Clay mineral crystals are mostly formed by stacking layers of silicon-oxygen tetrahedral sheets and aluminum-oxygen octahedral sheets. They basically have water absorption and expansion because of their unique layered crystal structure. Clay minerals after hydration and expansion usually cause serious engineering problems, which have a negative impact on engineering construction. They have received extensive research attention. It is generally believed that the hydration expansion of clay minerals is mainly divided into two stages, i.e., crystal expansion and osmotic expansion. Crystal expansion is caused by the expansion of water molecules into the interlayer of clay minerals. Permeation expansion is due to the lattice substitution of clay minerals, which leads to the imbalance of valence and electricity of the crystal. Massive exchangeable ions are gathered on the surface of the crystal. After these ions are dissociated in water, they will repel each other with negative charge under the action of the diffusion double layer, resulting in expansion. Compared with osmotic expansion, the degree of crystal expansion is small, kaolinite, illite, pennine and other interlayer cation-free clay minerals do not have an expansibility. However, the problem of expansion disaster occurs under the working condition rich in pennine, indicating the research value of pennine hydration expansion. However, the water absorption characteristics, expansion characteristics and hydration mechanism of pennine in nano-scale are not yet clear, and related research needs to be carried out. In this paper, a molecular dynamics study on water absorption of mesophyll pennine was carried out to explain the hydration characteristics of mesophyll pennine nanocrystal structure. The changes of energy, structure and chemical bond of mesophyll pennine in the process of hydration expansion were discussed.

The ring cutter samples with different pennine contents (i.e., 0%, 20% and 100%) were prepared with pennine mixed with quartz. The no-load expansion rate was measured. The particle size of the soil sample was controlled to be 200 mesh (0.075 μm), the density of the soil sample was 1.8 g/cm³, and the initial water content was 10%. The hydration degree of pennine with different water contents was analyzed by thermogravimetric analyzer, and the water content controlled was 0%, 5% and 10%. The microstructure and crystal parameters of pennine samples were analyzed by X-ray diffractometer and scanning electron microscope. The crystal model was established based on the results of the microscopic test. The sorption module was used to carry out the adsorption test. A hydration model containing different amounts of water molecules was established through the adsorption test. The geometry optimization task under the Forcite module was used to optimize the structure of the model. The molecular dynamics simulation of the model was carried out using the Dynamics task under the Forcite module, and the expansion deformation of pennine was simulated via dynamic calculation under the NPT ensemble. The Clayff force field suitable for clay minerals was used in the simulation process. The simulated temperature is 298 K and the simulated pressure is 0.001 GPa. The time step is 1 fs, the number of iteration steps is 100 000, and the truncation radius is 12.5 Å. The charge calculation method is the Forcefield Assigned. The non-bond energy Coulomb interaction was calculated by the Ewald sum method. The van der Waals interaction energy was calculated by an atom-based method.

The experimental results of the no-load expansion rate show that the no-load expansion rate of the ring knife sample increases with the increase of the content of pennine, indicating that the pennine has an expansibility. The thermogravimetric analysis shows that the higher the initial water content is, the higher the degree of hydration of the pennine will be. In addition to the free water adsorbed between the particles, some water molecules are bonded between the crystal layers via hydrogen bonding. The results of molecular dynamics simulation show that pennine is electrically neutral due to the simultaneous substitution of high-valence cations and low-valence cations, so the crystal expansion occurs. After the water molecules enter the interlayer, they are embedded in the hexagonal holes of the silicon-oxygen backbone layer. The oxygen atoms in the water molecules form a hydrogen bond connection with the hydroxide ions in the talc layer, which controls the hydration limit of the pennine crystal. In the process of hydration and expansion of pennine, it is dominated by electrostatic interaction energy, and followed by van der Waals force, and the bond stretching energy is the smallest. Compared with montmorillonite, pennine hydration is more difficult. The peak of the radial distribution function of water molecules shifts to the right as the degree of hydration increases, indicating that the spacing of water molecules and the diffusivity of water molecules increase. After massive water molecules enter the crystal, the total number of hydrogen bonds increases, the average coordination number of oxygen atoms and hydrogen atoms increases. However, the hydrogen bond length increases, the bond angle decreases, and the crystal expands.

The experimental and simulation results showed that when water molecules entered the interlayer of the crystal, pennine expanded slightly, which was consistent with kaolinite and illite without cations in the interlayer. The hydration expansion of pennine conformed to the linear growth law as a whole. Pennine crystals continued to expand until the limit as the hydration degree increased. The lattice constants in the limit state were a of 21.52 Å, b of 18.61 Å, and c of 14.54 Å. The limit adsorption amount of the crystal was controlled by the crystal structure. After water molecules entered the interlayer of the crystal, the adsorption site was in the hexagonal holes of the silica backbone layer, and each hexagonal hole could only adsorb one water molecule. When the water-absorbed pennine expanded under dynamic conditions, the electrostatic interaction energy was the largest, the van der Waals force was the second, and the bond stretching energy was the smallest. When water molecules entered the interlayer of pennine, hydrogen bonds could be formed or strengthened. The coordination number of hydrogen and oxygen and the length of hydrogen bond formed increased, but the bond angle decreased with the increase of the number of water molecules.

