For the purpose of improving the deterioration diagnosis accuracy of lithium-ion batteries, we aim to establish a model-based deterioration diagnosis method. An equivalent circuit model is derived using electrochemical impedance spectroscopy that can accurately represent the dynamic characteristics of lithium ion batteries. By estimating the parameters of the model by the particle swarm optimization method, it is possible to follow the change of the parameter due to deterioration considering the relationship with deterioration from the parameter change.