Anchoring Interfacial Nickel Cations by Tunable Coordinative Structure for Highly Stabilized Nickel-Rich Layered Oxide Cathodes

Abstract

Ni-rich LiNixCoyMn1−x-yO2 (NCM) cathode materials have received extensive attention on account of their high specific capacities and great application prospects in electric vehicles. While increasing Ni content in NCM can greatly increase initial discharge capacities, more highly reactive Ni4+ species in the delithiated state may facilitate irreversible phase transformation and undesirable interfacial reactions, leading to severe capacity degradation. Here we demonstrate an organic surface modification approach to modulate the surface coordinative structure of NCM cathode for enhanced cycling stability. We discover that the highly reactive Ni4+ cations can be anchored by strong electron-donating organic groups, especially under bidentate coordination, which mitigates excessive electrolyte decomposition and Ni dissolution into the electrolyte, inhibits the layered-to-rock salt phase transformation and suppresses the initiation and propagation of microcracks within the NCM cathodes. In consequence, the nickel-rich cathode coated with poly (acetoacetoxyethyl methacrylate) (PAAEM) with multiple ester groups exhibits a remarkable improvement in cycling stability, showing 91.3% retention of the initial capacity after 200 cycles. The present findings demonstrate that regulating surface coordinative structure is an efficient and practical strategy to modify the interfacial reactions for enhanced cyclability in Ni-rich layered oxide cathodes.