Examining the effects of silicon based additives on the long-term cycling capabilities of cylindrical cells

Abstract

There is an ever increasing demand for higher power and energy in EVs and the use of anodes with a percentage of silicon (Si) is becoming more prevalent to meet those demands. This article describes the results of a systematic study on electrochemical performance and the impact of mechanical changes within two types of batteries of commercial relevance that are nominally identical except their anode chemistry. We analyse 32 cells with a composite anode comprising graphite and a silicon-based component, and 30 cells with conventional graphite anodes and reveal through X-ray computed tomography that jelly roll deformations nucleate as a result of the swelling of the anode layers towards the centre of the cell. Furthermore, although Si causes large mechanical changes in the architecture of the jelly roll, with respect to the SOH window relevant for EVs, the presence of a small percentage of Si does not have a highly detrimental impact on the cycling performance of the cells. In fact, with respect to cell degradation, it appears that commercial cells have not yet reached the limit of Si loading in composite anodes, and there is room for improvement in cell capacities to meet the increasing demands on EVs.