U.S. patent application number 08/997992 was filed with the patent office on 2001-11-15 for electrode and battery using the same.
Invention is credited to MITANI, TETSUO, SHIOTA, HISASHI, UCHIKAWA, FUSAOKI, URUSHIBATA, HIROAKI.
Application Number | 20010041285 08/997992 |
Document ID | / |
Family ID | 18391307 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041285 |
Kind Code |
A1 |
SHIOTA, HISASHI ; et
al. |
November 15, 2001 |
ELECTRODE AND BATTERY USING THE SAME
Abstract
An electrode in which an active material 11 or 7, an electron
conducting material 12 or a current collector 5 or 6 has PTC
characteristics is used as at least one of positive and negative
electrodes 1 and 2.
Inventors: |
SHIOTA, HISASHI; (TOKYO,
JP) ; URUSHIBATA, HIROAKI; (TOKYO, JP) ;
MITANI, TETSUO; (TOKYO, JP) ; UCHIKAWA, FUSAOKI;
(TOKYO, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Family ID: |
18391307 |
Appl. No.: |
08/997992 |
Filed: |
December 24, 1997 |
Current U.S.
Class: |
429/62 ; 429/212;
429/232 |
Current CPC
Class: |
H01M 2200/106 20130101;
H01M 4/624 20130101; H01M 4/131 20130101; H01M 4/66 20130101; H01M
4/36 20130101; H01M 4/02 20130101; H01M 4/133 20130101; H01M
10/0525 20130101; Y02E 60/10 20130101; H01M 4/13 20130101 |
Class at
Publication: |
429/62 ; 429/212;
429/232 |
International
Class: |
H01M 002/34; H01M
004/62 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 1996 |
JP |
8-347598 |
Claims
What is claimed is:
1. An electrode comprising: an electrode active material layer
containing an active material; and an electronic conducting current
collector on which the electrode active material layer are formed
wherein said electrode active material layer has the property of
increasing its resistance with a rise in temperature(PTC).
2. The electrode according to claim 1, wherein said active material
has the property of increasing its resistance with a rise in
temperature(PTC).
3. The electrode according to claim 1, wherein said electrode
active material layer comprises an active material particle and an
electronic conducting material, and the electronic conducting
material has the property of increasing its resistance with a rise
in temperature(PTC).
4. The electrode according to claim 1, wherein said electrode
active material layer is composed of an active region having an
electrode activity and a non-active region having no electrode
activity by which said active region is isolated into a plurality
of parts, and said non active region has the property of increasing
resistance with a rise in temperature.
5. The electrode according to claim 1, wherein said electrode
active material layer is composed of an active region having an
electrode activity and a non-active region having no electrode
activity by which said active region is isolated into a plurality
of parts, and said active region has the property of increasing
resistance with a rise in temperature.
6. The electrode according to claim 1, wherein said active material
is made up of secondary particles comprising a plurality of active
material particles having adhered on the surface thereof electronic
conducting particles having the property of increasing resistance
with a rise in temperature.
7. The electrode according to claim 1, wherein said electronic
conducting current collector has the property of increasing its
resistance with a rise in temperature(PTC).
8. The electrode according to claim 7, wherein said electronic
conducting current collection is composed of conductive plate to
which an electronic conducting material having the property of
increasing resistance with a rise in temperature is bonded.
9. The electrode according to claim 6, wherein said electronic
conducting material is a polymer having a softening point not
higher than 150.degree. C.
10. A battery comprising: a positive electrode a negative
electrode; and an electrolysis held between said positive electrode
and said negative electrode, wherein at least one of the positive
electrode and negative electrode comprises an electrode active
material layer containing an active material and an electronic
conducting current collector on which the electrode active material
layer are formed, and said electrode active material layer has the
property of increasing its resistance with a rise in
temperature(PTC).
11. The battery according to claim 10, wherein said electrode
active material layer is composed of an active region having an
electrode activity and a non-active region having no electrode
activity by which said active region is isolated into a plurality
of parts, and said non active region has the property of increasing
resistance with a rise in temperature.
12. The battery according to claim 10, wherein said electrode
active material layer is composed of an active region having an
electrode activity and a non-active region having no electrode
activity by which said active region is isolated into a plurality
of parts, and said active region has the property of increasing
resistance with a rise in temperature.
13. The battery according to claim 10, wherein said active material
is made up of secondary particles comprising a plurality of active
material particles having adhered on the surface thereof electronic
conducting particles having the property of increasing resistance
with a rise in temperature.
14. The battery according to claim 10, wherein said electronic
conducting current collector has the property of increasing its
resistance with a rise in temperature(PTC).
15. The battery according to claim 14, wherein said electronic
conducting current collector is composed of metal to which an
electronic conducting material having the property of increasing
resistance with a rise in temperature is bonded.
