The Role of Li-Rich Disordered Domain in Li-Rich Cathodes

Li-rich cathodes suffer from electrochemical degradation due to structural incompatibility between the Li-rich and LiTMO₂-like phases (transition metal [TM] = Mn, Ni). This study identifies and characterizes a previously overlooked transitional phase, the Li-rich disordered (LRD) domain, which bridges these two primary phases and is the fundamental origin of heterogeneous redox-driven strain and lattice displacements. Advanced structural analyses reveal that transition metals, particularly Ni, occupy Li sites within this LRD domain. We demonstrate that tailoring the synthesis to constrict the LRD domain effectively mitigates its structural evolution during (de)lithiation. This constricted domain acts as a buffer layer, isolating the anisotropic lattice strain between adjacent domains, thereby suppressing oxygen loss and enhancing structural integrity. In situ high-temperature XRD further tracks the formation of this domain during synthesis. Consequently, the engineered cathode delivers a 15% (25 mA g⁻¹, 50 cycles) and 26% (250 mA g⁻¹, 300 cycles) increase in specific capacity than pristine within 2.0–4.8 V, alongside enhanced long-term cycling stability. This work elucidates the critical role of the constricted LRD domain in stabilizing anionic redox, offering a fundamental insight for designing advanced Li-rich cathodes.