Silver niobate (i.e., AgNbO₃, AN) as a lead-free antiferroelectric material has a promising application in energy storage and photocatalysis. However, a lack of theoretical understanding due to the heterogeneity of ceramic microstructures affects its further development. In this study, high-quality [001]-oriented AN single crystal was grown with AgCl as a co-solvent. This crystal exhibited energy storage density and efficiency comparable to AN ceramic, along with superior photovoltaic performance. The [001]-oriented AN single crystal demonstrated exceptional withstand voltage characteristics, surpassing those of AN ceramic. This work could provide crucial insights into the optoelectronic performance of AN single crystals, paving a way for potential applications in high-energy storage capacitors, piezoelectric devices, and photocatalysis.

In this study, pure-phase raw materials were synthesized by a solid-state reaction method, followed by the growth of AN single crystals by a modified co-solvent method. The raw materials from Sinopharm Chemical Reagent Co., Ltd., China, were Ag₂O (99.7% purity) and Nb₂O₅ (99.5% purity), which were ground, dried, and then calcined in an oxygen atmosphere at 900℃ for 6 h to obtain pure-phase AN. The raw materials were mixed with a specific amount of AgCl (99.5% purity), and heated in double corundum crucibles in an oxygen atmosphere at 1180 ℃ for melting. The melt was then slowly cooled to 1140 ℃ for nucleation and further cooled to room temperature to obtain single crystals. Finally, the residual AgCl was removed through ammonia treatment.

The [001]-oriented AgNbO₃ (AN) single crystals exhibit higher phase transition temperatures, compared to conventional AN ceramics, due to their high crystallinity and specific orientation. These crystals also demonstrate exceptional optoelectronic properties, with a forbidden bandwidth of 2.82eV, enabling an effective UV absorption at below 440nm and stable visible light transmittance at above 470 nm. Furthermore, the [001]-oriented AN single crystal shows remarkable withstand voltage characteristics, maintaining a stability at a bias voltage of up to 190 V, significantly exceeding those of AN ceramic (i.e., ~10V). The leakage current increases linearly and symmetrically with voltage and optical power, highlighting their potential for high-voltage, high-power applications. In summary, the [001]-oriented AN single crystal offers unique advantages for photodetectors and optoelectronic devices due to their enhanced phase transition temperatures, superior optoelectronic properties, and exceptional withstand voltage characteristics. A future research can focus on further optimizing their performance and expanding their applications in optoelectronic technology.

In this study, high-quality [001]-oriented AgNbO₃ (AN) single crystals were grown with AgCl as a co-solvent. The crystals exhibited comparable energy density and conversion efficiency to the same-composition ceramics with higher phase transition temperatures due to their crystallinity and orientation. The forbidden bandwidth of 2.82 eV enabled an effective UV light absorption at below 440 nm and a good visible light transmittance at above 470 nm. The crystals demonstrated excellent withstand voltage characteristics, maintaining a stability at high bias voltage and exhibiting a linear relationship between leakage current and voltage/optical power. These results could underscore a potential of [001]-oriented AN single crystal for high-voltage, high-power optoelectronic applications.

Ultra-wide bandgap (UWBG) semiconductor materials have attracted extensive attention in the fields of optoelectronics, sensing systems, and high-power devices due to their high critical electric field, high-temperature resistance, and excellent photoelectric properties. In this paper, high-quality Sn⁴⁺-doped ZnGa₂O₄ crystals with a volume of approximately 10 cm³ were successfully obtained by the VGF method. The crystal structure of the grown Sn⁴⁺∶ ZnGa₂O₄ crystals was detected by single crystal X-ray diffraction (XRD), and their crystal quality was studied by high-resolution X-ray diffraction (HRXRD). In addition, the optical and electrical properties of the grown Sn⁴⁺∶ ZnGa₂O₄ crystals were investigated by UV-Vis spectroscopy, XPS, and Hall measurements. The results show that the optical properties are affected by the Sn⁴⁺ concentration, and it is demonstrated for the first time that the electrical properties of ZnGa₂O₄ single crystals can be controlled by the concentration of doped Sn⁴⁺. The carrier concentration of the grown Sn⁴⁺-doped ZnGa₂O₄ single crystal at room temperature is higher than that of previously studied ZnGa₂O₄ single crystals (1.39 × 10¹⁹ cm^-3) and Sn⁴⁺-doped β-Ga₂O₃ (3 × 10¹⁸ - 3 ×10¹⁹ cm^-3). The improved photoelectric properties of ZnGa₂O₄ crystals after Sn⁴⁺ doping are expected to find applications in high-power devices and optoelectronic devices.

