Yuanyuan Li

With the capacity of generators continuing to increase, higher demands are placed on the heat dissipation of epoxy resin (EP), the main insulation material used in stator bars and windings. To overcome its low thermal conductivity, a multiscale hybrid filler strategy was adopted to investigate the effects of spherical Al₂O₃ (10 and 1 μm), platelet BN (1 μm), and SiO₂ (50 nm) on the thermal and insulating properties of EP composites. Unlike conventional studies focusing on individual fillers, this work highlights the synergistic design of fillers with different sizes and morphologies. The filler ratios were optimized by finite element simulation, and the composites were prepared by melt blending. The results show that, at a total filler loading of 38.5 wt%, the EP composite filled with spherical Al₂O₃ particles of 10 and 1 μm, platelet BN of 1 μm, and nano-SiO₂ of 50 nm achieves a thermal conductivity of 0.5497 W/(m·K), corresponding to an increase of 158.2% compared with pure EP (0.2129 W/(m·K)). This enhancement is attributed to the synergistic effect of multiscale and multishape fillers, where large Al₂O₃ particles form the main thermally conductive framework, small Al₂O₃ particles fill the gaps, platelet BN acts as a bridging filler, and nano-SiO₂ improves the interfacial region. In addition, the composite exhibits low relative permittivity and dissipation factor tanδ in the frequency range of 10⁻²–10⁶ Hz, and its breakdown strength reaches 65.99 kV/mm. These results demonstrate that simulation-guided multiscale hybrid filler design is an effective strategy for improving the thermal conductivity of EP while maintaining acceptable insulating performance.

In this work, the effects of different sintering temperatures and TiO₂ concentrations on the dielectric properties of ZrO₂ and Nb₂O₅ pre-doped CaCu₃Ti₄O₁₂ (CCTO) ceramics were investigated. These doped ceramics were sintered at temperatures of 1020, 1030, and 1040 °C, exhibiting the lowest dielectric loss of 0.01, which consistently remained below 0.03 across a wide frequency range from 10 to 10⁵ Hz. Simultaneously, they maintained a high dielectric constant of more than 3000 and remarkably met the requirements for an X8P capacitor (Δε′ ≤ ±10% at temperature range from −55 to 150 °C). It was clarified that TiO₂ doping increased grain boundary resistance, leading to the reduced dielectric loss, and elevated the grain boundary activation energy, thereby enhancing the temperature stability. The TiO₂-doped CCTO-based ceramics also demonstrated reduced sensitivity to variations in sintering temperature, highlighting their excellent manufacturability. This characteristic holds great promise for the fabrication of CCTO-based ceramics, which usually exhibit poor repetitiveness.

Here, we investigate structure and mechanical change of Cu and Al current collector during cycling and analyze the contribution to capacity attenuation of Sb-based lithium-ion batteries (LIBs). There exists migration of C, Sb, and Li atoms to the inside of Cu current collector, and diffusion of Li, Co, and O atoms to the inside of Al current collector during cycling, which results in the formation of a porous film of Li₂SbCu (with the thickness of 21 µm after 100 cycles) and a relatively dense film of Al₂O₃ (with the thickness of 23 µm after 100 cycles) on the surface of Cu and Al current collector, respectively. The formation of films results in a weak bond between active layer and current collector, and the increase of hardness of 0.84 GPa and modulus of 22.5 GPa for Cu current collector after 100 cycles, which is adverse to the charge capacity and cycling stability. Nevertheless, Al₂O₃ films caused hardness decrease of 0.53 GPa and modulus decrease of 18.93 GPa of Al current collector after 100 cycles, which contributes to the improvement of cycling stability and charge capacity. This study provides an understanding of the capacity loss of Sb-based LIBs from the perspective of structural degradation of current collectors.

In this work, electrical tree inception and ageing experiments were conducted to investigate the initiation, growth characteristics and structural characteristics of electrical trees of nano‐SiO ₂ doped epoxy resin at different temperatures. Electrical tree inception and ageing experiments were conducted using power frequency voltage of 15 kV at 20, 40, 60, 80 and 100°C. Electrical breakdown properties of epoxy resin were investigated by applying AC and DC voltages at 20, 40, 80 and 120°C. There are two major observations based on the experimental results. With the increase of temperature, the morphological structure of the electrical trees changes from dendritic to plexiform, the tree inception voltage decreases and the growth rate of the electrical trees increases obviously. Either under DC or AC voltage, the breakdown strength of the nano‐SiO ₂ doped epoxy resin decreases as the temperature increases. Finally, based on the space charge and the trap level measurement, the mechanism of the electrical tree propagation and breakdown in nano‐SiO ₂ doped epoxy resin was analysed.

Epoxy resin (EP) nanodielectrics with the mass fraction of nano-silica (SiO ₂ ) between 0 and 5 wt% were manufactured. The influence of SiO ₂ content on the dielectric properties of EP nanodielectrics was studied. It is found that the dielectric properties are the best when the SiO ₂ content is 0.5 wt%. We further tested and analyzed the dielectric properties of pure EP and EP nanodielectrics with 0.5 wt% SiO ₂ at the temperature ranging from 40 to 200 °C. The results show that the complexity permittivity and space charge accumulation of the samples increase significantly at low frequency and the temperature above T _g . The complexity permittivity and space charge accumulation of the nanocomposites with the loading of 0.5 wt%, however, are smaller than that of pure EP. These results indicate that the interface area between nano-silica and EP matrix suppresses the motions of molecular chains and the migration of charge carriers.