Progress Towards the Development and Understanding of Energy Dense Rechargeable Batteries Utilizing Zn and Cu

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.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 Zn batteries are a strong candidate for electrical grid storage applications due to Zn’s high capacity (820 mAh/g), established materials supply chain and low cost. To realize the highest energy dense batteries, Zn needs to be coupled with a similarly low cost, abundant and high-capacity cathode. CuO (674 mAh/g) is an intriguing high-capacity cathode when paired with Zn in alkaline electrolyte, a battery that until recently has been relegated to the history books as a primary system. In 2021 Schorr et al. reported a rechargeable Zn/CuO battery that utilized a Bi additive to help facilitate the electrochemical reversibility of the Cu conversion electrode. Bi 2 O 3 , a species with comparable redox potentials to Cu 2 O, promoted reversibility and minimized passivation in the historically non-reversible system. The battery cycled without any observable Cu and Bi mixed oxide phases, cycling between metallic Cu and Bi and Cu 2 O/Cu(OH) 2 and Bi 2 O 3 , respectively. Although the Bi additive did not eliminate capacity fade completely, limiting the cells to a 30% depth of discharge (relative to CuO) enabled 250 cycles at > 124 Wh/L. Alternatively, compensating for capacity loss with additional Cu metal provided for very high areal capacities (∼40 mA h/cm 2 ) and energy densities (∼260 W h/L), despite only 65% active material cathode loadings and ∼10% Zn anode utilization; preliminary tests indicated these batteries were prone to shorting. Seeking to improve performance and minimize the spatial segregation of Cu- and Bi-phases observed upon cycling in the prior system, D. Arnot et al. prepared nanoscale carbon coated (Cu/Bi) particles, where the coating partially minimized dissolution and diffusion of soluble cuprate and bismuthate complexes, where ~ 200 cycles at 300 mAh/g was demonstrated (@ ~ 100 Wh/L). CuBi 2 O 4 and CuO phases were formed upon oxidation, indicating carbon coatings can affect the battery cycling mechanism and may have future roles increasing performance. Data collected from a variety of experimental techniques, including cyclic voltammetry, rotating ring-disk electrode voltammetry, electrochemical impedance spectroscopy, electron microscopy, transmission electron microscopy, Raman spectroscopy, operando energy-dispersive X-ray diffraction measurements, battery cycling along with recent DFT modeling will be presented to help elucidate the role of additives, carbon coatings, and ion selective polymers in enabling reversible Zn/Cu based batteries. In addition, the general challenges of achieving a highly reversible energy dense battery based on two conversion electrodes operating in highly alkaline environment will be discussed. 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 the 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. N. B. Schorr et al. Rechargeable Alkaline Zinc/Copper Oxide Batteries. ACS Applied Energy Mater. 2021 , 4, 7, 7073–7082. https://doi.org/10.1021/acsaem.1c01133. D. J. Arnot et al. Rechargeable Alkaline Zn-Cu Batteries Enabled by Carbon Coated Cu/Bi Particles. J. Power Sources 2022 , 529 , 231168. https://doi.org/10.1016/j.jpowsour.2022.231168. 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.