Propylene Carbonate Molecules Research Articles

Diffusion and structure of propylene carbonate-metal salt electrolyte solutions for post-lithium-ion batteries: From experiment to simulation.

The diffusion of cations in organic solvent solutions is important for the performance of metal-ion batteries. In this article, pulsed field gradient nuclear magnetic resonance experiments and fully atomistic molecular dynamic simulations were employed to study the temperature-dependent diffusive behavior of various liquid electrolytes representing 1M propylene carbonate solutions of metal salts with bis(trifluoromethylsulfonyl)imide (TFSI-) or hexafluorophosphate (PF6-) anions commonly used in lithium-ion batteries and beyond. The experimental studies revealed the temperature dependence of the diffusion coefficients for the propylene carbonate (PC) solvent and for the anions following an Arrhenius type of behavior. It was observed that the PC molecules are the faster species. For the monovalent cations (Li+, Na+, K+), the PC solvent diffusion was enhanced as the cation size increased, while for the divalent cations (Mg2+, Ca2+, Sr2+, Ba2+), the opposite trend was observed, i.e., the diffusion coefficients decreased as the cation size increased. The anion diffusion in LiTFSI and NaTFSI solutions was found to be similar, while in electrolytes with divalent cations, a decrease in anion diffusion with increasing cation size was observed. It was shown that non-polarizable charge-scaled force fields could correspond perfectly to the experimental values of the anion and PC solvent diffusion coefficients in salt solutions of both monovalent (Li+, Na+, K+) and divalent (Mg2+, Ca2+, Sr2+, Ba2+) cations at a range of operational temperatures. Finally, after calculating the radial distribution functions between cations, anions, and solvent molecules, the increase in the PC diffusion coefficient established with the increase in cation size for monovalent cations was clearly explained by the large hydration shell of small Li+ cations, due to their strong interaction with the PC solvent. In solutions with larger monovalent cations, such as Na+, and with a smaller solvation shell of PC, the PC diffusion is faster due to more liberated solvent molecules. In the salt solutions with divalent cations, both the anion and the PC diffusion coefficients decreased as the cation size increased due to an enhanced cation-anion coordination, which was accompanied by an increase in the amount of PC in the cation solvation shell due to the presence of anions.

Exploring the Molecular-Scale Structures at Solid/Liquid Interfaces of Li-Ion Battery Materials: A Force Spectroscopy Analysis with Sparse Modeling.

In this study, we clarify the liquid structure formed at the interface between LiCoO2 (LCO), the cathode material of Li-ion batteries, and propylene carbonate (PC), which is used as a solvent in the electrolyte, on a molecular scale. We apply sparse modeling-based modal analysis to force spectroscopy data measured by frequency modulation atomic force microscopy (FM-AFM) and show that each component in the FM-AFM force curve, such as oscillatory solvation force, background, and noise, can be automatically decomposed. Moreover, by combining detailed force curve analysis with solid/liquid interface simulations based on first-principles calculation, we have identified that there are distinct damped vibrational modes in the force curves at the LCO/PC interface with a period of about 0.57 nm and those with shorter periods, which likely correspond to the solvation forces associated with bulk-state PC molecules and those with PC molecules in "lying down" orientations.

