Lithium batteries compose a dominant portion of the global battery market. The reason for their popularity is because lithium is an excellent anode material, carrying the highest theoretical capacity and lowest electrochemical potential of all known candidate elements. Topped with the fact that elemental lithium is naturally abundant and inexpensive, it is no surprise that lithium batteries are powering most of our portable electronic devices, electric vehicles, unmanned aerial vehicles and other devices.
Lithium batteries come in two dominant types: lithium-ion and lithium-metal. Lithium-ion batteries (LIBs) are a type of rechargeable battery in which lithium ions move between electrodes during charging and discharging. LIBs use an intercalated lithium compound as the material for one of the electrodes, as opposed to lithium-metal batteries (LMBs) that use metallic lithium electrodes. Although LMBs stand apart from other batteries in their high charge density (long life), two concerns have prevented their wide-scale use in consumer electronics: these batteries are non-rechargeable, because of degradation or dendrite formation on the electrodes, and the explosive reactivity of elemental lithium when exposed to water or even moisture from air.
New technology is now being put to use to bypass these two concerns, enabling LMBs for competition on energy-demanding markets such as electric vehicles. One recent solution makes use of phosphorus-sulfur chemical compounds that create a thin coating over the lithium electrode. The coating protects the electrode from accidental exposure to water. Another solution employs a thin film of graphene oxide (GO) as the protective layer.
Apart from protecting the lithium electrode from accidental exposure to water or air, the GO layer prevents formation of dendrites. Dendrites grow on lithium-metal electrodes during the charging cycle when lithium re-deposits on the electrode unevenly. These dendrites can eventually grow through the electrolyte, causing the two electrodes to touch, which in turn may cause the battery to explode. A thin GO layer, which is spray-coated on a standard fiberglass separator, slows the passage of lithium ions through the battery enough to prevent the formation of dendrites. The relation between the rate of passage of lithium ions and the way that they deposit on the counter-electrode was resolved with theoretical modeling and computation, in a paper recently published in the journal Advanced Functional Materials.
The potential of graphene to enhance battery technology and enable novel high-power, long-lasting solutions is a known fact, with a continuous stream of scientific results adding to the certainty that the material will play an important role in future energy storage solutions. This most recent result goes in a new direction, bringing lithium-metal batteries closer to wide-scale use.