Integrating SnS₂ Quantum Dots with Nitrogen-Doped Ti₃C₂T_x MXene Nanosheets for Robust Sodium Storage Performance

Transition-metal dichalcogenides with a lamellar structure have been recognized as a class of attractive host materials for Na+ insertion, and intensively investigated as anodes for sodium-ion batteries. However, large-scale applications are severely restricted by their intrinsic inferior conductivity and large volume expansion during deep cycles. Herein, a unique 0D/2D heterostructure of SnS2 quantum dots (QDs) with N-doped Ti3C2Tx MXene (namely, SnS2 QDs/Ti3C2) has been successfully designed via an ingenious solvent spatial confinement growth strategy. During the hydrothermal process, the nucleation and growth of SnS2 nanoparticles can be effectively regulated by N-methyl pyrrolidone, which results in the uniform growth of SnS2 QDs of about 3 nm onto the Ti3C2Tx MXene matrix. Meanwhile, in situ N-doping of Ti3C2Tx MXene can also be realized because of the NH3 released from the decomposition of the sulfur precursor, which greatly enhances the interfacial Na+ transport. Such a rational design endows the newly developed SnS2 QDs/Ti3C2 electrode with fascinating sodium storage properties including a high specific capacity of 763.2 mA h g–1 at 100 mA g–1 and ultrastable cycling stability (345.3 mA h g–1 at 100 mA g–1 after 600 cycles). The experimental and theoretical simulation results demonstrate that the ultrafine SnS2 QDs with abundantly active sites on the interface and stronger Na+ adsorption energy on the heterojunction formed between N-doped Ti3C2 MXenes contribute to the superior sodium storage capability.