Aqueous interphase formed by CO2 brings electrolytes back to salt-in-water regime

Super-concentrated water-in-salt electrolytes make high-voltage aqueous batteries possible, but at the expense of high cost and several adverse effects, including high viscosity, low

conductivity and slow kinetics. Here, we observe a concentration-dependent association between CO2 and TFSI anions in water that reaches maximum strength at 5 mol kg−1 LiTFSI. This TFSI–CO2

complex and its reduction chemistry allow us to decouple the interphasial responsibility of an aqueous electrolyte from its bulk properties, hence making high-voltage aqueous Li-ion

batteries practical in dilute salt-in-water electrolytes. The CO2/salt-in-water electrolyte not only inherits the wide electrochemical stability window and non-flammability from

water-in-salt electrolytes but also successfully circumvents the numerous disadvantages induced by excessive salt. This work represents a deviation from the water-in-salt pathway that not

only benefits the development of practical aqueous batteries, but also highlights how the complex interactions between electrolyte components can be used to manipulate interphasial

chemistry.

All the data generated or analysed during this study are included in this article and its Supplementary Information. The details of the molecular dynamics simulation are available in

Supplementary Data 1. Source data are provided with this paper.

All authors except K.X. acknowledge the support of the National Natural Science Foundation of China (51872322) and the Center for Clean Energy. J.Z., M.C. and G.F. thank the Hubei Provincial

Natural Science Foundation of China (2020CFA093) and the Program for Huazhong University of Science and Technology, Academic Frontier Youth Team. K.X. thanks the Joint Center of Energy

Storage Research, an energy hub funded by the US Department of Energy, Basic Energy Sciences, for support.

Beijing Advanced Innovation Center for Materials Genome Engineering, Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Beijing National

Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China

Jinming Yue, Yuxin Tong, Lilu Liu, Liwei Jiang, Tianshi Lv, Yong-sheng Hu, Hong Li, Xuejie Huang, Lin Gu, Liumin Suo & Liquan Chen

Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, China

Jinming Yue, Yuxin Tong, Liwei Jiang, Tianshi Lv & Liumin Suo

State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, China

Battery Science Branch, Sensor and Electron Devices Directorate, US Army Research Laboratory, Adelphi, MD, USA

Yangtze River Delta Physics Research Center Co. Ltd, Liyang, China

L.S. and K.X. conceived the idea. J.Y. and L.S. designed the experiments. J.Y. performed the material preparation, electrochemical measurements and data analysis. L.J. performed the NMR

measurements. Y.T. collected the TEM images, and L.L. measured the XPS spectra. T.L. performed the cost analysis of the electrolyte. J.Z., M.C. and G.F. performed the molecular dynamics

simulations and analysed the data. J.Y., G.F., K.X. and L.S. wrote the manuscript. All authors discussed the results and commented on the manuscript.

Peer review information Nature Chemistry thanks Jin Han and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary Figs. 1–39, Tables 1–3 and experimental details.

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