U.S. patent application number 09/284617 was filed with the patent office on 2002-02-14 for carbon-containing material and a method of making porous electrodes for chemical sources of electric current.
Invention is credited to AFANASIEV, VLADIMIR LEONIDOVICH, ALEXANDROV, ALEXANDR BORISOVICH, GALITSKY, ALEXANDR ANATOLIEVICH, JUDANOV, MIKOLAI FEDOROVICH, MITKIN, VALENTIN NIKOLAEVICH, MUKHIN, VIKTOR VASILIKEVICH, ROMASHKIN, VASILY PETROVICH, ROZHKOV, VLADIMIR VLADIMIROVICH, TELEZHKIN, VLADLEN VLADIMIROVICH.
Application Number | 20020018933 09/284617 |
Document ID | / |
Family ID | 23090877 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020018933 |
Kind Code |
A1 |
MITKIN, VALENTIN NIKOLAEVICH ;
et al. |
February 14, 2002 |
CARBON-CONTAINING MATERIAL AND A METHOD OF MAKING POROUS ELECTRODES
FOR CHEMICAL SOURCES OF ELECTRIC CURRENT
Abstract
The proposed carbon-containing material comprises an
electrode-active material, preferably a fluorocarbon, containing
58-67 wt. % fluorine, a binder, an agent adding to the conductance
of the electrode-active material, and an expanding agent, in the
capacity of which graphite oxyfluoride, is used is used. The
proposed method of making a porous electrode comprises the
following steps: a step-by-step mixing of the abovesaid components,
at the first of which graphite oxyfluoride is mixed together with
the electrode-active material, the resultant mixture is modified,
predominantly by subjecting it to impact action to prepare an
intermediate product which at the second step is mixed together
with the binder and the agent adding to the conductance of the
electrode-active material, followed by forming an electrode and its
heat-treatment to establish pores in its structure without
destruction thereof.
Inventors: |
MITKIN, VALENTIN NIKOLAEVICH;
(NOVOSIBIRSK, RU) ; JUDANOV, MIKOLAI FEDOROVICH;
(NOVOSIBIRSK, RU) ; GALITSKY, ALEXANDR ANATOLIEVICH;
(NOVOSIBIRSK, RU) ; ALEXANDROV, ALEXANDR BORISOVICH;
(NOVOSIBIRSK, RU) ; AFANASIEV, VLADIMIR LEONIDOVICH;
(NOVOSIBIRSK, RU) ; MUKHIN, VIKTOR VASILIKEVICH;
(NOVOSIBIRSK, RU) ; ROZHKOV, VLADIMIR VLADIMIROVICH;
(NOVOSIBIRSK, RU) ; ROMASHKIN, VASILY PETROVICH;
(NOVOSIBIRSK, RU) ; TELEZHKIN, VLADLEN VLADIMIROVICH;
(NOVOSIBIRSK, RU) |
Correspondence
Address: |
JOHN B HARDAWAY III
HARDAWAY LAW FIRM
PO BOX 10107
FEDERAL STATION
GREENVILLE
SC
296030107
|
Family ID: |
23090877 |
Appl. No.: |
09/284617 |
Filed: |
April 28, 1999 |
PCT Filed: |
July 31, 1996 |
PCT NO: |
PCT/RU96/00206 |
Current U.S.
Class: |
429/212 ;
423/415.1; 423/448; 429/220; 429/224; 429/231.8 |
Current CPC
Class: |
H01M 4/5815 20130101;
H01M 4/131 20130101; H01M 4/139 20130101; H01M 4/485 20130101; H01M
4/625 20130101; Y02E 60/10 20130101 |
Class at
Publication: |
429/212 ;
429/231.8; 429/224; 429/220; 423/415.1; 423/448 |
International
Class: |
H01M 004/58; H01M
004/50; H01M 004/48; C01B 031/04 |
Claims
1. A carbon-containing material for electrodes of electrochemical
cells, comprising an electrode-active material, a binder, an agent
adding to electrical conductance of the electrode-active material,
and an expanding agent, CHARACTERIZED in that used as the expanding
agent is graphite oxyfluoride.
2. The carbon-containing material of claim 1, CHARACTERIZED in that
it comprises graphite oxyfluoride of the following general
formula:C.sub.x.zCyO.nH.sub.2O.CF,where x=1.5-15, y=2.2-2.5,
=0.5-1.4, n=0.1-0.5:
3. The carbon-containing material of claim 1, CHARACTERIZED in that
fluorocarbon containing 58 to 67 wt. % fluorine is therein used as
the electrode-active material.
4. The carbon-containing material of claim 1, CHARACTERIZED in that
compounds of transition metals taken either separately or in
combination are therein used as the electrode-active material.
5. The carbon-containing material of claim 4, CHARACTERIZED in that
manganese dioxide is therein used as the compounds of transition
metals.
6. The carbon-containing material of claim 4, CHARACTERIZED in that
copper oxide is therein used as the compounds of transition
metals.
7. The carbon-containing material of claim 4, CHARACTERIZED in that
pyrite or chalcopyrite is therein used as the compounds of
transition metals.
8. The carbon-containing material of claim 4, CHARACTERIZED in that
a mixture of copper oxide and pyrite is therein used as a mixture
of the compounds of transition metals.
9. The carbon-containing material of claim 4, CHARACTERIZED in that
a mixture of copper oxide and chalcopyrite is therein used as the a
mixture of the compounds of transition metals.
10. A method of making porous electrodes for electrochemical cells,
predominantly lithium ones, comprising mixing an electrode-active
material, a binder, an agent increasing the conductance of the
electrode-active material, and an expanding agent, and forming a
finished product, CHARACTERIZED in that used as the expanding agent
is graphite oxyfluoride and mixing the components are effected in
several steps so that at the first step graphite oxyfluoride is
mixed with the electrode-active material, then the resultant
mixture is modified until an intermediate product is obtained,
which is then mixed with the binder and the agent increasing the
conductance of the electrode-active material, and formation of a
finished product is followed by its heat-treatment till forming
pores in the structure of the finished electrode without its
destruction.
11. The method of claim 10, CHARACTERIZED in that the graphite
oxyfluoride of the following general
formula:C.sub.x.zCyO.nH.sub.2O.CF,where x=1.5-15, y=2.2-2.5,
z=0.5-1.4, n=0.01-0.5. is therein used.
12. The method of claim 10, CHARACTERIZED in that fluorocarbon
containing 58-67 wt. % fluorine is therein used as the
electrode-active material.
13. The method of claim 10, CHARACTERIZED in that compounds of
transition metals taken either separately or in combination, are
used as the electrode-active material.
14. The method of claim 10, CHARACTERIZED in that manganese dioxide
is therein used as the electrode-active material.
15. The method of claim 10, CHARACTERIZED in that copper oxide is
therein used as the electrode-active material.
16. The method of claim 10, CHARACTERIZED in that pyrite or
chalcopyrite is therein used as the electrode-active material.
17. The method of claim 10, CHARACTERIZED in that a mixture of
copper oxide and pyrite is therein used as the electrode-active
material.
18. The method of claim 10, CHARACTERIZED in that a mixture of
copper oxide and chalcopyrite is therein used as the
electrode-active material.
19. The method according to any one of the preceding claims 11-18,
CHARACTERIZED in that the powdered electrode-active material and
graphite oxyfluoride are mixed together in a weight ratio of from
8:1 to 40:1, respectively.
20. The method of claim 19, CHARACTERIZED in that a diluent is
added to the mixture at the second step of mixing until a
paste-like mass is obtained.
21. The method of claim 10, CHARACTERIZED in that a
polytetrafluoroethylene suspension is used as the binder.
22. The method of claim 10, CHARACTERIZED in that heat-treatment is
performed at 150-350.degree. C.
23. The method of claim 10, CHARACTERIZED in that modification is
effected by virtue of an impact action produced on a mixture of the
two said components.
24. The method of claim 23, CHARACTERIZED in that the impact action
is carried out with an acceleration of the tumbling bodies of from
10 to 75 g, where g is gravitational acceleration.
