Anionic Redox in Alkali-Rich Chalcogenides for Energy-Dense, Lithium-Ion Batteries

Abstract

Lithium-rich transition-metal oxides and chalcogenides exhibit reversible charge-storage reactions centered at anionic sites (e.g., O2–, S2–, or Se2–), augmenting well-established metal cation-sited redox reactions to increase the energy density of lithium-ion or sodium-ion batteries by up to 100%.1 Despite these promising characteristics, the structure–property relationships that govern cation- and anion-coupled redox reactions in chalcogenides remain poorly understood. We deconvolve the cation/anion redox mechanisms of Li+-insertion in alkali-rich chalcogenides by modulating the transition metal–sulfide electronic band structure via systematic metal substitution for iron in Li2Fe1–xMxS2. Key electrochemical characteristics (cation/anion redox potential, Li+-insertion capacity, reversibility) will be correlated with electronic and structural properties as a function of chalcogenide composition using such techniques as X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering. Experimental results will be compared with density functional theory (DFT) calculations of analogous model systems. Understanding the relationship between band structure and reversible charge-storage will guide the design of alkali-rich chalcogenides that are candidates to transition into commercial Li-ion batteries. Due to the absence of oxygen in the chalcogenide crystal structure, batteries that use these as cathode materials will be inherently safer to operate at elevated temperatures and challenging charge–discharge duty cycles. C.J. Hansen, J.J. Zak, A.J. Martinolich, N.H. Bashian, F. Kaboudvand, A. Van der Ven, B.C. Melot, J.N. Welker, and K.A. See. Multielectron, Cation and Anion Redox in Lithium-Rich Iron Sulfide Cathodes. J. Am. Chem. Soc. 142 (2020) 6737–6749.