New battery security rules regarding thermal runaway have prompted an evolution in pack design
In 2020, the Chinese language authorities issued GB 38031, a brand new nationwide security customary for electrical autos. It set a brand new requirement for automobile security through which passengers should obtain at the least a five-minute warning to exit the automobile if a battery thermal runaway occasion is detected. Earlier this 12 months, a revised customary was issued, which tightened these security necessities significantly. Whereas the five-minute egress rule nonetheless stands, the usual is now extra prescriptive round failure modes, testing, documentation and efficiency.
Thermal boundaries are one of many key applied sciences required to fulfill this customary. In pouch- or prismatic designs, thermal boundaries are usually positioned between every cell to function a firewall. If one cell goes into thermal runaway, thermal boundaries reduce off the cell-to-cell conduction that’s the first pathway for thermal power to journey. Thermal boundaries can not cease the spark, however that may delay or stop it from lighting the fuse. Whereas GB 38031-2025 doesn’t explicitly require thermal boundaries, it’s now a lot tougher to adjust to the usual with out them.
On the similar time, EV batteries are getting larger. Increased power densities, tighter packaging, and shorter design cycles imply there’s much less room — actually and figuratively — for error. To stop a single-cell thermal runaway from propagating into adjoining cells, designers must pack as a lot thermal resistance as potential into the tiny gaps between cells. However how a lot is critical?
It seems there’s a easy proportionality between the power content material of the cells, the cell-face space, and the vital thermal resistance of the thermal barrier. That proportionality may be discovered by conducting a number of thermal runaway assessments through which thermal boundaries of various thickness are trapped between two cells in an open-air setting. By triggering one cell into thermal runaway and monitoring whether or not the opposite cell follows it, two populations may be recognized: propagating and non-propagating designs. These populations are separated by a boundary denoting the vital thermal resistance beneath which thermal propagation will happen.
This evaluation reveals that thicker, extra energetic cells require additional thermal resistance to stop propagation by cell-to-cell warmth switch. When the identical kind of testing is carried out on NMC cells, an identical linear boundary exists however with a taller slope. On account of their decrease trigger- and better peak-temperatures throughout runaway, NMC designs can require 50-60% extra insulation for a pack of the identical power capability.
Aspen Aerogels’ engineers have an in-depth understanding of the complicated mechanisms of thermal runaway. They design PyroThin cell-to-cell boundaries with a system-level method to not solely deal with thermal propagation but in addition maintain cell well being and efficiency all through the pack’s lifecycle.
