U.S. patent application number 13/972003 was filed with the patent office on 2013-12-19 for nonaqueous electrolytic solution and nonaqueous electrolyte secondary battery.
This patent application is currently assigned to MITSUBISHI CHEMICAL CORPORATION. The applicant listed for this patent is MITSUBISHI CHEMICAL CORPORATION. Invention is credited to Takashi Fujii, Shinichi Kinoshita, Youichi Ohashi.
Application Number | 20130337318 13/972003 |
Document ID | / |
Family ID | 39492145 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130337318 |
Kind Code |
A1 |
Fujii; Takashi ; et
al. |
December 19, 2013 |
NONAQUEOUS ELECTROLYTIC SOLUTION AND NONAQUEOUS ELECTROLYTE
SECONDARY BATTERY
Abstract
A nonaqueous electrolytic solution that can provide a high
energy density nonaqueous electrolyte secondary battery having a
high capacity, excellent storage characteristics, and excellent
cycle characteristics and suppressing the decomposition of an
electrolytic solution and the deterioration thereof when used in a
high-temperature environment includes an electrolyte, a nonaqueous
solvent, and a compound represented by general formula (1):
##STR00001## wherein R.sup.1, R.sup.2, and R.sup.3 each
independently represent a hydrogen atom, a cyano group, or an
optionally halogen atom-substituted hydrocarbon group having 1 to
10 carbon atoms, with the proviso that R.sup.1 and R.sup.2 do not
simultaneously represent hydrogen atoms.
Inventors: |
Fujii; Takashi; (Ibaraki,
JP) ; Ohashi; Youichi; (Ibaraki, JP) ;
Kinoshita; Shinichi; (Ibaraki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI CHEMICAL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
MITSUBISHI CHEMICAL
CORPORATION
Tokyo
JP
|
Family ID: |
39492145 |
Appl. No.: |
13/972003 |
Filed: |
August 21, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13476598 |
May 21, 2012 |
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13972003 |
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12518188 |
Sep 14, 2009 |
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PCT/JP2007/073572 |
Dec 6, 2007 |
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13476598 |
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Current U.S.
Class: |
429/200 ;
429/188; 429/199 |
Current CPC
Class: |
H01M 2300/0025 20130101;
H01M 10/0567 20130101; H01M 10/052 20130101; H01M 10/0525 20130101;
H01M 10/056 20130101; H01M 2300/0037 20130101; H01M 10/4235
20130101; Y02E 60/10 20130101; H01M 4/134 20130101 |
Class at
Publication: |
429/200 ;
429/199; 429/188 |
International
Class: |
H01M 10/056 20060101
H01M010/056; H01M 10/052 20060101 H01M010/052 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 2006 |
JP |
2006-329935 |
Jun 28, 2007 |
JP |
2007-170651 |
Claims
1-24. (canceled)
25. A nonaqueous electrolytic solution comprising: an electrolyte,
a nonaqueous solvent, at least one compound selected from the group
consisting of a halogen atom-containing cyclic carbonate, a
monofluorophosphate, and a difluorophosphate, and a compound of
formula (1): ##STR00009## wherein R.sup.1, R.sup.2, and R.sup.3 are
each independently a hydrogen atom, a cyano group, a hydrocarbon
group having 1 to 10 atoms, or a halogen atom-substituted
hydrocarbon group having 1 to 10 carbon atoms, wherein the solution
is suitable for a nonaqueous electrolyte secondary battery that
comprises a negative electrode, a positive electrode, and a
nonaqueous electrolytic solution, the negative electrode and the
positive electrode being capable of storing and releasing metal
ions.
26. The nonaqueous electrolytic solution according to claim 25,
wherein the solution is suitable for a nonaqueous electrolyte
secondary battery that comprises a negative electrode comprising a
carbonaceous material serving as an active material.
27-30. (canceled)
31. A nonaqueous electrolyte secondary battery comprising: a
negative electrode, a positive electrode, and the nonaqueous
electrolytic solution of claim 25, wherein the negative electrode
and the positive electrode are each capable of storing and
releasing metal ions.
32. The nonaqueous electrolyte secondary battery according to claim
31, wherein the negative electrode comprises a carbonaceous
material serving as an active material.
Description
TECHNICAL FIELD
[0001] The present invention relates to nonaqueous electrolytic
solutions and nonaqueous electrolyte secondary batteries.
Specifically, the present invention relates to a specific
component-containing nonaqueous electrolytic solution that can
realize a secondary battery having improved battery
characteristics, such as cycle characteristics and high-temperature
storage characteristics, and relates to a nonaqueous electrolyte
secondary battery including the nonaqueous electrolytic
solution.
BACKGROUND ART
[0002] In recent years, there have been advances in the development
of nonaqueous electrolyte secondary batteries with higher energy
densities as progress toward a reduction in the size and weight of
electric appliances. Furthermore, the expansion of fields of
application of nonaqueous electrolyte secondary batteries require
further improvement in battery characteristics.
[0003] Hitherto, metallic lithium, metal compounds, such as
elemental metals, oxides, and alloys of lithium, capable of storing
and releasing lithium, and carbonaceous materials have been used as
negative-electrode active materials for use in nonaqueous
electrolyte secondary batteries. With respect to carbonaceous
materials, in particular, for example, nonaqueous electrolyte
secondary batteries including carbonaceous materials, such as coke,
artificial graphite, and natural graphite, capable of storing and
releasing lithium have been reported. In such nonaqueous
electrolyte secondary batteries, lithium does not exist in the
metallic state, suppressing the formation of dendrites and
improving the life and safety of batteries. In particular,
nonaqueous electrolyte secondary batteries including graphite-based
carbonaceous materials such as artificial and natural graphite have
been receiving attention because they should meet the demand for
higher capacity.
[0004] In nonaqueous electrolyte secondary batteries including the
carbonaceous materials, usually, cyclic carbonic esters, such as
propylene carbonate and ethylene carbonate, are widely used as
high-dielectric solvents for use in nonaqueous electrolytic
solutions. In particular, for nonaqueous electrolyte secondary
batteries including non-graphite-based carbonaceous materials,
e.g., coke, propylene carbonate-containing solvents are suitably
used.
[0005] In the case of using solvents containing propylene carbonate
in nonaqueous electrolyte secondary batteries including negative
electrodes composed of graphite-based carbonaceous materials alone
or mixtures of graphite-based carbonaceous materials and other
negative-electrode materials capable of storing and releasing
lithium, however, the decomposition reaction of propylene carbonate
proceeds vigorously on surfaces of the electrodes during charging.
This makes it impossible to smoothly store and release lithium at
the graphite-based carbonaceous negative electrodes.
[0006] In contrast, ethylene carbonate is not vigorously
decomposed; hence, in nonaqueous electrolyte secondary batteries
including graphite-based carbonaceous negative electrodes, ethylene
carbonate is often used as a high-dielectric solvent in
electrolytic solutions. Even in the case of using ethylene
carbonate as a main solvent, however, there are problems of
reductions in charge and discharge efficiency and cycle
characteristics, an increase in internal battery pressure due to
gas generated by the decomposition of electrolytic solutions on
surfaces of the electrodes during charging and discharging, and the
like.
[0007] To improve characteristics of nonaqueous electrolyte
secondary batteries, electrolytic solutions containing various
additives have been reported.
[0008] To suppress the decomposition of electrolytic solutions of
nonaqueous electrolyte batteries including graphite-based negative
electrodes, for example, the following electrolytic solutions have
been reported: electrolytic solutions containing vinylene carbonate
and its derivatives (Patent Document 1), electrolytic solutions
containing ethylene carbonate derivatives having non-conjugated
unsaturated bonds in their side chains (Patent Document 2), and
electrolytic solutions containing halogen atom-substituted cyclic
carbonates (Patent Document 3). These compounds contained in the
electrolytic solutions are reductively decomposed on surfaces of
negative electrodes to form films that suppress excessive
decomposition of the electrolytic solutions.
[0009] These compounds, however, do not necessarily meet the
requirements for storage characteristics under a high-temperature
environment, battery characteristics in a high-voltage state, or
gas generation. Vinylene carbonate compounds react readily with
positive electrode materials in a charged state. A higher vinylene
carbonate compound content is liable to cause a further reduction
in storage characteristics.
[0010] Meanwhile, in place of vinylene carbonate and its
derivatives and ethylene carbonates having nonconjugated
unsaturated bonds in their side chains and their derivatives,
nitrile compounds having unsaturated bonds have been reported as
additives capable of being reductively decomposed to form films
(Patent Document 4). The patent document discloses that also in
electrolytic solutions containing these compounds, the reductive
decomposition of solvents can be suppressed at a low level during
charging. Also in the case of using these compounds, however, there
are still issues of battery characteristics under a
high-temperature environment and high-voltage conditions or gas
generation.
[0011] The suppression of the reactivity of electrode materials in
a charged state to solvents, vinylene carbonate and its
derivatives, ethylene carbonates having nonconjugated unsaturated
bonds in their side chains and their derivatives, or halogen
atom-substituted cyclic carbonates, which are additives, results in
improvements in battery characteristics under high-temperature
conditions and the suppression of gas generation. It is desirable
to develop a technique for suppressing the reactivity.
[0012] In place of propylene carbonate and ethylene carbonate, a
halogen atom-substituted cyclic carbonate used as a high-dielectric
solvent has been reported (Patent Document 5). The document
describes that the incorporation of a fluorine atom or a chlorine
atom serving as an electron-withdrawing group in ethylene carbonate
suppresses the decomposition and improves charge and discharge
efficiency. This effect, however, is still insufficient under a
high-temperature environment. Thus, further improvements are
required.
[0013] In recent years, negative-electrode active materials
composed of elemental metals, such as silicon (Si), tin (Sn), and
lead (Pb), capable of being alloyed with lithium, alloys containing
at least these metal elements, and metal compounds containing these
metal elements (hereinafter, referred to as "negative-electrode
active materials containing Si, Sn, Pb, and the like") have been
reported. The capacity of these materials are about 2,000
mAhcm.sup.-3 or more and is about four or more times those of
graphite and the like. Thus, the use of these materials results in
a higher capacity.
[0014] Secondary batteries including the negative-electrode active
materials containing Si, Sn, Pb, and the like can have higher
capacities but have problems of a reduction in safety, a reduction
in charge and discharge efficiency due to the deterioration of the
negative-electrode active materials by charge and discharge, a
reduction in battery characteristics under a high-temperature
environment and high-voltage conditions, gas generation, and a
reduction in cycle characteristics.
[0015] To ensure safety and prevent a reduction in the discharge
capacity of such batteries, a nonaqueous electrolytic solution
containing a phosphotriester and a cyclic carbonate or a multimer
of a carbonate has been reported as a nonaqueous electrolytic
solution used for secondary batteries (Patent Document 6). To
improve charge-discharge cycle characteristics of batteries, a
method for improving charge-discharge cycle characteristics of a
battery by adding a heterocyclic compound having a sulfur atom
and/or an oxygen atom in its ring to a nonaqueous electrolytic
solution and forming a film on a surface of a negative-electrode
active material has been reported (Patent Document 7). To suppress
gas generation when a battery is stored in a charged state at a
high temperature, a negative electrode provided with a fired
mixture layer containing negative-electrode active material
particles, lithium oxide, and a binder arranged on a surface of a
current collector has been reported (Patent Document 8). [0016]
[Patent Document 1] Japanese Unexamined Patent Application
Publication No. 8-45545 [0017] [Patent Document 2] Japanese
Unexamined Patent Application Publication No. 2000-40526 [0018]
[Patent Document 3] WO98/15024 [Patent Document 4] Japanese
Unexamined Patent Application Publication No. 2003-86247 [0019]
[Patent Document 5] Japanese Unexamined Patent Application
Publication No. 62-290072 [0020] [Patent Document 6] Japanese
Unexamined Patent Application Publication No. 11-176470 [0021]
[Patent Document 7] Japanese Unexamined Patent Application
Publication No. 2004-87284 [0022] [Patent Document 8] Japanese
Unexamined Patent Application Publication No. 2007-66726
DISCLOSURE OF INVENTION
[0023] In conventional secondary batteries described in Patent
Documents 6, 7, and the like, the use of an element such as silicon
(Si) as a material constituting negative electrodes results in a
higher capacity. However, the performance, in particular, discharge
capacity retention rates of the secondary batteries in
charge-discharge cycles over longer periods of time, is still
insufficient.
[0024] Furthermore, the conventional secondary batteries described
above do not sufficiently overcome all problems of gas generation,
the reduction in cycle characteristics, and the like when stored in
a charged state at a high temperature.
[0025] The present invention has been made in light of the
circumstances described above. It is an object of the present
invention to provide a nonaqueous electrolytic solution for use in
a nonaqueous electrolytic secondary battery, the nonaqueous
electrolytic solution suppressing gas generation during
high-temperature storage in a charged state and affording
satisfactory cycle characteristics, and provide a secondary battery
including the nonaqueous electrolytic solution.
[0026] To overcome the foregoing problems relating to the graphite
negative electrodes, it is another object of the present invention
to provide a high energy density nonaqueous electrolyte secondary
battery having a high capacity, excellent storage characteristics,
and excellent cycle characteristics and suppressing the
decomposition of an electrolytic solution used in the nonaqueous
electrolyte secondary battery and the deterioration thereof when
used in a high-temperature environment.
[0027] The inventors have conducted various studies and have found
that the use of a nitrile compound having a specific structure
minimizes the decomposition reaction of an electrolytic solution
and, if an additive for forming a film on a negative electrode is
added, also minimizes the decomposition reaction of the additive,
thereby improving charge and discharge efficiency, storage
characteristics, and cycle characteristics. The finding has led to
the completion of the present invention.
[0028] A nonaqueous electrolytic solution according to a first
aspect of the present invention is a nonaqueous electrolytic
solution for use in a nonaqueous electrolyte secondary battery
including a positive electrode having a positive-electrode active
material capable of storing and releasing metal ions and a negative
electrode having a negative-electrode active material containing at
least one atom selected from the group consisting of Si, Sn, and Pb
and capable of storing and releasing metal ions and includes a
compound represented by general formula (1) and/or a compound
having 2 to 4 cyano groups in its structural formula:
##STR00002##
[0029] In general formula (1), R.sup.1, R.sup.2, and R.sup.3 each
independently represent a hydrogen atom, a cyano group, or an
optionally halogen atom-substituted hydrocarbon group having 1 to
10 carbon atoms.
[0030] A nonaqueous electrolytic solution according to a second
aspect of the present invention is a nonaqueous electrolytic
solution for use in a nonaqueous electrolyte secondary battery
including a negative electrode, a positive electrode, and a
nonaqueous electrolytic solution, the negative electrode and the
positive electrode being capable of storing and releasing metal
ions, and includes an electrolyte, a nonaqueous solvent, and a
compound represented by general formula (2):
##STR00003##
[0031] In general formula (2), R.sup.4, R.sup.5, and R.sup.6 each
independently represent a hydrogen atom, a cyano group, or an
optionally halogen atom-substituted hydrocarbon group having 1 to
10 carbon atoms, with the proviso that R.sup.4 and R.sup.5 do not
simultaneously represent hydrogen atoms.
[0032] A nonaqueous electrolytic solution according to a third
aspect of the present invention is a nonaqueous electrolytic
solution for use in a nonaqueous electrolyte secondary battery
including a negative electrode, a positive electrode, and a
nonaqueous electrolytic solution, the negative electrode and the
positive electrode being capable of storing and releasing metal
ions, and includes an electrolyte, a nonaqueous solvent, a compound
represented by general formula (1), and at least one compound
selected from the group consisting of halogen atom-containing
cyclic carbonates, monofluorophosphates, and
difluorophosphates:
##STR00004##
[0033] In general formula (1), R.sup.1, R.sup.2, and R.sup.3 each
independently represent a hydrogen atom, a cyano group, or an
optionally halogen atom-substituted hydrocarbon group having 1 to
10 carbon atoms.
[0034] A nonaqueous electrolyte secondary battery according to a
fourth aspect of the present invention includes a positive
electrode having a positive-electrode active material capable of
storing and releasing metal ions, a negative electrode having a
negative-electrode active material containing at least one atom
selected from the group consisting of Si, Sn, and Pb and capable of
storing and releasing metal ions, and the nonaqueous electrolytic
solution according to the first aspect.
[0035] A nonaqueous electrolyte secondary battery according to a
fifth aspect of the present invention includes a positive electrode
having a positive-electrode active material capable of storing and
releasing metal ions, a negative electrode having a
negative-electrode active material containing at least one atom
selected from the group consisting of Si, Sn, and Pb and capable of
storing and releasing metal ions, and the nonaqueous electrolytic
solution according to the second aspect.
[0036] A nonaqueous electrolyte secondary battery according to a
sixth aspect of the present invention includes a negative
electrode, a positive electrode, and a nonaqueous electrolytic
solution, the negative electrode and the positive electrode being
capable of storing and releasing metal ions, wherein the nonaqueous
electrolytic solution is the nonaqueous electrolytic solution
according to the second aspect.
[0037] A nonaqueous electrolyte secondary battery according to a
seventh aspect of the present invention includes a negative
electrode, a positive electrode, and a nonaqueous electrolytic
solution, the negative electrode and the positive electrode being
capable of storing and releasing metal ions, wherein the nonaqueous
electrolytic solution is the nonaqueous electrolytic solution
according to the third aspect.
DETAILED DESCRIPTION OF THE INVENTION
[0038] According to the present invention, it is possible to
provide a nonaqueous electrolyte secondary battery inhibiting gas
generation during high-temperature storage in a charged state and
having excellent cycle characteristics.
[0039] Furthermore, according to the present invention, it is
possible to provide a nonaqueous electrolyte secondary battery that
does not readily deteriorate when used in a high-temperature
environment and that has high capacity, excellent storage
characteristics, and excellent cycle characteristics.
[0040] While embodiments of the present invention will be described
in detail below, the present invention is not limited to the
following description. Any modification can be made within the
scope of the invention.
[Nonaqueous Electrolytic Solution]
[0041] A nonaqueous electrolytic solution according to a first
aspect of the present invention is a nonaqueous electrolytic
solution for use in a nonaqueous electrolyte secondary battery
including a nonaqueous electrolytic solution, a negative electrode,
and a positive electrode, the negative electrode and the positive
electrode being capable of storing and releasing metal ions, and
the negative electrode having a negative-electrode active material
containing at least one atom selected from the group consisting of
Si, Sn, and Pb, and contains an unsaturated nitrile compound
represented by general formula (1) described below and/or a
compound having 2 to 4 cyano groups in its structural formula
described below.
[0042] A nonaqueous electrolytic solution according to a second
aspect of the present invention is a nonaqueous electrolytic
solution for use in a nonaqueous electrolyte secondary battery
including a nonaqueous electrolytic solution, a negative electrode,
and a positive electrode, the negative electrode and the positive
electrode being capable of storing and releasing metal ions,
contains an electrolyte and a nonaqueous solvent that dissolves the
electrolyte, and further contains an unsaturated nitrile compound
represented by general formula (2) described below.
[0043] A nonaqueous electrolytic solution according to a third
aspect of the present invention is a nonaqueous electrolytic
solution for use in a nonaqueous electrolyte secondary battery
including a nonaqueous electrolytic solution, a negative electrode,
and a positive electrode, the negative electrode and the positive
electrode being capable of storing and releasing metal ions,
contains an electrolyte and a nonaqueous solvent that dissolves the
electrolyte, and further contains an unsaturated nitrile compound
represented by general formula (1) described below and at least one
compound selected from the group consisting of halogen
atom-containing cyclic carbonates, monofluorophosphates, and
difluorophosphates.
[0044] Details of the effect of the present invention are not
clear. It is believed that in the unsaturated nitrile compound
represented by general formula (1) described below and the
unsaturated nitrile compound represented by general formula (2),
each of the unsaturated nitrile compounds is subjected to reduction
reaction on a surface of the negative electrode at a more
electropositive potential than the other constituents in the
nonaqueous electrolytic solution to form a coating component,
thereby suppressing the decomposition of the other components
constituting the nonaqueous electrolytic solution and thus
improving battery characteristics and cycle characteristics under a
high-temperature environment.
[0045] In the compound having 2 to 4 cyano groups in its structural
formula and contained in the nonaqueous electrolytic solution, the
presence of 2 or more cyano groups results in some strong
interactions, such as coordination and adsorption, with a
transition metal contained in a positive-electrode active material
compared with a mononitrile compound, thereby stabilizing the
positive electrode in a charged state. This permits the suppression
of the reaction between the positive electrode in a charged state
and the nonaqueous electrolytic solution during high-temperature
storage and the suppression of gas generation and a deterioration
in battery characteristics.
[0046] The excellent effect attributed to the compound having 2 to
4 cyano groups in its structural formula is noticeable when a
negative electrode having a negative-electrode active material
containing at least one atom selected from the group consisting of
Si, Sn, and Pb is used, as compared with the case of using a
carbon-based negative-electrode active material as a
negative-electrode active material.
[0047] The reason for this is not necessarily clear. It is
speculated that in the case of using the negative electrode having
the negative-electrode active material containing at least one atom
selected from the group consisting of Si, Sn, and Pb, the potential
of a positive electrode is high compared with the case of using a
carbon-based negative electrode even when the same battery voltage
is obtained, thereby facilitating the reaction between the positive
electrode and the nonaqueous electrolytic solution during
high-temperature storage in a charged state. In this case, the
stabilizing effect of the compound having 2 to 4 cyano groups in
its structural formula on the positive electrode in the nonaqueous
electrolytic solution is believed to be more clearly provided.
[0048] Furthermore, a secondary battery including the negative
electrode having the negative-electrode active material containing
at least one atom selected from the group consisting of Si, Sn, and
Pb is less likely to degrade cycle characteristics without reducing
charge and discharge efficiency and thus can satisfy both storage
characteristics and cycle characteristics.
[0049] Although the reason for this is not clear, it is speculated
that the difference in reactivity of the compound, having 2 to 4
cyano groups in its structural formula contained in the nonaqueous
electrolytic solution, on the negative electrode is affected.
[Nonaqueous Electrolytic Solution According to First Aspect]
[0050] A nonaqueous electrolytic solution according to the first
aspect of the present invention is a nonaqueous electrolytic
solution for use in a nonaqueous electrolyte secondary battery
including a nonaqueous electrolytic solution, a negative electrode,
and a positive electrode, the negative electrode and the positive
electrode being capable of storing and releasing metal ions, and
the negative electrode having a negative-electrode active material
containing at least one atom selected from the group consisting of
Si, Sn, and Pb, the negative-electrode active material being
capable of storing and releasing metal ions, and always contains a
compound represented by general formula (1) described below
(hereinafter, also referred to as "unsaturated nitrile compound
(1)") and/or a compound having 2 to 4 cyano groups in its
structural formula.
{Unsaturated Nitrile Compound (1)}
[0051] Unsaturated nitrile compound (1) is represented by general
formula (1) below.
##STR00005##
[0052] In general formula (1), R.sup.1, R.sup.2, and R.sup.3 each
independently represent a hydrogen atom, a cyano group, or an
optionally halogen atom-substituted hydrocarbon group having 1 to
10 carbon atoms.
[0053] In general formula (1) described above, a specific example
of a compound in which each of R.sup.1 to R.sup.3 represents a
hydrogen atom is acrylonitrile.
[0054] In general formula (1) described above, specific examples of
a compound in which at least any one of R.sup.1 to R.sup.3
represents a cyano group include fumaronitrile,
1,1,2-tricyanoethylene, and tetracyanoethylene.
[0055] In general formula (1) described above, in the case where at
least one of R.sup.1 to R.sup.3 represents a hydrocarbon group, the
lower limit of the number of carbon atoms in the hydrocarbon group
is usually 1 or more. The upper limit is usually 10 or less,
preferably 8 or less, and more preferably 6 or less.
[0056] In general formula (1) described above, the type of
hydrocarbon group of each of R.sup.1 to R.sup.3 is not particularly
limited. That is, each of R.sup.1 to R.sup.3 may represent an
aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a
group in which an aliphatic hydrocarbon group is linked to an
aromatic hydrocarbon group. The aliphatic hydrocarbon group may be
a saturated hydrocarbon group or may have an unsaturated bond (a
carbon-carbon double bond or carbon-carbon triple bond).
Furthermore, the aliphatic hydrocarbon group may have a chain or
cyclic structure. In the case of the chain structure, a linear or
branched structure may be used. Moreover, the aliphatic hydrocarbon
group may have a structure in which a linear moiety is linked to a
cyclic moiety.
[0057] Specific examples of a preferred substituent as a
hydrocarbon group of each of R.sup.1 to R.sup.3 are described
below.
<Specific Example of Saturated Chain Hydrocarbon Group>
[0058] Examples thereof include a methyl group, an ethyl group, a
n-propyl group, an isopropyl group, a n-butyl group, an isobutyl
group, a sec-butyl group, and a tert-butyl group.
<Specific Example of Saturated Cyclic Hydrocarbon Group>
[0059] Examples thereof include a cyclopropyl group, a cyclopentyl
group, a cyclohexyl group, and a cycloheptyl group.
<Specific Example of Hydrocarbon Group Having Unsaturated Bond
(Hereinafter, Also Referred to as an "Unsaturated Hydrocarbon
Group")>
[0060] Examples thereof include a vinyl group, a 1-propen-1-yl
group, a 1-propen-2-yl group, an allyl group, a crotyl group, an
ethynyl group, a propargyl group, a phenyl group, a 2-toluoyl
group, a 3-toluoyl group, a 4-toluoyl group, a xylyl group, a
benzyl group, and a cinnamoyl group.
<Preferred Example of Hydrocarbon Group>
[0061] Among exemplified hydrocarbon groups described above, the
following hydrocarbon groups of R.sup.1 to R.sup.3 are preferred
from the viewpoint of solubility in a nonaqueous electrolytic
solution and the ease of industrial availability: a methyl group,
an ethyl group, a n-propyl group, an isopropyl group, a n-butyl
group, an isobutyl group, a tert-butyl group, a cyclopentyl group,
a cyclohexyl group, a phenyl group, a 2-toluoyl group, a 3-toluoyl
group, a 4-toluoyl group, a vinyl group, an allyl group, an ethynyl
group, a propargyl group, a benzyl group, and the like.
