U.S. patent application number 11/267107 was filed with the patent office on 2006-10-05 for positive electrode for use in lithium cell and lithium cell using the same.
Invention is credited to Eriko Ishiko, Michiyuki Kono.
Application Number | 20060222952 11/267107 |
Document ID | / |
Family ID | 35892464 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060222952 |
Kind Code |
A1 |
Kono; Michiyuki ; et
al. |
October 5, 2006 |
Positive electrode for use in lithium cell and lithium cell using
the same
Abstract
A positive electrode for use in a lithium battery using water as
a dispersion medium, not causing a problem of deteriorating the
battery performance due to corrosion of a collector or the like and
not forming unevenness on the coating surface, as well as a lithium
battery using the positive electrode, the positive electrode used
being formed from a positive electrode paste containing a positive
electrode active material represented by the following formula (I),
a binder ingredient comprising a water dispersible elastomer and a
water soluble polymer as a viscosity improver, water as a
dispersion medium and a dispersing agent: Li.sub.xMPO.sub.4 (I) (in
the general formula (I) above, M represents a metal atom containing
at least one of metal atoms selected from the group consisting of
Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B and Mo,
and 0<x<2).
Inventors: |
Kono; Michiyuki; (Osaka,
JP) ; Ishiko; Eriko; (Kyoto-shi, JP) |
Correspondence
Address: |
JORDAN AND HAMBURG LLP
122 EAST 42ND STREET
SUITE 4000
NEW YORK
NY
10168
US
|
Family ID: |
35892464 |
Appl. No.: |
11/267107 |
Filed: |
November 3, 2005 |
Current U.S.
Class: |
429/231.95 ;
252/182.1; 429/217; 429/221; 429/223; 429/224; 429/231.5;
429/231.6 |
Current CPC
Class: |
H01M 4/5825 20130101;
H01M 10/0525 20130101; H01M 4/136 20130101; Y02E 60/10 20130101;
Y10T 29/49115 20150115; H01M 2300/004 20130101 |
Class at
Publication: |
429/231.95 ;
429/224; 429/217; 429/221; 429/223; 429/231.6; 429/231.5;
252/182.1 |
International
Class: |
H01M 4/58 20060101
H01M004/58; H01M 4/62 20060101 H01M004/62 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2004 |
JP |
2004-324339 |
Claims
1. A positive electrode formed from a positive electrode paste
comprising a positive electrode active material represented by the
following general formula (I), a binder ingredient comprising a
water dispersible elastomer and a water soluble polymer as a
viscosity improver, water as a dispersion medium and a dispersing
agent: Li.sub.xMPO.sub.4 (I) (in the general formula (I) above, M
represents a metal atom containing at least one of metal atoms
selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn,
V, Ca, Sr, Ba, Ti, Al, Si, B and Mo, and 0<x<2).
2. A positive electrode according to claim 1, wherein the positive
electrode active material is LiFePO.sub.4.
3. A positive electrode according to claim 1 or 2, wherein the
dispersing agent is one or more of materials selected from the
group consisting of nonionic sufactants, polycarboxylic acid
compounds, compounds having a sulfonic group, and compounds having
a vinyl pyrrolidone structure.
4. A lithium secondary battery having a positive electrode
according to claim 1 or 2, a negative electrode using an active
material capable of intercalating/deintercalating metallic lithium
or lithium ion, and an electrolyte layer.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention concerns a positive electrode for use
in lithium cell and a lithium cell using the same.
[0002] As electrode materials for lithium secondary cell, it is
generally to use carbon compounds such as graphite for a negative
electrode and a composite oxide as an electrode active material for
a positive electrode. Such positive and negative electrodes are
manufactured, for example, by slurryfying an electrode active
material, a binder and a electrically conducting agent such as
conductive carbon used optionally for improving the electron
conductivity with a dispersion medium to prepare a paste or a
coating solution, coating the same to an electrode collector by a
coater and evaporating the dispersion medium.
[0003] An organic dispersion medium such as N-methyl-2-pyrrolidone
has been used as the dispersion medium for manufacturing the
coating solution but it involves a problem of toxicity in the
manufacturing premise, a problem in view of safety, effects of the
dispersion medium wastes on environments, a problem of processing
cost, etc. In view of the above, it has been demanded to use water
which reduces manufacturing cost and does not cause such
problems.
[0004] In the manufacture of the negative electrode, use of water
has been enabled recently as a dispersion medium by using a
synthetic rubber latex type adhesive and a viscosity improver, and
a manufacturing method capable of avoiding the problems described
above has become popular.
[0005] On the other hand, in the manufacture of the positive
electrode, while LiCoO.sub.2 has been widely used generally as the
positive electrode active material, when water is used as the
dispersion medium upon preparing a positive electrode by a positive
electrode paste using LiCoO.sub.2 as the positive electrode active
material, this results in a problem that LiOR, etc. are formed by
reaction of lithium ion in the active material and water to cause
corrosion of a collector and deteriorate the cell performance.
Accordingly, it is still customary at present to use a styrene
butadiene rubber or polyvinylidene fluoride (PVDF) for the binder
and a non-aqueous dispersion medium such as N-methyl-2-pyrrolidone
for the dispersion medium.
[0006] For solving the problem such as corrosion of the collector
and enabling the use of water as the dispersion medium, JP-A No.
2000-294252 describes a positive electrode formed by coating the
surface of a collector with a protective film of an oxalate salt or
a compound of elements selected from silicon, chromiun, and
phosphorus. Further, JP-A No. 2003-157836 proposes to coat the
surface of the positive electrode active material with a protective
film having electroconductivity.
[0007] However, the positive electrodes described above are not
still sufficient in view of the cell performance and since they
require a step of covering the collector, etc., they involve a
problem that they are disadvantageous also in view of the cost.
[0008] On the other hand, the present inventors have noted on
lithium phosphate materials such as LiFePO.sub.4 as the positive
electrode active material use of lithium phosphate in the organic
dispersion medium system as the positive electrode active material
is shown, for example, in JP-T No. 2000-509193, JP-A Nos. 9-134724,
2004-55493, etc.
[0009] When the present inventors have attempted to manufacture of
a positive electrode by using lithium phosphates such as
LiFePO.sub.4 in an aqueous system, it has been found that the
problem of the corrosion for the collector less occurs. However, it
has been found that the positive electrode active material
agglomerates upon preparing the paste, tending to cause unevenness
on the paste coated surface.