Although the application of electrospinning technology address certain issues with lithium-ion batteries and a significant number of controllable negative electrode materials are reported, several factors must be taken into consideration when designing the more optimal structures to meet the market demand for high-performance lithium-ion batteries. Developing nanofibers with a diameter less than 50 nm as smaller nanofiber materials can provide shorter diffusion paths and faster lithium ion intercalation kinetics. The preparation of micro-/nano-structured composite fibers, such as using multi-nozzle electrospinning technology to achieve composite fibers with controllable size and morphology, introducing heteroatoms into nanofibers, the presence of heteroatoms on the carbon surface can improve the reaction activity and conductivity, thereby enhancing the storage capacity of lithium ions. Electrospinning flexible batteries can be also developed. For lithium-ion battery flexible negative materials, flexible negative materials have high porosity and interconnected open-hole structures, which can improve the ionic conductivity and mechanical strength, so they can be more suitable for electrode materials used in lithium-ion batteries. In addition, electrospun nanofiber materials can be applied in energy conversion and storage devices such as fuel cells, solar cells, lithium-ion batteries, and supercapacitors. This review is of great significance for the development of these energy storage devices and also paves a way for advanced battery systems such as lithium sulfur batteries, sodium-ion batteries, and lithium-air batterie. It is indicated that high-performance electrospinning technology could be applied in high-performance advanced battery systems in the near future.

Recent research on co solutions for the growth of SiC single crystals by HTSG method through various methods is represented. The research scope of solvents involves thermal physical performance parameters, C dissolution, thermochemical properties, thermodynamic properties, and other aspects. However, the existing research has not yet identified the optimal solubilizing system from a theoretical perspective, as well as the substantial impact of element ratios in various solution systems on crystal growth. There are still several difficulties in the research of solutions as follows:

1) It is difficult to test the mixed solution due to the high experimental temperature of the HTSG method. At present, it is possible to roughly predict the thermal and physical performance parameters of solutions through theoretical calculations, but equipment for the related experiments is unavailable and the cost is also high. Effectively improving the accuracy of simulation and conducing accurate predictions for experiments can be achieved via in-depth research on the changes in thermal and physical performance parameters of solutions.

2) The concentration of C in the solution is a key factor affecting the quality of crystal growth. The concentration of C is investigated both theoretically and experimentally under ideal conditions of thermal equilibrium. The seed crystals can experience melt-through during the remelting process of crystal growth, if the concentration of C in the solution is too low. On the contrary, if the concentration of C in the solution is too high, it is likely that crystallization can occur before the impurities on the surface of the seed crystal are completely melted. The situations above could seriously affect the quality of the crystal growth. It plays an important role in improving crystal quality via in-situ detecting the changes in C concentration inside the crucible.

3) The existing HTSG method usually uses graphite crucibles as a C source for crystal growth. As the temperature inside the crucible increases, graphite crucible is continuously corroded by the solution, presenting different shapes. Different shaped crucibles can seriously affect the stability of the flow field inside the crucible, and even change the trajectory of the flow field. In-depth research on the corrosion process of graphite crucibles by auxiliary solutions can effectively avoid negative effects caused by changes in flow field and temperature field in the later stage of growth.

Although there are still some difficulties to overcome in the study of solvents for the growth of SiC single crystals by the HTSG method with the continuous efforts of numerous research teams, some key issues are constantly proposed and solved. The research on solvents can also accelerate the pace of HTSG method for growing SiC single crystals, opening a door to low-cost and low-energy SiC single crystal growth.

This review provided a brief summary of the research progress in the application of machine learning to crystal growth, and discussed mainly three aspects, i.e., crystal structure prediction, optimization of crystal growth conditions, and methods of controlling crystal growth. In terms of crystal structure prediction, machine learning achieves significant results, but the accuracy and computational efficiency still need to be improved, especially for large-size, multi-component complex systems. In the future, it is necessary to further improve and develop algorithms to increase the accuracy and computational efficiency of prediction models. Regarding the optimization of crystal growth conditions, machine learning methods can predict the optimum parameter combinations, speeding up the optimization process. However, there are still some issues with data accuracy, process complexity, and model interpretability that need to be addressed. Future work should involve the integration of more machine learning algorithms, combined with theoretical and practical research, to develop reliable and interpretable models. In terms of methods for crystal growth control, machine learning algorithms can precisely control the crystal growth process, improving the stability and quality of crystal growth. However, there are still some challenges such as in-depth studies on the physical mechanisms of crystal growth, the laws of control, and the simulation of complex systems with multiple coupled factors. In the future, it is necessary to combine advanced machine learning algorithms and optimization methods to enhance the simulation of multi-factor coupling and complex systems, further improving the control capability of crystal growth.

