Ionic Conduction Mechanism Research Articles

Ionic conduction mechanisms in 70Li2S−30P2S5 type electrolytes: experimental and atomic simulation studies

Although understanding the structure-property relationship in solid electrolytes is pivotal to develop electrolytes with improved properties, previous studies examined only the partial effect of the structures and did not consider the realistic operating environments. Here, experimental investigations and theoretical simulations are used to explore the collective effects of crystal structure, temperature, and electric field on the ionic conductivity of various electrolytes with the 70Li 2 S−30P 2 S 5 composition. Each electrolyte sample is composed of a mixture of three distinct crystalline phases: γ-Li 3 PS 4 , Li 7 P 3 S 11 , and Li 4 P 2 S 6 , each of which is comprised of the PS 4 , P 2 S 7 , and P 2 S 6 substructures in varying fractions and spatial distributions. Atomic simulations confirm that the abundant stable Li interstitial sites in these crystals, particularly Li 7 P 3 S 11 , shorten the jumping distance for Li self-diffusion. On the other hand, charge polarization of the P 2 S 7 cluster amplifies its oscillatory motion in the presence of an electric field and at ambient temperatures, thereby widening the Li diffusion passage. The reduction in the Li jumping distance, as well as the widening of the diffusion passage, reduce the energy barriers for Li diffusion, allowing for fast Li transport. While the present findings fill the knowledge gaps regarding the ionic conduction mechanisms of the 70Li 2 S−30P 2 S 5 electrolytes, they also provide design criteria for developing highly conductive solid electrolytes.

Diffusion mechanism in a sodium superionic sulfide-based solid electrolyte: Na11Sn2AsS12

Recently, in all solid-state batteries, sulfide-based solid electrolytes have received increased attention due to their high ionic conductivity, good mechanical features, and better chemical stability. Therefore, in the present study, we have synthesized a novel sodium superionic conducting sulfide-based inorganic solid electrolyte (Na11Sn2AsS12) using a solid-state reaction method. The prepared solid electrolyte (Na11Sn2AsS12) is characterized by different techniques such as x-ray diffractometry (XRD), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy, thermogravimetric analysis (TGA), electrochemical impedance spectroscopy, and linear sweep voltammetry to study its various properties such as structure, surface morphology, thermal stability, dielectric properties, ionic conductivity, and electrochemical stability window for sodium ion battery (SIB) applications. The XRD analysis confirms two coexisting phases—tetragonal and cubic, with phase fractions of 0.69 and 0.31, respectively. The SEM study reveals the irregular shape and dense morphology of the solid electrolyte. On the other hand, TGA shows that the prepared solid electrolyte is suitable for high temperature battery applications. The ionic and transport studies confirm that the synthesized Na11Sn2AsS12 is purely ionic in nature, with ionic conductivity found to be S cm−1 and negligible electronic conductivity ∼ S cm−1 at room temperature. Furthermore, the detailed ionic conduction mechanism is studied using temperature and frequency-dependent AC impedance analysis. In addition, the synthesized solid electrolyte Na11Sn2AsS12 exhibits a wide electrochemical window (∼7.0 V) and a high diffusion coefficient ( cm2 s−1) showing suitable electrolyte properties for solid-state SIB applications.

Ionic Conduction Mechanism and Design of Metal-Organic Framework Based Quasi-Solid-State Electrolytes.

We report the theoretical and experimental investigation of two polyoxometalate-based metal–organic frameworks (MOFs), [(MnMo6)2(TFPM)]imine and [(AlMo6)2(TFPM)]imine, as quasi-solid-state electrolytes. Classical molecular dynamics coupled with quantum chemistry and grand canonical Monte Carlo are utilized to model the corresponding diffusion and ionic conduction in the two materials. Using different approximate levels of ion diffusion behavior, the primary ionic conduction mechanism was identified as solvent-assisted hopping (>77%). Detailed static and dynamic solvation structures were obtained to interpret Li+ motion with high spatial and temporal resolution. A rationally designed noninterpenetrating MOF-688(one-fold) material is proposed to achieve 6–8 times better performance (1.6–1.7 mS cm–1) than the current state-of-the-art (0.19–0.35 mS cm–1).

