UCLA researchers in the Department of Chemistry have developed a safety switch that prevents overcharging of lithium-ion batteries without impacting battery operation.
Lithium-ion batteries (LIBs) are the leading type of portable energy storage due to their high energy density and rechargeability. As the energy market demands higher voltages, power, and lifetimes, safety concerns are becoming more prevalent amidst hazardous events due to LIB failure. One main failure mechanism, “overcharging”, has resulted in dangerous or fatal outcomes such as fires or explosions. Different approaches have been suggested to prevent battery destruction and thermal runaway but these systems often have reaction times that are too slow or have adverse effects on the battery performance in terms of voltage, current or conductivity.
UCLA researchers have developed a silicon expansion safety switch that mechanically switches off current to the anode when the cell is fully charged. The safety switch’s mechanism is based on the large volumetric change that occurs in silicon when lithium ions permeate it (lithiation).The switch consists of two pieces of silicon built into the anode.As lithiation proceeds, the silicon pieces expand, ultimately to the point where they separate the anode from the power source. Incorporating these safety switches into batteries can prevent “overcharging”, or the dangerous continuation of charging beyond the adequate cell voltage.
This battery shutdown is reversible, with the silicon volume condensing back to its original size after the potential is reduced, allowing regular operation of the battery once the potential is within safe levels. The safety switch does not negatively impact standard battery operation. Thus, this supplementary safety equipment will allow for high performing batteries that do not compromise safety.
Safety switch, Li-ion batteries, Silicon expansion, overcharging, lithium, battery