Alternating-current Impedance Research Articles

Preparation of Solid Electrolytes Containing Highly Concentrated Electrolytes and Effects of Solidifying on Physicochemical Properties

Currently, safety improvements for the electrolyte of conventional lithium-ion batteries is desired owing to their apprehending accidents of firing by contained flammable organic solvents. Safety ensuring is a very important issue for the expansion of larger sizes and applications. Recently, highly concentrated electrolytes containing an extremely high concentration of electrolyte salts are drawing attention as a new electrolyte design. The highly concentrated electrolytes reported unique characteristics such as greatly improved thermal stability and expanded electrochemical window(1). However, the solvation structure of highly concentrated electrolytes remains unclear. In this study, we proposed gel polymer electrolytes (GPEs) composed of highly concentrated liquid electrolytes using chemically cross-linked polyether-based polymers. We investigated the physicochemical properties and battery characteristics of GPEs. The aim of this study is to develop an electrolyte design that improved the safety and performance of rechargeable batteries.In this study, all GPEs were prepared in an Ar-filled glovebox. LiFSA+xEC (0.8≦x≦4) liquid electrolytes (LE) were prepared by mixing EC and LiFSA, and GPEs were also prepared by LiFSA+xEC (0.8≦x≦4), polyether-based polymers (P(EO/PO = 0.8/0.2)) and DMPA as a photoinitiator, and irradiated UV for 5 min. Prepared GPEs samples were evaluated for thermal properties, ionic conductivity, and solvation structure by thermogravimetry (TG), The self-diffusion coefficients (D) and Raman spectrometric method, respectively.To analyze the solvation structure of Li+ in the highly concentrated electrolytes, Raman spectra were measured in the wavenumber range of 680-860 cm−1. Figure 1 shows the obtained Raman spectra of prepared GPEs. The observed peak was attributed to the symmetric stretching mode of FSA- anion and confirmed shift to high wavenumber with LiFSA concentration. The peak shift of FSA- was suggested for the formation of aggregate structures by change of dissociation properties to contact ion pair (bound FSA-) from separated solvent ion pair (free FSA-).Figure 2 shows the TG curves of each GPEs. TG data was obtained the heating scan rate of 10 K min-1 from 303 K to 753 K. The thermal stability of GPEs improved with LiFSA concentrations. GPEs of high Li salt concentration were suggested the formation of aggregate structure, and the strong interaction between Li+- ethylene carbonate, formed a quite strong solvation structure. In general, the aggregate structure is caused by strong interaction between lithium cation and ethylene carbonate. Also, LiFSA+xEC electrolyte solution exhibited decreasing tendency of free EC and improvement of thermal stability(2). From the above results, a change of solvation structure in GPEs was suggested to improve thermal stability. Although LiFSA+xEC electrolytes showed multiple steps of thermal weight loss processes, prepared GPEs exhibited that in one step. Therefore, proposed component materials of GPEs achieved sufficient homogeneously without phase separation and lower thermodynamic activity of the solvent.The ionic conductivity(σ) of prepared GPEs was evaluated by alternating current(AC) impedance measurements using hermetically sealed cells. AC impedance measurements were conducted by cooling from 333 K to 263 K at 10 K intervals. The temperature dependence of the σ for the electrolyte using Arrhenius-type plots is shown in Figure 3. σ decreased with LiFSA concentration. σ also increased with temperature following with VFT equation. Also, LiFSA+xEC electrolyte solution exhibited tendency of the viscosity increased with LiFSA concentration(2). From the above results, decreased of σ with increasing concentration was due to increase viscosity.The self-diffusion coefficients (D) were measured by PFG-NMR with a superconducting magnet and equipped with a pulsed-field gradient multiprobe. Figure 4 shows the self-diffusion coefficients (D GPE and D LE) of ions and EC were measured between 333 K and 303 K to evaluate the diffusion behaviors in the electrolytes of x = 4.0.The order of D is D EC > D FSA > D Li for the diluted electrolyte of x = 4.0 and increasing D GPE with temperature. D GPE decreased with solidification compared to D LE. Figure 5 also shows the D GPE of ions and EC were measured between 333 K and 303 K to evaluate the diffusion behaviors in the electrolytes of x = 0.8. D Li increased compared to the electrolytes of x=4 relatively. Also, the order of D is D Li > D EC > D FSA in highly concentrated electrolytes at 333 K.The calculated t Li of the electrolyte at 333 K is shown in Figure 6. The t Li increases with the increased LiFSA concentration. The highest t Li was obtained when x = 0.80. The significant increase in the t Li at high LiFSA concentrations reflects faster diffusion of Li+ compared with anions.[1] Y. Yamada, A. Yamada, J. Electrochem. Soc., 162(14), A2406-A2423 (2015).[2] R. Furui, et.al, J. Phys. Chem. C, 127, 10748-10756 (2023). Figure 1

