An in-situ technique for monitoring the pressure evolution of volumetrically constrained Li-ion pouch cells has previously been introduced by Louli et al. When constrained, changes in cell volume cause a pressure response that is measured. A reversible pressure change is observed due to the reversible electrode volume expansion and contraction during charge and discharge of the cell. Here, it is shown that in addition to this reversible pressure evolution, pouch cells with silicon-containing negative electrodes exhibit an irreversible pressure growth over the course of tens of cycles, and that large irreversible pressure growth correlates with poor lifetime. It is hypothesized that this is caused by the growth of the solid electrolyte interphase (SEI), resulting in irreversible capacity loss as well as volume growth which is manifest in the irreversible pressure growth measurements. Li(Ni1-x-yCoxAly)O2/SiO-graphite, LiCoO2/Si Alloy-graphite and Li(Ni1-x-yCoxAly)O2/nano Si-C pouch cell chemistries were tested in this work. The lifetime of these cells are ranked and shown to agree with the ranking of irreversible pressure growth. Impedance measurements are also presented to further rationalize the apparent correlation between lifetime, irreversible pressure growth and SEI growth. We propose that in-situ pressure measurements can be used as a non-destructive technique to gauge SEI growth and thus rank the performance of Li-ion cells.
- A. J. Louli, Jing Li, S. Trussler, Christopher R. Fell, and J. R. Dahn, Volume, Pressure and Thickness Evolution of Li-Ion Pouch Cells with Silicon-Composite Negative Electrodes, J. Electrochem. Soc., 164 (2017).