U.S. patent application number 11/115172 was filed with the patent office on 2005-11-03 for electrode, electrochemical device, and method of making electrode.
This patent application is currently assigned to TDK CORPORATION. Invention is credited to Kurihara, Masato, Maruyama, Satoshi, Suzuki, Hisashi, Suzuki, Tadashi.
Application Number | 20050241137 11/115172 |
Document ID | / |
Family ID | 35185562 |
Filed Date | 2005-11-03 |
United States Patent
Application |
20050241137 |
Kind Code |
A1 |
Suzuki, Tadashi ; et
al. |
November 3, 2005 |
Electrode, electrochemical device, and method of making
electrode
Abstract
An electrode comprises a planar collector, and an active
material containing layer disposed on the collector. The active
material containing layer comprises a plurality of particles
containing an active material, and a binder for binding the
particles containing the active material to each other and the
particles containing the active material to the collector. The
collector has a surface depressed in conformity to a form of the
particles containing the active material.
Inventors: |
Suzuki, Tadashi; (Tokyo,
JP) ; Suzuki, Hisashi; (Tokyo, JP) ; Kurihara,
Masato; (Tokyo, JP) ; Maruyama, Satoshi;
(Tokyo, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
TDK CORPORATION
Tokyo
JP
103-8272
|
Family ID: |
35185562 |
Appl. No.: |
11/115172 |
Filed: |
April 27, 2005 |
Current U.S.
Class: |
29/592.1 ;
204/290.01 |
Current CPC
Class: |
H01G 11/28 20130101;
H01M 4/0435 20130101; Y02E 60/10 20130101; Y02E 60/13 20130101;
H01M 10/0525 20130101; H01G 11/42 20130101; H01G 11/38 20130101;
H01M 2004/021 20130101; Y10T 29/49002 20150115; H01M 4/70 20130101;
H01M 4/0471 20130101; H01G 9/042 20130101; H01M 4/139 20130101 |
Class at
Publication: |
029/592.1 ;
204/290.01 |
International
Class: |
C25D 017/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2004 |
JP |
P2004-134294 |
Claims
What is claimed is:
1. An electrode comprising a planar collector, and an active
material containing layer disposed on the collector; wherein the
active material containing layer comprises a plurality of particles
containing an active material, and a binder for binding the
particles containing the active material to each other and the
particles containing the active material to the collector, the
collector having a surface depressed in conformity to a form of the
particles containing the active material.
2. The electrode according to claim 1, wherein a conductive
auxiliary agent particle is contained in the binder in the active
material containing layer.
3. The electrode according to claim 1, wherein the particles
containing the active material in the active material containing
layer have a particle size of 0.1 to 500 .mu.m.
4. An electrochemical device comprising a pair of electrodes and an
electrolyte interposed between the electrodes; wherein at least one
of the pair of electrodes includes a planar collector, and an
active material containing layer disposed on the collector; and
wherein the active material containing layer comprises a plurality
of particles containing an active material, and a binder for
binding the particles containing the active material to each other
and the particles containing the active material to the collector,
the collector having a surface depressed in conformity to a form of
the particles containing the active material.
5. A method of manufacturing an electrode, the method comprising: a
particle layer forming step of forming a particle layer including a
binder meltable by heating and a plurality of particles containing
an active material on a planar collector, and a rolling step of
heating the particle layer and extending the particle layer by
passing the collector and the particle layer between rotating
rollers, so as to bind the particles containing the active material
to each other with the binder and bind the particles containing the
active material to the collector with the binder.
6. The method of manufacturing an electrode according to claim 5,
wherein the particle layer further includes a conductive auxiliary
agent particle.
7. The method of manufacturing an electrode according to claim 6,
wherein the particle layer includes a plurality of composite
particles each comprising the particles containing the active
material integrated with each other beforehand by the binder
including the conductive auxiliary agent particle.
8. The method of manufacturing an electrode according to one of
claim 5, wherein the rolling step is carried out by passing the
collector and particle layer between heated rollers.
9. The method of manufacturing an electrode according to one of
claim 5, wherein a line pressure of 200.times.10.sup.2 to
2000.times.10.sup.2 N/m is applied between the rollers in the
rolling step.
10. The method of manufacturing an electrode according to one of
claim 5, wherein, in the particle layer forming step, a binder
layer, meltable by heating, including a conductive auxiliary agent
particle is disposed beforehand on a surface of the collector, and
the particle layer is formed on the binder layer.
11. The method of manufacturing an electrode according to one of
claim 5, wherein the particles containing the active material have
a particle size of 0.1 to 500 .mu.m.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electrode usable in
electrochemical devices such as primary batteries, secondary
batteries (lithium-ion secondary batteries in particular),
electrolytic cells, and capacitors (electrochemical capacitors in
particular), an electrochemical device equipped therewith, and a
method of manufacturing an electrode.
[0003] 2. Related Background Art
[0004] Electrochemical devices such as high-energy batteries
typified by lithium ion secondary batteries and electrochemical
capacitors typified by electric double layer capacitors have widely
been in use in portable devices and the like. Such an
electrochemical device mainly comprises a pair of electrodes and an
electrolyte (e.g., a liquid electrolyte or solid electrolyte)
interposed between the electrodes.
[0005] In general, such an electrode of the electrochemical device
comprises an active material containing layer stacked on a planar
collector, whereas the active material containing layer includes a
number of particles containing an active material. Proposed as a
method of manufacturing such an electrode is one comprising the
steps of preparing a kneaded product including a particle
containing an active material, a binder, and a conductive auxiliary
agent particle; extending the kneaded product wit a hot roller
machine or hot press machine, so as to yield an active material
containing sheet, and bonding the active material containing sheet
to the collector (see, for example, Japanese Patent Application
Laid-Open No. 2004-2105).
SUMMARY OF THE INVENTION
[0006] However, the electrode manufactured by the above-mentioned
method has been found to exhibit a relatively high contact
resistance between the particle containing the active material and
the collector. When such an electrode is used in an electrochemical
device, the internal resistance of the electrochemical device
becomes higher, whereby the electrochemical device may be
obstructed from achieving higher output or higher energy
density.
[0007] A view of the problem mentioned above, it is an object of
the present invention to provide an electrode which can filly lower
the contact resistance between a particle containing an active
material and a collector, an electrode equipped therewith, and a
method of manufacturing the electrode.
[0008] The inventors conducted diligent studies in order to achieve
the above-mentioned object and, as a result, have found the
following. Namely, the conventional active material containing
sheet formed by expanding a material kneaded product with a pair of
rollers has a relatively smooth surface, whereby the conventional
electrode comprises such an active material containing sheet having
a relatively smooth surface and a planar collector bonded thereto.
Therefore, the contact area between the active material containing
sheet and the collector is not sufficient, whereby the contact
resistance between the particle containing the active material and
the collector is high.
[0009] Therefore, m one aspect, the present invention provides an
electrode comprising a planar collector, and an active material
containing layer disposed on the collector; wherein the active
material containing layer comprises a plurality of particles
containing an active material and a binder for binding the
particles containing the active material to each other and the
particles containing the active material to the collector, the
collector having a surface depressed in conformity to a form of the
particles containing the active material.
[0010] In another aspect, the present invention provides an
electrochemical device comprising a pair of electrodes and an
electrolyte interposed between the electrodes; wherein at least one
of the pair of electrodes includes an active material containing
layer comprising a plurality of particles containing an active
material, and a binder for binding the particles containing the
active material to each other and the particles containing the
active material to the collector, the collector having a surface
depressed in conformity to a form of the particles containing the
active material.
[0011] In such an electrode, the collector is depressed in
conformity to the form of particles containing an active material
whereby the contact area between the particles containing the
active material and the collector can be made larger than the
conventional one. This can lower the internal resistance of the
electrochemical device using such an electrode, thereby enabling
the electrochemical device to raise its power and improve its
energy density.
