U.S. patent application number 15/296777 was filed with the patent office on 2017-02-09 for power storage device, lithium-ion secondary battery, electric double layer capacitor and lithium-ion capacitor.
The applicant listed for this patent is SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. Invention is credited to Toru ITAKURA, Kyosuke ITO.
Application Number | 20170040642 15/296777 |
Document ID | / |
Family ID | 45399581 |
Filed Date | 2017-02-09 |
United States Patent
Application |
20170040642 |
Kind Code |
A1 |
ITO; Kyosuke ; et
al. |
February 9, 2017 |
POWER STORAGE DEVICE, LITHIUM-ION SECONDARY BATTERY, ELECTRIC
DOUBLE LAYER CAPACITOR AND LITHIUM-ION CAPACITOR
Abstract
One object is to provide a power storage device including an
electrolyte using a room-temperature ionic liquid which includes a
univalent anion and a cyclic quaternary ammonium cation having
excellent reduction resistance. Another object is to provide a
high-performance power storage device. A room-temperature ionic
liquid which includes a cyclic quaternary ammonium cation
represented by a general formula (G1) below is used for an
electrolyte of a power storage device. In the general formula (G1),
one or two of R.sub.1 to R.sub.5 are any of an alkyl group having 1
to 20 carbon atoms, a methoxy group, a methoxymethyl group, and a
methoxyethyl group. The other three or four of R.sub.1 to R.sub.5
are hydrogen atoms. A.sup.- is a univalent imide anion, a univalent
methide anion, a perfluoroalkyl sulfonic acid anion,
tetrafluoroborate (BF.sub.4.sup.-), or hexafluorophosphate
(PF.sub.6.sup.-).
Inventors: |
ITO; Kyosuke; (Hadano,
JP) ; ITAKURA; Toru; (Atsugi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEMICONDUCTOR ENERGY LABORATORY CO., LTD. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
45399581 |
Appl. No.: |
15/296777 |
Filed: |
October 18, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14450786 |
Aug 4, 2014 |
9478368 |
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15296777 |
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13167030 |
Jun 23, 2011 |
8795544 |
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14450786 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G 11/22 20130101;
H01M 10/0525 20130101; H01M 2300/0034 20130101; Y02E 60/10
20130101; H01M 10/0566 20130101; Y02T 10/70 20130101; H01M 10/0569
20130101; Y02E 60/13 20130101; H01G 11/62 20130101; H01M 10/0563
20130101; H01M 10/0561 20130101; H01G 11/58 20130101 |
International
Class: |
H01M 10/0569 20060101
H01M010/0569; H01G 11/22 20060101 H01G011/22; H01M 10/0525 20060101
H01M010/0525; H01G 11/62 20060101 H01G011/62 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2010 |
JP |
2010-149169 |
Claims
1. (canceled)
2. A power storage device comprising: a first positive electrode; a
first negative electrode; a first electrolyte salt comprising a
lithium ion; and an ionic liquid represented by a general formula
(G2) ##STR00015## and 1-ethyl-3-methylimidazolium
bis(trifluoromethanesulfonyl)imide; wherein R.sub.2 represents an
alkyl group having 1 to 4 carbon atoms, wherein R.sub.1 represents
a hydrogen atom, and wherein A.sup.- represents a univalent imide
anion selected from (C.sub.nF.sub.2n+1SO.sub.2).sub.2N.sup.- (n=0
to 4), (C.sub.mF.sub.2m+1SO.sub.3).sup.- (m=0 to 4), and
CF.sub.2(CF.sub.2SO.sub.2).sub.2N.sup.-.
3. The power storage device according to claim 2, wherein the power
storage device is a lithium-ion secondary battery.
4. The power storage device according to claim 2, the power storage
device further comprising: a first solvent, wherein the first
solvent is a room-temperature ionic liquid other than the ionic
liquid represented by the general formula (G2).
5. The power storage device according to claim 2, further
comprising: a second positive electrode; and a second negative
electrode, wherein the second positive electrode is not
electrically connected to the first positive electrode.
6. The power storage device according to claim 2, further
comprising a reference electrode, the reference electrode
comprising: the 1-ethyl-3-methylimidazolium
bis(trifluoromethanesulfonyl)imide; and a second electrolyte
salt.
7. The power storage device according to claim 6, wherein the
second electrolyte salt is different from the first electrolyte
salt.
8. The power storage device according to claim 7, wherein the
second electrolyte salt comprises a silver ion.
9. The power storage device according to claim 2, wherein the
A.sup.- is (FSO.sub.2).sub.2N.sup.- or
(CF.sub.3SO.sub.2).sub.2N.sup.-.
10. An electronic appliance comprising the power storage device
according to claim 2.
11. A power storage device comprising: a first positive electrode;
a first negative electrode; a first electrolyte salt comprising a
lithium ion; and an ionic liquid represented by a general formula
(G2) ##STR00016## and a reference electrode comprising: a second
positive electrode; a second negative electrode; a second
electrolyte salt; and 1-ethyl-3-methylimidazolium
bis(trifluoromethanesulfonyl)imide, wherein R.sub.2 represents an
alkyl group having 1 to 4 carbon atoms, wherein R.sub.1 represents
a hydrogen atom, and wherein A.sup.- represents a univalent imide
anion selected from (C.sub.nF.sub.2n+1SO.sub.2).sub.2N.sup.- (n=0
to 4), (C.sub.mF.sub.2m+1SO.sub.3).sup.- (m=0 to 4), and
CF.sub.2(CF.sub.2SO.sub.2).sub.2N.sup.-.
12. The power storage device according to claim 11, wherein the
power storage device is a lithium-ion secondary battery.
13. The power storage device according to claim 11, the power
storage device further comprising: a first solvent, wherein the
first solvent is a room-temperature ionic liquid other than the
ionic liquid represented by the general formula (G2).
14. The power storage device according to claim 11, wherein the
second electrolyte salt is different from the first electrolyte
salt.
15. The power storage device according to claim 11, wherein the
second electrolyte salt comprises a silver ion.
16. The power storage device according to claim 11, wherein the
A.sup.- is (FSO.sub.2).sub.2N.sup.- or
(CF.sub.3SO.sub.2).sub.2N.sup.-.
17. The power storage device according to claim 11, wherein the
ionic liquid is represented by a general formula (G4)
##STR00017##
18. An electronic appliance comprising the power storage device
according to claim 11.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a room-temperature ionic
liquid and a power storage device using the room-temperature ionic
liquid.
[0003] Note that the power storage device indicates all elements
and devices which have a function of storing power.
[0004] 2. Description of the Related Art
[0005] A lithium-ion secondary battery which is one of power
storage devices is used in a variety of applications including
mobile phones, electric vehicles (EV), and the like.
Characteristics such as high energy density, cycle characteristics,
and safety under various operating environments are required for a
lithium-ion secondary battery.
[0006] As an organic solvent for an electrolyte of a lithium-ion
secondary battery, a cyclic carbonate which has high dielectric
constant and excellent ion conductivity is often used. Among the
cyclic carbonate, ethylene carbonate is often used.
[0007] However, not only ethylene carbonate but many organic
solvents have volatility and a low flash point. For this reason, in
the case where an organic solvent is used for an electrolyte of a
lithium-ion secondary battery, the temperature inside the
lithium-ion secondary battery might rise due to a short circuit,
overcharge, or the like and the lithium-ion secondary battery might
burst or catch fire.
[0008] In view of the above, it has been considered to use a
room-temperature ionic liquid which is less likely to burn and
volatilize as an electrolyte of a lithium-ion secondary
battery.
REFERENCE
Patent Document
[0009] [Patent Document 1] Japanese Published Patent Application
No. 2003-331918
SUMMARY OF THE INVENTION
[0010] When a room-temperature ionic liquid is used for an
electrolyte of a lithium-ion secondary battery, there is a problem
in that a low potential negative electrode material cannot be used
because of low reduction resistance of a room-temperature ionic
liquid. Thus, a technique has been disclosed, which enables
dissolution and precipitation of lithium which is a low potential
negative electrode material without an additive by improving the
reduction resistance of a room-temperature ionic liquid using
quaternary ammonium salt (see Patent Document 1). However, the
reduction potential of a room-temperature ionic liquid whose
reduction resistance is thus improved is substantially equivalent
to an oxidation-reduction potential of lithium. Further improvement
is required for the reduction resistance of a room-temperature
ionic liquid.