ZnGa₂O₄ bulk single crystals doped with Sn⁴⁺ were grown by the VGF method. High-purity (99.999%) Ga₂O₃, ZnO and SnO₂ powders were used as starting materials. The three powders were mixed for 80 h at a speed of 40 revolutions per minute, and then the mixed powders were cold-pressed into blocks at a pressure of 2000 bar and calcined in air at 600 ℃ in an alumina crucible for 16 h. Subsequently, ZnGa₂O₄ bulk single crystals doped with Sn⁴⁺ were grown in a crucible with an inner diameter of 60 mm and a height of 60 mm. The furnace was heated to 1900 ℃ at a rate of 250 ℃/h in an atmosphere of argon and 12% oxygen, and maintained at this temperature for about 2 h. Then the furnace was cooled slowly at a rate of 2-3 ℃ per minute. Sn⁴⁺ doped ZnGa₂O₄ bulk single crystals were obtained.

XRD analysis indicates that the Sn⁴⁺-doped ZnGa₂O₄ crystal maintains a pure spinel phase without any impurity phases, and the lattice constant slightly increases due to the introduction of Sn⁴⁺. The high-resolution X-ray diffraction (HRXRD) results show that the full width at half maximum (FWHM) of the rocking curve of the crystal is only 82 arcsec, indicating excellent crystal quality. X-ray photoelectron spectroscopy (XPS) analysis confirms that Sn⁴⁺ mainly enters the octahedral sites of the lattice by replacing Ga³⁺. X-ray fluorescence spectroscopy (XRF) analysis indicates that Sn⁴⁺ is successfully doped into the crystal, but the actual doping concentration is lower than the theoretical value due to the volatility of SnO₂. Optical performance tests show that Sn⁴⁺ doping slightly reduces the optical band gap of ZnGa₂O₄ crystals and increases the absorption in the near-infrared band, which is related to the increase in carrier concentration. Hall measurement results show that Sn⁴⁺ doping significantly increases the carrier concentration of the crystal (up to 3.32×10¹⁹ cm^-3) and reduces the resistivity (0.006 Ω·cm), outperforming undoped ZnGa₂O₄ and Sn⁴⁺-doped β-Ga₂O₃ crystals.

In this study, high-quality Sn⁴⁺-doped ZnGa₂O₄ single crystals with a volume of 10 cm³ were successfully grown by the vertical gradient freezing (VGF) method. The obtained Sn⁴⁺-doped ZnGa₂O₄ crystals showed no significant shift in diffraction peaks and a full width at half maximum (FWHM) of the rocking curve as low as 82 arc seconds, confirming the extremely high quality of the single crystals. X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectroscopy (XPS) analyses respectively confirmed the contents of Zn, Ga, O, and Sn elements, as well as the fact that Sn⁴⁺ were mainly incorporated into the ZnGa₂O₄ crystal by replacing Ga³⁺ at octahedral sites in the spinel structure. With the increase of Sn⁴⁺ doping concentration, the optical band gap of ZnGa₂O₄ crystals decreased to 4.58 eV and 4.56 eV, respectively. The introduction of Sn⁴⁺ did not cause significant changes in the cutoff absorption edge at about 275 nm, but increased absorption in the near-infrared wavelength range, which was related to the increase in carrier concentration. Hall measurements verified the effect of Sn⁴⁺ doping on the electrical properties of ZnGa₂O₄ single crystals. The results indicated that the introduction of Sn⁴⁺ significantly increased the carrier concentration of ZnGa₂O₄ crystals (2.65×10¹⁹-3.32×10¹⁹ cm^-3) and decreased the resistivity (0.006-0.008 Ω·cm). These properties were superior to undoped ZnGa₂O₄ single crystals and Sn⁴⁺-doped β-Ga₂O₃ single crystals. Overall, the Sn⁴⁺-doped ZnGa₂O₄ crystals grown in this study demonstrated significant application potential in power devices and solar-blind detection, and are expected to play a key role in the development of future high-power and high-frequency electronic and optoelectronic devices.

