Autonomic shutdown of Lithium-ion batteries using thermoresponsive microspheres

Autonomic, thermally-induced shutdown of Lithium-ion (Li-ion) batteries is demonstrated by incorporating thermoresponsive polymer microspheres (ca. 4 μm) onto battery anodes or separators. When the internal battery environment reaches a critical temperature, the microspheres melt and coat the anode/separator with a nonconductive barrier, halting Li-ion transport and shutting down the cell permanently. Three functionalization schemes are shown to perform cell shutdown: 1) poly(ethylene) (PE) microspheres coated on the anode, 2) paraffin wax microspheres coated on the anode, and 3) PE microspheres coated on the separator. Charge and discharge capacity is measured for Li-ion coin cells containing microsphere-coated anodes or separators as a function of capsule coverage. For PE coated on the anode, the initial capacity of the battery is unaffected by the presence of the PE microspheres up to a coverage of 12 mg cm ^-2 (when cycled at 1C), and full shutdown ( >98% loss of initial capacity) is achieved in cells containing greater than 3.5 mg cm ^-2. For paraffin microspheres coated on the anode and PE microspheres coated on the separator, shutdown is achieved in cells containing coverages greater than 2.9 and 13.7 mg cm ^-2, respectively. Scanning electron microscopy images of electrode surfaces from cells that have undergone autonomic shutdown provides evidence of melting, wetting, and resolidification of PE into the anode and polymer film formation at the anode/separator interface.