[0011] In view of the above problem, one object of the present
invention is to provide a power storage device including an
electrolyte using a room-temperature ionic liquid which is
excellent in reduction resistance. Another object is to provide a
high-performance power storage device.
[0012] One embodiment of the present invention is a power storage
device including a room-temperature ionic liquid represented by a
general formula (G1) below, which includes a cyclic quaternary
ammonium cation.
##STR00001##
[0013] In the general formula (G1), one or two of R.sub.1 to
R.sub.5 are any of an alkyl group having 1 to 20 carbon atoms, a
methoxy group, a methoxymethyl group, and a methoxyethyl group; the
other three or four of R.sub.1 to R.sub.5 are hydrogen atoms; and
A.sup.- is a univalent imide anion, a univalent methide anion, a
perfluoroalkyl sulfonic acid anion, tetrafluoroborate
(BF.sub.4.sup.-), or hexafluorophosphate (PF.sub.6.sup.-).
[0014] Specifically, one or two of R.sub.1 to R.sub.5 in the
room-temperature ionic liquid represented by the general formula
(G1) are preferably an alkyl group having 1 to 4 carbon atoms.
[0015] Another embodiment of the present invention is a power
storage device including an electrolyte using a room-temperature
ionic liquid represented by a general formula (G2) below, which
includes a cyclic quaternary ammonium cation.
##STR00002##
[0016] In the general formula (G2), one of R.sub.1 and R.sub.2 is
any of an alkyl group having 1 to 20 carbon atoms, a methoxy group,
a methoxymethyl group, and a methoxyethyl group; the other of
R.sub.1 and R.sub.2 is a hydrogen atom; and A.sup.- is a univalent
imide anion, a univalent methide anion, a perfluoroalkyl sulfonic
acid anion, tetrafluoroborate (BF.sub.4.sup.-), or
hexafluorophosphate (PF.sub.6.sup.-).
[0017] Another embodiment of the present invention is a power
storage device including an electrolyte using the room-temperature
ionic liquid represented by the general formula (G2), in which one
of R.sub.1 and R.sub.2 is an alkyl group having 1 to 4 carbon
atoms.
[0018] Another embodiment of the present invention is a power
storage device including an electrolyte using a room-temperature
ionic liquid represented by a general formula (G3) below, which
includes a cyclic quaternary ammonium cation.
##STR00003##
[0019] In the general formula (G3), A.sup.- is a univalent imide
anion, a univalent methide anion, a perfluoroalkyl sulfonic acid
anion, tetrafluoroborate (BF.sub.4.sup.-), or hexafluorophosphate
(PF.sub.6.sup.-).
[0020] Another embodiment of the present invention is a power
storage device including an electrolyte using a room-temperature
ionic liquid represented by a general formula (G4) below, which
includes a cyclic quaternary ammonium cation.
##STR00004##
[0021] In the general formula (G4), A.sup.- is a univalent imide
anion, a univalent methide anion, a perfluoroalkyl sulfonic acid
anion, tetrafluoroborate (BF.sub.4.sup.-), or hexafluorophosphate
(PF.sub.6.sup.-).
[0022] Another embodiment of the present invention is a power
storage device including an electrolyte using a room-temperature
ionic liquid which includes any one of univalent anions selected
from (C.sub.nF.sub.2n+1SO.sub.2).sub.2N.sup.- (n=0 to 4),
(C.sub.mF.sub.2m+1SO.sub.3).sup.- (m=0 to 4), and CF.sub.2
(CF.sub.2SO.sub.2).sub.2N.sup.- for A.sup.- in the general formulae
(G1) to (G4).
[0023] Another embodiment of the present invention is a lithium-ion
secondary battery at least including a positive electrode, a
negative electrode, any one of the room-temperature ionic liquids
represented by the general formulae (G1) to (G4), and electrolyte
salt including lithium. Any one of the room-temperature ionic
liquids represented by the general formulae (G1) to (G4) and the
electrolyte salt including lithium are included in an
electrolyte.
[0024] Another embodiment of the present invention is an electric
double layer capacitor at least including a positive electrode, a
negative electrode, and any one of the room-temperature ionic
liquids represented by the general formulae (G1) to (G4) which is
used for an electrolyte.
[0025] Another embodiment of the present invention is a lithium-ion
capacitor at least including a positive electrode, a negative
electrode, any one of the room-temperature ionic liquids
represented by the general formulae (G1) to (G4), and electrolyte
salt including lithium. Any one of the room-temperature ionic
liquids represented by the general formulae (G1) to (G4) and the
electrolyte salt including lithium are included in an
electrolyte.
[0026] According to one embodiment of the present invention, a
power storage device including an electrolyte using a
room-temperature ionic liquid which is excellent in reduction
resistance can be provided. Further, a high-performance power
storage device can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIGS. 1A and 1B are cross-sectional views of lithium-ion
secondary batteries.
[0028] FIG. 2A is a top view of a lithium-ion secondary battery and
FIG. 2B is a perspective view of a lithium-ion secondary
battery.
[0029] FIGS. 3A and 3B are perspective views showing a
manufacturing method of a lithium-ion secondary battery.
[0030] FIG. 4 is a perspective view showing a manufacturing method
of the lithium-ion secondary battery.
[0031] FIG. 5 is a perspective view showing an example of an
application mode of a power storage device.
[0032] FIGS. 6A and 6B are graphs each showing NMR charts of
1,2-dimethyl-1-propylpiperidinium
bis(trifluoromethanesulfonyl)imide.
[0033] FIGS. 7A and 7B are graphs each showing NMR charts of
1,3-dimethyl-1-propylpiperidinium
bis(trifluoromethanesulfonyl)imide.
[0034] FIG. 8 is a graph showing linear sweep voltammograms of
synthesized samples and a comparative sample.
[0035] FIGS. 9A and 9B are graphs each showing NMR charts of
1,3-dimethyl-1-propylpiperidinium bis(fluorosulfonyl)imide.
[0036] FIG. 10 is a perspective view showing a manufacturing method
of a lithium-ion secondary battery.
[0037] FIG. 11 is a graph showing charge and discharge
characteristics of a manufactured lithium-ion secondary
battery.
DETAILED DESCRIPTION OF THE INVENTION
[0038] Hereinafter embodiments of the present invention will be
described in detail with reference to the accompanying drawings.
Note that the present invention is not limited to the following
description and it is easily understood by those skilled in the art
that the mode and details can be variously changed without
departing from the scope and spirit of the present invention.
Therefore the invention should not be construed as being limited to
the description of the embodiment below. In describing structures
of the present invention with reference to the drawings, the same
reference numerals are used in common for the same portions in
different drawings. The same hatching pattern is applied to similar
parts, and the similar parts are not especially denoted by
reference numerals in some cases. In addition, an insulating layer
is not illustrated in a top view for convenience in some cases.
Note that the size, the layer thickness, or the region of each
structure shown in each drawing is exaggerated for clarity in some
cases. Consequently, the present invention is not necessarily
limited to such scales shown in the drawings.
Embodiment 1
[0039] In this embodiment, an electrolyte of a power storage device
which is one embodiment of the present invention, and a
room-temperature ionic liquid which is used for the electrolyte,
which is one embodiment of the present invention, will be
described.
[0040] A room-temperature ionic liquid of one embodiment of the
present invention includes a cyclic quaternary ammonium cation and
a univalent anion. The room-temperature ionic liquid can be
represented by a general formula (G1) below.
##STR00005##
[0041] In the general formula (G1), one or two of R.sub.1 to
R.sub.5 are any of an alkyl group having 1 to 20 carbon atoms, a
methoxy group, a methoxymethyl group, and a methoxyethyl group. The
other three or four of R.sub.1 to R.sub.5 are hydrogen atoms.
A.sup.- is a univalent imide anion, a univalent methide anion, a
perfluoroalkyl sulfonic acid anion, tetrafluoroborate
(BF.sub.4.sup.-), or hexafluorophosphate (PF.sub.6.sup.-).
[0042] In the case where R.sub.1 to R.sub.5 in the general formula
(G1) are an alkyl group having 1 to 20 carbon atoms, carbon atoms
having small carbon number (for example, 1 to 4 carbon atoms) is
used because the viscosity of the synthesized room-temperature
ionic liquid can be reduced; which is preferable for a power
storage device.
[0043] When a room-temperature ionic liquid having low reduction
resistance (also referred to as stability against reduction) is
used for an electrolyte of a power storage device, the
room-temperature ionic liquid is reduced by receiving electrons
from a positive electrode material or a negative electrode material
and therefore decomposed. Characteristics of the power storage
device deteriorate as a result.
