Capacitor starts its journey from 1745, and still moves forward in form of supercapacitor. Supercapacitor is one of the advanced forms of capacitor with higher energy density that bridges between...

Hybrid supercapacitors are the most desirable electrochemical energy storage devices, owing to their versatile and tunable performance characteristics, specifically in energy and power densities, towards applications in research and development. Construction‐wise, optimized assembly of batteries (energy devices) and supercapacitors (power devices) are the key for hybrid supercapacitors. Based on scientific advancements and technological achievements, hybrid ion capacitors are the most important segments in hybrid supercapacitors, as well as in the overall energy storage arena. Herein, opportunities and challenges of hybrid ion capacitors are intensively addressed in light of lithium‐ion, sodium‐ion, potassium‐ion, magnesium‐ion, calcium‐ion, zinc‐ion, and aluminum‐ion capacitors. The historical origins and their developmental pathways are identified for each type of capacitor. Possible classes of materials for every hybrid ion capacitor are discussed, and relevant mechanisms are demonstrated. These discussions reveal that a rich materials bank exists for lithium‐ion, sodium‐ion, and zinc‐ion capacitors, but the same is not applicable for potassium‐ion, magnesium‐ion, calcium‐ion, and aluminum‐ion capacitors. Consequently, such hybrid ion capacitors have not yet reached the level of commercial benchmarks like lithium‐ion, sodium‐ion, and zinc‐ion capacitors. However, this Review focuses on mostly full‐cell device data that synchronize the performances of practical scaled‐up systems. Several electrolytes based on solvent media (aqueous, organic, and ionic liquid), phase (liquid, gel, and solid), and redox activity (active and passive) are exemplified in different sections of hybrid ion capacitors. Various device constructions are elaborated upon, such as liquid‐electrolyte devices, polymeric gel devices, all‐solid‐state devices, flexible‐cum‐wearable devices, microdevices, solar‐charging devices, and so forth. The Review culminates with feasible future directions for the commercial success of hybrid ion capacitors, which are in the nascent stages of developments. To the best of our knowledge, it is the first holistic account of hybrid ion capacitors from their historical perspectives to present developments.

Recent developments in supercapacitor technology in terms of materials and devices are reviewed herein. Beyond the conventional materials (i. e., carbonaceous matters, metallic compounds and conducting polymers), various multifunctional materials are reported in literature as future supercapacitive materials. A comprehensive account on such materials is lacking due to the diversified electrochemical characteristics of these materials. In this review, we bring all such non‐conventional multifunctional energy storage materials under a same umbrella for summarizing the recent advancements in supercapacitors. The envisaged multifunctional materials include metal‐organic‐frameworks (MOFs), covalent‐organic‐frameworks (COFs), heteroatom‐doped carbonaceous materials, biomass‐derived porous carbons, black phosphorous, mixed conductors, perovskite nanoparticles, polyoxometalates (POMs), redox active electrolytes, slurry materials for flow supercapacitors, thermal self‐charging materials, thermal self‐protective materials, piezoelectric materials and electrochromic materials. Inherent pros and cons of each class of material are discussed, and materials modifications towards the successful device fabrications are highlighted herewith. While the MOF‐based supercapacitors are drawing some attentions, other non‐conventional energy storage materials are truly in the nascent stage of developments. This review culminates with summary and proposed future directions for product developments. In brief, this article provides a holistic view regarding all non‐conventional multifunctional energy storage materials for future supercapacitor technology.

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