Graphical depiction of the battery anode layers (left) Harold Kung (right)
While working with battery technology, Northwestern University Professor Harold Kung has come up with a novel configuration for lithium batteries that yield 10 times the capacity with a tenth of the charge time versus industry standard. The development is an elegant mix of old and new that
The research team took the concept of a graphene based anode and combined it with the old tried and true silicon. Graphene can store 1 lithium atom for every 6 carbon atoms. The team tried a purely silicon anode, and was able to store 4 lithium atoms for every 1 silicon. However, silicon expands greatly during rapid recharging, making it not usable for most purposes. Their first step was to sandwich layers of silicon between those of the graphene.
Kung explained, "Now we almost have the best of both worlds. We have much higher-energy density because of the silicon, and the sandwiching reduces the capacity loss caused by the silicon expanding and contracting. Even if the silicon clusters break up, the silicon won’t be lost.”
Charging time still remained an issue for the team. The charging time was limited by the shape of the graphene sheets, which have rather large overall surface area. In the charging process, a lithium-ion must travel to the edges of the graphene sheet before finding its place somewhere between the layers. The result is a long charge time. To combat this issue, the team used chemical oxidation to make 10-20 nanometer holes in the graphene layers, they budded "in-plane defects." The defects create a shortcut for the ions to the silicon storage layers. In the end, the team saw a charge time 10 times faster than anything currently available.
I am most interested in the portable gadget arena for their tech. No longer worrying about charging every 4 hours, or waiting 8 hours to replenish, sounds like a dream come true. Graphene finally finds a wide spread use. I am looking forward to more news from Northwestern.