Water-Mediated Surface\nEngineering Enhances High-Voltage\nStability of Fast-Charge LiCoO<sub>2</sub> Cathodes

Maintaining the surface structure stability of LiCoO<sub>2</sub> (LCO) during rapid charge–discharge processes (>5C)\nand under\nhigh-voltage conditions (>4.2 V) is challenging due to interfacial\nside reactions, cobalt dissolution, and oxygen redox activity at deeply\ndelithiated states, all of which contribute to performance degradation.\nHerein, different from traditional surface coating methods, we report\na water-mediated strategy that modifies the surface architecture of\nLCO, creating a passivating layer to inhibit surface degradation and\nenhance cycling stability under fast charging conditions. The surface\netching of LCO by H<sub>2</sub>O is accompanied by a concurrent Li<sup>+</sup>/H<sup>+</sup> cation exchange, which passivates surface oxygen\nwith H<sup>+</sup> ions, thereby enhancing both the hydrophobicity\nand structural stability. Consequently, the modified LCO exhibits\nsuperior capacity retention, which is 2.5 times that of the pristine\nLCO, after 100 cycles at a current density of 1000 mA g<sup>–1</sup> (∼6C at 4.5 V). Even at an elevated temperature of 45 °C,\nit maintains impressive cycling stability at a current density of\n500 mA g<sup>–1</sup> (∼3C), as demonstrated in practical\nfull-cell configurations. Investigation with multiple samples confirmed\nthat the water-mediated strategy demonstrated broad applicability.\nWe emphasize that the water-mediated modification of the surface architecture\non cathode materials offers significant insights into enhancing the\nstability of high-energy-density lithium-ion batteries (LIBs).