Ionic Conduction Mechanism Research Articles

High ionic conductivity and ion conduction mechanism in ZIF-8 based quasi-solid-state electrolytes: a positron annihilation and broadband dielectric spectroscopy study.

The low ionic conductivity and electrode-electrolyte interface instability issues with solid polymer electrolytes jeopardize their electrochemical performances in lithium-ion batteries (LIBs). The use of quasi-solid-state electrolytes (QSSEs) with concentrated Li salt embedded inside the pore networks of metal organic frameworks (MOFs) can successfully address the aforementioned issues. Owing to the sieve effect of zeolitic imidazolate framework-8 (ZIF-8) towards selective cation permeability over anions through the interconnected pore network, a unique QSSE with LiTFSI salt concentrated in the ZIF-8 skeleton used as a filler in poly(ethylene oxide) has been synthesized. LiTFSI gets embedded inside the interconnected pore network of ZIF-8 that furnishes unhindered pathways for Li+ ion migration leading to a very high ionic conductivity of ∼6 × 10-4 S cm-1. The higher ionic conductivity is directly related to the Li+ ion conduction through the pore network of ZIF-8 which has been experimentally evident from complementary methods viz. Positron annihilation and broadband dielectric spectroscopy. The design route towards these types of QSSEs encompassing porous MOFs paves the way for realizing Li superionic conductors suitable for practical application in commercial LIBs with high safety and stability.

A new universal force-field for the Li2S-P2S5 system.

Lithium thiophosphate electrolyte is a promising material for application in all-solid-state batteries. Ab initio molecular dynamics (AIMD) simulations have been used to investigate the ion conduction mechanisms in single-crystalline and glassy compounds. However, the complexity of real materials (e.g., materials with grain boundaries and multiphase glass-ceramics) causes AIMD simulations to have high computational cost. To overcome this computational limitation, we developed a new interatomic potential for classical molecular dynamics (CMD) simulations of Li solid-state electrolytes. The training datasets were generated from representative sulfide electrolytes (β-Li3PS4, γ-Li3PS4, Li4P2S6, Li7P3S11, and Li7PS6 crystals and 70Li2S-30P2S5 glass). Using the functional forms of the Class II and Stillinger-Weber potentials, all parameters were optimized by minimizing the differences in forces on atoms, stresses, and potential energies between the CMD and AIMD results. Subsequent validation showed that the optimized parameters can reproduce the dynamics of Li+ as well as the structures of the crystalline and glassy materials. The ionic conductivity of Li7P3S11 crystal was approximately five times that of the isostoichiometric 70Li2S-30P2S5 glass, indicating that CMD simulations using the developed force-field accurately reproduced the effective conduction path in Li7P3S11 from AIMD. The developed force-field parameters make it possible to simulate complex materials including amorphous-crystalline interfaces and multiphase glass-ceramics in the CMD framework.

Transient behavior of electrical conductivity in low‐density polyethylene in the presence of acetophenone

AbstractThe transient current in low‐density polyethylene (LDPE) is studied, particularly in the presence of the small organic molecule acetophenone (ACP). Crosslinked LDPE is used extensively in high‐voltage power transmission, and acetophenone is a common byproduct of the crosslinking chemistry. Time‐dependent current measurements of LDPE with and without ACP soaked into the polymer as well as at one or both electrodes are performed by applying step voltages. The results demonstrate that the presence of ACP causes a deviation in the predicted power‐law current decay, suggesting that electron and hole injection at the anode and cathode, respectively, are affected by the presence of this small organic molecule. ACP contributes both to the ionic conduction and charge hopping mechanism. The charge mobility depends on the applied electric field and the sample thickness. The results suggests that the dispersive charge transport phenomenon influences the measured current. This study shows how such a molecule may alter charge transport in polyethylene.