As a semiconductor material with superior optical properties, amorphous TiO₂ with the valence band, conduction band, and bandgap structure of crystalline TiO₂ is prone to forming a loose porous structure with more surface defects. During the photocatalytic reaction process, it can generate a large number of electron and hole capture traps, which is conducive to improving a photocatalytic efficiency. However, its photocatalytic activity still needs to be improved. Widening its absorption range, narrowing its band gap and promoting the migration of the internal electron-hole to the surface to react with the target product are all still the current important research aspects.

Doping or loading is a normal modification method of TiO₂. The doping with rare-earth element La is simple and effective, narrowing the band gap of TiO₂ and reducing the energy consumption of photocatalytic reaction. To further improve the photocatalytic activity, loading La-TiO₂ on SBA-15 can be an effective option. The high specific surface area and the mesopores of SBA-15 can be beneficial to the dispersion of the active component and the diffusion of reactants, thereby improving the photocatalytic performance. In this paper, TiO₂ was firstly doped with La, and La-TiO₂ was then supported on mesoporous molecular sieves SBA-15. The obtained catalyst La-TiO₂/SBA-15 was characterized and applied in the photocatalytic oxidation desulfurization for the model and real diesel oil. In addition, the photocatalytic reaction mechanism was also proposed.

4 mmol tetrabutyl titanate was dropped slowly into a solution of 0.9 mL of deionized water with 10 mL of absolute ethanol under magnetically stirring until a white gel was generated. After stirring for 0.5 h, the white gel was aged at 25 ℃ for 14 h, and then stirred at 40 ℃ until the absolute ethanol was completely evaporated. This white powder becomes an amorphous TiO₂ after drying at 100 ℃ and grinding. The synthesis process of La-TiO₂ was similar to that of amorphous TiO₂. However, deionized water was replaced with a solution of lanthanum nitrate (Its concentration was calculated according to the doping amount of La). To support La-TiO₂ on SBA-15, lanthanum nitrate and tetrabutyl titanate were put into 10 mL absolute ethanol. The ratio of the feed stocks in this mixture is same as that of the synthesis of La-TiO₂. SBA-15 mesoporous molecular sieve was also put into this mixture, and the loading of La-TiO₂ on the supported catalyst was 10% (in mass content). 1 mL deionized water was dropped slowly into the mixture under stirring.

The X-ray diffraction (XRD) patterns of the samples were determined on a model D/max-RB X-ray diffractometer with Cu-Kα radiation operating at 40 kV and 150 mA. The composition of the catalyst was identified by a model D/max-R X-ray fluorescence spectrometer (XRF) with a tungsten target at 40 kV and 50 mA. The elemental quantitative or semi-quantitative analysis was carried out based on the characteristic peak intensity of each element. The pore structure was characterized by a model ASAP 2010 physical adsorption instrument (BET). After 16-h pretreatment in vacuum at 110 ℃, N₂ adsorption-desorption was operated at -196 ℃. The transmission electron microscope (TEM) images were determined on a model JEM-2010CX electron microscope at 200 kV. The Fourier-transform infrared spectra (FT-IR) in the range of 4 000-400 cm^-1 were recorded on a model WQF 510 spectrometer at a resolution of 4 cm^-1. The UV-Vis diffuse reflection spectra (UV-Vis) were recorded on a model Cary 2450 UV-Vis spectrometer with BaSO₄ as a reference sample in the wavelength range of 200-800 nm. The photoluminescence (PL) spectra were recorded on a model FluoroMax-4 spectrofluorometer, which was excited at 240 nm in the scanning range of 260-460 nm. The valence-band X-ray photoemission spectroscopic data (VB-XPS) were obtained on a model ESCALAB 250 X-ray photoelectron spectrometer equipped with an Al Kα X-ray source and the spot size of 500 μm. At ambient temperature, PODS reaction was operated in a beaker under magnetically stirring. 10 mL model or real fuel was added firstly into a beaker, and then some amount of CH₃OH as an extractant (calculated in volume ratio of the extractant to the fuel), a catalyst (calculated in the mass percent in the model fuel) and H₂O₂ (calculated in n(O)/n(S)) were added. The beaker was placed in the dark under magnetically stirring for 0.5 h to establish adsorption-desorption equilibrium of DBT on catalysts. PODS proceed under the visible light irradiation and the samples were withdrawn periodically every 0.5 h from the upper phase, and the sulfur content of the clear liquid sample was detected on a model TSN-5000 sulfur nitrogen detector after high-speed centrifuge.

