Title: Inferring solid-state diffusivity in lithium-ion battery active materials: improving upon the classical GITT method

Abstract: The Galvanostatic Intermittent Titration Technique (GITT) is a ubiquitous method for determining the solid-state diffusivity in lithium-ion battery materials. However, it is notoriously time-consuming and relies upon assumptions whose applicability is questionable. We propose a novel methodology that allows inference of the diffusivity for a more general class of data that is simpler and faster to harvest. We infer the diffusivity (as a function of stoichiometry) by minimising the residual sum of squares between data and solutions to a spherically-symmetric diffusion model in a single representative active material particle. Using data harvested from the NMC cathode of a commercial LG M50 cell we first demonstrate that our method is able to reproduce the diffusivities inferred by the GITT, which requires ten days of galvanostatic intermittent titration data. We then demonstrate that our method reliably reconstructs diffusivity using significantly less data. Despite arising from quick-to-measure data, our method more accurately infers diffusivities. This work is a contribution towards developing faster and more reliable techniques in parameter inference for lithium-ion batteries.