INVESTIGATION OF SOLVATION IN LITHIUM PERCHLORATE -PROPYLENE CARBONATE-DIMETHYL CARBONATE SYSTEM BY RAMAN SPECTROSCOPY

The difference of solvent properties can significantly affect the solvation phenomena in individual and, especially, in mixed solutions. In particular, it can be assumed that in mixed solvents, i.e. in systems with intermediate dielectric permittivity (mixtures of linear and cyclic carbonic acid esters), cations will bind molecules of linear esters more strongly and bind molecules of cyclic esters more weakly than it takes place in individual solvents. In the present work the Raman spectra of lithium perchlorate solvents in propylene carbonate (PC), dimethyl carbonate (DMC) and their mixture in a wide range of salt concentrations are studied. It is shown that the solvation effects of the cation are clearly traced in the region of symmetric ring vibrations (~690-730 cm-1) of propylene carbonate and in the region of deformation vibrations of CCA (~520 cm-1) of dimethyl carbonate. These effects are also evident in the mixed solvent. The so-called method of differential spectroscopy was used to judge the structural changes of mixed-solvent systems. It consisted in constructing spectra of lithium salt solutions in mixed solvents, additive sum of spectra of lithium salt solutions in PC and DMC, as well as their difference (differential spectra). The analysis of differential spectra allows us to conclude that in systems with mixed solvent there is a weakening of interaction of propylene carbonate molecules with ions, and there is a preferential solvation of cations and anions by dimethyl carbonate molecules. Also, unlike propylene carbonate, dimethyl carbonate solvates perchlorate ions, which follows from the line contour changes in the region of CH3-group vibrations (2970 cm-1) solvation of anions is also observed in the mixed solvent. For citation: Rabadanov K.Sh., Gafurov M.M., Akhmedov M.A., Rabadanova D.I., Magomedova A.G. Investigation of solvation in lithium perchlorate -propylene carbonate-dimethyl carbonate system by raman spectroscopy. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 5. P. 36-42. DOI: 10.6060/ivkkt.20246705.6967.

Local structure of concentrated NaFSA solutions in propylene carbonate studied by X-ray and neutron diffraction methods

Abstract The microscopic structure of 10 mol% NaFSA [FSA: bis(fluorosulfonyl)amide]-propylene carbonate (PC) solution has been investigated by means of X-ray and neutron diffraction techniques. The solvation structure of Na+ has been determined from least-squares fitting analysis of X-ray intermolecular difference interference terms observed for 10 mol% NaFSA-PC solution and pure liquid PC. In the present solution, onaverage, 6(1) PC molecules are involved in the first solvation shell of Na+ with intermolecular distance rNaO = 2.26(7) Å, and bond angle ∠Na+…O = C = 169(9)°. Intermolecular correlation between neighboring PC molecules in the solution has been derived from simultaneous least-squares fitting analysis of observed H–H, H–X, and X–X (X: atoms except for H) intermolecular partial structure factors determined from neutron diffraction data for H/D isotopically-substituted sample solutions. An indication of anti-parallel configuration of the nearest neighbor PC molecules has been suggested.

Designing of high‐performance dye‐sensitized solar cells by using a new electrolyte based on deep eutectic solvents

SummaryThe present research is aimed to develop an efficient electrolyte based on deep eutectic solvents (DESs) for dye‐sensitized solar cells (DSSCs). In this regard, the performance of the propylene carbonate (PC) and tetrabutylammonium iodide (TBAI) based DES (PC/TBAI‐DES) as a new electrolyte solvent for DSSCs is evaluated for the first time. Herein, the effects of various electrolyte components, namely the amount of acetonitrile (AN), iodine, and 1‐ethyl‐3‐methylimidazolium iodide (EmimI), are investigated. The optimal conditions are achieved with an electrolyte composition of 0.1 M of iodine and EmimI in a binary mixture of PC/TBAI‐DES and AN (volume ratio 80:20). The DSSCs based on this electrolyte attained a significant conversion efficiency of 10.04% (Jsc = 21.94 mA cm2, Voc = 0.78 V, and FF = 0.58) under 1 sun (AM 1.5) illumination. Moreover, a detailed view of the molecular arrangement of PC/TBAI‐DES solution near the titanium dioxide and platinum solid surfaces as electrodes of DSSCs is investigated using molecular dynamics simulations. Besides, the interaction parameters between TBAI ion pair and PC molecule are determined through density functional theory.

