Deformation from Formation Until End of Life: Micro X-ray Computed Tomography of Silicon Alloy Containing 18650 Li-Ion Cells

Abstract

The use of Si-containing negative electrodes is one of the most promising options to increase the energy density of Li-ion batteries. Nonetheless, increasing the Si content in the anode above 5–10 weight % is still a challenge because of the expansion/contraction behavior of the Si upon lithiation/de-lithiation. Due to a 2 to 3 fold volume increase of Si during charging, it is paramount to understand and manage structural changes from the formation until the end of life. This applies not only at electrode, but also at cell level and specifically for cells with high electrode loadings close to mass production format. To this aim, we report here on the structural changes in Si-blended anode/manganese nickel cobalt oxide (NMC) 622 cathode 18650 format cells from production through formation until end of life by means of micro X-ray computed tomography (CT). We constructed specially designed 18650 cells in which the jelly roll does not fill the full volume of the case. The volume change without external constraint led to the identification of three main deformation mechanisms at the jelly roll level and shed some light on the effect of the cell geometry on the use and performance of anodes with high Si-content.