Ionic Conduction Mechanism Research Articles

Ionic conduction mechanism in high concentration lithium ion electrolytes.

The conduction mechanism of a family of high concentration lithium electrolytes (HCEs) is investigated. It is found in all HCEs that the molecular motions are regulated by the anion size and correlated to the HCE ionic resistivity. From the results, a mechanism involving highly correlated ionic networks is derived.

Mixed electronic and oxide ionic conduction and migration mechanisms in digermanate La2-xCaxGe2O7-x/2.

Mixed electronic and oxide ionic conduction was enabled in digermanate-type La2-xCaxGe2O7-x/2 containing Ge3O10 chains and isolated GeO4 units by substitution of La3+ with Ca2+. The structure and solid solution limit of Ca doped La2Ge2O7 were studied by systematic experiments, including rotation electron diffraction (RED), X-ray diffraction (XRD) and neutron powder diffraction (NPD) experiments, etc. The preferred occupation of Ca2+ and oxygen vacancies was investigated by Rietveld analysis of the NPD data. The obtained conducting material La1.925Ca0.075Ge2O6.963 exhibits superior thermal stability and an order of magnitude improvement in conductivity compared to the parent La2Ge2O7 (∼9 × 10-5 S cm-1 at 1000 °C). BVEL calculations reveal that the oxygen vacancies were stabilized and transported within the framework of La2Ge2O7 by sharing oxygen and oxygen exchange between the adjacent Ge3O10 chains and GeO4 units, exhibiting a three-dimensional oxide ion transport nature.

Anolyte Enhances Catalyst Utilization and Ion Transport Inside a CO2 Electrolyzer Cathode

Electrochemical CO2 reduction is a promising technology to capture and convert CO2 to valuable chemicals. High Faradaic efficiencies of CO2 reduction products are achieved with zero-gap alkaline CO2 electrolyzers with a supporting electrolyte at the anode (anolyte). Herein, we investigate the effect of anolyte on the electrode properties such as catalyst utilization, ionic accessibility etc. of a CO2 reduction cathode using electrochemical techniques and cell configurations that avoid the complexities related to co-electrolysis. Using 1M KOH as the anolyte and a Cu gas-diffusion-electrode with low Nafion content as the model CO2 reduction electrode, we find that electrode capacitance (proxy for electrochemically active surface area) and ionic conductivity inside the cathode increase approximately 4 and 447 times, respectively, in presence of KOH. Liquid anolyte wets the electrode’s pore structure more efficiently than capillary condensation of feed water vapor. The ionomer coverage is very low, and its distribution inside the electrode is highly fragmented. Surface ion conduction mechanisms inside the electrode are orders of magnitude lower than the bulk ion conduction in presence of anolyte. This study shows that when an anolyte (e.g., KOH) is used, catalyst utilization and ionic accessibility inside the electrode increase significantly.

Theoretical insight into lithium triborates as solid-state electrolytes

Owing to the inherent properties combining high ionic conductivity and electrochemical stability, the lithium triborates (LBOs) have emerged as a promising solid-state electrolyte for next-generation batteries. Specific fundamental details of the ionic conduction mechanism and related physicochemical properties remain to be understood. In this study, using the first-principles density functional theory calculations, we present a systematic computational investigation on LBOs in the respect of electronic structures, mechanical and thermodynamic properties, Li-ion transport, and interfacial (with Li metal) behaviors. Our results show that LBO is a thermodynamically and mechanically stable insulator with an indirect wide bandgap of 6.4 eV. Notably, LBOs could behave as a fast Li-ion conductor with a low migration energy barrier (15 meV) and are characterized by a zig–zag Li+-diffusion path along the c direction. We found that the interface between Li metal and LBO is both physically and chemically stable with no new phase formed while exhibiting a metallic character due to the charge transfer from a Li metal. Our study highlights the intriguing promise of LBOs as solid-state electrolytes for high-energy cells.

