Understanding the complex surface and interphase chemistry of Ni-rich layered oxide cathodes

Owing to the high theoretical capacity (274 mAh g −1 ) and operating voltage (4.3 V vs. Li + /Li), Ni-rich layered oxide (NRLO) cathodes are the premier choice for high-energy-density Li-ion batteries (LIBs). However, the practical applications of NRLO cathodes are hindered by their high thermal, chemical, and structural instabilities, leading to poor performance and long-term safety risks. Unlike the other cathodes for LIBs, the deterioration of NRLO originates at the surface/interphase region and propagates towards the bulk. The high surface reactivity of NRLO cathodes leads to the phase transitions from layered to spinel to rock-salt, Li + /Ni 2+ cation mixing, crack formation, and surface alkaline Li residues. Thus, a comprehensive understanding of their intricate surface chemistry is essential for rationally designing high-performance NRLO cathodes. Numerous reviews cover NRLO degradation, surface modifications, and the dynamics of the cathode electrolyte interphase (CEI). However, the critical interfacial phenomena: Li + -transport barriers in multilayer interphases, interlinked degradation pathways, interface-induced bulk degradation, the complexity of probing interphases, and anode-cathode crosstalk remain necessary for comprehensive integration. Thus, this review provides a concise overview of NRLO cathode structures and degradation mechanisms; surface/interphase challenges; interconnected degradation pathways; complexities of interphase characterization; challenges in translating lab-scale NRLO data to industry scale; and prospects for high-energy-density LIBs.