Moore and colleagues are applying their "automatic healing" technique in Li-ion batteries in an attempt to prevent thermal runaway.
According to Patrick Glynn, DOE Office of Science, in his article "Preventing Laptop Fires and "Thermal Runaway,"" the technique was to coat either the anode layer or separator layer with heat-sensitive "microspheres," or tiny solid capsules, ranging from two to forty-some nanometers in diameter. When the battery reached a certain temperature, the microspheres would melt, blocking the pores in the separator through which lithium ions pass and shutting down battery operation. The researchers fabricated two sets of microspheres, one made of polyethylene and another of paraffin wax. They tested the system using coin-shaped CR2032 Li-ion batteries (the type you find in the keyless remote to your car). They experimented with different levels of coating to maximize both battery operation at room temperature and the effectiveness of shutdown at high temperatures. They were able to demonstrate shutdown (reduced charge capacity by 98 percent) at 110º Celsius with PE microspheres and shutdown at 65º C with the paraffin wax, while sustaining normal battery operation at room temperature. The safety advantage is that these triggering temperatures are considerably lower than the melting point of the two materials in the separator (PE at 130º C. and PP at 165º C.), so battery operation is shut down with the separator still safely intact. Examination of the surfaces with scanning electron microscopy confirmed the melting pattern.
So the hope is that the choice of material can be fine-tuned eventually to achieve the desired performance and to expand the application of the system to other types of batteries. "Since the melt transition temperature . . . dictates the triggering temperature of the cell shutdown," the researchers wrote, "this highly customizable mechanism should be applicable to a wide variety of battery chemistries and their unique shutdown requirements." The work was supported primarily by the DOE Office of Science.
For the full U.S. Department of Energy article about the research, please click here.