Minimal TiO2 Coupled with Conductive Polymer-Stimulated Synergistic Effect on Fast and Reversible Sodium-Ion Storage for Bismuth Sulfide.

Designing multiphase composition is believed to availably boost the structural integrity and electrochemical properties of sodium-ion battery anodes. Herein, a conceive of nanoflowers, assembled with Bi2S3 nanorods, is demonstrated to construct the multiphase composition involving TiO2 coating and polypyrrole (PPy) encapsulation. Bi2S3 acted as the dominating active material, in consideration of the low content of TiO2, which ensured the high capacity of the composite. The dual-structural restrain of the TiO2 and PPy coatings can effectively alleviate volume variation based on the pseudo-"zero-strain" effect of TiO2 and high flexibility of PPy shells. Meanwhile, the heterointerface greatly enhanced the coupling effect between Bi2S3 and TiO2 and thus improved the electrochemical performance, which was proved by the results of density functional theory calculation and electrochemical tests. Combining the regulation from the Bi2S3/TiO2 heterojunction and the dual-structural restrain effect, the Bi2S3/TiO2@PPy electrode exhibited excellent rate performance and superior cycle stability (275.8 mA h g-1 over 500 cycles at 10 A g-1). This study indicates that designing multiphase composition can be very promising and provides a structural insight to construct high stability in electrodes for sodium-ion batteries.