Engineering fluoride-rich interphase and inhibiting grain coarsening for highly reversible bismuth sulfide anode for sodium storage

Abstract

Bismuth sulfide is considered as a promising anode material for sodium-ion battery due to the high theoretical capacity originates from conversion and alloying reaction. However, large volume expansion during cycling, unstable solid electrolyte interphase (SEI) and poor reaction reversibility limit its practical application. Herein, taking Bi2S3 nanorods as example, we first investigated the capacity fading mechanism of Bi2S3 nanorods in electrolytes with different composition and revealed that although ether electrolyte could improve the reversibility, the coarsening of bismuth during cycling is the culprit to the capacity fading. Then, a tailored two-pronged approach including carbon coating and Fe-doping was proposed to induce F-rich SEI and inhibit grain coarsening during cycling. As a result, the optimized electrode exhibited enhanced low-plateau alloying reaction and a high specific capacity as 382 mA h/g, which is in sharp contrast to 180 mA h/g of pure Bi2S3 which dominated by high-plateau conversion reaction. In addition, high-capacity retention as 76% could be maintained even at 10 A/g due to the enhanced reaction kinetics by Fe-doping. Thanks to the stable SEI and enhanced reversibility, full cell with high energy density as 156 W h/kg could be achieved without any pre-sodiation or assistant from complex nanostructure.