| Lithium-sulfur battery is a kind of advanced battery with low cost,high energy density and long-term stability.However,due to the current commercialization of liquid electrolyte is easy to leak,prone to safety accidents,researchers will focus on solid polymer electrolyte,in order to obtain more safe and higher energy density of lithium sulfur battery.However,due to the lack of a liquid component,the solid electrolyte has very low ionic conductivity,poor interface contact with the electrode and narrow electrochemical window.A kind of electrolyte between liquid and solid electrolyte,namely gel electrolyte,was developed to solve these problems.Gel electrolyte is a kind of electrolyte that fixed liquid electrolyte in solid polymer matrix.Combined with the advantages of liquid and solid electrolyte,it can be used in lithium-sulfur battery to improve the comprehensive performance of the battery.In this paper,PVDF-HFP-based gel electrolyte was prepared and applied to lithium-sulfur batteries.The main research contents are as follows:（1）PVDF-HFP gel electrolyte was prepared in three different ways to test the physical and electrochemical properties of the gel electrolyte membrane,and then assembled into a lithium-sulfur battery to test the comprehensive performance of the battery.The membrane prepared by electrospinning method has large specific surface area and high porosity,which can speed up the transport of Li+,improve the ionic conductivity of the membrane and the migration number of lithium ions,so that the comprehensive performance of the battery is improved.At the rate of 0.1C,the discharge capacity of the first cycle is as high as 1284.8 m Ah g-1,and the capacity retention rate of the battery is 24.3%after 50 cycles.The cycle stability of the battery is much higher than that of evaporation and phase separation methods.Considering the advantages of low cost,simple operation and so on,electrospinning membrane has great potential application in the preparation of gel electrolyte membrane.（2）PVDF-HFP/PEO composite gel electrolyte was prepared by electrospinning using PVDF-HFP and PEO as polymer matrix materials.The two polymer combinations can give full play to their respective advantages,which is more conducive to improving the electrochemical performance of lithium-sulfur batteries.With the addition of PEO,its functional groups can anchor polysulfide and inhibit the shuttle effect.At the same time,the effects of different proportions of PVDF-HFP and PEO on the performance of the gel electrolyte and the comprehensive performance of the assembled cells were explored.Experimental results show that PVDF-HFP-30%PEO has the best effect.At20℃,PVDF-HFP-30%PEO has high ionic conductivity(4.3×10-3 S cm-1),high lithium ion migration number（0.768V）and wide electrochemical stability window（4.6629V）.At the rate of 0.2C,the discharge capacity of the assembled lithium-sulfur battery is 1280.8 m Ah g-1 in the first cycle,and the discharge capacity is still up to430.3 m Ah g-1 after 50 cycles.The coulomb efficiency is nearly 100%,and the cycle stability is excellent.（3）ZrO2 modified PVDF-HFP-30%PEO gel electrolyte was prepared by electrospinning technology and applied to lithium-sulfur batteries.An appropriate amount of ZrO2 can reduce the crystallinity of the polymer system,improve the ionic conductivity and lithium ion migration number of the membrane,and thus improve the comprehensive performance of the battery.At the same time,the appropriate proportion of ZrO2 was explored,and it was proved that PVDF-HFP-30%PEO-8%ZrO2 gel had the best electrolyte performance.PVDF-HFP-30%PEO-8%ZrO2 gel electrolyte membrane at 20℃has an ionic conductivity of 6.5×10-3 S cm-1,a lithium ion transfer number of0.89,an electrochemical window of 4.81V,and a good interface stability,which can effectively inhibit the growth of lithium dendrite.At the rate of 0.5C,the discharge capacity of the assembled lithium-sulfur battery is up to 1122.7 m Ah g-1 in the first cycle,and still 472.9 m Ah g-1 after 100 cycles,showing excellent comprehensive performance. |
