Lithium Electrolyte Solutions Research Articles

(Digital Presentation) Hybrid Membranes Engineered from Sustainable Sources Exhibit Improved Ionic Conductivity

Ion-conducting membranes are crucial in electrochemical storage and energy conversion technologies such as fuel cells, alkaline ion batteries, and redox-flow batteries. The purpose of the membrane is to prevent direct contact between the electrodes while allowing selective ions to pass through. The characteristics of the ion-conducting membranes include excellent mechanical and thermal stability, chemical resistance, high ionic conductivity, and selectivity. Polymers and polymer-based precursors make up the majority of the materials that have been used as ion-conducting membranes. However, most polymer-based membranes have issues related to poor chemical resistance, recyclability, and thermal and mechanical stability. In addition, as more sustainable materials are being sought to create a sustainable society, new environmentally friendly and economically viable materials are in high demand. The clay-based material could be an alternative for ion-conducting applications due to its porous structure, high surface area, tunable interlayer spacing, excellent thermal and mechanical stability, and high ion conductivity. Clay minerals are primarily used in water treatment, pharmaceutics, ceramics, paints, and coating industries. Furthermore, clay minerals have been used as a filler material in energy storage and conversion system to improve the thermal stability and ion conductivity in electrodes, electrolytes, and separators.Herein, we report a novel approach to making non-polymeric hybrid clay membranes using environmentally benign materials such as clay and zwitterion (i.e., sulfobetaine). These membranes with improved ionic conductivity will find immense potential in applications in energy storage and conversion systems. Such membranes have been synthesized by intercalating sulfobetaine molecules into the interlayer spacing of the bentonite clay matrix. Sulfobetaine is a zwitterion composed of quaternary ammonium cations and sulfonate anions. Leveraging the unique structure-property features that exist in zwitterions helps to alter the interlayer spacings in the clay matrix, thereby enabling ion diffusion through the silicate layers. Furthermore, it helps in the formation of a self-supporting membrane. The functionalized membrane's crystal structure and chemical composition were investigated using XRD, XPS, and ATR-FTIR. XRD was used to identify the layered structure of the silicates in clay and the increased interlayer spacing (1.15 nm to 1.8 nm) of the hybrid clay membrane. Data from XPS and ATR-FTIR confirmed the successful functionalization of clay with sulfobetaine. Furthermore, the ionic conductivity of the hybrid clay membrane was characterized using a non-aqueous lithium electrolyte solution, and found a conductivity of . This is one of the first reports showcasing how zwitterions can impart conductivity in clay silicate motifs. It suggests an easy and novel approach to transport lithium-ion through silicate layers, thereby making it suitable for use as membranes in batteries and supercapacitors. The current study demonstrates an easy and versatile approach to developing cost-effective and eco-friendly membranes from sustainable materials such as clay, which, when functionalized, has the potential to be a highly efficient ion-conducting material with applications in energy storage, devices, and technologies.

Thermodynamic modeling of aqueous lithium salt solutions with association electrolyte nonrandom two-liquid activity coefficient model

The high charge density of lithium ion and the resulting strong association phenomena make thermodynamic modeling of aqueous lithium electrolyte solutions extremely challenging. In this study, the association electrolyte nonrandom two-liquid activity coefficient model of Lin et al. (AIChE J. 2022, 68(2), e17422) is utilized to correlate and predict thermodynamic properties and solubility behavior of aqueous single electrolyte solutions of LiCl, LiBr, LiI, and LiNO3, and their mixed electrolyte solutions. Capturing self-association of water, cross-association of ion and water for hydration, and cross-association of cation and anion for ion-pairing, the association model accurately represents the literature experimental data up to saturation concentrations and at the temperature ranging from 263 K to 523 K. This study further investigated the effect of anions of the lithium salts, and re-confirmed that the order of solution non-ideality as LiI > LiBr > LiCl > LiNO3 because the anions with stronger association strengths are more likely to form ion pairs and thus lower the mean ionic activity coefficients.

