Total Ionic Conductivity Research Articles

Excess Li2O Additives to Promote Grain Boundary Growth and Improve Ionic Conductivity of LiTa2PO8 Solid Electrolytes

LiTa2PO8 (LTPO) is a new solid-state lithium ion electrolyte material reported in the latest research, which has high bulk ionic conductivity and low grain boundary ion conductivity. However, it is difficult to density with conventional sintering methods. Herein, in this work, the solid-phase synthesis method was used to prepared the LTPO solid-state electrolyte, and the influence of the amount of lithium on the structure and performance of LTPO electrolyte material was investigated. The results show that the excess Li2O does not increase other impurities and does not change the structure of the material, but the liquid phase produced by the excess Li2O can promote the elimination of interfacial pores, accelerate the direct bonding of grains and improve the ionic conductivity of grain boundary, thus improving the overall ionic conductivity of the material. Considering the volatilization of lithium and the impact of liquid phase sintering at high temperatures and the content restructuring, after adding 20 wt% excess formulation of Li2O, the resultant of LTPO density is 5.0 g/cm3, the density reaches 85.58%. As a result, the total ionic conductivity of the electrolyte is 3.28 × 10–4 S/cm at 25°C, and the Li-ion diffusion activation energy is 0.27 eV. In addition, after loading this electrolyte into a Li–Li symmetric battery, it is proved that the electrolyte has lithium ion transport performance and can be used in all-solid-state batteries. However, it is also found from cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) analysis that the interface between LTPO material and Li is unstable, and Ta5+ ions are reduced, which will be another key issue to be addressed in the future.

Effects of monovalent alkali metals on grain boundary conductivity and electrochemical properties of gadolinia-doped ceria electrolyte

In the present work, 1 mol% alkali metals (Li, Na, K) doped Ce0.9Gd0.1O2-δ (GDC) electrolytes are prepared by citrate-nitrate sol-gel autoignition process. The effects of monovalent alkali metals on the phase structure, micromorphology and grain boundary conductivity of GDC electrolyte are investigated. All Ce0.89Gd0.1A0.01O2-δ (AGDC, A = Li, Na, K) ceramics exhibit a complete fluorite-type structure. SEM results show that all samples sintered at 1400 °C for 5 h have been achieved high densification, and the addition of alkali metals is conducive to the growth of grains. The space charge potential calculated by impedance data has decreased obviously after alkali metals are incorporated into GDC and the value of Ce0.89Gd0.1K0.01O2-δ ceramic is apparently reduced from 0.063 V (GDC) to 0.033 V at 400 °C. These results indicate monovalent alkali metals are beneficial to improve grain boundary conductivity and even total electrical conductivity. Additionally, among all the samples, the Ce0.89Gd0.1K0.01O2-δ electrolyte shows the highest total ionic conductivity of 2.64 × 10−2 S/cm at 700 °C in dry air. The single cell with Ce0.89Gd0.1K0.01O2-δ electrolyte promises the best power density of 624.5 mW cm−2 at working temperature of 700 °C. Therefore, the monovalent alkali metals dopants have promoting effects on improving the grain boundary conductivity, enhancing the sintering activity and output performance of GDC as an electrolyte for IT-SOFCs.

Impact of Total Ionic- and Individual Li+-Conduction in Dual-Cation Electrolytes on Power Performances for Thick Electrode Li4Ti5O12//AC Hybrid Capacitors

The utilization of dual-cation electrolytes constructed with a Li-based electrolyte (LiBF4) and an additional supporting electrolyte (quaternary ammonium salts or ionic liquids) is a promising strategy toward simultaneously achieving thick-electrode (∼100 μm) Li-based energy storage devices with high power and high energy densities. We observed that 1-ethyl-3-methylimidazolium tetrafluoroborate was suitable for the dual-cation electrolyte in a Li4Ti5O12 (LTO)//activated carbon (AC) (LTO//AC) hybrid capacitor, showing 64% capacity retention at a high current density of 200 mA cm–2. The EMI-based dual-cation system exhibited the highest total ionic conductivity and output characteristics compared to other dual-cation systems even with lowered Li+ transport in the bulk electrolyte. The simulation of the charge-transfer resistance (Rct) based on the transmission line model shows that the dual-cation electrolyte with high ionic conduction mitigates the Rct distribution within the macropores of a 200 μm thick LTO electrode, resulting in a decrease of the mean value of Rct. A combination of spectroscopic analysis and electrochemical characterization at different electrolyte compositions revealed that a good balance between the total ionic and individual Li+-conductivities should be found by controlling the concentration ratio between Li-based and supporting electrolytic salts in order to extract the maximum performance of the thick-electrode LTO//AC systems.

