Thickness- and morphology-controlled vanadium pentoxide/polyaniline (V2O5/PANI) core/shell hybrid nanofibers are fabricated by electropolymerization of PANI on V2O5 nanofibers for enhanced energy storage. By simply adjusting the electrodeposition time, the thickness of the PANI shells can be controlled from 5nm to 47nm, and the morphology can be changed from coaxial to branched. The influence of shell thickness on the improved Li-ion storage performance of the V2O5/PANI core/shell nanofibers is systematically investigated, and this enhancement of charge capability and cycling stability strongly varies with the shell thickness. Thickness-dependent synergistic electron transport, Li-ion diffusion distances, and shell mechanical strength mechanisms are also proposed. These results provide meaningful references for developing new functional core/shell materials and high-performance energy storage composite materials.