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

Na0.67Mn0.65Fe0.35-xNixO2 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 Na0.67Mn0.65Fe0.35O2 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 Na0.67Mn0.65Fe0.2Ni0.15O2 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 Na0.67Mn0.65Fe0.2Ni0.15O2 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 Na0.67Mn0.65Fe0.2Ni0.15O2 possibly serves as a promising high capacity and stable cathode material for sodium ion battery applications.