Batteries are easy to use, remotely monitorable, not fuel dependent, easily permitted and installed, and start automatically and reliably during an electrical outage. This makes them optimal for stationary storage and power assurance applications. Within battery-based grid storage, as of mid-2017, lithium-ion, sodium-ion, and lead-acid systems are the leaders, comprising 59% (~1.1 GW), 8% (0.15 GW), and 3% (0.06 GW) of global operational electrochemical storage, respectively.¹ However, these batteries suffer from low energy density, high cost, poor safety, environmental concerns, and/or cycle life. Existing battery options on the market also do not meet the required market needs for long-duration backup power. For example, lead-acid batteries require too much space, are heavy, and contain toxic materials. Lithium-ion batteries, while compact and capable of excellent cycle life, are too expensive to serve long outages and have notable flammability and environmental risks.

Alkaline zinc-based batteries are a strong candidate for electrical grid storage applications due to zinc’s high capacity (820 mAh/g), established materials supply chain and low cost.¹ Alkaline-based cells are generally considered safe and do not have the temperature limitations of Li-ion or Pb-acid batteries, thereby removing the need for complicated thermal management control strategies and providing for simpler systems with lower integration costs. To realize the highest energy density batteries, Zn needs to be coupled with a similarly low cost, abundant and high-capacity cathode. Historically Zn has been paired with MnO₂ (616 mAh/g), CuO (674 mAh/g) and S (1675 mAh/g) cathodes to produce energy dense primary batteries. If reversibility can be proven for these conversion cathodes, they would be enticing candidates for grid storage systems.

In this presentation, we will report on the development of electrochemically reversible conversion cathodes for alkaline Zn-batteries. Specifically, we will focus on copper oxide-based cathodes and their use in alkaline Zn/CuO batteries with application for large scale grid storage.² Sandia has recently developed rechargeable alkaline Zn/CuO batteries with very high areal capacities of ~ 40 mAh/cm² and energy densities of > 200 Wh/L. This is among the highest ever energy density reported for a laboratory scale alkaline Zn–based battery using a conversion cathode. In this example, the rechargeability is enabled by the addition of a bismuth (Bi₂O₃) additive that facilitates the electrochemical reversibility of Cu₂O and Cu(OH)₂ species. Data collected from a variety of techniques, including cyclic voltammetry (CV), rotating ring-disk electrode (RRDE) voltammetry, electrochemical impedance spectroscopy (EIS), electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and operando energy-dispersive X-ray diffraction measurements will be presented to elucidate the role of the additive in enabling reversibility in Zn/CuO batteries. In addition, the general challenges of achieving high-capacity Zn anodes and the pairing of two high-capacity conversion electrodes to form the battery, each which cycles through the formation of soluble “-ate” complexes [i.e., cuprate, Cu(OH)₄^2- and zincate, Zn(OH)₄^2-] will also be covered.

The goal is to demonstrate a Zn/CuO battery with long lifetime, at appreciable energy densities (> 200 Wh/L), with excellent safety, lower toxicity and sufficiently low cost to be manufactured and installed on the grid. While these laboratory scale Zn/CuO battery builds have very promising characteristics to date they have not been optimized or adapted for consumer or market-based needs in terms of power performance, energy density, cycle life or stability in terms of shelf life and the ability to tolerate partial state of charge. Progress towards these goals may also 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-mission 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.

References:

1. M. B. Lim, T. N. Lambert, B. R. Chalamala. “Rechargeable Alkaline Zinc–Manganese Oxide Batteries for Grid Storage: Mechanisms, Challenges and Developments” Mater. Sci. Eng. R Rep. 2021, 143, 100593.
2. N. B. Schorr, D. Arnot, A. M. Bruck, J. Duay, M. Kelly, R. L. Habing, L. S. Ricketts, J. A. Vigil, J. W. Gallaway and T. N. Lambert “Rechargeable Alkaline Zinc/Copper Oxide Batteries” ACS Applied Energy Mater. 2021, 4, 7, 7073–7082.