Catalyst was separated from the reaction mixture via filtration and washing with deionized ethanol, dried at 80 ℃ and then directly used for the next run.

Four PODS processes were repeated, and in each process 1.0 mmol/L a kind of active intermediate capture agent was added. Isopropanol (IPA), p-benzoquinone (p-BQ) and disodium ethylenediaminetetraacetate (EDTA-2Na) were used for detecting hydroxyl radicals, superoxide radicals and holes, respectively.

The XRD patterns show that La-TiO₂/SBA-15 retains a two-dimensional hexagonal highly ordered mesoporous structure of SBA-15. TiO₂, La-TiO₂ and La-TiO₂/SBA-15 do not show any characteristic diffraction peaks, indicating that they all are amorphous. Compared with the sample SBA-15, the specific surface area, pore volume and pore size of sample La-TiO₂/SBA-15 decrease due to the loading of La-TiO₂. However, its specific surface area is still higher than that of amorphous TiO₂. The TEM images present an ordered mesoporous structure of La-TiO₂/SBA-15, and La-TiO₂ is also evenly dispersive in the pore channels. The UV-Vis analysis shows that the absorption edge of La-TiO₂ is higher than that of TiO₂. A reason is that lanthanum doping reduces a band gap energy of TiO₂ and improves a light absorption ability of the catalyst. Although a band gap width is almost unchanged for loading. The PL spectra indicate that the intensity of fluorescence emission peak decreases after doping and loading, proving that the doping and loading both can reduce an electron-hole recombination rate, thereby prolonging the photogenerated carrier lifetime of amorphous titania material.

The effect of reaction condition on the results of PODS was investigated and optimized. The results are obtained under optimum conditions (i.e., catalyst dosage of 1% (in mass fraction), n(O)∶n(S) of 15∶1, and the of agent: oil ratio of 1∶1). Under such conditions, the desulfurization rate is 95.12%, and it can still reach more than 85% after four runs of reusing. For La-TiO₂/SBA-15 as a catalyst, the active intermediate species in PODS were ·O₂^- and h⁺ based on active intermediate species capture experiments.

La-TiO₂/SBA-15 prepared had a two-dimensional hexagonal pore structure, a high specific surface area, and well-dispersion. Lanthanum doping broadened a light response range, increased the absorbance of the light, and reduced the photogenerated electron-hole recombination rate of TiO₂. La-TiO₂/SBA-15 had a higher catalytic activity rather than TiO₂ and La-TiO₂, and a good reusability. The main active intermediate species were ·O₂^- and h⁺.

With the continuous growth in energy storage demands for portable electronic devices, electric vehicles, and grid energy storage, rechargeable metal-ion batteries have found extensive applications in energy supply and storage due to their advantages of low self-discharge, high energy density, and environmental friendliness. One of the essential components of metal-ion batteries is the negative electrode material, and its physical and chemical properties are crucial for battery performance. However, in practical applications, there is still a shortage of high-performance negative electrode materials for metal-ion batteries. Traditional three-dimensional electrode materials suffer from limited storage capacity and less than ideal charge-discharge rates, primarily because of the limited number of lattice vacancies in their structure. This limitation hinders their ability to meet market demands, particularly in scenarios where faster charge-discharge rates are required, such as electric vehicles and grid energy storage. In contrast, two-dimensional materials offer advantages such as a larger specific surface area and enhanced metal ion diffusion, making them suitable for energy storage in batteries. Among two-dimensional materials, the emerging class of two-dimensional transition metal borides (MBenes) exhibits excellent electrical conductivity, structural stability, and high specific capacity. As a result, an increasing amount of research work is considering them as electrode materials for energy storage systems. Compared to traditional experimental research methods, first-principles computational techniques can better assist in designing novel high-performance electrode materials at the atomic and electronic scale. In this paper, we aim to explore the potential of h-Mo₂B₂ MBene as a negative electrode material for metal-ion batteries using first-principles calculation methods. We systematically investigate its structural stability, electronic structure, and electrochemical properties. The studies suggest that h-Mo₂B₂ holds promise as a prospective negative electrode material for application in metal-ion batteries.

