Electrolyte Solutions For Batteries Research Articles

Aprotic Lithium-Oxygen Batteries Based on Nonsolid Discharge Products.

Aprotic lithium-oxygen (Li-O2) batteries are considered to be a promising alternative option to lithium-ion batteries for high gravimetric energy storage devices. However, the sluggish electrochemical kinetics, the passivation, and the structural damage to the cathode caused by the solid discharge products have greatly hindered the practical application of Li-O2 batteries. Herein, the nonsolid-state discharge products of the off-stoichiometric Li1-xO2 in the electrolyte solutions are achieved by iridium (Ir) single-atom-based porous organic polymers (termed as Ir/AP-POP) as a homogeneous, soluble electrocatalyst for Li-O2 batteries. In particular, the numerous atomic active sites act as the main nucleation sites of O2-related discharge reactions, which are favorable to interacting with O2-/LiO2 intermediates in the electrolyte solutions, owing to the highly similar lattice-matching effect between the in situ-formed Ir3Li and LiO2, achieving a nonsolid LiO2 as the final discharge product in the electrolyte solutions for Li-O2 batteries. Consequently, the Li-O2 battery with a soluble Ir/AP-POP electrocatalyst exhibits an ultrahigh discharge capacity of 12.8 mAh, an ultralow overpotential of 0.03 V, and a long cyclic life of 700 h with the carbon cloth cathode. The manipulation of nonsolid discharge products in aprotic Li-O2 batteries breaks the traditional growth mode of Li2O2, bringing Li-O2 batteries closer to being a viable technology.

Anodic dissolution of aluminum in non-aqueous electrolyte solutions for sodium-ion batteries

The respective impact of the electrolyte and solvent, during anodic dissolution or passivation of aluminum was investigated in electrolyte solutions developed for sodium-ion batteries.

A smart membrane with negative thermo-responsiveness in battery electrolyte solution

The challenge of thermal runaway in lithium-ion batteries necessitates innovative solutions to enhance their safety. In this work, a negatively thermo-responsive membrane is proposed with grafting poly (N-isopropylacrylamide) onto polydopamine-modified polypropylene (PP) membrane via the Michael addition reaction. The implementation of such smart membrane is achieved based on the upper critical solution temperature (UCST) of the PNIPAM in the electrolyte solution containing 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), ethylene carbonate/diethyl carbonate (EC/DEC), and lithium tetrafluoroborate (LiBF4). The conformational transition of the PNIPAM in the electrolyte solution is intricately influenced by the competing salting-out effect of [EMIM][BF4] and salting-in effect of LiBF4. By maintaining a constant 1.0 M LiBF4 concentration in the electrolyte solution, the UCST of the PNIPAM that is precisely adjusted according to the 45.5 wt%-50 wt% of [EMIM][BF4] in the mixed EC/DEC solution provides the gating temperature. When below the gating temperature, the PNIPAM gating polymer grafted on the PP membrane remains in a shrinkable state to let the electrolyte ions shuttle feely between the electrodes. Conversely, in the event of overheating stemming from inadvertent Li-ion battery mismanagement, the PNIPAM gating polymer becomes extensible above the gating temperatures, resulting in the closure of the separator membrane. This mechanism effectively arrests the mobility of electrolyte ions, thereby contributing to the enhanced safety and security of lithium-ion batteries. The finding in this work offers valuable insights into the design and development of smart battery membranes with enhanced safety features to advance the progress of lithium-ion battery technology.

Correlations between Molecular Structure, Solvation Topology, and Transport Properties of Aqueous Organic Flow Battery Electrolyte Solutions

Correlations between Molecular Structure, Solvation Topology, and Transport Properties of Aqueous Organic Flow Battery Electrolyte Solutions

Is "Water in Salt" Electrolytes the Ultimate Solution? Achieving High Stability of Organic Anodes in Diluted Electrolyte Solutions Via a Wise Anions Selection.

