U.S. patent application number 14/176288 was filed with the patent office on 2014-06-12 for anode and battery.
This patent application is currently assigned to Sony Corporation. The applicant listed for this patent is Sony Corporation. Invention is credited to Takayuki Fujii, Rikako Imoto, Kenichi Kawase, Hideki Nakai, Kensuke Yamamoto.
Application Number | 20140162120 14/176288 |
Document ID | / |
Family ID | 40534550 |
Filed Date | 2014-06-12 |
United States Patent
Application |
20140162120 |
Kind Code |
A1 |
Fujii; Takayuki ; et
al. |
June 12, 2014 |
ANODE AND BATTERY
Abstract
A battery including a cathode, an anode, and an electrolytic
solution. The electrolytic solution is impregnated in a separator
provided between the cathode and the anode. The anode has an
insulative coat on an anode active material layer provided on an
anode current collector. The coat contains an insulating material
such as a meal hydroxide and a metal oxide. The coat is in a form
of plate divided into a plurality of portions. The insulation
property of the coat prevents internal short circuit. A plurality
of portions of the coat prevent separation of the anode active
material layer and decomposition of the electrolytic solution.
Further, even when short circuit occurs, heat generation is
prevented by heat absorption characteristics of the coat.
Inventors: |
Fujii; Takayuki; (Fukushima,
JP) ; Kawase; Kenichi; (Fukushima, JP) ;
Nakai; Hideki; (Fukushima, JP) ; Imoto; Rikako;
(Fukushima, JP) ; Yamamoto; Kensuke; (Fukushima,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sony Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Sony Corporation
Tokyo
JP
|
Family ID: |
40534550 |
Appl. No.: |
14/176288 |
Filed: |
February 10, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12247364 |
Oct 8, 2008 |
|
|
|
14176288 |
|
|
|
|
Current U.S.
Class: |
429/211 |
Current CPC
Class: |
H01M 4/48 20130101; H01M
2220/00 20130101; H01M 10/0525 20130101; H01M 10/4235 20130101;
H01M 4/386 20130101; H01M 4/02 20130101; H01M 4/62 20130101; H01M
2004/027 20130101; H01M 2004/021 20130101; H01M 4/366 20130101;
Y02E 60/10 20130101; H01M 4/134 20130101 |
Class at
Publication: |
429/211 |
International
Class: |
H01M 10/42 20060101
H01M010/42; H01M 10/0525 20060101 H01M010/0525; H01M 4/134 20060101
H01M004/134 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 15, 2007 |
JP |
2007-268348 |
Claims
1. An anode comprising: an anode current collector; an active
material layer on the anode current collector; and an insulative
coat on the anode active material layer, wherein, the insulative
coat is divided into a plurality of spaced apart portions across an
outer surface of the anode active material layer and is configured
to provide a migration path for an electrode reactant to the active
material layer between the portions, the anode active material
layer contains a plurality of anode active material particles, and
the coat extends along a partial surface of two or more of the
anode active material particles while continuously covering the
partial surface.
2. The anode according to claim 1, wherein the insulative coat is
in the form of a plate.
3. The anode according to claim 1, wherein the insulative coat is
formed by electrolytic plating method.
4. The anode according to claim 1, wherein the anode active
material layer contains a plurality of anode active material
particles containing silicon.
5. The anode according to claim 1, wherein where an area of the
anode active material layer is S1 and an area of the insulative
coat is S2, and an area ratio S2/S1 is in the range from 0.2 to
0.9, inclusive.
6. The anode according to claim 1, wherein a weight per unit area
of the insulative coat is in the range from 0.02 mg/cm2 to 1
mg/cm2, inclusive.
7. A battery comprising: a cathode; an anode; and an electrolytic
solution, wherein, the insulative coat is divided into a plurality
of spaced apart portions across an outer surface of the anode
active material layer and is configured to provide a migration path
for an electrode reactant to the active material layer between the
portions, the anode active material layer contains a plurality of
anode active material particles, and the coat extends along a
partial surface of two or more of the anode active material
particles while continuously covering the partial surface.
8. The battery according to claim 7, wherein the insulative coat is
in the form of a plate.
9. The battery according to claim 7, wherein the insulative coat is
formed by electrolytic plating method.
10. The battery according to claim 7, wherein the anode active
material layer contains a plurality of anode active material
particles containing silicon.
11. The battery according to claim 7, wherein where an area of the
anode active material layer is S1 and an area of the coat is S2,
and an area ratio S2/S1 is in the range from 0.2 to 0.9,
inclusive.
12. The battery according to claim 7, wherein a weight per unit
area of the coat is in the range from 0.02 mg/cm2 to 1 mg/cm2,
inclusive.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/248,374 filed Oct. 8, 2008, the entirety of
which is incorporated herein by reference to the extent permitted
by law. The present invention claims priority to and contains
subject matter related to Japanese Patent Application JP
2007-268348 filed in the Japanese Patent Office on Oct. 15, 2007,
the entire contents of which being incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an anode having an anode
active material layer on an anode current collector and a battery
including the same.
[0004] 2. Description of the Related Art
[0005] In recent years, portable electronic devices such as
combination cameras (videotape recorder), mobile phones, and
notebook personal computers have been widely used, and it is
strongly demanded to reduce their size and weight and to achieve
their long life. Accordingly, as a power source, a battery, in
particular a light-weight secondary batter capable of providing a
high energy density has been developed.
[0006] Specially, a secondary battery using insertion and
extraction of lithium for charge and discharge reaction (so-called
lithium ion secondary battery) is extremely prospective, since such
a lithium ion secondary battery provides a higher energy density
compared to a lead battery and a nickel cadmium battery. The
lithium ion secondary battery includes a cathode and an anode that
are opposed to each other with a separator in between and an
electrolytic solution impregnated in the separator. The anode has
an anode active material layer on an anode current collector.
[0007] As an anode active material contained in the anode active
material layer, a carbon material such as graphite has been widely
used. However, in recent years, as the high performance and the
multi functions of the portable electronic devices are developed,
improving the battery capacity is further demanded. Thus, it has
been considered to use silicon or the like instead of the carbon
material. Since the theoretical capacity of silicon (4199 mAh/g) is
significantly higher than the theoretical capacity of graphite (372
mAh/g), it is prospected that the battery capacity is thereby
significantly improved.
[0008] The lithium ion secondary battery provides a high energy
density. Meanwhile, the lithium ion secondary battery has some
disadvantages that should be solved. Firstly, when charged, the
anode active material inserting lithium is highly active. Thus, the
electrolytic solution tends to be easily decomposed and lithium
tends to be inactivated. Secondly, when the separator is broken by
strong external force, internal short circuit may be generated.
Thirdly, when the anode active material is swollen and shrunk
during charge and discharge, the anode active material layer may be
separated. All the foregoing disadvantages may become a cause to
lower the cycle characteristics and the safety.
[0009] To solve the various disadvantages of the lithium ion
secondary battery, various techniques have been considered.
Specifically, to improve the cycle characteristics and the load
characteristics, a technique of coating the surface of carbon
particles as an anode active material with a hydrate of aluminum
oxide by dipping method has been proposed (for example, refer to
Japanese Unexamined Patent Application Publication No.
2003-257419). Further, to prevent abnormal overheat due to internal
short circuit, a technique of forming a porous insulating layer
such as alumina on the surface of the anode active material layer
by vapor-phase deposition method such as sputtering method has been
proposed (for example, refer to Japanese Unexamined Patent
Application Publication No. 2005-183179). Furthermore, to prevent
internal short circuit due to overheat, a technique of forming a
porous heat-resistant layer containing an insulative filler such as
alumina and a binder between the separator and the anode active
material layer by coating method has been proposed (for example,
refer to Japanese Unexamined Patent Application Publication No.
2006-120604). Moreover, to prevent internal short circuit, a
technique of forming a porous protective film composed of solid
particles such as alumina powder and a resin binder on the surface
of the anode active material layer by coating method has been
proposed (for example, refer to Japanese Unexamined Patent
Application Publication No. 07-220759). Moreover, to improve the
capacity characteristics and the cycle characteristics, a technique
of covering the surface of the anode active material with an
inorganic ion conductive film composed of lithium-aluminum
hydroxide compound by dipping method has been proposed (for
example, refer to Japanese Unexamined Patent Application
Publication No. 09-171813). Moreover, to improve the cycle
characteristics, a technique of covering a partial surface of the
anode active material with a metal oxide by liquid-phase deposition
method has been proposed (for example, refer to Japanese Unexamined
Patent Application Publication No. 2007-141666).
SUMMARY OF THE INVENTION
[0010] In recent years, in the portable electronic devices, the
high performance and the multi functions tend to be increasingly
developed and thus, electric power consumption thereof tends be
increased. Accordingly, there is a tendency that charge and
discharge of the secondary battery used for the portable electronic
devices are frequently repeated, and thus the cycle characteristics
and the safety are easily lowered. Therefore, further improvement
of the cycle characteristics and the safety of the secondary
battery is aspired.
[0011] In view of the foregoing, in the invention, it is desirable
to provide an anode and a battery capable of obtaining superior
cycle characteristics and safety.
[0012] According to an embodiment of the invention, there is
provided an anode having an insulative coat divided into a
plurality of portions on an anode active material layer provided on
an anode current collector. According to an embodiment of the
invention, there is provided a battery including a cathode, an
anode, and an electrolytic solution, in which the anode has an
insulative coat divided into a plurality of portions on an anode
active material layer provided on an anode current collector.
[0013] According to the anode of the embodiment of the invention,
the anode has the insulative coat divided into a plurality of
portions on the anode active material layer. Therefore, in the case
where the anode is used for an electrochemical device such as a
battery, the insulation property of the coat prevents internal
short circuit, and the plurality of portions of the coat prevent
separation of the anode active material layer and decomposition of
the electrolytic solution. Further, even when short circuit occurs,
heat generation is prevented by heat absorption characteristics of
the coat. Thereby, according to the battery including the anode of
the invention, superior cycle characteristics and safety are
obtained.
[0014] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a cross section view showing a structure of an
anode according to an embodiment of the invention;
[0016] FIG. 2 is a cross section view showing an enlarged part of
the anode shown in FIG. 1;
[0017] FIG. 3 is another cross section view showing an enlarged
part of the anode shown in FIG. 1;
[0018] FIG. 4 is a cross section view showing a structure of an
anode of a comparative example;
[0019] FIG. 5 is another cross section view showing a structure of
the anode of the comparative example;
[0020] FIG. 6 is a cross section view showing a structure of a
first battery including the anode according to the embodiment of
the invention;
[0021] FIG. 7 is a cross section view taken along line VII-VII of
the first battery shown in FIG. 6;
[0022] FIG. 8 is a cross section view showing an enlarged part of
the battery element shown in FIG. 7;
[0023] FIG. 9 is a cross section view showing a structure of a
second battery including the anode according to the embodiment of
the invention;
[0024] FIG. 10 is a cross section view showing an enlarged part of
the spirally wound electrode body shown in FIG. 9;
[0025] FIG. 11 is a perspective view showing a structure of a third
battery including the anode according to the embodiment of the
invention;
[0026] FIG. 12 is a cross section view taken along line XII-XII of
the spirally wound electrode body shown in FIG. 11;
[0027] FIG. 13 is a cross section view showing an enlarged part of
the spirally wound electrode body shown in FIG. 12; and
[0028] FIG. 14 is a cross section view showing a structure of a
battery fabricated in examples.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] An embodiment of the invention will be hereinafter described
in detail with reference to the drawings.
[0030] FIG. 1 schematically shows a cross sectional structure of an
anode according to an embodiment of the invention. The anode is
used, for example, for an electrochemical device such as a battery.
