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As promising cathode materials for sodium-ion batteries, P2–Na 0.67 Ni 0.33 Mn 0.67 O 2 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–Na 0.67 Ni 0.33 Mn 0.67 O 2 through proper Co doping and Al 1.8 Co 0.2 O 3 surface coating. Without Co doping and Al 1.8 Co 0.2 O 3 coating, the initial specific discharge capacity of P2–Na 0.67 Ni 0.33 Mn 0.67 O 2 in the voltage range of 2–4.3 V is 154.7 mAh·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, Al 1.8 Co 0.2 O 3 coating can improve the cycle stability with a reduced capacity. The coated sample exhibits a retention rate of 84.8% after 100 cycles. [ABSTRACT FROM AUTHOR]