Scientists from Germany and Japan are using a porous polymer framework to potentially double the amount of energy that can be stored in lithium-ion batteries.
When batteries were built with lithium, the lightest of all metals, it was a breakthrough, opening a new realm of compact and portable electronic devices. But the applications are limited as power demands increase and transition metals the batteries use are becoming increasingly scarce, reports Chemistry World.
Ken Sakaushi of the Dresden University of Technology believes he has a solution to both problems. He and his team developed a novel energy storage principle for a cathode based on a porous organic polymer framework material.
In a traditional lithium battery, electrons transfer from the anode to the cathode by reducing a positive charge (p-doping) or creating a negative charge (n-doping) within the cathode, while there are corresponding movements of either anions or cations, respectively.
“Our idea is to combine these into one process,” Sakaushi says. “It uses both anions and cations to transfer electrons during the discharge.”
The key to the development was an idea to use a triazine-based polymer as the cathode material. Triazine — an organic chemical similar to a six-member benzene ring but with three carbon atoms replaced by nitrogen — has an electrical behavior that makes it uniquely suited for better energy storage because it can exist both in p-doped and n-doped states. “The most important feature of our cathode is a continuous, linear transition between these states during charge and discharge,” Sakaushi says, which doubles the capacity when compared with traditional cathodes.
Another advantage of the polymeric framework is that it gives precise control over the pore size and distribution to deliver high-surface area and allow for rapid transport of the ions into and out of the electrode. “These are very interesting materials,” says Laurence Hardwick from the University of Liverpool in the United Kingdom. “People are now trying to use them in applications such as energy storage — this is the first or second paper in this area. It’s a very interesting, novel approach for ion storage in this class of solids.”
John Owens, a professor of electrochemistry at the University of Southampton, U.K., says the development is an important step toward realizing the benefits of organic polymers. “Nickel and cobalt are good for energy storage, but they’re becoming expensive… [T]his doesn’t use any mineral resource, so it’s sustainable in that respect. And it’s easy to make.”
Sakaushi wants to continue his research with the new materials. “First of all, we have to find out how the ions are stored in the polymer,” he says. “The polymeric frameworks also have honeycomb structures, so they might inherit some features of graphene.’
Dale McGeehon has been a journalist and editor for more than 25 years, covering chemical regulation and testing for Pesticides and Toxic Chemical News and innovations in material sciences for the National Technology Transfer Center. His writing credits include Omni and College Park magazines and The New York Times.