Ion Migration Process Research Articles

Characterization of Sr-doped lithium lanthanum titanate with improved transport properties

Safety issues affecting traditional lithium-ion batteries with liquid electrolyte can be successfully overcome by application of a solid electrolyte. Among various candidate materials, perovskite-type compounds, typically from Li3xLa2/3−xTiO3 group, are known to exhibit superior Li+ ionic conductivity. However, the ever-increasing requirement for high ionic conductivity necessitates the improvement of its structure and composition. In this work, Sr2+ cations, having ionic radius larger than La3+, are doped at the La-site in order to enlarge the unit lattice parameter and so facilitate the lithium ion migration process. At the same time, Sr doping can increase the lithium ion concentration of Li0.33+xLa0.56−xSrxTiO3 oxides as charge compensation. Both of them favor the increase of lithium ion conductivity. The Sr substitution induces structure transformation from tetragonal to cubic structure. The prepared dense Li0.36La0.53Sr0.03TiO3 (x = 0.03) ceramic electrolyte exhibits a high ionic conductivity of 1.95 × 10−3 S cm−1 at 303 K, which is about twice as high as that of the pristine material.

Understanding the role of water-based electrolytes on magnesium-ion insertion/extraction into λ-MnO2 lattice structure

In rechargeable batteries, the different anionic groups of the electrolyte salt having same cation play an importance role in improving electrode material performance due to their intrinsic characteristics which affect ion migration process, structural stability and self-discharge. To this end, we investigate Mg2+ ion insertion into λ-MnO2 structure with aqueous electrolytes that contain three different salts of Mg. Experimental study includes both material characterizations performed to describe the physical properties of the active material and battery performance tests of the working electrode in Mg-based aqueous mediums. Herein, λ-MnO2 that functions as an inorganic electroactive template is synthesized by extracting Li+ ion from LiMn2O4 through acid leaching method. Electrochemical performance of the spinel-type positive electrode material is evaluated by means of cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. In charge-discharge tests conducted at C/10 current density, λ-MnO2 electrode deliver approximately a reversible discharge capacity of 70 mAh g−1 in 1 M MgSO4, 20 mAh g−1 in both 1 M MgCI2 and 1 M Mg(NO3)2 after 100 cycles. C-rate performance tests are carried out for the samples in which the electrolyte contained MgSO4 salt, and the result is found to be around 220 mAh g−1 capacity at C/40 current rate. Concurrently, the insertion of Mg2+ ion is confirmed by EDX-mapping and XPS analysis after the first reduction step.

Enabling High Lithium Conductivity in Polymerized Ionic Liquid Block Copolymer Electrolytes

AbstractHerein, the use of a novel block copolymer host, based on a polymerized ionic liquid block copolymer, is proposed. Mechanically robust solid polymer electrolytes (SPEs) with high lithium conductivity are developed using a ternary polymer electrolyte system, consisting of a poly(styrene‐b‐1‐((2‐acryloyloxy)ethyl)‐3‐butylimidazolium bis(trifluoromethanesulfo‐nyl)imide) (S‐PIL64‐16) block copolymer, a N‐propyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI) ionic liquid (IL) and a lithium bis (fluorosulfonyl) imide (LiFSI) salt. The impact of both IL and lithium salt concentration on the morphology, ion migration processes and electrochemical performance of the electrolytes is characterized. High lithium ion conductivity is achieved when anion to Li+ molar ratio was kept below a value of 1.5, resulting in a lithium transport number ( ) as high as 0.53 at 50 °C. Finally, the cycling performance in a Li|LiFePO4 full cell is assessed using an in‐house formulated solid‐state high loading cathode (LiFePO4 loading=10 mg cm−2, 1.8 mAh cm−2). 98 % of the theoretical discharge capacity (167 mA g−1) is achieved for the first cycle at a C‐rate of C/20 at 50 °C. The results herein reported are the first demonstration of a PIL block copolymer‐IL‐salt composite electrolyte operating at near‐practical levels, making them a promising choice of electrolyte for the next generation of solid‐state high capacity lithium‐metal batteries.

