Northwestern Univ. researchers report on a new high-power Si–graphene composite anode material for Li-ion batteries .
With current technology, the capabilities of a lithium-ion battery are limited in two ways: energy capacity is limited by the charge density, and charge rate is limited by the speed at which the lithium ions can make their way from the electrolyte into the anode.
The Northwestern research team combined two techniques to combat both these problems. First, to stabilize the silicon in order to maintain maximize charge capacity, they sandwiched clusters of silicon between the graphene sheets. This allowed for a greater number of lithium ions in the electrode while utilizing the flexibility of graphene sheets to accommodate the volume changes of silicon during use.
The team also used a chemical oxidation process to create minuscule holes (10-20 nanometers) in the graphene sheets—i.e., “in-plane defects”—so the lithium ions would have a “shortcut” into the anode. This reduced the time it takes the battery to recharge by up to 10 times
Next the researchers will begin studying changes in the cathode that could further increase effectiveness of the batteries. They will also look into developing an electrolyte system that will allow the battery to automatically shut off at high temperatures.
