A Simple One-Dimensional Transport Model to Explain Inverse Signatures in Lithium-Metal Batteries

Abstract

Lithium metal as the negative electrode in lithium batteries provides high theoretical capacity (3,860 mAh g–1) and negative electrochemical potential (-3.040 V vs standard hydrogen electrode) 1. However, using lithium metal poses several challenges, including dendritic electrodeposition and accumulation of dead lithium. These phenomena can cause the cell to short, and also contribute to poor cyclability 2.Lithium deposition and stripping can be observed on the cell’s voltage response as unique signatures. These signatures can give insight on the morphology of the deposit 3. Physics-based continuum models can be used to understand lithium ion transport effects on deposition and stripping, and on the emergent voltage signatures.Our past work studied one-dimensional models for lithium symmetric cells to model charge transport and capture the transitions in voltage observed experimentally 4. In this work, we propose a simple diffusion-based one-dimensional moving boundary that shows inverse signatures of lithium ion concentration and overpotential for the lithium deposition reaction. We show that using a transport model alone can produce unique inverse voltage signatures. The deposition of lithium is modeled as a moving interface.The model was tested with different design parameters such as salt concentration, and different applied current densities and ion diffusivities to study their effect on the formation of signatures. These parameters affect the interface motion and ion transport in the electrolyte. The interplay between these two phenomena then determines characteristic signatures of the overpotential and the cell voltage. Acknowledgement This work at the University of Texas at Austin was supported by U.S. DOE award DEAC05- 76RL01830 through PNNL subcontract 475525 and the assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the US Department of Energy (DoE) through the Advanced Battery Materials Research Program (Battery500 Consortium).