Assessment of processing route on the performance of ceria‐based composites

Gd-doped ceria (GDC)-based composites, including a eutectic mixture of lithium and sodium carbonate (NLC) as second phase, were prepared using several processing routes, namely chemical synthesis, co-firing of both phases, or impregnation of a presintered porous matrix. LiAlO2-based composites were also prepared and used as reference. The structural, microstructural, and electrical properties (impedance spectroscopy in air, up to 700°C) of these materials were assessed in detail. A limited set of compositions was also used in measurements of total electrical conductivity at different oxygen partial pressures (from 0.21 to <10−25 atm), in the 600°C to 700°C range. The results obtained confirmed the enormous impact of the processing route on the percolation of the ceramic phase. In the exploited range of operating conditions, GDC-NLC composites prepared by infiltration of molten carbonates within a mechanically robust ceramic matrix exhibit a high total ionic conductivity strongly influenced by the contribution of the molten salt while the ceramic phase is decisive in the appearance of a significant component of electronic conductivity under reducing conditions.

The solvation structure, transport properties and reduction behavior of carbonate-based electrolytes of lithium-ion batteries.

Despite the extensive employment of binary/ternary mixed-carbonate electrolytes (MCEs) for Li-ion batteries, the role of each ingredient with regards to the solvation structure, transport properties, and reduction behavior is not fully understood. Herein, we report the atomistic modeling and transport property measurements of the Gen2 (1.2 M LiPF6 in ethylene carbonate (EC) and ethyl methyl carbonate (EMC)) and EC-base (1.2 M LiPF6 in EC) electrolytes, as well as their mixtures with 10 mol% fluoroethylene carbonate (FEC). Due to the mixing of cyclic and linear carbonates, the Gen2 electrolyte is found to have a 60% lower ion dissociation rate and a 44% faster Li+ self-diffusion rate than the EC-base electrolyte, while the total ionic conductivities are similar. Moreover, we propose for the first time the anion–solvent exchange mechanism in MCEs with identified energetic and electrostatic origins. For electrolytes with additive, up to 25% FEC coordinates with Li+, which exhibits a preferential reduction that helps passivate the anode and facilitates an improved solid electrolyte interphase. The work provides a coherent computational framework for evaluating mixed electrolyte systems.

Communication—Fast Li+ Ion Conducting NASICON-Type Li1.15Y0.15Zr1.85P3O12 Glass Ceramics

Herein, NASICON-type Li1.15Y0.15Zr1.85P3O12 glass ceramics (a-LYZP) were synthesized from amorphous materials. Compared with samples prepared by the solid-state reaction (s-LYZP), a-LYZP showed a higher total ionic conductivity of 7.0 × 10−5 S cm−1 at 298 K and improved inter-particle contact. The structure of this glass ceramic effectively reduced the resistance of the Li1.15Y0.15Zr1.85P3O12. In the temperature range 263–298 K, the activation energy of a-LYZP was 0.43 eV, which was smaller than that for s-LYZP (0.63 eV). Rietveld analysis of XRD patterns suggested that the longer a-axis and larger unit lattice volume of a-LYZP prevented phase change from rhombohedral to triclinic.

Stability of Solid-State Sintered Li1.5Al0.5Ge1.5(PO4)3 Solid Electrolytes in Var-ious Mediums for All Solid-State Li-ion Batteries

