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 compounds may be used to obtain different electrochemical properties, which can be used to develop improved electrode materials for Li-ion batteries.