The new bendable supercapacitor made from graphene, which charges quickly and safely, and stores a record-high level of energy for use over a long period. Photo: Dr Zhuangnan Li (UCL).
The new bendable supercapacitor made from graphene, which charges quickly and safely, and stores a record-high level of energy for use over a long period. Photo: Dr Zhuangnan Li (UCL).

A new bendable supercapacitor made from graphene, which charges quickly and can safely store a record-high level of energy for use over a long period, has been developed and demonstrated by researchers at University College London (UCL) in the UK and the Chinese Academy of Sciences.

While still at the proof-of-concept stage, the new supercapacitor shows enormous potential as a portable power supply for several practical applications, including electric vehicles, phones and wearable technology. The discovery, reported in a paper in Nature Energy, overcomes the issue usually faced by high-powered, fast-charging supercapacitors – that they cannot hold a large amount of energy in a small space.

"Our new supercapacitor is extremely promising for next-generation energy storage technology as either a replacement for current battery technology, or for use alongside it, to provide the user with more power," said UCL’s Zhuangnan Li, first author of the paper. "We designed materials which would give our supercapacitor a high-power density – that is how fast it can charge or discharge – and a high energy density – which will determine how long it can run for. Normally, you can only have one of these characteristics, but our supercapacitor provides both, which is a critical breakthrough.

"Moreover, the supercapacitor can bend to 180° without affecting performance and doesn't use a liquid electrolyte, which minimizes any risk of explosion and makes it perfect for integrating into bendy phones or wearable electronics."

A team of chemists, engineers and physicists worked on the new design, which uses an innovative graphene electrode material with pores that can be changed in size to store charge more efficiently. This tuning maximizes the energy density of the supercapacitor to a record 88.1Wh/L (Watt-hour per liter), which is the highest ever reported energy density for carbon-based supercapacitors.

Similar fast-charging commercial technology has a relatively poor energy density of 5–8Wh/L while traditional slow-charging but long-running lead-acid batteries used in electric vehicles typically have 50–90Wh/L. While the supercapacitor developed by the team has a comparable energy density to state-of-the-art lead-acid batteries, its power density is two orders of magnitude higher at over 10,000 Watt per liter.

"Successfully storing a huge amount of energy safely in a compact system is a significant step towards improved energy storage technology," said Ivan Parkin, dean of Mathematical & Physical Sciences at UCL and senior author of the paper. "We have shown it charges quickly, we can control its output and it has excellent durability and flexibility, making it ideal for development for use in miniaturized electronics and electric vehicles. Imagine needing only 10 minutes to fully charge your electric car, or a couple of minutes for your phone and it lasting all day."

The researchers made electrodes from multiple layers of graphene, creating a dense but porous material capable of trapping charged ions of different sizes. They characterized it using a range of techniques and found it performed best when the pore sizes matched the diameter of the ions in the electrolyte.

The optimized material, which forms a thin film, was used to build a proof-of-concept device with both a high-power density and high-energy density. The 6cm x 6cm supercapacitor was made from two identical electrodes layered either side of a gel-like substance that acted as a chemical medium for the transfer of electrical charge.

This supercapacitor was used to power dozens of light-emitting diodes (LEDs) and was found to be highly robust, flexible and stable. Even when bent at 180°, it performed almost the same as when it was flat, and after 5,000 cycles it retained 97.8% of its capacity.

"Over the next 30 years, the world of intelligent technology will accelerate, which will greatly change communication, transportation and our daily lives," said Feng Li from the Chinese Academy of Sciences, another senior author of the paper. "By making energy storage smarter, devices will become invisible to us by working automatically and interactively with appliances. Our smart cells are a great example of how the user experience might be improved and they show enormous potential as portable power supply in future applications."

This story is adapted from material from UCL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.