[0044] "Reduction of a room-temperature ionic liquid" means that a
room-temperature ionic liquid receives electrons from a positive
electrode material or a negative electrode material. Thus, the
stability against reduction can be improved by making it difficult
particularly for a cation having a positive charge, which is
included in the room-temperature ionic liquid, to receive
electrons, i.e., lowering the reduction potential of the
room-temperature ionic liquid.
[0045] Inductive effects are caused by an electron donating
substituent included in the room-temperature ionic liquids of
embodiments of the present invention. In the room-temperature ionic
liquid, electric polarization of a cation which is an ion having a
positive charge is alleviated due to inductive effects, so that it
is difficult for the cation to receive electrons. Consequently, the
reduction resistance of the room-temperature ionic liquid is
improved.
[0046] As described above, the electron donating substituent can be
any one of an alkyl group having 1 to 20 carbon atoms, a methoxy
group, a methoxymethyl group, and a methoxyethyl group. The alkyl
group having 1 to 20 carbon atoms may be either a straight-chain
alkyl group or a branched-chain alkyl group.
[0047] The reduction potential of the room-temperature ionic liquid
can be lowered and the reduction resistance of the room-temperature
ionic liquid can be improved even when the general formula (G1)
includes either one or two electron donating substituents.
[0048] A room-temperature ionic liquid of one embodiment of the
present invention includes a cyclic quaternary ammonium cation and
a univalent anion. The room-temperature ionic liquid can be
represented by a general formula (G2) below.
##STR00006##
[0049] One of R.sub.1 and R.sub.2 in the general formula (G2) is
any one of an alkyl group having 1 to 20 carbon atoms, a methoxy
group, a methoxymethyl group, and a methoxyethyl group. The other
of R.sub.1 and R.sub.2 is a hydrogen atom. A.sup.- is a univalent
imide anion, a univalent methide anion, a perfluoroalkyl sulfonic
acid anion, BF.sub.4.sup.-, or PF.sub.6.sup.-.
[0050] It is preferable to use a carbon atom having small carbon
number for an alkyl group in the general formula (G2) as in the
general formula (G1) because a cyclic quaternary ammonium cation
can be easily synthesized.
[0051] In the general formula (G2), R.sub.3 to R.sub.5 of the
general formula (G1) are hydrogen atoms, so that the general
formula (G2) is a room-temperature ionic liquid whose reduction
resistance is improved.
[0052] Further, one embodiment of the present invention is a
room-temperature ionic liquid including a methyl group as R.sub.1
and a hydrogen atom as R.sub.2 in the general formula (G2). The
room-temperature ionic liquid can be represented by a general
formula (G3) below. A.sup.- is any one of a univalent imide anion,
a univalent methide anion, a perfluoroalkyl sulfonic acid anion,
BF.sub.4.sup.-, and PF.sub.6.sup.-.
##STR00007##
[0053] Furthermore, one embodiment of the present invention is a
room-temperature ionic liquid including a hydrogen atom as R.sub.1
and a methyl group as R.sub.2 in the general formula (G2). The
room-temperature ionic liquid can be represented by a general
formula (G4) below. A.sup.- is any one of a univalent imide anion,
a univalent methide anion, a perfluoroalkyl sulfonic acid anion,
BF.sub.4.sup.-, and PF.sub.6.sup.-.
##STR00008##
[0054] The general formulae (G3) and (G4) are room-temperature
ionic liquids based on the general formula (G2) and further based
on the general formula (G1). Therefore, the general formulae (G3)
and (G4) are room-temperature ionic liquids whose reduction
resistance is improved.
[0055] Further, A.sup.- in the general formulae (G1) to (G4) is any
one of a univalent imide anion, a univalent methide anion, a
perfluoroalkyl sulfonic acid anion, BF.sub.4.sup.-, and
PF.sub.6.sup.-; however, A.sup.- is not limited to this. Any anion
may be used as A.sup.- as long as it serves as a room-temperature
ionic liquid with a cyclic quaternary ammonium cation of one
embodiment of the present invention.
[0056] Here, calculation results of an improvement of the reduction
resistance caused by an electron donating substituent are
shown.
[0057] A lowest unoccupied molecular orbital level (LUMO level) of
a cation in each of six kinds of room-temperature ionic liquids
determined by a quantum chemistry computational program is shown in
Table 1. The six kinds of room-temperature ionic liquids each
include a methyl group as substituents of R.sub.1 to R.sub.5 in the
general formula (G1). The six kinds of room-temperature ionic
liquids are represented by structural formulae (.alpha.-1) to
(.alpha.-8) below. In addition, as a comparative example, a lowest
unoccupied molecular orbital level (LUMO level) of a
(N-methyl-N-propylpiperidinium) cation represented by a structural
formula (.alpha.-9) below is shown in the Table 1. A
(N-methyl-N-propylpiperidinium) cation is a room-temperature ionic
liquid having a reduction potential which is the same degree as
that of an oxidation-reduction potential of lithium which is used
as a negative electrode of a power storage device.
##STR00009## ##STR00010##
TABLE-US-00001 TABLE 1 LUMO Level Structural Formula (.alpha.-1)
-3.047 [eV] Structural Formula (.alpha.-2) -3.174 [eV] Structural
Formula (.alpha.-3) -3.192 [eV] Structural Formula (.alpha.-4)
-2.941 [eV] Structural Formula (.alpha.-5) -3.013 [eV] Structural
Formula (.alpha.-6) -2.877 [eV] Structural Formula (.alpha.-7)
-3.125 [eV] Structural Formula (.alpha.-8) -3.102 [eV] Structural
Formula (.alpha.-9) -3.244 [eV]
[0058] In the quantum chemistry computation of this embodiment, the
optimal molecular structures in the ground state and a triplet
state of a cation in each of the room-temperature ionic liquids of
embodiments of the present invention and a
(N-methyl-N-propylpiperidinium) cation are calculated by using the
density functional theory (DFT). The total energy of the DFT is
represented as the sum of potential energy, electrostatic energy
between electrons, electronic kinetic energy, and
exchange-correlation energy including all the complicated
interactions between electrons. Also in the DFT, an
exchange-correlation interaction is approximated by a functional (a
function of another function) of one electron potential represented
in terms of electron density to enable high-speed and
highly-accurate calculations. Here, B3LYP, which is a hybrid
functional, is used to specify the weight of each parameter related
to exchange-correlation energy. In addition, as a basis function,
6-311 (a basis function of a triple-split valence basis set using
three contraction functions for each valence orbital) is applied to
all the atoms. By the above basis function, for example, orbits of
1s to 3s are considered in the case of hydrogen atoms while orbits
of 1s to 4s and 2p to 4p are considered in the case of carbon
atoms. Furthermore, to improve calculation accuracy, the p function
and the d function as polarization basis sets are added to hydrogen
atoms and atoms other than hydrogen atoms respectively.
[0059] Note that Gaussian 09 is used as the quantum chemistry
computational program. A high performance computer (Altix 4700,
manufactured by SGI Japan, Ltd.) is used for the calculations. The
quantum chemistry computation is performed assuming that all of the
cations represented by the structural formulae (.alpha.-1) to
(.alpha.-9) have the most stable structure and are in a vacuum.
[0060] In the case where a room-temperature ionic liquid is used
for an electrolyte of a power storage device, the reduction
resistance of the room-temperature ionic liquid results in the
degree of electrons received from a positive electrode or a
negative electrode by a cation included in the room-temperature
ionic liquid, as described above.
[0061] For example, when the LUMO level of a cation is higher than
a conduction band of a negative electrode material, a
room-temperature ionic liquid including the cation is not reduced.
The reduction resistance of the cation with respect to lithium can
be evaluated by comparing the LUMO level of the cation with the
LUMO level of a (N-methyl-N-propylpiperidinium) cation having a
reduction potential substantially equivalent to an
oxidation-reduction potential of lithium that is a typical low
potential negative electrode material. In other words, it can be
said that when the LUMO level of a cation in the room-temperature
ionic liquids of embodiments of the present invention is higher
than the LUMO level of a (N-methyl-N-propylpiperidinium) cation,
the room-temperature ionic liquids of embodiments of the present
invention are excellent in reduction resistance.
