Sulfolane Research Articles

Highly selective extraction of aromatics from diesel fuel using dual N-containing heterocyclic deep eutectic solvents

Separation of aromatics and alkanes in diesel fuel is significant for its diversified utilization. In this study, a series of dual N-containing heterocyclic deep eutectic solvents (DESs) were designed and synthesized to separate alkanes/aromatics. The optimal DES (2EmimCl:Trtz) was determined to be 1-Ethyl-3-methylimidazole chloride salt (EmimCl) and 1,2,4-triazole (Trtz) with a molar ratio of 2:1. Sulfolane (SUL) was added as a co-extractant with an optimal molar ratio of 3:1. The extractant ([2EmimCl:Trtz]3SUL) was adopted in the model oil containing dodecane and tetraline. The effects of experimental parameters on the extraction performance were studied, and under optimal conditions, the separation factor for tetraline reached 145.2 with a distribution coefficient of 0.1500. The recycling ability of [2EmimCl:Trtz]3SUL was found to be good. The mechanism of selective extraction was studied using density functional theory (DFT), which indicated that the difference in interaction forces between extractants and aromatics/alkanes is the key to achieving selective separation. Finally, multistage cross-flow extractions of [2EmimCl:Trtz]3SUL were adopted in the six-component model oil and real diesel oil to demonstrate its performance in complex and diesel oil systems.

Eutectic Electrolytes Composed of Li Salt and Sulfones

Sulfone-based highly concentrated electrolytes are promising electrolytes for high-voltage Li-ion batteries (LIBs), owing to the high thermal and oxidative stabilities of sulfones. In addition, highly concentrated Li salt/sulfone electrolytes exhibit unique Li+ ion hopping/exchange conduction mechanism and high Li+ ion transference number (>0.6).1,2 However, the application of these electrolytes at low temperatures is limited due to the precipitation of a stable crystalline solvate. In this study, the applicability of ternary mixtures of Li salt, sulfolane (SL), and dimethyl sulfone (DMS) as LIB electrolytes was assessed. Due to the increased entropy of mixing, the crystallization of the solvates was suppressed in the ternary electrolytes, resulting in a wide temperature range of liquid sate of the electrolytes.3 In the ternary electrolytes, the network structures of Li+–sulfone–Li+ and Li+–anion–Li+ were formed, and Li+ ion dynamically exchanges sulfones and anions and diffuses more rapidly than these ligands, resulting in a relatively high Li+ transference number. Highly reversible charge–discharge behaviors of the LiCoO2 and graphite electrodes were attained using the ternary electrolyte. Despite the lower ionic conductivity of the sulfone-based electrolyte, the rate capability of the Li/LiCoO2 cell with the ternary electrolyte was comparable to that in a conventional carbonate-based electrolytes. Acknowledgements This study was partially supported by the JSPS KAKENHI (Grant No. JP19H05813 and JP22H00340). References K. Dokko et. al., J. Phys. Chem. B 2018, 122, 10736.Y. Ugata et. al., J. Phys. Chem. B 2021, 125, 6600.Y. Ugata et. al., J. Phys. Chem. C 2022, 126, 10024.

Triple-function Hydrated Eutectic Electrolyte for Enhanced Aqueous Zinc Batteries.

Aqueous rechargeable zinc-ion batteries (ARZBs) are impeded by the mutual problems of unstable cathode, electrolyte parasitic reactions, and dendritic growth of zinc (Zn) anode. Herein, a triple-functional strategy by introducing the tetramethylene sulfone (TMS) to form a hydrated eutectic electrolyte is reported to ameliorate these issues. The activity of H2O is inhabited by reconstructing hydrogen bonds due to the strong interaction of TMS and H2O. Meanwhile, the preferentially adsorbed TMS on the Zn surface increases the thickness of double electric layer (EDL) structure, which provides a shielding buffer layer to suppress dendrite growth. Interestingly, TMS modulates the primary solvation shell of Zn2+-6H2O ultimately to achieve a novel solvent co-intercalation ((Zn-TMS)2+) mechanism, and the intercalated TMS works as a "pillar" that provides more zincophilic sites and stabilize the structure of cathode (NH4V4O10, (NVO)). Consequently, the Zn||NVO battery exhibits a remarkable high specific capacity of 515.6 mAh g-1 at a low current density of 0.2 A g-1 for over 40 days. This multi-functional electrolytes and solvent co-intercalation mechanism will significantly propel the practical development of aqueous batteries.

