U.S. patent application number 13/485108 was filed with the patent office on 2013-02-07 for aqueous slurry for battery electrodes.
The applicant listed for this patent is Pierre Blanc, Hilmi Buqa, Werner Scheifele. Invention is credited to Pierre Blanc, Hilmi Buqa, Werner Scheifele.
Application Number | 20130034651 13/485108 |
Document ID | / |
Family ID | 44735378 |
Filed Date | 2013-02-07 |
United States Patent
Application |
20130034651 |
Kind Code |
A1 |
Buqa; Hilmi ; et
al. |
February 7, 2013 |
Aqueous Slurry For Battery Electrodes
Abstract
A slurry or paste for the manufacture of electrodes for
secondary batteries such as lithium ion containing electrochemical
cells. The slurry comprises a water based binder with CMC, SBR and
PVDF as binder materials.
Inventors: |
Buqa; Hilmi; (Oberentfelden,
CH) ; Scheifele; Werner; (Oberkirch, DE) ;
Blanc; Pierre; (Morges, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Buqa; Hilmi
Scheifele; Werner
Blanc; Pierre |
Oberentfelden
Oberkirch
Morges |
|
CH
DE
CH |
|
|
Family ID: |
44735378 |
Appl. No.: |
13/485108 |
Filed: |
May 31, 2012 |
Current U.S.
Class: |
427/58 ;
252/182.1 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 4/8828 20130101; H01M 4/623 20130101; H01M 4/0404 20130101;
H01M 4/622 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
427/58 ;
252/182.1 |
International
Class: |
H01M 4/62 20060101
H01M004/62; H01M 4/04 20060101 H01M004/04; H01M 4/485 20100101
H01M004/485; H01M 4/38 20060101 H01M004/38; H01M 4/48 20100101
H01M004/48 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 3, 2011 |
GB |
1113378.2 |
Claims
1. A slurry for the manufacture of an electrode for an (lithium ion
containing) electrochemical cell, the slurry comprising a
combination of at least three of polyacrylic acid (PAA),
carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) and
polyvinylidene fluoride (PVDF) in an aqueous solution and an
electrochemically activateable compound.
2. The slurry of claim 1, comprising the polyvinylidene fluoride
(PVDF) and at least two of polyacrylic acid (PAA), carboxymethyl
cellulose (CMC), styrene-butadiene rubber (SBR).
3. The slurry of claim 1, further comprising latex in the aqueous
solution.
4. The slurry of claim 3, comprising a dispersion of the
polyvinylidene fluoride (PVDF) and the latex in the aqueous
solution.
5. The slurry of claim 1, wherein in the aqueous solution comprises
de-ionized water.
6. The slurry of claim 1, wherein the composition is free of
organic solvent.
7. The slurry of claim 1, wherein the concentration of each one of
the at least three of the polyacryilic acid (PAA), the
carboxymethyl cellulose, the styrene-butadiene rubber and the
polyvinylidene fluoride is about 0.5% to about 10% by weight.
8. The slurry of claim 1, wherein the slurry is an electrode slurry
of a lithium ion battery.
9. The slurry of claim 1, wherein the electrochemically
activateable material comprises at least one of graphite, titanate,
lithium metal oxides such as LMO, Li--NCA, LCO, LNCM, LFP and other
metal oxides or other materials known in the art, as well as their
blends.
10. A method for the manufacture of an electrode for use in an
electrochemical cell, the method comprising: preparing a slurry
comprising a combination of at least three of polyacylic acid
(PAA), carboxymethyl cellulose (CMC), styrene-butadiene rubber
(SBR) and polyvinylidene fluoride (PVDF) as binder in an aqueous
solution, coating or laminating the slurry on a current
collector.
11. The method of claim 10, wherein preparing the slurry comprises
dispersing latex in the aqueous solution for stabilizing the
aqueous solution.
12. The method of claim 10, further comprising adding a non-aqueous
electrolyte.
13. The method of claim 10, wherein the concentration of each one
of the at least three of the polyacrylic acid (PAA), the
carboxymethyl cellulose, the styrene-butadiene rubber and the
polyvinylidene fluoride is about 0.5% to about 10% by weight.