16. The electrode according to claim 13, wherein said electronic
conducting material is a polymer having a softening point not
higher than 150.degree. C.
17. An electrode comprising: an electrode active material layer
containing an active material; and an electronic conducting current
collector on which the electrode active material layer are formed,
wherein said electronic conducting current collector has the
property of increasing its resistance with a rise in temperature
(PTC) electrode active material layer and said electrode active
material layer is made of an plurality of parts electrical isolated
each other.
18. The electrode according to claim 17, wherein said electronic
conducting current collector is made of a conductive plate to which
an electronic conducting material has the property of increasing
its resistance with a rise in temperature(PTC) is bonded.
19. A battery comprising: a positive electrode; a negative
electrode; and an electrolysis held between said positive electrode
and said negative electrode, wherein at least one of the positive
electrode and negative electrode comprises an electrode active
material layer made of an plurality of parts electrical isolated
each other and an electronic conducting current collector on which
the electrode active material layer are formed, and said electronic
conducting current collector has the property of increasing its
resistance with a rise in temperature (PTC).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to an electrode to be used in a
battery and to a battery using the same. In particular, it relates
to a lithium ion secondary battery with improved safety.
[0003] 2. Description of the Related Art
[0004] With the recent improvement of performance of electronic
equipment, there has been a demand for improvement on batteries for
use as a power source of the electronic equipment, especially
rechargeable secondary batteries. Lithium ion secondary batteries
have been attracting attention for their light weight, portability,
and high capacity. Lithium ion secondary batteries, while
advantageous for their high energy density, require sufficient
safety measures because they use metallic lithium and a nonaqueous
electrolytic solution.
[0005] A safety valve for escape of increased inner pressure and a
PTC (positive temperature coefficient) element which increases
resistance according to heat generation caused by an external
short-circuit to cut off an electric current have been proposed to
date as safety measures.
[0006] For example, JP-A-4-328278 (the term "JP-A" as used herein
means an "unexamined published Japanese patent application")
proposes a cylindrical battery having a safety valve and a PTC
element in the positive electrode cap. However, it is a generally
followed practice that a safety valve is designed not to work so
easily because, on the safety valve's working, moisture in the air
tends to enter the battery and react with lithium present in the
negative electrode.
[0007] A PTC element, on the other hand, cuts off the circuit in
case of an external short-circuit and causes no adverse influence.
It could be the first safety component to work in case of
abnormality by designing to work when the inner temperature
reaches, for example, 120.degree. C. due to a short-circuit.
Problem to be Solved by the Invention
[0008] When a short-circuit occurs in the inside of a battery, the
cutoff of the external circuit by a PTC element does not mean a
cutoff of a short-circuit inside the battery. If a short-circuit
occurs in the battery, and the inner temperature rises, the
separator made of polyethylene, polypropylene, etc. which is
interposed between a positive electrode and a negative electrode is
expected to melt by the heat. The molten separator is expected to
exude or enclose the nonaqueous electrolytic solution that has been
held in the separator so that the ion conducting properties of the
separator may be reduced to weaken the short-circuit current.
However, a separator away from the heat generating part does not
always melt.
[0009] In an attempt to solve the above problem, JP-A-7-161389
proposes using an active material having PTC characteristics in
itself in the positive electrode. However, since the resistance of
a positive electrode active material having PTC characteristics is
about 10.sup.-5 S/cm at a working temperature (room temperature),
the battery will not function unless such a positive electrode
active material is used in combination with an electrical
conduction aid as demonstrated in Examples of the publication. With
a conduction aid having no PTC behavior being added, even though a
positive electrode active material exhibits PTC characteristics, a
short-circuit current is to flow via the conduction aid.
SUMMARY OF THE INVENTION
[0010] An object of the present invention is to settle the
above-mentioned problems and to provide a highly safe lithium ion
secondary buttery which controls heat generation in case of an
external and/or internal short-circuit.
[0011] A first aspect of the electrode of the present invention is
an electrode which comprises:
[0012] an electrode active material layer containing an active
material;
[0013] and an electronic conducting current collector on which the
electrode active material layer are formed wherein said electrode
active material layer has the property of increasing its resistance
with a rise in temperature(PTC).
[0014] A second aspect of the electrode of the present invention
according to the first aspect is an electrode wherein said active
material has the property of increasing its resistance with a rise
in temperature(PTC).
[0015] A third aspect of the electrode of the present invention
according to the first aspect is an electrode wherein said
electrode active material layer comprises an active material
particle and an electronic conducting material, and the electronic
conducting material has the property of increasing its resistance
with a rise in temperature(PTC).
[0016] A fourth aspect of the electrode of the present invention
according to the first aspect is an electrode wherein said
electrode active material layer is composed of an active region
having an electrode activity and a non-active region having no
electrode activity by which said active region is isolated into a
plurality of parts, and said non active region has the property of
increasing resistance with a rise in temperature.
