Decrease In Ionic Conductivity Research Articles

Thermophysical and transport properties of a pyrrolidinium-based ionic liquid confined in silica

Ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyrrTFSI) was confined in silica (Aerosil A380) by direct mixing. The resulting BMPyrrTFSI/xSiO2 ionogel (x – from 2.3 to 6.7 wt%) was studied by TG, DSC, conductometry and viscometric methods. For confined IL, a decrease in the Tm and Ts-s by 14–16 °C and an increase in the Tg, and Tcc by 4–5 °C were found. With an increase in xSiO2, the opposite dynamics of the decomposition temperatures Tonset and Tpeak, and a disproportionate decrease in ionic conductivity were observed. The change in the properties of BMPyrrTFSI under conditions of limited geometry of the silica matrix is explained in the terms by the interaction of the IL and SiO2, as well as the conformation features of the cation and anion. In the first time, parameters such as the fragility index D and the formation factor F were also discussed for such systems. As a result, BMPyrrTFSI/4.5 wt% SiO2 ionogel (0.2 S m−1, 20 °C) was proposed as a promising electrolyte for application in electrochemical devices. This study may be useful for creating quasi-solid electrolytes based on ILs and inorganic materials.

Coarse-Grained Simulations of Columnar Ionic Liquid Crystals: Comparison with Experiments.

We simulate a homologous series of guanidinium-based columnar ionic liquid crystals (ILCs) using coarse-grained molecular dynamics (MD) simulations with the Martini force field. We systematically vary the length of alkyl side chains, ILC-n (n = 8, 12, 16), and compare our results with previous experimental findings. Experimentally, ILC-8 exhibits a narrow mesophase window and weak columnar order, while ILC-12 and ILC-16 display a broad mesophase window and high columnar order. The MD simulations show that ILC-8 forms a percolated structure, whereas the longer chain analogues self-assemble into columns, with columnar assembly becoming more prominent as the side chain length increases, in qualitative agreement with the experiments. Furthermore, the intercolumnar distance increases monotonically with increasing side chain length and decreases with increasing temperature. Finally, we find that the diffusion coefficient and ionic conductivity decrease substantially with increasing chain length, consistent with experimental observations. We attribute this decrease in mobility to the formation of hexagonally ordered columns, which restrict transport more than percolated networks.

The influence of defects on conduction processes in chalcogenide semiconductor compounds

Due to the strong dependence on the intrinsic defectiveness of structures, semiconductor compounds based on metal chalcogenides have a wide spread in kinetic properties and high growth temperatures of materials, as well as a tendency to self-compensation of defects. It has been shown that an increase in defectivity in the cation sublattice leads to a decrease in ionic conductivity in copper chalcogenides, and an increase in temperature leads to an increase in ionic conductivity due to a change in mobility. The low activation energy indicates a strong intrinsic disorder of the cation part of the lattice. In copper chalcogenides, the presence of hopping conductivity at small deviations from stoichiometry is explained by compensation and a high concentration of vacancies. Under such conditions, this activation energy is the activation energy for the movement of copper ions throughout the crystal and almost all metal ions contribute to the ionic electrical conductivity. In semiconductor compounds based on metal chalcogenides with deviations from stoichiometry, the activation energy of cationic conductivity does not change, since the defects that arise in this case do not introduce large changes in ionic conductivity with temperature. The increase in ionic conductivity with increasing temperature is due to a change in mobility, since the carrier concentration remains unchanged. The latter is determined only by the structural features of the phases. Deviation from stoichiometry in compounds makes it necessary to take into account the movement of the main charge carriers in the allowed zones, and the movement of carriers along vacancies. The properties of metal chalcogenides are largely determined by the characteristics of their preparation and depend on the relative ratio of metal and chalcogen atoms, as well as the presence of intrinsic defects and their influence on the mechanism of behavior of charge carriers and transfer phenomena.