Progress in Gel Polymer Electrolytes for Sodium‐Ion Batteries

Sodium‐ion battery is a potential application system for large‐scale energy storage due to the advantage of higher nature abundance and lower production cost of sodium‐based materials. However, there exist inevitably the safety problems such as flammability due to the use of the same type of organic liquid electrolyte with lithium‐ion battery. Gel polymer electrolytes are being considered as an effective solution to replace conventional organic liquid electrolytes for building safer sodium‐ion batteries. In this review paper, the authors present a comprehensive overview of the research progress in electrochemical and physical properties of the gel polymer electrolyte‐based sodium batteries. The gel polymer electrolytes based on different polymer hosts namely poly(ethylene oxide), poly(acrylonitrile), poly(methyl methacrylate), poly(vinylidene fluoride), poly(vinylidene fluoride‐hexafluoro propylene), and other new polymer networks are summarized. The ionic conductivity, ion transference number, electrochemical window, thermal stability, mechanical property, and interfacial issue with electrodes of gel polymer electrolytes, and the corresponding influence factors are described in detail. Furthermore, the ion transport pathway and ion conduction mechanism are analyzed and discussed. In addition, the advanced gel polymer electrolyte systems including flame‐retardant polymer electrolytes, composite gel polymer electrolytes, copolymerization, single‐ion conducting polymer electrolytes, etc. with more superior and functional performance are classified and summarized. Finally, the application prospects, development opportunities, remaining challenges, and possible solutions are discussed.

Surface and interfacial conduction using gadolinium-doped ceria electrolyte for advanced low temperature 400–500 °C fuel cell

Lowering the operating temperature with enhanced performance and better efficiency is considered a universal R&D bottleneck for the progress of low-temperature (<520 °C) solid oxide fuel cells (SOFCs) or ceramic fuel cells (CFCs) to avail the opportunities of commercialization. Bulk doping is the primary ionic conduction mechanism in traditional electrolyte materials for CFC, mainly influenced by the operating temperature and bulk density, thus resulting in high operational temperature. Herein, we proposed a new mechanism for tunning Ce0.9Gd0.1O2-δ (GDC) electrolyte based on a nanocrystalline structure from surface or grain boundary conduction to interfacial conduction by introducing the carbonates to form the heterostructure, exhibiting an extremely high ionic conductivity of (0.2 S·cm−1) at 520 °C. At first, we noticed that the grain boundary conduction of GDC is causing to enhance the charge carrier leading to establishing surface conduction. We further modify the GDC with carbonates to form the core–shell heterostructure to boost ionic conduction. The constructed cell with core–shell heterostructure has exhibited a remarkable performance of 968 mW/cm2.In contrast, 578 mW/cm2 was achieved from the surface conduction of GDC, and at the same time, we observed immensely low grain-boundary resistance from the impedance analysis. The mechanism of core–shell structure formation has been discussed in detail, and the ionic conduction at the surface and interfaces can be considered the dominant conduction mechanism for GDC electrolytes. This work has explored a new approach by tuning the ionic property from surface to interface to develop advanced CFCs, significantly improving the state-of-art GDC electrolyte via enhancing surface/interface conductions. This may be developed as a more functional approach for advanced energy materials, e.g., battery and electrolysis devices.

Onset of vacancy-mediated high activation energy leads to large ionic conductivity in two-dimensional layered Cs2PbI2Cl2 Ruddlesden-Popper halide perovskite

