Making Supercapacitors Higher in Energy Density: Wisdoms on Electrolytes and Device Architecture

The pursuit of higher energy density is central to advancing supercapacitor technology. While most existing reviews concentrate discretely on novel electrode materials or electrolytes, this work establishes a distinctive framework by linking the core device components directly to the energy density equation (E = 1/2 CV²). We systematically dissect how the electrode, electrolyte, separator, and current collector individually and collectively influence the specific capacitance (C) and operating voltage (V). The discussion is extended to the device level, examining how symmetric and asymmetric architectures can be strategically designed to further push the energy density limits. Key topics include the engineering of high-capacitance materials such as MXenes and metal-organic frameworks, the development of wide-voltage-window electrolytes such as "water-in-salt" systems, and optimization of auxiliary components. This component-to-device analysis offers a holistic guide for performance enhancement, critically addresses existing limitations, and proposes informed perspectives for future research towards high-energy-density supercapacitors.