U.S. patent application number 10/902174 was filed with the patent office on 2005-02-17 for cathode material for polymer batteries and method of preparing same.
Invention is credited to Brouillette, Dany, Gagnon, Regis, Lavoie, Paul-Andre, Leblanc, Patrick, Regisser, Fabrice, Vallee, Alain.
Application Number | 20050037262 10/902174 |
Document ID | / |
Family ID | 34115514 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050037262 |
Kind Code |
A1 |
Vallee, Alain ; et
al. |
February 17, 2005 |
Cathode material for polymer batteries and method of preparing
same
Abstract
The invention provides a pre-mix of positive electrode material
in transportable solid form comprising polymer and solid particles
of electrochemically active material and/or electronically
conductive additives and a process for preparing a pre-mix positive
electrode in transportable solid form. The pre-mix positive
electrode material may also comprise an alkali metal salt either
dissolved or dispersed in the mixture. The invention also provides
making a cathode film from the transportable solid pre-mix of
positive electrode material.
Inventors: |
Vallee, Alain; (Varennes,
CA) ; Lavoie, Paul-Andre; (Montreal, CA) ;
Leblanc, Patrick; (Boucherville, CA) ; Gagnon,
Regis; (St-Jean-Sur-Richelieu, CA) ; Regisser,
Fabrice; (Varennes, CA) ; Brouillette, Dany;
(Brossard, CA) |
Correspondence
Address: |
SMART & BIGGAR
Suite 3300
1000 de La Gauchetiere Street West
Montreal
QC
H3B 4W5
CA
|
Family ID: |
34115514 |
Appl. No.: |
10/902174 |
Filed: |
July 30, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60491532 |
Aug 1, 2003 |
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Current U.S.
Class: |
429/217 ;
252/182.1; 264/105; 264/211.23; 429/232 |
Current CPC
Class: |
H01M 4/139 20130101;
H01M 2004/028 20130101; H01M 4/0419 20130101; H01M 4/02 20130101;
H01M 4/36 20130101; H01M 4/62 20130101; H01M 4/485 20130101; H01M
4/0404 20130101; H01M 4/625 20130101; H01M 4/04 20130101; H01M
4/0483 20130101; C08J 3/205 20130101; H01M 4/0416 20130101; H01M
4/0411 20130101; H01M 4/505 20130101; H01M 4/13 20130101; H01M
4/525 20130101; H01M 4/48 20130101; H01M 10/052 20130101; Y02E
60/10 20130101; H01M 4/0402 20130101 |
Class at
Publication: |
429/217 ;
252/182.1; 429/232; 264/211.23; 264/105 |
International
Class: |
H01M 004/62; H01M
004/04 |
Claims
We claim:
1. A pre-mix positive electrode material comprising a polymer and
solid particles of electrochemically active material and
electronically conductive additives, wherein the pre-mix positive
electrode material is a transportable solid.
2. A pre-mix of positive electrode material as defined in claim 1
wherein the pre-mix of positive electrode material further
comprises an alkali metal salt or alkali metal salt mix.
3. A pre-mix of positive electrode material as defined in claim 2
wherein the alkali metal salt is dispersed in the pre-mix of
positive electrode material.
4. A pre-mix of positive electrode material as defined in claim 2
wherein the alkali metal salt is dissolved in the polymer of the
pre-mix of positive electrode material.
5. A pre-mix of positive electrode material as defined in claim 1
further comprising an electronic conductive additive selected from
the group consisting of carbon, graphite and combinations
thereof.
6. A pre-mix of positive electrode material as defined in claim 1
wherein the transportable solid is in a form selected from the
group consisting of chunks, pucks, carrots, stripes, pellets,
granules, powder, flakes and combinations thereof.
7. A pre-mix of positive electrode material as defined in claim 1
wherein the pre-mix of positive electrode material further
comprises a small amount of water in the range of 1000 ppm to
10,000 ppm
8. A pre-mix of positive electrode material as defined in claim 2
further comprising fumed silica to inhibit adhesion of the
transportable solids during transport or storage.
9. A process for preparing a pre-mix positive electrode in
transportable solid form comprising the steps of: (a) In a mixing
device, mixing together a polymer, at least one solvent and solid
particles of electrochemically active material to form an mixture
of polymer-solid particles; (b) evaporating the at least one
solvent present in the mixture of polymer-solid particles; and (c)
transforming the polymer-solid particles mixture into a
transportable solid selected from the group consisting of chunks,
pucks, carrots, stripes pellets, granules, powder, flakes and
combinations thereof.
