Impact of Manufacturing Tolerance on Lithium Ion Electrode and Cell Physical Properties

Abstract

In both laboratory and commercial scale manufacturing of lithium ion cells, variability is introduced in numerous stages of the production process. The acceptable tolerances on these produced parts can have a large impact on the final product’s reliability, repeatability, and functionality. In this study, the range of electrode porosity, electrode internal void volume, cell capacity, and capacity ratio that result from electrode coating and calendering tolerance are investigated and offered as one possible explanation for cell-to-cell and lot-to-lot performance variation. Based on an electrode coating tolerance of ± 0.4 mg/cm2 and calender tolerance of ± 3.0 μm the resulting range of physical properties is investigated. For a target positive electrode porosity of 30%, the resulting porosity can range from 19.6-38.6%. To account for this variation during the manufacturing process, as much as 41% excess or as little as 59% of the target electrolyte quantity should be added to cells to match the positive electrode void volume. Similar results are observed for a negative electrode of 40% target porosity, where a range from 30.8% to 48.0% porosity is possible. For the negative electrode as little as 72% up to 28% excess electrolyte should be added to fill the internal void space. Although the results are specific to each electrode composition, density, chemistry, and loading the presented process highlight possible variability of produced parts. These results are further magnified as cell designs moves toward higher power applications with thinner electrode coatings.