For the research, development, and eventual manufacture of lithium-ion batteries, it is necessary to understand the phenomena limiting cell performance and incorporate this knowledge into battery design. While methods exist for the determination of electrotyte-phase properties, procedures for the assessment of analogous solid-state properties in battery electrode materials are more difficult to implement. The perturbation solution derived in this work is implemented to determine the intercalate diffusion coefficient in a solvent-cast porous electrode containing carbonized poly(acrylonitrile) fibers suitable for a lithium-ion battery. It is shown that both intercalate and vacant site contributions to the excess free energy of the solid phase influence significantly the nonequilibrium behavior of the electrode. In addition, the analysis is shown to provide insight into the processes that govern the pulse-power performance of batteries based on insertion electrodes (e.g., lithium-ion and metal-hydride batteries).