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

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. A novel strategy for MXene electrode-electrolyte composite inks is proposed. Li+ is inserted into MXene nanosheets to expand the interlayer spacing, thus boosting ion diffusion kinetics. Micro-supercapacitors obtained by screen printing exhibit high capacitance, excellent rate performance, and stability. This work provides a new idea for future wearable electronic energy storage devices. image