Electrochemical and Surface Analysis of Li10GeP2S12 Solid Electrolytes Synthesized Using a Solution-Based Method

All-solid-state batteries using flame-retardant inorganic solid electrolytes are expected to be the next-generation batteries with high safety and high output characteristics. For these, solid sulfide electrolytes with high ionic conductivity are required. Li10GeP2S12 represents a promising solid-electrolyte material for all-solid-state batteries owing to its high Li ionic conductivity (12 mS cm-1) at 27 °C [1]. To achieve practical application, Li10GeP2S12 should be synthesized using the liquid-phase method, which facilitates mass production. Our group has succeeded in a rapid synthesis of Li10GeP2S12 using excess sulfur as a solubilizer and a mixture of acetonitrile (ACN), tetrahydrofuran (THF), and a trace of ethanol (EtOH) as solvents [2]. However, Li10GeP2S12 synthesized using this approach exhibits lower ionic conductivity than that achieved using mechanical milling. In this study, Li10GeP2S12 were synthesized through the solution synthesis as the improved version. In addition, the particle characteristics of the sample synthesized by the solution synthesis were analyzed by transmission electron microscopy, particle size analysis, impedance measurements at low temperatures at 190 K, and X-ray photoelectron spectroscopy.Starting materials Li2S (Mitsuwa, 99.9 %), GeS2 (Wako, 99.9 %), P2S5 (Aldrich, 99%), and S (Aldrich, 99.8%) were mixed at a molar ratio of 5:1:1:10. The mixed powder was then added to an ACN-THF-EtOH solvent. After stirring and dissolution for 30 min, the obtained solution was vacuum-dried at 130 °C for 1 h. The precursor powder was then pelletized via uniaxial pressing. The pellet was then placed in a SiO2 tube using boats of different materials, such as quartz (SiO2), alumina (Al2O3), and titanium (Ti). Subsequently, the precursor pellet was subjected to heat treatment in a tube furnace at different temperatures (550, 650, and 750 °C) for 8 h to obtain the Li10GeP2S12 solid electrolyte powder. For comparison, this sulfite was also synthesized by mechanical milling. The crystal structure was evaluated by X-ray diffraction (XRD) measurements, the surface state was determined by X-ray photoelectron spectroscopy (XPS), and the grain size and morphology were determined by field-emission scanning electron microscopy. The ionic conductivity was also evaluated using alternating-current impedance measurements, and particle size distribution measurements and transmission electron microscopy observations were performed.The solution synthesis sample with the Ti boat exhibited an ionic conductivity of 5.5 mS cm-1, which is the highest among the extant liquid phase synthesis studies. According to the XRD patterns, impurity peaks (e.g., at SiS2) were hardly observed in the sample heat-treated in the Ti boat, and a decrease in the full-width-at-half-maximum metric was observed (Fig. 1). This result indicates that the use of a Ti boat can improve crystallinity and suppress side reactions. In comparison, the Li10GeP2S12 samples synthesized by mechanical milling exhibited ionic conductivities of 7.9 mS cm-1, higher than those achieved using solution synthesis, although the solution-synthesized sample exhibited a smaller particle size. This smaller particle size correlates with a higher grain boundary resistance, which leads to a lower total ionic conductivity. Moreover, a surface layer from the solvent was detected on the solution-synthesized particle surfaces according to XPS measurements. This surface layer contributes to a more stable interface of Li-In/Li10GeP2S12. We expect that these findings will enable the effective harnessing of particle states to develop sulfide solid electrolytes with high ionic conductivity and fine particles. Acknowledgments: This work was supported by JSPS KAKENHI (Grant Number JP 21K14716 and JP 22H04614), and the SOLiD-EV project (JPNP18003), SOLiD-NEXT project (JPNP23005) of the New Energy and Industrial Technology Development Organization (NEDO), and the GteX Program (JPMJGX23S5) of the Japan Science and Technology Agency (JST), Japan. The XPS experiments were conducted at the BL7U beamline in the Aichi Synchrotron Radiation Center, Aichi Science & Technology Foundation, Aichi, Japan (Proposal Nos. 202204118 and 202302109).

