Preparation Of Vanadium-Based Heterojunction And Application In Lithium-Sulfur Batteries

Lithium-sulfur batteries(LSBs)are considered to be one of the most promising rechargeable batteries due to their ultra-high energy density.However,the practical application has been hindered due to the shuttle effect of soluble polysulfides and sluggish reaction kinetics.Here,this thesis reported the synthesis of two kinds of vanadium-based heterojunctions as sulfur host to alleviate the shuttle effect and promote the redox kinetics of poly sulfides.(1)By a simple partial nitridation method,a flexible three-dimensional nitrogen-doped graphene-supported vanadium trioxide/vanadium nitride(V2O3@VN/NG)heterojunction material was synthesized.By integrating the strong adsorption capacity of V2O3 for polysulfides and the rapid catalytic conversion capacity of VN,synergistically promote the redox kinetics of poly sulfides and alleviate the shuttle effect.Therefore,the V2O3@VN-20 has an initial specific capacity of 1130 mAh g-1 and 980 mAh g-1 at a current density of 1 C and 2 C,respectively.It has an initial specific capacity of 784 mAh g-1 at 5 C.After 300 cycles,the capacity retention rate is 70%,and the capacity decay rate per cycle is only 0.1%.At the same time,it still has a reversible specific capacity of 862 mAh g-1 after cycling for 100 cycles at a current density of 0.5 C with a sulfur loading of 5 mg cm-2.(2)Using vanadium disulfide(VS2)as the precursor,a flexible three-dimensional sulfur and nitrogen co-doped graphene-supported vanadium tetrasulfide vanadium nitride(V3S4@VN/SNG)heterostructure material was synthesized by the local nitridation method.V3S4 usually exists in the form of V0.5VS2,with a monolithic stacked block structure of VS2 subunits and V atoms linking the two layers.This structure is very conducive to the insertion and extraction of alkali metals,and the multilayer sheet structure provides a path for the rapid diffusion of ions and electrons.The experimental results show that V3S4@VN/SNG has an initial specific capacity of 1381 mAh g-1 at a current density of 0.1 C,and a maximum reversible specific capacity of 591 mAh g-1 at a current density of 5 C.After 100 cycles,the capacity retention rate is 93%,and the capacity decay rate per cycle is 0.07%.