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Non-fluorinated electrolyte for high-voltage anode-free sodium metal battery

Nature Sustainability volume 9, pages 306–316 (2026)Cite this article

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Abstract

Abundant sodium (Na) batteries are a sustainable alternative to resource-constrained lithium-ion batteries, offering huge cost advantages. However, developing high-voltage anode-free sodium metal batteries (SMBs) to narrow the energy density gap with lithium-ion batteries is hindered by a critical challenge: existing electrolytes cannot simultaneously achieve ultra-high Na coulombic efficiency and anodic stability. Here we present a rationally designed non-fluorinated electrolyte (1.0 M NaPF6 in 1,2-diethoxyethane/1,2-di-tert-butoxyethane) to address this key limitation, achieving Na coulombic efficiency of >99.95% and anodic stability of >4.8 V. For coin cells (2.0 mAh cm−2, N/P = 1.7), our electrolyte design enables 4.0 V Na | |Na3V2(PO4)3 (NVP) at 5 C and 4.3 V Na | |NaNi0.6Mn0.2Co0.2O2 (NMC622) at 0.3 C for 5,000 and 500 cycles with a capacity retention >80%. Remarkably, the 50 mAh anode-free pouch cells 4.0 V Al | |NVP and 4.3 V Al | |NMC622 also achieve 500 and 300 cycles (retention >75%) with a specific energy of >360 Wh kg(electrode)−1. This work focuses on electrolyte optimization and conceptual advances, whereas critical aspects such as safety, large-scale manufacturability and practical feasibility of SMBs require further investigation. The electrolyte design using non-fluorinated solvents enhances the anodic stability without sacrificing Na efficiency, laying groundwork for advancing low-cost, high-energy SMBs and supporting the transition to sustainable battery technologies.

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Fig. 1: Molecular electrolyte design towards high-voltage glyme-based electrolytes for SMBs.
Fig. 2: Solvation structure of the investigated electrolytes.
Fig. 3: The electrochemical performance of Na metal anode in different electrolytes.
Fig. 4: SMBs full cell performance with NVP cathode.
Fig. 5: SMBs full cell performance with NMC622 cathode.
Fig. 6: Interphase chemistry investigation on the cathode.

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Data availability

The authors declare that the data supporting the findings of this study are available within the article and its Supplementary Information files. Source data are provided with this paper.

Code availability

Gaussian and VASP are commercial codes, RDKIT and CREST are freely available at https://www.rdkit.org and https://crest-lab.github.io/crest-docs/, and a MD simulation code is provided in Supplementary Materials. A specific version of the simulation code is attached as supporting archive to this paper together with the force field files and initial configurations. DFT calculations were performed using Gaussian 16 C.02 package, and VASP 5.4.4. rdkit and Crest were used to sample DME, DBE, TTE conformers.

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Acknowledgements

This work was supported by the US Department of Energy (DOE) under award number DE-EE0008202 (C.W.) at the University of Maryland (UMD) and subcontract number 725470 with Pacific Northwest National Laboratory (PNNL). Modelling work was supported by U.S. Army Combat Capabilities Development Command Army Research Laboratory (DEVCOM ARL) and Center for Research in Extreme Batteries (CREB) (O.B. and T.P.P.). The work at Brookhaven National Laboratory is supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of US DOE through the Advanced Battery Materials Research (BMR) Program under contract number DE-SC0012704 (E.H. and X.-Q.Y.). This research used 28-ID-2 beamline of the National Synchrotron Light Source II, US DOE Office of Science User Facilities, operated for the DOE Office of Science by Brookhaven National Laboratory under contract number DE-SC0012704 (E.H. and X.-Q.Y.).

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Authors and Affiliations

  1. Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD, USA

    Ai-Min Li, Zeyi Wang, Nan Zhang & Chunsheng Wang

  2. Battery Science Branch, DEVCOM Army Research Laboratory, Adelphi, MD, USA

    Travis P. Pollard & Oleg Borodin

  3. Pacific Northwest National Laboratory, Richland, WA, USA

    Fred Omenya & Xiaolin Li

  4. Chemistry Division, Brookhaven National Laboratory, Upton, NY, USA

    Sha Tan, Enyuan Hu & Xiao-Qing Yang

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Contributions

A.-M.L. and C.W. conceived the idea for the project and wrote the paper. O.B. and T.P.P. conducted and analysed the DFT calculations and MD simulations, and participated in the paper revision and mechanism identification. Z.W. assisted with DFT analysis. N.Z. helped with Raman data collection. F.O. and X.L. helped with the NMC622 cathode preparation and discussion. S.T., E.H. and X.-Q.Y. helped with synchrotron data collection and analysis. All authors participated in discussion of the paper.

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Correspondence to Oleg Borodin or Chunsheng Wang.

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Li, AM., Pollard, T.P., Wang, Z. et al. Non-fluorinated electrolyte for high-voltage anode-free sodium metal battery. Nat Sustain 9, 306–316 (2026). https://doi.org/10.1038/s41893-025-01710-w

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