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

High-sodium manganese-based layered oxide (Na_xTM_1−yMn_yO₂, 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 3d orbitals, which hinders the reversible (de)intercalation of Na⁺. Herein, by simultaneously modulating the electron configuration and crystal structures, the P2-Na_0.7Li_0.1Ni_0.266Nb_0.0056Fe_0.1Mn_0.56O₂ (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 Mn³⁺ (t_2g³-e_g⁰) effectively eliminates the asymmetric 3d 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.