The anode has an anode current collector 1 having a pair of opposed
faces, an anode active material layer 2 provided on the anode
current collector 1, and a coat 3 provided on the anode active
material layer 2. The anode active material layer 2 and the coat 3
may be provided on the both faces of the anode current collector 1
or on only a single face thereof.
[0031] The anode current collector 1 is preferably made of a metal
material having favorable electrochemical stability, favorable
electric conductivity, and favorable mechanical strength. As such a
kind of metal material, for example, copper (Co), nickel (Ni),
stainless or the like is cited. Among them, copper is preferable
since high electric conductivity is thereby obtained.
[0032] In particular, the foregoing metal material preferably
contains one or more metal elements not forming an intermetallic
compound with an electrode reactant. If the intermetallic compound
is formed with the electrode reactant, lowering of the current
collectivity characteristics and separation of the anode active
material layer 2 from the anode current collector 1 may occur,
because it is easily affected by stress due to expansion and
shrinkage of the anode active material layer 2 during the operation
of the electrochemical device (for example, during charge and
discharge of battery). As such a kind of metal element, for
example, copper, nickel, titanium, iron (Fe), chromium (Cr) or the
like is cited.
[0033] The foregoing metal material preferably contains one or more
metal elements being alloyed with the anode active material layer
2. Thereby, the contact characteristics between the anode current
collector 1 and the anode active material layer 2 are improved, and
thus the anode active material layer 2 is less likely to be
separated from the anode current collector 1. As a metal element
that does not form an intermetallic compound with the electrode
reactant and is alloyed with the anode active material layer 2, for
example, in the case where the anode active material layer 2
contains silicon as an anode active material, copper, nickel, iron
or the like is cited. These metal elements are preferable in terms
of the strength and the electric conductivity as well.
[0034] The anode current collector 1 may have a single layer
structure or a multilayer structure. In the case where the anode
current collector 1 has the multilayer structure, for example, it
is preferable that the layer adjacent to the anode active material
layer 2 is made of a metal material being alloyed with the anode
active material layer 2, and layers not adjacent to the anode
active material layer 2 are made of other metal material.
[0035] The surface of the anode current collector 1 is preferably
roughened. Thereby, due to so-called anchor effect, the contact
characteristics between the anode current collector 1 and the anode
active material layer 2 are improved. In this case, it is enough
that at least the surface of the anode current collector 1 opposed
to the anode active material layer 2 is roughened. As a roughening
method, for example, a method of forming fine particles by
electrolytic treatment and the like are used. The electrolytic
treatment is a method of providing concavity and convexity by
forming fine particles on the surface of the anode current
collector 1 by electrolytic method in an electrolytic bath. A
copper foil provided with the electrolytic treatment is generally
called "electrolytic copper foil."
[0036] The anode active material layer 2 contains one or more anode
materials capable of inserting and extracting an electrode reactant
as an anode active material. The anode active material layer 2 may
also contain other materials such as a conductive agent and a
binder according to needs.
[0037] As the anode material capable of inserting and extracting
the electrode reactant, for example, a material that is able to
insert and extract the electrode reactant and contains at least one
of metal elements and metalloid elements as an element is cited.
Such an anode material is preferably used, since a high energy
density is thereby obtained. Such a kind of anode material may be a
simple substance, an alloy, or a compound of a metal element or a
metalloid element, or may have one or more phases thereof at least
in part.
[0038] In the invention, "the alloy" includes an alloy containing
one or more metal elements and one or more metalloid elements, in
addition to an alloy composed of two or more metal elements.
Further, "the alloy" may contain a nonmetallic element. The texture
thereof includes a solid solution, a eutectic crystal (eutectic
mixture), an intermetallic compound, and a texture in which two or
more thereof coexist.
[0039] As the foregoing metal element or the foregoing metalloid
element, for example, a metal element or a metalloid element
capable of forming an alloy with the electrode reactant is cited.
Specifically, magnesium (Mg), boron (B), aluminum, gallium (Ga),
indium (In), silicon, germanium (Ge), tin (Sn), lead (Pb), bismuth
(Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf),
zirconium, yttrium (Y), palladium (Pd), platinum (Pt) and the like
are cited. Specially, at least one of silicon and tin is preferably
used, and silicon is preferable to tin, because silicon has the
high ability to insert and extract the electrode reactant, and
provides a high energy density.
[0040] As an anode material containing at least one of silicon and
tin, for example, the simple substance, an alloy, or a compound of
silicon; the simple substance, an alloy, or a compound of tin; or a
material having one or more phases thereof at least in part is
cited. Each thereof may be used singly, or a plurality thereof may
be used by mixture.
[0041] As the alloy of silicon, for example, an alloy containing at
least one selected from the group consisting of tin, nickel,
copper, iron, cobalt, manganese, zinc, indium, silver, titanium,
germanium, bismuth, antimony, and chromium as the second element
other than silicon is cited. As the compound of silicon, for
example, a compound containing oxygen or carbon (C) is cited, and
the compound of silicon may contain the foregoing second element in
addition to silicon. Examples of an alloy or a compound of silicon
include SiB.sub.4, SiB.sub.6, Mg.sub.2Si, Ni.sub.2Si, TiSi.sub.2,
MoSi.sub.2, CoSi.sub.2, NiSi.sub.2, CaSi.sub.2, CrSi.sub.2,
Cu.sub.5Si, FeSi.sub.2, MnSi.sub.2, NbSi.sub.2, TaSi.sub.2,
VSi.sub.2, WSi.sub.2, ZnSi.sub.2, SiC, Si.sub.3N.sub.4,
Si.sub.2N.sub.2O, SiO.sub.v (0<v.ltoreq.2), SnO.sub.w
(0<w.ltoreq.2), LiSiO and the like.
[0042] As the alloy of tin, for example, an alloy containing at
least one selected from the group consisting of silicon, nickel,
copper, iron, cobalt, manganese, zinc, indium, silver, titanium,
germanium, bismuth, antimony, and chromium as the second element
other than tin is cited. As the compound of tin, for example, a
compound containing oxygen or carbon is cited, and may contain the
foregoing second element in addition to tin. Examples of an alloy
or a compound of tin include SnSiO.sub.3, LiSnO, Mg.sub.2Sn and the
like.
[0043] In particular, as the anode material containing at least one
of silicon and tin, for example, an anode material containing the
second element and the third element in addition to tin as the
first element is preferable. As the second element, at least one
selected from the group consisting of cobalt, iron, magnesium,
titanium, vanadium (V), chromium, manganese, nickel, copper, zinc,
gallium, zirconium, niobium (Nb), molybdenum, silver, indium,
cerium (Ce), hafnium, tantalum (Ta), tungsten (W), bismuth, and
silicon is cited. As the third element, at least one selected from
the group consisting of boron, carbon, aluminum, and phosphorus (P)
is cited. When the second element and the third element are
contained, the cycle characteristics are improved.
[0044] Specially, a SnCoC-containing material that contains tin,
cobalt, and carbon as an element in which the carbon content is in
the range from 9.9 wt % to 29.7 wt %, and the cobalt ratio to the
total of tin and cobalt (Co/(Sn+Co)) is in the range from 30 wt %
to 70 wt % is preferable. In such a composition range, a high
energy density is obtained.
[0045] The SnCoC-containing material may further contain other
element according to needs. As other element, for example, silicon,
iron, nickel, chromium, indium, niobium, germanium, titanium,
molybdenum, aluminum, phosphorus, gallium, bismuth or the like is
preferable. Two or more thereof may be contained, since thereby
higher effects are obtained.
[0046] The SnCoC-containing material has a phase containing tin,
cobalt, and carbon. Such a phase preferably has a low crystallinity
structure or an amorphous structure. Further, in the
SnCoC-containing material, at least part of carbon as an element is
preferably bonded to a metal element or a metalloid element as
other element. Cohesion or crystallization of tin or the like is
thereby inhibited.
[0047] The SnCoC-containing material may be formed by, for example,
mixing raw materials of each element, dissolving the resultant
mixture in an electric furnace, a high frequency induction furnace,
an arc melting furnace or the like and then solidifying the
resultant. Otherwise, the SnCoC-containing material may be formed
by various atomization methods such as gas atomizing and water
atomizing; various roll methods; or a method using mechanochemical
reaction such as mechanical alloying method and mechanical milling
method. Specially, the SnCoC-containing material is preferably
formed by the method using mechanochemical reaction, since thereby
the anode active material is able to have a low crystalline
structure or an amorphous structure. For the method using the
mechanochemical reaction, for example, a manufacturing apparatus
such as a planetary ball mill and an attliter may be used.
[0048] As a measurement method for examining bonding state of
elements, for example, X-ray Photoelectron Spectroscopy (XPS) may
be used. In XPS, in the case of graphite, the peak of is orbit of
carbon (C1s) is observed at 284.5 eV in the apparatus in which
energy calibration is made so that the peak of 4f orbit of gold
atom (Au4f) is obtained in 84.0 eV. In the case of surface
contamination carbon, the peak is observed at 284.8 eV. Meanwhile,
in the case of higher electric charge density of carbon element,
for example, when carbon is bonded to a metal element or a
metalloid element, the peak of C1s is observed in the region lower
than 284.5 eV. That is, when the peak of the composite wave of C1s
obtained for the SnCoC-containing material is observed in the
region lower than 284.5 eV, at least part of carbon contained in
the SnCoC-containing material is bonded to the metal element or the
metalloid element as other element.
[0049] In XPS, for example, the peak of C1s is used for correcting
the energy axis of spectrums. Since surface contamination carbon
generally exists on the surface, the peak of C1s of the surface
contamination carbon is set to in 284.8 eV, which is used as an
energy reference. In XPS, the waveform of the peak of C1s is
obtained as a form including the peak of the surface contamination
carbon and the peak of carbon in the SnCoC-containing material.
Therefore, for example, by analyzing the waveform with the use of
commercially available software, the peak of the surface
contamination carbon and the peak of carbon in the SnCoC-containing
material are separated. In the analysis of the waveform, the
position of the main peak existing on the lowest bound energy side
is set to the energy reference (284.8 eV).
[0050] The anode active material layer 2 using the simple
substance, an alloy, or a compound of silicon; the simple
substance, an alloy, or a compound of tin; or a material having one
or more phases thereof at least in part as an anode material is
preferably formed by, for example, vapor-phase deposition method,
liquid-phase deposition method, spraying method, coating method,
firing method, or a combination of two or more of these methods. In
this case, the anode current collector 1 and the anode active
material layer 2 are preferably alloyed in at least part of the
interface thereof. Specifically, at the interface thereof, the
element of the anode current collector 1 may be diffused in the
anode active material layer 2; or the element of the anode active
material layer 2 may be diffused in the anode current collector 1;
or these elements may be diffused in each other. Thereby,
destruction due to expansion and shrinkage of the anode active
material layer 2 in charge and discharge is prevented, and the
electron conductivity between the anode current collector 1 and the
anode active material layer 2 is improved.
[0051] As vapor-phase deposition method, for example, physical
deposition method or chemical deposition method is cited.
Specifically, vacuum evaporation method, sputtering method, ion
plating method, laser ablation method, thermal CVD (Chemical Vapor
Deposition) method, plasma CVD method and the like are cited. As
liquid-phase deposition method, a known technique such as
electrolytic plating and electroless plating is used. Coating
method is, for example, a method in which a particulate anode
active material mixed with a binder or the like is dispersed in a
solvent and the anode current collector is coated with the
resultant. Firing method is, for example, a method in which coating
is provided by coating method and then heat treatment is provided
at a temperature higher than the melting point of the binder or the
like. For firing method, a known technique such as atmosphere
firing method, reactive firing method, and hot press firing method
is available as well.