10. A process as defined in claim 9 wherein the dried polymer-solid
particles mixture resulting from step (b) is transformed into a
transportable solid by melting it through a melting and pumping
device, thereafter cooling and hardening the melted polymer-solid
particles mixture and thereafter breaking down the hardened
polymer-solid particles mixture into a transportable solid shape
through a mechanical cutting device.
11. A process as defined in claim 9 wherein the at least one
solvent is evaporated and the polymer-solid particles mixture is
transformed into a transportable solid by spray drying the
polymer-solid particles mixture still in solution in the solvent
through a nozzle thereby yielding a pre-mix positive electrode in
transportable solid form selected from the group consisting of
granules, powder and flakes.
12. A process as defined in claim 9 wherein the solid particles
further comprise an electronic conductive additive selected from
the group consisting of carbon, graphite and combinations
thereof.
13. A process for preparing a pre-mix positive electrode in
transportable solid form comprising the steps of: (a) In a mixing
device, mixing together a polymer, at least one solvent, an alkali
metal salt and solid particles of electrochemically active material
to form an mixture of polymer-salt-solid particles; (b) evaporating
the at least one solvent present in the mixture of
polymer-salt-solid particles; and (c) transforming the
polymer-salt-solid particles mixture into a transportable solid
selected from the group consisting of chunks, pucks, carrots,
stripes, pellets, granules, powder, flakes and combinations
thereof.
14. A process as defined in claim 13 wherein the dried
polymer-salt-solid particles mixture resulting from step (b) is
transformed into a transportable solid by melting it through a
melting and pumping device, thereafter cooling and hardening the
melted polymer-salt-solid particles mixture and thereafter breaking
down the hardened polymer-salt-solid particles mixture into a
transportable solid shape through a mechanical cutting device
15. A process as defined in claim 13 wherein the at least one
solvent is a polar solvent.
16. A process as defined in claim 13 wherein the at least one
solvent is a non-polar solvent.
17. A process as defined in claim 16 wherein the polymer, the
non-polar solvent, the alkali metal salt and the solid particles
are heated to a temperature of 40.degree. C. or more while being
mixed together in step (a).
18. A process as defined in claim 13 wherein the dried
polymer-salt-solid particles mixture resulting from step (b) is
transformed into a transportable solid by melting it through a
melting and pumping device, thereafter cooling and hardening the
melted polymer-salt-solid particles mixture and thereafter breaking
down the hardened polymer-salt-solid particles mixture into a
transportable solid shape through a mechanical cutting device.
19. A process as defined in claim 13 wherein the at least one
solvent is evaporated and the polymer-salt-solid particles mixture
is transformed into a transportable solid by spray drying the
polymer-salt-solid particles mixture still in solution in the
solvent through a nozzle thereby yielding a pre-mix positive
electrode in transportable solid form selected from the group
consisting of granules, powder and flakes.
20. A process as defined in claim 13 wherein the pre-mix positive
electrode in transportable solid form is mixed with fumed silica to
inhibit adhesion of the transportable solids during transport or
storage
21. A process as defined in claim 13 wherein the solid particles
further comprise an electronic conductive additive selected from
the group consisting of carbon, graphite and combinations
thereof.
22. A process for extruding a thin positive electrode sheet having
at least 40%/wt solid content for a lithium polymer battery through
a single or twin screw extruder, said process comprises the steps
of: (a) introducing a pre-mix of positive electrode material in
solid form comprising a polymer and solid particles of
electrochemically active cathode material, into a first feed throat
of the extruder; (b) melting the polymer and mixing said pre-mix of
positive electrode material in the extruder; (c) introducing in a
second feed throat of the extruder an alkali metal salt which is
dissolved in the polymer of the pre-mix of positive electrode
material; (d) extruding the positive electrode material through a
die in the form of a thin sheet.
23. A process for extruding d thin positive electrode sheet as
defined in claim 22 wherein said pre-mix of positive electrode
material in solid form further comprises an electronic conductive
additive selected from the group consisting of carbon, graphite and
combinations thereof.
24. A process for extruding a thin positive electrode sheet as
defined in claim 23 wherein an electronic conductive additive
selected from the group consisting of carbon, graphite and
combinations thereof is introduced into the extruder downstream
from the pre-mix of positive electrode material in solid form.
25. A process for extruding a thin positive electrode sheet as
defined in claim 22 wherein said thin sheet is from 5 to 200 .mu.m
thick.