Solid electrolytes are strong candidates for next-generation Li-ion bat-teries for Electrical Vehicle (EV) applications. However, their usage is not widely spread because of their relatively poor ionic conductivity and high electrode/electrolyte interfacial resistance compared to their com-mercial counterparts, organic based liquid electrolytes. Sodium Superi-onic Conductor (NASICON) type solid electrolytes could be an option to overcome these problems. Li1.5Al0.5Ge1.5(PO4)3 (LAGP) stands forward among other NASICON type solid electrolytes with their easy synthesis and processing. Yet, their stability against various mediums remain un-known and needs to be enlightened. In this study, the stability of LAGP against water, air at 85°C and 1M LiOH solution was discussed. LAGP re-sults after sintering at 900°C for 3 hours showed impurity-free, highly dense structure with a restricted grain growth. Water and air aged sam-ples showed a dramatical reduction on grain boundary contribution of to-tal ionic conductivity whereas the sample aged at 1M LiOH solution ex-hibited both reduction in ionic conductivity and increase on grain boundary conductivity. The highest reduction on total ionic conductivity was observed on the sample aged in water. On the contrary, the sample aged in 1M LiOH solution resulted in a net increase on total ionic con-ductivity. The highest total conductivity of 4.3 x 10-4 S/cm was obtained from the sample aged in 1M LiOH. On the other hand, the sample aged the lowest conductivity – 1.8 x 10-4 S/cm – showed the lowest total con-ductivity of all samples.

Glass Transition Temperature and Ion Binding Determine Conductivity and Lithium–Ion Transport in Polymer Electrolytes

Polymer electrolytes with high Li+-ion conductivity provide a route toward improved safety and performance of Li+-ion batteries. However, most polymer electrolytes suffer from low ionic conduction and an even lower Li+-ion contribution to the conductivity (the transport number, t+), with the anion typically transporting over 80% of the charge. Here, we show that subtle and potentially undetected associations within a polymer electrolyte can entrain both the anion and the cation. When removed, the conductivity performance of the electrolyte can be improved by almost 2 orders of magnitude. Importantly, while some of this improvement can be attributed to a decreased glass transition temperature, Tg, the removal of the amide functional group reduces interactions between the polymer and the Li+ cations, doubling the Li+ t+ to 0.43, as measured using pulsed-field-gradient NMR. This work highlights the importance of strategic synthetic design and emphasizes the dual role of Tg and ion binding for the development of polymer electrolytes with increased total ionic conductivity and the Li+ ion contribution to it.

Dual-Cation Electrolyte System Using Quaternary Ammonium Salts and Ionic Liquid for High Power and High Energy Li4Ti5O12//AC Hybrid Capacitor System