Adsorption of Halides on Au (111) Electrode in Aprotic Solvents: AC- Voltammetry, EIS, XPS and Surface-Enhanced Infrared Spectroscopy

Specific adsorption of ions on the electrode surface has a significant impact on the electric double layer (EDL) structure and the kinetics of electrode processes[1]. The ion adsorption at aqueous solution interfaces[2] on various metals has been examined intensively, but much fewer studies from non-aqueous solvents have been conducted[3]. Such studies are important because the metal-solvent [4] and ion-solvent interaction energy [5] depend on the chemical nature of the solvent.In this study, three organic solvents (propylene carbonate (PC), diglyme (DG), and dimethyl sulfoxide (DMSO)) were investigated for the adsorption of iodide and bromide ions on Au(111) single crystal electrode. This analysis was conducted by using differential capacity measurements, cyclic voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and Surface-Enhanced Infrared Spectroscopy (SEIRAS).The magnitude of anion adsorption on Au(111) electrode increases in the series of halides I- ˃ Br- due to better solvation [6] and in the solvent order PC ˃ DG ˃ DMSO[7]. As well, the influence of water content on the adsorption rate of iodide on Au(111) electrode in PC and DMSO was studied. This effect, and the much higher adsorption rate in water is explained by the closer approach of the solvated halogen ion to the surface and the resulting stronger interaction of the transition state with the electrode. Quantification of the adsorbed iodide amount from XPS spectra confirms the coverage estimated from the adsorption charge in CVs. During SEIRAS measurements, a bipolar band is observed at around 1805 cm−1 which correlates to the C-O-vibration of PC as reported on silver electrodes from SERS measurements[8]. A stronger electrical field with decreasing potential is observed in absence of iodine leads to higher absorbance of PC molecules on the surface. Acknowledgments Financial support by the German Federal Ministry of Education and Research (BMBF) of the “LuCaMag” project (Fkz: 03EK3051A) under the framework of “Vom Material zur Innovation” program is acknowledged.

On the Differential Capacitance and Potential of Zero Charge of Au(111) in Some Aprotic Solvents

AbstractVoltammetric and Gouy‐Chapman capacitance minimum measurements were conducted on Au(111) and roughened Au(111) electrodes in aprotic electrolytes in the absence and presence of specifically adsorbed ions for concentrations ranging from 0.001 to 0.5 M. Negative of the point of zero charge (pzc), the capacitance maximum increases in the order Ca2+<Li+<K+, but the pzc value is independent of cation nature. The capacitance values have a slight dependence on cation type at a more negative potential. The pzc depends on the solvent and is influenced by the dielectric constant, metal‐solvent interactions and donor number; it is shifted to more positive values with increasing water content. Specific anion adsorption shifts the pzc to more negative values. The pzc value is more negative for the roughened electrode compared to the single crystal electrode. Propylene carbonate (PC) adsorption in the presence of perchlorate and iodide was examined on gold film by surface‐enhanced infrared absorption spectroscopy (SEIRAS). The potential dependent intensity is explained by a stronger electric field and thus a better alignment of the PC molecules when the absolute potential difference to the pzc is large.The capacitance curves were theoretically modelled. From the capacitance maxima on both sides of the pzc the ionic volume and thus the solvation numbers were estimated. The width of the capacitance minimum is believed to be related to the layer of adsorbed solvent molecules.

Adsorption of propylene carbonate on the LiMn2O4 (100) surface investigated by DFT + U calculations* *Project supported by the National Natural Science Foundation of China (Grant No. 51962010).

Understanding the mechanism of the interfacial reaction between the cathode material and the electrolyte is a significant work because the interfacial reaction is an important factor affecting the stability, capacity, and cycling performance of Li-ion batteries. In this work, spin-polarized density functional theory calculations with on-site Coulomb energy have been employed to study the adsorption of electrolyte components propylene carbonate (PC) on the LiMn2O4 (100) surface. The findings show that the PC molecule prefers to interact with the Mn atom on the LiMn2O4 (100) surface via the carbonyl oxygen (Oc), with the adsorption energy of −1.16 eV, which is an exothermic reaction. As the adsorption of organic molecule PC increases the Mn atoms coordination with O atoms on the (100) surface, the Mn3 + ions on the surface lose charge and the reactivity is substantially decreased, which improves the stability of the surface and benefits the cycling performance.

