| Lithium sulfur battery because of its high theoretical capacity of 1675 mAh g-1,theoretical energy density of 2800 Wh L-1 and outstanding output power,is expected to meet the requirements of high performance electrochemical energy storage devices for the rapid development of new energy electric vehicles and electronic information products.However,the problems of low conductivity,poor rate performance and short cycle life have been restricting the industrialization development of lithium sulfur battery.This paper is mainly about enhancing the conductivity of lithium sulfur battery and inhibiting“shuttle effect”through modifying the traditional separator.Three kinds of separator modified coating were prepared,namely active carbon/polyvinylidene fluoride modified coating?AC/PVDF?,active carbon/carbon nanotubes modified coating?AC/CNT?and isopropyl/active carbon modified coating?IPA/AC?.And used the nitrogen physical adsorption apparatus to analyze the surface area,pore volume and pore size distribution of active carbon and active carbon/carbon nanotubes composite.The surface morphology and element distribution of the coating were measured by scanning electron microscope and energy dispersive spectrometer before and after cycling.A series of performance tests for these three kinds of batteries were carried out by using LAND battery test system and electrochemical workstation.1.Mechanical grinding method was used to make AC/PVDF coating composite materials with mass ratio of 7:1,8:1 and 9:1.Then the AC-X?X=7,8,9?modified separator were prepared by blade coating technique.It is found that the battery has the prominent performance when the mass ratio of AC/PVDF is 9:1,especially after 400 cycles under 0.2C,the battery has only 0.15%per cycle capacity attenuation rate.In addition,this battery has the longest discharge platform and the weakest polarization as well as the minimum charge transfer resistance.This is because the AC-9 coating has excellent electrical conductivity and maximum surface area on the premise of ensuring the stable structure,making the modified separator with the best inhibition effect on polysulfides.2.The coating composite of AC/CNT=7:1,8:1,9:1 were obtained by mechanical grinding.The AC/CNT-X?X=7,8,9?modified separators were prepared by using the blade coating technique.It is found that the battery with AC/CNT-8 coated separator can obtain the highest first discharge capacity of 1495 mAh g-1 and can remain 742 mAh g-1 after 200cycles at 0.2C,which is obviously better than the other two kinds of modified batteries.Moreover,under varying current rate?0.2C?1C?0.2C?,the AC/CNT-8 coated separator also has an ideal rate performance.These can be attributed to the effective interception of AC/CNT-8 modified coating on polysulfide ions and the improved conductivity of the battery.3.The active carbon was successfully hydroxylated by isopropyl solution immersion and magnetic stirring,and then the IPA/AC composite material was used as modified coating for separator.The X-ray photoelectron spectroscopy was used to determine the amount of hydroxyl functional groups introduced in active carbon,and a series of electrochemical tests were used to analyze the electrochemical properties of the modified battery.It is found that the content of C-OH in IPA/AC composite is up to 40%,and the modified coating can successfully integrates the strong physical adsorption of active carbon and the electrostatic repulsion between the hydroxyl and negatively charged polysulfide ions,which can obviously reduce the loss of active substances and make the performance of the batteries more prominent. |
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