Hierarchical ZnS-SnS2 @C nanocomposite as superior-rate and long-life anode for sodium ion batteries

Two-dimensional SnS2 are known as potential anodes for Na-ion batteries owing to high energy density and low voltage plateau. However, SnS2 suffers from structural instability, material fragmentation, and low electrical conductivity. We propose to design a hierarchical structure in which the outer layer is conductive carbon, the middle layer is SnS2, and the inner layer is ZnS. Such a design can effectively solve the problem of SnS2: the conductive carbon can improve the conductivity of the composite, and the ZnS in the inner layer stabilizes the structure. ZnS-SnS2 @C has superior rate performance (257.7 mAh g−1 at 5 A g−1) and cycle durability (234.4 mAh g−1 after 500 cycles with the capacity retention rate of 61.33%). In situ EIS reveals that ZnS-SnS2 @C has lower charge transfer resistance during cycling. Theoretical calculations also confirmed that the diffusion energy barrier of Na ions in ZnS-SnS2 @C is lower than that of ZnS and SnS2. The synergistic effect between SnS2 and ZnS and carbon coating with well-designed hierarchical structure provides an effective strategy to improve Na intercalation performance for anode materials.