Ionic Conductivity Research Articles

Chitosan-based gel polymer electrolytes for high performance Li-ion battery

This study explores the use of glutaraldehyde-crosslinked chitosan-based gel polymer electrolytes (GPEs) in lithium-ion batteries (LIBs). GPEs are prepared by solution casting using two different molecular weights of chitosan including 150 kDa as medium and 400 kDa as high molecular weight (MMWCS and HMWCS, respectively) with varying amounts of crosslinker. Degree of crystallinity was 25.9 and 24.1 % for HMWCS and MMWCS, respectively that was decreased to 18.3 and 22.7 % by using 5 % crosslinker and 17.8 and 21.1 % by using 10 % crosslinker, and 17.2 and 17.6 % by using 20 % crosslinker. The obtained ionic conductivity for HMWCS and MMWCS was 3.1 × 10−3 and 2.9 × 10−3 S.cm−1. After crosslinking by 5, 10, and 20 % crosslinker, the ionic conductivity was obtained to 0.9 × 10−3 and 0.3 × 10−3 S.cm−1, 6.3 × 10−3 and 5 × 10−3 S.cm−1, and 1.1 × 10−3 and 0.5 × 10−3 S.cm−1 for high and medium molecular weight, respectively. Lithium-ion transfer number was obtained between 0.34 and 0.83 and the highest t+ value was obtained for the MMWCS-GA10. Electrochemical stability window of the prepared polymer electrolytes was >5 V and samples showed no remarkable dendrite growth after cycling analyses. The symmetric cells demonstrated reliable performance, operating for over 300 h without any short-circuiting, which indicates excellent reversible cycling stability for chitosan-based lithium-ion batteries. Furthermore, the Gr/GPE cell exhibited very low voltage polarization, with the over-potential decreasing from 10 mV initially to 6 mV after 300 h at the same current density. Discharge capacity was obtained higher than 170 mAh/g at 0.2C with CE = 97 % for both HMWCS-GA20 and HMWCS-GA20.

Influence of calcium-doped on the conductivity of NASICON-type Na3Zr2Si2PO4 solid electrolyte

Sodium-ion solid electrolyte has many advantages such as high safety, good ionic conductivity, and strong chemical stability. NASICON-type Na3Zr2Si2PO4 solid electrolyte was prepared by high-temperature Solid State Reaction (SSR). X-ray Diffraction (XRD) show that the 20% excess addition of Na and P elements will reduce the formation of ZrO2 impurity phase and increase the ionic conductivity to 1.01×10−4 S cm−1. On the basis of this experiment, Ca was added to dope the Na site in Na3Zr2Si2PO4 with different contents. Electrochemical impedance spectroscopy (EIS) results show that the conductivity of Ca2+ doped Na2.7Ca0.15Zr2Si2PO4 is significantly increased to 1.53×10−4 S cm−1, the electronic conductivity is 3.99×10−8 S cm−1, and the activation energy is 0.32 eV. Cyclic voltammetry testing demonstrated stable chemical properties below to 5 V. Na | Na2.7Ca0.15Zr2Si2PO4 | Na3V2(PO4)3 battery still maintains a high capacity retention rate of 98.76% after 200 cycles at 25oC-0.2C. It indicating that the new 0.15molCa-doped Na2.7Ca0.15Zr2Si2PO4 has the highest electrical conductivity, which provides a new research idea for sodium-ion solid-state batteries and has great potential in solid-state battery applications.

Pre-existing mobile Zn2+ ions in ZnZr4(PO4)6 for capacitive- and battery- type energy storage systems

Zinc-ion based energy storage systems with a pure intrinsic Zn2+ ion conductor, ZnZr4(PO4)6 (ZnZrP), and consisting of variable valence Zr sites, are fabricated for the first time. Zn2+ ions are loosely held within the voids of the Zr-phosphate framework enabling ionic conduction in the solid matrix. By combining with activated carbon (AC), the resulting ZnZrP-AC composite exhibits a high mixed ionic-electronic conductivity of 1.25 mS cm−1. Benefitting from the high conductivity, fast charge transfer and transport across the ZnZrP-AC cross-section are enabled through short diffusion pathways in the resulting hybrid supercapacitor (HSC) or Zn-ion battery (ZIB). The HSC (ZnZrP-AC/ZnCl2-γ-butyrolactone/Zn-AC) delivers a specific capacitance of 275F g−1, energy and power density maxima of 153 Wh kg−1 and 7.2 kW kg−1 and a cycling life of 10,000 cycles, with 87.2 % capacitance retention. In the ZIB configuration of ZnZrP-AC/Zn(CF3SO3)2-acetonitrile/Zn-AC, a capacity of 136 mAh/g (at 50 mA g−1), with capacity retention of 95 % after 100 cycles is achieved, with a mixed diffusive and surface-confined fast charge storage mechanism. The active materials remain largely intact after cycling confirming the durability of the cell architecture with potential for scale-up and practical applications.

