Unraveling the Role of Surficial Oxygen Vacancies in Stabilizing Li-Rich Layered Oxides

Li-rich layered oxides based on the anionic redox chemistry provide the highest practical capacity among all transition metal (TM) oxide cathodes but still struggle with poor cycling stability. Here, a certain amount of oxygen vacancies (OVs) are introduced into the ≈10 nm-thick surface region of LiNiCoMnO through a long-time medium-temperature post-annealing. These surficial enriched OVs significantly suppress the generation of O-O dimers (O, 0 < n < 4) and the associated side reactions, thus facilitating the construction of a uniform and compact cathode/electrolyte interphase (CEI) layer on the surface. The CEI layer then decreases the further side reactions and TM dissolution and protects the bulk structure upon cycling, eventually leading to enhanced cycling stability, demonstrated in both half cells and full cells. An in-depth understanding of OVs is expected to benefit the design of stable cathode materials based on anionic redox chemistry.