Regulating Cathode‐Electrolyte Interphase by Confining Functional Aluminum Compound within Ni‐Rich Cathodes

Abstract The oxidative capability of Ni 4+ and high operation voltage of nickel‐rich LiNi 1−x−y Co x Mn y O 2 (Ni‐rich NCM) cause its continuous and deleterious side reactions with electrolyte and irreversible phase transition, which hinder its industrial application. To mitigate these issues, Al (CF 3 SO 3 ) 3 is proposed as a solid electrolyte additive that can be readily oxidized to regulate the cathode‐electrolyte interphase (CEI) due to the highest occupied molecular orbital‐level of CF 3 SO 3 − , meanwhile being confined within the single‐crystalline NCM811. CF 3 SO 3 − prior to the electrolyte is oxidized upon increasing voltage to produce sulfur components and involve CEI formation. Concurrently, the released Al 3+ ions are combined with reactive oxygen from NCM811 particles and HF from the electrolyte to form Al 2 O 3 and AlF 3 , respectively. A robust sandwich CEI film containing sulfur and aluminum species is formed, which cannot only prevent decomposition of the electrolyte, but also alleviate the formation of inactive rock‐salt phase on NCM811 surface. Consequently, such CEI leads to high‐performance batteries with a high‐capacity retention of 91.5% after 200 cycles under 0.5 C compared to 72.4% of pristine NCM811. This facile and environmentally benign method provides a new avenue to develop high‐capacity and durable cathodes for lithium‐ion batteries.