26. A process for extruding a thin positive electrode sheet having
at least 40%/wt of solid content for a lithium polymer battery
through a single or twin screw extruder, the process comprises the
steps of: (a) introducing into a first feed throat of the extruder
an alkali metal salt; (b) introducing into a second feed throat of
the extruder a pre-mix of positive electrode material in solid form
comprising a polymer and solid particles of electrochemically
active cathode material; (b) melting and mixing said pre-mix of
positive electrode material in the extruder and dissolving said
alkali metal salt in the melted polymer; and (c) extruding the
positive electrode material through a die in the form of a thin
sheet.
27. A process for extruding a thin positive electrode sheet as
defined in claim 26 wherein said pre-mix of positive electrode
material in solid form further comprises an electronic conductive
additive selected from the group consisting of carbon, graphite and
combinations thereof.
28. A process for extruding a thin positive electrode sheet as
defined in claim 26 wherein an electronic conductive additive
selected from the group consisting of carbon, graphite and
combinations thereof is introduced into the extruder separate from
the pre-mix of positive electrode material in solid form.
29. A process for extruding a thin positive electrode sheet as
defined in claim 28 wherein said thin sheet is from 5 to 200 .mu.m
thick.
30. A process for extruding a thin positive electrode sheet having
at least 40%/wt of solid content for a lithium polymer battery
through a single or twin screw extruder, the process comprises the
steps of: (a) introducing a pre-mix of positive electrode material
in solid form comprising a polymer, an alkali metal salt and solid
particles of electrochemically active cathode material and
electronically conductive additives, into a first feed throat of
the extruder; (b) melting the polymer and mixing said pre-mix of
positive electrode material in the extruder; and (c) extruding the
positive electrode material through a die in the form of a thin
sheet.
31. A process for extruding a thin positive electrode sheet as
defined in claim 30 wherein said thin sheet is from 5 to 200 .mu.m
thick.
32. A process for making a positive electrode having at least
40%/wt of solid content for a lithium polymer battery, the process
comprising the steps of: (a) In a mixing device, mixing together a
polymer, a solvent, and solid particles of electrochemically active
material to form an mixture of polymer-solid particles; (b)
evaporating the solvent present in the mixture of polymer-solid
particles; (c) introducing the mixture of polymer-solid particles
into a first feed throat of the extruder; (b) melting the polymer
and blending said mixture of polymer-solid particles in the
extruder to form a positive electrode material; and (c) extruding
the positive electrode material through a die in the form of a thin
sheet.
33. A process for making a positive electrode as defined in claim
32, wherein said solid particles further comprise an electronic
conductive additive selected from the group consisting of carbon,
graphite and combinations thereof.
34. A process for making a positive electrode as defined in claim
32, wherein said solid particles further comprise an alkali metal
salt.
35. A process for making a positive electrode as defined in claim
32, further comprising the step of introducing an alkali metal salt
into a second feed throat of the extruder.
36. A process for making a positive electrode as defined in claim
32, further comprising the step of introducing an electronic
conductive additive into a second feed throat of the extruder.
Description
FIELD OF INVENTION
[0001] The present invention relates generally to polymer batteries
and more specifically to the preparation of cathode materials for
polymer batteries.
BACKGROUND OF THE INVENTION
[0002] Lithium/polymer electrolyte batteries are manufactured by
superposing three main types of films: a film of metallic lithium,
a film of an electrolyte comprising a polymer and a lithium salt,
and a film of a positive electrode. Each of these films has a
thickness between 5 and 200 .mu.m, for a total thickness of 100 to
300 .mu.m for the elementary film of battery.
[0003] The film of positive electrode is typically prepared by
coating or extrusion, on a support film or directly on an aluminum
foil or metallized plastic film, used as an electrical current
collector, a dispersion containing an electrochemically active
material such as a transitional metal oxide, carbon black and/or
graphite to ensure electronic conduction, a polymer-salt
electrolyte to ensure ionic conduction and the mechanical bond
between the solid particles mentioned above and most often
appropriate solvent or solvent mixtures which are evaporated
totally or partially during the coating process or extrusion
process.
[0004] In the coating process, the mixing and blending of the
electrochemically active material, the electronic conduction
additives, the polymer binder and the lithium salt forming the
positive electrode is done in a compatible solvent or solvent
mixtures that will dissolve the salt and the polymer immediately
prior to coating. The solution is then coated through a coating
head in the form of a thin film. The solvent is then evaporated and
recovered, usually by condensation, for obvious environmental
reasons.
