Ti3C2Tx MXene supported SnO2 quantum dots with oxygen vacancies as anode for Li-ion capacitors

Abstract Li-ion capacitors (LICs) based on battery-type anodes and capacitive cathodes have the potential to become the candidate of the next generation of electrochemical energy storage (EES) devices because of their high energy density (ED) along with large power density (PD) which are basically determined by the physical and chemical properties of their anodes and cathodes. In this work, the coating of SnO2 quantum dots (QDs, ca. 4–5 nm) with oxygen vacancies on the surface of Ti3C2Tx MXene sheets with different contents has been achieved through one-step solvothermal method. The optimized SnO2 QDs/Ti3C2Tx-50 composite anode displays a large reversible discharge capacity (1000.4 mAh g−1@0.2 A g−1), distinguished cycling stability (the discharge capacity of 1004.0 mAh g−1 at the end of 300 cycles under the same current density), and good rate performance, and in which the reaction kinetics is dominated by the fast capacitive process to a large extent, due to the reduced Li+ ion diffusion path and oxygen vacancies in SnO2 QDs, the prominent electrical conductivity along with outstanding mechanical property for Ti3C2Tx MXene, and the large specific surface area of this composite. And a high-capacity N, S co-doped biomass derived porous carbon (NS-BPC) cathode (95.8 mAh g−1@0.2 A g−1) is synthesized, and constructed with the SnO2 QDs/Ti3C2Tx-50 anode to give rise to a superior-performance Li-ion capacitor possessing ED being 148.5 to 17.5 Wh kg−1 with the corresponding PD of 200.4 W kg−1 to 10.0 kW kg−1, additionally exceedingly good cycling stability (96.5% capacity retention ratio after 5000 cycles).