Enhancement Of Ionic Conductivity Research Articles

Surface Carbon Shell-Functionalized ZrO2 as Nanofiller in Polymer Gel Electrolyte-Based Dye-Sensitized Solar Cells.

We prepare dye-sensitized solar cells (DSSCs) fabricated with a poly (ethylene glycol) based polymer gel electrolytes (PGEs) incorporating surface carbon shell-functionalized ZrO2 nanoparticles (ZrO2-C) as nanofillers (NFs). ZrO2 are polymerized via atom transfer radical polymerization (ATRP) using poly (ethylene glycol) methyl ether methacrylate (POEM) as a scaffold to prepare the ZrO2-C through carbonization. The power conversion efficiency of DSSC with 12 wt% ZrO2-C/PGEs is 5.6%, exceeding that with PGEs (4.4%). The enhanced efficiency is attributed to Lewis acid-base interactions of ZrO2-C and poly (ethylene glycol), catalytic effect of the carbon shells of ZrO2-C, which results in reduced crystallinity, enhanced ion conductivity of electrolytes, decreased counterelectrode/electrolyte interfacial resistance, and improved charge transfer rate. These results demonstrate that ZrO2-C introduction to PGEs effectively improves the performance of DSSCs.

Comments on "Enhanced ionic conductivity of yttria-stabilized ZrO2 with natural CuFe-oxide mineral heterogeneous composite for low temperature solid oxide fuel cells, Int. J. Hydrogen Energy 42 (2017) 17495–17503"

Recently, in this journal the phenomenon of ionic conductivity enhancement has again been claimed to boost the electrical characteristics of a solid electrolyte, this time of the classical oxygen ion conductor yttria-stabilized zirconia. It is demonstrated that the arguments to support the claim are flawed and that the criticized article is another example of a fallacy with regard to ionic conductivity enhancement.

Correlated Migration Invokes Higher Na+‐Ion Conductivity in NaSICON‐Type Solid Electrolytes

AbstractNa super ion conductor (NaSICON), Na1+nZr2SinP3–nO12 is considered one of the most promising solid electrolytes; however, the underlying mechanism governing ion transport is still not fully understood. Here, the existence of a previously unreported Na5 site in monoclinic Na3Zr2Si2PO12 is unveiled. It is revealed that Na+‐ions tend to migrate in a correlated mechanism, as suggested by a much lower energy barrier compared to the single‐ion migration barrier. Furthermore, computational work uncovers the origin of the improved conductivity in the NaSICON structure, that is, the enhanced correlated migration induced by increasing the Na+‐ion concentration. Systematic impedance studies on doped NaSICON materials bolster this finding. Significant improvements in both the bulk and total ion conductivity (e.g., σbulk = 4.0 mS cm−1, σtotal = 2.4 mS cm−1 at 25 °C) are achieved by increasing the Na content from 3.0 to 3.30–3.55 mol formula unit−1. These improvements stem from the enhanced correlated migration invoked by the increased Coulombic repulsions when more Na+‐ions populate the structure rather than solely from the increased mobile ion carrier concentration. The studies also verify a strategy to enhance ion conductivity, namely, pushing the cations into high energy sites to therefore lower the energy barrier for cation migration.

Fast Oxygen Transport in Bottlelike Channels for Y-Doped BaZrO3: A Reactive Molecular Dynamics Investigation

Yttrium-doped barium zirconate (BZY) has emerged as an attractive candidate of oxygen ion (O2–) conducting solid electrolyte because of its high ionic conductivity and excellent chemical stability. In this work, the O2– transport properties and mechanisms of BZY coexisting oxygen vacancies, dopants, and edge dislocations are simulated by reactive molecular dynamics for the first time, and the yttrium concentration (Y%) and temperature (T) dependences of thermodynamic and kinetic properties are studied for the bulk and dislocation (Bulk and Disl) systems, respectively. It is concluded that the Y% under 20 mol % for Bulk BZY can promote O2– conduction, while 30 mol % Y-doped Disl BZY has the highest O2– diffusion coefficient. Besides, dislocations will accelerate O2– diffusion when T is less than 1173.15 K due to the formation of double-bottle diffusion channels that enables facile reorientation of oxygen polyhedron. Therefore, it is feasible to introduce line defects to enhance ion conductivity at low temp...