[0017] A fifth aspect of the electrode of the present invention
according to the first aspect is an electrode wherein said
electrode active material layer is composed of an active region
having an electrode activity and a non-active region having no
electrode activity by which said active region is isolated into a
plurality of parts, and said active region has the property of
increasing resistance with a rise in temperature.
[0018] A sixth aspect of the electrode of the present invention
according to the first aspect is an electrode wherein said active
material is made up of secondary particles comprising a plurality
of active material particles having adhered on the surface thereof
electronic conducting particles having the property of increasing
resistance with a rise in temperature.
[0019] A eighth aspect of the electrode of the present invention
according to the first aspect is an electrode wherein said
electronic conducting current collector has the property of
increasing its resistance with a rise in temperature(PTC).
[0020] A eighth aspect of the electrode of the present invention
according to the eighth aspect is an electrode, wherein said
electronic conducting current collector is composed of conductive
plate to which an electronic conducting material having the
property of increasing resistance with a rise in temperature is
bonded.
[0021] A ninth aspect of the electrode of the present invention
according to the sixth aspect is an electrode, wherein said
electronic conducting material is a polymer having a softening
point not higher than 150.degree. C.
[0022] A tenth aspect of the battery of the present invention
battery which comprises: a positive electrode; a negative
electrode; and an electrolysis held between said positive electrode
and said negative electrode, wherein at least one of the positive
electrode and negative electrode comprises an electrode active
material layer containing an active material and an electronic
conducting current collector on which the electrode active material
layer are formed, and said electrode active material layer has the
property of increasing its resistance with a rise in
temperature(PTC).
[0023] A eleventh aspect of the battery of the present invention
according to the tenth aspect is a battery, wherein said electrode
active material layer is composed of an active region having an
electrode activity and a non-active region having no electrode
activity by which said active region is isolated into a plurality
of parts, and said non active region has the property of increasing
resistance with a rise in temperature.
[0024] A twelfth aspect of the battery of the present invention
according to the tenth aspect is a battery, wherein said electrode
active material layer is composed of an active region having an
electrode activity and a non-active region having no electrode
activity by which said active region is isolated into a plurality
of parts, and said active region has the property of increasing
resistance with a rise in temperature.
[0025] A thirteenth aspect of the battery of the present invention
according to the tenth aspect is a battery, wherein said active
material is made up of secondary particles comprising a plurality
of active material particles having adhered on the surface thereof
electronic conducting particles having the property of increasing
resistance with a rise in temperature.
[0026] A fourteenth aspect of the battery of the present invention
according to the tenth aspect is a battery, wherein said electronic
conducting current collector has the property of increasing its
resistance with a rise in temperature(PTC).
[0027] A fifteenth aspect of the battery of the present invention
according to the fourteenth aspect is a battery, wherein said
electronic conducting current collector is composed of metal to
which an electronic conducting material having the property of
increasing resistance with a rise in temperature is bonded.
[0028] A sixteenth aspect of the battery of the present invention
according to the thirteenth aspect is a battery, wherein said
electronic conducting material is a polymer having a softening
point not higher than 150.degree. C.
[0029] A seventeenth aspect of the battery of the present invention
is a battery which comprises:
[0030] an electrode active material layer containing an active
material;
[0031] and an electronic conducting current collector on which the
electrode active material layer are formed,
[0032] wherein said electronic conducting current collector has the
property of increasing its resistance with a rise in
temperature(PTC) electrode active material layer and
[0033] said electrode active material layer is made of an plurality
of parts electrical isolated each other.
[0034] A eighteenth aspect of the battery of the present invention
according to the seventeenth aspect is a battery, wherein said
electronic conducting current collector is made of a conductive
plate to which an electronic conducting material has the property
of increasing its resistance with a rise in temperature(PTC) is
bonded.
[0035] A ninteenth aspect of the battery of the present invention
is a battery which comprises: a positive electrode; a negative
electrode; and an electrolysis held between said positive electrode
and said negative electrode,
[0036] wherein at least one of the positive electrode and negative
electrode comprises an electrode active material layer made of an
plurality of parts electrical isolated each other and an electronic
conducting current collector on which the electrode active material
layer are formed,
[0037] and said electronic conducting current collector has the
property of increasing its resistance with a rise in temperature
(PTC).
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a schematic cross section of the main part of an
example of the lithium ion secondary battery according to the
present invention.
[0039] FIG. 2 is a schematic cross section of the same battery as
shown in FIG. 1, in which the behavior of the positive electrode in
case of an internal short-circuit is illustrated.
[0040] FIG. 3 shows changes in battery voltage and temperature with
time in a simulation of a short-circuit in the lithium ion
secondary battery according to the present invention.
[0041] FIG. 4 shows a schematic cross section of the electrode of
the third embodiment of the present invention.
