Inhibiting Thermal Runaway in Large Format Li-Ion Batteries

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NOHMs Technologies is developing novel safe solvent hybrid electrolytes for safe, high energy density, high voltage, and high-power lithium-ion batteries for mobility and consumer applications. Over the past 25 years there has been a proliferation in the use of lithium ion technology and with that ever-increasing market demand for higher energy density cells – demand primarily met by advancements in the cathode and anode. This proliferation has come with the increased rise of safety concerns. There have been high profile incidents of what is known as thermal runaway across a wide variety of applications ranging from consumer electronics to electric vehicles. It is well understood that thermal runaway occurs when the self-heating rate in the cell exceeds the heat dissipation out of the cell. This self-heating is the product of undesired side-reactions in the cell which are onset by abuse conditions such as excess heat, internal short circuits, etc. The key to inhibiting thermal runaway is to modify the cell such that the self-heating rate under abuse conditions is significantly reduced. Reducing the self-heating rate is important when considering battery packs that consist of many cells as is the case in electric vehicles, so that if one cell fails in a pack the thermal runaway does not propagate to adjacent cells. Given that market trends are moving away from low energy electrodes, our approach therefore is to modify the electrolyte system to reduce the overall cell self-heating rate. This is a tunable, drop-in solution to addressing the need for improving battery safety. The incorporation of NOHMs novel safe solvents into the electrolyte formulation is shown to impact the abuse tolerance of cells on both the material level, i.e. the electrolyte-electrode interaction and on the cell level. The presented electrolyte systems demonstrate reduced overall energy and peak heat flow in the exotherm profiles of high-nickel cathode materials as well as lithiated graphite via differential scanning calorimetry (DSC). With this approach, we demonstrate significantly lower self-heating rates in an accelerating rate calorimeter (ARC) heat-wait-seek test on 30 Ah and above high-nickel cathode lithium ion cells. Combined with good rate capability and cycle life NOHMs’ novel safe solvents present an improvement in battery safety without compromising battery performance. This approach carries significance in not just safer individual cells but also in safer overall battery packs.