Innovators at NASA Johnson Space Center have developed a high-powered infrared (IR) laser that can trigger Li-ion battery cells into thermal runaway (TR) without perforating the battery’s wall like previous methods. Inducing TR in a battery cell allows engineers to test and improve the safety performance of overheated batteries that can potentially catch fire or explode. The primary advantage of this method is the heat energy delivered by the laser can be localized to the exact target spot on the battery cell minimizing thermal biasing to adjacent cells.
This technology is based upon a 120-watt IR laser coupled to a fiber optic cable that is routed from the output of the laser into a series of focusing optics which directs energy onto a battery cell mounted to a test stand. When activated, heat from the laser penetrates the metal housing, heating the internals of the cell. At a specific temperature, the separator in the first few layers of the cell melts allowing the anode and cathode to make contact and initiates an internal short circuit. The internal short circuit then propagates throughout the battery eventually causing thermal runaway.
The lower the wavelength of the laser used to produce the thermal runaway the more heat-energy will be absorbed into the cell producing a faster result. The fiber optic cable can be terminated into a series of optics to focus the laser at a specific target, or the fiber optic cable can be stripped bare and placed next to the target to heat an isolated location. This method can also be used on a wide variety of cells, including Li-ion pouch cells, Li-ion cylindrical cells and Li-ion large format cells.
This laser method does not require any internal modification of the test subject cell design nor require patch heating to trigger a short-circuit. Triggering Li-ion cells with laser radiation could work on any commercial battery cell design with only exterior surface treatment required, which can be done by the user. The technology has several potential applications including human-occupied vehicular transport applications that require a high level of rigor in determining margins of safety (automotive, aircraft, sea vessels, spacecraft).