“Water-in-salt” electrolyte enables high-voltage aqueous lithium-ion chemistries

Suo, Liumin; Borodin, Oleg; Gao, Tao; Olguin, Marco; Ho, Janet; Fan, Xiulin; Luo, Chao; Wang, Chunsheng; Xu, Ke

doi:10.1126/science.aab1595

Cited by 2,952 publications

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“…Upon closer comparison with the well-known redox processes of sulfur in nonaqueous media at 2.1∼2.4 V (Fig. 1A, black dashed line) (19), an apparent positive shift of ∼0.3 V occurred in the aqueous solution, which has been observed previously and attributed to the high Li salt concentration in WiBS electrolyte (12). More noticeable is the drastic change from the characteristic two-stage lithiation process in nonaqueous media to a seemingly single-stage redox process in aqueous media, as well as the much reduced potential hysteresis in the latter.…”

Section: Resultsmentioning

confidence: 81%

“…Remarkably, at a slow rate of 0.2C (discharge/ charge of full theoretical capacity in 5 h), the cell being cycled between 2.2 and ∼0.5 V exhibited a single discharge plateau with an average voltage of 1.60 V, delivering a discharge capacity of 84.40 mAh·g of total electrode mass (i.e., 1,327 mAh·g −1 of sulfur mass) or an areal capacity of 10.6 mAh·cm −2 . The energy density was conservatively estimated to be ∼135 Wh/(kg of total electrode mass), which represents a marked improvement not only over all conventional aqueous Li-ion systems (<75 Wh·kg −1 ) (9, 11), but in particular also over what was achieved by the highly concentrated aqueous electrolytes (12,13,18). At a rate five times higher (1C), the capacity dropped only slightly, to 68.24 mAh·g −1 , reflecting the fast kinetics of the cell reactions.…”

Section: Resultsmentioning

confidence: 99%

“…In particular, wide electrochemical stability windows (>3.0 V) comparable to those of nonaqueous electrolytes have been recently demonstrated by water-in-salt (WiS) and waterin-bisalt (WiBS) electrolytes. With water molecules still far outnumbering that of Li salts, this class of completely nonflammable WiS and WiBS electrolytes realized a dramatic improvement in safety, while placing many Li-ion and even beyond Li-ion chemistries within the reach of aqueous electrolytes (12,13). Historically, it has been very challenging to use elemental sulfur as the cathode material in aqueous electrolytes, primarily because of the high solubility of short-chain lithium polysulfide (Li 2 S x , x < 6) and Li 2 S in aqueous media, and the strong parasitic shuttling reaction occurring thereafter (14).…”

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Unique aqueous Li-ion/sulfur chemistry with high energy density and reversibility

Yang

Suo

Borodin

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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177

182

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Leveraging the most recent success in expanding the electrochemical stability window of aqueous electrolytes, in this work we create a unique Li-ion/sulfur chemistry of both high energy density and safety. We show that in the superconcentrated aqueous electrolyte, lithiation of sulfur experiences phase change from a highorder polysulfide to low-order polysulfides through solid-liquid two-phase reaction pathway, where the liquid polysulfide phase in the sulfide electrode is thermodynamically phase-separated from the superconcentrated aqueous electrolyte. The sulfur with solid-liquid two-phase exhibits a reversible capacity of 1,327 mAh/(g of S), along with fast reaction kinetics and negligible polysulfide dissolution. By coupling a sulfur anode with different Li-ion cathode materials, the aqueous Li-ion/sulfur full cell delivers record-high energy densities up to 200 Wh/(kg of total electrode mass) for >1,000 cycles at ∼100% coulombic efficiency. These performances already approach that of commercial lithium-ion batteries (LIBs) using a nonaqueous electrolyte, along with intrinsic safety not possessed by the latter. The excellent performance of this aqueous battery chemistry significantly promotes the practical possibility of aqueous LIBs in large-format applications.water-in-salt | rechargeable aqueous battery | aqueous sulfur battery | gel polymer electrolyte | phase separation I n the past two decades, rechargeable lithium-ion batteries (LIBs) have revolutionized consumer electronics with their high energy density and excellent cycling stability, and are the state-of-the-art candidates for applications ranging from kilowatt hours for electric vehicles up to megawatt hours for grids (1, 2). The latter applications in large-format present much more stringent requirements for safety, cost, and environmental friendliness, besides energy density and cycle life. The shortcomings of LIB are mostly due to the flammable and toxic nonaqueous electrolytes and moderate energy densities (<400 Wh·kg −1 ) provided by the electrochemical couples currently used (3). Among the various "beyond Li-ion" high-energy chemistries (>500 Wh·kg −1 ) explored currently, the nonaqueous lithium/sulfur (Li/S) battery based on sulfur as a cathode (theoretical capacity of 1,675 mAh·g −1 ) and metallic lithium as an anode seems to be the most practical, as evidenced by the mushrooming literature and significant advances in this system in the past 5 y (4-7). However, commercialization of this system still faces challenges because of severe safety concerns associated with the dendrite growth of metallic Li anode in highly inflammable ether-based electrolytes (8), and the high self-discharge associated with parasitic shuttling of the intermediate polysulfide species. Moreover, the moisture-sensitive nature of the nonaqueous electrolyte would contribute significantly to the cost of the Li/S battery pack due to the stringent moisture-exclusion infrastructure required during the manufacturing, processing, and packaging of the cells. The indispensabl...