The introduction of the water-in-salt (WIS) electrolytes concept to prevent water splitting and widen the electrochemical stability window, has spurred extensive research efforts toward development of improved aqueous batteries. The successful implementation of these electrolyte solutions in many electrochemical systems shifts the focus from diluted to WIS electrolyte solutions. Considering the high costs and the tendency of these nearly saturated solutions to crystallize, this trend can be carefully re-evaluated. Herein we show that the stability of organic electrodes comprising the active material perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), is strongly influenced by the solvation character of the anions rather than the concentration of the electrolyte solution. Even though the charging process of PTCDA involves solely insertion of cations (i.e., principal counter-ions), surprisingly, the dominant factor influencing its electrochemical performance, including long-term electrode stability, is the type of the co-ions (i.e., electrolytic anions). Using systematic electrochemical analysis combined with theoretical simulations, we show that the selection of kosmotropic anions results in fast fading of the PTCDA anodes, while a selection of chaotropic anions leads to excellent stability, even at electrolytes concentrations as low as 0.2 M. These findings provide a new conceptual approach for designing advanced electrolyte solutions for aqueous batteries.

Is “Water in Salt” Electrolytes the Ultimate Solution? Achieving High Stability of Organic Anodes in Diluted Electrolyte Solutions Via a Wise Anions Selection

AbstractThe introduction of the water‐in‐salt (WIS) electrolytes concept to prevent water splitting and widen the electrochemical stability window, has spurred extensive research efforts toward development of improved aqueous batteries. The successful implementation of these electrolyte solutions in many electrochemical systems shifts the focus from diluted to WIS electrolyte solutions. Considering the high costs and the tendency of these nearly saturated solutions to crystallize, this trend can be carefully re‐evaluated. Herein we show that the stability of organic electrodes comprising the active material perylene‐3,4,9,10‐tetracarboxylic dianhydride (PTCDA), is strongly influenced by the solvation character of the anions rather than the concentration of the electrolyte solution. Even though the charging process of PTCDA involves solely insertion of cations (i.e., principal counter‐ions), surprisingly, the dominant factor influencing its electrochemical performance, including long‐term electrode stability, is the type of the co‐ions (i.e., electrolytic anions). Using systematic electrochemical analysis combined with theoretical simulations, we show that the selection of kosmotropic anions results in fast fading of the PTCDA anodes, while a selection of chaotropic anions leads to excellent stability, even at electrolytes concentrations as low as 0.2 M. These findings provide a new conceptual approach for designing advanced electrolyte solutions for aqueous batteries.

The Effect of Chlorides on the Performance of DME/Mg[B(HFIP)4]2 Solutions for Rechargeable Mg Batteries

One of the major issues in developing electrolyte solutions for rechargeable magnesium batteries is understanding the positive effect of chloride anions on Mg deposition-dissolution processes on the anode side, as well as intercalation-deintercalation of Mg2+ ions on the cathode side. Our previous results suggested that Cl− ions are adsorbed on the surface of Mg anodes and Chevrel phase MgxMo6S8 cathodes. This creates a surface add-layer that reduces the activation energy for the interfacial Mg ions transportation and related charge transfer, as well as promotes the transport of Mg2+ from the solution phase to the Mg anode surface and into the cathodes’ host materials. Here, this work further examines the effect of adding chlorides to the state-of-the-art Mg[B(HFIP)4]2/DME electrolyte solution, specifically focusing on reversible magnesium deposition, as well as the performance of Mg cells with benchmark Chevrel phase cathodes. It was observed that the presence of chlorides in these solutions facilitates both Mg deposition, and Mg2+ ions intercalation, whereby this effect is more pronounced as the purity level of the solution is lowered.