Robust, transparent, self-healable, recyclable all-starch-based gel with thermoelectric capability for wearable sensor

Conventional all-starch-based (ASB) gels are weak and lack ductility. The preparation of a robust ASB gel with multi-functionalities e.g., self-healing, anti-freezing, conductivity, and so forth, is highly desirable but challenging. Herein, a new kind of ASB gel was prepared by gelatinizing starch in urea and choline chloride solution (UC) with the aid of water. Its tensile strength was up to 1.08 MPa with a tensile strain of 313 %, and this value hardly changed after 10 days ageing. A high healing efficiency of 98 % can be achieved after 1 h of healing at room temperature, and the healed tensile strength reaches up to ca. 1.06 MPa, which is almost the highest value for ASB gel. The resultant ASB gel can surfer from bending and twisting at −80 °C. Moreover, ASB gel also exhibits excellent biocompatibility and biodegradability. In addition, UC endowed the ASB gel with ion conductivity, allowing it to be used as a flexible strain sensor to monitor human movement. The ion-conductive ASB gel also exhibited thermoelectric ability with a Seebeck coefficient of 2.5 mV K−1, which can be further improved to 5 mV K−1 with a maximum output voltage of 252 mV by introducing a gradient of ionic concentration.

Revealing the Interplay of Local Environments and Ionic Transport in Perovskite Solid Electrolytes.

Solid-state ionic conduction is significantly influenced by bottleneck sizes, which impede ion diffusion within solid lattices. Using aberration-corrected scanning transmission electron microscopy and multislice electron ptychography, we directly observed that increased La occupancy in the perovskite solid electrolyte Li0.5La0.5TiO3 correlates with reduced bottleneck sizes formed by four oxygen atoms connecting neighboring A-site cages. This correlation was also confirmed in local aperiodic regions, where smaller bottleneck sizes due to increased La occupancies affect the directionality and dimensionality of the Li+ ion conductivity. Furthermore, while prior studies have focused on averaged Li+ ion diffusion across different bottleneck areas or chemical environments, by devising a molecular dynamics (MD)-based methodology, we quantify the diffusivity of Li+ ions through specific bottleneck regions. Atomistic simulations, including nudged elastic band calculations and this MD-based methodology, revealed that larger bottleneck sizes correlate with smaller local migration barriers and higher local diffusivity. This study elucidates the relationship among local chemistry, lattice structure, and Li+ ion transport, providing insights for the design of advanced oxide solid electrolytes.

Polymer Electrolytes with High Ionic Conductivities at Freezing Temperature for Aqueous Hybrid Batteries.

Rechargeable and flexible aqueous batteries (ABs) have emerged as one of promising energy devices which is primarily due to the safety, environmental friendliness and economic efficiency. However, because of the freezing behavior of aqueous electrolytes, most ABs possess poor performance when the working temperature drops below zero. To solve this problem, a gel polymer electrolyte (GPE) with high ionic conductivity (IC) and frost-resistance is designed for aqueous Zn-Li hybrid batteries by a biomass-based polymers complex consisting of carboxyl modified sodium alginate (SA) and zwitterionic betaine (BA). Introducing iminodiacetic acid to enrich -COOH groups along the SA main chains could improve IC of the prepared GPEs to 41.27 and 20.96 mS cm-1 at 20 and -20 oC, respectively. At -20 oC, the discharge capacity of the resultant cell is two times higher than that of the liquid electrolyte-based cell, and the cell presents a capacity retention of 91.6% after 300 charge/discharge cycles at 1 C. This proposed strategy greatly improve the IC of GPEs at freezing temperature, which is expected to broaden the practical application of GPEs in wide range of temperature.

