Process for fabrication of low basis weight electrode active blanks
View Patent ↗The present invention is directed to calendaring an electrode active admixture, such as of a transition metal oxide, and particularly silver vanadium oxide, into an electrode structure. To obtain electrode structures of a desired low basis weight requires calendaring a paste of the active material into a first sheet tape, which is subsequently subjected to secondary and ternary calendering steps. Secondary calendaring is performed in a direction reverse or orthogonal to that used to form the initial sheet tape. The final calendaring step is performed in a third direction aligned 180° with respect to the first direction, but with the second structure rotated bottom over top with respect to the orientation that formed the first and second structures. The ternary calendaring step provides for fibrillation of the fluoro-polymeric binder in a direction reverse to the initial direction to form the product low basis weight electrode active structure.
1. A method for preparing an electrode, comprising the steps of:
a) providing an electrode active material;
b) mixing the electrode active material with a fluoro-polymeric material in a solvent to form an electrode admixture paste comprising the electrode active material;
c) calendering the paste into a first structure of the electrode admixture having a first thickness by contacting the paste in a first direction;
d) calendering the first structure into a second structure having a second thickness less than the first thickness by contacting the electrode admixture in a second direction having the first structure rotated bottom over top with respect to the orientation that formed the first structure to thereby form an electrode active structure; and
e) contacting the electrode active structure to at least one of a first and second major surfaces of a conductive substrate.
2. The method of claim 1 including calendaring the first structure into an intermediate structure before forming the second structure, the intermediate structure having an intermediate thickness less than the first thickness by contacting the electrode admixture in a direction substantially orthogonal to or in a reverse direction to that which formed the first structure.
3. The method of claim 1 including adding a conductor material to the electrode admixture.
4. The method of claim 1 including providing the paste comprised of about 3 weight percent carbon, 3 weight percent of the fluoro-polymeric material and about 94 weight percent of the electrode active material.
5. The method of claim 1 including providing the electrode active material comprising a metal-containing material.
6. The method of claim 1 including selecting the solvent from the group consisting of water and an inert organic material.
7. The method of claim 1 including subjecting the electrode active material to a grinding step that reduces its particle size from a granular electrode active material to a finely divided particle size prior to mixing with the fluoro-polymeric material and the solvent forming the paste.
8. The method of claim 1 including forming the paste into the cathode sheet by feeding the paste through a series of roll mills as the first calendering step forming the first structure.
9. The method of claim 1 including the step of first feeding the paste into a compaction mill that serves to provide the electrode active material in a pellet form prior to introduction to the first calendaring step.
10. The method of claim 1 including selecting the electrode active material from the group consisting of carbon, fluorinated carbon, silver vanadium oxide, copper silver vanadium oxide, manganese dioxide, titanium disulfide, cobalt oxide, nickel oxide, copper vanadium oxide, LiNiO 2 , LiMn 2 O 4 , LiCoO 2 , LiCO 0.92 Sn 0.08 O 2 , LiCo 1−x Ni x O 2 , and mixtures thereof.
11. The method of claim 1 wherein the step of forming the paste into the electrode active structure further comprises the dropwise addition of a liquid electrolyte.
12. The method of claim 1 wherein the electrode active structure has a thickness in the range of from about 0.004 inches to about 0.020 inches.
13. The method of claim 1 including removing residual solvent from the electrode active material by drying the electrode active material.