High-Performance Energy Storage Polymers for Lithium-Ion Batteries

Redox-active organic materials are promising for energy storage due to their low cost, versatility, and favorable mechanical properties. However, organic materials generally exhibit lower specific, volumetric, and areal capacities compared with intercalation layered transition metal oxides. Here, we show that side-chain engineering of redox-active conjugated polymers significantly increases charge storage capacity. We studied a series of conjugated polymers with varying contents of oligo(ethylene glycol) (EG) side-chains and found that the EG side-chains increased ionic and electronic conductivities in nanocomposite and pure polymer electrodes. This led to improved rate performance, with 85 % capacity retention at 200C, and increased capacities in thick electrodes. The EG side-chains also enabled nanocomposite electrodes with a much higher content of redox-active polymer, including pure polymer electrodes with significant electrochemical activity. Finally, the EG side-chains led to additional charge storage processes. Altogether, these findings demonstrate that side-chain engineering is a powerful approach to improving the specific, volumetric, and areal capacities of organic electrodes based on redox-active conjugated polymers.