Dual modification of P2-Na0.67Ni0.33Mn0.67O2 by Co doping and Al1.8Co0.2O3 coating

As promising cathode materials for sodium-ion batteries, P2-Na0.67Ni0.33Mn0.67O2 has the characteristics of high capacity and high working voltage. However, the application is strongly limited because of the rapidly deteriorated electrochemical performances during cycling. Therefore, we present in this study the optimization of the cycling stability of P2-Na0.67Ni0.33Mn0.67O2 through proper Co doping and Al1.8Co0.2O3 surface coating. Without Co doping and Al1.8Co0.2O3 coating, the initial specific discharge capacity of P2-Na0.67Ni0.33Mn0.67O2 in the voltage range of 2-4.3 V is 154.7 mAh center dot g(-1), and the capacity retention rate after 100 cycles is 26.4%. Co doping can improve the cycling stability and rate capability. However, the initial capacity also reduces with the Co doping amount. Furthermore, Al1.8Co0.2O3 coating can improve the cycle stability with a reduced capacity. The coated sample exhibits a retention rate of 84.8% after 100 cycles.