[0012] It will be preferred if the binder in the active material
containing layer includes a conductive auxiliary agent particle,
since a conduction path is further formed thereby between the
particles containing the active material and the collector, whereby
the contact resistance can further be lowered. This is also more
preferable in that a conduction path is further formed between the
particles containing the active material, so that the contact
resistance between the particles containing the active material can
be reduced, whereby the resistance of the active material
containing layer itself can greatly be lowered.
[0013] Preferably, the particles containing an active material in
the active material containing layer have a particle size of 0.1 to
500 .mu.m. When the particle size of the particles containing the
active material is smaller than 0.1 .mu.m the particles containing
the active material tend to flocculate and thus are less likely to
disperse uniformly in the active material containing layer. When
the active material containing layer includes a conductive
auxiliary agent particle in particular, the contact between the
particles containing the active material and the conductive
auxiliary agent particle may become uneven, and the contact between
the particles containing the active material, the conductive
auxiliary agent particle, and the binder may become uneven, whereby
problems may occur in their adhesions. When the particles
containing the active material have a particle size exceeding 500
.mu.m, on the other hand, the electrolyte and the like in the
particles containing the active material tend to exhibit a greater
resistance to diffuse, whereas the specific surface area of the
particles containing the active material tends to become smaller.
Therefore, the capacity of the electrochemical device is harder
to
[0014] In still another aspect, the present invention provides a
method of manufacturing an electrode, the method comprising a
particle layer forming step of forming a particle layer including a
binder meltable by heating and a plurality of particles containing
an active material on a planar collector; and a rolling step of
heating the particle layer and extending the particle layer by
passing the collector and the particle layer between rotating
rollers, so as to bind the particles containing the active material
to each other with the binder and bind the particles containing the
active material to the collector with the binder.
[0015] In the rolling step in this aspect of the present invention,
the particles containing the active material are pressed against
the collector, so as to dent the surface of the collector.
Therefore, the electrode having a surface depressed in conformity
to the form of the particles containing the active material such as
the one mentioned above can be manufactured favorably. Since the
forming of the active material containing layer and the binding
(bonding) of the active material containing layer and collector can
be carried out at the same time, the number of steps can be made
smaller than that conventionally required, whereby the cost can be
cut down.
[0016] When the particle layer further includes a conductive
auxiliary agent particle in the particle layer forming step, the
electrode whose binder includes the conductive auxiliary agent
particle as mentioned above can be obtained. Such an electrode is
more preferable in that it can further reduce the contact
resistance between the particles containing the active material and
the collector, and can also lower the contact resistance between
the particles containing the active material.
[0017] Here, it will be preferred if the particle layer includes a
plurality of composite particles each comprising the particles
containing the active material integrated with each other
beforehand by the binder including the conductive auxiliary agent
particle.
[0018] This can favorably disperse the particles containing the
active material and the conductive auxiliary agent particle in the
composite particle beforehand Hot-rolling such a particle layer
including the composite particles can form a quite favorable
electronic conduction path in the active material containing layer.
Therefore, the resistance of the active material containing layer
can further be reduced.
[0019] It will be preferred if the rolling step is carried out by
passing the collector and the particle layer between heated
rollers, since this allows a single apparatus to perform the
heating and rolling.
[0020] It will be preferred if a line pressure of
200.times.10.sup.2 to 2000.times.10.sup.2 N/m (about 20 to 200
kgf/cm) is applied between the rollers in the rolling step. When
the line pressure the rollers is less than 200.times.10.sup.2 N/n,
the particles containing the active material are less likely to
dent the collector sufficiently. When the line pressure of the
rollers exceeds 2000.times.10.sup.2 N/m, on the other hand, the
active material containing layer is consolidated so much that the
electrolyte is harder to diffuse in the active material containing
layer. Accordingly, the above range of the line pressure can reduce
the impedance sufficiently.
[0021] It will be preferred in the particle layer forming step if a
binder layer, meltable by heating, including a conductive auxiliary
agent particle is disposed beforehand on a surface of the
collector, and the particle layer is formed on the binder
layer.
[0022] In this case, the binder layer is also molten at the time of
hot rolling, whereby the particles containing the active material
and the collector can be bound to each other more favorably. Here,
the particles containing the active material dent the molten binder
layer, and then the collector. Since the binder layer includes the
conductive auxiliary agent particle, employing such a binder layer
can also sufficiently lower the contact resistance between the
particles containing the active material and the collector.
[0023] It will be preferred if the particles containing the active
material have a particle size of 0.1 to 500 .mu.m. When the
particle size of the particles containing the active material is
smaller than 0.1 .mu.m, the particles containing the active
material tend to flocculate and thus are less likely to disperse
uniformly in the active material containing layer. When the active
material containing layer includes a conductive auxiliary agent
particle in particular, the contact between the particles
containing the active material and the conductive auxiliary agent
particle may become uneven, and the contact between the particles
containing the active material, the conductive auxiliary agent
particle, and the binder may become uneven, whereby problems may
occur in their adhesions. When the particles of the active material
containing the active material have a particle size exceeding 500
.mu.m, on the other hand, the electrolyte and the like in the
particles containing the active material tend to exhibit a greater
resistance to diffuse, whereas the specific surface area of the
particles containing the active material tends to become smaller.
Therefore, the capacity of the electrochemical device is harder to
increase.
[0024] In the present invention, the "active material" refers to
the following materials depending on the electrode to be formed.
Namely, the "active material" refers to a reducer and an oxidizer
when the electrode to be formed is an electrode wed as an anode and
a cathode of a primary battery, respectively. The "particles
containing the active material" can contain materials other the
active material to such an extent that functions of the active
material are not deteriorated thereby.
[0025] When the electrode to be formed is an anode (at the time of
discharging) used in a secondary battery, the "active material"
refers to a reducer, while being a material which can chemically
stably exist either in its reduced or oxidized state, whereas a
reducing reaction from the oxidized state to the reduced state and
an oxidizing reaction from the reduced state to the oxidized state
can proceed reversibly. When the electrode to be formed is a
cathode (at the time of discharging) used in a secondary battery,
the "active material" refers to an oxidizer, while being a material
which can chemically stably exist either in its reduced or oxidized
state, whereas a reducing reaction from the oxidized state to the
reduced state and an oxidizing reaction from the reduced state to
the oxidized state can proceed reversibly.
[0026] When the electrode to be formed is an electrode used in a
primary or secondary battery, the "active material" may be a
material capable of occluding or releasing metal ions involved in
an electrode reaction (by intercalating/deintercalating or
doping/undoping) in addition to those mentioned above. Examples of
such a material include carbon materials used in anodes and/or
cathodes of lithium-ion secondary batteries and metal oxides
(including mixed metal oxides).
[0027] When the electrode to be formed is an electrode used in an
electrolytic cell or an electrode used in a capacitor (condenser),
the "active material" refers to electronically conductive metals
(including metal alloys), metal oxides, and carbon materials.
[0028] The "electrolyte" in the electrochemical device in the
present invention refers to (1) a porous separator formed from an
insulative material and impregnated with an electrolytic solution
(or a gel-like electrolyte obtained by adding a gelling agent to an
electrolytic solution); (2) a solid electrolyte film (a film made
of a solid polymer electrolyte or a film including an ionically
conductive inorganic material); (3) a layer made of a gel-like
electrolyte obtained by adding a gelling agent to an electrolytic
solution; and (4) a layer made of an electrolytic solution.