25. The method of claim 10, CHARACTERIZED in that the impact action
is carried out in the presence of water or a low-boiling organic
solvent taken in an amount of 0.1-5 wt. %.
26. The method according to any one of claims 23-25, CHARACTERIZED
in that the impact action is performed a density of the
intermediate product from 1.0 to 1.5 g/cu.cm is obtained.
27. The method of claim 10, CHARACTERIZED in that at the second
step of the mixing process use is made of water, ethanol, a mixture
of both, or a low-boiling hydrocarbon having a boiling point below
100.degree. C.
28. A porous electrode of an electrochemical cell, CHARACTERIZED in
that it is made of the material described in any one of claims
1-9.
29. The porous electrode of an electrochemical cell, CHARACTERIZED
in that it is prepared according to the method described in any one
of claims 10-27.
Description
TECHNICAL FIELD
[0001] The present invention relates in general to electrochemical
cells and more specifically to a carbon-containing material for
electrodes of electrochemical cells and to a method of making
porous electrodes from said material.
[0002] The herein-proposed invention can find application in
establishing novel carbon-containing energy-saturated electrode
materials made use of in electrochemical cells, largely in 1.5- and
3-volt lithium cells.
BACKGROUND ART
[0003] There exists at present a problem in electrochemical cells
using solid-state electrodes how to provide high energy-capacity of
electrodes and simultaneously high operating density of discharge
current. The problem concerns predominantly cathodes because anodes
of electrochemical cells based on active metals, i.e., lithium,
sodium, zinc, and others are most frequently used in constructions
of electrochemical cells in their compact state, that is, with
their density which is realized to a maximum extent in anodes and
is equal to or approximates their pycnometric density realizable in
crystal lattices of said materials.
[0004] To realize maximum characteristics of electrochemical cells
as to energy capacity thereof, it is necessary to use
electrode-active materials having high specific weight and volume
characteristics with a maximum possible filling of the electrode
construction with an electrode-active material. However, a higher
electrode density due to a more complete filling of the electrode
volume with an electrode-active material reduces the electrode
surface available for a current-generating reaction to proceed,
whereby the effective density of the electrode discharge current as
a whole is adversely affected.
[0005] On the other hand, the effective density of the electrode
discharge current can be increased due to a larger effective
electrode surface attainable by a finer dividing of the electrode
components and adding to its composition such materials that
enhance the electrode conductance. This in turn results in higher
electrode porosity but also leads to a lower content of the
principal electrode component, that is, an electrode-active
material.
[0006] Therefore resolving the problem of creating a high
energy-capacity electrochemical cell featuring a larger discharge
current density is inevitably concerned with a search for
compromise between reduction in a total energy capacity of the
electrode and an increase in its porosity and electrical
conductance with the electrode volume remaining invariable.
[0007] The electrode of an electrochemical cell is usually
comprised of a mixed composition consisting of an electrode-active
material, a binder, and an electrode conductance increasing
material. To establish porous structure in electrodes use is made
of pore-formation materials (expanding agents) in the capacity of
which such substances and materials are applied that are liable to
dissolve or volatile upon physico-chemical treatment of preformed
electrodes. As a result, a porous structure is established in the
electrode, required for lodging therein electrolyte and depositing
solid products of the current-producing reaction (cf. a textbook
"Electrochemical cells with lithium electrode" by I. A. Kedrinski
et al., Krasnoyarsk University Publishers, Krasnoyarsk, 1983, pp.
248, 144-147 (in Russian) [1].
[0008] Known in prior art are a variety of expanding agents such as
expanded granulated graphite (expandate) (cf. "Active mass of
positive electrode of a primary cell" by Peter Faber. USSR
Inventor's Certificate #488,432, IPC Holm 13/02, 21/00, published
on Oct. 15, 1975 in Bulletin #38 [2]; "Positive electrode of an
electrochemical cell" by B. K. Makarenko et al., USSR Inventor's
Certificate #564,668, IPC H01m 4/98, 6/14, published on Jul. 5,
1977 in Bulletin #25 [3]); some organic substances, e.g., camphor
(cf. French Patent #2,093,287, IPC H01m 13/00, 1972 [4]) or soluble
inorganic compounds such as potassium hexafluorophosphate (cf.
"Process for producing porous electrode for an electrochemical cell
with nonaqueous electrolyte" by N. S. Lidorenko et al., USSR
Inventor's Certificate #527,775, IPC H01m 4/62, published on Sep.
5, 1976 in Bulletin #33 [5]). Used for the same purpose are also
insoluble inorganic compounds and materials featuring a porous
structure per se, i.e., zeolites (cf. "An electric cell with
organic electrolyte" by N. Watanabe et al., Japan Patents
61-264,679, 61-264,680, 61-264,682, 61-264,681, IPC H01m 6/16 of
May 20, 1985 [61]), or activated alumina(cf. "Element of the
lithium--fluorocarbon system" by Suetsugu Satiko, Japan Patent N
63-334,457, IPC H01m 4/06 of Dec. 28, 1988 [7]). All the materials
mentioned above when introduced in the composition are liable to
improve discharge characteristics; however, this reduces the
electrode density, with the result that the capacitance of the
electrochemical cell is reduced due to a lower content of the
electrode-active material.
[0009] Methods for making porous cathodes for electrochemical cells
boils down to a combination of sequences of the steps of preparing,
mixing, and treating the parent components, a most frequently used
practice is to mix all the prepared ingredients in a single step
(cf. references 1 to 7), in the presence of water or organic
solvents, whereupon the semifinished items of a cathode material
are isolated, dried, and disintegrated. Then the cathodes are
formed, provided with current leads (by, e.g., pressing them into
cathode casings) are subjected either to washing out the expanding
agent with an appropriate solvent or to thermal treatment for
removing the sublimating expanding agents from the cathode. As a
result, a porous structure necessary for normal operation of an
electrochemical cell is established in the cathode (cf. references
2, 4, 5). However, porous cathodes of electrochemical cells,
wherein used as expanding agents are such soluble compounds as
camphor [4] or potassium hexafluorophosphate [5] are rather hard to
be washed out from an expanding agent. This is concerned with the
fact that the particles of the spent expanding agent are occluded
during the cathode forming process with a binder or an energy
carrier, which affects adversely the properties of a cathode and of
an electrochemical cell based thereon. For that reason many times
repeated procedures are used for completely removing the expanding
agent, which involves the use of further amounts of solvents. In
addition, use of said materials and methods of making electrodes
for electrochemical cells renders impossible realizing higher
energy characteristics in a lithium electrochemical cell having a
porosity of 35-50% adequate for serviceability of an
electrochemical cell, because porous cathodes of electrochemical
cells, wherein used as expanding agents is zeolite [6] or activated
alumina [7] feature a reduced weight and volume energy capacity,
that is, such expanding agents fail to exhibit electrical activity
being therefore no more than useless ballast.
[0010] Use of a known active cathode mass in electrochemical cell
electrodes which contains a metal oxide (such as manganese dioxide,
lead monoxide or mixtures thereof) as an electrode-active material,
and graphite expandate [2] as an electrical conductance increasing
agent, affects adversely the electrode specific energy capacity.
Graphite expandate (expanded graphite) serves in cathode material
also as an expanding agent due to its low density (0.007-0.05
g/cu.cm), large specific surface [2], and high porosity. Used for
making electrode material is a natural graphite expandate of the
coral-like structure which makes up to 25% of the weight of energy
carrier. The coral-like structure of the graphite expandate is
realized in case of a separately conducted thermolysis of various
graphite compounds, such as fluorinated graphite [3]. Adding
graphite expandate to the electrode composite is an inconvenient
procedure due to its material being a badly dusting one.
