Towards the Rational Design of Ni & Co free Chalcogen Anion Redox Cathode Materials

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Global energy demands and a desire for decreased reliance on fossil fuels have intensified research toward large-scale energy storage capabilities. Even though many years of active research in Li-ion battery technologies, the current battery materials still rely heavily on conventional transition-metal cathode materials. These cathode materials have limited capacity, and geopolitical issues raise concerns over their continued availability. Recently, researchers have been exploring the so-called “Lithium-rich anion redox” cathode chemistry, where both transition metals and anions participate in the electrochemical redox reactions, resulting in significantly higher energy storage capability. Despite delivering high capacity, these Li-rich cathodes suffer from fundamental stability issues. This project seeks to gain the fundamental insights necessary for the design of next-generation low-cost and high-capacity cathode materials that are free from Nickel and Cobalt metals. For broader impacts, a specific outreach mission will be formed to provide research experience to the students in community colleges around Detroit, MI where the majority of students are from underrepresented groups. Li-rich anion-redox cathode chemistry is emerging as conventional cationic-redox of transition metal-based layered oxides are reaching their theoretical capacity limit. Though the combined redox of both anion and cation towards higher energy storage capability, the cathodes suffer from voltage fade, large voltage hysteresis, and irreversible oxygen release, which originate mysteriously from the anionic redox activity of oxygen ligand itself. The technical objective of this project is to construct a structural framework for Li-rich anion redox cathodes by tuning metal-ligand covalency using commercially viable metal-cations and less electronegative chalcogen ligands (sulfides and selenides). The proposed research is based on the hypothesis that the improved metal-ligand covalency can be achieved by bringing metal cation d-band close to chalcogen anion p-band in lithium-rich chalcogenide thereby utilizing highly reversible multi-electron redox chemistry. The successful outcome of the project is to elucidate the core understanding of lithiation (discharge)-delithiation (charge) kinetics in chalcogen anion redox compounds and anion redox induced structural transformation in various metal d-band and ligand p-band environments. Thus, this research aims to define fresh perspectives on chalcogen redox chemistry to advance the fundamental understanding of the next-generation cathode materials.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.