Most electrochemical models fail to accurately simulate lithium-ion battery behaviors at high C-rates (generally above 2C) and thus limit lithium-ion battery usage in many of today's applications, including electric vehicles and hybrid electric vehicles. To address this issue, the non-uniform concentration distribution effects that occur within the electrodes at higher C-rates must be included in the electrochemical model. The essential modifications to the model must incorporate solid-phase diffusion, liquid-phase diffusion, and reaction polarization. This paper develops an electrochemical model that considers high C-rate performance and assesses the model's performance for LiCoO2 batteries with charge/discharge rates up to 4C, and LiFePO4 batteries up to 5C.