Construction of internal electric field to suppress oxygen evolution of Ni-rich cathode materials at a high cutoff voltage

Abstract

The Nickel-rich layered cathode materials have been considered as promising cathode for lithium-ion batteries (LIBs), which due to it can achieve a high capacity of than 200 mAh g−1 under a high cutoff voltage of 4.5 V. However, the nickel-rich layered cathode materials show severely capacity fading at high voltage cycling, induced by the hybrid O anion and cation redox promote Oα− (α< 2) migration in the crystal lattice under high charge voltage, lead to the instability of the oxygen skeleton and oxygen evolution, promote the phase transition and electrolyte decomposition. Here, Li1−xTMO2−y/Li2SO4 hybrid layer is designed by a simple pyrolysis method to enhance the high voltage cycle stability of NCM. In such constructed hybrid layer, the inner spinel structure of Li1−xTMO2−y layer is the electron-rich state, which could form an electron cloud coupling with the NCM with surface oxygen vacancies, while Li2SO4 is p-type semiconductors, thus constructing a heterojunction interface of Li1−xTMO2−y//Li2SO4 and Li1−xTMO2−y//NCM, thereby generating internal self-built electric fields to inhibit the outward migration of bulk oxygen anions. Moreover, the internal self-built electric fields could not only strengthen the bonding force between the Li1−xTMO2−y/Li2SO4 hybrid layer and host NCM material, but also boost the charge transfer. As consequence, the modified NCM materials show excellent electrochemical performance with capacity retention of 97.7% and 90.1% after 200 cycles at 4.3 V and 4.5 V, respectively. This work provides a new idea for the development of high energy density applications of Nickel-rich layered cathode materials.