Cathode properties of nanocrystalline Li₃V_1.8Al_0.2(PO₄)₃/multi-walled carbon nanotube composites for hybrid capacitor prepared via ultra-centrifugation treatment

Highly-dispersed Li₃V_1.8Al_0.2(PO₄)₃ nanoparticles which are directly impregnated onto the surface of multi-walled carbon nanotubes (MWCNT) were successfully synthesized via a unique two-step process using an ultracentrifugation at 75,000 g. The synthetic procedure of the Li₃V_1.8Al_0.2(PO₄ )₃/MWCNT composite involves the following two steps: i) precipitation of V_1.8Al_0.2O₃ (10-100nm) nanoparticles on the surface of MWCNT, and ii) the subsequent transformation of the V_1.8Al_0.2O₃ into the Li₃V_1.8Al_0.2(PO₄)₃ nanoparticles without any change of their shape and dimensions. The 10% of Al-doping brought out an increase in the discharge capacity from 119 to 124mAhg^-1 per Li₃V_2-xAl_x(PO₄) ₃, which corresponds to a 14% increase of the Li₃V_2-xAl_x(PO₄)₃ utilization ratio. The Al-doping also reduced its electric resistance by 26%. The Li₃V_1.8Al_0.2(PO₄)₃/MWCNT with such an efficient electron transport can deliver excellent electrochemical performances ever attained to date; capacity density of 85mAh g^-1 at a high discharge rate of 480C and stable cycle performance over 10,000 cycles at 10C rate with 85% retention of the initial capacity.