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Microwave-assisted hydrothermal synthesis of NH4V3O8 microcrystals with controllable morphology

Water-free NH4V3O8 microcrystals have been successfully synthesized by a microwave-assisted hydrothermal method. The products were characterized by means of X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, cyclic voltammetry, and galvanostatic cycling. The results show phase-pure products whose particle size and morphology can be tailored by varying the reaction conditions, i.e., reaction temperature, synthesis duration, and initial pH value. For instance, at low pH (2.5 to 3), flower-like agglomerates with primary particles of 20 to 30 microm length are found, while at pH = 5.5 single microplates with hexagonal outline (30 to 40 microm) prevail. The sample with the comparably highest specific surface area (11 m2/g) was studied regarding its electrochemical performance. It shows an extraordinary initial discharge capacity of 378 mA h g-1 at 10 mA g-1, which corresponds to the intercalation of 4.2 Li+/f.u.