Electrochemical evaluation of porous CaFe₂O₄ anode material prepared via solution combustion synthesis at increasing fuel-to-oxidizer ratios and calcination temperatures

The drawbacks of common anodes in lithium-ion batteries (LIBs) and hybrid supercapacitors (HSCs), such as the high voltage plateau of Li₄Ti₅O₁₂ (1.55 V vs. Li/Li⁺) and the moderate capacity of graphite (372 mAh-g^-1), have established a need for better materials. Conversion materials, and in particular iron oxide and CaFe₂O₄ (CFO), have amassed recent attention as potential anode replacements. In this study, we evaluate the material and electrochemical effects of the solution combustion synthesis (SCS) of porous CFO across novel fuel-to-oxidizer ratios and calcination temperatures. We demonstrate that nearly doubling the amount of fuel used during synthesis increases capacities between 120 and 150% at high current densities (~ 1000 mA-g^-1) and across 500 additional charging-discharging cycles, an effect brought on in part by enhanced compositional purity in these samples. However, in order to ensure long-term cyclic stability, it is necessary to also calcine porous CFO to 900 °C to enhance crystallite size, particle size and spacing, and compositional purity.