[0029] The present invention can provide an electrode which can
sufficiently reduce the contact resistance between a particle
containing an active material and a collector, an electrochemical
device equipped therewith, and a method of manufacturing the
electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a schematic sectional view of the anode in
accordance with an embodiment of the present invention;
[0031] FIG. 2 is a schematic sectional view of the cathode in
accordance with an embodiment of the present invention;
[0032] FIG. 3 is a schematic sectional view showing an
electrochemical device using the anode of FIG. 1 and the cathode of
FIG. 2;
[0033] FIG. 4 is a schematic sectional view of a composite particle
used when manufacturing an electrode;
[0034] FIG. 5 is an explanatory view showing an example of
granulating step when manufacturing composite particles;
[0035] FIG. 6 is an explanatory view showing an example of rolling
step when manufacturing an electrode; and
[0036] FIG. 7 is a table showing impedance values of
electrochemical devices in examples A1-A4 and a comparative example
A1.
[0037] FIG. 8 is a table showing impedance values of
electrochemical devices in examples B1-B11.
[0038] FIG. 9 is a table showing impedance values of
electrochemical devices in examples C1-C10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] In the following, preferred embodiments of the present
invention will be explained in detail with reference to the
drawings. In the following explanations, parts identical or
equivalent to each other will be referred to with numerals
identical to each other without repeating their overlapping
descriptions.
[0040] Anode
[0041] FIG. 1 shows a preferred embodiment of an anode 2 as an
electrode for a lithium-ion secondary battery in accordance with
the present invention. As shown in FIG. 1, the anode 2 comprises a
planar (film-like) collector 22 and an active material containing
layer 24 formed on the collector 22. The form of the anode 2 is not
restricted in particular, and may be a thin film as depicted, for
example.
[0042] Collector of Anode
[0043] It will be sufficient ff the collector 22 is a conductive
planar material. For example, a thin metal sheet such as a copper
foil can be used
[0044] Active Material Containing Layer
[0045] The active material containing layer 24 mainly comprises
particles 25 containing an active material, conductive auxiliary
agent particles 26, and a binder 27.
[0046] Particles Containing Active Material
[0047] Particles containing known active materials for
electrochemical devices can be used as the particles 25 containing
the active material. Examples of such particles 25 containing the
active material include those containing carbon materials which can
occlude/release lithium ions (by intercalating/deintercalating or
doping/undoping), such as graphite, carbon which is hard to
graphitize, carbon which is easy to graphitize, and carbon sintered
at a low temperature; metals adapted to combine with lithium, such
as AL, Si, and Sn; amorphous compounds mainly composed of oxides,
such as SiO.sub.2 and SnO.sub.2; and litium titanate
(Li.sub.3Ti.sub.5O.sub.12). The particles 25 containing the active
material may consist of the active material alone, or include
ingredients other than the active material.
[0048] The average particle size of the particles 25 is preferably
0.1 to 500 .mu.m. When the particle size of the particles 25
containing the active material is lower than 0.1 .mu.m, the
particles 25 containing the active material tend to flocculate and
thus are less likely to disperse uniformly in the active material
containing layer. When the particles 25 containing the active
material have a particle size exceeding 500 .mu.m, on the other
hand, the electrolyte and the like in the particles 25 containing
the active material tend to exhibit a greater resistance to
diffuse. Namely, when the particle size of the particles 25
containing the active material is larger than 500 .mu.m, ionic
diffusion resistance in the particles 25 containing the active
material becomes very large, and thus an impedance tends to become
larger. The preferable particle size of the particles 25 containing
the active material is 0.1 to 50 m.
[0049] Binder
[0050] The binder 27 binds the particles 25 containing the active
material to each other such that the particles 25 containing the
active material come into contact with each other, and the
particles 25 containing the active material to the collector 22
such that the particles 25 containing the active material and the
collector 22 come into contact with each other.
[0051] As long as the above-mentioned binding is possible, the
material of the binder 27 is not limited, examples of which include
fluorine resins such as polyvinylidene fluoride (PVDF),
polytetrafluoroethylene (PTFE),
tetrafluoroethylene/hexafluoropropylene copolymer (my),
tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA),
ethylene/tetrafluoroethylene copolymer (ETFE),
polychlorotrifluoroethylen- e (PCTFE),
ethylene/chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl
fluoride (PVF).
[0052] Examples of the binder 27 other than those mentioned above
include vinylidene-fluoride-based fluorine rubbers such as
vinylidene-fluoride/hexafluoropropylene-based fluorine rubber
(VDF/HFP-based fluorine rubber),
vinylidene-fluoride/hexafluoropropylene/- tetrafluoroethylene-based
fluorine rubber (VDF/HFP/TFE-based fluorine rubber),
vinylidene-fluoride/pentafluoropropylene-based fluorine rubber
(VDF/PFP/TFE-based fluorine rubber),
vinylidene-fluoride/pentafluoropropy-
lene/tetrafluoroethylene-based fluorine rubber (VDF/PFP/TFE-based
fluorine rubber),
vinylidene-fluoride/perfluoromethylvinyl-ether/tetrafluoroethyle-
ne-based fluorine rubber (VDF/PFMVE/TFE-based fluorine rubber), and
vinylidene-fluoride/chlorotrifluoroethylene-based fluorine rubber
(VDF/CTFE-based fluorine rubber).
[0053] Examples of the binder 27 other than those mentioned above
include polyethylene, polypropylene, polyethylene terephthalate,
aromatic polyamide, cellulose, styrene/butadiene rubber, isoprene
rubber, butadiene rubber; and ethylene/propylene rubber. Also
employable are thermoplastic elastomeric polymers such as
styrene/butadiene/styrene block copolymer, its hydrogenetated
products, styrene/ethylene/butadiene/- styrene copolymer,
styrene/isoprene/styrene block copolymer, and its hydrogenated
products. Further, syndiotactic 1,2-polybutadiene, ethylene/vinyl
acetate copolymer, propylene-.alpha.-olefin (whose carbon number is
2 to 12) copolymers, and the like may be used.
[0054] Electronically conductive polymers and ionically conductive
polymers may also be used as the binder 27. An example of the
electronically conductive polymers is polyacetylene. In this case,
the binder 27 also functions as a conductive auxiliary agent
particle, thereby making it unnecessary to add the conductive
auxiliary agent particles 26.
[0055] As the ionically conductive polymers, those exhibiting
conductivity for ions such as lithium ion can be used, for
instance. Examples of the ionically conductive polymers include
those in which monomers of polymer compounds (polyether-based
polymer compounds such as polyethylene oxide and polypropylene
oxide, crosslinked polymers of polyether compounds,
polyepichlorohydrin, polyphosphazene, polysiloxane, polyvinyl
pyrrolidone, polyvinylidene carbonate, polyacrylonitrile, etc.) are
complexed with lithium salts such as LiClO.sub.4, LiBF.sub.4,
LiPF.sub.6, LiAsF.sub.6, LiCl, LiBr, Li(CF.sub.3SO.sub.2).sub.2N,
and LIN(C.sub.2F.sub.5SO.sub.2).sub.2 or alkali metal salts mainly
composed of lithium. Examples of polymerization initiators used for
complexing include photopolymerization initiators and thermal
polymerization initiators suitable for the above-mentioned
monomers.
[0056] The content of the binder 27 included in the active material
containing layer 24 is preferably 0.5 to 6 mass % based on the mass
of the active material containing layer 24. When the content of the
binder 27 is less than 0.5 mass %, the amount of the binder 27 is
so small that the active material containing layer 24 is less
likely to be formed firmly. When the content of the binder 27
exceeds 6 mass %, on the other hand, the amount of binder 27 not
contributing to the electric capacity increases so much that a
sufficient volume energy density is harder to attain When the
electronic conductivity of the binder 27 is low in particular in
this case, the electric resistance of the active material
containing layer 24 rises so much that a sufficient electric
capacity is harder to attain.
[0057] Conductive Auxiliary Agent Particles
[0058] The conductive auxiliary agent particles 26 are not
restricted in particular, whereby known conductive auxiliary agent
particles may be used. Examples of the conductive auxiliary agent
particles include carbon materials such as carbon blacks, highly
crystalline synthetic graphite, and natural graphite; fine powders
of metals such as copper, nickel, stainless, and iron; mixtures of
the above-mentioned carbon materials and fine powders of metals,
and powder materials of conductive oxides such as ITO and the like.
