Li-storage performance of binder-free and flexible iron fluoride@graphene cathodes

Abstract

As flexible devices have become increasingly popular in our daily life, flexible energy-supply devices, especially flexible lithium-ion batteries (LIBs), have attracted great attention. Graphene foam is a lightweight, flexible and conductive interconnected network that can be directly used as a current collector material to disperse active materials. FeF₃·0.33H₂O is a suitable active cathode material with a high theoretical capacity and natural abundance. But its poor ionic and electrical conductivity limits its application. In order to combine the superior qualities of GF and FeF₃·0.33H₂O, we developed a scCO₂-assisted method to grow FeF₃·0.33H₂O flower-like arrays perpendicularly on GF. Consequently, the designed composites efficiently combine the good flexibility of GF and high energy storage capacity of FeF₃·0.33H₂O. The strong interaction between GF and FeF₃·0.33H₂O established by the scCO₂ method greatly improves the electron transport and ion migration. Thus, the obtained flexible electrode requires no binder, metal current collectors and conducting agents. It shows a capacity of about 145 mA h g⁻¹ at a current density of 1C (200 mA g⁻¹) after assembled as a cathode electrode.