Si–C/G based anode swelling and porosity evolution in 18650 casing and in pouch cell

Abstract : Silicon lithiation induces a high material expansion which leads to significant swelling and mechanical pressure at the anode and cell level. In this study, the effect of the various mechanical constrains on the swelling behaviour of pouch cell and cylindrical cell (18650) with high performance silicon carbon graphite (Si–C/G) anode material was evaluated. In case of 18650 cells, strain gauges were used to evaluate the strains and pressure generated from anode swelling during cycling process; in addition, individual cell components thickness change was captured at 8 different states of charge (SOC) during a cycle by in situ 3D imaging with X-Ray micro computed-tomography (voxel size 1.6 μm) combined with a specific image treatment. For bi-layer pouch cells, operando swelling was measured using an in-house high precision (<0.1 μm) compression set-up with simultaneous pressure and thickness recording as well as dynamic pressure regulation system. Combining these unique experimental techniques and the modelling of Si–C/G active material swelling in function of the SOC we were able to provide insights in porosity changes of anodes for the two cell formats.