[0010] The present invention has been achieved in view of the above
and it intends to provide a positive electrode for use in a lithium
cell excellent both in electric characteristics and physical
properties and a lithium cell using the same, by manufacture from
an aqueous coating solution using safe water as a dispersion medium
instead of organic dispersion media used so far thereby solving the
problem of toxicity in the manufacturing premise, the problem of
safety, and the problem of the effects of dispersion medium wastes
on environments and the problem of the processing cost, as well as
solving the problem of degradation of the cell performance caused
by corrosion etc. of collectors and the problem for the occurrence
of unevenness on the coated surface,
SUMMARY OF THE INVENTION
[0011] In order to solve the foregoing subject, the positive
electrode for use in the lithium cell according to the present
invention is formed from a positive electrode paste containing a
positive electrode active material represented by the following
formula (I), a binder ingredient comprising a water dispersible
elastomer and a water soluble polymer as a viscosity improver,
water as a dispersion medium, and a dispersing agent:
Li.sub.xMPO.sub.4 (I) (in the general formula (I) above, M
represents a metal atom containing at least one of metal atoms
selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn,
V, Ca, Sr, Ba, Ti, Al, Si, B and Mo, and 0<x<2).
[0012] The "dispersion medium" used herein is a material for
dispersing the constituent ingredients of the positive electrode
paste and it includes those dissolving a portion of the constituent
ingredients, that is, functioning also as a solvent.
[0013] A preferred example of the positive electrode active
material includes LiFePO.sub.4.
[0014] As the dispersing agent, one or more of materials selected
from the group consisting of nonionic surfactants, polycarboxylic
acid compounds, compounds having sulfonic acid groups, and
compounds having vinyl pyrrolidone structure can be used
suitably.
[0015] The lithium secondary cell according to the invention has a
positive electrode of the invention described above, a negative
electrode using an active material capable of
intercalating/deintercalating metal lithium or lithium ion, and an
electrolyte layer.
[0016] In the invention, since a lithium phosphate compound such as
LiFePO.sub.4 is used as the positive electrode active material and
a specified positive electrode material composition containing a
dispersing agent is adopted, even in a case where water is used as
a dispersion medium in the positive electrode preparing step,
corrosion of a collector less occurs and the problem of degrading
the cell performance can be overcome without covering the collector
differently from the prior art, and the problem for the occurrence
of unevenness during paste coating can also be overcome. Further,
the lithium phosphate compound is an active material capable of
solving the problems in view of the resource, cost and safety of
existent electrode active materials, being inexpensive and having
high safety. Accordingly, a positive electrode for use in a lithium
cell having high thermal stability as the cell characteristics and
also excellent in the rate characteristic and the cycle
characteristic can be provided at a reduce cost.
[0017] That is, according to the invention, a lithium cell of high
performance can be provided, as well as an effect in view of the
manufacture capable of using safe water instead of organic
dispersion media having high risk and involving various problems in
view of handling can be obtained and it is also advantageous in
view of the raw material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1(a) is a graph showing the result of a rate
characteristic test at 10.2 C, 1 C, 3 C, and 5 C for beaker cells
of Example 1;
[0019] FIG. 1(b) is a graph showing the result of a rate
characteristic test at 0.2 C, 1 C, 3 C, and 5 C for beaker cells of
Comparative Example 1;
[0020] FIG. 1(c) is a graph showing the result of a rate
characteristic test at 0.2 C, 1C, 3 C, and 5 C for beaker cells of
Comparative Example 2;
[0021] FIG. 2(a) is a graph showing the result of a cycle
characteristic test at IC charge/discharge for beaker cells of
Example 1;
[0022] FIG. 2(b) is a graph showing the result of a cycle
characteristic test at IC charge/discharge for beaker cells of
Comparative Example 1; and
[0023] FIG. 2(c) is a graph showing the result of a cycle
characteristic test at IC charge/discharge for beaker cells of
Comparative Example 2.
DESCRIPTION OF PREFERRED EMBODIMENTS
1. Positive Electrode
[0024] The positive electrode active material used as a positive
electrode for use in a lithium secondary cell according to the
invention is represented by the following formula (I):
Li.sub.xMPO.sub.4 (I) (in the general formula (I) above, M
represents metal species containing at least one of metal atoms
selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn,
V, Ca, Sr, Ba, Ti, Al, Si, B and Mo, and 0<x<2). Among them
those containing Fe for M are preferred and LiFePO.sub.4 is
particularly preferred.
[0025] Olivine type LiFePO.sub.4 has a theoretical capacitance as
high as 170 mAh/g and is inexpensive, and can greatly save the cell
manufacturing cost. Further it also has excellent properties as the
positive electrode material such as showing scarce toxicity to
human bodies or environments, causing less oxygen deintercalation
and having high thermal stability.
[0026] The starting material for the positive electrode active
material includes, for example, Li salts such as LiOH,
Li.sub.2CO.sub.3, CH.sub.3COOLi, and LiCl as the Li source, Fe
salts such as FeC.sub.2O.sub.4, (CH.sub.3COO).sub.2Fe, FeCl.sub.2,
and FeBr.sub.2 as the Fe source, Mn salts such as MnCl.sub.2 as the
Mn source, Ni salt such as NiCl as the Ni source, and
Co.sub.3O.sub.4 as the Co source.
[0027] Also in a case where M is other elements, metal salts for
each of the elements can be used.
[0028] For the P source, H.sub.3PO.sub.4,
(NH.sub.4).sub.2HPO.sub.4, NH.sub.4H.sub.2PO.sub.4, etc. can be
used.
[0029] The positive electrode active material can be obtained
usually by blending the starting materials at an aimed molar ratio
and sintering them at a high temperature.
[0030] While the grain size of the positive electrode active
material is not particularly limited, the average grain size of
primary particles is usually about from 10 nm to 100 .mu.m and 30
to 250 nm of grain size is preferred and 60 to 200 nm grain size is
more preferred in that the electron conductivity is favorable.
[0031] While lithium phosphate compound may be used as it is, a
positive electrode active material of low conductivity such as
LiFePO.sub.4 may be compensated for electron conductivity by
coating the surface of particles with carbon. The coating amount of
carbon is, preferably, 1 part by weight or more and 20 parts by
weight or less and, most preferably, 1 part by weight or more and
10 parts by weight or less based on 100 parts by weight of the
positive electrode active material.