Four-armed branching and thermally integrated imidazolium-based polymerized ionic liquid as an all-solid-state polymer electrolyte for lithium metal battery

The low ionic conductivity and poor interfacial contact are the main obstacles restricting the practical application of all-solid-state polymer electrolyte in lithium metal batteries. Herein, four-armed and imidazolium cation-tethered polymeric ionic liquid (IMFPIL) is prepared through atom transfer radical polymerization of hydroxyethyl acrylate and subsequent functionalization. The branching architecture of the organic scaffold endows IMFPIL with high thermal stability, low glass transition temperature and loosely packed polymer backbones. The derived more free paths and volumes for Li-ion migration confer much enhanced ion conductivity on the as-prepared all-solid-state polymer electrolyte (IMFSPE), which is 22 times that of the linear counterpart with the same composition. High-temperature thermal integration of IMFSPE into the lithium metal battery effectively eliminates the gaps between the electrolyte and the two electrodes, rendering excellent interfacial contact and stability. The volume variation of the electrodes during the charge-discharge can be effectively mediated. As a result, in sharp contrast to the battery failure of the linear counterpart, such an integrated LiFePO4/IMFSPE/Li all-solid-state battery presents a high discharge capacity of 153 mAh g−1 at 0.2 C with 99% of coulombic efficiency, and the capacity retention ratio reaches 73% after 150 cycles. Compared with IMLSPE, IMFSPE-2 efficiently weakens the formation of dendritic lithium. The branching design combining with the thermal integration strategy and superior electrochemical features of imidazole make IMFSPE behave as an all-solid-state polymer electrolyte, which paves a new way for developing PILs as ideal SPEs in energy storage device.

An Entropically Stabilized Fast-Ion Conductor: Li3.25[Si0.25P0.75]S4

We report on a family of lithium fast ion conductors, Li3+x[SixP1–x]S4, that exhibit an entropically stabilized structure type in a solid solution regime (0.15 < x < 0.33) with superionic conductivity above 1 mS·cm–1. Exploration of the influence of aliovalent substitution in the thermodynamically unstable β-Li3PS4 lattice using a combination of single crystal X-ray and powder neutron diffraction, the maximum entropy method, and impedance spectroscopy reveals that substitution induces structural splitting of the localized Li sites, effectively stabilizing bulk β-Li3PS4 at room temperature and delocalizing lithium ion density. The optimal material, Li3.25[Si0.25P0.75]S4, exhibits inherent entropic site disorder and a frustrated energy landscape, resulting in a high conductivity of 1.22 mS·cm–1 that represents an increase of three orders of magnitude compared to bulk β-Li3PS4 and one order of magnitude higher than the nanoporous form. The enhanced ion conduction and lowered activation barrier with increasin...

(Invited) ALD and MLD of Functional Thin-Film Coatings for Enhanced Performance in Li-Ion and Li-Metal Solid-State Batteries

The key figures of merit for batteries are Energy density, charging time (C-rate) and cycling Life time. In this invited talk we will focus on the application of continuous closed thin films as artificial interfaces in large capacity batteries or for the fabrication of functional battery components in micro-batteries. We will deal mostly with the perspective of device performance where the ALD and MLD processes merely provide the films and enable their ultrathin, continuous and conformal nature. Nanoscale film thickness allows for low interface and cell resistance even when the materials themselves are poor conductors. For example. LiPON (N-doped Li3PO4) is a solid electrolyte interesting because it is stable against metallic lithium but, because of its poor ionic conductivity (<10-6 S/cm) only practically useful for thicknesses under few hundred nanometers. Even further, materials which are not solid electrolytes by their own merit (e.g. TiO2) still have ion-transparent properties up to several tens of nanometer and can be used as ion transparent artificial interfaces in contrast to alumina which is an insulator for Li-ions. For coating of individual particles, ideally coatings which have both electronic and ionic conducting (or transparent) properties. Doping is one approach to enhance either conductivity. When scaling down of the film thickness also finite size effects have to be considered, for example, the thickness of the electrical double layer, diffusion layer thickness and the electric field over the dielectric. ALD and MLD can be used also to fabricate functional nanomaterials; i.e. by harvesting nanoscale effects. For example, nanocomposite solid electrolyte films of a few tens of nanometers were fabricated by a combination of MLD of inorganic-organic hybrid alucone thin-films, etching the organic fraction in water and functionalization by ALD of Li2CO3 and Li3PO4. For the first time, enhanced ion conductivity is shown by harvesting the enhanced ion conductivity at oxide/ion conductor interfaces. Finally, volume changes during charge and discharge are limiting the cycle life-time of batteries, especially for rigid solid-state batteries. Also ALD thin-films suffer from the mechanical strain and the benefits of the “closed” protective film are lost. Therefore, MLD of hybrid organic/inorganic coatings is explored to enable more elastic coatings for improved cycle life time.