Triple‐function Hydrated Eutectic Electrolyte for Enhanced Aqueous Zinc Batteries

AbstractAqueous rechargeable zinc‐ion batteries (ARZBs) are impeded by the mutual problems of unstable cathode, electrolyte parasitic reactions, and dendritic growth of zinc (Zn) anode. Herein, a triple‐functional strategy by introducing the tetramethylene sulfone (TMS) to form a hydrated eutectic electrolyte is reported to ameliorate these issues. The activity of H2O is inhibited by reconstructing hydrogen bonds due to the strong interaction between TMS and H2O. Meanwhile, the preferentially adsorbed TMS on the Zn surface increases the thickness of double electric layer (EDL) structure, which provides a shielding buffer layer to suppress dendrite growth. Interestingly, TMS modulates the primary solvation shell of Zn2+ ultimately to achieve a novel solvent co‐intercalation ((Zn‐TMS)2+) mechanism, and the intercalated TMS works as a “pillar” that provides more zincophilic sites and stabilizes the structure of cathode (NH4V4O10, (NVO)). Consequently, the Zn||NVO battery exhibits a remarkably high specific capacity of 515.6 mAh g−1 at a low current density of 0.2 A g−1 for over 40 days. This multi‐functional electrolytes and solvent co‐intercalation mechanism will significantly propel the practical development of aqueous batteries.

Sulfolane as an additive to regulate Zn anode in aqueous Zn-ion batteries

Aqueous Zn-ion batteries (AZIBs) have attracted strong attention for widespread applications because of their safety, cheapness and ecological amiability. Nevertheless, challenges exist at the Zn anode such as the side reactions. Here, a small amount of sulfolane (SL) (1 vol%) was added into the typical ZnSO4 electrolyte as an additive. Detailed studies shown that SL adjusts the solvation structure of Zn2+, reduces the water activity and regulates the Zn deposition. Consequently, the side reactions are suppressed. Therefore, with only addition of 1% SL, the symmetric cells exhibit long cycling lifespan of more than 2000 h and high Coulombic efficiency of 99.7% at 1 mA cm−2 and 1 mAh cm−2. Even under harsh conditions of 5 mA cm−2 and 5 mAh cm−2, the Zn anode still displays long cycling performance of 1000 h. Furthermore, Zn||MnO2 full batteries with SL/ZnSO4 electrolyte shows a high capacity of about 120 mAh g−1 after 500 cycles at 0.5 A g−1.

In situ generated of hybrid interface in poly(1,3-dioxolane) quasi solid electrolyte and extended sulfone cosolvent for lithium-metal batteries

The practical application of lithium metal batteries with high energy density are difficult to apply due to the problem of uncontrolled lithium dendrite growth with commercial liquid electrolytes. Herein, we designed a poly 1,3-dioxolane (PDOL) based quasi solid polymer electrolyte with in-situ polymerization. A small amount of lithium difluoro(oxalato)borate (LiDFOB) provides cationic initiation center for the polymerization of dioxolane (DOL). Sulfolane (SL) were further introduced into the system as a cosolvent and the ionic conductivity was increased to 3.22 × 10-4 S cm-1followed with a high Li+ transfer number of 0.73 at room temperature. Trace amount of SbF3 was introduced to form a robustness inorganic-rich hybrid interface that reduces the decomposition of electrolyte components and retards the formation of lithium dendrites during cycling. The superior rate performance and stable 5C long cycle performance are obtained in LiFePO4||Li full cell owing to the interaction between Li+, SL and PDOL. This work expands the choice of components in quasi solid electrolytes to manufacture qualified LMBs with enhanced performance.

Li-Ion Transport and Solution Structure in Sulfolane-Based Localized High-Concentration Electrolytes

Localized high-concentration electrolytes (LHCEs), which are mixtures of highly concentrated electrolytes (HCEs) and non-coordinating diluents, have attracted significant interest as promising liquid electrolytes for next-generation Li secondary batteries, owing to their various beneficial properties both in the bulk and at the electrode/electrolyte interface. We previously reported that the large Li+-ion transference number in sulfolane (SL)-based HCEs, attributed to the unique exchange/hopping-like Li+-ion conduction, decreased upon dilution with the non-coordinating hydrofluoroether (HFE) despite the retention of the local Li+-ion coordination structure. Therefore, in this study, we investigated the effects of HFE dilution on the Li+ transference number and the solution structure of SL-based LHCEs via the analysis of dynamic ion correlations and molecular dynamics simulations. The addition of HFE caused nano-segregation in the SL-based LHCEs to afford polar and nonpolar domains and fragmentation of the polar ion-conducting pathway into smaller clusters with increasing HFE content. Analysis of the dynamic ion correlations revealed that the anti-correlated Li+–Li+ motions were more pronounced upon HFE addition, suggesting that the Li+ exchange/hopping conduction is obstructed by the non-ion-conducting HFE-rich domains. Thus, the HFE addition affects the entire solution structure and ion transport without significantly affecting the local Li+-ion coordination structure. Further studies on ion transport in LHCEs would help obtain a design principle for liquid electrolytes with high ionic conductivity and large Li+-ion transference numbers.

