<p>Supercapacitors are promising high‐power energy storage devices, but are often limited by low energy density and mechanical instability. Here, we present an epoxy‐silica hybrid ionogel polymer electrolyte (HIGPE) synthesized via an in situ sol–gel reaction combined with thermal polymerization. Two epoxy monomers, one rigid and one flexible, were combined with silica precursors and subjected to in situ sol–gel processing to generate nanophase-separated domains. The subsequent thermal curing in an ionic liquid medium produced a free-standing HIGPE featuring chemically bonded SiO₂ nanoparticles, which uniformly disperse and modulate polymerization-induced phase separation (PIPS), yielding a finely structured nanoscale network. At room temperature, HIGPE exhibits an ionic conductivity of 1.5 × 10^–3 S/cm and a mechanical modulus of 0.9&#xa0;MPa. When assembled into symmetric activated carbon supercapacitors, HIGPE enables a specific capacitance of 145 F/g at 0.2 A/g, which is 2.5 times higher than that of SiO₂-free IGPE, and achieves an energy density of 45 Wh/kg. Moreover, capacity retention remains above 80% after 5000 cycles, and bending tests confirm excellent flexibility with negligible performance loss. These results demonstrate that controlling PIPS through in situ nanoparticle incorporation produces a mechanically robust, high-conductivity electrolyte, addressing key shortcomings of conventional supercapacitors and paving the way for next-generation flexible energy storage.</p> Graphical abstract <p>A new hybrid epoxy-silica ionogel polymer electrolyte (HIGPE) was developed to address the challenges of low energy density and mechanical instability in supercapacitors. Created through an in situ sol-gel process followed by thermal polymerization, HIGPE features silica particles that form a nanoscale network. This structure not only enhances ionic conductivity but also maintains mechanical flexibility. HIGPE-based supercapacitors show great promise for advancing energy storage technology.</p>