High capacity and stability induced by sandwich-like structure and metal–O configuration for CoNi2S4/Ti3C2Tx heterostructure electrode

A two-dimensional heterostructure, combined with the collective advantages of single building blocks, has attracted considerable interest as a new paradigm in the materials design of electrochemical energy storage. In the present study, a sandwich-like CoNi2S4/Ti3C2Tx heterostructure electrode was successfully acquired using a simple one-step hydrothermal procedure, where CoNi2S4 nanosheets are distributed uniformly within the MXene interlayers and on surfaces. The layered structure of MXene restricts the overgrowth of CoNi2S4. The tiny size shortens the charge transfer and ion diffusion pathway and minimises the volume change in CoNi2S4. The introduction of CoNi2S4 expands the interlayer distance of the host MXene, enabling fast ion movement and efficiently accommodating the volume expansion of CoNi2S4. The electronic coupling of the metal in CoNi2S4 and O in Ti3C2Tx improves the electrical conductivity and optimises the absorbability and stability of OH– on the heterostructure. The CoNi2S4/Ti3C2Tx heterostructure delivered a capacity of 320 mAh g–1 (2398 F g–1) at 1 A g–1 and a capacity retention of 80% at 25 A g–1 after 40, 000 cycles, outperforming most supercapacitor electrode materials reported to date owing to the synergy between the structural configuration and electronic interactions. This work provides valuable insights for designing high-performance electrode materials by manipulating the structural configuration and interface electronic interaction.