[Introduction] The Use of thick electrodes (> 100 µm) is a simple approach to increase the energy density of electrochemical energy storage devices. However, the high ionic resistance in thick electrodes limits the high-power applications of such devices. “Dual-cation” electrolytes for thick-electrode hybrid capacitor systems, typically composed of Li4Ti5O12 (LTO, 200 µm) and activated carbon (AC, 400 µm) electrodes, have been developed[1]. A dual-cation electrolyte is composed of lithium tetrafluoroborate (LiBF4) and spiro-(1,1')-bipyrrolidinium tetrafluoroborate (SBPBF4) dissolved in propylene carbonate (PC). An SBP-based dual-cation electrolyte, comprising 1 M LiBF4 + 2 M SBPBF4 / PC, exhibits a higher total ionic conductivity (7.67 S cm-1) than the single-cation electrolyte (3.40 S cm-1), consisting of 1 M LiBF4 / PC, while Li+ conductivity decreases with an increase of SBPBF4 concentration. Our interesting finding was that the presence of SBP+, despite the low Li+ transport in the electrolyte bulk, reduces overvoltage associated with migration limitation in the thick LTO electrode, and thus enhances power density in LTO//AC hybrid capacitor systems.In this study, we propose another dual-cation electrolyte using a 1-ethyl-3-methylimidazolium (EMI) cation in place of the SBP cation, which further enhances the power performance of LTO//AC hybrid capacitor systems. It has been shown that an EMI-based electrolyte exhibits a higher total ionic conductivity (10.9 S cm-1) than the SBP-based electrolyte. Herein we provide a detailed account of factors that improve the discharge properties of the EMI-based dual-cation electrolyte by using electrochemical and spectroscopic methods.[Experimental] The dual-cation electrolytes were prepared by dissolving 1 M LiBF4 and x M SBPBF4 (0 < x < 3) or x' M EMIBF4 (0 < x' < 4), in PC. The ionic conductivity of the prepared electrolytes was measured using a conductivity meter. The LTO(200 μm)//AC(400 μm) hybrid capacitor system assumed a coin type cell assembly; charge-discharge measurements were conducted at 1 mA cm-2 (at the charge) and 1 to 200 mA cm-2 (at the discharge). Pulsed Gradient Spin Echo (PGSE) NMR analysis was conducted to determine the self-diffusion coefficients of the Li(7Li), SBP (1H), and EMI (1H) cations and the BF4 (19F) anion in the electrolytes.. Electrochemical impedance spectroscopy (EIS) was performed to evaluate the resistance of the LTO electrode using LTO//LTO symmetric cells designed at both the delithiated (SOC of LTO = 0%) and lithiated (SOC of LTO = 25%) states.[Results and discussion]The results of the ionic conductivity for all electrolytes are shown in Figure 1. The EMI-based dual-cation electrolyte exhibited higher ionic conductivity than the SBP-based electrolyte. The results of the charge-discharge test (Figure 2) showed that the EMI-based dual-cation electrolyte exhibits optimal discharge properties among the electrolytes. Moreover, the PGSE NMR analysis results indicated that the self-diffusion coefficient for all ions including Li+ decreased with an increase in EMIBF4 concentration. In contrast, the ionic resistance (R ion) of the LTO negative electrode calculated from the EIS results at the delithiated state (SOC of LTO = 0%) yielded lower values for the EMI-based dual-cation electrolyte (11.1 Ω cm2) than that for the SBP-based (14.0 Ω cm2) and single-cation (27.1 Ω cm2) electrolytes. We also evaluated the charge-transfer resistance (R ct) from the EIS results using LTO//LTO symmetric cells at the lithiated state (SOC of LTO = 25%). The R ct was found to be lower in the EMI-based dual-cation electrolyte (1.71 Ω cm2) than that in the SBP-based (2.28 Ω cm2) and single-cation (3.57 Ω cm2) electrolytes. These results showed that charge-transfer reactions at the LTO electrodes occur more readily in the dual-cation electrolyte.The results indicated that a reduction in R ct occurs because ion potential suppression occurs owing to the accelerated ion transport in the electrode, as well as in our previous study[1]. The suppression of the ionic potential increased the Li+ concentration and reaction current at the collector side, which decreased the R ct. This is because the advantage of an increase in total ionic conductivity is effective even when the transport ofLi+ is reduced in a thick-electrode system. This study confirms that the use of the EMI-based electrolyte, which has a higher total ionic conductivity than the SBP-based electrolyte, exhibits a remarkable suppression of R ion and R ct. The use of thick electrodes, therefore, facilitates an increase in total ionic conductivity, which has a more desirable effect than that of high Li+ conductivity, especially in the EMI-based dual-cation electrolyte, wherein the power density of the thick-electrode LTO//AC hybrid capacitor systems was significantly improved.[1] Y. Chikaoka et al., J. Phys. Chem. C, in press(doi.org/10.1021/acs.jpcc.0c01916). Figure 1

Mechanochemical Synthesis of Modified Li2ohbr to Improve Ionic Conductivity

All-solid-state lithium batteries have gained more attention as the next-generation batteries with high energy density, high safety and long life. Recently, cubic-phase lithium-rich anti-perovskite (LiRAP: Li3-x OH x X (X = Cl, Br), including x = 0) compounds have been actively investigated due to their certain advantages to overcome the problems faced by other solid electrolytes [1]. In this work, we investigated the ionic conductivity of Li2OHBr by chemical doping.Li2OHBr was mechanochemically synthesized using LiOH and LiBr [2]. Powder X-ray diffraction (PXRD) pattern of the synthesized sample well agreed with cubic Li2OHBr with a lattice constant of 4.046 Å and no impurities were observed as shown in Fig. 1(a). In the Nyquist plot of Au/Li2OHBr/Au symmetrical cell measured at 25 ºC, one semicircular arc was observed (Fig. 1(b)). The total ionic conductivity of Li2OHBr evaluated based on this semicircular arc was 1.1 × 10–6 S cm–1 at 25 ˚C. In an attempt to improve the ionic conductivity, Li2OHBr1-x Cl x , Li1.8M0.1OHBr (M = Mg, Ca, Sr, Ba) and Li2+x OH1-x Br were synthesized by the same manner as Li2OHBr. The PXRD measurements revealed that most of the modified Li2OHBr formed cubic phase without impurities and the lattice constant slightly changed by chemical doping (Fig. 1(a)). The total ionic conductivity of Li2OHBr0.75Cl0.25, Li1.8Ca0.1OHBr and Li2.2OH0.8Br were 9.3 × 10–7, 4.9 × 10–7 and 3.6 × 10–6 S cm–1 at 25 ºC, respectively. It has been reported that grain-boundary resistance is generally larger than bulk resistance in LiRAPs[3] and also, the LiRAPs have a tendency to form Li vacancy around the grain boundary [4]. Thus, the reason why Li2.2OH0.8Br has larger ionic conductivity than Li2OHBr is because, the Li concentration around grain boundary is increased. So, it can be one of the strategies to improve ionic conductivity of LiRAPs. Acknowledgement: This work was supported by JSPS KAKENHI Grant Number JP18K14318 and in part JP19H05813 (Grant-in-Aid for Scientific Research on Innovative Areas “Interface IONICS”). One of the authors Manoj Krishna Sugumar thankfully acknowledges the financial assistance from Yoshida Scholarship Foundation.