Extractive Distillation Approach to the Separation of Styrene from Pyrolysis Gasoline Feedstock Coupled with Deep Desulfurization

The separation of mixtures with close boiling points is a critical task in the petrochemical industry, and one such mixture that requires separation is o-xylene/styrene. The STED process is used to separate o-xylene/styrene, which contains a certain amount of organic sulfur in the product due to the limitations of the process. In this study, the process underwent enhancements to attain the effective separation of styrene and accomplish deep desulfurization. A mixture of sulfolane (SUL) and N-methylpyrrolidone (NMP) was selected as the extraction solvent after calculating the UNIFAC group contributions. An orthogonal experiment was conducted to investigate the effects of the solvent/oil ratio, reflux ratio, water addition rate, and solvent ratio on the product. The correspondence between each factor and the indexes examined was determined, enabling the optimization and prediction of the styrene product quality. The final optimized conditions for the extractive distillation column are as follows: solvent/oil ratio of 7, reflux ratio of 4.5, water addition rate of 6000 kg/h, and a solvent ratio of 9:1. Under optimal conditions, the purity of the product was observed to be greater than that of the original process and the sulfur content of the product can be reduced to lower than 10 ppm at the cost of an increase of 12.31% in energy consumption.

Phase Behaviors and Ion Transport Properties of LiN(SO<sub>2</sub>CF<sub>3</sub>)<sub>2</sub>/Sulfone Binary Mixtures

Highly concentrated Li salt/aprotic solvent solutions are promising electrolytes for next-generation batteries. Understanding the Li+ ion transport process is crucial for designing novel battery electrolytes. In this study, we systematically investigated the phase behavior, solvate structures, and Li+ transport properties of binary mixtures comprising lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and various sulfones, such as sulfolane (SL), 3-methyl sulfolane (MSL), dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), and ethyl isopropyl sulfone (EiPS). Except for the MSL system, the [LiTFSA]/[sulfone] = 1/2 mixtures remained in a liquid state at room temperature, thus enabling a systematic comparison of the Li+ transport properties in the highly concentrated electrolytes. In highly concentrated liquid electrolytes, Li+ ions diffuse by exchanging ligands (sulfone and TFSA). Li+ ions diffuse faster than TFSA in all electrolytes except the EiPS-based electrolyte at a composition of [LiTFSA]/[sulfone] = 1/2, resulting in high Li+ transference numbers. SL-based electrolytes show higher ionic conductivity and Li+ transference numbers than other sulfone-based electrolytes. Consequently, sulfone solvents with compact molecular sizes and low energy barriers of conformational change are favorable for enhancing the Li+ ion transport in the electrolytes.

Screening Physical Solvents for Methyl Mercaptan Absorption Using Quantum Chemical Calculation Coupled with Experiments.

This work presents a screening method of physical solvents for methyl mercaptan (MeSH) absorption using quantum chemical calculations. The absorption solubility and thermodynamic behaviors of dimethyl sulfoxide (DMSO), sulfolane (SUL), propylene carbonate (PC), N,N-dimethylformamide (DMF), and 1-methyl-2-pyrrolidinone (NMP) for MeSH were calculated and analyzed using the COSMO-RS model, and the absorption mechanism was probed combining the quantum theory of atoms in molecules (QTAIM) and reduced density gradient (RDG). Results show that the absorption solubility of the five solvents for MeSH by COSMO-RS model calculations follow the order of NMP > PC > DMSO > SUL > DMF, and the van der Waals forces and hydrogen bond forces determine the absorption solubility of physical solvents for MeSH. In addition, the experimental results of MeSH Henry coefficients in the above five solvents follow the same order as the calculated results. However, the calculated Henry coefficients' value largely deviates from the experimental value; therefore, we believe that this calculation method is only available for qualitative screening. This work provided a feasible approach to screening high-performance physical solvents for MeSH removal.