[0011] One prior-art electrochemical cell electrode and a method of
making same (EP Patent N 0146764, IPC H01m 4/06, 4/88 [8] are
known, the electrode material comprising an electrode-active
material in the capacity of which carbon monofluoride is used, a
binding agent (fluopolymer), and an agent increasing electrical
conductance of the electrode-active material. During the electrode
producing process an expanding agent is added, a nonpolymer
additive (alcohols, hydrocarbons, solutions) being used as said
agent. The expanding agent is introduced into a mixture of
ingredients during their intermixing at the very beginning of the
electrode producing process so as to prepare a dough-like mass and
make a finished resilient microporous carbon-containing electrode
therefrom by removing the expanding agent. The porous structure of
the cathode is formed after the expanding agent has been
evaporation removed, which follows the electrode making process
comprising intermixing all the components and applying a high
shearing force to to the resultant mixture so as to form therein a
homogeneous filamentary structure, followed by electrode forming by
extruding or calendering, pressing, and stacking the packages till
obtaining a finished electrode cathode plate for an electrochemical
cell.
[0012] The aforedescribed material and method of making an
electrode (cathode) therefrom are quite acceptable for use in a
lithium electrochemical cell. However, said material and method
suffer from the following disadvantages stemming from the specific
features of the components used in the electrode and of the method
for making an electrochemical cell electrode therefrom:
[0013] relatively low energy, effectiveness, namely, capacitance of
the resultant carbon-containing cathode material which is due to an
inadequate amount of one of its principal components, i.e., the
electrode-active material in the capacity of which carbon
monofluoride is used. In a worldwide practice of producing the
cathodes of the "fluorocarbon-lithium" system cell batteries used
are as a rule fluorocarbon materials, such as dicarbon monofluoride
(C.sub.2F) and carbon monofluoride (CF.sub.1.0) which contain up to
59 wt. % fluorine, for instance, fluorinated petroleum coke having
a composition CF.sub.0.92-1.0. Theoretical capacitance of carbon
monofluoride is 861 mAh/g;
[0014] carbon monofluoride also has a relatively low bulk density
(about 1.0 g/cu.cm) which prevents one to introduce a greater
amount of energy carrier into the actual volume of the positive
electrode of a lithium electrochemical cell in order to increase
the specific volumetric energy capacity thereof;
[0015] carbon monofluoride has relatively low operating discharge
current density values in standard fluorocarbon cathodes (not over
0.1 mA/sq.cm) and is featured by a badly reduced initial discharge
voltage under higher current loads, which is due to deposition of
solid lithium fluoride on the cathode surface. This phenomenon
occurs due to the fact in an actual electrochemical cell under such
increased discharge current conditions the total volume of its
pores is inadequate for lodging a required amount of electrolyte
for dissolving the resultant diffusion layer of solid lithium
fluoride, i.e., the product of reaction between fluorocarbon and
lithium. Of importance is also the fact that fluorocarbon cathodes
offer high ohmic resistance and hence feature high overvoltage
value which reveals itself in that the value of the running
discharge voltage under a nominal load of 30 kOhm drops to 2.6-2.7
V during the electrochemical cell operation;
[0016] when being discharged, an electrochemical cell with a
fluorocarbon electrode is frequently liable to swell. This
phenomenon is allowed for in constructing a lithium electrochemical
cell by introducing a lower amount of fluorocarbon into the
electrode to prevent the cell from swelling;
[0017] as a result of intermixing the parent components of the
carbon-containing electrode material and the following steps of
electrode forming by extruding or calendering, pressing, and
stacking the packages till obtaining a finished porous cathode
plate for an electrochemical cell, the resultant cathode plate is
homogeneous but rigid due to a strong volume cohesion of composite
by the binding agent, i.e., fluoropolymer;
[0018] when making the electrode using the known method, that is,
by mixing all components in a single step and applying a high
shearing force to the resultant mixture so as to form therein a
homogeneous filamentary structure of the electrode material, the
particles of the electrode-active material and those of the agent
adding to electrical conductance of said material are excessively
occluded with the binder so that the particles of the active mass
are frequently found to be coated-with a layer of the binder which
results either in a badly reduced capacitance of the electrode
under nominal discharge conditions (0.1 mA/sq.cm) or in failure to
operate such an electrode at increased discharge current density
values in a lithium electrochemical cell, because such a
fluorocarbon electrode in combination with lithium has an output
voltage below 2 V with a discharge current density of 0.1 mA/sq.cm
and over;
[0019] it is rather difficult to effect control over pore formation
in the cathode by the known method during production of a finished
product (electrode) as pores are formed in such an
carbon-containing electrode by virtue of fine droplets of an
expanding agent, namely a liquid nonpolymer additive (such as
alcohols, hydrocarbons, solutions) which is spread over the cathode
composite as result of mixing and volume cohesion during
calendering at the expense of a binder. The resultant pores get rid
of the expanding agent by volatilizing the nonpolymer liquid
used;
[0020] as a result of the aforesaid process of making the electrode
mass of a carbon-containing material, adhesion of the resultant
rigid porous cathode plate to the current lead gets rather low
(with a untight press-fitting), wheres in case of a more tight
press-fitting (under a higher pressure) the cathode porosity is
reduced due to forcing the liquid out of the pores. Thus, an
intermediate variant is selected by using such pressure values (or
press-fitting on an additional current lead welded on to the
cathode cover) at which adhesion is retained and an acceptable
cathode porosity is attained.
[0021] By and large, practical application of the electrochemical
cell production process technique according to the known method
affects adversely the discharge characteristics of an
electrochemical cell during its operation.
DISCLOSURE OF THE INVENTION
[0022] It is a principal object of the present invention to provide
a carbon-containing material having such components, and such a
method of making porous electrodes from said material that are
instrumental in attaining higher specific energy characteristics of
the carbon-containing material in the electrode of an
electrochemical cell, including volume- and weight electrical
capacitance and energy capacity, as well as higher operating
density of discharge current and voltage, and in simplifying the
method of making such electrodes.
[0023] The foregoing object is accomplished due to the provision a
carbon-containing material for electrodes of electrochemical cells,
said material comprising an electrode-active material, a binder, an
agent adding to electrical conductance of the electrode-active
material, and an expanding agent, wherein, according to the
invention, used as the expanding agent is graphite oxyfluoride.
[0024] A positive effect of applying such an expanding agent
resides in that an adequate number of pores for lodging a
nonaqueous electrolyte therein are established in the structure of
the active mass for making a carbon-containing electrode after the
steps of mixing and heat-treatment. In addition, heat-treatment of
graphite oxyfluoride results in formation of thermally expanded
graphite inside the electrode which is in fact an agent increasing
electrical conductance of the electrode. Moreover, use of the
aforementioned expanding agent makes possible unifying electrode
materials by using a single expanding agent for the various types
of 1.5- and 3-volt electrochemical cells using different
electrode-active materials. Use of such a common expanding agent
increases the aforementioned specific energy characteristics of the
proposed material in the electrode of an electrochemical cell.
[0025] As a rule, graphite oxyfluoride is assigned the following
general formula:
C.sub.x.zCyO.nH.sub.2O.CF,
[0026] where
[0027] x=1.5-12,
[0028] y=2.2-2.5,
[0029] z=0.5-1.4,
[0030] n=0.1-0.5
[0031] cf. USSR Inventor's Certificate N 955,654 by L. L.
Gornostaev et al., registered on May 4, 1982 for "Graphite
oxyfluorides and process for producing same", IPC C01B 31/00 [9]).
However, use of such a product as an expanding agent is efficient
only in rather expensive cathode masses based on fluorocarbon as an
electrode-active material, whereas it proves to be more expedient
that used as an expanding agent in cathode masses based on oxides
and sulfides of metals or mixtures thereof is another less
expensive type of graphite oxyfluoride featuring a modified phase
ratio (i.e., an increased content of the graphite phase and reduced
content of the graphite oxyfluoride phase), expressed by another
general formula:
C.sub.x.zCyO.nH.sub.2O.CF,
[0032] where
[0033] x=5-15,
[0034] y=2.2-2.5,
[0035] z=0.2-2.0,
[0036] n=0.1-2.0.
[0037] This is due to the- fact that graphite oxyfluoride prepared
by known processes appears nearly always as a close mixture of the
three phases, wherein present in the graphite phase (C.sub.x) are
the phases of graphite oxide (zCy.sub.O) and fluorinated graphite
(CF) which have been etched out during oxidation. Accordingly,
chemical behavior of graphite oxyfluoride and hence conditions for
its use as an expanding agent are dependent on the ratio between
and behavior of all the three phases at a variable temperature.
