Synthesis of Jarosite and Vanadium Jarosite Analogues Using Microwave Hydrothermal Reaction and Evaluation of Composition-Dependent Electrochemical Properties

Polyanion compounds are attractive as electrode materials for Li-ion batteries due to their low cost, good stability, and safety. Here we used microwave hydrothermal synthesis to prepare a series of jarosite compounds, AM3(SO4)2(OH)6, where A = K, Na and M = Fe, V. Both morphology and electrochemical properties of the materials in Li half-cells showed a composition dependence. At potentials >1.5 V vs Li/Li+, an insertion-type reaction was observed in Na,Fe-jarosite but not in K,Fe-jarosite, likely due to the presence of intercalated H3O+. Reversible insertion-type reactions were observed in both vanadium jarosites between 1–4 V with capacities around 40–60 mAh/g. Below 1 V vs Li/Li+, all four jarosite compounds underwent conversion reactions with capacities ∼500 mAh/g observed for the Fe-jarosites. X-ray diffraction showed the jarosites became mostly amorphous at low potentials but that Li+ may insert into empty channels at higher voltages. These results show how tuning the composition of jarosite compoun...