Coordination Regulation Strategy in Fabricating Bi<sub>2</sub>S<sub>3</sub>@CNFs Composites with Uniform Dispersion for\nRobust Sodium Storage

To\nsolve large volume change and low conductivity of Bi<sub>2</sub>S<sub>3</sub>-based anodes, a coordination regulation strategy is\nproposed to prepare Bi<sub>2</sub>S<sub>3</sub> nanoparticles dispersed\nin carbon fiber (Bi<sub>2</sub>S<sub>3</sub>@CNF) composites. It has\nbeen discovered that introducing trimesic acid as a ligand can significantly\nimprove the loading and dispersion of Bi<sup>3+</sup> in polyacrylonitrile\nfibers. The results exhibit that Bi<sub>2</sub>S<sub>3</sub> nanoparticles\nof 200–300 nm are uniformly anchored on the superficial surface\nlayer of CNFs, and Bi<sub>2</sub>S<sub>3</sub> nanoparticles of about\n20 nm are evenly dispersed in the interior of CNFs. Assessed as sodium-ion\nbatteries’ anode material, the discharge capacity of the Bi<sub>2</sub>S<sub>3</sub>@CNF anode in the second cycle is 669.3 mAh g<sup>–1</sup> at 0.1 A g<sup>–1</sup> and still retains\n620.2 mAh g<sup>–1</sup> after 100 cycles, with the capacity\nretention rate of 92.7%. Even at 0.5 A g<sup>–1</sup>, the\nspecific capacity of the second cycle is 432.99 mAh g<sup>–1</sup>, which still keeps 400.9 mAh g<sup>–1</sup> after 800 cycles,\nwith a retention rate of 92.5%. The excellent cycle stability is mainly\nattributed to the uniform distribution of small Bi<sub>2</sub>S<sub>3</sub> nanoparticles in CNFs providing abundant active sites, preventing\nside reactions, relieving volume expansion, improving the electrical\nconductivity, and accelerating the electrochemical reaction kinetics.