Electrode materials and processes for their preparation
This application describes an electrode material comprising particles of an electrochemically active material dispersed in a polymer binder, where the polymer binder is an acidic polymer or a mixture comprising a binder soluble in an aqueous solvent or a non-aqueous solvent (e.g. NMP) and an acidic polymer. The application also further relates to processes for the preparation of the electrode material and electrodes containing the material, as well as to the electrochemical cells and their use.
1. An electrode material comprising particles of an electrochemically active material dispersed in a polymer binder, wherein the polymer binder consists of:
i. a mixture consisting of an aqueous binder and an acidic polymer;
ii. an acidic polymer; or
iii. a mixture consisting of a non-aqueous binder and an acidic polymer;
wherein the acidic polymer is selected from poly(acrylic acid), poly(methacrylic acid) and combinations thereof and has an average molecular weight within the range of from about 200 000 g/mol to about 600 000 g/mol.
2. The electrode material of claim 1 , wherein the acidic polymer is poly(methacrylic acid).
3. The electrode material of claim 1 , wherein the acidic polymer is poly(acrylic acid).
4. The electrode material of claim 1 , wherein the polymer binder is (i) a mixture consisting of an aqueous binder and an acidic polymer, and the aqueous binder is selected from SBR (styrene butadiene rubber), NBR (butadiene acrylonitrile rubber), HNBR (hydrogenated NBR), CHR (epichlorohydrin rubber), ACM (acrylate rubber), and combinations thereof.
5. The electrode material of claim 4 , wherein the aqueous binder comprises SBR (styrene butadiene rubber) or the aqueous binder is SBR (styrene butadiene rubber).
6. The electrode material of claim 1 , wherein the polymer binder is (i) or (iii) and the ratio (aqueous binder):(acidic polymer) or (non-aqueous binder):(acidic polymer) is within the range of from about 1:8 to about 8:1, or from about 1:5 to about 5:1, or from about 1:3 to about 3:1.
7. The electrode material of claim 1 , wherein the acidic polymer further comprises lithium ions.
8. The electrode material of claim 1 , wherein the electrochemically active material comprises a material selected from the group consisting of titanates, lithium titanates, lithium metal phosphates, vanadium oxides, lithium metal oxides, and combinations thereof.
9. The electrode material of claim 8 , wherein the electrochemically active material is selected from TiO 2 , Li 2 TiO 3 , Li 4 Ti 5 O 12 , H 2 Ti 5 O 11 and H 2 Ti 4 O 9 , or a combination thereof, LiM′PO 4 wherein M′ is Fe, Ni, Mn, Co, or a combination thereof, LiV 3 O 8 , V 2 O 5 , LiMn 2 O 4 , LiM″O 2 , wherein M″ is Mn, Co, Ni, or a combination thereof, Li(NiM″)O 2 , wherein M′″ is Mn, Co, Al, Fe, Cr, Ti, or Zr, and combinations thereof.
10. The electrode material of claim 8 , wherein the electrochemically active material is selected from lithium titanates and lithium metal phosphates.
11. The electrode material of claim 1 , wherein said particles further comprise a carbon coating.
12. A process for producing an electrode comprising an electrode material as defined in claim 1 , comprising the steps of:
a) mixing, in any order:
i. particles of electrochemically active material, the mixture consisting of the aqueous binder and the acidic polymer in an aqueous solvent to obtain a slurry;
ii. particles of electrochemically active material and the binder consisting of the acidic polymer in a solvent to obtain a slurry; or
iii. particles of electrochemically active material, the mixture consisting of the non-aqueous binder and the acidic polymer in an unreactive organic solvent to obtain a slurry;
b) casting the slurry of step (a) on a current collector; and
c) drying the casted slurry to obtain an electrode.
13. The process of claim 12 , further comprising a step of neutralizing the acidic polymer prior to step (a) with a lithium-containing base such as lithium hydroxide.
14. The process of claim 12 , wherein the current collector is aluminum or an alloy having aluminum as the main component.
15. The process of claim 12 , wherein the solvent in step (a)(ii) is an aqueous solvent.
16. The process of claim 12 , wherein the solvent in step (a)(ii) or (a)(iii) is an unreactive organic solvent.
17. The electrode material of claim 1 , wherein the polymer binder is (iii) a mixture consisting of a non-aqueous binder and an acidic polymer, and the non-aqueous binder is selected from fluorinated binders.
18. The electrode material of claim 17 , wherein the fluorinated binder comprises PVDF or the fluorinated binder is PVDF.
19. An electrode comprising the electrode material as defined in claim 1 , on a current collector, preferably the current collector is aluminum or an alloy having aluminum as the main component.
20. An electrochemical cell comprising an electrode as defined in claim 19 , an electrolyte and a counter-electrode.
21. The electrode material of claim 11 , wherein the carbon coating is a nano-layer of carbon comprising fibers on the surface of the particles and/or the carbon coating comprises a polyaromatic structure of graphene comprising heteroatoms selected from oxygen, nitrogen, sulfur and combinations thereof.