We report the dielectric properties of a two-dimensional layered Ruddlesden-Popper halide perovskite ${\mathrm{Cs}}_{2}{\mathrm{PbI}}_{2}{\mathrm{Cl}}_{2}$ synthesized via a simple mechanochemical process to explore fundamental aspects of ionic conduction and relaxation mechanism over a wide temperature and frequency range. Several experimental techniques, such as complex impedance spectroscopy, alternating current (AC) conductivity spectroscopy, and complex electric modulus spectroscopy, have been employed to investigate the nuances of ionic conduction and relaxation mechanisms, and the results have been corroborated using different theoretical models, such as the Maxwell-Wagner equivalent circuit model, the modified Jonscher power law, the Havrilliak-Negami (HN), and the Kohlrausch-Williams-Watts (KWW) model. The contribution of the grains and grain boundaries to the total impedance in the system is estimated by the analysis of the Nyquist plots. In temperature-dependent AC conductivity spectra, a critical temperature (413 K) is observed, beyond which the conductivity increases abruptly. This critical temperature also defines two distinct temperature ranges: the low-temperature (303--413 K) and the high-temperature (423--463 K) regimes, where the ionic transport mechanism switches from the normal ionic transport to a vacancy-mediated ionic transport mechanism. A substantially high activation energy $\ensuremath{\sim}1.82\phantom{\rule{0.16em}{0ex}}(\ifmmode\pm\else\textpm\fi{}0.02)\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ is calculated from the Arrhenius plot of the ionic conductivity in the high-temperature region, while at the low-temperature region, the activation energy is found to be $\ensuremath{\sim}0.48\phantom{\rule{0.28em}{0ex}}(\ifmmode\pm\else\textpm\fi{}0.02)\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$. The abrupt jump in the ionic conductivity beyond the critical temperature is attributed to the onset of the anionic vacancy-mediated enhanced ionic conductivity. Polaronic models have been used to interpret the AC conductivity and its power-law exponent. The activation energy obtained from ionic conductivity measurements is consistent with those calculated from relaxation time using the HN and KWW models. The presence of two master curves in time-temperature superposition scaling of AC conductivity and modulus loss spectra specifies the validity of two different conduction mechanisms.

On the impact of the type of anion on the properties of solid-state electrolytes

Solid-state batteries are a valuable option for sustainable energy storage. Their performance is strongly dependent on the ionic conductivity of the solid-state electrolyte (SSE). The mechanism of ion conduction in solid polymer electrolytes has been extensively studied in terms of flexibility of the polymer chains and their interactions with mobile cations that hop between conduction sites carrying the charge. The role of the counterion (i.e. anion) interacting with both the polymer and the cation has not been explored in detail. In this study we show however, that the anion can severely impact the conduction as well. The effect of the anion (I−, SCN−, BF4− and PF6−) on the thermal, structural and electrical properties of a solid polymer electrolyte (15C5BA polymer) was investigated. The results clearly show that the nature of the anions can be used as a parameter to actually tune the properties of the polymer electrolyte.

(Digital) Ionic Conduction Mechanism and Design of Metal–Organic Framework Based Quasi-Solid-State Electrolytes

Recently, anionic metal–organic frameworks (MOFs) with superior ionic conductivity and Li+ transference numbers have opened a new avenue in the development of quasi-solid-state electrolytes (QSSEs). Given the superior performance and the characterization challenges associated with transport property measurements, it is vitally important to understand the Li+ transport and conduction mechanisms of this new prototype of QSSEs. In this presentation, we will discuss the theoretical and experimental investigation of two polyoxometalate (POM) -based MOFs, [(MnMo6)2(TFPM)] imine and [(AlMo6)2(TFPM)] imine , as QSSEs. 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%), revealing the critical role of the solvent in MOF-based QSSEs. Detailed static and dynamic solvation structures were obtained to interpret Li+ motion with high spatial and temporal resolution. We found that the local charge distribution on POM surface largely determines the interaction between Li+ and the framework. Based on the prevalent mechanism of Li+ motion, we propose a hypothesized MOF design with a non-interpenetrating structure that is expected to achieve 6–8 times better ionic conduction performance (1.6–1.7 mS cm−1) than the current state-of-the-art (0.19–0.35 mS cm−1), approaching the conductivity range of liquid electrolytes. Figure 1

Role of the Membrane Transport Mechanism in Electrochemical Nitrogen Reduction Experiments.