Particularly preferred hydrocarbon groups are as follows: a methyl
group, an ethyl group, a n-propyl group, a n-butyl group, a
cyclohexyl group, and a phenyl group.
[0062] A hydrocarbon group of each of R.sup.1 to R.sup.3 shown in
general formula (1) described above may have a structure in which
hydrogen atoms bonded to carbon atoms are partially or completely
substituted with halogen atoms.
[0063] Examples of the halogen atom include a fluorine atom, a
chlorine atom, a bromine atom, and an iodine atom. A fluorine atom,
a chlorine atom, and a bromine atom are preferred. A fluorine atom
and a chlorine atom are more preferred from the viewpoints of
chemical stability and electrochemical stability.
[0064] In the case of a halogen atom-substituted hydrocarbon group
of each of R.sup.1 to R.sup.3, the number of halogen atoms is not
particularly limited. Hydrogen atoms in the hydrocarbon group may
be partially substituted with a halogen atom. Furthermore, all
hydrogen atoms in the hydrocarbon group may be substituted with
halogen atoms. In the case where a hydrocarbon group of each of
R.sup.1 to R.sup.3 has a plurality of halogen atoms, these halogen
atoms may be the same or different.
[0065] Specific examples of a halogen atom-substituted hydrocarbon
group suitable as a hydrocarbon group of each of R.sup.1 to R.sup.3
are described below.
<Specific Example of Fluorine Atom-Substituted Chain Saturated
Hydrocarbon Group>
[0066] Examples thereof include a fluoromethyl group,
difluoromethyl group, a trifluoromethyl group, a 1-fluoroethyl
group, a 2-fluoroethyl group, a 1,1-difluoroethyl group, a
1,2-difluoroethyl group, a 2,2-difluoroethyl group, a
2,2,2-trifluoroethyl group, a perfluoroethyl group, a
1-fluoro-n-propyl group, a 2-fluoro-n-propyl group, a
3-fluoro-n-propyl group, a 1,1-difluoro-n-propyl group, a
1,2-difluoro-n-propyl group, a 1,3-difluoro-n-propyl group, a
2,2-difluoro-n-propyl group, a 2,3-difluoro-n-propyl group, a
3,3-difluoro-n-propyl group, a 3,3,3-trifluoro-n-propyl group, a
2,2,3,3,3-pentafluoro-n-propyl group, a perfluoro-n-propyl group, a
1-fluoroisopropyl group, a 2-fluoroisopropyl group, a
1,2-difluoroisopropyl group, a 2,2-difluoroisopropyl group, a
2,2'-difluoroisopropyl group, 2,2,2,2',2',2'-hexafluoroisopropyl
group, a 1-fluoro-n-butyl group, a 2-fluoro-n-butyl group, a
3-fluoro-n-butyl group, a 4-fluoro-n-butyl group, a
4,4,4-trifluoro-n-butyl group, a perfluoro-n-butyl group, a
2-fluoro-tert-butyl group, and a perfluoro-tert-butyl group.
<Specific Example of Fluorine Atom-Substituted Cyclic Saturated
Hydrocarbon Group>
[0067] Examples thereof include a 1-fluorocyclopropyl group, a
2-fluorocyclopropyl group, a perfluorocyclopropyl group, a
1-fluorocyclopentyl group, a 2-fluorocyclopentyl group, a
3-fluorocyclopentyl group, a perfluorocyclopentyl group, a
1-fluorocyclohexyl group, a 2-fluorocyclohexyl group, a
3-fluorocyclohexyl group, a 4-fluorocyclohexyl group, and a
perfluorocyclohexyl group.
<Specific Example of Fluorine Atom-Substituted Unsaturated
Hydrocarbon Group>
[0068] Examples thereof include a 2-fluorophenyl group, a
3-fluorophenyl group, a 4-fluorophenyl group, a 2,3-difluorophenyl
group, a 2,4-difluorophenyl group, a 3,5-difluorophenyl group, a
2,4,6-trifluorophenyl group, a perfluorophenyl group, a
3-fluoro-2-methylphenyl group, a 4-fluoro-2-methylphenyl group, a
5-fluoro-2-methylphenyl group, a 6-fluoro-2-methylphenyl group, a
2-fluoro-3-methylphenyl group, a 4-fluoro-3-methylphenyl group, a
5-fluoro-3-methylphenyl group, a 6-fluoro-3-methylphenyl group, a
2-fluoro-4-methylphenyl group, a 3-fluoro-4-methylphenyl group, a
perfluorotoluoyl group, a perfluoronaphthyl group, a 1-fluorovinyl
group, a 2-fluorovinyl group, a 1,2-difluorovinyl group, a
2,2-difluorovinyl group, a perfluorovinyl group, a 1-fluoroallyl
group, a 2-fluoroallyl group, a 3-fluoroallyl group, a
perfluoroallyl group, a (2-fluorophenyl)methyl group, a
(3-fluorophenyl)methyl group, a (4-fluorophenyl)methyl group, and a
(perfluorophenyl)methyl group.
<Specific Example of Chlorine Atom-Substituted Chain Saturated
Hydrocarbon Group>
[0069] Examples thereof include a chloromethyl group, a
dichloromethyl group, a trichloromethyl group, a 1-chloroethyl
group, a 2-chloroethyl group, a 1,1-dichloroethyl group, a
1,2-dichloroethyl group, a 2,2-dichloroethyl group, a
2,2,2-trichloroethyl group, a perchloroethyl group, a
1-chloro-n-propyl group, a 2-chloro-n-propyl group, a
3-chloro-n-propyl group, a 1,1-dichloro-n-propyl group, a
1,2-dichloro-n-propyl group, a 1,3-dichloro-n-propyl group, a
2,2-dichloro-n-propyl group, a 2,3-dichloro-n-propyl group, a
3,3-dichloro-n-propyl group, a 3,3,3-trichloro-n-propyl group, a
2,2,3,3,3-pentachloro-n-propyl group, a perchloro-n-propyl group, a
1-chloroisopropyl group, a 2-chloroisopropyl group, a
1,2-dichloroisopropyl group, a 2,2-dichloroisopropyl group, a
2,2'-dichloroisopropyl group, a 2,2,2,2',2',2'-hexachloroisopropyl
group, a 1-chloro-n-butyl group, a 2-chloro-n-butyl group, a
3-chloro-n-butyl group, a 4-chloro-n-butyl group, a
4,4,4-trichloro-n-butyl group, a perchloro-n-butyl group, a
2-chloro-tert-butyl group, and a perchloro-tert-butyl group.
<Specific Example of Chlorine Atom-Substituted Cyclic Saturated
Hydrocarbon Group>
[0070] Examples thereof include a 1-chlorocyclopropyl group, a
2-chlorocyclopropyl group, a perchlorocyclopropyl group, a
1-chlorocyclopentyl group, a 2-chlorocyclopentyl group, a
3-chlorocyclopentyl group, a perchlorocyclopentyl group, a
1-chlorocyclohexyl group, a 2-chlorocyclohexyl group, a
3-chlorocyclohexyl group, a 4-chlorocyclohexyl group, and a
perchlorocyclohexyl group.
<Specific Example of Chlorine Atom-Substituted Unsaturated
Hydrocarbon Group>
[0071] Examples thereof include a 2-chlorophenyl group, a
3-chlorophenyl group, a 4-chlorophenyl group, a 2,3-dichlorophenyl
group, a 2,4-dichlorophenyl group, a 3,5-dichlorophenyl group, a
2,4,6-trichlorophenyl group, a perchlorophenyl group, a
3-chloro-2-methylphenyl group, a 4-chloro-2-methylphenyl group, a
5-chloro-2-methylphenyl group, a 6-chloro-2-methylphenyl group, a
2-chloro-3-methylphenyl group, a 4-chloro-3-methylphenyl group, a
5-chloro-3-methylphenyl group, a 6-chloro-3-methylphenyl group, a
2-chloro-4-methylphenyl group, a 3-chloro-4-methylphenyl group, a
perchlorotoluoyl group, a perchloronaphthyl group, a 1-chlorovinyl
group, a 2-chlorovinyl group, a 1,2-dichlorovinyl group, a
2,2-dichlorovinyl group, a perchlorovinyl group, a 1-chloroallyl
group, a 2-chloroallyl group, a 3-chloroallyl group, a
perchloroallyl group, a (2-chlorophenyl)methyl group, a
(3-chlorophenyl)methyl group, a (4-chlorophenyl)methyl group, and a
(perchlorophenyl)methyl group.
<Preferred Example of Halogen Atom-Substituted Hydrocarbon
Group>
[0072] Among these, a fluorine atom-substituted hydrocarbon group
is preferred from the viewpoints of chemical and electrochemical
stability and the ease of industrial availability. Specific
examples thereof are described below.
[0073] Examples thereof include a fluoromethyl group, a
difluoromethyl group, a trifluoromethyl group, a 1-fluoroethyl
group, a 2-fluoroethyl group, a 2,2,2-trifluoroethyl group, a
perfluoroethyl group, a 3,3,3-trifluoro-n-propyl group, a
2,2,3,3,3-pentafluoro-n-propyl group, a perfluoro-n-propyl group, a
2,2,2,2',2',2'-hexafluoroisopropyl group, a perfluoro-n-butyl
group, a 2-fluoro-tert-butyl group, a perfluoro-tert-butyl group, a
2-fluorocyclohexyl group, a 3-fluorocyclohexyl group, a
4-fluorocyclohexyl group, a perfluorocyclohexyl group, a
2-fluorophenyl group, a 3-fluorophenyl group, a 4-fluorophenyl
group, a 2,3-difluorophenyl group, a 2,4-difluorophenyl group, a
3,5-difluorophenyl group, a 2,4,6-trifluorophenyl group, a
perfluorophenyl group, a 1-fluorovinyl group, a 2-fluorovinyl
group, a perfluorovinyl group, a (2-fluorophenyl)methyl group, a
(3-fluorophenyl)methyl group, a (4-fluorophenyl)methyl group, and a
(perfluorophenyl)methyl group.
[0074] Specific examples of a compound which is represented by
general formula (1) and in which at least one of R.sup.1 to R.sup.3
represents any of the foregoing hydrocarbon group are described
below.
<Specific Examples of Compound Having Chain Saturated
Hydrocarbon Group>
[0075] Examples thereof include methacrylonitrile,
2-ethyl-acrylonitrile, crotononitrile, 3-methylcrotononitrile,
2-methyl-2-butenenitrile, 2-pentenenitrile,
2-methyl-2-pentenenitrile, 3-methyl-2-pentenenitrile, and
2-hexenenitrile.
<Specific Examples of Compound Having Cyclic Saturated
Hydrocarbon Group>
[0076] Examples thereof include 1-cyano-1-cyclopentene and
1-cyano-1-cyclohexene.
<Specific Examples of Compound Having Unsaturated Hydrocarbon
Group>
[0077] Examples thereof include 2-vinylacrylonitrile,
geranylnitrile and cinnamonitrile.
<Specific Examples of Compound Having Chain Saturated
Hydrocarbon Group Substituted with Fluorine Atom>
[0078] Examples thereof include 2-fluoroacrylonitrile,
3-fluoroacrylonitrile, 3-fluoro-methacrylonitrile,
2-(fluoromethyl)acrylonitrile, 2-(difluoromethyl)acrylonitrile,
2-(trifluoromethyl)acrylonitrile, 3-fluorocrotononitrile,
4-fluorocrotononitrile, 4,4-difluorocrotononitrile,
4,4,4-trifluorocrotononitrile, 3-(fluoromethyl)crotononitrile,
4-fluoro-3-(fluoromethyl)-2-butenenitrile,
4-fluoro-2-pentenenitrile, and 5-fluoro-2-pentenenitrile.
<Specific Examples of Compound Having Cyclic Saturated
Hydrocarbon Group Substituted with Fluorine Atom>
[0079] Examples thereof include 3-fluoro-1-cyano-1-cyclopentene,
4-fluoro-1-cyano-1-cyclopentene, 5-fluoro-1-cyano-1-cyclopentene,
3-fluoro-1-cyano-1-cyclohexene, 4-fluoro-1-cyano-1-cyclohexene,
5-fluoro-1-cyano-1-cyclohexene, and
6-fluoro-1-cyano-1-cyclohexene.
<Specific Examples of Compound Having Unsaturated Hydrocarbon
Group Substituted with Fluorine Atom>
[0080] Examples thereof include 2-(1-fluorovinyl)acrylonitrile,
[0081] 2-(2-fluorovinyl)acrylonitrile,
2-(1-fluoroallyl)acrylonitrile, 2-(2-fluoroallyl)acrylonitrile,
2-(3-fluoroallyl)acrylonitrile, 2-(2-fluorophenyl)acrylonitrile,
2-(3-fluorophenyl)acrylonitrile, 2-(4-fluorophenyl)acrylonitrile,
3-(2-fluorophenyl)propenenitrile, 3-(3-fluorophenyl)propenenitrile,
3-(4-fluorophenyl)propenenitrile, and 3-fluorogeranylnitrile.
<Preferred Example of Unsaturated Nitrile Compound (1)>
[0082] Among these nitrile compounds exemplified above, the
following compounds are particularly preferred as unsaturated
nitrile compound (1) according to the present invention from the
viewpoint of easy synthesis or from the industrial standpoint.
[0083] Examples thereof include acrylonitrile, methacrylonitrile,
crotononitrile, 3-methylcrotononitrile, 2-methyl-2-butenenitrile,
2-pentenenitrile, 2-methyl-2-pentenenitrile,
1-cyano-1-cyclopentene, 1-cyano-1-cyclohexene, geranylnitrile,
cinnamonitrile, 2-furonitrile, fumaronitrile, and
tetracyanoethylene.
[0084] In unsaturated nitrile compound (1) according to the present
invention shown in general formula (1), preferably, R.sup.1 and
R.sup.2 do not simultaneously represent hydrogen atoms, and either
or both of R.sup.1 and R.sup.2 each independently represent a cyano
group or an optionally halogen atom-substituted hydrocarbon group
having 1 to 10 carbon atoms. Examples of unsaturated nitrile
compound (1) include preferred compounds for unsaturated nitrile
compound (2) represented by general formula (2) described
below.
[0085] The molecular weight of unsaturated nitrile compound (1) is
not limited. Unsaturated nitrile compound (1) may have any
molecular weight unless the effect of the present invention is
significantly impaired. Unsaturated nitrile compound (1) has a
molecular weight of usually 40 or more and preferably 50 or more.
The upper limit of the molecular weight is not particularly
limited. For practical purposes, the upper limit is usually 400 or
less and preferably 300 or less because an excessively high
molecular weight is liable to cause an increase in the viscosity of
an electrolytic solution.
[0086] A method for producing unsaturated nitrile compound (1) is
not particularly limited. Any of known methods can be selected to
produce it.
[0087] A single type of unsaturated nitrile compound (1) may be
used alone. Alternatively, two or more types of unsaturated nitrile
compounds (1) may be used in combination as a mixture.
[0088] The nonaqueous electrolytic solution according to the first
aspect has an unsaturated nitrile compound (1) content of usually
0.001% by weight or more, preferably 0.01% by weight or more, and
more preferably 0.1% by weight, and usually 10% by weight or less,
preferably 5% by weight, and more preferably 2% by weight with
respect to the total weight of the nonaqueous electrolytic
solution. An unsaturated nitrile compound (1) content of less than
the lower limit described above can result in insufficient
suppression of the decomposition of other components, constituting
the nonaqueous electrolytic solution, on a surface of the
electrode, so that the effect of the present invention may not be
readily provided. Meanwhile, an unsaturated nitrile compound (1)
content exceeding the upper limit described above can result in
excessive progress of the reaction on the electrode surface,
thereby deteriorating various battery characteristics.
[0089] Furthermore, two or more types of unsaturated nitrile
compounds (1) may be used in combination. Also in the case where
the two or more types of unsaturated nitrile compounds are used in
combination, the total content of the two or more types of
unsaturated nitrile compounds (1) is the same as above.
{Compound Having 2 to 4 Cyano Groups in its Structural Formula}
[0090] The number of cyano groups in the compound having 2 to 4
cyano groups in its structural formula is usually 2 or more and
usually 4 or less, preferably 3 or less, and particularly
preferably 2.
[0091] Furthermore, the compound having 2 to 4 cyano groups in its
structural formula is preferably a compound represented by general
formula (3) (hereinafter, also referred to as "dicyano compound
(3)").
[0092] NC--(X).sub.n--CN (3) In general formula (3), X represents
CH.sub.2, CFH, CF.sub.2, CHR, CFR, CR.sub.2, C.dbd.O, O, S, NH, or
NR. R represents an optionally substituted hydrocarbon group having
5 or less carbon atoms or a cyano group. n represents an integer of
1 or more. n X's may be the same or different.
[0093] In general formula (3), n represents an integer of 1 or
more. Preferably, n represents an integer of 2 or more. More
preferably, n represents an integer of 5 or more. An excessively
small n results in an excessively small distance between two cyano
groups in general formula (3), so that both cyano groups cannot
sufficiently affect a transition metal in the positive-electrode
active material. The upper limit of n is not particularly limited.
The upper limit is usually 12 or less and particularly preferably 8
or less from the viewpoint of sufficiently ensuring the proportion
of the cyano groups, serving as an agent, per weight of dicyano
compound (3) incorporated in the nonaqueous electrolytic
solution.
[0094] X represents one or more groups selected from the group
consisting of CH.sub.2, CFH, CF.sub.2, CHR, CFR, CR.sub.2, C.dbd.O,
O, S, NH, and NR, in which the one or more groups may be the same
or different (wherein R represents an optionally substituted
hydrocarbon group having 5 or less carbon atoms or a cyano group).
Among these, from the viewpoint of stability in a battery,
preferably, X represents one or more groups selected from the group
consisting of CH.sub.2, CFH, CF.sub.2, CHR, CFR, CR.sub.2, O, S,
and NR, wherein the one or more groups may be the same or
different. Particularly preferably, X represents one or more groups
selected from the group consisting of CH.sub.2, CFH, CF.sub.2, CHR,
CFR, CR.sub.2, and O, wherein the one or more groups may be the
same or different. Most preferably, X represents one or more groups
selected from the group consisting of CH.sub.2, CFH, CF.sub.2, CHR,
CFR, and CR.sub.2, wherein the one or more groups may be the same
or different.
[0095] R in each of CHR, CFR, and CR.sub.2 of X represents a cyano
group or a hydrocarbon group having 5 or less carbon atoms and
optionally having a substituent such as a cyano group. Specific
examples of R include the following hydrocarbon groups, hydrocarbon
groups having substituents, and a cyano group.
<Hydrocarbon Group>
[0096] Examples thereof include a methyl group, an ethyl group, a
propyl group, an isopropyl group, a butyl group, a 1-methylpropyl
group, a 2-methylbutyl group, a tert-butyl group, a pentyl group, a
1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group,
and a neopentyl group.
<Hydrocarbon Group Having Substituent>
[0097] Examples thereof include a fluoromethyl group, a
difluoromethyl group, a trifluoromethyl group, a 2-fluoroethyl
group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a
1,1,2,2,2-pentafluoroethyl group, a methoxymethyl group, an
ethoxymethyl group, a 2-methoxyethyl group, a cyanomethyl group, a
2-cyanoethyl group, a 3-cyanopropyl group, a methoxycarbonylmethyl
group, an ethoxycarbonylmethyl group, and a 2-methoxycarbonylethyl
group.
[0098] R may be a cyano group.
[0099] In the case where X represents CR.sub.2, two R's may be the
same or different.
[0100] Specific examples of dicyano compound (3) are described
below.
<Specific Examples of Dicyano Compound (3)>
[0101] Examples thereof include malononitrile, succinonitrile,
glutaronitrile, adiponitrile, pimelonitrile, suberonitrile,
azelanitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile,
methylmalononitrile, ethylmalononitrile, isopropylmalononitrile,
tert-butylmalononitrile, methylsuccinonitrile,
2,2-dimethylsuccinonitrile, 2,3-dimethylsuccinonitrile,
trimethylsuccinonitrile, tetramethylsuccinonitrile,
3,3'-oxydipropionitrile, 3,3'-thiodipropionitrile,
3,3'-(ethylenedioxy)dipropionitrile,
3,3'-(ethylenedithio)dipropionitrile, 1,2,3-propanetricarbonitrile,
1,3,5-pentanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, and
tris(2-cyanoethyl)amine.
[0102] Among these specific examples described above, the following
compounds are preferred because the effect of the present invention
is readily provided.
<Preferred Examples of Dicyano Compound (3)>
[0103] Examples thereof include succinonitrile, glutaronitrile,
adiponitrile, pimelonitrile, suberonitrile, azelanitrile,
sebaconitrile, 3,3'-oxydipropionitrile, 3,3'-thiodipropionitrile,
1,2,3-propanetricarbonitrile, and 1,3,5-pentanetricarbonitrile.
[0104] Among these preferred specific examples described above, in
particular, pimelonitrile, suberonitrile, azelanitrile,
sebaconitrile, 3,3'-oxydipropionitrile, and
1,3,5-pentanetricarbonitrile, in which n represents 5 or more in
general formula (3), are more preferred.
[0105] A method for producing dicyano compound (3) is not
particularly limited. Any of known methods can be selected to
produce it.
[0106] Compounds having 2 to 4 cyano groups in their structural
formulae, e.g., dicyano compound (3), may be contained alone in the
nonaqueous electrolytic solution of the present invention.
Alternatively, any two or more types of compounds may be combined
in any proportion.
[0107] Furthermore, the proportion of a compound having 2 to 4
cyano groups in its structural formula, e.g., dicyano compound (3),
in a nonaqueous electrolytic solution according to the first aspect
is not particularly limited. Any proportion thereof may be used
unless the effect of the present invention is significantly
impaired. The nonaqueous electrolytic solution has a concentration
of the compound of usually 0.001% by weight or more, preferably
0.01% by weight or more, and more preferably 0.1% by weight, and
usually 10% by weight or less, preferably 5% by weight or less, and
more preferably 2% by weight or less. At a concentration of the
compound of less than the lower limit of this range, in the case of
using this nonaqueous electrolytic solution for a secondary
battery, the nonaqueous electrolyte secondary battery does not have
sufficiently improved characteristics, in some cases. A
concentration of the compound exceeding the upper limit of this
range can increase reactivity in the nonaqueous electrolytic
solution to deteriorate the battery characteristics of the
nonaqueous electrolyte secondary battery.
{Halogen Atom-Containing Cyclic Carbonate}
[0108] The nonaqueous electrolytic solution according to the first
aspect may further contain a halogen atom-containing cyclic
carbonate.
[0109] An example of the halogen atom-containing cyclic carbonate
is a cyclic carbonate in which a halogen atom is bonded to either
or both of the main skeleton and a hydrocarbon group linked to the
cyclic carbonate.
[0110] Specific examples of the cyclic carbonate include
five-membered cyclic carbonates, six-membered cyclic carbonates,
and seven-membered cyclic carbonates.
[0111] Examples of the hydrocarbon group linked to the cyclic
carbonate include hydrocarbon groups exemplified as the hydrocarbon
groups of R.sup.1 to R.sup.3 of unsaturated nitrile dicyano
compound (3) described above.
[0112] Specific examples of the halogen atom in the halogen
atom-containing cyclic carbonate include a fluorine atom, a
chlorine atom, a bromine atom, and an iodine atom. Among these, a
fluorine atom and a chlorine atom are preferred. A fluorine atom is
particularly preferred. The number of halogen atoms of the halogen
atom-containing cyclic carbonate is not particularly limited as
long as the number of halogen atoms is 1 or more. The number of
halogen atoms is usually 6 or less and preferably 4 or less. In the
case where the halogen atom-containing cyclic carbonate has a
plurality of halogen atoms, they may be the same or different.
SPECIFIC EXAMPLES
[0113] Specific examples of the halogen atom-containing cyclic
carbonate include fluoroethylene carbonate, chloroethylene
carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene
carbonate, 4,4-dichloroethylene carbonate, 4,5-dichloroethylene
carbonate, 4-fluoro-4-methylethylene carbonate,
4-chloro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylene
carbonate, 4,5-dichloro-4-methylethylene carbonate,
4-fluoro-5-methylethylene carbonate, 4-chloro-5-methylethylene
carbonate, 4,4-difluoro-5-methylethylene carbonate,
4,4-dichloro-5-methylethylene carbonate, 4-(fluoromethyl)-ethylene
carbonate, 4-(chloromethyl)-ethylene carbonate,
4-(difluoromethyl)-ethylene carbonate, 4-(dichloromethyl)-ethylene
carbonate, 4-(trifluoromethyl)-ethylene carbonate,
4-(trichloromethyl)-ethylene carbonate,
4-(fluoromethyl)-4-fluoroethylene carbonate,
4-(chloromethyl)-4-chloroethylene carbonate,
4-(fluoromethyl)-5-fluoroethylene carbonate,
4-(chloromethyl)-5-chloroethylene carbonate,
4-fluoro-4,5-dimethylethylene carbonate,
4-chloro-4,5-dimethylethylene carbonate,
4,5-difluoro-4,5-dimethylethylene carbonate,
4,5-dichloro-4,5-dimethylethylene carbonate,
4,4-difluoro-5,5-dimethylethylene carbonate,
4,4-dichloro-5,5-dimethylethylene carbonate, and
fluorotrifluoromethylethylene carbonate.
PREFERRED EXAMPLE
[0114] Among these halogen atom-containing cyclic carbonates,
fluorine atom-containing cyclic carbonate derivatives are
preferred. In particular, fluoroethylene carbonate,
4-(fluoromethyl)-ethylene carbonate, 4-(trifluoromethyl)-ethylene
carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene
carbonate, 4-(fluoromethyl)-4-fluoroethylene carbonate, and
fluorotrifluoromethylethylene carbonate are more preferably used
because they form interface-protecting films.
[0115] A method for producing the halogen atom-containing cyclic
carbonate is not particularly limited. Any known method can be
selected to produce it.
