Strong Coordination Interaction in Amorphous Sn-Ti-Ethylene Glycol Compound for Stable Li-ion Storage

Abstract

Sn has been considered among the most promising metallic anode materials for lithium-ion batteries (LIBs) thanks to its high specific capacity. Herein, we report a novel amorphous tin-titanium-ethylene glycol (Sn-Ti-EG) bimetal organic compound as anode for LIBs. The Sn-Ti-EG electrode exhibits exceptional cyclic stability with high Li-ion storage capacities. Even after 700 cycles at a current density of 1.0 A g^-1, the anode maintains a capacity of 345 mAh g^-1. The unique bimetal organic structure of the Sn-Ti-EG anode and the strong coordination interaction between Sn/Ti and O within the framework effectively suppress the aggregation of Sn atoms, eliminating the usual pulverization of bulk Sn through volume expansion. Further, the Sn M-edge of X-ray absorption near edge structure spectra obtained from the soft X-ray absorption spectroscopy signifies the conversion of Sn²⁺ ions to Sn⁰ during the initial lithiation process, which is reversible to Sn²⁺ upon de-lithiation. These findings manifest Sn being among the most active components that account for the excellent electrochemical performance of the Sn-Ti-EG electrode, while Ti has no practical contribution to the electrode’s capacity. The reversible formation of organic functional groups on the solid electrolyte interphase is also partly responsible for its cyclic stability.