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

Abstract The optimization of anode materials such as Sn, P and Sn 4 P 3 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 retard 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 Sn 4 P 3 into phase-separated crystalline Sn and amorphous P in a carbonaceous framework can be finely controlled, producing a series of binary (Sn 4 P 3 /C), quaternary (Sn 4 P 3 /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 Sn 4 P 3 /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 Na 15 Sn 4 and Na 3 P in the ex-situ X-ray diffraction patterns, suggesting the crystallite growth of sodiation products can be depressed. Moreover, Sn 4 P 3 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.