Mitigating Jahn–Teller Distortion toward High‐Capacity P2‐Type Layered Oxide Cathodes for Sodium‐Ion Batteries

Abstract High‐sodium manganese‐based layered oxide (Na _x TM _{1− y} Mn _y O ₂ , 0.7 < x ≤ 1) cathodes have attracted growing attention in sodium‐ion batteries (SIBs) due to their high theoretical capacities. However, the actual discharge capacity (≈90 mAh g ⁻¹ at 2–4 V) of layered oxide cathodes is significantly lower than its theoretical capacity of ≈250 mAh g ⁻¹ . It is mainly due to the Jahn‐Teller distortion caused by the asymmetric electron occupancy of transition‐metal (TM) ions in 3 d orbitals, which hinders the reversible (de)intercalation of Na ⁺ . Herein, by simultaneously modulating the electron configuration and crystal structures, the P2‐Na _0.7 Li _0.1 Ni _0.266 Nb _0.0056 Fe _0.1 Mn _0.56 O ₂ (LNNFM) is designed with ultrahigh capacity (193.6 mAh g ⁻¹ , up to 79.0% Na utilization with a charge cutoff voltage of 2.0–4.0 V), exceptional cyclability (capacity retention of 80.2% after 1000 cycles at 10 C) and remarkable rate capability (83.9 mAh g ⁻¹ at 30 C). It is verified that the obtained low‐spin Mn ³⁺ ( t _2g ³ ‐ e _g ⁰ ) effectively eliminates the asymmetric 3 d electron configuration, gaining the volume change of only 0.097% in the LNNFM. This work challenges the traditional opinion that a low cut‐off voltage leads to decreased energy density and provides a new route for realizing high‐energy‐density batteries.