Sustainable MXene/Conductive Cellulose Heteroinks for 3D Printed High Areal Energy Density Micro‐Supercapacitors and Self‐Powered Integrated Systems

The additive manufacturing of micro-supercapacitors (MSCs) with outstanding areal energy density and scalable integration remains challenging due to the incompatibility between printability and functionality of electronic ink. Here, a thixotropic MXene/conductive cellulose heteroink is formulated, eliminating the need for tedious processing and toxic organic additives, to construct MSCs with high areal energy density. Conductive cellulose with radially graded structure containing defect-rich graphitic shells not only inhibits MXene re-stacking through hydrogen-bonded 3D porous networks, but also establishes sp²-carbon pathways for rapid electron transport. The optimized 3D printed MSCs achieve record-breaking metrics: high areal capacitance of 3.12 F cm^-2 (1 mA cm^-2), outstanding energy density of 1.25 mWh cm^-2, and 95% capacitance retention after 10 000 bending cycles. Notably, the 3D printed MSCs can operate stably within a temperature range of -40 to 60 °C. In addition, an integrated flexible sensing system incorporating 3D printed MSCs and strain sensors is demonstrated, which is highly sensitive for real-time motion monitoring. This work establishes a materials-by-design paradigm for customizable micro-energy systems, advancing wearable and implantable electronics.