Preferential solvation and solvation shell composition of sunitinib malate, an anti-tumor compound, in some binary mixed solvents at 298.15 K

Preferential solvation of sunitinib malate (STM) was investigated in the binary mixtures of water, ethanol, ethylene glycol (EG), and propylene carbonate (PC) solvents at 298.15 K. Similar to its pharmaceutical formulation steps, dimethyl sulfoxide (DMSO) was used as the base solvent during our experiments. Bosch–Rose model was utilized to estimate the electronic transition energies, ET, and other preferential solvation parameters, demonstrating solute–solvent and solute–solute interactions. Shifting λmax situation with respect to the dielectric constant of the pure solvents was carefully monitored indicating that STM had the lowest λmax in water and PC among HBD and HBA solvents, respectively. Moreover, ET showed positive deviation with respect to ideality for ethanol–EG, ethanol–PC, and ethanol–DMSO binary systems while negative deviation was obtained for the others which was explainable based on the model assumptions. According to the results, STM molecules preferred to be solvated by PC, ethanol, EG, and DMSO solvent molecules rather than water in the binary mixtures of the aforementioned solvents, meaning that the presence of water in the cybotactic region is least probable compared to the others. Based on the local mole fractions, the abundance of pure solvents and/or complex solvent molecules in the cybotactic region around the solute was discussed in detail, illustrating the specific and non-specific interactions between solute and solvent molecules.

Specific features of the interaction of a mechanically renewable graphite electrode with solutions based on propylene carbonate

The electrochemical behavior of a mechanically renewable graphite electrode at its interface with LiClO4 solutions in propylene carbonate (PC) is studied by cyclic voltammetry (CVA) and impedance methods. It is shown that in the potential region from −1.0 to 0.5 V (vs. aqueous saturated calomel electrode), this electrode can be considered as ideally polarizable. This allows the dependences of the electric double layer capacitance С on the graphite-electrode potential E to be obtained. These С vs. E curves are characterized by the presence of a minimum at the potential independent of the salt concentration; moreover, the minimum itself deepens with electrolyte dilution. The analysis shows that the position of this minimum in the С vs. E curves corresponds to the potential of zero charge (PZC) of this electrode. An essential feature of these С vs. E curves is that they demonstrate the capacitance values (in the vicinity of PZC and at the potentials corresponding to positive surface charges) substantially lower as compared with the similar dependences observed on electrodes of mercury and other s,p-metals. Assuming that this peculiarity of graphite electrode is associated with its semiconductor properties, the procedure of processing experimental results is developed based on the approach known from the literature. With the use of this procedure, the components of the overall potential drop (φ) at the electrode-solution interface which correspond to the potential drops in the space charge region in graphite surface layer (φ1) and in the electric double layer at its interface with solution (φ2) are calculated. The results obtained make it possible to quantitatively assess the semiconductor characteristics of the graphite material such as the flat band potential and the concentration of charge carriers in the conduction band and also to propose and substantiate the conclusion that the chemisorption properties of graphite and mercury electrodes with respect to PC molecules are close.

Molecular dynamics investigation of electric field altered behavior of lithium ion battery electrolytes

Electric field alters the behavior of electrolytes. In spite of its importance, the dynamic behavior of lithium ion battery (LIB) electrolytes in the presence of electric field is not well studied. In this study, we probe 1 M ethylene carbonate (EC) and propylene carbonate (PC) based electrolytes of LiPF6 salt in the presence of unidirectional electric field to understand its effect on their transport and structural properties. Drift and diffusivity of the ions increase exponentially with the electric field strength. More importantly, the diffusivity becomes direction dependent. The changes in the molecular level organization of the electrolyte is responsible for the observed variations in the transport properties. Comparison of EC and PC based electrolytes suggest that various entities of PC electrolyte are dynamically lethargic. In the presence of electric field, PC molecules solvate lithium ion strongly compared to EC, throwing insights into the issue of PC co-intercalation that results in the rapid degradation of the LIB. The distinct solvation behavior shown by the electrolytes in response to the electric field emphasizes the need for study of electrolytes of advanced batteries in the presence of electric field.

