Physics-Based Modeling and Parameter Estimation Strategies for Rechargeable Lithium-Metal Battery Cells

Abstract

This thesis develops physics-based models for rechargeable lithium-metal battery (LMB) cells and strategies for estimating the values of the model parameters from cell-level measurements. Highlighting the need for accurate models to optimize battery performance and lifespan, the author discusses the structure and operation of LMBs and their primary failure mechanisms—formation of dendritic lithium (Li) at the Li-metal electrode during recharging and loss of electrolyte. The work develops a Newman-based model for LMB structured in such a way that cell-level measurements determine all parameter values without the need for cell teardown. A number of simplified models—including a transfer-function model, an equilibrium-perturbation model, a high-frequency edge model, and a second-harmonic model—are developed for full LMB cells for the first time. These models are used to devise a strategy to estimate the values of the model parameters by regression to open-circuit potential (OCP) and electrochemical-impedance spectroscopy (EIS) measurements. Before application to a single-layer LMB pouch cell, the author validates the strategy against simulated measurements derived from a synthetic cell with known parameter values. The voltage RMSE between the fully identified model’s predictions and laboratory measurements is about 4.2mV for a GITT discharge profile and 10.3mV for a C/4-average half-sine discharge profile. In addition, estimates of the solid-diffusion coefficient derived from model regression agree with those estimated from an independent GITT experiment. MATLAB code is provided to simulate the Newman model in COMSOL, compute cell impedance and the internal electrochemical variables from the TF model, and perform the model regressions. As an avenue for future work, the possibility of incorporating explicit models for the growth of dendritic Li is discussed.