A SnO2/MXene hybrid nanocomposite as a negative electrode material for asymmetric supercapacitors

In this report, we synthesised a SnO2/Ti3C2Tx composite through a single-step hydrothermal route with varying quantities of Ti3C2Tx (from 50 mg to 100 mg). The formation of a hybrid increases the interlayer spacing of Ti3C2Tx, and this increment in the interlayer spacing supports the charge transport in the electroactive material. Thus, the resultant composite with 80 mg of Ti3C2Tx (SnO2/Ti3C2Tx-80) displays a specific capacitance of 620 F g(-1) at 2 A g(-1) current density. Density Functional Theory (DFT) calculations have been performed to comprehend the structural and electronic properties of SnO2 and hybrid SnO2/Ti3C2Tx systems. The formation of a hybrid structure has significantly increased the conductivity of the SnO2 system due to the charge transfer from Ti3C2Tx to SnO2. The quantum capacitance is higher in the hybrid system than in the pristine SnO2 system. This validates and supports our experimental results that the hybrid system has enhanced charge storage performance. For practical realisation, an asymmetric supercapacitor (ASC) device is fabricated using SnO2/Ti3C2Tx-80 as a negative electroactive material and cobalt phosphate as a positive electroactive material. The fabricated device delivers a specific capacitance of 100 F g(-1) at 3 A g(-1) current density. The ASC shows an energy density of 32 W h kg(-1) with a power density of 5118.5 W kg(-1). The device retains 93% of its initial capacitance even after 15 000 GCD cycles at 4.5 A g(-1) with a coulombic efficiency of 98%.