The electrical properties of codoping LaInO<sub>3</sub> perovskite

This paper is devoted to the study of LaInO3 based co-doped materials. Solid solutions in which lanthanum is substituted for strontium have sufficiently high conductivity values, but a low level of oxygen deficiency is realized. Mg2+ and Ca2+ ions were chosen as co-dopants for the B sublattice. Both series of the investigated La0.9Sr0.1In1-xCaxO2.95–0.5x and La0.9Sr0.1In1-yMgyO2.95-0.5y solid solutions crystallize in orthorhombic symmetry with sp. gr. Pnma. The ionic conductivity in a dry atmosphere is determined by the oxygen ions transport. Oxygen-ion transfer in solid solutions is ~30–40% at high temperatures (T 700°C) and increases to 80% as the temperature decreases to 400–300°C. The substitution Ca2+ with In3+ increases the electrical conductivity of the oxygen ions; the highest values are achieved for the compositions La0.9Sr0.1In0.95Ca0.05O2.925 and La0.9Sr0.1In0.9Ca0.1O2.9. The introduction of Mg2+ co-dopant at the In3+ positions leads to a decrease in ionic conductivity compared to La0.9Sr0.1InO2.95. The effects of changing oxygen mobility with changing geometric factors (cell volume, critical radius) are discussed.

Nematic liquid crystal dispersed with two-dimensional functionalised graphene oxide (fGO): insights on improving the nematic ordering and reducing electro-optic response time

ABSTRACT Doping a nematic liquid crystal (NLC) with nanoparticles (NPs) of varied dimensions and properties to form LC-NP nanocomposites with improved electro-optic and dielectric properties has recently been a much-explored field of work. But still, NLC nanocomposites based on two-dimensional (2D) NPs have not been studied vividly because of the high tendency of 2D NPs to aggregate together. In the present work, we have studied the effect of incorporating hexadecanethiol functionalised graphene oxide (fGO), a 2D NP, in a conventional NLC medium under varying doping concentrations. We found that at a lower doping concentration (⁓10−4 wt.%), the NLC nanocomposite showed a substantial increase in dielectric anisotropy (Δε) and birefringence (Δµ) values as compared to pure NLC sample. A significant decrease (⁓50%) in ionic conductivity as well as reduced electro-optic response time (⁓75%) was also observed in this NLC nanocomposite. As the fGO doping concentration was increased (⁓10−2 wt.%), a reverse trend was observed for Δε, Δµ and response time values, which declined sharply with increasing doping concentration. Hence, the present work highlights two different working mechanisms at low- and high-doping concentrations of 2D NPs.

Design of Novel Types of Phosphorus-Containing Flame-Retardant Hybrid Solid Electrolytes with Enhanced Ionic Conductivities

Hybrid polymer/inorganic solid electrolytes have been considered one of the promising routes toward improved safety and higher energy density compared to today’s liquid electrolytes. Herein, flame-retardant phosphorus-containing random copolymers, namely poly(oligo(ethylene glycol) methyl ether methacrylate)-co-(dimethyl(methacryloyloxy)methyl phosphonate) (P(xPEGMA-co-yMAPC1)), were synthesized with different ratio of monomer compositions and further used as the polymer matrix. By mixing P(xPEGMA-co-yMAPC1) with lithium perchlorate (LiClO4) and acetonitrile (ACN), the solid polymer electrolytes were obtained after vacuum evaporation of ACN. Among the P(xPEGMA-co-yMAPC1) copolymer electrolytes, the P(9PEGMA-co-1MAPC1) with 10wt% LiClO4 presented an ionic conductivity of 1.0×10-4 S cm-1 at 60℃ and 3.1×10-5 S cm-1 at 30℃ and showed good flame-retardant performance compared to pure PPEGMA. The increase in MAPC1 content upgraded the flame-retardant performances but enhanced the glass transition temperature (Tg) of the copolymers, leading to a decrease in ionic conductivity. To further enhance the ionic conductivity of the copolymer electrolytes, hybrid polymer/inorganic solid electrolytes are synthesized by adding Li1.3Al0.3Ti1.7(PO4)3 (LATP) and SiO2 inorganic fillers, respectively. P(9PEGMA-co-1MAPC1) with 10wt% LATP exhibits a higher ionic conductivity of 1.4×10-4 S cm-1 at 60℃, while P(9PEGMA-co-1MAPC1) with SiO2 fillers show a lower ionic conductivity of 8.5×10-5 S cm-1 at 60. Finally, the cycling performances of hybrid solid electrolytes containing LiFePO4|P(9PEGMA-co-1MAPC1) + LiClO4 + LATP/SiO2|Li batteries were tested. The capacity reaches 164.2 mAh g−1 at 0.05 C, and the capacity retention reaches 90% after 200 cycles at 0.1 C. Figure 1

