Multiscale Analysis and Safety Assessment of Fresh and Electrical Aged Lithium-Ion Pouch Cells Focusing on Mechanical Behavior

Marvin Sprenger,Norbert Dölle,Marco Raffler,Florian Schauwecker,Christian Ellersdorfer,Wolfgang Sinz

doi:10.3390/en15030847

Marvin Sprenger, Norbert Dölle + Show 4 more

Open Access

https://doi.org/10.3390/en15030847

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Journal: Energies	Publication Date: Jan 24, 2022
Citations: 13	License type: CC BY 4.0

Affiliation: Mercedes-Benz (Germany), Graz University of Technology

Abstract

Analyzing the impact of electrical aging on the lithium-ion cell’s mechanical behavior and safety is an important factor to assess the crash safety of electric vehicles during their lifetime. In this study, fresh and electrical aged state-of-the-art NCM pouch cells were investigated. Aged cells, which were cycled electrically to 90% state of health, under laboratory conditions in electric vehicle battery modules were used. The used charging/discharging strategy represents real customer behavior based on accelerated driving profiles. First, it is shown that electrical aging has a significant influence on the anodes’ and separators’ mechanical properties, which had a lower mechanical strength and stiffness under tension. Additionally, quasi-static cylindrical indentation and three-point bending tests were performed to investigate aging effects on cell level at varying state of charge (SOC). Aged cells with 0% SOC showed a right-shifted force–displacement curve and a 29% lower maximum force compared to fresh cells. Fully charged, aged cells reached a similar maximum force to fresh cells, but faster temperature increase and higher temperature peaks after internal short circuit. Inductively coupled plasma optical emission spectrometry analyses confirmed an increased lithium content on the anode surface, which is indicated in literature as a reason for the increased exothermic reaction of the aged cells. The results indicate a higher safety risk for the aged investigated pouch cells under mechanical loads based on their changed mechanical properties and thermal runaway behavior.

Highlights

The usage of lithium-ion batteries (LIBs) is of high importance in current, as well as future, electric vehicles (EV) due to a fast increasing market, which is accelerated by ambitious goals against climate change [1]
Fresh and electrical aged lithium-ion pouch cells were compared with a focus on their mechanical behavior in crash situations
In order to analyze the main changes of aged cells relevant for crash safety, multiscale investigations in terms of mechanical cell component and cell level tests at 0% and 100% state of charge (SOC) were performed

Summary

Introduction

The usage of lithium-ion batteries (LIBs) is of high importance in current, as well as future, electric vehicles (EV) due to a fast increasing market, which is accelerated by ambitious goals against climate change [1]. External short circuits (ESC) can result in the deformation of electrical conducting components such as cell tabs, high-voltage busbars or cables, and the resulting failure of their insulation layers as described in [5,6,7]. A mechanical, electrical, or thermal abuse of the battery cell itself can lead to an internal short circuit (ISC) caused by separator failure followed by a thermal runaway (TR) [5,8]. After the final failure of the separator layer during this process, a high-electric-energy release due to ISC takes place. This can lead to burning electrolytes and, in the worst case, explosions [8]

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