Nitrogen-doped Ti3C2Tx/TiO2-graphene hybrid materials with 3D interconnected structure compatible with ionic liquid-based electrolyte for high performance supercapacitors

Ti3C2Tx, a typical MXene, bears tremendous attention as a type of potential electrode materials for supercapacitors. Regrettably, though Ti3C2Tx electrode has excellent capacitance in aqueous electrolytes, it cannot achieve high energy density due to a narrow operating potential window of the aqueous electrolytes. Herein, we demonstrate a well-designed hybrid material: nitrogen-doped Ti3C2Tx-reduced graphene oxide with in situ formed TiO2 nanopaticles bridged by -NH- (N-Ti3C2Tx/TiO2-RGO), and meanwhile formulate a ternary mixed electrolyte of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EmimTFSI), acetonitrile (ACN), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to match the hybrid material. The N-Ti3C2Tx/TiO2-RGO hybrid possesses a 3D cross-linked porous structure with rapid transport channels for the electrolyte ions. The formulated ionic liquid-based electrolyte has a wide electrochemical stability window and free lithium ions are able to conduct Faradaic redox reactions. Benefiting from its unique architectural structure, the N-Ti3C2Tx/TiO2-RGO material delivers an enhanced specific capacitance (specific capacity) of 188 F g−1 (338 C g−1) at 1 A g−1 and exhibits a high rate capability. Furthermore, the assembled asymmetrical supercapacitor with the N-Ti3C2Tx/TiO2-RGO-5 anode and the self-synthesized p-phenylenediamine functionalized reduced graphene oxide (PPD-RGO) cathode delivers a high energy density of 46 Wh kg−1 at a high-power density of 1550 W kg−1. This work develops a simple strategy to assemble 2D MXene sheets into 3D porous electrode materials compatible to the ionic liquid-based electrolyte for high performance supercapacitors.