Solvent-free electrode fabrication
The invention relates to an electrode formed by the blending of dry active powdery electrode forming materials with an aqueous binder dispersion, and the subsequent adhering of the wet binder/dry active powdery electrode-forming materials blend to an electroconductive substrate, resulting in an electrode. The aqueous binder is preferably a fluoropolymer, and more preferably polyvinylidene fluoride (PVDF). The hybrid process provides the good dispersion and small particle size of a wet process, with the energy savings and reduced environmental impact of a dry process. The resulting electrode is useful in energy-storage devices.
1. A method for forming an energy storing device, comprising the steps of:
a) forming an aqueous binder dispersion composition having discrete particles of one or more polymers;
b) adding said aqueous binder dispersion to one or more types of dry active powdery electrode-forming materials to form a uniform damp solid blend,
c) drying said uniform damp solid blend of binder and dry active powdery electrode-forming materials, and
d) applying said uniform blend to at least one surface of an electroconductive substrate to form an electrode.
2. The method of claim 1 , wherein said binder is selected from the group consisting of fluoropolymers, SBR, ethylene vinyl acetate (EVA), acrylic polymers, polyurethanes, styrenic polymers, polyamides, polyesters, polycarbonate and thermoplastic polyurethane (TPU).
3. The method of claim 2 , wherein said binder comprises a fluoropolymer.
4. The method of claim 3 , wherein said fluoropolymer comprises at least 50 weight percent of polyvinylidene fluoride homopolymer or copolymer.
5. The method of claim 3 , wherein said fluoropolymer is a copolymer comprising from 5 to 30 weight percent of hexafluoropropene and 70 to 95 weight percent of vinylidene fluoride monomer units.
6. The method of claim 3 , wherein the fluoropolymer has a melt viscosity of greater than 5 Kpoise, according to ASTM method D-3835 measured at 450° F. and 100 sec −1 .
7. The method of claim 6 , wherein the fluoropolymer has a melt viscosity of greater than 15 Kpoise, according to ASTM method D-3835 measured at 450° F. and 100 sec −1 .
8. The method of claim 1 , wherein said aqueous binder dispersion composition, comprises the polymer binder and one or more additives selected from the group consisting of surfactants, anti-settling agents, wetting agents, thickeners, rheology modifiers, fugitive adhesion promoters, fillers, anti-foaming agents, pH buffers.
9. The method of claim 1 , wherein said dry active powdery electrode-forming materials are selected from the group consisting of an oxide, sulfide or hydroxide of lithium and a transition metal; carbonaceous materials; and nano-titanates.
10. The method of claim 1 , further comprising the step of forming an energy storage device using said electrode.
11. An electrode formed by the process of claim 1 .
12. A dry blend comprising a fluoropolymer binder and active powdery electrode-forming materials, wherein said fluoropolymer binder exists at least 75 percent by weight as single binder particles, said single binder particles having a weight average particle size of less than 500 nm.
13. Said dry blend of claim 12 , wherein said single polymer particles have a weight average particle size of from 20 to 400 nm.
14. Said dry blend of claim 13 , wherein said single polymer particles have a weight average particle size of from 50 to 300 nm.
15. A method for forming an energy storing device, comprising the steps of:
a) forming an aqueous binder dispersion composition having discrete particles of one or more polymers;
b) spraying said aqueous binder dispersion onto carbon or activated carbon to form a uniform damp blend, and
c) applying said uniform blend to at least one surface of an electroconductive substrate to form an electrode.