Local Electron Spin‐State Modulation at Mn Site for Advanced Sodium‐Ion Batteries with Fast‐Kinetic NaNi0.33Fe0.33Mn0.33O2 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 Mn 3+ , lead to the inferior cycling lifespan. Herein, the nonequilibrium‐driven local electron spin‐state modulation at Mn site with Sn 4+ substitution is proposed to stabilize the NaNi 0.33 Fe 0.33 Mn 0.33 O 2 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 0.33 Fe 0.33 Mn 0.33 O 2 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.