[0042] FIG. 5 shows a schematic cross section of the conventional
electrode in comparison with the FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] The embodiments for carrying out the present invention are
described below with reference to the accompanying drawings.
[0044] FIG. 1 is a schematic cross section of the main part of an
embodiment of the lithium ion secondary battery according to the
present invention. In FIG. 1 numeral 1 indicates a positive
electrode comprising a positive electrode current collector 5
having formed thereon a positive active material layer made up of a
positive electrode active material 11, an electronic conducting
material 12 that is in contact with the active material 11, and a
binder 14. Numeral 2 is a negative electrode comprising a negative
electrode current collector 6 having formed thereon a negative
electrode active material layer mode up of a negative active
material 7, such as carbon particles, and a binder. Numeral 3
indicates a separator holding an electrolytic solution containing
lithium ions.
[0045] The electrode according to the present invention having the
above-described structure is characterized in that the positive
electrode active material 11, the positive electrode current
collector 6 or the electronic conducting material 12 in contact
with the positive electrode active material 11 has PTC
characteristics (the property of increasing electrical resistance
with a rise in temperature).
[0046] While FIG. 1 is to illustrate the structure of the positive
electrode 1, the same structure also applies to the negative
electrode 2. In that case, a particulate negative electrode active
material 7 and an electronic conducting material in contact with
the active material 7 are formed into a negative electrode by means
of a binder, and the negative electrode material 7, the electronic
conducting material or the current collector 6 has PTC
characteristics.
[0047] FIG. 2 is a schematic cross section of the same battery as
shown in FIG. 1, in which the behavior of the positive electrode in
case of an internal short-circuit is illustrated. When an internal
short-circuit takes place due to, for example a mediator 4, for
example, dendrite shape of metallic lithium grown from the negative
electrode 2 as shown in FIG. 2, short-circuit currents 51 and 52
flow along the path indicated by arrows toward the internal
short-circuited part. The short-circuit current 51 is an
electronically conducting current, while the short-circuit current
52 is an ionically conducting current. The part in which the
short-circuit currents 51 and 52 are concentrated generates Joule's
heat. In short, the inner temperature rises at the part where the
short-circuit currents 51 and 52 flow (in the vicinities of the
short-circuit caused by the mediator 4).
[0048] According to the present invention, since the positive
electrode active material 11, the electronic conducting material 12
or the electronic conducting material 13 constituting the positive
electrode current collector 5 has PTC characteristics, the
short-circuit current 51 is decayed with the rise in temperature
caused by the short-circuit.
[0049] In a battery, a voltage loss due to internal resistance is
about 1 to 5% of the battery voltage at a generally employed
current. Supposing the total voltage is applied to the internal
resistant portion, if a short-circuit takes place, the
short-circuit current would be 20 to 100 times the ordinary
current. Therefore, it is expected that a short-circuit current
would be reduced down to a normal level or even less if the
internal resistance at the short-circuited part could be increased
100 times or more by a PTC function.
[0050] The possibility of thermal runaway, while varying depending
on the materials making up a battery, seems to increase after the
battery temperature exceeds 150.degree. C. Therefore, it is
desirable that the PTC function works at a temperature of
150.degree. C. so as to inhibit thermal runaway. Taking the time
lag between the start and the completion of the FTC function into
consideration, it is desirable for the PTC function to work from
120.degree. C.
[0051] In FIG. 1, at least one of the current collectors 5 and 6,
the active materials 7 and 11, and the electronic conducting
material 12 must be endowed with PTC characteristics.
[0052] Because a short-circuit current has its rise in the active
materials 11 and 7 of the positive and negative electrodes 1 and 2,
it is the most effective that the active material 7 or 11 is made
to have PTC characteristics. With an increase in temperature due to
a short-circuit, the active material 7 or 11 increases its
resistance to reaction to reduce the short-circuit current.
[0053] The "resistance to reaction" of an electrode active material
is considered to be the sum of resistance to electronic conduction
and ionic conduction in the inside of the active material 7 or 11
and resistance to charge transfer on the surface of the active
material 7 or 11. Many of the active materials 11 have high
resistance to electronic conduction originally so that the
resistance to ionic conduction in the inside of the active material
11 and the resistance to charge transfer on the surface of the
active material 11 usually takes the main part of resistance to
reaction. In one feature of the present invention, the resistance
to reaction has PTC behavior. More specifically, electronic
conducting particles having PTC characteristics are adhered to the
surface of the active material particles to form secondary
particles of the active material 7 or 11 having an active part and
a non-active part having PTC characteristics.
[0054] It is also effective that the electronic conducting material
has PTC characteristics. Since the positive electrode active
material 11 usually has in itself low electron conductivity, the
electronic conducting material 12 is incorporated to form the
positive electrode 1 in which the active material 11 and the
electronic conducting material 12 are brought into contact. Use of
an electronic conducting material having PTC characteristics
enables the electrode to decay the short-circuit current.