[0032] Examples of the elastomer usable in the invention include a
copolymer of acrylonitrile and butadiene (NBR), a copolymer of
acrylonitrile and hydrogenated butadiene (HNBR), a copolymer of
styrene ad butadiene (SBR), a copolymer of styrene and
acrylonitrile (SAN), a terpolymer of acrylonitrile, butadiene and
styrene (ABS), a terpolymer of styrene, acrylonitrile and styrene
(SAS), a terpolymer of styrene, isoprene and styrene (SIS), a
terpolymer of styrene, butadiene and styrene (SBS), a terpolymer of
ethylene, propylene and diene (EPDM)), a
styrene/ethylene/butene/styrene (SEES) polymer, a polyurethane
elastomer, polychloroprene (CR) or 2-chloro-1,3-butadiene,
polyisobutylene (PIB), polyisoprene, polybutadiene, an
ethylene/propylene copolymer (EPR), a copolymer of ethylene and
vinyl acetate (EVA), a copolymer of ethylene and acrylate ester
(EMA, EEA, etc.), a vinyl pyrrolidone/vinyl acetate copolymer, and
mixtures thereof. The polymers may have a cross-linked
structure.
[0033] Among the elastomers described above, the styrene butadiene
copolymer (SBR) and an acrylonitrile butadiene copolymer (NBR) are
preferred, SBER being particularly preferred.
[0034] As the water soluble polymer, one or more members selected
from celluloses such as carboxymethyl cellulose (CMC), methyl
cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl
methyl cellulose, and hydroxyethyl methyl cellulose; polycarboxylic
acid compounds such as polyacrylic acid, and sodium polyacrylate;
compounds having a vinyl pyrrolidone structure such as polyvinyl
pyrrolidone; polyacrylamide, polyethylene oxide, polyvinyl alcohol,
sodium alginate, xanthane gum, carrageenan, guar gum, agar, and
starch can be used, and among them, carboxymethyl cellulose salt is
preferred.
[0035] In a case where the water soluble polymer is a carboxymethyl
cellulose salt, the etherification degree thereof is preferably
from 0.3 to 2.0, particularly preferably, from 0.45 to 1 in view of
solubility to water, storage stability and manufacturing cost.
[0036] In a case of using the dispersible elastomer and the water
soluble polymer are used for the positive electrode, the same
combination can be applied for the negative electrode to provide an
advantage that the same material can be used for both
electrodes.
[0037] As the water, distilled water, ion-exchanged water, and
superpure water are preferred, and the ionic conductivity thereof
is preferably 0.5 mS/m or less, more preferably, 0.1 mS/m or less,
and organic carbon is, preferably, 100 .mu.g C/L or less, more
preferably, 50 .mu.g C/L or less, zinc is, preferably, 0.5 .mu.g
Zn/L or less, more preferably, 0.1 .mu.g C/L or less, silica is
preferably 50 .mu.g SiO.sub.2/L or less, more preferably, 2.5 .mu.g
SiO.sub.2/L or less, chloride ions are preferably, 10 .mu.g
Cl.sup.-/L or less, more preferably, 1 .mu.g Cl.sup.-/L, and
sulfate ions are, preferably 10 .mu.g SO.sub.4.sup.-2/L or less
and, more preferably, 1 .mu.g SO.sub.4.sup.-2/L or less.
[0038] In the invention, use of the dispersing agent can prevent
agglomeration of particles and makes the coating of the active
material layer smooth upon manufacture of the positive
electrode.
[0039] Examples of the dispersing agent include nonionic
surfactants such as polyoxyethylene tridecylether, polyoxyethylene
branched decyl ether, polyoxyethylene isodecyl ether,
polyoxyethylene lauryl ether, polyoxyalkylene lauryl ether,
polyoxyethylene oleylether, polyoxyethylene alkyl ether,
polyoxyethylene styrenated phenyl ether, polyoxyethylene castor
oil, polyoxyethylene hardened castor oil, polyoxyethylene oleate
ester, polyoxyethylene distearate ester, polyoxyethylene polyoxy
propylene block polymer, sorbitan trioleate, sorbitan sesquioleate,
sorbitan monooleate, sorbitan inonostearate, sorbitan mono coconut
fatty acid ester, polyoxyethylene sorbitan mono coconut fatty acid
ester, polyoxyethylene sorbitan monostearate, polyoxyethylene
sorbitan monostearate, polyoxyethylene sorbitan monooleate,
polyoxyethylene lanolin alcohol ether, polyoxyethylene lanoline
fatty acid ester, polyoxyethylene alkyl amine ether, coconut fatty
acid diethanolamide, acetylene glycol, acetylene alcohol, acetylene
glycol alkylene oxide adduct, acetylene alcohol alkylene oxide
adduct; compounds having a sulfonic acid group such as aromatic
sulfonic acid formalin condensation products such as sodium
.beta.-naphthalene sulfate formalin condensation products, special
sodium aromatic sulfate formalin condensation products, sodium
alkyl naphthalene sulfonate formalin condensation products, and
sodium polystyrene sulfonate, and sodium lignine sulfonate;
polycarboxylic acid compounds such as ammonium polycarboxylate
salts, sodium polycarboxylate salts, polyoxyethylene alkyl ether
sulfate salts, polyacrylic acid, and sodium polyacrylate; compounds
having a vinyl pyrrolidone structure such as polyvinyl pyrolidone
and a copolymer of vinyl pyrrolidone and acrylic acid; and anionic
surfactants such as polyoxyethylene alkyl ether, and among them,
the nonionic surfactants, polycarboxylic acid compounds, compounds
having a sulfonic acid group and compounds having a vinyl
pyrrolidone structure are particularly preferred one or more
dispersing agents may be used in combination.
[0040] The blending ratio of the positive electrode active
material, water dispersible elastomer, water soluble polymer,
dispersing agent and water, as a ratio based on 100 parts by weight
of the positive electrode active material (as solids) is as
follows. The elastomer is, preferably, 0.5 part by weight or more
and 12 parts by weight or less, more preferably, 1 part by weight
or more and 6 parts by weight or less. The water soluble polymer,
is preferably, 0.1 part by weight or more and 12 parts by weight or
less, more preferably, 0.5 part by weight or more and 4 parts by
weight or less. The dispersing agent is, preferably, 0.05 part by
weight or more and 10 parts by weight or less, more preferably, 0.2
part by weight or more and 5 parts by weight or less. Water is,
preferably, 20% by weight or more and 95% by weight or less, more
preferably, 40 parts by weight or more and 70% by weight or less in
the paste.
[0041] In order to enhance the dispersing effect, an organic
dispersion medium such as N-methyl-2-pyrrolidone, acetonitrile,
methanol, ethanol, and isopropyl alcohol may be incorporated at the
ratio of 20% by weight or less in the dispersion medium component
within a range not departing the purpose object of the
invention.
[0042] As an ingredient other than those described above, an
electrically conducting agent may be added in order to enhance
electroconductivity, and one or more carbonaceous materials such as
carbon black, acetylene black and graphite which has been used so
fat for the positive electrode can be used.