[0038] It is most expedient that fluorocarbon containing 58 to 67
wt. % fluorine be used as the electrode-active material of a
carbon-containing material with a view to increasing the energy
capacity thereof to a maximum possible level, because such a
fluorocarbon is superior to the known fluorocarbon materials
(namely, carbon monofluoride or fluorinated petroleum coke) as for
the amount of fluorine and hence contains more energy, whereby the
object of the invention as to increasing specific energy capacity
of the electrode and of an electrochemical cell as a whole is
accomplished.
[0039] It is also expedient, with a view to increasing specific
energy capacity of the material and of an electrode based thereon,
that used as the electrode-active material be high specific energy
capacity compounds of transition metals, such as oxides and
sulfides of metals taken either separately or in combination.
[0040] It is expedient that with a view to increasing specific
energy capacity of three-volt lithium electrochemical cells, used
as the electrode-active material be less expensive manganese
dioxide.
[0041] It is also expedient to use graphite oxyfluoride in
combination with the electrode-active materials used in one and a
half-volt electrochemical cells, namely, copper oxide, as well as a
mixture of copper oxide with pyrite or chalcopyrite.
[0042] A good effect is attained when using copper oxide, as well
as a mixture of copper oxide with pyrite or chalcopyrite in
combination with graphite oxyfluoride, a binder, and a
conductance-increasing agent which increases electrical conductance
of the carbon-containing materials for electrodes of one and a
half-volt electrochemical cells.
[0043] Thus, practical use of the herein-proposed carbon-containing
material for electrodes of electrochemical cells makes possible
producing porous electrodes for electrochemical cells, which
electrodes being superior to known electrodes as to capacitance.
This is attained due to forming pores in the structure of an
electrode made from the proposed carbon-containing material. Pores
in an electrode are necessary for lodging electrolyte therein. In
addition, a close mixture of the products of thermolysis of
graphite oxyfluoride with the electrode-active material makes it
possible to attain higher factors of utilization of the
electrode-active material as will hereinafter be demonstrated.
[0044] The foregoing object is accomplished also due to the
provision of a method of making porous electrodes for
electrochemical cells, comprising mixing an electrode-active
material, a binder, an agent increasing the conductance of the
electrode-active material, and an expanding agent, and forming a
finished product, wherein, according to the invention, used as the
expanding agent is graphite oxyfluoride and mixing the components
are effected in several steps so that at the first step graphite
oxyfluoride is mixed with the electrode-active material, then the
resultant mixture is modified until an intermediate product is
obtained, which is then mixed with the binder and the agent
increasing the conductance of the electrode-active material, and
formation of a finished product is followed by its heat-treatment
till forming pores in the structure of the finished electrode
without its destruction.
[0045] A step-by-step mixing of components and modification of the
resultant mixture at the first step are conducive to a close mixing
of the electrode-active material together with the expanding agent
which is accompanied by further disintegration of the components
and by an increase in the bulk density of the mixture of the
electrode-active material with graphite oxyfluoride, thus adding to
the electrical conductance of the latter. In addition, such
step-by-step mixing of the components enables one to control final
density and porosity of the electrode material by regulating the
mixing conditions at the second step to obtain an elastic active
mass. Provision of said elastic resulting from the second step of
final mixing of all the components facilitates the electrode
forming process and control of its density. A positive effect of
such a method of making a porous electrode consists in a
possibility of attaining higher energy capacity of the electrode
under nominal discharge conditions (0.1 mA/sq.cm) which is due to
combining a number of newly arising effects:
[0046] lodging in the electrode free space an adequately large
amount of any of the aforelisted electrode-active materials
modified in a mixture with the expanding agent makes it possible to
attain a substantially higher specific energy capacity of such
electrodes than that in the best of the heretofore-known 1-.5- and
3-volt lithium 17 lithium electrochemical cells;
[0047] use of the herein-proposed expanding agent, viz, graphite
oxyfluoride in the electrode and a method for making said electrode
makes possible attaining a higher density of continuous discharge
current (0.75-1.0 mA/sq.cm and over) with a high capacitance
remaining unaffected, which is attained due to heat-treatment of
the finished product, since thermal decomposition of graphite
oxyfluoride is accompanied by forming pores therefrom in the
electrode without destruction of the latter, as well as by forming
thermally expanded graphite uniformly distributed in the electrode
material, the presence of which adds to the conductance of both
said material and said electrode and hence makes it possible to
reduce a voltage drop of the current source as a whole due to its
internal resistance.
[0048] Used as graphite oxyfluoride may be any of the known ones,
though it is most expedient to use graphite oxyfluoride of the
following general formula:
C.sub.x.zCyO.nH.sub.2O.CF,
[0049] where
[0050] x=1.5-15,
[0051] y=2.2-2.5,
[0052] z=0.5-1.4,
[0053] n=0.01-0.5.
[0054] It is expedient that used as electrode-active materials for
attaining higher specific energy capacity of electrodes and
electrochemical cells are substances which feature maximum energy
capacity, viz, fluorocarbon and manganese dioxide for making the
cathodes of three-voltage lithium electrochemical cells, as well as
oxides and sulfides of transition metals, in particular, copper
oxide, pyrite, chalcopyrite taken either separately or in
combination.
[0055] Use of each of the aforementioned electrode-active materials
as components of the electrode masses for lithium electrochemical
cells in combination with the rest of the components of a
carbon-containing material makes it possible to provide electrodes
of lithium electrochemical cells having higher specific energy
capacity.
[0056] It is desirable that the electrode-active material and
graphite oxyfluoride be mixed together in a weight ratio of from
8:1 to 40:1, respectively which has been found experimentally. The
lower limit of said ratio is determined by the fact that when the
graphite oxyfluoride content of the composition is below 40:1, this
renders the effect of adding the expanding agent immaterial and
does not virtually increase the energy capacity of an
electrochemical cell and the attainable operating density of
discharge current. The upper limit of said ratio is determined by
the fact that with the graphite oxyfluoride content of the
composition exceeding 8:1 the resultant electrode though being
highly porous, features a reduced content of the electrode-active
material, which result in an affected capacitance of a lithium
electrochemical cell.
[0057] It is favorable that at the second step of mixing a diluent
is added to the mixture until a paste-like mass is obtained,
whereby a homogeneous elastic paste-like material can be
obtained.
[0058] It is expedient to use a polytetrafluoroethylene suspension
as the binder, whereby an adequately strong elastic homogeneous
material can be obtained which can readily be rolled on roll.
[0059] Heat-treatment is desirable to perform at 150 to 350.degree.
C.
[0060] The aforementioned temperature range is characteristic of
thermolysis of the graphite oxyfluoride having the above-specified
composition and is adequate for a uniformly running complete
thermolysis of graphite oxyfluoride and forming pores in the
structure of a carbon-containing electrode without collapsing the
shape thereof.
[0061] It is expedient that modification be effected by virtue of
an impact action, the most efficient being such action with a
gravitational acceleration of tumbling bodies ranging from 10 g to
75 g, where g is gravitational acceleration. As a result of such a
treatment fluorocarbon materials get modified, that is, the
aforedescribed changes occur, in particular, bulk density is
increased, concentration of paramagnetic centers rises, and the
size of crystallites or particles is reduced which is accompanied
with reduced coherent scattering areas. This in turn leads to
increased discharge characteristics of fluorocarbon materials and
higher energy capacity of cathode materials made therefrom. An
averaged interplanar spacing (according to X-ray diffraction
findings) is likewise somewhat reduced due to an abruptly
diminished quantity of combined-layer structures.
[0062] It is desirable that the impact action be carried out in the
presence of water or a low-boiling organic solvent taken in an
amount of from 0.1 (which is the level of natural moisture-content
of an electrode-active material) to 5 wt. % in the mixture. In this
case the impact action is favorable to effect before obtaining an
intermediate product having a bulk density of from 1.0 to 1.5
g/cu.cm.
[0063] Presence of water or a low-boiling organic solvent in
mechanical impact treatment of a mixture of fluorocarbon
and-graphite oxyfluoride provides further effect due to the fact
that in the presence if 0.1-5 wt. % water or a low-boiling organic
solvent the material becomes no longer dusty but retains looseness
and a required intermediate product density (1.0-1.5 g/cu.cm) is
attained faster than without using a liquid additive.
