Trends in Nanoparticle Use in Polymer Composites for Energy Storage Applications: From Interfacial Design to Scalable Production

Nanoparticle‐modified polymer blends (NMPBs) have emerged as a transformative class of materials for advanced capacitive and electrochemical energy storage. This review evaluates progress over the past decade in integrating conductive nanomaterials such as carbon nanotubes, graphene derivatives, and MXenes, together with high k‐ceramic fillers, into miscible and immiscible polymer blend matrices for film capacitors, supercapacitors, and batteries. We benchmark gains in permittivity, breakdown strength, AC conductivity, dielectric loss, electric modulus, and device‐level electrochemical performance. Particular attention is given to trade‐offs that govern energy density, leakage, and operational stability. The analysis distills fundamental design strategies grounded in interfacial control, dispersion stability, and morphology management. These strategies target suppression of leakage pathways and dielectric loss, improvement of field uniformity, and retention of mechanical integrity under high electric fields and elevated temperature. Persistent technical challenges are addressed, including high‐field dielectric losses, thermal and interfacial instability during cycling, sensitivity to moisture and oxidation, and the scalability gap between laboratory casting and industrial roll‐to‐roll processing. Emerging directions are mapped, including two‐dimensional (2D) materials with tunable surface terminations, machine‐learning‐guided formulation discovery, and multiscale computational modeling to guide composition and architecture while linking interfacial physics to device‐level reliability. The review provides a critical framework and a practical roadmap for translating polymer‐based nanocomposite energy storage from concept to manufacturable, sustainable technologies.