Study On Modification Of Sulfur Cathode By Surface Functionalization Of Acetylene Black

Lithium-sulfur batteries(Li-S)have attracted much attention due to their high specific capacity(1672 mAh g-1)and high energy density(2600 Wh Kg-1).However,the shuttle effect and volume expansion have seriously affected the cycling stability of the Li-S system,which restricts its commercial application.In this paper,based on the functional modification principle of carbon materials,functional acetylene black was prepared as a sulfur carrier,and the inhibition effects of different modified materials and processes on polysulfides were compared.Based on the active sulfur reserved void space process route,a gradient structure lithium-sulfur battery cathode electrode sheet was designed,this paper discussed the influence of heating temperature and carbon coating thickness on cycle stability,and proposes a new idea to solve the volume expansion problem from the electrode sheet level.The main research contents and results of the paper are as follows:(1)On the basis of the acidification(pretreatment)of acetylene black with concentrated nitric acid,select materials such as egg liquid,melamine,m-aminobenzene sulfonic acid,milk powder,etc.,through the method of liquid film wetting combined with thermal decomposition,to the acidified polarity acetylene black was functionalized and modified,the mechanism of functional acetylene black inhibiting the dissolution of polysulfides was analyzed,and an orthogonal experiment was designed to optimize the modification process.The research shows that the functional acetylene black(HAB-75-E)with 30%egg liquid added and thermally decomposed at 800℃ for 2 h has the best electrochemical performance after being loaded with sulfur,and the specific capacity is 786.49 mAh g-1 after 100 cycles at 1C current density,the capacity retention rate is 90.29%.(2)In this paper,the concept of gradient structure lithium-sulfur battery cathode sheet is proposed,and the carbon coating film technology is introduced to control the sublimation and condensation process of active sulfur in the cathode sheet through heat treatment.A gradientstructured lithium-sulfur battery cathode sheet with a decreasing sulfur content along the cathode sheet to the carbon coating film is prepared,which reserves space for the expansion of active sulfur and relieves the volume expansion during charging and discharging;further,The preparation process of the gradient structure electrode sheet was optimized by adjusting the heat treatment temperature and the thickness of the carbon film.The electrochemical performance results show that the specific capacity of the gradient-structured electrode sheet with a carbon film thickness of 10 μm after heat treatment at 120℃ for 2 h after 100 cycles at 1C current density is 744 mAh g-1,and the capacity retention rate is 94.03%;after 200 cycles the specific capacity is 684.4 mAh g-1,and the cycle retention is 86.2%.