Electrohydrodynamic conduction pumping of a viscoelastic dielectric fluid with the Onsager–Wien effect

Due to the Onsager–Wien effect (enhanced electric field dissociation), electrohydrodynamic (EHD) conduction pumping problems in the Oldroyd-B viscoelastic dielectric liquid are solved using the finite volume method. Fully coupled nonlinear equations, including the Naiver–Stokes (N–S) equation, the Nernst–Plank equation of the ion conduction mechanism, and the constitutive equation of viscoelastic fluid, are thoroughly implemented. Our numerical model is fully verified with two benchmark cases, and simulations are performed under different conduction numbers C0 (0.01–103), Weissenberg numbers Wi (0.01–50), and viscosity ratios (0.3–0.9). Two limiting operating states of EHD conduction pumping, the Ohmic and the saturation regimes, are discussed in detail. Elastic instability is more likely to occur in the Ohmic regime, and the thickness of the heterocharge layer (called the dissociation layer) remains sensitive to C0 and the elasticity values. Current density and pressure generation show crucial degrees of dependence on the fluid elasticity and viscosity ratio.

Study of Crown Ether - Lithium Salt Complexes for Solid-State Electrolyte of Li Ion Battery

Electrolyte plays a pivotal role in Li-ion battery (LIB). Generally, it has been considered as a liquid phase material that allows for reasonable dissolution ability of inorganic salt and ion transportability across the electrodes. Since conventional liquid electrolytes faced limitations to improve battery performance, the solid-state electrolyte has raised rapidly to replace the liquid electrolyte. Solid polymer electrolyte (SPE) is one of the most promising solid-state electrolytes, it has attracted attention due to its strength as an electrolyte such as high accessibility, tolerance against volume change of electrodes, and reasonable chemical/thermal stability. Especially poly(ethylene oxide) (PEO) or PEO-based electrolytes have been widely developed, because of their outstanding Li salt dissolution ability. PEO forms a unique helical complex structure with Li salt, the complex is highly stable. It allows PEO to dissolve Li salt much easier than other polyethers, such as poly(propylene oxide) or poly(oxymethylene). However, the high stability of the complex could disturb fast ionic conduction in electrolyte medium, it is the reason why PEO electrolyte has poor ionic conductivity at ambient temperature (10-7 to 10-6S/cm at room temperature). Crown ethers, the macrocycles composed of ethylene oxide, also attract attention for SPEs. Even though the monomer is the same (ethylene oxide) for both PEO and Crown ethers, the properties of each complex are different. Crown ether electrolyte shows higher ionic conductivity than PEO electrolyte at ambient temperature, it is assumed that the crown ether electrolyte is an amorphous phase while PEO electrolyte has high crystallinity below the melting point (60~80%). Crown ether is also promising for Li metal batteries. Crown ether is the hosting material that has a preorganized acceptor structure (also well-known as macrocyclic effect), therefore it can adjust kinetics of reduction on the surface of Li metal anode. Even though promising abilities of crown ether electrolytes have been reported, their ion conduction mechanisms are yet understood well. Therefore, it is worth studying about complex structure and ion conduction mechanism of crown ether electrolyte for a better understanding of SPE, and further, it can be a milestone to design new SPEs. To understand the complex structure and ion conduction mechanism in crown ether electrolytes, we performed both experimental and theoretical analysis. We synthesized the complexes of different sizes of crown ethers (12-crown-4, 15-crown-5, and 18-crown-6) and Li salts (LiTFSI, LiClO4, LiBF4, and LiI). The complexes are characterized by Fourier transformed infrared (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA), and AC impedance analysis. DFT calculation and molecular dynamics for each complex were performed to obtain an atomistic description of the complexes.

Electric and Dielectric Studies on Modified Lithium Germanate

Titanium doped Lithium Germanate (Li4TiGe2O8) is synthesized by ceramic double sintering route. Germanate is sintered at a temperature of 900o C for 30 min in a microwave furnace. The formation of glass was confirmed by the X-ray diffraction technique. Electric, dielectric, ferroelectric and piezoelectric properties are investigated. Dielectric studies performed from room temperature to 500o C showed a steady dielectric constant of approximately 75 throughout the investigated temperature. AC conductivity of the glass showed very high resistivity of the order of 107 Ω-cm. Further, an ionic hopping conduction mechanism is suggested from the conductivity behaviour as a function of frequency. Ferroelectric hysteresis recorded at room temperature has exhibited a square loop suggesting very good ferroelectric nature of the glass. From the obtained high resistivity and piezoelectric coefficient, the glass can be explored for MMIC and MLCC device fabrication.

