Electrochemically Rechargeable and Mechanically Replaceable Zinc Electrodes for Nickel-Zinc Batteries, Zinc-Air Fuel Cells, and Hydrogen-on-Demand Systems
Authors: Kogan Iakov , Khomenko Anna 
Published: December 2020

This presentation provides a brief review of Panisolar’s research associated with rechargeable zinc electrodes for three alkaline energy storage devices. A new technology for fabrication of the electrochemically rechargeable and mechanically replaceable zinc electrode (also named as a replaceable zinc cartridge) included only room temperature processes. Electrochemical regeneration decreased the cost of the electrode substantially, and extended the cycle life of the related energy storage device.
Original idea was to replace hydrogen in cylinders by zinc cartridges that could be conveniently stored and generate hydrogen on demand [1]. The system appeared to be very simple: the zinc cartridge was connected to a hydrogen evolution electrode through a variable resistor that controlled hydrogen flow [2]. The zinc electrode could be electrochemically reduced internally or externally after discharge for repeated use. The whole system included two devices: the hydrogen generator and a hydrogen fuel cell.
It was appealing to simplify the system by eliminating hydrogen evolution and hydrogen oxidation by incorporation of the zinc cartridge in the fuel cell instead of hydrogen. The project was switched to the design of the rechargeable zinc-air batteries/fuel cells [2]. In addition to traditional two electrode cell a three electrode device was assembled and tested. The front and back sides of the cell were formed by the air and oxygen evolution electrodes, while the replaceable zinc cartridge took the whole internal space of the cell. Oxygen evolution electrode was formed from the surface modified stainless steel mesh while the air electrode was based on a catalyst prepared by pyrolization of phenylenediamine metal complexes to produce N-doped carbon [3]. 11cm*9cm*0.75cm fuel cell could be charged-discharged at 2A for 7h and 0.5A for 24h. Recently a cylindrical zinc-air battery of AA size was assembled and tested.
A large-sized storage system was expected to be charged-discharged with high conversion efficiency. An inherent problem of the zinc-air storage device is low recharging efficiency about 0.5 because of irreversibility of the air electrode. This deficiency was eliminated by design of the nickel-zinc battery with the replaceable cartridges.
Battery grade nickel hydroxide was produced in a proprietary chemical reactor. Numerous problems, which included poor filtration and longtime drying were resolved. An in house assembled spray-dry system was adopted for express drying nickel hydroxide.
The nickel-zinc battery with the rechargeable zinc electrode [4,5] has high power capability about 300A/kg, good recharging efficiency 0.85-0.9 and cycle life about 800 cycles, which had been demonstrate in 6 months test. This experiment was performed two years ago. Panisolar’s new electrodes are expected to have recharging efficiency more than 1000. It is well known that the nickel hydroxide electrode has exclusively long cycle life that exceeds 20,000 cycles. Therefore after the deterioration of the zinc electrode it can be replaced at about 5%-15% of the battery cost once in two years to extend battery life to 20,000 cycles.
The energy density of the nickel-zinc battery is lower than that of the lithium battery. This problem was mitigated by adjusting the shape of the storage device. A flat battery, only 1cm-2cm thickness can be assembled by joining cells side-by-side. This flat battery can be used as a wall mounted battery [6], which will not take much space inside the building. Which imaginable wall mounted battery a customer will prefer to install at home: 1cm thickness flammable lithium battery or 2cm safe to operate zinc storage device?
High power, long cycle life, safety, and abundance of natural resources of components make the nickel-zinc battery a strong competitor for stationary energy storage applications.

References

[1] I. Kogan, A. Khomenko, Zinc Modules as Universal Energy Storage Units for Future Economy, International Conference for Hydrogen Energy, June 4, 2012, Toronto, ON.
[2] I. Kogan, A. Khomenko US Patent 9,711,830.
[3] I. Kogan, A. Khomenko US Patent 9,502,717.
[4] I. Kogan, A. Khomenko, Rechargeable Zinc-Air and Nickel-Zinc Batteries as a Practical Alternative to Lithium Storage Devices, 2016 Spring Meeting of Canadian Section of ECS.
[5] I. Kogan, A. Khomenko US Patent 10,608,243.
[6] I. Kogan, A. Khomenko US Pat. Appl. 2016/0204441.