Conversion-type anode materials for sodium ion batteries have received extensive attention because of their relatively high theoretical capacity. However, multiple challenging obstacles stand in the way of their commercial application, especially their poor cycling stability resulting from the bad reversibility of the conversion reaction. Herein, Ni-Co bimetal sulfide was selected and investigated with the goal of improving the reversibility of the conversion reaction owing to the similarity of Ni and Co. As expected, when three-dimensional hierarchical Ni@NiCo