Elastic Restraint Induced by Carbon Coating Enhances Potassium-Ion Batteries' Performance via Phase Transition

Potassium-ion batteries (PIBs) possess great potential in the next generation of large-scale energy storage due to their abundant sources and suitable operating voltage. However, the serious volume expansion resulting from the large radius of K⁺ makes it difficult to insert and extract, which greatly limits the development of PIBs. Herein, tin phosphide coated with carbon (Sn₄P₃@C) is designed for the PIB anode material by in situ construction of robust physical barriers of carbonaceous materials to accommodate the strain induced by volume expansion. Furthermore, the unique elastic restraint induced by the carbon coating in Sn₄P₃@C blocks the phase transition of α-Sn to β-Sn during the process of potassiation. Meanwhile, the existence of α-Sn facilitates K⁺ diffusion dynamics, endowing the Sn₄P₃@C electrode with high reversible discharge ability, good circularity, and a low discharge plateau. Moreover, the electrode can maintain a capacity of 187 mAh g^-1 over repeated 1500 cycles at 1 A g^-1. This work not only explores the chemical kinetics of K⁺ in Sn₄P₃ but also provides a new idea for basic research of tin-based anode materials.