Polyepichlorohydrin grafted poly(phenylene oxide) to construct hydrophilic and hydrophobic microphase separation anion exchange membrane

An anion exchange membrane (QAPECH-g-PPO) with polyepichlorohydrin (PECH) as the main chain and poly(phenylene oxide) (PPO) as the side chain was prepared by Williamson etherification reaction. Atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) characterization indicate that PECH grafted with PPO can effectively form a hydrophilic and hydrophobic phase separation structure. The amount of and molecular weight of PPO grafted has different effects on the membrane properties. As the amount of PPO grafted increases, the tensile strength of the membrane gradually increases. When the amount of PPO grafted exceeds 44%, the excessive hydrophobic phase prevents the formation of continuous ionic channels in the hydrophilic phase, leading to a significant decrease in ionic conductivity. When the amount of PPO is 38%, the ionic conductivity can reach 72 mS cm−1 (80 °C), while the swelling ratio is only 15%. Moreover, higher molecular weight PPO at 38% amount improves tensile strength of QAPECH-g-PPO membrane. The higher the molecular weight of PPO, the more stable the π - π stacking structure is formed, leading to more aggregation of hydrophobic phases in the anion exchange membrane and weakened constraints on ion clusters. Therefore, the water absorption and ion conductivity slightly increase.

Understanding the Surprising Ionic Conductivity Maximum in Zn(TFSI)2 Water/Acetonitrile Mixture Electrolytes.

Aqueous electrolytes composed of 0.1 M zinc bis(trifluoromethylsulfonyl)imide (Zn(TFSI)2) and acetonitrile (ACN) were studied using combined experimental and simulation techniques. The electrolyte was found to be electrochemically stable when the ACN V% is higher than 74.4. In addition, it was found that the ionic conductivity of the mixed solvent electrolytes changes as a function of ACN composition, and a maximum was observed at 91.7 V% of ACN although the salt concentration is the same. This behavior was qualitatively reproduced by molecular dynamics (MD) simulations. Detailed analyses based on experiments and MD simulations show that at high ACN composition the water network existing in the high water composition solutions breaks. As a result, the screening effect of the solvent weakens and the correlation among ions increases, which causes a decrease in ionic conductivity at high ACN V%. This study provides a fundamental understanding of this complex mixed solvent electrolyte system.

The synergistic effects of dual substitution of Bi and Ce on ionic conductivity of Li7La3Zr2O12 solid electrolyte

Li7La3Zr2O12 (LLZO) is a promising solid-state electrolytes (SSE) candidate with high ionic conductivity, wide electrochemical window, good chemical stability and thermal stability. However, LLZO is unstable at room temperature and is easily converted from a cubic structure to a tetragonal structure, resulting in a decrease in ionic conductivity. Stable cubic phase LLZO can be obtained by element doping and the ionic conductivity can be improved. We found that the doping of Bi and Ce can reduce the sintering temperature and increase the ionic conductivity, among which the Li7La2.5Ce0.5Zr1.625Bi0.3O12 (LLCZBO) solid electrolyte has the highest ionic conductivity of 5.12 × 10−4 S cm−1 and the electronic conductivity of 2.72 × 10−10 at room temperature. LLCZBO prepared by sol-gel method can reduce the sintering temperature and improve the degree of densification. These results indicate that double-doped Bi and Ce is a simple and effective strategy to develop oxide solid electrolytes with high ionic conductivity.

Enhancing low-temperature characteristics of graphite anode by comprehensive modification of electrolyte

