Three‐Phase Boundary in Cross‐Coupled Micro‐Mesoporous Networks Enabling 3D‐Printed and Ionogel‐Based Quasi‐Solid‐State Micro‐Supercapacitors

Abstract The construction of advanced micro‐supercapacitors (MSCs) with both wide working‐voltage and high energy density is promising but still challenging. In this work, a series of nitrogen‐doped, cross‐coupled micro‐mesoporous carbon–metal networks (N‐STC/M_xO_y) is developed as robust additives to 3D printing inks for MSCs fabrication. Taking the N‐STC/Fe₂O₃ nanocomposite as an example, both experimental results and theoretical simulations reveal that the well‐developed hierarchical networks with abundantly decorated ultrafine Fe₂O₃ nanoparticles not only significantly facilitate the ion adsorption at its three‐phase boundaries (Fe₂O₃, N‐STC, and electrolyte), but also greatly favor ionic diffusion/transport with shortened pathways. Consequently, the as‐prepared N‐STC/Fe₂O₃ electrode delivers a high gravimetric capacitance (267 F g⁻¹ at 2 mV s⁻¹) and outstanding stability in a liquid‐electrolyte‐based symmetric device, as well as a record‐high energy density of 114 Wh kg⁻¹ for an asymmetric supercapacitor. Particularly, the gravimetric capacitance of the ionogel‐based quasi‐solid‐state MSCs by 3D printing reaches 377 F g⁻¹ and the device can operate under a wide temperature range (−10 to 60 °C).