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Layered double hydroxides (LDH) can be transformed from alkaline supercapacitor material into metal-cation storage cathode working in neutral electrolytes through electrochemical activation. However, the rate performance for storing large cations is restricted by the small interlayer distance of LDH. Herein, the interlayer distance of NiCo-LDH is expanded by replacing the interlayer nitrate ions with 1,4-benzenedicarboxylic anions (BDC), leading to the enhanced rate performance for storing large cations (Na+, Mg2+, and Zn2+), whereas almost the unchanged one for storing small-radius Li+ ions. The improved rate performance of the BDC-pillared LDH (LDH-BDC) stems from the reduced charge-transfer and Warburg resistances during charge/discharge due to the increased interlayer distance, as revealed by in situ electrochemical impedance spectra. The asymmetric zinc-ion supercapacitor assembled with LDH-BDC and activated carbon presents high energy density and cycling stability. This study demonstrates an effective strategy to improve the large cation storage performance of LDH electrodes by increasing the interlayer distance. [ABSTRACT FROM AUTHOR]

Charge accumulation on the surface of insulation dielectric used in high voltage DC equipment is one of the important causes of surface flashover. Surface charge accumulation is closely related to surface trap characteristics. In this paper, the surface trap energy level distribution of polyimide (PI) was calculated and analyzed by the corona charging method and surface potential decay method. Besides, electron and hole trap characteristics were studied by changing the polarity and amplitude of the charging voltage. Furthermore, the influence of surface charge polarity and quantity on the flashover voltage was researched. Experimental results indicate that the energy level of traps corresponding to the maximum trapped charge density ranges around 0.94 eV. In addition, the energy level of the hole trap is slightly higher than that of the electron trap. The maximum charge density captured by the electron trap and hole trap is about 1.17 × 1021 and 1.03 × 1021 eV−1 m−3, respectively. The polarity of the surface charge can influence the conductivity characteristics of PI, the surface heterocharge reduces the volume conductivity by about 80% while the surface homocharge improves the volume conductivity of PI by about 6.4 times. Besides, both negative and positive surface charges can improve surface conductivity. The polarity of surface charge influences the flashover characteristics of PI, the flashover voltage increases by about 37.8% with the increase of homocharge density and decreases by about 23.8% with the increase of heterocharge density, which is related to the change of electric field near the cathode caused by surface charge accumulation. [ABSTRACT FROM AUTHOR]

The type of matrix resin of the semi‐conductive shielding layer directly affects the thermal aging characteristics of the semi‐conductive shielding layer and the high‐voltage cable. In this paper, ethylene vinyl acetate (EVA), ethylene ethyl acrylate (EEA), and ethylene butyl acrylate (EBA) resins were used as matrix to prepare carbon black (CB) + EVA, CB + EEA, and CB + EBA shielding materials. The law of physicochemical, electrical, and mechanical properties of different matrix resin shielding materials with aging time was studied, and the influence mechanism of matrix resin on the aging characteristics of shielding materials was analyzed. The results show: with the increase of aging time, the crystallization area and the number of functional groups of the three shielding materials decreased to varying degrees. The number of functional groups in CB + EBA shielding materials decreased evenly with aging time, but that of CB + EVA and CB + EEA shielding materials changed significantly after 7 days of aging. After 60 days of aging, the crystallization area of CB + EBA shielding material changed slightly, but that of CB + EVA and CB + EEA shielding material decrease significantly. The electrical properties of the three shielding materials showed different decreasing trend with aging time. When the aging time is 7 days, the positive temperature coefficient (PTC) effect of CB + EEA shielding material decreases obviously. When the aging time is 30 days, the resistivity of CB + EVA and CB + EEA shielding material increases slowly (9 Ω cm–12 Ω cm) with the increase of temperature. When the aging time is 60 days, the resistivity of CB + EBA shielding material decreases obviously, and the PTC effect weakens obviously. Taking the mechanical properties of the shielding material as reference, the rapid deterioration stage of the mechanical properties of the three shielding materials is different. The CB + EVA and CB + EEA shielding material rapid deterioration time is 0–7 days, and the tensile strength and elongation of the shielding material are greatly reduced. The rapid deterioration stage of CB + EBA shielding material is 7–30 days, and the tensile strength and elongation decrease from 24.38 MPa and 499.5% to 14 MPa and 155.7%, respectively. This work can provide data support for the selection of matrix resin of shielding material and the fault analysis of shielding layer of high voltage cable. [ABSTRACT FROM AUTHOR]

Developing multicomponent composite materials with delicate morphology and tailored structure is of vital importance for designing advanced sodium‐ion batteries (SIBs). Herein, a confinement‐structured Fe2Mo3O8@C@MoS2 with local‐expanded interlayer spacing is designed via high‐temperature phase transition from FeMoO4 to Fe2Mo3O8 and the tactically introducing dopamine molecules into the interlayer of MoS2 nanosheets. By analysis of the in situ generated solid electrolyte interphase film in different electrolytes, the favorable compatibility of Fe2Mo3O8@C@MoS2 in ether‐based electrolytes is well illustrated. Importantly, the sodium storage mechanism and detailed structural evolution of Fe2Mo3O8 are established for the first time by in situ X‐ray diffraction. Furthermore, theoretical calculations indicate the unique structure facilitates internal charge transfer and enhances Na+ adsorption ability. Thanks to the unique confinement structure, local‐expanded interlayers and robust framework, the Fe2Mo3O8@C@MoS2 composite achieves a high reversible specific capacity of 636 mAh g‒1 at 0.1 A g‒1, excellent rate capability (301 mAh g‒1 at 5.0 A g‒1) and ultralong cycling stability (365 mAh g–1 after 6000 cycles at 2.0 A g–1). The study provides an essential understanding of the Na storage mechanism of Fe2Mo3O8 and a promising strategy for constructing high‐performance anodes for SIBs. [ABSTRACT FROM AUTHOR]