[0005] In the extrusion process, the mixing and blending of the
electrochemically active material, the electronic conduction
additives, the polymer binder and the lithium salt forming the
positive electrode material is carried out by the screw or screws
of the extruder itself. The polymer and lithium salt are generally
introduced first in the extruder and melted followed by the
introduction downstream from the polymer-salt melt of the
electrochemically active material and the electronic conduction
additives which are mixed and dispersed in the polymer-salt melt by
the screw or screws of the extruder. Frequently, an appropriate
solvent or solvent mixtures is added to reduce the viscosity of the
melt and to help in the mixing of the solid particles of active
material and electronic conduction additives, the solvent(s) which
must be evaporated after the positive electrode material is
extruded onto a support film, directly on a current collector or as
a free-standing film. Preferably, a twin screw extruder is used for
its superior ability over a single screw extruder for mixing and
blending the various components of the positive electrode
material.
[0006] However, even with a twin screw extruder, the mixing and
blending of the various components of positive electrode material
is sometime inadequate. Specifically, the solid particles (active
material and electronic conduction additive particles) are not
properly mixed and dispersed, resulting in a less homogenous
positive electrode material resulting in poor electrochemical
performance of the electrochemical cells. In addition, the use of a
twin screw extruder involves high shear events which may
potentially degrade the polymer thereby further decreasing the
electrochemical performance of the cell during the cycles of charge
and discharge.
[0007] Thus there is a need for a method or process of mixing and
blending the various components of a positive electrode material to
improve the dispersion and consistency of mixing of the solid
particles as well as a positive electrode material with homogenous
dispersion of its solid particles constituents.
STATEMENT OF THE INVENTION
[0008] It is therefore an object of the present invention to
provide a method for mixing the various components of a positive
electrode material having solid content for a polymer battery.
[0009] It is another object of the present invention to provide an
improved positive electrode material having dispersed solid content
for a lithium polymer battery.
[0010] As embodied and broadly described, the invention provides a
pre-mix of positive electrode material in solid transportable form
comprising a polymer and solid particles of electrochemically
active material and preferably an electronic conductive additive.
Preferably, the pre-mix of positive electrode material in solid
transportable form comprises a polymer and at least 40% of solid
particles of electrochemically active material and electronic
conductive additives. Also preferably, the pre-mix of positive
electrode material comprises a alkali metal salt either dissolved
or dispersed in the polymer. Preferably, the pre-mix of positive
electrode material is in the form of small to medium size chunks,
pucks, carrots, stripes, etc. or in pellet, granule, powder or
flake form. Preferably, the pre-mix of positive electrode material
in solid transportable form comprises a polymer and between 40%/wt
and 80%/wt of solid particles of electrochemically active material
and electronic conductive additives. The polymer of the pre-mix of
positive electrode material may contain a small amount of water
within the range of 1000 ppm to 10,000 ppm.
[0011] The active material of the cathode may be selected from
lithium cobalt/nickel oxide, lithium manganese oxide
(LiMn.sub.2O.sub.4), layered lithium manganese nickel oxide and
their derivatives, mixtures and analogs for so-called 4V cathodes
or among cathodes discharging below 4V such as phosphates or other
polyanions of transition metals such as LiFePO.sub.4 and Nasicon
structures, also including V.sub.2O.sub.5, and Li.sub.xV3O8. The
alkali metal salt(s) may be for example salts based on lithium
trifluorosulfonimide (LiTFSi) as described in U.S. Pat. No.
4,505,997, LIPF.sub.6, LiBF.sub.4, LiSO.sub.3CF.sub.3, LiClO.sub.4,
and LiSCN, etc. and combinations thereof. The nature of the salt or
of the active material is not a limitation of the present
invention.
[0012] As embodied and broadly described, the invention also
provides a process for preparing a pre-mix positive electrode in
solid transportable form comprising the steps of:
[0013] (a) In a mixing device, mixing together a polymer, at least
one solvent and solid particles of electrochemically active
material to form an mixture of polymer-solid particles;
[0014] (b) evaporating the at least one solvent present in the
mixture of polymer-solid particles; and
[0015] (c) transforming the polymer-solid particles mixture into a
transportable solid selected from the group consisting of chunks,
pucks, carrots, stripes, pellets, granules, powder, flakes and
combinations thereof.
[0016] As embodied and broadly described, the invention also
provides for a process for preparing a pre-mix positive electrode
in transportable solid form comprising the steps of:
[0017] (a) In a mixing device, mixing together a polymer, at least
one solvent, an alkali metal salt and solid particles of
electrochemically active material to form an mixture of
polymer-salt-solid particles;
[0018] (b) evaporating the at least one solvent present in the
mixture of polymer-salt-solid particles; and
[0019] (c)transforming the polymer-salt-solid particles mixture
into a transportable solid selected from the group consisting of
chunks, pucks, carrots, stripes, pellets, granules, powder, flakes
and combinations thereof.
