Stabilizing the oxygen anionic redox chemistry using a Li-deficient and Li-rich biphasic structure for high-energy Li-ion batteries

Li-rich layered oxides (LLOs) with a large specific capacity of ∼300 mAh g^-1 show promise for developing high-energy Li-ion batteries (LIBs). However, the thermodynamic instability of the oxygen-anionic redox couple leads to lattice oxygen loss and structural transformation, resulting in a rapid decline in voltage and capacity. In this work, we rationally engineer Li-deficient phase formation in LLOs to stabilize oxygen-anionic redox chemistry and improve structural stability. The Li-deficient and Li-rich biphasic intergrowth composite is synthesized via ion exchange from the P3/O3 intermediate mixed-phase oxides. It is found that the incorporation of the Li-deficient phase makes the movement of the O 2p non-bonding energy band toward lower energy, which further alleviates the lattice oxygen release and stabilizes the oxygen-anionic redox chemistry upon Li⁺ de-intercalation. Consequently, the cycling stability is significantly enhanced in the biphasic LLOs, retaining superior capacity/voltage retention of ∼86%/88% after 400 cycles with a low capacity decay rate of 0.034% and voltage decline of 1.06 mV per cycle. The biphasic design offers a simple and feasible strategy for regulating the oxygen-anionic redox chemistry and boosting the structural stability of high-capacity LLOs.