Achieving thermodynamic stability of single-crystal ultrahigh-nickel cathodes via an alcohol-assisted mechanical fusion

Elevating the operating voltage is an effective approach to improve the reversible capacity of ultra-high nickel layered oxide cathode LiNi_xCo_yMn_zO₂ (NCM, x ≥ 0.8) and solve the “range anxiety” confusion of electric vehicles. However, the undesirable surface reconstruction induced by the high cut-off voltage has a fatal impact on the thermodynamic stability of the material, inevitably leading to fast capacity degradation. Herein, a mechanical fusion aided by alcohol is suggested to create a stable olivine structure for the single-crystal (SC) ultrahigh-nickel cathode LiNi_0.92Co_0.04Mn_0.04O₂. The addition of nanoparticles effectively bridges the void of SC-NCM, builds an ideal particle grading, and significantly raises the cost efficiency, as well as promotes the cycling stability and safety of the full cell. Remarkably, the layered/olivine mixture forms a perfect shield by lowering the surface area between the NCM cathode and electrolyte, hence mitigating side reactions and contributing to an incredibly thin and stable cathode/electrolyte interface. Furthermore, the thermodynamic stability of highly delithiated NCM is improved, as both the particle cracks and structural degradation are simultaneously postponed. Consequently, the maximum temperature of the single-crystal LiNi_0.92Co_0.04Mn_0.04O₂@LiFePO₄‖graphite pouch full cell is dramatically reduced from 599.4 to 351.4 °C, and the full cell achieves 88.2% capacity retention after 800 cycles, demonstrating excellent thermal stability and cycling stability. This facile strategy provides a feasible technical reference for further exploiting the ultrahigh-capacity, high-safety, and long-life Ni-rich cathode for commercial application of lithium-ion batteries (LIBs).