A Coupled Electrochemical-Mechanical Pressure Model for Lithium Metal Batteries

Abstract

The application of mechanical pressure is receiving interest for controlling the deposition morphology of Lithium metal (Li metal) anodes.1 Pressure has been observed to induce constrained Li growth and result in more uniform deposition, in contrast to the high surface-area, mossy Li deposits that are typically observed.2 The prevention of undesirable phenomena such as mossy or dendritic lithium can potentially result in significant increases in the cycle life of high-energy Li metal cells.3 Modeling and experimental investigations at electrode and cell levels have identified the modification of interfacial kinetics and plastic deformation of Li as key mechanisms leading to dense deposition.1,2,4 Further insights can be obtained by the study of these coupled electrochemical-mechanical effects during the dynamic evolution of the electrode-electrolyte interface, and its correlation with cell-level measurements, e.g. voltage evolution during extended cycling.5 This article proposes a multiscale-continuum model applicable to both Li metal anodes and full cells under pressure. In the first iteration, the effect of interfacial deformation on kinetics is studied at different external pressures using a two-dimensional mechanical model. This model will employ more recent constitutive equations for the mechanical response of Li metal.6 The modified parameters obtained thus are combined with a cell-level macrohomogenous pseudo two-dimensional (p2D) model for the cathode and separator, which relates the effect of the modified kinetics on voltage. The voltage response from this ‘pressure-aware p2D model’ is studied both for symmetric cells and full Li metal cells, with different mathematical coupling techniques evaluated by comparison against experimental cycling data from cells under pressure. Efficient solutions are also presented for the two-dimensional mechanical model, which are envisaged to aid the computationally fast evaluation of the cell-level model. The two-dimensional interface model serves as the basis for addition of localized transport models. This in turn will introduce the ability to simulate the dynamic evolution of the anode-electrolyte interface, with attendant improvements in connecting morphological evolution to the evolution of cell-level variables during practical operation. AcknowledgmentsThe authors are thankful for financial support by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program (Battery500 Consortium).