[0055] In order for the positive electrode current collector 5 to
have PTC characteristics, the current collector 5 can be made up of
metal 15 to which the electronic conducting material 13 having PTC
characteristics is contacted as shown in FIG. 1. The negative
electrode current collector 6 can also be made to have PTC
characteristics in the same manner.
[0056] Where only the current collectors 5 and 6 are made to have
PTC characteristics, and the active material layers each formed of
the active material 11 or 7 and the binder 14 have good electron
conductivity in the lateral direction, cases are sometimes met with
in which the active material layers become bypass for letting the
short-circuit current to flow, failing to sufficiently decaying the
short-circuit current, even when the current collectors 5 and 6
increase their resistance in case of a short-circuit. Then as shown
in FIG. 4, it is desirable to limit the electron conductivity of
the active material layers in their lateral detection by isolating
the active material layer 20 into plural of active material regions
by electron insulator 21.
[0057] According to the feature, the electron insulator 21 prevents
the short-circuit current from bypassing. And the short-circuit
current is cut early by means of the PTC function of the PTC layer
22 formed on the conductive layer 22 such as a metal plate or
carbon plate. Therefore energy discharge owing to short-circuit is
kept low, and safety of the secondary battery is kept.
[0058] With respect to isolation region, such as electron
insulating material, by which active material regions are isolated,
any size, any pitch and any kindness of electron insulating
material are effective without being limited. As the electron
insulating material, any material has electron insulating
characteristic under the circumference in which the electrode is
used, for example in the electrode for a lithium ion secondary
battery, electron insulating material used as other element of the
battery, can be used. The size of the isolation region is desirably
small in a range wherein a function of preventing a short-circuit
current from bypassing can be kept. And pitch is desirably large
with respect to acting as the real function of the electrode.
[0059] In contradiction that, as shown in FIG. 5 in the case of
conventional electrode in which only the current collectors is made
to have RTC characteristics, and the active material layers 20
formed on a whole surface of PTC layer 22 on the conductive layer
23, the active material layers 20 has a good electron conductivity
in the lateral direction, the short-circuit current is continued
flowing by bypassing the cutting zone formed by the PTC function.
And by continuing flowing a range of heated zone is expanded, the
short-circuit current is continued flowing by further bypassing.
Therefore in the case of a battery, large amount of energy is
discharged.
[0060] Accordingly in such a case, it is required to previously
limit the electron conductivity of the active material layers in
their lateral direction by, for example, dividing the active
material layers.
[0061] Materials having no PTC characteristics are used as an
active material which forms the active material particles per se or
the aforesaid secondary particles. Examples of useful positive
electrode active materials are LiCoO.sub.2, LiNiO.sub.2,
LiCo.sub.1-xNi.sub.xO.sub.- 2, and LiMn.sub.2O.sub.4. Examples of
useful negative electrode active materials are carbon particles,
such as mesophase carbon microbeads (MCHB), graphite, and acetylene
black.
[0062] Specific but non-limiting examples of useful electronic
conducting materials or electronic conducting particles having PTC
characteristics include barium titanate, barium titanate doped with
Sr, Pb, etc. (complex oxides), and electrically conductive
polymers, such as polyethylene mixed with carbon black.
[0063] The PTC function of the conductive polymer controlled by the
mixing ratio of a plastic and an electrically conducting material,
such as carbon black. When the conductive polymer is used, the
plastic melts by the heat of the short-circuit to cut off both the
electron conducting path and the ion conducting path in the active
material comprising the secondary particles, thereby to enhance the
resistance to electronic conduction. When the conductive polymer is
applied to the electronic conducting material 12 or 13, the
electronic conducting path is to be cut.
[0064] The present invention will now be illustrated in greater
detail by way of Examples of the lithium ion secondary battery
shown in FIG. 1.
Preparation of Positive Electrode
[0065] Ten parts of fine particles (average particle size 10 .mu.m)
of an electronic conducting material having an electrical
conductivity of 5 S/cm at room temperature and 5 .mu.S/cm at a
working temperature of 120.degree. C. (selected from barium
titanate, Sr-doped barium titanate, Pb-doped barium titanate, and a
graphite/polyethylone mixture), 85 parts by weight of LiCoO.sub.2
as an active material, and 5 parts by weight of polyvinylidene
fluoride (hereinafter abbreviated as PVDF) were dispersed in
N-methylpyrrolidone (hereinafter abbreviated as NMP) to prepare a
positive electrode active material paste. The paste was applied to
20 .mu.m thick aluminum foil as a positive electrode current
collector with a doctor blade to a thickness of 150 .mu.m, dried at
80.degree. C., and pressed to prepare a positive electrode 1 having
a positive electrode active material layer 3 having a thickness of
100 .mu.m.