[0116] A single type of halogen atom-containing cyclic carbonate
may be used alone. Alternatively, two or more types of halogen
atom-containing cyclic carbonates may be used in combination as a
mixture.
[0117] The halogen atom-containing cyclic carbonate provides
different functions in response to its concentration in an
electrolytic solution. That is, in the case where the halogen
atom-containing cyclic carbonate is used as an additive at a
concentration of 0.001% by weight to 10% by weight with respect to
the total weight of a nonaqueous electrolytic solution, the halogen
atom-containing cyclic carbonate is decomposed on a surface of a
negative electrode to form a negative-electrode-surface-protecting
film in the same way as in a carbon-carbon unsaturated cyclic
carbonate described below. Meanwhile, in the case where the halogen
atom-containing cyclic carbonate is used as a solvent at a
concentration of 10% by weight to 70% by weight, the halogen
atom-containing cyclic carbonate has not only the function as the
additive described above but also the function of improving the
oxidation resistance of the nonaqueous electrolytic solution.
[0118] In the case where the halogen atom-containing cyclic
carbonate is used as an additive, the concentration of the halogen
atom-containing cyclic carbonate is usually 0.001% by weight or
more and preferably 0.01% by weight or more and usually 10% by
weight or less, preferably 8% by weight or less, and more
preferably 5% by weight or less with respect to the total weight of
a nonaqueous electrolytic solution. At an excessively low
proportion thereof, in some cases, the film is not sufficiently
formed by reductive decomposition on the negative electrode, so
that battery characteristics may not be sufficiently provided.
[0119] In the case where the halogen atom-containing cyclic
carbonate is used as a solvent, the concentration of the halogen
atom-containing cyclic carbonate is usually 10% by weight or more,
preferably 12% by weight or more, more preferably 15% by weight or
more, still more preferably 20% by weight or more, and usually 70%
by weight or less, preferably 60% by weight or less, and more
preferably 50% by weight or less with respect to the total weight
of a nonaqueous electrolytic solution. A concentration of less than
the lower limit described above can result in insufficient
suppression of the oxidative decomposition of other components,
constituting a nonaqueous electrolytic solution, on a surface of a
positive electrode, so that the effect of the present invention may
not be provided. Meanwhile, a concentration exceeding the upper
limit described above can result in an increase in the viscosity of
an electrolytic solution, thereby deteriorating various battery
characteristics.
[0120] The halogen atom-containing cyclic carbonate can be used as
a mixture obtained by mixing the halogen atom-containing cyclic
carbonate and a nonaqueous solvent described below in a desired
ratio. Examples of a combination of components constituting the
mixture are described below.
[0121] That is, examples thereof include a halogen atom-containing
cyclic carbonate and a halogen atom-free cyclic carbonate; a
halogen atom-containing cyclic carbonate and a chain carbonate; a
halogen atom-containing cyclic carbonate and a cyclic ether; a
halogen atom-containing cyclic carbonate and a chain ether; a
halogen atom-containing cyclic carbonate and a
phosphorus-containing organic solvent; a halogen atom-containing
cyclic carbonate, a halogen atom-free cyclic carbonate, and a chain
carbonate; a halogen atom-containing cyclic carbonate, a halogen
atom-free cyclic carbonate, and a cyclic carbonate; a halogen
atom-containing cyclic carbonate, a halogen atom-free cyclic
carbonate, a cyclic carbonate, and a chain carbonate; a halogen
atom-containing cyclic carbonate, a halogen atom-free cyclic
carbonate, a cyclic ether, and a chain carbonate; and a halogen
atom-containing cyclic carbonate, a halogen atom-free cyclic
carbonate, a phosphorus-containing organic solvent, and a chain
carbonate.
{Cyclic Carbonate Having Carbon-Carbon Unsaturated Bond}
[0122] The nonaqueous electrolytic solution according to the first
aspect may further contain a cyclic carbonate having a
carbon-carbon unsaturated bond.
[0123] Examples of the cyclic carbonate having a carbon-carbon
unsaturated bond include vinylene carbonate-based compounds, vinyl
ethylene carbonate-based compounds, and methylene ethylene
carbonate-based compounds.
[0124] Examples of methylene ethylene carbonate-based compounds
include methylene ethylene carbonate, 4,4-dimethyl-5-methylene
ethylene carbonate, and 4,4-diethyl-5-methylene ethylene
carbonate.
PREFERRED EXAMPLE
[0125] Preferred examples of the cyclic carbonate having a
carbon-carbon unsaturated bond include vinylene carbonate,
methylvinylene carbonate, ethylvinylene carbonate,
4,5-dimethylvinylene carbonate, 4,5-diethylvinylene carbonate,
fluorovinylene carbonate, trifluoromethylvinylene carbonate,
4-vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate,
4-ethyl-4-vinylethylene carbonate, 4-n-propyl-4-vinylethylene
carbonate, 5-methyl-4-vinylethylene carbonate, 4,4-divinylethylene
carbonate, and 4,5-divinylethylene carbonate.
[0126] Among these cyclic carbonates having carbon-carbon
unsaturated bonds, vinylene carbonate, 4-methylvinylene carbonate,
4,5-dimethylvinylene carbonate, 4-vinylethylene carbonate, and
5-methyl-4-vinylethylene carbonate are preferred. Vinylene
carbonate and 4-vinylethylene carbonate are more preferred.
[0127] The cyclic carbonates having carbon-carbon unsaturated bonds
may be used separately or in combination as a mixture.
[0128] A cyclic carbonate having both of an unsaturated bond and a
halogen atom (appropriately referred to as a "halogenated
unsaturated cyclic carbonate") is not particularly limited. Any
halogenated unsaturated cyclic carbonate may be used unless the
effect of the present invention is significantly impaired.
[0129] Examples of the halogenated unsaturated cyclic carbonate
include vinylene carbonate derivatives; and ethylene carbonate
derivatives substituted with substituent groups each having an
aromatic ring or a carbon-carbon unsaturated bond.
[0130] Specific examples of vinylene carbonate derivatives include
fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate,
4-fluoro-5-phenylvinylene carbonate, chlorovinylene carbonate,
4-chloro-5-methylvinylene carbonate, and 4-chloro-5-phenylvinylene
carbonate.
[0131] Specific examples of the ethylene carbonate derivatives
substituted with substituent groups each having an aromatic ring or
a carbon-carbon unsaturated bond include 4-fluoro-4-vinylethylene
carbonate, 4-fluoro-5-vinylethylene carbonate,
4,4-difluoro-5-vinylethylene carbonate,
4,5-difluoro-4-vinylethylene carbonate, 4-chloro-5-vinylethylene
carbonate, 4,4-dichloro-5-vinylethylene carbonate,
4,5-dichloro-4-vinylethylene carbonate,
4-fluoro-4,5-divinylethylene carbonate,
4,5-difluoro-4,5-divinylethylene carbonate,
4-chloro-4,5-divinylethylene carbonate,
4,5-dichloro-4,5-divinylethylene carbonate,
4-fluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene
carbonate, 4,4-difluoro-5-phenylethylene carbonate,
4,5-difluoro-4-phenylethylene carbonate, 4-chloro-4-phenylethylene
carbonate, 4-chloro-5-phenylethylene carbonate,
4,4-dichloro-5-phenylethylene carbonate,
4,5-dichloro-4-phenylethylene carbonate,
4,5-difluoro-4,5-diphenylethylene carbonate, and
4,5-dichloro-4,5-diphenylethylene carbonate.
[0132] With respect to the foregoing halogen atom-containing cyclic
carbonate and the foregoing cyclic carbonate having a carbon-carbon
unsaturated bond, a single type or two or more types of one of the
cyclic carbonates may be used. Alternatively, a single type or two
or more types of each of the cyclic carbonates may be used in
combination. In the case where one of the halogen atom-containing
cyclic carbonate and the cyclic carbonate having a carbon-carbon
unsaturated bond is used, the halogen atom-containing cyclic
carbonate is preferably contained from the viewpoint of improving
the oxidation resistance of a nonaqueous electrolytic solution to
suppress a deterioration in battery characteristics. Furthermore,
in the case where any two or more types of cyclic carbonates are
combined in any proportion, a film formed on a surface of a
negative electrode has complex characteristics, which is more
preferred.
[0133] In the case where the nonaqueous electrolytic solution
according to the first aspect contains a cyclic carbonate having a
carbon-carbon unsaturated bond, the proportion of the cyclic
carbonate having a carbon-carbon unsaturated bond is usually 0.001%
by weight or more and preferably 0.01% by weight, and usually 10%
by weight or less and preferably 5% by weight or less with respect
to the total weight of the nonaqueous electrolytic solution. At an
excessively low proportion thereof, in some cases, a film is not
sufficiently formed by reductive decomposition on the negative
electrode, so that battery characteristics may not be sufficiently
provided. Meanwhile, an excessively high proportion thereof may
lead to gas generation due to the oxidative decomposition of an
excess of the carbonate and a deterioration in battery
characteristics.
[0134] In the case where the nonaqueous electrolytic solution
according to the first aspect contains both of the halogen
atom-containing cyclic carbonate and the cyclic carbonate having a
carbon-carbon unsaturated bond, the proportion of the halogen
atom-containing cyclic carbonate is usually 0.001% by weight or
more and preferably 0.01% by weight or more and usually 0.1% by
weight or less and preferably 70% by weight or less with respect to
the total weight of the nonaqueous electrolytic solution, the
proportion of the cyclic carbonate having a carbon-carbon
unsaturated bond is usually 0.001% by weight or more and preferably
0.01% by weight or more and usually 10% by weight or less and
preferably 5% by weight or less with respect to the total weight of
the nonaqueous electrolytic solution, and the total proportion of
these components is usually 0.002% by weight or more and preferably
0.01% by weight or more and usually 80% by weight or less and
preferably 70% by weight or less with respect to the total weight
of the nonaqueous electrolytic solution.
{Monofluorophosphate and Difluorophosphate}
[0135] The nonaqueous electrolytic solution according to the first
aspect may further contain a monofluorophosphate and/or a
difluorophosphate.
[0136] The type of monofluorophosphate and/or difluorophosphate
used in the present invention is not particularly limited as long
as it is constituted by a cation and one or more
monofluorophosphate ions and/or one or more difluorophosphate ions.
The type monofluorophosphate and/or difluorophosphate needs to be
selected in consideration of the fact that an ultimately produced
nonaqueous electrolytic solution needs to be useful as an
electrolytic solution of a nonaqueous electrolyte secondary
battery.
[0137] Thus, preferably, each of the monofluorophosphate and the
difluorophosphate in the present invention is a salt of one or more
ions of a metal (hereinafter, also referred to as a "salt-forming
metal") selected from the elements in groups 1, 2, and 13 of the
periodic table or a quaternary onium ion and one or more
monofluorophosphate ions or one or more difluorophosphate ions. A
single type of monofluorophosphate and/or difluorophosphate may be
used. Alternatively, two or more types of monofluorophosphate
and/or difluorophosphate may be used in combination.
<Metal Monofluorophosphate and Metal Difluorophosphate>
[0138] In the case where the monofluorophosphate and the
difluorophosphate of the present invention are a salt of a
salt-forming metal ion and a monofluorophosphate ion (hereinafter,
the salt being also referred to as a "metal monofluorophosphate")
and a salt of a salt-forming metal ion and a difluorophosphate ion
(hereinafter, the salt being also referred to as a "metal
difluorophosphate"), respectively, among the salt-forming metals
constituting the metal monofluorophosphate and the metal
difluorophosphate, examples of the metals in group 1 of the
periodic table include lithium, sodium, potassium, and cesium.
Among these metals, lithium or sodium is preferred. Lithium is
particularly preferred.
[0139] Specific examples of the metals in group 2 of the periodic
table include magnesium, calcium, strontium, and barium. Among
these metals, magnesium or calcium is preferred. Magnesium is
particularly preferred.
[0140] Specific examples of the metals in group 13 of the periodic
table include aluminum, gallium, indium, and thallium. Among these
metals, aluminum or gallium is preferred. Aluminum is particularly
preferred.
[0141] The number of atoms of the salt-forming metal present in one
molecule of each of the metal monofluorophosphate and the metal
difluorophosphate of the present invention is not limited. Only one
atom may be present. Alternatively, two or more atoms may be
present.
[0142] In the case where each of the metal monofluorophosphate and
the metal difluorophosphate of the present invention contains two
or more atoms of the salt-forming metal in one molecule, the types
of these salt-forming metal atoms may be the same or different.
Furthermore, one or two or more metal atoms other than the
salt-forming metal may be contained.
[0143] Specific examples of the metal monofluorophosphate and the
metal difluorophosphate include Li.sub.2PO.sub.3F,
Na.sub.2PO.sub.3F, MgPO.sub.3F, CaPO.sub.3F,
Al.sub.2(PO.sub.3F).sub.2, Ga.sub.2(PO.sub.3F).sub.3,
LiPO.sub.2F.sub.2, NaPO.sub.2F.sub.2, Mg (PO.sub.2F.sub.2).sub.2,
Ca(PO.sub.2F.sub.2).sub.2, Al(PO.sub.2F.sub.2).sub.3, and
Ga(PO.sub.2F.sub.2).sub.3. Among these compounds,
Li.sub.2PO.sub.3F, LiPO.sub.2F.sub.2, Na.sub.2PO.sub.22F, Mg
(PO.sub.2F.sub.2).sub.2, and the like are preferred from the
viewpoints of easy availability and battery characteristics
provided.
<Monofluorophosphate Quaternary Onium Salt and Difluorophosphate
Quaternary Onium Salt>
[0144] In the case where the monofluorophosphate and the
difluorophosphate of the present invention are a salt of a
quaternary onium ion and a monofluorophosphate ion (hereinafter,
the salt being also referred to as a "monofluorophosphate
quaternary onium salt") and a salt of a quaternary onium ion and a
difluorophosphate ion (hereinafter, the salt being also referred to
as a "difluorophosphate quaternary onium salt"), the quaternary
onium ions constituting the monofluorophosphate quaternary onium
salt and the difluorophosphate quaternary onium salt are usually
cations. Specific examples thereof include cations represented by
general formula (4) described below.
##STR00006##
wherein in general formula (4), R.sup.11 to R.sup.14 each
independently represent an optionally substituted hydrocarbon
group; and Q represents an atom in group 15 of the periodic
table.
[0145] In the general formula (4), the type of each of R.sup.11 to
R.sup.14 is not limited. Each of R.sup.11 to R.sup.14 may represent
an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a
group in which both groups are linked. The aliphatic hydrocarbon
group may have a chain structure, a cyclic structure, or a
structure in which a linear moiety is linked to a cyclic moiety. In
the case of the chain structure, a linear or branched structure may
be used. Furthermore, each of R.sup.11 to R.sup.14 may be a
saturated hydrocarbon group or may have an unsaturated bond.
[0146] Examples of the hydrocarbon group of each of R.sup.11 to
R.sup.14 include alkyl groups, cycloalkyl groups, aryl groups, and
aralkyl groups.
[0147] Specific examples of alkyl groups include a methyl group, an
ethyl group, a 1-propyl group, a 1-methylethyl group, a 1-butyl
group, a 1-methylpropyl group, a 2-methylproplyl group, and a
1,1-dimethylethyl group. Among these, a methyl group, an ethyl
group, a 1-propyl group, a 1-butyl group, and the like are
preferred.
[0148] Specific examples of cycloalkyl groups include a cyclopentyl
group, a 2-methylcyclopentyl group, a 3-methylcyclopentyl group, a
2,2-dimethylcyclopentyl group, a 2,3-dimethylcyclopentyl group, a
2,4-dimethylcyclopentyl group, a 2,5-dimethylcyclopentyl group, a
3,3-dimethylcyclopentyl group, a 3,4-dimethylcyclopentyl group, a
2-ethylcyclopentyl group, a 3-ethylcyclopentyl group, a cyclohexyl
group, a 2-methylcyclohexyl group, a 3-methylcyclohexyl group, a
4-methylcyclohexyl group, a 2,2-dimethylcyclohexyl group, a
2,3-dimethylcyclohexyl group, a 2,4-dimethylcyclohexyl group, a
2,5-dimethylcyclohexyl group, a 2,6-dimethylcyclohexyl group, a
3,4-dimethylcyclohexyl group, a 3,5-dimethylcyclohexyl group, a
2-ethylcyclohexyl group, a 3-ethylcyclohexyl group, a
4-ethylcyclohexyl group, a bicyclo[3.2.1]octan-1-yl group, and a
bicyclo[3.2.1]octan-2-yl group. Among these, a cyclopentyl group, a
2-methylcyclopentyl group, a 3-methylcyclopentyl group, a
cyclohexyl group, a 2-methylcyclohexyl group, a 3-methylcyclohexyl
group, and a 4-methylcyclohexyl group are preferred.
[0149] Specific examples of aryl groups include a phenyl group, a
2-methylphenyl group, a 3-methylphenyl group, a 4-methylphenyl
group, and a 2,3-dimethylphenyl group. Among these, a phenyl group
is preferred.
[0150] Specific examples of aralkyl groups include a phenylmethyl
group, a 1-phenylethyl group, a 2-phenylethyl group, a
diphenylmethyl group, and a triphenylmethyl group. Among these, a
phenylmethyl group and a 2-phenylethyl group are preferred.
[0151] The hydrocarbon group of each of R.sup.11 to R.sup.14 may be
substituted with one or two or more substituents. The type of
substituent is not limited unless the effect of the present
invention is significantly impaired. Examples of the substituent
include a halogen atom, a hydroxy group, an amino group, a nitro
group, a cyano group, a carboxy group, an ether group, and an
aldehyde group. In the case where each of R.sup.11 to R.sup.14 has
two or more substituents, these substituents may be the same or
different.
[0152] When any two or more hydrocarbon groups of R.sup.11 to
R.sup.14 are compared with one another, the hydrocarbon groups may
be the same or different. In the case where the hydrocarbon groups
of R.sup.11 to R.sup.14 have substituents, the hydrocarbon groups
including the substituents may be the same or different.
[0153] Furthermore, any two or more hydrocarbon groups of R.sup.11
to R.sup.14 or any two or more their substituents may be bonded
together to form a cyclic structure.
[0154] The number of carbon atoms in the hydrocarbon group of each
of R.sup.11 to R.sup.14 is usually 1 or more, and usually 20 or
less, preferably 10 or less, and more preferably 5 or less. An
excessively large hydrocarbon group having a large number of carbon
atoms reduces the number of moles per weight and is liable to cause
the deterioration of various effects. In the case where the
hydrocarbon group of each of R.sup.11 to R.sup.14 has a
substituent, the number of carbon atoms in the hydrocarbon group
including the substituent needs to satisfy the above range.
[0155] In general formula (4), Q represents an atom that belongs to
group 15 of the periodic table and preferably represents a nitrogen
atom or a phosphorus atom.
[0156] Preferred examples of the quaternary onium salt represented
by general formula (4) described above include aliphatic chain
quaternary salts, aliphatic cyclic ammonium, aliphatic cyclic
phosphonium, and nitrogen-containing heteroaromatic cations.
[0157] Among the aliphatic chain quaternary salts,
tetraalkylammonium, tetraalkylphosphonium, and the like are
particularly preferred.
[0158] Specific examples of tetraalkylammonium include
tetramethylammonium, ethyltrimethylammonium,
diethyldimethylammonium, triethylmethylammonium,
tetraethylammonium, and tetra-n-butylammonium.
[0159] Specific examples of tetraalkylphosphonium include
tetramethylphosphonium, ethyltrimethylphosphonium,
diethyldimethylphosphonium, triethylmethylphosphonium,
tetraethylphosphonium, and tetra-n-butylphosphonium.
[0160] As aliphatic cyclic ammonium, pyrrolidiniums, morpholiniums,
imidazoliniums, tetrahydropyrimidiniums, piperaziniums, and
piperidiniums are particularly preferred.
[0161] Specific examples of pyrrolidiniums include
N,N-dimethylpyrrolidinium, N-ethyl-N-methylpyrrolidinium, and
N,N-diethylpyrrolidinium.
[0162] Specific examples of morpholiniums include
N,N-dimethylmorpholinium, N-ethyl-N-methylmorpholinium, and
N,N-diethylmorpholinium.
[0163] Specific examples of imidazoliniums include
N,N'-dimethylimidazolinium, N-ethyl-N'-methylimidazolinium,
N,N'-diethylimidazolinium, and 1,2,3-trimethylimidazolinium.
[0164] Specific examples of tetrahydropyrimidiniums include
N,N'-dimethyltetrahydropyrimidinium,
N-ethyl-N'-methyltetrahydropyrimidinium,
N,N'-diethyltetrahydropyrimidinium, and
1,2,3-trimethyltetrahydropyrimidinium.
[0165] Specific examples of piperaziniums include
N,N,N',N'-tetramethylpiperazinium,
N-ethyl-N,N',N'-trimethylpiperazipium,
N,N-diethyl-N',N'-dimethylpiperazinium,
N,N,N'-triethyl-N'-methylpiperazinium, and
N,N,N',N'-tetraethylpiperazinium.
[0166] Specific examples of piperidiniums include
N,N-dimethylpiperidinium, N-ethyl-N-methylpiperidinium, and
N,N-diethylpiperidinium.
[0167] Among nitrogen-containing heteroaromatic cations,
pyridiniums, imidazoliums, and the like are particularly
preferred.
[0168] Specific examples of pyridiniums include N-methylpyridinium,
N-ethylpyridinium, 1,2-dimethylpyridinium, 1,3-dimethylpyridinium,
1,4-dimethylpyridinium, and 1-ethyl-2-methylpyridinium.
[0169] Specific examples of imidazoliums include
N,N'-dimethylimidazolium, N-ethyl-N'-methylimidazolium,
N,N'-diethylimidazolium, and 1,2,3-trimethylimidazolium.
[0170] Salts of the quaternary onium ions and the
monofluorophosphate ions and salts of the quaternary onium ions and
the difluorophosphate ions exemplified above are preferred examples
of the monofluorophosphate onium salt and the difluorophosphate
quaternary onium salt of the present invention.
[0171] In the nonaqueous electrolytic solution according to the
first aspect, a single type of monofluorophosphate or
difluorophosphate may be used alone. Alternatively, any two or more
types of monofluorophosphate and/or difluorophosphate may be
combined in any proportion. A single type of monofluorophosphate or
difluorophosphate is usually used from the viewpoint of efficiently
operating a secondary battery. In the nonaqueous electrolytic
solution, when the use of a mixture of two or more types of salts
is preferred, a mixture of two or more types of
monofluorophosphates and/or difluorophosphates may be used.
[0172] The molecular weight of each of monofluorophosphate and
difluorophosphate is not limited. Each of monofluorophosphate and
difluorophosphate may have any molecular weight unless the effect
of the present invention is significantly impaired. Each of
monofluorophosphate and difluorophosphate usually has a molecular
weight of 100 or more. The upper limit of the molecular weight is
not particularly limited. In view of reactivity in a reaction, the
upper limit is usually 1,000 or less and preferably 500 or less,
for practical purposes.
[0173] A method for producing each of the monofluorophosphate and
the difluorophosphate is not particularly limited. Any of known
methods can be selected to produce them.
[0174] In the case where the nonaqueous electrolytic solution
according to the first aspect contains the monofluorophosphate
and/or the difluorophosphate, the total proportion of the
monofluorophosphate and/or the difluorophosphate is preferably
0.001% by weight or more, more preferably 0.01% by weight or more,
still more preferably 0.05% by weight or more, and particularly
preferably 0.1% by weight or more with respect to the total amount
of the nonaqueous electrolytic solution. The upper limit of the
total proportion is preferably 5% by weight or less, more
preferably 4% by weight or less, and still more preferably 3% by
weight or less.
[0175] At an excessively low proportion of the monofluorophosphate
and/or the difluorophosphate in the nonaqueous electrolytic
solution, in some cases, a film is not sufficiently formed by the
decomposition of them, so that battery characteristics may not be
sufficiently provided. Meanwhile, an excessively high proportion
thereof may lead to a deterioration in battery characteristics due
to the decomposition of an excess of thereof.
[0176] When a nonaqueous electrolyte secondary battery including a
nonaqueous electrolytic solution containing the monofluorophosphate
and the difluorophosphate is practically produced and then
disassembled to take out the nonaqueous electrolytic solution, the
proportions of the monofluorophosphate and the difluorophosphate in
the resulting nonaqueous electrolytic solution are often
significantly reduced. In the case where at least one type of
monofluorophosphate and/or difluorophosphate can be detected,
albeit at a low level, the nonaqueous electrolytic solution is
assumed to have contained the monofluorophosphate and/or the
difluorophosphate.
[0177] Furthermore, even in the case where a nonaqueous
electrolytic solution obtained by practically producing a
nonaqueous electrolyte secondary battery including the nonaqueous
electrolytic solution containing the monofluorophosphate and the
difluorophosphate and then disassembling the battery to take out
the nonaqueous electrolytic solution does not contain the
monofluorophosphate and/or the difluorophosphate, the
monofluorophosphate and/or the difluorophosphate is often detected
on a positive electrode, a negative electrode, or a separator,
which are other components of the nonaqueous electrolyte secondary
battery. Thus, also in the case where at least one type of
monofluorophosphate and/or difluorophosphate can be detected on at
least one component selected from the positive electrode, the
negative electrode, and the separator, the nonaqueous electrolytic
solution is assumed to have contained the monofluorophosphate
and/or the difluorophosphate.
[0178] The case where the monofluorophosphate and/or the
difluorophosphate is contained in a nonaqueous electrolytic
solution and at least one component selected from a positive
electrode, a negative electrode, and a separator, is also the same
as above.
[0179] The monofluorophosphate and/or the difluorophosphate may be
incorporated in advance in a positive electrode or on a surface of
a positive electrode of a nonaqueous electrolyte secondary battery
produced. In this case, the incorporated monofluorophosphate and/or
difluorophosphate should be partially or completely dissolved in
the nonaqueous electrolytic solution to provide the function.
[0180] Means for incorporating the monofluorophosphate and/or the
difluorophosphate in advance in the positive electrode or on the
surface of the positive electrode is not particularly limited.