Measurement of Transport Number of Lithium in Glycerol Assisted by Fourier Transform Spectroscopy Analysis: Progress towards Elaboration of Optimal Electrolyte of Friendly Environmental Battery

Up to now, a great deal of research investigations on lithium ion conductors has been carried out, because they are potentially utilized in the solid electrolytes of the batteries and the electrochemical devices. However, in order to elaborate new ecological batteries of lithium, it becomes primordial to study and understand the properties of transport of the lithium electrolytes using eco-friendly solvents, with view perhaps to find out the best electrolyte for such devices. In fact, the electromotive forces (EMFs) of lithium chloride electrolyte in the hydrogen-bonded solvents glycerol, were measured using the concentration cells (CCs) 0.005/0.05 and 0.05/0.5. Then the transport numbers of the lithium-ion were deduced by means of the Nernst equation in combination with the Debye-Huckel limiting law. Whilst the activation energy values were calculated from the parameters of the fitting of the transference number data to the empirical power law, yielding a regression coefficient of 95.9% for the most concentrated concentration cell. The structure and interactions in the lithium electrolyte solution were studied by vibrational Infra-Red spectroscopy. The experimental data were discussed and compared to those obtained previously, using impedance spectroscopy of glass-forming glycerolate lithium electrolytes for the same purpose. Despite the enormous difference between their viscosities; glycerol shows similar activation energy (i.e. 31.40 kJ.mol–1) with water (i.e. 31.73 kJ.mol–1), in particular at very low concentration, confirming both solvents being hydrogen-bonded. Besides, this study suggests the utilization of the glycerol-lithium ion electrolyte for future conception of ecological lithium-ion battery, rather than those using ion electrolyte polymer currently on the market. Similarly to relaxation and conductivity, the transport number data suggests that the diffusion of conformational states is also monitoring the overall lithium ion transport mechanism.

Tracking ion transport in radical polymers

A ready supply of thin, lightweight, flexible batteries could push development of stretchable and foldable electronics into high gear. For that reason, researchers have combed through libraries of organic compounds looking for high-performance electronic conductors. Organic radical polymers—molecules with radical sites hanging off a polymer backbone—recently jumped ahead of the pack, showing themselves to be promising electrode materials for fast-charging batteries. But the mechanism by which these polymers conduct charge has remained unclear, hampering their development. To sort out the details, especially the role of ion transport, a team led by Jodie L. Lutkenhaus of Texas A&M University devised a quartz crystal microbalance method to monitor nanogram-scale mass changes in a polymer electrode during charging cycles (Nat. Mater. 2018, DOI: 10.1038/s41563-018-0215-1). The electrochemical system consisted of PTMA, a poly(methyl methacrylate)–based polymer with pendant nitroxyl radical groups, infused with common lithium electrolyte solutions. The group found that as anions latch on

The Effect of Ionic Aggregates on the Transport of Charged Species in Lithium Electrolyte Solutions

In this investigation we focus on the problem of modeling the transport of the charged species (lithium ions) in electrolyte solutions with moderate and high salt concentrations (0.1M to > 2M), and consider the Nernst-Planck equation as a model of such processes. First, using a combination of magnetic resonance imaging (MRI) and inverse modeling (IM) we demonstrate that at higher concentrations the Nernst-Planck equation requires negative transference numbers in order to accurately describe the concentration profiles obtained from experiments. The need for such a physically inconsistent constitutive relation indicates the loss of validity of the Nernst-Planck equation as a model for this process. Next we consider the formation of ion pairs and clusters as a possible effect responsible for the appearance of negative transference numbers and derive an extended version of the Nernst-Planck system which accounts for these additional species. However, a careful analysis of this model reveals that incorporation of ion-pairing effects into the modeling will not change the transference numbers inferred from the experimental data via inverse modeling. This demonstrates that physical effects other than formation of ion pairs and clusters must be incorporated into the Nernst-Planck model in order for it to correctly describe ion transport at higher salt concentrations. One prime candidate for such effects is the motion of the reaction surface resulting from dendrite growth.