[0043] The positive electrode of the invention is manufactured by
preparing a paste-like positive electrode material by mixing each
of the ingredients described above, coating the same to an aluminum
foil or the like to be a collector and evaporating the dispersion
medium. It is preferred that the elastomer is prepared into an
emulsion, and the water soluble polymer is previously prepared into
an aqueous solution of about from 0.5 to 10%.
[0044] The method, the order, and the like of mixing each of the
ingredients described above are not particularly limited, and for
example, the active material and the electrically conducting agent
can be used while being mixed previously. For the mixing in this
case, a mortar, a mill mixer, a ball mill such as a planetary ball
mill or a shaker type ball mill, mechanotusion or the like can be
used. Also the method for the addition of the dispersing agent is
also not particularly restricted, and it can be used as an aqueous
solution at a concentration of 0.5% by weight or more or can be
used as it is. In addition, the electrically conducting agent can
be used in a state of a liquid electrifying dispersion in which the
electrically conducting agent is previously dispersed in an aqueous
solution of the dispersing agent.
2. Lithium Secondary Battery
[0045] The lithium secondary battery of the invention is composed
of the positive electrode, the negative electrode and the
electrolyte layer for the lithium secondary battery of the
invention.
[0046] The negative electrode is preferably capable of
intercalating/deintercalating metalic lithium or lithium ions, and
the material constitution is not particularly limited but known
materials can be used.
[0047] As a specific example, a negative electrode prepared by
coating a material obtained by mixing a negative electrode active
material and a binder to a collector can be used.
[0048] As the negative active material, known active materials can
be used with no particular restriction. For example, carbon
materials such as natural graphite, artificial graphite, less
graphitizing carbon, easily graphitizing carbon, metal materials
such as metallic or alloyed lithium, or tin compounds, lithium
transition metal nitrides, crystalline metal oxides, amorphous
metal oxides and electroconductive polymers can be used.
[0049] As the binder, organic or inorganic binders can be used, and
for example, all of aqueous dispersible elastomers mentioned as
those usable for the positive electrode such as polyvinylidene
fluoride and styrene butadiene copolymers, and water soluble
polymers as a viscosity improver can be used.
[0050] As a collector for the negative electrode, for example,
copper, nickel and the like fabricated in the form of a mesh,
punched metal, expanded metal or a planar shaped foil can be
used.
[0051] The electrolyte layer is a layer put between the positive
electrode and the negative electrode, which is a layer containing
an electrolyte solution or a polymer having an electrolyte salt
dissolved therein or a polymeric gel electrolyte. In a case of
using the electrolyte solution or the polymeric gel electrolyte, it
is preferred to use a separator in combination.
[0052] The electrolyte may be an electrolyte which is used in
ordinary lithium secondary batteries, and comprises an electrolyte
salt and a non-aqueous medium.
[0053] The electrolytic salt includes, for example, LiPF.sub.6,
LiBF.sub.4, LiClO.sub.4, LiAsF.sub.6, LiCl, LiBr,
LiCF.sub.3SO.sub.3, LiN(CF.sub.3SO.sub.2).sub.2,
LiC(CF.sub.3SO.sub.2).sub.3, LiI, LiAlCl.sub.4, NaClO.sub.4,
NaBF.sub.4, NaI, and the like, and particularly includes inorganic
lithium salts such as LiPF.sub.6, LiBF.sub.4, LiClO.sub.4,
LiAsF.sub.6, and organic lithium salts represented by
LiN(SO.sub.2C.sub.xF.sub.2x+1)(SO.sub.2C.sub.yF.sub.2y+1), in which
x and y each represents 0 or an integer of from 1 to 4, and x+y is
from 2 to 8.
[0054] The organic lithium salt includes, specifically,
LiN(SO.sub.2F).sub.2, LiN
(SO.sub.2CF.sub.3)(SO.sub.2C.sub.2F.sub.5) ,
LiN(SO.sub.2CF.sub.3)(SO.sub.2C.sub.3F.sub.7),
LiN(SO.sub.2C.sub.4F.sub.3)(SO.sub.2C.sub.4F.sub.9),
LiN(SO.sub.2C.sub.2F.sub.5).sub.2,
LiN(SO.sub.2C.sub.2F.sub.5)(SO.sub.2C.sub.3F.sub.7),
LiN(SO.sub.2C.sub.2F.sub.5)(SO.sub.2C.sub.4F.sub.9), etc.
[0055] Among them, LiPF.sub.6, LiBF.sub.4, LiN
(CF.sub.3SO.sub.2).sub.2, LiN(SO.sub.2F).sub.2,
LiN(SO.sub.2C.sub.2F.sub.5).sub.2, etc, are preferably used as the
electrolyte since they are excellent in electric
characteristics.
[0056] One or more kinds of electrolyte salts may be used.
[0057] The organic solvent in which the electrolyte salt is
dissolved is not particularly restricted so long as it is an
organic solvent to be used for a non-aqueous electrolyte solution
of ordinary lithium secondary batteries, and includes, for example,
carbonate compounds, lactone compounds, ether compounds, sulfolane
compounds, dioxolane compounds, ketone compounds, nitrile compounds
and halogenated hydrocarbon compounds. They specifically include
carbonates such as dimethyl carbonate, methyl ethyl carbonate,
diethylcarbonate, ethylene carbonate, propylene carbonate, ethylene
glycol dimethylcarbonate, propylene glycol dimethyl carbonate,
ethylene glycol diethyl carbonate, and vinylene carbonate, lactones
such as .gamma.-butyrolactone, ethers such as dimethoxyethane,
tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, and
1,4-dioxane, sulfolans such as sulfolane and 3-methyl sulfolane,
dioxolanes such as 1,3-dioxolane, ketones such as
4-methyl-2-pentanone, nitrites such as acetonitrile, propionitrile,
valeronitrile, benzonitrile, halogenated hydrocarbons such as
1,2-dichloroethane, and other ionic liquids such as methyl formate,
dimethyl formamide, diethyl tormamide, dimethyl sulfoxide,
imidazolium salts, and quaternary ammonium. Further mixtures
thereof may also be used.
[0058] Among the organic solvents described above, it is
particularly preferred that one or more kinds of non-aqueous media
selected from carbonates are contained since they provide excellent
solubility, dielectric constant and viscosity of the
electrolyte.