Specific examples thereof include a method in which the
monofluorophosphate and/or the difluorophosphate is dissolved in a
slurry prepared in forming a positive electrode described below;
and a method in which an already formed positive electrode is
subjected to application of or impregnation with a solution of the
monofluorophosphate and/or the difluorophosphate dissolved in any
nonaqueous solvent, followed by drying to remove the solvent.
[0181] The monofluorophosphate and/or the difluorophosphate may be
incorporated in a positive electrode or a surface of a positive
electrode from a nonaqueous electrolytic solution containing at
least one type of monofluorophosphate and/or difluorophosphate when
a nonaqueous electrolyte secondary battery is practically produced.
In the case where a nonaqueous electrolyte secondary battery is
produced, a positive electrode is impregnated with a nonaqueous
electrolytic solution; hence, the monofluorophosphate and the
difluorophosphate are often incorporated in the positive electrode
or a surface of the positive electrode. When the
monofluorophosphate and/or the difluorophosphate can be detected,
albeit at a low level, from a positive electrode recovered in
disassembling a battery, a nonaqueous electrolytic solution is
assumed to have contained the monofluorophosphate and/or the
difluorophosphate.
[0182] The monofluorophosphate and/or the difluorophosphate may be
incorporated in advance in a negative electrode or a surface of a
negative electrode of a nonaqueous electrolyte secondary battery
produced. In this case, the incorporated monofluorophosphate and/or
difluorophosphate should be partially or completely dissolved in
the nonaqueous electrolytic solution to provide the function.
[0183] Means for incorporating the monofluorophosphate and/or the
difluorophosphate in advance in the negative electrode or on the
surface of the negative electrode is not particularly limited.
Specific examples thereof include a method in which the
monofluorophosphate and/or the difluorophosphate is dissolved in a
slurry prepared in forming a negative electrode described below;
and a method in which an already formed negative electrode is
subjected to application of or impregnation with a solution of the
monofluorophosphate and/or the difluorophosphate dissolved in any
nonaqueous solvent, followed by drying to remove the solvent.
[0184] The monofluorophosphate and/or the difluorophosphate may be
incorporated in a negative electrode or a surface of a negative
electrode from a nonaqueous electrolytic solution containing at
least one type of monofluorophosphate and/or difluorophosphate when
a nonaqueous electrolyte secondary battery is practically produced.
In the case where a nonaqueous electrolyte secondary battery is
produced, a negative electrode is impregnated with a nonaqueous
electrolytic solution; hence, the monofluorophosphate and/or the
difluorophosphate are often incorporated in the negative electrode
or a surface of the negative electrode. When the
monofluorophosphate and/or the difluorophosphate can be detected,
albeit at a low level, from a negative electrode recovered in
disassembling a battery, a nonaqueous electrolytic solution is
assumed to have contained the monofluorophosphate and/or the
difluorophosphate.
[0185] The monofluorophosphate and/or the difluorophosphate may be
incorporated in advance in a separator or a surface of a separator
of a nonaqueous electrolyte secondary battery produced. In this
case, the incorporated monofluorophosphate and/or difluorophosphate
should be partially or completely dissolved in the nonaqueous
electrolytic solution to provide the function.
[0186] Means for incorporating the monofluorophosphate and/or the
difluorophosphate in advance in the separator or a surface of the
separator is not particularly limited. Specific examples thereof
include a method in which the monofluorophosphate and/or the
difluorophosphate is mixed when a separator is formed; and a method
in which before the formation of a nonaqueous electrolyte secondary
battery, a separator is subjected to application of or impregnation
with a solution of the monofluorophosphate and/or the
difluorophosphate dissolved in any nonaqueous solvent, followed by
drying to remove the solvent.
[0187] The monofluorophosphate and/or the difluorophosphate may be
incorporated in a separator or a surface of a separator from a
nonaqueous electrolytic solution containing the monofluorophosphate
and/or the difluorophosphate when a nonaqueous electrolyte
secondary battery is practically produced. In the case where a
nonaqueous electrolyte secondary battery is produced, a separator
is impregnated with a nonaqueous electrolytic solution; hence, the
monofluorophosphate and/or the difluorophosphate are often
incorporated in the separator or a surface of the separator. When
the monofluorophosphate and/or the difluorophosphate can be
detected, albeit at a low level, from a separator recovered in
disassembling a battery, a nonaqueous electrolytic solution is
assumed to have contained the monofluorophosphate and/or the
difluorophosphate.
[0188] The incorporation of the monofluorophosphate and/or the
difluorophosphate and the halogen atom-containing cyclic carbonate
in a nonaqueous electrolytic solution probably permits improvement
in high-temperature storage characteristics of a nonaqueous
electrolyte secondary battery including the nonaqueous electrolytic
solution. The detailed reason for this is not clear. The present
invention is not limited to the reason. The reason for this is
probably that a satisfactory protective film is formed on a surface
of a negative-electrode active material by the reaction between the
halogen atom-containing cyclic carbonate and the
monofluorophosphate and/or the difluorophosphate in the nonaqueous
electrolytic solution, thereby suppressing a side reaction and
deterioration due to high-temperature storage. Furthermore, the
simultaneous presence of the halogen atom-containing cyclic
carbonate and the monofluorophosphate and/or the difluorophosphate
in the electrolytic solution is believed to contribute to
improvement in characteristics of the protective film.
[0189] In the case where the nonaqueous electrolytic solution
according to the first aspect contains the halogen atom-containing
cyclic carbonate and the monofluorophosphate and/or the
difluorophosphate, the proportion of the monofluorophosphate and/or
the difluorophosphate is usually 0.001% by weight or more and
preferably 0.01% by weight or more and usually 5% by weight or less
and preferably 4% by weight or less with respect to the total
weight of the nonaqueous electrolytic solution, the proportion of
the halogen atom-containing cyclic carbonate usually 0.001% by
weight or more and preferably 0.01% by weight or more and usually
70% by weight or less with respect to the total weight of the
nonaqueous electrolytic solution, and the total proportion of these
components is usually 0.002% by weight or more and preferably 0.01%
by weight or more and usually 75% by weight or less and preferably
70% by weight or less with respect to the total weight of the
nonaqueous electrolytic solution.
{Nonaqueous Solvent}
[0190] With respect to a nonaqueous solvent the nonaqueous
electrolytic solution according to the first embodiment, any known
solvent for use in a nonaqueous electrolytic solution may be used.
Usually, an organic solvent is used. Examples of the organic
solvent include chain and cyclic carbonates, chain and cyclic
carboxylates, chain and cyclic ethers, and phosphorus-containing
organic solvents.
[0191] Examples of cyclic carbonate include alkylene carbonates
with alkylene groups each having 2 to 4 carbon atoms, e.g.,
ethylene carbonate, propylene carbonate, butylene carbonate,
fluoroethylene carbonate, difluoroethylene carbonate, and
trifluoromethylethylene carbonate. Among these, ethylene carbonate,
propylene carbonate, and fluoroethylene carbonate are preferred. In
particular, propylene carbonate has high reactivity at the
interface between a negative electrode and an electrolytic
solution. Thus, it is difficult to use propylene carbonate for a
battery, in some cases. In a nonaqueous electrolytic solution of
the present invention, however, propylene carbonate can be suitably
used because the reactivity at the interface between the negative
electrode and the electrolytic solution.
[0192] Examples of chain carbonate include dialkyl carbonates with
alkyl groups each having 1 to 4 carbon atoms, e.g., dimethyl
carbonate, diethyl carbonate, di-n-propyl carbonate, ethylmethyl
carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate;
and dialkyl carbonates with alkyl groups each having 1 to 4 carbon
atoms and having hydrogen atoms partially or completely substituted
with fluorine atoms, e.g., bis(fluoromethyl) carbonate,
bis(difluoromethyl) carbonate, bis(trifluoromethyl) carbonate,
bis(2-fluoroethyl) carbonate, bis(2,2-difluoroethyl) carbonate,
bis(2,2,2-trifluoroethyl) carbonate, fluoromethylmethyl carbonate,
difluoromethylmethyl carbonate, trifluoromethylmethyl carbonate,
2-fluoroethylmethyl carbonate, 2,2-difluoroethylmethyl carbonate,
2,2,2-trifluoroethylmethyl carbonate, fluoromethylethyl carbonate,
difluoromethylethyl carbonate, trifluoromethylethyl carbonate,
2-fluoroethylethyl carbonate, 2,2-difluoroethylethyl carbonate, and
2,2,2-trifluoroethylethyl carbonate. Among these, dimethyl
carbonate, diethyl carbonate, and ethylmethyl carbonate are
preferred.
[0193] Examples of cyclic carboxylates include
.gamma.-butyrolactone and .gamma.-valerolactone.
[0194] Examples of chain carboxylates include methyl acetate, ethyl
acetate, methyl propionate, ethyl propionate, and methyl
butyrate.
[0195] Examples of cyclic ethers include tetrahydrofuran and
2-methyltetrahydrofuran.
[0196] Examples of chain ethers include diethoxyethane,
dimethoxyethane, and dimethoxymethane.
[0197] Examples of phosphorus-containing organic solvents include
trimethyl phosphate, triethyl phosphate, dimethylethyl phosphate,
methyldiethyl phosphate, ethylenemethyl phosphate, and
ethyleneethyl phosphate.
[0198] These nonaqueous solvents may be used alone. Alternatively,
any two or more nonaqueous solvents may be combined in any
proportions. Two or more compounds are preferably used in
combination. For example, a high-dielectric solvent, e.g., cyclic
carbonate or cyclic carboxylate, and a low-viscosity solvent, e.g.,
chain carbonate or chain carboxylate, are preferably used in
combination.
[0199] In the case of using a chain carboxylate as a nonaqueous
solvent, the proportion of the chain carboxylate in the nonaqueous
solvent is usually 50% by weight or less, preferably 30% by weight
or less, and more preferably 20% by weight or less. A proportion
exceeding the upper limit may result in a reduction in
conductivity. Note that the chain carboxylate is not an essential
component of the nonaqueous solvent. The nonaqueous solvent may not
contain the chain carboxylate.
[0200] In the case of using a cyclic carboxylate as a nonaqueous
solvent, the proportion of the cyclic carboxylate in the nonaqueous
solvent is usually 60% by weight or less, preferably 55% by weight
or less, and more preferably 50% by weight or less. A proportion
exceeding the upper limit may result in a reduction in flowability
or a deterioration in output characteristics at a low temperature.
Note that the cyclic carboxylate is not an essential component of
the nonaqueous solvent. The nonaqueous solvent may not contain the
cyclic carboxylate.
[0201] Furthermore, in the case of using a chain ether as a
nonaqueous solvent, the proportion of the chain ether in the
nonaqueous solvent is usually 60% by weight or less, preferably 40%
by weight or less, and more preferably 30% by weight or less. A
proportion exceeding the upper limit may result in a reduction in
conductivity. Note that the chain ether is not an essential
component of the nonaqueous solvent. The nonaqueous solvent may not
contain the chain ether.
[0202] Furthermore, in the case of using a cyclic ether as a
nonaqueous solvent, the proportion of the cyclic ether in the
nonaqueous solvent is usually 60% by weight or less, preferably 50%
by weight or less, and more preferably 40% by weight or less. A
proportion exceeding the upper limit may result in a deterioration
in storage characteristics. Note that the cyclic ether is not an
essential component of the nonaqueous solvent. The nonaqueous
solvent may not contain the cyclic ether.
[0203] A preferred example of the nonaqueous solvent is a
combination of a cyclic carbonate and a chain carbonate, the
carbonates serving as main components. In particular, the total
proportion of the cyclic carbonate and the chain carbonate in the
nonaqueous solvent is usually 85% by weight or more, preferably 90%
by weight or more, and more preferably 95% by weight or more, and
the volume ratio of the cyclic carbonate to the chain carbonate is
5:95 or more, preferably 10:90 or more, and more preferably 15:85
or more, and usually 45:55 or less and preferably 40:60 or less.
The use of a nonaqueous electrolytic solution containing a lithium
salt and an additive characteristic of the present invention, in
particular, unsaturated nitrile compound (1) or unsaturated nitrile
compound (2) described below and/or the compound having 2 to 4
cyano groups in its structural formula, in this mixed solvents
achieves a good balance among cycle characteristics, large-current
discharge characteristics, and the suppression of gas generation
and is thus preferred.
[0204] Examples of a preferred combination of the cyclic carbonate
and the chain carbonate include combinations of ethylene carbonate
and dialkyl carbonates. Specific examples of the combination
include ethylene carbonate and dimethyl carbonate; ethylene
carbonate and diethyl carbonate; ethylene carbonate and ethylmethyl
carbonate; ethylene carbonate, dimethyl carbonate, and diethyl
carbonate; ethylene carbonate, dimethyl carbonate, and ethylmethyl
carbonate; ethylene carbonate, diethyl carbonate, and ethylmethyl
carbonate; and ethylene carbonate, dimethyl carbonate, diethyl
carbonate, and ethylmethyl carbonate.
[0205] Combinations of propylene carbonate, ethylene carbonate, and
dialkyl carbonates are also preferred. In this case, the volume
ratio of ethylene carbonate to propylene carbonate is usually 99:1
or less and preferably 95:5 or less and usually 1:99 or more and
preferably 20:80 or more.
[0206] Furthermore, combinations of propylene carbonate and the
foregoing dialkyl carbonates are preferred.
[0207] Another preferred example of the nonaqueous solvent is a
nonaqueous solvent containing 50% by weight or more of an organic
solvent selected from ethylene carbonate, propylene carbonate, the
halogen atom-containing cyclic carbonate, .gamma.-butyrolactone,
and .gamma.-valerolactone. A nonaqueous electrolytic solution
containing a lithium salt and an additive characteristic of the
present invention, in particular, unsaturated nitrile compound (1)
or unsaturated nitrile compound (2) described below in this mixed
solvent results in the suppression of evaporation of the solvent
and the suppression of fluid leaks even when the solution is used
at a high temperature.
[0208] In particular, a nonaqueous solvent in which the total
amount of ethylene carbonate and .gamma.-butyrolactone in the
nonaqueous solvent is 70% by weight or more and preferably 80% by
weight or more and in which the volume ratio of ethylene carbonate
to .gamma.-butyrolactone is in the range of 5:95 to 45:55 is
preferred. A nonaqueous solvent in which the total amount of
ethylene carbonate and propylene carbonate in the nonaqueous
solvent is 70% by weight or more and preferably 80 weight or more
and in which the volume ratio of ethylene carbonate to propylene
carbonate is in the range of 30:70 to 80:20 is preferred. The use
of a nonaqueous electrolytic solution containing a lithium salt and
an additive characteristic of the present invention, in particular,
unsaturated nitrile compound (1) or unsaturated nitrile compound
(2) described below and/or the compound having 2 to 4 cyano groups
in its structural formula, in this mixed solvent achieves a good
balance between storage characteristics and the suppression of gas
generation and is thus preferred.
[0209] Moreover, the phosphorus-containing organic solvent is
preferably used as a nonaqueous solvent. The incorporation of the
phosphorus-containing organic solvent in the nonaqueous solvent in
a concentration of usually 10% by weight or more and preferably 10%
to 80% by weight results in a reduction in the flammability of the
resulting electrolytic solution. In particular, the use of the
phosphorus-containing organic solvent in combination with a
nonaqueous solvent selected from ethylene carbonate, propylene
carbonate, the halogen atom-containing cyclic carbonate,
.gamma.-butyrolactone, .gamma.-valerolactone, and dialkyl
carbonates achieves a good balance between cycle characteristics
and large-current discharge characteristics and is thus
preferred.
[0210] In this specification, the volume ratio of the nonaqueous
solvents is measured at 25.degree. C. For a solvent that is in the
form of a solid at 25.degree. C., e.g., ethylene carbonate, a
measurement value at its melting point is used.
{Electrolyte}
[0211] An electrolyte is not particularly limited. Any known
electrolyte can be used as long as it is used as an electrolyte in
a target secondary battery. For nonaqueous electrolyte secondary
batteries, usually, lithium salts can be used as electrolytes.
[0212] Specific examples of the lithium salt include inorganic
lithium salts, such as LiClO.sub.4, LiAsF.sub.6, LiPF.sub.6,
Li.sub.2CO.sub.3, and LiBF.sub.4; fluorine-containing organic
lithium salts, such as LiCF.sub.3SO.sub.3,
LiC.sub.4F.sub.9SO.sub.3, LiN(CF.sub.3SO.sub.2).sub.2,
LiN(C.sub.2F.sub.5SO.sub.2).sub.2, lithium cyclic
1,2-perfluoroethanedisulfonylimide, lithium cyclic
1,3-perfluoropropanedisulfonylimide, LiN(CF.sub.3SO.sub.2)
(C.sub.4F.sub.9SO.sub.2) LiC(CF.sub.3SO.sub.2).sub.3, LiPF.sub.4
(CF.sub.3).sub.2, LiPF.sub.4 (C.sub.2F.sub.5).sub.2,
LiPF.sub.4(CF.sub.3SO.sub.2).sub.2, LiPF.sub.4
(C.sub.2F.sub.5SO.sub.2).sub.2, LiBF.sub.2 (CF.sub.3).sub.2,
LiBF.sub.2 (C.sub.2F.sub.5).sub.2, LiBF.sub.2
(CF.sub.3SO.sub.2).sub.2, LiBF.sub.2
(C.sub.2F.sub.5SO.sub.2).sub.2, LiB (OCOCF.sub.3), LiB
(OCOC.sub.2F.sub.5).sub.4; oxalatophosphate salts, such as lithium
tetrafluoro(oxalato)phosphate, lithium
difluorobis(oxalato)phosphate, and lithium tris(oxalato)phosphate;
oxalatoborate salts, such as lithium bis(oxalato)borate and lithium
difluorooxalatoborate; and sodium salts and potassium salts, such
as KPF.sub.6, NaPF.sub.6, NaBF.sub.4, and Na.sub.2CF.sub.3SO.sub.3.
Among these, LiPF.sub.6, LiBF.sub.4, LiCF.sub.3SO.sub.3,
LiN(CF.sub.3SO.sub.2).sub.2, LiN(C.sub.2F.sub.5SO.sub.2).sub.2 are
preferred. In particular, LiPF.sub.6 or LiBF.sub.4 is
preferred.
[0213] The foregoing lithium salts may be used alone.
Alternatively, any two or more types of lithium salts may be
combined in any proportion. Combinations of two or more types of
inorganic lithium salts or combinations of the inorganic lithium
salts and phosphorus-containing organic lithium salts are preferred
because gas generation is suppressed during continuous charge or
deterioration after high-temperature storage is suppressed. In
particular, a combination of LiPF.sub.6 and LiBF.sub.4 and a
combination of an inorganic lithium salt, e.g., LiPF.sub.6 or
LiBF.sub.4, and a fluorine-containing organic lithium salt, e.g.,
LiCF.sub.3SO.sub.3, LiN(CF.sub.3SO.sub.2).sub.2, or
LiN(C.sub.2F.sub.5SO.sub.2).sub.2, are preferred. In the
combination of LiPF.sub.6 and LiBF.sub.4, preferably, the
proportion of LiBF.sub.4 is usually in the range of 0.01% by weight
to 50% by weight with respect to the total amount of the lithium
salts. In the combination of the inorganic salt, e.g., LiPF.sub.6
or LiBF.sub.4, and the fluorine-containing organic lithium salt,
e.g., LiCF.sub.3SO.sub.3, LiN(CF.sub.3SO.sub.2).sub.2,
LiN(C.sub.2F.sub.5SO.sub.2).sub.2, preferably, the proportion of
the inorganic lithium salt is in the range of usually 70% by weight
to 99% by weight with respect to the total amount of the lithium
salts.
[0214] Furthermore, in the case of a nonaqueous solvent containing
50% by weight or more of .gamma.-butyrolactone, LiBF.sub.4 is
preferably contained in a concentration of 40 mol % or more with
respect to the total amount of the lithium salts. In particular,
more preferably, LiBF.sub.4 is contained in a concentration of 40
mol % to 95 mol % with respect to the total amount of the lithium
salts, and the remainder is composed of a compound selected from
the group consisting of LiPF.sub.6, LiCF.sub.3SO.sub.3,
LiN(CF.sub.3SO.sub.2).sub.2 and
LiN(C.sub.2F.sub.5S.sup.O.sub.2).sub.2.
[0215] The concentration of the lithium salt in a nonaqueous
electrolytic solution is usually 0.5 mol/L or more, preferably 0.6
mol/L or more, and more preferably 0.8 mol/L or more, and usually 3
mol/L or less, preferably 2 mol/L or less, and more preferably 1.5
mol/L or less. An excessively low concentration of the lithium salt
in the nonaqueous electrolytic solution results in the insufficient
electrical conductivity of the electrolytic solution. An
excessively high concentration may result in a deterioration in
battery performance due to an increase in viscosity.
{Additional Additive}
[0216] To improve wettability for a separator described below, the
nonaqueous electrolytic solution according to the first aspect may
further contain one or two or more types of surfactants such as
trioctyl phosphate, perfluoroalkyl group-containing
poly(oxyethylene ether), and perfluorooctane sulfonate in addition
to unsaturated nitrile compound (1) and/or the compound having 2 to
4 cyano groups in its structural formula described above, the
nonaqueous solvent, and the electrolyte. The surfactant content is
preferably in the range of 0.01% to 1% by weight with respect to
the total weight of the nonaqueous electrolytic solution. At a
surfactant content of less than the lower limit, the effect
expected may not be provided. Meanwhile, a surfactant content
exceeding the upper limit may result in a deterioration in battery
characteristics.
[0217] The nonaqueous electrolytic solution may further contain
various overcharge-preventing agents, other film-forming agents,
and additional aids.
[0218] Examples of the overcharge-preventing agents include
aromatic compounds, such as biphenyl, alkylbiphenyl, terphenyl,
partially hydrogenated terphenyl, cyclohexylbenzene,
tert-butylbenzene, tert-amylbenzene, diphenyl ether, and
dibenzofuran; partially fluorinated aromatic compounds described
above, e.g., 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and
p-cyclohexylfluorobenzene; and fluorine-containing anisoles, such
as 2,4-difluoroanisole, 2,5-difluoroanisole, and
2,6-difluoroanisole.
[0219] The overcharge-preventing agents may be used alone.
Alternatively, any two or more types of overcharge-preventing
agents may be combined in any proportion.
[0220] The overcharge-preventing agent is preferably contained in
the nonaqueous electrolytic solution in a concentration of 0.1% to
5% by weight. At an overcharge-preventing agent concentration of
less than the lower limit, the effect expected may not be provided.
Meanwhile, an overcharge-preventing agent concentration exceeding
the upper limit may result in a deterioration in battery
characteristics.
[0221] As other film-forming agents, fluorinated carbonate,
aryl-substituted carbonate, cyclic carboxylic anhydride, sulfonic
acid derivatives, sulfone compounds, and sulfite compounds are
preferably used.
[0222] As aryl-substituted carbonate, for example, 4-phenylethylene
carbonate and methylphenyl carbonate are used.
[0223] As cyclic carboxylic anhydride, for example, succinic
anhydride, maleic anhydride, glutaric anhydride, trimellitic
anhydride, and phthalic anhydride are used.
[0224] As sulfonic acid derivatives, for example, 1,3-propane
sultone, 1,4-butane sultone, 1,3-propen sultone, 1,4-butene
sultone, methyl methanesulfonate, ethyl methanesulfonate,
dimethylmethanesulfonic acid amide are used.
[0225] As sulfone compounds, for example, dimethyl sulfone,
sulfolane, and 3-sulfolene are used.
[0226] As sulfite compounds, for example, ethylene sulfite,
trimethylene sulfite, erythritan sulfite, vinylethylene sulfite,
dimethyl sulfite, ethylmethyl sulfite, and diethyl sulfite are
used.
[0227] These may be used separately or in any combination of two or
more of them in any proportion.
[0228] In the case where the film-forming agent is contained, a
nonaqueous electrolytic solution has a film-forming agent content
of 0.01% by weight or more and preferably 0.1% by weight or more
and 10% by weight or less and preferably 8% by weight or less, so
that a battery has satisfactory capacity retention characteristics
and cycle characteristics.
[0229] Examples of additional aids include carbonate compounds,
such as erythritan carbonate, spiro-bis-dimethylene carbonate, and
methoxyethylmethyl carbonate; carboxylic anhydrides, such as
citraconic anhydride, glutaconic anhydride, itaconic anhydride,
trimellitic anhydride, diglycolic anhydride,
cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic
dianhydride, and phenylsuccinic anhydride; sulfur-containing
compounds, such as 1,3-propane sultone, 1,4-butane sultone, methyl
methanesulfonate, busulfan, and tetramethylthiuram monosulfide,
N,N-dimethylmethanesulfonamide, and N,N-diethylmethanesulfonamide;
nitrogen-containing compounds, such as 1-methyl-2-pyrrolidinone,
1-methyl-2-piperidone, 3-methyl-2-oxazolidinone,
1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide;
hydrocarbon compounds, such as heptane, octane, and cycloheptane;
and fluorine-containing aromatic compounds, such as fluorobenzene,
difluorobenzene, hexafluorobenzene, and benzotrifluoride. These may
be used separately or in any combination of two or more of them in
any proportion.
[0230] In the case where a nonaqueous electrolytic solution
contains these aids, the proportion of the aids is usually in the
range of 0.01% by weight to 10% by weight with respect to the
nonaqueous electrolytic solution. The incorporation of these aids
in a nonaqueous electrolytic solution of the present invention
results in improvement in capacity retention characteristics and
cycle characteristics after high-temperature storage.
{Method for Producing Nonaqueous Electrolytic Solution}
[0231] The nonaqueous electrolytic solution according to the first
aspect can be prepared by dissolving the unsaturated nitrile
compound (1) and/or the compound having 2 to 4 cyano groups in its
structural formula, the electrolyte, and, if necessary, additional
aids into the nonaqueous solvent.
[0232] Components such as the nonaqueous solvent are preferably
dehydrated in advance when the nonaqueous electrolytic solution is
prepared. Specifically, the components are preferably dehydrated so
as to have a water content of usually 50 ppm or less and
particularly 20 ppm or less. Any dehydration method can be
selected. Examples thereof include a method in which a component is
heated under reduced pressure; and a method in which a component is
passed through molecular sieves.