In this paper the calculations are based on Density Functional Theory (DFT) first-principles methods, implemented using the Vienna Ab initio Simulation Package (VASP). The Projector Augmented Wave (PAW) pseudopotential approach is utilized, with a plane wave cutoff energy of 500 eV. The Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) is employed for the exchange-correlation functional. To account for the interaction between metal cations and 2D materials, van der Waals interactions are considered in the calculations. During the geometric structure optimization, energy and force convergence criteria are set to 10^-5 eV/atom and 0.01 eV/Å, respectively. The K-point grids used for h-Mo₂B₂ unit cell and 2×2×1 supercell calculations are 20×20×1 and 5×5×1, respectively. A vacuum layer with a thickness of 20 Å is included to eliminate the spurious interaction. Phonon spectra calculations are performed using density functional perturbation theory. Differential charge calculations are employed to study charge redistribution and transfer between adsorbed metal atoms and 2D materials. Bader charge analysis is utilized to assess the amount of charge transfer between the metal ions and the 2D material. The Climbing Image Nudged Elastic Band (CI-NEB) method is used to calculate the migration energy barriers and migration pathways of metal ions on h-Mo₂B₂.

The 2D h-Mo₂B₂ studied in this paper belongs to the P6/mmm space group within the hexagonal crystal system. It comprises three atomic layers stacked in a Mo-B-Mo sequence, with hexagonal B atomic layers situated between the upper and lower Mo atomic planes. To evaluate the dynamical stability of h-Mo₂B₂, phonon spectrum calculations were conducted, and no imaginary frequencies were observed throughout the entire Brillouin zone. This indicates that h-Mo₂B₂ exhibits dynamical stability. The band structure of h-Mo₂B₂ reveals numerous bands crossing the Fermi level, confirming its metallic nature. This exceptional electrical conductivity of h-Mo₂B₂ can significantly enhance the rate performance of electrodes. Adsorption energy is a fundamental criterion for assessing whether a material can be utilized as a negative electrode. The adsorption energies of Li, Na, Mg, and K on the h-Mo₂B₂ surface were calculated, and all exhibited negative values, indicating effective adsorption of all metal atoms on a monolayer of h-Mo₂B₂. Rapid charge-discharge rates are crucial for secondary batteries, and the migration energy barrier of metal ions is a key factor determining the charge-discharge rate. The migration energy barriers for the four metal atoms on the h-Mo₂B₂ surface are ranked as K (7 meV)<Na (10 meV)<Mg (37 meV)<Li (39 meV). The extremely low migration energy barriers suggest that Li, Na, Mg, and K can easily diffuse on h-Mo₂B₂, making it a promising high-rate electrode material. As a negative electrode material for lithium-ion batteries, h-Mo₂B₂ exhibits a theoretical specific capacity of 735 mA·h·g^-1, significantly surpassing graphite's 372 mA·h·g^-1. For sodium ion, h-Mo₂B₂ boasts a theoretical specific capacity of 314 mA·h·g^-1, while for magnesium ion, due to multilayer adsorption and divalent ions carrying more charge, it reaches 1 506 mA·h·g^-1, far exceeding the capacity for Li and Na. Theoretical calculations also indicate that h-Mo₂B₂ possesses low average open-circuit voltages of 0.36 V (Li), 0.47 V (Na), and 0.63 V (Mg), all within the 0-1 V range. This lowers the likelihood of dendrite formation in the negative electrode, thereby enhancing the safety and stability of metal-ion batteries. This paper, from a theoretical standpoint, elucidates and confirms the potential of h-Mo₂B₂ as a negative electrode material for rechargeable metal-ion batteries. It paves the way and provides valuable insights for the design of high-performance electrode materials.

Based on first-principles calculations, we systematically investigated the physical properties and electrochemical performance of 2D h-Mo₂B₂ MBene. It was found that h-Mo₂B₂ is dynamically stable and exhibits metallic conductivity. The diffusion barriers for metal atoms (M=Li, Na, Mg, K) on h-Mo₂B₂ are remarkably low, all being less than 0.04 eV, indicating that h-Mo₂B₂ can facilitate rapid charge and discharge when employed as a negative electrode material in metal-ion batteries. The theoretical specific capacities of h-Mo₂B₂ for Li, Na, and Mg are 753, 314, and 1 506 mA·h·g^-1, respectively. Furthermore, the average open-circuit voltages (OCV) for h-Mo₂B₂ with Li, Na, and Mg are calculated to be 0.36, 0.47, and 0.63 V, respectively. All these findings collectively support that 2D h-Mo₂B₂ MBene can serve as a high-performance negative electrode material for lithium, sodium, and magnesium ion batteries.

Polymer based dielectric capacitors are used in pulse power systems due to their ultrafast charge-discharge speed, mechanical flexibility, good reliability, light weight, and low cost. Although the breakdown strength of the commercial biaxially oriented polypropylene film (BOPP) capacitor is greater than 700 MV/m and the dielectric loss is less than 0.02%, its energy density is only 2-3 J/cm³, and its long-term service temperature does not exceed 105 ℃. Poly(ether imide) (PEI) as a linear polymer with excellent thermal and chemical stability has a high breakdown strength (E_b) and an extremely low loss, thus is widely used at high temperatures. Nevertheless, the discharged energy density of pristine PEI as low as 2.90 J/cm³ inhibits the enhanced energy storage performance. Composites composed of dielectric ceramic particle and polymer matrix have the combined advantages of a large dielectric constant of ceramic and a high breakdown strength of polymer. In this paper, titanium dioxide (TiO₂) particles were introduced into the PEI matrix to prepare a TiO₂/PEI composite, and the dielectric properties were analyzed.

