The rise of flexible zinc-ion hybrid capacitors: advances, challenges, and outlooks

The advent of flexible electronic devices has given rise to urgent demand for compatible flexible power sources. Zinc-ion hybrid capacitors (ZIHCs) combine the complementary advantages of zinc-ion batteries— for high energy density—and supercapacitors— for exceptional power density and cycling stability—and thus they have been vigorously studied as a very promising energy storage candidate in recent years. In this review, we systematically summarize the fundamental principles and recent progress of ZIHCs, including the critical challenges faced by electrode materials, electrolytes, and electrode–electrolyte interfaces. Furthermore, special focus is given toward their functionalities (e.g., environmental adaptability, stimuli-responsive properties, and miniaturization) commensurate with the flexible devices. A perspective on future directions of flexible ZIHCs is also presented. This timely and comprehensive review is expected to give a fresh impetus toward the rational design and development of flexible ZIHCs to fully realize their potential as flexible energy storage devices.