Boron-doped high-entropy oxide toward high-rate and long-cycle layered cathodes for wide-temperature sodium-ion batteries

Abstract

O3-type layered metal oxides hold great promise for sodium-ion batteries cathodes owing to their energy density advantage. However, the severe irreversible phase transition and sluggish Na+ diffusion kinetics pose significant challenges to achieve high-performance layered cathodes. Herein, a boron-doped O3-type high entropy oxide Na(Fe0.2Co0.15Cu0.05Ni0.2Mn0.2Ti0.2)B0.02O2 (NFCCNMT-B0.02) is designed and the covalent B–O bonds with high entropy configuration ensure a robust layered structure. The obtained cathode NFCCNMT-B0.02 exhibits impressive cycling performance (capacity retention of 95% and 82% after 100 cycles and 300 cycles at 1 and 10 C, respectively) and outstanding rate capability (capacity of 83 mAh g−1 at 10 C). Furthermore, the NFCCNMT-B0.02 demonstrates a superior wide-temperature performance, maintaining the same capacity level (113.4 mAh g−1@−20 °C, 121 mAh g−1@25 °C, and 119 mAh g−1@60 °C) and superior cycle stability (90% capacity retention after 100 cycles at 1 C at −20 °C). The high-entropy configuration design with boron doping strategy contributes to the excellent sodium-ion storage performance. The high-entropy configuration design effectively suppresses irreversible phase transitions accompanied by small volume changes (ΔV = 0.65 Å3). B ions doping expands the Na layer distance and enlarges the P3 phase region, thereby enhancing Na+ diffusion kinetics. This work offers valuable insights into design of high-performance layered cathodes for sodium-ion batteries operating across a wide temperature.