Synthesis of hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres and their Na storage performance

In order to study the electrochemical performance of ternary transition metal oxide as a sodium electrode, hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres with a diameter of approximately 230 nm were prepared through hydrothermal method. The prepared hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres have a high specific surface area of 32.6 m²/g and good dispersibility. Hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres show good cycle life and rate performance when used as the negative electrode of sodium ion batteries: After 800 cycles at a current density of 200 mA/g, there is still a discharge specific capacity of 178.5 mA·h/g, and the capacity retention rate is as high as 91.6%; After 800 cycles at a current density of 500 mA/g, the capacity retention rate is 89.3%. In addition, when the current density is 100, 200, 500, 1 000 and 2 000 mA/g, the average discharge specific capacity is 212.7, 191.4, 148, 121.8 and 100 mA·h/g, respectively. The good electrochemical performance of the hollow Ni_0.75Zn_0.25Fe₂O₄ nanosphere electrode can be due to its unique hollow structure of the nanosphere, high specific surface area and shortened electron and ion transmission path, which improve its electrochemical performance during the Na⁺ insertion/desorption process.