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

Abstract

P2-Na_0.67Ni_0.33Mn_0.67O₂ 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_0.67Ni_0.33Mn_0.67O₂, 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 TMO₂ layer under high pressure and produces a solid solution reaction that is nearly zero phase transition. The assembled full-cell devices with Na_0.67Li_0.1Ni_0.18Cu_0.05Mn_0.67O₂ 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.