Improvement Of Polymer Gel On Electrochemical Performance Of Lithium-sulfur Battery

In the rapidly changing 21^st century,lithium-ion batteries have been used in all aspects of people's lives,at the same time,due to the extraction and consumption of traditional fossil energy,many researchers have applied lithium-ion batteries to new energy hybrid vehicles.However,as a common negative electrode material of commercial lithium-ion batteries,graphite materials have gradually become fatigued due to their theoretical specific capacity values(372 mAh·g^-1)in the endurance of electronic equipment and long-distance demand for hybrid vehicles.To this end,many scientists are pursuing a new generation of battery systems to promote the upgrading of the battery industry.Lithium-sulfur batteries are widely favored by researchers because of their high specific capacity(1675 mAh·g^-1),energy density(2600 Wh·kg^-1),abundant active material sulfur reserves and environmentally friendly.As the most important sulfur cathode material in lithium-sulfur batteries,problems such as volume expansion and poor conductivity occur during operation,which affects battery performance.During the reaction,the resulting product is also dissolved in the electrolyte and followed by the flow to the negative electrode causes a loss of capacity,which is the most famous problem of shuttle effect.Generally,people use carbon materials and sulfur for mixing and melting to provide a conductive network while adsorbing the generated polysulfide,but the effect is not significant.In recent years,researchers have used solid or gel electrolytes to solve safety problems such as short circuits and explosions that may occur during battery operation.This measure not only suppresses the shuttle effect of polysulfide ions,but also the gel polymer meets the future pursuit of flexible batteries due to its high mechanical properties and good toughness.In this paper,by applying polymethyl methacrylate?PMMA?and polyvinylidene fluoride copolymerized hexafluoropropylene?PVDFHFP?gel polymers to lithium-sulfur batteries,the shuttle effect of the battery is suppressed to a certain extent.And by adding bistrifluorosulfonylmethylimine lithium salt?LiNTFSI?to improve the cycle stability,the main content of this paper is as follows:?1?Using PMMA and PVDFHFP polymers as the coating slurry,composite electrode with gel porous coating was prepared by phase separation method.Characterized by SEM,TGA,EDS,etc.,confirmed that this experiment successfully prepared a porous composite electrode made of PMMA and PVDFHFP,and the influence of coating thickness on the electrochemical performance of electrode sheet was studied.In the battery assembled with three composite electrode pieces,the specific discharge capacity of P50?the coating thickness is 21.90?m?in the first circle reached1003.99 mAh·g^-1,and the Coulomb efficiency could remain stable at 99.7%,the specific capacity was still 817.23 mAh·g^-1 after 100 cycles,the retention rate is as high as 81.40%,the unretouched original electrode piece retains only 59.68%after 100cycles.At the same time,even at a high rate of 2 C,the specific capacity of the battery can have 420.8 mAh·g^-1.Obviously,the design of the coated composite electrode has a positive effect on the suppression of the shuttle effect of lithium-sulfur batteries.?2?PVDFHFP gel interlayer material was prepared by using phase separation to form a porous membrane,and bistrifluorosulfonylmethylimide?LiNTFSI?lithium salt was added to improve its performance.The result shows:the addition of lithium salt can promote the swelling of the polymer gel and be able to absorb more electrolyte.When the cycle rate is 0.5 C,the coulomb efficiency of the composite interlayer can be maintained at about 99.8%,which proves that the material is reversible.The lithium ion-added PIL-F has a specific discharge capacity of 999.2 mAh·g^-1 in the first cycle,and the retention rate can still reach 89.1%after one hundred cycles,the original electrode sheet without interlayer is only 59.68%,showing excellent cycle stability.Although the performance of PIL-F is slightly insufficient under high magnification,its specific capacity can still reach 345.4 mAh·g^-1.