Parameter Optimization of Semiconductor Gas Sensor under AC Impedance Measurement.

Semiconductor gas sensors were confirmed to perform high linearity and a stable baseline under alternating current (AC) impedance measurements. However, a procedure to determine the optimal parameters of AC impedance measurements is still lacking. Taking the detection of SF6 decomposition gas as an example, this work has established a model of semiconductor gas sensors under AC impedance measurement. Employing four types of sensors to detect three gases (H2S, SO2, and CO), the effectiveness of the optimization method has been validated, as well. With the high linearity and stable baseline obtained from AC impedance measurement, it enables rapid correction of temperature drift within environmental temperatures ranging from 10 to 30 °C. Overall, the proposed method can provide a novel approach to inhibit the drift failure of semiconductor gas sensors.

Pressure-induced amorphization in α-GeO2: Structural evolution and improved dielectric properties

In this paper, we report the investigation of the structure evolution and dielectric properties of α-GeO2 under compression using in-situ Raman spectroscopic measurements, alternate current impedance spectroscopic measurements, and first-principal calculations. It is discovered that the coordination number of Ge in α-GeO2 increases from 4 to 6 at 5.0 GPa, while an amorphous state forms at 11.5 GPa and maintains to ambient conditions. The alternate current impedance spectroscopy measurements revealed that the variation of electrical resistance shows opposite tendencies at pressures against that of the coordination number. This phenomenon is ascribed to the pressure-induced emergence of unbonded oxygen atoms, and thus the increase of the concentration of oxygen ions in the GeO4 tetrahedra. Meanwhile，it is found that the application of pressure-induced amorphization improves the dielectric properties to a certain extent, which is of significant importance to provide a valuable approach for the synthesis of amorphous oxides with better dielectric properties.

Application of the upgraded design of the STM32F103 battery monitoring system based on hospital power

This paper presents a battery monitoring system based on an STM32F103 microcontroller for hospital power applications. The system adopts a modular design to improve reliability and maintainability. It can monitor the terminal voltage and alternating current (AC) impedance of each battery in a battery pack with up to 128 cells, as well as the ambient temperature, relative humidity and hydrogen concentration. The device includes a keyboard for parameter input, a liquid crystal display (LCD) for information display, and multiple communication interfaces. The proposed solution can automatically monitor the battery voltage and AC impedance. It also provides alarms to greatly improve the stability of hospital power system operation and reduce the workload of maintenance personnel.