Ion‐Conducting Hydrogels and Their Applications in Bioelectronics

AbstractBioelectronics focuses on the interface between biological systems and electronics. Most biological systems are soft and wet, while electronics are typically hard and dry. Information in the form of charge is carried by electrons and holes in electronics, while ions and charged molecules are the charge carriers in biological systems. As such, finding the right material for the bioelectronic interface is challenging. Hydrogels are water swollen porous polymer networks and, similarly to biological systems, hydrogels are wet, soft, and ion conducting. These properties make hydrogels an ideal choice for the bioelectronic interface between electronics and biological systems. This review focuses on polyelectrolyte hydrogels, a class of hydrogels that has fixed charges as part of the polymer network. In order to maintain charge neutrality, these charges attract mobile ions of the opposite charge in the water swollen pores. These mobile ions give the hydrogels selective ionic conductivity. Here, it is discussed brief fundamentals of hydrogels, ionic conduction mechanism and optimization of the conductivity, and applications in bioelectronic sensors and mechanical actuators.

Influence of activation energy on charge conduction mechanism and giant dielectric relaxation of sol-gel derived C3H7NH3PbBr3 perovskite; Act as high performing UV photodetector

This work contains an extensive study on temperature dependent complex dielectric behavior over 4 Hz≤ f≤ 8 MHz of a promising hybrid perovskite, propylammonium lead bromide. The structural, as well as morphological property of this sol-gel derived sample have been analyzed with the help of XRD and SEM respectively. The obtained energy band gap and thermal stability study ensure the capability of this material in device fabrication. Possessing a wide band gap, this perovskite fascinatingly serves as a UV photodetector. The individual impact of grain and grain boundary over the entire resistance has been resolved by Maxwell – Wagner Cole–Cole model. This material holds an amazing property; giant dielectric constant near room temperature at low frequency limit which escalates rapidly in the influence of thermal effect. Modified cole – cole plot assures that both space and free charge conductivities ascend with temperature. The asymmetrical nature of the imaginary part of electric modulus is analyzed by Kohlrausch – Williams – Watts which confirms its non – Debye nature diminishes with rising temperature. The thermally triggered AC conductivity follows Jonscher’s power law and is emphasized with the jump relaxation model. The bulk conductivity of the sample depends on temperature and is elucidated with variable range hopping of localized charge carriers. Activation energy plays a key role in the ionic conduction mechanism within the sample, described elaborately. The overall substantial studies on its application as UV detector and different dielectric properties of this sample construct the basis of appreciable acceptability of the sample in energy harvesting.

Alkali-Activated Cement Sensors for Sodium Chloride Monitoring

Chloride-induced corrosion of reinforced concrete costs the global economy billions of dollars every year. Despite concerted research effort, the non-invasive, continuous monitoring of sodium chloride in concrete structures is still an unsolved problem. Here, we outline a first-time demonstration of a sodium chloride sensor based on alkali-activated cements: a class of cementitious, electrolytically conductive materials which are typically used for concrete construction and repair. In this work, internal sodium chloride concentrations ranging from 0–22 wt% were measured independently of moisture contents via shifts in electrical impedance. The typical sodium chloride measurement precision was 0.85 wt%. Non-linearity of the sensor response due to signal saturation began at sodium chloride concentrations >5 wt%. We use experimental measures of ion dynamics to link this saturation to the deleterious effect of high concentrations on ion mobility. This study demonstrates sensor feasibility, and provides new experimental evidence to further our understanding of ionic conductivity mechanisms in these materials. The work will allow for the development of self-sensing repair and construction materials for locating and quantifying sodium chloride levels within concrete structures — a valuable technology for supporting concrete health monitoring and maintenance.