High-safety composite solid electrolyte based on inorganic matrix for solid-state lithium-metal batteries

Composite solid electrolytes (CSEs) combine the advantages of polymer electrolytes and inorganic ceramic electrolytes, which have attracted increasing attention for solid-state lithium-metal batteries. However, the most studied polymer-based CSEs are easily ignited and can be penetrated by lithium (Li) dendrite, leading to safety issue. Herein, we report CSEs with very high inorganic ceramic loadings of >90% by a cold sintering method at a low temperature of 200°C. The ceramic-based CSEs show better safety and mechanical properties than polymer-based CSEs. The Li symmetric cell–symmetric Li-ion cells have the same material as the positive and negative electrode [when cells are assembled one would already contain lithium and the other would not]–using the ceramic-based CSE delivers a stable cycling performance of over 550 h at the current density of 0.3 mA/cm2. More importantly, according to the electrochemical impedance spectroscopy (EIS), Debye diagram, and power law equation, the Li-ion conduction mechanism in CSEs is systematically investigated. Using a modified brick layer model, the conductivities for Li-ions transport parallel with ceramic/polymer interfaces are calculated to be five orders of magnitudes higher than that perpendicular to the interfaces. This work provides a new analytical method for inorganic matrix based CSEs for high-safety batteries and conducts an in-depth research on the ion conduction mechanism.

Front Cover Image

COVER CAPTION: The Front cover image is based on the Review Ionic conductivity and ion transport mechanisms of solid-state lithium-ion battery electrolytes: A review by Hui Yang and Nianqiang Wu, https://doi.org/10.1002/ese3.1163.

Ionic conductivity and ion transport mechanisms of solid‐state lithium‐ion battery electrolytes: A review

AbstractThis review article deals with the ionic conductivity of solid‐state electrolytes for lithium batteries. It has discussed the mechanisms of ion conduction in ceramics, polymers, and ceramic‐polymer composite electrolytes. In ceramic electrolytes, ion transport is accomplished with mobile point defects in a crystal. Li+ ions migrate mainly via the vacancy mechanism, interstitial mechanism, or interstitial‐substitutional exchange mechanism. In solid polymer electrolytes, Li+ ions are transported mainly via the segment motion, ion hopping (Grotthuss mechanism), or vehicle mechanism (mass diffusion). This study has also introduced various electrolyte materials including perovskite oxides, garnet oxides, sodium superionic conductors, phosphates, sulfides, halides, cross‐linked polymers, block‐copolymers, metal‐organic frameworks, covalent organic frameworks, as well as ceramic‐polymer composites. In addition, it has highlighted some strategies to improve the ionic conductivity of solid‐state electrolytes, such as doping, defect engineering, microstructure tuning, and interface modification.

Impedance spectroscopic study of biodegradable PVA/PVP doped TBAI ionic liquid polymer electrolyte

This work aims to understand the ion conduction mechanism in polymer electrolyte membranes. Polyvinyl alcohol and polyvinyl pyrrolidone are chosen as polymer matrix and tetrabutylammonium-iodide as the ionic liquid among various synthetic polymers. Four samples named A-1, A-2, A-3, and A-4 have been synthesized by various concentrations and characterized the membranes through impedance spectroscopy analysis which uncovers the conductivity features of the electrolyte. Out of the four samples, the one with 25 wt.% ionic liquid sample shows better performance than the rest of the samples. The prepared membrane was analysed and understood various parameters such as impedance analysis, dielectric constant, dielectric loss, and electric modulus. The activation energy was calculated for the samples A-2, A-3, and A-4, as 0.27 eV, 0.96 eV and 2.97 eV, respectively. The Arrhenius models for carrier transport have been explained to interpret the conduction mechanism in polymer membranes. The present work has been focused on studying the effect of tetrabutylammonium-iodide ionic liquid on polyvinyl alcohol and polyvinyl pyrrolidone polymer matrix as an electrolyte membrane and the possibility of using this as an electrolyte membrane in devices such as fuel cells, supercapacitors, and batteries.