[0062] From Table 1, the LUMO level of the cation represented by
the structural formula (.alpha.-1) is -3.047 eV; the LUMO level of
the cation represented by the structural formula (.alpha.-2) is
-3.174 eV; the LUMO level of the cation represented by the
structural formula (.alpha.-3) is -3.192 eV; the LUMO level of the
cation represented by the structural formula (.alpha.-4) is -2.941
eV; the LUMO level of the cation represented by the structural
formula (.alpha.-5) is -3.013 eV; the LUMO level of the cation
represented by the structural formula (.alpha.-6) is -2.877 eV; the
LUMO level of the cation represented by the structural formula
(.alpha.-7) is -3.125 eV; and the LUMO level of the cation
represented by the structural formula (.alpha.-8) is -3.102 eV.
[0063] The LUMO level of the (N-methyl-N-propylpiperidinium) cation
that is a comparative example represented by the structural formula
(.alpha.-9) is -3.244 eV. The LUMO levels of all of the cations in
the room-temperature ionic liquids of embodiments of the present
invention are higher than -3.244 eV. Therefore, the
room-temperature ionic liquids of embodiments of the present
invention are excellent in the reduction resistance.
[0064] That is, reduction resistance of a room-temperature ionic
liquid is improved by an advantageous effect of introducing an
electron donating substituent into a molecule.
[0065] The oxidation potential of a room-temperature ionic liquid
changes depending on anion species. When any one of
(C.sub.nF.sub.2n+1SO.sub.2).sub.2N.sup.- (n=0 to 4),
(C.sub.mF.sub.2m+1SO.sub.3).sup.- (m=0 to 4), and CF.sub.2
(CF.sub.2SO.sub.2).sub.2N.sup.- is used as a univalent anion of the
room-temperature ionic liquids of embodiments of the present
invention, the oxidation potential can be high. When the oxidation
potential is high, it means that the oxidation resistance (also
referred to as stability against oxidation) is improved. The
oxidation resistance of the room-temperature ionic liquids of
embodiments of the present invention is improved by the interaction
between a cation in which electric polarization is alleviated
because of an electron donating substituent and the anion described
above.
[0066] An electrolyte of a power storage device having low
reduction potential and high oxidation potential, that is, a wide
oxidation-reduction potential window can increase the number of
materials which can be selected for a positive electrode and a
negative electrode and make the electrolyte stable to the selected
positive electrode material and negative electrode material.
Therefore, a power storage device having excellent reliability can
be realized.
[0067] The energy density of a power storage device is caused by a
difference between an oxidation potential of a positive electrode
material and a reduction potential of a negative electrode
material. Thus, a low potential negative electrode material and a
high potential positive electrode material can be selected by using
an electrolyte having wide reduction-oxidation potential window.
Consequently, a power storage device having high energy density can
be realized.
[0068] In this embodiment, the case where R.sub.1 to R.sub.5 in the
general formula (G1) or (G2) are an alkyl group having 1 to 4
carbon atoms is described; however, the number of carbon atoms is
not limited to this. The number of carbon atoms may be 1 to 20. For
example, the number of carbon atoms can be greater than or equal to
5. The freezing point can be changed by adjusting the number of
carbon atoms. By changing the freezing point, a storage device
which can be used in a variety of applications can be
manufactured.
[0069] According to this embodiment, a room-temperature ionic
liquid having excellent reduction resistance and oxidation
resistance is used for an electrolyte of a power storage device;
thus, a high-performance power storage device having high energy
density and excellent reliability can be obtained.
[0070] This embodiment can be implemented in appropriate
combination with any of the structures described in the other
embodiments.
Embodiment 2
[0071] An electrolyte in a power storage device of one embodiment
of the present invention includes a nonaqueous solvent and
electrolyte salt. The room-temperature ionic liquid of one
embodiment of the present invention can be used for the nonaqueous
solvent in which the electrolyte salt dissolves. The electrolyte
salt dissolved in the nonaqueous solvent may be electrolyte salt
including carrier ions such as an alkali metal ion, an alkaline
earth metal ion, a beryllium ion, or a manganese ion. Examples of
the alkali metal ion include a lithium ion, a sodium ion, or a
potassium ion. Examples of the alkaline earth metal ion include a
calcium ion, a strontium ion, or a barium ion. Electrolyte salt
including a lithium ion is used as the electrolyte salt of this
embodiment. Further, a lithium-ion secondary battery or a
lithium-ion capacitor can be formed by using at least a positive
electrode, a negative electrode, and a separator. In this
structure, an electric double layer capacitor can be obtained by
using the room-temperature ionic liquid of one embodiment of the
present invention for an electrolyte, without using the electrolyte
salt.
[0072] In this embodiment, among the above described power storage
devices, a lithium-ion secondary battery using an electrolyte which
includes a room-temperature ionic liquid and electrolyte salt
including lithium and a manufacturing method of the lithium-ion
secondary battery are described with reference to FIGS. 1A and
1B.
[0073] A structural example of a lithium-ion secondary battery 130
is shown in FIG. 1A.
[0074] The lithium-ion secondary battery 130 in this embodiment
includes a positive electrode 148 including a positive electrode
current collector 142 and a positive electrode active material
layer 143, and a negative electrode 149 including a negative
electrode current collector 101 and a negative electrode active
material layer 104. The lithium-ion secondary battery 130 in FIG.
1A includes a separator 147, a housing 141, and an electrolyte 146.
The separator 147 is provided between the positive electrode 148
and the negative electrode 149. The positive electrode 148, the
negative electrode 149, and the separator 147 are provided in the
housing 141. The electrolyte 146 is included in the housing
141.
[0075] For the positive electrode current collector 142, for
example, a conductive material can be used. As the conductive
material, aluminum (Al), copper (Cu), nickel (Ni), or titanium (Ti)
can be used, for example. In addition, an alloy material containing
two or more of the above-mentioned conductive materials can be used
as the positive electrode current collector 142. As the alloy
material, an Al--Ni alloy or an Al--Cu alloy can be used, for
example. Furthermore, a conductive layer provided by deposition
separately on a substrate and then separated from the substrate can
be also used as the positive electrode current collector 142.
[0076] As the positive electrode active material layer 143, a
material containing ions serving as carriers and a transition metal
can be used, for example. As the material containing ions serving
as carriers and a transition metal, a material represented by a
general formula A.sub.hM.sub.iPO.sub.j (h>0, i>0, j>0) can
be used, for example. Here, A represents, for example, an alkaline
metal such as lithium, sodium, or potassium; or an alkaline earth
metal such as calcium, strontium, or barium; beryllium; or
magnesium. M indicates a transition metal such as iron, nickel,
manganese, or cobalt. As the material represented by the general
formula A.sub.hM.sub.iPO.sub.j (h>0, i>0, j>0), lithium
iron phosphate, sodium iron phosphate, or the like can be given.
The material represented by A and the material represented by M may
be selected from one or more of each of the above materials.
[0077] Alternatively, a material represented by a general formula
A.sub.hM.sub.iO.sub.j (h>0, i>0, j>0) can be used. Here, A
represents, for example, an alkaline metal such as lithium, sodium,
or potassium; or an alkaline earth metal such as calcium,
strontium, or barium; beryllium; or magnesium. M indicates a
transition metal such as iron, nickel, manganese, or cobalt. As the
material represented by the general formula A.sub.hM.sub.iO.sub.j
(h>0, i>0, j>0), lithium cobaltate, lithium manganate,
lithium nickel oxide, or the like can be given. The material
represented by A and the material represented by M may be selected
from one or more of each of the above materials.
[0078] A material containing lithium is preferably selected for the
positive electrode active material layer 143 of the lithium-ion
secondary battery in this embodiment. In other words, A in the
above general formulae A.sub.hM.sub.iPO.sub.j (h>0, i>0,
j>0) or A.sub.hM.sub.iO.sub.j (h>0, i>0, j>0) is
preferably lithium.
[0079] The positive electrode active material layer 143 may be
formed by applying a paste mixed with a conductive additive (for
example, acetylene black (AB) or a binder (for example,
polyvinylidene fluoride (PVDF))) onto the positive electrode
current collector 142, or formed by sputtering. In the case of
forming the positive electrode active material layer 143 by a
coating method, pressure forming may also be employed, if
necessary.
[0080] Note that strictly speaking, "active material" refers only
to a material that relates to insertion and elimination of ions
functioning as carriers. In this specification, however, in the
case of using a coating method to form the positive electrode
active material layer 143, for the sake of convenience, the
positive electrode active material layer 143 collectively refers to
the material of the positive electrode active material layer 143,
that is, a substance that is actually a "positive electrode active
material," a conductive additive, a binder, etc.
