Tin and tin-zinc plated substrates to improve Ni-Zn cell performance
View Patent ↗An improved Ni—Zn cell with a negative electrode substrate plated with tin or tin and zinc during manufacturing has a reduced gassing rate. The copper or brass substrate is electrolytic cleaned, activated, electroplated with a matte surface to a defined thickness range, pasted with zinc oxide electrochemically active material, and baked. The defined plating thickness range of 40-80 μIn maximizes formation of an intermetallic compound Cu 3 Sn that helps to suppress the copper diffusion from under plating layer to the surface and eliminates formation of an intermetallic compound Cu 6 Sn 5 during baking to provide adequate corrosion resistance during battery operation.
1. A method to manufacture a zinc electrode substrate for a nickel zinc battery cell, the method comprising:
(a) providing a strip of substrate material, said substrate material comprising copper;
(b) electrolytically cleaning the strip;
(c) electroplating 40-80 μIn of metal onto the strip in an electrolyte bath comprising a tin ion source;
(d) pasting a layer of zinc oxide based electrochemically active material onto the plated substrate; and
(e) baking the plated substrate and paste by maintaining a higher than ambient temperature for a period of time to form an intermetallic compound layer comprising less than 10% Cu 6 Sn 5 with the balance Cu 3 Sn.
2. The method of claim 1 , wherein the metal deposited further comprises zinc from a zinc ion source in the electrolyte bath.
3. The method of claim 2 , wherein the metal deposited comprises about 75-100% weight tin and about 0-25% weight zinc.
4. The method of claim 1 , wherein the substrate material further comprises zinc, wherein the copper and zinc form a brass alloy.
5. The method of claim 1 , wherein the electrolytic cleaning is performed for a period of about 5-10 minutes in an alkaline soak solution.
6. The method of claim 5 , wherein the alkaline soak solution has a pH of about 10-13.
7. The method of claim 6 , wherein the alkaline soak solution comprises an alkaline hydroxide, an alkaline carbonate, and an alkaline phosphate.
8. The method of claim 1 , further comprising activating the strip, after (b) and before (c), wherein the activation operation comprises immersing the strip in an activation solution comprising an acid.
9. The method of claim 8 , wherein the activation solution has a pH of about 0.2-3.
10. The method of claim 8 , wherein the activation solution comprises sulfuric acid at an acid concentration of 4-20%.
11. The method of claim 1 , wherein the electroplating operation occurs at a current density about 40-80 A/m 2 for a period of about 4-6 minutes.
12. The method of claim 1 , wherein the electroplating bath comprises a current carrier source and no brightening agent.
13. The method of claim 1 , wherein the plating bath has a pH of about 0.1-3.
14. The method of claim 13 , wherein the electroplating bath further comprises an oxidation retardant and an anti-treeing agent.
15. The method of claim 14 , wherein the tin ion source is stannous sulfate, the oxidation retardant is a sulfonic acid, and the anti-treeing agent is selected from the group consisting of naphthol, gelatin, and cresol.
16. The method of claim 2 , wherein the electroplating bath comprises a current carrier source and no brightening agent.
17. The method of claim 16 , wherein the electroplating bath further comprises an oxidation retardant and an anti-treeing agent, and wherein the tin ion source is stannous sulfate, the zinc ion source is zinc sulfate, the current carrier source is an acid, the oxidation retardant is a sulfonic acid, and the anti-treeing agent is selected from the group consisting of naphthol, gelatin, and cresol.
18. The method of claim 1 , wherein the baking operation comprises maintaining the substrate at a temperature of about 200-350° C. for a period of about 30 minutes to 2 hours.
19. The method of claim 1 , wherein (c) comprises electroplating metal consisting essentially of
(i) tin or
(ii) tin and zinc.