Achieving Fast Charging and Superior Cycling Stability Single-Crystal Ni-Rich Cathodes by Ultrafast Aqueous Washing

Single-crystal Ni-rich layered oxides represent ideal cathodes for high-energy-density lithium-ion batteries due to their high compaction density and volumetric capacity. However, lithium-excess high-temperature synthesis generates substantial residual lithium compounds (RLCs; e.g., Li₂CO₃/LiOH) on particle surfaces. These RLCs elevate interfacial impedance, while protracted Li⁺ diffusion pathways in micrometer-sized crystals collectively degrade fast-charge capability and cycling stability. To address these challenges, we develop an efficient strategy employing 3-min ultrafast washing followed by 600°C annealing for LiNi_0.85Co_0.1Mn_0.05O₂ single crystals. This approach achieves 80% capacity retention at 5 C charging meeting extreme fast-charging targets while maintaining superior cycling stability at 1 C. The ultrafast wash removes 94.5% of surface RLCs while confining structural deterioration to a mere 2-4 nm rock-salt reconstruction layer. Complementarily, in situ X-ray diffraction (XRD) reveals that this attenuated surface rock-salt phase enables smooth bulk phase transitions during Li⁺ (de)intercalation, thereby enhancing structural reversibility, ionic conductivity, and long-term stability.