[0052] In addition to the foregoing anode material, as the anode
material capable of inserting and extracting the electrode
reactant, for example, a carbon material is cited. As the carbon
material, for example, graphitizable carbon, non-graphitizable
carbon in which the spacing of (002) plane is 0.37 nm or more,
graphite in which the spacing of (002) plane is 0.34 nm or less and
the like are cited. More specifically, pyrolytic carbons, coke,
glassy carbon fiber, an organic polymer compound fired body,
activated carbon, carbon black or the like is cited. The coke
includes pitch coke, needle coke, petroleum coke and the like. The
organic polymer compound fired body is obtained by firing and
carbonizing a phenol resin, a furan resin or the like at an
appropriate temperature. In the carbon material, the crystal
structure change associated with inserting and extracting the
electrode reactant is very small. Therefore, for example, by using
the carbon material together with other anode material, a high
energy density is obtained together with superior cycle
characteristics. In addition, the carbon material also functions as
an electrical conductor, and thus the carbon material is preferably
used. The shape of the carbon material may be any of a fibrous
shape, a spherical shape, a granular shape, and a scale-like
shape.
[0053] Further, as the anode material capable of inserting and
extracting the electrode reactant, for example, a metal oxide, a
polymer compound and the like capable of inserting and extracting
the electrode reactant are cited. As the metal oxide, for example,
iron oxide, ruthenium oxide, molybdenum oxide or the like is cited.
As the polymer compound, for example, polyacetylene, polyaniline,
polypyrrole or the like is cited.
[0054] It is needless to say that these anode materials may be used
together with the above-mentioned anode material. Further, a
mixture of two or more of anode materials may be used in any
combination.
[0055] As the electrical conductor, for example, a carbon material
such as graphite, carbon black, acetylene black, and Ketjen black
is cited. Such a carbon material may be used singly, or a plurality
thereof may be used by mixture. The electrical conductor may be a
metal material, a conductive polymer or the like as long as the
material has the electric conductivity.
[0056] As the binder, for example, a synthetic rubber such as
styrene-butadiene rubber, fluorinated rubber, and
ethylenepropylenediene; or a polymer material such as
polyvinylidene fluoride is cited. One thereof may be used singly,
or two or more thereof may be used by mixture.
[0057] FIG. 2 and FIG. 3 show an enlarged part of the anode shown
in FIG. 1. The anode active material layer 2 has several modes
according to the type of the anode active material and the method
of forming the anode active material layer 2.
[0058] Specifically, for example, in the case where the anode
active material contains a material that is capable of inserting
and extracting the electrode reactant and that contains at least
one of metal elements and metalloid elements, and the anode active
material is formed by vapor-phase deposition method or the like, as
shown in FIG. 2, the anode active material layer 2 contains a
plurality of particulate anode active materials (anode active
material particles 2A) extending in the vertical direction (in a
direction away from the surface of the anode current collector 1).
In the case where the anode current collector 1 is made of a
roughened foil such as an electrolytic copper foil and a plurality
of projection sections 1P exist on the surface thereof, the anode
active material particle 2A is grown for every projection 1P in the
thickness direction, and is linked to the anode current collector 1
at the root. The plurality of anode active material particles 2A
may be adjacent to each other, or may be spaced from each other at
intervals (gap 2G). In the case where the anode active material is
deposited on the anode current collector 1 by vapor-phase
deposition method or the like, the anode active material particles
2A may have a single layer structure formed by one deposition step,
or may have multilayer structure formed by a plurality of
deposition steps. In this case, it is preferable that the anode
active material is deposited by vapor-phase deposition method, and
at lest part of the interface between the anode current collector 1
and the anode active material particles 2A is alloyed.
[0059] Further, for example, when the anode active material
contains the carbon material, as shown in FIG. 3, the anode active
material layer 2 contains a plurality of anode active material
particles 2B. The anode active material particles 2B are carbon
material particles. Two or more of carbon material particles may
aggregate to form the anode active material particle 2B in some
cases. In the case where the carbon material is used as an anode
active material, the anode active material is generally mixed with
a binder or the like. However, in FIG. 3, the binder or the like is
not shown. If the binder is shown in FIG. 3, the binder should
exist in a gap between each anode active material particle 2B. In
FIG. 3, the projection section 1P shown in FIG. 2 is not shown.
However, in the case shown in FIG. 3, the anode current collector 1
may have the projection section 1P.
[0060] The coat 3 contains an insulating material, and is divided
into a plurality of portions. The divided insulative coat 3 is
provided on the anode active material layer 2 for the following
reasons. Firstly, the insulation property of the coat 3 prevents
internal short circuit of an electrochemical device. Secondly,
since part of the anode active material layer 2 is covered with the
coat 3, the anode active material layer 2 is prevented from being
separated while securing a migration path of the electrode reactant
(insertion and extraction path). Thirdly, the heat absorption
characteristics of the coat 3 prevents heat generation when an
electrochemical device is short-circuited.
[0061] As shown in FIG. 2 and FIG. 3, the divided coat 3 has a
plate shape (so-called plate-like). While the coat 3 extends along
a partial surface of the anode active material particle 2A or 2B,
the coat 3 covers the partial surface. "The coat 3 has a plate
shape" means that the coat 3 is in a state of a mass made of an
insulating material, and is not in a state of a particle. That is,
the coat 3 is not a complex system containing an insulating
material particle, a binder or the like.
[0062] In some cases, each coat 3 exists on one anode active
material particle 2A or 2B, extends along a partial surface thereof
while covering the partial surface. In some cases, each coat 3
extends and lies on two or more anode active material particles 2A
or 2B, extends along a partial surface thereof while continuously
covering the partial surface. For the covering state, the latter is
preferable to the former, and a case of including the both covering
states is preferable to a case of including only one covering
state. This is because the separation of the anode active material
layer 2 is further prevented. Accordingly, in the case where the
both covering states are included, a larger ratio of the latter
covering state is preferable. FIG. 2 shows the former and the
latter covering states, and FIG. 3 shows only the former covering
state. It is needless to say that the latter covering state may be
included in the case shown in FIG. 3.
[0063] The type of the insulating material composing the coat 3 is
not particularly limited, but an insulating material having a high
heat capacity is preferable to improve heat absorption
characteristics. For example, an insulating material which has heat
resistance (decomposition temperature) of 500 deg C. or more, and
in which the volume heat capacity (specific heat) at 300K is 1.7
J/Kg or more is preferable.
[0064] Specifically, the coat 3 preferably contains at least one of
a metal hydroxide and a metal oxide, since such a compound has a
high heat capacity and a high specific heat and thus the heat
absorption ability is improved. Between them, the metal hydroxide
is preferable. Although the metal hydroxide and the metal oxide are
finally decomposed by being heated, the metal oxide is directly
decomposed, whereas the metal hydroxide is changed to a metal oxide
and then decomposed. Thus, the heat absorption ability in the case
of using the metal hydroxide is higher than that in the case of
using the metal oxide. As the foregoing metal hydroxide, for
example, at least one selected from the group consisting of
aluminum hydroxide, zirconium hydroxide, and a substitute hydroxide
is cited. As the metal oxide, for example, at least one selected
from the group consisting of aluminum oxide, zirconium oxide, and
titanium oxide is cited. It is needless to say that a metal
hydroxide and a metal oxide other than the foregoing metal
hydroxides and the foregoing metal oxides may be used.
[0065] The method of forming the coat 3 is not particularly
limited. However, a method capable of collectively forming the coat
3 that is divided into a plurality of portions is preferable. As
such a kind of forming method, for example, electrolytic plating
method or electroless plating method is cited. Specially, the
electrolytic plating method is preferable, since thereby the
divided coat 3 is able to be easily formed on the anode active
material layer 2 by one step under general plating conditions.
However, forming methods other than the foregoing forming methods
may be used.
[0066] In the case where the coat 3 is formed by electrolytic
plating method, as shown in FIG. 2, the growth process of the
plating film is affected by so-called edge effect. Thus, the
thickness of the coat 3 in the end portion tends to be relatively
thick, and t in the central portion thereof tends to be relatively
thin. In some cases, the end portion of the coat 3 is grown from
the surface of the anode active material particle 2A adjacent to
the anode active material particle 2A covered with the end portion
of the coat 3 with a distance, while extending the surface thereof.
Such a mode is one of the characteristics caused when the coat 3
divided into a plurality of portions is formed by electrolytic
plating method. It is needless to say that the foregoing mode may
be caused in the case shown in FIG. 3 as well.
[0067] Whether or not the coat 3 is formed by electrolytic plating
method may be checked after the fact. In the case where the coat 3
is formed by using a plating solution containing a nitrate salt,
nitrogen component should remain in the coat 3. The nitrate salt
is, for example, aluminum nitrate nonahydrate
(Al(NO.sub.3).sub.3.9H.sub.2O) or the like in the case of using
aluminum hydroxide as a material of the coat 3. In the case where
the coat 3 is formed by coating method, vapor-phase deposition
method or the like, nitrogen component should not remain in the
coat 3 unless the coat 3 is formed by using an insulating material
containing nitrogen as an element. A fact that the coat 3 contains
the nitrogen component is a supporting evidence that the coat 3 is
formed by electrolytic plating method. The amount of the nitrogen
component remaining in the coat 3 is about in the range from 0.5%
to 3% at an atomic ratio in the case of using the foregoing plating
solution containing a nitrate salt, and is able to be confirmed by
element analysis by XPS, for example.
[0068] In particular, where the area of the anode active material
layer 2 is S1 and the area of the coat 3 is S2, the area ratio
S2/S1 is preferably in the range from 0.2 to 0.9. Thereby, the
foregoing function of the coat 3 is sufficiently demonstrated. More
specifically, if the area ratio S2/S1 is smaller than 0.2, the
covering range of the coat 3 is extremely small and thus it may be
difficult to prevent the separation of the anode active material
layer 2. Meanwhile, if the area ratio S2/S1 is larger than 0.9, the
formation range of the coat 3 is extremely large and thus it is
difficult to insert and extract the electrode reactant.
[0069] The foregoing areas S1 and S2 may be calculated by observing
the surface of the anode by a Scanning Electron Microscope
(SEM)-Energy Dispersive X-ray spectrometer (EDX) or the like,
defining a given formation range of the anode active material layer
2 (area S1) as a reference, and then determining the formation
range of the coat 3 (area S2) in the foregoing range. In this case,
the areas S1 and S2 may be artificially calculated, but the areas
S1 and S2 are preferably calculated mechanically by image-editing
software or the like, since thereby high measurement precision is
obtained and the reproducibility of the measurement numerical value
becomes high.
[0070] Further, the weight per unit area of the coat 3 is
preferably in the range from 0.02 mg/cm.sup.2 to 1 mg/cm.sup.2,
since thereby the foregoing function of the coat 3 is sufficiently
demonstrated. More specifically, if the weight per unit area is
smaller than 0.02 mg/cm.sup.2 or larger than 1 mg/cm.sup.2, as in
the case described for the area ratio S2/S1, it is difficult to
prevent the separation of the anode active material layer 2, and to
insert and extract the electrode reactant.
[0071] The foregoing weight per unit area of the coat 3 may be also
calculated by examining a weight difference of the anode between
the weight before forming the coat 3 and the weight after forming
the coat 3.
[0072] The anode is formed, for example, by the following
procedure.