Toward All-Ceramic Solid State Lithium Battery: Hot-Pressing Nasicon Electrolyte

In this presentation we show the influence of pressure during the hot sintering stage on the ionic conductivity of the lithium super ionic conductor Li1.5Al0.5Ge1.5(PO4)3 (LAGP) as electrolyte for solid state lithium battery 1. A new method is developed to obtain high ionic conductivities at only 650 °C by applying pressure (56 MPa) instead of standard 850-900°C. Considering the possible decomposition reactions when cathode materials are annealed at high temperature (typically ≥700 °C), the use of high pressure at 650 °C can significantly limit the formation of side-products. In this presentation we show the criteria required to optimize the pressure and temperature parameters for enhancing the total ionic conductivity. Finally, this study reports an all solid-state battery based on a LiFePO4 olivine cathode prepared at 650 °C showing very good Li-intercalation/deintercalation performance. Good ionic interfacial contact is achieved without using polymer and liquid electrolyte at the positive electrode. 1 Paolella et al. Advanced Materials Interfaces, 2020, Just Accepted Manuscript DOI: 10.1002/admi.202000164 Figure 1

One-step low-temperature synthesis of Li0.33La0.55TiO3 solid electrolytes by tape casting method

Li0.33La0.55TiO3 (LLTO) is a solid Li-ion conductor with high bulk ionic conductivity. However, a high processing temperature, typically around 1300 °C, is generally required for obtaining its crystallization. In this work, LLTO was successfully synthesized at temperatures as low as 900 °C by tape casting method. Thermogravimetric analysis was carried out on the precursors for clarifying the weight loss and related phase transformations, and powder X-ray diffraction analysis was performed on the final products for verifying the crystallinity and phase purity in the low-temperature-processed LLTO electrolytes. The morphology of the synthesized LLTO powders was observed by scanning electron microscopy for understanding the microstructural evolution with increase of the sintering temperature. The ionic conductivity and activation energy of LLTO solid electrolytes were measured. A typical ionic conducting behavior with a moderate total conductivity of 4.3 × 10−6 S/cm and a quite low activation energy of 0.29 eV was obtained in the 900 °C-derived LLTO sample. When the processing temperature was raised to 1350 °C, the total ionic conductivity was further enhanced, reaching 6.13 × 10−5 S/cm. When the LLTO pellets were subject to cold isostatic pressing, the low-temperature (900 °C)-processed LLTO sample also presented a high conductivity of 2.1 × 10−5 S/cm. This work sheds light on the low-temperature synthesis of LLTO-based solid electrolytes for solid-state lithium battery applications.

Impact of Precrystallized NaYSi4O12 Powders in the Synthesis of Sodium Conducting Solid Electrolytes

The glass crystallization route for Na‐ion conducting glass ceramics with conductive N5 modification of Na5YSi4O12 has been explored. P2O5 is used to modify the glass frit for optimization of the sintering and crystallization process. Mass spectroscopy reveals that the evaporation of CO2 in the sintered microstructure is responsible for enhanced porosity. The glass is not fully transformed to the highly conductive phase (N5) by crystallization and thereby lower conductivities in sintered samples is observed. A pre‐crystallization step of the initial glass powder is evaluated as suitable to eliminate the gas evolution and subsequent sintering of material crystallized in desired N5 modification is successfully performed. With the powder of the pre‐crystallized material, homogenous sintered microstructures consisting of crystalline and glassy phases are obtained. Despite the higher temperature needed for sintering, low porosity and a mechanical strength up to 60 N mm−2 are achieved for samples from pre‐crystallized powder. The analysis of impedance spectra of sintered samples reveal high impact of grain boundaries on total ionic conductivity. Samples made from pre‐crystallized powder show higher overall ionic conductivity of 8.3 × 10−6 S cm−1 at room temperature which is lower than the conductivity of crystallized N5 phase grains (1.4 × 10−4 S cm−1).

