Development of Alkaline Zn-Based Batteries for Grid Storage

Abstract

For energy storage to become ubiquitous in the electric grid, safe, reliable low-cost electrochemical storage technologies manufactured at high volumes with low capital expenditures are needed. Alkaline batteries based on high capacity multi-electron conversion electrodes from low cost, abundant and safe materials, such as a Zn/MnO2 are a promising technology. These batteries have a theoretical specific energy rivaling that of Li-ion systems (Zn @820 mAh/g and MnO2 @617 mAh/g, with ~400 Wh/L) and costs reducible to <$50/kWh, when produced at scale (S. Banerjee et al.). While recent advances by Yadav et al. have demonstrated highly reversible Bi- and Cu-stabilized MnO2 electrodes that can achieve the full 2e- capacity of MnO2 in alkaline electrolyte, the ability to pair this electrode with Zn over 5000+ cycles, which equates to ~10-15 years of battery life, remains a difficult challenge. Zn anodes suffer from irreversible shape change, the redistribution of active material, and passivation over repeated charge and discharge, limiting their achievable capacity and lifetime. Pre-saturating the electrolyte with zincate [Zn(OH)4 2-], which minimizes dissolution of Zn from the anode and reduces the rate of hydrogen evolution, has recently been shown to enhance cycle life for ~10-35% depth-of-discharge (DOD) Zn anodes by ~100-200% (M. Lim et al.); however, Zn(OH)4 2- saturated electrolyte is incompatible with high DOD MnO2, and exacerbates the formation of electrochemically inactive phases, such as ZnMn2O4 at the cathode. Hence, using zincate-blocking separators, able to entrap the zincate within the anode and effectively isolate the MnO2 cathode from Zn(OH)4 2- crossover, while maintaining hydroxide/cation conductivity, is one approach to improve the reversible cycling of a Zn/MnO2 cell at high DOD of both MnO2 and Zn. More recently we have developed a series of permselective polymeric separators (Kolesnichenko et al.) and screened them using our newly-developed anodic stripping voltammetry crossover assay (Duay et al.) to identify those with Zn(OH)4 2- blocking ability. A primary discharge of MnO2 was used to demonstrate that a sustained 2nd e- discharge plateau, indicative of the absence of zinc species at the cathode, was observed only for Zn/MnO2 batteries that utilized our selective polymeric separators. Finally, application of these polymeric separators in rechargeable Zn/MnO2 batteries increased cycle life with higher coulombic efficiencies. Various aspects involved in improving the cycle life of Zn anodes at increased DOD, and of the application of polymeric separators in isolating the MnO2 cathode from soluble zincate and their ability to enable higher DOD cycling in Zn, will be discussed. This work was supported by the U.S. Department of Energy, Office of Electricity, and the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by National Technology and 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-NA-0003525. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.