[0073] First, the anode current collector 1 made of an electrolytic
copper foil or the like is prepared. After that, the anode active
material layer 2 is formed on the anode current collector 1 by
selecting the forming method according to the type of the anode
active material or the like. Specifically, in the case where a
material that is capable of inserting and extracting the electrode
reactant and that contains at least one of metal elements and
metalloid elements is used as an anode active material, the anode
active material is deposited on the anode current collector 1 by
vapor-phase deposition method or the like to form the plurality of
anode active material particles 2A to form the anode active
material layer 2. Further, in the case where the carbon material is
used as an anode active material, the anode current collector 1 is
coated with a slurry containing the particulate anode active
material (anode active material particles 2B) by coating method or
the like, the resultant is dried and compression-molded according
to needs to form the anode active material layer 2. Finally, the
coat 3 is formed on the anode active material layer 2 by
electrolytic plating method or the like. When the insulating
material such as the metal hydroxide and the metal oxide is plated
and grown after the anode active material layer 2 is formed, the
plating film is not grown to fill in the gap between the anode
active material particles 2A or 2B, but is grown to locally cover
the top portion thereof. Thus, the coat 3 is formed and divided
into a plurality of portions. Accordingly, the anode is formed.
[0074] With this anode, since the insulative coat 3 divided into a
plurality of portions is provided on the anode active material
layer 2, in the case where the anode is used for an electrochemical
device, superior cycle characteristics and safety are able to be
obtained for the following reasons.
[0075] FIG. 4 and FIG. 5 show a cross sectional structure of an
anode of a comparative example, and respectively correspond to FIG.
2 and FIG. 3. In the anode of the comparative example, the surface
of the anode active material layer 2 is coated with a slurry
containing insulating material particles and a binder by coating
method, and thereby a coat 4 in a state of a plurality of particles
is formed on the anode active material layer 2. In the anode of
this embodiment, the following advantages are obtained compared to
the anode of the comparative example.
[0076] Firstly, since the insulative coat 3 is in a state of a
plate divided into a plurality of portions, the anode active
material particle 2A or 2B is insulated from outside more than the
case that the insulative coat 4 is in a state of a particle. The
plate-like coat 3 not generating a gap in the covering range allows
the anode active material particle 2A or 2B to be insulated from
outside over a large range. Meanwhile, the particulate coat 4 that
is dotted locally and generates a number of gaps in the covering
range insulates the anode active material particle 2A or 2B only in
a small range. Thereby, since the anode is less likely to be
conducted to the outside due to the insulation property of the coat
3, internal short circuit of the electrochemical device is
prevented.
[0077] Secondly, the plate-like coat 3 covers the anode active
material particle 2A or 2B, and thus physical pressure force
applied by the coat 3 to the anode active material particle 2A or
2B is larger than in the case that the particulate coat 4 covers
the anode active material particle 2A or 2B. The plate-like coat 3
is able to press the anode active material particle 2A or 2B over a
large range. Meanwhile, the particulate coat 4 is able to press the
anode active material particle 2A or 2B only in a small range.
Thereby, the anode active material layer 2 is less likely to be
expanded and shrunk when charged and discharged. Therefore, the
anode active material layer 2 is prevented from being separated in
the place where the anode active material layer 2 is covered while
securing a migration path of the electrode reactant (insertion and
extraction path) in the place where the anode active material layer
2 is not covered. In this case, when the anode is used together
with an electrolytic solution for an electrochemical device, the
coat 3 works as a protective film for the anode active material
layer 2 and thus decomposition reaction of the electrolytic
solution is also prevented.
[0078] Thirdly, since the plate-like coat 3 has heat absorption
characteristics, the heat absorption ability is higher than in the
case that the particulate coat 4 has heat absorption
characteristics. Since the plate-like coat 3 has a larger volume
than the particulate coat 4, the heat absorption amount thereof is
also larger than that of the particulate coat 4. Thereby, even when
the electrochemical device is short-circuited, heat generation is
inhibited by the heat absorption characteristics of the coat 3.
[0079] Accordingly, in the anode of this embodiment, internal short
circuit in the electrochemical device is prevented, and separation
of the anode active material layer, decomposition of the
electrolytic solution, and heat generation when short-circuited are
prevented. As a result, superior cycle characteristics and safety
are obtained.
[0080] In particular, when the coat 3 contains the metal hydroxide
or the metal oxide, favorable insulation property and favorable
heat absorption characteristics are obtained in the coat 3, and
thus high effects are obtained.
[0081] Further, in the case where the anode active material layer 2
contains the plurality of anode active material particles 2A or 2B,
when the coat 3 extends along a partial surface of two or more
anode active material particles 2A or 2B, while continuously
covering the partial surface, the anode active material layer 2 is
more less likely to be separated in the place where the anode
active material layer 2 is covered and thus higher effects are able
to be obtained.
[0082] Further, when the area ratio S2/S1 is in the range from 0.2
to 0.9, or when the weight per unit area of the coat 3 is in the
range from 0.02 mg/cm.sup.2 to 1 mg/cm.sup.2, higher effects are
able to be obtained.
[0083] Further, when the coat 3 is formed by electrolytic plating
method, the coat 3 divided into a plurality of portions is able to
be easily formed on the anode active material layer 2 by one
step.
[0084] In addition, when the anode active material layer 2 contains
silicon, the anode active material layer 2 is expanded and shrunk
and is easily separated in electrode reaction. However, in the
anode of this embodiment, such separation of the anode active
material layer 2 is effectively prevented, and thus higher effects
are able to be obtained.
[0085] Next, a description will be hereinafter given of a usage
example of the foregoing anode. As an example of the
electrochemical devices, batteries are herein taken. The anode is
used for the batteries as follows.
[0086] First Battery
[0087] FIG. 6 and FIG. 7 show cross sectional structures of a first
battery. FIG. 7 shows a cross section taken along line VII-VII
shown in FIG. 6. The battery herein described is, for example, a
lithium ion secondary battery in which the capacity of an anode 22
is expressed based on insertion and extraction of lithium as an
electrode reactant.
[0088] In the secondary battery, the battery element 20 having a
flat spirally wound structure is mainly contained in a battery can
11.
[0089] The battery can 11 is, for example, a square package member.
As shown in FIG. 7, the square package member has a shape with a
cross section in the longitudinal direction of a rectangle or an
approximate rectangle (including curved lines in part). The square
package member structures not only a square battery in the shape of
a rectangle, but also a square battery in the shape of an oval.
That is, the square package member means a rectangle vessel-like
member with the bottom or an oval vessel-like member with the
bottom, which respectively has an opening in the shape of a
rectangle or in the shape of an approximate rectangle (oval shape)
formed by connecting circular arcs by straight lines. FIG. 7 shows
a case that the battery can 11 has a rectangular cross sectional
shape. The battery structure including the battery can 11 is called
square structure.
[0090] The battery can 11 is made of, for example, a metal material
such as iron, aluminum, or an alloy thereof. The battery can 11 may
have a function as an electrode terminal as well. Specially, to
prevent the secondary battery from being swollen by using the
rigidity (less likely to deform) of the battery can 11 when charged
and discharged, rigid iron is preferable to aluminum. In the case
where the battery can 11 is made of iron, the battery can 11 may be
plated by nickel or the like.
[0091] The battery can 11 has a hollow structure in which one end
of the battery can 11 is closed and the other end thereof is
opened. At the open end of the battery can 11, an insulating plate
12 and a battery cover 13 are attached, and thereby inside of the
battery can 11 is hermetically closed. The insulating plate 12 is
located between the battery element 20 and the battery cover 13, is
arranged perpendicularly to the spirally wound circumferential face
of the battery element 20, and is made of, for example,
polypropylene or the like. The battery cover 13 is, for example,
made of a material similar to that of the battery can 11, and also
has a function as an electrode terminal as the battery can 11
does.
[0092] Outside of the battery cover 13, a terminal plate 14 as a
cathode terminal is provided. The terminal plate 14 is electrically
insulated from the battery cover 13 with an insulating case 16 in
between. The insulating case 16 is made of, for example,
polybutylene terephthalate or the like. In the approximate center
of the battery cover 13, a through-hole is provided. A cathode pin
15 is inserted in the through-hole so that the cathode pin 15 is
electrically connected to the terminal plate 14 and is electrically
insulated from the battery cover 13 with a gasket 17 in between.
The gasket 17 is made of, for example, an insulating material, and
the surface thereof is coated with asphalt.
[0093] In the vicinity of the rim of the battery cover 13, a
cleavage valve 18 and an injection hole 19 are provided. The
cleavage valve 18 is electrically connected to the battery cover
13. If the internal pressure of the battery becomes a certain level
or more by internal short circuit, external heating or the like,
the cleavage valve 18 is separated from the battery cover 13 to
release the internal pressure. The injection hole 19 is sealed by a
sealing member 19A made of, for example, a stainless steel
ball.
[0094] The battery element 20 is formed by layering a cathode 21
and the anode 22 with a separator 23 in between and then spirally
winding the resultant laminated body. The battery element 20 is
flat according to the shape of the battery can 11. A cathode lead
24 made of aluminum or the like is attached to an end of the
cathode 21 (for example, the internal end thereof). An anode lead
25 made of nickel or the like is attached to an end of the anode 22
(for example, the outer end thereof). The cathode lead 24 is
electrically connected to the terminal plate 14 by being welded to
an end of the cathode pin 15. The anode lead 25 is welded and
electrically connected to the battery can 11.
[0095] FIG. 8 shows an enlarged part of the battery element 20
shown in FIG. 7. In the cathode 21, for example, a cathode active
material layer 21B is provided on the both faces of a strip-shaped
cathode current collector 21A. The cathode current collector 21A is
made of, for example, a metal material such as aluminum, nickel,
and stainless. The cathode active material layer 21B contains a
cathode active material, and if necessary, may also contain other
material such as a binder and an electrical conductor.
[0096] The cathode active material contains one or more cathode
materials capable of inserting and extracting lithium as an
electrode reactant. As the cathode material, for example, a
lithium-containing compound is preferable, since thereby a high
energy density is obtained. As the lithium-containing compound, for
example, a complex oxide containing lithium and a transition metal
element or a phosphate compound containing lithium and a transition
metal element is cited. In particular, a compound containing at
least one selected from the group consisting of cobalt, nickel,
manganese, and iron as a transition metal element is preferable,
since thereby a higher voltage is obtained. The chemical formula
thereof is expressed as, for example, Li.sub.xM1O.sub.2 or
Li.sub.yM2PO.sub.4. In the formula, M1 and M2 represent one or more
transition metal elements. Values of x and y vary according to the
charge and discharge state of the battery, and are generally in the
range of 0.05.ltoreq.x.ltoreq.1.10 and
0.05.ltoreq.y.ltoreq.1.10.
[0097] As the complex oxide containing lithium and a transition
metal element, for example, a lithium cobalt complex oxide
(Li.sub.xCoO.sub.2), a lithium nickel complex oxide
(Li.sub.xNiO.sub.2), a lithium nickel cobalt complex oxide
(Li.sub.xNi.sub.(1-z)CO.sub.xO.sub.2 (z<1)), a lithium nickel
cobalt manganese complex oxide
(Li.sub.xNi.sub.(1-v-w)CO.sub.vMn.sub.wO.sub.2) (v+w<1)),
lithium manganese complex oxide having a spinel structure
(LiMn.sub.2O.sub.4) or the like is cited. Specially, a complex
oxide containing cobalt is preferable, since thereby a high
capacity is obtained and superior cycle characteristics are
obtained. As the phosphate compound containing lithium and a
transition metal element, for example, lithium iron phosphate
compound (LiFePO.sub.4) or a lithium iron manganese phosphate
compound (LiFe.sub.(1-u)Mn.sub.uPO.sub.4(u<1)) or the like is
cited.