First isolation of solvated MgCl+ species as the sole cations in electrolyte solutions for rechargeable Mg batteries

First isolation of solvated MgCl+ species as the sole cations in electrolyte solutions for rechargeable Mg batteries

Highly swollen ROMP-based gels

The leakage of organic solvent during the transportation and storage is one of the major threats to the environment. Networks/gels acting as the absorbing materials for organic solvents are the most promising solution for the organic solvent pollution. Here, we report the synthesis of highly swollen networks/gels in high yield (≥95%) via ring opening metathesis polymerization (ROMP) using Grubbs’ first generation catalyst/initiator (G1), a crosslinker (1,1′-(methylenedi-4,1-phenylene)bis-exo-7-oxanorbornenecarboximide) and monofunctional monomer/diluent (exo-N-phenyl-7-oxanorbornenecarboximide). The mesh size of the network was varied by keeping the concentration of monomer constant while changing the concentrations of crosslinker and G1 (initiator). The swelling capacity of the network in N,N-dimethylformamide (DMF) solvent increased from 41 to 53 and to 61 with the increase of theoretical mesh size (molar ratio of monomer to crosslinker) from 20 to 40 and to 60, respectively. By further increasing the mesh size from 60 to 80 there was no significant change in swelling capacities (63). Thus, the gel with the mesh size of 60 was selected for swelling capacity analysis in other polar organic solvents such as dimethyl sulfoxide (DMSO), dichloromethane (DCM), chloroform and lithium-ion battery electrolyte solution (1.0 M LiPF6 in ethylene carbonate (EC)/diethyl carbonate (DEC) = 50/50 (v/v)). They showed the decreased swelling capacity value from 61 to 57, 40, 31 and 5, respectively. For a controlled mesh size ROMP-based gel, we observed the highest swelling capacity values to date.

Quantifying Dissolved Transition Metals in Battery Electrolyte Solutions with NMR Paramagnetic Relaxation Enhancement.

Transition metal dissolution is an important contributor to capacity fade in lithium-ion cells. NMR relaxation rates are proportional to the concentration of paramagnetic species, making them suitable to quantify dissolved transition metals in battery electrolytes. In this work, 7Li, 31P, 19F, and 1H longitudinal and transverse relaxation rates were measured to study LiPF6 electrolyte solutions containing Ni2+, Mn2+, Co2+, or Cu2+ salts and Mn dissolved from LiMn2O4. Sensitivities were found to vary by nuclide and by transition metal. 19F (PF6-) and 1H (solvent) measurements were more sensitive than 7Li and 31P measurements due to the higher likelihood that the observed species are in closer proximity to the metal center. Mn2+ induced the greatest relaxation enhancement, yielding a limit of detection of ∼0.005 mM for 19F and 1H measurements. Relaxometric analysis of a sample containing Mn dissolved from LiMn2O4 at ∼20 °C showed good sensitivity and accuracy (suggesting dissolution of Mn2+), but analysis of a sample stored at 60 °C showed that the relaxometric quantification is less accurate for heat-degraded LiPF6 electrolytes. This is attributed to degradation processes causing changes to the metal solvation shell (changing the fractions of PF6-, EC, and EMC coordinated to Mn2+), such that calibration measurements performed with pristine electrolyte solutions are not applicable to degraded solutions-a potential complication for efforts to quantify metal dissolution during operando NMR studies of batteries employing widely-used LiPF6 electrolytes. Ex situ nondestructive quantification of transition metals in lithium-ion battery electrolytes is shown to be possible by NMR relaxometry; further, the method's sensitivity to the metal solvation shell also suggests potential use in assessing the coordination spheres of dissolved transition metals.

Solution NMR of Battery Electrolytes: Assessing and Mitigating Spectral Broadening Caused by Transition Metal Dissolution.