Preparation of Negative Electrode
[0066] Ninety-five parts by weight of mesophase carbon microbeads
(hereinafter abbreviated as MCMB) and 5 parts by weight of PVDF
were dispersed in NMP to prepare a negative electrode active
material paste. The paste was applied to 20 .mu.m thick copper foil
with a doctor blade to a thickness of 300 .mu.m, dried at
80.degree. C., and pressed to form a negative electrode 4 having a
negative electrode active material layer 6 having a thickness of
100 .mu.m.
Preparation of Batter
[0067] A 5 parts by weight of PVDF solution in NMP was applied to
both sides of a porous polypropylene sheet (Cellguard #2400,
produced by Hoechst Celanese Plastics Ltd.) as a separator 7.
Before the adhesive dried, the positive electrode 1 and the
negative electrode 4 were stuck to each side of the separator 7,
followed by drying at 80.degree. C. to prepare an electrode
laminate.
[0068] Ten electrode laminates were laid one on another, and
current collecting tabs each connected to the end of every positive
or negative current collector were spot-welded among the positive
electrode laminates and the negative electrode laminated,
respectively, to form a single battery body in which the positive
electrodes and the negative electrodes were each connected in
parallel.
[0069] The battery body was immersed in an electrolytic solution
consisting of 1.0 mol/dm.sup.3 of lithium hezafluorophosphate in a
1:1 (by mole) mixed solvent of ethylene carbonate and dimethyl
carbonate, and the impregnated battery body was sealed into an
aluminum laminate film (resin coated aluminum film) pack by heat
sealing to complete a battery.
[0070] The resulting battery was charged at 500 mA to 4.2 V at an
ambient temperature of 25.degree. C. After completion of the
charge, an iron nail having a diameter of 2.5 mm was put in the
center of the battery to run a simulation of an internal
short-circuit. FIG. 3 shows the changes in battery voltage and
temperature with time. As shown, in the instant the iron nail was
put in (time 0), the terminal voltage fell to 0 V but was gradually
restored with time, which seemed to be because heat was generated
at the short-circuited part immediately after the short-circuit
whereby the electronic conducting particles having PTC
characteristics in the vicinities of the short-circuited part
functioned to decay the short-circuit current. The battery
temperature started rising after the short-circuit, reaching the
peak in about 5 minutes. Then it gradually dropped to room
temperature. This shift of the peak of temperature is considered
due to the time required for heat conduction because of the
positional difference of the measuring point from the heat
generating point (the short-circuited part).
[0071] For comparison, a battery having no PTC function was
produced in the same manner as described above, except for using
artificial graphite (KS-6, produced by Lonza Ltd.) as electronic
conducting particles. As a result of the same simulation of a
short-circuit, the peak temperature exceeded 150.degree. C., and
restoration of the battery voltage was not observed.
EMBODIMENT 2
Preparation of Positive Electrode
[0072] LiCoO.sub.2 particles having an average particle size of 1
.mu.m were made into secondary particles having an average particle
size of 50 .mu.m while powdering with high-density polyethylene
having a softening point of 120.degree. C. Eighty-five parts by
weight of the resulting secondary particles, 10 parts by weight of
artificial graphite (KS-6, produced by Lonza Ltd.) as electronic
conducting particles, and 5 parts by weight of PVDF as a binder
were dispersed in NMP to prepare a positive electrode active
material paste. The paste was applied to 20 .mu.m thick aluminum
foil as a positive electrode current collector 2 with a doctor
blade to a thickness of 150 .mu.m, dried at 80.degree. C., and
pressed to prepare a positive electrode 1 having a positive
electrode active material layer 3 having a thickness of 100
.mu.m.
Preparation of Negative Electrode
[0073] Ninety-five parts by weight of MCMB and 5 parts by weight of
PVDF were dispersed in NMP to prepare a negative electrode active
material paste. The paste was applied to 20 .mu.m thick copper foil
with a doctor blade to a thickness of 150 .mu.m, dried at
80.degree. C., and pressed to form a negative electrode 4 having a
negative electrode active material layer 6 having a thickness of
100 .mu.m.
Preparation of Battery
[0074] A 5 parts by weight of PVMF solution in NMP was applied to
both sides of a porous polypropylene sheet (Cellguard #2400,
produced by Hoechst Celanese Plastics Ltd.) as a separator 7.
Before the adhesive dried, the positive electrode 1 and the
negative electrode 4 were stuck to each side of the separator 7,
followed by drying at 80.degree. C. to prepare an electrode
laminate.
[0075] Ten electrode laminates were laid one on another, and
current collecting tabs each connected to the end of every positive
and negative current collector were spot-welded among the positive
electrode laminates and the negative electrode laminates,
respectively, to form a single battery body in which the positive
electrode laminates and the negative electrode laminates were each
connected in parallel.
