High‐voltage stabilized high‐entropy oxyfluoride cathode for high‐rate sodium‐ion batteries

Abstract Complex phase transitions occur in P2‐type materials during charging and discharging. A high‐entropy structure can effectively inhibit the structural phase transition of a P2‐type layered material. In this study, a high‐temperature solid‐phase method is used to synthesize the P2‐type high‐entropy fluorine oxide (HEFO) Na 0.7 Li 0.08 Mn(IV) 0.21 Mn(III) 0.43 Mg 0.11 Ni 0.11 W 0.04 Nb 0.02 O 1.9 F 0.1 [♦‐NLM(IV) 0.21 M(III) 0.43 F (♦ = NMNW‐O)], with a superlattice structure and Na 2 WO 4 coating. Na 2 WO 4 can effectively inhibit the complex phase transition to improve the structural stability of the material and overcome the limitations of P2‐type Na x TMO 2 (TM = transition metal) via additional charge compensation. Adjusting the Mn 3+ /Mn 4+ ratio to increase the average valence state of Mn and introducing F − and Li + to inhibit the Jahn–Teller effect suppress the complex phase transition during charging and discharging. The material exhibits a good multiplicative performance (discharge specific capacity of 88.4 mAh g −1 at a multiplicative rate of 10C) and capacity retention (99.22% after 200 cycles at 1C in the potential window of 1.5–4.3 V). The structural stabilities of HEFO are effectively demonstrated using electrochemical in situ X‐ray diffraction and ex situ X‐ray photoelectron spectroscopy. Theoretical calculations reveal that the high‐entropy structure effectively improves the electronic structure and charge distribution of the layered oxide material. This study provides new concepts for use in developing novel energy batteries.