NMR spectroscopy is a powerful tool that is commonly used to assess the degradation of lithium-ion battery electrolyte solutions. However, dissolution of paramagnetic Ni2+ and Mn2+ ions from cathode materials may affect the NMR spectra of the electrolyte solution, with the unpaired electron spins in these paramagnetic solutes inducing rapid nuclear relaxation and spectral broadening (and often peak shifts). This work establishes how dissolved Ni2+ and Mn2+ in LiPF6 electrolyte solutions affect 1H, 19F, and 31P NMR spectra of pristine and degraded electrolyte solutions, including whether the peaks from degradation species are at risk of being lost and whether the spectral broadening can be mitigated. Mn2+ is shown to cause far greater peak broadening than Ni2+, with the effect of Mn2+ observable at just 10 μM. Generally, 19F peaks from PF6 - degradation species are most affected by the presence of the paramagnetic metals, followed by 31P and 1H peaks. Surprisingly, when NMR solvents are added to acquire the spectra, the degree of broadening is heavily solvent-dependent, following the trend of solvent donor number (increased broadening with lower solvent donicity). Severe spectral broadening is shown to occur whether Mn is introduced via the salt Mn(TFSI)2 or is dissolved from LiMn2O4. We show that the weak 19F and 31P peaks in spectra of electrolyte samples containing micromolar levels of dissolved Mn2+ are broadened to an extent that they are no longer visible, but this broadening can be minimized by diluting electrolyte samples with a suitably coordinating NMR solvent. Li3PO4 addition to the sample is also shown to return 19F and 31P spectral resolution by precipitating Mn2+ out of electrolyte samples, although this method consumes any HF in the electrolyte solution.

Non-polar ether-based electrolyte solutions for stable high-voltage non-aqueous lithium metal batteries

The electrochemical instability of ether-based electrolyte solutions hinders their practical applications in high-voltage Li metal batteries. To circumvent this issue, here, we propose a dilution strategy to lose the Li+/solvent interaction and use the dilute non-aqueous electrolyte solution in high-voltage lithium metal batteries. We demonstrate that in a non-polar dipropyl ether (DPE)-based electrolyte solution with lithium bis(fluorosulfonyl) imide salt, the decomposition order of solvated species can be adjusted to promote the Li+/salt-derived anion clusters decomposition over free ether solvent molecules. This selective mechanism favors the formation of a robust cathode electrolyte interphase (CEI) and a solvent-deficient electric double-layer structure at the positive electrode interface. When the DPE-based electrolyte is tested in combination with a Li metal negative electrode (50 μm thick) and a LiNi0.8Co0.1Mn0.1O2-based positive electrode (3.3 mAh/cm2) in pouch cell configuration at 25 °C, a specific discharge capacity retention of about 74% after 150 cycles (0.33 and 1 mA/cm2 charge and discharge, respectively) is obtained.

Antiaromatic Covalent Organic Frameworks Based on Dibenzopentalenes

Despite their inherent instability, 4n π systems have recently received significant attention due to their unique optical and electronic properties. In dibenzopentalene (DBP), benzanellation stabilizes the highly antiaromatic pentalene core, without compromising its amphoteric redox behavior or small HOMO-LUMO energy gap. However, incorporating such molecules in organic devices as discrete small molecules or amorphous polymers can limit the performance (e.g., due to solubility in the battery electrolyte solution or low internal surface area). Covalent organic frameworks (COFs), on the contrary, are highly ordered, porous, and crystalline materials that can provide a platform to align molecules with specific properties in a well-defined, ordered environment. We synthesized the first antiaromatic framework materials and obtained a series of three highly crystalline and porous COFs based on DBP. Potential applications of such antiaromatic bulk materials were explored: COF films show a conductivity of 4 × 10-8 S cm-1 upon doping and exhibit photoconductivity upon irradiation with visible light. Application as positive electrode materials in Li-organic batteries demonstrates a significant enhancement of performance when the antiaromaticity of the DBP unit in the COF is exploited in its redox activity with a discharge capacity of 26 mA h g-1 at a potential of 3.9 V vs. Li/Li+. This work showcases antiaromaticity as a new design principle for functional framework materials.

