Regulating anionic redox activity of lithium-rich layered oxides via LiNbO3 integrated modification

Abstract

Lithium-rich layered oxide cathodes suffer from severe interfacial degradation, capacity attenuation and voltage fading which mainly result from poor reversibility of anionic redox. In this study, a LiNbO3 integrated strategy including LiNbO3 coating, spinel heterostructure and Nb5+ doping has been proposed for stabilizing lattice oxygen and improving structural stability. Among them, the LiNbO3 coating layer can protect highly active peroxo-like oxygen from the electrolyte and spinel heterostructure with three-dimensional (3D) lithium transport channels facilitates the diffusion kinetics. More importantly, Nb5+ dopants inserting into subsurface lattice regulate localized electron configuration and strengthen the reversibility of anionic redox. Theoretical calculation results including density of states and crystal orbital overlap populations unravel the active O-O dimer still coordinates with crystal framework under fully delithiated state after Nb doping exhibiting enhanced anionic redox reversibility and structural stability. Corresponding analysis suggest that doping Nb5+ cations possessing no valence electron (4d0) and low electronegativity could transform Mn-O system into electrochemical inactive Nb-O system with large charge transfer and low d orbital repulsion (Mott-Hubbard regime). Moreover, this inactive Nb-O system cannot provide any reactive electron from Nb5+ cation and oxygen holes have to be isolated on O 2p orbitals, leading to the enhanced reversibility of anionic redox. This integrated modification strategy provides inspiring insights for understanding and regulating the reversibility of anionic redox, showing great potential in designing high-performance lithium-rich Mn-based cathodes.