Ultrahigh proton conductivity of four ionic hydrogen-bonded organic frameworks based on functionalized terephthalates

Recently, the utilization of hydrogen-bonded organic frameworks (HOFs) with high crystallinity and inherent well-defined H-bonding networks in the field of proton conduction has received increasing attention, but obtaining HOFs with excellent water stability and prominent proton conductivity (σ) remains challenging. Herein, by employing functionalized terephthalic acids, 2,5-dihydroxyterephthalic acid, 2-hydroxyterephthalic acid, 2-nitro terephthalic acid, and terephthalic acid, respectively, four highly water-stable ionic HOFs (iHOFs), [(C8H5O6)(Me2NH2)]∙2H2O (iHOF 1), [(C8H5O5)(Me2NH2)] (iHOF 2), [(C8H4NO6)(Me2NH2)] (iHOF 3) and [(C8H5O4)(Me2NH2)] (iHOF 4) were efficiently prepared by a straightforward synthesis approach in DMF and H2O solutions. The alternating-current (AC) impedance testing in humid conditions revealed that all four iHOFs were temperature- and humidity-dependent σ, with the greatest value reaching 10-2 S·cm−1. As expected, the high density of free carboxylic acid groups, crystallization water, and protonated [Me2NH2]+ units offer adequate protons and hydrophilic environments for effective proton transport. Furthermore, the σ values of these iHOFs with different functional groups were compared. It was discovered that it dropped in the following order under 100 °C and 98 % relative humidity (RH): σ iHOF 1 (1.72 × 10−2 S·cm−1) > σ iHOF 2 (4.03 × 10−3 S·cm−1) > σ iHOF 3 (1.46 × 10−3 S·cm−1) > σ iHOF 4 (4.86 × 10−4 S·cm−1). Finally, we investigated the causes of the above differences and the proton transport mechanism inside the framework using crystal structure data, water contact angle tests, and activation energy values. This study provides new motivation to develop highly proton-conductive materials.

Electrical modeling of an electrochemical sensor operating at the redox cycling mode

In this work, the direct current vs. voltage (DC) characteristics, and the alternate current (AC) impedance of a 1D four-electrode electrochemical cell, operating under redox-cycling conditions, are presented and discussed. The analysis refers to a four-electrode electrochemical system with one positively biased working electrode, one negatively biased working electrode, one auxiliary electrode, and one reference electrode operating in a redox cycling mode. This configuration is useful, for example, for electrochemical biosensors that can benefit from the inherent redox-cycling amplification of the apparatus. An aqueous buffered electrolyte is assumed, containing electrochemically active species that can be oxidized on the anode, with a positive overpotential. Meanwhile, the product of the oxidation reaction can diffuse to the other working electrode which has a negative overpotential, where the product is reduced. The analysis in this paper assumes that oxidation is the dominant mechanism at the anode, reduction is the dominant mechanism at the cathode, and the transport between them is dominated by diffusion. Since it is a 1D model, an ideal lossless redox cycling, i.e. both working electrodes’ currents (anodic and cathodic) are of the same magnitude with opposite signs, is assumed. Next, the small signal (AC) impedance of the electrochemical cell was calculated assuming that the AC signal modifies the oxidation reaction rate at the anode while the reduction reaction rate at the cathode is fixed. The impedance under redox cycling is calculated vs. frequency for various oxidation and reduction rates and both Bodé and Nyquist plots of the impedance are presented. The last part of the paper presents measured data for both DC and AC (i.e. Bodé and Nyquist plots) experiments with interdigitated array (IDA) electrodes, 5 & 10 μm spacing, operating under redox cycling conditions. The DC measurements were conducted in a 6 mM ferricyanide [K3Fe(CN)6] in 0.1 M Phosphate Buffer Saline (PBS) solution, pH 7.4. The AC measurements were conducted in 10 mM & 100 nM ferricyanide (K3Fe(CN)6) in 100 mM KNO3 aqueous electrolyte. A critical discussion follows the results section where the highlights and problems of the models are discussed.