[0020] As embodied and broadly described, the invention also
provides a process for extruding a thin positive electrode sheet
having at least 40%/wt solid content for a lithium polymer battery
through a single or twin screw extruder, said process comprises the
steps of:
[0021] (a) introducing a pre-mix of positive electrode material in
solid form comprising a polymer and solid particles of
electrochemically active cathode material, into a first feed throat
of the extruder;
[0022] (b) melting the polymer and mixing said pre-mix of positive
electrode material in the extruder;
[0023] (c) introducing in a second feed throat of the extruder an
alkali metal salt which is dissolved in the polymer of the pre-mix
of positive electrode material;
[0024] (d) extruding the positive electrode material through a die
in the form of a thin sheet.
[0025] As embodied and broadly described, the invention also
provides a process for extruding a thin positive electrode sheet
having at least 40%/wt of solid content for a lithium polymer
battery through a single or twin screw extruder, the process
comprises the steps of:
[0026] (a) introducing into a first feed throat of the extruder an
alkali metal salt;
[0027] (b) introducing into a second feed throat of the extruder a
pre-mix of positive electrode material in solid form comprising a
polymer and solid particles of electrochemically active cathode
material;
[0028] (b) melting and mixing said pre-mix of positive electrode
material in the extruder and dissolving said alkali metal salt in
the melted polymer; and
[0029] (c) extruding the positive electrode material through a die
in the form of a thin sheet.
[0030] As embodied and broadly described, the invention also
provides a process for extruding a thin positive electrode sheet
having at least 40%/wt of solid content for a lithium polymer
battery through a single or twin screw extruder, the process
comprises the steps of:
[0031] (a) introducing a pre-mix of positive electrode material in
solid form comprising a polymer, an alkali metal salt and solid
particles of electrochemically active cathode material and
electronically conductive additives, into a first feed throat of
the extruder;
[0032] (b) melting the polymer and mixing said pre-mix of positive
electrode material in the extruder; and
[0033] (c) extruding the positive electrode material through a die
in the form of a thin sheet.
[0034] As embodied and broadly described, the invention also
provides a process for making a positive electrode having at least
40%/wt of solid content for a lithium polymer battery, the process
comprising the steps of:
[0035] (a) In a mixing device, mixing together a polymer, a
solvent, and solid particles of electrochemically active material
to form an mixture of polymer-solid particles;
[0036] (b) evaporating the solvent present in the mixture of
polymer-solid particles;
[0037] (c) introducing the mixture of polymer-solid particles into
a first feed throat of the extruder;
[0038] (b) melting the polymer and blending said mixture of
polymer-solid particles in the extruder to form a positive
electrode material; and
[0039] (c) extruding the positive electrode material through a die
in the form of a thin sheet.
[0040] As embodied and broadly described, the invention further
provides an electrochemical generator having a electrode thin film
obtained by the process of extruding pre-mix positive electrode
material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] The invention will be better understood and other advantages
will appear by means of the following description and the following
drawings in which:
[0042] FIG. 1 is a flow chart illustrating the various step for
preparing the cathode material according to one embodiment of the
invention; and
[0043] FIG. 2 is a flow chart illustrating the various step for
preparing the cathode material according to a second embodiment of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0044] With reference to FIG. 1, a solution of polymer in solvent
or mixture of solvents is mixed with solid particles of active
cathode material and electronic conductive additives. The polymer
solution could be obtained by the dissolution of a polymer in a
solvent(s) or directly at the outlet of a polymerization reactor if
the polymer is already in solution. In a preferred embodiment the
active cathode material and electronic conductive additives have
been blended together prior to introduction into the polymer
solution. However, the active cathode material and the electronic
conductive additives may be introduced separately into the polymer
solution. The polymer solution and the solid particles are mixed in
any type of mixing device(s) capable of proper dispersion for a
sufficient time to obtain a good dispersion of the solid particles
in the polymer solution and/or in any equipment that homogenize the
mixture in order to achieve the same dispersion. The mixing process
may be done in one step in a single mixing device or through
multiple steps through a two or more mixing device with different
mixing properties. Further solvent may be added if necessary to the
mixture to facilitate the dispersion of the solid particles.
Solvent typically used in this process are polar or non-polar
solvents into which the polymer is soluble such as Toluene,
Acetonitrile, Methanol, Acetone, Benzene, and Methyl Ethyl Ketone
(MEK) to name a few. The polymer may be an homo- or co-polymer, may
comprise two or more polymers, and may be cross linkable or not.
Anti-oxidants and other additives such as stabilizers, dispersion
agents and fillers may be added to the polymer solution as
necessary.
