Three‐dimensional (3D)‐printed MXene high‐voltage aqueous micro‐supercapacitors with ultrahigh areal energy density and low‐temperature tolerance

Abstract The rapid advancement in the miniaturization, integration, and intelligence of electronic devices has escalated the demand for customizable micro‐supercapacitors (MSCs) with high energy density. However, efficient microfabrication of safe and high‐energy MXene MSCs for integrating microelectronics remains a significant challenge due to the low voltage window in aqueous electrolytes (typically ≤0.6 V) and limited areal mass loading of MXene microelectrodes. Here, we tackle these challenges by developing a high‐concentration (18 mol kg⁻¹) “water‐in‐LiBr” (WiB) gel electrolyte for MXene symmetric MSCs (M‐SMSCs), demonstrating a record high voltage window of 1.8 V. Subsequently, additive‐free aqueous MXene ink with excellent rheological behavior is developed for three‐dimensional (3D) printing customizable all‐MXene microelectrodes on various substrates. Leveraging the synergy of a high‐voltage WiB gel electrolyte and 3D‐printed microelectrodes, quasi‐solid‐state M‐SMSCs operating stably at 1.8 V are constructed, and achieve an ultrahigh areal energy density of 1772 μWh cm⁻² and excellent low‐temperature tolerance, with a long‐term operation at −40°C. Finally, by extending the 3D printing protocol, M‐SMSCs are integrated with humidity sensors on a single planar substrate, demonstrating their reliability in miniaturized integrated microsystems.