Direct Fluorination of Iron (II, III) Oxide Conversion Electrodes

Multivalent conversion-based transition metal (TM) compounds have significantly higher specific capacity due to their multiple red-ox states contributing towards transfer of> 1 lithium per transition metal atom. 1-2 Iron oxides (Fe2O3 and Fe3O4) are examples of such high capacity conversion electrodes having other advantages such as low cost, natural abundance and environmental benignity.3 A relatively lower redox potential with respect to Li/Li+ makes them more suitable as anodes for lithium batteries.4 On the other hand, their fluoride counterparts such as FeF3 have higher redox potential, and capacity contribution derived from intercalation and conversion mechanisms. The major drawback of iron fluoride is their poor electronic conductivity due to the higher ionicity of the Fe-F bonds.5 One of the approaches for overcoming this barrier is developing synthesis methods for converting fluorides to oxyfluorides.6 In this work, we demonstrate a novel approach where we use a direct fluorination method to convert iron oxides to oxyfluoride using a fluidized bed reactor. Fluorination of nano-Fe3O4 (n-Fe3O4) powder was carried out using a fluidized bed reactor by controlling F2 partial pressure and reaction temperature (T). XPS study confirmed that with increase in fluorination temperatures, more F was introduced into Fe3O4 with concomitant reduction of surface oxygen species, especially for T&gt