Anti‐perovskite materials for energy storage batteries

AbstractAnti‐perovskites X3BA, as the electrically inverted derivatives of perovskites ABX3, have attracted tremendous attention for their good performances in multiple disciplines, especially in energy storage batteries. The Li/Na‐rich antiperovskite (LiRAP/NaRAP) solid‐state electrolytes (SSEs) typically show high ionic conductivities and high chemical/electrochemical stability toward the Li‐metal anode, illustrating their great potential for applications in the Li‐metal batteries (LMBs) using nonaqueous liquid electrolyte or all‐solid‐state electrolyte. The antiperovskites have been studied as artificial solid electrolyte interphase for Li‐metal anode protection, film SSEs for thin‐film batteries, and low melting temperature solid electrolyte enabling melt‐infiltration for the manufacture of all‐solid‐state lithium batteries. Transition metal‐doped LiRAPs as cathodes have demonstrated a high discharge specific capacity and good rate capability in the Li‐ion batteries (LIBs). Additionally, the underlying scientific principles in antiperovskites with flexible structural features have also been extensively studied. In this review, we comprehensively summarize the development, structural design, ionic conductivity and ion transportation mechanism, chemical/electrochemical stability, and applications of some antiperovskite materials in energy storage batteries. The perspective for enhancing the performance of the antiperovskites is also provided as a guide for future development and applications in energy storage.image

Insights into the Ionic Conduction Mechanism of Quasi-Solid Polymer Electrolytes through Multispectral Characterization.

Quasi-solid polymer electrolytes (QPE) composed of Li salts, polymer matrix, and solvent, are beneficial for improving the security and energy density of batteries. However, the ionic conduction mechanism, existential form of solvent molecules, and interactions between different components of QPE remain unclear. Here we develop a multispectral characterization strategy combined with first-principles calculations to unravel aforesaid mysteries. The results indicate that the existential state of solvent in QPE is quite different from that in liquid electrolyte. The Li cations in gel polymer electrolyte are fully solvated by partial solvent molecules to form a local high concentration of Li+ , while the other solvent molecules are fastened by polymer matrix in QPE. As a result, the solvation structure and conduction mechanism of Li+ are similar to those in high-concentrated liquid electrolyte. This work provides a new insight into the ionic conduction mechanism of QPE and will promote its application for safe and high-energy batteries.

Insights into the Ionic Conduction Mechanism of Quasi‐Solid Polymer Electrolytes through Multispectral Characterization

AbstractQuasi‐solid polymer electrolytes (QPE) composed of Li salts, polymer matrix, and solvent, are beneficial for improving the security and energy density of batteries. However, the ionic conduction mechanism, existential form of solvent molecules, and interactions between different components of QPE remain unclear. Here we develop a multispectral characterization strategy combined with first‐principles calculations to unravel aforesaid mysteries. The results indicate that the existential state of solvent in QPE is quite different from that in liquid electrolyte. The Li cations in gel polymer electrolyte are fully solvated by partial solvent molecules to form a local high concentration of Li+, while the other solvent molecules are fastened by polymer matrix in QPE. As a result, the solvation structure and conduction mechanism of Li+ are similar to those in high‐concentrated liquid electrolyte. This work provides a new insight into the ionic conduction mechanism of QPE and will promote its application for safe and high‐energy batteries.

A high ion-conductive and stable porous membrane for neutral aqueous Zn-based flow batteries

Zn-based flow batteries (ZFBs) with low cost and high efficiency have become one of promising energy storage technologies for renewable energy development. However, in ZFBs, an anion exchange membrane (AEM) losses ion conductivity because of the presence of Zn2+. The side reaction of Zn2+ precipitation resulted in ion exchange decomposition of AEM with quaternary groups. While a cation exchange membrane (CEM) hinders anion conductivity because of electrostatic interaction between ion-exchange groups and anions. To address poor ion conductivity of ion exchange membrane in ZFBs, a polyetherimide (PEI)-based porous ion conductive membrane is developed via water phase inversion technology for ZFBs. The ion conductive mechanism is based on pore size exclusion, which mitigates the effects of ion exchange groups on ion conductivity. The membrane performance is further improved by introducing suitable polyvinylpyrrolidone (PVP) and controlling tetrahydrofuran (THF) volatilization time. The results demonstrate that in Zn/4-Hydroxy-2,2,6,6-tetramethyl-piperidine 1-Oxyl (TEMPO-OH) flow battery, a coulombic efficiency (CE) of more than 98% and an energy efficiency (EE) of ~77% was achieved at 20 mA cm−2, and the flow battery assembled with 20PEI-1PVP-90s can stably run for 150 cycles. The PEI-based porous membrane with low cost and high efficiency is considered as a promising strategy for ZFBs.

