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June 16, 2022

Nickel-Zinc Battery Chemistry FAQ

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Nickel Zinc Cells

Anode: Zinc

Cathode: Nickel oxide

Electrolyte: Potassium hydroxide

Applications:Electric vehicles, standby load service

The combination of nickel and zinc is very interesting because of the low cost and low toxicity of the constituents. There have been many technical obstacles, but a string of recent patents and a commercial start-up based on a KOH electrolyte holds great promise for applications where light weight is an issue.

The nickel/zinc battery uses zinc as the negative electrode and nickel hydroxide as the positive. The discharge reactions are:

Location Half Reaction Voltage
Anode Zn + 2OH- —> Zn(OH)2+ 2e 1.24 V
Cathode 2NiOOH + 2H2O —> 2Ni(OH)2 + 2OH- 0.49 V
Overall 2NiOOH + Zn + 2H2O —> 2Ni(OH)2 + Zn(OH)2 1.73

These cells run between 1.55 and 1.65 V. Theoretical energy density is 334 Wh/kg, or about 1.3 kg of nickel and 0.7 kg of zinc per kilowatt-hour. The internal resistance of nickel/zinc batteries is remarkably low, which makes this system particularly attractive for high charge and discharge rates

Practical specific energy is around 60 Wh/kg. The technical problems that have plagued these batteries so far are dissolution of the zinc in the electrolyte, and uneven redepositing of the zinc during charging. Progress in these batteries has been mostly in the improvement of the zinc electrode. The charging is tricky because the termination voltage is a strong function of temperature.

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