Design of a p-Type Electrode for Enhancing Electronic Conduction in High-Mn, Li-Rich Oxides

Abstract

We report the introduction of p-type conductivity in high-Mn, Li-rich oxides (HMLOs) by the introduction of Cu doping to improve intrinsic electronic conduction. The study is based on experimental observations and a fundamental understanding through first-principles electronic structure analysis. Although the Cu-doped HMLO (CuHMLO) has a crystal structure identical to the original HMLO, the electrochemical performance of CuHMLO is superior in terms of specific energy and power characteristics. Specifically, CuHMLO exhibits a larger specific capacity with enhanced rate capability, and could be charged at lower voltages and discharged at higher voltages. For the first-principles calculations, HMLO and CuHMLO structures are modeled based on Rietveld refinement of the powder X-ray diffraction data of the powders synthesized herein. The electronic structure of CuHMLO reveals the generation of an electron hole in the valence band, above the Fermi level, indicating p-type conductivity and improving the electronic conductivity. The interpretation based on the crystal field theory elucidates that the generation of this electron hole is responsible for the relatively reduced character of Cu than Mn in the highly oxidized HMLO environment. Combination of this observed enhancement with a fundamental understanding on the origin of the p-type conductivity could assist in improving the specific energy and power characteristics of Li-rich oxides.