[0076] The battery body was immersed in an electrolytic solution
consisting of 1.0 mol/dm.sup.3 of lithium hexafluorophosphate in a
1:1 (by mole) mixed solvent of ethylene carbonate and dimethyl
carbonate, and the impregnated battery body was sealed into an
aluminum laminate film pack by heat sealing to complete a
battery.
[0077] The resulting battery was charged at 500 mA to 4.2 V at an
ambient temperature of 25.degree. C. After completion of the
charge, an iron nail having a diameter of 2.5 mm was put in the
center of the battery to run a simulation of an internal
short-circuit. Similarly to the behavior shown in FIG. 3, in the
instant the iron nail was put in (time 0), the terminal voltage
fell to 0 V but was gradually restored with time. The voltage
restoration seems to be because heat was generated at the
short-circuited part immediately after the short-circuit whereby
the high-density polyethylene clinging to the active material
particles in the vicinities of the short-circuited part was
softened and expanded to cut the electronic conducting path to the
active material to thereby decay the short-circuit current.
EMBODIMENT 3
Preparation of Positive Electrode
[0078] Eighty-five parts by weight of LiCoO.sub.2 having an average
particle size of 1 .mu.m, 10 parts by weight of artificial graphite
(KS-6, produced by Lonza Ltd.) as electronic conducting particles,
and 5 parts by weight of PVDF as a binder were dispersed in NMP to
prepare a positive electrode active material paste.
[0079] Separately, a 50 .mu.m thick sheet of an electrically
conductive polymer consisting of 30% polyethylene and 70% carbon
black and having an electrical conductivity of 5 S/cm at room
temperature and 5 .mu.S/cm at a working temperature of 120.degree.
C. was stuck to a 20 .mu.m thick aluminum net to prepare a positive
electrode current collector 2. The positive electrode active
material paste prepared above was applied to the current collector
2 through a mask having slits at an opening ratio of 70% by means
of a doctor blade to a thickness of 150 .mu.m, dried at 80.degree.
C. so that the positive electrode active material layer made of an
plurality of parts electrical isolated each other(referring to the
FIG. 4), and pressed to prepare a positive electrode 1 having a
positive electrode active material layer 3 having a thickness of
100 .mu.m.
Preparation of Negative Electrode
[0080] Ninety-five parts by weight of MCMB and 5 parts by weight of
PVDF as a binder were dispersed in NMP to prepare a negative
electrode active material paste. The paste was applied to 20 .mu.m
thick copper foil with a doctor blade to a thickness of 150 .mu.m,
dried at 80.degree. C., and pressed to form a negative electrode 4
having a negative electrode active material layer 6 having a
thickness of 100 .mu.m.
Preparation of Battery
[0081] A 5 parts by weight of PVDF solution in NMP was applied to
both sides of a porous polypropylene-sheet (Cellguard #2400,
produced by Hoechst Celanese Plastics Ltd.) as a separator 7.
Before the adhesive dried, the positive electrode 1 and the
negative electrode 4 were stuck to each side of the separator 7,
followed by drying at 80.degree. C. to prepare an electrode
laminate.
[0082] Ten electrode laminates were laid one on another, and
current collecting tabs each connected to the end of every positive
or negative current collector were spot-welded among the positive
electrode laminates and the negative electrode laminates,
respectively, to form a single battery body in which the positive
electrode laminates and the negative electrode laminates were each
connected in parallel.
[0083] The battery body was immersed in an electrolytic solution
consisting of 1.0 mol/dm.sup.3 of lithium hexafluorophosphate in a
1:1 (by mole) mixed solvent of ethylene carbonate and dimethyl
carbonate, and the impregnated battery body was sealed into an
aluminum laminate film pack by heat sealing to complete a
battery.
[0084] The resulting battery was charged at 500 mA to 4.2 V at an
ambient temperature of 25.degree. C. After completion of the
charge, an iron nail having a diameter of 2.5 mm was put in the
center of the battery to run a simulation of an internal
short-circuit. As a result, the same changes in battery temperature
and voltage as in FIG. 3 were observed. That is, in the instant the
iron nail was put in (time 0), the terminal voltage fell to 0 V but
was gradually restored with time. The voltage restoration seems to
be because heat was generated at the short-circuited part
immediately after the short-circuit whereby the electrically
conductive polymer having PTC characteristics in the vicinities of
the short-circuited part functioned to cut off the electronic
conducting path to the active material to thereby decay the
short-circuit current.
Preparation of Positive Electrode
[0085] Eighty-five parts by weight of LiCoO.sub.2 particles having
an average particle size of 1 .mu.m, 10 parts by weight of
artificial graphite (KS-6, produced by Lonza Ltd.) as electronic
conducting particles, and 5 parts by weight of PVDF as a binder
were dispersed in NMP to prepare a positive electrode active
material paste. The paste was applied to 20 .mu.m thick aluminum
foil as a positive electrode current collector 2 with a doctor
blade to a thickness of 150 .mu.m, dried at 80.degree. C., and
pressed to prepare a positive electrode 1 having a positive
electrode active material layer 3 having a thickness of 100
.mu.m.
