Synthesis and optimization of NASICON-type Li3V2(PO4)3 by adipic acid-mediated solid-state approach

We report the synthesis and optimization of NASICON-type carbon-coated Li 3 V 2 (PO 4 ) 3 by solid-state approach. Adipic acid (AA) is used as the source material for the carbon. Initially, the synthesis of monoclinic Li 3 V 2 (PO 4 ) 3 is optimized at a precalcination temperature of 300 °C for 4 h and 900 °C for 8 h under Ar flow to yield a single phase. Powder characterizations such as thermogravimetric–differential thermal analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and particle size distribution are conducted, and the results are presented. The AA concentration is varied according to the total metal ion composition in the compound (0.05, 0.1, and 0.15 M). Electrochemical Li-insertion properties are evaluated in half-cell configurations between 3 and 4.8 V vs. Li at a current density of 0.1 mA cm −2 at room temperature. Compared with the lower AA concentrations, Li/Li 3 V 2 (PO 4 ) 3 (0.15 M AA) cell exhibited discharge capacities of 178 and 147 mAh g −1 for the 1st and 50th cycles, respectively, and a capacity retention of 83 % after 50 cycles, which is 11 % higher than that of the native compound. Li/Li 3 V 2 (PO 4 ) 3 (0.15 M AA) showed better rate performances and delivered discharge capacities of 173, 165, 150, 132, 105, and 76 mAh g −1 at rates of 0.1, 0.2, 0.5, 1, 5, and 12 C, respectively. Electrochemical impedance spectroscopy reveals the enhancement in electronic conductivity profile after carbon coating.