To enhance the performance and lifespan of SOFCs, the academic community has undertaken multidisciplinary and multifaceted optimization research. Among these efforts, optimizing the microstructure of electrodes has yielded increasingly reliable results and remains a focal area of study, with numerous innovative approaches continuously emerging. The integration of advanced optimization methods has deepened researchers' understanding of the relationship between anode microstructure and the overall performance of SOFCs, enabling the intentional design of specific microstructural morphologies and the preparation of real samples for validation. Multi-objective optimization is anticipated to play a prominent role in future microstructural studies, opening new pathways for developing SOFC samples with controllable morphologies to further advance microstructural optimization.

Based on this foundation, the future directions for research include:

1) Employing modern advanced characterization techniques to comprehensively quantify the evolution of SOFC microstructure throughout its lifecycle. Building upon current observation and three-dimensional reconstruction techniques, future research should systematically investigate microstructural changes in various states, including sintering preparation, operation, and degradation. Advances in image processing and analytical algorithms hold significant potential for providing a thorough understanding of SOFC microstructural behavior.

2) Integrating simulation and experimental preparation closely to identify the most effective anode microstructure. By decorating anodes with materials featuring specific morphologies, researchers can design electrodes with superior performance, promoting research into gradient anodes and anode modification. Active design of anode microstructures, with extensive use of multi-objective optimization methods, will allow for the successful fabrication of electrodes that meet anticipated performance targets. Further stability-enhancing strategies for SOFC anodes could be achieved by adjusting operating conditions and preparation techniques.

3) Increasing attention is being given to the combination of artificial intelligence (AI) and big data in SOFC optimization. Using machine learning to identify optimized parameters and ideal models, rather than relying on trial-and-error, can significantly streamline resource use. Deep learning will be a powerful tool in designing unique functional anodes. Additionally, nanoscale 3D printing—an economical and practical technology for producing electrodes with special microstructural features—holds great promise in microstructure optimization design and may facilitate the successful fabrication of advanced electrodes.

Solid-state electrolytes are critical for advancing lithium-ion battery technologies due to their potential to provide higher safety, improved energy density, and better long-term stability, compared to conventional liquid electrolytes. Among solid-state electrolytes, sulfide-based materials such as Li₆PS₅Cl (LPSC) are especially promising because of their high ionic conductivity, low interface impedance, and mechanical flexibility. LPSC has an argyrodite structure that inherently offers abundant lithium-ion migration pathways, ensuring efficient ionic transport. However, practical applications of LPSC are often hindered in the presence of intrinsic defects, such as lithium vacancies and LiCl substitutions, thus altering the local atomic environments and macroscopic ionic transport properties. Conventional computational methods like ab initio molecular dynamics (AIMD) offer a quantum-level precision, but are computationally prohibitive in large scales, whereas classical empirical potentials lack the accuracy to capture complex defect-induced local rearrangements. Therefore, developing a computational method that combines quantum accuracy with large-scale simulations remains an important challenge.

This study used a deep learning-based large-atom model (DPA-SSE), employing a "pretraining-fine-tuning-distillation" strategy specifically designed for sulfide solid electrolytes. Initially, the model was pretrained based on extensive density functional theory (DFT) data covering diverse sulfide materials and defect structures. Subsequently, it was fine-tuned using a carefully selected subset of 551 high-value DFT configurations specifically related to LPSC and its defect environments, chosen from a larger dataset of 11 631 configurations. These configurations included comprehensive DFT-calculated energies, atomic forces, and virial stress tensors. The fine-tuned model could achieve a quantum-level precision with a significantly reduced mean absolute error in predicting energies and forces. Finally, a distilled model was proposed via leveraging the fine-tuned model to label extensive datasets efficiently, enabling simulations of large-scale systems with thousands to millions of atoms in nanosecond time scales.

