The Effect of Fluoroethylene Carbonate in Lithium-Ion Pouch Cells with Chemical Silicon-Carbon/Graphite Composite Negative Electrodes

Improving energy density and cycle life of lithium-ion batteries (LiBs), while maintaining or improving safety is important. Introducing silicon-containing materials to graphite negative electrodes is a promising way to increase LiB energy density. This study focuses on the impact of varying concentrations (0–10 wt%) of fluoroethylene carbonate (FEC), on the performance of Li-ion pouch cells that include 20 wt% chemical silicon-carbon (chemical SiC) in their negative electrodes. Long-term cycling tests at 40 °C and 55 °C along with long-term storage experiments at 60 °C were carried out to evaluate the effect of FEC on cell lifetime. Upon reaching 90% capacity retention, post-mortem analyses were performed using electrochemical impedance spectroscopy (EIS), while gas chromatography-mass spectrometry (GC-MS) was performed to investigate electrolyte degradation products. Scanning electron microscopy (SEM) was utilized to examine changes in the negative electrode surface after cycling at 40 °C until 90% capacity. The results demonstrate that employing FEC as an additive, in the range of 0 to 4%, has little effect on capacity retention and voltage polarization during long-term cycling or storage for cells that contain chemical SiC (at least for the sample tested here) in the negative electrode, while cells with 8 and 10% FEC performed worse.