The average particle size of the conductive auxiliary agent
particles is smaller than that of the particles containing the
active material, preferably on the order of 1 to 500 nm.
[0059] The conductive auxiliary agent particles 26 are included in
the binder 27 by a large amount. The conductive auxiliary agent
particles 26 exist singly or in series between the particles 25
containing the active material or between the particles 25
containing the active material and the collector 22, thereby
forming further conduction paths therebetween. This is effective in
flirter lowering the contact resistance between the particles 25
containing the active material and the contact resistance between
the particles 25 containing the active material and the collector
22 within the active material containing layer 24.
[0060] The content of the conductive auxiliary agent particles 26
included in the active material containing layer 24 is preferably
0.5 to 6 mass % based on the total mass of the active material
containing layer 24. When the content of the conductive auxiliary
agent particles 26 is less than 0.5 mass %, the amount of the
conductive auxiliary agent particles 26 is so small that
appropriate conduction paths are harder to be formed in the active
material containing layer 24. When the content of the conductive
auxiliary agent particles 26 exceeds 6 mass %/, on the other hand,
the amount of conductive auxiliary agent particles 26 not
contributing to the electric capacity increases so much that a
sufficient volume energy density is harder to attain.
[0061] Such an active material containing layer 24 includes
conduction paths in which the particles 25 containing the active
material are directly in contact with each other, and conduction
paths in which the particles 25 containing the active material are
in contact with each other by way of one or a plurality of
conductive auxiliary agent particles 26. Therefore, the particles
25 containing the active material form a three-dimensional network
structure in which they are electrically connected to each other
without being isolated.
[0062] Also, such an active material containing layer 24 includes
conduction paths in which the particles 25 containing the active
material are directly in contact with the collector 22, and
conduction paths in which the particles 25 containing the active
material are in contact with the collector 22 by way of one or a
plurality of conductive auxiliary agent particles 26, whereby the
particles 25 containing the active material are electrically
connected to the collector 22 by the conduction paths.
[0063] In particular, the particles 25 containing the active
material dent the surface of the collector 22 in this embodiment,
so that the surface of the collector 22 is depressed in conformity
to the form of the particles 25 containing the active material thus
forming depressions 22a.
[0064] Cathode
[0065] FIG. 2 shows a preferred embodiment of the cathode 3 as an
electrode for the lithium-ion secondary battery in accordance with
the present invention. The cathode 3 comprises a planar collector
32 and an active material containing layer 34 formed on the
collector 32.
[0066] Collector of Cathode
[0067] Employable as the collector 32 are conductive planar
materials, an example of which is an aluminum foil.
[0068] Active Material Containing Layer of Cathode
[0069] The active material containing layer 34 mainly comprises
particles 35 containing an active material, conductive auxiliary
agent particles 36, and a binder 37.
[0070] Particles Containing Active Material
[0071] The particles 35 containing the active material are not
restricted in particular, whereby particles containing known active
materials for electrochemical devices can be used therefor.
Examples of the particles 35 containing the active material include
those containing lithium cobaltate (LiCoO.sub.2), lithium nickelate
(LiNiO.sub.2), lithium manganese spinel (LiMn.sub.2O.sub.4), mixed
metal oxides represented by the general formula of
LiNi.sub.xMN.sub.yCo.sub.zO.sub.2 (x +y+z =1), lithium vanadium
compounds, V.sub.2O.sub.5, olivine-type LiMPO.sub.4 (where M is Co,
Ni, Mn, or Fe), and lithium titanate (Li.sub.3Ti.sub.5O.sub.12).
The particles 35 containing the active material may consist of the
active material alone or include other materials as a matter of
course.
[0072] The average panicle size of the particles 35 containing the
active material is preferably 0.1 to 500 .mu.m in the cathode 3.
When the particle size of the particles 35 containing the active
material is less than 0.1 .mu.m, the particles 35 containing the
active material tend to flocculate and thus are less likely to
disperse uniformly in the active material containing layer. When
the particles 35 containing the active material have a particle
size exceeding 500 .mu.m, on the other hand, the electrolyte and
the like in the particles 35 containing the active material tend to
exhibit a greater resistance to diffuse. Namely, when the particle
size of the particles 35 containing the active material is larger
than 500 .mu.m, ionic diffusion resistance in the particles 35
containing the active material becomes very large, and thus an
impedance tends to become larger. The preferable particle size of
the particles 35 containing the active material is 0.1 to 50
.mu.m.
[0073] Binder Conductive Auxiliary Agent etc.
[0074] As the conductive auxiliary agent particles 36 and binder
37, materials similar to the conductive auxiliary agent particles
26 and binder 27 in the active material containing layer of the
anode 2 can be used in a similar mode. Operations and effects of
the conductive auxiliary agent particles 36 and binder 37 are
similar to those in the anode 2. Preferably, the contents of the
conductive auxiliary agent particles 36 and binder 37 included in
the active material containing layer 34 are made similar to those
in the anode 2.
[0075] From the viewpoint of forming contact interfaces between the
particles 35 containing the active material and the electrolyte
three-dimensionally with a sufficient size, the BET specific
surface area of the particles 35 containing the active material is
preferably 0.1 to 10 m.sup.2/g, more preferably 0.1 to 5
m.sup.2/g.
[0076] The active material containing layer 34 includes conduction
paths in which the particles 35 containing the active material are
directly in contact with each other, and conduction paths in which
the particles 35 containing the active material are in contact with
each other by way of one or a plurality of conductive auxiliary
agent particles 36, whereby the particles 35 containing the active
material form a three dimensional network structure in which they
are electrically connected to each other without being isolated
[0077] Also, such an active material containing layer 34 includes
conduction paths in which the particles 35 containing the active
material are directly in contact with the collector 32, and
conduction paths in which the particles 35 containing the active
material are in contact with the collector 32 by way of one or a
plurality of conductive auxiliary agent particles 36, whereby the
particles 35 containing the active material are electrically
connected to the collector 32 by the conduction paths.
[0078] In particular, the particles 35 containing the active
material dent the surface of the collector 32 in this embodiment,
so that the surface of the collector 32 is depressed in conformity
to the form of the particles 35 containing the active materials
thus forming depressions 32a.
[0079] Operations and effects of such anode 2 and cathode 3 will
now be explained. In the anode 2 and cathode 3, the surfaces of the
collectors 22, 32 are formed with the depressions 22a, 32a in
conformity to the forms of the particles 25, 35 containing the
active materials, whereby the particles 25, 35 containing the
active materials partly fit into the depressions 22a, 32a,
Therefore, the anode 2 and cathode 3 in this embodiment can yield
wider contact areas between the particles 25, 35 containing the
active material and the collectors 22, 32 than those in the
conventional anode 2 and cathode 3 with no depressions. Therefore,
the contact resistance between the collectors 22, 32 and the
particles 25, 35 containing the active material becomes smaller.
This can lower the internal resistance of the electrochemical
device using the anode 2 and cathode 3, thereby allowing the
electrochemical device to increase its output and improve its
energy density.
[0080] Electrochemical Device
[0081] An example of the lithium-ion secondary battery 1 as an
electrochemical device using the above-mentioned anode 2 and
cathode 3 will now be explained
[0082] FIG. 3 is a schematic sectional view showing a basic
configuration of the lithium-ion secondary battery 1 in accordance
with an embodiment. The lithium-ion secondary battery 1 is mainly
constituted by a unit cell 5 including the anode 2, the cathode 3,
and an electrolyte layer 4 disposed between the anode 2 and cathode
3; and a case 7 sealing the unit cell 5 therein. At the time of
charging, the anode 2 is connected to an anode of an external power
supply (none of which is depicted), so as to function as a cathode.