Boron group element doping of Li1.5Al0.5Ge1.5(PO4)3 based on microwave sintering

We report effectiveness of dopants selected from group 13, such as B, Ga, and In, on the conductivity of Li1.5Al0.5Ge1.5(PO4)3 (LAGP) that is recognized as one of the promising solid electrolytes for next-generation solid-state lithium batteries. To minimize loss of versatile element, crystallization of LAGP using a microwave irradiation is introduced. Experimental results demonstrate that B enhances grain boundary conductivity, while Ga improves the bulk ionic conductivity. Co-doping of B and Ga leads to enhanced total ionic conductivity and remarkably reduced activation energy.

A simple and effective method to prepare dense Li1.3Al0.3Ti1.7(PO4)3 solid–state electrolyte for lithium-oxygen batteries

A simple and effective method was developed and used to improve the conductivity and density of Li1.3Al0.3Ti1.7(PO4)3 solid–state electrolyte. The raw powders were synthesized through two different methods to expand the particle size distribution, which could improve the sintered density and the grain boundary connection of the of LATP electrolyte. Through this method, the relative density of the electrolyte made of mixed powders can reach to 97% compared with the 92% and 95% for electrolyte made of single solid-state reaction powder and sol-gel reaction powder, respectively. The conductivity test shows that this electrolyte has high total ion conductivity of 5.23 × 10−4 S cm−1 at room temperature with the grain boundary conductivity of 6.11 × 10−4 S cm−1. With the merits of high density and ion conductivity, this solid-state electrolyte shows good rate capability and cycle performance in aqueous lithium-oxygen batteries.

Effects of Cr/Ti co-doping on the electrical and thermal properties of tantalum-based electrolyte materials for solid oxide fuel cells

New triclinic oxide material Ta1−x−yTixCryO2.5−δ (x = 0.077, y = 0–0.053) was synthesized via an oxalate co-precipitation method and tested as a novel electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Structural, electrical, and thermal properties of tantalum-based electrolyte co-doping with Cr3+/Ti4+ content were studied. X-ray powder diffraction showed that the crystal structure changed from orthorhombic to triclinic due to co-doped, and its high-temperature triclinic (pseudo-tetragonal) phase of tantalum pentoxide (H-Ta2O5) structure was stabilized to room temperature by doping. The crystalline phase facilitates the generation of more oxygen vacancies, which increases the electrical conductivity. The appearance of oxygen vacancies in the crystal with triclinic structure was confirmed with Raman spectroscopy and X-ray photoelectron spectroscopy. Scanning electron microscopy results exhibited the grain size decreases gradually with doping. Impedance curves showed high total ionic conductivity (1.48 × 10–1 S/cm at 700 °C) and low activation energy (Ea = 0.857 eV) for Ta0.9Ti0.067Cr0.033O2.5−δ. Thermal expansion coefficients (3.09 × 10–6 K−1) for co-doped samples were much lower in comparison to other electrolytes. Based on the results reported in this work, Ta1−x−yTixCryO2.5−δ can be an excellent oxygen conductor and recommended as solid electrolytes for IT-SOFC applications.

Boost in the thermal stability, ionic conductivity and director relaxation frequency in the composite of liquid crystal and functionalised multi-walled carbon nanotubes

ABSTRACT In the present work, we have prepared a liquid crystal-carbon nanotube (LC-CNT) composite by dispersing a low concentration of carboxylic group (-COOH) functionalised multi-walled CNTs (MWCNTs) in a liquid-crystal 6CHBT and studied in detail the alterations in thermal and electrical parameters. Thermodynamic studies reveal that transition processes are becoming fast due to the dispersion of MWCNTs. The change in the behaviour of transitions is credited to the reduction in ionic impurities owing to the ion trapping characteristic of CNTs. The isotropic liquid to nematic transition temperature of the composite system is increasing for the exothermic cycle as compared to that of the pure sample. The average transition enthalpies and entropies for various transitions of the composite system are increasing as compared to those of the virgin sample. Longitudinal component of the permittivity and dielectric anisotropy of the composite system is slightly reduced as compared to those of the virgin sample. Relaxation frequencies of an observed relaxation mechanism corresponding to the rotation of molecules about their short axes of the composite system are enhanced as compared to the undispersed sample. Total ionic conductivity of the composite system is boosted as compared to those of the pure sample.

