Enhancing High‐Temperature Electrochemical Performance of Single‐Crystal Ultra‐High Nickel Cathodes via High‐Valence Nb Gradient Doping

ABSTRACT High‐capacity, low‐cost ultra‐high Ni (Ni ≥ 0.9, NCM9) single‐crystal layered oxides have emerged as the most promising cathode materials for lithium‐ion batteries. However, they undergo lattice distortion and severe structural degradation after high‐temperature storage. In this study, a high‐valence Nb gradient doping modification strategy is employed to achieve the fabrication of structurally stable ultra‐high Ni single‐crystal cathode materials (SNCM9‐xNb) under high‐temperature storage. The introduction of Nb inhibits harmful phase transitions, alleviates stress accumulation, reduces intracrystalline microcracks, and prolongs cycle life. Meanwhile, the formation of Nb─O bonds suppress lattice oxygen release and mitigates structural collapse caused by high‐temperature storage. Consequently, SNCM9‐0.02Nb (after 60°C storage for 90 days) exhibits a high discharge capacity of 6.82Ah and a high‐retention of 82.1% following 600 cycles of the pouch‐type full‐cells. Despite undergoing 90 days of storage under elevated temperature conditions (60°C), the capacity retention and recovery rates exhibit minimal degradation, maintaining 90.87% and 93.28%, respectively, thus demonstrating remarkable stability and resilience. The high‐valence Nb gradient doping modification strategy reported in this work has been shown to mitigate the high‐temperature structural degradation of ultra‐high Ni single‐crystal cathode materials, thus offering a valuable insight into the development of cathode materials with stable performance at high temperatures.