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

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.