Oxides As Cathode Materials for Mg-Ion Batteries

Abstract

Magnesium (Mg) batteries have the potential to revolutionize energy storage. Theoretically these batteries far outperform current Li-ion batteries in both volumetric and gravimetric capacities. [1] Additionally, Mg is a more earth abundant (13.9% Mg in earth’s crust compared to 7x10-4 % Li) and less expensive alternative ($2700/ton Mg and $64000/ton Li), ideal for automobile electrification and thus transforming society. [2] Despite these attractive properties, implementation of Mg-ion batteries has been hindered by several challenges. Most significantly, 1) electrolytes which allow for reversible Mg deposition have limited stability, and 2) reversible intercalation of Mg2+in cathode materials is kinetically slow and often irreversible. Thus, future Mg-ion batteries must incorporate stable high voltage and capacity cathode materials with fast and reversible Mg intercalation kinetics. Mg battery prototypes have used Chevrel phase cathodes, Mo6S8, and its derivatives. [3] These cathodes incorporate a delocalized framework to accommodate the charge and diffusion of hard Mg2+ ions. The multiple Mo ions allow for a diffuse charge network to accommodate intercalated Mg2+ ions. However, Chevrel phase cathodes suffer from low voltages (~1.1 V vs Mg/Mg2+) and only partial reversibility, where the total capacity drops by ~40% after the first discharge cycle. [4] For Mg batteries to be realized commercially, the cathode’s voltage and reversibility must be improved. In this talk we discuss our efforts using transition-metal oxides with open and delocalized structures as cathode materials for Mg-ion batteries. We investigate various bronzes and polyoxometalates, which have known magnesiated forms and high redox potentials. We find that these oxides exhibit reversible electrochemical behavior in various non-aqueous electrolytes and report on our efforts at confining these materials to electrode surfaces. [1] Yoo, H.; Shterenberg, I.; Gofer, Y.; Gershinsky, G.; Pour, N.; Aurbach D. Energy Environ. Sci. 2013, 6, 2265. [2] Saha, P.; Jampani, P.; Datta, M.; Okoli, C.; Manivannan, A.; Kumta, P. J. Electrochem.Soc. 2014, 161, A593. [3] Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman R.; Cohen, Y.; Moshkovich, M.; Levi, E. Nature, 2000, 407, 724. [4] Saha, P.; Datta, M.; Velikokhatnyi, O.; Manivanna, A.; Alman, D.; Kumta P. Prog. Mater. Sci. 2014, 66, 1.