Phase pure Sn₄P₃ nanotops by solution-liquid-solid growth for anode application in sodium ion batteries

Sn₄P₃ is a promising anode material for sodium ion batteries due to its high capacity and suitable redox potentials relative to Na/Na⁺. In Sn₄P₃ obtained by conventional fabrication methods, its large size (when obtained by ball milling) or the phosphorus (P) impurity left in the sample (when obtained by solvothermal treatment) is detrimental to the anode performance. In the present work, a facile solution chemistry method was developed to grow phase pure Sn₄P₃ nanotops with controllable size. Using trioctylphosphine (TOP) as the P source, the present method avoids the usage of flammable yellow P and the shelf-stable red P, the residue of which is difficult to remove after the reaction. The experimental results suggest solution-liquid-solid as the mechanism guiding the Sn₄P₃ growth. The Sn precursor plays an important role in determining the size and the morphology of the final Sn₄P₃ product. Such Sn₄P₃ nanotops show good electrochemical performance when employed as the anode for sodium ion batteries, giving an initial capacity of 719.8 mA h g^-1 at a current density of 50 mA g^-1, an initial coulombic efficiency of about 72.7%, and reasonably good cyclability.