What is “the diffusion coefficient”? A harder question than we first thought. In a new paper in ACS Applied Energy Materials, we show a more objective and accurate way to calculate the diffusion coefficient from GITT data specific to its end use. We realized that the diffusion coefficient used in a non-ideal (non-Fickian) diffusion model is different than the standard Fickian one. The value you calculate depends on its end use. Also interesting was that the non-ideal diffusion model fit discharge data across discharge rates much better than the Fickian model, even when each used their best fit diffusion coefficients. DOI: 10.1021/acsaem.1c02218