[0233] The nonaqueous electrolytic solution according to the first
aspect may be gelatinized with a genatinizer such as a polymer so
as to have a semi-solid form. The proportion of the nonaqueous
electrolytic solution in the semi-solid electrolyte is usually 30%
by weight or more, preferably 50% by weight or more, and more
preferably 75% by weight or more, and usually 99.95% by weight or
less, preferably 99% by weight or less, and more preferably 98% by
weight or less with respect to the total amount of the semi-solid
electrolyte. An excessively high proportion of the nonaqueous
electrolytic solution results in difficulty in holding the
nonaqueous electrolytic solution, thus readily causing fluid leaks.
In contrast, an excessively low proportion of the nonaqueous
electrolytic solution may result in insufficient charge and
discharge efficiency and capacity.
[Nonaqueous Electrolytic Solution According to Second Aspect]
[0234] A nonaqueous electrolytic solution according to a second
aspect of the present invention always contains a compound general
formula (2) described below (hereinafter, also referred to as
"unsaturated nitrile compound (2)"). To more efficiently suppress
the decomposition of an nonaqueous electrolytic solution on a
surface of a negative electrode, preferably, the nonaqueous
electrolytic solution further contains at least one compound
selected from the group consisting of halogen atom-containing
cyclic carbonate, cyclic carbonate having a carbon-carbon
unsaturated bond, monofluorophosphate, and difluorophosphate.
##STR00007##
[0235] In general formula (2), R.sup.4, R.sup.5, and R.sup.6 each
independently represent a hydrogen atom, a cyano group, or an
optionally halogen atom-substituted hydrocarbon group having 1 to
10 carbon atoms, with the proviso that R.sup.4 and R.sup.5 do not
simultaneously represent hydrogen atoms.
[0236] In the case where at least one of R.sup.4, R.sup.5, and
R.sup.6 in general formula (2) represents a cyano group, examples
thereof include fumaronitrile, 1,1,2-tricyanoethylene, and
tetracyanoethylene.
[0237] In the case where at least one of R.sup.4, R.sup.5, and
R.sup.6 in general formula (2) represents a hydrocarbon group,
examples of the hydrocarbon group are the same as those listed as
the examples of the hydrocarbon groups of R.sup.1 to R.sup.3 in
general formula (1).
[0238] Furthermore, in the case where hydrocarbon groups of
R.sup.4, R.sup.5, and R.sup.6 in general formula (2) are
substituted with halogen atoms, the halogen atom-substituted
hydrocarbon groups are the same as those listed as the examples of
the halogen atom-substituted hydrocarbon groups of R.sup.1 to
R.sup.3 in general formula (1).
[0239] When the compound represented by general formula (2) has a
hydrocarbon group as any one of R.sup.4 to R.sup.6, specific
examples of the compound are described below.
<Specific Example of Compound Having Chain Saturated Hydrocarbon
Group>
[0240] Examples thereof include crotononitrile,
3-methylcrotononitrile, 2-methyl-2-butenenitrile, 2-pentenenitrile,
2-methyl-2-pentenenitrile, 3-methyl-2-pentenenitrile, and
2-hexenenitrile.
<Specific Examples of Compound Having Cyclic Saturated
Hydrocarbon Group>
[0241] Examples thereof include 1-cyano-1-cyclopentene and
1-cyano-1-cyclohexene.
<Specific Examples of Compound Having Unsaturated Hydrocarbon
Group>
[0242] Examples thereof include geranylnitrile and
cinnamonitrile.
<Specific Examples of Compound Having Chain Saturated
Hydrocarbon Group Substituted with Fluorine Atom>
[0243] Examples thereof include 3-fluorocrotononitrile,
4-fluorocrotononitrile, 4,4-difluorocrotononitrile,
4,4,4-trifluorocrotononitrile, 3-(fluoromethyl)crotononitrile,
4-fluoro-3-(fluoromethyl)-2-butenenitrile,
4-fluoro-2-pentenenitrile, and 5-fluoro-2-pentenenitrile.
<Specific Examples of Compound Having Cyclic Saturated
Hydrocarbon Group Substituted with Fluorine Atom>
[0244] Examples thereof include 3-fluoro-1-cyano-1-cyclopentene,
4-fluoro-1-cyano-1-cyclopentene, 5-fluoro-1-cyano-1-cyclopentene,
3-fluoro-1-cyano-1-cyclohexene, 4-fluoro-1-cyano-1-cyclohexene,
5-fluoro-1-cyano-1-cyclohexene, and
6-fluoro-1-cyano-1-cyclohexene.
<Specific Examples of Compound Having Unsaturated Hydrocarbon
Group Substituted with Fluorine Atom>
[0245] Examples thereof include 3-(2-fluorophenyl)propenenitrile,
3-(3-fluorophenyl)propenenitrile, 3-(4-fluorophenyl)propenenitrile,
and 3-fluorogeranylnitrile.
<Preferred Example of Unsaturated Nitrile Compound (2)>
[0246] Among these nitrile compounds exemplified above, the
following compounds are particularly preferred as unsaturated
nitrile compound (2) according to the present invention from the
viewpoint of easy synthesis or from the industrial standpoint.
[0247] Examples thereof include crotononitrile,
3-methylcrotononitrile, 2-methyl-2-butenenitrile, 2-pentenenitrile,
2-methyl-2-pentenenitrile, 1-cyano-1-cyclopentene,
1-cyano-1-cyclohexene, geranylnitrile, cinnamonitrile,
fumaronitrile, and tetracyanoethylene.
[0248] The molecular weight of unsaturated nitrile compound (2) is
not limited. Unsaturated nitrile compound (2) may have any
molecular weight unless the effect of the present invention is
significantly impaired. Unsaturated nitrile compound (2) has a
molecular weight of usually 40 or more and preferably 50 or more.
The upper limit of the molecular weight is not particularly
limited. For practical purposes, the upper limit is usually 400 or
less and preferably 300 or less because an excessively high
molecular weight is liable to cause an increase in the viscosity of
an electrolytic solution.
[0249] A method for producing unsaturated nitrile compound (2) is
not particularly limited. Any of known methods can be selected to
produce it.
[0250] A single type of unsaturated nitrile compound (2) may be
used alone. Alternatively, two or more types of unsaturated nitrile
compounds (2) may be used in combination as a mixture.
[0251] The nonaqueous electrolytic solution according to the first
aspect has an unsaturated nitrile compound (2) content of usually
0.001% by weight or more, preferably 0.01% by weight or more, and
more preferably 0.1% by weight, and usually 10% by weight or less,
preferably 5% by weight, and more preferably 2% by weight with
respect to the total weight of the nonaqueous electrolytic
solution. An unsaturated nitrile compound (2) content of less than
the lower limit described above can result in insufficient
suppression of the decomposition of other components, constituting
the nonaqueous electrolytic solution, on a surface of the
electrode, so that the effect of the present invention may not be
readily provided. Meanwhile, an unsaturated nitrile compound (2)
content exceeding the upper limit described above can result in
excessive progress of the reaction on the electrode surface,
thereby deteriorating various battery characteristics.
[0252] Furthermore, two or more types of unsaturated nitrile
compounds (2) may be used in combination. Also in the case where
the two or more types are used in combination, the total content of
the two or more types of unsaturated nitrile compounds (2) is the
same as above.
[0253] The nonaqueous electrolytic solution according to the second
aspect may contain one or two or more compounds selected from the
group consisting of a halogen atom-containing cyclic carbonate, a
cyclic carbonate having a carbon-carbon unsaturated bond, a
monofluorophosphate, and a difluorophosphate as in the nonaqueous
electrolytic solution according to the first aspect. With respect
to the compounds, specific examples, preferred examples, preferred
proportions in the nonaqueous electrolytic solution, existence
forms, and mechanisms of action are the same as those in the above
description of the first aspect.
[0254] Also for a nonaqueous solvent, an electrolyte, and
additional additives which can be incorporated in the nonaqueous
electrolytic solution according to the second aspect, specific
examples, preferred examples, preferred proportions in the
nonaqueous electrolytic solution, existence forms, and mechanisms
of action are the same as those in the above description of the
first aspect.
[0255] The nonaqueous electrolytic solution according to the second
aspect can be produced by the same method as that for producing the
nonaqueous electrolytic solution according to the first aspect.
[Nonaqueous Electrolytic Solution According to Third Aspect]
[0256] A nonaqueous electrolytic solution according to a third
aspect of the present invention is a nonaqueous electrolytic
solution for use in a nonaqueous electrolyte secondary battery
including a nonaqueous electrolytic solution, a negative electrode,
and a positive electrode, the negative electrode and the positive
electrode being capable of storing and releasing metal ions,
contains an electrolyte and a nonaqueous solvent, and further
contains an unsaturated nitrile compound represented by general
formula (1) (i.e., unsaturated nitrile compound (1)) and at least
one compound selected from the group consisting of halogen
atom-containing cyclic carbonates, monofluorophosphates, and
difluorophosphates.
##STR00008##
[0257] In general formula (1), R.sup.1, R.sup.2, and R.sup.3 each
independently represent a hydrogen atom, a cyano group, or an
optionally halogen atom-substituted hydrocarbon group having 1 to
10 carbon atoms.
[0258] The nonaqueous electrolytic solution is preferably used in a
nonaqueous electrolyte secondary battery including a negative
electrode containing a carbonaceous material serving as an active
material.
[0259] For unsaturated nitrile compound (1), the halogen
atom-containing cyclic carbonate, the monofluorophosphate, and the
difluorophosphate which are contained in the nonaqueous
electrolytic solution according to the third aspect, specific
examples, preferred examples, preferred proportions in the
nonaqueous electrolytic solution, existence forms, and mechanisms
of action are the same as those in the above description of the
first aspect.
[0260] Preferably, the nonaqueous electrolytic solution according
to the third aspect further contains a cyclic carbonate having a
carbon-carbon unsaturated bond as in the nonaqueous electrolytic
solution according to the first aspect because a more stable
interface-protecting film can be formed. In this case, with respect
to the compound, specific examples, preferred examples, preferred
proportions in the nonaqueous electrolytic solution, existence
forms, and mechanisms of action are the same as those in the above
description of the first aspect.
[0261] Also for a nonaqueous solvent, an electrolyte, and
additional additives which can be incorporated in the nonaqueous
electrolytic solution according to the third aspect, specific
examples, preferred examples, preferred proportions in the
nonaqueous electrolytic solution, existence forms, and mechanisms
of action are the same as those in the above description of the
first aspect.
[0262] The nonaqueous electrolytic solution according to the third
aspect can be produced by the same method as that for producing the
nonaqueous electrolytic solution according to the first aspect.
[Nonaqueous Electrolyte Secondary Battery]
[0263] A nonaqueous electrolyte secondary battery of the present
invention includes a negative electrode, a positive electrode, and
the foregoing nonaqueous electrolytic solution of the present
invention, the negative electrode and the positive electrode being
capable of storing and releasing metal ions such as lithium
ions.
[0264] That is, the nonaqueous electrolyte secondary battery of the
present invention is the same as a known nonaqueous electrolyte
secondary battery, except for the nonaqueous electrolytic solution.
The nonaqueous electrolyte secondary battery of the present
invention usually has a structure in which a positive electrode and
a negative electrode are stacked with a porous film (separator)
provided therebetween, the porous film containing the nonaqueous
electrolytic solution of the present invention, and in which these
components are accommodated in a case. Thus, the shape of the
nonaqueous electrolyte secondary battery of the present invention
is not particularly limited and may have a cylindrical shape, an
angular shape, a laminate shape, a coin shape, a large shape, or
the like.
[Positive Electrode]
[0265] Examples of a positive-electrode active material contained
in the secondary battery of the present invention include inorganic
compounds, such as oxides of transition metals, complex oxides of
transition metals and lithium (lithium-transition metal complex
oxides), sulfides of transition metals, and metal oxides, metallic
lithium, lithium alloys, and complexes thereof.
[0266] Specific examples thereof include transition metal oxides,
such as MnO, V.sub.2O.sub.5, V.sub.6O.sub.13, and TiO.sub.2;
lithium-transition metal complex oxides, such as LiCoO.sub.2 and
lithium-cobalt complex oxides each having a basic composition of
LiCoO.sub.2, LiNiO.sub.2 and lithium-nickel complex oxides each
having a basic composition of LiNiO.sub.2, LiMn.sub.2O.sub.4 and
LiMnO.sub.2 and lithium-manganese complex oxides each having a
basic composition of LiMn.sub.2O.sub.4 and LiMnO.sub.2,
lithium-nickel-manganese-cobalt complex oxides, and
lithium-nickel-cobalt-aluminum composite oxides; sulfides of
transition metals, such as TiS and FeS; and metal oxides, such as
SnO.sub.2 and SiO.sub.2.
[0267] Among these, lithium-transition metal complex oxides,
specifically, in particular, LiCoO.sub.2 and lithium-cobalt complex
oxides each having a basic composition of LiCoO.sub.2, LiNiO.sub.2
and lithium-nickel complex oxides each having a basic composition
of LiNiO.sub.2, LiMn.sub.2O.sub.4 and LiMnO.sub.2 and
lithium-manganese complex oxides each having a basic composition of
LiMn.sub.2O.sub.4 and LiMnO.sub.2, lithium-nickel-manganese-cobalt
complex oxides, and lithium-nickel-cobalt-aluminum composite oxides
are preferably used because they can achieve a good balance between
high capacity and high cycle characteristics. Furthermore,
lithium-transition metal complex oxides are preferred because their
structures can be stabilized by partially substituting other
metals, such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga,
and Zr, for cobalt, nickel, and manganese.
[0268] These positive-electrode active materials may be used
separately or in any combination of two or more of them in any
proportion.
[0269] The positive electrode for use in the nonaqueous electrolyte
secondary battery of the present invention can be produced by a
common method. Specific examples of a method for producing the
positive electrode include a method in which a mixture of the
positive-electrode active material, a binder, a conductive
material, and the like is subjected to roll forming to form a sheet
electrode; a method in which compression molding is performed to
form a pellet electrode; a method in which a positive-electrode
active material is applied to a current collector for the positive
electrode (hereinafter, also referred to as a "positive electrode
current collector") to form a positive-electrode active material
layer (application method); and a method in which a thin layer
(positive-electrode active material layer) containing the foregoing
positive-electrode active material is formed on a positive
electrode current collector by evaporation, sputtering, plating, or
the like. Usually, a positive-electrode active material layer is
formed by the application method.
[0270] In the case of employing the application method, a binder, a
thickener, a conductive material, a solvent, and the like are added
to the positive-electrode active material to form a slurry. The
resulting slurry is applied to a positive electrode current
collector, followed by drying and pressing to increase density.
Thereby, the positive-electrode active material layer is formed on
the positive electrode current collector.
[0271] Examples of a material constituting the positive electrode
current collector include aluminum, titanium, and tantalum, and
alloys containing one or two or more thereof. Among these, aluminum
and its alloys are preferred.
[0272] The positive electrode current collector has a thickness of
usually 1 .mu.m or more and preferably 5 .mu.m or more and usually
100 .mu.m or less and preferably 50 .mu.m or less. An excessively
large thickness of the positive electrode current collector results
in an excessively reduction in the capacity of a battery as a
whole. In contrast, an excessively small thickness of the positive
electrode current collector may lead to poor handleability.
[0273] To improve the binding effect on the positive-electrode
active material layer formed on the surface, the surface of the
positive electrode current collector is preferably subjected to
roughening treatment in advance. Examples of a method for
roughening the surface include blasting; rolling with a
rough-surface roll; mechanical polishing in which a surface of a
current collector is polished with an abrasive particle-coated
abrasive, a grindstone, an emery wheel, a wire brush having steel
wire, or the like; electropolishing, and chemical polishing.
[0274] To reduce the weight of the positive electrode current
collector to improve the energy density per weight of the battery,
a perforated positive electrode current collector having an
expanded metal form or a perforated metal form may also be used. In
this type of positive electrode current collector, the weight can
be desirably changed by changing the opening ratio. In the case
where positive-electrode active material layers are formed on both
sides of this type of positive electrode current collector, the
positive-electrode active material layers are not very easily
detached owing to a rivet effect provided through the openings. An
excessively high opening ratio, however, may result in a reduction
in the contact area between the positive-electrode active material
layers and the positive electrode current collector, thereby
reducing bonding strength.
[0275] To increase conductivity, the conductive material is usually
incorporated in the positive-electrode active material layer. The
type of conductive material is not limited. Examples of the
conductive material include metal materials, such as copper and
nickel; carbon materials, such as graphite, e.g., natural graphite
and artificial graphite, carbon black, e.g., acetylene black, and
amorphous carbon, e.g., needle coke. These materials may be used
separately or in combination of two or more of them in any
proportion.
[0276] The proportion of the conductive material in the
positive-electrode active material layer is usually 0.01% by weight
or more, preferably 0.1% by weight or more, and more preferably 1%
by weight or more, and usually 50% by weight or less, preferably
30% by weight or less, and more preferably 15% by weight or less.
An excessively low proportion of the conductive material may result
in insufficient conductivity. In contrast, an excessively high
proportion of the conductive material may result in a reduction in
battery capacity.
[0277] The binder used for the production of the positive-electrode
active material layer is not particularly limited. In the case of
employing the application method, any binder can be used as long as
it is composed of a material stable for a liquid medium used in
producing the electrode. Specific examples thereof include
resin-like polymers, such as polyethylene, polypropylene,
polyethylene terephthalate, polymethyl methacrylate, aromatic
polyamide, cellulose, and nitrocellulose; rubbery polymers, such as
styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber
(NBR), fluorocarbon rubber, isoprene rubber, butadiene rubber, and
ethylene-propylene rubber; thermoplastic elastomer-based polymers,
such as styrene-butadiene-styrene block copolymers and hydrogenated
products thereof, ethylene-propylene-diene ternary copolymers
(EPDM), styrene-ethylene-butadiene-ethylene copolymers, and
styrene-isoprene-styrene block copolymers and hydrogenated products
thereof; flexible resin-like polymers, such as
syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl
acetate copolymers, and propylene-.alpha.-olefin copolymers;
fluorinated polymers, such as polyvinylidene fluoride,
polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and
polytetrafluoroethylene-ethylene copolymers; and polymeric
compositions having ionic conductivity of alkali metal ions (in
particular, lithium ions). These materials may be used separately
or in combination of two or more of them in any proportion.
[0278] The proportion of the binder in the positive-electrode
active material layer is usually 0.1% by weight or more, preferably
1% by weight or more, and more preferably 5% by weight or more, and
usually 80% by weight or less, preferably 60% by weight or less,
more preferably 40% by weight or less, and most preferably 10% by
weight or less. At an excessively low proportion of the binder, the
positive-electrode active material is not sufficiently held, and
the positive electrode has insufficient mechanical strength, so
that battery performance such as cycle characteristics may be
deteriorated. An excessively high proportion of the binder may lead
to a reduction in battery capacitance and conductivity.
[0279] The type of liquid medium used for forming a slurry is not
particularly limited as long as the positive-electrode active
material, a conductive agent, the binder, and, if necessary, the
thickener can be dissolved or dispersed in the liquid medium.
Aqueous solvents and organic solvents may be used.
[0280] Examples of aqueous solvents include water and mixed
solvents of alcohol and water.
[0281] Examples of organic solvents include aliphatic hydrocarbons
such as hexane; aromatic hydrocarbons such as benzene, toluene,
xylene, and methylnaphthalene; heterocyclic compounds, such as
quinoline and pyridine; ketones, such as acetone, methyl ethyl
ketone, and cyclohexanone; esters, such as methyl acetate and
methyl acrylate; amines, such as diethylenetriamine, and
N,N-dimethylaminopropylamine; ethers, such as diethyl ether,
propyleneoxide, and tetrahydrofuran (THF); amides, such as
N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide;
and aprotic polar solvents, such as hexamethylphosphoramide and
dimethyl sulfoxide. These materials may be used separately or in
combination of two or more of them in any proportion.
[0282] In particular, in the case of using the aqueous solvent, a
slurry is preferably formed using the thickener and latex of
styrene-butadiene rubber (SBR) or the like. The thickener is
usually used to adjust the viscosity of the slurry. Non-limiting
examples of the thickener include carboxymethyl cellulose, methyl
cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl
alcohol, starch oxide, starch phosphate, and casein, and salts
thereof. These materials may be used separately or in combination
of two or more of them in any proportion.
[0283] In the case of incorporating the thickener, the proportion
of the thickener is 0.1% by weight or more, preferably 0.5% by
weight or more, and more preferably 0.6% by weight or more with
respect to the active material. The upper limit is 5% by weight or
less, preferably 3% by weight or less, and more preferably 2% by
weight or less. A proportion of the thickener of less than the
above range may result in a significant reduction in applicability.
A proportion of the thickener exceeding the above range may result
in a reduction in the proportion of the active material in the
positive-electrode active material layer, thereby causing problems
of a reduction in the capacity of the battery and an increase in
the resistance between the positive-electrode active material
particles.
[0284] The viscosity of the slurry is not particularly limited as
long as the slurry can be applied to the current collector. The
viscosity may be appropriately adjusted by changing the amount of
solvent used in preparing the slurry to the extent that application
can be performed.
[0285] The resulting slurry is applied to the positive electrode
current collector, followed by drying and pressing to form a
positive-electrode active material layer. Any known application
method can be employed without limitation. Also, a drying method is
not particularly limited. Known methods, such as air drying, drying
by heating, and drying under reduced pressure, can be employed.
[0286] The positive-electrode active material layer obtained by
application and drying is preferably compacted by hand pressing,
roller pressing, or the like in order to increase packing density
of the positive-electrode active material.
[0287] The positive-electrode active material layer has a density
of preferably 1.5 g/cm.sup.3 or more, more preferably 2 g/cm.sup.3
or more, and still more preferably 2.2 g/cm.sup.3 or more. The
upper limit is preferably 3.9 g/cm.sup.3 or less, more preferably
3.5 g/cm.sup.3 or less, and still more preferably 3.0 g/cm.sup.3 or
less. A density exceeding the above range may result in a reduction
in permeability of the nonaqueous electrolytic solution to and
around the interface between the current collector and the active
material, particularly reducing charge and discharge
characteristics at a high current density. A density of less than
the above range may result in a reduction in the conductivity
between active material particles, thus increasing battery
resistance.
[Negative Electrode]
[0288] Examples of a negative-electrode active material that can be
used include carbonaceous materials, metal compounds, metallic
lithium, and lithium alloys capable of storing and releasing metal
ions. Among these, carbonaceous materials, in particular, graphite
and a graphite material covered with more amorphous carbon than
graphite, are preferred.
[0289] Furthermore, a metal compound capable of storing and
releasing metal ions can be used as the negative-electrode active
material. Examples of the metal compound include compounds
containing metals, such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P,
Pb, Sb, Si, Sn, Sr, and Zn. These metals may be used in any forms
of elemental forms, oxides, alloys with lithium, and the like. In
particular, a negative-electrode active material containing at
least one atom selected from the group consisting of a silicon (Si)
atom, a tin (Sn) atom, and a lead (Pb) atom is preferably
selected.
[0290] Examples of the negative-electrode active material
containing at least one atom selected from the group consisting of
a Si atom, a Sn atom, and a Pb atom include the elemental metal of
one metal element selected from Si, Sn, and Pb; alloys of two or
more of Si, Sn, and Pb; alloys of one or two or more metal elements
selected from Si, Sn, and Pb and one or two or more other metal
elements; and compounds containing one or two or more metal
elements selected from Si, Sn, and Pb. The use of the elemental
metal, alloy, or metal compound as the negative-electrode active
material results in a higher capacity of a battery.
[0291] These negative-electrode active materials may be used
separately or in combination of two or more of them in any
proportion.
[0292] Graphite has a d value (interlayer distance) of the lattice
plane (002 plane) obtained by X-ray diffraction according to the
Japan Society for the Promotion of Science (JSPS) method of usually
0.335 to 0.340 nm, preferably 0.335 to 0.338 nm, and particularly
preferably 0.335 to 0.337 nm. The crystallite size (Lc) obtained by
X-ray diffraction according to the JSPS method is usually 30 nm or
more, preferably 50 nm or more, and particularly preferably 100 nm
or more. The ash content is usually 1% by weight or less,
preferably 0.5% by weight or less, and particularly preferably 0.1%
by weight or less.
[0293] The graphite material covered with amorphous carbon
preferably has a structure such that graphite having a d value of
the lattice plane (002 plane) on X-ray diffraction of 0.335 to
0.338 nm is used as a core material and that a carbonaceous
material having a d value of the lattice plane (002 plane) on X-ray
diffraction larger than that of the core material is attached to
the core material, in which the weight ratio of the core material
to the carbonaceous material having d value of the lattice plane
(002 plane) on X-ray diffraction, larger than that of the core
material is in the range of 99/1 to 80/20. Use of the graphite
material results in a high-capacity negative electrode having low
reactivity to the electrolytic solution.
[0294] The particle diameter of the carbonaceous material is
usually 1 .mu.m or more, preferably 3 .mu.m or more, more
preferably 5 .mu.m or more, and most preferably 7 .mu.m or more,
and usually 100 .mu.m or less, preferably 50 .mu.m or less, more
preferably 40 .mu.m or less, and most preferably 30 .mu.m or less,
in terms of a median diameter by the laser diffraction and
scattering method.
[0295] The specific surface area of the carbonaceous material by
the BET method is usually 0.3 m.sup.2/g or more, preferably 0.5
m.sup.2/g or more, more preferably 0.7 m.sup.2/g or more, and most
preferably 0.8 m.sup.2/g or more, and usually 25 m.sup.2/g or less,
preferably 20 m.sup.2/g or less, more preferably 15 m.sup.2/g or
less, and most preferably 10 m.sup.2/g or less.