The molecular dynamics simulations are conducted to systematically investigate the effect of LiCl defect concentration on the ionic conductivity in LPSC at different temperatures by the distilled DPA-SSE model. At a lower temperature (i.e., 333 K), the simulations show that introducing LiCl defects moderately improves the ionic conductivity, compared to pristine LPSC, indicating that defects at a low concentration can create a beneficial local disorder facilitating ion transport. However, at an elevated temperature (i.e., 500 K), the simulations clearly demonstrate a negative correlation between ionic conductivity and increasing defect concentrations. Specifically, the measured ionic conductivities at different defect concentrations (i.e., 0%, 3.8%, and 7.7%) are approximately 3.23 × 10^-2, 2.06 × 10^-2 S/cm, and 1.36 × 10^-2 S/cm, respectively. The reduced ionic conductivity at higher defect concentrations is attributed to an increased structural instability, leading to a partial decomposition or a significant rearrangement of PS4 tetrahedral units, which form critical frameworks for efficient ion migration. The radial distribution function (RDF) analysis further corroborates these findings, showing intensified local coordination and disrupted ion diffusion pathways at higher defect levels.

This work demonstrated the feasibility and effectiveness of using a deep learning-based large-atom model to accurately and efficiently simulate ionic transport in defect-rich sulfide solid electrolytes. The "pretraining-fine-tuning-distillation" approach significantly reduced the computational cost associated with conventional quantum mechanical simulations, while maintaining a high predictive accuracy. This study provided valuable theoretical insights that could inform the design and optimization of high-performance solid-state electrolytes via revealing the intricate relationship among defect concentrations, local structural dynamics and ionic conductivity. Moreover, the methodological framework presented could have a broad applicability, offering a powerful and scalable computational tool for studying a variety of complex materials in energy storage applications.

Solid polymer electrolytes (SPEs) are pivotal for advancing all-solid-state lithium batteries (ASSLBs) due to their flexibility, processability, and compatibility with existing manufacturing processes. However, their practical application is hindered due to their low ionic conductivity and insufficient mechanical strength at room temperature. The existing research focuses on enhancing ionic conductivity through lithium salt optimization, polymer modification, or nanoparticle incorporation, the interplay between mechanical deformation and electrochemical performance remains underexplored. Previous studies reported that the mechanical pre-deformation (e.g., stretching or compression) can alter the microstructure of SPEs, thereby affecting ion transport. A unified understanding of how mechanical pre-deformation synchronously improves both ionic conductivity and mechanical properties (i.e., critical for structural integrity during battery operation) is still lacking. This study was to address this gap via systematically investigating the mechanical-electrochemical coupling effects on poly(ethylene oxide)-lithium bis(trifluoromethanesulfonyl)imide (PEO-LiTFSI) SPEs under mechanical pre-deformation. This work was to establish a predictive model for SPE performance optimization and provide guidelines for designing high-performance ASSLBs.

PEO-LiTFSI membranes were synthesized by dissolving PEO (M_w=600 000) and LiTFSI (mass ratio 1.000∶0.404) in acetonitrile, followed by casting and drying under controlled humidity (H₂O≤0.1 mg/L). The samples were subjected to tensile or compressive pre-strain (i.e., 10%-20% compression, 50%-80% tension) at elevated temperatures (above melting point) by universal testing machines, followed by rapid cooling to room temperature. The ionic conductivity was determined by electrochemical impedance spectroscopy (EIS) in a CHI660E workstation. The elastic modulus and yield strength were measured via quasi-static tensile tests. The free volume changes were analyzed by positron annihilation lifetime spectroscopy (PALS). Then, a coupled electrochemical-mechanical model was proposed in COMSOL to simulate the stress distribution and lithium diffusion in ASSLBs. The model incorporated temperature- and strain-dependent material parameters derived from the related experimental data.

This study reveals that the mechanical pre-deformation, particularly compression, significantly enhances both the ionic conductivity and mechanical properties of PEO-LiTFSI solid polymer electrolytes (SPEs). The results demonstrate that in the presence of 20% pre-compression, the ionic conductivity is increased by 4.4 times at 20 ℃, while the elastic modulus and yield strength can be enhanced by 1.60 times and 1.45 times, respectively. These enhancements are attributed to the microstructural changes induced by pre-deformation. The results by positron annihilation lifetime spectroscopy (PALS) confirm an 18% increase in normalized free volume (v_f/v_fo), which reduces Li⁺ migration barriers and facilitates ion transport. Polymer chain alignment under compression strengthens interchain interactions, countering a potential mechanical weakening from free volume expansion and improving stress distribution homogeneity. The simulations further validate these findings, showing that pre-compressed SPEs exhibit more uniform tensile stress near the electrolyte/electrode interface, thereby delaying the plastic deformation and extending the elastic working range. Despite a modest 7.7% increase in interfacial stress, the concurrent 17.5% increase in yield strength ensures a mechanical integrity during high-rate operation. In addition, a unified Arrhenius-based model incorporating temperature- and strain-dependent parameters accurately predicts the SPE behavior, with average relative errors of 8.4% for ionic conductivity and 3.6% for elastic modulus, confirming its utility for performance optimization. These results highlight the dual benefits of mechanical pre-compression, i.e., enhancing ion transport while fortifying structural robustness, and provide actionable insights for designing high-performance, durable all-solid-state lithium batteries.

