In order to assess the impact of cell degradation on rate capability, we employ multiphase porous electrode theory (MPET) simulations based on nonequilibrium thermodynamics , to compare the pulse response of a degraded cell and the response prior to degradation. Importantly, MPET captures the rate-dependent populations of active particles sustaining the applied current , which control internal resistance and parasitic side reactions . Degradation manifests itself by gradually altering the current or potential response from cycle to cycle, and the model is able to attribute these changes to a number of physical mechanisms.