[0296] The carbonaceous material preferably has an R value (=IB/IA)
of 0.01 to 0.7, in which the R value is represented by the ratio of
IB to IA, where IA represents the peak strength of a peak PA
observed in the range of 1,570 to 1,620 cm.sup.1 in a Raman
spectrum with argon ion laser light, and IB represents the peak
strength of a peak PB observed in the range of 1,300 to 1,400
cm.sup.-1 in the spectrum. The half-width of a peak observed in the
range of 1,570 to 1,620 cm.sup.1 is usually 26 cm.sup.1 or less and
preferably 25 cm.sup.-1 or less.
[0297] Examples of the compound containing one or two or more metal
elements selected from Si, Sn, and Pb include complex compounds,
such as carbides, oxides, nitrides, sulfides, and phosphides, each
containing one or two or more metal elements selected from Si, Sn,
and Pb.
[0298] Furthermore, compounds in which these complex compounds are
complexly bonded to several elements such as metal elements,
alloys, and nonmetallic elements are also exemplified. More
specifically, with respect to Si and Sn, alloys of a metal that
does not serve as a negative electrode and either Si or Sn can be
used, for example.
[0299] With respect to Sn, for example, a complex compound
containing 5 to 6 elements and composed of a combination of Sn, a
metal serving as a negative electrode and being different from Si,
Sn, and Pb, a metal not serving as a negative electrode, and a
nonmetallic element, can also be used.
[0300] Among these negative-electrode active materials, the
elemental metal of one metal element selected from Si, Sn, and Pb,
alloys of two or more of Si, Sn, and Pb, and oxides, carbides,
nitrides, and the like of one or two or more metal elements
selected from Si, Sn, and Pb are preferred because when batteries
including these materials are produced, the resulting batteries
have large capacities per unit weight. In particular, the elemental
metal, alloys, oxides, carbides, nitrides, and the like of Si
and/or Sn are preferred from the viewpoint of capacity per unit
weight and environmental load.
[0301] The following compounds containing Si and/or Sn are also
preferred because they have lower capacities per unit weight than
elemental metals or alloys but have excellent cycle
characteristics: [0302] Oxides of Si and/or Sn, in which the
element ratio of Si and/or Sn to oxygen is usually 0.5 or more,
preferably 0.7 or more, more preferably 0.9 or more, and usually
1.5 or less, preferably 1.3 or less, and more preferably 1.1 or
less; [0303] Nitrides of Si and/or Sn, in which the element ratio
of Si and/or Sn to nitrogen is usually 0.5 or more, preferably 0.7
or more, and more preferably 0.9 or more, and usually 1.5 or less,
preferably 1.3 or less, and more preferably 1.1 or less; and [0304]
Carbides of Si and/or Sn, in which the element ratio of Si and/or
Sn to carbon is usually 0.5 or more, preferably 0.7 or more, and
more preferably 0.9 or more, and usually 1.5 or less, preferably
1.3 or less, and more preferably 1.1 or less.
[0305] These negative-electrode active materials may be used
separately or in combination of two or more of them in any
proportion.
[0306] The negative electrode for use in the nonaqueous electrolyte
secondary battery of the present invention can be produced by a
common method. Specific examples of a method for producing the
negative electrode include a method in which a mixture of the
negative-electrode active material, a binder, a conductive
material, and the like is subjected to roll forming to form a sheet
electrode; and a method in which compression molding is performed
to form a pellet electrode. Usually, a method in which a thin layer
(negative-electrode active material layer) containing the foregoing
negative-electrode active material is formed on a current collector
for the negative electrode (hereinafter, also referred to as a
"negative electrode current collector") by application,
evaporation, sputtering, plating, or the like. In this case, a
binder, a thickener, a conductive material, a solvent, and the like
are added to the negative-electrode active material to form a
slurry. The resulting slurry is applied to a negative electrode
current collector, followed by drying and pressing to increase
density. Thereby, the negative-electrode active material layer is
formed on the negative electrode current collector.
[0307] Examples of a material constituting the negative electrode
current collector include steel, copper alloys, nickel, nickel
alloys, and stainless steel. Among these, copper foil is preferred
from the viewpoint of easy processing for thin films and cost.
[0308] The negative electrode current collector has a thickness of
usually 1 .mu.m or more and preferably 5 .mu.m or more and usually
100 .mu.m or less and preferably 50 .mu.m or less. An excessively
large thickness of the negative electrode current collector may
result in an excessively reduction in the capacity of a battery as
a whole. In contrast, an excessively small thickness of the
negative electrode current collector may lead to poor
handleability.
[0309] To improve the binding effect on the negative-electrode
active material layer formed on the surface, the surface of the
negative electrode current collector is preferably subjected to
roughening treatment in advance. Examples of a method for
roughening the surface include blasting; rolling with a
rough-surface roll; mechanical polishing in which a surface of a
current collector is polished with an abrasive particle-coated
abrasive, a grindstone, an emery wheel, a wire brush having steel
wire, or the like; electropolishing, and chemical polishing.
[0310] To reduce the weight of the negative electrode current
collector to improve the energy density per weight of the battery,
a perforated negative electrode current collector having an
expanded metal form or a perforated metal form may also be used. In
this type of negative electrode current collector, the weight can
be desirably changed by changing the opening ratio. In the case
where negative-electrode active material layers are formed on both
sides of this type of negative electrode current collector, the
negative-electrode active material layers are not very easily
detached owing to a rivet effect provided through the openings. An
excessively high opening ratio, however, may result in a reduction
in the contact area between the negative-electrode active material
layers and the negative electrode current collector, thereby
reducing bonding strength.
[0311] A slurry for forming the negative-electrode active material
layer is usually prepared by adding a binder, a thickener, and the
like to a negative-electrode material. The term "negative-electrode
material" used in this specification indicates a material including
the negative-electrode active material and the conductive
material.
[0312] The proportion of the negative-electrode active material in
the negative-electrode material is usually 70% by weight or more
and preferably 75% by weight or more and usually 97% by weight or
less and preferably 95% by weight or less. An excessively low
proportion of the negative-electrode active material is liable to
cause a secondary battery including the resulting negative
electrode to have an insufficient capacity. An excessively high
proportion of the negative-electrode active material is liable to
lead to the resultant negative electrode having insufficient
strength because the proportions of the binder and the like are
relatively reduced. In the case of using two or more
negative-electrode active materials in combination, the total
amount of the negative-electrode active materials may satisfy the
above range.
[0313] Examples of the conductive material used for the negative
electrode include metal materials, such as copper and nickel; and
carbon materials, such as graphite and carbon black. These
materials may be used separately or in combination of two or more
of them in any proportion. In particular, a carbon material as the
conductive material is preferably used because the carbon material
functions also as an active material. The proportion of the
conductive material in the negative-electrode material is usually
3% by weight or more and preferably 5% by weight or more and
usually 30% by weight or less and preferably 25% by weight or less.
An excessively low proportion of the conductive material is liable
to lead to insufficient conductivity. An excessively high
proportion of the conductive material is liable to cause a
reduction in battery capacity and strength because the proportions
of the negative-electrode active material and the like are
relatively reduced. In the case of using two or more conductive
materials in combination, the total amount of the conductive
materials may satisfy the above range.
[0314] With respect to the binder for use in the negative
electrode, any binder can be used as long as it is safe for a
solvent and an electrolytic solution used in producing the
electrode. Examples thereof include polyvinylidene fluoride,
polytetrafluoroethylene, polyethylene, polypropylene,
styrene-butadiene rubber, isoprene rubber, butadiene rubber,
ethylene-acrylic acid copolymers, and ethylene-methacrylic acid
copolymers. These materials may be used separately or in
combination of two or more of them in any proportion.
[0315] The proportion of the binder is usually 0.5% by weight or
more and preferably 1% by weight or more and usually 10% by weight
or less and preferably 8% by weight or less with respect to 100% by
weight of the negative-electrode material. An excessively low
proportion of the binder is liable to lead to the resultant
negative electrode having insufficient strength. An excessively
high proportion of the binder is liable to cause a reduction in
battery capacity and strength because the proportions of the
negative-electrode active material and the like are relatively
reduced. In the case of using two or more binders in combination,
the total amount of the binders may satisfy the above range.
[0316] Examples of the thickener for use in the negative electrode
include carboxymethyl cellulose, methyl cellulose, hydroxymethyl
cellulose, ethyl cellulose, polyvinyl alcohol, starch oxide, starch
phosphate, and casein. These materials may be used separately or in
combination of two or more of them in any proportion. The thickener
may be used as needed. In the case of using the thickener, the
thickener is preferably used in the negative-electrode active
material layer in a proportion of usually 0.5% by weight to 5% by
weight.
[0317] A slurry for forming the negative-electrode active material
layer is prepared by adding the conductive material, the binder,
and the thickener, as needed, to the negative-electrode active
material with an aqueous solvent or an organic solvent serving as a
dispersant. As the aqueous solvent, water is usually used.
Alternatively, a mixed solvent in which an organic solvent, such as
alcohol, e.g., ethanol, or cyclic amide, e.g., N-methylpyrrolidone,
is incorporated in water in a concentration of 30% by weight or
less with respect to water may be used. Examples of the organic
solvent include cyclic amides such as N-methylpyrrolidone; linear
amides, such as N,N-dimethylformamide and N,N-dimethylacetamide;
aromatic hydrocarbons, such as anisole, toluene, and xylene; and
alcohols, such as butanol and cyclohexanol. Among these, cyclic
amides such as N-methylpyrrolidone and linear amides, such as
N,N-dimethylformamide and N,N-dimethylacetamide, are preferred.
These materials may be used separately or in combination of two or
more of them in any proportion.
[0318] The resulting slurry is applied to the negative electrode
current collector, followed by drying and pressing to form a
negative-electrode active material layer. Any known application
method can be employed without limitation. Also, a drying method is
not particularly limited. Known methods, such as air drying, drying
by heating, and drying under reduced pressure, can be employed.
[0319] The electrode structure of an electrode produced from the
negative-electrode active material by the foregoing method is not
particularly limited. The active material present on the current
collector preferably has a density of 1 g/cm.sup.3 or more, more
preferably 1.2 g/cm.sup.3 or more, and still more preferably 1.3
g/cm.sup.3 or more. The upper limit is preferably 2 g/cm.sup.3 or
less, preferably 1.9 g/cm.sup.3 or less, more preferably 1.8
g/cm.sup.3 or less, and still more preferably 1.7 g/cm.sup.3 or
less. A density exceeding the above range may cause the break of
active material particles, thereby increasing the initial
irreversible capacity and reducing the permeability of the
nonaqueous electrolytic solution to and around the interface
between the current collector and the active material to cause a
deterioration in charge and discharge characteristics at a high
current density. A density of less than the above range may result
in a reduction in the conductivity between active material
particles, thus increasing battery resistance to cause a reduction
in capacity per unit volume.
[Separator]
[0320] Usually, a separator is interposed between the positive
electrode and the negative electrode to prevent shorting. In this
case, usually, the separator is impregnated with the nonaqueous
electrolytic solution of the present invention.
[0321] The material and shape of the separator are not particularly
limited. A porous sheet or nonwoven fabric having excellent
liquid-holding properties and composed of a material stable for the
nonaqueous electrolytic solution of the present invention is
preferably used. Examples of a material that can be used for the
separator include polyolefins, such as polyethylene and
polypropylene; polytetrafluoroethylene, and polyether sulfone.
Polyolefins are preferred.
[0322] The separator usually has 1 .mu.m or more, preferably 5
.mu.m or more, and more preferably 10 .mu.m or more, and usually 50
.mu.m or less, preferably 40 .mu.m or less, and more preferably 30
.mu.m or less. An excessively small thickness of the separator may
result in a reduction in insulation performance and mechanical
strength. An excessively large thickness cause a deterioration in
battery performance such as rate characteristic and a reduction in
the energy density of the battery as a whole.
[0323] The separator usually has a porosity of 20% or more,
preferably 35% or more, and more preferably 45% or more, and
usually 90% or less, preferably 85% or less, and more preferably
75% or less. An excessively low porosity is liable to cause an
increase in film resistance to deteriorate rate characteristics. An
excessively high porosity is liable to cause a reduction in the
mechanical strength of the separator to reduce insulation
performance.
[0324] The separator usually has an average pore size of 0.5 .mu.m
or less and preferably 0.2 .mu.m or less and usually 0.05 .mu.m or
more. An excessively large average pore size is liable to lead to
cause a short circuit. An excessively small average pore size may
result in an increase in film resistance, deteriorating rate
characteristics.
[Housing]
[0325] A housing used for the nonaqueous electrolyte secondary
battery of the present invention may be composed of any material.
Examples of the material include nickel-plated iron, stainless
steel, aluminum and alloys thereof, nickel, and titanium.
[0326] The present invention relates to a nonaqueous electrolytic
solution for use in a lithium secondary battery having improved
battery characteristics, such as cycle characteristics and
high-temperature storage characteristics and relates to a
nonaqueous electrolyte secondary battery including the nonaqueous
electrolytic solution.
[0327] More specifically, as described in the following Examples,
advantages are demonstrated in terms of a remaining capacity, a
recovery capacity, the amount of gas generated, a storage gas, a
gas-generation inhibition rate, load characteristics after storage,
a cycle capacity retention rate, and the ratio of cycle capacity
retention rates.
[0328] The gas-generation inhibition rate and the ratio of cycle
capacity retention rates are determined as described below.
[0329] Hereinafter, a "cyano group-containing compound" is used to
indicate a unsaturated nitrile compound (1), unsaturated nitrile
compound (2), which are characteristic of the present invention, or
a compound having 2 to 4 cyano groups in its structural
formula.
<Evaluation of Battery Characteristics>
1. Storage Test
[0330] A sheet battery held between glass plates to improve contact
between electrodes was charged at a constant current corresponding
to 0.2 C until the battery voltage reached a charge cut-off voltage
of 4.2 V and discharged at a constant current corresponding to 0.2
C until the battery voltage reached a discharge cut-off voltage of
3 V at 25.degree. C. This charge-discharge operation was repeated 3
cycles to stabilize the battery. Then, the battery was subjected to
4.2-V-CCCV charge (0.05 C cut) and stored at 85.degree. C. for 24
hours. The sheet battery was immersed in an ethanol bath before and
after the high-temperature storage. The amount of gas generated
(storage gas) was determined from the change in volume.
[0331] The battery after the storage was discharged at 25.degree.
C. at a constant current of 0.2 C until the battery voltage reached
a discharge cut-off voltage of 3 V, subjected to 4.2 V-CCCV charge
(0.05 C cut), and discharged at a current corresponding to 0.2 C
until the battery voltage reached 3 V, and then a 0.2-C capacity
was measured. Next, the battery was subjected to 4.2-V-CCCV charge
(0.05 C cut) and discharged at a current corresponding to 1.0 C
until the battery voltage reached 3 V, and then a 1.0-C capacity
was measured. The ratio of the 1.0-C capacity after the storage to
the 0.2-C capacity after the storage (1.0-C capacity/0.2-C
capacity) is defined as the load characteristics after storage.
[0332] Furthermore, a value calculated by the subtraction of the
ratio (%) of the amount of gas generated from a battery including a
nonaqueous electrolytic solution that contains a cyano
group-containing compound of the present invention to the amount of
gas generated from a corresponding battery including a nonaqueous
electrolytic solution that does not contain a cyano
group-containing compound of the present invention from 100, i.e.,
100-{(amount of gas generated from battery including nonaqueous
electrolytic solution that contains cyano group-containing compound
of the invention/amount of gas generated from battery including
nonaqueous electrolytic solution that does not contain cyano
group-containing compound of the invention).times.100}, is defined
as the gas-generation inhibition rate (%). The term "1 C" indicates
a current value when a battery is fully charged in one hour.
2. Cycle Test
[0333] The sheet battery held between glass plates to improve
contact between the electrodes was charged at a constant current
corresponding to 0.2 C until the battery voltage reached a charge
cut-off voltage of 4.2 V and discharged at a constant current
corresponding to 0.2 C until the battery voltage reached a
discharge cut-off voltage of 3 V at 25.degree. C. This
charge-discharge operation was repeated three cycles to stabilize
the battery. A cycle test was performed as follows: the
charge-discharge operation of 0.5-C-CCCV charge (0.05 C cut) and
constant-current discharge at 0.5 C until 3 V was repeated. The
rate of a discharge capacity in the 100th cycle to a discharge
capacity in the fourth cycle, i.e., (discharge capacity in 100th
cycle/discharge capacity in 4th cycle), is defined as the cycle
capacity retention rate.
[0334] The ratio of the cycle capacity retention rate of a battery
including a nonaqueous electrolytic solution that contains a cyano
group-containing compound of the present invention to the cycle
capacity retention rate of a corresponding battery including a
nonaqueous electrolytic solution that does not contain a cyano
group-containing compound of the present invention, i.e., (cycle
capacity retention rate of battery including nonaqueous
electrolytic solution that contains cyano group-containing compound
of the invention/cycle capacity retention rate of battery including
nonaqueous electrolytic solution that does not contain cyano
group-containing compound of the invention), is defined as the
ratio of the cycle capacity retention rates.
[0335] The gas-generation inhibition rate is usually 5% or more,
preferably 10% or more, more preferably 15% or more, particularly
preferably 30% or more, and most preferably 60% or more from the
viewpoint of suppressing the expansion of a battery.
[0336] The ratio of the cycle capacity retention rates is usually
0.6 or more, preferably 0.7 or more, more preferably 0.8 or more,
particularly preferably 0.9 or more, and most preferably 1.0 or
more from the viewpoint of improving the lifetime of a battery.
EXAMPLES
[0337] While the present invention will now be described in further
detail by means of examples, the present invention, the present
invention is not limited to these examples without departing from
the scope of the present invention.
Examples 1 to 25 and Comparative Examples 1 to 18
[0338] Nonaqueous electrolyte secondary batteries were produced
according to the following procedure and evaluated. Tables 1 to 5
show the results.
[Production of Positive Electrode]
[0339] First, 85 parts by weight of LiCoO.sub.2 ("C5", manufactured
by Nippon Chemical Industrial Co., Ltd.) serving as a
positive-electrode active material, 6 parts by weight of carbon
black, and 9 parts by weight of polyvinylidene fluoride (trade
name: "KF-1000", manufactured by Kureha Corporation) were mixed,
followed by addition of N-methyl-2-pyrrolidone to form a slurry.
The resulting slurry was uniformly applied to both surfaces of
aluminum foil having a thickness of 15 .mu.m, followed by drying.
The resulting foil was pressed in such a manner that
positive-electrode active material layers had a density of 3.0
g/cm.sup.3, thereby forming a positive electrode.
[Production of Graphite Negative Electrode]
[0340] First, 94 parts by weight of natural graphite having a d
value of the lattice plane (002 plane) on X-ray diffraction of
0.336 nm, a crystallite size (Lc) of 652 nm, an ash content of
0.07% by weight, a median diameter by the laser diffraction and
scattering method of 12 .mu.m, a BET specific surface area of 7.5
m.sup.2/g, an R value (IB/IA) determined by Raman spectrum analysis
with argon ion laser light of 0.12, and a half-width of a peak
observed in the range of 1,570 to 1,620 cm.sup.-1 of 19.9 cm.sup.-1
and 6 parts by weight of polyvinylidene fluoride were mixed,
followed by addition of N-methyl-2-pyrrolidone to form a slurry.
The resulting slurry was uniformly applied to a surface of copper
foil having a thickness of 12 .mu.m, naturally dried, and finally
dried at 85.degree. C. for whole day and night under reduced
pressure. Then the copper foil was pressed in such a manner that a
negative-electrode active material layer had a density of 1.5
g/cm.sup.3, thereby forming a negative electrode.
[Preparation of Electrolytic Solution]
[0341] Under a dry argon atmosphere, compounds described in solvent
and additive sections of each of the rows of [Examples] and
[Comparative Examples] in Tables 1 to 5 described below were mixed
in proportions described in the sections, and then LiPF.sub.6
serving as an electrolytic salt was dissolved therein in such a
manner that the concentration of LiPF.sub.6 was 1 mol/L, thereby
preparing nonaqueous electrolytic solutions (nonaqueous
electrolytic solutions in Examples 1 to 25 and Comparative Examples
1 to 18).
[Production of Nonaqueous Electrolyte Secondary Battery]
[0342] The positive electrode, the negative electrodes, and a
separator composed of polyethylene were stacked in a sequence of
negative electrode/separator/positive electrode/separator/negative
electrode, thereby forming a battery element. The battery element
was placed in a bag formed of a laminate film in which both
surfaces of an aluminum film (with a thickness of 40 .mu.m) were
covered with resin layers in such a manner that terminals of the
positive electrode and the negative electrode were protruded. The
nonaqueous electrolytic solution prepared according to the
foregoing procedure was fed into the bag, followed by vacuum
sealing to produce a sheet battery.
[Evaluation of Battery]
[0343] The sheet battery held between glass plates to improve
contact between the electrodes was charged at a constant current
corresponding to 0.2 C until the battery voltage reached a charge
cut-off voltage of 4.2 V and discharged at a constant current
corresponding to 0.2 C until the battery voltage reached a
discharge cut-off voltage of 3 V at 25.degree. C. This
charge-discharge operation was repeated three cycles to stabilize
the battery. In the fourth cycle, the battery was subjected to
4.4-V-constant-current constant-voltage charge (CCCV charge) (0.05
C cut) in which the battery was charged at a current corresponding
to 0.5 C until the battery voltage reached a charge cut-off voltage
of 4.4 V and then charged until a charging current reached a value
corresponding to 0.05 C. Then the battery was discharged at a
constant current corresponding to 0.2 C until the battery voltage
reached 3 V, and the discharge capacity was measured before
high-temperature storage. Next, the battery was subjected to
4.4-V-CCCV charge (0.05 C cut) and then high-temperature storage at
85.degree. C. for 24 hours. The sheet battery was immersed in an
ethanol bath before and after the high-temperature storage. The
amount of gas generated was determined from the change in volume.
Tables 1 to 5 show the amount of gas.
[0344] After the storage, the battery was discharged at a constant
current of 0.2 C until the battery voltage reached a discharge
cut-off voltage of 3 V at 25.degree. C., and the remaining capacity
after the storage test was determined. Next, the battery was
subjected to 4.4-V-CCCV charge (0.05 C cut). The battery was
discharged at a current corresponding to 0.2 C until the battery
voltage reached a discharge cut-off voltage of 3 V, and the 0.2-C
capacity was measured. Thereby, the 0.2-C capacity after the
storage test was determined and defined as the recovery capacity.
The term "1 C" indicates a current value when a battery is fully
charged in one hour.
[0345] Tables 1 to 5 show the remaining capacity and the recovery
capacity (%) when the discharge capacity before the
high-temperature storage was defined as 100%.
[0346] In Tables 1 to 5, the values of parts by weight correspond
to the solvents and the additives. That is, in Example 1 in Table
1, the expression "ethylene carbonate+ethylmethyl carbonate
(35.32+63.43)" in the solvent section is used to indicate that
35.32 parts by weight of ethylene carbonate and 63.43 parts by
weight of ethylmethyl carbonate were mixed. The expression
"vinylene carbonate+crotononitrile (1+0.25)" in the additive
section is used to indicate that 1 part by weight of vinylene
carbonate and 0.25 parts by weight of crotononitrile were mixed.
The same is true for Table 6 and other Tables.
