P2-type Na0.67Mn0.6Fe0.4-x-yZnxNiyO2 cathode material with high-capacity for sodium-ion battery

The P2-type Na0.67Mn0.6Fe0.4O2 (NaMnFe), Na0.67Mn0.6Fe0.3Zn0.1O2 (NaMnFeZn), and Na0.67Mn0.6Fe0.2Zn0.1Ni0.1O2 (NaMnFeZnNi) are prepared using an acetate decomposition reaction and developed as promising cathode materials for high-capacity sodium-ion batteries. The XRD patterns show that Zn2+ and Ni2+ ions are successfully incorporated into the lattice of the Na-Mn-Fe-O system, and the P2-type structure remains unchanged after substitution. The charging/discharging tests exhibit that the Na0.67Mn0.6Fe0.4O2, Na0.67Mn0.6Fe0.3Zn0.1O2, and Na0.67Mn0.6Fe0.2Zn0.1Ni0.1O2 electrodes have the capacities of 200.4, 182.0, and 202.2 mAhg(-1), respectively. The Na0.67Mn0.6Fe0.4O2 electrode has a higher initial capacity but faster capacity decay. When partially substituting Zn and Ni for Fe, the Na0.67Mn0.6Fe0.3Zn0.1O2 and Na0.67Mn0.6Fe0.2Zn0.1Ni0.1O2 electrodes exhibit lower reversible capacity but improved cycling stability (88.3 and 93.4% capacity retention over 100 cycles). The greatly improved electrochemical performance of the Na0.67Mn0.6Fe0.2Zn0.1Ni0.1O2 electrode apparently belongs to the contribution of the Zn2+ and Ni2+ substitution, which facilitates to alleviate the Jahn-Teller distortion of Mn and suppresses the polarization.