Investigation of Alkaline Zinc Anode Performance with Increasing Addition of Calcium Zincate (Ca[Zn(OH)3]2·2H2o) Under Industrially Relevant Conditions
Authors: Yang Patrick K , Turney Damon E. , Nyce Michael , Wygant Bryan Russell , Lambert Timothy N. , O'Brien Stephen , Yadav Gautam Ganapati , Weiner Meir , Yang Shinju , Hawkins Brendan , Banerjee Sanjoy 
Published: December 2024

There is a need for safe, affordable, low cost, and reliable grid scale energy storage as the world transitions from fossil fuels towards intermittent renewable sources of energy. Metallic zinc (Zn) anodes are investigated and produced industrially for anodes for primary and rechargeable Zn batteries due to their high theoretical capacity, relative abundance, non-toxic, and non-flammable nature. Zn in alkaline electrolytes have poor reversibility at high Zn utilization due to passivation, shape change/redistribution, dendrite formation, hydrogen evolution, and the crossover of zincate ion (Zn(OH)4
2−) into the cathode. Zinc oxide (ZnO) anodes with additives such as calcium hydroxide (Ca(OH)2) have shown improvements on cyclability compared to metallic Zn anodes due to the in-situ formation of lower solubility calcium zincate (CaZn, (Ca[Zn(OH)3]2·2H2O)).
Ex-situ synthesized CaZn has been cycled vs nickel under alkaline conditions showing great improvement in cyclability but to be economically feasible, it must be paired with MnO2 cathodes. Due to a charge in balance between the discharged CaZn and charged MnO2, practical anode recipes will include a higher percentage of charged Zn to prevent the requirement of additional formation steps. To understand how CaZn could be incorporated into commercial alkaline Zn/MnO2 batteries, anode formulations with increasing CaZn (0%, 30%, 70%, 100%) in mixtures with metallic Zn are investigated in 20 wt% KOH along with minor additions of Bi2O3, acetylene carbon, and CTAB surfactant. The total molar zinc content is normalized; thus, electrode capacity is kept comparable, resulting in electrodes relevant to real world use cases. At high 50% Zn utilization, pure CaZn anodes achieved ~280 cycles while Zn anodes achieved ~50 cycles, a five-time improvement in cycle life resulting in four times cost reduction per cycle. Not only do we compare cyclability of the different formulations but also compare the different failure mechanisms of the majority Zn with CaZn vs a pure CaZn anode to understand why there is an increase in the cycling performance.
Acknowledgement: This work was supported by the U.S. Department of Energy Office of Electricity. Dr. Imre Gyuk, Director of Energy Storage Research at the U.S. Department of Energy Office of Electricity, is thanked for his financial support of this project. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. The views expressed in this article do not necessarily represent the views of the U.S. Department of Energy or the United States Government. This article has been authored by an employee of National Technology & Engineering Solutions of Sandia, LLC under Contract No. DE-NA0003525 with the U.S. Department of Energy (DOE). The National Technology & Engineering Solutions of Sandia, LLC employee owns all right, title and interest to their contribution to the article and is responsible for its contents. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this article or allow others to do so, for United States Government purposes. The DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan