Deciphering the catalysis essence of vanadium self-intercalated two-dimensional vanadium sulfides (V5S8) on lithium polysulfide towards high-rate and ultra-stable Li-S batteries

Atom-intercalated transition metal disulfides (TMDs) have attached much attention mainly due to their highly improved conductivity. But it is few reported that the atom intercalation can enable the TMDs have unexpected catalytic properties, caused by the unit-cell deformation in them. In this work, a type of V 0.25 -intercalated VS 2 (V 5 S 8 ) nanoflakes was designed via a direct vulcanization method combining Kirkendall heat diffusion effect, and used as the promotor for lithium-sulfur batteries (LSBs). The V 5 S 8 possesses a NiAs crystal structure, in which V atoms occupy the interlayer spacing between VS 2 monolayers, which will unavoidably cause the unit-cell deformation. As expected, the CNF@V 5 S 8 /S cathodes show a specific capacity of 1260 mAh g −1 at 0.2 C, and can keep 73.65% of the capacity with charge/discharge rate increasing 10 times; while the CNF@VS 2 /S ones can only retain 54.0% of the initial capacity. Moreover, the CNF@V 5 S 8 /S cathodes show an ultralow decay rate of only 0.0312% per cycle for 1500 cycles at 5 C. Furthermore, the catalysis effect of V 5 S 8 on the conversion of lithium polysulfide (Li 2 S n , n = 1, 2, 4, 6 and 8) and S 8 clusters were systematically discusses. Besides, the V 5 S 8 can further enable LSBs achieve a high areal capacity (8.2 mAh cm −2 with sulfur loading of 7.8 mg cm −2 ) and a high dynamic flexible stability at bending angle between 0 and 180 °.