[0045] Thereafter, the solvent or solvents are evaporated by any
means known to those skilled in the art such as an evaporator or
spray dryer amongst others, to obtain a polymer-solid particles
mixture adapted for a coating process or an extrusion process. The
polymer-solid particles mixture is then transformed into a
transportable solid such as small or medium size chunks, carrots
pucks or stripes, or granules, powder, pellets or flakes. There are
no limitation to the geometric shapes the polymer-solid particles
mixture may take. In one specific embodiment, the polymer-solid
particles mixture is introduced in a melting and pumping device
such as extruder, where the polymer is melted and the composite is
further mixed, then pumped into a cooling device where it hardens.
This hardened mixture is brought to a mechanical cutting device
that transforms the hardened polymer-solid particles mixture into
the desired shape such as a pelletizer which transforms the
hardened polymer-solid particles mixture into pellets of a few
millimeters in length and width or diameter. In another embodiment
the polymer-solid particles mixture still in solution in the
solvent is spay dried through a nozzle which yields a polymer-solid
particles mixture in the form of granules, powder or flakes. The
pre-mix cathode material in chunks, carrots, pucks, granules,
pellets or powder form is then ready for shipment or for processing
by extrusion or coating to be transformed into thin films. In the
present text the term solid transportable form includes solids of
any shapes which can be safely shipped in containers such as
chunks, pucks, carrots, stripes, pellets, granules, powder and
flakes.
[0046] Preferably, the pre-mix cathode material in transportable
solid form is stored and/or transported in a controlled
environment. Specifically, it is preferable to maintain the
temperature of the pre-mix cathode material in transportable solid
form below 30.degree. C. to prevent unwanted degradation of the
performance of the cathode material.
[0047] In the extrusion process, the pre-mixed cathode material is
introduced in a first feed throat of either a single (reciprocating
or non-reciprocating) or twin screw extruder where it begins to
melt. In a second feed throat downstream from the first feed throat
is added an alkali metal salt which is dissolved and mixed in the
melted cathode material. As a variant of the process, the alkali
metal salt may be introduced first and the pre-mix cathode material
second. The alkali metal salt provides ionic conductivity to the
cathode material. The cathode material including the dissolved
alkali metal salt is extruded through a die as a thin sheet of
between 5 and 200 .mu.m thick, either directly onto a substrate
support such as a metal foil current collector or a plastic film,
or as a self-supporting sheet which is later on laminated onto a
current collector. The alkali metal salt(s) may be for example
salts based on lithium trifluorosulfonimide (LiTFSi) as described
in U.S. Pat. No. 4,505,997, LIPF.sub.6, LiBF.sub.4,
LiSO.sub.3CF.sub.3, LiClO.sub.4, and LiSCN, etc. and combination
thereof. The nature of the salt is not a limitation of the present
invention.
[0048] In the extruder, the pre-mixed solid particles (active
material and electronic conduction additive particles) are further
mixed and blended and are therefore thoroughly mixed and dispersed
resulting in an homogenous positive electrode material having a
optimal energy content and excellent electrochemical performance or
improved cyclability of the electrochemical cells produced
thereafter. In addition, the fact that the cathode material has
been previously mixed and blended allows the use of an extruder
having a screw designed to produce low shear as opposed to the high
shear previously required to thoroughly mix and blend the cathode
material. This results in a less energetic mixing and melting of
the polymer that avoids potential degradation of the polymer with
the result of improving the electrochemical performance of the
electrochemical cells produced thereafter during the cycles of
charge and discharge. The pre-mixing of the solid particles into a
polymer solution also enables an increased proportion of solid
particles and specifically of active material into the resulting
cathode which may contain up to 80%/wt of active material.
[0049] The polymer included in the pre-mixed cathode material in
solid form may comprise a small amount of water such as between
1000 ppm and 10,000 ppm and preferably within the range of 2000 ppm
to 5000 ppm, in order to adjust the rheological properties of the
pre-mixed cathode material, for example, by lowering the viscosity
of the material and therefore improving the processability the
pre-mixed cathode material through an extruder.
