Tin phosphide-carbon composite as a high-performance anode active material for sodium-ion batteries with high energy density

Tin phosphide (Sn₄P₃) is a promising anode material for sodium-ion batteries because of its relatively large theoretical capacity, appropriate Na⁺ alloying potential, and good cyclic stability. Herein, the Sn₄P₃ embedded into a carbon matrix with good rate performance and long cycle life is reported. The Sn₄P₃-C composite exhibits excellent rate performance (540 mAh g⁻¹ at 5 A g⁻¹) and the highest reversible capacity (844 mAh g⁻¹ at 0.5 A g⁻¹) among Sn₄P₃-based anodes reported so far. Its reversible capacity is as high as 705 mAh g⁻¹ even after 100 cycles at 0.5 A g⁻¹. Besides, its initial Coulomb efficiency can reach 85.6%, with the average Coulomb efficiency exceeding 99.75% from the 3rd to 100th cycles. Na₂C₆O₆ is firstly used as a cathode when Sn₄P₃ acts as anode, and the Na-Sn₄P₃-C//Na₂C₆O₆ full cell shows excellent electrochemical performance. These results demonstrate that the Sn₄P₃-C composite prepared in this work displays high-rate capability and superior cyclic performance, and thus is a potential anode for sodium ion batteries.