Redox-active conjugated polymers are an emerging class of organic charge storage materials for lithium-ion batteries. These materials are expected to have fast electron transfer kinetics and high stability. The long polymer chains prevent dissolution of the redox active species while the π-conjugated polymer backbone provides a high conductivity path linking the localized redox moieties. The high electronic conductivity provided by the conjugated polymer backbone enables fast electron transfer kinetics improving capacity retention at high rates of charge and discharge. Redox moieties with fast and reversible stable redox activity and high redox potentials with respect to the Li+/Li redox need to be chosen to design these polymers for use as cathodes in Li-ion batteries. Herein, we propose diketopyrrolopyrrole (DPP) as a suitable building block for the development of redox-active conjugated polymers. The electron deficient nature of the DPP moiety enables high redox potentials (&gt; 2V vs. Li+/Li). Further, the redox active carbonyl groups provide stable and fast redox activity. In this work, we show stable cycling of DPP-based π-conjugated redox polymers as Li-ion cathodes with less than 6% fade in capacity over 1000 cycles along with very good rate performance (70% capacity retention at 500C). The DPP-based cathodes have an average potential of ~2.2 V with respect to Li+/Li along with ~100% of the theoretical capacities being accessible at reasonably high rates. We also explore the role of the sidechain on the performance of the polymers. We demonstrate that these polymers could potentially find applications as cathode materials for other ion-intercalation chemistries, for example, Na-ion batteries. Our results set an encouraging precedent for the design of versatile, high energy density and long-life charge storage materials based on DPP-based redox-active conjugated polymers.

Diketopyrrolopyrrole-based redox active π-conjugated polymers as high-rate lithium-ion cathodes

ACS Spring Meeting 2021

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