Cyclic electrochemical reactions on a Li-metal negative electrode having a low-resistance interface with a solid-state electrolyte

Li metal is a promising negative-electrode material for high-energy-density all-solid-state batteries. However, the surface of Li metal is prone to oxidation, which results in the formation of a contamination layer at the Li metal–solid electrolyte interface. This interfacial contamination layer is the root cause of short-circuiting and poor cycle stability, thus hindering the development of all-solid-state batteries. Prior studies have not quantitatively assessed the effect of the above layer on battery performance. Herein, the degradation mechanisms affecting the interface are investigated using alternating-current impedance measurements and Li plating–stripping cycle tests for a symmetric cell. A thin contamination layer results in a Li–electrolyte interface with a low resistance of 0.20 kΩ cm2 and stable Li plating–stripping behavior at a current density of 3 mA cm−2, whereas a thick contamination layer results in a high interfacial resistance of 2.0 kΩ cm2. The thinning of the contamination layer on Li metal enhances the stability of the Li–electrolyte interface and Li plating–stripping kinetics.

Frequency varying heating strategy for lithium-ion battery rapid preheating under subzero temperature considering the limitation of on-board current

The electrical performance of lithium-ion battery gradually deteriorates with the temperature decrease. Alternating current (AC) heating is an efficient manner to improve the lithium-ion battery (LIB) discharge ability at low temperature. This paper proposes an effective method to quickly preheat battery under low temperature based on sinusoidal AC. An electrothermal coupled model is established to precisely characterize the battery electrical and thermal behavior characteristics. Subsequently, the impedance characteristics of large format prismatic LIB are investigated through electrochemical impedance spectroscopy testing. The amplitude and frequency of sine wave current exploited for battery pack heating are optimized at different temperatures and SOC based on the analysis of AC impedance. Finally, the sinusoidal AC heating for battery pack is achieved leveraging the designed full bridge inverter circuit-based heater and the heating efficiency with respect to different amplitudes and frequencies are comprehensively compared. On this basis, a frequency varying heating strategy with fixed amplitude considering the current limitation of hardware circuit is proposed. The experimental results show that the battery pack can be rapidly heated from −30 °C to 0 °C with the maximum average temperature rise rate of 3.78 °C/min, and the heating energy consumption rate is less than 0.27% SOC/°C with the proposed strategy. On this account, the battery pack discharge capacity under frigid environment can be distinctly enhanced based on the proposed heating strategy.

Study on influencing factors and regularity analysis of eddy current method applied to detection of reinforcement corrosion

Abstract Rebar corrosion is one of the main reasons for the deterioration of concrete structures. In order to ensure the safe operation of reinforced concrete structures, it is necessary to detect the corrosion rate of rebars in time. This article adopts the eddy current method based on electromagnetic induction to detect steel corrosion, studies the mechanism of alternating current (AC) impedance change induced by steel corrosion in coils, and establishes a mathematical model between steel corrosion and coil AC impedance. Meanwhile, the quantitative relationship between excitation signal frequency, concrete thickness, coil parameters, and coil impedance is studied. Through experiments, it was found that in the early stages of steel corrosion, there is a linear relationship between the scanning peak value of the coil impedance and the mass loss rate of the steel bars, and the slope of the fitting curve decays exponentially with the increase of the concrete thickness. The method used in this paper has an absolute error of less than 0.01 and a relative error of less than 8 % in detecting the mass loss rate of rebars at the initial stage of steel corrosion. When the concrete thickness is less than 20 mm, the relative error is lower than 4 %.

Discovery of eight-coordinated layered phase of SbBr3 under high pressure

Layered trihalides have attracted significant interest due to their potential applications in optical and spintronic devices. Herein, we report a combined experimental and theoretical investigation of antimony tribromide (SbBr3) under high pressure (up to 30 GPa) using synchrotron x-ray diffraction, Raman spectroscopy, alternating current (AC) impedance measurements, and first-principles calculations. The results indicate that SbBr3 transforms from a molecular phase (space group Pbnm) to an eight-coordinated layered phase (space group P21/a) at 7.6 GPa. A partial density of states analysis reveals that the eight-coordinated layered geometry of SbBr3 is rooted in the electron transfer from the Sb p orbital to the Br p orbital. Furthermore, based on AC impedance measurements, the resistance decreases with increasing pressure due to the gradual narrowing of the bandgap of SbBr3 in the Pbnm phase. The positive resistance–pressure relationship in the P21/a phase is attributed to the low carrier mobility caused by lattice distortion. Our current findings not only provide information on the phase diagram and electronic transport of SbBr3 but also expand the realm of layered functional materials in molecular trihalides.

