Synergistic enhancement of 4.8 V cycling stability in Li-rich layered oxide cathode via single-crystal formation and consequent spontaneous Cl− incorporation

Li-rich layered oxide cathodes (LLOs) exhibit inherent instability during high-voltage cycling at 4.8 V. The design of single-crystal morphology is one of the strategies to enhance the high-voltage stability of LLOs. This study challenges the conventional single-crystal-focused view by revealing a novel synergistic mechanism between spontaneous Cl^- doping and single-crystal formation during the LiCl molten salt synthesis process. By optimizing the LiCl-to-TM molar ratio to 1.65, the liquid-phase isolation effect of the molten salt leads to uniform single-crystal particles, thereby effectively eliminating grain boundary fracture risks. Concurrently, high-temperature processing drives spontaneous Cl^- substitution for O^2- within the lattice. Multi-scale characterizations confirm uniform solid-phase doping and demonstrate c-axis lattice expansion. The high bond energy of TM-Cl bonds, effectively stabilizes the lattice structure and suppresses transition metal migration. Consequently, the combined effects of single-crystal integrity and Cl-bonding significantly reduce Mn dissolution and make the layered structure preserved after cycling. Optimized SCCl-3 exhibits 99.2 % capacity retention after 200 cycles at 4.8 V, compared with the 81 % degradation observed in the control group. Furthermore, the enhanced lithium-ion diffusion performance in optimized SCCl-3 leads to a capacity of 160.52 mAh g^-1 at 2C. This work establishes a new physicochemical dual-regulation paradigm for the design of high-voltage LLOs.