Enhanced sodium ion conduction in Al-substituted Na2ZrO3

A variety of promising applications are found relying on the ionic conductivity of sodium zirconate (Na2ZrO3). The ionic conductivity of Na2ZrO3 can be further enhanced by introducing metallic ions into the lattice of Na2ZrO3, which is becoming an emerging subject of interest. In the context of these, this letter presents a wet chemical method to obtain Na2ZrO3 by intentional substitution of Al at Zr sites. The obtained Al-substituted Na2ZrO3 was found to be crystalline, with enhanced sodium ion conduction (5.3 × 10−5 S/cm). Furthermore, we propose a mechanism for the sodium ion conduction in Al-substituted Na2ZrO3.

Crystal Structure, Electrical Properties, and Energy Storage Capacity of STCN Modified BNT-BKT Based Lead-Free Dielectrics

Perovskite solid solutions of SrTi(Cu1/3Nb2/3)O3 (STCN) modified 0.8Bi0.5Na0.5TiO3−0.2Bi0.5K0.5TiO3 (BNT-BKT) in the vicinity of morphotropic phase boundary composition were prepared. The dielectric and impedance properties associated with their structural evolution were investigated. Strong unsteadiness and large hysteresis (dielectric loss) under elevated temperature and variational frequency restrict the development of BNT-BKT based ceramics. Here we show a distinct phase transition from ferroelectric to ergodic relaxor phase that occurs with increasing STCN. Incremental chemical defects resulted from the substitution of the A/B site facilitate the distributions of polar nanoregions. The flatter and smoother dielectric curves between T s and T m illustrate good temperature stability. The complex impedance spectrums demonstrate that the compositions possess a mixed electronic and ionic conduction mechanism. More oxygen vacancies can be introduced into the lattice, contributing to a decremental impedance as the increased dopant. Meanwhile, will suppress p-type conduction and reduce dielectric loss. Favorable stabilities of dielectric permittivity, energy storage, and electrostrictive strain were achieved, attributed to the existence of nanodomains.

Ion Conduction Mechanism as a Fingerprint of Potassium Channels.

K+-channels are membrane proteins that regulate the selective conduction of potassium ions across cell membranes. Although the atomic mechanisms of K+ permeation have been extensively investigated, previous work focused on characterizing the selectivity and occupancy of the binding sites, the role of water molecules in the conduction process, or the identification of the minimum energy pathways enabling permeation. Here, we exploit molecular dynamics simulations and the analytical power of Markov state models to perform a comparative study of ion conduction in three distinct channel models. Significant differences emerged in terms of permeation mechanisms and binding site occupancy by potassium ions and/or water molecules from 100 μs cumulative trajectories. We found that, at odds with the current paradigm, each system displays a characteristic permeation mechanism, and thus, there is not a unique way by which potassium ions move through K+-channels. The high functional diversity of K+-channels can be attributed in part to the differences in conduction features that have emerged from this work. This study provides crucial information and further inspiration for wet-lab chemists designing new synthetic strategies to produce versatile artificial ion channels that emulate membrane transport for their applications in diagnosis, sensors, the next generation of water treatment technologies, etc., as the ability of synthetic channels to transport molecular ions across a bilayer in a controlled way is usually governed through the choice of metal ions, their oxidation states, or their coordination geometries.

