: Lithium-ion batteries, which are lightweight and have a high energy density, are commonly used in consumer electronics, such as laptops and hoverboards. However, because they contain a flammable electrolyte, they can catch fire if they become overheated. To prevent such spontaneous combustion, Yi Cui of Stanford University and colleagues have developed a heat-sensitive polymer film
embedded with nickel nanoparticles, which can be incorporated inside the batteries. If the battery gets too hot, the film swells and the nickel nanoparticles are pushed apart. That causes the conductivity to drop, and the battery stops working. Once the battery’s temperature cools to an acceptable level, the polymer relaxes and becomes conductive again, and the battery can resume functioning.