Long-term investigation of uniaxial compressive and self-sensing performances of ultra-high performance seawater sea-sand concrete incorporating superfine stainless wires: Insights into underlying mechanisms and theoretical models

Developing intrinsic self-sensing concrete is expected to provide a digital intelligence solution to address the infrastructure’s challenges in terms of safety, lifespan, resilience, and carbon emission reduction. Using seawater and sea-sand as well as corrosion-resistant conductive fillers to fabricate self-sensing ultra-high seawater sea-sand performance concrete (UHPSSC) with outstanding mechanical and durability performances is the prerequisite for realizing localized resource utilization and in-situ monitoring of marine infrastructure. However, the potential effect of ions from seawater and sea-sand on the long-term stability of mechanical and electrical performances cannot be ignored. This paper presents a long-term investigation of uniaxial compressive, electrical, and self-sensing performances of superfine stainless wires (SWs) reinforced UHPSSC under natural curing. The results show that incorporating 1.5% SWs improves the compressive strength, elastic modulus, peak strain, and toughness of UHPSSC by 25.0%, 11.7%, 33.8%, and 119.2%, respectively. The established statistical damage constitutive models based on Weibull strength theory highlight the roles of SWs in delaying crack initiation. The dense microstructure of SWs-reinforced UHPSSC inhibits the growth of expansive hydration products formed by corrosive ions, thus guaranteeing its long-term strength development. Additionally, due to incorporating 1.5% SWs, the electrical resistivity of UHPSSC is reduced by seven orders of magnitude, with a strain sensitivity of 119.1 under monotonic compressive loading and a monitoring stress range of 0-148.4 MPa, indicating that SWs-reinforced UHPSSC can sense its stress and strain while providing early warning of crack initiation and propagation. Benefiting from the rust-free property, micron diameter, and high aspect ratio of SWs, the primary conductive path of composites comprises the overlapping networks formed by low-content SWs, which are not influenced by the ion conduction of conductive ions. Hence, SWs-reinforced UHPSSC exhibits stable electrical resistivity and sensitivity during long-term curing, suggesting its considerable potential for long-term in-situ monitoring of marine infrastructure.

Characterization of Oxygen Diffusion and Catalytic Behavior of Composite Materials in Solid Oxide Fuel Cells Using the Non-destructive Adler-Lane-Steele Method

Solid oxide fuel cells (SOFCs) are technologically interesting because they provide high-efficiency energy conversion via an electrochemical reaction within the cells. To bring SOFC to market, researchers must develop highly electroactive, low-cost devices that are chemically stable in both high (800 – 1000 °C) and low (600 – 800 °C) temperatures, as well as optimize oxygen reduction in electrodes. The electrochemical performance of SOFC is highly dependent on the catalytic activity (or catalyst behaviours) of the electrode materials involved in the oxygen reduction reaction due to the slower oxygen reduction kinetics at lower temperatures. Understanding the fundamental properties of oxygen self-diffusion in solid-state ionic systems is critical for developing nextgeneration electrolyte and electrode material compositions and microstructures that enable SOFCs to operate at lower temperatures more effectively, durably, and affordably. To date, the most common method for evaluating electrocatalytic performance is electrochemical impedance spectroscopy (EIS), which causes sample damage due to its set-up procedure. As a result, modelling approaches have been used to better understand the reaction mechanism, oxygen diffusion coefficient, and kinetics of SOFC electrode reactions, including the mixed ionic electronic conductor (MIEC)-based electrode. Several models have recently been developed to represent the reaction mechanisms of SOFCs, with Adler-Lane-Steele (ASL) mathematical theory believed to be suitable for predicting oxygen gas diffusion through the pores of the MIEC-based materials. Hence, the aim of this paper is to validate the area-specific resistance of composite electrodes using the ASL modeling technique rather than the standard EIS analysis. The findings are significant in contributing to the development of a new non-destructive method for analyzing the catalytic behavior of SOFC components.

