High rate capability Li3V2xNix(PO4)3/C (x = 0, 0.05, and 0.1) cathodes for Li-ion asymmetric supercapacitors

Nanostructured Li3V2xNix(PO4)3 (x ¼ 0, 0.05, and 0.1) cathode materials, with a mean particle dimension ranging from 200 to 63 nm, are successfully synthesized with poly(acrylic acid) and D-(+)-glucose as carbon sources. All three samples show a monoclinic crystalline structure as confirmed by X-ray diffraction and Rietveld analysis. Ni-doping improves the specific capacity of Li3V2(PO4)3/C. Between 3.0 and 4.3 V vs. Li+/Li, all cathodes exhibit good rate capability, even at high C-rates. For these reasons, they are good candidates for high power and energy applications, in particular for the development of high energy density supercapacitors. Li3V1.95Ni0.05(PO4)3/C, because of its highest specific discharge capacity (93 mA h g1 at 100 C) and capacity retention of 97% after 1000 cycles, is selected for building an asymmetric supercapacitor with activated carbon as the anode. At a power density of 2.8 kW L1, the asymmetric system delivers 18.7 W h L1, a value five orders of magnitude higher than that of the symmetric capacitor at the same power level.