TiO₂ particles were prepared by a sol-gel method, and TiO₂/PEI composites were prepared by a tape casting method. TiO₂ particles with a target content were firstly dispersed in NMP solvent under ultrasound for 60 min to form a stable suspension, and then the PEI particles were added into the suspension in a small amount repeatedly and stirred for several hours until a uniform and stable solution was formed. Subsequently, the suspension was cast on a smooth glass plate, and the thickness of the composite was controlled by a scraper. The composites were further dried in a vacuum oven at 120 ℃ for several hours to thoroughly remove the solvent. Finally, the electrode with the diameter of 2 mm was coated onto the film via ion sputtering before testing.

The relative dielectric constant of the composite is improved as TiO₂ content is increased. When the volume fraction of TiO₂ content is 9%, the relative dielectric constant of composite increases to 4.9, which is 1.75 times greater than that of pristine PEI. Moreover, at 25-150 ℃, the dielectric constant of 5% TiO₂/PEI composite increases from 4.3 to 4.5, showing that its dielectric properties are stable and independent of temperature. The conductivity polarization caused by diffusion current in the Cole-Cole curve shows a straight line with a certain slope, indicating that there are a few conductive paths in the composite. Thus, the characteristic breakdown strength E_b of composite is significantly enhanced in comparison with pristine PEI. The E_b of 5% TiO₂/PEI composite reaches 615 MV/m. The improvement of E_b is since TiO₂ particles hinder the expansion path of the electrical branches inside the composite, reducing the possibility of electrical breakdown, and the uniform distribution of TiO₂ particles in the PEI matrix weakens the distortion of the local electric field of the composite, and the uniform distribution of electric field can effectively improve the E_b of the composite. Also, the addition of TiO₂ improves the elastic modulus of the composite, which is conducive to the improvement of E_b. Its energy storage density U_dis of composite is 7.10 J/cm³, which is 2.3 times higher than that of pristine PEI and the discharged efficiency η is 94.9% due to the synchronous improvement of dielectric constant and breakdown strength. However, excessive TiO₂ ceramic particles form some inevitable defects such as holes and agglomerations that increase the electrical breakdown paths, thus weakening the breakdown strength and energy storage performance. While the breakdown strength and energy storage performance of the composite film at 150 ℃ are tested. Although E_b is lower than that at 25 ℃, its value is still as high as 487 MV/m. Compared with the case at 25 ℃, U_dis and η at 150 ℃ also decrease. At 150 ℃, the maximum U_dis of 5% TiO₂/PEI composite is 5.05 J/cm³, and η is 88.5%. The stability comparison of U_dis and η of 5% TiO₂/PEI composite film under 300 MV/m is further conducted at different temperatures. As the temperature increases to 150 ℃, the U_dis stability of 5% TiO₂/PEI composite remains 98.5% with a η stability of 97.4% in comparison with an U_dis stability of 99.5% and a η stability of 99.2% for pristine PEI. The faint decrease of U_dis and η at high temperature is due to the unavoidable massive dielectric loss and joule heat during the frequent charge-discharge processes. All these results prove that benefiting from an inherent low dielectric loss, TiO₂/PEI composite basically possesses a satisfactory fatigue resistance at room temperature and even at high temperatures.

TiO₂ particles were prepared by a sol-gel method, and TiO₂/PEI composites were prepared by a tape casting method. The addition of TiO₂ particles increased the dielectric constant and breakdown strength of the composite, improving its energy storage performance. At room temperature, the breakdown strength of TiO₂/PEI composite reached 615 MV/m, and the energy storage density was 7.10 J/cm³, which was 2.3 times greater than that of pristine PEI. And the charge-discharge efficiency could reach 94.9%. Moreover, when the temperature increased to 150 ℃, the maximum energy storage density of 5% TiO₂/PEI composite film was 5.05 J/cm³, while the charge-discharge density stability remained 98.5% with an efficiency stability of 97.4%. TiO₂/PEI composite prepared could have a great potential in high temperature capacitors due to the excellent energy storage performance and stability.

PCCs is a key technology for renewable energy conversion and storage. The degradation of oxygen electrode greatly increases the polarization resistance of the cell and causes obviously declined performance. It is thus urgent to improve the stability of oxygen electrode materials. A further research can be conducted in the following fields, i.e., the relationship between the composition and electrochemical performance of the oxygen electrode, the influence of microstructure evolution and morphology changes under a high humidity on electrochemical performance, and the corresponding degradation mechanisms; the thermal cycle stability and interface stability of oxygen electrode materials under actual operating conditions; the mechanism of the PCCs oxygen electrode poisoned by Cr and Si in a high humidified atmosphere, as well as corresponding detoxification strategies; and it is necessary for commercial application requirements to investigate the stability of large-area PCCs under typical operating conditions.

