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

Nature Energy volume 1, Article number: 16129 (2016) Cite this article

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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).

There is a growing demand for rechargeable batteries that are high energy density and retain a high level of safety1,2,3. Lithium-ion batteries have relied to date on non-aqueous electrolytes (with wide potential windows)4,5 in combination with low-potential and high-capacity negative electrodes, for example, graphite (0.15 V versus Li+/Li, 372 mAh g−1) and spinel Li4Ti5O12 (1.55 V versus Li+/Li, 175 mAh g−1), to store the high energies per weight (∼150–400 Wh kg−1 based on total electrode weight) found in commercially available batteries1,2,3,6. However, the use of highly volatile, flammable, and toxic non-aqueous electrolytes compromises battery safety4,5. Although various measures have been taken to minimize the safety risk7, accidental fires due to non-aqueous Li-ion batteries in notebook computers, automobiles, and aeroplanes have still occurred8,9. In most cases, these accidents have been aggravated by leakage of the highly flammable electrolyte induced by thermal runaway (that is, out-of-control exothermic reactions)7,9.

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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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Authors and Affiliations

  1. Department of Chemical System Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

    Yuki Yamada, Kenji Usui, Seongjae Ko & Atsuo Yamada

  2. Elements Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University, 1-30, Goryo-Ohara, Nishikyo-ku, Kyoto 615-8245, Japan

    Yuki Yamada, Keitaro Sodeyama, Yoshitaka Tateyama & Atsuo Yamada

  3. PRESTO, Japan Science and Technology Agency (JST), 4-1-8, Honcho, Kawaguchi, Saitama 333-0012, Japan

    Keitaro Sodeyama

  4. Center for Green Research on Energy and Environmental Materials and Center for Materials Research by Information Integration, National Institute for Materials Science (NIMS), 1-1, Namiki, Tsukuba, Ibaraki 305-0044, Japan

    Keitaro Sodeyama & Yoshitaka Tateyama

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  1. Yuki Yamada
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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.

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Correspondence to Atsuo Yamada.

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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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