[0064] It is desirable that at the second step of the mixing
process the latter is performed in the presence of water, ethanol,
a mixture of both, or a low-boiling hydrocarbon-having a boiling
point below 100.degree. C. This makes possible producing a
past-like mass from which electrode bands and finished electrodes
are readily shaped and which is easily press onto current leads
during the electrode shaping procedure.
[0065] Thus, the herein-proposed carbon-containing material for
electrodes of electrochemical cells and a method of making porous
electrodes therefrom is instrumental in attaining the following
advantages in an electrochemical cell, predominantly a lithium
one:
[0066] higher specific volume and weight energy capacity of a
carbon-containing electrode which is attained due to a combination
of an increased utilization factor of the electrode-active material
with an adequately high content of the latter in the electrode;
[0067] higher ultimate operating density of the electrode discharge
current in electrochemical cells attainable due to the provision of
a porous electrode, as well as due to modifying of a mixture of an
electrode-active material and an expanding agent to obtain an
intermediate product, followed by making a porous electrode;
[0068] provision of a standard production procedure of electrodes
featuring in creased energy capacity, using a broad range of
electrode-active materials for creating efficient lithium
electrochemical cells of both 1.5- and 3-volt systems.
[0069] Use of graphite oxyfluoride as the expanding agent makes
possible applying for making the electrode of a higher energy
capacity electrochemical cell a fluorocarbon leaner in fluorine
(and hence less expensive), containing as low as 58 wt. % fluorine
(which corresponds to CF.sub.0.87) rather than 61.29 wt. % (as
required for carbon monofluoride CF.sub.1.0) which enables one to
extend the range of electrode-active materials used.
BEST METHOD OF CARRYING OUT THE INVENTION
[0070] The following starting materials are used for carrying the
invention into effect.
[0071] Used as electrode-active materials are fluorocarbons with a
fluorine content of 58-67 wt. % or compounds of transition metals,
such as oxides and sulfides of such metals taken either separately
or in combination, e.g., copper oxide, a mixture of copper oxide
with pyrite or chalcopyrite.
[0072] Use of fluorocarbon materials having a fluorine content
below 58 wt. % is of low efficiency, since electrodes and
electrochemical cells thus produced possess lower energy capacity
than that attained for the heretofore-known "fluorocarbon-lithium"
system. Use of fluorocarbon materials having a fluorine content
above 67 wt. % which is the case with polytetrafluoroethylene
containing 76 wt. % fluorine, as the electrode-active material
proves to be inefficient because such fluorine-rich materials are
in fact electrochemically inactive. Therefore use is made as a rule
of a fluorocarbon having a fluorine content of 65-67 wt. %.
[0073] Used as the binder may be a polytetrafluoroethylene
suspension.
[0074] Used as the expanding agent is graphite oxyfluoride having
the following general formula:
C.sub.x.zCyO.nH.sub.2O.CF,
[0075] where
[0076] x=1.5-15,
[0077] y=2.2-2.5,
[0078] z=0.5-1.4,
[0079] n=0.1-0.5.
[0080] It is basically practicable to use graphite oxyfluorides
prepared by the heretofore-known processes and featuring another
composition; however, said processes are very complicated, whereby
such graphite oxyfluorides are more expensive and hence less
efficient products. Moreover, graphite oxyfluorides of other
compositions are not considerably superior to that proposed herein
as to the energy capacity and discharge current density attainable
in the electrode of a electrochemical cell.
[0081] A minimum value of x=1.5 in the general formula of graphite
oxyfluoride is dictated by experimental capabilities of producing
said material according to the process [8] and also by the fact
that with value of x below 1.5 one does not so far succeed in
selecting an electrode composition with the use of which the
electrode would not be destructed during the heat-treatment
procedure due to vigorous thermolysis of such a graphite
oxyfluoride.
[0082] A maximum value of x=15 in the general formula of graphite
oxyfluoride is selected on account of the fact that its further
increase, that is, further increase in the proportion of the
graphite phase in the mass of graphite oxyfluoride neither results
in a considerable pore formation effect nor further increases
discharge characteristics of an electrochemical cell electrode.
[0083] It is common practice to use a graphite oxyfluoride having
the value of x=12-15 as the most inexpensive expanding agent.
[0084] As a rule, used as the agent increasing the conductance of
the electrode-active material (and of the electrode as a whole) is
acetylene black.
[0085] Usually there is taken 78-85 wt. % of an electrode-active
material, e.g., fluorocarbon material having a fluorine content of
58-67 wt. % and a natural moisture content of from 0.1 to 1.0 wt.
%, whereupon said material is mixed directly in the drum of a
mechano-chemical activator (cf., e.g., Centrifugal barrel mill,
USSR Inventor's Certificate N 101,874, Bulletin N 11, 1955) [11]
with graphite oxyfluoride of the following general formula:
C.sub.x.zCyO.nH.sub.2O.CF,
[0086] where
[0087] x=1.5-15,
[0088] y=2.2-2.5,
[0089] z=0.5-1.4,
[0090] n=0.1-0.5,
[0091] with their weight ratio of from 8:1 to 40:1, whereupon water
or a low-boiling solvent (ethanol, acetone, volatile hydrocarbon)
is added to the resultant mixture in an amount of 1.0-5.0 wt. %,
and the mixture is modified, at the first step of mixing, by
subjecting it to mechanical impact treatment until an intermediate
product is obtained, having a bulk density of from 1.0 to 1.5
g/cu.cm, said treatment being carried out in, e.g., a
planetary-friction apparatus at a gravitational acceleration of
10-75 g, the treatment time being usually 2.5 min. A minimum
gravitational acceleration 10 g (where g stands for free fall
acceleration) is obtained experimentally as a result of checking
for absence of a substantial impact action on the fluorocarbon
material in various treatment apparatus (in particular, effects
described in Example 2 hereinbelow occur at a gravitational
acceleration of 10 g after a prolonged impact action and at a
higher power consumption and a longer treatment time, accordingly).
A maximum value of gravitational acceleration used is 75 g. When
said acceleration value exceeds 75 g this leads to badly increased
power consumption and to higher construction requirements imposed
on the components of treatment apparatus, especially as to
wear-resistance thereof (it is not permissible to allow
considerable amounts of metal resulting from attrition of rubbing
surfaces to get in cathode masses) without further substantial
modification of the properties of the fluorocarbon materials
involved.
[0092] Routine mechanical treatment, viz, extensively known
disintegration of material in traditional disintegrators or
grinders (with an acceleration of grinding or tumbling bodies of
from 1 to 5 g in, e.g., ball mills or disk-type grinders) fails to
provide an increased number of paramagnetic centers and to change
other important properties of an electrode-active material. It is
practicable, however, to use other modification methods by virtue
of mechanical action exerted by other apparatus capable of
providing impact conditions, i.e., from 10 to 75 g. It is also
practicable to use chemical methods for modifying the surface of an
electrode-active material, e.g., by treating fluorocarbon materials
in a controlled gaseous medium at an elevated temperature (over
350.degree. C.). However, application of such methods to a mixture
of graphite oxyfluoride with an electrode-active material might
provoke a premature "swelling" of the intermediate product due to
graphite oxyfluoride thermolysis, thus rendering it unfit for
further making carbon-containing porous electrodes for higher
energy capacity electrochemical cells.
[0093] It is found experimentally that the best density of the
resultant intermediate product (viz, a modified mixture of graphite
oxyfluoride with a fluorocarbon material) lies within 1.0 and 1.5
g/cu.cm. With lower density values of the intermediate product the
resultant finished electrode though being of high porosity but has
a lower volumetric energy capacity than is required for
electrochemical cells. Though higher density values are basically
attainable in the course of the modification process, it is,
however, difficult to produce from the obtained intermediate
product an elastic paste-like material necessary for a successful
electrode shaping procedure. Furthermore, attempts to attain higher
intermediate product density lead to badly increased consumption of
the material the tumbling bodies are made from, with the resultant
contamination of the electrode with foreign impurities and
adversely affected the durability of the electrode properties and
the service life of an electrochemical cell proper.