This study demonstrated that the mechanical pre-compression (i.e., 10%-20% strain) could be an effective strategy to simultaneously enhance the ionic conductivity, elastic modulus, and yield strength of PEO-LiTFSI solid polymer electrolytes (SPEs), addressing critical challenges in their engineering application. The improvements could be attributed to the synergistic effects of increased free volume, facilitating Li⁺ ion transport and polymer chain orientation, which strengthening interchain interactions and homogenizes stress distribution. A unified Arrhenius-based model could capture the temperature- and strain-dependent evolution of SPE properties, enabling the predictive optimization for diverse operating conditions. The simulations further revealed that the pre-compressed SPEs exhibited more uniform interfacial stress profiles and higher mechanical resilience, expanding a usable rate capability of all-solid-state lithium batteries while maintaining structural integrity. These findings could establish mechanical pre-deformation as a viable pathway to design high-performance SPEs and advance the development of durable, high-energy-density solid-state batteries.

Advancements in sealing materials are pivotal for the progression of solid oxide fuel cell (SOFC) technology. These materials must maintain a long-term stability under extreme operating conditions, i.e., high temperatures, elevated pressures, and chemically aggressive environments. In addition, they also require excellent thermal expansion compatibility and gas impermeability to ensure the structural integrity and operational longevity of SOFC stacks. Future developments in SOFC sealing materials should focus on glass-ceramic composites, offering superior chemical stability, tailored thermal expansion behavior, and robust mechanical properties at elevated temperatures. These characteristics make them well-suited for ensuring the long-term stability of SOFC systems. The microstructure of these composites can be engineered to enhance gas tightness, self-healing capabilities, and overall durability via optimizing the composition of glass and ceramic phases, as well as refining heat treatment processes. The development of high-performance glass-ceramic composite sealing materials will address the critical challenges associated with the existing SOFC sealing technologies, providing some essential solutions for the commercialization and large-scale deployment of SOFC systems. Advancements in this field will facilitate a widespread adoption of clean energy technologies, contributing to the global transition toward a low-carbon economy and sustainable energy infrastructure.

FPM is proven to be an advanced computational method with broad application prospects in electrochemical research, such as exploring the potential effects in electrocatalytic water splitting, the activation polarization in the kinetics of lithium-ion batteries, and the concerted mechanism of proton-electron transfer within the electric double layer. These applications reveal the profound potential effects on the catalytic intermediate adsorption, charge transfer, and reaction pathways in both OER and ORR. Some researches on material phase transitions in lithium-ion batteries and their impact on battery performance also offer new avenues for improving cycle stability and energy density. Furthermore, studies on proton migration mechanisms provide theoretical guidance for optimizing proton transport at electrochemical interfaces, enhancing reaction selectivity, and boosting energy conversion efficiency. As computing power is enhanced and theoretical models are refined, the application of the FPM in electrochemical research becomes more widespread and in-depth. In addition, FPM enhances the accuracy and reliability of simulations, providing theoretical backing for the design of novel electrochemical materials, and shows promising potential for application in frontier fields like gate-controlled material phase transitions, magnetism, and electrosynthesis, offering innovative solutions to energy and environmental challenges with prospects.

However, FPM has its limitations. It can control the system to achieve fractional electron numbers, thereby realizing the grand canonical ensemble for electrons, but the complex interactions among multiple atoms are difficult to accurately describe. As a result, it cannot achieve non-integer changes in ion numbers to maintain a constant chemical potential, particularly for the systems with dynamic ion concentrations at chemical reaction interfaces. It is possible that machine learning potential fitting approaches based on first-principles calculations can offer a way to balance accuracy with the advantages of large-scale simulations. Nevertheless, the development of machine learning potentials for constant potential simulations is still in its early stage. Therefore, addressing large-scale and complex simulations under constant potential remains a challenge in future theoretical developments.