Direct relations between ion diffusion constants and ionic conductivity for lithium electrolyte solutions

Lithium cation and anion diffusion constants (DLi and DAnion) are plotted versus ionic conductivity (σ) (σ–D relation) for lithium organic electrolyte solutions which are important to investigate Li secondary batteries. Lithium salts studied are LiPF6, LiBF4, LiN(SO2CF3)2 (LiTFSA), LiN(SO2C2F5)2 (LiBETI), LiC4BO8 (LiBOB), LiSO3CF3 and Li2B12F12. Main organic solvents are propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone (GBL), diethyl carbonate (DEC), four glymes and polyethylene glycol (PEG) dimethyl ethers of average molecular weights of 400 and 1,000. Mixing effects of two solvents are shown for EC-DEC-LiPF6 systems. In total, about 20 organic electrolyte solutions were studied. In addition, for six binary ionic liquid systems, σ–D relations are plotted. Values for the degree of apparent ion dissociation (α) were calculated from the DLi, DAnion and σ using the Nernst-Einstein (NE) relation and are plotted against σ (σ–α relation). The number of charge-carrying ions (Ncarrier) was estimated from the α and salt concentration, and plotted versus σ (σ-Ncarrier relation). To estimate the velocity of ions, the σ–Dsolvent relations are plotted. Also, the apparent lithium transference number (tLi) obtained simply from the DLi and Danion values are plotted versus σ (σ −tLi relation). While we have already reported all the data in our previous papers, we did not plot directly the ion diffusion constants and other parameters versus ionic conductivity. In this paper, the importance of the direct relations of σ–D, σ–α, and σ-Ncarrier is demonstrated to understand functions of lithium electrolyte solutions.The numerical data are freely available in Supplementary Information (SI), covering broad aspects of the fundamental and practical lithium electrolyte solution systems. We believe that they will contribute to the research and development for next generation Li battery systems.

Ionic Conduction of Non-Aqueous Lithium Electrolyte Solution through Surface Modified Anodized Alumina Membrane Prepared By LPD Process Using Aqueous-Organic Mixed Solvent

The reduction of the internal resistance by the accelerations of Li+ transport and electron transfer promotes the high-speed charge/discharge of lithium ion batteries (LIBs). Recently, the improving charge/discharge has been attempted by exploiting model porous electrodes which have mesoporous structures such as anodic aluminum oxide (AAO) [1]. AAO is a suitable template for the preparation of the multi layered structures using its regular nanopore array. TiO2 thin films have potential application in the negative electrodes of LIBs, so we prepared the SiO2 or TiO2/AAO nanocomposite by the liquid phase deposition (LPD) procedure in this work. The LPD method involves a metal oxide and hydroxide thin films synthetic procedure using the hydrolysis equilibria reactions of metal-fluoro complexes as follows; (Hydrolysis reaction) MF x (x-2n)- + H2O → MO n + xF- + 2nH+ (F- scavenging reaction) Al3+ + 6HF → H3AlF6 + 3/2H2 Previously, TiO2 was deposited on the surface of AAO mesopores by the LPD within 250 nm, and in this study, the TiO2 thin film onto AAO mesopore wall which has the extreme small diameter, i.e., ca. 20-40 nm, was prepared by the LPD. In this research, the achievement of the LPD reaction at 0 °C or less by the use of the H2O/EtOH mixed solvent and the deposition of oxide thin film to mesopore inner wall owing to the decrease of the LPD reaction activity under low temperature were executed. Furthermore, the specific ion conductivity of the electrolyte solution in the mesopore channels in the prepared TiO2/AAO nanocomposites was evaluated. AAO membranes were prepared by two-step anodization as previous report [1,2]. AAO template whose thichness is ca. 500 m (i.e. the aspect ratio of a AAO membrane thichness to a mesopore diameter is ca. 5000) was dipped in (NH4)2SiF6 or (NH4)2TiF6 solution of various concentration for 0-60 h at -20-40 °C. Prepared SiO2 or TiO2/AAO nanocomposite was used as a separator of a four-electrode cell and an impedance measurement was carried out. LiClO4/EC:DEC = 1:1 (v/v) of 0.5 to 2.5 mol L-1was used as an electrolyte solution. The results of LPD reaction using (NH4)2TiF6 solution of 10 mol L-1 in 1 : 1 (v/v) H2O/EtOH at -20-5 °C (The LPD reaction solution was still liquid-state at -20 °C) for 10 h were shown in Fig. 1. The TiO2 thin film deposition within the deep mesopores without collapse of the mesopore structure was achieved at -13.5 °C. The AAO mesopore structure collapsed because the LPD reaction reactivity was too high at 5 °C, and the TiO2 thin film was not generated because the reactivity was too low at -20 °C. It is suggested that the moderate decrease in the LPD reaction activity by using an aqueous/organic solvent mixture was necessary to achieve oxide thin films deposition on the AAO mesopore wall, while retaining the AAO mesoporous structure. The Nyquist plots for four-electrode cells using SiO2 or TiO2/AAO nanocomposites show two semicircles for each nanocomposite. The lower frequency region of the semi-circle was assigned as ion transport resistance in the SiO2 and TiO2 modified mesopore walls, and the fitting of the semicircle in the low frequency region, the specific conductivity in the pore was calculated. For a LiClO4 solution of 0.5-2.5 mol L-1, the specific Li+ ion conductivities after SiO2 or TiO2 thin film coating by LPD in the mesopore of the AAO nanocomposites was compared with those without thin film coating (i.e. as-prepared AAO). The conductivity for the TiO2/AAO nanocomposite is 3 times that for as-prepared AAO, whereas that the conductivity for the SiO2/AAO nanocomposite is similar for as-prepared AAO. Even if the concentration was changed, the ratios of the specific Li+ ion conductivity in the SiO2 or TiO2 modified mesopore to the electrolyte solution and as-prepared AAO were almost constant. These activation energies of Li+ ion conduction in mesopores for each sample are 14.6 (as-prepared AAO), 13.8 (SiO2/AAO), 13.2 kJ mol-1 (TiO2/AAO), respectively. It is suggested that the ionic conduction are influenced by surface electric potential of oxides. This work was supported by CREST, JST. [1] T. Fukutsuka, et al., Electrochim. Acta., 199, 380 (2016) [2] H. Masuda et al., Science, 268, 1466 (1995) Figure 1

