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Batteries: Widening voltage windows

Nature Energy volume 1, Article number: 16161 (2016) Cite this article

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The energy output of aqueous batteries is largely limited by the narrow voltage window of their electrolytes. Now, a hydrate melt consisting of lithium salts is shown to expand such voltage windows, leading to a high-energy aqueous battery.

Aqueous Li-ion batteries offer advantages in terms of safety, toxicity and cost over their non-aqueous counterparts. However, their energy density (typically less than 80 Wh kg−1 based on the total mass of electrodes) is much smaller than that of the state-of-the-art non-aqueous Li-ion batteries1 (250–400 Wh kg−1). This is because the electrochemical stability window of aqueous electrolytes is much narrower than that of the non-aqueous ones. This stability window is determined by the reductive and oxidative reactions of salts, solvents or additive components in the electrolyte2. To ensure the reversibility (and hence rechargeability) of batteries, redox reactions of both the negative and positive electrodes must take place within such a window. In aqueous electrolytes, however, the stable operating voltage window of water is only 1.23 V, beyond which undesired water hydrolysis occurs. Expanding the operating voltage window therefore represents the core challenge in the development of practical aqueous Li-ion batteries. Recently, a highly concentrated aqueous electrolyte, dubbed water in salt, was shown to expand the voltage window to ∼3.0 V on stainless steel electrodes, but the energy density remains around 100 Wh kg−1 (ref. 3). Writing in Nature Energy, Atsuo Yamada and colleagues now report a eutectic system of organic Li salts as a new class of stable aqueous electrolytes with a voltage window larger than 3.1 V when measured on platinum (Pt) for anodic and on aluminium (Al) for cathodic limits, and demonstrate an aqueous battery with an energy density above 130 Wh kg−1, competitive with non-aqueous Li-ion batteries4.

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Figure 1: Electrochemical stability windows of aqueous electrolytes and redox potentials of electrode materials.

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Authors and Affiliations

  1. Kang Xu is at the Electrochemistry Branch of the US Army Research Laboratory, Maryland 20783, USA.,

    Kang Xu

  2. Chunsheng Wang is at the Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20740, USA.,

    Chunsheng Wang

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  1. Kang Xu
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  2. Chunsheng Wang
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Correspondence to Kang Xu or Chunsheng Wang.

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Xu, K., Wang, C. Batteries: Widening voltage windows. Nat Energy 1, 16161 (2016). https://doi.org/10.1038/nenergy.2016.161

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