Exploring the Synergistic Potential: A Comprehensive Review of MXene-Based Composite Electrocatalysts

MXenes, a prominent category of 2D materials consisting of transition metal carbides, nitrides, and carbonitrides, have garnered significant interest since the introduction of Ti3C2Tx. This fascination arises from their exceptional attributes like their high special surface area, superb electrical conductivity, and remarkable mechanical strength. These qualities have established MXenes as top materials for electrocatalysis, a critical component of clean energy conversion technologies. Crucially, MXenes serve as the foundation for the next generation of electrocatalysts, aiming at high activity, selectivity, and sustainability.In electrocatalysis, MXene composites enhance the performance of various reactions, such as water splitting and fuel cell operations. When combined with metals, metal oxides, or other conductive materials, MXenes exhibit improved electrical conductivity and catalytic activity. These composites can achieve higher efficiency and selectivity in electrochemical reactions, making them suitable for sustainable energy applications. MXene composites also play an significant role in the development of supercapacitors, which are energy storage devices characterized by rapid charge and discharge capabilities. The high special surface area and excellent conductivity of MXenes increase charge storage and improve energy and power density. When MXene composites are mixed with materials such as polymers or other nanomaterials, they can further optimize these properties, leading to increased performance and longevity. Also in battery technology, MXene composites are used to improve the performance of anodes and cathodes. Their high capacity for ion storage and conduction contributes to higher energy density and faster charge/discharge rates. By combining MXenes with other materials, researchers are able to create advanced battery systems that overcome traditional limitations, resulting in batteries that are more efficient, durable, and capable of delivering higher performance. In this study MXene–Carbon composites, MXene-LDH composites, MXene-Polymer composites, MXene-MOF composites are reviewed and discussed. The versatility of MXenes is further enhanced when they are composited with various other materials. Such compositions allow for tailoring their innate properties, enabling a widespread range of applications. In terms of environmental implications, MXenes and their composites boast excellent reducibility, conductivity, and biocompatibility, making them very appropriate for use in environmental clean-up and protection applications.

Investigation of Ceria based Heterostructure Composite Mixed Matrix Membrane with Polybenzimidazole for Polymer Electrolyte Fuel Cell Application at High Temperature

In recent years Ceria based heterostructure composites are considered as one of the highest performing solid state ionic conductors, therefore we wanted to leverage the benefits of using these materials for high temperature Proton Exchange Membrane Fuel Cells (PEMFCs). In this study a Polybenzimidazole (PBI)/Ceria carbonate CHC (Ceria based heterostructure composite) membrane was prepared by drop casting method and tested as an electrolyte for a high temperature H2/Air PEMFC application in anhydrous condition. Inorganic composite of ceria and alkali metal carbonates (Li2CO3, Na2CO3) was prepared by solid state route to obtain Ceria carbonate CHC. X-Ray diffraction (XRD) study confirmed the formation of the heterostructure and their successful incorporation into the PBI membranes. Homogeneity of fillers inside the membrane was further verified by Energy Dispersive X-Ray Analysis (EDAX) and Scanning Electron Microscopy (SEM). 5wt% of inorganic powder induced inside the PBI fillers reduced the phosphoric acid uptake of composite membrane (∼17% less) compared to pristine PBI membrane, which ultimately resulted into a lower swelling and dimensional change of the composite membrane. Thermal robustness of the phosphoric acid doped composite and pristine PBI membranes was investigated by thermogravimetric analysis (TGA) which showed that the prepared membranes were gone under a less than 10% reduction in weight up till 200ºC, ensuring their validity of application in high temp PEM fuel cells. The added inorganic functionalities resulted in a slight increase in the proton conductivity of PA doped composite PBI membranes i.e., 42.3 mS cm-1 at 180 ºC while for pristine PBI membrane it is 36 mS cm-1 at same temperature. A single cell with composite PBI membranes outperformed a pristine PBI membrane resulted into a ∼120% higher peak power density i.e., 320.88 mW cm-2. The composite membrane also displayed the excellent durability and showed a less than 10-4 mV/h degradation in cell potential till 180 ºC.

