Cu₄SnP₁₀ as a promising anode material for sodium ion batteries

High theoretical capacity of metal phosphides makes them promising candidates for anode application in sodium ion batteries. In this work, we report a ternary compound phosphide—copper tin phosphide (Cu₄SnP₁₀) nanowires for sodium ion battery anode applications. The introduction of Cu helps to stabilize a rather high P content in the compound (as compared to Sn₄P₃, for example), enabling a high capacity of 811 mA h g⁻¹ at a current density of 25 mA g⁻¹ for phase pure Cn₄SnP₁₀ nanowire anode. Cu incorporation is also found to effectively alleviate Sn aggregation in the anode during charge/discharge cycles, which is known as a major contributor to the faded cycle performance of Sn-P compound. On the other hand, we show that possible volume expansion and instability of the solid electrolyte interface in the Cn₄SnP₁₀ nanowire anode remain as problems causing cycle instability of the electrode. By forming composite with multiwall carbon nanotubes, we demonstrate significantly improved cycle performance of the composite anode, which delivers a stable capacity of 512 mA h g⁻¹ after 100th cycle at a current density of 100 mA g⁻¹. At higher current density of 1 A g⁻¹, the capacity of the composite electrode retains at 412 mA h g⁻¹, showing its good rate performance.