Electrochemical Modeling of Hierarchically Structured Lithium‐Ion Battery Electrodes

Oleg Birkholz,Marc Kamlah

doi:10.1002/ente.202000910

Abstract

Hierarchically structured active materials in lithium‐ion battery (LIB) electrodes with porous secondary particles are promising candidates to increase the gravimetric energy density and rate performance of the cell. However, there are still aspects to this technology which are not fully understood. Herein, a mathematical model for half cells with hierarchically structured electrodes aiming at delivering a better insight and obtaining a deeper knowledge to this matter is presented. First, the classical half‐cell model originating back to Newman and coworkers is revisited and the basic assumptions for the electrochemically based equations are presented. As a next step, the mathematical framework of the volume averaging method is used to consistently extend the classical to the hierarchically structured half‐cell model. For both models, the full set of boundary conditions for the half‐cell setup is presented. Finally, the hierarchically structured half‐cell model is validated by experiments taken from literature and parametric studies are conducted. The results suggest that, while the rate‐limiting factor for the classical half‐cells is the diffusion coefficient of the active material, in case of the hierarchically structured half‐cells, it is the combination of electronic conductivity and inner morphology of the secondary particles.

Highlights

Due to the flexible nature of this cell model, it was extended in many directions.[25]
To help commercialization des, an impedance model for an agglomerate secondary particle was proposed in various studies,[26,27] and in the study by Wu et al.,[28] an electrochemical–mechanical model was develof lithiumion battery (LIB) in electric vehicles and for them to become a real alternative to, say, gasoline engine cars, energy density must approximately be doubled to 350 W h kgÀ1.[6]. One way to increase energy density and rate capability is to use nanostructured or hierarchically structured active material particles.[7,8,9,10,11]
Given that the results clearly show a qualitatively good agreement with experiments, the proposed hierarchically structured half-cell model can be regarded as validated in a sense that it allows for investigations to predict the influence of geometry, structure, and material on electrochemical performance

Summary

Introduction

Due to the flexible nature of this cell model, it was extended in many directions.[25] As for nanostructured active material catho-. In the study by Lueth et al.,[29] an agglomerate Newman-type cell model was proposed, where the porous secondary particle structure was modeled by replacing the compact particles by porous particles and adding additional balance laws. The goal of this article is to develop a half-cell model for hierarchically structured electrodes, to model the porous structure of nanostructured secondary particles including transport of

Objectives

Results

Conclusion