Pressure Prediction Modeling and Validation for Lithium-Ion Pouch Cells in Buffered Module Assemblies

Abstract

Lithium-ion pouch cells must be constrained for optimal performance and lifetime. By introducing buffer layers to the module, beneficial medium pressures can be maintained over long aging periods. In this work, we review the irreversible cell growth mechanism for an automotive cell by multifaceted post-mortem analysis. Quantitative analysis of scanning electron imaging, growth and compression data as well as elemental analysis reveal anode dominated growth attributed to solid electrolyte interphase growth and thus correlated to loss of active lithium for aged cells. Based on this, a relaxed 1D force equilibrium model is developed that may predict module pressures both at begin-of-life and over aging for buffered and unbuffered module assemblies. The pressure evolution predictions over lifetime for both module types are successfully validated by optical ex-situ measurements of 22 modules aged on system level. The presented framework may guide pouch-type module design choices and engineering tradeoffs to optimize energy density, safety, stability, lifetime and performance.