Asymmetric supercapacitors by integrating high content Na+/K+-inserted MnO2 nanosheets and layered Ti3C2Tx paper

In this work, Na+/K+-inserted MnO2 (NaxKyMnO2) nanosheets are synthesized on Ni foam via a facile and efficient route based on an electro-deposition and electro-oxidation reaction process. The NaxKyMnO2 nanosheet arrays has a broad potential window, which can be extended to 1.0 V versus standard calomel electrode (vs. SCE). The NaxKyMnO2 with iso-oriented feature and unique nanoarchitectures provides shortened diffusion path lengths for both Na+, K+ and electronic transport, and reduces the stress associated with Na+, K+ insertion and extraction. The layered Ti3C2Tx paper on Ni foam (Ti3C2Tx@NF) are also synthesized successfully that can act as a negative electrode, stably in a negative potential window of -0.8-0 V (vs. SCE). Subsequently, an aqueous asymmetric supercapacitor is demonstrated with a high potential of 1.8-2.0 V by using NaxKyMnO2@NF as the positive electrode and Ti3C2Tx@NF as the negative electrode. The asymmetric device achieves a high power density of 9.396 mW/cm(2) and improved energy density of 0.11 mWh/cm(2), as well as great cycling performance. (C) 2019 Elsevier Ltd. All rights reserved.