Influence of the Morphological Characteristics of Separator Membranes on Ionic Mobility in Lithium Secondary Batteries

Microviscosity components influencing the ionic mobility of lithium electrolyte solution in separator membranes were evaluated and the ionic mobility was correlated with membrane morphology. The microviscosity component responsible for the anion–cation Coulombic interactions (α) was anomalously large in low porosity membranes compared to that in the free electrolyte solution, owing to restricted ionic motion in the narrow pore spaces within the membrane. With increase in the membrane porosity, α diminished owing to the enlarged space and motional freedom for the ionic species, whereas βcation, which is responsible for the cation/membrane interactions, appeared. This behavior may be due to the specific charge on the walls of the pore spaces and the increased collision frequency for the ions. Consequently, the cationic mobility (Dcation) selectively decreased, whereas the anionic mobility (Danion) increased in high porosity membranes. Despite the positive correlation between the diffusion coefficient distribution width (σ) and averaged diffusion value for the anion and solvent species, a clear correlation between σ and Dcation was not observed, which is attributed to the fact that the cation is specifically affected by the membrane, perhaps via Coulombic interactions, as evidenced by the appearance of βcation. Controlling the microviscosities of the ions in the electrolyte by controlling the porous morphology of the separator membrane is significant for designing high-performing battery systems.

Measurement on isolated lithium iron phosphate particles reveals heterogeneity in material properties distribution

We present herein localized galvanostatic and potentiodynamic measurements on lithium iron phosphate (LFP) particles, using the combination of a scanning micropipette contact method (SMCM) and scanning electron microscopy (SEM). The proposed technique allows small substrate areas (∼10 μm in diameter) decorated with LFP particles to be probed within a lithium electrolyte solution in organic carbonate solvents (0.1 M LiClO4 in propylene carbonate in the present study). SEM images of the scanned area allow the correlation of each electrochemical response to the number, and volume of the probed particles. Under favorable conditions, single particles are found within the measurement areas, thus enabling the determination of single particle properties in an anaerobic environment without the additional complications arising from the presence of binders and electronically conductive fillers. The ability to analyze a material with complementary experimental techniques at the single particle level should create new opportunities for fundamental studies and for the quality control of granular materials.

