10.1021/acs.chemmater.9b01334.s001 Kijae Kim Kijae Kim Yasunobu Ando Yasunobu Ando Akira Sugahara Akira Sugahara Seongjae Ko Seongjae Ko Yuki Yamada Yuki Yamada Minoru Otani Minoru Otani Masashi Okubo Masashi Okubo Atsuo Yamada Atsuo Yamada Dense Charge Accumulation in MXene with a Hydrate-Melt Electrolyte American Chemical Society 2019 Hydrate-Melt Electrolyte Electrochemical double-layer Dense Charge Accumulation large-capacitance MXene Ti 2 CT x Aqueous EDL capacitors show supercapacitor hydrate-melt electrolyte Li titanium carbide MXene electrode electrochemical window electrochemical energy storage devices 2019-06-11 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Dense_Charge_Accumulation_in_MXene_with_a_Hydrate-Melt_Electrolyte/8313920 Electrochemical double-layer (EDL) capacitors operating at high charge/discharge rates are an important class of electrochemical energy storage devices. Aqueous EDL capacitors show great potential for use as inexpensive devices with much higher power; however, their energy density is severely limited by the narrow electrochemical window of water (1.23 V) and the small specific capacity of the electrodes. Here, we develop a high-voltage aqueous supercapacitor based on a highly concentrated Li<sup>+</sup> aqueous electrolyte (hydrate melt) and a two-dimensional titanium carbide MXene electrode. Experimental and theoretical analyses reveal the existence of dense hydrated Li<sup>+</sup> in the interlayer space of the deeply charged MXene, which is realized by the wide electrochemical window of a hydrate-melt electrolyte. The hydrate-melt electrolyte together with the large-capacitance MXene Ti<sub>2</sub>CT<sub><i>x</i></sub> improves the performance of an aqueous lithium-ion supercapacitor, offering a promising strategy for advanced aqueous capacitors.