Homogeneous separator
View Patent ↗A battery separator for use in zinc alkaline batteries having improved mechanical strength and higher resistance to oxidation comprising cellulose that has been crosslinked with a saturated hydrocarbon group containing between four and sixteen carbon atoms.
1. A separator for use in an alkaline zinc alkaline battery comprising;
a cellulose film regenerated from a solution of cellulose, said cellulose have saturated hydrocarbon cross-links containing 4 to 16 carbon atoms, said cross-links obtained by a nucleophilic substitution reaction, and said cross-links are attached to hydroxyl sites on the cellulose.
2. A separator according to claim 1 in which 0.5% to 10% of the available hydroxyl sites contain said cross-links.
3. A separator according to claim 2 in which the cross-linking agent is a saturated alkylene chain containing 4 to 12 carbon atoms.
4. A separator according to claim 3 in which saturated alkylene is selected from the group consisting of hexyl and decyl.
5. A zinc alkaline battery combining in combination;
an alkali resistant battery case;
a body of alkaline electrolyte;
a zinc electrode having a portion thereof in contact with said body of electrolyte;
a counter electrode having a portion thereof in contact with said body of electrolyte; and
a cellulose separator disposed between said electrodes having no more than 10% of hydroxyl sites on cellulose chains cross-linked with a saturated hydrocarbon group containing 4 to 16 carbon atoms, obtained via a nuclophilic substitution reaction.
6. A battery according to claim 5 in which the saturated hydrocarbon group is a saturated alkylene group containing 6 to 12 carbon atoms.
7. A battery according to claim 6 in which the cellulose is selected from the group consisting of microcrystalline cellulose, microgranular cellulose, cotton fiber and paper.
8. A battery according to claim 7 in which the counter electrode comprises silver.
9. A method of forming a separator for an alkaline zinc alkaline battery comprising the steps of:
dissolving cellulose in an organic solvent to form a solution;
deprotonizing from 0.5% to 10% of hydroxyl groups on the cellulose;
adding a saturated hydrocarbon polyhalide cross-linking agent containing 4 to 16 carbon atoms to the solution and reacting the halide atoms with the deprotonizing sites to form cross-links;
forming a film of said solution containing cross-linked cellulose; and
drying the film to form a separator.
10. A method according to claim 9 in which the separator has a thickness from 12 microns to 250 microns.
11. A method according to claim 10 in which the cellulose is selected from the group consisting of microgranular cellulose, cotton fiber, paper and microcrystalline cellulose.
12. A method according to claim 11 in which the cellulose has a degree of polymerization from 200 to 1200.
13. A method according to claim 9 in which substantially all the deprotonized sites are reacted with the saturated dihalide cross-linking agent.
14. A method according to claim 9 in which the halide is an iodide.
15. A method according to claim 9 in which the solvent comprises a polar aprotic solvent and an alkali metal salt.
16. A method according to claim 15 in which the 3 to 8% by weight of the alkali metal salt is present based on weight of polar aprotic solvent.
17. A method according to claim 16 in which the metal salt is lithium chloride and the polar aprotic solvent is DMAC.
18. A method according to claim 15 in which the solvent is present in the solution in an amount of 1 to 11% by weight.
19. A method according to claim 9 in which the cellulose is deprotonized by adding an inorganic base to the solution.