Electrochemical Characteristics of Vertically-Aligned Ti3C2 Nanosheet Electrode for High-Speed Charge/Discharge Supercapacitors

Abstract

Two-dimensional titanium carbide (Ti3C2) nanosheets have recently received attention as a supercapacitor electrode material capable of achieving high capacity and rapid charge-discharge due to psudocapacitance associated with redox reaction on the surface1. To effectively use the surface of each single Ti3C2 nanosheet, nanosheet electrodes with well-controlled porous structures are necessary to increase ion and electron transfer pathway. Here, electrochemical performance of vertically-aligned Ti3C2 nanosheet electrodes, fabricated based on our proposed nanosheet vertical alignment method combined with electrophoretic deposition and freeze drying2, was examined. To check the importance of the vertically aligned structure to improve electrochemical performance, a vertically-aligned and a horizontally-stacked nanosheet electrode were fabricated by using Ti3C2 nanosheets with lateral size of 200 nm. Cyclic voltammograms of the vertically-aligned electrode show redox peaks at approximately 1.0 V and 1.6 V versus Li/ Li+ at a scan rate of 2 mV s−1, whereas that of the horizontally-stacked electrode gives no significant peaks from Ti3C2 (Figure 1). The capacity obtained from the vertically-aligned electrode was larger than that obtained from horizontally-stacked electrode, suggesting that the vertically-aligned structure improved ion diffusion path to the surface. To investigate the effect of the sheet size on the electrochemical characteristics, vertically-aligned electrodes composed of three different-sized Ti3C2 nanosheets (100, 200 and 600 nm) were prepared and evaluated. It should be noted that the amount of the nanosheets loaded on each electrode was kept constant at 0.68-0.70 mg cm-2. The capacity reached approximately 153 (100 nm), 140 (200 nm) and 136 mAh g−1 (600 nm), at 0.2C current rate, respectively, suggesting that small Ti3C2 nanosheets could effectively improve Li ion accessibility to their active sites compared with large nanosheets. Thus the vertically-aligned Ti3C2 nanosheet electrode could be useful for supercapacitors with high capacity and high-speed charge/discharge ability. This research was partly supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) (JPMJAL1008) from Japan Science and Technology Agency (JST). References M. Naguib, V. N. Mochalin, M. W. Barsoum and Y. Gogotsi, MXenes: A new family of two-dimensional materials, Adv. Mater., 26, 992 (2014).D. Mochizuki, R. Tanaka, Y. Ayato, S. Makino and W. Sugimoto, Vertically Aligned Reduced Graphite Oxide Nanosheet Film and its Application in a High-Speed Charge/Discharge Electrochemical Capacitor, ACS Appl. Energy Mater., 2, 1033 (2019). Figure 1