Zinc doped P2-type layered cathode for high-voltage and long-life sodium ion batteries: impacts of calcination temperature and cooling methods

Sodium ion batteries (SIBs) are promising technique for energy storage applications. Cathode materials are keys to improve the energy density of SIBs. P2-type layered cathodes with low Na ion diffusion barrier attract great attention. However, it suffers structural instability at a high working voltage. Though many attempts were made, the cycle stability of P2-type layered cathodes with a high working voltage is still not satisfactory. In this work, zinc was used as a doping element for modification. When the doping amount is x = 0.1 (Na0.7Ni0.25Mn0.65Zn0.1O2), it presents enhanced cycle stability in the voltage range of 2.5–4.2 V. The impacts of calcination temperature and cooling methods were investigated. It was found that the material shows excellent stability when the material was calcined at 950 °C followed by natural cooling, the discharge capacity is 64.9 mAh g−1 over 1000 cycles with a capacity retention of 84.0% after 1000 cycles at 170 mA g−1, superior to those reported in literature. In situ XRD reveals a reversible phase transition from P2 to OP4 at the high voltage contributes to the excellent cycle stability.