Factors Controlling the Ionic Mobility of Lithium Electrolyte Solutions in Separator Membranes

The interactions between the mobile ions and membrane substrate were investigated for lithium electrolyte solutions confined within the separator membrane in lithium batteries through NMR and electrochemical measurements as well as theoretical analyses. Fundamental dynamic properties such as ionic mobility, dissociation degree of the salt, and microviscosities of the ion, which are responsible for ionic mobility, were different for the electrolyte confined within the membranes compared with the corresponding values for the free electrolyte. We also found that the interactions between the ion and membrane substrate depend on the type of membrane. The results of this study suggest that the ionic mobility of the electrolyte in a lithium battery can be controlled by selecting separator membranes with suitable chemical or physical properties, which would be significant for improving the performance of the battery system.

NMR Determination of the Relative Binding Affinity of Crown Ethers for Manganese Cations in Aprotic Nonaqueous Lithium Electrolyte Solutions

Polymeric chelating agents placed in the interelectrode space of a Li-ion battery (LIB) have been suggested as a means of sequestering Mn cations dissolved from positive electrodes of LIBs to prevent their migration to, and deposition onto, negative electrodes and thus mitigate the associated degradation of LIB performance and life. In order to select the most effective chelating agent and optimize its polymeric form, it is desirable to determine the binding affinity of various chelating agents for manganese cations. The present study evaluates the relative binding affinity of crown ethers for manganese cations in a lithium-containing environment through the detection of the 7Li nucleus chemical shift. Results are presented for the relative binding affinities of 15-crown-5 and 1-aza-15-crown-5 ethers for Mn2+ and Mn3+. Significant differences in relative binding affinity were discovered with particular crown ether–manganese oxidation state combinations. Additionally, a substantial decrease in binding affi...

Ion Transport in Separator Membranes of Lithium Secondary Batteries

The migration properties of cations and anions in lithium electrolyte solutions through separator membranes were evaluated on the basis of diffusion coefficients. The observed diffusion coefficients for the cationic (DLi), anionic (DF), and solvent species (DH) of the electrolyte solution in the membrane are lower than those of the free electrolyte solution. Two main effects are responsible for the reduction in D. One is the physical barrier effect of the membrane substrate. The magnitude of this effect depends on the size, configuration, and the total volume of the pore spaces which hold the solution. The other is a chemical interaction effect, which is associated with polar groups or sites in the membrane substrate. For example, DF values are anomalously lower than DLi values for solutions in polyvinylidene difluoride- (PVDF-) based membranes, leading to an increase in the apparent cation transport number. This would indicate that the anions selectively interact with the membrane substrate through a Cou...

Effect of Solid Surface Properties on Transport Numbers of Non-Aqueous Lithium Electrolyte Solutions

not Available.

Transport properties of non-aqueous lithium electrolyte coexisting with porous solid materials: Montmorillonite-based electrolyte composite system

In order to discuss the hetero-phase effect of the coexisting solid phase on the ionic conduction in non-aqueous lithium electrolyte solution, the conductivity and transport number of ionic species in non-aqueous lithium perchlorate solution/montmorillonite clay composite system were measured using Hittorf's cell. Transport number of lithium ion rapidly increased as the clay content increased, while total conductivity gradually decreased. The calculated ionic mobility of lithium ion was constant in the liquid content range of 75–90 vol.%. The activation energy of the conductivity for both ions separately obtained from the temperature dependence of the ionic mobilities. The activation energy of lithium ion was ca. 10 kJ mol −1 and extremely lower than anion species. It is proved that the lithium ion transfer is promoted by the cation exchange materials using inorganic clay materials. It is suggested that the lithium ions can transfer through the inside of clay structure and anion transfer is hindered by the repulsion between anion species and clay skeleton structure.

Carrier Diffusivity in Porous Membranes

Carrier diffusivity of a lithium electrolyte solution in porous membranes was evaluated by observation of diffusion behavior of ionic species using NMR spectroscopy. We performed analysis on the basis of the restricted diffusion model and a new idea of diffusion distribution. That new concept is engendered in the assumption that observed diffusion values are distributed according to pore size distribution and nonuniformity of pore and polymer density in a membrane. Carrier diffusivity in polyethylene (PE) porous membranes showed characteristic echo attenuation, which differs from echo behavior as a result of random walk migration. We first tried to simulate the echo change on the basis of the restricted diffusion model in porous structure, resulting in disagreement with the observed echo change. As a result, the idea that diffusion values are distributed concurrent with porous geometry was applied to interpret the situation. Introduction of a Gaussian function to represent the distributed condition yielde...