Robust solid slippery surface for anti-corrosion: Experimental and simulation

Corrosion has long been an enduring obstacle for researchers. It is a challenge to make progress in corrosion protection technology and understanding corrosion mechanisms for quite some time. In recent years, the slippery surface has been applied for anti-corrosion. This novel surface gives new expectation to corrosion protection technicians. Even though some researchers have constructed lots of slippery surfaces for anti-corrosion, the robustness should be improved and the intrinsic anti-corrosion mechanism also needs to be clarified. Therefore, we fabricated a solid slippery surface (SSS) via electrodeposition combined with hydrothermal method followed by solid lubricant infused into a micro-nano “metasequoia” structure. The anti-abrasion performance was enhanced due to the special structure as well as the solid lubricant. Besides, the SSS showed thermal assisted self-healing property even after experienced abrasion. The corrosion resistance was evaluated by electrochemical experimental with the potentiodynamic polarization curve and alternating-current impedance technique. The Ecorr and Icorr of SSS were 0.029 V and 2.121 × 10−9 A·cm−2, respectively. Furthermore, the diffusion behavior and relative concentration of corrosive particles were analyzed by the molecular dynamics simulation method. The simulation results showed that the as-prepared SSS can provide a very superior anti-corrosion property with a simulated diffusion coefficient of 2.2 × 10−9 m2·s−1 for Cl−. This work provides technical guidance and theoretical support for the application of SSS in corrosion protection and can provide a reference for the anti-corrosion mechanism of SSS.

Extraction of Ag3Sn nanowires bundle and its electrochemical characteristics

The Ag3Sn nanowires (NWs) bundle embedded in the Sn-3.5Ag eutectic alloy bar directionally solidified was extracted by utilizing electrochemical selective corrosion, during which the Sn-base was dissolved and the Ag3Sn fibrous phase was remained. The diameter of Ag3Sn NWs decreases with the increasing of directional solidification rate, and their length increases with the corrosion duration. Utilizing the electrochemical alternative current (AC) impedance method and the cyclic voltammetry (CV), the interfacial impedance and the charge storage capacity of electrodes with Ag3Sn NWs bundle were tested in 0.9 % NaCl aqueous solution. The measuring results indicated that the lowest interfacial impedance appeared at the average length of nanowires with 8 µm, whereas the charge storage capacity was increased constantly with the length of Ag3Sn NWs. These electrochemical characteristics make the Ag3Sn NWs bundle electrodes possible to be applied as the electrophysiological electrode. A series of trial EEG (electroencephalogram) tests showed that the EEG signals of Ag3Sn NWs dry electrodes had a higher correlation to that of Ag/AgCl wet electrodes.

Corrosion Susceptibility of Blued Steel Reinforcement in Concrete by Electrochemical Impedance Spectroscopy

The main aim of this study is to quantify the rate of corrosion in reinforced steel bars embedded within concrete structures exposed to a simulated high-chloride marine environment. This involved selecting specific frequencies that corresponded to the solution resistance and charge transfer resistance, enabling faster measurements. A total of five cement mortar specimens were meticulously prepared for the investigation. The study focused on assessing the impact of variations in bluing temperature on corrosion minimization. Bluing was carried out at 450, 550, 650, and 750oC, and then immersing the specimens in a 3 wt.% NaCl solution for 21 days. Frequent tests, just after immersion, 7,14-, and 21-days immersions. Measurements through alternative current (AC) impedance were conducted across a frequency spectrum ranging from 100kHz to 10MHz. The results showed a significant decrease in the corrosion rate for specimens blued at 750, which was attributed to the development of thicker protective layers on the rebar. Higher corrosion rates were observed for bluing at lower temperatures.

