| Lithium-sulfur battery is regarded as one of the most promising rechargeable batteries for next generation,because it has advantages of high theoretical energy density,natural abundance and low cost.However,Li-S battery suffers from low columbic efficiency and fast capacity decays which can be ascribed to the dissolution of the intermediate polysulfides generated during the charge and discharge cycles.The previous reports show that lithium nitrates can effectively inhibit the shuttle phenomenon and improve columbic efficiency.However,lithium nitrates also cause irreversible oxidation of the positive active material,which results in capacity loss.Therefore,it is very important to find a more suitable method to suppress the shuttle phenomenon without use of lithium nitrate in the electrolyte.the single-ion conductive polymer electrolyte has the characteristic of selective ion permeability.It only allowed a single ion to get through the membrane,So it is also regarded as the ultimate strategy to solve the problem of lithium polysulfide shuttled between the anode and cathode.Lithium perfluorinated sulfonyl dicyanomethide?Li-PFSD?is a kind of novel polymer electrolyte with high Li-ion transference number,but Li-PFSD has generally low mechanical strength,low ionic conductivity,and it is easy swelling in liquid electrolyte,which results in possible physical degeneration.and LiPFSD has relatively higher density?about 1 g/cm3?than microporous polypropylene film?Celgard 2400?,which brings the problems such as the low weight energy density,which hindered its wide application.In this paper,we add respectively Li-GO and PVDF/SiO2 mixture into LiPFSD polymer electrolyte to enhance the ionic conductivity,solvent resistance,and improve the mechanical properties.It is found that the elastic modulus of the membrane increased from 3.2 Mpa to 4.85 Mpa,and the ion conductivity of the membrane increased from 2.26×10-44 S/cm to 2.65×10-44 S/cm when adding 0.1%Li-GO into the Li-PFSD polymer.However,the improvement of the cycling performance of lithium-sulfur battery was not significant.When adding 20%PVDF and SiO2 into the Li-PFSD polymer,its elastic modulus increased from 3.75 MPa to 13.5 MPa,and the ionic conductivity increased from 2.45×10-4 S/cm to 3.27×10-4 S/cm.Therefore,we can conclude that the PVDF and SiO2 mixture could greatly improve the ion conductivity and mechanical properties of the modified ternary electrolyte membranes.In order to improve the weight energy density of the Li-S battery,we cast the ternary electrolyte onto a microporous polypropylene film,which can reduce the thickness of the composite membrane to 25 um,and get a composite membrane with higher mechanical strength which can also restrain the shuttling effect effectively.This paper systematically studied the effect of the use of composite membrane on the cycling performance and the irreversible oxidation of lithium-sulfur battery without lithium nitrate addition.Results shows that the initial specific discharge capacity was995 mAh/g.After 50 cycles,it still maintains 798 mAh/g with a capacity retention of80.2%and columbic efficiency of 80%.In addition,the irreversible oxidation of the positive electrode reduces from 50%to about 18.4%PEDOT-co-PEG/PVDF was coated onto the metal lithium as a protective layer.The conductive polymer layer with coating thickness of 30?m can suppress the corrosion of the lithium metal and stabilize the interface between lithium electrode and electrolyte,and columbic efficiency was also improved.The specific discharge capacity of the Li-S battery with a protected Li anode and no lithium nitrates addition and composite membrane maintains high initial discharge capacity of 1287 mAh/g at 0.1C with a good specific discharge capacity of 698 mAh/g and capacity retention of 54.2%and the coulombic efficiency of above 95%after 100 cycles... |
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