One-Step Hydrothermal Synthesis of SnS₂/SnO₂/C Hierarchical Heterostructures for Li-ion Batteries Anode with Superior Rate Capabilities

Novel three-dimensional hierarchical heterostructures composed of two-dimensional SnS₂ nanoflakes and zero-dimensional SnO₂ nanoparticles were fabricated via a one-step hydrothermal method. Size of the heterostructures was ca. 2 μm in diameter, and individual SnS₂ nanoflakes with thickness of ca. 150 nm were connected to central core of the heterostructures. The SnO₂ nanoparticles in a diameter of ca. 5 nm uniformly covered entire surface of the SnS₂ nanoflakes. Moreover, both of these structures were highly crystalline. Meanwhile, amorphous carbon was formed within the heterostructures. The SnS₂/SnO₂/C hierarchical heterostructures had a high initial specific reversible capacity of 1065.7 mAh g^-1, stable cycling stability of 638 mAh g^-1 after 30 cycles, and superior rate capability of 550.8 mAh g^-1 at 1C rate. These SnS₂/SnO₂/C hierarchical heterostructures showed better performance than individual SnS₂ and SnO₂ nanomaterials, and the performance was even higher than the graphene-SnS₂ and graphene-SnO₂ nanohybrid materials. This is attributed to a synergistic effect of high surface area, which is provided by the unique SnS₂ internal nanoflake layered structures decorated with ultra-fine SnO₂ nanoparticles, and an effective beneficial buffer matrix to accommodate the large volume change upon cycling, which is caused by the side-products such as Li₂S or Li₂O. The SnS₂ nanoflake was deduced to play a similar role as graphene material, since both possess 2D conducting layer structures. The uniform carbon dispersion within the structures also stabilizes the structures and improves electrical conductivity of the hierarchical heterostructures.