The electrochemical synthesis of ammonia through the nitrogen reduction reaction (NRR) is receiving much attention, since it is considered a promising alternative to the Haber–Bosch process. In NRR experiments, a Nafion membrane is generally adopted as a separator. However, its use is controversial since ammonia can be trapped in the membrane, to some extent, or even pass through it. We systematically investigate the interaction of a Nafion membrane with ammonia and with an electrolyte and compare it with Zirfon as a possible alternative separator. We show that Nafion containing ammonia can easily release it when immersed in a 0.1 M Na2SO4 ammonia-free electrolyte, due to the cation exchange mechanism (Na+-NH4+). Since Na2SO4 is a commonly adopted electrolyte for NRR experiments, this may cause serious measurement errors and non-reproducible results. The same experiments performed using the polysulfone Zirfon separator clearly show that it is immune to interactions with ammonia, because of its different ion conduction mechanism. The findings provide a deeper understanding of the choice of membrane and electrolyte to be adopted for NRR tests, and may allow one to obtain more accurate and reliable results.

Demonstration of a 2-D SnS/MXene Nanohybrid Asymmetric Memristor

This article demonstrates the fabrication and characterization of a low-cost, energy-efficient, easy-to-fabricate SnS/MXene memristor in which an SnS/Ti3C2Tx active layer is sandwiched in between two copper electrodes. The device has been showing substantial merits with an experimental <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text{off}}$ </tex-math></inline-formula> : <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text{on}}$ </tex-math></inline-formula> ratio of ~22 with good cyclic stability, exceptional reproducibility, and data retention capability up to 1000 cycles. This article explains the detailed physics governing the various regions of the proposed memristor characteristics in terms of the dual ionic conduction mechanism. Furthermore, the article explains the memristor’s asymmetric behavior using the concept of the trapping and de-trapping of charge carriers. Real-time band structures extracted using sophisticated ultraviolet photoelectron spectroscopy (UPS) strongly support the claims reported in this article. Finally, this article concludes with a practical application of the fabricated device as a low-cost, tunable asymmetric clock generator circuit.

Electrolytes for Multivalent Metal-Ion Batteries: Current Status and Future Prospect.

Electrochemical energy storage has experienced unprecedented advancements in recent years and extensive discussions and reviews on the progress of multivalent metal-ion batteries have been made mainly from the aspect of electrode materials, but relatively little work comprehensively discusses and provides an outlook on the development of electrolytes in these systems. Under this circumstance, this Review will initially introduce different types of electrolytes in current multivalent metal-ion batteries and explain the basic ion conduction mechanisms, preparation methods, and pros and cons. On this basis, we will discuss in detail the research and development of electrolytes for multivalent metal-ion batteries in recent years, and finally, critical challenges and prospects for the application of electrolytes in multivalent metal-ion batteries will be put forward.

An Account on Functional Polymer Composite for Multivariant Application: A Mechanistic Approach

The presented article reports a detailed review of the polymer composite and its applications in multifaceted areas. The novelty of the report is in establishing the mechanistic overview on the functionalization of polymer for selective applications. The most important and established application of polymer is in sensing, polymer electrolyte, biomedical application, point of care application etc. The utilization of functional polymer in fluorescence thermometers is dependent on the maintenance of their lower critical solubility temperature. Polyelectrolytes like conducting polymers are widely applied for chemo sensing applications. The primary mechanism for the functionality of these conducting polymers is the presence of altering single and double bonds which enables the thorough flow of charge within the matrix system. Furthermore, the macromolecular synthetic polymer is subjected to functionalization through composite upon combing with specific salts and filler components. The addition of unreactive/reactive filler components in minute amounts is reported to significantly reduce the polarization loss and increase the cyclability of the matrix when applied to solid-state devices like sensors, fuel cells for stationary and mobile applications, etc. Fuels cells being an example of renewable energy is reported to attract the modern market with emphasis on polymer membrane-based system wherein sulphonic acid-based electrolyte membrane act as the ionic electrolyte conductor. The mechanism of ion conduction within the polymer matrix plays an important role in the application in solid-state devices like sensors, fuel cells, batteries, etc. The review briefly explains the role of ionic conduction as explained using two primary mechanisms like Arrhenius and Vogel Tammann Fulcher. Finally, the role of polymer bio composites is discussed in light of biomedical applications.