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Section: Resultsmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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Unique aqueous Li-ion/sulfur chemistry with high energy density and reversibility

Yang

Suo

Borodin

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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182

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“…Through using concentrated electrolytes of water-in-ionic liquid (water in 1-butyl-3-methylimidazolium chloride, BMImCl) [19,20] or water-in-salt (water in lithium, bis(trifluoromethylsulphonyl)imide, LiTFSI) [21], the onset of oxygen evolution and hydrogen reactions can be shifted to more positive and negative potentials, respectively. Broad electrochemical window of about 3 V has been achieved accordingly ( Figure 3).…”

Section: Redox Electrochemistry Of Flow Batteriesmentioning

confidence: 99%

Redox Flow Batteries: Fundamentals and Applications

Chen¹,

Kim²,

Chang³

2017

Redox - Principles and Advanced Applications

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A redox flow battery is an electrochemical energy storage device that converts chemical energy into electrical energy through reversible oxidation and reduction of working fluids. The concept was initially conceived in 1970s. Clean and sustainable energy supplied from renewable sources in future requires efficient, reliable and cost-effective energy storage systems. Due to the flexibility in system design and competence in scaling cost, redox flow batteries are promising in stationary storage of energy from intermittent sources such as solar and wind. This chapter covers basic principles of electrochemistry in redox flow batteries and provides an overview of status and future challenges. Recent progress in redox couples, membranes and electrode materials will be discussed. New demonstration and commercial development will be addressed.

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“…Due to the increase in the oxidative stability of the glymes and the presence of the ligandexchange conduction mode, the solvate ILs can be used as battery electrolytes and are compatible with 4 V-class cathodes such as LiCoO 2 in the cell voltage range of 3.0-4.2 V. This is true regardless of the use of ether-based electrolytes because the ligand exchange rate is much faster than the electrode reaction rate. 95 The discovery that oxidative stability is increased by the coordination of solvent molecules to Li + has inspired many researchers to use concentrated organic 123 and aqueous 124 electrolyte solutions to widen the potential windows and to apply these electrolytes in innovative batteries.…”

confidence: 99%

Design and Materialization of Ionic Liquids Based on an Understanding of Their Fundamental Properties

Watanabe

2016

Electrochemistry

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Ionic liquids (ILs) are defined as salts that have melting points lower than 100°C. Most are organic salts, and these may be designed and tailored to have suitable properties. ILs are recognized as a third group of solvents (and electrolytes), after water and organic solvents. They are characterized by their unique properties such as nonvolatilities, high thermal stabilities, and high ionic conductivities. In this article, our work on the design and preparation of ILs is briefly reviewed. The concept of ionicity is proposed as a metric to characterize the basic nature (dissociativity) of ILs, which is affected by the Lewis acidity/basicity of cations/anions (i.e., coulombic interactions), the directionality of interactions between cations and anions, and van der Waals interactions between ions. The ionicity of ILs is dominated by a subtle balance between coulombic and van der Waals interactions, which clearly discriminates ILs from conventional high-temperature inorganic molten salts. Here, the design of protic ILs for fuel cell electrolytes, electron-transporting ILs for dye-sensitized solar cell electrolytes, and Li + -conducting solvate ILs for lithium battery electrolytes are discussed based on an understanding of the fundamental properties of ILs. Furthermore, the combination of ILs with polymers and colloidal particles affords intriguing quasi-solid materials (ion gels), and the ion transport in these gels is decoupled from the mechanical relaxation time of these materials, yielding new solid electrolytes. The possibility of temperature and photo-sensitive solubility dependence of polymers in ILs allows the creation of stimuli-responsive materials. Finally, protic ILs/protic salts are demonstrated to be good precursors for N-doped carbon materials.

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“Water-in-salt” electrolyte enables high-voltage aqueous lithium-ion chemistries

Cited by 2,952 publications

References 62 publications

Unique aqueous Li-ion/sulfur chemistry with high energy density and reversibility

Unique aqueous Li-ion/sulfur chemistry with high energy density and reversibility

Redox Flow Batteries: Fundamentals and Applications

Design and Materialization of Ionic Liquids Based on an Understanding of Their Fundamental Properties

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