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Asymmetric ether solvents for high-rate lithium metal batteries

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Abstract

Recent electrolyte solvent design based on weakening lithium-ion solvation have shown promise in enhancing cycling performance of Li-metal batteries. However, they often face slow redox kinetics and poor cycling reversibility at high rate. Here we report using asymmetric solvent molecules substantially accelerates Li redox kinetics. Asymmetric ethers (1-ethoxy-2-methoxyethane, 1-methoxy-2-propoxyethane) showed higher exchange current densities and enhanced high-rate Li0 plating/stripping reversibility compared to symmetric ethers. Adjusting fluorination levels further improved oxidative stability and Li0 reversibility. The asymmetric 1-(2,2,2-trifluoro)-ethoxy-2-methoxyethane, with 2 M lithium bis(fluorosulfonyl)imide, exhibited high exchange current density, oxidative stability, compact solid–electrolyte interphase (~10 nm). This electrolyte exhibited superior performance among state-of-the-art electrolytes, enabling over 220 cycles in high-rate Li (50 μm)||LiNi0.8Mn0.1Co0.1O2 (NMC811, 4.9 mAh cm−2) cells and for the first time over 600 cycles in anode-free Cu | |Ni95 pouch cells (200 mAh) under electric vertical take-off and landing cycling protocols. Our findings on asymmetric molecular design strategy points to a new pathway towards achieving fast redox kinetics for high-power Li-metal batteries.

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Fig. 1: Design of asymmetric solvent molecule for high-rate performance Li-metal batteries.
Fig. 2: Effect of solvent asymmetry on lithium-metal compatibility–optimization of non-fluorinated backbone structure.
Fig. 3: Investigation on the different degree of fluorination on EME.
Fig. 4: Comparison of electrolyte properties and high-rate Li0 plating/stripping reversibility between FxEME and FxDEE.
Fig. 5: Proposed mechanism of asymmetric ether solvents showing fast redox kinetic.
Fig. 6: High-rate LMBs full-cell cycling with FxEME and FxDEE electrolytes.
Fig. 7: Superior high-rate LMBs performance of F3EME electrolyte and its practicality tests using eVTOL protocol.

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All relevant data are included in the paper and its Supplementary Information. Source data are provided with this paper.

Code availability

The code and data used to determine dipole orientations is available at https://github.com/Adi1008/asymmetric-solvents.

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Acknowledgements

We acknowledge support from the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the US Department of Energy (DOE) under the Battery Materials Research (BMR) Program and Battery 500 Consortium. The cryo-TEM work was supported by the US DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under contract DE-AC02-76SF00515. Part of this work was performed at the Stanford Nano Shared Facilities (SNSF), supported by the National Science Foundation under award ECCS-2026822. DFT calculations and MD simulations were conducted on the Sherlock cluster, operated by Stanford University and the Stanford Research Computing Center, to whom we would like to express our gratitude for their computational resources and support. I.R.C. acknowledges support from Stanford Graduate Fellowship (SGF) and SBS Foundation Fellowship for graduate studies at Stanford University. A.S. is grateful for support from the NSF Graduate Research Fellowship and SGF. S.C.K. acknowledges support from Stanford Energy Postdoctoral Fellowship.

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Authors

Contributions

I.R.C., Z.B. and Y. Cui conceived the idea. I.R.C. conducted the experiments and analysed the results under the guidance of Z.B., Y. Cui, and J.Q. I.R.C. performed synthesis, electrochemical measurements and materials characterization. Y. Chen carried out DOSY NMR. J.F. measured XPS measurements and GEIS. H.L. performed FIB-SEM and made UME. E.Z. performed H2O titration techniques and viscosity measurements. C.S. conducted cryo-TEM. J.H. and A.S. carried out the DFT and MD simulations. J.H.L. conducted SEM images. Y.L. and I.R.C. synthesized and provided EME, MPE and FxEME. S.C.K. and I.R.C. measured solvation energies and entropy. H.P. measured 13C, 19F-NMR and heteronuclear single quantum coherence for solvents. P.Z., and J.L. provided technical help and helpful discussions. I.R.C., Y. Chen, A.S., J.Q., Y. Cui and Z.B. cowrote and revised the manuscript.

Corresponding authors

Correspondence to Jian Qin, Yi Cui or Zhenan Bao.

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Competing interests

Z.B., Y. Cui and I.R.C. declare that this work has been filed as US Provisional Patent Application No. 63/689,564 and some molecules in this work have been included in previously filed International Application No. PCT/US2022/047472. A license related to PCT/US2022/047472 has been assigned to Feon Energy, Inc., in which Z.B. and I.R.C. owns equity. The remaining authors declare no competing interests.

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Nature Energy thanks Kai Liu and the other, anonymous, reviewer for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–71 and Tables 1–7.

Supplementary Video 1

Flammability test.

Source data

Source Data Fig. 2

Li || Cu cycling performance data, voltage profile.

Source Data Fig. 3

Voltage profile, Li || Cu cycling performance data, statistical source data, Li || NMC full-cell cycling performance data.

Source Data Fig. 4

Statistical source data, Li || Cu cycling performance data, voltage profile.

Source Data Fig. 5

Statistical source data.

Source Data Fig. 6

Full-cell cycling performance data.

Source Data Fig. 7

Full-cell cycling performance data.

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Choi, I.R., Chen, Y., Shah, A. et al. Asymmetric ether solvents for high-rate lithium metal batteries. Nat Energy 10, 365–379 (2025). https://doi.org/10.1038/s41560-025-01716-w

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