(491g) Optimization of Hydrogels for Non-Spillable Zn|MnO2 Rechargeable Batteries Allowing for 2nd Electron MnO2 Cycling

Zn|MnO₂ batteries are a research and industrial interest due to high theoretical capacity, low cost, and intrinsic safety. Typically, liquid potassium hydroxide solution is used as an electrolyte. It is widely known, however, many industrial applications require non-spillable electrolyte, and, further, many Zn|MnO₂ failure mechanisms are enabled by liquid electrolytes, such as uncontrollable active material redistribution and cross-cell migration of zinc that results in electrochemically inert hetaerolite (ZnMn₂O₄). Hydrogels were thus developed as an alternative to liquid electrolytes, expecting that the mitigation of Zn would be reduced thus reducing hetaerolite formation, and ultimately creating a battery without the evaporation or spillage risks of liquid electrolytes.

Alkaline hydrogels were prepared via in situ polymerization and optimized for Zn|MnO₂ battery performance by modifying parameters that affect polymer hydrogel properties, such as reaction kinetics via temperature, KOH concentration, and the concentrations of initiator, cross-linker (N,N’-methylenebisacrylamide), and monomer. Polymer chain length, volume fraction with respect to water, and degree of cross-linking were optimized to allow sufficient ionic mass transfer that sustains the battery during typical cycling rates and extracting the 2^nd electron from the MnO₂.

The Code of Federal Regulations for non-spillable battery electrolyte tests were followed to adhere to industrial and governmental standards. As a lab-proxy test to follow these regulations, capillary tubes were used to test the spill ability of experimental hydrogels. Maximum volume fraction of water was sought while maintaining non-spillable rheology. Cycling data was then collected with this optimized non-spillable electrolyte. EIS of these alkaline hydrogel electrolytes was also performed to analyze ionic transport.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. Dr. Imre Gyuk, Energy Storage Program Manager, Office of Electricity is thanked for the financial support.