[0050] FIG. 2 illustrates a variant of the process previously
described where the polymer solution is prepared with a polar
solvent into which both the polymer and the alkali metal salt are
soluble as is well known in the art. Polar solvents typically used
in this process are Acetonitrile, Methanol, Acetone, and Methyl
Ethyl Ketone (MEK) to name a few. To this polymer solution is added
all solid particles of active cathode material and electronic
conductive additives already pre-blended together and a alkali
metal salt soluble in the polar solvent. The mixture of
polymer-salt and solid particles is mixed in any type of mixing
device(s) or homogenizer capable of proper dispersion for a
sufficient time to obtain a good dispersion of the solid particles
in the polymer-salt solution. Thereafter the solvent is removed
through evaporation or other means from the mixture, and the
remaining polymer-salt/solid particles mixture is transformed into
a transportable solid such as small to medium size chunks pucks,
carrots, stripes, granules, powder, pellets or flakes as previously
described. If necessary, to prevent the transportable solid pre-mix
cathode material which now includes an alkali metal salt from
partially melting and agglomerating during transport or storage,
rendering it difficult to further process, the transportable solid
pre-mix cathode material may be mixed into a substance like fumed
silica which is compatible with the electrochemistry of the cells
and microscopically separates the transportable solid, especially
the pellets, granules, powder or flakes to inhibit their adhesion
to each other.
[0051] When brought to the extruder, or any types of melting and
pumping device, for processing into thin sheets of between 5 and
200 .mu.m thick, the pre-mix polymer-salt/solid particles (active
material and electronic conduction additive particles) are further
mixed and blended and are therefore thoroughly dispersed resulting
in excellent electrochemical performance or improved cyclability of
the electrochemical cells produced thereafter. The pre-mixed
cathode material in solid form is introduced into a feed throat of
either a single (reciprocating or non-reciprocating) or twin screw
extruder where it is melted and extruded through a die as a thin
sheet of between 5 and 200 .mu.m thick, either directly onto a
substrate support such as a metal foil current collector or a
plastic film, or as a self-supporting or free-standing sheet which
is later on laminated onto a current collector.
[0052] The solid particles are therefore thoroughly mixed resulting
in an homogenous positive electrode material having a optimal
energy content in terms of volume as well as of mass. In addition,
as previously stated, the fact that the cathode material has been
previously mixed and blended allows the use of an extruder having a
screw designed to produce low shear as opposed to the high shear
previously required to thoroughly mix and blend the cathode
material. This results in a less energetic mixing and melting of
the polymer that avoids potential degradation of the polymer with
the result of improving the electrochemical performance of the
electrochemical cells produced thereafter during the cycles of
charge and discharge.
[0053] As a further variant of the process described with reference
to FIG. 2, the polymer solution is prepared with a solvent or
solvent mixture, into which the polymer is soluble but the alkali
metal salt is not soluble, such as a non-polar solvent like Toluene
or Benzene. To this polymer solution is added all solid particles
of active cathode material and electronic conductive additives
already pre-blended together and the alkali metal salt. The alkali
metal salt is not dissolved but dispersed into the polymer
solution. The mixture of polymer, salt and solid particles is mixed
in any type of mixing device or devices (one or more) capable of
good dispersion for a sufficient time to obtain solid particles and
salt particles that are thoroughly dispersed within the polymer
solution. Thereafter the solvent is removed through evaporation or
other means from the mixture, and the remaining polymer/salt/solid
particles mixture is transformed into a transportable solid such as
the shapes or forms previously described.
[0054] In some cases, and under certain conditions, the alkali
metal salt may be dissolved in the non-polar solvent. For example,
raising the temperature of the mixture of polymer, salt and solid
particles in solution in the non-polar solvent may enable the salt
to dissolve in the polymer solution. The mixture of polymer, salt
and solid particles in solution in the non-polar solvent may be
heated to a temperature of about 40.degree. C. or more during
mixing to enable the salt to dissolve in the polymer solution.
Also, a combination of two or more solvents, one of which being a
non-polar solvent, may enable the salt to dissolve in the polymer
solution. Thereafter the solvent(s) is/are removed through
evaporation or other means from the mixture, and the remaining
polymer/salt/solid particles mixture is transformed into a
transportable solid such as the shapes or forms previously
described.
[0055] When brought to the extruder for processing into thin sheets
of between 5 and 200 .mu.m thick, the pre-mix polymer/salt/solid
particles (active material and electronic conduction additive
particles) are further mixed and blended and are therefore
thoroughly mixed and dispersed resulting in excellent
electrochemical performance or improved cyclability of the
electrochemical cells produced thereafter. The pre-mixed cathode
material is introduced in a feed throat of either a single
(reciprocating or non-reciprocating) or twin screw extruder where
the polymer is melted, the alkali metal salt is dissolved in the
polymer and the solid particles are re-dispersed into the
polymer-salt solution. The cathode material is extruded through a
die as a thin sheet of between 5 and 200 .mu.m thick, either
directly onto a substrate support such as a metal foil current
collector or a plastic film, or as a self-supporting sheet which is
later on laminated onto a current collector.
