Lithium-ion batteries in electric vehicles (EVs) store and release power through the movement of lithium ions back and forth between electrodes via a liquid electrolyte. Such ion movement slows considerably in cold temperatures, reducing both battery power as well as the charging rate. A solution devised at the University of Michigan could enable high ranges and fast charging in cold weather without sacrificing the energy density of battery.
The researchers previously improved battery charging capability by creating pathways roughly 40 microns in size in the graphite anode. Drilling through the graphite by blasting it with lasers enabled lithium ions to find places to lodge faster, even deep within the electrode, ensuring more uniform charging. However, cold charging still proved inefficient due to the formation of a lithium metal chemical layer on the electrode surface.
Formation of this unwanted layer can now be avoided by coating the battery with a glassy material composed of lithium borate-carbonate, approximately 20 nanometers thick. Application of this coating was demonstrated to speed up cold charging, and when combined with the drilled channels enabled test cells to charge 500% faster in temperatures as low as 14° F (-10° C).
The battery modifications described in Joule result in EV batteries that maintain 97% of their capacity even after being fast-charged 100 times at very cold temperatures.
