Cu/Li Heterotopic Doping to Enable Long‐Term Cyclicity for P2‐Type Nickel Manganese Based Sodium‑Ion Batteries

Abstract P2‐Na 0.67 Ni 0.33 Mn 0.67 O 2 is regarded as a viable cathode material for sodium ion batteries due to its high theoretical energy density. However, it also has challenges that impair its electrochemical performance, like the P2‐O2 phase transition, the strong Jahn‐Teller distortion effect, and the Na + /vacancy ordering at high voltage. Here, an approach is proposed to use the Cu/Li binary doping modification of P2‐Na 0.67 Ni 0.33 Mn 0.67 O 2 , which stabilizes the cathode structure by introducing Li into alkali metal sites and Cu at transition metal sites. Due to its anti‐site doping, Li acts as an interlayer stationary point that suppresses the relative slip of the TMO 2 layer under high pressure and produces a solid solution reaction that is nearly zero phase transition. The assembled full‐cell devices with Na 0.67 Li 0.1 Ni 0.18 Cu 0.05 Mn 0.67 O 2 cathode and commercial hard carbon anode can deliver a high energy density of 379.3 Wh kg −1 . In addition, due to the proposed unique dual‐site doping, the full‐cell also exhibits excellent cycling stability, which maintains a capacity retention rate of 84% and 71% over 200 and 1000 cycles at 1 C and 10 C, respectively. As a result, the proposed doping technique offers an effective approach to designing cathode materials with excellent cycling stability.