Transition metal sulfides and selenides are common electrode materials in supercapacitors. However, the slow redox kinetics and structural collapse during charge–discharge cycles of single-component materials have impeded their electrochemical performance. In this study, hollow Co9S8 nanotubes were synthesized through a rational morphology design approach. Subsequently, NiSe2 or Co0.85Se was electrodeposited onto the Co9S8 nanotubes, yielding two core–shell heterostructure arrays, namely, NiSe2@Co9S8 and Co0.85Se@Co9S8. By fully leveraging the advantages and synergistic effects of these dual-phase heterostructures, the NiSe2@Co9S8 and Co0.85Se@Co9S8 configurations demonstrated outstanding areal capacitances of 12.54 F cm−2 and 9.61 F cm−2, respectively, at 2 mA cm−2. When integrated with activated carbon in hybrid supercapacitors, the NiSe2@Co9S8//AC and Co0.85Se@Co9S8//AC devices exhibited excellent energy storage performance, with energy densities of 0.959 mW h at 1.681 mW and 0.745 mW h at 1.569 mW, respectively. Additionally, these hybrid supercapacitors demonstrated remarkable cycling stability, with capacitance retention of 87.5% and 89.5% after 5000 cycles for NiSe2@Co9S8//AC and Co0.85Se@Co9S8//AC, respectively. This study provides a novel approach to the synthesis of multiphase core–shell heterostructures based on metal sulfides and selenides, opening new avenues for future research. [ABSTRACT FROM AUTHOR]

Transition metal sulfides are promising electrode materials for supercapacitors due to their excellent electrochemical performance and high conductivity. Unfortunately, the low rate performance and poor cycling stability limited their progress towards commercial applications. Herein, the core–shell structure of MoO42−-intercalated LDHs coated on Co9S8 nanotubes was rationally designed and prepared to improve their electrochemical performance and cycling stability by adjusting the composition of LDHs. Compared to NiMo-LDH@Co9S8 and CoMo-LDH@Co9S8, the optimized NiCoMo-LDH@Co9S8 electrode exhibits excellent areal specific capacitance (11 F cm−2 at 3 mA cm−2) and excellent cycling stability (94.4% after 5000 cycles). In addition, asymmetric supercapacitor devices were assembled with NiCoMo-LDH@Co9S8 and activated carbon (AC), which delivered a high energy density of 0.94 mWh cm−2, at a power density of 1.70 mW cm−2, and good cycling stability (89.4% after 5000 cycles). These results indicate that the introduction of MoO42− can enhance the synergistic effect of multiple metals and the synthesized NiCoMo-LDH@Co9S8 core–shell composite has great potential in the development of high-performance electrode materials for supercapacitors. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) becomes a superior candidate material for new environmentally friendly cable main insulation with its excellent heat resistance, electrical properties, and degradability. However, in practical application, PP material is aging and vulnerable and its toughness is poor. The mechanical properties of PP material can be improved by elastomer modification, but the effects of different elastomers on the comprehensive properties of composite specimens are quite different. In this paper, the electrical and mechanical properties of different types of elastomer‐modified PP composites are compared and analyzed by combining experimental and molecular simulation (MS) methods. The experimental results show that the SEBS/PP composite material has the lowest trap energy levels among all kinds of composite materials, its space charge accumulation is 1.96 × 10−9C, and the mechanical and rheological properties improvement of the composite is the most remarkable. Meanwhile, the volume resistivity is reduced by two orders of magnitude compared with pure PP. However, the breakdown strength of all kinds of composite materials decreases by different degrees after the modification. The solubility parameters (δ) and the free volume are further investigated by the molecular simulation, which shows that the δ of SEBS is similar to that of PP, which represents the best compatibility. Moreover, the SEBS/PP composite material has the strongest inter‐molecular force and the most excellent toughness improvement for PP. This work provides a theoretical basis for elastomer selection in PP modification. [ABSTRACT FROM AUTHOR]

Limited by sluggish reaction kinetics, insufficient electrode utilization and severe volume deformation, designing nickel‐based materials with high capacity and rate capability is still a challenge. Herein, a carbon nanotubes threaded NiSe2/Co3Se4 quantum dots embedded in carbon nanospheres with rich Se vacancies both in NiSe2 and Co3Se4 is elaborately designed via MOF template method. The formation mechanism of the Se vacancies is elucidated for the first time, which is ascribed to the release of gas during the decomposition of organic ligand inhibits the ordered arrangement of atoms. The CNT‐V‐NiCoSe possesses many significant superiorities, such as sufficiently exposed active sites, high electrode utilization, favorable charge‐carrier migration, and relaxed structure deformation. Consequently, the CNT‐V‐NiCoSe electrode shows top‐level specific capacity (384 mAh g−1 at 1 A g−1), ultrahigh rate capability (209 mAh g−1 at 150 A g−1) and remarkable cycling durability. The CNT‐V‐NiCoSe//Zn battery achieves maximum energy density of 615.6 Wh kg−1 and maximum power density of 81.7 kW kg−1. Density functional theory calculations elucidate the Se vacancies improve the density of states at Fermi level, facilitates internal charge transfer, and enhances OH− adsorption ability. This study provides guidance for the preparation of high‐performance electrode materials with rich vacancies by template method. [ABSTRACT FROM AUTHOR]