Multistage redox reactions of conductive-polymer nanostructures with lithium ions: potential for high-performance organic anodes

Conducive polymers have a wide range of applications originating from their π-conjugated systems. The redox reactions of conductive polymers with doping and dedoping of anions have been applied to cathodes for charge storage. In contrast, the redox reactions with cations have not been fully studied in anodes for charge storage. Here, we found that the nanostructures of conductive polymers, such as polypyrrole (PPy) and polythiophene (PTp) derivatives, have reversible redox reactions with cations. The PPy and PTp nanostructures acted as anodes with specific capacities of 157 and 44.4 mA h g–1, respectively, at a current density of 20 mA g–1. The introduction of a carboxy group to the pyrrole and thiophene rings enhanced the specific capacities up to 730 and 963 mAh g–1, respectively. The enhanced electrochemical properties were not observed in the bulk-size conductive polymers. The results suggest that conductive-polymer nanostructures have potential for developing metal-free, high-performance charge storage devices. A targeted synthesis of nanoscale conductive polymers can help designers make the switch to organic anode materials for rechargeable lithium batteries. Yuya Oaki and colleagues from Keio University in Yokohama, Japan, report that modifying nanoscale conductive polymers with carbonyl groups can improve how these organic materials store and extract energy from lithium ions. Initial tests with nanoscale polypyrrole and polythiophene compounds revealed these polymers could act as anodes and store lithium ions into their ring-based frameworks through a series of reversible redox reactions. Adding carbonyl groups to these polymers boosted the lithium-storage capacity of these anodes by up to 5-fold—an enhancement, they suggest, which arises from better access to unoccupied polymer energy states. The absence of anode-like behavior in bulk forms of the conducting polymers highlights the importance of nanoscale morphologies. Conductive polymers have the overlooked electrochemical properties. Nanostructures of conductive polymers, such as polypyrrole (PPy) and polythiophene (PTp) derivatives, showed the reversible redox reactions with multiple lithium ions for application to high-performance anode of lithium-ion battery. The PPy and PTp with the carboxy substituents have the enhanced specific capacity up to 730 and 963 mAh g–1, respectively.