P2-Na-2/3 Ni2/3Te1/3O2 Cathode for Na-ion Batteries with High Voltage and Excellent Stability

Air-stable layered structured cathodes with high voltage and good cycling stability are highly desired for the practical application of Na-ion batteries. Herein, we report a P2-Na-2/3 Ni2/3Te1/3O2 cathode that is stable in ambient air with an average operating voltage of similar to 3.8 V, demonstrating excellent cycling stability with a capacity retention of more than 92.7% after 500 cycles at 20 mA g(-1) and good rate capability with 91.9% capacity utilization at 500 mA g(-1) with respect to capacity at S mA g(-1) between 2.0 and 4.0 V. When the upper cutoff voltage is increased to 4.4 V, P2-Na-2/3 Ni2/3Te1/3O2 delivers a reversible capacity of 71.9 mAh g(-1) and retains 91.8% of the capacity after 100 cycles at 20 mA g(-1). The charge compensation during charge/discharge is mainly due to the redox couple of Ni2+ /Ni3+ in the host with a small amount of contribution from oxygen. The stable structure of the material without phase transformation and with small volume change during charge-discharge allows it to give excellent cycle performance especially when the upper cutoff voltage is not higher than 4.2 V.