[0098] In addition, as the cathode material, for example, an oxide
such as titanium oxide, vanadium oxide, and manganese dioxide; a
disulfide such as titanium disulfide and molybdenum sulfide; a
chalcogenide such as niobium selenide; sulfur; a conductive polymer
such as polyaniline and polythiophene are cited.
[0099] The anode 22 has a structure similar to that of the anode
described above. For example, in the anode 22, an anode active
material layer 22B and a coat 22C are provided on the both faces of
a strip-shaped anode current collector 22A. The structures of the
anode current collector 22A, the anode active material layer 22B,
and the coat 22C are respectively similar to the structures of the
anode current collector 1, the anode active material layer 2, and
the coat 3 in the anode described above. In the anode 22, the
charge capacity of the anode active material capable of inserting
and extracting lithium is preferably larger than the charge
capacity of the cathode 21.
[0100] The separator 23 separates the cathode 21 from the anode 22,
and passes ions as an electrode reactant while preventing current
short circuit due to contact of the both electrodes. The separator
23 is made of, for example, a porous film made of a synthetic resin
such as polytetrafluoroethylene, polypropylene, and polyethylene,
or a ceramic porous film. The separator 23 may have a structure in
which two or more porous films as the foregoing porous films are
layered.
[0101] An electrolytic solution as a liquid electrolyte is
impregnated in the separator 23. The electrolytic solution
contains, for example, a solvent and an electrolyte salt dissolved
therein.
[0102] The solvent contains, for example, one or more nonaqueous
solvents such as an organic solvent. The nonaqueous solvents
include, for example, an ester carbonate solvent such as ethylene
carbonate, propylene carbonate, butylene carbonate, dimethyl
carbonate, diethyl carbonate, ethyl methyl carbonate, and
methylpropyl carbonate. Thereby, superior capacity characteristics,
superior cycle characteristics, and superior storage
characteristics are obtained. Above all, a mixture of a
high-viscosity solvent such as ethylene carbonate and propylene
carbonate and a low-viscosity solvent such as dimethyl carbonate,
ethyl methyl carbonate, and diethyl carbonate is preferable.
Thereby, the dissociation property of the electrolyte salt and the
ion mobility are improved, and thus higher effects are
obtained.
[0103] The solvent may contain halogenated ester carbonate, since
thereby a stable coat is formed on the surface of the anode 22, and
thus the decomposition reaction of the electrolytic solution is
prevented and the cycle characteristics are improved. The
halogenated ester carbonate may be a chain compound or a cyclic
compound. The type of halogen is not particularly limited, but
fluorine is especially preferable since thereby high effects are
obtained. As a fluorinated ester carbonate, for example, a chain
compound such as fluoromethylmethyl carbonate and bis(fluoromethyl)
carbonate and a cyclic compound such as
4-fluoro-1,3-dioxolane-2-one and 4,5-difluoro-1,3-dioxolane-2-one
is cited. One thereof may be singly, or a plurality thereof may be
used by mixture. As 4,5-difluoro-1,3-dioxolane-2-one, a
trans-isomer is more preferable than a cis-isomer, since the former
is easily available and provides higher effects.
[0104] Further, the solvent may contains a cyclic ester carbonate
having an unsaturated bond, since thereby the cycle characteristics
are improved. As the cyclic ester carbonate having an unsaturated
bond, for example, vinylene carbonate, vinyl ethylene carbonate and
the like are cited. One thereof may be singly, or a plurality
thereof may be used by mixture.
[0105] Further, the solvent may contain sultone, since thereby the
cycle characteristics are improved, and the secondary battery is
inhibited from being swollen. As the sultone, for example,
1,3-propene sultone or the like is cited.
[0106] In addition, the solvent may contain an acid anhydride,
since thereby the cycle characteristics are improved. As the acid
anhydride, for example, a succinic anhydride, a glutaric anhydride,
a maleic anhydride, a sulfobenzoic anhydride, a sulfopropionic
anhydride, a sulfobutyrate anhydride, an ethanedisulfonic
anhydride, a propanedisulfonic anhydride, a benzenedisulfonic
anhydride or the like is cited. One thereof may be used singly, or
a plurality thereof may be used by mixture.
[0107] The electrolyte salt contains, for example, one or more
light metal salts such as a lithium salt. As the lithium salt, for
example, lithium hexafluorophosphate (LiPF6), lithium
tetrafluoroborate (LiBF.sub.4), lithium perchlorate (LiClO.sub.4),
lithium hexafluoroarsenate (LiAsF6) or the like is cited. Thereby,
superior capacity characteristics, superior cycle characteristics,
and superior storage characteristics are obtained. Specially,
lithium hexafluorophosphate is preferable, since the internal
resistance is lowered, and thus higher effects are obtained.
[0108] The content of the electrolyte salt in the solvent is, for
example, in the range from 0.3 mol/kg to 3.0 mol/kg, since thereby
superior capacity characteristics are obtained.
[0109] The secondary battery is manufactured, for example, by the
following procedure.
[0110] First, the cathode 21 is formed. At first, a cathode active
material, a binder, and an electrical conductor are mixed to
prepare a cathode mixture, which is dispersed in an organic solvent
to form paste cathode mixture slurry. Subsequently, the both faces
of the cathode current collector 21A are uniformly coated with the
cathode mixture slurry by using a doctor blade, a bar coater or the
like, which is dried. Finally, the resultant is compression-molded
by a rolling press machine or the like while being heated if
necessary to form the cathode active material layer 21B. In this
case, the resultant may be compression-molded over several
times.
[0111] Further, the anode 22 is formed by forming the anode active
material layer 22B and the coat 22C on the both faces of the anode
current collector 22A by the same procedure as that of forming the
anode described above.
[0112] Next, the battery element 20 is formed by using the cathode
21 and the anode 22. First, the cathode lead 24 is attached to the
cathode current collector 21A by welding or the like, and the anode
lead 25 is attached to the anode current collector 22A by welding
or the like. Subsequently, the cathode 21 and the anode 22 are
layered with the separator 23 in between, and spirally wound in the
longitudinal direction. Finally, the resultant is shaped in the
flat shape.
[0113] The secondary battery is assembled as follows. First, after
the battery element 20 is contained in the battery can 11, the
insulating plate 12 is arranged on the battery element 20.
Subsequently, the cathode lead 24 is connected to the cathode pin
15 by welding or the like and the anode lead 25 is connected to the
battery can 11 by welding or the like. After that, the battery
cover 13 is fixed on the open end of the battery can 11 by laser
welding or the like. Finally, the electrolytic solution is injected
into the battery can 11 from the injection hole 19, and impregnated
in the separator 23. After that, the injection hole 19 is sealed by
the sealing member 19A. The secondary battery shown in FIG. 6 to
FIG. 8 is thereby completed.
[0114] In the secondary battery, when charged, for example, lithium
ions are extracted from the cathode 21, and are inserted in the
anode 22 through the electrolytic solution impregnated in the
separator 23. Meanwhile, when discharged, for example, lithium ions
are extracted from the anode 22, and are inserted in the cathode 21
through the electrolytic solution impregnated in the separator
23.
[0115] According to the square secondary battery, since the anode
22 has the structure similar to that of the foregoing anode,
superior cycle characteristics and safety are obtained. In this
case, even when the anode 22 contains silicon advantageous for
obtaining a high capacity, the cycle characteristics are improved.
Thus, higher effects are thereby obtained than in a case where the
anode contains other anode material such as a carbon material.
Effects of the secondary battery other than the foregoing effects
are similar to those of the foregoing anode.
Second Battery
[0116] FIG. 9 and FIG. 10 show a cross sectional structure of a
second battery. FIG. 10 shows an enlarged part of a spirally wound
electrode body 40 shown in FIG. 9. The battery is a lithium ion
secondary battery as the foregoing first battery. The second
battery contains the spirally wound electrode body 40 in which a
cathode 41 and an anode 42 are spirally wound with a separator 43
in between, and a pair of insulating plates 32 and 33 inside a
battery can 31 in the shape of an approximately hollow cylinder.
The battery structure including the battery can 31 is a so-called
cylindrical secondary battery.
[0117] The battery can 31 is made of, for example, a metal material
similar to that of the battery can 11 in the foregoing first
battery. One end of the battery can 31 is closed, and the other end
thereof is opened. The pair of insulating plates 32 and 33 is
arranged to sandwich the spirally wound electrode body 40 in
between and to extend perpendicularly to the spirally wound
periphery face.
[0118] At the open end of the battery can 31, a battery cover 34,
and a safety valve mechanism 35 and a PTC (Positive Temperature
Coefficient) device 36 provided inside the battery cover 34 are
attached by being caulked with a gasket 37. Inside of the battery
can 31 is thereby hermetically sealed. The battery cover 34 is made
of, for example, a material similar to that of the battery can 31.
The safety valve mechanism 35 is electrically connected to the
battery cover 34 through the PTC device 36. In the safety valve
mechanism 35, if the internal pressure becomes a certain level or
more by internal short circuit, external heating or the like, a
disk plate 35A flips to cut the electric connection between the
battery cover 34 and the spirally wound electrode body 40. The PTC
device 36 increases the resistance in accordance with temperature
rise to limit a current and thereby preventing abnormal heat
generation resulting from a large current. The gasket 37 is made
of, for example, an insulating material and its surface is coated
with asphalt.
[0119] A center pin 44 may be inserted in the center of the
spirally wound electrode body 40. In the spirally wound electrode
body 40, a cathode lead 45 made of aluminum or the like is
connected to the cathode 41, and an anode lead 46 made of nickel or
the like is connected to the anode 42. The cathode lead 45 is
electrically connected to the battery cover 34 by being welded to
the safety valve mechanism 35. The anode lead 46 is welded and
thereby electrically connected to the battery can 31.
[0120] The cathode 41 has a structure in which, for example, a
cathode active material layer 41B is provided on the both faces of
a strip-shaped cathode current collector 41A. The anode 42 has a
structure similar to that of the anode described above, for
example, has a structure in which an anode active material layer
42B and a coat 42C are provided on the both faces of a strip-shaped
anode current collector 42A. The structures of the cathode current
collector 41A, the cathode active material layer 41B, the anode
current collector 42A, the anode active material layer 42B, the
coat 42C, and the separator 43 and the composition of the
electrolytic solution are respectively similar to the structures of
the cathode current collector 21A, the cathode active material
layer 21B, the anode current collector 22A, the anode active
material layer 22B, the coat 22C, and the separator 23 and the
composition of the electrolytic solution in the foregoing first
battery.
[0121] The secondary battery is manufactured, for example, as
follows. First, for example, the cathode 41 is formed by forming
the cathode active material layer 41B on the both faces of the
cathode current collector 41A, and the anode 42 is formed by
forming the anode active material layer 42B and the coat 42C on the
both faces of the anode current collector 42A by respective
procedures similar to the procedures of forming the cathode 21 and
the anode 22 in the foregoing first battery. Subsequently, the
cathode lead 45 is attached to the cathode 41, and the anode lead
46 is attached to the anode 42. Subsequently, the cathode 41 and
the anode 42 are spirally wound with the separator 43 in between,
and thereby the spirally wound electrode body 40 is formed. The end
of the cathode lead 45 is connected to the safety valve mechanism
35, and the end of the anode lead 46 is connected to the battery
can 31. After that, the spirally wound electrode body 40 is
sandwiched between the pair of insulating plates 32 and 33, and
contained in the battery can 31. Subsequently, the electrolytic
solution is injected into the battery can 31 and impregnated in the
separator 43. Finally, at the open end of the battery can 31, the
battery cover 34, the safety valve mechanism 35, and the PTC device
36 are fixed by being caulked with the gasket 37. The secondary
battery shown in FIG. 9 and FIG. 10 is thereby completed.
