A Universal Approach to Aqueous Energy Storage via Ultralow‐Cost Electrolyte with Super‐Concentrated Sugar as Hydrogen‐Bond‐Regulated Solute

Abstract

Compared with the organic, ionic liquid, and solid-state electrolytes, aqueous electrolytes have the advantages of good security, environmental friendliness, high ionic conductivity, low cost, and high operability in ordinary environments. [1][2][3][4][5] Therefore, aqueous secondary ion batteries/capacitors are more attractive in large-scale energy storage, and have greater application prospects. [6][7][8][9] However, even so, there still exists several disadvantages as follows: 1) The thermodynamic electrochemical stability window (ESW) of water is as narrow as 1.23 V. Even considering the existence of overpotential, the ESWs of conventional aqueous electrolytes are not higher than 2 V. 2) Usually, the electrode materials cannot form stable interface in water, so it is difficult to ensure the cycling stability. 3) Dissolution and even decomposition of electrode materials and discharge/charge products limit the choice of electrode materials. [10] These factors have limited the improvement of key electrochemical performance indicators such as energy density, output voltage, and cycle life of aqueous energy-storage devices Aqueous energy-storage systems have attracted wide attention due to their advantages such as high security, low cost, and environmental friendliness. However, the specific chemical properties of water induce the problems of narrow electrochemical stability window, low stability of water-electrode interface reactions, and dissolution of electrode materials and intermediate products. Therefore, new low-cost aqueous electrolytes with different water chemistry are required. The nature of water depends largely on its hydroxylbased hydrogen bonding structure. Therefore, the super-concentrated hydroxyl-rich sugar solutions are designed to change the original hydrogen bonding structure of water. The super-concentrated sugars can reduce the free water molecules and destroy the tetrahedral structure, thus lowering the binding degree of water molecules by breaking the hydrogen bonds. The ionic electrolytes based on super-concentrated sugars have the expanded electrochemical stability window (up to 2.812 V), wide temperature adaptability (-50 to 80 °C), and fair ionic conductivity (8.536 mS cm −1 ). Aqueous lithium-, sodium-, potassium-ion batteries and supercapacitors using super-concentrated sugar-based electrolytes demonstrate an excellent electrochemical performance. The advantages of ultralow cost and high universality enable a great practical application potential of the superconcentrated sugar-based aqueous electrolytes, which can also provide great experimental and theoretical assistance for further research in water chemistry.

Stable, high-performance, dendrite-free, seawater-based aqueous batteries

“…The seawater-based electrolyte (2 M ZnSO 4 in seawater) has a wider electrochemical window increased from 2.4 V to 2.6 V as compared with DI water-based electrolyte (2 M ZnSO 4 in DI water). When using seawater as a solvent, the content of free water molecules decreases, which has been proven to be an effective strategy to expand the electrochemical stability window 21 , 40 . Moreover, the Zn 3 Mn electrode shows a significantly improved anti-corrosion ability in the seawater-based electrolyte as compared to the Zn electrode (Supplementary Fig.…”

Perspective on High‐Energy Carbon‐Based Supercapacitors

“…In addition, the organic components of the hybrid electrolytes can be extended to macromolecules. Recently, Xue et al [203] reported that the mixture of lowcost hydroxyl-rich sugar and water can act as a solvent to dissolve metal salts. The resultant electrolyte exhibits high ESW (2.8 V on Pt electrodes), moderate ionic conductivity (8 mS cm −1 ), and wide applicable temperature range (-50 to 80°C).…”

The Applications of Water‐in‐Salt Electrolytes in Electrochemical Energy Storage Devices

“…These data are summarized from the following references: 21 m LiTFSI, [2] 30 m ZnCl 2 , [41] 17 m NaClO 4 , [25] 22 m LiNO 3 , [35] 12 m NaNO 3 , [26] 25 m NH 4 CH 3 COO, [15] 22 m KCF 3 SO 3 , [79] 21 m LiTFSI + 7 m LiOTF, [16] 32 m KOAc + 8 m LiOAc, [19] 9.26 m NaCF 3 SO 3 + 1 m Na 2 SO 4 , [68] 9 m NaOTF + 22 m TEAOTF, [42] 42 m LiTFSI + 21 m Me 3 EtN•TFSI, [43] [30] 21 m LiTFSI-H 2 O/9.25 m LiTFSI-DMC (1:1), [32] [29] LiTFSI + 94%PEG + 6%H 2 O, [44] 2 M NaNO 3 + 66.7 wt% sucrose. [122] the motion of ions follows Stokes-Einstein law. [37] In contrast, the ion transport mechanism of WISEs is not consistent with the above because of the unusual solvation structure.…”