[0081] For the negative electrode current collector 101, a simple
substance of copper (Cu), aluminum (Al), nickel (Ni), or titanium
(Ti), or a compound of any of these elements can be used.
[0082] There is no particular limitation on a material used for the
negative electrode active material layer 104 as long as it can
dissolve and precipitate lithium and can be doped and dedoped with
a lithium ion. For example, a lithium metal, a carbon based
material, silicon, a silicon alloy, or tin can be used. For carbon
to/from which a lithium ion can be inserted and extracted, graphite
based carbon such as a fine graphite powder, a graphite fiber, or
graphite can be used.
[0083] For a nonaqueous solvent of the electrolyte 146, the
room-temperature ionic liquids described in Embodiment 1 can be
used. For electrolyte salt of the electrolyte 146, electrolyte salt
including lithium can be used. Further, the nonaqueous solvent of
the electrolyte 146 in which the electrolyte salt dissolves is not
necessarily a single solvent of the room-temperature ionic liquids
described in Embodiment 1. The nonaqueous solvent may be a mixed
solvent of plural kinds of solvents in which any one of the
room-temperature ionic liquids described in Embodiment 1 and
another room-temperature ionic liquid are mixed.
[0084] Examples of the electrolyte salt including lithium include
lithium chloride (LiCl), lithium fluoride (LiF), lithium
perchlorate (LiClO.sub.4), lithium fluoroborate (LiBF.sub.4),
LiAsF.sub.6, LiPF.sub.6, Li(CF.sub.3SO.sub.2).sub.2N, and the like.
The electrolyte salt dissolved in the nonaqueous solvent of the
room-temperature ionic liquids described in Embodiment 1 may be
electrolyte salt which includes a carrier ion and corresponds with
the positive electrode active material layer 143. In this
embodiment, the electrolyte salt including lithium is used as the
electrolyte salt because lithium is contained in the material used
for the positive electrode active material layer 143. However, it
is preferable to use electrolyte salt including sodium as the
electrolyte salt when a material containing sodium is used for the
positive electrode active material layer 143, for example.
[0085] As the separator 147, paper, nonwoven fabric, a glass fiber,
a synthetic fiber such as nylon (polyimide), vinylon (a polyvinyl
alcohol based fiber), polyester, acrylic, polyolefin, or
polyurethane, or the like may be used. Note that a material which
does not dissolve in the electrolyte should be selected.
[0086] More specific examples of the materials for the separator
147 are high-molecular compounds based on fluorine-based polymer,
polyether such as polyethylene oxide and polypropylene oxide,
polyolefin such as polyethylene and polypropylene,
polyacrylonitrile, polyvinylidene chloride, polymethyl
methacrylate, polymethylacrylate, polyvinyl alcohol,
polymethacrylonitrile, polyvinyl acetate, polyvinylpyrrolidone,
polyethyleneimine, polybutadiene, polystyrene, polyisoprene, and
polyurethane; derivatives thereof; cellulose; paper; and nonwoven
fabric, all of which can be used either alone or in a
combination.
[0087] Next, a lithium-ion secondary battery 131 having a different
structure from that in FIG. 1A will be described with reference to
FIG. 1B. The lithium-ion secondary battery 131 shown in FIG. 1B
includes the positive electrode 148 including the positive
electrode current collector 142 and the positive electrode active
material layer 143, and the negative electrode 149 including the
negative electrode current collector 101 and the negative electrode
active material layer 104. In the lithium-ion secondary battery, a
separator 156 is provided between the positive electrode 148 and
the negative electrode 149 and is impregnated with an
electrolyte.
[0088] The components shown in the lithium-ion secondary battery
130 can be used as the negative electrode current collector 101,
the negative electrode active material layer 104, the positive
electrode current collector 142, and the positive electrode active
material layer 143, which are in FIG. 1B.
[0089] The separator 156 is preferably a porous film. As a material
of the porous film, a glass fiber, a synthetic resin material, a
ceramic material, or the like may be used.
[0090] As the electrolyte with which the separator 156 is
impregnated, the electrolyte in the lithium-ion secondary battery
130 can be used.
<Method for Manufacturing Lithium-Ion Secondary Battery>
[0091] Here, a method for manufacturing the positive electrode 148
including the positive electrode active material layer 143 on the
positive electrode current collector 142 will be described.
[0092] For the material of each of the positive electrode current
collector 142 and the positive electrode active material layer 143,
the above described materials can be used.
[0093] Then, the positive electrode active material layer 143 is
formed on the positive electrode current collector 142. The
positive electrode active material layer 143 may be formed by a
sputtering method or a coating method as described above. In the
case of forming the positive electrode active material layer 143 by
a coating method, the material for the positive electrode active
material layer 143 is mixed with a conduction auxiliary agent, a
binder, etc. to form a paste, and the paste is applied onto the
positive electrode current collector 142 and dried to form the
positive electrode active material layer 143. In the case of
forming the positive electrode active material layer 143 by a
coating method, pressure forming may be employed, if necessary. As
described above, the positive electrode 148 includes the positive
electrode active material layer 143 formed on the positive
electrode current collector 142.
[0094] Note that as the conduction auxiliary agent, an
electron-conductive material which does not cause chemical change
in the power storage device may be used. For example, a carbon
material such as graphite or carbon fibers; a metal material such
as copper, nickel, aluminum, or silver; or a powder or a fiber of a
mixture thereof can be used.
[0095] Note that as the binder, a polysaccharide, a thermoplastic
resin, a polymer with rubber elasticity, or the like such as
starch, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl
cellulose, regenerated cellulose, or diacetyl cellulose, polyvinyl
chloride, polyvinyl pyrrolidone, polytetrafluoroethylene,
polyvinylide fluoride, polyethylene, or polypropylene,
ethylene-propylene-diene monomer (EPDM), sulfonated EPDM,
styrene-butadiene rubber, butadiene rubber, fluorine rubber, or
polyethylene oxide can be given.
[0096] Next, a method for manufacturing the negative electrode 149
including the negative electrode current collector 101 and the
negative electrode active material layer 104 will be described.
[0097] For the material of each of the negative electrode current
collector 101 and the negative electrode active material layer 104,
the above described materials can be used.
[0098] Next, the negative electrode active material layer 104 is
formed on the negative electrode current collector 101. In this
embodiment a lithium foil is used. The room-temperature ionic
liquid of one embodiment of the present invention is excellent in
reduction resistance and is stable to lithium which is a negative
electrode material having the lowest potential. Consequently, when
the room-temperature ionic liquid is used for the electrolyte, the
lithium-ion secondary batteries 130 and 131 which have high energy
density and excellent reliability can be obtained.
[0099] In the case where a material other than a lithium foil is
used for the negative electrode active material layer 104, the
negative electrode active material layer 104 can be manufactured in
a manner similar to that of the positive electrode active material
layer 143. For example, when silicon is used as the negative
electrode active material layer 104, a material obtained by
depositing microcrystalline silicon and then removing amorphous
silicon from the microcrystalline silicon by etching may be used.
When amorphous silicon is removed from microcrystalline silicon,
the surface area of the remaining microcrystalline silicon is
increased. A chemical vapor deposition method or a physical vapor
deposition method can be used as the deposition method of the
microcrystalline silicon. For example, a plasma CVD method can be
used as the chemical vapor deposition method and a sputtering
method can be used as the physical vapor deposition method. Note
that the above described conduction auxiliary agent and the binder
can also be used.
[0100] The electrolyte 146 and the electrolyte with which the
separator 156 is impregnated can be manufactured by mixing
electrolyte salt including a carrier ion and any one of the
room-temperature ionic liquids described in Embodiment 1. In this
embodiment, Li(CF.sub.3SO.sub.2).sub.2N is used as the electrolyte
salt including lithium.
[0101] A variety of reactions can be applied to a method for
synthesizing the room-temperature ionic liquids described in
Embodiment 1. As an example, Synthesis Scheme (S-1) can be
employed.
##STR00011##
[0102] In the above Scheme (S-1), the reaction from a general
formula (.alpha.-10) to a general formula (.alpha.-11) is
alkylation of amine by an amine compound and a carbonyl compound in
the presence of hydrido. For example, excessive formic acid can be
used as the hydrido source. CH.sub.2O is used as the carbonyl
compound in the room-temperature ionic liquid of one embodiment of
the present invention.
