Nanosized α-LiFeO2 as electrochemical supercapacitor electrode in neutral sulfate electrolytes

In this work we have explored the electrochemical properties of two lithiated iron oxide powders for supercapacitor purposes. These samples mainly consisted of α-LiFeO2 in nanosized or micrometric form. Electrolyte was an aqueous 0.5 M Li2SO4 solution and voltage range studied was between 0 and -0.7 V vs. a Ag/AgCl reference electrode. As expected, electrochemical performance was dependent on the particle size. When electrolyte was deaerated a stable capacitance of ∼50 F g-1 is provided by the nanosized sample for several hundred cycles. Other sulfate based salts (Na2SO4, K2SO4, Cs2SO4) were investigated as electrolytes but only Li2SO4 leads to a stable capacitance upon cycling, probably due to lithium intercalation. An hybrid cell consisting of this sample and MnO2 as negative and positive electrodes, respectively, delivered 0.3 F cm-2 (10 F g-1). Although these values are lower than reported for other aqueous hybrid cell, α-LiFeO2/MnO2 asymmetric capacitor is interesting from both, an economic and an environmental point of view.