Electric and Thermal Performance Enhancement of Silicone Gel by Nano-SiO₂ under DC Stress

As power electronic devices become increasingly integrated, their encapsulation materials are exposed to elevated electrical and thermal stresses. In practical applications, the operating temperature of power modules often exceeds 150 °C, presenting significant challenges to insulation reliability. Under high-temperature DC voltages, space charge accumulation and electric field distortion can accelerate insulation aging. This study investigates the influence of nano-SiO₂ doping on space charge characteristics, insulation properties, and thermal stability of silicone gel composites. Nanocomposites with varying SiO₂ loadings were prepared using fumed silica and characterized through pulsed electro-acoustic measurements, DC breakdown tests, DC conductivity measurements, and thermally stimulated depolarization current testing. Thermal stability was assessed via thermogravimetric analysis and differential scanning calorimetry. Results indicate that nanocomposite with 1.0 wt% SiO₂ content exhibits optimal performance, which features enhanced trap levels, significant suppression of space charge accumulation, a 16.1% increase in DC breakdown strength, a tenfold rise in volume resistivity, and a 60 °C increase in thermal decomposition onset temperature. These findings demonstrate the potential of SiO₂-doped silicone gel as high-performance materials for power module encapsulation.