[0094] The post-modification intermediate product consisting of a
close mixture of graphite oxyfluoride with an electrode-active
material, at the second step is mixed in a separate container with
a binder (usually a polytetrafluoroethylene suspension) and with an
agent increasing conductance of the electrode-active material
(usually acetylene black). The binder is usually added in an amount
of 5-10 wt. % and the amount of the agent increasing conductance of
the electrode-active material and of the carbon-containing
electrode in electrochemical cells equals usually 5-10 wt. % of a
total weight of the material. Mixing is effected in, e.g., a
standard propeller (or another-type) stirrer until a homogeneous
mass of the carbon-containing material for electrochemical cell
electrodes is obtained.
[0095] The mixture obtained at the second step may be doped with
two- or five-fold amount of water, ethanol or a volatile
hydrocarbon (such as hexane, heptane, gasoline) for a better mixing
procedure, which is carried out in, e.g., a standard propeller
stirrer until a paste-like mass is obtained. Once the paste-like
mass has been separated, the carbon-containing material for
electrochemical cell electrodes is dried at, e.g., 100-150.degree.
C. for a main proportion of moisture or diluent to eliminate.
[0096] The resultant carbon-containing material for electrochemical
cell electrodes is wetted with ethanol or heptane using, e.g., a
standard technique disclosed in [1] and the resultant paste-like
electrode mass is rolled on rolls to obtain a blank of the
electrode band. Then carbon-containing electrodes are cut out of
said band and pressed onto electrical leads, e.g., metal cases of
disk-type electrochemical cells or metal screens of roll-type
electrochemical cells, or else they are pressed into, e.g., metal
cylindrical jars of packed-type chemical cells, which jars also
serve as electrical leads. The electrode blanks together with
electrical leads are subjected heat-treatment in, e.g., a vacuum
drying cabinet at 150-350.degree. C. The drying conditions (i.e.,
rate of temperature elevation and a drying cabinet holding time)
should be so selected as to prevent destruction of finished
electrodes but to provide elimination of volatile products (water,
organic solvents, and products of thermolysis of graphite
oxyfluoride) resulting in pore formation inside the electrode
structure. Finally, electrochemical cells, e.g., lithium cells of
the disk or cylindrical construction are assembled.
[0097] For a better understanding of the invention given below are
some specific exemplary embodiments thereof.
EXAMPLE 1
[0098] Porous electrodes having specific preset parameters were
made, using the abovedescribed technique, whereupon disk-type
lithium electrochemical cells were assembled from said electrodes
with use of standard electrolyte grade 1M LiClO.sub.4 in a mixture
with propylene carbonate and dimethoxyethane. The assembled cells
were of the following standard size: BR2325 (the
"fluorocarbon-lithium electrochemical system) and CR2325 (the
manganese dioxide-lithium electrochemical system). The discharge
tests of the cells were conducted at room temperature under a 30
kOhm load. The test results are tabulated in Table 1 below.
1 TABLE 1 Electrode- NN active Fluorocarbon Manganese nn material
material dioxide 1 2 3 4 Specific 515 590 630 320 electrode
capacitance, mah/g Fluorocarbon 58.0 63.0 67.0 -- fluorine content,
wt. % Electrode- 85.0 82.0 78.0 80.0 active material content of
mixture in wt. % with respect to electrode weight Binder 5.0 5.0
5.0 7.0 content, wt. % Value of "x" 1.5 12.0 15.0 15.0 in graphite
oxyfluoride formula Weight ratio 1:8 1:12 1:20 1:40 of graphite
oxyfluoride to electroac- tive material Intermediate 1.2 1.5 1.3 --
product density, g/cu. cm Acceleration 45 10 75 -- of tubling
bodies, "g" units Content of 0.1 1.0 5.0 -- water or low- boiling
organic solvent during modification, wt. % Heat- 250 270 350 150
treatment temperature, .degree. C.
[0099] In what follows are further exemplary embodiments of the
present invention making use of various materials for making porous
electrodes for lithium electrochemical cells.
EXAMPLE 2
[0100] Fluorocarbon materials appearing as powders containing 63-67
wt. % fluorine, as well as disintegrated fluorinated fabric
containing 58-61 wt. % fluorine and appearing as pieces of
fluorinated fabric and dust resulting from cutting said fabric into
pieces, were mechanically treated in standard ball mills for 8-20
hours at a rotation speed of 2 to 20 rpm, the acceleration of a
free falling tumbling body, i.e., a ball being virtually equal to
gravitational acceleration (g). After such a treatment the bulk
density of the resultant disintegrated fluorocarbon materials
increases but insignificantly compared with the initial one,
namely, by 3-7 wt. % for the material containing 65-67 wt. %
fluorine, by 10-15 wt. % for the material containing 63-65 wt. %
fluorine, and by 10-15% for the disintegrated fluorinated fabric.
Concentration of paramagnetic centers for all types of
fluorocarbons remains virtually unaffected (within the sensitivity
of the electronic paramagnetic-resonance method). The size of the
coherent scattering areas (that is, the size of microparticles of
fluorocarbon materials) within the accuracy tolerance of the X-ray
diffraction method remains likewise invariable. It is particle size
distribution alone (determined by means of sieve analysis) that is
found to have changed; in particular, for the two former of
abovedescribed materials an average size of macroparticles
(aggregates of microparticles) decreases two- or fourfold. The
fluorine content (within accuracy tolerance of the analysis) of the
disintegrated fluorocarbon materials remains the same as in the
starting materials.
[0101] Carbon-containing electrodes made from disintegrated
fluorocarbon materials by a standard procedure of mixing them with
acetylene black and a binder, viz, polytetrafluoroethylene
suspension taken according to same formulation (i.e., 80 wt. %
powdered fluorocarbon, 10 wt. % acetylene black, and 10 wt. %
polytetrafluoroethylene suspension), and preparing according to the
flowsheet of the known method (except for using a strong shearing
force) were tested on stacks of BR2325 type lithium electrochemical
cells. The following findings were obtained as to the capacitance
of lithium electrochemical cells with a discharge current density
of 0.1 mA/sq.cm: for the first material, 190 +13 mAh, for the
second material, 160+15 mAh, and for the powdered fluorocarbon
prepared from disintegrated fluorinated fabric, 140+20 mAh. With a
discharge current density of 1.0 mA/sq.cm the results of
capacitance measurement were by approximately 20-6-% lower, while
the worst results were exhibited by electrochemical cells based on
the second and third materials.
[0102] The minimum number of the electrochemical cells produced and
of electrical measurements conducted in each series for each
material is 10.
[0103] For the sake of comparison there were tested electrochemical
cells made on the base of fluorocarbon cathodes of the same
composition made from nondisintegrated first and second materials.
The test findings as to capacitance after mechanical impact
treatment are tabulated in Table 2 below.
2TABLE 2 Results of impact treatment of various fluorocarbon
materials Characteristic Starting material Treated material 1 2 3
Powdered fluorocarbon with 65-67 wt. % fluorine content Bulk
density, 0.85 + 0.05 1.3 + 0.10 g/cu. cm Size of coherent 22.5 +
1.5 16.5 + 2.5 scattering area, A Average size on 6.64 + 0.02 6.61
+ 0.01 "C", A Weight 16 * 1018 28 * 1018 concentration of
paramagnetic centers, g.sup.-3 Volume 13 * 1018 39 * 1018
concentration of paramagnetic centers, cm.sup.-3 Capacitance of 190
+ 13 225 + 12 disk-type lithium electrochemical cell, mAh Powdered
fluorocarbon with 63-65 wt. % fluorine content Bulk density, 0.45 +
0.15 1.3 + 0.10 g/cu. cm Size of coherent 22.5 + 1.0 17.0 + 1.5
scattering area, A Average size on 7.64 + 0.02 6.71 + 0.02 "C"
axis, A Weight 4.5 * 1018 6.4 * 1018 concentration of paramagnetic
centers, g.sup.-1 Volume 1.6 * 1018 8.3 * 1018 concentration of
paramagnetic centers, cm.sup.-3 Capacitance of 165 + 25 205 + 10
disk-type lithium electrochemical cell, mAh 1 6 7 Powdered
fluorocarbon with 65-67 wt. % fluorine content obtained from
fluorinated fabric Bulk density, 0.80 + 0.20 1.2 + 0.15 g/cu. cm
Size of coherent 35-50 19.5 + 0.5 scattering area, A Average size
on 7.44 + 0.20 6.67 + 0.05 "C" axis, A Weight 4.5 * 1018 6.4 * 1018
concentration of paramagnetic centers, g.sup.-1 Volume 1 * 1018 29
* 1018 concentration of paramagnetic centers, cm.sup.-3 Capacitance
of 150 + 25 180 + 10 disk-type lithium electrochemical cell, mAh
Treatment conditions: gravitational acceleration, 10-75 g,
treatment time, 3-5 min
[0104] cell capacitance with discharge current density of 0.1
mA/sq.cm: for powdered fluorocarbon materials, 165+35 mAh; for
powdered fluorocarbon materials from fluorinated fabric, 150+35
mAh.
