An “Ether‐In‐Water” Electrolyte Boosts Stable Interfacial Chemistry for Aqueous Lithium‐Ion Batteries

Abstract

water (1.23 V) limits both the operating voltage and energy density of aqueous batteries. Although adjusting the pH can effectively suppress hydrogen evolution at the anode, owing to the inherent voltage limit, another electrode compromise would occur. Fortunately, the solid-electrolyte interphase (SEI) acts to kinetically stabilize the electrolyte at potentials beyond their thermodynamic stability limits. Early research on SEI focused on the electrodes, and the findings have since been applied extensively to carbonate-based nonaqueous electrolytes, with successful outcomes. [9-13] However, SEI has many restrictive requirements in the standard aqueous battery. In traditional aqueous electrolytes, the decomposition products are H 2 and O 2 , which fail to deposit as solids on the surface of the electrodes. A superconcentrated (Li + (H 2 O) 2) n polymerlike chain aqueous electrolyte based on LiNO 3 salt was reported, achieving a 2.55 V stability window without forming a protective SEI. [14] But a high cathodic potential (2.35 V vs Li) to satisfy the demands of commercial anode materials such as Li 4 Ti 5 O 12 (1.55 V vs Li) remain challenging. Furthermore, the absence of SEI leads to a low energy density and limited cycle life in aqueous batteries. [15,16] More recently, some pioneering works offered new directions by developing high concentration aqueous electrolytes: 21 m (m = molality, mol kg −1) "water-in-salt" electrolyte, [17] 28 m "water-in-bisalt" electrolyte, [18] "water-in-ionomer" electrolyte, [19] hybrid aqueous-nonaqueous electrolyte, [20] molecular crowding electrolytes, [21] hydrate melt electrolytes, [22] and 63 m "water-in-hybrid-salt" electrolyte. [23] These approaches help to broaden the limited electrochemical stability window of aqueous electrolytes. Some of these modified electrolytes exhibited impressive energy density, compatibility with electrodes, and exceptional stable cycle performance. Although these efforts on aqueous electrolytes have introduced a new prospect for electrode protection by reducing water activity, the in situ SEI formation is still infancy. There is a need for in-depth research of SEI to reach the desired cycle stability and energy density. For instance, the thermodynamics and kinetics of expanding voltage windows in the SEI formation mechanism need to be investigated. In addition, no electrolyte has been identified to address the challenges of cycle stability and discharge capacity, nor has and study evaluated the correlation between SEIs' unique structures and their electrochemical Aqueous batteries are promising devices for electrochemical energy storage because of their high ionic conductivity, safety, low cost, and environmental friendliness. However, their voltage output and energy density are limited by the failure to form a solid-electrolyte interphase (SEI) that can expand the inherently narrow electrochemical window of water (1.23 V) imposed by hydrogen and oxygen evolution. Here, a novel (Li 4 (TEGDME)(H 2 O) 7) is proposed as a solvation electrolyte with sta...

Preparation and electrochemical properties of ionic-liquid-modified Na3SbS4 membrane composite electrolytes

“…This indicates IL incorporation effectively inhibits the formation of Na dendrite [48]. High current density may result in severe decomposition of the ionic liquid, especially with the existence of salts [16,49]. This may explain the higher polarization voltage of 0.17 M NaTFSI-Pyr 14 TFSI-NGE than that of Pyr 14 TFSI-NGE at high current densities (Fig.…”

Ultra‐High Initial Coulombic Efficiency Induced by Interface Engineering Enables Rapid, Stable Sodium Storage

“…According to XPS C 1s and O 1s spectrum of FeS 2 /N,S‐C (Figure 5 e,f, Figure S27a, 28a), contents of C−H/C−O (285.80 eV), [38] polyether (533.21 eV) [39] and C‐O‐Na (531.6 eV), [39] as organic decomposition products, are much lower than those of N,S‐C, suggesting fewer organic components in its thin SEI. Besides, XPS elemental analysis after different Ar + sputtering times shows that CF x greatly decreases with increasing sputtering time and NaF dominates F 1s spectra after sputtering 40 s, indicating a homogeneous and ultra‐thin SEI (Figure 5 e,f,h, Figure S27a, 28a).…”

Solid electrolyte interphase in water-in-salt electrolytes

“…After all, the SEI is not a simple combination of each ingredient; the morphology and distribution of diverse chemical components might be as important as the components themselves. So far, the main methods used to enhance the SEI include increasing the salt concentration and introducing additional components in the SEI via adding organic co-solvents, for example, DMC, AN, and urea [33,35,46,47]. In consideration of the electrolyte additives, which have been extensively investigated in the organic system, additives for WiSEs can also be developed to manipulate the SEI in the aqueous system.…”