Decoupling reaction rate and diffusion limitation to fast-charging electrodes by extended modeling of cyclic voltammetry data

Abstract

Fast charging performance is essential for electrode materials of batteries in portable devices as well as electric vehicles. In order to support the further development of fast charging batteries, a better understanding of the relation between the intrinsic properties and the fast charging performance is urgently required, which can be achieved by the separation of mass transfer and charge transfer limitations to the fast charging performance. However, this ability is beyond the reach of the current theoretical models. In this work, a new theoretical framework is proposed to decouple the influences of ohmic resistance, reaction rate, and ion diffusion to the fast-charging properties of electrodes. The electrode geometry and dimensions are also incorporated in the model. The new model was successfully validated by analyzing cyclic voltammetry data of 4 typical electrode materials, i.e., lithium titanate, lithium iron phosphate, titanium oxide (anatase), and niobium oxide. Surprisingly, we found that the reaction rate limits the fast charging performance in all materials that we analyzed. The extended model also allows to determine the three contributions in different reaction stages. The new model is considered to facilitate electrode design and boost the development of the next generations of fast-charging batteries.