Scientists in Sweden have made a paper-thin material that can act as a supercapacitor. Only 0.5 millimeters (0.02 inches) thick, this jet black “power paper” has the ability to store remarkable amounts of electricity while being light, portable, and even waterproof. This new design is detailed in a study in the journal Advanced Science.
Our entire global infrastructure depends on our capacity to store electricity. Generally speaking, we have two ways of storing it: batteries, and capacitors. Unlike the long-term storage capacity of the former, the latter can absorb, retain and deposit huge amounts of energy in an instant. Supercapacitors typically store around 10 to 100 times the amount of energy of traditional capacitors; they are an essential component of modern electronic systems, from computing to transportation.
Although thin films behaving as supercapacitors aren't new, this is the first time that the material has been produced in true 3D; the thickness of the sheets can be altered at the whim of the scientists. At the thinner end of the scale, the material can be folded into many shapes that can fit into any electrical system that an electrical engineer may desire. The researchers demonstrated this flexibility by folding a sheet of “power paper” into an origami swan.
Image credit: Demonstrating the ability of the “power paper” to take on different shapes and withstand the pull of weights. Malti et al./Advanced Science
In order to construct their supercapacitor, a mixture of renewable cellulose and a readily available plastic polymer were used. High-pressure water was used to break down long cellulose fibers, strands that to begin with only measured 20 nanometers. A solution containing an electrically charged polymer was used to coat the fragmented, smaller fibers, which tangled themselves up somewhat irregularly, leaving spaces between them.
The liquid that permeates these spaces contains electrolytes and thus can conduct electricity. It is the free ability of electrically excited particles (ions) to travel through these liquid-filled pores, and of free electrons to travel through the polymer, that gives the material its remarkable ability to rapidly conduct electricity.
This means that the material can be charged up in only a few seconds, and can last for hundreds of charge cycles, transmitting an electrical current using both ions and electrons. This makes it a rare material called an organic mixed ionic-electronic conductor (MIEC). This highly versatile supercapacitor, according to the authors of the study, has the potential to be made into “giant” volumes using the readily available, sustainably sourced construction materials.
By producing single sheets of “power paper,” rather than attaching multiple, 2D sheets together to make a thicker one, this new material is inherently stronger than its predecessors, which are vulnerable to cracking and breaking. The lattice of plastic polymers means that, although it relies on pore space liquids in order to work, the material itself is actually waterproof.
The only wrinkle in the manufacturing process so far is that, like conventional paper, it has to be dehydrated to make the final sheets. This removes much of the pore space fluids, which will dramatically reduce its ionic conductivity. If this dehydration process can take place in a way that leaves the pore fluids “locked in” to the material, then the research team will have a truly groundbreaking new supercapacitor on their hands.
