Anode materials with a high initial coulombic efficiency and a long lifespan are highly desirable for sodium-ion batteries. Here, bimetallic μ-BiSn microspheres well combine the high capacity of Sn and the good stability of Bi together, exhibiting superior electrochemical performance, such as a high initial Coulombic efficiency (90.6%), a good cycling stability (541 mA h g -1 after 3000 cycles at 2 A g -1 ) and an excellent rate capability (393 mA h g -1 at 10 A g -1 ).