Battery Thermal Runaway and Solutions
Transportation will likely be dominated by electric vehicles in the future. They are expected to reign the market in the next decade as their market share grows. Despite this, lithium-ion batteries pose a significant safety concern for consumers. Recently at an electric vehicle charging station in Delhi, India, over 90 vehicles caught fire because of a short circuit.
With high energy density, lithium-ion batteries release a great deal of electric current, resulting in increased cell temperatures. At high temperatures, organic electrolyte decomposes. This process generates flammable gases such as hydrogen and methane, causing the cell pressure to grow, the seals to open, the reaction with oxygen in the air, and finally, the battery explosion. The result is the development of several methods to stop or delay the current overflow in the cell.
Positive temperature coefficient (PCT) polymers are a solution with an increase in electrical resistance as the temperature rises. It isolates a single cell from the pack to prevent heat transfer. Shutdown separators are another solution for cell protection. In advanced multilayer separators, an additional layer melts at a critical temperature, closes pores, and blocks the lithium-ion transfer path between electrodes. Furthermore, the electrodes are physically separated by the backbone polypropylene (PP). In overcharged batteries, electrolyte additives such as redox shuttles can react and lock the battery potential.
Battscout's analysis shows that over 1400 patents are published on thermal runaway controlling methods. Asahi Glass is one of the top companies with the most extensive patent portfolio with its flame retardant electrolyte, which includes fluorine-containing ethers and carboxylic acid esters. These compounds improve liquid electrolyte's high-temperature stability. Separator manufacturer Celgrad develops three-layer separators made of an outer PP layer and an inner polyethylene (PE) layer; while the PE layer acts via a quick shutdown effect described before; the PE layer acts through the immediate shutdown effect described earlier. Meanwhile, Cadenza Innovations has introduced pack designs with thermal insulating materials. BYD, JEVE, and Svolt are introducing unique packing designs for thermal management. Besides, BYD also is focused on polymeric separators and Svolt developing thermal condition prediction procedures.
