Printed electronics have been suggested for a wide range of applications. Perhaps one of the most interesting and innovative possibilities is a paper supercapacitor, capable of storing and releasing energy. The capacitor would be both thin and flexible, and ideal for applications ranging from the IoT to building walls.

The Digital Cellulose Center (DCC), a competence center coordinated by RISE Research Institutes of Sweden, has already developed prototypes. The competence center is run by RISE, Linkoping University and KTH Royal Institute of Technology, and has 14 industrial partners. The DCC is working on numerous projects, including sensors, bio-medical devices and energy harvesting. It has also formed spin-outs, including Cellfion, which produces battery membranes from cellulose.

Dr. Jesper Edberg, scientific leader at the Digital Cellulose Center and researcher at RISE Research Institutes of Sweden, spoke about these paper supercapacitors, which utilize cellulose harvested from Sweden’s plentiful forests.

“The aim here is to make sustainable electronics by using materials from forests, which we have a lot of in Sweden,” Dr. Edberg said. “We are looking at how we can use our resources and move away from plastics, so why not make electronics from natural materials? There have been several initiatives – we joined up with companies in the forest and industrial sectors and with funding, we set up this competence center.”

The supercapacitors are a blend of cellulose and electroactive materials which can be formed in a machine that can produce paper. The papers are coated with aluminum, which functions as the device’s current collector as well as a moisture and oxygen barrier. The paper is produced by papermaking equipment, and the circuits are then screenprinted.

“By mixing cellulose and electroactive paticles, we got something similar to paper,” Dr. Edberg reported. “We did see it had some amazing properties, and today we have reached an actual paper that we can make in a paper making machine. It is a thin flexible substrate that can be run through a roll-to-roll process.

“In parallel, we worked on the printed supercapacitors – it’s a mixture of electronic particles and cellulose,” he added. “These capacitors are made on paper, and every layer of the stack has some bio-based materials, even carbon from coconuts. The future goal is to use the papermaking process to make the electrodes, and we can make them thin and flexible.”

Dr. Edberg noted that they are seeing capacitance, and that it is more or less equal to commercial supercapacitors.

“Our supercapacitors store electrical energy,” Dr. Edberg said. “A supercapacitor can’t store as much energy, but it releases it much quicker than a battery. It can be used for a million cycles, and our supercapacitor is renewable and carbon neutral.

“When you are using paper, it is not as stable as plastics, but plastics don’t break down if they end up in landfills,” he noted. “For wearable devices or a sensor on the body, you would want it to energy autonomous, and we have many ways of harvesting energy form the environment, including light and body heat.”

There are plenty of applications that could utilize these supercapacitors.

“We could use these supercapacitors for sustainable buildings to store the solar energy,” Dr. Edberg noted. “You could store energy in these supercapacitors, which can be placed in the walls. We could also think about IoT devices – we can make them very large or very small –and wearable electronics need a power source though. There could also be short-term uses.”

There are challenges that have had to be overcome.

“One of the challenges is they like to absorb water and it starts to mold, but there are many ways of counteracting that,” said Dr. Edberg. “We can make it hydrophobic and flame retardant. There are also other things we need to improve – its lifetime and how long it will last. This is something we are looking at. We also need to do stress tests to simulate aging.”

The next step is to take the prototype to market.

“We have working prototypes, but since we are a research institute, we now need a company to take on this project,” said Dr. Edberg. “We’d like to get a pilot project going with a building company. We have 14 industrial partners in the DCC. The other ways are for an external company to license this technology, or even create a spinout.”