A one-step polyvinyl alcohol/polyacrylamide/polyacrylic acid/dimethyl sulfoxide/CaCl2 hybrid hydrogel enabling anti-fatigue, anti-freeze and anti-dehydration for wearable strain sensor

Hydrogel with fatigue resistance, freezing tolerant and dehydration resistance are peculiarly attractive in strain sensors. The hydrogel soaked in organic solvent is an effective strategy to improve freezing resistance and dehydration resistance, while this may result in poor conductivity. Moreover, ion-incorporation is considered to be the most feasible method for solving above concern, while high concentration of salt ions will result in weak mechanical properties. Therefore, the facile preparation of anti-freezing and anti-dehydration hydrogels with excellent fatigue resistance remains a challenge. Herein, a polyvinyl alcohol/polyacrylamide/polyacrylic acid/dimethyl sulfoxide/CaCl2 hybrid hydrogel was designed and fabricated through a facile one-step method to balance a variety of outstanding properties. On account of the hybridization design of multi-materials, the hybrid hydrogel exhibited high ionic conductivity (∼0.2 S/m), strength (∼0.36 MPa) and stretchability (∼825 %). Meanwhile, the hybrid hydrogel demonstrated prominent freezing resistance, dehydration resistance and fatigue resistance. The mechanical properties almost no deterioration after 1000 stretching cycle at 100 % strain, exposure to environment for 30 days or freeze at low temperature. Besides, the hybrid hydrogel-based stain sensor showed a linear sensitivity (GF = 1.12 over 0–400 % strain), quickly responsivity (200 ms), and could monitor various human activities steadily, demonstrating distinguished potential for use in wearable health monitoring and flexible electric skins.

Conduction channel creation by interstitial site engineering in otherwise insulating Na6ZnS4 for Na-conducting solid-state electrolytes

Na5.6Zn0.6Ga0.4S4, which retains the crystalline structure of its parent form Na6ZnS4, is described as a new class of Na-conducting solid-state electrolytes (SSEs) for all-solid-state batteries. We demonstrate that while Na6ZnS4 is ionically insulating (1.4 nS cm-1), Ga-substitution results in an astonishing improvement of ionic conductivity (σion) to 70.1 μS cm-1, making Na5.6Zn0.6Ga0.4S4 a practical SSE. This dramatic increase in σion (5 × 104 fold) is associated with an increased Na+ occupancy in interstitial sites as ‘x’ increases in Na6-xZn1-xGaxS4, where interstitial Na ions facilitate long-range Na+ conduction, which is otherwise immobile. Ga-substitution also results in phase-pure Na6-xZn1-xGaxS4, contributing at least partially to the enhancement of σion. Furthermore, Na6-xZn1-xGaxS4 exhibits neither releasing H2S gas nor compromising its crystalline structure for several hours under ambient conditions. Ga-substitution also enhances electrochemical stability. While the anodic limit remains largely unchanged, the cathodic limit is significantly lowered from 0.99 V vs. Na2Sn in Na6ZnS4 to 0.35 V in Na5.6Zn0.6Ga0.4S4, resulting in stable Na alloying/dealloying reactions in a symmetric Na2Sn ‖ Na2Sn cell. These findings are comprehensively supported by various experimental and theoretical methods. Finally, we construct a full cell (Na2Sn ‖ TiS2) and demonstrate the practicality of Na5.6Zn0.6Ga0.4S4 as a promising SSE in all solid-state Na ion batteries.

Radiation synthesis of high conductivity hydrogel based on tragacanth gum/poly (ionic liquids) for multimodal sensors and supercapacitor

Natural polymer-based hydrogels have found extensive use in flexible sensing, energy storage, and other fields because of their environmental sustainability and biocompatibility. Nonetheless, numerous challenges persist in the development of hydrogels with outstanding conductivity solely from natural polymers. Herein, we have successfully synthesized hydrogels based on natural polymer (tragacanth gum) and ionic liquids (1-vinyl-3-ethylimidazolium bromide) using a convenient and efficient one-step ionizing radiation method (TG/PIL hydrogels). The TG/PIL hydrogels exhibit high ionic conductivity (7.1 S m−1 at 25 °C), and can be used for multimodal sensors, including strain and temperature sensors. It has exceptional capabilities in monitoring human motor behavior, capturing subtle facial expressions and pulses beat. TG/PIL hydrogel can also accurately sense changes in the temperature of the external environment, and have significant thermal sensitivity within the range of 40 to 60 °C (−3.22 % /°C). Furthermore, the high conductivity of TG/PIL hydrogels enables them to exhibit outstanding performance in supercapacitor electrolytes, it has good stability in a certain load bearing range, temperature range, folding angle range. This work offers a straightforward technique for creating a multimodal hydrogel sensor, with promising applications in flexible wearable devices, energy storage, and beyond.

