Preparation Of Modified Glass Fiber Membrane And Its Application In Lithium-sulfur Batteries

With the rapid development of electric vehicles and portable devices,the demand for high-performance batteries is increasing.Lithium sulphur batteries have attracted wide attention due to it’s high theoretical specific capacity（1675 mAh/g）and energy density（2600 Wh/kg）.However,due to low electric conductivity of sulfur and“shuttle effect”caused by diffusion of soluble polysulfides to the anode,resulting in rapid decay of capacity,limits the commercial application of lithium sulfur batteries.Currently,Celgard polyolefin membranes are used in both lithium sulfur batteries and lithium ion batteries.In this paper,we use glass fiber membrane replaced Celgard polyolefin membrane as a lithium sulfur battery separator,and we further modified glass fiber membrane to prepare high-performance lithium sulfur batteries.The main work is as follows:（1）The feasibility of replacing commercial membrane with glass fiber membrane as a lithium sulfur battery separator.Commercial Celgard membrane has low liquid absorption rate and poor thermal stability.In this paper,commercial Celgard membrane was replaced by glass fiber membrane as a lithium sulfur battery separator.We compared the two membranes physical properties,as well as assembled batteries electrochemical and cycliing performance.Results show that,the liquid absorption rate,porosity and ionic conductivity of glass fiber membrane was 727.5%,65%and2.54 mS/cm,which of 6 times,2 times and 6 times than commercial Celgard membrane,respectively.Glass fiber membrane also has high thermal stability,after 2 h under 150℃heated,it still can kept the shapes as before.Using glass fiber membrane assemble batteries,the batteries impedance was low,and the cycling performance was stable,furthermore,there were no side reaction in battery.To sum up,the glass fiber membrane can replace the commercial Celgard membrane as a lithium sulfur battery separator.（2）Preparation of mesoporous TiO₂ and its application in lithium sulfur battery separator.The strong interaction between metal oxides and polysulfides can inhibit the diffusion of polysulfides and alleviate the"shuttle effect".In this paper,mesoporous TiO₂ was prepared by soft template method.We mixed mesoporous TiO₂ with Ketjen Black and coated the hybrids on the surface of glass fiber membrane to modify the separator.Mesoporous TiO₂ can adsorb polysulfides effectively,alleviating the"shuttle effect",at the same time,Ketjen Black with excellent conductivity can activate the adsorbed polysulfides,increasing the discharge specific capacity.The batteries using modified separators electrochemical test results show that the initial specific discharge capacity was 1130.3 mAh/g at the rate of 0.2 C,and 991.8 mAh/g remained after 60 cycles,showing a excellent cycling performance.（3）Preparation of magnetic mesoporous Fe₃O₄ nanoparticles and it’s application in lithium sulfur battery separator.The charged particles moving in magnetic field were affected by lorentz force,so it can using the magnetic field to concentrate the polysulfides and limit the diffusion of polysulfides to anode.In this paper,the Fe₃O₄ nanoparticles were prepared by ahydrothermal method,then heated the Fe₃O₄ nanoparticles to 600℃for 2 h under nitrogen protection,get the magnetic mesoporous Fe₃O₄ nanoparticles.Then we mixed the magnetic mesoporous Fe₃O₄ nanoparticles with Ketjen Black,and coated the hybrids on the surface of glass fiber membrane to modify the separator.Polysulfides moving in the magnetic field were subjected by lorentz force,and it were concentrated around the magnetic mesoporous Fe₃O₄ nanoparticles,which can beadsorbed by magnetic mesoporous Fe₃O₄ nanoparticles easily,at the same time,Ketjen Black with excellent conductivity can activate the adsorbed polysulfides,increasing the discharge specific capacity.The batteries using modified separators electrochemical test results show that the initial specific discharge capacity was 1274.5 mAh/g,at the rate of 0.2 C,and 896.3 mAh/g remained after 50cycles,showing a excellent cycling performance.（4）The application of metal organic frameworks in lithium sulfur battery separator.Metal organic frameworks（MOFs）has abundant pore structure and it can adsorb polysulfides to some extent.In this paper,three kinds of MOFs UiO-66,MOF-5 and ZIF-8 with different pore sizes were grown in situ on the glass fiber membrane,and then Ketjen Black was coated on the surface of glass fiber membrane to modify the separator.MOFs with abundant pore structure can adsorb the polysulfides,at the same time,Ketjen Black with excellent conductivity can activate the adsorbed polysulfides,increasing the discharge specific capacity.The batteries using modified separators electrochemical test results show that the UiO-66 modified separator battery had the best cycling performance,with the initial discharge capacity of 1270.1 mAh/g at the rate of 0.2 C,and 827.7 mAh/g remained after 100 cycles,showing a excellent cycling performance.