Evaluating safety behavior of Li-ion batteries regarding negative electrode composition

Li-ion battery performance is highly dependent on the electrode materials. The composition of the negative and positive electrodes influences crucial aspects of the Li-ion cell, including energy density, ageing behavior and thermal stability. Recent Li-ion technologies include the use of composite graphite-silicon negative electrodes to improve the energy storage capacity of the otherwise graphite-only negative electrode. This article evaluates the impact of negative electrode composition (standard graphite vs. Si-Gr) on the performance of two recent technologies of Li-ion batteries from the same manufacturer, focusing on electrical performance and safety behavior. The studied technologies are the LG M50LT and LG M58T, the latest one introducing a considerable increase of capacity, passing from 4.80 to 5.65 in nominal capacity. This article abords the comparison of both technologies in electric performance, electrode composition, cell design and thermal stability. Electrical characterization confirmed that the LG M58T cells possess 12.5% more capacity than the LG M50LT technology. Material characterization proved the key difference between both technologies: Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX) confirmed that the LG M50LT negative electrodes are composed of graphite, while the M58T features a blended graphite-silicon oxide (SiOx) electrode. After the analyses regarding cell characterization, the capacity increase of the LG M58T technology was attributed to the presence of silicon particles in its negative electrode composition. Safety tests showed that critical events of the exothermic chain reaction during thermal runaway occurred at similar temperatures for both technologies. Nonetheless, maximal pressure reached during thermal runaway and mass loss during the thermal event were higher for the M58T cells. These first safety results indicate a higher reactivity on the M58T technology related to the higher capacity of the cell.