Effect of Electrolyte Concentration on the Solvation Structure of Gold/LITFSI–DMSO Solution Interface

Abstract

The use of high-concentration electrolytes in lithium metal batteries enables the effective suppression of lithium dendrite growth at the lithium anode. The issue of the solvation structure at the electrolyte/electrode interface in low-and high-concentration electrolytes must be addressed to understand the electroreduction stability and solid− electrolyte interphase (SEI) formation. The concentration-dependent solvation structure of lithium bis(trifluoromethanesulfonyl)imide (LITFSI)−dimethyl sulfoxide (DMSO) on a gold model electrode has been investigated with various electrolyte concentrations using surface-enhanced Raman spectroscopy. At low concentrations, free DMSO and TFSI − were found to be chemisorbed on the gold surface to form an adsorption layer. Among these, TFSI − was chemisorbed via its oxygen atoms based on the observation of the ν(Au−O) bond. Besides, chemisorbed TFSI − at the gold surface did not coordinate with Li + in the lowconcentration electrolyte. As the concentration gradually increased up to 2.31 M, chemisorbed TFSI − started to coordinate with Li + . On further increase in LITFSI concentration above 2.31 M, chemisorbed DMSO was absent in the adsorption layer; instead, chemisorbed TFSI − became the only species. The chemisorbed TFSI − is proposed to be coordinated with Li + by two of its oxygens in such high concentration, making its coordination saturated. The DMSO-free adsorption layer in electrolytes with concentration above 2.31 M might help to form a dense and uniform SEI once an electrical field is applied, which contributes to improve the long-term cyclability of batteries.

Hopping in High Concentration Electrolytes - Long Time Bulk and Single-Particle Signatures, Free Energy Barriers, and Structural Insights

“…One of the ways to achieve safer high-voltage Li-ion batteries is to use highly concentrated electrolytes (HCEs), which reduces flammability. , Further, anion-derived solid electrolyte interphase (SEI) formed in HCEs enable greater stability and longer term cycling compared to present-day dilute electrolyte batteries wherein solvent-derived SEI is generated. − High-energy density and voltage needs are also met by HCEs ( solvent-in-salt electrolytes ). Some specific advantages of using HCEs are increased battery life-span, higher Coulombic efficiency, ultrafast charging, prevention of solvent degradation, , larger and more stable electrochemical windows, higher rate capability, and higher transport numbers of alkali ions. , Although HCEs are generally thought to suffer from the drawback of low ionic conductivity, this drawback has been overcome in part recently by an appropriate choice of anions in mixed-anion HCEs, and in part by adding a nonsolvating and/or low-viscosity additive solvent. − …”

In Situ Formation of “Dimethyl Sulfoxide/Water‐in‐Salt”‐Based Chitosan Hydrogel Electrolyte for Advanced All‐Solid‐State Supercapacitors

“…The boiling point of this binary solvent system can be further increased by adjusting the salt concentration to saturation. Besides, DMSO with its moderately high donor number can be adsorbed on the substrate to interact with the anions and promote the formation of a dense and stable solid–electrolyte interphase (SEI) layer on the surface of electrodes [13] . Lu et al introduced a eutectic mixture of DMSO and H 2 O into electrolytes so that the supercapacitor exhibited a broad operational temperature window of 100 °C (−35 to 65 °C) [14]…”

“…Besides, DMSO with its moderately high donor number can be adsorbed on the substrate to interact with the anions and promote the formation of a dense and stable solid-electrolyte interphase (SEI) layer on the surface of electrodes. [13] Lu et al introduced a eutectic mixture of DMSO and H 2 O into electrolytes so that the supercapacitor exhibited a broad operational temperature window of 100°C (À 35 to 65°C). [14] Furthermore, a wide electrochemical voltage window is often difficult to achieve due to the water splitting at 1.23 V, which greatly limits the energy supplies of supercapacitors.…”

Nonaqueous Solvent Adsorption on Transition Metal Surfaces with Density Functional Theory: Interaction of N,N-Dimethylformamide (DMF), Tetrahydrofuran (THF), and Dimethyl Sulfoxide (DMSO) with Ag, Cu, Pt, Rh, and Re Surfaces

“…Nonaqueous solvents, and their interfaces with metals, are of critical importance to the performance of a variety of important technologies and applications, such as batteries, − surface modification, nanoparticle synthesis and stability, − and catalysis − including in electrocatalysis. − Polar aprotic solvents are useful in many applications, such as when it is desired to restrict access to protons for improved selectivity in electrochemical reactions. ,,, Among the many available polar aprotic solvents, some commonly used solvents include dimethyl sulfoxide (DMSO), tetrahydrofuran, also known as oxolane (THF), N , N -dimethylformamide (DMF), and acetonitrile. , A wide variety of important properties are influenced by the composition of the solvent and electrolyte. In batteries, critical properties such as the electrolyte conductivity and the formation of passivation layers are strongly affected by the choice of solvent . Similarly, in catalysis, the solvent affects transport processes, and also potentially interacts directly with the catalyst/surface and intermediates/adsorbates, significantly affecting rates and selectivities of catalytic reactions .…”

“…For example, spectroscopic evidence indicates a strong chemisorption of DMSO on Pt, and also significant interaction with Au , and Ag, displaying preferential adsorption to step sites . Raman spectroscopy was used to show that DMSO chemisorbs to Au at low electrolyte concentrations, but at higher electrolyte concentrations, it is displaced by adsorption of an electrolyte ion; this is hypothesized to critically affect the formation of an SEI in batteries. On Ag, DMSO has been hypothesized to bind in a potential-dependent way, flipping between binding through O at positive potentials and S at negative potentials, with reorientation of solvent molecules near the PZC. , Interestingly, the differential capacitance of DMSO/Au electrodes , was shown to be significantly smaller than that of solvents with similarly large permanent dipole moments, such as acetonitrile, which would not be expected if the molecule could freely reorient near the interface.…”