Promising sodium storage of bismuthinite by conversion chemistry

Chalcogenide materials are emerging as promising anode materials for sodium-ion batteries because of their reasonable capacity, which stems from two consecutive conversion and de/alloy reactions. Herein, we introduce the layer-structured Bi2S3 that shows long-term cyclability for sodium storage. Since deep sodiation induces the de/alloy reaction accompanied by a large volume change, we intentionally limit the reaction to the conversion process, resulting in long-term stable cyclability followed by a two-step conversion reaction: Bi2S3 + 3Na+ + 3e− → NaBiS2 + Bi0 + Na2S followed by NaBiS2 + 3Na+ + 3e− → Bi0 + 2Na2S, which was confirmed by operando X-ray diffraction, X-ray photoelectron spectroscopy and time-of-flight secondary-ion mass spectroscopy. During the electrochemical reaction, the presence of reduced graphene oxide (rGO) anchored with Bi2S3 assists to improve the charge transfer and buffers the electrode integrity, resulting in enhanced electrode performance of the Bi2S3/rGO composite compared with that of bare Bi2S3. The feasibility of using the Bi2S3/rGO composite is further confirmed in a full cell by pairing it with a Na0.67[Ni0.1Fe0.1Mn0.8]O2 cathode, resulting in reasonable capacity retention of ~74 % of the initial capacity for 300 cycles.