Nitrogen-doped carbon dots modified double transition metal MXene (Ti2NbC2Tx) for superior lithium/sodium-ion storage

Two-dimensional transition metal carbides/nitrides or MXenes, show great promising in energy storage field owing to its excellent electrical and chemical properties, especially for the modifiable surface functional groups, adjustable interlayer spacing and metal-like conductivity. Here, a hybrid electrode based on double transition metal MXene (Ti2NbC2Tx) is designed and synthesized, where nitrogen-doped carbon dots are uniformly anchored on the edge-crumpled Ti2NbC2Tx nanosheets. The unique structure of the hybrid electrode can effectively suppress the self-stacking of MXenes nanosheets, improve the ions/electron transport efficiency and the cycling stability. The Ti2NbC2Tx@CDs hybrid electrode achieves outstanding rate capability and cycling performance for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). At 5 A g-1, up to 10,000 cycles, it can deliver 217.3 mAh g-1 for LIBs and 109.2 mAh g-1 for SIBs. The Ti2NbC2Tx@CDs hybrids show high capacitive contribution, owing to the rapid ions/electrons transporting. The Ti2NbC2Tx@CDs hybrids also show ideal electrochemical reversibility from the in-situ XRD study. This work will help to develop novel double transition metal MXenes and their composite electrode materials for LIBs/SIBs with better performance.