Understanding the Electrochemical and Interfacial Behavior of Sulfolane based Electrolyte in LiNi0.5Mn1.5O4‐Graphite Full‐Cells

AbstractAn ethylene carbonate‐free electrolyte composed of 1 M lithium bis(fluorosulfonyl) imide (LiFSI) in sulfolane (SL) is studied here for LiNi0.5Mn1.5O4‐graphite full‐cells. An important focus on the evaluation of the anodic stability of the SL electrolyte and the passivation layers formed on LiNi0.5Mn1.5O4 (LNMO) and graphite is being analysed along with intermittent current interruption (ICI) technique to observe the resistance while cycling. The results show that the sulfolane electrolyte shows more degradation at higher potentials unlike previous reports which suggested higher oxidative stability. However, the passivation layers formed due to this electrolyte degradation prevents further degradation. The resistance measurements show that major resistance arises from the cathode. The pressure evolution during the formation cycles suggests that there is lower gas evolution with sulfolane electrolyte than in the conventional electrolyte. The study opens a new outlook on the sulfolane based electrolyte especially on its oxidative/anodic stability.

Fine pore tailoring of PSf-b-PEG membrane in sub-5 nm via phase-inversion

It is highly important but challenging to fabricate polymeric separation membranes with pore size in sub-5 nm via the non-solvent induced phase separation (NIPS) process. Herein, we reported a simple but effective method to precisely tailor the pore size of polysulfone-block-polyethylene glycol (PSf-b-PEG) membrane in sub-5 nm via NIPS. Selective solvents of tetramethylene sulfone (Ts) and tetrahydrofuran (THF) towards the corresponding PEG block and PSf block in PSf-b-PEG were mixed at various ratios to tailor the casting solution properties and to finely tailor the pore size of the PSf-b-PEG membranes. The membrane formation mechanism was also investigated to reveal that the PSf-b-PEG membrane exhibited intertwined and fused nanofibrous structure with relatively high porosity and extremely strong mechanical strength. As the content of evaporative THF in the casting solution increased from 42.5 wt% to 85.0 wt%, the MWCO of the PSf-b-PEG membranes decreased from 127 kDa to 6.6 kDa, and the mean effective pore size of the membranes shrank from 15 nm to 2 nm, greatly exceeding the tailorable range and the minimum threshold of the pore size of PSf and PES membranes. Impressively, even if the pore size of the membrane was 2 nm, the pure water permeance of the membrane was still as high as 7 L m−2 h−1 bar−1, indicating the great potential of the PSf-b-PEG membranes for practical applications.

Reconstructing anode/electrolyte interface and solvation structure towards high stable zinc anode

The dendrite growth and side-reactions at unstable anode/electrolyte interface severely impair the electrochemical performance of aqueous zinc-ion battery. Herein, guided by the metal-coordination chemistry, a multifunctional electrolyte additive, sulfolane (SL), is introduced into aqueous ZnSO4 electrolyte to achieve uniform Zn deposition for highly stable and reversible zinc-ion batteries. Experimental results and theoretical calculations prove that the SL molecules can simultanously modulate Zn2+ solvation structure and anode/electrolyte interface. The electrolyte engineering is capable of modulating the primary solvation structure through expelling some active water to mitigate common parasitic reaction. Concomitantly, SL molecules are inclined to adsorb on the Zn metal surface, forming H2O-poor electrical double layer and regulating the nucleation and growth of Zn ions, and thus protecting the Zn anode from the detrimental side-reactions induced by water and dendrite growth. Benefiting from this versatility, the batteries exhibit high reversibility with 99.64 % coulombic efficiency and outstanding stability (over 600 h at 10 mA·cm−2/10 mAh·cm−2). Even cycled at harsh conditions of 20 mA·cm−2/20 mAh·cm−2, the remarkable stability of 100 h is obtained. The Zn//V2O5 full battery delivers high specific capacity of 249 mAh/g with capacity retention of 87.1 % after 5000 cycles.

High-concentration LiPF6/sulfone electrolytes: structure, transport properties, and battery application.

