Mechanistic Investigation of Metal Sulfide Electrodes for High-Energy Non-Aqueous Anion Batteries

Oregon State University, Corvallis OR

Investigators

Abstract

The energy density of the current Li-ion batteries has nearly reached their ceiling; however, driving range anxiety still hinders the market growth of electric vehicles. In addition, the current high-energy batteries rely on expensive elements of cobalt and nickel with poor earth abundance and in cobalt’s case not plentiful domestically. Therefore, manufacturing such batteries is not sustainable for transforming a large percentage of vehicles to be electrified to mitigate climate change. Current high-energy batteries employ Li-ions (positive charged ions) as the charge carrier to compensate for the charge neutrality of metal oxides during charge and discharge. In theory, the operation of battery electrodes can use anions (negative charged ions) as charge carriers, but this research direction has yet to receive much attention, particularly to achieve high energy density. This project will study earth abundant materials that are plentiful domestically such as copper and sulfur. This fundamental research project will fill the knowledge gap by employing light (low molecular weight) anions as the charge carriers to couple with the redox reactions of inexpensive metal sulfides as the electrode. The project will build upon the preliminary findings of the reversible storage of anions in conversion electrode reactions. In addition, the PI will study nonaqueous electrolytes to facilitate the new battery reactions. As a part of the research, the project will provide high-quality research opportunities for underserved undergraduate and high school students. The project aims to elucidate the operation mechanism of a high-energy cathode converted reversibly between Cu2S mixed with a lithium salt and the composite comprising a cupric salt, CuA2, and sulfur. The targeted Cu2S, as a natural mineral, is a promising anion-hosting cathode material because Cu2S is a conductor of both electrons and copper ions. The project will generate knowledge about the interplays and transport of three ions in a seemingly complicated conversion reaction. In the electrochemical conversion reactions between Cu2S+LiA and CuA2+S, four electrons are transferred. Li-ions never interact with redox centers of copper or sulfur but only with A-anion; however, copper ions and anions transport between the redox centers of Cu2S, CuS, and CuA2. This electrode design causes the decoupling of device charge compensation and electrode charge compensation. The outcomes of this project will be a new addition to solid-state ionics and electrochemical systems. Unlike that of the sulfur cathode in Li-S batteries, the presence of copper ions eliminates polysulfide formation due to the strong binding between copper ions and sulfides. The insoluble nature of Cu2S and CuS allows the characterization of the solid electrode at different state of charge on detailed structural and kinetic properties. The project will delineate the correlations that affect the utilization, the kinetic properties, and the reversibility of the electrodes. The project will establish synergistic selection rules of anion charge carriers and electrolytes to promote the proposed battery chemistry performance. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.