Mitigating Jahn–Teller Distortion toward High‐Capacity P2‐Type Layered Oxide Cathodes for Sodium‐Ion Batteries
Qiaojun Li, Yu Li, Yu Li, Qiannan Zhou, Bo Long, Yuanhao Wang, Ying Li, Ying Li, Zhixu Qiu, Zilu Wang, Yufei Zhang, Chuan Wu, Ying Bai
Abstract
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.