How the utilised SOC window in commercial Li-ion pouch cells influence battery ageing

Evelina Wikner,Johan Fridner,Torbjörn Thiringer,Daniel Brandell,Erik Björklund

doi:10.1016/j.powera.2021.100054

Evelina Wikner, Johan Fridner + Show 3 more

Open Access

https://doi.org/10.1016/j.powera.2021.100054

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Abstract

In many lithium-ion battery (LIB) applications, e.g. hybrid vehicles and load-levelling storage systems, only part of the state-of-charge (SOC) range needs to be utilised. This offers the possibility to use an optimal SOC window to avoid LIB ageing. Here, a large test matrix is designed to study LIB ageing in a commercial 26 Ah pouch cell, in order to map the ageing behaviour at different SOC levels with respect to temperature and current. A quantification of the degradation modes, loss of lithium inventory (LLI), loss of active positive (LAMPE) and negative (LAMNE) electrode materials is made by analysing the change in the open circuit voltage (OCV). A key result is that lower SOC intervals significantly improved battery ageing. Even during harsh test conditions, such as high C-rates and temperatures, the cells deliver more than three times the expected number of full cycle equivalents. High SOC combined with high C-rate increase ageing where the dominating ageing mechanisms are LLI, followed by LAMPE.

Highlights

The established knowledge is that Lithium-ion batteries (LIB) degrade faster when operated at either high or low state of charge (SOC), high temperature and high C-rate [1,2,3,4,5,6,7,8]
We focus on investigating ageing in high-quality automotive pouch cells
For the tests conducted in 0–90% SOC intervals, Fig. 2, faster ageing at higher temperatures can be seen

Summary

Introduction

The established knowledge is that Lithium-ion batteries (LIB) degrade faster when operated at either high or low state of charge (SOC), high temperature and high C-rate [1,2,3,4,5,6,7,8]. It has been shown that using a limited part of the available SOC window, which is applicable in applications such as hybrid vehicles and stationary battery storages for load-levelling, improves the battery lifetime [9,10,11]. High-quality vehicle batteries is very expensive and time consuming. Post mortem (PM) analysis is the main method used to characterise LIB ageing mechanisms. This requires a material lab facility with advanced equipment and several time consuming analysis methods [12]. Various mathematical and non-invasive approaches have been developed to make use of the characteristics in the potential curve [4, 13,14,15,16,17,18]

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