Top-down synthesis of iron fluoride/reduced graphene nanocomposite for high performance lithium-ion battery

Highlights: • A top-down strategy is designed to fabricate iron fluoride/reduced graphene nanocomposite. • FeF₃·3H₂O and graphene oxide are chosen as starting materials for the first time. • The as-prepared composites including FeF₃·0.33H₂O/rGO and FeF₂/rGO display outstanding electrochemical performances. -- Abstract: To fabricate reliable conducting matrix for highly insulated iron fluoride, we design a facile, green and low-cost solvothermal based synthesis method using graphene oxide powders and commercial FeF₃·3H₂O as precursors for the preparation of FeF₃·0.33H₂O/reduced graphene oxide (denoted as FeF₃·0.33H₂O/rGO) nanocomposite, as it is achieved by a combination of self-assembly, top-down phase transformation and solvothermal reduction processes. The 1D tunnel structure of FeF₃·0.33H₂O phase, nanoscale size and graphene conductive matrix together ensure ultrafast Li ion and electron transport. When applied as a cathode in lithium-ion batteries, the FeF₃·0.33H₂O/rGO electrode displays durable long-term cyclability (98% capacity retention over 100 cycles at 0.5C) and impressive rate capability (122 mAh g⁻¹ at 10C), wherein surface-induced capacitive process plays an important role. Meanwhile, we also demonstrate the successful preparation of FeF₂/reduced graphene oxide (denoted as FeF₂/rGO) nanocomposite through adaption of reaction temperature, which has been seldom synthesized and here also exhibits high electroactivity.