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

A series of silver ferrite/maghemite composite materials (Ag_xFeO_y, where Ag_xFeO_y = 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 Ag_0.2FeO_1.6. Notably, following 30 discharge-charge cycles, the one-pot Ag_0.2FeO_1.6 composite delivers an energy density (156 mWh/g) profoundly higher than the mechanical mixture Ag_0.2FeO_1.6 (67 mWh/g). Ag_xFeO_y composites with the lowest Ag (x) content and smallest crystallite size, Ag_0.2FeO_1.6, 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 Ag_xFeO_y 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.