A theoretical approach for estimating a best constant coefficient to use in an electrode model is presented for the case where experimental data exist on the diffusion coefficient as a function of the state of charge of an intercalation material. this method uses a model of diffusion in a single particle as its basis. From examining the surface concentration vs. average concentration curve for diffusion in a single particle, we can determine a diffusion coefficient that is a function of the dimensionless flux rate of material into the particle. This diffusion coefficient function can then be used in a model of a porous electrode.