Improved electrode reversibility of anionic redox with highly concentrated electrolyte solution and aramid-coated polyolefin separator

Abstract

High-capacity electrode materials made of abundant elements are necessary to develop cost-effective energy storage applications. An emerging new chemistry has involved a series of electrode materials with a cation-disordered rock salt structure, and Li-excess and Mn-based oxides with disordered structures are attractive candidates for this purpose. Large reversible capacities for these electrode materials are obtained through both cationic/anionic redox. However, cyclability associated with insufficient reversibility of anionic redox in carbonate-based electrolyte solutions is not acceptable for practical applications. Herein, a significant improvement of electrode reversibility was achieved with highly concentrated electrolyte consisting of LiN(SO₂F)₂ and dimethyl carbonate. A practical problem when using high-viscosity concentrated electrolyte, i.e., non-wettability of concentrated electrolyte to polyolefin separators with small pores, was also effectively solved by using an aramid-coated polyolefin membrane. The improvement of reversibility for anionic redox associated with the suppression of oxygen loss, was clearly demonstrated by the results of X-ray absorption spectroscopy of nanosized Li_1.14Ti_0.29Mn_0.57O₂ with the concentrated electrolyte solution and aramid-coated separator. These findings have shown the future possibility of developing applications of high-energy batteries without ions of non-abundant nickel/cobalt.