[0103] In the above Scheme (S-1), the reaction from the general
formula (.alpha.-11) to a general formula (.alpha.-12) is
alkylation by a tertiary amine compound and an alkyl halide
compound, which synthesizes quaternary ammonium salt. Propane
halide is used as the alkyl halide compound in the room-temperature
ionic liquid of one embodiment of the present invention. X is
halogen, preferably bromine or iodine, which has high reactivity,
more preferably iodine.
[0104] Through ion exchange between the quaternary ammonium salt
represented by the general formula (.alpha.-12) and desired metal
salt, the room-temperature ionic liquid of one embodiment of the
present invention can be obtained. Lithium metal salt can be used
in the Synthesis Scheme (S-1).
[0105] Next, a top view of a specific structure of the lithium-ion
secondary battery 130 in FIG. 1A which is laminated is shown in
FIG. 2A. A perspective view of a specific structure of the
lithium-ion secondary battery 131 in FIG. 1B which is a button type
is shown in FIG. 2B. A method for assembling the button-type
lithium-ion secondary battery 131 in FIG. 2B is shown in FIGS. 3A
and 3B and FIG. 4.
[0106] The laminated lithium-ion secondary battery 130 in FIG. 2A
includes the positive electrode 148 including the positive
electrode current collector 142 and the positive electrode active
material layer 143, and the negative electrode 149 including the
negative electrode current collector 101 and the negative electrode
active material layer 104, which are described above. The laminated
lithium-ion secondary battery 130 in FIG. 2A includes the separator
147 between the positive electrode 148 and the negative electrode
149. In the lithium-ion secondary battery 130, the positive
electrode 148, the negative electrode 149, and the separator 147
are placed in the housing 141 and the electrolyte 146 is included
in the housing 141.
[0107] In FIG. 2A, the negative electrode current collector 101,
the negative electrode active material layer 104, the separator
147, the positive electrode active material layer 143, and the
positive electrode current collector 142 are arranged in this order
from the bottom side. The negative electrode current collector 101,
the negative electrode active material layer 104, the separator
147, the positive electrode active material layer 143, and the
positive electrode current collector 142 are provided in the
housing 141. The housing 141 is filled with the electrolyte
146.
[0108] The positive electrode current collector 142 and the
negative electrode current collector 101 in FIG. 2A also function
as terminals for electrical contact with the outside. For this
reason, part of each of the positive electrode current collector
142 and the negative electrode current collector 101 is arranged
outside the housing 141 so as to be exposed.
[0109] Note that FIG. 2A shows one example of the laminated
lithium-ion secondary battery 130 and the laminated lithium-ion
secondary battery 130 may have other structures.
[0110] The button-type lithium-ion secondary battery 131 in FIG. 2B
includes the separator 156 provided between the positive electrode
148 and the negative electrode 149. The separator 156 is
impregnated with an electrolyte. The specific structure and the
assembling method of the button-type lithium-ion secondary battery
131 in FIG. 2B will be described with reference to FIGS. 3A and 3B
and FIG. 4.
[0111] First, a first housing 171 is prepared. A bottom surface of
the first housing 171 is a circle and the side of the first housing
171 is a rectangle. That is, the first housing 171 is a dish having
a columnar shape. It is necessary to use a conductive material for
the first housing 171 in order that the positive electrode 148 can
be electrically connected to the outside. For example, the first
housing 171 may be formed of a metal material. The positive
electrode 148 including the positive electrode current collector
142 and the positive electrode active material layer 143 is
provided in the first housing 171 (see FIG. 3A).
[0112] In addition, a second housing 172 is prepared. A bottom
surface of the second housing 172 is a circle and the side of the
second housing 172 is a trapezoid in which an upper base is longer
than a lower base. That is, the second housing 172 is a dish having
a columnar shape. The diameter of the dish is smallest at the
bottom and increases upward. Note that the diameter of the second
housing 172 is smaller than the diameter of the bottom surface of
the first housing 171. The reason is described later.
[0113] It is necessary to use a conductive material for the second
housing 172 in order that the negative electrode 149 can be
electrically connected to the outside. For example, the second
housing 172 may be formed of a metal material. The negative
electrode 149 including the negative electrode current collector
101 and the negative electrode active material layer 104 is
provided in the second housing 172.
[0114] A ring-shaped insulator 173 is provided so as to surround
the side of the positive electrode 148 provided in the first
housing 171. The ring-shaped insulator 173 has a function of
insulating the negative electrode 149 and the positive electrode
148 from each other. The ring-shaped insulator 173 is preferably
formed using an insulating resin.
[0115] The second housing 172 in which the negative electrode 149
is provided shown in FIG. 3B is installed in the first housing 171
in which the ring-shaped insulator 173 is provided, with the
separator 156 which is already impregnated with the electrolyte
interposed therebetween. The second housing 172 can be fit in the
first housing 171 because the diameter of the second housing 172 is
smaller than the diameter of the bottom surface of the first
housing 171 (see FIG. 4).
[0116] As described above, the positive electrode 148 and the
negative electrode 149 are insulated from each other by the
ring-shaped insulator 173, so that the positive electrode 148 and
the negative electrode 149 do not short-circuit.
[0117] Note that one example of the button-type lithium-ion
secondary battery 131 is shown in FIG. 2B and the button-type
lithium-ion secondary battery 131 may have other structures.
[0118] In FIG. 2A, an example of the lithium-ion secondary battery
130 in FIG. 1A which is laminated is shown, and in FIGS. 3A and 3B
and FIG. 4, an example of the lithium-ion secondary battery 131 in
FIG. 2B which is button type is shown; however, structures of the
lithium-ion secondary batteries 130 and 131 are not limited to
these. The lithium-ion secondary batteries 130 and 131 shown in
FIGS. 1A and 1B may have various structures such as a button type,
a stack type, a cylinder type, and a laminate type.
[0119] As described above, according to this embodiment, a
room-temperature ionic liquid having excellent reduction resistance
and oxidation resistance is used for an electrolyte of a power
storage device; thus, a high-performance power storage device
having high energy density and excellent reliability can be
obtained.
[0120] This embodiment can be implemented in appropriate
combination with any of the structures described in the other
embodiments.
Embodiment 3
[0121] In this embodiment, an application mode of the power storage
device described in Embodiment 2 will be described with reference
to FIG. 5.
[0122] The power storage device described in Embodiment 2 can be
used in electronic appliances, e.g., cameras such as digital
cameras or video cameras, digital photo frames, mobile phones (also
referred to as cellular phones or cellular phone devices), portable
game machines, portable information terminals, and audio
reproducing devices. Further, the power storage device can be used
in electric propulsion vehicles such as electric vehicles, hybrid
electric vehicles, train vehicles, maintenance vehicles, carts, and
wheelchairs. Here, as a typical example of the electric propulsion
vehicles, a wheelchair is described.
[0123] FIG. 5 is a perspective view of an electric wheelchair 501.
The electric wheelchair 501 includes a seat 503 where a user sits
down, a backrest 505 provided behind the seat 503, a footrest 507
provided at the front of and below the seat 503, armrests 509
provided on the left and right of the seat 503, and a handle 511
provided above and behind the backrest 505. A controller 513 for
controlling the operation of the wheelchair is provided for one of
the armrests 509. A pair of front wheels 517 is provided at the
front of and below the seat 503 through a frame 515 provided below
the seat 503. A pair of rear wheels 519 is provided behind and
below the seat 503. The rear wheels 519 are connected to a driving
portion 521 including a motor, a brake, a gear, and the like. A
control portion 523 including a battery, a power controller, a
control means, and the like is provided under the seat 503. The
control portion 523 is connected to the controller 513 and the
driving portion 521. The driving portion 521 is driven through the
control portion 523 with the operation of the controller 513 by the
user. The control portion 523 controls the operation of moving
forward, moving back, turning around, and the like, and the speed
of the electric wheelchair 501.
[0124] The power storage device described in Embodiment 2 can be
used in the battery of the control portion 523. The battery of the
control portion 523 can be externally charged by electric power
supply using plug-in systems or contactless power feeding. Note
that in the case where the electric propulsion vehicle is a train
vehicle, the train vehicle can be charged by electric power supply
from an overhead cable or a conductor rail.
Example 1
[0125] In this example, an example of a method for producing
1,2-dimethyl-1-propylpiperidinium
bis(trifluoromethanesulfonyl)imide (abbreviation: 2mPP13-TFSA)
represented by a structural formula (.alpha.-13) will be
described.
