Biomimetic Sn₄P₃ Anchored on Carbon Nanotubes as an Anode for High-Performance Sodium-Ion Batteries

Recently, Sn₄P₃ has emerged as a promising anode for sodium-ion batteries (SIBs) due to the high specific capacity. However, the use of Sn₄P₃ has been impeded by capacity fade and an inferior rate performance. Herein, a biomimetic heterostructure is reported by using a simple hydrothermal reaction followed by thermal treatment. This bottlebrush-like structure consists of a stem-like carbon nanotube (CNT) as the electron expressway and mechanical support; fructus-like Sn₄P₃ nanoparticles as the active material; and the permeable stoma-like thin carbon coating as the buffer layer. Having benefited from the biomimetic structure, a superior electrochemical performance is obtained in the SIBs. It exhibits a high capacity of 742 mA h g^-1 after 150 cycles at 0.2C, and superior rate performance with 449 mA h g^-1 at 2C after 500 cycles. Moreover, the sodium storage mechanism is confirmed by cyclic voltammetry and <i>ex situ</i> X-ray diffraction and transmission electron microscopy. <i>In situ</i> electrochemical impedance spectroscopy was adopted to analyze the reaction dynamics. This research represents a further step toward figuring out the inferior electrochemical performance of other metal phosphide materials.