Boosting Ion Diffusion Kinetics of MXene Inks with Water‐in‐Salt Electrolyte for Screen‐Printed Micro‐Supercapacitors

Abstract Flexible wearable electronics are in urgent need of advanced micro‐energy storage devices. MXenes are widely used in supercapacitors because of their excellent conductivity and hydrophilicity. Nevertheless, MXene‐based supercapacitors typically exhibit low capacitance and unsatisfied rate performance, particularly in the solid compact MXene film electrode with limited porosity and/or ion diffusion paths. Here, the synthesis of MXene inks with enlarged interlayer spacing for facilitated ion diffusion kinetics by intercalating lithium ions is reported. The ion‐intercalated MXene inks are further screen‐printed for scalable production of MXene‐based micro‐supercapacitors (MSCs). Benefiting from such an electrode architecture design, as well as the wide voltage window of 21 m bis(trifluoromethane)sulfonimide lithium (LiTFSI) water‐in‐salt electrolyte, the device exhibits impressive areal capacitance (252 mF cm −2 ), much‐improved rate performance (capacitance retention rate as high as 80%), excellent cyclic stability (retains 98.4% of initial capacitance after 10 000 cycles) and flexibility, showing great potential in the field of wearable intelligent electronics.