Design Guidelines for Sulfonyl/Sulfamoyl Fluoride Electrolyte Additives for Modulation of Lithium Anode Coulombic Efficiency

Owing to its high theoretical capacity (3860 mAh/g, over 10 times that of graphite) and its lowest theoretical electrochemical potential (-3.04 V vs SHE), Li metal is an ideal anode material for improving the capacity of rechargeable Li batteries [1]. However, the practical application of the Li anode is severely hindered by its high reactivity with standard electrolyte compositions, which results in limited Coulombic efficiency (CE) in those electrolytes (for instance, 85-90% with 1 M LiPF6 EC:DEC [2]). Strategies to improve CE have focused on electrolyte engineering, including development of highly concentrated electrolytes (HCE) and more recently, local high-concentration electrolytes (LHCE) [3]. A feature shared by these strategies is the promotion of contact-ion pairing, which enhances anion contributions to the solid electrolyte interphase (SEI). Among the best-performing salts are fluorinated lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), which are believed to promote stable inorganic-rich SEIs and correlate with higher CE [4]. A second strategy of interest is to pursue development of additives incorporated at relatively low concentrations (e.g., 2-5 wt%) that can favorably alter the SEI, such as carbonates (e.g., vinylene carbonate (VC) [5] and fluoroethylene carbonate (FEC) [6]), sulfates (e.g., ethylene sulfate (DTD) and 1,3-propanesulfonate (PS) [7]), and borates (e.g., lithium difluoro(oxoalate) borate (LiDFOB) [8] and tris (2,2,2-trifluoroethyl) borate (TTFEB) [9]). An advantage of this strategy is the possibility to ultimately lower reliance on high fluorinated salt concentrations, which are costly and can be corrosive towards the Al current collector, and potentially expand the versatility of available electrolyte frameworks having competitive CE. However, compared to the principles developed for salt and solvent selection in HCE and LHCE, the mechanism behind successful additive activation needs elucidation.In this work, we examined the potential of "FSI-like," neutral sulfonyl/sulfamoyl fluorides (R-SO2F and R-R’-NSO2F, Figure 1) as functional additives for Li cycling, motivated by their structural similarity to the high-performance FSI- anion. The examined baseline electrolytes include high-CE systems consisting of LiFSI dissolved in various solvents: fluoroethylene carbonate (FEC, 1 and 4 M salt), 1,2-dimethoxyethane (DME, 4 M), and dimethyl carbonate (DMC, 6 M). The ability for each additive to coordinate with Li+ was first examined by NMR, with trends rationalized in part by supporting microcalorimetry data on the degree of solvent coordination strength. We relate these to CE and cycling outcomes in each electrolyte. Interestingly, we find that additives have negligible effect on CE in FEC-based electrolytes, whereas significant impacts were observed in DME and DMC. We relate these diverse outcomes to the SEI chemical compositions and gases evolved during galvanostatic cycling, as characterized by X-ray photoelectron spectroscopy (XPS) and gas chromatography (GC), which help to rationalize competitive reactions among solvent, anion, and additive. Unfortunately, additives had a negative-to-neutral impact on CE in these systems. Thus, we finally examined a LiPF6 in carbonate electrolyte, 1 M LiPF6 in EC/DMC (LP40), where we hypothesized that competitive reduction of coordinating additives over problematic carbonate solvent would lead to performance gains. Indeed, significant improvements (up to 94%, compared to baseline 89% over the initial 50 cycles) in CE were observed for two additives, with their structural advantages further discussed. Overall, our findings provide insights into the effects of sulfonyl/sulfamoyl fluoride additive structures on Li metal cyclability and the compositions of baseline electrolytes whose electrochemical cycling stability can be effectively modulated by these additives. Xu, W., et al., Lithium metal anodes for rechargeable batteries. Energy & Environmental Science, 2014.7(2):p.513-537.Genovese, M., et al., Combinatorial methods for improving lithium metal cycling efficiency. Journal of The Electrochemical Society, 2018.165(13):p.A3000.Hobold, G.M., et al., Moving beyond 99.9% Coulombic efficiency for lithium anodes in liquid electrolytes. Nature Energy, 2021.6(10):p.951-960.Suo, L., et al., Fluorine-donating electrolytes enable highly reversible 5-V-class Li metal batteries. Proceedings of the National Academy of Sciences, 2018.115(6):p.1156-1161.Aurbach, D., et al., On the use of vinylene carbonate (VC) as an additive to electrolyte solutions for Li-ion batteries. Electrochimica acta, 2002.47(9):p.1423-1439.Markevich, E., et al., Fluoroethylene carbonate as an important component in electrolyte solutions for high-voltage lithium batteries: role of surface chemistry on the cathode. Langmuir, 2014.30(25):p.7414-7424.Han, B., et al., Poor Stability of Li2CO3 in the Solid Electrolyte Interphase of a Lithium ‐Metal Anode Revealed by Cryo ‐Electron Microscopy. Advanced Materials, 2021.33(22):p.2100404.Liu, J., et al., Lithium difluoro (oxalato) borate as a functional additive for lithium-ion batteries. Electrochemistry communications, 2007.9(3):p.475-479.Ma, Y., et al., Enabling reliable lithium metal batteries by a bifunctional anionic electrolyte additive. Energy Storage Materials, 2018.11:p.197-204. Figure 1. (a) Sulfonyl/sulfamoyl fluoride chemical structures and (b) R-S and S-F bond lengths calculated by density functional theory. Figure 1

