Silver ferrite/maghemite composites and mixtures: Impact of one-pot composite preparation on battery-relevant electrochemistry

Abstract A series of silver ferrite/maghemite composite materials (AgxFeOy, where AgxFeOy = composites of xAgFeO2 + [(1 − x)/2] γ-Fe2O3 and y = 2 − (1 − x)/2) have been prepared via a non-stoichiometric, one-pot co-precipitation strategy. The impact of a one-pot composite preparation on electrochemistry was determined by comparison to a mechanical mixture of nanocrystalline AgFeO2 and γ-Fe2O3 powders, which were combined to afford an overall composition of Ag0.2FeO1.6. Notably, following 30 discharge-charge cycles, the one-pot Ag0.2FeO1.6 composite delivers an energy density (156 mWh/g) profoundly higher than the mechanical mixture Ag0.2FeO1.6 (67 mWh/g). AgxFeOy composites with the lowest Ag (x) content and smallest crystallite size, Ag0.2FeO1.6, deliver twice the discharge energy density (169 mWh/g) of stoichiometric AgFeO2 with no maghemite component and exhibited good capacity retention over 50 cycles. The notable electrochemistry of one-pot AgxFeOy composites may involve reduced AgFeO2 and γ-Fe2O3 aggregate sizes and a concomitant increase in AgFeO2/γ-Fe2O3 crystallite contact not achievable through mechanical mixing.