[0059] The polymeric compounds to be used for the polymeric
electrolyte or the polymeric gel electrolyte include, for example,
polymers such as of ether, ester, siloxane, acrylonitrile,
vinylidene fluoride, hexafluoropropylene, acrylate, methacrylate,
styrene, vinyl acetate, vinyl chloride, and oxetane or polymeric
materials having a copolymer structure thereof or a cross-linked
product thereof, and one or more polymeric materials may be used.
The polymeric structure is not particularly restricted, and,
polymeric materials having an ether structure such as polyethylene
oxide are particularly preferred.
[0060] The electrolyte is contained in a battery container, as a
liquid electrolyte in liquid-type batteries, as a precursor
solution having a polymer dissolved in the liquid electrolyte in
gel-type batteries, and as a polymer before cross-linking having an
electrolyte salt dissolved therein in solid electrolyte-type
batteries.
[0061] Also for the separator, separators used for ordinary lithium
secondary batteries can be used with no particular restriction, and
for example, porous resins and non-woven fabrics made, for example,
of polyethylene, polypropylene, polyolefin or
polytetrafluoroethylene can be used.
[0062] Examples of the invention will be described below, but the
invention is not limited to the following examples.
EXAMPLE 1
[0063] 100 g of LiFePO.sub.4 with 5% by weight of a carbon coating
amount as a positive electrode active material, 10 g of acetylene
black (manufactured by Denki Kagaku Kogyo Co.) as an electrically
conducting agent, 120 g of an aqueous 2 wt % solution of
carboxynethyl cellulose with an etherfying degree of from 0.45 to
0.55 (CELOGEN PL-15, manufactured by Daiichi Kogyo Seiyaku Co.) as
a viscosity improver, and 0.5 g of a nonionic surfactant having a
polyoxyethylene styrenated phenyl ether structure (trade name of
products: NOIGEN EA-137, manufactured by Daiichi Kogyo Seiyaku Co.)
as a dispersing agent were mixed by a homo-mixer for 30 min. 10 g
of an aqueous 40 wt % solution of the SBR emulsion (trade name of
products: MB-400B, manufactured by Nippon Zeon Co.) as a binder and
50 g of water as a dispersion medium were added to the mixed
solution, stirred by a homo-mixer for 15 min and, further, mixed by
a ball mill for 6 hours, to prepare a positive electrode paste.
[0064] The positive electrode paste was coated to an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0065] For the thus prepared positive electrode, it was visually
observed whether agglomerates of 0.5 mm diameter or more were
present or not in the active material layer.
[0066] Further, a charge/discharge test was conducted by using the
obtained positive electrode in a 2-electrode type beaker cell.
Metallic lithium was used for the negative electrode, and an
LiPF.sub.6 solution (1 mol/L) with a solvent of ethylene carbonate
(EC)/.gamma.-butyrolactone (GBL)/ethyl methyl carbonate (EMC)=3/2/5
(by volume ratio) is used as an electrolyte.
[0067] The test cell was charged/discharge for one cycle at 0.25
mAh/g, and the discharge capacitance was defined as an effective
capacitance. In the cycle test, the effective capacitance was
defined as 1 C for identical cell. Using the same cell, a test was
conducted for 200 cycles under the condition for charge discharge
at 1 C, and the retention ratio of the discharge capacitance at 200
cycle was determined based on the discharge capacitance at the
initial 1 C discharge in the cycle test as the standard
capacitance. The voltage was 4.0 V to 2.0 V and the temperature was
at 20.degree. C.
[0068] Table 1 shows the result of observation for the active
material layer, the effective capacitance, and the capacitance
retention ratio after 200 cycles.
EXAMPLE 2
[0069] 100 g of LiFePO.sub.4 with 2% by weight of a carbon coating
amount as a positive electrode active material, 6 g of acetylene
black (manufactured by Denki Kagaku Kogyo Co.) as an electrically
conducting agent, 100 g of an aqueous 2 wt % solution of
carboxymethyl cellulose with etherfying degree from 0.6 to 0.7
(CELOGEN WS-C, trade name of products, manufactured by Daiichi
Kogyo Seiyaku Co.) and 1 g of a nonionic surfactant of a
polyoxyethylene styrenated phenyl ether structure as a dispersing
agent (NOIGEN EA-187, trade name of products manufactured by
Daiichi Kogyo Seiyaku Co.) were mixed by a homo-mixer for 30 min. 5
g of a 40 wt % solution of an SBR einulsion (BM-400B, trade name of
products manufactured by Nippon Zeon Co.) as a binder, and 50 g of
water as a dispersion medium were added to the mixed solution,
stirred by a homo-mixer for 15 min and, further mixed by a ball
mill for 6 hours, to obtain a positive electrode paste.
[0070] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0071] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode.
EXAMPLE 3
[0072] 100 g of LiCoPO.sub.4 with 5% by weight of a carbon coating
amount as a positive electrode active material, 3 g of carbon black
(trade name of products: Ketchen Black EC, manufactured by AKZO
NOBEL Co.) as an electrically conducting agent, 100 g of an aqueous
1 wt % solution of carboxyrethyl cellulose with an etherfying
degree of from 0.55 to 0.65 (CELOGEN 3H, manufactured by Daiichi
Kogyo Seiyaku Co.) as a viscosity improver, and 2 g of a sodium
naphthalene sulfonate formalin condensation product (trade name of
products: Lavelin FM-P, Daiuchi Kogyo Seiyaku Co.) as a dispersing
agent were mixed by a homo-mixer for 30 min. 7.5 g of an aqueous 40
wt % solution of an SBR emulsion (trade name of products: BM-400B,
manufactured by Nippon Zeon Co.) as a binder and 50 g of water as a
dispersion medium were added to the mixed solution, stirred by a
homo-mixer for 15 min and, further, mixed by a ball mill for 6
hours, to prepare a positive electrode paste.
[0073] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0074] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode, and an
LiBF.sub.4 solution (2 mol/L) with a solvent of ethylene carbonate
(EC)/.gamma.-butyrolactone (GBL)=3/7 (volume ratio) as an
electrolyte.
EXAMPLE 4
[0075] 100 g of LiFePO.sub.4 with 3% by weight of a carbon coating
amount as a positive electrode active material, 3 g of carbon black
(trade name of products: Kenchen Black EC, manufactured by AKZO
NOBEL Co.) as an electrically conducting agent, 90 g of an aqueous
1 wt % solution of carboxymethyl cellulose with an etherfying
degree of from 1.15 to 1.45 (CELOGEN HE-1500F, manufactured by
Daiichi Kogyo Seiyaku Co.) as a viscosity improver, and 0.4 g of
polycarboxylic acid (trade name of products: POLITY 335S,
manufactured by Lion Corp.) as a dispersing agent were mixed by a
homo-mixer for 30 min. 7.5 g of an aqueous 40 wt % solution of an
acrylonitrile butadiene emulsion (trade name of products: BM-400B,
manufactured by Nippon Zeon Co.) as a binder and 50 g of water as a
dispersion medium were added to the mixed solution, stirred by a
homo-mixer for 15 min and, further, mixed by a ball mill for 6
hours, to prepare a positive electrode paste.
