La³⁺ Doped Nickel-Manganese Oxide as High-Capacity Cathode for Sodium-Ion Batteries Guided by Bayesian Optimization

In sodium-ion batteries, the layered transition metal oxides used as cathode often experience interlayer sliding of interlayer spacing and lattice variations during charge/discharge, leading to structural damage and capacity degradation. To address this challenge, a La³⁺ doping strategy guided by Bayesian optimization has been employed to prepare the high-performance O3-NaNi_0.39Mn_0.50Cu_0.06La_0.05O₂ (NMCL) cathode material. Density functional theory calculations reveal that the O 2p orbital overlaps with the t_2g orbital of transition metals in NMCL, facilitating the formation of Na-O-La bonds and promoting the oxygen redox reaction kinetics. During the Na⁺ (de)intercalation process, NMCL exhibits significant negative lattice expansion, characterized by an increase in the c lattice parameter and exceptionally low volume expansion of 1.8 % and 3.1 %, respectively. Consequently, it delivers an excellent specific capacity of 243.3 mAh g^-1 over a wide voltage range of 2.0 V to 4.5 V, which can be attributed to La³⁺ doping that promotes oxidation of O^2- to peroxide O₂ ^n- (n<2) during charge.