Robust polymer electrolytes with fast ion-transport nanochannels constructed by carbon dots for long lifespan Li metal batteries

As an anode material in energy storage systems, Li metal has exceptional merits, including high specific capacity, low density, and low redox potential. However, challenges such as lithium dendrites and unstable solid electrolyte interphase (SEI) hinder the practical application of lithium metal batteries (LMBs). Solid polymer electrolytes (SPEs), notably PVDF-HFP, are expected to overcome the above problems because of their mechanical merits and safe features, but their limited ion transportation behaviors result in insufficient ionic conductivity at room temperature. Herein, we invent an approach to prepare high performance electrolytes composed by porous PVDF-HFP and functionalized carbon dots (CDs). Such porous PVDF-HFP polymer membranes are created by a subtle phase inversion process, possessing a sponge-like structure, vertical lithium-ion transport channels and CDs decorated surfaces, thus able to uptake the liquid electrolyte (LE) to form gel polymer electrolytes (GPEs). The CDs fillers are produced in large scale with adjustable surface states, which can enhance Li salts disassociation to release free Li ions. As a result, the optimal conductivity of the as-prepared GPEs at room temperature is up to 8.7 mS cm−1 and the lithium transference number reaches 0.64. Our GPEs endow Li symmetric batteries with very stable SEI and long cycling life over 2200 h, and help realize high capacities and retention rates of the LMBs using LiFePO4(LFP) or LiCoO2(LCO) cathodes.

Improved ionic conductivity of La and Mg co-doped ceria nanocrystals synthesized by auto-combustion method

Ionic conductivity of La3+ and Mg2+ co-doped ceria, synthesized by auto-combustion method, is investigated here as electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFCs, operating below 800 °C). The prepared nanocrystalline electrolytes, LMDC10 (Ce0.9La0.05Mg0.05O2-δ) and LMDC20 (Ce0.8La0.1Mg0.1O2-δ) have exhibited improved ionic conductivities of 1.31 × 10−2 and 1.39 × 10−1 S cm−1 at 1073 K with reduced activation energies of 0.93 and 0.97 eV, respectively, when compared to conventional electrolytes like yttria-stabilized zirconia. The prepared samples are characterized by XRD, Raman spectra, XPS and FESEM which confirmed the formation of single-phasic cubic fluorite structure. Thus, the potential for La3+ and Mg2+ co-doped ceria electrolytes to offer cost-effective alternatives with low sintering temperatures and high performance for IT-SOFCs.

Effect of glycine doping on structure, linear optical properties, and ionic conductivity of ammonium dihydrogen phosphate crystals

Effect of glycine doping on structure, linear optical properties, and ionic conductivity of ammonium dihydrogen phosphate crystals

Chemical and electrochemical repair methods for the anchorage regions of grouted, post-tensioned concrete systems

Grouted, post-tensioned concrete systems are commonly used for constructing bridges with an intended corrosion-free service life of 100+ years. However, the use of inadequate grout materials and improper grouting techniques have caused voids at the anchorage regions – resulting in premature corrosion (say, within one or two decades) of strands. In addition, re-grouting the voids with repair grout has aggravated the corrosion of strands at the interface between the base grout (usually carbonated) and repair grout due to the differences in their chemical properties – raising concerns and leading to reluctance in re-grouting the voids in tendons. This work focused on developing non-invasive chemical (re-alkalization) and electrochemical (galvanic cathodic protection) methods to repair the anchorages of grouted, post-tensioned concrete systems. Immersion experiments were conducted to assess the efficiency of alkaline solutions in re-alkalizing the carbonated grouts. It was found that 1M Ca(OH)2 solution can restore the pH of the carbonated grouts in about a day. Moreover, the electrochemical impedance spectroscopy studies indicated that 1M Ca(OH)2 solution can re-passivate the embedded strands within a week. It can be sometimes challenging to achieve complete re-alkalization and re-grouting of voids; hence, a redundant electrochemical system that could work from outside the anchorage was found necessary. Therefore, experiments were conducted to evaluate the viability of galvanic anodes in protecting the anchorages. It was found that a thin layer of grout surrounding the strand would be sufficient to provide ionic conductivity for the galvanic anode (connected to the strand-end outside the anchorage) to protect the strand portions inside the anchorage. Based on the study, recommendations for the repair of the anchorage regions using chemical and electrochemical methods are presented.

