Insight into the Relationship between Transition Metal and Anionic Redox As Found in Simple Li-Rich CuO-Li2O Composite Cathode Materials

Abstract

Conventional lithium ion battery cathode materials derive their capacity exclusively from transition metal cation redox. Many recent studies on novel Li-rich cathode materials have found substantial reversible anionic redox that shows promise to greatly enhance battery capacity. Unfortunately, this anionic (oxygen) redox contribution to the charge compensation of lithium extraction and insertion typically results in cathode degradation and oxygen gas release. While previous studies have emphasized methods such as the doping of 4d or 5d transition metals to stabilize the formation of peroxo-like species, the mechanism of anionic redox in relation to the transition metals present is still largely unknown. This study employs simple Li-rich cathode materials as a model for further understanding of the mechanism of anionic redox. Here we have synthesized a number of materials including simple 3d transition metal (e.g., Cu) doped lithium oxide to more closely examine the relationship between oxygen redox and the transition metal present in the cathode material. The materials studied contain a high ratio of lithium to transition metal to probe the maximum anionic redox activity. We will discuss our results in which galvanostatic measurements are combined with quantitative gas evolution analysis, in addition to ex-situ resonant inelastic X-ray scattering and X-ray photoelectron spectroscopy on cycled electrodes, to continue to clarify the required conditions for anionic redox in lithium ion battery cathode materials.