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Non-flammable electrolytes with high salt-to-solvent ratios for Li-ion and Li-metal batteries

Abstract

Non-flammable electrolytes could intrinsically eliminate fire hazards and improve battery safety, but their compatibility with electrode materials, especially graphite anodes, remains an obstacle owing to the strong catalytic activity of the anode surfaces. Here, we report an approach that improves the stability of non-flammable phosphate electrolytes by adjusting the molar ratio of Li salt to solvent. At a high Li salt-to-solvent molar ratio (~1:2), the phosphate solvent molecules are mostly coordinated with the Li+ cations, and the undesired reactivity of the solvent molecules toward the graphite anode can be effectively suppressed. High cycling Coulombic efficiency (99.7%), good cycle life and safe operation of commercial 18650 Li-ion cells with these electrolytes are demonstrated. In addition, these non-flammable electrolytes show reduced reactivity toward Li-metal electrodes. Non-dendritic Li-metal plating and stripping in Li–Cu half-cells are demonstrated with high Coulombic efficiency (>99%) and good stability.

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Fig. 1: Electrochemical performance of graphite anode.
Fig. 2: Electrochemical behaviour with a LiCoO2 cathode and a 18650 cell.
Fig. 3: Optical and SEM images of the Li-metal plating, and electrochemical performance of Li-metal plating and stripping on Cu substrates.
Fig. 4: Raman analysis of LiFSI–TEP electrolyte.
Fig. 5: Characterization of solution structure.

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Acknowledgements

The main idea of the paper was jointly developed by Wuhan University and Pacific Northwest National Laboratory (PNNL), with support from the US Department of Energy, Office of Science, Basic Energy Sciences, Division of Materials Sciences and Engineering, under award KC020105-FWP12152 and by the National Key Research Program of China (no. 2016YFB0100200) and the National Nature Science Foundation of China (nos. 21673165 and 21333007). The NMR testing was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Division of Materials Sciences and Engineering, under award KC020105-FWP12152. Simulations were performed using PNNL Institutional Computing Resources. PNNL is operated by Battelle for the US Department of Energy under contract no. DE-AC05-76RL01830. The electrochemical study was supported by Wuhan University, and supported by the National Key Research Program of China (no. 2016YFB0100200) and the National Nature Science Foundation of China (nos. 21673165 and 21333007). The preparation of 18650 cells was supported by EVE Energy Co. Ltd. The safety tests were supported by the staff of the Battery Safety Laboratory of BST Power (Shenzhen) Limited.

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J.L., L.X. and Y.C. conceived the idea of the high-molar-ratio non-flammable electrolyte. Z.Z. and X.J. synthesized a series of non-flammable electrolytes and carried out the electrochemical measurements of the electrode materials and 18650 cells. K.S.H. and L.X. conducted NMR measurements. V.M. conducted DFT calculations. Z.Z., L.X., Y.C. and J.L. participated in the manuscript writing. X.A., H.Y., J.-G.Z. and M.L.S. provided advice and helped in editing the manuscript. All authors participated in the analysis of the experimental data, the discussions of the results and the preparation of the paper.

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Correspondence to Yuliang Cao, Lifen Xiao or Jun Liu.

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Zeng, Z., Murugesan, V., Han, K.S. et al. Non-flammable electrolytes with high salt-to-solvent ratios for Li-ion and Li-metal batteries. Nat Energy 3, 674–681 (2018). https://doi.org/10.1038/s41560-018-0196-y

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