One-step hydrothermal reduction synthesis of tiny Sn/SnO2 nanoparticles sandwiching between spherical graphene with excellent lithium storage cycling performances

Highlights: • Tiny Sn/SnO₂ NPs sandwiching between SG is designed to solve Sn anode's problem. • Sn/SnO₂/SG is prepared by one-step low temperature hydrothermal reduction method. • Li₂O generated from SnO₂ acts as buffer matrix for Sn at subsequent alloy process. • Li₂O and excess nano-sized Sn can react easily to reversibly transform into SnO₂. • Excellent cycle stability is presented in Sn/SnO₂/SG composite. The reunion of Sn is always a troublesome issue when it's used as the energy storage materials, on the one hand it comes from the preparation process due to its low melting point, and on the other hand it comes from the Li-Sn alloying process because of its natural tendency of migration. The Sn/SnO₂/spherical graphene composite prepared by one-step low temperature hydrothermal reduction method can effectively solve this problem. In the composite, Sn/SnO₂ tiny nanoparticles with average diameter of 5 nm distribute evenly between multilayers of graphene sheets presenting a hollow spherical structure. The introduction of SnO₂ can effectively restrain the agglomeration of Sn nanoparticles during alloying process since an amorphous Li₂O matrix is formed to separate the adjacent active particles. The sandwich graphene hollow sphere skeleton effectively buffers the volume expansion of Sn/SnO₂ and further restricts their migration and agglomeration. Due to the above advantages, the nano-Li₂O generating from the decomposition of SnO₂ can contact closely with excessive nano-Sn in restricted area, promoting facile conversed conversion reaction. Therefore, the composite exhibits high reversible capacity and excellent cycle performance. A stable and high specific capacity of 843.8 mAh g⁻¹ is obtained after 100 cycles at 0.1 C.