Reverse Monte Carlo analysis of NaI-LiI solid electrolyte based on the neutron total scattering data

In the present study, the origin of Li+ ion conduction in an Li+/Na+ mixed solid electrolyte, 9NaI∙LiI, was investigated from the perspective of atomic configuration. The co-existence of Li+ and Na+ ions in solid electrolytes is known to result in a deterioration in conductivity, known as the mixed alkali effect. While dominant Li+ conduction has been reported in Li+-doped NaI where 10 mol% of Li+ ions are substituted for the host Na+ ions in NaI, the structural origin of the Li+ conduction in NaI is not well understood. From the results of reverse Monte Carlo (RMC) modeling based on the neutron total scattering data, it was revealed that the position of the Li+ is significantly off-centered from the ideal LiI6 octahedra despite the symmetrical distribution of the Na+ ions in the cation sites. The peculiar distribution of Li+ was explained by the large mismatch between the size of the Li+ ion and the lattice volume of NaI. These off-centered Li+ ions were shown to result in void spaces in the LiI6 octahedra. It is likely that the free volume in the LiI6 octahedra provides the hopping sites for the neighboring Li+ ions. Since the ionic radius of Na+ ions is larger than that of Li+ ions, the spaces in the LiI6 and NaI6 octahedra were not sufficient for Na+ hopping. One of the factors which contributed to the different ion conduction mechanism for Li+ and Na+ in the Li+/Na+ mixed solid electrolytes was shown to be the different local structures around Li+ and the host Na+ in Na compounds.

(Invited) Ion Conduction and Interface Stability of Sulfide Based Solid State Electrolytes – an Atomistic Perspective

All-solid-state batteries are promising in terms of safety as well as high energy density compared to the conventional organic liquid-based lithium batteries. However, the characteristic low ionic conductivity of solid-state electrolytes is a major challenge towards commercialization of solid-state sodium ion batteries. Sulfide-based electrolytes especially in amorphous form have been reported as promising solid electrolytes owing to their relatively high ionic conductivity at room temperature. However, a fundamental understanding of the local structure of these amorphous electrolytes and its subsequent impact on the ion transport could be instrumental in establishing guidelines for designing novel solid electrolytes. In the present work, we utilize first principles and classical atomistic simulations to characterize the local structure and investigate the ion transport in amorphous sulfide electrolytes. We selected sodium thiosilicate [xNa2S – (1-x) SiS2] and sodium thiophosphate [xNa2S – (1-x) P2S5] based electrolytes as a model system wherein we characterized the local structure, ion conduction mechanism and ultimately calculated the ionic conductivity of these electrolytes. We utilized experimental X-ray and neutron scattering data for model validation. Our theoretical calculations provide fundamental insights into ion conduction mechanisms as well as correlate ionic conductivity with electrolyte structure and composition.Along with ionic conductivity, interfacial stability is extremely important factor influencing the overall performance of solid-state batteries. Interfacial instability with sulfide electrolytes is detrimental to Li-ion transport, leading to poor cycling performance. Inherent thermodynamic instability of sulfide-based solid electrolytes drives the chemical reaction across the interface leading to formation of undesired secondary phases. The secondary phases are formed dynamically during the cycling and therefore a careful investigation into the dynamics at the electrolyte-cathode interfaces is crucial. To generate fundamental understanding of the interface stability, we utilized ab initio molecular dynamics (AIMD) simulations to carefully investigate the dynamics of secondary phase formation across the Li3PS4 | LiCoO2 interfaces. High-resolution microscopy and spectroscopy studies were used to complement the the first principles simulations methods and unravel the interphases formed under different cycling conditions. These calculations provide crucial insights into formation of secondary phases across the interface, which could be leveraged to evaluate possible avenues to inhibit formation of such undesirable secondary phases.

