Super-iron nanoparticles with facile cathodic charge transfer

Super-irons contain the + 6 valence state of iron. One advantage of this is that it provides a multiple electron opportunity to store additional battery charge. A decrease of particle size from the micrometer to the nanometer domain provides a higher surface area to volume ratio, and opportunity to facilitate charge transfer, and improve the power, voltage and depth of discharge of cathodes made from such salts. However, super-iron salts are fragile, readily reduced to the ferric state, with both heat and contact with water, and little is known of the resultant passivating and non-passivating ferric oxide products. A pathway to decrease the super-iron particle size to the nano-domain is introduced, which overcomes this fragility, and retains the battery capacity advantage of their Fe(VI) valence state. Time and power controlled mechanosynthesis, through less aggressive, dry ball milling, leads to facile charge transfer of super-iron nanoparticles. Ex-situ X-ray Absorption Spectroscopy is used to explore the oxidation state and structure of these iron oxides during discharge and shows the significant change in stability of the ferrate structure to lower oxidation state when the particle size is in the nano-domain.

Research highlights
► A pathway is shown decreasing K2FeO4, super-iron particles to the nanometer domain.
► Nano super-irons particles are achieved through less aggressive, dry, ball milling.
► Nano super-irons exhibit improved, facile cathodic charge transfer.
► Nano super-irons retain a high battery storage advantage of the Fe(VI) valence state.
► X-ray is used to explore the iron oxides’ valence and structure during discharge.