Toward Garnet-Based Electrolyte Li-Metal Batteries: A Highly Effective Solid-State Electrolyte- Li Metal Interface

The widespread adoption of electric-powered vehicles (electric vehicles, plug-in hybrids, etc.) stimulated the desire to pursue solid-state batteries (SSBs) with energy densities beyond those of lithium-ion batteries as well as long cycle life and safety. Many technological elements are involved in successful development and commercialization of SSBs, including solid-state electrolyte (SSE) materials, ionic conductivity enhancement, electrolyte/electrode interface stability, enabling Li metal anode, cell and pack manufacturing methods, battery management system, and battery pack design. The principle focus of this talk will be a discussion centered on charge transfer at the Li metal-SSE interface and its effect on electrolyte/electrode interface stability during Li plating/striping to enable Li metal anode. Further discussion will focus on the impact of lithiated interfacial coating layers on the interfacial impedance, which has enabled the uniform plating of Li at the Li-SSE interfaces. In this study, garnet-type oxide with nominal composition of Li7La3Zr2O12 (LLZO) has been used as model system due to its simultaneous fast-ion conductivity and stability against metallic Li.

Enhancement of Mechanical Stability and Ionic Conductivity of Chitosan‐based Solid Polymer Electrolytes Using Silver Nanowires as Fillers

With the emergence of wearable devices and internet of things, it is expected that small flat, and flexible electrochemical devices will be required for these applications. One of the prerequisites for these devices to be applied to such fields is the development of solid polymer electrolytes with high ionic conductivity. Because most solid polymer electrolytes have low ionic conductivity, small organic molecules have been used as plasticizers to increase their ionic conductivity. Since these plasticizers can increase amorphous regions that play the role of ion channels in polymer, their ionic conductivity increases; however, their mechanical stability decreases inversely. Conventionally, to overcome this drawback, inert nanoparticles are added into solid polymer electrolytes as fillers. Herein, we show that 1‐dimensional silver nanowires can increase the mechanical stability of chitosan‐based solid polymer electrolytes as well as their ionic conductivity more than nanospheres can, and discuss a plausible mechanism for such an enhancement.

Molecular dynamics simulations of point/line defect structures and oxygen diffusion mechanism in yttrium-doped barium zirconate

Yttrium-doped barium zirconate is one of the most attractive electrolyte candidates for solid oxide fuel cells due to its excellent chemical stability and ionic conductivity. For the first time, this paper studies the barium zirconate systems coexisting point defects and line defects by classical molecular dynamics simulations in combination with the Coulomb-Buckingham potential, and the influences of yttrium dopants and oxygen vacancies concentrations and the edge dislocations on the structures and oxygen transport properties. The calculated results have shown that the diffusion coefficient is related to concentration of dopant, and it is not conducive to oxygen conduction when the dopant concentration is too high or too low. And it is concluded that 30% Y-doped barium zirconates have the highest diffusion coefficients regardless of the presence of edge dislocation defects. In addition, at the temperature of 1073.15 K, the diffusion of oxygen ion has been accelerated by edge dislocations when the dopant concentration is less than 30%, which could be explained by the gathering-jogging transport mechanism among edge dislocation, oxygen vacancy and oxygen ion. Therefore, the dopant concentration of barium zirconate should not be too high in practical applications of solid electrolytes, and it is feasible to introduce line defects to enhance ion conductivity.

