MXene/TiO2 Heterostructure-Decorated Hard Carbon with Stable Ti-O-C Bonding for Enhanced Sodium-Ion Storage.

Hard carbon (HC) has attracted considerable attention in the application of sodium-ion battery (SIB) anodes, but the poor realistic capacity and low rate performance severely hinder their practical application. Herein we report a solvent mechanochemical protocol for the in situ fabrication of the HC-MXene/TiO2 electrode by functionalizing MXene to improve the electrochemical performance of the batteries. MXene (Ti3C2Tx) with abundant oxygen-containing functional groups reacts with HC particles in the ball milling process to form a Ti-O-C covalent cross-linked HC-MXene composite, in which the edge of the MXene nanosheets is in situ oxidized by air to form TiO2 nanorods, forming a regular 1D/2D MXene/TiO2 heterojunction structure. Ti-O-C covalent bonding can protect the heterojunction structures from pulverization and detachment from the current collector during charge/discharge cycles due to sodium-ion intercalation/detachment, thus improving the stability of the electrode structure. Meanwhile, the MXene/TiO2 heterojunction can form a 3D conductive network and provide more active sites. The resulting HC-MXene/TiO2 electrode exhibits superior electrode capacity (660 mAh g-1), making it a promising anode material for SIBs. This simple and efficient method for preparing MXene/TiO2 heterojunction-decorated HC provides a new perspective on the structural design of MXene and carbon material composites for SIBs.