Electrical properties and redox stability of series novel high-entropy Bi2VO5.5-based oxides

Exceptional high ionic conductivities have been well documented in the Bi2VO5.5-based materials. However, the poor phase and redox stabilities under a reducing atmosphere hindered their wide applications. Herein, with the aim to improve the phase and redox stabilities under a reducing atmosphere, a high-entropy strategy of multiple-metal-doping was applied to prepare series Bi2V1–4x(GaSiTaZr)xO5.5-δ (0 ≤ x ≤ 0.1) materials by a traditional solid state reaction method. The results revealed that multiple-metal-doping could stabilize the tetragonal phase of Bi2VO5.5 to room temperature and shown good phase and structural stabilities under inert or high oxygen partial pressure atmospheres, as well as pure oxide ion conduction which was about two orders of magnitude higher than that of the parent material, e.g. ∼2.0×10−2 S/cm at 400 ºC for the x = 0.05 sample while ∼1.5×10−4 S/cm for the x = 0 sample. Although the Bi2V1–4x(CuNiNbTi)xO5.5-δ materials would still be readily reduced under a reducing environment and introduce strong electronic conduction, the phase stability was apparently improved. Thus, improving the redox stability and suppressing the electronic conduction of the stabilized Bi2VO5.5-based materials under a reducing atmosphere is still the direction we should strive for.

Biopolymers as three-dimensional structural binders for nickel-cobalt sulfide supercapacitor electrodes

Ion diffusion and electron transfer are hindered by commonly used hydrophobic binders, which directly affect the electrochemical performance of the electrodes. Hydrophilic binders are selected to efficaciously solve the problem of relatively low actual specific capacitance and rate performance in the field of nickel cobalt sulfide electrode materials. In the paper, RuCoNiS electrodes were prepared using polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), xanthan gum (XG), and chitosan (CS) as binders. The surface wettability, morphological structure, specific surface area, and electrochemical performance of electrodes with different binders were analyzed by XRD, SEM, BET, CV, GCD, and EIS, etc. It's shown that the synthesis of CoNi2S is confirmed by XRD. The XPS results verify the existence of RuO2 and Ni2+/Ni3+ and Co2+/Co3+ redox couples. A cross-linked network structure is formed on the surface of the RuCoNiS by CS. The CS-RuCoNiS electrode has the largest specific surface area and microporosity. Ion migration in the electrolyte is facilitated by the excellent wettability of the CS-RuCoNiS electrode. The CS-RuCoNiS electrode reachs 1193.52 F g-1, which is 1.74 times higher than that of the PTFE-RuCoNiS electrode at 1 A g-1. The CS binder with its three-dimensional structure has the highest ionic conductivity of 2.29 × 10-4 S cm-1, a lower Rct, good cycling stability with a capacity retention of 84.3% after 5000 cycles at 200 mV s-1, and excellent rate performance of 85.6%. It can provide a practical application in supercapacitors.

Optimizing oxygen ion conductivity by modulating crystalline homogeneity

Keeping the stoichiometry at the optimal value required for electrical conduction throughout polycrystalline ceramics is crucial for various polycrystalline oxygen ion conductors. Using the photoluminescence spectrum of Eu3+ as a structural probe, the dependence between composition uniformity and conductivity was confirmed. We found that, for apatite La9.67×0.99Eu9.67×0.01Si6O26.505 (LSO) oxygen ion conductors synthesized by glycine nitrate combustion method, higher glycine content enhances the La/Si ratio uniformity, thereby improving the bulk conductivity. Surprisingly, thermal diffusion even at 1550°C cannot achieve uniform distribution when the precursor materials are not sufficiently homogeneous. Slight non-uniformity in the La/Si ratio is beneficial for impurities aggregation at high-density grain boundary regions, thereby alleviating the blocking effect of grain boundary on oxygen ion conduction. Both the bulk and total conductivities are higher than the best reported values in polycrystalline apatite by optimizing the La/Si ratio uniformity. The insight gained in this work is beneficial for enhancing conductivity by modulating crystalline homogeneity, and it facilitates further enhancement of ionic conductivity through cations doping for various polycrystalline oxygen ion conductors.