Tetrahydrothiophene 1-oxide as highly effective co-solvent for propylene carbonate-based electrolytes

Propylene carbonate (PC) together with cyclic sulfur compounds such as tetrahydrothiophene 1-oxide (THT1oxide) as co-solvent and lithium hexafluorophosphate (LiPF6) as conducting salt are introduced as new aprotic liquid electrolytes for lithium-ion batteries. Starting with the single solvent electrolyte LiPF6 in PC, by addition of THT1oxide, the ion transport properties even at temperatures down to −20 °C are improved by the different solvation behavior of Li+ ions due to the high Li+ ion affinity of the sulfinyl (-S=O) group and by the resulting decrease of the Li+ ion complex size. Electrolytes that contain Li+ ion complexes with both PC and THT1oxide molecules in the solvation shell are able to form protective interphase layers on graphite and NCM111 (LiNi1/3Co1/3Mn1/3O2) electrodes that are both permeable for Li+ ions while ensuring good electronic insulation, thus enabling stable cycling in lithium-ion cells with only minor capacity fading. THT1oxide/PC-based electrolytes afford better long-term as well as low temperature cycling behavior compared to established state-of-the-art (SOTA) organic carbonate-based electrolytes. The obtained results allow for the design of new co-solvents for PC and comparable cyclic organic carbonates, and provide a non-toxic and cheap alternative to crown ethers without affecting the Li+ ion transference/transport numbers.

The Volumetric and Transport Properties of 1-Ethyl-3-Methylimidazolium Trifluoromethanesulfonate Ionic Liquid and Propylene Carbonate Binary System

In the present work, a new binary mixture system composed of the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([Emim][CF3SO3]) and propylene carbonate (PC) was prepared. The densities, dynamic viscosities, and electrical conductivities of ([Emim][CF3SO3] + PC) were measured over the whole concentration range (mole fractions of IL from 0 to 1) for temperatures from 288.15 to 353.15 K. The excess molar volumes (VE) and viscosity deviations (Δη) of the binary systems were calculated to characterize the volume contraction and intermolecular interactions in the mixture system, and both were correlated with the Redlich–Kister polynomial equation. The Vogel–Fulcher–Tamman equation was used to describe the temperature dependences of the dynamic viscosities and the electrical conductivities of the binary system. Further, density functional theory calculations were employed to obtain the structure, energy, and COSMO charge distributions of the cation and anion of the IL and the PC molecule, and the intermolecular interactions in the binary mixture system were evaluated.

Interparticle interactions and dynamics in BmimBF4 and LiBF4 solutions in propylene carbonate: MD simulation

Ionic liquids have gained immense popularity in recent decades due to a combination of unique properties. Despite the widespread use of ionic liquids mixtures with aprotic dipolar solvents in electrochemistry, it remains relevant to predict their macroscopic, primarily transport, properties based on the microscopic picture of the entire set of interparticle interactions in such systems. The method of molecular dynamics simulation (MDS) is one of the most powerful tools for solving problems of this kind. However, one of the unsolved problems of the classical MDS of ion-molecular systems is the correct accounting of polarization effects. Recently it was proposed to use a variation of the effective ion charges in solutions to solve this task. This paper presents the results of the MDS structural and dynamic properties of 1-butyl-3-methylimidazolium (BmimBF4) and lithium (LiBF4) tetrafluoroborates solutions in propylene carbonate (PC) at 298.15 K in NPT ensemble using GROMACS and MDNAES software packages. The possibility of reproducing the experimental dynamic properties (diffusion coefficients of cations and solvent, viscosity, and electrical conductivity) of binary systems based on mixtures of ionic liquids with PC in a wide concentration range was shown. Polarization effects were taken into account by reducing the partial charges of the ion atoms. The structure of the solvation shell of cations was studied within the framework of radial distribution functions, distribution of coordination numbers and the presence of hydrogen bonds between the organic cation and solvent molecules. The results point to stronger and more structured solvation shell of the Li+ cation compared to Bmim+, which is consistent with the conclusions about the mobility of these cations. The reorientation times of propylene carbonate molecules and their lifetimes in the framework of the first solvation shells of the cations are several times higher for the lithium cation.

