Intermediate phase regulation in Ni-rich cathodes via soft oxidation-lithiation for enhanced electrochemical performance

Cation disordering is a common issue in Ni-rich cathodes that significantly degrades cycle life and compromises safety. The cubic rock-salt phase formation and the slow oxidation kinetics of Ni²⁺ during solid-state sintering are widely recognized as the principal causes of these structural defects. To solve this issue, a topotactic soft-chemical precursor engineering strategy is proposed for use in aqueous solution. By utilizing the layered structure of the precursor, this method allows for selective proton extraction and efficient Ni²⁺ oxidation, along with rapid Li⁺ intercalation to form a layered lithiated intermediate. This intermediate crystallizes without further phase transitions during subsequent heat treatment, preventing structural defects caused by complex phase evolution and slow ion diffusion. The resulting cathode exhibits a long-range ordered layered structure and a uniform phase distribution, enabling efficient Li⁺ insertion and extraction. Electrochemical tests reveal a high discharge capacity of 229.6 mAh g⁻¹ and an initial coulombic efficiency of 95.77 % at 0.1 C, greatly exceeding the performance of a conventionally synthesized cathode (210.3 mAh g⁻¹, 88.93 %). Improved Li⁺ transport kinetics reduces phase-transition hysteresis and alleviates stress concentration, resulting in better cycling stability with a capacity retention of 85.3 % after 300 cycles, compared to 61.5 % for the conventional sample. This work presents a scalable and effective synthesis route for Ni-rich cathodes with reduced structural disorder and extended lifespan, providing valuable insights into how the regulation of intermediate phases influences electrochemical performance in high-performance Ni-rich cathodes.