Non-flammable and oxidatively stable sulfones are promising electrolyte solvents for thermally stable high-voltage Li batteries. In addition, sulfolane-based high-concentration electrolytes (HCEs) show high Li+ ion transference numbers. However, LiPF6 has not yet been investigated as the main salt in sulfone-based HCEs for Li batteries. In this study, we investigated the phase behaviors, solvate structures, and transport properties of binary and ternary mixtures of LiPF6 and the following sulfone solvents: sulfolane (SL), dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), and 3-methyl sulfolane (MSL). The stable crystalline solvates Li(SL)4PF6 and Li(DMS)2.5PF6 with high melting points were formed in the LiPF6/SL and LiPF6/DMS mixtures, respectively. In contrast, LiPF6/EMS, LiPF6/MSL, and LiPF6/SL/another sulfone mixtures remained liquids over a wide temperature range. Raman spectroscopy revealed that SL and another sulfone are competitively coordinated to Li+ ions to dissociate LiPF6 in the ternary mixtures. Although the ionic conductivity decreased with increasing LiPF6 concentration due to an increase in viscosity, Li+ ions diffused faster than PF6-via exchanging ligands in the HCE [LiPF6]/[SL]/[DMS] = 1/2/2, resulting in a higher Li ion transference number than that in conventional Li battery electrolytes.

The role of ethylene carbonate (EC) and tetramethylene sulfone (SL) in the dissolution of transition metals from lithium-ion cathodes.

Transition metal (TM) dissolution is a direct consequence of cathode-electrolyte interaction, having implications not only for the loss of redox-active material from the cathode but also for the alteration of solid electrolyte interphase (SEI) composition and stability at the counter electrode. It has widely been reported that the limited anodic stability of typical carbonate-based electrolytes, specifically ethylene carbonate (EC)-based electrolytes, makes high-voltage cathode performance problematic. Hence, the more anodically stable tetramethylene sulfone (SL) has herein been utilized as a co-solvent and a substitute for EC in combination with diethyl carbonate (DEC) to investigate the TM dissolution behavior of LiN0.8C0.17Al0.03 (NCA) and LiMn2O4 (LMO). EC|DEC and SL|DEC solvents in combination with either LiPF6 or LiBOB salts have been evaluated, with LFP as a counter electrode to eliminate the influence of low potential anodes. Oxidative degradation of EC is shown to propagate HF generation, which is conversely reflected by an increased TM dissolution. Therefore, TM dissolution is accelerated by the acidification of the electrolyte. Although replacing EC with the anodically stable SL reduces HF generation and effectively mitigates TM dissolution, SL containing electrolytes are demonstrated to be less capable of supporting Li-ion transport and thus show lower cycling stability.

QC and MD Modelling for Predicting the Electrochemical Stability Window of Electrolytes: New Estimating Algorithm

The electrolyte is an important component of lithium-ion batteries, especially when it comes to cycling high-voltage cathode materials. In this paper, we propose an algorithm for estimating both the oxidising and reducing potential of electrolytes using molecular dynamics and quantum chemistry techniques. This algorithm can help to determine the composition and structure of the solvate complexes formed when a salt is dissolved in a mixture of solvents. To develop and confirm the efficiency of the algorithm, LiBF4 solutions in binary mixtures of ethylene carbonate (EC)/dimethyl carbonate (DMC) and sulfolane (SL)/dimethyl carbonate (DMC) were studied. The structure and composition of the complexes formed in these systems were determined according to molecular dynamics. Quantum chemical estimation of the thermodynamic and oxidative stability of solvate complexes made it possible to establish which complexes make the most significant contribution to the electrochemical stability of the electrolyte system. This method can also be used to determine the additive value of the oxidation and reduction potentials of the electrolyte, along with the contribution of each complex to the overall stability of the electrolyte. Theoretical calculations were confirmed experimentally in the course of studying electrolytes by step-by-step polarisation using inert electrodes. Thus, the main aim of the study is to demonstrate the possibility of using the developed algorithm to select the optimal composition and solvent ratio to achieve predicted redox stability.

High-Capacity Zinc Anode with 96 % Utilization Rate Enabled by Solvation Structure Design.

Aqueous zinc-ion batteries (AZBs) show promises for large-scale energy storage. However, the zinc utilization rate (ZUR) is generally low due to side reactions in the aqueous electrolyte caused by the active water molecules. Here, we design a novel solvation structure in the electrolyte by introduction of sulfolane (SL). Theoretical calculations, molecular dynamics simulations and experimental tests show that SL remodels the primary solvation shell of Zn2+ , which significantly reduces the side reactions of Zn anode and achieves high ZUR under large capacities. Specifically, the symmetric and asymmetric cells could achieve a maximum of ∼96 % ZUR at an areal capacity of 24 mAh cm-2 . In a ZUR of ∼67 %, the developed Zn-V2 O5 full cell can be stably cycled for 500 cycles with an energy density of 180 Wh kg-1 and Zn-AC capacitor is stable for 5000 cycles. This electrolyte structural engineering strategy provides new insight into achieving high ZUR of Zn anodes for high performance AZBs.

