Surficial and Interior Incorporation of Borates Mitigating the Inherent Jahn–Teller Distortion in a P2 Mn‐Rich Layered Cathode for Na‐Ion Batteries

Abstract Layered Mn‐rich materials are regarded as a promising cathode candidate for Na‐ion batteries (NIBs) owing to its environmentally friendly nature, decent theoretical capacities, and relatively low cost. However, the irreversible phase transition originating from the Jahn–Teller distortion attributed to high‐spin Mn 3+ (t 2g 3 eg 1 ) during deep sodiation triggers serious structural degradation followed by capacity decay. Herein, the incorporation of borate‐anion groups either into the bulk (BO 3 3− ) or on the surface (BO 4 5− ) successfully modulates the local‐structure environment of the P2‐type layered cathode, changing the lattice parameters and valence states of the transition metals inside. The optimized Na 0.734 Ni 0.207 Mn 0.694 Co 0.098 (B 0.063 O x )O 2‐x (B‐NCM) can remit a P2‐P’2 phase transition by mitigating the inherent Jahn–Teller distortion of MnO 6 octahedra, allowing a reversible phase transition with reduced strain even after deep sodiation to 1.5 V. The B‐NCM cathode exhibits excellent capacity retention, reaching 82.02% after 200 cycles. In addition, the modulated local structure inside B‐NCM helps to relieve Na + /vacancy ordering, enhancing Na + diffusivity and rate capability compared to a pristine NCM analo. This work demonstrates a novel approach based on the incorporation of glassy anion groups into both surface and bulk to improve the electrochemical properties of layered Mn‐rich cathode materials.