In summary, the rational design and optimization of electrolytes is an effective approach to enhancing the performance of RT Na-S batteries. This review outlines the working principles and major challenges faced by RT Na-S batteries and systematically discusses the research advancements in carbonate-based, ether-based electrolytes, and electrolyte additives for RT Na-S batteries. In RT Na-S batteries, carbonate, and ether-based electrolytes exhibit different properties. The solubility of NaPSs is lower in carbonate-based electrolytes, but they can undergo side reactions with the carbonate solvent, thus leading to the loss of active sulfur and consumption of the electrolyte. The design of carbonate electrolytes focuses on avoiding side reactions between the carbonate solvent and NaPSs, such as selecting appropriate solvents or additives to induce the formation of a stable CEI layer, preventing direct contact between the carbonate solvent and NaPSs. In contrast, NaPSs are more stable in ether-based electrolytes, but their high solubility in ether electrolytes results in severe shuttle effects and corrosion of the sodium metal anode. The design of ether-based electrolytes emphasizes the suppression of NaPSs shuttle effect and the interface modification of the sodium metal anode. This can be achieved via selecting specific solvents and additives that form coordination bonds with NaPSs and a stable SEI to inhibit NaPSs shuttle and stabilize the sodium metal anode. Some strategies involving high-concentration or localized high-concentration electrolytes have some positive effects in the design of both carbonate and ether-based electrolytes. In addition, the introduction of flame-retardant solvents into the electrolyte can also enhance the safety of the battery to some extent.

Despite significant research progress on RT Na-S battery electrolytes, there are still some scientific problems to be addressed to promote the commercial application of RT Na-S batteries. Future research should be as follows:

1) Theoretical calculations can be employed to reveal the dissolution and diffusion mechanisms of NaPSs in electrolytes, as well as the general interactions between solvent molecules, additives, and NaPSs. This can then enable the efficient screening of suitable solvents and additives for sodium-sulfur battery electrolytes through machine learning.

2) The sodium metal used in the anode of sodium-sulfur batteries is excessive, which increases manufacturing costs and reduces energy density. Developing sodium-sulfur batteries with Na₂S as a cathode and a current collector as an anode (i.e., anode-free sodium-sulfur batteries) represents a promising avenue for future development, as it can maximize the energy density of sodium-sulfur batteries. However, the sodium in anode-free sodium-sulfur batteries is limited as it is sourced from Na₂S. It is thus necessary to develop electrolytes with a high coulombic efficiency to minimize sodium loss and enhance the cycling stability of the battery.

3) Although the operating temperature of sodium-sulfur batteries reduces from high temperatures (~350 ℃) to room temperature, a future research should focus on the development of low-melting-point solvents or ionic liquids for the design of low-temperature electrolytes, to accommodate more extreme operating environments. It is of great significance to promote the practical application of sodium-sulfur batteries.

4) Solid-state electrolytes can effectively suppress the shuttle effect of NaPSs and the growth of sodium dendrites, while also avoiding the risks associated with electrolyte leakage. Therefore, the development of novel solid-state electrolytes shows a great promise for enabling higher performance and safety sodium-sulfur batteries.

Polyetherimide with its high glass transition temperature (i.e., 217 ℃) and melting point (i.e., 247 ℃) is considered as a promising high-temperature dielectric material. However, the π-π conjugated structure of its benzene rings leads to a sharp increase in conductivity loss at high temperatures and electric fields, thus reducing efficiency and energy storage density. Montmorillonite possesses a large bandgap and good insulation properties. Incorporating montmorillonite nanosheets into the polymer matrix is an effective approach to enhance the carrier transition barrier and dissipate carriers in the in-plane direction, thereby suppressing conduction current and improving the high-temperature energy storage performance of the polymer. However, the significant differences between the flexible matrix and the rigid inorganic filler pose some challenges for the compatibility at the organic-inorganic interface. In this paper, polyethylenimine was modified onto the surface of montmorillonite nanosheets to improve their interface compatibility with polyetherimide, allowing for uniform dispersion within the organic matrix. In addition, the impact of modified montmorillonite on the dielectric constant, breakdown strength and energy storage performance of polyetherimide composites was also investigated.