Preparation of Negative Electrode
[0086] MCMB was powdered with high-density polyethylene having a
softening point of 120.degree. C. into particles having an average
particle size of 50 .mu.m. Ninety-five parts by weight of the
resulting particles and 5 parts by weight of PVDF were dispersed in
NMP to prepare a negative electrode active material paste. The
paste was applied to 20 .mu.m thick copper foil with a doctor blade
to a thickness of 150 .mu.m, dried at 80.degree. C., and pressed to
form a negative electrode 4 having a negative electrode active
material layer 6 having a thickness of 100 .mu.m.
Preparation of Battery
[0087] A 5 parts by weight of PVDF solution in NMP was applied to
both sides of a porous polypropylene sheet (Cellguard #2400,
produced by Hoechst Celanese Plastics Ltd.) as a separator 7.
Before the adhesive dried, the positive electrode 1 and the
negative electrode 4 were stuck to each side of the separator 7,
followed by drying at 80.degree. C. to prepare an electrode
laminate.
[0088] Ten electrode laminates were laid one on another, and
current collecting tabs each connected to the end of every positive
or negative current collector were spot-welded among the positive
electrode laminates and the negative electrode laminates,
respectively, to form a single battery body in which the positive
electrode laminates and the negative electrode laminates were each
connected in parallel.
[0089] The battery body was immersed in an electrolytic solution
consisting of 1.0 mol/dm.sup.3 of lithium hexafluorophosphate in a
1:1 (by mole) mixed solvent of ethylene carbonate and dimethyl
carbonate, and the impregnated battery body was sealed into an
aluminum laminate film pack by heat sealing to complete a
battery.
[0090] The resulting battery was charged at 500 mA to 4.2 V at an
ambient temperature of 25.degree. C. After completion of the
charge, an iron nail having a diameter of 2.5 mm was put in the
center of the battery to run a simulation of an internal
short-circuit. As a result, the same changes in battery temperature
and voltage as in FIG. 3 were observed. That is, in the instant the
iron nail was put in (time 0), the terminal voltage fell to 0 V but
was gradually restored with time. The voltage restoration seems to
be because heat was generated at the short-circuited part
immediately after the short-circuit whereby the electrically
conductive polymer having PTC characteristics in the vicinities of
the short-circuited part functioned to cut off the electronic
conducting path to the active material to thereby decay the
short-circuit current.
[0091] The present invention is applicable to the electrode for
Electrolysis apparatus, the electrode for electroplating the
electrode for liquid crystal display and so on.
[0092] As described above, the electrode according to the present
invention comprises an active material, an electronic conducting
material in contact with tie active material, and an electronic
conducting current collector to which the active material and the
electronic conducting material are bonded with a binder, in which
the active material, electronic conducting material or electronic
conducting current collector has the property of increasing its
resistance with a rise in temperature. Accordingly, in case of an
internal short-circuit, the PTC function of the active material,
the electronic conducting material or the electronic conducting
material constituting the current collector which is in the path of
the short-circuit current works to decay the short-circuit current
thereby suppressing a rise in temperature. In the case that only
electronic conducting current collector has the property of
increasing its resistance with a rise in temperature, it is
required that electrode active material layer is made of an
plurality of parts electrical isolated each other for improving a
safety.
[0093] Where the active material is composed of a part having an
electrode activity and a part having no electron activity, with the
part having no electron activity exhibiting the property of
increasing its resistance with a rise in temperature, the
resistance to reaction of the active material increases at the time
of a short-circuit to control the rise in temperature.
[0094] Where the active material is made up of secondary particles
comprising a plurality of active material particles to which
electronic conducting particles having the property of increasing
the resistance with a rise in temperature are clinging, the
resistance to reaction or the active material increases at the time
of a short-circuit to control the rise in temperature.
[0095] The electronic conducting current collector can be endowed
with PTC characteristics by the structure composed of metal to
which an electronic conducting material having the property of
increasing its resistance with a rise in temperature is joined.
[0096] Where the electronic conducting material is a polymer having
a softening point lower than 150.degree. C., the polymer melts by
the heat of a short-circuit. Where the polymer is applied to the
active material, the melt cuts both the electron conducting path
and the ion conducting path to increase the resistance to electron
conduction. Where the polymer is applied to the electron conducting
material, the melt cuts the electron conducting path.
[0097] The battery according to the present invention comprises a
positive electrode, a negative electrode, and an electrolytic
solution held between the positive and negative electrodes, in
which the above-described electrode endowed with PTC
characteristics is used as a positive or negative electrode. The
battery is of high safety because the temperature rise in case of
an internal short-circuit can be suppressed.
* * * * *