Direct Measurement of Enhanced Ion Conductivity at an Ionic Liquid Electrolyte (ILE)/SiO2 Interface with Interdigitated Electrode Array

Recently, our group reported a novel solid-state electrolyte material which is constituted of a nano-porous SiO2 monolith and an ionic liquid electrolyte (ILE) which occupies the pores. The unique feature of this solid nano-composite electrolyte (nano-SCE) is its ion conductivity which is higher than that of the ILE itself [1]. Here, we report a direct measurement of this enhanced ion conductivity by measuring the ion conductivity of a thin-film ILE on a planar SiO2 substrate. The enhanced ion conductivity is directly measured with interdigitated electrode arrays deposited on a planar SiO2 substrate, as shown in Figure 1. By depositing a thin-film ILE film on these electrodes, the impedance response of the ILE/SiO2 interface could be measured by impedance spectroscopy (IS). The ion conductivity on the ILE/SiO2 interface could subsequently be quantified by analysis of the equivalent circuit model and by measuring the ILE film thickness. The ILE film thickness is scaled down to the nanometer regime. This is the first time that such thin ILE films could be deposited using liquid processing techniques. The enhanced ion conductivity is revealed when the ILE film thickness is reduced to 20 nm thicknesses and below. The ion conductivity of the ILE films with a thickness around 80 nm have a similar conductivity compared to the bulk ILE. Enhanced ion conductivity along interfaces has been observed before and is typically referred to as heterogenous doping [2]. The mechanism that governs the enhanced conductivity in the nano-SCE are similar to those described by heterogenous doping. However, the ion conductivities measured in this work are many times higher compared to those reported before. In conclusion, for the first time ILE thin-films with thicknesses in the nanometer regime are deposited with liquid processing. Moreover, the ion conductivity at the ILE/SiO2 interface could be quantified and showed an increased conductivity compared to the bulk ILE value.

A Novel Material Class of Solid-State Nano-Composite Electrolytes with High Li-Ion Conductivity

All-solid-state Li-ion cells are expected to become the next major cell technology. Besides the fact that they are intrinsically safer compared to today’s cells with a flammable liquid organic electrolyte, a solid-state electrolyte also enables the introduction of a metallic lithium anode, resulting in cell energy densities of >1000 Wh/L. This is significantly higher compared to the practical limit of 800 Wh/L of the liquid Li-ion cell technology. Applying metallic lithium electrodes with a liquid electrolyte is challenging due to the likelihood of dendrite formation during cell charging (i.e. during lithium plating) [1]. It is expected that a solid-state electrolyte is a better candidate to deal with the lithium dendrite formation problem, as it forms a physical barrier for the dendrites to grow [2]. For many years, it was considered practically impossible to engineer solid-state materials having ionic conductivities that are equally high and surpassing those of the liquid electrolytes, as ion diffusion in solids is typically much slower compared to diffusion in liquids. A high Li-ion conductivity through the electrolyte is essential for the Li-ion cells to be charged and discharged at high rate. We here present a novel class of nano-composite electrolytes (nano-SCEs) for which ion conductivity values are obtained higher than those seen in conventional liquid electrolytes. These nano-SCEs constitute a nano-porous SiO2 monolith that encloses an adsorbed ionic liquid electrolyte. Different from to so-called ionogel electrolytes – which follow a similar approach in that they confine an ILE in a porous oxide matrix [3] – our electrolytes feature the unique property that the ionic conductivity of the composite is higher than to that of the ionic liquid electrolyte [4]. The so-called enhancement factor reaches values of > 200 %, as shown in the Figure 1. The high ion conductivity and enhancement factor were established by engineering the surface chemistry in the nano-SCE [4]. Along the pore walls of the oxide matrix, the ionic liquid electrolyte molecules are organizing themselves such that “highway” conduction paths are created for fast Li-ion transport. The exact nature of these highway conduction paths strongly depends on the chemistry of the ionic liquid electrolyte. Figure 1 show the influence of the ILE chemistry on the nano-SCE enhancement factor. Interestingly, the enhancement factor increases with increasing ILE viscosity. In conclusion, a new material class of composite electrolytes is presented having the unique feature of enhanced ion conductivity. The conduction promotion arises from the chemical interaction between the ILE and the nano-porous SiO2 matrix. Furthermore, the enhancement factor can be controlled by engineering the ILE viscosity.

