Introducing high-valence element into P2-type layered cathode material for high-rate sodium-ion batteries

Abstract

P2-type layered transition-metal oxides with high energy density and rich variety have attracted extensive attention for sodium-ion batteries (SIBs) in grid-scale energy storage application, but they usually suffer from sluggish kinetics and large volume change upon cycling. Herein, we designed a high-performance P2-type Na_0.67Ni_0.31Mn_0.67Mo_0.02O₂ (NNMMO) cathode with regulated electronic environment and Na⁺ zigzag ordering modulation via high-valence Mo⁶⁺ stabilization engineering. The achieved NNMMO cathode exhibits a high-rate capability with a reversible capacity of 77.2 mAh/g at 10 C and a long cycle life with a capacity retention of 75 % at 2 C after 1000 cycles. In addition, in situ X-ray diffraction and ex-situ X-ray absorption fine structure spectroscopy characterizations verify that the presence of Mo⁶⁺ also stabilizes the desodiated structure through a pinning effect, achieving an extremely low volume change of 1.04 % upon Na⁺ extraction. The quantified diffusional analysis and theoretical calculations demonstrate that the Mo⁶⁺-doping improves the Na⁺ diffusion kinetics, optimizes the energy band structure and enhances the TM-O bond strength. Additionally, the as-fabricated pouch cells by paring NNMMO cathode and hard carbon anode show impressive cycling stability with an energy density of 296.7 Wh/kg. This study broadens the perspective for high-valence metal ion doping to obtain superior cathode materials and pave the way for developing high-energy-density SIBs.