Technological roadmap for potassium-ion hybrid capacitors

Potassium-ion hybrid capacitors (PIHCs) are in principle advantageous over the traditional metal-ion hybrid capacitors (MIHCs) in terms of low cost, safety, and reliability, holding enormous potential for the massive market, yet they remain largely an uncharted field. Herein, we provide a comprehensive review of recent advances on PIHCs, including fundamental understanding, device configurations, and design rationale. Then, technical hurdles that essentially impede the development of PIHCs are discussed, accompanied by corresponding improvement strategies for all aspects of PIHCs. Lastly, how far we are from the lab bench to the consumer market is highlighted, and a comprehensive roadmap starting from cooperative components integration and ending with the future direction of next-generation PIHCs for grid-scale energy storage is clearly described. We anticipate that this review will timely arouse strong interest and attention from both academic and industrial communities to this rising technology and make a revolutionary step forward toward commercial applications.