[0122] In the secondary battery, when charged, for example, lithium
ions are extracted from the cathode 41 and inserted in the anode 42
through the electrolytic solution impregnated in the separator 43.
Meanwhile, when discharged, for example, lithium ions are extracted
from the anode 42, and inserted in the cathode 41 through the
electrolytic solution impregnated in the separator 43.
[0123] According to the cylindrical secondary battery, the anode 42
has the structure similar to that of the foregoing anode. Thus,
superior cycle characteristics and safety are obtained. Effects of
the secondary battery other than the foregoing effects are similar
to those of the first battery.
Third Battery
[0124] FIG. 11 shows an exploded perspective view of a third
battery. FIG. 12 shows an exploded cross section taken along line
XII-XII shown in FIG. 11. In the battery, a spirally wound
electrode body 50 on which a cathode lead 51 and an anode lead 52
are attached is contained in a film package member 60. The battery
structure including the package member 60 is a so-called laminated
film structure.
[0125] The cathode lead 51 and the anode lead 52 are respectively
directed from inside to outside of the package member 60 in the
same direction, for example. The cathode lead 51 is made of, for
example, a metal material such as aluminum, and the anode lead 52
is made of, for example, a metal material such as copper, nickel,
and stainless. The metal materials are in the shape of a thin plate
or mesh.
[0126] The package member 60 is made of an aluminum laminated film
in which, for example, a nylon film, an aluminum foil, and a
polyethylene film are bonded together in this order. The package
member 60 has, for example, a structure in which the respective
outer edges of two pieces of rectangle aluminum laminated films are
bonded to each other by fusion bonding or an adhesive so that the
polyethylene film and the spirally wound electrode body 50 are
opposed to each other.
[0127] An adhesive film 61 to protect from entering of outside air
is inserted between the package member 60 and the cathode lead 51,
the anode lead 52. The adhesive film 61 is made of a material
having contact characteristics to the cathode lead 51 and the anode
lead 52. Examples of such a material include, for example, a
polyolefin resin such as polyethylene, polypropylene, modified
polyethylene, and modified polypropylene.
[0128] The package member 60 may be made of a laminated film having
other lamination structure, a polymer film such as polypropylene,
or a metal film, instead of the foregoing aluminum laminated
film.
[0129] In the spirally wound electrode body 50, a cathode 53 and an
anode 54 are layered with a separator 55 and an electrolyte 56 in
between and then spirally wound. The outermost periphery thereof is
protected by a protective tape 57.
[0130] FIG. 13 shows an enlarged part of the spirally wound
electrode body 50 shown in FIG. 12. The cathode 53 has a structure
in which, for example, a cathode active material layer 53B is
provided on the both faces of a strip-shaped cathode current
collector 53A. The anode 54 has a structure similar to that of the
anode described above, for example, has a structure in which an
anode active material layer 54B and a coat 54C are provided on the
both faces of a strip-shaped anode current collector 54A. The
structures of the cathode current collector 53A, the cathode active
material layer 53B, the anode current collector 54A, the anode
active material layer 54B, the coat 54C, and the separator 55 are
respectively similar to those of the cathode current collector 21A,
the cathode active material layer 21B, the anode current collector
22A, the anode active material layer 22B, the coat 22C, and the
separator 23 of the foregoing first battery.
[0131] The electrolyte 56 is so-called gelatinous (gel
electrolyte), containing an electrolytic solution and a polymer
compound that holds the electrolytic solution. The gel electrolyte
is preferable, since thereby high ion conductivity (for example, 1
mS/cm or more at room temperature) is obtained and liquid leakage
is prevented. The electrolyte 56 is provided, for example, between
the cathode 53 and the separator 55, and between the anode 54 and
the separator 55.
[0132] As the polymer compound, for example, polyacrylonitrile,
polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and
polyhexafluoropropylene, polytetrafluoroethylene,
polyhexafluoropropylene, polyethylene oxide, polypropylene oxide,
polyphosphazene, polysiloxane, polyvinyl acetate, polyvinyl
alcohol, polymethacrylic acid methyl, polyacrylic acid,
polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene
rubber, polystyrene, polycarbonate or the like is cited. One of
these polymer compounds may be used singly, or a plurality thereof
may be used by mixture. Specially, as the polymer compound,
polyacrylonitrile, polyvinylidene fluoride,
polyhexafluoropropylene, polyethylene oxide or the like is
preferably used, since thereby the electrochemical stability is
obtained.
[0133] The composition of the electrolytic solution is similar to
the composition of the electrolytic solution in the first battery.
However, in this case, the solvent means a wide concept including
not only the liquid solvent but also a solvent having ion
conductivity capable of dissociating the electrolyte salt.
Therefore, when the polymer compound having ion conductivity is
used, the polymer compound is also included in the solvent.
[0134] Instead of the gel electrolyte 56 in which the electrolytic
solution is held by the polymer compound, the electrolytic solution
may be directly used. In this case, the electrolytic solution is
impregnated in the separator 55.
[0135] The secondary battery including the gel electrolyte 56 is
manufactured, for example, by the following three manufacturing
methods.
[0136] In a first manufacturing method, first, for example, the
cathode 53 is formed by forming the cathode active material layer
53B on the both faces of the cathode current collector 53A, and the
anode 54 is formed by forming the anode active material layer 54B
and the coat 54C on the both faces of the anode current collector
54A by a procedure similar to that of the method of forming the
cathode 21 and the anode 22 in the foregoing first battery.
Subsequently, a precursor solution containing an electrolytic
solution, a polymer compound, and a solvent is prepared. After the
cathode 53 and the anode 54 are coated with the precursor solution,
the solvent is volatilized to form the gel electrolyte 56.
Subsequently, the cathode lead 51 is attached to the cathode
current collector 53A and the anode lead 52 is attached to the
anode current collector 54A. Subsequently, the cathode 53 and the
anode 54 provided with the electrolyte 56 are layered with the
separator 55 in between to obtain a laminated body. After that, the
laminated body is spirally wound in the longitudinal direction, the
protective tape 57 is adhered to the outermost periphery thereof to
form the spirally wound electrode body 50. Finally, for example,
after the spirally wound electrode body 50 is sandwiched between
two pieces of the film package members 60, outer edges of the
package members 60 are contacted by thermal fusion bonding or the
like to enclose the spirally wound electrode body 50. At this time,
the adhesive films 61 are inserted between the cathode lead 51, the
anode lead 52 and the package member 60. Thereby, the secondary
battery shown in FIG. 11 to FIG. 13 is completed.
[0137] In a second manufacturing method, first, the cathode lead 51
is attached to the cathode 53, and the anode lead 52 is attached to
the anode 54. After that, the cathode 53 and the anode 54 are
layered with the separator 55 in between and spirally wound. The
protective tape 57 is adhered to the outermost periphery thereof,
and thereby a spirally wound body as a precursor of the spirally
wound electrode body 50 is formed. Subsequently, after the spirally
wound body is sandwiched between two pieces of the film package
members 60, the outermost peripheries except for one side are
bonded by thermal fusion-bonding or the like to obtain a pouched
state, and the spirally wound body is contained in the pouch-like
package member 60. Subsequently, a composition of matter for
electrolyte containing an electrolytic solution, a monomer as a raw
material for the polymer compound, a polymerization initiator, and
if necessary other material such as a polymerization inhibitor is
prepared, which is injected into the pouch-like package member 60.
After that, the opening of the package member 60 is hermetically
sealed by thermal fusion bonding or the like. Finally, the monomer
is thermally polymerized to obtain a polymer compound. Thereby, the
gel electrolyte 56 is formed. Accordingly, the secondary battery is
completed.
[0138] In a third manufacturing method, first, the spirally wound
body is formed and contained in the pouch-like package member 60 in
the same manner as that of the foregoing first manufacturing
method, except that the separator 55 with the both faces coated
with a polymer compound is used. As the polymer compound with which
the separator 55 is coated, for example, a polymer containing
vinylidene fluoride as a component, that is, a homopolymer, a
copolymer, a multicomponent copolymer and the like are cited.
Specifically, polyvinylidene fluoride, a binary copolymer
containing vinylidene fluoride and hexafluoropropylene as a
component, a ternary copolymer containing vinylidene fluoride,
hexafluoropropylene, and chlorotrifluoroethylene as a component and
the like are cited. As a polymer compound, in addition to the
foregoing polymer containing vinylidene fluoride as a component,
another one or more polymer compounds may be used. Subsequently, an
electrolytic solution is prepared and injected into the package
member 60. After that, the opening of the package member 60 is
sealed by thermal fusion bonding or the like. Finally, the
resultant is heated while a weight is applied to the package member
60, and the separator 55 is contacted to the cathode 53 and the
anode 54 with the polymer compound in between. Thereby, the
electrolytic solution is impregnated into the polymer compound, and
the polymer compound is gelated to form the electrolyte 56.
Accordingly, the secondary battery is completed.
[0139] Further, in the third manufacturing method, swollenness of
the secondary battery is suppressed compared to in the first
manufacturing method. Further, in the third manufacturing method,
the monomer as a raw material of the polymer compound, the solvent
and the like are hardly left in the electrolyte 56 compared to the
second manufacturing method, and the formation step of the polymer
compound is favorably controlled. Thus, sufficient contact
characteristics are obtained between the cathode 53/the anode
54/the separator 55 and the electrolyte 56.
[0140] According to the laminated film secondary battery, the anode
54 has the structure similar to that of the foregoing anode. Thus,
superior cycle characteristics and safety are obtained. Effects of
the secondary battery other than the foregoing effects are similar
to those of the first battery.
EXAMPLES
[0141] Examples of the invention will be described in detail
Example 1-1
[0142] To examine the cycle characteristics, the coin-type
secondary battery shown in FIG. 14 was fabricated by the following
procedure. The secondary battery was fabricated as a lithium ion
secondary battery in which the capacity of an anode 72 was
expressed based on insertion and extraction of lithium.
[0143] First, a cathode 71 was formed. First, lithium carbonate
(Li.sub.2CO.sub.3) and cobalt carbonate (CoCO.sub.3) were mixed at
a molar ratio of 0.5:1. After that, the mixture was fired in the
air at 900 deg C. for 5 hours. Thereby, lithium cobalt complex
oxide (LiCoO2) was obtained. Subsequently, 91 parts by weight of
the lithium cobalt complex oxide as a cathode active material, 6
parts by weight of graphite as an electrical conductor, and 3 parts
by weight of polyvinylidene fluoride as a binder were mixed to
obtain a cathode mixture. After that, the cathode mixture was
dispersed in N-methyl-2-pyrrolidone (NMP) to obtain paste slurry.
Subsequently, a single face of a cathode current collector 71A made
of a strip-shaped aluminum foil (thickness: 12 .mu.m thick) was
uniformly coated with the slurry, which was dried. After that, the
resultant was compression-molded by a roll pressing machine to form
a cathode active material layer 71B. Finally, the cathode current
collector 71A on which the cathode active material layer 71B was
formed was punched out in a state of a pellet being 15.2 mm in
diameter.