The performance of lithium-ion batteries is significantly deteriorated at low temperatures due to the components’ properties limitations such as the electrolyte viscosity increase and freezing accompanied with a decrease in ionic conductivity, rise of charge transfer resistance, and a substantial capacity loss (over 50 % of room-temperature capacity) in batteries with commercial electrolytes and graphite anodes, even at 0 °C. In this work, a complex modification of lithium salt and solvents of the electrolyte was applied simultaneously to develop an optimal electrolyte system with improved low-temperature characteristics for a Li/graphite half-cell. Various concentrations of commercial and alternative lithium salts (lithium hexafluorophosphate and lithium difluoro(oxalato)borate), dissolved in a mixture of solvents, were studied as electrolytes to determine the best interaction with a graphite electrode at low temperature. A solvent mixture of non-carbonate, low-freezing-point, organic ester ethyl acetate and solid electrolyte interphase (SEI) forming fluorinated co-solvent fluoroethylene carbonate in a ratio of 9:1 was used to prevent freezing of the electrolyte and ensure the formation of a more conductive SEI layer, respectively. The Li/graphite half-cell with the designed electrolyte system has retained about 80 % of its room-temperature capacity at −20 °C, demonstrating a new perspective for the development of low-temperature type electrolytes.

Anomalous Impact of Mechanochemical Treatment on the Na-ion Conductivity of Sodium Closo-Carbadodecaborate Probed by X-Ray Raman Scattering Spectroscopy.

Solid-state sodium ion conductors are crucial for the next generation of all-solid-state sodium batteries with high capacity, low cost, and improved safety. Sodium closo-carbadodecaborate (NaCB11 H12 ) is an attractive Na-ion conductor owing to its high thermal, electrochemical, and interfacial stability. Mechanical milling has recently been shown to increase conductivity by five orders of magnitude at room temperature, making it appealing for application in all-solid-state sodium batteries. Intriguingly, milling longer than 2 h led to a significant decrease in conductivity. In this study, X-ray Raman scattering (XRS) spectroscopy is used to probe the origin of the anomalous impact of mechanical treatment on the ionic conductivity of NaCB11 H12 . The B, C, and Na K-edge XRS spectra are successfully measured for the first time, and ab initio calculations are employed to interpret the results. The experimental and computational results reveal that the decrease in ionic conductivity upon prolonged milling is due to the increased proximity of Na to the CB11 H12 cage, caused by severe distortion of the long-range structure. Overall, this work demonstrates how the XRS technique, allowing investigation of low Z elements such as C and B in the bulk, can be used to acquire valuable information on the electronic structure of solid electrolytes and battery materials in general.

Unveiling frequency-dependent dielectric behavior of cellulose-based polymer electrolyte at various temperature and salt concentration

Dielectric behavior of cellulose-based polymer electrolyte was studied at various temperature and salt concentration. A polymer electrolyte membrane based on cellulose acetate (CA) as the polymer host and LiClO4 as the dopant salt was fabricated using the solution casting technique. The dopant salt concentration was varied as 0.3, 0.5, 0.67, and 1M. Dielectric relaxation spectroscopy characterization were performed using potentiostat at frequency ranging from 0.1 Hz to 1 MHz. Measurements were performed by sandwiching the membrane between stainless steel plates. The ionic conductivity was then calculated based on the Cole–Cole plot obtained from the impedance measurement. It was found that sample 1 M had the highest ionic conductivity at high frequencies. However, the frequency-dependent conductance plot showed that the ionic conductivity of the 1 M sample significantly decreased at low frequencies, i.e. from 3.41×10-5 S/cm at 1 MHz to 1.9×10-8 S/cm at 0.1 Hz. Other samples did not experience this phenomenon, including those with a Celgard© commercial membrane to represent commercial Li-ion batteries. This is caused by excess charge accumulation, leading to a high concentration of immobile charge carriers, which reduces the available free volume surrounding the polymer chain. This resulted in a significant decrease in ionic conductivity at low frequencies. Temperature variation was also performed on the conductivity measurement at 30-70 °C. Temperature variation showed more predictable behavior, where increasing the temperature activated charge carriers and enhanced ionic conductivity, from 1.81×10-5 S/cm at room temperature to 9.04×10-5 at 70°C. Sweeping across the frequency range results in a consistent sequence of ionic conductivities among the samples at various temperatures. This work is beneficial for evaluating a biomass-based polymer electrolyte complex in a Li-ion battery environment. Feasibility studies can be performed at various concentrations and temperatures to determine the optimal level of dopant salt input across a broad frequency range.