[0076] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0077] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode, and a
solution of LiN(CF.sub.3SO.sub.2).sub.2 (0.5 mol/L) and
LiN(SO2F).sub.2 (1 mol/L) with a solvent of ethylene carbonate
(EC)/.gamma.-butyrolacton (GBL)/propylene carbonate (PC)=2/2/6
(volume ratio) as an electrolyte.
EXAMPLE 5
[0078] 100 g of LiFePO.sub.4 as a positive electrode active
material, 10 g of acetylene black (manufactured by Denki Kagaku
Kogyo Co.) as an electrically conducting agent, 100 g of an aqueous
2 wt % solution of hydroxypropyl methylcellulose as a viscosity
improver, and 1 g of a non-ionic surfactant of a polyoxyethylene
styrenated phenylether structure (trade name of products: NOIGEN
EA-187 manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing
agent were mixed by a homo-mixer for 30 min. 10 g of an aqueous 40
wt % solution of an SBR emulsion (trade name of products: BM-400B,
manufactured by Nippon Zeon Co.) as a binder and 50 g of water as a
dispersion medium were added to the mixed solution, stirred by a
homo-mixer for 15 min and, further, mixed by a ball mill for 6
hours, to prepare a positive electrode paste.
[0079] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0080] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode, and a
solution of LiPF.sub.4 (1 Mol/L) with a solvent of ethylene
carbonate (EC)/.gamma.-butyrolactone (GEL)/ethylmethyl carbonate
(EMC) 3/3/4 (volume ratio) as an electrolyte.
EXAMPLE 6
[0081] 100 g of LiFe.sub.0.25Ti.sub.0.75PO.sub.4 with 5% by weight
of a carbon coating amount as a positive electrode active material,
6 g of acetylene black (manufactured by Denki Kagaku Kogyo Co.) as
an electrically conducting agent, 70 g of an aqueous 0.5 wt %
solution of carboxymethyl cellulose with an etherfying degree of
from 0.65 to 0.75 (CELOGEN BSH-12, manufactured by Daiichi Kogyo
Seiyaku Co.) as a viscosity improver, and 0.8 g of an anionic
surfactant (trade name of products: Hitenol NE-05, manufactured by
Daiichi Kogyo Seiyaku Co.) as a dispersing agent were mixed by a
homo-mixer for 30 min. 8 g of an aqueous 40 wt % solution of an SBR
emulsion (trade name of products: BM-400B, manufactured by Nippon
zeon Co.) as a binder and 50 g of water as a dispersion medium were
added to the mixed solution, stirred by a homo-mixer for 15 min
and, further, mixed by a ball mill for 6 hours, to prepare a
positive electrode paste.
[0082] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0083] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode, and a
solution of LiBF.sub.4 (1.5 mol/L) with a solvent of ethylene
carbonate (EC)/.gamma.-butyrolacton (GBL)/dimethyl carbonate
(DMC)=3/6/1 (volume ratio) as an electrolyte.
EXAMPLE 7
[0084] 100 g of LiFePO.sub.4 with 2% by weight of a carbon coating
amount as a positive electrode active material, 6 g of acetylene
black (manufactured by Denki Kagaku Kogyo Co.) as an electrically
conducting agent, 100 g of an aqueous 2 wt % solution of
carboxymethyl cellulose with an etherfying degree of from 0.6 to
0.7 (CELOGEN WS-C, manufactured by Daiichi Kogyo Seiyaku Co.) as a
viscosity improver, and 3 g of an aqueous 10% solution of polyvinyl
pyrrolidone (trade name of products: PITZCOL K-30, manufactured by
Daiichi Kogyo Seiyaku Co.) as a dispersing agent were mixed by a
homo-mixer for 30 min. 10 g of an aqueous 40 wt % solution of an
SBR emulsion (trade name of products: BM-400B, manufactured by
Nippon Zeon Co.) as a binder and 50 g of water as a dispersion
medium were added to the mixed solution, stirred by a homo-mixer
for 15 min and, further, mixed by a ball mill for 6 hours, to
prepare a positive electrode paste.
[0085] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0086] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode, and a
solution of LiN(CF.sub.3SO.sub.2).sub.2 (1 mol/L) with a solvent of
ethylene carbonate (EC)/.gamma.-butyrolacton (GBL)/diethyl
carbonate (DEC)=4/3/3 (volume ratio) as an electrolyte
EXAMPLE 8
[0087] 100 g of LiFe.sub.0.5Mn.sub.0.5PO.sub.4 with 2% by weight of
a carbon coating amount as a positive electrode active material, 6
g of acetylene black (manufactured by Denki Kagaku Kogyo Co.) as an
electrically conducting agent, 100 g of an aqueous 2 wt % solution
of carboxymethyl cellulose with an etherfying degree of from 0.6 to
0.7 (CELOGEN WS-C, manufactured by Daiichi Kogyo Seiyaku Co.) as a
viscosity improver, and 1 g of a nonionic surfactant having a
polyoxyethylene styrenated phenol ether structure (trade name of
products: NOIGEN EA-187, manufactured by Daiichi Kogyo Seiyaku Co.)
as a dispersing agent were mixed by a homo-mixer for 30 min. 3 g of
an aqueous 40% solution of an SBR emulsion (trade name of products:
BM-400B, manufactured by Nippon zeon Co.) as a binder, 2g of a 40
wt % solution of an acrylic emulsion, and 50 g of water as a
dispersion medium were added to the mixed solution, stirred by a
homo-mixer for 15 min and, further, mixed by a ball mill for 6
hours, to prepare a positive electrode paste.
[0088] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0089] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode, and a
solution of LiPF.sub.6 (1 mol/L) with a solvent of ethylene
carbonate (EC)/.gamma.-butyrolacton (GBL)/ethyl methyl carbonate
(EMC)=3/5/2 (volume ratio) as an electrolyte.
