Reversible Configurations of 3-Coordinate and 4-Coordinate Boron Stabilize Ultrahigh-Ni Cathodes with Superior Cycling Stability for Practical Li-Ion Batteries

Abstract

Ultrahigh-Ni layered oxide cathodes are the leading candidate for next-generation high-energy Li-ion batteries owing to their cost-effectiveness and ultrahigh capacity. However, the increased Ni content causes larger volume variations and worse lattice oxygen stability during cycling, resulting in capacity attenuation and kinetics hysteresis. Herein, a Li₂SiO₃-coated Li(Ni_0.95Co_0.04Mn_0.01)_0.99B_0.01O₂ ultrahigh-Ni cathode that well-addresses all the above issues, which is also the first time to realize the real doping of B ions is demonstrated. The as-obtained cathode delivers a reversible capacity of up to 237.4 mAh g⁻¹ (924 Wh kg⁻¹_cathode) and a superior capacity retention of 84.2% after 500 cycles at 1C in pouch-type full-cells. Advanced characterizations and calculations verify that the boron-doping is existed in terms of 3-coordinate and 4-coordinate configurations and their high electrochemical reversibility during de-/lithiation, which greatly stabilizes oxygen anions and impedes Ni-ion migration to Li layer. Furthermore, the B-doping engineers the primary particle microstructure for better relaxing the lattice strain and accelerating Li-ion diffusion. This work advances the energy density of cathode materials into the domain of above 900 Wh kg⁻¹, and the concept will inspire more intensive study on ultrahigh-Ni cathodes.