[0056] As a further variant of the process illustrated in FIG. 1, a
solution of polymer in solvent is mixed with solid particles of
active cathode material only. The mixture of polymer and solid
particles of active cathode material is mixed in any type of mixing
device(s) capable of good dispersion for a sufficient time to
obtain solid particles that are thoroughly dispersed within the
polymer solution. Thereafter the solvent is removed through
evaporation or other means from the mixture, and the remaining
polymer/solid particles of active cathode material mixture is
transformed into a transportable solids as previously described.
When brought to the extruder for processing into thin sheets of
between 5 and 200 .mu.m thick, the pre-mix polymer/solid particles
(active material only) in solid form is introduced into a feed
throat of the extruder, the alkali metal salt and the electronic
conduction additive are fed into other feed throat(s); the various
components are mixed and dispersed or dissolved in the molten
polymer. The alkali metal salt is dissolved in the polymer and the
solid particles (active material and electronic conductive
additives) are re-dispersed into the polymer-salt solution. The
cathode material is extruded through a die as a thin sheet of
between 5 and 200 .mu.m thick, either directly onto a substrate
support such as a metal foil current collector or a plastic film,
or as a self-supporting sheet which is later on laminated onto a
current collector.
[0057] As yet another variant of the process illustrated in FIG. 1,
a solution of polymer in solvent is mixed with solid particles of
electronic conductive additives material only. The mixture of
polymer and solid particles of electronic conductive additives is
mixed in any type of mixing device(s) capable of good dispersion
for a sufficient time to obtain solid particles of electronic
conductive additives that are thoroughly dispersed within the
polymer solution. Thereafter the solvent is removed through
evaporation or other means from the mixture, and the remaining
polymer/solid particles of electronic conductive additives mixture
is transformed into a transportable solid as previously described.
When brought to the extruder for processing into thin sheets of
between 5 and 200 .mu.m thick, the pre-mix polymer/solid particles
(electronic conductive additives only) in solid transportable form
is introduced into a feed throat of the extruder, the alkali metal
salt and the active cathode material are fed into other feed
throat(s); the various components are mixed and dispersed or
dissolved in the molten polymer. The alkali metal salt is dissolved
in the polymer and the solid particles (active cathode material and
electronic conductive additives) are re-dispersed into the
polymer-salt solution. The cathode material is extruded through a
die as a thin sheet of between 5 and 200 .mu.m thick, either
directly onto a substrate support such as a metal foil current
collector or a plastic film, or as a self-supporting sheet which is
later on laminated onto a current collector.
[0058] For each of the above variants or embodiments described, if
the pre-mix cathode material is prepared within the vicinity of the
extruder, the solvent or solvents of the solution of the pre-mix
cathode material may be evaporated or dried just prior to the
introduction of the pre-mix cathode material into the extruder such
that the pre-mix cathode material remains in a fluid state and is
never transformed into a transportable solid. The pre-mix cathode
material is introduced directly into the extruder while still in a
fluid state and processed as described in the previous variants or
embodiments thereby eliminating the necessity to transform it into
a transportable solid.
[0059] In a preferred embodiment, the polymer is a polyether such
as polyethylene oxide based polymer, the alkali metal salt is a
lithium salt such as LiTFSi, the active material is a transition
metal oxide such as lithium vanadium oxide
(Li.sub.xV.sub.3O.sub.8), the electronic conductive additive is
carbon black or a binary mixture of carbon black and graphite. The
positive electrode material includes between 15%/wt and 45%/wt of
polyether; between 40%/wt and 80%/wt of lithiated vanadium oxide;
between 1.0%/wt and 5%/wt of Carbon black and Graphite particles
and between 2%/wt and 15%/wt of lithium salt. An antioxidant and
other additives in minute proportion may also be added to the
mixture.
[0060] If the transformation of the solid pre-mix cathode material
is done by coating process, the process is simplified since most if
not all the components of the cathode are already pre-mixed,
permitting reduction of mixing time, energy and hardware thereby
reducing production cost.
[0061] An electrochemical generator comprising a plurality of
electrochemical laminates is then constructed; each laminates
comprises an anode film which is preferably a lithium metal sheet
or a lithium alloy sheet, an electrolyte separator capable of
Lithium ion transport, and a cathode thin film obtained by the
process of extruding or coating pre-mixed positive electrode
materials.
[0062] Although the present invention has been described in
relation to particular variations thereof, other variations and
modifications are contemplated and are within the scope of the
present invention. Therefore the present invention is not to be
limited by the above description but is defined by the appended
claims.
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