Interstitialcy diffusion of fluoride ions in LaOF by DFT-based first-principles calculations

Ionic conduction in LaOF was investigated by density functional theory-based first-principles calculations. The origin and microscopic mechanism of selective fluoride ion conduction in LaOF were investigated by evaluating the formation energy of the Frenkel pair and by performing ab initio molecular dynamics (MD) simulations for both tetragonal (anion order along the [0 0 1] direction) and rhombohedral (anion order along the [1 1 1] direction) structures experimentally obtained in LaO1−xF1+2x. In both structures, the formation of an F Frenkel pair was energetically favored over that of an O Frenkel pair, and the F Frenkel pair predominantly contributed to the conduction of fluoride ions. From the trajectory of MD simulations with an F or O Frenkel pair in the two structures, it was found that fluoride ion conduction mainly occurred via an interstitialcy mechanism. This fluoride ion migration occurred only in the tetragonal structure along the (0 0 1) plane. This observation was further confirmed by migration barriers evaluated by the climbing-image nudged elastic band method. The results suggested the possibility of the enhancement of ionic conductivity by controlling the anion ordering in mixed anion compounds.

Enhanced electrochemical properties of metal oxide interspersed polymer gel electrolyte for QSDSSC application

Improved ionic conductivity of polymer gel electrolyte by the addition of inorganic fillers is an innovation in electrochromic devices. This work reports preparation of polymethyl methacrylate (PMMA) based gel electrolyte via ‘solvation-unfolding-swelling’ process. The properties of the gel electrolyte after adding inorganic nano fillers have been studied. An enhancement in the physical and electrochemical properties of the PMMA gel electrolyte is observed with the introduction of fillers such as TiO2 and ZnO. The modified gel electrolyte shows an enhancement in ionic conductivity due to the synergistic effect of the fillers. A maximum conductivity is observed for an optimum filler concentration which is 3 wt% for ZnO and 2 wt% for TiO2 with conductivities respectively 18.41 × 10−4 and 17.54 × 10−4 mho cm−1. FTIR and thermogravimetric analyses are performed to study the interaction of the fillers with the polymer matrix. Stability study of these gel electrolytes is carried out by monitoring their electrochemical behavior under ambient temperature. Performance of the PMMA gel electrolyte before and after adding the filler is checked in a solar cell assembly under 1 sun illumination. The result shows that the fillers has a direct bearing on the performance of the solar cell.

Solid Nano-Composite Electrolytes (nano-SCE) with Ion Conductivity Promotion at an Interfacial Ice Layer on the Mesoporous Silica Matrix

