Study On Suppressing Shuttle Effect Of Li-S Battery By Transition Metal Doped Cathode Materials

Lithium-sulfur（Li-S）battery is one of the most promising new-generation energy storage battery systems for the advantages of its high energy density and low cost.However,the insulation of sulfur,large volume change during charge and discharge process,and the shuttle effect have severely limited the application prospects of lithium-sulfur batteries.Vanadium Nitride（VN）has excellent electrical conductivity,which could significantly improve the conductivity of the cathodes as sulfur host material,and suppress the shuttle effect as well.In this study,VN was doped with transition metal elements.The electronic structure of VN was modulated by heteroatom doping to further suppress shuttle effect.The theoretical calculations and the experimental tests were carried out to verify the proposed strategy for improving the electrochemical performance of lithium-sulfur batteries.The main contents are as follows:1.Theoretical calculation was used to explore the efficiency of different metal-doped substrate materials in suppressing the shuttle effect.First-principles calculations were used to obtain the most stable adsorption configuration between VN and polysulfide;The polysulfide adsorption capability of different metals（Mn,Fe,Co,Ni）doped VN under this stable configuration was investigated as well;The calculation of density of electronic states（DOS）was further used to describe the mechanism of metal doping for optimizing the surface electronic structure and promote the interaction between VN and polysulfide.The results show that these metal doping elements could effectively improve the polysulfide adsorption capability of VN,and Co metal element is competitive among them.2.Substrate materials doped with different transition metals were synthesized and the electrochemical performance of the samples was tested.Different metals（Mn,Fe,Co,Ni）doped VN micro-flower structure materials were prepared through hydrothermal reaction and ammonia heat treatment reaction.The cycle performance and rate performance of prepared cathodes were tested.The results show that metal doping could significantly improve the electrochemical performance of Li-S battery,especially for Co-doped VN cathodes.The initial discharge specific capacity of Co-doped VN cathode can reach 640 m Ah g^-1 at a high rate of 3.0 C,and 452 m Ah g^-1 was still maintained after 500 cycling,which shows excellent electrochemical performance.3.Substrate materials with different metal doping amounts were prepared and the electrochemical performance of the samples was tested.Co doped VN with different Co doping amount was prepared（the atomic ratio of Co/V is 0%,3%,5%,7%）,and the electrochemical performance of these cathodes was tested.The test results show that when the element ratio of Co/V is 5%,the electrochemical performance of the lithium-sulfur battery is optimized to the extent.The specific discharge capacity of the Co_0.05-VN/S electrode can reach to 706 m Ah g^-1 at 2.0 C,and the capacity decay of each cycle is only0.034%among 500 cycles.