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

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 of4.5 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 O^(α-)(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,Li_(1-x)TMO_(2-y)/Li_(2)SO_(4) 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 Li_(1-x)TMO_(2-y)layer is the electron-rich state,which could form an electron cloud coupling with the NCM with surface oxygen vacancies,while Li_(2)SO_(4) is p-type semiconductors,thus constructing a heterojunction interface of Li_(1-x)TMO_(2-y)//Li_(2)SO_(4) and Li_(1-x)TMO_(2-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 Li_(1-x)TMO_(2-y)/Li_(2)SO_(4) 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.