The transition to solid-state Li-ion batteries requires solid electrolytes with Li-ion conductivity exceeding 1 mS/cm. Solid composite electrolytes or SCEs consisting of an ionic conductor and a dielectric matrix offers an elegant strategy to enhance the ionic conductivity of electrolytes by engineering the interface conduction. Composite electrolyte materials with inorganic oxide matrixes such as silica, alumina or titania with, for example, inorganic or polymer electrolytes have indeed shown enhancements in ion conductivity, however, the total ion conductivity was still well below 1mS/cm due to the low conductivity of the starting individual electrolytes used. Also composites of mesoporous oxide matrix filled with non-volatile ionic liquid electrolyte (ILE) fillers have been explored as solid electrolyte option. The advantage is that ILE can already have quite high ionic conductivity as individual electrolyte component. However, simple confinement of an electrolyte solution in nanometer size pores results in lower conductivity as its effective viscosity increases. The decrease in ion conductivity is expected the worse for mesoporous channels (~10nm in diameter) where the ionic liquid can even turn solid. To achieve higher ion conductivity, interface enhancement has to exceed the decrease in conductivity by confinement. Monolithic nanoporous silica with ILE confined in the porous structures, also named “ionogels” have shown ion conductivities approaching that of the ILE bulk conductivity, indeed, indicating the presence of interface enhancement in these materials. However, so far, the ionic conductivity of the confined ILE in the nanoporous oxide has never exceeded that of the ILE conductivity itself. These ionogels are fabricated by a sol-gel process e.g. by hydrolysis-condensation reaction with tetra-ethylorthosilicate (TEOS) precursor and typically formic acid where the ILE is added in the solution as the template for the silica to grow around. In this paper we demonstrate that the Li-ion conductivity of nano-composites consisting of a mesoporous silica monolith with an ionic liquid electrolyte as filler can be several times higher than that of the pure ionic liquid electrolyte itself when the silica surface is appropriately hydroxylated. Interfacial ice layers induce strong adsorption and ordering of the ionic liquid molecules through H-bonding rendering it immobile and solid-like as for the interfacial ice layer itself. The dipole over the adsorbate results in solvation of the Li+ ions for enhanced conduction. The existence of an interfacial mesophase layer is proven by Infrared and Raman spectroscopy. Higher Li-ion diffusion coefficients for the nanocomposite compared to the pure ionic liquid electrolyte reference is shown by Pulsed-Field-Gradient NMR. The principle of ion conduction enhancement is generic and could be applied to different ion systems. The concept also allows for further (nano)engineering towards specific properties of ion conduction, transport number, electrochemical window, safety and cost for future battery cell generations. The nano-SCE was fabricated in a similar way as the ionogels: a single-step sol-gel process with a TEOS precursor and with the ionic liquid electrolyte in the homogeneous precursor solution, except we did not use formic acid but water. We will focus on systematic study of our nano-SCE model system with (N-butyl- N-methyl pyrrolidinium bis(trifluoromethanesulfonyl) imide ([BMP]TFSI) and bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSI). Figure caption: Ball-and-stick model for the adsorbed mesophase layer on silica with an interfacial ice water layer. The strong H-bonding between TFSI anions and OH surface groups result in polarization of the adsorbed ILE layer and the dissociation of Li+ from TFSI- anion. The free Li-ions can move faster through the liquid-like layer just above the adsorbed mesophase layer resulting in enhanced ion conductivity. Figure 1

Ionic conduction in Li3Na(NH2)4: Study of the material design for the enhancement of ion conductivity in double-cation complex hydrides

Complex hydrides have collected recent attention as a new class of solid electrolytes with potential applications in all-solid-state batteries. To improve ionic conduction in the complex hydrides, multi-cation crystal structure can be attractive. It will allow tuning the cation dynamics via structure modification depending on types and number of additional cations. However, multi-cation crystal structure struggles with the inter-cation scattering among different cations. To address this issue, understanding the conduction mechanisms in the multi-cationic crystals is indispensable. Here, we study cationic conduction in a double-cation (Li and Na) complex hydride Li3Na(NH2)4, which is formed by replacing Li (with Na) from specific lattice site of LiNH2 without altering the crystal symmetry. The nuclear magnetic resonance (NMR) measurements found that Li3Na(NH2)4 is a Li-ion conductor with negligibly small Na-ion conduction. This finding is critically important to elucidate Li-ion conduction mechanism in Li3Na(NH2)4. Enhanced Li-ion conduction in Li3Na(NH2)4 is achieved by (a) suppressing diffusion of Na cation trapped at the strategically located 2c lattice sites under deep potential well; and (b) by increasing the Li defect concentration influenced by the larger volume of the Li metastable sites due to Na substitution into LiNH2. Our study will provide the design principle for multi-cation complex hydrides, and accelerate development of superior solid electrolytes for all-solid-state batteries.

Exploring Side-Chain Designs for Enhanced Ion Conductivity of Anion-Exchange Membranes by Mesoscale Simulations

Anion-exchange membranes (AEM) are polyelectrolytes functionalized with cationic groups. Studies of AEM in the past few decades suggest that AEM is a competitive alternative to conventional proton-...

