Extremely high-rate capacity and stable cycling of a highly ordered nanostructured carbon–FeF2 battery cathode

Abstract

FeF₂, as a promising cathode material for Li-ion batteries, has a high specific capacity of 571 mA h g⁻¹, and a lot of research has been focused on overcoming its poor cycling stability associated with low electron conduction and large volume effect, mostly through nanostructured material design. However, FeF₂ nanodesign itself is a challenge. Herein, we report the incorporation of an ordered mesoporous carbon (CMK-3) into FeF₂-based cathodes. The FeF₂ nanoparticles inside the conducting CMK-3 by topochemical conversion from an iron oxide precursor to iron fluoride hydrate in situ, form a well-connected three dimensional network structure. Such a hierarchical framework combines multiple advantageous features, including a continuous electrically conductive network and porous space for the volume expansion of the FeF₂ particles. With this cathode, we demonstrate a cycle life of 1000 cycles with little capacity decay (less than 0.3‰ per cycle). The FeF₂@CMK-3 electrode shows stable cycling and an extremely high-rate capacity, owing to the special porous structure and the nano-sized particles. In the potential range of 1.5–4.5 V, discharge capacities of 500, 400 and 320 mA h g⁻¹ can be delivered at the high rates of 500, 2000 and 4000 mA g⁻¹ after 100 cycles, respectively, which is the highest level for FeF₂ so far.