Aqueous zinc-ion battery is considered as one of the most promising candidates for large-scale energy storage device due to its low cost, high safety and recyclability. Compared with other alkali-based batteries, zinc-based batteries can realize energy storage through 2-electron charge transfer delivering a high specific capacity (820 mA·h/g) and low price. However, the existing development of zinc-ion battery is far from commercialization. Main challenges exhibit in three aspects, i.e., a serious dendrite effect caused by the uneven deposition of zinc ions in the battery; uncontrollable water-induced parasitic reactions such as hydrogen evolution reaction (HER) in acidic electrolyte; and metal corrosion and irreversible side reactions on surface of anode. These challenges result in a low coulombic efficiency, a shorten cycle life of battery and even serious security risks. In order to solve the shortcomings of zinc anode, some methods (i.e., zinc anode structure modification, electrolyte optimization and artificial interface layer (SEI) construction) are developed. Among them, a tunning electrolyte is a directive method to avoid negative side reactions and inhibit the dendrite growth. Electrolyte modification can realize a long-cycle-life zinc anode and a high efficient battery. In this paper, tetraethylene glycol dimethyl ether (TEGDME) was added into ZnSO₄ based electrolyte as s co-solvent to investigate the plating/stripping behavior of Zn metal. The reaction mechanism of co-solvation effect from multi-scale was analyzed.

All reagents with analytical purity were used without any treatment. For the preparation of bare electrolyte, 2.87 g of ZnSO₄·7H₂O was dissolved into 10 mL distilled water to prepare 1 mol/L ZnSO₄ electrolyte. For the preparation of co-solvent electrolyte, 2.87 g of dried lithium bistrifluoromethyl sulfonate (LITFSI) was dissolved into 10 mL dehydrated tetraethylene glycol dimethyl ether (TEGDME) in an argon glove box under stirring for overnight. The final concentration was controlled to 1 mol/L LITFSI/TEGDME. A mixed electrolyte was prepared via dissolving 5 mL aqueous ZnSO₄ electrolyte, 3 mL of LITFSI/TEGDME electrolyte, and 2 mL of distilled water. The mixture was stirred at room temperature for 2 h, and then aged for 12 h to obtain the final electrolyte.

The monitoring during charge/discharge process was carried out on a model EQCM-D instrument (AWS, A-20, Spain). In this experiment, a 12 mm diameter titanium-gold quartz wafer was used as a cathode, and a high purity zinc foil was used as an anode. The amount of electrolyte was 2 mL. Before the measurement, the cell was active at a low current density. Afterwards, the frequency and dissipation were recorded during the electrochemical process.

The surface roughness was determined by ex-situ atomic force microscopy (AFM) (EIS) method, The impedance detection during electrochemical process was carried out by in-situ electrochemical impedance. The distribution of relaxation times (DRT) analysis was carried out based on the in-situ EIS results. The electrochemical performance was measured on 1470E electrochemical workstation. The surface conditions of the two electrodes were analyzed by X-ray diffraction.

An electrolyte (Co-Solv) for aqueous zinc battery was designed via mixing aqueous electrolyte with TEGDME/LITFSI. The electrochemical measurement reveals that the Coulomb efficiencies (CE) of Co-Solv is 97.2%, which is higher than that of bare electrolyte based battery (i.e., 94.4%). The main reason is due to the co-solvent effect from water and TEGDME in Co-Solv electrolyte. This further confirmed by in-situ E-QCM results. Compared to the frequency and dissipation evolution during charge/discharge process, the surface electro-deposition process can be revealed. A rigid film with TEGDME/LITFSI can form on the top of anode, which further inhibits the occurrence of side reaction such as HER.

Based on the results by AFM, the roughness in the bare electrolyte increases after electrochemical process. The roughness surface is closely related to the side reactions. The formation of irreversible basic zinc sulfate affects the anode performance. In the Co-Solv based battery, the roughness decreases and a rigid film appears on the top of anode to avoid the side reactions. This protected film is dense and firm to inhibit the formation of dendrite.

According to the results from DRT analysis, the co-solvation effect can affect the double electric layer structure of the metal surface, and induce the uniform deposition of metal zinc via maintaining the stability of the local electric field on the electrode surface. Combined with the results by E-QCM and AFM, the addition of TEGDME/LITFSI can improve the electrochemical performance via inhibiting dendrite growth, reducing side reactions and blocking the HER.

