Boosting the sodium storage of the 1T/2H MoS2@SnO2 heterostructure via a fast surface redox reaction

Abstract

The sluggish kinetics and large volume expansion arising from the large ionic radius of Na⁺ remain elusive weaknesses of sodium ion batteries (SIBs). Here, we report a transition from bulk diffusion to surface-dominant pseudocapacitive charge storage by nanoscaling and heterostructuring, which enables fast and stable charge storage kinetics for SIBs. An electronic attraction induced self-assembly strategy was developed for the synthesis of the 1T/2H MoS₂@SnO₂ heterostructure. Ultrasmall SnO₂ nanoparticles with a low crystallinity were uniformly distributed on the basal plane of MoS₂. The intercalated SnO₂ serves as an interfacial pillar to restrict the restacking of MoS₂ nanosheets, whereas dual-phase 1T/2H MoS₂ provides a continuous network for efficient charge transfer and restrains the aggregation of Na_xSn. As a result, the 1T/2H MoS₂@SnO₂ heterostructure exhibits a higher specific capacity (626 mA h g⁻¹ at 0.1 A g⁻¹), and superior cycling and rate capabilities (262 mA h g⁻¹ at 2 A g⁻¹ for 500 cycles) compared to the raw MoS₂ and 2H MoS₂@SnO₂ counterparts. Electrochemical kinetics analyses reveal that the charge transfer kinetics are boosted by the synergistic effect between the 1T/2H MoS₂ and SnO₂ nanoparticles. Quantitative examination into the origin demonstrated that the Na⁺ storage is dominated by the fast surface redox reaction, which endows the heterostructure with a durable high rate capability.