Tuning Ionic Conductivity and Stability of Li10GeP2S12 Solid-State Electrolyte

All-solid-state Li-ion batteries gained a huge attention because they exhibit higher power density, wider electrochemical stability windows, and overall safety of solid-state electrolytes (SSE) compared to conventional liquid electrolyte-based batteries. Unfortunately, most of the SSE materials have not matched the ionic conductivity of their liquid counterpart. But, recent research and the synthesis of new materials have shown SSE can conduct ions at an equivalent or even higher rate. However, the electrochemical stability needs to be improved. There is a growing research effort in identifying a solid electrolyte that is both electrochemically stable and has a very high ionic conductivity. The Li10GeP2S12 (LGPS) is one of the superionic conductors, is known for its high ionic conductivity that can be deployed as a solid electrolyte in batteries. However, LGPS is not stable as exposed to air and moisture, posing challenges during its manufacturing, and designing process. Thus, in an attempt to optimize the stability and ionic conductivity, the effect of antimony (Sb), tin (Sn), and oxygen (O) substitution on conductivity and stability of LGPS is investigated using Density Functional Theory (DFT). The systematic study of compositional variation, phase stability, defects chemistry, and the impact on electronic properties and ionic conductivity is performed. Thus, this study will provide significant insights on ion conduction mechanisms and strategies that can tune the ionic conductivity and stability of LGPS based electrolytes. This project was supported in part by COE SJSU, DOE NERSC, and XSEDE.

(Invited) Novel Nature-Inspired Concepts to Design Ionomeric Nanomaterials for Energy Conversion and Storage Devices

Ion-conducting polymers (ionomers) are an integral part of renewable energy-driven technologies. Proton exchange membrane fuel cells (PEMFCs) have already been incorporated into low-duty vehicles and are now being adopted in heavy-duty vehicles. Therefore, we need more durable and efficient fuel cell materials than ever. A major technical challenge of PEMFCs is the ion transport limitation at the ionomer-catalyst interface which negatively impacts the efficiency of the cells. The current state-of-the-art fuel cell ionomers (both fluorocarbon- and hydrocarbon-based) conduct protons efficiently in bulk, several tens of micron thick, free-standing membranes, but poorly in sub-micron thick films. This needs attention as sub-micron thick ionomer layers are used as catalyst binders on electrodes of PEMFCs and other energy conversion and storage devices. However, the nanoscale behavior of these existing ionomers within complex hydration environment is not well-understood yet. More importantly, ionomers are rarely designed to improve the thin film ion conduction properties. To address and overcome these issues, we do not only design innovative nanoscale materials characterization techniques to explore the distribution of ion conduction environment across ionomer films/membrane, but also design novel classes of ionomers inspired by natural living systems to facilitate ion conduction in thin films. We experimentally measure the ion conductivity, morphology, and mechanical properties, and combine them with computational studies to elevate our understanding of ion conduction mechanism within 10-200 nm thick films of these newly designed ionomers. The results suggest the great promise of these new classes of ionomers as efficiently ion-transporting catalyst binders for fuel cells, electrolyzers, and batteries.

Microscopic insight into anion conduction in covalent−organic framework membranes: A molecular simulation study

Recently there has been considerable interest in the utilization of covalent-organic frameworks (COFs) as ion-exchange membranes. While rapid ion conduction is experimentally observed in COF membranes, the underlying mechanism remains elusive. Herein, we report a molecular simulation study on chloride ion (Cl−) conduction in four COF membranes functionalized with quaternary ammonium groups (QA-2, QA-4, QA-6 and QA-EO) of different side chains (ethyl, butyl, hexyl and diethyl ether). It is revealed that membrane flexibility is crucial to be incorporated in simulation for reliable predictions. The Cl− conductivities in the four membranes are predicted to decrease as COF-QA-2 > COF-QA-4 ≈ COF-QA-EO > COF-QA-6, which is in good agreement with experimental data. The pore size, rather than membrane-Cl− interaction, is unravelled to be the key factor governing the trend of conductivity. The microscopic insight provided by simulation is useful to elucidate the fundamental mechanism of ion conduction, and might facilitate the design of new COF membranes for optimal ion conduction.

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.