The discharge capacities of V2O5/carbon composites at various current densities were measured and calculated using a mathematical diffusion controlled reaction model to estimate the lithium diffusion distance, i.e.. V2O5 layer thickness, required to achieve high-rate performances in lithium ion batteries. V2O5/carbon composites were prepared by mixing a V2O5 sol, carbon and a surfactant, followed by drying. V2O5/carbon composites with a short lithium diffusion distance and a high electronic conductivity exhibited highrate performances and the discharge capacity of a V2O5/carbon composite was 286 mAh/g at a high current density of 80 A/g. It was possible to estimate discharge capacities depending on current density and V2O5 layer thickness by lithium diffusion simulation. The simulation revealed that a V2O5/carbon composite with a V2O5 layer thickness of 4.5 nm can achieve a large discharge capacity at a sufficiently high current density of 200 A/g in the case of a composite that has a sufficiently high electronic conductivity. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.