Batteries, such as lithium-ion, sold for consumer use in portable electronic devices and other applications such as electrical cars, occasionally fail in the field over time. These cells have typically passed a wide variety of safety tests such as those required by governmental shipping regulations and other certification organizations. Nevertheless, they sometimes fail by overheating, which triggers thermal runaway in the battery. This action may engulf the entire device such as a cellphone or tablet-type devices.
To better understand these failure modes, innovators at NASA Johnson Space Center and the DOE National Energy Renewable Laboratory have developed a battery test device that introduces latent flaws into the test batteries to produce an internal short circuit. This device can help battery manufacturers and testers determine which battery design will best minimize the spread of a thermal runaway-induced fire in the battery or bank of batteries.
The uniqueness of this device can be attributed to its simplicity. In a particular embodiment, it is comprised of a small copper and aluminum disc, a copper puck, polyethylene or polypropylene separator, and a layer of wax as thin as the diameter of one human hair. After implantation of the device in a cell, an internal short circuit is induced by exposing the cell to higher temperatures and melting the wax, which is then wicked away by the separator, cathode, and anode, leaving the remaining metal components to come into contact and induce an internal short. Sensors record the cell's reactions. Testing the battery response to the induced internal short provides a 100% reliable testing method to safely test battery containment designs for thermal runaway.