Sn4P3-induced crystalline/amorphous composite structures for enhanced sodium-ion battery anodes

Abstract

The optimization of anode materials such as Sn, P and Sn4P3 in terms of capacity and cyclability is crucial to improve the overall performance of sodium-ion batteries. However, the delicate fabrication of these materials, including the balanced crystalline/amorphous domains, reasonable particle size and distribution, complementary components exhibiting synergetic reactions, among others, still greatly retards the realization of maximum performance. Herein, a series of Sn/P-based composite materials with a plum pudding configuration were fabricated to achieve controlled crystalline/amorphous structures as well as optimized size and distribution in a carbon framework. By using a facile and low-cost ball milling method, the structural transformation of Sn4P3 into phase-separated crystalline Sn and amorphous P in a carbonaceous framework can be finely controlled, producing a series of binary (Sn4P3/C), quaternary (Sn4P3/Sn/P/C) and ternary (Sn/P/C) composites. Due to the complementary components, crystalline/amorphous adjustment, crystallite sizes and well-integrated interfaces, the quaternary Sn4P3/Sn/P/C composite showed the best electrochemical performance, with a noticeable long-cycle performance of 382 mA h g−1 and 86% capacity retention for nearly 300 cycles. Different from binary and ternary composites, the discharge of quaternary composite generates no noticeable signals of Na15Sn4 and Na3P in the ex-situ X-ray diffraction patterns, suggesting the crystallite growth of sodiation products can be depressed. Moreover, Sn4P3 in the quaternary composite can be partially regenerated in the desodiation reaction, implying the significant short-range interaction and thus better synergetic reactions between Sn and P components. The results demonstrate that the design and organization of crystalline/amorphous structures can serve as an efficient strategy to develop novel electrode materials for sodium ion batteries.