Regulating π-Type Interactions between O 2p and TM t2g Orbitals via Ti Doping and Surface Dielectric Coatings for Li-Rich Cathode

Abstract

The irreversible anionic redox reaction and oxygen release of Li-rich layered oxide cathodes seriously hinder their commercial application. Here, a synergistic modification strategy of surface dielectric coating (TiNb2O7) and bulk phase Ti doping is proposed in this paper. TiNb2O7, as a dielectric oxide, can generate a reversed electric field during charging to block the migration path of anions inside the material. In addition, the unique three-dimensional Li+ diffusion channels of TiNb2O7 can improve the lithium-ion diffusion kinetics. The bulk-phase Ti doping can increase the energy barrier of the oxygen release reaction, and the stronger Ti-O bond can regulate the electronic structure and π-hybridization of the transition metal and thus stabilize the oxygen skeleton. The results of XPS, CV, and HRTEM show that the synergistic modification strategy fundamentally inhibits oxygen loss and enhances the reversibility of anion redox, while constructing a uniform and stable CEI interface. The co-modification strategy effectively improves the electrochemical performance of the materials. The modified sample can maintain a high capacity of 175.1 mAh g-1 after 500 cycles at 1C. This work provides new insights to improve the oxygen loss problem of Li-rich layered oxide cathodes.