Niobium Gradient Doping-Driven Microstructural Engineering for High-Performance Nickel-Rich Cathode Materials in Lithium-Ion Batteries

Implementing Ni-enriched (Ni ≥ 60%) layered cathodes in high-energy lithium-ion battery (LIB) presents a host of hurdles, including issues with maintaining structural integrity, the volatile nature of the reactive Ni⁴⁺ ions, and the risk of thermal breakdown. Herein, we propose a two-step strategy for Nb modification, which enables gradient Nb doping in Li[Ni_0.6Co_0.2Mn_0.2]O₂ (NCM622). In which, the low concentration of Nb doping within the NCM622 particles increases the interplanar spacing, facilitating lithium-ion diffusion and enhances crystallographic stability by preventing excessive Nb doping from interfering with lithium-ion sites, thereby delivering a progressively higher specific capacity and effectively mitigates the degradation of the Ni-enriched layered cathode; Nb densely decorates primary-particle grain boundaries and secondary-particle surfaces, which not only effectively suppresses electrolyte decomposition and side reactions, but also enhances electronic conductivity, which is attributed to the nature of fast ionic conductors refer to Nb-based compounds. Additionally, Nb incorporation elongates and radially aligns primary particles, forming a framework that effectively dissipates sudden internal strain during phase transformations, while ion deintercalation preferentially proceeds along these extended edges. The Nb-NCM622 cathode retains 86% of its initial capacity after 300 cycles at 5C (1C = 180 mA g^-1), significantly surpassing that of the pristine counterpart (68.34%). Moreover, to design a battery with high specific power and energy, Nb-modified NCM622 is cooperated with 8% graphene to form capacitor-LIB hybrid electrode. A 7 Ah pouch full-cell pairing the hybrid cathode with hard carbon retains ≈90% capacity after 7000 cycles at 70 A. This simple tactic extends lifespan, permits rapid charging, and meets safety benchmarks─while preserving capacity for next-gen electric vehicles.