Argyrodite-type advanced lithium conductors and transport mechanisms beyond paddle-wheel effect

Development of next-generation solid-state Li-ion batteries requires not only electrolytes with high room-temperature (RT) ionic conductivities but also a fundamental understanding of the ionic transport in solids. In spite of considerable work, only a few lithium conductors are known with the highest RT ionic conductivities ~ 0.01 S/cm and the lowest activation energies ~0.2 eV. New design strategy and novel ionic conduction mechanism are needed to expand the pool of high-performance lithium conductors as well as achieve even higher RT ionic conductivities. Here, we theoretically show that lithium conductors with RT ionic conductivity over 0.1 S/cm and low activation energies ~ 0.1 eV can be achieved by incorporating cluster-dynamics into an argyrodite structure. The extraordinary superionic metrics are supported by conduction mechanism characterized as a relay between local and long-range ionic diffusions, as well as correlational dynamics beyond the paddle-wheel effect.

Bioinspired Tough Solid-State Electrolyte for Flexible Ultralong-Life Zinc-Air Battery.

Manufacturing advanced solid-state electrolytes (SSEs) for flexible rechargeable batteries becomes increasingly important but remains grand challenge. The sophisticated structure of robust animal dermis and good water-retention of plant cell in nature grant germane inspirations for designing high-performance SSEs. Herein, tough bioinspired SSEs with intrinsic hydroxide ion (OH- ) conduction are constructed by in situ formation of OH- conductive ionomer network within a hollow-polymeric-microcapsule-decorated hydrogel polymer network. By virtue of the bioinspired design and dynamic dual-penetrating network structure, the bioinspired SSEs simultaneously obtain mechanical robustness with 1800% stretchability, good water uptake of 107g g-1 and water retention, and superhigh ion conductivity of 215 mS cm-1 . The nanostructure of bioinspired SSE and related ion-conduction mechanism are revealed and visualized by molecular dynamics simulation, where plenty of compact and superfast ion-transport channels are constructed, contributing to superhigh ion conductivity. As a result, the flexible solid-state zinc-air batteries assembled with bioinspired SSEs witness high power density of 148 mW cm-2 , specific capacity of 758 mAh g-1 and ultralong cycling stability of 320 h as well as outstanding flexibility. The bioinspired methodology and deep insight of ion-conduction mechanism will shed light on the design of advanced SSEs for flexible energy conversion and storage systems.

EIS and FTIR approaches to study the ion transport parameters and relaxation dynamics of Na+1 ion in SPE based on MC polymer inserted with sodium salt

In this work deep insights on ion transport parameters based on EIS and FTIR were presented. MC based biopolymer was used as the host material to prepare solid polymer electrolyte (SPE). The XRD equipment was used to study the structural changes happening in the SPE films upon addition of various rate of NaSCN salt. The polymer-salt interactions were observed from the shifting and changing of intensity of FTIR transmittance peaks. The EIS plots were fitted with EECs to detect the electrical properties of the films. Transport parameters including number density (n), mobility (μ) and diffusion coefficient (D) were evaluated using impedance and FTIR methodologies. The percentage of free ions was found to influence the transport parameters utilizing FTIR approach. The maximum DC conductivity of 3.6 × 10−6 Scm−1 was obtained for the MC film incorporated with 40 wt% of NaSCN salt. The temperature variation of DC conductivity follows Arrhenius behavior model. The dielectric properties of the films were studied at ambient temperature. The effects of temperature on dielectric properties were examined on the highest conducting sample. The relaxation processes were analyzed in terms of loss tangent and electric modulus. Broad peaks of M'' pattern and tanδ plot are marks for non-Debye type relaxation of Na+ ions. The ion conduction mechanisms as a complicated subject in SPEs were focused in this work. The noticeable results achieved from the dielectric properties and electric modulus indicated the coupled motion between cations of the dissolved salt and polymer segmental motions. The transport of ions followed Arrhenius model in which polymer chains assist ion jumping.

A facile in situ Mg surface chemistry strategy for conditioning-free Mg[AlCl4]2 electrolytes

Developing a simple and reliable strategy for modulating overpotential of Mg plating/stripping is crucial for realizing overall high performance of rechargeable Mg batteries, which have been demonstrated to be rather challenging. Herein, we report a facile LiI-assisted Mg surface chemistry to reduce Mg plating/stripping overpotential via in situ solubilization mechanism and ion conductive surface layer formation mechanism. As a result, we successfully formulate a new conditioning-free Mg[AlCl4]2-based Mg electrolyte system that improves Mg plating/stripping from the very first cycle. The overpotential of Mg plating/stripping of the as-prepared electrolyte with a LiI electrolyte additive is remarkably reduced to 240/240 mV at a current density of 1000 µA cm−2. Using this electrolyte, a rechargeable Mg battery coupled with PANi intercalated V2O5 (V2O5-PANi) cathode and Mg anode delivers a stable discharge specific capacity of nearly 50 mA h g−1 after an impressively prolonged cycle life of 500 cycles. Our finding provides a new inspiration of in situ Mg surface chemistry to activate Mg anode surface with high Mg ion conductivity.