Computational Modelling of Ceria-Based Solid Oxide Fuel Cell Electrolyte Materials

The significant advances in materials development for solid oxide fuel cells (SOFCs) and modelling techniques have challenged researchers to develop streamlined methodologies aiming at faster and more reliable fabrication of highly efficient cells. Instead of adopting a trial-and-error technique to discover the optimal composition of fuel cell component materials, alternative tools and techniques should be developed for predicting the likely best compositions in a cost-effective and timely manner. Many formulations have been studied for application as SOFC electrolytes over the years and doubly-doped ceria materials have been of considerable recent interest.Here, a simulation methodology to calculate the lattice parameter and the oxygen ion migration energy of ceria-based electrolyte formulations was developed, and the results were analysed and benchmarked against corresponding results obtained experimentally in order to verify the efficacy of the simulation methodology. To this end, a supercell consisting of 2 x 2 x 2 ceria unit cells doubly-doped with samarium and gadolinium was modelled and simulated using molecular mechanics force field methods using the CP2K computational chemistry suite. Two compositional series were modelled with the general formula Ce32-(x+y)SmxGdyO64-(x+y)/2 where x and y are the number of samarium and gadolinium dopant atoms per supercell respectively. The first compositional series, Series One, had equal amounts of dopants but different total dopant concentration with values of x = y = 1, 2, 8, or 16. Series Two had a fixed total dopant concentration (x + y = 8) but different amounts of each dopant in each structure such that x had integer values from 0 to 8 (x = 0 ... 8) and y = 8 - x. Moreover, two doping strategies were simulated for each compositional series depending on how the dopant atoms and resulting vacancies were distributed throughout the crystal. The first doping strategy places one dopant atom in two or more of the eight minicubes comprising the 2 x 2 x 2 supercell for Series One structures and, for Series Two structures, one dopant atom is placed in each minicube starting with one gadolinium atom in each minicube and then progressively replacing one gadolinium atom with one samarium atom in each of the subsequent structures of this series until there is one samarium atom in each minicube. The second doping strategy places the dopants exclusively in the four minicubes that let the dopants be as far as possible from each other. In all cases, the oxygen vacancies are chosen to be the nearest neighbours, i.e., in the nearest lattice positions, to the dopant atoms.For each structure, the lattice parameter was calculated using a cell optimisation technique utilizing the conjugate gradient method where the soft particle mesh Ewald (SPME) sums method and the DIPole Polarizable Ion Model (DIPPIM) for the long- and short-range potentials respectively. To estimate the activation energies associated with hopping of an oxygen ion from a specific site to a neighbouring site in the structures studied, the following steps were applied: The positions of the dopant atoms in the pure crystal were assigned.The at a distance within 3.0 Å was generated.The climbing image nudged elastic band (CI-NEB) method was applied to determine all the activation barriers of the doped crystal.The average energy barrier was calculated. The results obtained for the lattice parameter were comparable to those observed experimentally and exhibited the same linear trends satisfying Vegard's law, albeit the trend for the fixed dopant concentration series had a slight negative slope. Simulation-derived values of the activation energy showed the same trends as those observed experimentally. The simulations also produced transition state curves showing the saddle point and energy minima for each structure; information that could not be obtained experimentally and that can shed some light on the mechanism of ionic conduction. It was found that the position of oxygen vacancies within the crystal structure play a key role in determining the activation energy of ion hopping, and that the different patterns of doping do not affect the overall trends in lattice parameter and activation energy. They do however produce different patterns in the energy profiles contributing to the energy barriers to ion hopping within the crystal structure.This work demonstrates that computational simulations of SOFC electrolyte materials provide results comparable with those obtained experimentally and could also provide insights into the mechanisms of ionic conduction. The incongruence of the computational and experimental results was attributed to the limitations of the molecular mechanics force field methodology utilised, with the expectation that an ab initio density functional theory (DFT) calculation would yield closer conformance. Figure 1

Lignin-Based Gel Polymer Electrolyte for Cationic Conductivity.

