Lithium-ion Cell Safety Improve by Reduced Pressure

Electrolytes are one of the key components in lithium ion batteries because of their interaction with all materials inside the lithium cell. Usually, they consist of mixtures of organic carbonates as solvents, lithium containing conducting salts, and various additives. During a thermal runaway accident, the electrolyte is one of the most critical compounds due to its potential to form highly toxic and flammable decomposition products. A thermal runaway accident can arise due to various cell failures and usually happens in several steps. In dependence of the cause of the cell failure, different mechanisms led to a worst-case scenario in which the cell becomes un-controllable and a fire accident takes place, as can be observed in the current Li-ion safety problematic. In the process, various gases can be formed at elevated temperatures and will cause a cell bloat and in the end an ignition of the whole cell. During a thermal runaway, the initial “electrolyte burn” will ignite also high-energy electrode material and cause a more pronounced accident. Such a fire can release lots of toxic gaseous electrode metals (Ni, Co, Mn) and fluorine-rich compounds. ... mehrThus, not only the fire accident must be brought under control but also the toxic combustion products have to be considered. In this study we developed an approach for preventing Li-ion cell explosions and burns by using reduced pressure. It is demonstrated in proof-of-concept experiments that it is possible by using a vacuum pump as well as a suction unit to prevent a cell explosion successfully. A vacuum pump is often used in the lab to produce a reduced pressure, but such an advice is expensive and unpractical for various applications. Therefore, a suction unit which is much more appropriate in products and applications is also investigated in the study. It is shown that reduced pressure can be used during a thermal runaway accident on cell level to enhance the safety of the unit significantly. Within a thermal runaway a strong temperature increase happens, but the Li-ion cells remain tightly closed. Additionally we present a model how this approach could be used in larger cells and battery packs. Such a control would be advantageous in particular when the battery pack is located in a sensitive area or is used under risky conditions.