Reaction Kinetics of Carbonation at the Surface of Garnet-Type Li7La3Zr2O12 as Solid Electrolytes for All-Solid-State Li Ion Batteries

Garnet-type Li7La3Zr2O12 has attracted attention as a promising candidate for solid electrolytes in all-solid-state lithium ion metal batteries because it exhibits high Li ion conductivity and is inert in the presence of metallic Li. However, this material is known to react with water and carbon dioxide gas, even under ambient conditions, which can cause degradation, such as a decrease in ionic conductivity. In this study, the reaction rate of the carbonation processes under both humid and dry conditions was evaluated using thermal analysis. We confirmed that carbonation did not occur at <700 K under dry conditions. The reaction kinetics were found to initially be phase-boundary controlled and then diffusion controlled, and the corresponding activation energies were estimated to be 0.5 and 0.8 eV, respectively.

Aging of lithium-ion battery separators during battery cycling

The separator is a core component of lithium-ion batteries, and its service life impacts the electrochemical performance and device safety. This study reports the performance of aluminum oxide ceramic-coated polyethylene separators (PE-Al2O3 separators) before and after aging. During lithium-ion battery cycling, degradation products from the electrolyte and graphite were found at the separator surface, leading to a decrease in porosity and ionic conductivity and an increase in the internal resistance of the separator. The mechanical properties of the separators gradually deteriorated with the increase in current rates and the number of cycles. After 200 cycles at 1.5C, the tensile strength of the aging separator decreased by about 6.70 % compared with the fresh separator. The contact angle between the separator and the electrolyte increased from 15.2° to 24.4°, over the first 200 cycles at 1.5C, and the wettability deteriorated with the aging of the separator. In addition, on aging, the separator maintained a stable thermal decomposition temperature and showed stable chemical properties.

Ionic conductivity prediction model for composite electrodes and quantification of ionic conductivity reduction factors in sulfide-based all-solid-state batteries

In recent years, all-solid-state batteries have been considered as suitable candidates for application in electric vehicles from the viewpoints of safety, rapid recharging, and energy density. Thus, vigorous efforts have been made to develop solid electrolytes (SE) with high ionic conductivity. However, it has been reported that the ionic conductivity of all-solid-state batteries decreases significantly when the electrodes are composed of a composite containing active materials. In this paper, we clarify the reason for the decrease in ionic conductivity both experimentally and via simulations. In addition, we propose a prediction model for the ionic conductivity of composite electrodes. First, to clarify the reason for the decrease in the ionic conductivity of SE, SE layers with controlled porosity are prepared. It is found that the contact ratio between the SE is the most significant factor in decreasing the ionic conductivity. In addition, a path-resistance-separation model is proposed to predict the overall ionic conductivity by separating the path inside the composite into macroscopic pathways that avoid the active material and microscopic pathways that avoid voids. The proposed model is expected to be used for improving the efficiency of all-solid-state battery design.

Improvement of Selectivity of RALEX-CM Membranes via Modification by Ceria with a Functionalized Surface.

Ion exchange membranes are widely used for water treatment and ion separation by electrodialysis. One of the ways to increase the efficiency of industrial membranes is their modification with various dopants. To improve the membrane permselectivity, a simple strategy of the membrane surface modification was proposed. Heterogeneous RALEX-CM membranes were surface-modified by ceria with a phosphate-functionalized surface. Despite a decrease in ionic conductivity of the prepared composite membranes, their cation transport numbers slightly increase. Moreover, the modified membranes show a threefold increase in Ca2+/Na+ permselectivity (from 2.1 to 6.1) at low current densities.

One-step in situ biosynthesis fabrication of double-network hydrogel electrolytes with satisfactory water retention capacity and excellent electrical conductivity for Zn-air batteries

• The BC-PVA composite hydrogel was successfully prepared by a one-step in situ biosynthesis method. • Benefiting from the double-network, the BC-PVA hydrogel had excellent water retention and electrical conductivity capacity. • The sandwich-type ZABs based on BC-PVA exhibited excellent electrochemical performance. In the semi-open environment of flexible Zn-air batteries, water in the electrolyte inevitably evaporates continuously leading to a drastic decrease in ionic conductivity. The development of novel electrolytes with excellent water retention capacity and superior electrochemical performance for long-term stability is the key to improve the life of Zn-Air batteries. In this paper, BC-PVA composite hydrogel was successfully prepared by adding polyvinyl alcohol (PVA) suspension to bacterial cellulose (BC) medium using a one-step in situ biosynthesis method. Benefiting from the double network structure, the hydrogel exhibited excellent performance. The experimental results showed that the BC-PVA-2 composite hydrogel had an excellent water retention rate of 97.90%. Compared with pure BC, the breaking strength and ionic conductivity of BC-PVA-2 containing 2 wt.% PVA were improved by about 42% and 600%, respectively. After assembling the sandwich-type Zn-air batteries (ZABs), the open circuit voltage was 1.32 V, the peak charge current density was 110 mA·cm -2 .

