Bi₂S₃/rGO nanocomposites with covalent heterojunctions as a high-performance aqueous zinc ion battery material

Bismuth(III) sulfide (Bi2S3) is a promising cathode material for aqueous zinc ion batteries (ZIBs), yet suffers from serious capacity issues due to its poor electrical conductivity and microstructural degradations. In this work, Bi2S3 anchored on reduced graphene oxide (rGO) is prepared through hydrothermal reaction and is used as cathode material for aqueous ZIBs. Raman and XPS characterizations confirmed that the oxygen bridge in Bi-O-C heterostructures is successfully created during the hydrothermal synthesis. These oxygen bridges are energy favourable in the Bi2S3/rGO composite materials and serve as the electron transfer channels for rapid charge compensation during Zn2+ incorporation/extraction. Rotating ring-disc electrode (RRDE) measurements demonstrate improved electrochemical stability of the Bi2S3/rGO composite material compared to pristine Bi2S3. As a result of these improved characteristics, Bi2S3/rGO composite shows notably better rate performance and cycling stability than unsupported Bi2S3. Ex-situ X-ray diffraction and XPS characterizations indicate that Zn2+ undergoes a reversible conversion reaction with Bi2S3 to form ZnS/Bi-0, rather than being intercalated into Bi2S3 crystal interlayers. The rGO substrate forms chemical bonds with bismuth in the composite material, and the strongly anchored bismuth on the rGO through a Bi-O-C bridge enables a highly reversible conversion reaction. As a result, the Bi2S3/rGO composite with 8 wt% rGO can deliver a reversible capacity of similar to 186 mAh g(-1) at the current density of 500 mA g(-1) after 150 cycles, showing high promise as Zn-ion battery material.