Y.Y. Zhu, S.H. Zheng, J.Q. Qin, J.X. Ma, P. Das, F. Zhou, Z.-S. Wu*

Fundamental Research, 2022.

DOI: 10.1016/j.fmre.2022.03.021 [PDF]

Two-dimensional MXene is a key high-capacitance electrode material of micro-supercapacitors (MSCs) for integrated microsystems. However, the narrow electrochemical voltage window of conventional aqueous electrolytes (≤1.23 V) and MXene symmetric MSCs (typically≤0.6 V) substantially limit their output voltage and energy density of MSCs. Highly concentrated electrolytes can reduce the activity of water molecules, inhibit water splitting, and consequently widen the operating voltage window of aqueous electrolytes. Herein, we report anultrahigh-voltage aqueousplanar asymmetric MSCs (AMSCs) based on highly concentrated LiCl-gel quasi-solid-state electrolyte, with MXene (Ti₃C₂T_x) negative electrode and MnO₂nanosheet positive electrode (MXene//MnO₂-AMSCs). Remarkably,MXene//MnO₂-AMSCs exhibita record voltage of up to 2.4 V among the reported aqueous MXene based MSCs, and in turn ultrahigh volumetric energy density of 53 mWh cm⁻³.Furthermore, the merits of in-plane geometry and quasi-solid-state electrolyte enable excellent mechanical flexibility and performance uniformity in the serially/parallelly connected packs of our AMSCs. Notably, MXene//MnO₂-AMSCs based integrated microsystem in conjuction with solar cells and consumer electronicscould simultaneously and efficiently realize energy harvesting, storage, and conversion.We believe this work will create many intriguing opportunities for constructing high-voltage aqueous MXene based AMSCs towards safe and self-sufficient micropower sources in smart integrated microsystems.