Microwave-Assisted Solvothermal Synthesis and Characterization of Various Polymorphs of LiVOPO4

All three polymorphs of LiVOPO4 have been synthesized, for the first time, by a microwave-assisted solvothermal (MW-ST) method by adjusting the reaction media and conditions. The triclinic polymorph (alpha-LiVOPO4) was obtained as the most stable and stoichiometric product and was thus chosen for optimization. Varying solvent mixtures consisting of water and alcohols/glycols proved to have significant effects on the particle size/morphology, with the water and glycol mixtures generally producing smaller particles. Particle size was also reduced with decreasing reaction time, decreasing reactant concentration, and CTAB surfactant addition. The electrochemical performance was analyzed in two potential ranges: 3.0-4.5 V corresponding to the insertion/extraction of one lithium and 2.0-4.5 V corresponding to the insertion/extraction of two lithium into/from the LiVOPO4 structure. Synthesis in a mixture of water and ethylene glycol in particular led to a high capacity of 134 mAh/g during the first cycle in the 3.0-4.5 V region. Initial attempts at coating the particles with PEDOT:PSS improved the cycling performance.