Sodium-Ion Battery Anode Construction with SnPx Crystal Domain in Amorphous Phosphorus Matrix

The high-capacity phosphorus- (P-) based anode materials for sodium-ion batteries (NIBs) often face poor performance retentions owing to the low conductivity and large volume expansion. It is thus essential to buffer these problems by appropriately alloying with other elements such as tin (Sn) and constructing well-designed microstructures. Herein, a series of P-/Sn-based composites have been synthesized by the facile and low-cost one-step ball milling. Pair distribution function (PDF) has been employed as a hardcore quantitative technique to elucidate their structures combined with other techniques, suggesting the formation and ratios of Sn4P3 and Sn crystalline domains embedded inside an amorphous P/carbon matrix. The composite with the largest amount of Sn4P3 in the P/C matrix can deliver the most balanced electrochemical performance, with a capacity of 422.3 mA-h g−1 for 300 cycles at a current density of 1000 mA g−1. The reaction mechanism has been elucidated by 23Na and 31P solid-state nuclear magnetic resonance (NMR) investigations. The study sheds light on the rational design and concrete identification of P-/Sn-based amorphous-dominant composite materials for NIBs.