Zn metal-free zinc ion hybrid supercapacitors: principles, innovations, and future directions

, and others) investigated for Type-II Zn metal-free hybrid supercapacitors is provided. Finally, the advantages, key bottlenecks, and viewpoints are highlighted to facilitate the future progress of Type-II ZHSs. It is anticipated that this review article will provide strategic guidance, with a primary focus on the design and development of high-performance Zn metal-free ZHSs, complementing the existing Type-I ZHSs.