14. The method of claim 10, further comprising drying the slurry.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to electrodes for secondary
batteries. In particular, the present disclosure relates to
slurries or pastes for the use in lithium ion containing
electrochemical cells.
[0003] 2. Introduction and Related Art
[0004] Electrodes for electrochemical cells are often manufactured
by attaching an electrochemically active electrode material to a
current collector. Known current collectors are rigid supports or
flexible foils made from a conducting material. Examples for widely
used current collector materials include copper or aluminium but
other materials may be used. Methods to attach the electrochemical
active electrode material to the current collector comprise
lamination, gluing using adhesives or coating. These methods for
manufacturing electrodes are widely used in the art.
[0005] A large variety of electrochemically activatable or active
electrode materials is known for manufacturing anodes and cathodes
in different battery systems and depending on the application of
the battery. The electrochemical active electrode material is
manufactured as a slurry or paste and subsequently coated onto the
current collector or the slurry is manufactured as a
self-supporting layer which is later attached to the current
collector.
[0006] The slurry or paste usually comprises a mixture of an
electrochemically activatable or active material and a binder
material for forming the paste/slurry. Further components are often
added, such as conductive additives (i.e. carbon black, graphite,
carbon fibers, VGCF (vapour grown carbon fibers), etc.)
[0007] A large number of binder materials is known in the art.
Polyvinylidene fluoride (PVDF) or polyvinyliden fluoride
hexafluoropropylene (PVDF-HFP) copolymers have been found to have
excellent chemical and mechanical properties when used as a binder
material in a slurry for positive and negative electrodes. In
particular, PVDF provides a good electrochemical stability and high
adhesion to the electrode materials and to current collectors. PVDF
is therefore a preferred binder material for electrode slurries.
PVDF, however, has the disadvantage that it can only be dissolved
in some specific organic solvent such as acetone has to be used
which requires specific handling, production standards and
recycling of the organic solvents in an environmentally-friendly
way. PVDF is also known for some long term instability in the cell
chemistry.
[0008] The use of aqueous solutions instead of organic solvents is
preferred for environmental and handling reasons and water-based
slurries have been considered. Possible binders for water-based
slurries known in the art comprise carboxymethyl cellulose (CMC)
and styrene-butadiene rubber (SBR). The publication of H. Buqa et
al.
[0009] "Study of a styrene butadiene rubber and sodium methyl
cellulose as binder for negative electrodes in lithium-ion
batteries" in Journal of Power Sources, 161 (2006), 617-622
describes the use of SBR and CMC as binders in aqueous solutions
and their electrochemical performances compared to PVDF in organic
solvent.
[0010] EP 0 907 214, corresponding to US 6,183,907, compares
acrylonitrile-butadiene rubber combined with CMC, combinations of
CMC and SBR as binder in an aqueous solution to polyvinylidene
fluoride in an organic solvent.
[0011] JP 2000 357505A describes the use of PVDF in an aqueous
dispersion acting as binder material. The organic solvent in
N-methyl-2-pyrrolidone (NMP) is added to the solution.
[0012] JP 2008 135334 suggests to use a polymeric layer made from
PVDF onto which a slurry comprising CMC and SBR as binder materials
is coated.
[0013] These and other attempts have been made to combine PVDF with
water based slurries in order to use the known advantages of PVDF
as a binder for electrode slurries without using organic solvents
that require specific treatment during manufacture, but no
successful implementation has been shown up to now.
[0014] It is an object of the present invention to overcome the
disadvantages of prior art.
SUMMARY OF THE INVENTION
[0015] The present disclosure provides a composition for a slurry
or a slurry for the manufacture of an electrode for an
electrochemical cell. The electrochemical cell can be an lithium
ion cell and can be a primary or a secondary battery. The slurry
comprises a combination of at least three of polyacrylic acid
(PAA), carboxymethyl cellulose (CMC), styrene butadiene rubber
(SBR) and polyvinylidene fluoride (PVDF) in an aqueous solution.