Search for Lithium Ion Conducting Oxides Using the Predicted Ionic Conductivity by Machine Learning

A machine learning method was developed, which predicts ionic conductivity based on chemical composition alone, aiming to develop an efficient method to search for lithium conductive oxides. Under the obtained guideline, the material search was focused on the Li2O–SiO2–MoO3 pseudo-ternary phase diagram, which is predicted to have high ionic conductivity (>10−4 S·cm−1). We investigated the formation range, ionic conductivity, and crystal structure of the lithium superionic conductor (LISICON) solid solution on the Li4SiO4–Li2MoO4 tie line. The ionic conductivity of the LISICON phases is about 10−7 S·cm−1, which is higher than that of the end members; however, two orders of magnitude lower than that of the analogous LISICON materials. In addition, the experimental values were two or three orders of magnitude lower than the predicted conductivity values by machine learning. However, the developed prediction model can be used as an initial guideline for material exploration since the predicted values follow the trend of practical conductivity in the phase diagram. The crystal structure analysis indicated that the distance between the lithium sites and the occupancy of each lithium site in the crystal structure contributed to the decrease in ionic conductivity. This strong correlation between crystal structure and ionic conductivity was one of the reasons for the discrepancy between the predicted ionic conductivity based on chemical composition alone and the experimental value.

The Effect of Annealing on the Grain Structure and Ionic Conductivity of Block Copolymer Electrolytes

Block copolymer electrolytes that microphase-separate into rigid non-conducting domains and soft ion-conducting domains are known to exhibit stability against lithium metal anodes. In these systems, order is confined to grains with concomitant defects. When these electrolytes are annealed, the grain size typically increases, which is assumed in the literature to lead to a decrease in the ionic conductivity. In this work, we study the interplay between grain size and ionic conductivity using a block polymer electrolyte composed of a polystyrene (PS) block with a molecular weight of 19 kg/mol and a poly(ethylene oxide) (PEO) block with a molecular weight 20 kg/mol mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt at a variety of salt concentrations. The electrolytes have lamellar morphologies at all salt concentrations. At low salt concentrations, the average grain size before annealing is large and ionic conductivity decreases upon annealing. At high salt concentrations, however, the average grain size before annealing is small and ionic conductivity increases upon annealing.

Preparation and characterization of La2-xSmxMo1.8Al0.2O8.7 as electrolyte for solid oxide fuel cells

Solid oxide fuel cells (SOFCs) have been regarded as promising eco-friendly power sources in recent years owing to their high energy conversion efficiency and fuel flexibility. La2Mo2O9-based ceramics draw researchers’ attention due to their good performance as electrolyte materials for SOFCs. In this study, the Sm and Al co-doped La2Mo2O9, La2-xSmxMo1.8Al0.2O8.7 (x=0.1,0.2,0.3 and 04, LSMAO), are successfully synthesized by the sol-gel method as electrolyte materials for SOFCs. The phase evolution, sintering, the microstructural and electrochemical performance of LSMAO were observed by TG-DSC, XRD, SEM, and impedance analyses, respectively. The results show that the highly phase-pure cubic LSMAO nanopowders can be obtained after calcining at 600 °C for 2 h. The as-synthesized LSMAO powders exhibited a better sintering activity. All these samples were found to have a relative density above 94.5% after sintering at 950 °C for 5 h. The electrical performance study shows that higher doping concentrations of Sm caused a decrease in ionic conductivity and an increase in activation energy. La1.9Sm0.1Mo1.8Al0.2O8.7 exhibited the highest oxide ionic conductivity (σ800 °C=0.033 S/cm) and lowest electrical activation energy (Ea=0.85 eV). This shows that LSMAO could be used as a potential electrolyte for intermediate temperature SOFCs (IT-SOFCs).