High rate capability Li3V2¬xNix(PO4)3/C (x = 0, 0.05, and 0.1) cathodes for Li-ion asymmetric supercapacitors

Abstract

Nanostructured Li₃V_2−xNi_x(PO₄)₃ (x = 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. Li₃V_1.95Ni_0.05(PO₄)₃/C, because of its highest specific discharge capacity (93 mA h g⁻¹ 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 L⁻¹, the asymmetric system delivers 18.7 W h L⁻¹, a value five orders of magnitude higher than that of the symmetric capacitor at the same power level.