Recent advances in carbon-based supercapacitors

Abstract

Rapid advancements in modern electronics have been starved of further breakthroughs to achieve high-energy, large-power, and long-running energy storage devices. Carbon-based supercapacitors (CSs) are promising large-power systems that can store electrical energy at the interface between the carbonaceous electrode surface and adsorbed electrolyte layer. However, commercial CSs using activated carbons suffer from limited energy densities in the organic electrolytes owing to sluggish mass diffusion and restricted charge accumulation. To overcome these issues, significant efforts have been devoted toward increasing the energy storage of CSs by the exploration of both large-capacitance electrodes and high-potential electrolytes. This paper reviews the recent advances made in the two core components (i.e., electrodes and electrolytes) of CSs. Firstly, we describe the involved energy storage mechanisms of CSs, followed by a brief overview of the key factors affecting the electrochemical performances. Then, novel design concepts have been summarized that can be used to fabricate carbon-based electrodes, such as microporous carbons, mesoporous carbons, hierarchical porous carbons, functionalized carbons, and carbon composites. Further, tailoring of the geometrical morphologies, pore structures, and surface functionalities can be discussed in pursuit of large-capacitance electrodes. Furthermore, various types of aqueous and nonaqueous electrolytes, such as water-in-salt, organic media, ionic liquids, and (quasi-)solid-state electrolytes, have been systematically investigated to settle the water hydrolysis concern of traditional electrolytes. Finally, the challenges in maximizing the synergistic effect between the electrodes and electrolytes are summarized, and we have proposed the future outlook for the development of advanced CSs.