Abstract
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.
Highlights
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
Of the three main types of anode materials, insertion, conversion, and alloy-type[20], the most widely used for LIBs and HSCs are insertion-type materials, which rely on bulk penetrations of L i+ ions to induce Faradaic charge transfers at specific voltages[21,22]
The efficacy of this strategy was recently demonstrated by Han et al.[34] when porous CaFe2O4 prepared via a simple sol–gel synthesis method showed considerable rate performance and cyclic stability compared to F e2O3, an improvement that was ascribed to the CaO spectator nanoparticles found only in the pCFO sample
Summary
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. PCFO prepared at a fuel-rich φ = 1.325 and calcined at 900 °C shows the best overall electrochemical performance out of all samples with an initial discharge capacity of 995 mAh-g-1, a nearly 100% capacity recovery after 20 cycles of high current charging-discharging, and an ending discharge capacity of 435 mAh-g-1 after an additional 500 cycle stability test at ~ 1000 mA-g-1.
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