The modified montmorillonite was prepared via cation exchanging with polyethylenimine, and MMT/PEI composites were prepared by a tape casting method. PEI particles were firstly dissolved in NMP solvent under heating and stirring at 50 ℃ for 6 h. Once the PEI particles were completely dissolved, modified montmorillonite with a target content were firstly dispersed in the solvent under ultrasonication for 0.5 h. The resulting suspension was then cast onto a clean glass plate with a scraper and dried in a vacuum oven at 80 ℃ for 12 h. Afterwards, the material was dried at 200 ℃ for 4 h to completely remove the NMP solvent. The glass substrate was then placed in deionized water and left to stand for 10 min, allowing for the composites film to detach from the glass substrate, resulting in a composite film with a thickness of approximately 10 μm.

The relative dielectric constant of the composites exhibits only a slight decrease in the frequency range of 10² Hz to10⁶ Hz, indicating a good stability. The dielectric constant of the composites at 1000 Hz increases from 3.25 for pure PEI to 3.54, while the dielectric loss remains below 0.02 in the entire frequency range as the amount of montmorillonite increases. Moreover, the dielectric constant of the composites increases from 3.13 to 3.32 with the addition of montmorillonite at 150 ℃ and 1000 Hz. The dielectric loss remains at a low level. Thus, the dielectric breakdown strength of pure PEI at 150 ℃ is 429 MV/m. After introducing modified montmorillonite, the breakdown strength of the composites initially increases and then decreases. At a doping modified montmorillonite amount of 0.1%, the breakdown strength increases to 487.2 MV/m, and with a doping modified montmorillonite amount of 0.2%, it further increases to 507.5 MV/m. However, the breakdown strength decreases to 459.5 MV/m when the doping modified montmorillonite amount continues to increase. The discharge energy density of pure PEI at 150 ℃ and at 450 MV/m is 2.56 J/cm³, with an efficiency of only 72.5%. After introducing the modified montmorillonite nanosheets, the breakdown strength and dielectric constant of the composites both are enhanced, leading to an improvement in charge storage capability. At 0.1% of modified montmorillonite doping amount, the maximum discharge energy density increases to 3.17 J/cm³ at 150 ℃ and 500 MV/m, although the efficiency remains low at 77.8%. When the doping modified montmorillonite amount increases to 0.2%, the maximum discharge energy density reaches 3.15 J/cm³ at 150 ℃ and 450 MV/m, with the efficiency improving to 90.1%, thus meeting the standard operational requirements for film capacitors. At 150 ℃ and 500 MV/m, the discharge energy density further increases to 3.54 J/cm³, while the efficiency stabilizes at 86.7%. However, when the doping modified montmorillonite amount increases to 0.3%, the maximum discharge energy density and efficiency both decline. This indicates that an appropriate amount of montmorillonite nanosheets can effectively enhance the energy storage properties of PEI-based composites. The excessive doping can lead to a negative effect on the energy storage performance of composites, likely due to aggregation or suboptimal dispersion of the nanosheets.

Polyethyleneimine molecules were effectively loaded onto the surface and interlayers of montmorillonite nanosheets through cation exchange. This process improved the dispersibility of the montmorillonite nanosheets in solvents and their compatibility with the polyetherimide matrix, ensuring the structural uniformity of the composite materials. After doping with modified montmorillonite, the energy storage performance of the composites exhibited the optimum performance observed at a doping modified montmorillonite amount of 0.2%. At this doping amount, the dielectric constant was 3.45 at 1000 Hz and 150 ℃, while the breakdown strength reached 507.5 MV/m. At an electric field strength of 450 MV/m, the charge-discharge efficiency achieved 90.1%, with a discharge energy density of 3.15 J/cm³; at 500 MV/m, the charge-discharge efficiency was 86.7%, and the maximum discharge energy density reached 3.54 J/cm³. The results of this work indicated that doping with montmorillonite nanosheets could be an effective strategy for enhancing the high-temperature energy storage performance of polyetherimide, paving a way for the development of high-strength, high-performance high-temperature dielectric polymers.

