A composite dielectric material having a plurality of particle cores, each surrounded by polymer strands that are chemically bonded to the surface of the particle core. Each polymer strand includes a linker, through which the polymer strand is attached to the surface, an interfacial core-shielding (ICS) group bound to the linker, and a polymer molecule bound to the ICS group. The ICS groups are designed to inhibit electrical breakdown of the composite dielectric material by (i) deflecting or scattering free electrons away from the particle cores and/or (ii) capturing free electrons by being transformed into relatively stable radical anions. Representative examples of the particle core material, linker, ICS group, and polymer molecule are titanium dioxide, a phosphonate group, a halogenated aromatic ring, and a polystyrene molecule, respectively.