Metal-free aqueous batteries can potentially address the projected shortages of strategic metals and safety issues found in lithium-ion batteries. More specifically, redox-active non-conjugated radical polymers are promising candidates for metal-free aqueous batteries because of the polymers’ high discharge voltage and fast redox kinetics. However, little is known regarding the energy storage mechanism of these polymers in an aqueous environment. The reaction itself is complex and difficult to resolve because of the simultaneous transfer of electrons, ions and water molecules. Here we demonstrate the nature of the redox reaction for poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl acrylamide) by examining aqueous electrolytes of varying chao-/kosmotropic character using electrochemical quartz crystal microbalance with dissipation monitoring at a range of timescales. Surprisingly, the capacity can vary by as much as 1,000% depending on the electrolyte, in which certain ions enable better kinetics, higher capacity and higher cycling stability.
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The experimental work was supported by grant DE-SC0014006 funded by the US Department of Energy, Office of Science (T.M., R.M.T. and J.L.L.). The MD simulation work was supported by grant NSF-DMR-2119672 funded by the National Science Foundation, and the Texas A&M Institute for Data Science Career Initiation Fellowship (C.-H.L. and D.P.T.). The use of the Texas A&M University Soft Matter Facility (RRID:SCR_022482) and contribution of P. Wei are acknowledged.
The authors declare no competing interests.
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Supplementary Tables 1–4, Figs. 1–45, discussions, references, PTAm synthesis, DFT computational details, MD computational details, kinetic investigations, Jones–Dole B coefficient, EQCM-D details, current collector|polymer film|electrolyte model, equations for anion and cation transfer in the PTAm reaction mechanism, and EIS calculations.
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Ma, T., Li, CH., Thakur, R.M. et al. The role of the electrolyte in non-conjugated radical polymers for metal-free aqueous energy storage electrodes. Nat. Mater. 22, 495–502 (2023). https://doi.org/10.1038/s41563-023-01518-z