Spatial confinement of free-standing graphene sponge enables excellent stability of conversion-type Fe2O3 anode for sodium storage

Conversion-type anode materials are highly desirable for Na-ion batteries (NIBs) due to their high theoretical capacity. Nevertheless, the active materials undergo severe expansion and pulverization during the sodiation, resulting in inferior cycling stability. Herein, a self-supporting three-dimensional (3D) graphene sponge decorated with Fe2O3 nanocubes (rGO@Fe2O3) is constructed. Specifically, the 3D graphene sponge with resilience and high porosity benefits to accommodate the volume expansion of the Fe2O3 nanocubes and facilitates the rapid electrons/ions transport, enabling spatial confinement to achieve outstanding results. Besides, the free-standing rGO@Fe2O3 can be directly used as an electrode without additional binders and conductive additives, which helps to obtain a higher energy density. Based on the total mass of the rGO@Fe2O3 material, the rGO@Fe2O3 anode presents a specific capacity of 859 mAh/g at 0.1 A/g. It also delivers an impressive cycling performance (327 mAh/g after 2000 cycles at 1 A/g) and a superior rate capacity (162 mAh/g at 20 A/g). The coin-type Na3V2(PO4)3@C//rGO@Fe2O3 NIB exhibits an energy density of 265.3 Wh/kg. This unique 3D ionic/electronic conductive network may provide new strategies to design advanced conversion-type anode materials for high-performance NIBs.