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

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.