In-situ solvothermal phosphorization from nano-sized tetragonal-Sn to rhombohedral-Sn4P3 embedded in hollow graphene sphere with high capacity and stability

Tin phosphide (Sn4P3) has a high theoretical specific capacity as anode material for lithium-ion batteries, nevertheless the large volumetric expansion during lithium insertion and Li-Sn alloying suppresses its application. Herein, we design sandwiched hollow spherical graphene-wrapping Sn4P3 nanoparticles composite by in-situ solvothermal phosphorization from nano-sized tetragonal-Sn. The product perfectly inherits the sandwich hollow spherical structure from the Sn precursor, a stable and high content COP covalent bond is formed between the Sn4P3 active substrate and graphene skeleton to improve the binding force and electrical conductivity. More importantly, the layer-structure Sn4P3 nanoparticles (20–50 nm) are inserted in the loosely stacking graphene shells, thus the radial volume expansion along c-axis and Sn aggregation can be effectively buffered. The synergy effect provides the transformed product with fewer structural changes comparing with metal Sn anodes, lithiation-generated Li3P and Sn can inter-support for each other to promote the conversion reaction with high reversibility. Thus, the sandwich-Sn4P3/spherical graphene composite exhibits excellent structural integrity and cycling stability, a high reversible capacity of 606.4 mAh g−1 is preserved at a rate of 0.1C over 100 cycles.