Intercalation Pseudocapacitance in 2D VS2/Ti3C2Tx MXene Hybrids for All-Climate and Long-Cycle Sodium-Ion Batteries

Abstract

Layered transition metal dichalcogenides have great potential as anodes of sodium-ion batteries (SIBs) due to their high theoretical specific capacity. However, the restacking severely limits their accessible sites, leading to undesirable specific capacity, cycle stability, and working temperature range. Herein, a hierarchical 2D VS2/Ti3C2Tx MXene hybrid is designed via a simple liquid-mixing method, where VS2 is confined in the conductive Ti3C2Tx matrix with chemical connections built between them. The in situ transmission electron microscopy analyses reveal that the hybrid depends on a very fast and reversible intercalation/de-intercalation process between VS2 and NaxVS2 (where x = 1) to store sodium. Theoretical calculations disclose that the Ti3C2Tx matrix remarkably enhances the charge transfer and alleviates the volume expansion of VS2 especially after Na+ is inserted. Consequently, such a rational design exhibits an intercalation pseudocapacitance-dominant mechanism, with excellent specific capacity (522 mAh g−1 at 0.2 A g−1), rate capability (342 mAh g−1 at 10 A g−1), cycle life (116% after 3000 cycles), and also all-climate workability (with high specific capacity and long-term cycle stability even at 70 and −40 °C). This study may open up a new vision to design fast-charging, long-cycle, and all-climate SIBs anodes based on the intercalation pseudocapacitance.