In situ synthesized carbon nanotubes-pillared MXene heterostructure integrated with CoSe₂ nanoparticles as high-performance anode for sodium-ion storage

Advancing sodium-ion batteries (SIBs) necessitates the development of high-performance anode materials. Two-dimensional MXene is recognized as a highly promising anode candidate. However, it suffers from severe layer restacking, which limits its active sites and ion transport. In this study, a novel hierarchical composite, CoSe₂@CNTs/Ti₃C₂T_x, is designed and synthesized. The composite is fabricated by intercalating Ti₃C₂T_x MXene with in situ grown carbon nanotubes (CNTs) between its layers, followed by a selenization process. This configuration gives rise to a “dot-tube-sheet” arrangement. The vertically aligned CNTs act as effective spacers, thereby preventing MXene restacking, increasing interlayer spacing, and enhancing electronic conductivity. The CoSe₂ nanoparticles, which are formed from the Co catalyst that is anchored at the tips of the CNTs, contribute to a high theoretical capacity. Consequently, the CoSe₂@CNTs/Ti₃C₂T_x anode demonstrates outstanding electrochemical performance, achieving a high reversible capacity of 235 mAh g−1 after 1000 cycles at 0.2 A g−1 with nearly full capacity retention, and an excellent rate capability of 179.6 mAh g−1 at 2 A g−1. Kinetic analysis reveals a predominantly pseudocapacitive charge storage mechanism and a low charge-transfer resistance, facilitated by the unique structure that promotes rapid Na+/electron transport. This work provides an effective strategy for designing high-performance MXene-based anodes for SIBs.