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 degrees 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.