Electrical Method for In Vivo Testing of Exhalation Sensors Based on Natural Clinoptilolite

Natural substances with a complex chemical structure can be advantageously used for functional applications. Such functional materials can be found both in the mineral and biological worlds. Owing to the presence of ionic charge carriers (i.e., extra-framework cations) in their crystal lattice, whose mobility is strictly depending on parameters of the external environment (e.g., temperature, humidity, presence of small gaseous polar molecules, etc.), zeolites can be industrially exploited as a novel functional material class with great potentialities in sensors and electric/electronic field. For fast-responding chemical-sensing applications, ionic transport at the zeolite surface is much more useful than bulk-transport, since molecular transport in the channel network takes place by a very slow diffusion mechanism. The environmental dependence of electrical conductivity of common natural zeolites characterized by an aluminous nature (e.g., chabasite, clinoptilolite, etc.) can be conveniently exploited to fabricate impedimetric water-vapor sensors for apnea syndrome monitoring. The high mechanical, thermal, and chemical stability of geomorphic clinoptilolite (the most widely spread natural zeolite type) makes this type of zeolite the most adequate mineral substance to fabricate self-supporting impedimetric water-vapor sensors. In the development of devices for medical monitoring (e.g., apnea-syndrome monitors), it is very important to combine these inexpensive nature-made sensors with a low-weight simplified electronic circuitry that can be easily integrated in wearable items (e.g., garments, wristwatch, etc.). Very low power square-wave voltage sources (micro-Watt voltage sources) show significant voltage drops under only a minimal electric load, and this property of the ac generator can be advantageously exploited for detecting the small impedimetric change observed in clinoptilolite sensors during their exposition to water vapor coming from the human respiratory exhalation. Owing to the ionic conduction mechanism (single-charge carrier) characterizing the zeolite slab surface, the sensor biasing by an ac signal is strictly required. Cheap handheld multimeters frequently include a very low power square-wave (or sinusoidal) voltage source of different frequency (typically 50 Hz or 1 kHz) that is used as a signal injector (signal tracer) to test audio amplifiers (low-frequency amplifies), tone control (equalizer), radios, etc. Such multimeter outputs can be connected in parallel with a true-RMS (Root-Mean-Square) ac voltmeter to detect the response of the clinoptilolite-based impedimetric sensors as voltage drop. The frequency of exhalation during breathing can be measured, and the exhalation behavior can be visualized, too, by using the voltmeter readings. Many handheld multimeters also include a data-logging possibility, which is extremely useful to record the voltage reading over time, thus giving a time-resolved voltage measurement that contains all information concerning the breathing test. Based on the same principle (i.e., voltage drop under minimal resistive load) a devoted electronic circuitry can also be made.

Direct Detection of Bound Ammonium Ions in the Selectivity Filter of Ion Channels by Solid-State NMR.

The flow of ions across cell membranes facilitated by ion channels is an important function for all living cells. Despite the huge amount of structural data provided by crystallography, elucidating the exact interactions between the selectivity filter atoms and bound ions is challenging. Here, we detect bound 15N-labeled ammonium ions as a mimic for potassium ions in ion channels using solid-state NMR under near-native conditions. The non-selective ion channel NaK showed two ammonium peaks corresponding to its two ion binding sites, while its potassium-selective mutant NaK2K that has a signature potassium-selective selectivity filter with four ion binding sites gave rise to four ammonium peaks. Ions bound in specific ion binding sites were identified based on magnetization transfer between the ions and carbon atoms in the selectivity filters. Magnetization transfer between bound ions and water molecules revealed that only one out of four ions in the selectivity filter of NaK2K is in close contact with water, which is in agreement with the direct knock-on ion conduction mechanism where ions are conducted through the channel by means of direct interactions without water molecules in between. Interestingly, the potassium-selective ion channels investigated here (NaK2K and, additionally, KcsA-Kv1.3) showed remarkably different chemical shifts for their bound ions, despite having identical amino acid sequences and crystal structures of their selectivity filters. Molecular dynamics simulations show similar ion binding and conduction behavior between ammonium and potassium ions and identify the origin of the differences between the investigated potassium channels.