[0144] Next, the anode 72 was formed. First, an anode current
collector 72A made of an electrolytic copper foil (thickness: 18
.mu.m) was prepared. After that, silicon as an anode active
material was deposited on a single face of the anode current
collector 72A by electron beam evaporation method to form a
plurality of anode active particles, and thereby an anode active
material layer 72B (thickness: 6 .mu.m) was formed. When the anode
active material layer 72B was formed, the anode active material was
deposited six times for every 1 .mu.m to obtain the six-layer anode
active material particles. Further, oxygen gas was introduced into
a chamber when the anode active material was deposited, and oxygen
in the air was continuously introduced into the chamber after
deposition was completed so that the anode active material particle
included a striped high-oxygen concentration region. Subsequently,
a plating solution for electrolytic plating was prepared by mixing
ethanol (C.sub.2H.sub.50H) and aluminum nitrate enneahydrate
(Al(NO.sub.3).sub.3.9H.sub.2O) at a weight ratio of 19:1. The
solution was prepared with the use of the plating solution in the
plating bath. An aluminum plate was connected to the anode at a
distance of 5 mm, and the anode current collector 72A on which the
anode active material layer 72B was formed was connected to the
cathode. Subsequently, electrolytic plating reaction was performed
under the conditions of an ambient temperature (23 deg) and a
constant voltage (15 V), aluminum hydroxide was precipitated on the
anode active material layer 72B, and thereby a plate-like coat 72C
that was divided into a plurality of portions was formed. The
reaction when the coat 72C was formed is expressed as
Al.sup.3++3OH.fwdarw.Al(OH).sub.3. When the coat 72C was formed,
the precipitation amount of aluminum hydroxide was adjusted by the
current amount applied to the plating solution, and the weight per
unit area of the coat 72C (hereinafter referred to as "unit weight"
(mg/cm.sup.2)) was 0.01 mg/cm.sup.2. The weight of the coat 72C was
calculated based on the weight difference between before
precipitation of aluminum hydroxide and after precipitation of
aluminum hydroxide. When the surface of the anode 72 was observed
by SEM-EDX, and the ratio of the area S2 of the coat 72C to the
area S1 of the anode active material layer 72B (the area ratio
S2/S1) was calculated, it was 0.2. Finally, the anode current
collector 72A on which the anode active material layer 72B and the
coat 72C were formed was punched out into a pellet being 15.5 mm in
diameter.
[0145] Next, 4-fluoro-1,3-dioxolane-2-one (FEC) and diethyl
carbonate (DEC) were mixed as a solvent, and lithium
hexafluorophosphate and lithium tetrafluoroborate were dissolved
therein as an electrolyte salt to prepare an electrolytic solution.
The composition of the solvent (FEC:DEC) was 50:50 at a weight
ratio. The concentration of lithium hexafluorophosphate in the
electrolytic solution was 1 mol/kg, and the concentration of
lithium tetrafluoroborate in the electrolytic solution was 0.1
mol/kg.
[0146] Finally, the secondary battery was assembled by using the
cathode 71, the anode 72, and the electrolytic solution. First, the
cathode 71 was contained in a package can 74, and the anode 72 was
bonded to a package cup 75. Subsequently, a separator 73
(thickness: 16 .mu.m) made of a porous propylene film was prepared,
and an electrolytic solution was impregnated in the separator 73.
Finally, the cathode 71 and the anode 72 were layered with the
separator 73 impregnated with the electrolytic solution in between.
After that, the package can 74 and the package cup 75 were caulked
with a gasket 76. Thereby, the coin-type secondary battery was
completed.
[0147] In examining the cycle characteristics, initial charge and
discharge were performed to stabilize the battery state. After
that, charge and discharge were performed 1 cycle in the atmosphere
at 23 deg C. and the discharge capacity was measured, and
continuously charge and discharge were performed 99 cycles in the
same atmosphere and the discharge capacity was measured. Thereby,
the discharge capacity retention ratio (%)=(discharge capacity at
the 100th cycle/discharge capacity at the first cycle).times.100
was calculated. The charge and discharge conditions for the initial
charge and discharge were as follows. That is, constant current
charge was performed at the current of 0.2 C until the upper
battery voltage of 4.2 V, charge was continuously performed at the
constant voltage of 4.2 V until the current became 0.05 C. After
that, discharge was performed at the constant current of 0.2 C
until the final voltage of 2.5 V. The charge and discharge
conditions for 1 cycle were as follows. That is, constant current
charge was performed at the current of 1 C until the upper battery
voltage of 4.2 V, charge was continuously performed at the constant
voltage of 4.2 V until the current became 0.05 C. After that,
discharge was performed at the constant current of 1 C until the
final voltage of 2.5 V. The foregoing "0.2 C" means a current value
with which the theoretical capacity is completely discharged in 5
hours. "0.05 C" means a current value with which the theoretical
capacity is completely discharged in 20 hours. "1 C" means a
current value with which the theoretical capacity is completely
discharged in 1 hour.
[0148] In addition to the foregoing coin-type secondary battery, to
examine the safety, the square secondary battery shown in FIG. 6 to
FIG. 8 was fabricated by a procedure similar to the procedure of
fabricating the coin-type secondary battery, except for the
following procedure. When the square secondary battery was
fabricated, first, the cathode 21 was formed by forming the cathode
active material layer 21B on the both faces of the cathode current
collector 21A, and the anode 22 was formed by forming the anode
active material layer 22B and the coat 22C on the both faces of the
anode current collector 22A. Subsequently, the cathode lead 24 made
of aluminum was welded to the cathode 21, and the anode lead 25
made of nickel was welded to the anode 22. Subsequently, the
cathode 21 and the anode 22 were layered with the separator 23 in
between, and spirally wound in the longitudinal direction. After
that, the resultant was shaped into the flat shape, and thereby the
battery element 20 was formed. Subsequently, after the battery
element 20 was contained in the battery can 11 made of aluminum,
the insulating plate 12 was arranged on the battery element 20.
Subsequently, the cathode lead 24 was welded to the cathode pin 15
and the anode lead 25 was welded to the battery can 11. After that,
the battery cover 13 was fixed on the open end of the battery can
11 by laser welding or the like. Finally, the electrolytic solution
was injected into the battery can 11 through the injection hole 19.
After that, the injection hole 19 was sealed by the sealing member
19A. The square secondary battery was thereby fabricated.
[0149] To examine the safety, a state when the battery was broken
was examined by performing round bar crush test. Specifically,
constant current and constant voltage charge was performed at the
current of 1 C until the upper battery voltage of 4.4 V. After
that, while the temperature of the battery can 11 was measured by a
thermocouple in the air (23 deg C.), a round bar (diameter: 10 mm)
was pressed on the planar portion thereof to totally crush the
battery. Thereby, temperature change after the test was evaluated
based on 4 grades. The evaluation was as follows in the order of
most favorable to the least favorable. That is, in the case that
the highest temperature did not exceed 100 deg C., it was graded as
"very good". In the case that the highest temperature did not
exceed 200 deg C., it was graded as "good". In the case that the
highest temperature did not exceed 300 deg C., it was graded as
"average". In the case that the highest temperature exceed 300 deg
C., it was graded as "poor".
Examples 1-2 to 1-11
[0150] A procedure was performed in the same manner as that of
Example 1-1, except that the unit weight was changed to 0.02
mg/cm.sup.2 (Example 1-2), 0.04 mg/cm.sup.2 (Example 1-3), 0.06
mg/cm.sup.2 (Example 1-4), 0.08 mg/cm.sup.2 (Example 1-5), 0.1
mg/cm.sup.2 (Example 1-6), 0.2 mg/cm.sup.2 (Example 1-7), 0.4
mg/cm.sup.2 (Example 1-8), 0.6 mg/cm.sup.2 (Example 1-9), 0.8
mg/cm.sup.2 (Example 1-10), or 1 mg/cm.sup.2 (Example 1-11). The
area ratio S2/S1 was 0.4 in Example 1-2, 0.8 in Example 1-3, and
0.9 in Examples 1-4 to 1-11.
Comparative Example 1-1
[0151] A procedure was performed in the same manner as that of
Example 1-1, except that the coats 72C and 22C were not formed.
Comparative Examples 1-2 to 1-12
[0152] A procedure was performed in the same manner as that of
Examples 1-1 to 1-11, except that a coat in a state of a plurality
of particles was formed instead of the plate-like coats 72C and 22C
divided into a plurality of portions. When the coat was formed,
aluminum hydroxide powder (average particle diameter: 1 .mu.m) and
polyvinylidene fluoride were mixed at a weight ratio of 95:5, the
mixture was dispersed in NMP to obtain slurry. While the coating
amount was adjusted so that the unit weight was equal to that of
Examples 1-1 to 1-11, the surface of the anode active material
layers 72B and 22B was coated with the slurry and the resultant was
dried. The foregoing average particle diameter was a median size
measured by laser diffractive particle size distribution size
measuring device. The same will be applied to the following
descriptions.
[0153] When the cycle characteristics and the safety of the
secondary batteries of Examples 1-1 to 1-11 and Comparative
examples 1-1 to 1-12 were examined, the results shown in Table 1
were obtained.
TABLE-US-00001 TABLE 1 Anode Anode active Discharge material layer
Coat capacity Anode Unit Area retention Round bar active Forming
Forming weight ratio ratio crush test material method Type method
(mg/cm.sup.2) S2/S1 (%) evaluation Example 1-1 Silicon Evaporation
Aluminum Plating 0.01 0.2 82 good Example 1-2 method hydroxide
method 0.02 0.4 83 very good Example 1-3 0.04 0.8 84 very good
Example 1-4 0.06 0.9 84 very good Example 1-5 0.08 0.9 84 very good
Example 1-6 0.1 0.9 84 very good Example 1-7 0.2 0.9 84 very good
Example 1-8 0.4 0.9 83 very good Example 1-9 0.6 0.9 82 very good
Example 1-10 0.8 0.9 81 very good Example 1-11 1 0.9 81 very good
Comparative Silicon Evaporation -- -- -- -- 81 poor example 1-1
method Comparative Aluminum Coating 0.01 -- 81 poor example 1-2
hydroxide method Comparative 0.02 81 poor example 1-3 Comparative
0.04 81 average example 1-4 Comparative 0.06 81 average example 1-5
Comparative 0.08 81 good example 1-6 Comparative 0.1 81 good
example 1-7 Comparative 0.2 80 very good example 1-8 Comparative
0.4 79 very good example 1-9 Comparative 0.6 77 very good example
1-10 Comparative 0.8 75 very good example 1-11 Comparative 1 73
very good example 1-12
[0154] As shown in FIG. 1, in Examples 1-1 to 1-11 in which the
coats 72C and 22C were formed, compared to Comparative example 1-1
in which the coats 72C and 22C were not formed, the discharge
capacity retention ratio was equal to or higher than that of
Comparative example 1-1, and the evaluation of the round bar crush
test was improved.
[0155] Further, in Examples 1-1 to 1-11 in which the plate-like
coats 72C and 22C divided into a plurality of portions were formed
by electrolytic plating method, compared to Comparative examples
1-2 to 1-12 in which the coat in a state of a plurality of
particles was formed by coating method, the discharge capacity
retention ratio was higher than those of Comparative examples 1-2
to 1-12 for every unit weight, and the evaluation of the round bar
crush test was equal to or higher than those of Comparative
examples 1-2 to 1-12.
[0156] For confirmation, as a representative of Examples 1-1 to
1-11, for the secondary battery of Example 1-5, element analysis
was performed for the coats 72C and 22C by XPS, resulting in 23
atomic % for aluminum and 77 atomic % for oxygen. From the results,
since the abundance ratio between aluminum and oxygen was 1:3 at a
ratio with the use of approximate integer numbers, it was
determined that the coats 72C and 22C were aluminum hydroxide.
[0157] Accordingly, in the secondary battery of the invention, it
was confirmed that when the anode active material layer was formed
by evaporation method with the use of silicon as an anode active
material, by forming aluminum hydroxide as an insulative coat
divided into a plurality of portions on the anode active material
layer, superior cycle characteristics and safety could be obtained.
In this case, it was also confirmed that it was enough that the
unit weight was in the range from 0.01 mg/cm.sup.2 to 1 mg/cm.sup.2
and the area ratio S2/S1 was in the range from 0.2 to 0.9.
