Unraveling the Design Principles of Battery‐Supercapacitor Hybrid Devices: From Fundamental Mechanisms to Microstructure Engineering and Challenging Perspectives

Abstract Battery‐supercapacitor hybrid devices (BSHDs) are aimed to be competitive complements to conventional batteries and supercapacitors by simultaneously achieving high energy density, high power density, and excellent cycling stability. However, the cooperative coupling of different energy storage mechanisms between batteries and supercapacitors is still challenging. Therefore, it is important to have a holistic understanding of BSHDs from material synthesis to final application. In this review, the basic concept and working principles of BSHDs are first discussed, which helps identify the related key scientific problems arising from hybridization. Then the ways in which some of these issues have been mitigated are discussed, for example by developing advanced microstructures and engineering the interface between electrode|current collector, electrode|electrolyte, and battery‐type(b‐type)|capacitor‐type(c‐type) materials. Furthermore, along with shedding light on innovative approaches for expanding the BSHDs’ cell voltage unconventional charge‐storage mechanisms and device configurations like dual ion and hydrogen ion hybrid supercapacitors are also summarized to push their performance even higher. Finally, a perspective on the technological challenges and future prospects of BSHDs from both an academic and industrial point of view is provided. This review is expected to serve as a window to look at the past and guide the future development of high‐performance BSHDs.