Oxygen ion conducting pyrochlore oxides prepared by an ultrasound-assisted wet chemistry route: Ca-doped Gd2Ti2O7 nanocrystals

Abstract Different compositions of pyrochlore-type oxides of general formula Gd2-xCaxTi2O7 (x = 0, 0.05 and 0.1), interesting solid oxide ion conducting materials, were prepared by a novel wet-chemistry method assisted by ultrasound. Titanium isopropoxide (TTIP), and Gd3+ and Ca2+ hydrated nitrates were used as metal sources; whereas, ethanol and ethylene glycol were used as solvents. The results corroborate the feasibility of this method to obtain nanometric particles of lanthanide titanates. Electrical properties of uniaxially pressed and sintered pellets (1200 and 1500 °C) were measured as a function of temperature (280–700 °C) and frequency (100 Hz-1MHz) by using impedance spectroscopy. The Analysis of electrical properties revealed an increasing of dc conductivity (σ) for higher contents of Ca2+ in the system, reaching a maximum of 3.55 × 10−3 S cm−1 at 700 °C for x = 0.1. Calculated activation energies for oxygen diffusion in the Ca-doped samples, are in the 0.68–0.89 eV range, well below that of pristine Gd2Ti2O7 (2.23 eV), which explains their enhanced conductivity. Increasing of dc conductivity is promoted by substitution of Gd3+ by Ca2+ in these titanates, generating oxygen vacancies in the structure, which facilitates the ion migration process.

Slow Response of Carrier Dynamics in Perovskite Interface upon Illumination.

The current-voltage hysteresis, as well as the performance instability of perovskite solar cells (PSCs) under a working condition, is serving as the major obstacle toward their commercialization while the exact fundamental mechanisms to these issues are still in debate. In this study, we investigated the slow variation of photogenerated carrier dynamics in a (FAPbI3)0.85(MAPbBr3)0.15 perovskite interface under continuous illumination. Different response behaviors of carrier dynamics in the perovskite interfaces with and without the hole transport layer, Spiro-OMeTAD (Spiro), were systematically studied by time-dependent, steady-state, and time-resolved photoluminescence. It was demonstrated that a light-induced defect curing process is dominantly responsible for the carrier dynamics evolution for the perovskite interface without Spiro, whereas both defect curing process and mobile ion migration should be accounted for the dynamic response of the perovskite interface contact with Spiro. When contacted with Spiro, the energy band curvature evolution in the perovskite interface induced by ion migration would decrease the hole transfer rate from the perovskite interface to Spiro upon illumination. This research work can faithfully highlight the strong correlation of slow photoresponse behaviors of the perovskite interface with both light-induced defect curing and ion migration processes, providing novel implications into the physical mechanism for the slow variation of PSC performances under a working condition.

Non-radiative processes in metal halide perovskite semiconductors probed by photoluminescence microscopy

Organo metal halide perovskites are solution processed semiconductors that recently attracted a great attention. They possess a rather “soft” and (photo) chemically active solid structure allowing for ion migration and other mass diffusion processes. This is a likely reason why non-radiative recombination centres in these materials are activated and deactivated on relatively slow time-scales. This dynamics reveals as photoluminescence (PL) fluctuations (blinking) of individual microcrystals and local areas of films and allows for application of a broad range of single molecule spectroscopy methods including optical super-resolution. Studying PL blinking resolves properties of individual non-radiative centres and helps to unravel their chemical nature.

A 1D Vanadium Dioxide Nanochannel Constructed via Electric-Field-Induced Ion Transport and its Superior Metal-Insulator Transition.

Nanoscale manipulation of materials' physicochemical properties offers distinguished possibility to the development of novel electronic devices with ultrasmall dimension, fast operation speed, and low energy consumption characteristics. This is especially important as the present semiconductor manufacturing technique is approaching the end of miniaturization campaign in the near future. Here, a superior metal-insulator transition (MIT) of a 1D VO2 nanochannel constructed through an electric-field-induced oxygen ion migration process in V2 O5 thin film is reported for the first time. A sharp and reliable MIT transition with a steep turn-on voltage slope of <0.5 mV dec-1 , fast switching speed of 17 ns, low energy consumption of 8 pJ, and low variability of <4.3% is demonstrated in the VO2 nanochannel device. High-resolution transmission electron microscopy observation and theoretical computation verify that the superior electrical properties of the present device can be ascribed to the electroformation of nanoscale VO2 nanochannel in V2 O5 thin films. More importantly, the incorporation of the present device into a Pt/HfO2 /Pt/VO2 /Pt 1S1R unit can ensure the correct reading of the HfO2 memory continuously for 107 cycles, therefore demonstrating its great possibility as a reliable selector in high-density crossbar memory arrays.

