A Review of Recent Advances in Supercapacitors: Materials, Electrolytes, and Device Engineering

Abstract

 Supercapacitors (SCs), also known as electrochemical capacitors, have garnered significant attention as vital energy storage devices due to their exceptional power density, rapid charge-discharge capabilities, and unparalleled cycle life. These attributes make them particularly promising for applications ranging from grid energy management and electric vehicles to portable and wearable electronics. This review aims to consolidate the latest research progress in the SC field, tracing the evolution from fundamental materials to advanced device architectures. The primary motivation is to address the central challenge of SCs—their relatively low energy density compared to batteries—by providing a clear overview of current strategies and future pathways. Recent years have witnessed remarkable activity: research on electrode materials has progressed from conventional activated carbons to the precise engineering of nanostructured materials like graphene and MXenes, alongside ongoing efforts to enhance the stability of pseudocapacitive materials such as metal oxides and conductive polymers. Concurrently, innovations in electrolytes, including "water-in-salt" solutions, ionic liquids, and solid-state systems, seek to widen the operational voltage window and improve safety. Device engineering, through asymmetric and hybrid configurations, has further boosted energy density, while flexible designs have unlocked novel application spaces. Despite these advances, critical challenges persist, including the fundamental trade-off between energy density, power density, and cycle life; the difficulties in scaling up the production of high-performance nanomaterials and managing performance degradation in practical, high-loading electrodes; and the unresolved issue of high interfacial resistance in solid-state electrolytes. This analysis concludes that future breakthroughs will hinge on the synergistic design of materials, electrolytes, and device configurations, moving beyond the isolated optimization of individual components.