Conformal Hollow Carbon Sphere Coated on Sn4P3 Microspheres as High-Rate and Cycle-Stable Anode Materials with Superior Sodium Storage Capability

Rational synthetic design of Sn4P3-based materials with unique morphological structure and superior sodium storage capability for sodium ion batteries (SIBs) is crucially and urgently needed. In this work, Sn4P3 microspheres encapsulated in hollow carbon spheres (Sn4P3(@C) are prepared by a low temperature phosphorized route using SnO2@C as the precursor. The XRD, XPS and TEM results show that multiple Sn4P3 microspheres with a diameter of 200 nm are conformally encapsulated in a hollow carbon shell. This void volume and the elasticity of protective carbon spherical shell can efficiently mitigate volume change of active Sn4P3 microspheres and form the stable solid electrolyte interface film on the surface of the carbon shell during charge/discharge process. When assembled as a negative electrode material into SIBs, the Sn4P3@C composite shows a stable specific capacity of 420 mAh g(-1) after 300 cycles at a current density of 0.2 A g(-1), as well as excellent rate capabilities of 424, 310, 253, 175, 111, 78, and 50 mAh g(-1) at the density of 0.2, 0.5, 1, 2, 5, 10, and 20 A g(-1), respectively. More importantly, as-prepared Sn4P3@C composite shows ultralong cycling performance (after 4000 cycles, of 2 and 5 A g(-1), the stable capacities are 205 and 103 mAh g(-1), respectively). It is demonstrated that the Sn4P3@C composite with the unique morphological design can improve electrochemical cycling performance and rate capability of Sn4P3. Therefore, it can be expected that our Sn4P3@C composite is a promising excellent anode material for SIBs.