The traditional electrolyte for lithium-ion batteries is a combination of 1 M LiPF6 with a cyclic carbonate-based solvent (for example, ethylene carbonate). The lack of a suitable alternative solvent has hindered further exploration of new functional electrolytes. Here we design and synthesize a fluorinated cyclic phosphate solvent, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane 2-oxide (TFEP), for use in lithium-ion batteries. Our design rationale is that this solvent molecule has a fused chemical structure of cyclic carbonates that can form a stable solid electrolyte interphase and organic phosphates that can trap hydrogen radicals and prevent combustion. An electrolyte formula composed of 0.95 M LiN(SO2F)2 in TFEP/2,2,2-trifluoroethyl methyl carbonate shows excellent non-flammability with zero self-extinguishing time and enables the highly stable operation of graphite anodes (~0.1 V versus lithium) and high-voltage LiNi0.5Mn1.5O4 cathodes (~4.7 V versus lithium), and thereby outperforms traditional electrolytes. This work opens up new frontiers in electrolyte developments towards safe lithium-ion batteries with higher energy densities.
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The datasets generated during and/or analysed during the current study are available from the corresponding author upon reasonable request.
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This work was supported by JSPS KAKENHI Specially Promoted Research (no. 15H05701 to A.Y. and no. 19H05459 to E.N.). Q.Z. is grateful to the Japan Society for the Promotion of Sciences (JSPS) for a JSPS Fellowship at The University of Tokyo (no. P18332) and the Grant-in-Aid for JSPS Fellows (no. 18F18332).
The authors have submitted a patent on this work with JP application No. 2020-24251.
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Supplementary Figs. 1–20 and Table 1.
Flammable test for the electrolyte of 1 M LiPF6 in EC/DMC.
Flammable test for the electrolyte of 0.98 M LiFSI in FEMC.
Flammable test for the electrolyte of 0.95 M LiFSI in TFEP/FEMC.
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Zheng, Q., Yamada, Y., Shang, R. et al. A cyclic phosphate-based battery electrolyte for high voltage and safe operation. Nat Energy 5, 291–298 (2020). https://doi.org/10.1038/s41560-020-0567-z
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