Preparation And Performance Of Dual-function Separator For Lithium Sulfur Battery

Lithium-sulfur batteries have become one of the future high-energy density battery systems due to their high theoretical specific capacity(1675 mAh g^-1)and energy density(2600 Wh kg^-1).However,the poor conductivity of the elemental sulfur and the discharge product Li₂S,the"shuttle effect",the deterioration of the lithium negative electrode caused by surface passivation,and volume change of the electrode material during charge and discharge process,all severely limite the commercialization process.It has been found that the"shuttle effect"caused by the dissolution of polysulfide and the deterioration of lithium metal anode are the main reasons for the rapid decline of lithium-sulfur battery capacity.In recent years,through cathode materials structural design,optimization of electrolyte composition and modification of separators,many progresses have been made in suppressing the"shuttle effect".In this work,three kinds of functional separators have been developed to inhibit polysulfide shuttle and protect lithium negative electrode.The details are as follows:1.Using lithified sulfonated polyether ether ketone?SPEEK?and Super-P?SP?particles to form dual-functional separator with cation selectivity on the surface of the PE separator.The SO₃^-group on SPEEK can provide transport channel for lithium ions and can repel polysulfide anions by coulomb interaction.SP has large specific surface area and can achieve good physical adsorption effect on polysulfide anions.At the same time,due to its good electronic conductivity,it can be used as additional current collector to promote electron transport and ensure the reactivation of the captured active material,thereby improving the electrochemical utilization of sulfur.Combination of them can suppress not only the diffusion of polysulfide,but also the formation of lithium dendrites.Capacity of the battery with this dual-functional separator remains at 576.8 mAh g^-1 and the lowest polarization?178 mV?after 200 cycles at 0.1 C.The SS-PE separator battery has high coulomb efficiency of up to 99%without the addition of LiNO₃.2.The KS-PE coated separator was prepared combining lithiated SPEEK and Ketjen black?KB?.The physical and electrochemical test results show that the high initial discharge capacity of 1114.6 mAh g^-1 is achieved at 0.1 C and can still maintain 850.5 mAh g^-1 after 100 cycles.The coulombic efficiency of the battery is 98%after 300 cycles at 0.1 C rate without the addition of LiNO₃,indicating the excellent cycle stability.Compared with the unmodified separator,the rate performance of the battery is significantly improved,especially at high rate?2 C?.It can also be seen from the FESEM photographs that the separator also has certain protective effect on the lithium negative electrode.3.Nano-TiO₂ is combined with lithiated SPEEK to form NTS-PE coated separator.Due to the strong adsorption of nano-titanium dioxide and electrostatic repulsion of SO₃^-group on polysulfide,the diffusion of polysulfide and the formation of lithium dendrites are suppressed effectively.Coulombic efficiency of the battery with this separator increases significantly?97%?,which is much higher than that of the unmodified separator?91%?.At the 0.1 C rate,the first capacity is as high as 1056.1 mAh g^-1,and the capacity of 516.2 mAh g^-1 can still be achieved after 200 cycles.