##STR00012##
[0126] 2-Methylpiperidine (1.98 g, 200 mmol) was gradually added to
formic acid (15.6 g, 300 mmol) while cooling with water. Next,
formaldehyde (22.5 ml, 300 mmol) was added to this solution. This
solution was heated to 100.degree. C. and cooled back to room
temperature after a bubble generation, and was stirred for about 30
minutes. Then, the solution was heated and refluxed for one
hour.
[0127] The formic acid was neutralized with sodium carbonate, the
solution was extracted with hexane and dried over magnesium
sulfate, and the solvent was distilled off, whereby
1,2-dimethylpiperidine (12.82 g, 113 mmol) which was light yellow
liquid was obtained.
[0128] Bromopropane (20.85 g, 170 mmol) was added to methylene
chloride (10 ml) to which the obtained light yellow liquid was
added, and was heated and refluxed for 24 hours, so that a white
precipitate was generated. After filtration, the remaining
substance was recrystallized from ethanol and ethyl acetate and
dried under reduced pressure at 80.degree. C. for 24 hours, whereby
1,2-dimethyl-1-propylpiperidinium bromide (11.93 g, 48 mmol) which
was a white solid was obtained.
[0129] 1,2-Dimethyl-1-propylpiperidinium bromide (5.3 g, 22 mmol)
and lithium bis(trifluoromethanesulfonyl)imide (7.09 g, 25 mmol)
were mixed and stirred in pure water, so that a room-temperature
ionic liquid which is insoluble in water was obtained immediately.
The obtained room-temperature ionic liquid was extracted with
methylene chloride and then washed with pure water six times and
dried in vacuum at 100.degree. C.; thus,
1,2-dimethyl-1-propylpiperidinium
bis(trifluoromethanesulfonyl)imide (9.37 g, 21 mmol) was
obtained.
[0130] The compound obtained through the above steps was identified
as 1,2-dimethyl-1-propylpiperidinium
bis(trifluoromethanesulfonyl)imide which is a target substance by
using a nuclear magnetic resonance (NMR) method and mass
spectrometry.
[0131] .sup.1H NMR data of the obtained compound is shown below.
.sup.1H-NMR (CDCl.sub.3, 400 MHz, 298 K): .delta. (ppm): 1.00,
1.03, 1.06 (t, 3H), 1.29, 1.34, 1.40 (d, 3H), 1.59-1.88 (m, 8H),
2.85, 2.90, 3.00, 3.07 (s, 3H), 2.85-2.98, 3.20-3.42 (m, 2H),
3.20-3.54 (m, 2H), 3.50-3.54 (m, 1H)
[0132] In addition, FIGS. 6A and 6B show .sup.1H NMR charts. Note
that FIG. 6B is a chart showing an enlargement of FIG. 6A in the
range of 0.750 ppm to 3.75 ppm.
[0133] The measurement results of the electro spray ionization mass
spectrum (ESI-MS) of the obtained compound are shown below.
[0134] MS (ESI-MS): m/z=156.2 (M).sup.+; C.sub.10H.sub.22N (156.2),
279.98 (M).sup.-; C.sub.2F.sub.6NO.sub.4S.sub.2 (280.15)
Example 2
[0135] Next, an example of a method for producing
1,3-dimethyl-1-propylpiperidinium
bis(trifluoromethanesulfonyl)imide (abbreviation: 3mPP13-TFSA)
represented by a structural formula (.alpha.-14) will be
described.
##STR00013##
[0136] 3-Methylpiperidine (1.98 g, 200 mmol) was gradually added to
formic acid (15.6 g, 300 mmol) while cooling with water. Next,
formaldehyde (22.5 ml, 300 mmol) was added to this solution. This
solution was heated to 100.degree. C. and brought back to room
temperature after a bubble generation, and was stirred for about 30
minutes. Then, the solution was heated and refluxed for one
hour.
[0137] The formic acid was neutralized with sodium carbonate, the
solution was extracted with hexane and dried over magnesium
sulfate, and the solvent was distilled off, whereby
1,3-dimethylpiperidine (12.82 g, 113 mmol) which was light yellow
liquid was obtained.
[0138] Bromopropane (20.85 g, 170 mmol) was added to methylene
chloride (10 ml) to which this light yellow liquid was added, and
was heated and refluxed for 24 hours, so that a white precipitate
was generated. After filtration, the remaining substance was
recrystallized from ethanol and ethyl acetate and dried under
reduced pressure at 80.degree. C. for 24 hours, whereby
1,3-dimethyl-1-propylpiperidinium bromide (19.42 g, 82 mmol) which
is a white solid was obtained.
[0139] 1,3-Dimethyl-1-propylpiperidinium bromide (10.60 g, 44 mmol)
and lithium bis(trifluoromethanesulfonyl)imide (14.18 g, 50 mmol)
were mixed and stirred to be in equimolar amounts in pure water, so
that a room-temperature ionic liquid which is insoluble in water
was obtained immediately.
[0140] The room-temperature ionic liquid was extracted with
methylene chloride and then washed with pure water six times and
dried in vacuum at 100.degree. C.; thus,
1,3-dimethyl-1-propylpiperidinium
bis(trifluoromethanesulfonyl)imide (18.31 g, 42 mmol) was
obtained.
[0141] The compound obtained through the above steps was identified
as 1,3-dimethyl-1-propylpiperidinium
bis(trifluoromethanesulfonyl)imide which is a target substance by
using a nuclear magnetic resonance (NMR) method and mass
spectrometry.
[0142] .sup.1H NMR data of the obtained compound is shown below.
.sup.1H-NMR (CDCl.sub.3, 400 MHz, 298 K): .delta. (ppm) 0.93-1.06
(m, 6H), 1.13-1.23, 1.75-1.95 (m, 2H), 1.60-1.95 (m, 2H), 1.75-1.95
(m, 2H), 1.95-2.12 (m, 1H), 2.72-2.84, 3.30-3.42 (m, 2H), 2.98,
3.01, 3.02, 3.07 (s, 3H), 3.07-3.52 (m, 2H), 3.19-3.28 (m, 2H)
[0143] In addition, FIGS. 7A and 7B show .sup.1H NMR charts. Note
that FIG. 7B is a chart showing an enlargement of FIG. 7A in the
range of 0.750 ppm to 3.75 ppm.
[0144] The measurement results of the electro spray ionization mass
spectrum (ESI-MS) of the obtained compound are shown below.
[0145] MS (ESI-MS): m/z=156.2 (M).sup.+; C.sub.10H.sub.22N (156.2),
279.98 (M).sup.-; C.sub.2F.sub.6NO.sub.4S.sub.2 (280.15)
Example 3
[0146] Linear sweep voltammograms of 2mPP13-TFSA and 3mPP13-TFSA
which are shown in the above Examples were measured and potential
windows of the above room-temperature ionic liquid were calculated.
N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide
produced by KANTO CHEMICAL CO., INC. was used as a comparative
sample.
[0147] The measurement was performed by using electrochemical
measurement system HZ-5000 produced by HOKUTO DENKO CORPORATION in
a glove box with an argon atmosphere. A glassy carbon electrode was
used as a working electrode and a platinum wire was used for an
opposite electrode. A silver wire immersed in a solution in which
silver trifluoromethanesulfonate was dissolved in
1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide at a
concentration of 0.1 M was used for a reference electrode.
Oxidation-reduction potential of the room-temperature ionic liquid
was corrected with reference to the oxidation-reduction potential
of ferrocene (Fc/Fc.sup.+).
[0148] A linear sweep voltammogram of each of 2mPP13-TFSA,
3mPP13-TFSA, and the comparative sample is shown in FIG. 8. A
"potential window" in this example indicates a difference between
an oxidation potential and a reduction potential. In FIG. 8, a
potential at which an electric current density of -1 mA/cm.sup.2
was detected during the scanning of potentials was calculated as a
reduction potential. Further, in FIG. 8, a potential at which an
electric current density of 1 mA/cm.sup.2 was detected during the
scanning of the potentials was calculated as an oxidation
potential. The potential window was calculated by subtracting a
"reduction potential" from an "oxidation potential".
