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Hydrate-melt electrolytes for high-energy-density aqueous batteries

Abstract

Aqueous Li-ion batteries are attracting increasing attention because they are potentially low in cost, safe and environmentally friendly. However, their low energy density (<100 Wh kg−1 based on total electrode weight), which results from the narrow operating potential window of water and the limited selection of suitable negative electrodes, is problematic for their future widespread application. Here, we explore optimized eutectic systems of several organic Li salts and show that a room-temperature hydrate melt of Li salts can be used as a stable aqueous electrolyte in which all water molecules participate in Li+ hydration shells while retaining fluidity. This hydrate-melt electrolyte enables a reversible reaction at a commercial Li4Ti5O12 negative electrode with a low reaction potential (1.55 V versus Li+/Li) and a high capacity (175 mAh g−1). The resultant aqueous Li-ion batteries with high energy density (>130 Wh kg−1) and high voltage (2.3–3.1 V) represent significant progress towards performance comparable to that of commercial non-aqueous batteries (with energy densities of 150–400 Wh kg−1 and voltages of 2.4–3.8 V).

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Figure 1: Preparation of a room-temperature hydrate melt.
Figure 2: Structural characterization of the hydrate melt.
Figure 3: Reversibility of Li+ intercalation/de-intercalation reactions.
Figure 4: High-energy-density aqueous Li-ion batteries with Li4Ti5O12 negative electrodes.
Figure 5: Thermodynamic and kinetic factors accounting for the battery operating mechanism.

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Acknowledgements

This work was supported by a JSPS Grant-in-Aid for Specially Promoted Research (No. 15H05701). The calculations in this work were performed on the K computer at the RIKEN AICS and on the Oakleaf-FX at the University of Tokyo with the support of the HPCI Systems Research Projects (Proposal Numbers hp150275 and hp150068) and on the supercomputers at NIMS, ISSP and ITC at the University of Tokyo and Kyushu University.

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Contributions

Y.Y. and A.Y. proposed the concept. Y.Y., K.U. and S.K. designed the experiments. K.U. developed the hydrate melt system and analysed the structures and basic physicochemical/electrochemical properties. S.K. designed the electrochemical cell and performed the cycling tests and the post-mortem electrode analyses. K.S. and Y.T. designed and performed the theoretical calculations. All authors contributed to the discussion. Y.Y. and A.Y. wrote the manuscript. A.Y. supervised the overall project.

Corresponding author

Correspondence to Atsuo Yamada.

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The authors declare no competing financial interests.

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Supplementary Information

Supplementary Figures 1–13, Supplementary Table 1, Supplementary Notes 1–2, Supplementary References (PDF 785 kb)

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Yamada, Y., Usui, K., Sodeyama, K. et al. Hydrate-melt electrolytes for high-energy-density aqueous batteries. Nat Energy 1, 16129 (2016). https://doi.org/10.1038/nenergy.2016.129

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