EXAMPLE 9
[0090] 100 g of LiFePO.sub.4 with 2% by weight of a carbon coating
amount as a positive electrode active material, 6 g of acetylene
black (manufactured by Denki Kagaku Kogyo Co.) as an electrically
conducting agent, 100 g of an aqueous 2 wt % solution of methyl
cellulose (trade name of products: SM-400, manufactured by
Shin-etsu Chemical Co.) as a viscosity improver, and 0.5 g of a
nonionic surfactant (trade name of products: NOIGEN EA-187,
manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing agent
were mixed by a homo-mixer for 30 min. 5 g of an aqueous 40%
solution of SBR emulsion (trade name of products: BM-400B,
manufactured by Nippon zeon Co.) as a binder, and 50 g of water as
a dispersion medium were added to the mixed solution, stirred by a
homo-mixer for 15 min and, further, mixed by a ball mill for 6
hours, to prepare a positive electrode paste.
[0091] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0092] A gel electrolyte was used for the electrolyte layer. For
the preparation of the gel electrolyte, tri-functional polyether
acrylate (trade name of products. ELEXEL TA-140) manufactured by
Daiichi Kogyo Seiyaku Co.) as a polymer ingredient and a solution
of LiBF.sub.4 (2 mol/L) with a solvent of ethylene carbonate
(EC)/.gamma.-butyrolactone (GBL)/ethylmethyl carbonate (EMC)=3/6/l
(volume ratio) as an electrolyte solution were used at 5:95(weight
ratio) Further, 2000 ppm of an organic peroxide (trade name of
products: PARKDOX 16 manufactured by Kayaku Akuzo Corp.) was added
as a heat polymerization initiator to obtain a precursor solution.
The precursor solution was poured into a beaker cell in which the
positive electrode and the negative electrode were previously
prepared, to conduct heat polymerization at 80.degree. C. for 1
hour to obtain an electrolyte.
[0093] Evaluation was conducted in the same manner as in Example 1
except for using the obtained positive electrode and the gel
electrolyte.
EXAMPLE 10
[0094] 100 g of LiFePO.sub.4 with 2% by weight of a carbon coating
amount as a positive electrode active material, 6 g of acetylene
black (manufactured by Denki Kagaku Kogyo Co.) as an electrically
conducting agent, 100 g of an aqueous 2 wt % solution of carboxyl
methyl cellulose with an etherifying degree of from 0.6 to 0.7
(trade name of products: CELOGEN WS-C, manufactured by Daiichi
Kogyo Seiyaku Co.) as a viscosity improver, and 0.2 g of a nonionic
surfactant having a polyoxyethylene styrenated phenol ether
structure (trade name of products: NOIGEN EA-187, manufactured by
Daiichi Kogyo Seiyaku Co.) as a dispersing agent were mixed by a
homo-mixer for 30 min. 5 g of an aqueous 40% solution of an SBR
emulsion (trade name of products: BM-400B, manufactured by Nippon
Zeon Co.) as a binder, and 50 g of water as a dispersion medium
were added to the mixed solution, stirred by a homo-mixer for 15
min and, further, mixed by a ball mill for 6 hours, to prepare a
positive electrode paste.
[0095] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0096] 100 g of graphite as a negative electrode active material, 2
g of acetylene black as an electrically conducting agent, 100 g of
an aqueous 2 wt % solution of carboxymethyl cellulose (CELOGEN
WS-C, trade name of products, manufactured by Daiichi Kogyo Seiyaku
Co.) as a viscosity improver were mixed by a homo-mixer for 30 min.
5 g of a 40 wt % solution of an SBR emulsion (BM-400B, trade name
of products manufactured by Nippon Zeon Co.) as a binder, and 50 g
of water as a dispersion medium were added to the mixed solution,
stirred by a homo-mixer for 15 min and, further mixed by a ball
mill for 16 hours, to obtain a negative electrode paste.
[0097] The negative electrode paste was coated on a copper foil as
a collector by an applicator and dried at 100.degree. C. to obtain
a negative electrode.
[0098] Tests were conducted in the same manner as in Example 1
except for using the thus obtained positive electrode, and the
negative electrode, and a solution of LiB.sub.4 (1.5 mol/L) with a
solvent of ethylene carbonate (EC)/.gamma.-butyrolacton (GBL)/ethyl
methyl carbonate (EMC)=5/4/1 (volume ratio) as an electrolyte.
EXAMPLE 11
[0099] 100 g of LiFe.sub.0.25Mo.sub.0.75PO.sub.4 with 3% by weight
of a carbon coating amount as a positive electrode active material,
10 g of acetylene black (manufactured by Denki Kagaku Kogyo Co.) as
an electrically conducting agent, 100 g of an aqueous 2 wt %
solution of hydroxypropyl methyl cellulose as a viscosity improver,
and 1 g of a nonionic surfactant having a polyoxyethylene
styrenated phenyl ether structure (trade name of products: NOIGEN
EA-187, manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing
agent were mixed by a homo-mixer for 30 min. 10 g of an aqueous 40%
solution of an SBR emulsion (trade name of products: BM-400B,
manufactured by Nippon zeon Co.) as a binder, and 50 g of water as
a dispersion medium were added to the mixed solution, stirred by a
homo-mixer for 15 min and, further, mixed by a ball mill for 6
hours, to prepare a positive electrode paste.
[0100] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0101] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode, and a
solution of LiBF.sub.4 (1 mol/L) with a solvent of ethylene
carbonate (EC)/.gamma.-butyrolactone (GBL)/ethyl methyl carbonate
(EMC)=3/5/2 (volume ratio) as an electrolyte.
EXAMPLE 12
[0102] 100 g of LiFe.sub.0.3Al.sub.0.7PO.sub.4 with 2% by weight of
a carbon coating amount as a positive electrode active material, 10
g of acetylene black (manufactured by Denki Kagaku Kogyo Co.) as an
electrically conducting agent, 70 g of an aqueous 1 wt % solution
of hydroxyethyl methyl cellulose as a viscosity improver, and 1 g
of a nonionic surfactant having a polyoxyethylene styrenated phenyl
ether structure (trade name of products: NOIGEN EA-187,
manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing agent
were mixed by a homo-mixer for 30 min. 8 g of an aqueous 40%
solution of an SBR emulsion (trade name of products: BM-400B,
manufactured by Nippon Zeon Co.) and 2 g of a 40 wt % vinyl acetate
emulsion as a binder, and 50 g of water as a dispersion medium were
added to the mixed solution, stirred by a homo-mixer for 15 min
and, further, mixed by a ball mill for 6 hours, to prepare a
positive electrode paste.
[0103] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0104] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode, and a
solution of LiBF.sub.4 (1.5 mol/L) with a solvent of ethylene
carbonate (EC)/.gamma.-butyrolactone (GBL)/ethyl methyl carbonate
(EMC)w-3/6/1 (volume ratio) as an electrolyte.
