Topologically Enhanced Charged Storage in Complex Particles for Redox-Flow Batteries

Self-assembled complex nanoparticles are promising charge carriers for energy storage and conversion systems. High specific capacities have been realized in these materials, which has been attributed to various factors such as their high surface area with complex topology and quantum effects caused by nanoscale dimensions. They have nevertheless found limited use in applications beyond metal-ion batteries. We have investigated the deployment of micron-sized FeSe 2 particles with nanostructured spikes as charge carriers in redox flow batteries. These so-called “hedgehog” particles (HPs) were found to be dispersible in aqueous media, and displayed shear-thinning rheology in suspension, which facilitated operation in a flow cell. Suspensions of HPs exhibited redox activity around -0.88 V vs Ag/AgCl at pH 14, leading to a 1.0 V open circuit voltage when deployed as the negolyte with ferro/ferricyanide as the posolyte. High current efficiencies (> 97 %) during cycling, and a volumetric capacity of up to 1.4 mol e /L (~ 36.4 Ah/L) were attained. Mechanisms for capacity fade and potential strategies for its mitigation will be discussed.