Bundled Defect-Rich MoS 2 for a High-Rate and Long-Life Sodium-Ion Battery: Achieving 3D Diffusion of Sodium Ion by Vacancies to Improve Kinetics.

Molybdenum disulfide (MoS2 ), a 2D-layered compound, is regarded as a promising anode for sodium-ion batteries (SIBs) due to its attractive theoretical capacity and low cost. The main challenges associated with MoS2 are the low rate capability suffering from the sluggish kinetics of Na+ intercalation and the poor cycling stability owning to the stack of MoS2 sheets. In this work, a unique architecture of bundled defect-rich MoS2 (BD-MoS2 ) that consists of MoS2 with large vacancies bundled by ultrathin MoO3 is achieved via a facile quenching process. When employed as anode for a SIB, the BD-MoS2 electrode exhibits an ultrafast charge/discharge due to the pseudocapacitive-controlled Na+ storage mechanism in it. Further experimental and theoretical calculations show that Na+ is able to cross the MoS2 layer by vacancies, not only limited to diffusion along the layer, thus realizing a 3D Na+ diffusion with faster kinetics. Meanwhile, the bundling architecture reduces the stack of sheets with a superior cycle life illustrating the highly reversible capacities of 350 and 272 mAh g-1 at 2 and 5 A g-1 after 1000 cycles.