At the time of charging, the cathode 3 is connected to a cathode of
an external power supply (none of which is depicted), so as to
function as an anode.
[0083] Electrolyte Layer
[0084] The electrolyte layer 4 may be a layer made of an
electrolytic solution, a solid electrolyte (ceramic solid
electrolyte or solid polymer electrolyte), or a layer constituted
by a separator and an electrolytic solution and/or solid
electrolyte infiltrated into the separator.
[0085] The electrolytic solution is prepared by dissolving a
lithium-containing electrolyte into a nonaqueous solvent. The
lithium-containing electrolyte may appropriately be chosen from
LiClO.sub.4, LiBF.sub.4, LiPF.sub.6, and the like, for example,
whereas lithium imide salts such as Li(CF.sub.3SO.sub.2).sub.2N and
Li(C.sub.2F.sub.5SO.sub.2).sub.2N, LiB(C.sub.2O.sub.4).sub.2, and
the like can also be used. The nonaqueous solvent can be selected
from organic solvents exemplified in Japanese Patent Application
Laid-Open No. SHO 63-121260 and the like, such as ethers, ketones,
and carbonates, for example. In particular, carbonates are
preferably used in the present invention.
[0086] Among the carbonates, a mixed solvent mainly composed of
ethylene carbonate with at least one species of other solvents
added thereto is preferably used in particular. In general, the
mixing ratio is preferably such that ethylene carbonate/other
solvents=5 to 70:95 to 30 (volume ratio). Ethylene carbonate has a
high solidifying point of 36.4.degree. C., so that it is solidified
at normal temperature and thus cannot be used alone as an
electrolytic solution for a battery. When at least one species of
other solvents having a lower solidifying point is added thereto,
however, the mixed solvent lowers its solidifying point, so as to
be usable.
[0087] As the other solvents in this case, any solvents can be used
as long as they can lower the solidifying point of ethylene
carbonate. Their examples include diethyl carbonate, dimethyl
carbonate, propylene carbonate, 1,2-dimethoxyethane, methylethyl
carbonate, .gamma.-butyrolactone, .gamma.-valerolactone,
.gamma.-octanoic lactone, 1,2-diethoxyethane,
1,2-ethoxymethoxyethane, 1,2-dibutoxyethane, 1,3-dioxolane,
tetrahydrofuran, 2-methyltetrahydrofuran, 4,4-dimethyl-1,3-dioxane,
butylene carbonate, and methyl formate. Employing the
above-mentioned mixed solvent while using a carbonaceous material
as an active material of the anode can remarkably improve the
battery capacity and fully lower the irreversible capacity
ratio.
[0088] Such an electrolytic solution infiltrates into pores of the
active material containing layer 24 in the anode 2 and pores of the
active material containing layer 34 in the cathode 3.
[0089] An example of the solid polymer electrode is a conductive
polymer having an ionic conductivity.
[0090] The above-mentioned conductive polymer, is not restricted in
particular as long as it has a lithium ion conductivity. Examples
of the conductive polymer include those in which monomers of
polymer compounds (polyether-based polymer compounds such as
polyethylene oxide and polypropylene oxide, crosslinked polymers of
polyether compounds, polyepichlorohydrin, polyphosphazene,
polysiloxane, polyvinyl pyrrolidone, polyvinylidene carbonate,
polyacrylonitrile, etc.) are complexed with lithium salts such as
LiClO.sub.4, LiBF.sub.4, LiPF.sub.6, LiAsF.sub.6, LiCl, LiBr,
Li(CF.sub.3SO.sub.2).sub.2N, and LiN(C.sub.2F.sub.5SO.sub.2).sub.2
or alkali metal salts mainly composed of lithium. Examples of
polymerization initiators used for complexing include
photopolymerization initiators and thermal polymerization
initiators suitable for the above-mentioned monomers.
[0091] Examples of support salts constituting the polymer solid
electrolyte include salts such as LiClO.sub.4, LiPF.sub.6,
LiBF.sub.4, LiAsF.sub.6, LiCF.sub.3SO.sub.3,
LiCF.sub.3CF.sub.2SO.sub.3, LiC(CF.sub.3SO.sub.2).sub.3,
LiN(CF.sub.3SO.sub.2).sub.2, LiN(CF.sub.3CF.sub.2O.sub.2).sub.2,
LiN(CF.sub.3SO.sub.2)(C.sub.4F.sub.9S- O.sub.2), and
LiN(CF.sub.3CF.sub.2CO).sub.2, and their mixtures.
[0092] When using the solid electrolyte, the solid electrolyte is
further added into pores of the active material containing layer 24
in the anode 2, and pores of the active material containing layer
34 in the cathode 3.
[0093] When a separator is used in the electrolyte layer 4,
examples of its constituent materials include one or more species
of polyolefins such as polyethylene and polypropylene (laminates of
two or more layers of films and the like when two or more species
can be used), polyesters such as polyethylene terephthalate,
thermoplastic fluorine resins such as ethylene/tetrafuoroethylene
copolymer, and celluloses. Modes of the sheet include microporous
films, woven fabrics, nonwoven fabrics, and the like having a
thickness of about 5 to 100 .mu.u while exhibiting an air permeance
of about 5 to 2000 sec/100 cc as measured by the method defined in
JIS-P8117. Monomers of the solid electrolyte may be infiltrated
into the separator and cured, so as to be polymerized for use. The
above-mentioned electrolytic solution may be used as being
contained in a porous separator.
[0094] The case 7 is not restricted in particular as long as it can
seal the unit cell 5. For example, metal cans, resin cases, and
metal laminate film packs can be used.
[0095] Since the contact resistance between the collectors 22, 32
of the anode 2 and cathode 3 and the active material containing
layers 24, 34 is low as mentioned above, such a lithium-ion
secondary battery 1 can reduce its DC electric resistance
(impedance). This allows the lithium-ion secondary battery 1 to
increase its output and improve its energy density.
[0096] Manufacturing Method
[0097] A preferred embodiment of methods of manufacturing the anode
2 and cathode 3 in accordance with the above-mentioned embodiments
will now be explained.
[0098] First, in this embodiment, composite particles 250 for the
anode 2 in which particles 25 containing an active material are
bound to each other with a binder 27 including conductive auxiliary
agent particles 26, and composite particles 350 for the cathode 3
in which particles 35 containing an active material are bound to
each other with a binder 37 including conductive auxiliary agent
particles 36 are made. Subsequently, a particle layer of the
composite particles 250 and a particle layer of the composite
particles 350 are stacked on their corresponding collectors, and
then thus obtained laminates are hot-rolled.
[0099] To begin with, a granulating step of making the composite
particles 250 will be explained. FIG. 4 is a schematic sectional
view of the composite particles 250, 350.
[0100] The composite particle 250 is a relatively loose aggregate
in which the particles 25 containing the active material are
integrated with each other |by the binder 27 including a large
number of conductive auxiliary agent particles 26. The binder 27
loosely binds the particles 25 containing the active material to
each other. Therefore, the particles 25 containing the active
material and the conductive auxiliary agent particles 26 are
favorably dispersed in the composite particle 250. On the other
hand, the composite particle 350 is one in which the particles 35
containing the active material are integrated with each other by
the binder 37 including the conductive auxiliary agent particles
36, and thus has the same structure as with the composite particle
250.
[0101] Such composite particles 250 are formed by way of the
following granulating step, for example. The granulating step will
be explained more specifically with reference to FIG. 5.
[0102] The granulating step includes a material liquid preparing
step of preparing a material liquid containing a binder, conductive
auxiliary agent particles, and a solvent; a fluidizing step of
fluidizing particles containing an active material within a
fluidizing tank; and a spray-drying step of spraying the material
liquid to the fluidized particles containing the active material so
as to flocculate the particles containing the active material, and
then eliminating the solvent from the material liquid so as to form
a composite particle.
