Abstract
Current electrolyte design for Li metal anodes emphasizes fluorination as the pre-eminent guiding principle for high Coulombic efficiency (CE) based largely on perceived benefits of LiF in the solid–electrolyte interphase (SEI). However, the lack of experimental techniques that accurately quantify SEI compositional breakdown impedes rigorous scrutiny of other potentially key phases. Here we demonstrate a quantitative titration approach to reveal Li2O content in cycled Li anodes, enabling this previously titration-silent phase to be compared statistically with a wide range of other leading SEI constituents including LiF. Across diverse electrolytes, CE correlates most strongly with Li2O above other phases, reaching its highest values when Li2O particles order along the SEI, demonstrating integrated chemical–structural function. The beneficial role of Li2O was exploited to create entirely fluorine-free electrolytes that breach >99% CE, highlighting electrolyte/SEI oxygenation as an underexplored design strategy.
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Acknowledgements
This work made use of the Massachusetts Institute of Technology (MIT) Materials Research Science and Engineering Center Shared Experimental Facilities, supported by the National Science Foundation under award number DMR-14-19807. This work also made use of the MIT Department of Chemistry Instrumentation Facility. Titration method development was supported in part by an Electrochemical Society–Toyota Young Investigator Award (B.M.G. and K.S.). The Cryo-HRTEM work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under award number DE-SC0022955 (Y.L. and C.W.). We also thank T. Buonassisi, MIT, for helpful discussions regarding the statistical analysis presented herein.
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G.M.H. and B.M.G. conceived the idea and designed the experiments. G.M.H. carried out experiments and measurements. C.W. and Y.L. co-designed Cryo-HRTEM experiments and performed imaging. K.S. assisted with method development. G.M.H. and B.M.G. analysed the data and prepared the initial draft of the paper. All authors discussed the results and contributed to the final version of the paper.
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Source data of all samples used for statistical analysis.
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Source data of all samples used for statistical analysis.
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Source data of all samples used for statistical analysis.
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Integrated NMR data of all samples.
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Source data of all samples used for statistical analysis.
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Source data of all samples used for statistical analysis.
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Hobold, G.M., Wang, C., Steinberg, K. et al. High lithium oxide prevalence in the lithium solid–electrolyte interphase for high Coulombic efficiency. Nat Energy 9, 580–591 (2024). https://doi.org/10.1038/s41560-024-01494-x
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DOI: https://doi.org/10.1038/s41560-024-01494-x
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