The performance of nickel hydroxide/carbon asymmetric supercapacitors has been studied with a range of positive and negative active material ratios. The utilisation of the nickel hydroxide electrode in asymmetric supercapacitors was found to be a function of the mass ratio of the positive and negative electrode materials and not independent as previously assumed. Previous models describing the behaviour of asymmetric supercapacitors assumed that the voltage swing was entirely due to the polarisable electrode. These models were found to be inadequate for describing the rate dependant charge/discharge behaviour of asymmetric supercapacitors. The mass ratio of the active materials was determined to be an important factor in predicting the observed behaviour and has been incorporated into an improved model. Crown Copyright (c) 2008 Published by Elsevier Ltd. All rights reserved.