Local Electron Spin‐State Modulation at Mn Site for Advanced Sodium‐Ion Batteries with Fast‐Kinetic NaNi_0.33Fe_0.33Mn_0.33O₂ Cathode

Abstract O3‐type cathode material with high theoretical capacity possesses significant potential for sodium ion batteries (SIBs). However, the irreversible phase transition, structural volume change and poor Na⁺ transmission efficiency, caused by Jahn–Teller distortion of Mn³⁺, lead to the inferior cycling lifespan. Herein, the nonequilibrium‐driven local electron spin‐state modulation at Mn site with Sn⁴⁺ substitution is proposed to stabilize the NaNi_0.33Fe_0.33Mn_0.33O₂ cathode. With this, the controlled irreversible phase transition and volume expansion during charge/discharge and fast Na⁺ transportation channel is achieved. Therefore, the modulated NaNi_0.33Fe_0.33Mn_0.33O₂ cathode can contribute to improved capacity of 144.8 mAh g⁻¹ at 0.1 C rate and long‐term cycling over 200 cycles with 80.1% retention by comparison with the counterpart (132.5 mAh g⁻¹ at 0.1 C) and 54.1% retention. Noted that the elevated Na⁺ diffusion kinetics corresponding to high‐rate capability is also demonstrated (93.2 mAh g⁻¹ at 10 C rate). Furthermore, the full battery equipped with hard carbon anode shows an energy density of 381.05 Wh kg⁻¹ and the 76.8% retention after 200 cycles. This work highlights the regulation of electron spin‐state from the insight of modification Jahn–Teller effect would shed a new perception on the design for the advanced layered cathode materials and SIBs.