Impedance behaviors under high pressure for DyFeO3 orthoferrite

An alternate current impedance spectrum up to 32.2 GPa was investigated to reflect the electrical properties of DyFeO3, where space charge plays the crucial role. Conductivity behaviors are determined by a universal dynamic response relationship. The band structure under various pressures was calculated by a density functional theory. The state density of d-shell electrons in conduction band varies with band gap, the reduction of which weakens the p-d coupling and leads to a conductivity transformation in the electrical transport process of O-phase. This work claims a reasonable electrical model for RFeO3 family, which is essentially impacted by high pressure.

Exploring the piezoresistive sensing behaviour of ultra-high performance concrete: Strategies for multiphase and multiscale functional additives and influence of electrical percolation

Self-sensing ultra-high performance concrete (UHPC) features superior mechanical capacity, excellent erosion resistance, long life cycle, and broad range of stress sensing, and is expected to be a pathway towards next-generation smart cementitious composites. This study presents a novel strategy to achieve electrical percolation and elevate the piezoresistive sensing capability of UHPC through the incorporation of multiphase and multiscale functional additives including graphene (G) and carbon nanotube (CNT). The workability, compressive strength, microstructural characteristics, and alternating current (AC) impedance response are investigated. The effect of electrical percolation on the piezoresistive behaviour is studied and discussed using various ratios of G/CNT. Results indicate that as the G/CNT ratio decreases from 4:0 to 0:4, the compressive strength is reduced from 194.7 MPa to 166.3 MPa due to the certain increase in the plastic viscosity of fresh mixture and the proportion of harmful pores, although the basic requirement of 150 MPa is met. Moreover, the AC impedance response significantly moves left and the radius of high-frequency arc reduces from 72910 Ω to 1295 Ω, suggesting electrical percolation. Bounded by percolation threshold, the fractional change of resistance curves can be divided into a two-stage pattern (i.e., linear and nonlinear stages) and a three-stage mode (i.e., linear decrease, balance, and abrupt increase stages). An underlying mechanism is proposed to explain the tremendous change in piezoresistive behaviour of self-sensing UHPC, considering the tunneling-percolation theory and electromechanical coupling behaviour. Additionally, the gauge factors range from 11 to 28, which is higher than most of the existing reported values, demonstrating the great potential of using hybrid functional nano-additives in self-sensing UHPC.

Relationship between Alternated Current Impedance Spectrum and Microstructure of Graphene Enhanced Concrete

This study presented experimental research on the alternating current (AC) impedance spectrum of graphene-enhanced cement matrix composites with dosage amounts of 0.1%, 0.2%, 0.4%, 0.8%, 1.6%, and 3.2%, respectively. The electrical properties were compared and analyzed with the Nyquist diagram, Bode diagram, and phase angle diagram. The microscopic pore structure was studied using mercury intrusion porosimetry (MIP) to establish the relationship between the pore structure parameters, the equivalent circuit fitting parameters of the AC impedance spectrum, and the mechanical properties. This study found that the incorporated graphene decreases the arc diameter of the impedance spectrum and causes the slope of the straight lines of the low-frequency region to drop. For the Bode curves, within low frequencies (1 Hz and 10 Hz), the impedance gradually increases as the graphene dosage increases. However, when the frequency is between 100 KHz and 1000 KHz, the impedance drops with an increase in the amount of graphene. According to the MIP test results, the proper incorporations of graphene increase the proportion of pores below 0.1 μm, which leads to a denser micro-structure and higher strength.