Polyacrylonitrile-based electrolytes: How processing and residual solvent affect ion transport and stability

Polyacrylonitrile (PAN) is one of the alternative candidate polymer hosts to form solid polymer electrolytes (SPEs) besides the widely used poly(ethylene oxide). In this study, we systematically investigate the processing of PAN based SPEs containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, using dimethylformamide (DMF) as the solvent. The effects of PAN processing procedure including solution mixing, casting, and drying on the morphology, ion transport, solvation structure, Li and oxidative stability of PAN electrolytes are thoroughly examined. In particular, four drying conditions are investigated and the amount of residual DMF is accurately determined using infrared (IR) spectroscopy. Varying the drying conditions can lead to five orders of magnitude decrease in the ionic conductivity. As DMF content decreases, the SPE's stability again Li metal dramatically improves. The practical oxidative stability is also strongly affected by the residual DMF content, ranging from 2.5 V to 3.5 V, much lower than reported values. Finally, the role of the residual DMF solvent is elucidated. DMF content vitally influences ion solvation structure at different concentration regimes, which ultimately dictates the ion conduction mechanism and oxidative stability of PAN based SPEs. This thorough study lays the groundwork for future development of PAN based electrolytes.

Ion conduction mechanism as a fingerprint of potassium channels

Potassium channels are found in virtually all living organisms where they control a large variety of cellular functions by facilitating selective K+ transport in and out of the cell. The molecular determinants responsible for this functional diversity are still poorly understood. More than 20 years after the first release of the atomic structure of a potassium channel, the mechanism of K+ conduction is still a matter of intense debate. An implicit assumption of previous work is that the mechanism of K+ conduction is a common feature of this extensive family of membrane proteins.

Diverse roles of lipids in ion conduction by TMEM16 lipid scramblases

Lipid scramblases from the TMEM16 protein family facilitate passive lipid transport between membrane leaflets but also operate as ion channels, with implication in diverse physiological processes such as cell volume regulation and apoptosis. Such dual functionality implies tight coupling between lipid and ion transport mediated by the scramblases. Here we used extensive atomistic molecular dynamics simulations and the computational electrophysiology method to study molecular mechanisms of ion conduction in fungal nhTMEM16 and human TMEM16K lipid scramblases with a particular focus on the roles that lipids play in ion permeability and selectivity.

Construction of polydopamine reduced graphene oxide/sodium carboxymethyl cellulose/polyacrylamide double network conductive hydrogel with high stretchable, pH-sensitive and strain-sensing properties

In recent years, electrically conductive hydrogels (ECHs) have attracted extensive attention for their potential applications in flexible wearable sensors and human motion monitoring. However, many ECHs are prone to damage during use, limiting their application. In this study, a quick and simple one-pot in situ copolymerization method was used to introduce the double network (DN) structure with good mechanical properties into the conductive hydrogel, providing a new method for preparing the multi-function DN hydrogel. A novel conductive hydrogel was prepared by introducing sodium carboxymethyl cellulose (CMCNa) and polydopamine (PDA) reduced graphene oxide (D-rGO) into polyacrylamide (PAM) hydrogel. Among them, the well-dispersed D-rGO nanofillers provided a good electron conduction pathway. CMCNa/PAM matrix was physically and chemically crosslinked with Fe3+ and N, N′-methylene-bis-acrylamide (MBA), which made the hydrogel had better mechanical properties and pH sensitivity than pure PAM hydrogel. The conductive hydrogel designed by us had better sensitivity (gauge factor (GF) value was 6.44), wider strain detection range (0–500%), better cycle stability and durability compared with other conductive hydrogels by using a composite conductive mechanism of electron and ion conductivity. More notably, D-rGO/CMCNa/PAM hydrogel could detect large-scale changes in human movement (such as bending of fingers and wrists) and sensitive signals without obvious allergic reactions to human skin, which offered great possibilities for practical applications as flexible strain sensors.

Mixed SYGnals in potassium channels: a mechanism for alternative ion conduction in human Kir3.2 channel mutations.

Mixed SYGnals in potassium channels: a mechanism for alternative ion conduction in human Kir3.2 channel mutations.

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.