Y.Y. Zhu†, S.H. Zheng†, P.F. Lu, J.X. Ma, P. Das, F. Su, H.-M. Cheng,*, Z.-S. Wu*
National Science Review, 2022, Accepted.
MXenes are one of the key materials for micro-supercapacitors (MSCs), integrating miniaturized energy storage components with microelectronics. However, the energy densities of MSCs are greatly hampered by MXene’s narrow working potential window (typically ≤ 0.6 V) in aqueous electrolytes. Here, we report the fabrication of high-voltageMXene MSCs through the efficient regulation of reaction kinetics in 2D Ti3C2TxMXene microelectrodesusingwater-in-LiCl (WIL, 20 m LiCl) saltgelelectrolyte.Importantly, the intrinsic energy storage mechanism of MXene microelectrodes in WIL, which is totally different from traditionalelectrolyte (1 m LiCl),was revealed throughin-situandex-situcharacterizations. We validated that the suppression of MXene oxidation at high anodic potential occurred due to the high content of WIL regulating anion intercalation in MXene electrodes, whicheffectively broadened the voltage window of MXene MSCs.Remarkably, the symmetricplanarMXeneMSCs presented a record operating voltage of 1.6 V, resulting in exceptionally high volumetric energy density of 31.7 mWh cm−3.With the ultrahigh ionic conductivity (69.5 mS cm−1) and ultralow freezing point (−57 °C) ofWIL gel electrolyte, our MSCs could be operated in a wide temperature range of −40 °C to 60°C, and worked for long duration even at −40 °C, demonstrative of its practicality in extreme environments.