[0103] First, in the material liquid preparing step, a solvent
adapted to dissolve the binder is used, so as to dissolve the
binder therein. The conductive auxiliary agent particles are
dispersed in thus obtained solution, so as to yield the material
liquid. The solvent may be a solvent (dispersant) which can
disperse the binder. The solvent adapted to dissolve the binder is
not restricted in particular as long as it can dissolve the binder
and disperse the conductive auxiliary agent particles. For example,
N-methyl-2-pyrrolidone or N,N-dimethylformamide can be used.
[0104] Next, in the fluidizing step, gas flows are generated in the
fluidizing tank 55 as shown in FIG. 5, and the particles 25
containing the active material are put into the gas flows, so as to
fluidize the particles 25 containing the active material.
[0105] Subsequently, in the spray-drying step, droplets 256 of the
material liquid are sprayed within the fluidizing tank 55, so as to
attach to the fluidized particles 25 containing the active
material, and are dried within the fluidizing tank 55 at the same
time. Here, the droplets 256 cause the particles 25 containing the
active material to attach to each other and flocculate, so as to be
integrated into predetermined aggregates, whereas the solvent is
eliminated from the droplets 256 of the material liquid, whereby
the composite particles 250 are obtained.
[0106] More specifically, the fluidizing tank 55 is a container
having a cylindrical form, for example, whose bottom is provided
with an opening 52 for introducing a warm air (or hot air) L5 from
the outside, so as to convect the panicles 25 containing the active
material within the fluidizing tank 55. The side face of the
fluidizing tank 55 is provided with an opening 54 for introducing
the droplets 256 of the material liquid sprayed to the particles 25
containing the active material convected within the fluidizing tank
55. The droplets 256 of the material liquid including the binder
27, conductive auxiliary agent particles 26, and solvent are
sprayed to the particles 25 containing the active material
convected within the fluidizing tank 55.
[0107] Here, the temperature of the warm air (or hot air) is
regulated, for example, such that the temperature of the atmosphere
in which the particles containing the active material are placed is
held at a predetermined temperature [preferably ranging from
50.degree. C. to a temperature not greatly exceeding the melting
point of the binder, more preferably ranging from 50.degree. C. to
a temperature not higher than the melting point of the binder
(e.g., 200.degree. C.)] at which the solvent can rapidly be
eliminated from the droplets 256 of the material liquid, whereby
the droplets 256 of the material liquid formed on the surfaces of
the particles 25 containing the active material are dried
substantially simultaneously with the spraying with the droplets
256 of the is material liquid. This can yield the composite
particles 250 in which the particles 25 containing the active
material are loosely bound to each other with the binder 27
containing the conductive auxiliary agent particles 26.
[0108] The amount of the conductive auxiliary agent particles 26
and binder 27 attached to the particles 25 containing the active
material is preferably 1 to 12 mass %, more preferably 3 to 12 mass
%, when expressed by the value of 100.times.(the mass of conductive
auxiliary agent particles+the mass of binder)/(the mass of
composite particles).
[0109] From the reasons mentioned above, it will be preferred if
the particles 25 containing the active material in use have a
particle size of 0.1 to 500 .mu.m.
[0110] The composite particles 350 can be manufactured in the same
manner as with the composite particles 250 explained above.
[0111] A preferred example of method of forming the anode 2 using
thus obtained composite particles 250 will now be explained with
reference to FIG. 6. The cathode 3 can be manufactured in the same
manner, while using the composite particles 350.
[0112] Specifically, the method can include a particle layer
forming step of supplying the collector 22 with the composite
particles 250, so as to form a particle layer 210 containing the
composite particles 250; and a rolling step of passing the
collector 22 and particle layer 210 between rotating rollers, while
heating the particle layer 210, so as to hot-roll the particle
layer 210.
[0113] Such steps can easily be carried out by a hot roll press
machine 300 shown in FIG. 6, for example.
[0114] Specifically, the collector 22 bridges feed rollers 302, 304
substantially horizontally. A conductive resin layer (binder layer)
22b is formed on the upper face of the collector 22 beforehand. The
conductive resin layer 22b can contain a binder meltable by heating
and conductive auxiliary agent particles. Specifically, it will be
preferred if the conductive resin layer 22b contains the binder 27
and conductive auxiliary agent particles 26 of the composite
particles 250.
[0115] Subsequently, a hopper 306 storing the composite particles
250 supplies the composite particles 250 onto the conductive resin
layer 22b of the collector 22, so as to form the particle layer 210
on the collector 22. Then, the collector 22 having the particle
layer 210 laminated thereon is passed between a pair of hot rollers
312, 314 rotating while being heated.
[0116] This melts the binder 27 of the composite particles 250 and
consolidates the composite particles 250, thereby forming the
active material containing layer 24 having the above-mentioned
structure on the collector 22.
[0117] The active material containing layer 24 is formed like a
single plate, and is bound to the collector 22 by the binder 27
including the conductive auxiliary agent particles 26.
[0118] Since the composite particles 250 are extended by the hot
rollers 312, 314 in this embodiment, the particles 25 containing
the active material are strongly pressed against the surface of the
collector 22, so as to dent the collector 22, whereby the surface
of the collector 22 is depressed in conformity to the form of the
particles 25 containing the active material. Therefore, an
electrode having the depressions 22a and exhibiting a low contact
resistance between the particles 25 containing the active material
and the collector 22 can easily be manufactured as mentioned above.
Also, since the forming of the sheet-like active material
containing layer 24 and the bonding of the active material
containing layer 24 to the collector 22 can be carried out at the
same time, the number of steps can be made smaller than that
conventionally required, whereby the cost can be cut down
[0119] Preferably, the surface temperature of the hot rollers 312
and 314 is 60 to 200.degree. C. Though depending on the melting
temperature of the binder 27, such a temperature range allows the
binder 27 to favorably bind the particles 25 containing the active
material to each other, and the particles 25 containing the active
material to the collector 22. When the temperature is lower than
60.degree. C., the binding property tends to deteriorate. When the
temperature exceeds 200.degree. C., on the other hand, it greatly
exceeds the melting point or softening point of binders used in
general, whereby a firm sheet is harder to make.
[0120] The line pressure applied between the hot rollers 312, 314
is preferably 200.times.10.sup.2 to 2000.times.10.sup.2 N/m (about
20 to 200 m kgf/cm). When the line pressure of the rollers is less
than 200.times.10.sup.2 N/n here, the particles 25 containing the
active material are less likely to dent the collector 22
sufficiently. When the line pressure of the rollers exceeds
2000.times.10.sup.2 N/n, on the other hand, the active material
containing layer 24 is consolidated so much that the electrolyte is
harder to diffuse within the active material containing layer 24.
Accordingly, the impedance of the electrochemical devices can be
sufficiently reduced by the range of 200.times.10.sup.2 to
2000.times.10.sup.2 N/m.
[0121] Since the composite particles 250 are used in this
embodiment, the particles 25 containing the active material and the
conductive auxiliary agent particles 26 can be dispersed in the
composite particles 250 beforehand, whereby the particles 25
containing the active material and the conductive auxiliary agent
particles 26 can attain a sufficient dispersibility in the active
material containing layer 24 formed by rolling. Therefore, the
particles 25 containing the active material and the conductive
auxiliary agent particles 26 can form a quite favorable
three-dimensional network of electronic conduction paths in the
active material containing layer 24.
[0122] When the conductive resin layer 22b is formed on the
collector 22 beforehand, the adhesion of the active material
containing layer 24, i.e., the particles 25 containing the active
material, to the collector 22 improves remarkably. Even when the
resin layer 22b exists on the collector 22 beforehand, the hot
rollers allow the particles 25 containing the active material to
penetrate through the resin layer 22b and dent the collector 22.
