Probing the Reversible and Irreversible Volume Expansion Observed in Li-Ion Pouch Cells
The electrodes used in Li-ion cells experience a change in volume during lithiation and de-lithiation. This electrode volume expansion will affect a Li-ion cell, causing an overall volume change in compliant cell formats such as pouch cells, or an increase in pressure in non-compliant cell formats such as hard can cylindrical cells. In this work, the effects of electrode volume expansion on Li-ion pouch cells are measured. In-situ volume and thickness measurements were performed on pouch cells to probe the reversible volume expansion and contraction of cells during charge and discharge. In-situ pressure measurements were performed on volumetrically constrained pouch cells to probe the reversible pressure change caused by electrode expansion and contraction. In addition to the reversible volume expansion and contraction observed with these techniques, an irreversible volume expansion was observed with in-situ pressure measurements. It was found that cells that experienced larger irreversible pressure growth consistently exhibited worse capacity retention. Therefore, it is proposed that monitoring irreversible volume expansion with in-situ pressure measurements may be a useful technique to rank the performance of Li-ion cell chemistries.