Dual design of electrodes and electrolytes ensures flexible symmetric micro-supercapacitors with high energy density

According to the energy density equation E = 0.5CV2, the energy density of aqueous symmetric micro-supercapacitors (AS-MSCs) can be significantly improved by increasing the working voltage of AS-MSCs. However, it is still challenging for the working voltage of AS-MSCs to break through the decomposition voltage of water (1.23 V). Herein, a flexible AS-MSCs device is assembled via in situ reconstructed zero-valence Ag on MXene nanosheets (ZV-AgNP-MXene) as film electrodes and utilizing polyacrylamide (PAM)/Na2SO4 hydrogel electrolyte. Gaining the choice of a neutral Na2SO4 electrolyte, the voltage of water decomposition (1.23 V) was suppressed, enabling the AS-MSC device to achieve an operation voltage output of 1.6 V. Meanwhile, in situ reconstruction of Ag nanoparticles as the conducting intercalator can alleviate the dense stacking of 2D MXene, providing fast ion and electron transport. Benefiting from the dual design of electrodes and electrolytes, the assembled flexible AS-MSC device achieves wide operation voltage window (1.6 V), high areal capacitance (151 mF cm-2) and landmark areal energy density (52 mu W h cm-2). This study provides a simple and efficient strategy to increase the operating voltage and energy density of MXene-based AS-MSCs. Benefiting from the dual design of electrodes and electrolytes, a flexible symmetric micro-supercapacitor device has been assembled to achieve a high areal energy density.