Abstract
A major impediment to Li–O2 battery commercialization is the low discharge capacities resulting from electronically insulating Li2O2 film growth on carbon electrodes. Redox mediation offers an effective strategy to drive oxygen chemistry into solution, avoiding surface-mediated Li2O2 film growth and extending discharge lifetimes. As such, the exploration of diverse redox mediator classes can aid the development of molecular design criteria. Here we report a class of triarylmethyl cations that are effective at enhancing discharge capacities up to 35-fold. Surprisingly, we observe that redox mediators with more positive reduction potentials lead to larger discharge capacities because of their improved ability to suppress the surface-mediated reduction pathway. This result provides important structure–property relationships for future improvements in redox-mediated O2/Li2O2 discharge capacities. Furthermore, we applied a chronopotentiometry model to investigate the zones of redox mediator standard reduction potentials and the concentrations needed to achieve efficient redox mediation at a given current density. We expect this analysis to guide future redox mediator exploration.
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Source data for figures in the main text have been uploaded to the Figshare public data repository and can be accessed at https://doi.org/10.6084/m9.figshare.21719882 (ref. 61). Source data are provided with this paper.
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Acknowledgements
K.D.G. acknowledges the support of the National Science Foundation and grant NSF 1954298. K.A. and L.A.C. thank the US Department of Energy for support under contract no. DE-AC02-06CH11357 from the Vehicle Technologies Office, which helped support the work done at ANL. We gratefully acknowledge the computing resources provided on Bebop, a high-performance computing cluster operated by the Laboratory Computing Resource Center (LCRC) at ANL. We also acknowledge the Electron Microscopy Core (EMC) at UIC’s Research Resource’s Center (RRC), where a substantial amount of post-discharge characterization was performed.
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E.J.A., M.R.Z., R.A., K.A. and K.D.G. helped with the conception of this manuscript. E.J.A., M.R.Z. and L.A.C. performed the DFT evaluations and analysis of redox mediators. E.J.A. performed the CV experiments and analysis. E.J.A. performed the battery discharge experiments and analysis. E.J.A. and R.A. performed the post-discharge product characterization. E.J.A. and M.L. performed the DEMS experiments and analysis. E.J.A. and K.D.G. analysed crucial data and wrote the manuscript.
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Supplementary Information
Supplementary discussion, Figs. 1–17, scheme 1 and Tables 1–6.
Supplementary Data 1
Additional redox mediator CV data.
Supplementary Data 2
CV and UV–vis titration data for chemically and electrochemically derived RO–OR species.
Supplementary Data 3
CV data for outer-sphere redox mediation experiments.
Supplementary Data 4
CV data for the Li+-coupling of outer-sphere redox mediation.
Supplementary Data 5
Scan rate-dependent peak CV current data.
Supplementary Data 6
CV data fitting in Ar-purged solutions.
Supplementary Data 7
CV data fitting in O2-saturated solutions.
Supplementary Data 8
Battery discharge data for Li anodes.
Supplementary Data 9
R+ concentration-dependent battery discharge data with LFP anodes.
Supplementary Data 10
R+ concentration-dependent battery discharge data with Li anodes.
Supplementary Data 11
Baseline and redox-mediated DEMS data.
Supplementary Data 12
Post discharge Raman data.
Supplementary Data 13
Data for comparison between extracted bimolecular rate constants and redox-mediated battery discharge capacity.
Supplementary Data 14
Unprocessed SEM image from pristine electrode.
Supplementary Data 15
Unprocessed SEM image from discharged electrode.
Supplementary Data 16
Unprocessed SEM image from discharged electrode.
Supplementary Data 17
Unprocessed SEM image from discharged electrode.
Supplementary Data 18
Unprocessed SEM image from discharged electrode.
Supplementary Data 19
Unprocessed SEM image from discharged electrode.
Supplementary Data 20
Unprocessed SEM image from discharged electrode.
Supplementary Data 21
Unprocessed SEM image from discharged electrode.
Source data
Source Data Fig. 2
Output energies (Ha) from DFT calculations of R+, R• and RO–OR.
Source Data Fig. 3
CVs presented in Fig. 3.
Source Data Fig. 4
Battery discharge curves presented in Fig. 4.
Source Data Fig. 5
Extracted kinetic rate constants and battery discharge values compared in Fig. 5.
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Askins, E.J., Zoric, M.R., Li, M. et al. Triarylmethyl cation redox mediators enhance Li–O2 battery discharge capacities. Nat. Chem. 15, 1247–1254 (2023). https://doi.org/10.1038/s41557-023-01268-0
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DOI: https://doi.org/10.1038/s41557-023-01268-0
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