Atomic-resolution imaging of electrically induced oxygen vacancy migration and phase transformation in SrCoO2.5-\u03c3

Oxygen ion transport is the key issue in redox processes. Visualizing the process of oxygen ion migration with atomic resolution is highly desirable for designing novel devices such as oxidation catalysts, oxygen permeation membranes, and solid oxide fuel cells. Here we show the process of electrically induced oxygen migration and subsequent reconstructive structural transformation in a SrCoO2.5−σ film by scanning transmission electron microscopy. We find that the extraction of oxygen from every second SrO layer occurs gradually under an electrical bias; beyond a critical voltage, the brownmillerite units collapse abruptly and evolve into a periodic nano-twined phase with a high c/a ratio and distorted tetrahedra. Our results show that oxygen vacancy rows are not only natural oxygen diffusion channels, but also preferred sites for the induced oxygen vacancies. These direct experimental results of oxygen migration may provide a common mechanism for the electrically induced structural evolution of oxides.

Influence of Cu, Au and Ag on structural and surface properties of bioactive coatings based on titanium

In this work influence of copper, silver and gold additives on structural and surface properties of biologically active thin films based on titanium have been described. Coatings were prepared by magnetron sputtering method. During each process metallic discs (targets) - Ti and the additive (Cu, Ag or Au) were co-sputtered in argon atmosphere. Structural investigation of as-deposited coatings was performed with the aid of XRD and SEM/EDS method. It was found that all prepared thin films were homogenous. Addition of Cu, Ag and Au resulted in nanocrystalline structure. Moreover, influence of these additives on hardness and antibacterial activity of titanium coatings was also studied. Ti-Cu, Ti-Ag and Ti-Au films had lower hardness as-compared to Ti. According to AAS results the difference of their activity was related to the ion migration process. It was found that Ti-Ag and Ti-Au coatings had biocidal effect related to direct contact of their surface with microorganisms. In the case of Ti-Cu antimicrobial activity had direct and indirect nature due to efficient ion migration process from the film surface to the surrounding environment. Functional features of coatings such as wettability and corrosion resistance were also examined and included in the comprehensive analysis.

Sulphate ion migration of cement concrete under the coupling action of corrosion solution and alternating loading

In this paper, the sulphate ion migration process of concrete under the coupling action of alternating loading and sulphate corrosion is investigated. Chemical analysis method is used to investigate the sulphate ion migration process of interior concrete. The results show that compared with the static loading and the no loading, the alternating loading can accelerate the sulphate ion migration in the cement concrete which is subjected to sulphate attack. The sulphate ion concentration on the surface of concrete under alternating loading is higher than static loading. With the increase of depth, the difference between the alternating loading and the static loading becomes smaller gradually. When the stress level is greater than 40%, the sulphate ion diffusion is improved obviously. It is also found that on the condition of that water–cement ratio met requirements of the concrete workability, low water–cement ratio will improve the durability of concrete under the coupling action of alternating loading and sulphate corrosion.

Electro-osmotic strengthening of silts based on selected electrode materials

Electro-osmosis is considered promising in effectively strengthening silts. This has been an urgent issue for engineers as large volumes of silts are being generated each year and need to be properly disposed. Electrode material is one of the key elements for the electro-osmosis technique. Inconsistent results have been reported in the existing literature on common electrode materials. To clarify these discrepancies and to optimize the electrode material, laboratory tests were performed with four common materials, namely, iron, graphite, copper and aluminum, under three levels of voltage gradient. Observations were performed from the perspectives of the electro-osmotic effect and the ionic strength. As for the former perspective, the electro-osmotic effect was denoted by the drainage, the water content and the effective potential. The graphite electrode was found to perform better at high potentials than iron or copper. The copper electrode exhibited a rapid decrease in the effective potential and current. As for the latter perspective, contents of Fe, Cu and Al were detected in the drainage and soils. Aluminum ions were demonstrated to have higher migration capacities than iron or cupric ions. Further analysis determined that electro-osmosis relies on ions in the original soils instead of those generated by electrode reactions. In conclusion, iron is recommended as the preferable electrode material for electro-osmosis. The performance of different electrode materials is directly reflected by the voltage loss rather than by the ion migration process. The voltage loss can be attributed to various factors, such as corrosion, electrochemical passivation, gas evolution, decomposition and electrochemical potential. The results of this paper provide deep insight into the influence of the electrode material on the electro-osmotic process.

