This review provides an overview of the fundamental principles of electrochemical energy storage in supercapacitors, highlighting various energy-storage materials and strategies for enhancing their performance, with a focus on manganese- and nickel-based materials. . The accelerating global demand for sustainable and efficient energy storage has driven substantial interest in supercapacitor technology due to its superior power density, fast charge–discharge capability, and long cycle life. However, the low energy density of supercapacitors remains a key. . Supercapacitors are among the most promising electrochemical energy-storage devices, bridging the gap between traditional capacitors and batteries in terms of power and energy density. Their charge-storage performance is largely influenced by the properties of electrode materials, electrolytes and. . A supercapacitor (SC), also called an ultracapacitor, is a high-capacity capacitor, with a capacitance value much higher than solid-state capacitors but with lower voltage limits. It bridges the gap between electrolytic capacitors and rechargeable batteries. It typically stores 10 to 100 times more. . Energy storage systems (ESSs) are a cornerstone technology that enables the implementation of inherently intermittent energy sources, such as wind and solar power. When power outages occur, ESSs also serve as backups for critical infrastructure. The power management systems, including converters. . This study presents an approach to improving the energy efficiency and longevity of batteries in electric vehicles by integrating super-capacitors (SC) into a parallel hybrid energy storage system (HESS). Unlike conventional systems that rely solely on batteries, this research highlights the. .