The article presents the results of the preparation and study of a gel-polymer electrolyte based on lignin obtained from Pinus sylvestris. Sulfonation and subsequent chlorination of lignin make possible implementation of the principle of mono-ionic conductivity in a natural biopolymer matrix, which provides predominantly cationic conductivity of the electrolyte. Based on the results of the qualitative and quantitative analysis of the synthesized samples, the mechanisms of the chemical conversion of the biopolymer, the structure models of the converted fragments of macromolecules, as well as the quantum-chemical calculation of their electronic and geometric parameters are presented. The key electronic characteristics of the gel polymer electrolytes (GPE) based on a composite of lignins with 20 wt.% polyvinyl alcohol are determined by impedance spectroscopy. The maximum value of the specific volume conductivity is 2.48 × 10−4 S cm−1, which is comparable with most commercial electrolytes of this type, but at the same time, record values are reached in the number of lithium cation transfer of 0.89. The studies allow to identify the basic laws of the effect of chemical modification on the structure of GPE and describe the mechanism of ionic conductivity.

Computational Modelling of Ceria-Based Solid Oxide Fuel Cell Electrolyte Materials

A simulation methodology for calculating the lattice parameter and oxygen ion migration energy of ceria-based electrolyte formulations is devised. The results are analysed and benchmarked against experimentally obtained values to verify the efficacy of the simulation methodology. A total of 26, 2 x 2 x 2 samarium (Sm)- and gadolinium (Gd)-doped supercells of different compositions and doping profiles were modelled and simulated by molecular mechanics force field methods using CP2K. The results of the computational simulations are comparable with those obtained experimentally, especially when there are equal amounts of Sm and Gd dopants in the structure. Simulation results can also provide insights into the mechanisms of ionic conduction. The incongruence of the computational and experimental results is attributed to the limitations of the molecular mechanics force field methodology utilised, with the expectation that an ab initio density functional theory (DFT) calculation would yield closer conformance.

Understanding the sodium-ion dynamics in NASICON (Na3Al2P3O12) glass containing NaF: Scaling of electrical conductivity spectra

Quest for high ion-conducting solid electrolyte materials for sodium-ion batteries has been tremendously increasing. Glass materials are a potential solid electrolyte for high-energy Na-ion batteries. Nevertheless, the effective research on glass materials for their applications in Na-ion batteries is dawdling due to its low ionic DC-conductivity and poor understanding of the dynamics of mobile cations. Herein, we have attempted to address the effect of substitution of NaF for Al2O3 on the conductivity of Na3Al2P3O12(NAP) glass (mol%: 37.5P2O5–25.0Al2O3–37.5 Na2O). Raman spectra reveal that the increase in the substituent NaF concentration significantly affects the coordination of Al3+ and the distribution of sodium cations in the network structure of NAP glass. Impedance spectra reveal that the change in conductivity of NAP glass with an increase in the NaF concentration is highly dependent on a specific temperature range. At a lower temperature range, (<150 °C), the conductivity increases initially with the increase in NaF concentration and it decreases with any further increase in the NaF concentration; whereas, at temperatures above 150 °C, the conductivity increases continuously with an increase in the NaF concentration. The frequency-dependent AC-conductivity has been analyzed using the time-temperature scaling principle (TTSP) based on Summerfield and Ghosh scaling procedures to probe the ion conduction mechanism. The NAP glass that contains low NaF concentrations (<7.5 mol%) obeys the AC-conductivity scaling, i.e., it satisfies the TTSP principle, with respect to temperature based on the Summerfield scaling procedure; this indicates that the sodium-ion dynamics are independent of the temperature. The scaled AC-conductivity curves for NAP glass containing high NaF concentrations (>10 mol%) have deviated from Summerfield scaling and further indicate that the fraction of sodium-ions responsible for the ionic conductivity is decreasing with an increase in the temperature. Scaling of AC-conductivity curves for all the glass samples using the Ghosh procedure suggests that the number density along with the hopping distance of sodium ions changes with increasing temperature. The Modified random network structural model has been further utilized to explain the variation in the NAP glass conductivity with an increase in the NaF concentrations. The outcome of this work will certainly aid in designing the chemical compositions of glasses for the development of solid electrolyte materials for their applications in Na-ion batteries.