Lithium iron phosphate-graphite (LFP-C) batteries are widely used in various fields due to their high energy density, low cost, high safety, good rate performance, long cycle life, and environmental friendliness. However, prolonged calendar aging leads to increased internal resistance and capacity decay, thereby shortening their service life. In this work, the impacts of storage temperature and SOC on the calendar aging performance of LFP-C batteries were investigated. The results show that the capacity decay is more severe under high temperature and high SOC conditions. The structural evolution of the anode and cathode materials, as well as the cathode-electrolyte interphase (CEI) and solid electrolyte interphase (SEI) layers were analyzed. It is indicated that the structure of LiFePO₄ cathode remains stable, while the degree of disorder in the graphite anode increases. The decomposition of the liquid electrolyte leads to an increase of LiF content in the CEI and SEI layers with decreasing Li₂CO₃ content in the SEI layer at 50 ℃.

In an inert atmosphere glove box, several LFP-C CR2025 coin cells were assembled. The cells were charged to the targeted SOC, and then divided into six groups and stored under different conditions (i.e., at 0°C-50%SOC, 0 ℃-100%SOC, 25 ℃-50%SOC, 25 ℃-100%SOC, 50 ℃-50%SOC, and 50 ℃-100%SOC) for one month. After storage, each group of cells was cycled at 1C to assess the impact of different storage conditions on the electrochemical performance of the cells. Other cells were disassembled, and then cleaned to obtain the positive and negative electrodes. The capacity degradation mechanisms of batteries during calendar aging were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy dispersive X-Ray spectroscopy (SEM-EDX), and X-ray photoelectron spectroscopy (XPS).

After 1-month storage, the LFP - graphite coin cells are charged and discharged at 1 C for 300 cycles. The results show that the cells stored at 50 ℃ cannot deliver any capacity. The cells stored at 0 ℃ exhibit a significantly higher discharge capacity, compared to the cells stored at 25 ℃. The cycling performance results of the cells after storage at different states of charge (SOC) indicate that the discharge capacity of coin cells stored at 50% SOC is higher than that of cells stored at 100% SOC.

It is revealed that there is a slight difference in the XRD patterns of LFP electrodes stored under various temperatures and SOC conditions, indicating that the structure of LFP maintains a high stability under various storage conditions. The XRD patterns of the graphite anodes also remain unchanged, and only the peaks attributed to the graphite and current collector Cu foil appear.

The results by Raman spectroscopy indicate that the LFP material remains stable after storage, while the degree of disorder in the graphite anode increases significantly and becomes more pronounced with the increase of storage temperatures and SOC. The results by FTIR reveal the side reaction products on the surfaces of both the cathode and anode materials (i.e., Li₂CO₃, (CH₂OCOOLi)₂, and ROCO₂Li).

The results by SEM-EDX indicate that there is a slight change in the elemental ratio on the surface of the cathode electrodes after storage under different conditions, further validating the stability of the LFP material. The surface of graphite particles becomes rough after storage, and the content of fluorine and phosphorus elements on the surface of graphite anodes increases under high-temperature and high-SOC conditions.

The results by XPS show that the content of LiF in the CEI layers increases with increasing the temperature and SOC. The storage temperature shows a more pronounced effect on the composition of the CEI rather than the SOC. The relative content of LiF and P—F in the SEI layers significantly increases, while the relative content of Li₂CO₃ decreases due to decomposition as the storage temperature increases.

LiFePO₄-graphite coin cells with different SOC (i.e., 50% and 100%) were stored at various temperatures (i.e., 0, 25 ℃ and 50 ℃) and for one month and then charged and discharged for 300 cycles. The results showed that cells stored at 50°C were completely inoperative. The battery capacity retention followed an order of 0 ℃-50%SOC > 0 ℃-100%SOC > 25 ℃-50%SOC > 2 ℃-100%SOC.

It was revealed that the LFP cathode exhibited a structural stability as the storage temperature and SOC increased. Conversely, the degree of disorder of graphite anode increased, having a detrimental effect on the lithium ion migration. It was evident that the temperature could have a dominant influence on the composition of the CEI rather than SOC. The relative content of Li₂CO₃ decreased, while the relative content of LiF decreased within the CEI layers as the storage temperatures and SOC increased. In addition, the relative content of LiF and P—F increased in the SEI layers with temperature, and the temperature had a more significant effect rather than SOC on the SEI layer.