Individual pieces of graphene have some pretty amazing properties, but finding a way to produce bulk materials that make good use of those properties has been rather challenging. Now, researchers have figured out a way to make graphene-based electrodes in bulk through a process so simple that it can be adapted to the manufacturing techniques that we currently use to make paper. And the resulting capacitors, at least in these test cases, had storage capacities that approached those of lead-acid batteries.

Those of us who have taken basic physics tend to think of capacitors as two parallel, charge-holding plates, since that's how they're taught to us. But electrochemical capacitors perform a similar trick on a much smaller scale by having the charges held by individual ions that absorb to an electrode. To boost capacity, the simplest thing to do is to increase the surface area for the ions to interact with. That's why graphene seems so appealing; since it's only a single atom thick, it should be possible to stick a tremendous amount of surface into a relatively small volume.

The problem, however, has been getting the ions into the graphene itself in order for them to interact. Once the graphene is prepared, lots of factors like pore size and inter-sheet spacing come into play, since these control how quickly ions can get into the graphene. A team at Australia's Monash University came up with an easy solution to this: put the ions in place during the manufacturing process.

The idea is to do solution-based processing of graphene oxide to form graphene, and then add a mixture of electrolyte and a volatile solvent to the mix. Once the graphene is formed and compressed, it's possible to start evaporating off the volatile solvent. As the process procedes, capillary action will gradually draw out more and more liquid, eventually compressing the graphene down so that there's only enough space between the layers to hold a thin film of electrolyte. The end result is a material with a packing density that's about double that of traditional porous carbon, an electrode material often used in capacitors.

The resulting material displays all the electrical properties associated with a capacitor, meaning that it can charge and discharge its full capacity almost instantly. But it has a storage density that's right at the low-end of the range seen in lead-acid batteries. It's also stable over multiple charge/discharge cycles and holds on to 90 percent of its capacity even after being charged for 300 hours straight.

The material's most promising feature, however, is the fact that it can be made with some simple solution-based processing. The authors suggest it can be made in bulk with some simple modifications to the process we use to make paper; the end result also seems to be about as flexible as paper (although it's completely black). As always, there will almost certainly be bumps in the road as the material is put to use, and this may very well not be the ultimate solution to our energy storage needs. But it's an appealingly simple one that seems to make a lot of sense.

Science, 2013. DOI: 10.1126/science.1239089 (About DOIs).