Since the resin layer 22b is a conductive resin layer, the contact
resistance between the particles 25 containing the active material
and the collector 22 can be made sufficiently low. Even if the
resin layer 22b is not formed on the collector 22 beforehand, an
electrode exhibiting operations and effects of the present
invention can be formed
[0123] The particle layer forming step may form the particle layer
by further mixing unintegrated single particles, i.e., at least one
species selected from the particles 25 containing the active
material, conductive auxiliary agent particles 26, and binder 27,
in addition to the composite particles 250. The electrode in
accordance with this embodiment can also be made when a particle
layer including unintegrated single particles, i.e., the particles
25 containing the active material, conductive auxiliary agent
particles 26, and binder 27, is formed without using the composite
particles 250 at all.
[0124] The particle layer 210 may be heated by an infrared lamp or
the like instead of the heated hot rollers, and then passed between
unheated rollers.
[0125] Thus manufactured electrode can easily be tamed into a
desirable electrochemical device by a known method.
[0126] Though preferred embodiments of the present invention are
explained in the foregoing, the present invention is not restricted
thereto.
[0127] For example, though the conductive auxiliary agent particles
26 are added in order to improve the electric contact between the
particles 25 containing the active material and/or between the
particles 25 containing the active material and the collector 22,
operations as an electrode are possible without the addition of the
conductive auxiliary agent particles 26 when the binder 27 has a
conductivity or the like or depending on characteristics of the
particles 25 containing the active material or the like.
[0128] Though the above-mentioned electrochemical device comprises
the electrode of the embodiment as each of the anode and cathode,
it will be sufficient if the electrode of the embodiment is
provided as at least one of the anode and cathode.
[0129] Though the above-mentioned electrochemical device includes
one unit cell 5, a plurality of unit cells may be laminated as
well. In this case, the unit cells may be connected either in
parallel or in series.
[0130] Though the above-mentioned embodiment of the electrochemical
device relates to a lithium-ion secondary battery, the
electrochemical device in accordance with the present invention may
be any of other secondary batteries and primary batteries, for
example, as long as it comprises at least an anode, a cathode, and
an ionically conductive electrolyte layer, while the anode and
cathode oppose each other by way of the electrolyte layer. As the
particles containing the active material for the active material
containing layer of the anode or cathode, not only those
exemplified above but those used in known primary batteries can
also be employed. The conductive auxiliary agent particles and
binder may be the same as the materials exemplified above.
[0131] The electrode of the present invention is not limited to
electrodes for batteries, but may be an electrode used in
electrolytic cells, electrochemical capacitors (electric double
layer capacitors, aluminum electrolytic capacitors, etc.), or
electrochemical sensors. In the case of an electrode for an
electric double layer capacitor, for example, carbon materials
having a high electric double layer capacity such as coconut shell
activated carbon, pitch-based activated carbon, and
phenol-resin-based activated carbon can be used as particles
containing the active material for the active material containing
layer of the anode or cathode. In the case of a double layer
capacitor, the specific surface area of the particles containing
the active material is preferably 500 to 3000 m.sup.2/g in each of
the cathode 3 and anode 2.
[0132] For an anode used for brine electrolysis, a pyrolyzed
product of ruthenium oxide (or a mixed oxide of ruthenium oxide and
other metal oxides) may be used as particles containing the active
material for the active material containing layer, for example.
[0133] When the electrochemical device of the present invention is
an electrochemical capacitor, any of aqueous electrolytic solutions
and nonaqueous electrolytic solutions (nonaqueous electrolytic
solutions using organic solvents) used in known electrochemical
capacitors such as electric double layer capacitors can be employed
as the electrolytic solution.
[0134] Species of the nonaqueous electrolytic solutions are not
restricted in particular, but are selected in view of the
solubility and degree of dissociation of the solute and the
viscosity of the liquid in general, and are desirably those having
a high conductivity and a wide potential window. Examples of the
organic solvents include propylene carbonate, diethylene carbonate,
and acetonitrile. Examples of the electrolytes include quaternary
ammonium salts such as tetraethylammonium tetrafluoroborate (boron
tetraethylammonium tetrafluoride). In this case, the mingling
moisture must be controlled strictly.
[0135] When the secondary battery 1 is a metal lithium secondary
battery, its anode (not depicted) may be an electrode solely
constituted by metal lithium or a lithium alloy also acting as a
collector. The lithium alloy is not restricted in particular,
examples of which include alloys such as Li--Al, LiSi, and LiSn
(LiSi being taken as an alloy here). In this case, it will be
sufficient if the cathode is constructed by composite particles 250
having a configuration which will be explained later.
EXAMPLES
[0136] In the following, the present invention will be explained in
more detail with reference to examples and a comparative example,
which do not restrict the present invention at all.
Example A1
[0137] First, electrodes for an electric double layer capacitor
were made.
[0138] (1) Making of Composite Particles
[0139] To begin with, composite particles 250 for use in the
manufacturing of active material containing layers in electrodes
for the electric double layer capacitor were made by the following
procedure. Here, the composite particles 250 were constituted by a
cathode/anode active material (90 mass %), conductive auxiliary
agent particles (5 mass %), and a binder (5 mass %).
[0140] As the cathode and the anode active material particles
containing the active material), activated carbon (having an
average particle size of 15 .mu.m) was used. As the conductive
auxiliary agent particles, carbon black (acetylene black) was used
As the binder, polyvinylidene fluoride PVDF) was used
[0141] First, a "material liquid" (containing 3 mass % of carbon
black and 2 mass % of polyvinylidene fluoride) in which carbon
black was dispersed in a solution in which polyvinylidene fluoride
had been dissolved in N,N-dimethylformamide acting as a solvent was
prepared.
[0142] Subsequently, air flows were generated in a container having
the same configuration as with the fluidizing tank 55 shown in FIG.
5, and particles of activated carbon were put therein, so as to be
fluidized. Then, the above-mentioned material liquid was sprayed to
the fluidized particles of activated carbon, so as to attach the
solution onto surfaces of the activated carbon particles, thereby
causing the particles to flocculate. The temperature in the
atmosphere in which the activated carbon particles were placed was
held constant at the time of spraying, so as to eliminate
NN-dimethylformamide from the particle surfaces substantially
simultaneously with the spraying. This yielded the composite
particles 250 (having an average particle size of 200 .mu.m) in
which the activated carbon particles were bound to each other with
polyvinylidene fluoride including carbon black, so as to be
integrated with each other.
[0143] The respective amounts of activated carbon, carbon black,
and polyvinylidene fluoride used in the granulating were regulated
such that the mass ratio of these components in the finally
obtained composite particles 250 became the above-mentioned
value.
[0144] (2) Making of Electrodes
[0145] Subsequently, electrodes (cathode and anode) were made. To
begin with, a conductive resin layer (having a thickness of 5
.mu.m) was formed on one side of an aluminum foil (having a
thickness of 20 .mu.m) acting as a collector. The conductive resin
layer was a layer (composed of 30 mass % of carbon black and 70
mass % of polyvinylidene fluoride) containing the same conductive
auxiliary agent particles (carbon black) as those contained in the
composite particles and the same binder (polyvinylidene fluoride)
as that contained in the composite particles.
[0146] Next, using a hot roll press machine having the same
configuration as that shown in FIG. 6, the composite particles
manufactured above were diffused over the resin layer of the
collector 22, so as to form a particle layer, and the collector
with the particle layer was rolled by hot rollers at a high
temperature. The rolling condition was such that the roller
temperature was 180.degree. C., and the line pressure applied
between the rollers (hereinafter referred to as "roller line
pressure") was 700.times.10.sup.2 N/m. As such, a pair of
electrodes (cathode and anode) each including an active material
containing layer with a thickness of 150 .mu.m, an active material
carrying amount of 45 mg/cm.sup.2, and a porosity of 25 vol % were
obtained.