Chemical Modification of Electrolytes for Lithium Batteries

AbstractFor Abstract see ChemInform Abstract in Full Text.

New Approached for Determining the Degree of Dissociation of a Salt by Measurements of Dynamic Properties of Lithium Ion Electrolytes

A new derivation idea for the dissociation degree of the salt of an electrolyte solution using the observed diffusion coefficient and ionic mobility was proposed. The dynamic values could be measured for individual species by the pulsed gradient spin−echo NMR technique. The observed diffusion coefficient is contributed from the dissociated ion and the associated ion pair. The observed mobility, on the other hand, reflects the migration behavior of only the ion. Combining these values, we independently derived the dissociation degree of the salt. This model was applied to the actual lithium electrolyte solution samples of Li-TFSI in EC/DEC (2/3, 1 M) dispersed with 10−15 wt % of PVDF−HFP. The estimated value of the dissociation degree of the salt was 0.75−0.90 using the observed mobility by NMR. When we applied the electrical conductivity for this estimation, the dissociation degree was in the range of 0.55 to 0.70. The difference in the absolute values between two estimations is due to the difference in the absolute values of the observed mobility attributed to the different measurement techniques of the dynamic value.

Structure and transport properties of polymer gel electrolytes based on PVdF-HFP and LiN(C 2F 5SO 2) 2

Gel polymer electrolytes composed of PVdF/HFP and a non-aqueous lithium electrolyte solution EC/DEC/LiN(C 2F 5SO 2) 2 (BETI) were prepared to investigate the conduction properties of the gel materials. Structural and micro-structural characterization was carried out by means of modulated differential scanning calorimetry (MDSC) and scanning electron microscopy (SEM). The samples with polymer/solution weight ratios higher than 0.5 contain at least an amorphous swollen gel phase and a crystalline one, while a pure liquid phase appears, which occupies cavities in the micrometer range in the gels with lower polymer content. The transport properties of the gels were investigated by means of impedance spectroscopy for conductivity and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) for diffusion coefficients. The results were compared with those of corresponding films prepared with LiN(CF 3SO 2) 2 (TFSI). The BETI-based samples showed diffusion values lower than the TFSI-based ones. Estimation of the carrier concentration change with the gel composition revealed that the interaction between the host polymer and the electrolyte in the gel especially in the polymer rich region (>50 wt%).

Investigation of the solution condition of lithium electrolyte solutions with LiCF3SO3 salt

Solution condition of the lithium electrolyte of LiCF3SO3 salt dissolved in propylene carbonate (PC), dimethoxyethane (DME) and tetrahydrofuran (THF) were investigated based on the measurements of the self-diffusion coefficients of lithium (DLi) and anion (DF) species using the pulsed-field gradient (PFG) NMR, viscosity and conductivity. DLi and DF decreased with the increase in the solution concentration for these electrolytes. This result reflects the change in the dissociation degree of the salt and the viscosity depending on the solution concentration. In the case of PC solution (the dielectric constant (∈) of PC: ∼65), measured DLi and DF were separated each other with the decrease in the concentration because the dissociation of the salt was promoted to increase the content of dissociated ions. With an increase in the concentration, the dissociation would be restricted and DLi and DF approximated each other, which means that the associated ion pairs are dominant in the solution. The effective ionic radius (reff) of cation species of PC solution estimated from the Stokes-Einstein relation using the diffusion coefficient and the viscosity results was four times greater than that of the naked lithium ion and independent of the dissociation degree. On the other hand, the reff of anion species changed depending on the dissociation degree. This suggests that the dissociated lithium ions are solvated by the PC solvent in the solution. DME and THF solutions did not show the solvation effect from the result of the change in reff with the concentration. This suggests that the dissociation degree of the dissolved salt was low due to the low ∈ of their solvents (∈ ∼ 7.2) and the ion pairs would dominant in the solutions independent of the solution concentration.