Autonomous optimization of non-aqueous Li-ion battery electrolytes via robotic experimentation and machine learning coupling

Developing high-energy and efficient battery technologies is a crucial aspect of advancing the electrification of transportation and aviation. However, battery innovations can take years to deliver. In the case of non-aqueous battery electrolyte solutions, the many design variables in selecting multiple solvents, salts and their relative ratios make electrolyte optimization time-consuming and laborious. To overcome these issues, we propose in this work an experimental design that couples robotics (a custom-built automated experiment named "Clio”) to machine-learning (a Bayesian optimization-based experiment planner named "Dragonfly”). An autonomous optimization of the electrolyte conductivity over a single-salt and ternary solvent design space identifies six fast-charging non-aqueous electrolyte solutions in two work-days and forty-two experiments. This result represents a six-fold time acceleration compared to a random search performed by the same automated experiment. To validate the practical use of these electrolytes, we tested them in a 220 mAh graphite∣∣LiNi0.5Mn0.3Co0.2O2 pouch cell configuration. All the pouch cells containing the robot-developed electrolytes demonstrate improved fast-charging capability against a baseline experiment that uses a non-aqueous electrolyte solution selected a priori from the design space.

Epidemiological Profile of Dermatosis among Automobile Repair and Maintenance Garages in the City of Parakou in 2020

Background: Occupational dermatoses, also called occupational dermatitis or occupational dermatitis, are very common in the workplace and are still a topical subject. All over the world, especially in developed countries. They handicap the professional activities of the workers. Purpose: To determine the epidemiological profile of dermatosis among automobile repair and maintenance garages in Parakou. Methods: It was a cross-sectional and descriptive study carried out from 20 April to 17 May 2020. The sampling method was non-probabilistic. Data collected from a questionnaire, clinical examination and worksite observation were analyzed with Epi Info 7.2.2.1 software. Results: The participation rate was 98.08%. The sex ratio (male/female) was 178. The mean age of the respondents was 25.80 ± 10.22 years. Respondents with less than 5 years of experience in the field were 61.22%. Mechanics were the most numerous. In the sample, 95.81% had frequent skin contact with fuels, 84.08% had contact with motor oils and 15.92% had contact with dilute battery electrolyte solutions. The frequency of dermatosis was 73.46%. Hands and wrists were the most affected seats (47.35%). Some (33.84%) wore them before the start of the activity in the garage but in 66.22% of them, the dermatosis had occurred because of their arrival in the garage. Among these skin diseases, keratoderma predominated at 80.01%. Conclusion: Dermatosis is very common among garage owners in Parakou.

