The first bio-derived pendant polymer cathode for lithium-ion batteries has been developed by researchers in Canada (Schon et al., Adv. Funct. Mater., (2016) DOI: 10.1002/adfm.201602114). The team has used a flavin molecule derived from vitamin B2, also known as riboflavin, as the redox-active energy storage unit and suggests that it could represent a sustainable way to make high-performance rechargeable batteries for a wide range of applications. The team's semi-synthetic route to the requisite pendant polymer in which two flavin units are coupled to a poly(norbornene) backbone allows for a high capacity and high voltage system to be built with a minimal number of synthetic steps.

According to Tyler Schon, Andrew Tilley, Colin Bridges, Mark Miltenburg, and Dwight Seferos of the University of Toronto, the growth in portable electronic gadgets and the emergence of the Internet of Things will increasingly require inexpensive, flexible, and versatile power sources to accommodate future device energy requirements. Unfortunately, current batteries use transition metal-based cathodes that need energy-intensive processing and extraction methods, all of which is less than environmentally benign. Moreover, about one third of the cost of such batteries, whether powering a smart phone or an electric smart car, is due to the metal oxide or phosphate cathode material.

The researchers explain that a lithium-ion battery built with their bio-derived polymer has a capacity of 125 milliamp hours per gram and an operational voltage of about 2.5 volts. Charge transport within the battery can be improved by forming hierarchical structures of the polymer with carbon black. The team also adds that preliminary experiments have offered new insights into the mechanisms that underlie electrode degradation and should help inform the design of polymer electrodes in general.

Redox active organic molecules have a high theoretical capacity, are low density, but strong materials, with tunable electronic properties. The polymers derived from a redox active molecule seem to be even more suited to a role in lithium-ion batteries than the small molecule systems. As such, "Our proposed new concept of using biologically derived polymers to store energy is an attractive strategy to address these issues," Seferos told Materials Today. "We have identified a very similar polymer that is stable at high capacity and is able to avoid degradation," Seferos adds. "We plan to make flexible batteries with this polymer. We hope to also extend this methodology to other redox-active bio-molecules in order to build a library of bio-derived electrode materials." He adds that the next step will be to extend this work towards flexible devices that can conform to the form factors required in many different applications."

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".