TABLE-US-00001 TABLE 1 Remaining Recovery Amount Solvent Additive
capacity capacity of gas (parts by weight) (parts by weight) (%)
(%) (mL) Example 1 Ethylene carbonate + Vinylene carbonate + 78 84
0.02 ethylmethyl carbonate crotononitrile (35.32 + 63.43) (1 +
0.25) Example 2 Ethylene carbonate + Vinylene carbonate + 78 81
0.03 ethylmethyl carbonate 2-methyl-2-pentenenitrile (35.32 +
63.43) (1 + 0.25) Example 3 Ethylene carbonate + Vinylene carbonate
+ 79 84 0.05 ethylmethyl carbonate cinnamonitrile (35.32 + 63.43)
(1 + 0.25) Example 4 Ethylene carbonate + Vinylene carbonate + 80
84 0.08 ethylmethyl carbonate crotononitrile (35.4 + 63.5) (1 +
0.1) Example 5 Ethylene carbonate + Vinylene carbonate + 77 78 0.03
ethylmethyl carbonate crotononitrile (35.2 + 63.3) (1 + 0.5)
Example 6 Ethylene carbonate + Crotononitrile 76 81 0.03
ethylmethyl carbonate (0.25) (35.67 + 64.08) Example 7 Ethylene
carbonate + Fluoroethylene carbonate 81 86 0.04 ethylmethyl
carbonate (1 + 0.25) (35.32 + 63.43) Example 8 Ethylene carbonate +
4,5-Difluoroethylene carbonate + 80 87 0.06 ethylmethyl carbonate
crotononitrile (35.32 + 63.43) (1 + 0.25) Example 9 Ethylene
carbonate + Lithium difluorophosphate + 80 85 0.05 ethylmethyl
carbonate crotononitrile (35.32 + 63.43) (1 + 0.25)
TABLE-US-00002 TABLE 2 Remaining Recovery Amount of Solvent
Additive capacity capacity gas (parts by weight) (parts by weight)
(%) (%) (mL) Example 10 Ethylene carbonate + Vinylene carbonate +
78 84 0.08 ethylmethyl carbonate fluoroethylene carbonate + (34.96
+ 62.79) crotononitrile (1 + 1 + 0.25) Example 11 Ethylene
carbonate + Vinylene carbonate + 79 86 0.09 ethylmethyl carbonate
4,5-difluoroethylene carbonate + (34.96 + 62.79) crotononitrile (1
+ 1 + 0.25) Example 12 Ethylene carbonate + Vinylene carbonate + 81
85 0.05 ethylmethyl carbonate lithium difluorophosphate + (35.37 +
62.88) crotononitrile (1 + 0.5 + 0.25) Example 13 Ethylene
carbonate + Fluoroethylene carbonate + 80 85 0.07 ethylmethyl
carbonate lithium difluorophosphate + (35.37 + 62.88)
crotononitrile (1 + 0.5 + 0.25) Example 14 Ethylene carbonate +
Vinylene carbonate + 82 86 0.07 ethylmethyl carbonate
fluoroethylene carbonate + (35.01 + 62.44) lithium
difluorophosphate + crotononitrile (1 + 1 + 0.5 + 0.25) Example 15
Fluoroethylene carbonate + Crotononitrile 73 82 0.20 ethylmethyl
carbonate (1) (38 + 61) Example 16 Fluoroethylene carbonate +
Acrylonitrile 73 83 0.22 ethylmethyl carbonate (1) (38 + 61)
Example 17 Fluoroethylene carbonate + Vinylene carbonate + 74 84
0.18 ethylmethyl carbonate crotononitrile (38 + 60) (1 + 1)
TABLE-US-00003 TABLE 3 Remaining Recovery Amount Solvent Additive
capacity capacity of gas (parts by weight) (parts by weight) (%)
(%) (mL) Example 18 Fluoroethylene carbonate + Vinylene carbonate +
73 82 0.24 ethylmethyl carbonate acrylonitrile (38 + 60) (1 + 1)
Example 19 Fluoroethylene carbonate + Vinylene carbonate + 75 84
0.26 ethylmethyl carbonate fumaronitrile (38 + 60) (1 + 1) Example
20 Fluoroethylene carbonate + Lithium difluorophosphate + 76 84
0.22 ethylmethyl carbonate crotononitrile (38 + 60) (1 + 1) Example
21 Fluoroethylene carbonate + Vinylene carbonate + 78 85 0.24
ethylmethyl carbonate lithium difluorophosphate + (38 + 60)
crotononitrile (1 + 0.5 + 1) Example 22 Ethylene carbonate +
Crotononitrile 74 83 0.22 fluoroethylene carbonate + (1)
ethylmethyl carbonate (17 + 20 + 62) Example 23 Ethylene carbonate
+ Vinylene carbonate + 75 83 0.21 fluoroethylene carbonate +
crotononitrile ethylmethyl carbonate (1 + 1) (17 + 20 + 61) Example
24 Ethylene carbonate + Lithium difluorophosphate + 76 84 0.20
fluoroethylene carbonate + crotononitrile ethylmethyl carbonate (1
+ 1) (17 + 20 + 61) Example 25 Ethylene carbonate + Vinylene
carbonate + 75 84 0.22 fluoroethylene carbonate + lithium
difluorophosphate + ethylmethyl carbonate crotononitrile (17 + 19 +
61) (1 + 0.5 + 1)
TABLE-US-00004 TABLE 4 Remaining Recovery Amount Solvent Additive
capacity capacity of gas (parts by weight) (parts by weight) (%)
(%) (mL) Comparative Ethylene carbonate + None 70 78 0.05 Example 1
ethylmethyl carbonate (36 + 64) Comparative Ethylene carbonate +
Vinylene carbonate 78 82 0.15 Example 2 ethylmethyl carbonate (1)
(35 + 64) Comparative Ethylene carbonate + Acrylonitrile 66 84 0.37
Example 3 ethylmethyl carbonate (0.25) (35.67 + 64.08) Comparative
Ethylene carbonate + Fluoroethylene carbonate 79 85 0.13 Example 4
ethylmethyl carbonate (1) (35 + 64) Comparative Ethylene carbonate
+ 4,5-Difluoroethylene 80 86 0.19 Example 5 ethylmethyl carbonate
carbonate (35 + 64) (1) Comparative Ethylene carbonate + Lithium
difluorophosphate 80 86 0.14 Example 6 ethylmethyl carbonate (1)
(35 + 64) Comparative Ethylene carbonate + Vinylene carbonate + 77
81 0.24 Example 7 ethylmethyl carbonate fluoroethylene (35 + 63)
carbonate (1 + 1) Comparative Ethylene carbonate + Vinylene
carbonate + 78 81 0.10 Example 8 ethylmethyl carbonate
acrylonitrile (35.32 + 63.43) (1 + 0.25) Comparative Ethylene
carbonate + Vinylene carbonate + 75 79 0.12 Example 9 ethylmethyl
carbonate methacrylonitrile (35.32 + 63.43) (1 + 0.25)
TABLE-US-00005 TABLE 5 Remaining Recovery Amount of Solvent
Additive capacity capacity gas (parts by weight) (parts by weight)
(%) (%) (mL) Comparative Ethylene carbonate + Vinylene carbonate +
76 81 0.13 Example 10 ethylmethyl carbonate acetonitrile (35.32 +
63.43) (1 + 0.25) Comparative Ethylene carbonate + Vinylene
carbonate + 67 70 0.08 Example 11 ethylmethyl carbonate
succinonitrile (35.32 + 63.43) (1 + 0.25) Comparative
Fluoroethylene carbonate + None 60 74 1.30 Example 12 ethylmethyl
carbonate (39 + 61) Comparative Fluoroethylene carbonate +
Acetonitrile 61 72 1.25 Example 13 ethylmethyl carbonate (1) (38 +
61) Comparative Fluoroethylene carbonate + Vinylene carbonate 72 82
1.25 Example 14 ethylmethyl carbonate (1) (38 + 61) Comparative
Fluoroethylene carbonate + Vinylene carbonate + 70 79 1.01 Example
15 ethylmethyl carbonate acetonitrile (38 + 60) (1 + 1) Comparative
Fluoroethylene carbonate + Vinylene carbonate + 65 71 0.85 Example
16 ethylmethyl carbonate succinonitrile (38 + 60) (1 + 1)
Comparative Ethylene carbonate + None 59 70 1.35 Example 17
fluoroethylene carbonate + ethylmethyl carbonate (17 + 20 + 63)
Comparative Ethylene carbonate + Vinylene carbonate 68 79 1.33
Example 18 fluoroethylene carbonate + (1) ethylmethyl carbonate (17
+ 20 + 62)
[0347] Tables 1 to 5 clearly show that in the case where the
nonaqueous electrolyte secondary batteries including the nonaqueous
electrolytic solutions each containing unsaturated nitrile compound
(1) or unsaturated nitrile compound (2) are produced, the gas
generation after the high-temperature storage is suppressed without
deteriorating the battery characteristics in terms of the remaining
capacity and the recovery capacity, as compared with the case where
the nonaqueous electrolyte secondary batteries including the
nonaqueous electrolytic solutions without unsaturated nitrile
compound (1) or unsaturated nitrile compound (2) are produced.
Specifically, in the electrolytic solutions prepared in Examples 1
to 25, the gas generation after the high-temperature storage is
suppressed without deteriorating the battery characteristics in
terms of the remaining capacity and the recovery capacity, as
compared with Comparative Examples 1 to 18.
[0348] In particular, in the case of using the compounds
represented by general formula (1) or general formula (2) wherein
at least one of R.sup.1 and R.sup.2 or at least one of R.sup.4 and
R.sup.5 represents a cyano group or an optionally halogen
atom-containing hydrocarbon group having 1 to 6 carbon atoms, the
effect is significant. Furthermore, in the case of using a
combination of fluoroethylene carbonate, which is a halogen
atom-containing cyclic carbonate, 4,5-difluoroethylene carbonate,
vinylene carbonate, which is a cyclic carbonate having a
carbon-carbon unsaturated bond, and lithium difluorophosphate
selected from the group consisting of monofluorophosphates and
difluorophosphates, the effect is particularly significant. In
particular, the results demonstrate that in the case where at least
one of the halogen atom-containing cyclic carbonate and at least
one compound selected from the group consisting of
monofluorophosphates and difluorophosphates is incorporated, the
remaining capacity and the recovery capacitance are high after the
high-temperature storage, which is effective. Moreover, the results
demonstrate that also in the case where both are incorporated, the
amount of gas generated after the high-temperature storage is
small, and the deterioration is suppressed in terms of the
remaining capacity and the recovery capacity, as compared with the
case where only unsaturated nitrile compound (1) is incorporated.
The results also demonstrate that even in the case where a large
amount of fluoroethylene carbonate, which is a halogen
atom-containing cyclic carbonate, is incorporated, the presence of
unsaturated nitrile compound (1) results in a significant
suppression of gas generation after the high-temperature storage
without deteriorating the battery characteristics.
Examples 26 to 36 and Comparative Examples 19 to 26
[0349] A battery was produced as in Example 1, except that the
negative electrode was replaced with a negative electrode formed by
a method described below, and the electrolytic solution was
replaced with a nonaqueous electrolytic solution prepared by mixing
compounds described in the solvent and additive sections of each of
the rows of [Examples] and [Comparative Examples] in Tables 6 and 7
in proportions described in the sections and dissolving LiPF.sub.6
serving as an electrolytic salt therein in such a manner that the
concentration of LiPF.sub.6 was 1 mol/L (nonaqueous electrolytic
solutions in Examples 26 to 36 and Comparative Examples 19 to
26).
[Production of Negative Electrode Composed of Silicon Alloy]
[0350] As negative-electrode active materials, 73.2 parts by weight
of silicon, which is a non-carbon material, 8.1 parts by weight of
copper, and 12.2 parts by weight of an artificial graphite powder
(trade name: "KS-6", manufactured by Timcal Ltd.) were used. To
these materials, 54.2 parts by weight of N-methylpyrrolidone
solution containing 12 parts by weight of polyvinylidene fluoride
and then 50 parts by weight of N-methylpyrrolidone were added. The
mixture was mixed using a disperser to form a slurry. The resulting
slurry was uniformly applied to 18-.mu.m-thick copper foil serving
as a negative electrode current collector, naturally dried, and
finally dried at 85.degree. C. for whole day and night under
reduced pressure. Then the copper foil was pressed in such a manner
that the electrode density was about 1.5 g/cm.sup.3, thereby
forming a negative electrode.
[Evaluation of Battery]
[0351] The sheet battery held between glass plates to improve
contact between the electrodes was charged at a constant current
corresponding to 0.2 C until the battery voltage reached a charge
cut-off voltage of 4.2 V and discharged at a constant current
corresponding to 0.2 C until the battery voltage reached a
discharge cut-off voltage of 3 V at 25.degree. C. This
charge-discharge operation was repeated three cycles to stabilize
the battery. In the fourth cycle, the battery was subjected to
4.2-V-constant-current constant-voltage charge (CCCV charge) (0.05
C cut) in which the battery was charged at a current corresponding
to 0.5 C until the battery voltage reached a charge cut-off voltage
of 4.2 V and then charged until a charging current reached a value
corresponding to 0.05 C. Then the battery was discharged at a
constant current corresponding to 0.2 C until the battery voltage
reached 3 V, and the discharge capacity was measured before
high-temperature storage. Next, the battery was subjected to
4.2-V-CCCV charge (0.05 C cut) and then high-temperature storage at
60.degree. C. for a week. The sheet battery was immersed in an
ethanol bath before and after the high-temperature storage. The
amount of gas generated was determined from the change in volume.
Tables 6 and 7 show the amount of gas.
[0352] After the storage, the battery was discharged at a constant
current of 0.2 C until the battery voltage reached a discharge
cut-off voltage of 3 V at 25.degree. C., and the remaining capacity
after the storage test was determined. Next, the battery was
subjected to 4.2-V-CCCV charge (0.05 C cut). The battery was
discharged at a current corresponding to 0.2 C until the battery
voltage reached a discharge cut-off voltage of 3 V, and the 0.2-C
capacity was measured. Thereby, the 0.2-C capacity after the
storage test was determined and defined as the recovery capacity.
The term "1 C" indicates a current value when a battery is fully
charged in one hour.
[0353] The discharge capacity before the high-temperature storage
was defined as 100%. In this case, the remaining capacity and the
recovery capacity (%) were shown in Tables 6 and 7.
TABLE-US-00006 TABLE 6 Remaining Recovery Amount Solvent Additive
capacity capacity of gas (parts by weight) (parts by weight) (%)
(%) (mL) Example 26 Ethylene carbonate + Fluoroethylene carbonate +
85 89 0.09 diethyl carbonate crotononitrile (34 + 60) (5 + 1)
Example 27 Ethylene carbonate + Fluoroethylene carbonate + 84 88
0.08 diethyl carbonate acrylonitrile (34 + 60) (5 + 1) Example 28
Ethylene carbonate + Fluoroethylene carbonate + 84 86 0.09 diethyl
carbonate methacrylonitrile (34 + 60) (5 + 1) Example 29 Ethylene
carbonate + Fluoroethylene carbonate + 88 90 0.22 diethyl carbonate
fumaronitrile (34 + 60) (5 + 1) Example 30 Ethylene carbonate +
4,5-Difluoroethylene 87 91 0.11 diethyl carbonate carbonate + (34 +
60) crotononitrile (5 + 1) Example 31 Ethylene carbonate + Vinylene
carbonate + 85 87 0.11 diethyl carbonate crotononitrile (34 + 60)
(5 + 1) Example 32 Ethylene carbonate + Lithium difluorophosphate +
88 90 0.10 diethyl carbonate crotononitrile (36 + 62) (1 + 1)
Example 33 Ethylene carbonate + Crotononitrile 83 87 0.11 diethyl
carbonate (1) (36 + 63) Example 34 Fluoroethylene carbonate +
Crotononitrile 87 90 0.20 diethyl carbonate (1) (39 + 60) Example
35 Fluoroethylene carbonate + Vinylene carbonate + 88 91 0.22
diethyl carbonate crotononitrile (37 + 57) (5 + 1) Example 36
Fluoroethylene carbonate + Lithium difluorophosphate + 87 91 0.20
diethyl carbonate crotononitrile (39 + 59) (1 + 1)
TABLE-US-00007 TABLE 7 Remaining Recovery Amount Solvent Additive
capacity capacity of gas (parts by weight) (parts by weight) (%)
(%) (mL) Comparative Ethylene carbonate + None 84 86 0.49 Example
19 diethyl carbonate (37 + 63) Comparative Ethylene carbonate +
Fluoroethylene carbonate 86 89 0.83 Example 20 diethyl carbonate
(5) (35 + 60) Comparative Ethylene carbonate + 4,5-Difluoroethylene
carbonate 87 90 0.90 Example 21 diethyl carbonate (5) (35 + 60)
Comparative Ethylene carbonate + Fluoroethylene carbonate + 56 59
0.51 Example 22 diethyl carbonate acetonitrile (34 + 60) (5 + 1)
Comparative Ethylene carbonate + Vinylene carbonate 85 88 0.95
Example 23 diethyl carbonate (5) (35 + 60) Comparative
Fluoroethylene carbonate + None 88 91 1.33 Example 24 diethyl
carbonate (40 + 60) Comparative Fluoroethylene carbonate + Vinylene
carbonate 88 90 1.31 Example 25 diethyl carbonate (5) (38 + 57)
Comparative Fluoroethylene carbonate + Lithium difluorophosphate 85
88 1.35 Example 26 diethyl carbonate (1) (39 + 60)
[0354] Tables 6 and 7 clearly show that also in the case of using
the negative electrode containing the specific metal element used
for the negative electrode, the nonaqueous electrolytic solution of
the present invention results in the same effect as the carbon
electrode, i.e., the gas generation after the high-temperature
storage is inhibited without deteriorating the battery
characteristics.
[Examples 37 to 47 and Comparative Examples 27 to 42]
[0355] A battery was produced as in each of Examples 26 to 36 and
Comparative Examples 19 to 26, except that under a dry argon
atmosphere, compounds described in solvent and additive sections of
each of the rows of [Examples] and [Comparative Examples] in Tables
8 and 9 described below were mixed in proportions described in the
sections, and then LiPF.sub.6 serving as an electrolytic salt was
dissolved therein in such a manner that the concentration of
LiPF.sub.6 was 1 mol/L, thereby preparing nonaqueous electrolytic
solutions (nonaqueous electrolytic solutions in Examples 37 to 47
and Comparative Examples 27 to 42) (in Tables, EC represents
ethylene carbonate, DEC represents diethylene carbonate, FEC
represents fluoroethylene carbonate, DFEC represents
4,5-difluoroethylene carbonate, VC represents vinylene carbonate,
and LiPO.sub.2F.sub.2 represents lithium difluorophosphate).
[0356] The resulting batteries were similarly evaluated. Tables 8
and 9 show the results. The storage test and the cycle test were
performed by methods described below.
[Evaluation of Battery]
1. Storage Test
[0357] A sheet battery held between glass plates to improve contact
between electrodes was charged at a constant current corresponding
to 0.2 C until the battery voltage reached a charge cut-off voltage
of 4.2 V and discharged at a constant current corresponding to 0.2
C until the battery voltage reached a discharge cut-off voltage of
3 V at 25.degree. C. This charge-discharge operation was repeated 3
cycles to stabilize the battery. Then, the battery was subjected to
4.2-V-CCCV charge (0.05 C cut) and stored at 85.degree. C. for 24
hours. The sheet battery was immersed in an ethanol bath before and
after the high-temperature storage. The amount of gas generated
(storage gas) was determined from the change in volume.
[0358] The battery after the storage was discharged at 25.degree.
C. at a constant current of 0.2 C until the battery voltage reached
a discharge cut-off voltage of 3 V, subjected to 4.2 V-CCCV charge
(0.05 C cut), and discharged at a current corresponding to 0.2 C
until the battery voltage reached 3 V, and then a 0.2-C capacity
was measured. Next, the battery was subjected to 4.2-V-CCCV charge
(0.05 C cut) and discharged at a current corresponding to 1.0 C
until the battery voltage reached 3 V, and then a 1.0-C capacity
was measured. The ratio of the 1.0-C capacity after the storage to
the 0.2-C capacity after the storage (1.0-C capacity/0.2-C
capacity) is defined as the load characteristics after storage.
[0359] Furthermore, a value calculated by the subtraction of the
ratio (%) of the amount of gas generated from a battery including a
nonaqueous electrolytic solution that contains unsaturated nitrile
compound (1) or unsaturated nitrile compound (2) to the amount of
gas generated from a corresponding battery including a nonaqueous
electrolytic solution that does not contain unsaturated nitrile
compound (1) or unsaturated nitrile compound (2) from 100, i.e.,
100-{(amount of gas generated from battery including nonaqueous
electrolytic solution that contains unsaturated nitrile compound
(1) or unsaturated nitrile compound (2)/amount of gas generated
from battery including nonaqueous electrolytic solution that does
not contain unsaturated nitrile compound (1) or unsaturated nitrile
compound (2)).times.100}, is defined as the gas-generation
inhibition rate (%). The term "1 C" indicates a current value when
a battery is fully charged in one hour.
2. Cycle Test
[0360] The sheet battery held between glass plates to improve
contact between the electrodes was charged at a constant current
corresponding to 0.2 C until the battery voltage reached a charge
cut-off voltage of 4.2 V and discharged at a constant current
corresponding to 0.2 C until the battery voltage reached a
discharge cut-off voltage of 3 V at 25.degree. C. This
charge-discharge operation was repeated three cycles to stabilize
the battery. A cycle test was performed as follows: the
charge-discharge operation of 0.5-C-CCCV charge (0.05 C cut) and
constant-current discharge at 0.5 C until 3 V was repeated. The
rate of a discharge capacity in the 100th cycle to a discharge
capacity in the fourth cycle, i.e., (discharge capacity in 100th
cycle/discharge capacity in 4th cycle), is defined as the cycle
capacity retention rate.
[0361] The ratio of the cycle capacity retention rate of a battery
including a nonaqueous electrolytic solution that contains
unsaturated nitrile compound (1) or unsaturated nitrile compound
(2) to the cycle capacity retention rate of a corresponding battery
including a nonaqueous electrolytic solution that does not contain
unsaturated nitrile compound (1) or unsaturated nitrile compound
(2), i.e., (cycle capacity retention rate of battery including
nonaqueous electrolytic solution that contains unsaturated nitrile
compound (1) or unsaturated nitrile compound (2)/cycle capacity
retention rate of battery including nonaqueous electrolytic
solution that does not contain unsaturated nitrile compound (1) or
unsaturated nitrile compound (2)), is defined as the ratio of the
cycle capacity retention rates.
<Evaluation Result>
TABLE-US-00008 [0362] TABLE 8 Unsaturated nitrile Cycle compound
(1) or High-temperature storage characteristics unsaturated nitrile
Additional characteristics Ratio of compound (2) additive Gas Load
Cycle cycle Negative Solvent Content Content Storage inhibition
characteristics retention retention electrode (wt %) Additive (wt
%) Additive (wt %) gas rate after storage rate rate Example37 Si EC
+ DEC Crotononitrile 1 -- -- 0.06 73.9 0.79 45.7 0.97 (36 + 63)
Comparative Si EC + DEC -- -- -- -- 0.23 -- 0.09 46.9 -- Example27
(37 + 63) Example38 Si EC + DEC Crotononitrile 0.5 FEC 5 0.15 77.9
0.51 -- -- (35.0 + 59.5) Example39 Si EC + DEC Crotononitrile 1 FEC
5 0.12 82.4 0.69 60.9 1.00 (34 + 60) Example40 Si EC + DEC
Crotononitrile 2 FEC 5 0.04 94.1 0.42 -- -- (34 + 59) Example41 Si
EC + DEC Acrylonitrile 1 FEC 5 0.08 88.2 0.74 -- -- (34 + 60)
Comparative Si EC + DEC -- 0 FEC 5 0.68 -- 0.23 60.8 -- Example28
(35 + 60) Example42 Si EC + DEC Crotononitrile 0.5 DFEC 2 0.08 83.3
0.19 74.6 1.00 (36.1 + 61.4) Comparative Si EC + DEC -- 0 DFEC 2
0.48 -- 0.83 74.5 -- Example29 (36 + 62) Example43 Si EC + DEC
Crotononitrile 0.5 VC 2 0.07 86.0 0.39 63.0 1.00 (36.1 + 61.4)
Comparative Si EC + DEC -- 0 VC 2 0.50 -- 0.25 63.1 -- Example30
(36 + 62) Example44 Si EC + DEC Crotononitrile 0.5 LiPO2F2 1 0.06
78.6 0.07 63.4 1.00 (36.4 + 62.1) Comparative Si EC + DEC -- 0
LiPO2F2 1 0.28 -- 0.39 63.2 -- Example31 (36 + 63)
TABLE-US-00009 TABLE 9 Unsaturated nitrile Cycle compound (1) or
High-temperature storage characteristics unsaturated nitrile
Additional characteristics Ratio of compound (2) additive Gas Load
Cycle cycle Negative Solvent Content Content Storage inhibition
characteristics retention retention electrode (wt %) Additive (wt
%) Additive (wt %) gas rate after storage rate rate Comparative
Carbon EC + DEC Crotononitrile 0.5 -- -- 0.05 37.5 0.27 51.0 0.65
Example 32 (35.0 + 59.5) Comparative Carbon EC + DEC -- 0 -- --
0.08 -- 0.46 79.0 -- Example 33 (37 + 63) Comparative Carbon EC +
DEC Crotononitrile 0.5 DFEC 2 0.12 65.7 0.36 87.0 0.96 Example 34
(36.1 + 61.4) Comparative Carbon EC + DEC -- 0 DFEC 2 0.35 -- 0.46
91.0 -- Example 35 (36 + 62) Comparative Carbon EC + DEC
Crotononitrile 0.5 LiPO2F2 1 0.03 66.7 0.44 91.5 0.99 Example 36
(36.4 + 62.1) Comparative Carbon EC + DEC -- 0 LiPO2F2 1 0.09 --
0.59 92.6 -- Example 37 (36 + 63) Example 45 Si FEC + DEC
Crotononitrile 0.5 -- 0 0.09 76.3 0.43 82.5 1.00 (39.8 + 59.7)
Comparative Si FEC + DEC -- -- -- -- 0.38 -- 0.77 82.7 -- Example
38 (40 + 60) Example 46 Si FEC + DEC Crotononitrile 0.5 DFEC 2 0.19
63.5 0.20 -- -- (39.0 + 58.5) Comparative Si FEC + DEC -- 0 DFEC 2
0.52 -- 0.83 -- -- Example 39 (39 + 59) Example 47 Carbon FEC + DEC
Crotononitrile 0.5 -- -- 0.09 85.5 0.32 93.4 1.00 (39.8 + 59.7)
Comparative Carbon FEC + DEC -- 0 -- -- 0.62 -- 0.52 93.5 --
Example 40 (40 + 60) Comparative Carbon FEC + DEC Crotononitrile
0.5 DFEC 2 0.14 78.1 0.43 -- -- Example 41 (39.0 + 58.5)
Comparative Carbon FEC + DEC -- 0 DFEC 2 0.64 -- 0.53 -- -- Example
42 (39 + 59)
[0363] Tables 8 and 9 show the following.
[0364] In Example 37, the amount of gas generated after the
high-temperature storage was reduced compared with Comparative
Example 27 (the Si negative electrode was used, and the nonaqueous
electrolytic solution did not contain unsaturated nitrile compound
(1)). Furthermore, in Example 37, the value of the load
characteristics after storage was large without a significant
reduction in cycle retention rate compared with Comparative Example
27.
[0365] In Example 39 (the Si negative electrode was used; and the
nonaqueous electrolytic solution contained 0.5% by weight of
crotononitrile and also contained fluoroethylene carbonate, which
is a halogen atom-containing cyclic carbonate), the amount of gas
generated after the high-temperature storage was reduced compared
with Comparative Example 28 (the Si negative electrode was used;
and the nonaqueous electrolytic solution did not contain
unsaturated nitrile compound (1) or unsaturated nitrile compound
(2) but contained fluoroethylene carbonate, which is a halogen
atom-containing cyclic carbonate). Also in each of Examples 40 to
42 (the Si negative electrode was used; and the nonaqueous
electrolytic solution contained unsaturated nitrile compound (1) or
unsaturated nitrile compound (2) and also contained fluoroethylene
carbonate, which is a halogen atom-containing cyclic carbonate),
the amount of gas generated after the high-temperature storage was
reduced. Furthermore, in Example 39, the load characteristics after
storage were further improved compared with Comparative Example 28.
A reduction in cycle retention rate was not observed.