[0147] (3) Making of Electric Double Layer Capacitor
[0148] The electrodes were opposed to each other so as to hold
therebetween a separator made of cellulose, whereas the separator
and the active material containing layers were impregnated with a
polycarbonate solution containing 1.2 mol/L of
TEMA.sup.+BF.sub.4.sup.- (triethylnethylammonium
tetrafluoroborate). They were sealed into an aluminum laminate
pack, so as to yield an electric double layer capacitor.
Examples A2 and A3
[0149] Examples A2 and A3 were the same as Example A1 except that
the roller line pressure was 200.times.10.sup.2 N/m and
2000.times.10.sup.2 N/m, respectively.
Example A4
[0150] A lithium-ion secondary battery was made in Example A4. For
the anode, the same electrode as that of Example Al was used. On
the other hand, the cathode was made by the same hot rolling as
with Example A1 while using the following composite particles and
collector.
[0151] The composite particles were made as in Example A1 while
using LiCoO.sub.2 particles (having an average particle size of 0.5
mm) as particles containing the active material, acetylene black
(Denka Black) as the conductive auxiliary agent particles, and
polyvinylidene fluoride (PVDF) as the binder. The particle size of
the composite particles was 200 .mu.m. The composite particles were
constituted by 90 mass % of the particles containing the active
material, 7 mass % of the conductive auxiliary agent particles, and
3 mass % of the binder.
[0152] Employed as the collector was an aluminum foil (with a
thickness of 20 .mu.m) having a surface formed with a conductive
resin layer (with a thickness of 5 .mu.m) including 30 mass % of
acetylene black and 70 mass % of polyvinylidene fluoride. An
Electrolytic solution containing 1.2 mol/L of LiBF.sub.4 as
electrolyte and mixture of ethylene carbonate and propylene
carbonate (70:30 by volume) as a solvent was used.
Comparative Example A1
[0153] Comparative Example A1 was the same as Example A1 except
that the composite particles were hot-rolled at a roller line
pressure of 700.times.10.sup.2 N/m by hot rollers at 120.degree.
C., so as to form an active material containing sheet, then the
active material containing sheet was overlaid on the collector, and
they were thermo-compressed at 5 MPa at 180.degree. C.
[0154] FIG. 7 shows DC impedance values of these electrochemical
devices at 1 kHz. It was verified that Examples 1 to 4 each having
formed the active material containing layer by hot-rolling the
particle layer formed on the collector as in the present invention
were able to lower the impedance of batteries and capacitors as
compared with Comparative Example 1 which formed a sheet of the
active material containing layer and then bonded it to the
collector as conventionally done.
Example B1
[0155] An electric double layer capacitor of Example B1 was made
under the same condition except that; the composite particles were
made using activated carbon having 2 .mu.m of particle size as the
particles containing the active material (90 mass%), acetylene
black as the conductive auxiliary agent particles (6 mass%), and
PVDF as the binder (4 mass%), the particle size of the composite
particles was .sup.60 .mu.m, the rolling condition was such that
the roller temperature was 120.degree. C., and the active material
carrying amount was 9.0 mg/cm.sup.2.
Example B2 to B6
[0156] Example B2 was the same as Example B1 except that the
particle size of the active carbon was 5 .mu.m and the particle
size of the composite particles was 120 .mu.m. Example B3 was the
same as Example B1 except that the particle size of the active
carbon was 15 .mu.m and the particle size of the composite
particles was 200 .mu.. Example B4 was the same as Example B1
except that the particle size of the active carbon was 18 .mu.m and
the particle size of the composite particles was 300 .mu.m. Example
B5 was the same as Example B1 except that the particle size of the
active carbon was 22 .mu.m and the particle size of the composite
particles was 450 .mu.m. Example B6 was the same as Example B1
except that the particle size of the active carbon was 28 .mu.m and
the particle size of the composite particles was 580 .mu.m.
Example B7 to B10
[0157] Example B7 was the same as Example B3 except that the roller
line pressure was 150.times.10.sup.2 N/m. Example B8 was the same
as Example B3 except that the roller line pressure was
250.times.10.sup.2 N/m. Example B9 was the same as Example B3
except that the roller line pressure was 1900.times.10.sup.2 N/m.
Example B10 was the same as Example B3 except that the roller line
pressure was 2200.times.10.sup.2 N/m.
Example B11
[0158] Example B11 was the same as Example B3 except that the
electrode was made under the condition that the particle layer
including unintegrated single particles, i.e., the activated carbon
as the particles containing the active material, the acetylene
black as conductive auxiliary agent particles, and the PVDF as
binder, was formed on the collectors without using the composite
particles at all.
Example C1
[0159] A Lithium ion secondary battery was made in the Example C1.
The anode was the same as the Example B3. On the other hand, the
cathode was made under the same condition of Example B3 except
that; the following composite particles and collector were used,
the active material carrying amount was 45 mg/cm.sup.2, and a
porosity was 28 vol %. The roller line pressure was
700.times.10.sup.2 N/m.
[0160] The composite particles were constituted by LiCoO.sub.2
particles (having 2 .mu.m of particle size) as the particles
containing the active material (90 mass %/o), acetylene black
(Denka Black) as the conductive auxiliary agent particles (7 mass
%), and the PVDF as a binder (3 mass %). The particle size of the
composite particles was 60 .mu.m.
[0161] The collector was an aluminum foil (having a thickness of 20
.mu.m). An conductive resin layer (composed of 30 mass % of
acetylene black and 70 mass % of polyvinylidene fluoride) was
formed on the collector. An Electrolytic solution containing 1
mol/L of LiBF.sub.4 as electrolyte and mixture of ethylene
carbonate and propylene carbonate (70:30 by volume) as a solvent
was used.
Example C2 to C5
[0162] Example C2 was the same as Example C1 except that the
particle size of the LiCoO.sub.2 particles was 5 .mu.m and the
particle size of the composite particles was 180 .mu.m for the
cathode. Example C3 was the same as Example C1 except that the
particle size of the LiCoO.sub.2 particles was 8 .mu.m and the
particle size of the composite particles was 250 .mu.m for the
cathode. Example C4 was the same as Example C1 except that the
particle size of the LiCoO.sub.2 particles was 12 .mu.m and the
particle size of the composite particles was 300 .mu.m for the
cathode. Example C5 was the same as Example C1 except that the
particle size of the LiCoO.sub.2 particles was 15 .mu.m and the
particle size of the composite particles was 420 .mu.m for the
cathode.
Example C6 to C9
[0163] Example C6 was the same as Example C2 except that the roller
line pressure was 150.times.10.sup.2 N/m for the cathode. Example
C7 was the same as Example C2 except that the roller line pressure
was 250.times.10.sup.2 N/m for the cathode. Example C8 was the same
as Example C2 except that the roller line pressure was
1800.times.10.sup.2 N/m for the cathode. Example C9 was the same as
Example C2 except that the roller line pressure was
2200.times.10.sup.2 N/m for the cathode.
Example C10
[0164] Example C10 was the same as Example C2 except that the
electrode was made under the condition that the particle layer
including unintegrated single particles, i.e., the LiCoO.sub.2
particles as the particles containing the active material, the
acetylene black as conductive auxiliary agent particles, and the
PVDF as binder, was formed on the collectors without using the
composite particles at all.
[0165] The electric double layer capacitors of Examples B1 to D11
and the Lithium ion secondary batteries of Examples C1 to C10 had
sufficient low impedance even at relatively low roller line
pressure, for example, about 700.times.10.sup.2 N/m (see FIG. 8 and
FIG. 9). The preferable roller line pressure seems to be in range
of 200.times.10.sup.2 to 2000.times.10.sup.2 N/m. It was found
that, when the particle size of the particles containing the active
material increase, the impedance tends to become increase.
[0166] It was also found that, when the composite particles were
used to form the particle layer on the collector, the impedance
tends to become decrease in contrast to the case without using the
composite particles.
* * * * *