Solvent molecule mobilities in propylene carbonate-based electrolyte solutions coexisting with fumed oxide nanoparticles

Non-aqueous LiClO4 solutions kneaded with various fumed oxides (fumed silica, fumed alumina, and fumed titania) were employed as model systems of lithium ion batteries. The properties of the solid phase and Li+ ions, which affect solvent molecules, were evaluated using 1H NMR spectroscopy and 1H NMR relaxation time (T1, T2) measurements. The 1H NMR signals of propylene carbonate (PC) molecules were influenced by the coexisting solid phase in the LiClO4-PC solution/fumed oxide nanoparticle dispersion. The mobilities of the PC molecules drastically decreased in the presence of only 1–2 vol% of the solid phase (liquid phase thickness is 15–20 nm or less), regardless of the fumed oxide employed. In the IR spectra of the PC/fumed alumina systems, the vibrations at higher wavenumbers were predominantly observed because of indirect electron-donation from the solid surface. The 1H NMR signal detection ratios depended on the fraction of the liquid phase influenced by the solid phase. In the LiClO4-PC solution/fumed alumina systems, the 1H NMR signal detection ratios greatly decreased because of this influence; here, the large positive zeta potential of the solid phase surface of fumed alumina attracted the PC molecules, which had local negative electric fields owing to polarization. Moreover, the T1 and T2 results confirmed that the interaction between the solid phase and PC molecules is much smaller than that between the solid phase and water molecules. Additionally, it was seen that the PC solution system was more significantly affected than the aqueous solution system; the network structure of the entire PC solvent is greatly affected by the addition of the Li+ ion, and the relaxation time decreased significantly.

Dielectric and electrical behaviour over the static permittivity frequency regime, the refractive indices and viscosities of PC–PEG binary mixtures

The complex permittivity, alternating current electrical conductivity, electric modulus and the impedance dispersion over the frequency range from 20Hz to 1MHz for the propylene carbonate (PC) and poly(ethylene glycol) (PEG; molecular weight 200gmol−1) mixtures spanning the entire mixing range have been investigated. The Nyquist plots of electric modulus and impedance for these polar liquid mixtures exhibit the Debye–type dispersion corresponding to the conductivity and electric double layers relaxation processes, respectively. The values of static permittivity, dc electrical conductivity, refractive index and viscosity of the PC–PEG mixtures in the temperature range 5–55°C have been reported. The excess properties of static permittivity, refractive index, and viscosity confirm the hydrogen-bond interactions between the PC and PEG molecules in their mixtures. The temperature dependent dc conductivity and viscosity of the PC–PEG mixtures obey the Arrhenius behaviour, and the activation energies of the mixtures decrease with an increase of PC concentration. The Stokes-Einstein relation for the conductivity in viscous media holds only for the PC-rich of PC–PEG mixtures.

Density and Solvation Effects of Imidazolium Based Ionic Liquids in Propylene Carbonate

