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.