[0149] In FIG. 8, a thin line denotes the comparative sample and
thick lines denote 2mPP13-TFSA and 3mPP13-TFSA which are
embodiments of the present invention. From FIG. 8, the reduction
potential of the comparative sample is -3.4 eV, the oxidation
potential thereof is 2.5 eV, and the potential window thereof is
5.9 eV. The reduction potential of 2mPP13-TFSA is -3.6 eV, the
oxidation potential thereof is 2.7 eV, and the potential window
thereof is 6.3 eV. The reduction potential of 3mPP13-TFSA is -3.6
eV, the oxidation potential thereof is 2.7 eV, and the potential
window thereof is 6.3 eV.
[0150] It was confirmed that 2mPP13-TFSA and 3mPP13-TFSA which are
one embodiment of the present invention each have a lower reduction
potential and a higher oxidation potential than those of the
comparative sample. Higher reduction resistance was confirmed
compared to the comparative sample. That is, stability against a
low potential negative electrode of a lithium metal, silicon, tin,
or the like was improved by introduction of an electron donating
substituent. Further, 2mPP13-TFSA and 3mPP13-TFSA which are one
embodiment of the present invention each have a higher oxidation
potential than that of the comparative sample, whereby the
oxidation resistance of 2mPP3-TFSA and 3mPP13-TFSA is excellent.
Consequently, 2mPP13-TFSA and 3mPP13-TFSA each have a wide
potential window. As described above, a low potential negative
electrode material and a high potential positive electrode material
can be selected by using the room-temperature ionic liquid of one
embodiment of the present invention for an electrolyte; thus, a
power storage device having high energy density can be
obtained.
Example 4
[0151] Next, an example of a method for producing
1,3-dimethyl-1-propylpiperidinium bis(fluorosulfonyl)imide
(abbreviation: 3mPP13-FSA) represented by a structural formula
(.alpha.-15) will be described.
##STR00014##
[0152] Since steps for obtaining 1,3-dimethyl-1-propylpiperidinium
bromide are the same as the steps described in Example 2, the
description is omitted here. 1,3-dimethyl-1-propylpiperidinium
bromide (17.02 g, 72 mmol) obtained in a manner similar to that in
Example 2 and potassium bis(fluorosulfonyl)imide (17.04 g, 78 mmol)
were mixed and stirred in pure water, so that a room-temperature
ionic liquid which is insoluble in water was obtained
immediately.
[0153] The room-temperature ionic liquid was extracted with
methylene chloride and then washed with pure water six times and
dried in vacuum at room temperature through a trap at -80.degree.
C.; thus, 1,3-dimethyl-1-propylpiperidinium
bis(fluorosulfonyl)imide (20.62 g, 61 mmol) which is a
room-temperature ionic liquid was obtained.
[0154] The compound obtained through the above steps was identified
as 1,3-dimethyl-1-propylpiperidinium bis(fluorosulfonyl)imide which
is a target substance by using a nuclear magnetic resonance (NMR)
method and mass spectrometry.
[0155] .sup.1H NMR data of the obtained compound is shown below.
.sup.1H-NMR (CDCl.sub.3, 400M Hz, 298 K): .delta. (ppm) 1.02-1.09
(m, 6H), 1.21-1.26, 1.69-1.75 (m, 2H), 1.83-1.91 (m, 2H), 1.94-1.97
(m, 2H), 1.97-2.15 (m, 1H), 2.77-2.87, 3.30-3.43 (m, 2H), 3.05,
3.10 (s, 3H), 3.15-3.54 (m, 2H), 3.25-3.29 (m, 2H)
[0156] Further, .sup.1H-NMR charts are shown in FIGS. 9A and 9B.
Note that FIG. 9B is a chart showing an enlargement of FIG. 9A in
the range of 0.750 ppm to 3.75 ppm.
[0157] The measurement results of the electro spray ionization mass
spectrum (ESI-MS) of the obtained compound are shown below.
[0158] MS (ESI-MS): m/z=156.2 (M).sup.+; C.sub.10H.sub.22N (156.2),
179.98 (M).sup.-; F.sub.2NO.sub.4S.sub.2 (180.13)
Example 5
[0159] Next, results of charge and discharge characteristics of a
coin-type lithium-ion secondary battery cell using 3mPP13-FSA in
Example 4 for a nonaqueous electrolyte are shown. Note that in this
example, a Sample A is the coin-type lithium-ion secondary battery
cell using 3mPP13-FSA for a nonaqueous electrolyte.
[0160] First, a method for manufacturing the Sample A will be
described with reference to FIG. 10. As a nonaqueous electrolyte of
the Sample A, 1.84 g (6.4 mmol) of lithium
bis(trifluoromethanesulfonyl)imide (abbreviation: LiTFSA) and 6.81
g (20.0 mmol) of 3mPP13-FSA were mixed in a glove box with an argon
atmosphere.
[0161] Commercially available products were used for the positive
electrode 148, the negative electrode 149, the ring-shaped
insulator 173, and the separator 156, other than the nonaqueous
electrolyte, which were in the Sample A. Specifically, an electrode
manufactured by Piotrek Co., Ltd. was used as the positive
electrode 148. The positive electrode active material layer 143 was
formed of lithium cobaltate and the positive electrode current
collector 142 was formed of an aluminum foil. The capacitance per
weight of the electrode used as the positive electrode 148 is 112
mAh/g. The negative electrode active material layer 104 in the
negative electrode 149 was formed of a lithium foil. For the
separator 156, GF/C which is a glass fiber filter produced by
Whatman Ltd. was used. Then, the positive electrode 148, the
negative electrode 149, and the separator 156 were impregnated with
the nonaqueous electrolyte. Commercially available objects were
used for the housings 171 and 172. The housing 171 electrically
connects the positive electrode 148 to the outside and the housing
172 electrically connects the negative electrode 149 to the
outside. The housings 171 and 172 were formed of stainless steel
(SUS). In addition, a spacer 181 and a washer 183 formed of
stainless steel (SUS) were prepared; commercially available objects
were used as the spacer 181 and the washer 183.
[0162] As shown in FIG. 10, the housing 171, the positive electrode
148, the separator 156, the ring-shaped insulator 173, the negative
electrode 149, the spacer 181, the washer 183, and the housing 172
were stacked in this order from the bottom side. The positive
electrode 148, the negative electrode 149 and the separator 156
were impregnated with the nonaqueous electrolyte. Then, the housing
171 and the housing 172 were crimped to each other with a "coin
cell crimper". Thus, the Sample A was manufactured.
[0163] Next, a coin-type lithium-ion secondary battery cell for
comparison (Sample B) was manufactured in a manner similar to that
of the Sample A (see FIG. 10). Note that the difference between the
Sample A and the Sample B is components of nonaqueous electrolytes.
For a nonaqueous electrolyte of the Sample B, LiTFSA and
N-methyl-N-propylpiperidinium bis(fluoromethanesulfonyl)imide
(abbreviation: PP13-FSA) were used. Specifically, 2.82 g (9.8 mmol)
of LiTFSA and 10.02 g (31.0 mmol) of PP13-FSA were mixed in a glove
box with an argon atmosphere.
[0164] The charge and discharge characteristics of each of the
Sample A and the Sample B were measured. The charge and discharge
characteristics were measured by using a charge-discharge measuring
device (produced by TOYO SYSTEM Co., LTD). For the measurements of
charge and discharge, a constant current mode was used. The charge
and discharge were performed with a current of 0.15 mA at a rate of
0.1 C. The upper limit voltage was 4.2 V and the lower limit
voltage was 2.5 V. Note that charging and discharging were in one
cycle. In this embodiment, 50 cycles were performed. The samples
were measured at room temperature.
[0165] The cycle characteristics of each of the Samples A and B
which were measured are shown in FIG. 11. The horizontal axis of
FIG. 11 indicates the number of cycles. The vertical axis of FIG.
11 indicates a capacity maintenance rate of the coin-type
lithium-ion secondary batteries. Note that the capacity maintenance
rate refers to a percentage of a capacitance after certain cycles
to the highest capacitance during 50 cycles. A solid line in FIG.
11 shows the charge and discharge characteristics of the Sample A.
A dotted line in FIG. 11 is the charge and discharge
characteristics of the Sample B. From FIG. 11, it was confirmed
that the Sample A is less likely to deteriorate because the
capacity maintenance rate after 50 cycles is high.
[0166] As described above, when a room-temperature ionic liquid
having excellent reduction resistance is used for a nonaqueous
electrolyte, a high-performance power storage device having
excellent charge and discharge characteristics can be obtained.
[0167] This application is based on Japanese Patent Application
serial no. 2010-149169 filed with Japan Patent Office on Jun. 30,
2010, the entire contents of which are hereby incorporated by
reference.
* * * * *