Boosting ion/e⁻ transfer of Ti₃C₂ via interlayered and interfacial co-modification for high-performance Li-ion capacitors

Owing to their unique structural and electronic characteristics, MXenes are considered to be the most potential anode materials for Li-ion capacitors (LICs). However, the stacking of layers, which would inevitably lead to the reduction of active sites and the sluggish lithiation kinetics, highly inhibits their electrochemical performance. Herein, to overcome the stacking and simultaneously improve the reversible capacity and cycle stability of MXenes, a kind of Ti₃C₂ with Sn⁴⁺ intercalated between the layers and amorphous SnO₂ layer modified (AS-Ti₃C₂) is proposed. The intercalated Sn⁴⁺ between the layers not only could facilitate Li-ion diffusion kinetics by expanding the interlayer spacing but also provide additional capacity by interlayered-alloying reactions. Meanwhile, the in-situ formed amorphous SnO₂ modified layers could offer abundant channels for fast Li-ion diffusion and provide a new interface between electrolyte and electrode to lower the energy barrier for interfacial charge transfer. Benefit from the synergy effects of faster ion diffusion kinetics and lower charge transfer barrier, AS-Ti₃C₂ delivers much improved rate performance and enhanced cycle stability in Li-ion half-cells, maintaining 91.5% capacity retention (after 1500 cycles @2000 mA g⁻¹). Moreover, LICs assembled by AS-Ti₃C₂ anodes and activated carbon (AC) cathodes deliver superior electrochemical properties including long cycle life (82.1% after 4000 cycles @2000 mA g⁻¹), high energy (105.7 Wh kg⁻¹) and power (8000 W kg⁻¹) densities. Our findings reveal that the interlayered and interfacial co-modification is feasible to improve the properties of MXenes.