Modulating anionic activities in layered Li-rich cathode materials with inverse spinel MnFe2O4 coating

Abstract

Layered Li-rich cathode oxides can provide high specific capacity due to oxygen anion redox involving in charge compensation process during cycling, but there is a severe structural transition from layered to spinel accompanying with irreversible oxygen loss during cycling, which lead to electrochemical degradation. The current researches show that the irreversible oxygen evolution reaction of layered lithiumrich materials in the first cycle mainly comes from the surface lattice oxygen, so the surface modification by the materials with more stable structure is one of the effective ways to improve the electrochemical performance of layered lithium-rich materials. In this paper, we report a modified layered lithium-rich cathode material by surface coating of inverse spinel MnFe2O4. The inverse spinel has strong polarization effect on anion migration due to its different atoms occupying octahedral sites from layered structure and it can also modulate the Fermi level and stretching the O-O bond, thereby increasing the energy barrier for surface oxygen oxidization. Furthermore, the three-dimensional connected tunnel structure of the inverse spinel also makes the surface layer of the material have a faster lithium ion transferring rate, and a large number of lithium storable vacancies inside of it improved the Li+ intercalation efficiency, initial coulombic efficiency and rate performance. Compared with the unmodified sample, the modified material coated with 2% MnFe2O4 has superior cycle stability and outstanding rate performance. It is hoped our work would provide the knowledge for the future development of high-performance cathode materials for Li-ion batteries.