Silicon Substituted Lithium Stannum Phosphate Ceramic Electrolytes: Structural, Electrical and Electrochemical Properties

Structural, electrical and electrochemical properties of silicon (Si) substituted NASICON-structured lithium stannum phosphate, Li1+ySn2P3-ySiyO12 with 0 &lt; y &lt; 1 that was prepared by the low-temperature water-based sol-gel method has been investigated. From the structural analysis, all samples in the system displayed rhombohedral symmetry. The total ionic conductivity, σt, and ionic mobility, µ was increased with the increase of silicon content, y. A high ionic conductivity value of 6.05 × 10-5 S cm-1 exhibited at y = 0.5 with a temperature of 500 °C. Linear sweep voltammetry analysis showed that the sample was electrochemically stable up to 5.1 V. Meanwhile, the ionic transference number value of the sample was 0.99, suggesting that the majority of mobile charge carriers were predominantly due to ions. Thus, from these results, it indicated that silicon substitution in LiSn2P3O12 ceramic electrolytes is significantly enhanced the electrical and electrochemical properties.

Effect of La3+, Pr3+, and Sm3+ triple-doping on structural, electrical, and thermal properties of ceria solid electrolytes for intermediate temperature solid oxide fuel cells

In the present study, we have investigated the effect of La3+, Pr3+, and Sm3+ triple-doping on structural, electrical, and thermal properties of ceria (Ce1–x(Lax/3Prx/3Smx/3)O2-δ). X-ray diffraction studies confirm the formation of samples with single-phase cubic-fluorite structure (JCPDS PDF File No: 34-0394). The lattice parameter values increases with increasing the dopant concentration (from 5.4190 Å to 5.4503 Å), shows that the dopants get totally dissolved into Cerium site. All the prepared samples were sintered at 1300 °C for 4 h. The values of relative densities were found to be higher than 95% and the high value is observed for the composition LPS8 i.e. 97.8%. The calculated crystalline size values were found to be in the range of 46 and 53 nm. Scanning electron microscope and energy dispersive spectroscopic techniques reveal the surface-microstructure and presence of elemental confirmation in the compositions. The average grain size values were found to be in between 231 and 366 nm. Raman spectroscopy study reveals the existence of oxygen vacancies in all the compositions and estimated concentration of oxygen vacancies is found to be high for LPS8 composition. The impedance spectroscopy revealed the total ionic conductivity and activation energies of all the compositions. The composition Ce0.76La0.08Pr0.08Sm0.08O2-δ (LPS8) displays the highest total ionic conductivity i.e. 0.043 S/cm with low activation energy i.e. 0.76 eV. Matched thermal expansion coefficient of the sample Ce0.76La0.08Pr0.08Sm0.08O2-δ with already existing electrode materials, makes it as an effective electrolyte material for the intermediate temperature–solid oxide fuel cell applications.

Increase in ionic conductivity of NASICON-type solid electrolyte Li1.5Al0.5Ti1.5(PO4)3 by Nb2O5 doping

A NASICON-type Li1.5Al0.5Ti1.5(PO4)3 (LATP) solid electrolyte was fabricated using a novel sol–gel approach with citric acid as a complex agent. An electrochemical impedance spectroscopy analysis shows that the ionic conductivity of the LATP solid electrolyte synthesized using the sol–gel route was low (8 × 10−5 S cm−1 at 303 K), owing to its large grain boundary impedance. To improve the ionic conductivity of the LATP conducting ceramic, we incorporated Nb2O5 as a doping agent into the LATP solid electrolyte. The effects of Nb2O5 on the phase composition, microstructure, and ionic conductivity of the LATP solid electrolyte were investigated. The LATP conducting ceramic with an 8-wt% Nb2O5 doping exhibited the highest total ionic conductivity of 3.54 × 10−4 S cm−1 at 303 K, relative density of 91.7%, and lowest activation energy of 0.271 eV. The fabricated LATP solid electrolyte doped with Nb2O5 is a promising material for electrochemical devices.