Electrolyte Motion Induced Salt Inhomogeneity in Si-Containing Cylindrical Cells – A Case Study

Electrolyte motion induced salt inhomogeneity (EMSI) is a failure mechanism in cylindrical and prismatic lithium-ion batteries that can lead to rapid capacity loss at high rates and eventually Li plating and cell failure. If a cell displaying EMSI is allowed to rest for several weeks before the onset of Li plating, capacity recovery is possible. This work studies the effect of varied anode silicon oxide (SiO x ) content (0 to 15% Si by weight) on EMSI in cylindrical 18650 cells by measuring capacity loss, changes in electrolyte resistance, and bulk movement of electrolyte via both moment of inertia measurements and X-ray CT imaging. With increased SiO x content, cells pump more electrolyte, display increasing electrolyte resistance with cycle number and show accelerated capacity loss. This trend did not hold true for the cell with the most SiO x , which showed electrolyte pumping without EMSI. This was possible due to a low porosity anode, which generates electrolyte pumping from both cathode and anode and does not lead to inhomogeneous salt distributions. This cell was also underfilled, likely reducing the amount of electrolyte motion. A simple model is presented for predicting the rest times required for a cell to equilibrate the electrolyte salt gradients, which agrees well with the experimental data. Three days is a typical “relaxation half-life” for these cells, with full capacity recovery after 30 1 C/1 C cycles taking up to two weeks.