Role of metal-oxide interfaces in the multiple resistance switching regimes of Pt/HfO2/TiN devices

The multiple resistive switching of Pt/HfO2/TiN devices is demonstrated as a result of a competition between the switching at opposite metal/oxide interfaces. Three switching operation modes are demonstrated: clockwise (CW) switching (set for negative voltage and reset for positive voltage at Pt electrode), as already reported in literature for similar material stacks; counterclockwise (CCW) switching and complementary switching (CS) that consist in a set and a reset for increasing voltage of the same polarity. The multiple switching operation modes are enabled by a deep-reset operation that brings the cell resistance close to the initial one. As a consequence, the set transition after a deep-reset occurs at the same voltage and currents as those of the forming and leads to a low resistance state whose resistance can be further decreased in a CCW switching or increased back with a CW switching. With a suitable choice of the stop voltage, a CS in obtained, as well. The coexistence of all three CW, CCW, and CS operations demonstrates that both metal-oxide interfaces are active in the formation and the dissolution of conductive filaments responsible for the switching. All these observations are discussed in terms of a competition between ion migration processes occurring at the opposite metal-oxide interfaces.

Copper diffusion in cable-insulating materials by chemiluminescence and DSC techniques

Chemiluminescence (CL) and differential scanning calorimetry (DSC) were applied for proving the copper ion migration processes occurring within the low- density polyethylene (LDPE) electrical insulator as a con- sequence of intimate contact. Thin LDPE slides of 0.5 mm thick were subjected to short-time thermal stress at tem- peratures between 80 and 120 C. Both CL and DSC ki- netic parameters revealed the acceleration of post- treatment oxidation at elevated temperatures (170-200 C) in copper-contacting polymer as in respect to the cases when Cu was absent. It was revealed that the oxidation rate measured by CL was more than two times higher for the samples heated in the presence of Cu than in its absence, while the oxidation induction time from DSC was con- siderably lowered for the same samples. Elemental analysis data provided by atomic absorption spectroscopy and par- ticle-induced X-ray emission techniques as well as SEM investigations confirmed the presence of copper within the samples subjected to thermal treatment when the polymer insulation was in contact with the metallic conductor. Chemiluminescence procedure has a remarkable sensitivity to detect the effect of copper in the polymer matrix even at low concentrations.

Electro- and magneto-modulated ion transport through graphene oxide membranes.

The control of ion trans-membrane transport through graphene oxide (GO) membranes is achieved by electric and magnetic fields. Electric field can either increase or decrease the ion transport through GO membranes depending on its direction, and magnetic field can enhance the ion penetration monotonically. When electric field is applied across GO membrane, excellent control of ion fluidic flows can be done. With the magnetic field, the effective anchoring of ions is demonstrated but the modulation of the ion flowing directions does not occur. The mechanism of the electro- and magneto-modulated ion trans-membrane transport is investigated, indicating that the electric fields dominate the ion migration process while the magnetic fields tune the structure of nanocapillaries within GO membranes. Results also show that the ion selectivity of GO membranes can be tuned with the electric fields while the transport of ions can be enhanced synchronously with the magnetic fields. These excellent properties make GO membranes promising in areas such as field-induced mass transport control and membrane separation.

Prelimenary Study on the Photovoltaic and Impedance Characteristics of Dye Sensitized Solar Cell (DSSC) using Polymer Gel Electrolyte

Dye sensitized solar cells (DSSC) have been fabricated by using polymer gel electrolyte consisting of ionic liquids in a composite polymers of siloxane and ethylene oxide groups. The structure of those DSSCs are ITO/Ti:ZnO/TiO2/Ru-dye/gel electrolyte/Pt/ITO, with active area of about 0,5 cm2. At this preliminary work, the structure parameters and fabrication procedures had not been optimized for achieving the best performance, but it had been carefully controlled to be same for all fabricated DSSCs. Those DSSCs shows the solar cell performance similar to that observed in DSSCs fabricated in the same cell structure but using conventional electrolyte solution. They exhibit better open voltage and filling factor, which is suggested to the reduction of charge carrier recombination probably taking place at the double layer region formed at the electrode interfaces. This is consistent with their impedance spectrum which is dominated by a Warburg-like characteristics indicating a diffusion limited migration process. It seems then the cell performances is improved by the reduction of charge recombination loss but restricted by diffusion limited ion migration process.