Ion Transport in Organic Electrolyte Solutions for Lithium-ion Batteries and Beyond

The performance of metal-ion batteries at low temperatures and their fast charge/discharge rates are determined mainly by the electrolyte (ion) transport. Accurate transport properties must be evaluated for designing and/or optimization of lithium-ion and other metal-ion batteries. In this review, we report and discuss experimental and atomistic computational studies on ion transport, in particular, ion diffusion/dynamics, transference number, and ionic conductivity. Although a large number of studies focusing on lithium-ion transport in organic liquids have been performed, only a few experimental studies have been conducted in the organic liquid electrolyte phase for other alkali metals that are used in batteries (such as sodium, potassium, magnesium, etc.). Atomistic computer simulations can play a primary role and predict ion transport in organic liquids. However, to date, atomistic force fields and models have not been explored and developed exhaustively to simulate such organic liquids in quantitative agreement to experimental measurements.

Construction of a spherically bent crystal analyzer through anodic bonding for a non-resonant inelastic X-ray scattering spectrometer

The anodic bonding method was used to construct spherically bent crystal analyzers for a synchrotron radiation based non-resonant inelastic X-ray scattering spectrometer to probe the local electronic and molecular structure. In order to test the performance of the fabricated analyzers, the O K-edge X-ray Raman scattering spectrum of a lithium-ion battery electrolyte solution was measured and compared to the spectrum in the literature, which was measured by using a conventional X-ray absorption spectroscopy. The X-ray Raman scattering spectrometer based on a 1 m Rowland circle provided to record the data with a resolution of 0.8 eV at ∼10 keV. The obtained experimental results showed that the anodic bonding was achieved with a high bonding quality.