Examples 2-1 and 2-2
[0158] A procedure was performed in the same manner as that of
Example 1-6, except that a plating solution was prepared by using
zirconium nitrate or titanium nitrate instead of aluminum nitrate,
and zirconium hydroxide (Example 2-1) or titanium hydroxide
(Example 2-2) instead of aluminum hydroxide was precipitated to
form the coats 72C and 22C.
Example 2-3
[0159] A procedure was performed in the same manner as that of
Example 1-6, except that aluminum hydroxide formed as the coats 72C
and 22C was heated in the vacuum atmosphere at 700 deg C. to obtain
aluminum oxide.
Examples 2-4 and 2-5
[0160] A procedure was performed in the same manner as that of
Examples 2-1 and 2-2, except that zirconium hydroxide or titanium
hydroxide formed as the coats 72C and 22C was heated in the vacuum
atmosphere at 700 deg C. to obtain zirconium oxide (Example 2-4) or
titanium oxide (Example 2-5).
[0161] When the cycle characteristics and the safety of the
secondary batteries of Examples 2-1 to 2-5 were examined, the
results shown in Table 2 were obtained.
TABLE-US-00002 TABLE 2 Anode Anode active Discharge material layer
Coat capacity Anode Unit Area retention Round bar active Forming
Forming weight ratio ratio crush test material method Type method
(mg/cm.sup.2) S2/S1 (%) evaluation Example 1-6 Silicon Evaporation
Aluminum Plating 0.1 0.9 84 very good method hydroxide method
Example 2-1 Zirconium 84 very good hydroxide Example 2-2 Titanium
84 very good hydroxide Example 2-3 Aluminum 81 very good oxide
Example 2-4 Zirconium 84 very good oxide Example 2-5 Titanium 84
very good oxide Comparative Silicon Evaporation -- -- -- -- 81 X
example 1-1 method Comparative Aluminum Coating 0.1 -- 81
.largecircle. example 1-7 hydroxide method
[0162] As shown in Table 2, in Examples 2-1 to 2-5 in which the
coats 72C and 22C were formed, compared to Comparative examples 1-1
and 1-7 in which the coats 72C and 22C were not formed, the
discharge capacity retention ratio was higher than that of
Comparative examples 1-1 and 1-7, and the evaluation of the round
bar crush test was improved as in Example 1-6.
[0163] For confirmation, as a representative of Examples 2-1 to
2-5, for the secondary battery of Example 2-3, element analysis was
performed for the coats 72C and 22C by XPS, resulting in 38 atomic
% for aluminum and 62 atomic % for oxygen. From the results, since
the abundance ratio between aluminum and oxygen was 2:3 at a ratio
with the use of approximate integer numbers, it was determined that
the coats 72C and 22C were aluminum.
[0164] Accordingly, in the secondary battery of the invention, it
was confirmed that when zirconium hydroxide was used as a material
for forming the coat, superior cycle characteristics and safety
were obtained as well.
Examples 3-1 to 3-5
[0165] A procedure was performed in the same manner as that of
Examples 1-2 to 1-6, except that the anode active material layers
72B and 22B were formed by coating method instead of electron beam
evaporation method. When the anode active material layers 72B and
22B were formed, silicon particles as an anode active material
(average particle diameter: 3 .mu.m) and 15 wt % NMP solution of
polyimide as a binder, and scale-like high crystalline artificial
graphite as an electrical conductor were mixed at a weight ratio of
70:10:10 to obtain slurry. After that, the surface of the anode
current collectors 72A and 22A was coated with the slurry, and then
the resultant was dried and then compression-molded.
Comparative Example 3
[0166] A procedure was performed in the same manner as that of
Comparative example 1-1, except that the anode active material
layers 72B and 22B were formed by coating method as in Examples 3-1
to 3-5.
[0167] When the cycle characteristics and the safety of the
secondary batteries of Examples 3-1 to 3-5 and Comparative example
3 were examined, the results shown in Table 3 were obtained.
TABLE-US-00003 TABLE 3 Anode Anode active Discharge material layer
Coat capacity Anode Unit Area retention Round bar active Forming
Forming weight ratio ratio crush test material method Type method
(mg/cm.sup.2) S2/S1 (%) evaluation Example 3-1 Silicon Coating
Aluminum Plating 0.02 0.4 80 average Example 3-2 method hydroxide
method 0.04 0.8 80 good Example 3-3 0.06 0.9 81 good Example 3-4
0.08 0.9 81 very good Example 3-5 0.1 0.9 81 very good Comparative
Silicon Coating -- -- -- -- 80 poor example 3 method
[0168] As shown in Table 3, in Examples 3-1 to 3-5 in which the
coats 72C and 22C were formed, compared to Comparative example 3 in
which the coats 72C and 22C were not formed, the discharge capacity
retention ratio was equal to or higher than that of Comparative
example 3, and the evaluation of the round bar crush test was
improved.
[0169] Accordingly, in the secondary battery of the invention, it
was confirmed that when the anode active material layer was formed
by coating method with the use of silicon as an anode active
material, by forming aluminum hydroxide as an insulative coat
divided into a plurality of portions on the anode active material
layer, superior cycle characteristics and safety were obtained as
well.
Examples 4-1 4-5
[0170] A procedure was performed in the same manner as that of
Examples 1-2 to 1-6, except that the anode active material layers
72B and 22B were formed by coating method with the use of Mesophase
Carbon Microbeads (MCMB) instead of silicon as an anode active
material. When the anode active material layers 72B and 22B were
formed, the MCMB as the anode active material (average particle
diameter: 20 .mu.m), polyvinylidene fluoride as a binder, and Vapor
Growth Carbon Fiber (VGCF) as an electrical conductor were mixed at
a weight ratio of 90:7:3, and the resultant mixture was dispersed
in NMP as an additional portion to obtain a slurry. The anode
current collectors 72A and 22A were coated with the slurry, the
resultant was dried, and then compression-molded.
Comparative Example 4
[0171] A procedure was performed in the same manner as that of
Comparative example 1-1, except that the anode active material
layers 72B and 22B were formed by coating method with the use of
MCMB as in Examples 4-1 to 4-5.
[0172] When the cycle characteristics and the safety of the
secondary batteries of Examples 4-1 to 4-5 and Comparative example
4 were examined, the results shown in Table 4 were obtained.
TABLE-US-00004 TABLE 4 Anode Anode active Discharge material layer
Coat capacity Anode Unit Area retention Round bar active Forming
Forming weight ratio ratio crush test material method Type method
(mg/cm.sup.2) S2/S1 (%) evaluation Example 4-1 MCMB Coating
Aluminum Plating 0.02 0.4 87 good Example 4-2 method hydroxide
method 0.04 0.8 87 good Example 4-3 0.06 0.9 87 good Example 4-4
0.08 0.9 87 very good Example 4-5 0.1 0.9 87 very good Comparative
MCMB Coating -- -- -- -- 87 average example 4 method
[0173] As shown in Table 4, in Examples 4-1 to 4-5 in which the
coats 72C and 22C were formed, compared to Comparative example 4 in
which the coats 72C and 22C were not formed, the discharge capacity
retention ratio was equal to that of Comparative example 4, and the
evaluation of the round bar crush test was improved.
[0174] Accordingly, in the secondary battery of the invention, it
was confirmed that when the anode active material layer was formed
by coating method with the use of MCMB as an anode active material,
by forming aluminum hydroxide as an insulative coat divided into a
plurality of portions on the anode active material layer, superior
cycle characteristics and safety were obtained as well.
[0175] As evidenced by the foregoing results of FIG. 1 to FIG. 4,
it was confirmed that into the secondary battery of the invention,
by forming the insulative coat segmented in a plurality of sections
on the anode active material layer, superior cycle characteristics
and superior safety were obtained irrespective of the type of the
anode active material and the method of forming the anode active
material layer.
[0176] When MCMB (carbon material) was used as an anode active
material, the discharge capacity retention ratio was not increased.
Meanwhile, when silicon (material that is able to insert and
extract lithium and contains at least one of metal elements and
metalloid elements) was used, the discharge capacity retention
ratio was increased. Thus, it was confirmed that higher effects
were obtained in the latter case. The result may show the
following. That is, when silicon advantageous for realizing a high
capacity was used as an anode active material, the electrolytic
solution tended to be easily decomposed than in the case of using a
carbon material. Thus, when silicon was used, effects of inhibiting
decomposition of the electrolytic solution was significantly
demonstrated.
[0177] The invention has been described with reference to the
embodiment and the examples. However, the invention is not limited
to the aspects described in the foregoing embodiment and the
foregoing examples, and various modifications may be made. For
example, the anode of the invention is not necessarily used for the
battery, but may be used for an electrochemical device other than
the battery. As other application, for example, a capacitor or the
like is cited.
[0178] Further, in the foregoing embodiment and the foregoing
examples, the descriptions have been given of the lithium ion
secondary battery in which the anode capacity is expressed based on
insertion and extraction of lithium as a battery type. However, the
battery type of the invention is not limited thereto. The invention
is similarly applicable to a battery in which the anode capacity
includes the capacity associated with insertion and extraction of
lithium and the capacity associated with precipitation and
dissolution of lithium, and the anode capacity is expressed as the
sum of these capacities, by setting the charge capacity of the
anode material capable of inserting and extracting lithium to a
smaller value than the charge capacity of the cathode.
[0179] Further, in the foregoing embodiment and the foregoing
examples, the descriptions have been given of the case using the
electrolytic solution or the gel electrolyte in which the
electrolytic solution is held by the polymer compound as an
electrolyte of the battery of the invention. However, other type of
electrolyte may be used. As other electrolyte, for example, a
mixture obtained by mixing an ion conductive inorganic compound
such as ion conductive ceramics, ion conductive glass, and ionic
crystal and an electrolytic solution; a mixture obtained by mixing
other inorganic compound and an electrolytic solution; a mixture of
the foregoing inorganic compound and a gel electrolyte or the like
is cited.
[0180] Further, in the foregoing embodiment and the foregoing
examples, the description has been given with the specific examples
of the square, cylindrical, laminated film, or coin-type secondary
battery as a battery structure, and with the specific example of
the battery in which the battery element has the spirally wound
structure. However, the invention is similarly applicable to a
battery having other battery structure such as a button-type
battery, or a battery in which the battery element has other
structure such as a lamination structure. The battery of the
invention is similarly applicable to other type of battery such as
a primary battery in addition to the secondary battery.
[0181] Further, in the foregoing embodiment and the foregoing
examples, the description has been given of the case using lithium
as an electrode reactant. However, as an electrode reactant, other
Group 1A element such as sodium (Na) and potassium (K), a Group 2A
element such as magnesium (Mg) and calcium (Ca), or other light
metal such as aluminum may be used. In these cases, the anode
material described in the foregoing embodiment may be used as an
anode active material as well.
[0182] Further, in the foregoing embodiment and the foregoing
examples, regarding the area ratio S2/S1 for the anode or the
battery of the invention, the numerical value range thereof derived
from the results of the examples has been described as the
appropriate range. However, such a description does not totally
eliminate the possibility that the area ratio S2/S1 may be out of
the foregoing range. That is, the foregoing appropriate range is
the range particularly preferable for obtaining the effects of the
invention. Therefore, as long as effects of the invention are
obtained, the area ratio S2/S1 may be out of the foregoing range in
some degrees. The same is applied to the weight per unit area of
the coat and the like, in addition to the foregoing area ratio
S2/S1.
[0183] It should be understood by those skilled in the art that
various modifications, combinations, sub-combinations and
alternations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
* * * * *