Adding salt to expand voltage window of humid ionic liquids

Chen, Ming; Wu, Jiedu; Ye, Ting; Ye, Jinyu; Zhao, Chang; Bi, Sheng; Yan, Jiawei; Mao, Bing‐Wei; Feng, Guang

doi:10.1038/s41467-020-19469-3

Cited by 67 publications

(88 citation statements)

References 85 publications

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“… 28 Inspired by the water-in-salt approach, Chen et al thus proposed dissolving small amounts of lithium ions in wet ionic liquids in order to “trap” these water molecules and expand the voltage window of the liquid. 29 Using small-angle neutron scattering combined with molecular dynamics, Borodin et al showed that water-in-salt electrolytes also display nanoheterogeneities with characteristic lengths of 1 to 2 nm. 30 However, instead of being formed of groups of different polarities, they are made of a 3D percolating lithium–water network dispersed inside a TFSI-rich matrix, as shown on Figure 1 a.…”

Section: Understanding Water-in-salt Electrolytes For Aqueous Li-ion mentioning

confidence: 99%

Confining Water in Ionic and Organic Solvents to Tune Its Adsorption and Reactivity at Electrified Interfaces

et al. 2021

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Conspectus The recent discovery of “water-in-salt” electrolytes has spurred a rebirth of research on aqueous batteries. Most of the attention has been focused on the formulation of salts enabling the electrochemical window to be expanded as much as possible, well beyond the 1.23 V allowed by thermodynamics in water. This approach has led to critical successes, with devices operating at voltages of up to 4 V. These efforts were accompanied by fundamental studies aiming at understanding water speciation and its link with the bulk and interfacial properties of water-in-salt electrolytes. This speciation was found to differ markedly from that in conventional aqueous solutions since most water molecules are involved in the solvation of the cationic species (in general Li + ) and thus cannot form their usual hydrogen-bonding network. Instead, it is the anions that tend to self-aggregate in nanodomains and dictate the interfacial and transport properties of the electrolyte. This particular speciation drastically alters the presence and reactivity of the water molecules at electrified interfaces, which enlarges the electrochemical windows of these aqueous electrolytes. Thanks to this fundamental understanding, a second very active lead was recently followed, which consists of using a scarce amount of water in nonaqueous electrolytes in order to control the interfacial properties. Following this path, it was proposed to use an organic solvent such as acetonitrile as a confinement matrix for water. Tuning the salt/water ratio in such systems leads to a whole family of systems that can be used to determine the reactivity of water and control the potential at which the hydrogen evolution reaction occurs. Put together, all of these efforts allow a shift of our view of the water molecule from a passive solvent to a reactant involved in many distinct fields ranging from electrochemical energy storage to (electro)catalysis. Combining spectroscopic and electrochemical techniques with molecular dynamics simulations, we have observed very interesting chemical phenomena such as immiscibility between two aqueous phases, specific adsorption properties of water molecules that strongly affect their reactivity, and complex diffusive mechanisms due to the formation of anionic and aqueous nanodomains.

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Section: Understanding Water-in-salt Electrolytes For Aqueous Li-ion mentioning

confidence: 99%

Confining Water in Ionic and Organic Solvents to Tune Its Adsorption and Reactivity at Electrified Interfaces

et al. 2021

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“…This effect was recently used by Chen et al . to expand the voltage window of humid ionic liquids [49] . At infinite dilution the first solvation shell of Li + is made of four water molecules.…”

Section: Resultsmentioning

confidence: 99%

Computational Screening of the Physical Properties of Water‐in‐Salt Electrolytes**

Méndez-Morales

Salanne

2020

Batteries & Supercaps

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Water‐in‐salts form a new family of electrolytes with properties distinct from the ones of conventional aqueous systems and ionic liquids. They are currently investigated for Li‐ion batteries and supercapacitors applications, but to date most of the focus was put on the system based on the LiTFSI salt. Here we study the structure and the dynamics of a series of water‐in‐salts with different anions. They have a similar parent structure but they vary systematically through their symmetric/asymmetric feature and the length of the fluorocarbonated chains. The simulations allow to determine their tendency to nanosegregate, as well as their transport properties (viscosity, ionic conductivity, diffusion coefficients) and the amount of free water, providing useful data for potential applications in energy storage devices.

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“…The most straightforward way is to distribute charges uniformly on electrode atoms (i.e., constant charge method, CCM) [4][5][6][7] . In contrast, the constant potential method (CPM), a computationally expensive but realistic approach, maintains electrode atoms at constant potential, adjusting the electrode charges self-consistently based on the electrode potential and ionic environment [8][9][10][11][12][13][14][15] . To explore the equilibrium performance of supercapacitors, CCM may be feasible for systems with open electrodes (e.g., those with planar 16 , cylindrical 7 , spherical 17 surfaces), but not for porous electrodes 11-13, 18, 19 .…”

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confidence: 99%

“…In studying charging and discharging supercapacitors, prior CPM simulations often 34 adopted the potential control mode: step-like, [8][9][10][11][12][13][14][15] linear, 21 or climbing-type 22,23 potential differences were applied between the positive and negative electrodes. These molecular simulations help to understand the fundamentals of charging and discharging supercapacitors.…”

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Modeling galvanostatic charge-discharge of nanoporous supercapacitors

Zeng

et al. 2021

Preprint

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Molecular modeling can study the energy storage of supercapacitors at the atomistic level and has become indispensable in this research. The constant potential method (CPM) allows keeping the electric potential uniform on the electrode, which is essential for a realistic description of the charge repartition and dynamics process in supercapacitors. Prior CPM studies have been limited to the potentiostatic mode. Though widely adopted in the experiment, the galvanostatic mode has been rarely investigated in CPM simulations due to a lack of effective methods. In this work, we developed a modeling approach to simulating the galvanostatic charge-discharge of supercapacitors under constant potential (GCD-CPM). We show that, for nanoporous electrodes, GCD-CPM can capture supercapacitor dynamics in excellent agreement with experimental measurements and delineate the ion adsorption-desorption dynamics underlying the hysteresis with molecular resolutions during charging and discharging. Therefore, this GCD-CPM modeling could open up new avenues for exploring the rich physics and electrochemistry of supercapacitor dynamics.

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Adding salt to expand voltage window of humid ionic liquids

Cited by 67 publications

References 85 publications

Confining Water in Ionic and Organic Solvents to Tune Its Adsorption and Reactivity at Electrified Interfaces

Confining Water in Ionic and Organic Solvents to Tune Its Adsorption and Reactivity at Electrified Interfaces

Computational Screening of the Physical Properties of Water‐in‐Salt Electrolytes**

Modeling galvanostatic charge-discharge of nanoporous supercapacitors

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