Evaluation of electrochemical performance of solid-oxide fuel cell anode with pillar-based electrolyte structures

Among the gas, ion, and electron diffusion processes in solid-oxide fuel cell (SOFC) electrodes, it is generally known that ionic conduction has the most impact on their electrochemical performance. Therefore, enhancement of the effective ionic conductivity of electrodes is a useful approach to reduce the overpotential. Yttria-stabilized zirconia (YSZ) pillars can be effective solutions to enhance the effective ionic conductivity of SOFC anodes. In this study, the influence of YSZ pillar structures on the electrochemical performance of SOFC anodes was evaluated by numerical simulation and experiments. First, to reveal the electrochemical reaction kinetics of anodes with pillar structures, a three-dimensional electrochemical simulation was conducted by the lattice Boltzmann method. The microstructure without pillars obtained by a focused ion beam scanning electron microscopy (FIB-SEM) measurement was used as the reference structure. Then, the original structure was replaced with YSZ phase to obtain virtual microstructures with YSZ pillars. With YSZ pillars, predicted area specific resistance became smaller than that of the reference structure, in spite of decrease in percolated TPB density. The electrochemical potential distribution of oxide ion and charge-transfer currents clearly show increase in the effective ionic conductivity. Relationships between overpotential and pillar geometries were parametrically discussed. Then, electrochemical performance of Ni-YSZ anode with the YSZ pillar structure formed by modifying the YSZ electrolyte surface was evaluated. By sputtering Ni-YSZ on pillar structures, stable electrochemical performance was obtained.

Precursor glass stability, microstructure and ionic conductivity of glass-ceramics from the Na1+xAlxGe2–x(PO4)3 NASICON series

Glass-ceramics from the Na1+xAlxGe2–x(PO4)3 system were synthesized for 0 ≤ x ≤ 1.0. The stability parameters of precursor glasses were analyzed indicating that systematic additions of aluminum in the NaGe2(PO4)3 composition improve the precursor glass forming ability. Considering the glass-ceramics, it is observed that an increase in the aluminum content, x, causes a decrease in the activation energy for conduction, and thus an increase in the ionic conductivity. As x increases, beyond the corresponding increase in the charge carrier (Na+) concentration, it is also observed an increase in the unit cell volume of the NASICON structure, which may also contribute to the enhancement of ionic conductivity. Concerning the microstructure, the addition of aluminum provokes an increase in the average grain-size of the obtained glass-ceramics. Ionic conductivity increases up to x = 0.8 but remains constant within the experimental error for the x = 1.0 sample, probably due to a limit in the solid solution range. Ionic conductivity of composition x = 0.8 is still improved by applying higher crystallization temperatures, which decreases the activation energy for ionic conduction.

Nanofiller-Induced Ionic Conductivity Enhancement and Relaxation Property Analysis of the Blend Polymer Electrolyte Using Non-Debye Electric Field Relaxation Function

The enhancement of conductivity of a composite polymer as a dielectric material is an essential requirement for electrostatic storage devices. We have modified the microstructure of the polymer matrix by introducing an insulating nanofiller SiO2. The effect of such a filler on the ionic conductivity of the composite polymer electrolyte has been investigated using a variety of experimental techniques along with the non-Debye type of relaxation functions. We have achieved optimum conductivity enhancement at a threshold filler concentration of 0.7 wt % in the blend polymer matrix composed of poly(ethylene oxide), poly(vinylidene fluoride) (80:20), and salt NH4 I (35 wt %). Such an enhancement of conductivity is a result of formation of a highly conducting interphase region around the nanofiller surface. The mobility of the conducting species is found to increase enormously in the presence of a filler. As a consequence, the ionic conductivity of the filler-induced blend polymer electrolyte increases 3 times of its magnitude (3.02 × 10–3 S/cm) compared to that without a filler. The occurrence of two different activation energies which decrease with increasing filler concentrations, as determined from temperature-dependent conductivity, has been well explained from the dynamics of free and contact ions. A non-Debye behavior of relaxation properties has been analyzed using a newly approached one-parameter Mittag-Leffler function. The experimental decay function fits very well using the Mittag-Leffler function as compared to the conventional non-Debye Kohlrausch–Williams–Watts function used in the literature.