P2-type Na0.67Mn0.65Fe0.2Ni0.15O2 Cathode Material with High-capacity for Sodium-ion Battery

Abstract Na 0.67 Mn 0.65 Fe 0.35-x Ni x O 2 as a Na storage cathode material was prepared by a sol-gel method. The XRD measurement demonstrated that these samples have a pure P2 phase. The charging/discharging tests exhibit that the Na 0.67 Mn 0.65 Fe 0.35 O 2 electrode has a high initial capacity of 204 mAh g −1 with a slow capacity decay to 136 mAh g −1 , showing higher capacity and considerable cycling performance. When partially substituting Ni for Fe, the Na 0.67 Mn 0.65 Fe 0.2 Ni 0.15 O 2 electrode exhibits higher reversible capacity of 208 mAh g −1 and improved cycling stability with 71% capacity retention over 50 cycles. The greatly improved electrochemical performance for the Na 0.67 Mn 0.65 Fe 0.2 Ni 0.15 O 2 electrode apparently belongs to the contribution of the Ni substitution, which facilitates to improve the electrochemical reversibility of the electrode and alleviate the Jahn-Teller distortion of Mn(III). Therefore, the Ni-substituted Na 0.67 Mn 0.65 Fe 0.2 Ni 0.15 O 2 possibly serves as a promising high capacity and stable cathode material for sodium ion battery applications.