Pressure-induced ionic–polaronic–ionic transition in LaAlO3

Combining alternate-current impedance spectrum measurement and first-principle calculations, we thoroughly analyzed the electrical transport behavior of LaAlO3 under high pressure. A pressure-induced ionic–polaronic–ionic transition has been discovered through impedance spectroscopy measurements. Through first-principle calculations, we have elucidated the physical origin of the emergence of polaronic conduction, which results from the distortion of electron density background around Al and O atoms. Furthermore, the discontinuous changes in the starting frequency of ion migration fW, relaxation frequency fb, and ionic resistance Ri have been found at around 13.2 GPa, which can be ascribed to the phase transition of LaAlO3 from rhombohedral to cubic phase. Pressure can enhance the migration of O2− ions, causing an increase in the ionic conductivity of LaAlO3. This research will deepen our comprehension on the ion migration in solid electrolytes.

Phosphate-based gel polymer electrolyte enabling remarkably long cycling stable sodium storage in a wide-operating-temperature

Gel polymer electrolytes are regarded as one of the efficient strategies to substitute traditional liquid electrolytes for achieving safer high energy density sodium ion batteries. However, operating under wide temperature range especially at low temperature under zero is still a great challenge for most gel polymer electrolytes and becomes a hindrance to sodium ion batteries further development. Herein, a multifunctional phosphate gel copolymer electrolyte with larger crosslinking degree and encapsulation over a broader operation temperature range (−20 to 70 °C) is designed and synthesized via in situ free radical copolymerization. This gel polymer electrolyte displays a wide electrochemical stability window up to 5.1 V (vs. Na+/Na) and high ionic conductivity even at low temperature of − 20 °C (>1.0 × 10−3 S cm−1). Moreover, its outstanding interfacial stability is confirmed via alternating-current impedance and Na plating/stripping experiments. The morphology and X-ray photoelectron spectroscopy data of separators after long cycling suggest the gel electrolyte has ability to inhibit the decomposition of liquid electrolyte and suppress the growth of sodium dendrite, hence enhance the cycling stability of battery efficiently at wide temperature range. As a result, the assembled gel Na||Na3V2(PO4)3 battery delivers outstanding ultralong cycling stability with superior discharge capacity retention over wide temperature range, including at room temperature (0.002% capacity decay per cycle for 3000 cycles), 60 °C (0.005% fade per cycle for 1500 cycles) and −10 °C (0.002% fade per cycle for 1200 cycles).

Proton Conductive Mononuclear Hydrogen-Bonded Cobalt(II) Spin Crossover Complex

The development of molecule-based switchable multifunctional materials remains an important challenge in molecular science. In particular, achieving high proton conductivities in spin crossover (SCO) compounds is of significant interest as the spin state can be controlled via proton transfer induced by an electric field, which leads to magnetoelectric effects and molecular spintronics. However, to the best of our knowledge, no studies have reported on proton-conductive SCO complexes. Thus, herein, we demonstrated the high proton conductivity of a mononuclear hydrogen-bonded Co(II) SCO compound, [Co(COOH-terpy)2](ClO4)2·4H2O (1·4H2O; COOH-terpy = 4′-carboxyl-2,2′:6′,2″-terpyridine). The [Co(COOH-terpy)2] 2+ cation assembled in the solid state via hydrogen-bonding between lattice water molecules and formed a 1D hydrogen-bonded chain. Each 1D chain was linked via CH−π interactions and C–C interactions and produced a complicated 3D supramolecular framework. Magnetic susceptibility and alternative current impedance measurements for 1·4H2O revealed incomplete spin transition behaviors and high-proton-conduction behaviors in identical temperature regions. 1·4H2O exhibited a proton conductivity of 1.68 × 10–3 S cm–1 at 353 K and 98% relative humidity. Notably, this is the first example of a proton-conductive mononuclear SCO compound having the hydrogen-bonding networks. Thus, the results of this study can be used to develop new design guidelines for molecular proton conductors, further leading to the development of multifunctional molecular switching materials.