Electrochromic (EC) devices show a promise to be the next major advance in the energy-efficient window technology. However, the development of higher value (performance and cost) EC windows is the key to promote the applications of these energy saving devices. To that end, computer modeling may play a powerful role in providing in-depth understanding in EC device design, performance enhancement, material selection and development of EC layers. In this work, we describe a 20 time-dependent finite element based solver, established to simulate large area Li ion electrochromic devices. The results of 2D-model development and corresponding simulations are presented utilizing literature-based material properties. The capability of the model is demonstrated in handling a very large width-to-thickness aspect ratio and examining the impacts of a voltage change due to the spreading resistance and a diffusivity variation inside electrodes on device performance and lithium ion transport kinetics. (C) 2013 Elsevier B.V. All rights reserved.