The results of densimetry investigation of the solutions of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), hexafluorophosphate (BMIMPF6) and bromide (BMIMBr) in propylene carbonate (PC) at 298.15, 318.15, 338.15 and 358.15 К are presented and discussed in terms of apparent partial molar volumes and solvation contribution. Density measurements were carried out using the vibrational tube densitometer Mettler Toledo DM 50 with accuracy ± 3∙10-5 g/cm3. The limiting partial molar volumes of investigated ionic liquids in PC were obtained from density experiment using Masson equation and divided into ionic contributions. Limiting partial molar volumes of BMIMBF4, BMIMPF6 and BMIMBr in PC slightly increase with the increase of temperature. The limiting partial molar volumes of BMIM+ cation obtained from three ionic liquids with different anions was found to have the same value, 115 cm3/mol at 298.15 K. The intrinsic volume of BMIM+ cation estimated from quantum chemical calculations at the M062X/6‑311++G(d,p) theory level exceeds one obtained from density experiment indicating that solvation of cation has a negative contribution to the volume of ion in propylene carbonate. In order to investigate the microscopic structure of the BMIM+ solvation shell in PC, molecular dynamics simulation of the infinitely dilute solution was carried out in the NVT ensemble at 298.15 K. The results of the simulation reveal that 5-6 PC molecules forming the first solvation shell penetrate into the inner space of the cation, which agrees with the results of a density experiment treatment. From the analysis of the cation-solvent site-site radial distribution functions and the running coordination numbers it was established that the most probable coordination center of PC molecule is carbonyl oxygen.

Benign Solvation Effect on Electrochemical Intercalation of Triethylmethyl Ammonium into Graphite from Propylene Carbonate

Tetraethyl ammonium/triethylmethyl ammonium tetrafluoroborates dissolved in propylene carbonate (PC) are the most common non-aqueous electrolyte solutions for supercapacitors using both carbonaceous electrodes. In this work, they are applied in the graphite/activated carbon asymmetric capacitors, in which the charge storage at graphite negative electrode is based on the intercalation of quaternary alkyl ammonium cations. The capacitor containing triethylmethyl ammonium (TEMA+) shows a much higher capacity and superior cycle-ability than that containing tetraethyl ammonium (TEA+). In situ X-ray diffraction and in situ dilatometry are combined to determine the larger recoverable expansion in graphite negative electrodes due to a reversible intercalation of TEMA+. Electrochemical quartz crystal microbalance verifies the dramatic structural changes stem from the considerable co-intercalation PC molecules together with TEMA+. A benign solvation effect is proposed for facilitating the transportation and storage of TEMA+ inside graphite.

Optimizing solid electrolyte interphase on graphite anode by adjusting the electrolyte solution structure with ionic liquid

N-allyl-N-methylpiperidinium bis(trifuoromethansulfonyl)imide (PP13*TFSI) ionic liquid was adopted as a solute replacing partial of lithium salt in a concentrated propylene carbonate (PC) electrolyte. Varying the concentration of PP13*TFSI ionic liquid can change the electrolyte solution structure and thus optimize the solid electrolyte interphase (SEI) on the graphite anode. The number of PC molecules coordinated with lithium ion is significantly altered and this results in a change of the SEI mechanism at the electrode/electrolyte interface. At an optimum molar ratio of 2:1 between LiTFSI and PP13*TFSI, the first coulombic efficiency and the cycling capability of the graphite anode are significantly improved. Fourier transform infrared spectroscopy (FTIR) verified the SEI mechanism change from two-electron reduction to one-electron reduction in the presence of PP13*TFSI ionic liquid. SEM and TEM observations reveal a thin, homogenous and compact SEI film formed on the graphite surface in the 3 mol L−1 LiTFSI+PP13*TFSI(2:1)/PC concentrated electrolyte.

Relationship between Ionic Interaction and NMR Relaxation Behavior in LiClO4-PC Solution Coexisting with Fumed Metal Oxide

Dynamic properties related to 1H NMR relaxation in SiO2 fine powder/non-aqueous LiClO4 solution was measured for using propylene carbonate (PC) and PC-1,2-dimethoxyethane (DME). The influence of solid phase and variation of effect of DME on ionic mobility is also discussed. For 1H NMR spectra of PC-DME binary solution, adding of SiO2 powder caused the broadening of NMR signal of 1H in PC and DME molecules. In pure PC-DME system, since DME is preferentially affected by solids rather than PC, as the ratio of DME increased, values of solvent molecules detected by NMR decreased. In 1 mol/L LiClO4/PC-DME system, as the ratio of DME in solution was higher, The interaction between the PC and the Li+ ion is weakened by the decrease of the dissociation degree, and the mobility of the PC was restored.