The slurry further comprises an electrochemical active or
activatable compound. In this way, PVDF can be used in a
water-based slurry, which allows for easier handling and less
environmental pollution and reduced costs while keeping the
chemical and electrochemical advantages of PVDF, i.e. the
electrochemical stability, possibility of lamination, lifetime
stability, reduced binder content enables higher C-rates, etc. The
combination of PVDF with SBR and CMC or PAA has also good adhesive
properties allowing lamination and/or coating of the slurry without
the use of additional adhesives.
[0016] It has been found that the combination consisting of PVDF
with CMC and SBR in an aqueous solution can be used as binder in a
positive or negative electrode slurry, wherein the CMC and SBR are
used as binder and PVDF is used as lamination agent.
[0017] Alternatively, CMC or SBR may be replaced by PAA as binder
material. A combination of PVDF with PAA and SBR can equally be
used in a positive or negative electrode slurry. PAA may be used to
reduce the PH of the slurry which helps to avoid or suppress
corrosion.
[0018] A combination of PVDF with SBR, CMC and PAA may also be used
in an aqueous solution combining the advantages of CMC and PAA.
[0019] A latex may be dispersed in this aqueous solution to
stabilise the PVDF in the aqueous solution. Using a PVDF-latex
dispersion makes it possible to use PVDF in aqueous solutions,
keeping the advantages of PVDF as lamination agent and in the same
time avoiding the use of organic solvents.
[0020] No organic solvents or other additional components besides
latex are needed or used to dissolve the PVDF in the aqueous
solution.
[0021] The aqueous solution is de-ionized water.
[0022] A concentration of about 0.5% to about 10% by weight of each
one of the CMC, SBR and the PVDF may be used for a stable slurry
with good chemical and electrical properties.
[0023] The composition of the slurry does not require organic
solvents, but such solvents could be used without changing the
spirit of the patent. The slurries may be free of any organic
solvent and the expensive and restrictive and complicated handling
of organic solvents is avoided or reduced during the manufacture of
the slurry.
[0024] In many cases it is important to have a water free effective
electrode material before the electrolyte is added. The slurry or
the manufactured electrode may therefore be dried.
[0025] The electrochemically activatable material may comprise at
least one of graphite, titanate, lithium metal oxides such as LMO
(lithium manganese oxide), Li-NCA (lithium nickel cobalt aluminium
oxide), LCO (lithium cobalt oxide), LNCM (lithium nickel cobalt
manganese oxide), LFP (lithium iron phosphate) and other metal
oxides or other materials known in the art, as well as their
blends. The slurry may be used for a positive electrode and/or for
a negative electrode.
[0026] The present disclosure also relates to a method or the
manufacture of an electrode for an electrochemical cell. The method
comprises preparing a slurry comprising a combination of at least
three of the PAA CMC, SBR and PVDF in an aqueous solution, coating
or laminating the slurry on a current collector, and drying the
slurry. Latex may be added to the aqueous solution to stabilise the
slurry.
[0027] Latex may be used in a dispersion with the PVDF in the
aqueous solution. The aqueous solution may further comprise at
least two of the PAA; CMC, SBR may be added to the dispersion
[0028] The method may further comprise adding a non-aqueous
electrolyte to the electrode.
[0029] The method and the slurry have the advantage that only
aqueous solutions are used that can be easily handled and a less
cost-intensive use.
BRIEF DESCRIPTION OF THE FIGURES
[0030] The present invention as defined by the claims will now be
described with respect to detailed examples and with reference to
the attached figures in which:
[0031] FIG. 1 shows cycle life characteristics for electrochemical
cells containing Li--NCO cathodes and graphite anode prepared with
water based binder mixture; and
[0032] FIG. 2 shows a discharge rate capability behaviour of the
Li--NCO/Graphite electrochemical cell of FIG. 1.
DETAILED DESCRIPTION
[0033] An electrochemical cell according to the present disclosure
can be prepared by standard methods known to a person skilled in
the art. It is common knowledge to a person skilled in the art to
use slurries for manufacturing positive or negative electrodes i.e.
cathodes or anodes. The slurry may be coated onto a current
collector. The current collector can be a metal foil and can
comprise materials such as copper or aluminium but other current
collectors can be used with the present invention.
