Extending phase-variation voltage zones in P2-type sodium cathodes through high-entropy doping for enhanced cycling stability and rate capability

P2-type layered sodium oxides hold great promise for grid-scale energy storage applications owing to their low-cost merit, while their detrimental structural and chemical transition lead to low reversible capacities and poor cycling stability. Herein, we leverage a high-entropy (HE) doping strategy to stabilize the P2-type Na0.667Mn0.667Ni0.167Co0.167O2 (NMNC) cathode. A novel Na0.667Mn0.667Ni0.167Co0.117Ti0.01Mg0.01Cu0.01-Mo0.01Nb0.01O2 (HE-NMNC) composite, with five equal content (1 at %) of cation substitution and exhib-iting a pure P63/mmc space group structure, is proposed. Interestingly, a reversible P2-type phase variation is identified for HE-NMNC at high degrees of charge, but such phase variation occurs in a wider voltage region and is much slower than that in the NMNC baseline. It is demonstrated that the HE-NMNC delivers outstanding rate capability and cycling stability under a charging cutoff voltage of 4.5 V, achieving a reversible capacity of 111 mAh/g at 5 C and retaining around 130 mAh/g after 100 cycles at 1 C. Apart from the charge compensation of main transition metals (Ni, Co, and Mn), the reversible redox of lattice oxygen also contributes to the capacity of HE-NMNC upon cycling. The proposed high-entropy doping strategy and reaction mechanism may provide new insights for developing advanced cathode materials.(c) 2023 Elsevier Ltd. All rights reserved.

Automated summary

This study successfully stabilizes the structure of P2-type layered sodium oxide Na0.667Mn0.667Ni0.167Co0.167O2 through a high-entropy doping strategy and proposes a novel HE-NMNC composite. The HE-NMNC demonstrates outstanding rate capability and cycling stability, providing new insights for the development of advanced cathode materials.