[0105] It follows from the Examples adduced hereinbefore that as
far as powdered fluorocarbon materials are concerned, standard
disintegration in ball mills does not virtually increase maximum
capacitance of a lithium electrochemical cell but tells only on the
root mean square (standard) deviation with a general average
capacitance decrease in a series. Thus, the role played by
mechanical treatment of the fluorocarbon material in a ball mill
boils down solely to producing finely ground powders without any
noticeable change in their properties.
[0106] Industrial applicability of the present invention is
supported by the following examples.
EXAMPLE 3
[0107] Fluorocarbon materials appearing as powders or pieces
((fibers)) of fluorinated fabric containing 0.1 wt. % water (which
is a natural moisture content of the materials) were charged in the
drums of a planetary-friction disintegration apparatus of any type
(use was made of APF-3, APF-7, and APF-8 units, as well as some
other laboratory apparatus capable of developing a tumbling body
acceleration of 10-7 g), wherein they were treated using the method
of mechanical impact action by virtue of, e.g., special grinding
bodies (balls) for 3-5 min. The data on the changes occurred in the
thus-treated fluorocarbon materials are tabulated in Table 2.
[0108] It follows from the data of Table 2 that mechanical impact
treatment is capable of changing in the properties of fluorocarbon
materials telling positively on accomplishing the object of the
invention, i.e., provision of higher energy capacity of
electrochemical cells.
[0109] Note: It is the abovedescribed mechanical impact treatment
of fluorocarbon materials that increases the values of the
open-circuit voltage in lithium electrochemical cells by 0.15-0.2 V
on the average, as well as the maximum attainable values of
discharge current density (approximately three- or fivefold and up
to
[0110] 5 mA/sq.cm) which gives evidence of a reduced overvoltage in
a fluorocarbon-lithium electrochemical cell. The said increase in
the specific energy capacity of the electrode of a lithium
electrochemical cell makes possible using even a fluorocarbon
having a relatively low fluorine content, that is, a powdered
material resulting from mechanical impact treatment of fluorocarbon
fabric, containing as low as 58 wt. % fluorine, that is, less than
the fluorine content of carbon monofluoride in the known
method.
EXAMPLE 4
[0111] There was carried out a mechanical impact treatment of
fluorocarbon materials having a fluorine content of 58-67 wt. % in
the presence of 1 wt. % water (an increased moisture content of the
materials which had been developed during storage in a humid
atmosphere) for 2-3 min. The resultant modified fluorocarbon
materials had the same characteristics which are specified in Table
2 with reference to the materials having a moisture content of 0.1
wt. %. Similar results as to the characteristics of the
fluorocarbon materials under treatment were obtained therefor when
they were wetted to a moisture content of 1-5 wt. % organic
solvents applied in the cathode mass production techniques, viz,
ethanol, acetone, and liquid hydrocarbons (hexane, heptane, and
decane). However, as a result the required treatment time was
decreased to 1-2 min, whereby the material became low-dusting.
[0112] Note: The method described in the above Example is
especially suitable and convenient for handling such a "dusty"
fluorocarbon material (having a relatively low bulk density) as
fluorinated black having a fluorine content of 63-65 wt. %.
EXAMPLE 5
[0113] A number of test series of fluorocarbon-based cathode
materials were made using the abovedescribed methods, said
materials having the following composition: 78-85 wt. % of the
fluorocarbon material of the three types stated in Example 2, 5-10
wt. % of a binder, 3-10 wt. % of graphite oxyfluoride of the
following general formula:
C.sub.x.zCyO.nH.sub.2O.CF,
[0114] where
[0115] x=1.5-15,
[0116] y=2.2-2.5,
[0117] z=0.5-1.4,
[0118] n=0.1-0.5,
[0119] as well as 5-15 wt. % of acetylene black. As a rule, use is
made of mean values of the above specified ranges of electrode
components. Then positive electrodes (cathodes) were made (shaped)
from said cathode masses, and type BR2325 fluorocarbon-lithium
electrochemical cells were assembled, using standard grade 1M
LiClO.sub.4 electrolyte in a mixture with propylene carbonate and
dimethoxyethane. Thereupon said cells were subjected to discharge
testing at room temperature under a 30 kOm load. The test findings
with reference to characteristics and composition of the cathodes
are tabulated in Table 3 below. The lower and upper limits of
content of the binder and of the agent increasing the conductance
of the electrode-active material and that of the electrode as a
whole are specified in the first two and the last four lines of
Table 3 for a powdered fluorocarbon material having a fluorine
content of 65-67 wt. %. For the sake of comparison the Table
contains data on the type BR2325 electrochemical cell available
from Matsushita Electric (cf. the textbook "Novelties in technology
of fluorine compounds", ed. by N. Ishikawa, Moscow, Mir Publishers,
1984, pp. 149, 592 (in Russian).
3TABLE 3 Attainable performance parameter of cathode material
Capacitance of type Average Acceleration BR2325, Average discharge
of tumbling electrochemi- discharge current, bodies, g cal cell,
mAh voltage, V mA/sq. cm For powdered fluorocarbon material with a
fluorine content of 65-67 wt. % there is indicated a maximum
parameter attained upon heating hte finished electrode to
270.degree. C. 75 205 2.58 0.20 For powdered fluorocarbon material
with a fluorine content of 65-67 wt. % heat-treatment is performed
at 180-270.degree. C. except for line 8 where heat-treatment
temperature is 350.degree. C. 10 10 2.64 0.35 45 209 2.68 0.50 45
222 2.68 0.60 75 224 2.70 0.75 75 216 2.73 0.75 45 201 2.70 0.75 45
177 2.68 0.60 10 184 2.70 0/75 10 185 2.73 0.75 10 172 2.70 0.75 10
181 2.50 0.05 Electrochemical cell, type BR2325 makes use of
fluorocarbon available from Matsushita Electric, Japan -- 160 2.60
0.04 Fluorocarbon with fluorine content of 58-61 wt. % in type
BR2325 electrochemical cell (nominal parameter) 75 165 2.58 0.20
Manganese dioxide in type CR 2325 electrochemical cell is available
from the Applicant 45 130 from 3 to 2 V 0.4 Specific energey
capacity mAh/g Wh/cu. cm Utilization factor For powdered
fluorocarbon material with a fluorine content of 65-67 wt. % there
is indicated a maximum parameter attained upon heating the finished
electrode to 270.degree. C. 506 2193 78 For powdered fluorocarbon
material with a fluorine content of 65-67 wt. % heat-treatment is
performed at 180-270.degree. C., except for line 8 where
heat-treatment temperature is 350.degree. C. 624 2488 83 577 2320
81 613 2399 87 607 2393 92 631 2446 94 588 2191 83 570 1955 78 615
2059 91 626 2085 82 620 1875 96 589 1650 86 Electrochemical cell,
type BR2325 makes use of fluorocarbon available from Matsushita
Electric, Japan 500 about 1560 Fluorocarbon with fluorine content
of 58-61 wt. % in type BR2325 electrochemical cell (nominal
parameter) 510 (78) 1815 Manganese dioxide in type CR2325
electrochemical, cell is available from the Applicant 262 about
525
[0120] Note: The value of specific weight capacitance in mAh/g is
followed by the parenthesized value of utilization factor (in
percent) of fluorocarbons in various cathode materials.