Electro-active polymer actuator based on PVDF with bacterial cellulose nano-whiskers (BCNW) via electrospinning method

Hybrid electro-active polymer actuator using poly(vinylidene fluoride)(PVDF) membranes enhanced with bacterial cellulose nanowhiskers (BCNW) are developed through an electrospinning method and hence characterized. PVDF is dissolved in DMF and acetone solvent to prepare the PVDF solution for the electrospinning. Nanowhiskers of bacterial cellulose are extracted by hydrolysis using sulfonic acid. PVDF-BCNW composite membranes with porous structure are prepared via an electrospinning method according to the BCNW contents. The crystallinity of the PVDF-BCNW composites through the XRD and DSC analysis are decreased as 50.2% and 43.7%, considerably, meanwhile, the electrolyte holding capacity of the PVDF-BCNW composite is increased as 760%, significantly. The actuating performance is also enhanced significantly as ±3.4 mm and 4.5 mm for the sinusoidal and step inputs. Electro active actuators based on the PVDF-BCNW composite produced by dipping and drying method showes significantly improved displacement because of the synergistic effect of ion migration and electrochemical doping process when the voltage is applied. A novel PVDF-BCNW actuators are useful for items such as biomimetic robots and other diverse applications.

Atomic-Scale Picture of the Ion Conduction Mechanism in a Tetrahedral Network of Lanthanum Barium Gallate

Combined experimental study of impedance spectroscopy, neutron powder diffraction, and quasielastic neutron scattering was performed to shed light onto the atomic-scale ion migration processes of protons and oxide ions in La0.8Ba1.2GaO3.9. This material consists of tetrahedral GaO4units, which are rather flexible, and rocking motion of these units promotes the ionic migration process. The oxide ion (vacancy) conduction takes place on channels along the c axis, involving a single elementary step, which occurs between adjacent tetrahedra (intertetrahedra jump). The proton conduction mechanism consists of intratetrahedron and intertetrahedra elementary processes. The intratetrahedron proton transport along the c axis is the rate-limiting process, with activation energy of 0.44 eV. The intertetrahedra proton transport has the activation energy of 0.068 eV.

Multiscale Simulation of Ion Migration for Battery Systems

ABSTRACTIn this paper we describe a multi-scale approach to ion migration processes, which involves a bridging from the atomic scale to the macroscopic scale. To this end, the diffusion coefficient of a material i.e. a macroscopic physical quantity, will be appropriately determined from molecular dynamics simulations on the microscale. This way, performance predictions become possible prior to material synthesis. However, standard methods produce in general wrong results for ensemble setups which correspond to battery or capacitor applications.We introduce a novel method to derive correct values also for such problems. These values are then used in a macroscopic system of partial differential equation (Poisson-Nernst-Planck system) for the numerical simulation of ion migration in a battery.

Performance and stability of (La,Sr)MnO3–Y2O3–ZrO2 composite oxygen electrodes under solid oxide electrolysis cell operation conditions

The electrochemical performance and stability of (La,Sr)MnO3–Y2O3–ZrO2 (LSM-YSZ) composite oxygen electrodes is studied in detail under solid oxide electrolysis cells (SOECs) operation conditions. The introduction of YSZ electrolyte phase to form an LSM-YSZ composite oxygen electrode substantially enhances the electrocatalytic activity for oxygen oxidation reaction. However, the composite electrode degrades significantly under SOEC mode tested at 500 mA cm−2 and 800 °C. The electrode degradation is characterized by deteriorated surface diffusion and oxygen ion exchange and migration processes. The degradation in electrode performance and stability is most likely associated with the breakup of LSM grains and formation of LSM nanoparticles at the electrode/electrolyte interface, and the formation of nano-patterns on YSZ electrolyte surface under the electrolysis polarization conditions. The results indicate that it is important to minimize the direct contact of LSM particles and YSZ electrolyte at the interface in order to prevent the detrimental effect of the LSM nanoparticle formation on the performance and stability of LSM-based composite oxygen electrodes.

Proton Conductivity Studies of Y-Doped Barium Zirconate: Theoretical and Experimental Approaches

The proton conductivities of BaZr1-xYxO3-δ (BYZ) pellet samples with x = 0.06 to 0.4 were studied. The analysis showed that the optimum doping concentrations for bulk and grain boundary proton conductivity were at x = 0.1 and 0.2, respectively. The activation energies of the proton conductivity in bulk were between 0.42-0.47 eV, and 0.68-0.82 eV in the grain boundary. To gain more insight into the ionic conductivity mechanism in BYZ, quantum simulations complemented with kinetic Monte Carlo technique was employed to simulate proton and oxide ion migration processes in 8-30 at.% BYZ supercell. The results reveal the effect of defect associations on the proton and oxide ion migration and confirm the domination of proton conductivity on the overall ionic conductivity at all doping concentrations throughout the temperature range of this study. The optimum doping concentrations for the proton and oxide ion conductivities were extracted and compared with the experimental results.