TEGDME/LITFSI was a mixture adding into ZnSO₄ based electrolyte to optimize the plating/stripping behavior of Zn metal. TEGDME could partly replace water to combine with Zn²⁺ and form the co-solvent structure of Zn²⁺-TEGDME/H₂O. It was indicated that the electrochemical reaction could related to the electric double layer structure near anode. Co-solvents could regulate the deposition of metallic zinc via affecting and stabilizing the local electric field. This work could provide a perspective potential for further development and mechanism analysis of co-solvent systems.

Aqueous zinc-ion batteries (AZIBs) as one of the highly anticipated areas in the new generation of battery technologies have broad application prospects and potential. Compared to conventional lithium-ion batteries, AZIBs have higher safety, cost-effectiveness, environmental friendliness, and higher energy density, making them highly sought after in energy storage and renewable energy. Nevertheless, a high concentration of water molecules in the AZIBs can result in the decomposition of water into H⁺ and OH^- during the charging/discharging process, which triggers significant hydrogen evolution reactions and corrosion problems, ultimately compromising the stability of the metal zinc electrode. Meanwhile, zinc dendrites are easily formed due to the uneven zinc deposition. To address these issues, this paper innovatively proposed an electrolyte additive of ethylene glycol methyl ether (MECS) to enhance the stability of the zinc electrode. The impact of MECS electrolyte additives on the AZIBs performance was systematically investigated via the experiments and theoretical calculations.

An electrolyte was prepared via adding different concentrations of MECS into 2 mol/L ZnSO₄ solution. The concentrations of MECS additives used were 2%, 4%, and 9% (in volume fraction, referred to as '2% MECS', '4% MECS', and '9% MECS').

V₆O₁₃·H₂O was prepared. Firstly, 2.73 g of V₂O₅ and 4.52 g of H₂C₂O₄ were added to 40 mL of deionized water (referred to as "solution A") and stirred at 90 ℃ for 1 h. Subsequently, 10 mL of H₂O₂ and 30 mL of ethanol were added to solution A, which was then transferred to a high-pressure vessel lined with PTFE. The vessel was heated at 180 ℃ for 3 h. Finally, the product was filtered, washed with ethanol and deionized water for at least 3 times, and then the washed material was dried in vacuum at 60 ℃ for 24 h. The preparation steps for the cathode plate were as follows: V₆O₁₃·H₂O, conductive agent (acetylene black), and PVDF were mixed at a weight ratio of 7∶2∶1, with NMP used as a solvent, and stirred evenly. The obtained slurry was coated on Ti foil, and dried in vacuum at 80 ℃ for 24 h. The samples were characterized by nuclear magnetic resonance (NMR), Fouier transform infrared spectroscopy (FTIR) and Raman spectroscopy (RS). Also, the binding energy was calculated based on the density functional theory (DFT).

Based on the results by BMR, FTIR and RS, the shift of ¹H peaks and the stretching vibrations of O—H both indicate a change in the solvation structure of Zn²⁺ in the solution with the MECS additives. The analysis of the DFT calculation results reveals that the binding energy between MECS and Zn²⁺ is significantly higher than that between Zn²⁺ and H₂O, indicating the preference of MECS to coordinate with Zn²⁺ and replace the positions of water molecules in the solvation structure of Zn²⁺. The restructured solvation structure of Zn²⁺ reduces the number of active water molecules in the electrolyte, thereby lowering the activity of parasitic reactions and enhancing the stability of the metal zinc anode.

The effect of MECS additives on the electrochemical performance of batteries was thoroughly investigated via assembling Zn//Zn symmetrical cells, Zn//Ti cells, and full cells. Under relatively mild testing conditions (i.e., 0.5 mA/cm² and 0.5 mA·h/cm²), Zn//Zn symmetrical cells with MECS additives can cycle stably for 1 250 h, while those without MECS additives only cycle for about 250 h before short-circuiting occurs. The batteries with MECS additives demonstrate an excellent performance even under different testing conditions due to the regulation effect of MECS at the zinc anode/electrolyte interface.

A novel electrolyte additive (MECS) was developed to stabilize zinc metal anode. Based on experimental and theoretical calculations, MECS molecules could participate in altering the solvation structure of Zn²⁺, reduce the quantity of active water molecules at the zinc anode interface through strong coordination with Zn²⁺, resulting in a smooth zinc deposition and a decreased by-product formation. Consequently, Zn//Zn symmetrical cells assembled with the improved electrolyte demonstrated stable cycling for over 1 250 h. In addition, the assembled Zn//V₆O₁₃·H₂O full cell also showed an excellent performance, maintaining a high capacity even after 800 cycles at a current density of 1 A/g. This study could present a simple, effective, and economic electrolyte modification approach to achieve effective utilization of zinc in aqueous zinc-ion batteries, providing innovative pathways for the development of next-generation secondary batteries.