[0034] A slurry according to the present disclosure is prepared by
mixing a binder with an active electrode material in an aqueous
solution. Further components may be added.
[0035] The binder comprises a composition of carboxymethyl
cellulose (CMC), styrene butadiene rubber (SBR) as binder and
polyvinylidene fluoride (PVDF) as lamination agent. No other binder
materials are used. Alternatively or in addition to CMC,
polyacrylic acid (PAA) may be used to reduce the PH of the slurry.
The total amount of binder in the slurry can be about 0.5% to about
30% by weight. Good results have been obtained with a total amount
of binder in the slurry of about 10% by weight. The binder can be
mixed in an aqueous solution made from de-ionized water. Latex at a
concentration of about 0.5-10% may be added to stabilize the
aqueous PVDF dispersion.
[0036] The slurry comprises an active electrode material and other
components such as carbon black and optionally further
additives.
[0037] Example for anode active electrode material may be graphite.
Examples for a cathode active electrode material comprises LFP,
LNCM, LCO, Li--NCA, LMO or other metal oxides and their blends.
EXAMPLE 1
Anode Electrode Slurry
[0038] A graphite electrode slurry may comprise 2% CMC or PAA, 5%
SBR, 3% PVDF, 2% carbon black and 88% graphite. The above
components may be mixed to a slurry in an aqueous solution. The
aqueous solution may be deionised water. Latex may be added to the
solution in order to maintain the PVDF in a stable dispersion. The
materials used are commercially available. No other materials are
used. The water contents depends on active materials, binder and
other conductive materials and their concentration used in the
slurry.
EXAMPLE 2
Cathode Electrode Slurry
[0039] A cathode electrode slurry may be mixed by using 4% CMC or
PAA, 6% SBR, 3% PVDF, 6% carbon black and 88% by weight of LFP or
another metal oxide. Latex may be added to the solution in order to
maintain the PVDF in a stable dispersion. The Li--NCO presented in
this draft is prepared using PVDF as Binder and acetone as a
solvent. Nevertheless, the Li--NCO electrodes can be prepeared
using: NMP, water, acetone, DMAC or other organic solvents.
[0040] The above slurries have been coated on an anode current
collector and onto a cathode count collector, respectively. The
current collector can be made from any known material such as for
example aluminium or copper and can be in form of a foil. The
cathode and the anode produced in this way were inserted in an
electrochemical cell, separated by a separator.
[0041] Electrochemical cells produced in such a manner have been
tested for their cycle life characteristics and for their discharge
rate capability behaviour depending on the temperature.
[0042] FIG. 1 shows cycle life characteristics for electrochemical
cells containing Li--NCO cathodes and graphite anodes prepared with
a water based binder mixture. The slurry is prepared using PVDF as
a binder and acetone as a solvent. The capacity retention in
constant over at least two hundred charging and recharging cycles
indicating a good cycle life of electrochemical cells based on
water based slurries.
[0043] FIG. 2 shows a discharge rate capability behaviour of
Li--NCO/graphite cells. The graphite electrodes were prepared with
the water based binder mixture of example 1. The results indicate
that there are no differences in using water based slurries
compared to slurries based on organic solvents or other slurries.
The use of the water based slurries therefore allows to reduce or
avoid the use of organic solvents in the slurries facilitating the
manufacture of the slurries.
[0044] It should be noted that organic solvent free slurries can be
prepared. However, a certain concentration of organic solvents can
be used in some applications of the present disclosure. The organic
solvent is, however, not necessary for dissolving the binder
material and the binder can be used in the aqueous solution.
[0045] While the above description of a detailed example has been
given for illustrative purposes only, other active electrode
materials can be used with, CMC, SBR and PVDF as binder materials
in an aqueous solution. A person skilled in the art will optimize
the concentrations of CMC, SBR and PVDF depending on the active
electrode material used and on the desired properties of the
slurry.
* * * * *