Physical and Electrolytic Properties of Dialkoxyethanes

1,2-Dimethoxyethane (DME, ethylene glycol dimethyl ether) and 1,2-diethoxyethane (DEE, ethylene glycol diethyl ether) are dialkyl ethers of ethylene glycol. DME shows a high boiling point as compared to diethyl ether and tetrahydrofuran. DME is also used as a reagent in organometallic chemistry and as a solvent in some electrolyte solutions for lithium batteries. The solubility of lithium salts in DEE is much less than that in DME. Partial fluorination of DEE can improve the solubility of lithium salts. In contrast, the polyfluorinated and perfluorinated organic solvents show very low polarity. These solvents are the so-called fluorous media and are often immiscible with organic solvents as well as water. We report the physical and electrochemical properties of fluorinated DEEs: monofluorinated, trifluorinated, and tetrafluorinated DEEs (EFEE, ETFEE, and FETFEE, respectively).The relative permittivity reflects the ease of progress of dielectric polarization. The relative permittivities of FETFEE, EFEE, and EFTEE decreased linearly with an increase in temperature. The relative permittivities of FETFEE, EFEE, and EFTEE decreased linearly with an increase in temperature. The relative permittivity of FETFEE was higher than those of ETFEE and EFEE: FETFEE > ETFEE ≈ EFEE > DEE. The viscosity is the property which opposes the relative motion of the adjacent layers of the liquid. It is regarded as the internal friction and affects electrolytic conductivity. The viscosity (η) of FETFEE was also higher than those of EFEE and ETFEE: FETFEE > EFEE > ETFEE > DEE. The kinematic viscositsiy (v) of ETFEE was as low as that of DEE above 323 K. The plots of log10(η/mPas) vs. T −1 and the plots of log10(v / 10−2 m2 s−1) vs. T −1 gave straight lines.The conductivity of an electrolyte solution is a key factor determining the internal resistance and rate performance of lithium batteries. The conductivities (κ) of electrolyte solutions in ETFEE and FETFEE increased with an increase in temperature (T). The viscosities of the fluorinated DEEs decreased rapidly with an increase in temperature and approached that of DEE at high temperatures. Interestingly, the conductivity of LiPF6 solution in FETFEE was higher than that in ETFEE: EFEE > FETFEE > ETFEE. The partial fluorination can increase the ability of the solvent molecules to form hydrogen bonds. The number of hydrogen atoms that are bound to the same terminal carbon atom as fluorine atoms are as given below: FETFEE (2), EFEE (2), ETFEE (0), and DEE (0). The attraction between FETFEE molecules can be based on nonconventional weak intermolecular hydrogen bonding (CF−H···O or C−H···F−C). The weak hydrogen-bonding system does not exchange its proton and therefore it is no more a genuine hydrogen bond; it is an electrostatic attraction between positive charge on the hydrogen and negative charge on the organic fluorine or the organic oxygen.The hydrogen bonding leads to the high acceptability of an electron-pair of a donor atom from a solute. This effect may result in the increased solvation of PF6 − ions and, consequently, in the higher degree of ionic dissociation. The fluoromethyl group (CH2F-) may serve as an anion-attracting group. In contrast, the polyfluorination can decrease the electron-pair donability of an oxygen atom of the C-O-C moiety. The trifluoromethyl group (CF3-) is a strong electron-withdrawing substituent. The anodic stability of FETFEE was higher than that of EFEE: FETFEE > ETFEE > EFEE. The finding suggests that the electron-pair donability decreases in the inverse order: FETFEE < ETFEE < EFEE. Fluorine is the most electronegative of all the elements. Most conventional measures for the electronic effect of substituents are provided as Taft constants (σ*) for substituents attached to aliphatic chains. The Taft constants of a trifluorometheyl group (CF3-: Taft σ* = 2.61, σ(calcd.) = 2.60) and a fluorometheyl group (CH2F-: Taft σ* = 1.10, σ(calcd.) = 1.17) are substantially larger than that of a metheyl group (CH3-: Taft σ* = 0, σ(calcd.) = −0.07). The value of 1.10 is comparable with a formyl group (-CHO: Taft σ* = 1.1, σ(calcd.) = 1.09).The product of conductivity and viscosity (κη) observed for FETFEE, ETFEE, and EFEE was slightly decreasing at high temperatures. The plots of log10(η/mPas) vs. T −1 gave straight lines. In contrast, the plots of log10(κ/mScm−1) vs. T −1 displayed upward curvature. The decrease in the κη and the convex curve show that the conductivities of LiPF6 solutions in FETFEE, ETFEE, and EFEE are not inversely proportional to the viscosities at elevated temperatures.

(Invited) Electrostriction Driven Preferential Solvation Processes for Divalent Cations in Non-Aqueous Electrolytes

The strong electric field from divalent cations (i.e. Mg2+, Zn2+ and Ca2+) can influence conformal structural evolution of organic solvent molecules and subsequently influence emergent properties of battery electrolyte solutions. This electrostriction process typically depends on the charge and size of the ion and on certain properties of the solvent such as molecular flexibility and permittivity. In this work, we focused on the effect of cationic size and structural flexibility of organic solvent molecules commonly used in multivalent batteries. In particular, we analyzed electrostriction driven preferential interactions that lead to contact-ion pair (CIP) and solvent separated ion pair (SSIP) formation in cyclic ether solvents such as tetrahydrofuran (THF) and 2-methyl-tetrahydrofuran (2-MeTHF) and linear structured ether solvents such as glymes (G1 and G2). The concentration and temperature dependent preferential interactions of these electrolyte systems were analyzed using multinuclear (1H,19F, 17O, 25Mg, 43Ca, and 67Zn) NMR spectroscopy and PFG-NMR diffusion measurement combined with classical MD and DFT based computational modeling. Our results show that the solvent-cation interaction is more favorable in the linear glyme-based electrolytes than in the cyclic THF-based electrolytes. In particular, the glyme-based solvents (G1 and G2) drive preferential dissociation of cation-anion pairs, resulting in a higher concentration of SSIPs in these multivalent electrolyte solutions. The correlation between such preferential solvation phenomena and emergent properties including conductivity and chemical stability will be discussed..