[0366] Also in each of Examples 42 to 44 (the Si negative electrode
was used; and the nonaqueous electrolytic solution contained 0.5%
by weight crotononitrile and difluoroethylene carbonate, which is a
halogen atom-containing cyclic carbonate, and either vinylene
carbonate, which is a cyclic carbonate having a carbon-carbon
unsaturated bond, or lithium difluorophosphate, which is a
difluorophosphate), the gas generation during high-temperature
storage was inhibited while the cycle retention rate was maintained
compared with Comparative Examples 29 to 31 (the Si negative
electrode was used; and the nonaqueous electrolytic solution did
not contain unsaturated nitrile compound (1) or unsaturated nitrile
compound (2) but contained difluoroethylene carbonate, which is a
halogen atom-containing cyclic carbonate, vinylene carbonate, which
is a cyclic carbonate having a carbon-carbon unsaturated bond, or
lithium difluorophosphate, which is a difluorophosphate). That is,
the combinations of these additives result in the same effects as
above.
[0367] In Comparative Example 32 (the carbon negative electrode was
used; and the nonaqueous electrolytic solution contained 0.5% by
weight crotononitrile), the amount of gas generated after the
high-temperature storage was reduced compared with Comparative
Example 33 (the carbon negative electrode was used; and the
nonaqueous electrolytic solution did not contained unsaturated
nitrile compound (1)). However, the gas-generation inhibition rate
was lower than that in Example 37 in which the Si negative
electrode was used. Furthermore, in Comparative Example 32, both of
the load characteristics after storage and the cycle capacity
retention rate were markedly deteriorated compared with Comparative
Example 33. From the results, in the case where unsaturated nitrile
compound (1) is used in the battery including the Si negative
electrode, unsaturated nitrile compound (1) is more effective in
inhibiting the gas generation during high-temperature storage than
the case where unsaturated nitrile compound (1) is used in the
battery including the carbon negative electrode. Furthermore, the
use of unsaturated nitrile compound (1) in the battery including
the Si negative electrode is also effective from the viewpoints of
the battery characteristics such as the load characteristics after
storage and the cycle characteristics.
[0368] Also in Example 46 (the Si negative electrode was used; and
the nonaqueous electrolytic solution contained unsaturated nitrile
compound (1) or unsaturated nitrile compound (2) and also contained
fluoroethylene carbonate, which is a halogen atom-containing cyclic
carbonate, as a solvent), the generation of the storage gas was
inhibited without causing a reduction in cycle retention rate, as
compared with Comparative Example 38 (the Si negative electrode was
used; and the nonaqueous electrolytic solution did not contain
unsaturated nitrile compound (1) or unsaturated nitrile compound
(2) but contained fluoroethylene carbonate, which is a halogen
atom-containing cyclic carbonate, as a solvent). That is, the
effect of the present invention is also exhibited to the nonaqueous
electrolytic solution containing the halogen atom-containing cyclic
carbonate serving as a solvent.
[0369] Furthermore, as shown in Example 47 (the carbon negative
electrode was used; and the nonaqueous electrolytic solution
contained unsaturated nitrile compound (1) or unsaturated nitrile
compound (2) and also contained fluoroethylene carbonate, which is
a halogen atom-containing cyclic carbonate, as a solvent), the use
of the halogen atom-containing cyclic carbonate as a solvent is
also effective for the case of using the carbon negative
electrode.
Examples 48 to 63 and Comparative Examples 43 to 55
Preparation of Nonaqueous Electrolytic Solution in Example 61,
Example 62, and Comparative Example 46
[0370] In each of Example 61, Example 62, and Comparative Example
46, under a dry argon atmosphere, sufficiently dried LiPF.sub.6 and
an additive described in Table 11 were dissolved in a mixture of
fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) (volume
ratio=3:7, weight ratio=40:60) in such a manner that the
concentration of LiPF.sub.6 was 1 moldm.sup.-3 and that the
concentration of the additive was the value described in Table 11,
thereby preparing a nonaqueous electrolytic solution (except that
in Comparative Example 46, the additive was not used). As the
halogen atom-containing cyclic carbonate, fluoroethylene carbonate
(FEC) was contained in the nonaqueous electrolytic solution as
described above.
<Preparation of Nonaqueous Electrolytic Solution in Examples and
Comparative Examples Other Than Example 61, Example 62, and
Comparative Example 46>
[0371] In each of Examples and Comparative Examples other than
Example 61, Example 62, and Comparative Example 46, under a dry
argon atmosphere, sufficiently dried LiPF.sub.6 and an additive
described in Table 10 or 11 were dissolved in a mixture of ethylene
carbonate (EC) and diethyl carbonate (DEC) (volume ratio=3:7,
weight ratio=37:63) in such a manner that the concentration of
LiPF.sub.6 was 1 moldm.sup.-3 and that the concentration of the
additive was the value described in Table 10 or 11, thereby
preparing a nonaqueous electrolytic solution (except that in
Comparative Examples 43 and 51, the additives were not used). As
the halogen atom-containing cyclic carbonate,
trans-4,5-difluoroethylene carbonate (DFEC) or fluoroethylene
carbonate (FEC) was used. As the difluorophosphate, lithium
difluorophosphate (LiPO.sub.2F.sub.2) was used.
<Production of Positive Electrode>
[0372] First, 94% by weight of lithium cobaltate (LiCoO.sub.2)
serving as a positive-electrode active material, 3% by weight of
acetylene black serving as a conductive material, and 3% by weight
of polyvinylidene fluoride (PVdF) serving as a binder were mixed in
an N-methylpyrrolidone solvent to form a slurry. The resulting
slurry was applied to both surfaces of aluminum foil having a
thickness of 15 .mu.m and dried in such a manner that the volume
was 90% of the volume of a negative electrode. The resulting
laminate was rolled so as to have a thickness of 85 .mu.m with a
press and then cut into a piece with active material layers each
having a width of 65 mm and a length of 150 mm. The piece was then
cut to form a positive electrode with active material portions each
having a width of 30 mm and a length of 40 mm. The positive
electrode was dried at 80.degree. C. for 12 hours under reduced
pressure before use.
<Production of Negative Electrode>
(Production of Negative Electrode Composed of Silicon Alloy)
[0373] As negative-electrode active materials, 73.2 parts by weight
of silicon, which is a non-carbon material, 8.1 parts by weight of
copper, and 12.2 parts by weight of an artificial graphite powder
(trade name: "KS-6", manufactured by Timcal Ltd.) were used. To
these materials, 54.2 parts by weight of N-methylpyrrolidone
solution containing 12 parts by weight of polyvinylidene fluoride
and then 50 parts by weight of N-methylpyrrolidone were added. The
mixture was mixed using a disperser to form a slurry. The resulting
slurry was uniformly applied to 18-.mu.m-thick copper foil serving
as a negative electrode current collector. The resulting copper
foil was pressed in such a manner that the electrode density was
about 1.5 g/cm.sup.3, and then cut into a piece with an active
material portion having a width of 30 mm and a length of 40 mm,
thereby forming a negative electrode (silicon-alloy negative
electrode). The negative electrode was dried at 60.degree. C. for
12 hours under reduced pressure before use. In Tables 8 and 9, the
Si negative electrode is used for convenience in writing.
(Production of Negative Electrode Composed of Carbon)
[0374] First, 98 parts by weight of an artificial graphite powder
(trade name: KS-44, manufactured by Timcal Ltd.) serving as a
negative-electrode active material, 100 parts by weight of an
aqueous dispersion of sodium carboxymethylcellulose (with a sodium
carboxymethylcellulose content of 1% by weight) serving as a
thickener, and 2 parts by weight of an aqueous dispersion of
styrene-butadiene rubber (with a styrene-butadiene rubber content
of 50% by weight) serving as a binder were mixed with a disperser
to form a slurry. The resulting slurry was applied to both surfaces
of copper foil having a thickness of 10 .mu.m, followed by drying.
The resulting laminate was rolled with a press so as to have a
thickness of 75 .mu.m. The laminate was cut into a piece with
active material portions each having a width of 30 mm and a length
of 40 mm, thereby forming a negative electrode. The negative
electrode was dried at 60.degree. C. for 12 hours under reduced
pressure before use.
<Production of Secondary Battery>
[0375] The positive electrodes, the negative electrode (alloy
negative electrode or carbon negative electrode), and separators
composed of polyethylene were stacked in a sequence of positive
electrode/separator/negative electrode/separator/positive
electrode, thereby forming a battery element. The battery element
was placed in a bag formed of a laminate film in which both
surfaces of an aluminum film (with a thickness of 40 .mu.m) were
covered with resin layers in such a manner that terminals of the
positive electrode and the negative electrode were protruded. Then
0.4 mL of the nonaqueous electrolytic solution was fed into the
bag, followed by vacuum sealing to produce a sheet battery.
[Evaluation of Battery]
1. Storage Test
[0376] A sheet battery held between glass plates to improve contact
between electrodes was charged at a constant current corresponding
to 0.2 C until the battery voltage reached a charge cut-off voltage
of 4.2 V and discharged at a constant current corresponding to 0.2
C until the battery voltage reached a discharge cut-off voltage of
3 V at 25.degree. C. This charge-discharge operation was repeated 3
cycles to stabilize the battery. Then, the battery was subjected to
4.2-V-CCCV charge (0.05 C cut) and stored at 85.degree. C. for 24
hours. The sheet battery was immersed in an ethanol bath before and
after the high-temperature storage. The amount of gas generated
(storage gas) was determined from the change in volume.
[0377] The battery after the storage was discharged at 25.degree.
C. at a constant current of 0.2 C until the battery voltage reached
a discharge cut-off voltage of 3 V, subjected to 4.2 V-CCCV charge
(0.05 C cut), and discharged at a current corresponding to 0.2 C
until the battery voltage reached 3 V, and then a 0.2-C capacity
was measured. Next, the battery was subjected to 4.2-V-CCCV charge
(0.05 C cut) and discharged at a current corresponding to 1.0 C
until the battery voltage reached 3 V, and then a 1.0-C capacity
was measured. The ratio of the 1.0-C capacity after the storage to
the 0.2-C capacity after the storage (1.0-C capacity/0.2-C
capacity) is defined as the load characteristics after storage.
[0378] Furthermore, a value calculated by the subtraction of the
ratio (%) of the amount of gas generated from a battery including a
nonaqueous electrolytic solution that contains dicyano compound (3)
to the amount of gas generated from a corresponding battery
including a nonaqueous electrolytic solution that does not contain
dicyano compound (3) from 100, 1(100-amount of gas generated from
battery including nonaqueous electrolytic solution that contains
dicyano compound (3)/amount of gas generated from battery including
nonaqueous electrolytic solution that does not contain dicyano
compound (3)).times.100), is defined as the gas-generation
inhibition rate (%). The term "1 C" indicates a current value when
a battery is fully charged in one hour.
2. Cycle Test
[0379] The sheet battery held between glass plates to improve
contact between the electrodes was charged at a constant current
corresponding to 0.2 C until the battery voltage reached a charge
cut-off voltage of 4.2 V and discharged at a constant current
corresponding to 0.2 C until the battery voltage reached a
discharge cut-off voltage of 3 V at 25.degree. C. This
charge-discharge operation was repeated three cycles to stabilize
the battery. A cycle test was performed as follows: the
charge-discharge operation of 0.5-C-CCCV charge (0.05 C cut) and
constant-current discharge at 0.5 C until 3 V was repeated. The
rate of a discharge capacity in the 100th cycle to a discharge
capacity in the fourth cycle, i.e., (discharge capacity in 100th
cycle/discharge capacity in 4th cycle), is defined as the cycle
capacity retention rate.
[0380] The ratio of the cycle capacity retention rate of a battery
including a nonaqueous electrolytic solution that contains dicyano
compound (3) to the cycle capacity retention rate of a
corresponding battery including a nonaqueous electrolytic solution
that does not contain dicyano compound (3), i.e., (cycle capacity
retention rate of battery including nonaqueous electrolytic
solution that contains dicyano compound (3)/cycle capacity
retention rate of battery including nonaqueous electrolytic
solution that does not contain dicyano compound (3)), is defined as
the ratio of the cycle capacity retention rates.
<Evaluation Result>
TABLE-US-00010 [0381] TABLE 10 Additive for nonaqueous electrolytic
solution Evaluation result Halogen Load atom- Gas- charac- Cycle
Ratio of Type containing generation teristics capacity cycle of
Dicyano compound (3) cyclic Storage inhibition after retention
capacity negative Content carbonate Difluorophosphate gas rate
storage rate retention Example electrode Type (wt %) (type: wt %)
(wt %) (mL) (%) (1.0 C/0.2 C) (%) rate Example 48 Si Succinonitrile
0.5 -- -- 0.07 69.6 0.46 32.2 0.69 Example 49 Si Glutaronitrile 0.5
-- -- 0.05 78.3 0.34 -- -- Example 50 Si Adiponitrile 0.5 -- --
0.06 73.9 0.26 -- -- Example 51 Si Pimelonitrile 0.5 -- -- 0.03 87
0.65 47.5 1.01 Example 52 Si Pimelonitrile 1 -- -- 0.01 95.7 0.54
47.5 1.01 Example 53 Si Sebaconitrile 0.5 -- -- 0.04 82.6 0.68 --
-- Example 54 Si 3,3'- 0.5 -- -- 0.06 73.9 0.23 48 1.02
oxydipropionitrile Example 55 Si 3,3'- 1 -- -- 0 100 0.22 48.1 1.03
oxydipropionitrile Comparative Si -- 0 -- -- 0.23 -- 0.09 46.9 1.00
Example 43 Example 56 Si Succinonitrile 0.5 DFEC: 2 -- 0.29 39.6
0.31 66.7 0.90 Example 57 Si Pimelonitrile 0.5 DFEC: 2 -- 0.22 54.2
0.21 75.5 1.01 Comparative Si -- 0 DFEC: 2 -- 0.48 -- 0.83 74.5
1.00 Example 44 Example 58 Si Succinonitrile 0.5 -- 1 0.16 42.9
0.03 59.4 0.94 Example 59 Si Pimelonitrile 0.5 -- 1 0.06 78.6 0.08
63.4 1.00 Example 60 Si 3,3'- 0.5 -- 1 0.06 78.6 0.04 64.1 1.01
oxydipropionitrile Comparative Si -- 0 -- 1 0.28 -- 0.39 63.2 1.00
Example 45
TABLE-US-00011 TABLE 11 Additive for nonaqueous Evaluation result
electrolytic solution Gas- Cycle Ratio of Type Halogen atom-
generation Load capacity cycle of Dicyano compound (3) containing
cyclic Difluoro- inhibition characteristics retention capacity
negative Content carbonate phosphate Storage gas rate after storage
rate retention Example electrode Type (wt %) (type: wt %) (wt %)
(mL) (%) (1.0 C/0.2 C) (%) rate Example 61 Si Malononitrile 0.25
.sup.2 -- 0.32 15.8 0.60 86.7 1.05 Example 62 Si Pimelonitrile 0.5
.sup.2 -- 0.1 73.7 0.71 82.2 0.99 Comparative Si -- 0 .sup.2 --
0.38 -- 0.77 82.7 1.00 Example 46 Example 63 Si Succinonitrile 1
FEC: 5 -- 0.23 66.2 0.59 -- -- Comparative Si Acetonitrile .sup.1 1
FEC: 5 -- 0.41 39.7 0.08 -- -- Example 47 Comparative Si -- 0 FEC:
5 -- 0.68 -- 0.23 -- -- Example 48 Comparative Carbon
Succinonitrile 0.5 -- -- 0.06 25.0 0.22 48.1 0.61 Example 49
Comparative Carbon Pimelonitrile 0.5 -- -- 0.04 50.0 0.32 65.4 0.83
Example 50 Comparative Carbon -- 0 -- -- 0.08 -- 0.46 79.0 1.00
Example 51 Comparative Carbon Pimelonitrile 0.5 DFEC: 2 -- 0.19
45.7 0.39 88 0.97 Example 52 Comparative Carbon -- 0 DFEC: 2 --
0.35 -- 0.46 91 1.00 Example 53 Comparative Carbon Pimelonitrile
0.5 -- 1 0.04 55.6 0.46 91.6 0.99 Example 54 Comparative Carbon --
0 -- 1 0.09 -- 0.59 92.6 1.00 Example 55 .sup.1 Nitrile compound
other than dicyano compound (3) .sup.2 Nonaqueous solvent (FEC/DEC
= 3/7 (volume ratio))
<Discussion>
[0382] Tables 10 and 11 show the following.
[0383] In each of Examples 48 to 55 (the Si negative electrode was
used; and the nonaqueous electrolytic solution contained 0.5% by
weight or 1% by weight of dicyano compound (3)), the amount of gas
generated after the high-temperature storage was reduced compared
with Comparative Example 43 (the Si negative electrode was used;
and the nonaqueous electrolytic solution did not contain dicyano
compound (3)). Furthermore, in each of Examples 48 to 55, the value
of the load characteristics after storage was larger than that in
Comparative Example 43. Among these, the particularly excellent
effects were observed in Examples 51 to 53. Moreover, in Example
48, the cycle capacity retention rate was smaller than that in
Comparative Example 43. In each of Examples 51, 52, 54, and 55, the
cycle capacity retention rate was large. The results demonstrate
that dicyano compound (3) has the effect of inhibiting gas
generation during high-temperature storage when the Si negative
electrode is used. In particular, the effect is significant when n
represents 5 or more in general formula (3) described above,
improving the load characteristics after storage, the cycle
capacity retention rate, and the ratio of the cycle capacity
retention rate.
[0384] Furthermore, A comparison between Examples 51 and 52 or a
comparison between Examples 54 and 55 show that an increase in
dicyano compound (3) content from 0.5% by weight to 1% by weight
particularly improves the gas-generation inhibition rate.
[0385] In Example 56 (the Si negative electrode was used; and the
nonaqueous electrolytic solution contained 0.5% by weight of
succinonitrile and also contained the halogen atom-containing
cyclic carbonate), the amount of gas generated after the
high-temperature storage was reduced compared with Comparative
Example 44 (the Si negative electrode was used; and the nonaqueous
electrolytic solution did not contain dicyano compound (3) but
contained the halogen atom-containing cyclic carbonate). In Example
57 (the Si negative electrode was used; and the nonaqueous
electrolytic solution contained 0.5% by weight of pimelonitrile and
also contained the halogen atom-containing cyclic carbonate), the
amount of gas generated after the high-temperature storage was
further reduced. In addition, in Example 57, the cycle capacity
retention rate was large. The results demonstrate that dicyano
compound (3) has the effect of inhibiting gas generation during
high-temperature storage when the Si negative electrode is used and
the nonaqueous electrolytic solution contains the halogen
atom-containing cyclic carbonate. In particular, the effect is
significant when n represents 5 or more in general formula (3)
described above, improving the cycle capacity retention rate.
[0386] In Example 58 (the Si negative electrode was used; and the
nonaqueous electrolytic solution contained 0.5% by weight of
succinonitrile and also contained difluorophosphate), the amount of
gas generated after the high-temperature storage was reduced
compared with Comparative Example 45 (the Si negative electrode was
used; and the nonaqueous electrolytic solution did not contain
dicyano compound (3) but contained difluorophosphate). In each of
Examples 59 and 60 (the Si negative electrode was used; and the
nonaqueous electrolytic solution contained 0.5% by weight of
pimelonitrile or 3,3'-oxydipropionitrile and also contained
difluorophosphate), the amount of gas generated after the
high-temperature storage was further reduced. Moreover, in each of
Examples 59 and 60, the cycle capacity retention rate was large.
The results demonstrate that dicyano compound (3) has the effect of
inhibiting gas generation during high-temperature storage when the
Si negative electrode is used and the nonaqueous electrolytic
solution contains monofluorophosphate and/or difluorophosphate. In
particular, the effect is significant when n represents 5 or more
in general formula (3) described above, maintaining or improving
the cycle capacity retention rate.
[0387] In each of Comparative Examples 49 and 50 (the carbon
negative electrode was used; and the nonaqueous electrolytic
solution contained 0.5% by weight of dicyano compound (3)), the
amount of gas generated after the high-temperature storage was
reduced compared with Comparative Example 51 (the carbon negative
electrode was used; and the nonaqueous electrolytic solution did
not contain dicyano compound (3)). However, the gas-generation
inhibition rate was lower than those in Examples 48, 51, and 52 in
which the Si negative electrodes were used. In each of Comparative
Examples 49 and 50, the load characteristics after storage and the
cycle capacity retention rate were markedly deteriorated compared
with those in Comparative Example 51. From the results, in the case
where dicyano compound (3) is used in the battery including the Si
negative electrode, dicyano compound (3) is more effective in
inhibiting the gas generation during high-temperature storage than
the case where dicyano compound (3) is used in the battery
including the carbon negative electrode. Furthermore, the use of
dicyano compound (3) in the battery including the Si negative
electrode is also effective from the viewpoints of the battery
characteristics such as the load characteristics after storage and
the cycle characteristics.
[0388] In Comparative Example 52 (the carbon negative electrode was
used; and the nonaqueous electrolytic solution contained 0.5% by
weight of pimelonitrile and also contained the halogen
atom-containing cyclic carbonate), the amount of gas generated
after the high-temperature storage was reduced compared with
Comparative Example 53 (the carbon negative electrode was used; and
the nonaqueous electrolytic solution did not contain dicyano
compound (3) but contained the halogen atom-containing cyclic
carbonate). However, the gas-generation inhibition rate was lower
than that in Example 57 in which the Si negative electrode was
used. Furthermore, in Comparative Example 52, the load
characteristics after storage and the cycle capacity retention rate
were markedly deteriorated compared with Comparative Example 53.
From the results, in the case where dicyano compound (3) is used in
the battery including the Si negative electrode, dicyano compound
(3) is more effective in inhibiting the gas generation during
high-temperature storage than the case where dicyano compound (3)
is used in the battery including the carbon negative electrode.
Furthermore, the use of dicyano compound (3) in the battery
including the Si negative electrode is also effective from the
viewpoints of the battery characteristics such as the load
characteristics after storage and the cycle characteristics.
[0389] In Comparative Example 54 (the carbon negative electrode was
used; and the nonaqueous electrolytic solution contained 0.5% by
weight of pimelonitrile and also contained difluorophosphate), the
amount of gas generated after the high-temperature storage was
reduced compared with Comparative Example 55 (the carbon negative
electrode was used; and the nonaqueous electrolytic solution did
not contain dicyano compound (3) but contained difluorophosphate).
However, the gas-generation inhibition rate was lower than that in
Example 59 in which the Si negative electrode was used.
Furthermore, in Comparative Example 54, the load characteristics
after storage and the cycle capacity retention rate were markedly
deteriorated compared with Comparative Example 55. From the
results, in the case where dicyano compound (3) is used in the
battery including the Si negative electrode, dicyano compound (3)
is more effective in inhibiting the gas generation during
high-temperature storage than the case where dicyano compound (3)
is used in the battery including the carbon negative electrode.
Furthermore, the use of dicyano compound (3) in the battery
including the Si negative electrode is also effective from the
viewpoints of the battery characteristics such as the load
characteristics after storage and the cycle characteristics.
[0390] In each of Examples 61 and 62 (the Si negative electrode was
used; and the FEC/DEC (3/7) nonaqueous solvent was used as the
nonaqueous electrolytic solution and 0.25% by weight of
malononitrile or 0.5% by weight of pimelonitrile), the amount of
gas generated after the high-temperature storage was reduced
compared with Comparative Example 46 (the Si negative electrode was
used; and the FEC/DEC (3/7) nonaqueous solvent was used as the
nonaqueous electrolytic solution and did not contained dicyano
compound (3)). Furthermore, in Example 62, the cycle
characteristics were also improved compared with Example 51.
[0391] In examples and comparative examples described above, the
advantages were proved by dicyano compound (3) having two cyano
groups. The present invention, however, is not limited to these
examples without departing from the scope of the invention. That
is, the present invention is characterized in that the electrolytic
solution contains the compound having 2 to 4 cyano groups in its
structural formula. With respect to the characteristics thereof, a
comparison of Example 63 in which the electrolytic solution
contains succinonitrile serving as a compound having two or more
cyano groups and Comparative Example 47 in which the electrolytic
solution contains acetonitrile serving as a compound having a
single cyano group clearly shows that the electrolytic solution in
Example 63 exhibits a reduction in storage gas and improvement in
load characteristics after storage, as compared with Comparative
Example 47. In Comparative Example 47, the load characteristics
after storage is impaired compared with Comparative Example 48.
These results clearly show that the electrolytic solution
containing the compound having 2 to 4 cyano groups in its
structural formula has the unique effect as described above. It is
thus speculated that an electrolytic solution containing a compound
having 3 to 4 cyano groups in its structural formula also has the
same effect as the electrolytic solution containing the compound
having 2 to 4 cyano groups in its structural formula.
[0392] According to the nonaqueous electrolytic solution of the
present invention, it is possible to produce a high energy density
nonaqueous electrolyte secondary battery having a high capacity and
excellent cycle characteristics and suppressing the decomposition
of an electrolytic solution used in the nonaqueous electrolyte
secondary battery and the deterioration thereof when used in a
high-temperature environment. Thus, the battery can be suitably
used in various fields such as electronic apparatuses for which
nonaqueous electrolyte secondary batteries are used.
[0393] Applications of the nonaqueous electrolytic solution for use
in secondary batteries and the nonaqueous electrolyte secondary
battery according to the present invention are not particularly
limited, and the battery can be used various known applications.
Examples thereof include notebook type personal computers,
pen-input personal computers, mobile personal computers, electronic
book players, portable telephones, portable facsimile telegraphs,
portable copiers, portable printers, headphone stereos, video
movies, liquid-crystal television sets, handy cleaners, portable
CDs, mini disks, transceivers, electronic pocketbooks, pocket
calculators, memory cards, portable tape recorders, radios, backup
power sources, motors, cars, motorcycles, small motor vehicles,
bicycles, illuminators, toys, game appliances, clocks,
stroboscopes, and cameras.
[0394] While the present invention has been described in detail
with reference to the specific embodiments, it will be understood
by the skilled person that various changes and modifications can be
made without departing from the spirit and scope of the invention.
The present invention contains subject matter related to Japanese
Patent Application No. 2006-329935 filed in the Japanese Patent
Office on Dec. 6, 2006 and Japanese Patent Application No.
2007-170651 filed in the Japanese Patent Office on Jun. 28, 2007,
the entire contents of which are incorporated herein by
reference.
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