Real-time insight into the doping mechanism of redox-active organic radical polymers

Abstract

Organic radical polymers for batteries represent some of the fastest-charging redox active materials available. Electron transport and charge storage must be accompanied by ion transport and doping for charge neutrality, but the nature of this process in organic radical polymers is not well understood. This is difficult to intuitively predict because the pendant radical group distinguishes organic radical polymers from conjugated, charged or polar polymers. Here we show for the first time a quantitative view of in situ ion transport and doping in organic radical polymers during the redox process. Two modes dominate: doping by lithium ion expulsion and doping by anion uptake. The dominance of one mode over the other is controlled by anion type, electrolyte concentration and timescale. These results apply in any scenario in which electrolyte is in contact with a non-conjugated redox active polymer and present a means of quantifying doping effects.

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Fig. 1: Schematic of the PTMA redox reaction.
Fig. 2: Comparison of in situ EQCM-D and cyclic voltammetry for varying scan rates.
Fig. 3: Δm/e and doping for various electrolytes.
Fig. 4: Three modes of anionic doping in a swollen PTMA electrode.
Fig. 5: Anionic doping in low-concentration electrolyte.

Data availability

The datasets collected and analysed in the current study are included in the Supplementary Information and/or are available from the corresponding author upon request.

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Acknowledgements

This work was supported by grant DE-SC0014006 funded by the US Department of Energy, Office of Science. We acknowledge A. Jaiswal and M. C. Dixon from Biolin Scientific Inc. for their help with analysing the EQCM-D data. We thank J. Ketter from Gamry Instruments for his help with analysing the cyclic voltammetry data. We thank W. Mustain of the University of South Carolina and E.-S. Oh of University of Ulsan for discussions.

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J.L.L and F.L. conceived the study. F.L. developed experimental procedures. S.W. planned and carried out the experiments and analysed the data. A.D.E. performed the comparison experiments and corrected the voltage in cyclic voltammetry using ferrocene as the internal standard. All authors discussed the results. S.W. and J.L.L wrote the manuscript with input from all authors.

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Correspondence to Jodie L. Lutkenhaus.

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Supplementary Figures 1–4, Supplementary Tables 1–3

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Wang, S., Li, F., Easley, A.D. et al. Real-time insight into the doping mechanism of redox-active organic radical polymers. Nature Mater 18, 69–75 (2019). https://doi.org/10.1038/s41563-018-0215-1

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