Nickel-doped manganese dioxide (Ni-MnO₂) synthesized by sol-gel method has been used as an electrode material for supercapacitors. The structure and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectrometry (EIS). Results showed that the nickel-doped manganese dioxide sample exhibited irregular particles with the diameter of about 500 nm. The crystallographic structure of MnO₂ was the poorly crystallized γ-MnO₂. The doping ratio had a great influence on the electrochemical properties of the materials. When the molar ratio of Ni/Mn was 3/100, the specific capacitance of Ni-MnO₂ achieved to 252.61 F/g. After 2000 charge/discharge cycles, the specific capacitance of Ni-MnO₂ was still maintained at 74.36%, which was attributed to its excellent cycling stability.

Polymer-based composites with the advantages of ceramics and polymers exhibit high dielectric constant, good processing properties and low dielectric loss. The composites with a varied content of irregular alumina ( i -Al ₂ O ₃ ) filler were prepared by UV-cured epoxy acrylic (EA). Spherical alumina ( s -Al ₂ O ₃ ) was used as a filler to further investigate the effect of alumina (Al ₂ O ₃ ) shapes on dielectric properties of composites in the frequency range of 50 Hz–1 MHz. Fourier transform infrared spectroscopy proved that the UV-cured epoxy acrylic/alumina (Al ₂ O ₃ /EA) composites were successfully fabricated. Scanning electron microscopy demonstrated that i -Al ₂ O ₃ particles have superior homodispersion in the matrix. Through testing, for all samples, with the addition of Al ₂ O ₃ , the relative permittivity of composites increased as expected, and the dielectric loss decreased accordingly. These data show that the incorporation of i -Al ₂ O ₃ particles presents better properties when compared with s -Al ₂ O ₃ /EA, which indicates that i -Al ₂ O ₃ particles have more influence on the dielectric properties of the composites than those of s -Al ₂ O ₃ particles. According to Weibull distribution, the characteristic breakdown strength of the Al ₂ O ₃ /EA composites was obtained and the results suggested that the composites of i -Al ₂ O ₃ /EA exhibited better breakdown performance.