The rapid growth of renewable energy generation has generated an urgent demand for effective and durable energy storage technologies. Among the various approaches, both redox flow batteries (RFBs) and lithium-ion batteries (LIBs) stand out as promising candidates for high capacity, safety, and high efficiency storage systems. However, their practical deployment is still limited by challenges related to interfacial kinetics, ion transport, and structural stability of key components such as electrodes and separators. In the first part of this thesis, efforts were devoted to improving the electrochemical performance of zinc-based flow batteries (ZBFBs) and vanadium flow batteries (VFBs). Both systems inherently suffer from low reaction rates and high overpotentials arising from sluggish interfacial kinetics and membrane crossover. To address these limitations, advanced electrode and separator design strategies were proposed to optimize interfacial properties and ion selectivity. The underlying mechanisms were systematically investigated through single-cell testing, electrochemical measurements, and scanning electron microscopy (SEM), providing insights into the correlation between surface architecture and electrochemical behavior. In the second part, the focus shifted to the development of functional polyimide (PI)-based separators for lithium-ion batteries (LIBs). Conventional polyolefin separators suffer from thermal shrinkage, low mechanical strength and poor electrolyte wettability, which compromise both safety and electrochemical performance. To address these challenges, two complementary strategies were explored. First, PI was synthesized and directly electrospun into freestanding membranes, enabling tunable morphology and high-temperature resistance through intrinsic polymer design. Second, a multilayer, layer-by-layer (LBL) architecture was fabricated by integrating electrospray and electrospinning techniques using commercially available PI (PI84) as the coating material. The resulting PI-based separators exhibit outstanding mechanical robustness with tensile strength up to 160 MPa, minimal thermal shrinkage below 5 %, and significantly enhanced electrolyte wettability. These improvements collectively contribute to superior electrolyte uptake and cycling stability in LIB cells, demonstrating the versatility and scalability of PI-based separator engineering. Overall, this work establishes a unified framework of functional separator and electrode designs to enhance the durability, safety, and electrochemical efficiency of next-generation energy storage devices, bridging the understanding between flow-based and solid-state electrochemical systems.