Characteristics of cathodes based of manganese dioxide are present
for comparison.
[0121] The results of electrical tests of carbon-containing
electrodes used in type BR 2325 electrochemical cell (carried out
under the following conditions: 10 kOm load, room temperature,
electrostatic discharge, end-point voltage, 2.0 V) are summarized
in Table 4 below.
4 TABLE 4 Initial height NN Short-circuit of electrochemi- nn
Cathode mass current, mA cal cell 1 2 3 4 1. Electrode 91 2.48 2.
material 234 2.44 3. free 95 2.45 4. from graphite 185 2.44 5.
oxyfluoride 83 2.44 6. 67 2.75 7. 66 2.44 8. 58 2.44 Average values
110 + 69 2.479 + 0.096 1. 28 2.47 2. 20 2.45 3. Electrode 16 2.52
4. material 18 2.64 5. doped with 19 2.45 6. graphite 13 2.68 7.
oxyfluoride 13 2.47 8. 15 2.44 9. 12 2.47 10. 17 2.55 Average
values 14.4 + 4.9 2.514 + 0.085 Final height of Average
electrochemical discharge Capacitance, Nos. cell voltage mAh 1 5 6
7 1. 2.48 2.55 212 2. 2.39 2.57 243 3. 2.65 2.53 183 4. 2.46 2.49
208 5. 2.46 2.56 202 6. 2.63 2.54 197 7. 2.46 2.54 201 8. 2.48 2.50
198 Average 2.503 + 0.087 2.54 + 0.03 208 + 8 values Utilization
factor = 83.12 + 3.32 1. 2.49 2.58 227 2. 2.42 2.60 229 3. 2.54
2.55 244 4. 2.51 2.59 205 5. 2.44 2.57 238 6. 2.43 2.58 232 7. 2.45
2.60 229 8. 2.45 2.57 208 9. 2.46 2.57 208 10. 2.52 2.53 222
Average 2.471 + 0.041 2.57 + 0.02 227 + 12 values Utilization
factor = 93.63 + 4.95
EXAMPLE 6
[0122] An electrochemical cell of the "manganese dioxide-lithium"
system There were prepared cathode masses comprising 80 wt. %
manganese dioxide, 5-7 wt. % polytetrafluoroethylene suspension,
3-5 wt. % acetylene black, as well as 2, 5, and 10 wt. % graphite
oxyfluoride of the following general formula:
C.sub.x.zCyO.nH.sub.2O.CF,
[0123] where
[0124] x=1.5-15,
[0125] y=2.2-2.5,
[0126] z=0.2-2.0,
[0127] n=0.1-2.0.
[0128] Then positive electrodes (cathodes) were made from said
cathode masses, and disc-type lithium electrochemical cells of the
CR2325 standard size were assembled using said cathodes, according
to a known technique. For the sake of comparing cell properties,
lithium electrochemical cells of the CR2325 standard size were
made, each of the positive electrodes thereof weighing 0.9 g and
comprising 80 wt. % manganese dioxide, 10 wt. %
polytetrafluoroethylene suspension, and 10 wt. % acetylene black.
The same electrolyte was used in both cell series, viz, 1M lithium
perchlorate solution in a mixture of propylene carbonate and
dimethoxyethane. The cells thus produced were subjected to
discharge testing against loading resistors of 5, 6, and 10 kOhm at
room temperature. It had been found as a result of the tests
conducted that the following electrical parameters of the CR2325
standard size electrochemical cells were attained in both cell
series:
5 Cells free from graphite oxyfluoride Cells with graphite R =
oxyfluoride 5.6 kOhm R = 10 kOhm R = 5.6 kOhm R = 10 kOhm Average
2.55 2.70 2.60-2.65 2.75-2.80 discharge voltage, V Average 115-120
125-135 145-160 165-185 discharge capacity, mAh
EXAMPLE 7
[0129] Electrochemical cell of the "copper oxide+pyrite-lithium"
and "copper oxide+chalcopyrite-lithium" systems.
[0130] There were prepared cathode masses comprising 80 wt. % of a
mixture of the compounds of transition metals, comprising 60 wt. %
copper oxide and 40 wt. % pyrite, 5-7 wt. % polytetrafluoroethylene
suspension, 3-5 wt. % acetylene black, and 2, 5, 10 wt. % graphite
oxyfluoride of the following general formula:
C.sub.x.zCyO.nH.sub.2O.CF,
[0131] where
[0132] x=1.5-15,
[0133] y=2.2-2.5,
[0134] z=0.5-1.4,
[0135] n=0.1-0.5.
[0136] Then roll-type positive electrodes (cathodes) were made from
said cathode masses, and roll-type lithium electrochemical cells of
the CR2325 standard size were assembled using said cathodes,
according to a known technique. For the sake of comparing cell
properties, roll-type lithium electrochemical cells of the GR6R
standard size were made, each of the positive electrodes thereof
weighing 0.9 g and comprising 80 wt. % of a mixture of the
compounds of transition metals containing 60 wt. % copper oxide and
40 wt. % pyrite, 10 wt. % polytetrafluoroethylene suspension, 20
wt. % acetylene black (free from an expanding agent).
[0137] The same electrolyte was used in both cell series, viz, 1M
lithium perchlorate solution in a mixture of propylene carbonate
and dimethoxyethane.
[0138] Then discharge characteristics of 1.5-volt roll-type lithium
electrochemical cells of the GR6R standard size were tested for the
following two electrochemical systems:
Li-FeS.sub.2+CuO (OM-P)and Li-CuO+CuFeS.sub.2 (OM-PCHP)
[0139] There were tested in cathode with a mixture of chalcopyrite
and pyrite a total of five positive electrodes prepared by various
techniques (said electrodes comprising graphite oxyfluoride
additives are indicated with the latter "M" in Table 5 below).
[0140] Then a comparative discharge testing of various electrodes
of pilot-series electrochemical cells of the GR6S standard size was
conducted under continuous test conditions and various current
loads, using 1M solution of LiClO.sub.4 in a mixture of propylene
carbonate and dimethoxyethane as electrolyte. Discharges were
carried out at room temperature using an automatic test bench until
an end-point voltage of 0.9 V is obtained. Averaged randomly
selected data of a preliminary testing of pilot-series lithium
electrochemical cells of the GR6S standard size are summarized in
Table 5 below.
6TABLE 5 Average Cathode Discharge Operating operating Nos material
voltage, V current, mA voltage, V 1 2 3 4 5 1 OM-CHP-m 2.4-2.9 5-20
1.30 2 OM-CHP 2.2-2.7 5-20 1.22 3 OM-CHP-m 2.0-2.4 20-60 1.33 4
OM-CHP 2.5-2.9 20-60 1.27 5 OM-P-m 2.9-3.1 80-100 1.40 6 OM-P
3.0-3.1 10-40 1.37 Internal Internal Output Utilization resistance,
resistance, Nos capacity, Ah factor, % Ohm Ohm 1 6 7 8 9 1 2.2-2.50
86-99 2.2-2.50 -- 2 2.1-2.26 77-89 2.1-2.26 -- 3 2.7-2.98 73-75
1.7-2.47 2.1-3.6 4 1.9-2.20 78-84 0.9-1.75 1.9-3.5 5 3.5-3.64 82-86
2.1-2.41 1.6-2.4 6 2.2-2.35 76-82 1.5-2.10 4.0-5.8
[0141] According to the performance characteristics attained in the
pilot-series electrochemical cells of the GR6P standard size, the
highest discharge characteristics are exhibited by the positive
electrodes prepared with the use of graphite oxyfluoride.
[0142] Thus, practical application of the herein-proposed
carbon-containing cathode material and the method of making a
porous electrode for electrochemical cells is instrumental in
increasing volume- and weight energy capacity of electrode-active
additives and hence discharge and capacitance characteristics of
the electrodes of lithium electrochemical cells of the various
electrochemical systems.
* * * * *