High‐Capacity Zinc Anode with 96 % Utilization Rate Enabled by Solvation Structure Design

AbstractAqueous zinc‐ion batteries (AZBs) show promises for large‐scale energy storage. However, the zinc utilization rate (ZUR) is generally low due to side reactions in the aqueous electrolyte caused by the active water molecules. Here, we design a novel solvation structure in the electrolyte by introduction of sulfolane (SL). Theoretical calculations, molecular dynamics simulations and experimental tests show that SL remodels the primary solvation shell of Zn2+, which significantly reduces the side reactions of Zn anode and achieves high ZUR under large capacities. Specifically, the symmetric and asymmetric cells could achieve a maximum of ∼96 % ZUR at an areal capacity of 24 mAh cm−2. In a ZUR of ∼67 %, the developed Zn−V2O5 full cell can be stably cycled for 500 cycles with an energy density of 180 Wh kg−1 and Zn‐AC capacitor is stable for 5000 cycles. This electrolyte structural engineering strategy provides new insight into achieving high ZUR of Zn anodes for high performance AZBs.

Regulating the solventized structure to achieve highly reversible zinc plating/stripping for dendrite-free Zn anode by sulfolane additive

Aqueous zinc ion batteries (AZIBs) are a kind of ideal rechargeable batteries due to their high theoretical capacity, low cost and good safety. However, dendrite growth and side reactions prevent AZIBs from becoming excellent energy storage devices. Herein, an electrolyte additive of sulfolane (SL) is added to ZnSO4 electrolyte to inhibit zinc dendrite growth and side reactions. It is found that SL molecules replace water molecules in the solventized structure of [Zn(H2O)6]2+, reducing the number of highly chemically active water molecules at the interface between anode and electrolyte, thus inhibiting the growth of zinc dendrites and side reactions. As a result, a super long cycle life of > 4300 h is achieved at 2 mA cm−2/0.5 mAh cm−2 (>5700 h at 1 mA cm−2/0.25 mAh cm−2) for the Zn-Zn symmetrical cell with SL additive, which is much higher than that of the symmetrical battery without additive (50 h). The present work provides a general strategy to achieve the inhibition of zinc dendrites and side reactions via tailoring the solventized structure of [Zn(H2O)6]2+ by using small organic molecular as electrolyte additive to reduce the number of highly chemically active water molecules at the interface between zinc metal and aqueous electrolyte.

Enhancing the reversibility of Li deposition/dissolution in sulfur batteries using high-concentration electrolytes to develop anode-less batteries with lithium sulfide cathode

The reversibility of Li deposition/dissolution onto/from a copper substrate is analyzed herein for fabricating anodeless Li2S-cathode-based batteries using sulfolane (SL)-based sparingly solvating electrolytes to prevent lithium-polysulfide dissolution. The composition of electrolytes—binary lithium bis(trifluoromethanesulfonyl)amide/lithium bis(fluorosulfonyl)amide (LiTFSA/LiFSA; 9:1 molar ratio) in SL solvent—considerably affects the reversibility; a high-concentration electrolyte (HCE) and a localized high-concentration electrolyte (LHCE: HCE diluted by non-coordinating hydrofluoroether) exhibit superior reversibility than that of 1 M solution. Solid electrolyte interphases (SEI) with high F compositions and relatively low O concentrations are formed on the HCE- and LHCE-deposited Li surfaces. SEI formation via FSA decomposition is promoted in the HCE and LHCE, whereas SL decomposition is prohibited by the fluorine-rich SEI. The Li-deposit morphology is significantly affected by the nucleation overpotential at the initial deposition, which is influenced by the nature of the formed SEIs. Small-surface-area deposits with a low nucleation overpotential suppress the electrolyte decomposition and the formation of dead Li, resulting in high reversibility. Optimal reversibility is achieved by performing low-current-density initial deposition at 60 °C with the LHCE. The charge/discharge characteristics of anode-less Cu||Li2S batteries are determined under the reversibility-optimized conditions; 75 charge/discharge cycles and a 50-cycle capacity retention rate of 47.5% are achieved.