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.

Key words: Sodium ion battery, Tin phosphides, Anode materials, Composite structure, Reaction mechanism