EXAMPLE 13
[0105] 100 g of LiFePO.sub.4 with 5% by weight of a carbon coating
amount as a positive electrode active material, 10 g of acetylene
black (trade name of products: Denka Black, manufactured by Denki
Kagaku Kogyo Co.) as an electrically conducting agent, 100 g of an
aqueous 2 wt % solution of carboxymethyl cellulose with an
etherifying degree of from 0.6 to 0.7 (CELOGEN WS-C, manufactured
by Daiichi Kogyo Seiyaku Co.) as a viscosity improver, and 1 g of a
nonionic surfactant having a polyoxyethylene styrenated phenyl
ether structure (trade name of products: NOIGEN EA-187,
manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing agent
were mixed by a homo-mixer for 30 min. 6.7 g of an aqueous 45%
solution of a nonionic urethane elastomer (trade name of products:
Superflex 500, manufactured by Daiichi Kogyo Seiyaku Co.) as a
binder, and 50 g of water as a dispersion medium were added to the
mixed solution, stirred by a homo-mixer for 15 min and, further,
mixed by a ball mill for 6 hours, to prepare a positive electrode
paste.
[0106] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0107] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode, and a
solution of LiPF.sub.6 (1 mol/L) with a solvent of ethylene
carbonate (EC)/propylene carbonate (PC)/ethyl methyl carbonate
(EMC)=2/1/7 (volume ratio) as an electrolyte.
EXAMPLE 14
[0108] 100 g of LiFe.sub.0.5Mn.sub.0.5PO.sub.4 with 5% by weight of
a carbon coating amount as a positive electrode active material, 10
g of acetylene black (manufactured by Denki Kagaku Kogyo Co.) as an
electrically conducting agent, 120 g of an aqueous 2 wt % solution
of carboxymethyl cellulose with an etherifying degree of from 0.45
to 0.55 (CELOGEN PL-15, manufactured by Daiichi Kogyo Seiyaku Co.)
as a viscosity improver, and 0.5 g of an acetylene alcoholic
nonionic surfactant (trade name of products: Olfin B, manufactured
by Nisshin Kagaku Kogyo Co.) as a dispersing agent were mixed by a
homo-mixer for 30 min. 9.4 g of an aqueous 32% solution of an
anionic urethane elastomer (trade name of products: Superflex 420,
manufactured by Daiichi Kogyo Seiyaku Co.) as a binder, and 50 g of
water as a dispersion medium were added to the mixed solution,
stirred by a homo-mixer for 15 min and, further, mixed by a ball
mill for 6 hours, to prepare a positive electrode paste.
[0109] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0110] Evaluation was conducted in the same manner as in Example 1
except for using the thus obtained positive electrode.
COMPARATIVE EXAMPLE 1
[0111] 100 g of LiFePO.sub.4 with 5% by weight of a carbon coating
amount as a positive electrode active material, 10 g of acetylene
black (manufactured by Denki Kagaku Kogyo Co.) as an electrically
conducting agent, 117 g of an aqueous 12 wt % solution of PVDF in
N-methyl-2-pyrrolidone (trade name of products: #1120, manufactured
by Kureha Kagaku Co.), and 50 g of N-methyl-2-pyrrolidone as a
dispersing agent were added to the mixed solution, stirred by a
homo-mixer for 1 hour, to prepare a positive electrode paste.
[0112] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 140.degree. C. to
obtain a positive electrode.
[0113] A beaker cell was prepared by using the thus obtained
positive electrode, the negative electrode and an electrolyte
similar to those in Example 1, and a charge/discharge test was
conducted.
COMPARATIVE EXAMPLE 2
[0114] 100 g of LiCoO.sub.2 (trade name of products: cellseed C5,
manufactured by Nippon Kagaku Kogyo Co.) as a positive electrode
active material, 6 g of acetylene black (manufactured by Denki
Kagaku Kogyo Co.) as an electrically conducting agent, 120 g of an
aqueous 2 wt % solution of an carboxymethyl cellulose (trade name
of products: PL-15 manufactured by Daiichi Kogyo Seiyaku Co.) were
mixed by a homo-mixer for 30 min. 5 g of an aqueous 40 wt %
solution of SBR emulsion (trade name of products: BM-400B,
manufactured by Nippon Zeon Co.) as a binder and 50 g of water as a
dispersion medium were added to the mixed liquid, stirred by a
homo-mixer for 15 min, and further mixed by a ball mill for 6 hours
to obtain a positive electrode.
[0115] The positive electrode paste was coated on an aluminum foil
as a collector by an applicator and dried at 100.degree. C. to
obtain a positive electrode.
[0116] A beaker cell was prepared by using the thus obtained
positive electrode and the negative electrode and an electrolyte
similar to those in Example 1, and a charge/discharge test was
conducted. The test was conducted within a range of the voltage
from 4.2 V to 2.8 V.
[0117] For the beaker cells under the conditions in Example 1 and
Comparative Examples 1, 2, a rate characteristic test at 0.2 C, 1
C, 3 C, and 5 C, and a cycle characteristic test at 1 C
charge/discharge were conducted. The results are shown in FIGS.
1(a)-1(c) and FIGS. 2(a)-2(c).
[0118] As can be seen from FIGS. 1(a)-1(c), for the battery using
the positive electrode of the invention, a battery excellent in the
bonding property with the collector by using a smaller amount of
binder than the positive electrode using PVDF of Comparative
Example 1 was obtained, and it was excellent in the characteristic
at high rate (5 C). Further, since the rate after 2 C was lowered
abruptly in Comparative Example 2, it can be seen that preparation
of a paste by using LiCoO.sub.2 and using water as the dispersion
medium is not preferred. Further, also in the cycle characteristic
test, like in the rate characteristic, the cells of Comparative
Examples 1, 2 caused lowering of capacitance not reaching the 200
cycles. TABLE-US-00001 TABLE 1 Presence or Capacitance absence of
Effective retention agglomerate capacitance ratio at No. particle
(mAh/g) 200 cycle (%) Example 1 none 160 99.6 Example 2 none 158
99.7 Example 3 none 134 97.5 Example 4 none 138 98.0 Example 5 none
138 98.9 Example 6 none 140 97.6 Example 7 none 144 99.5 Example 8
none 135 99.3 Example 9 none 145 99.7 Example 10 none 140 99.5
Example 11 none 148 99.8 Example 12 none 140 97.0 Example 13 none
160 99.5 Example 14 none 148 99.4 Comparative Example 1 present 153
50 or less somewhat Comparative Example 2 none 131 50 or less
* * * * *