Preparation And Properties Of Modified Nanofiber Membrane For Lithium Sulfur Battery

Lithium-sulfur batteries have high theoretical specific capacity and energy density,which have reached 1675 mAhg^-1 and 2600 Wh/kg,respectively,and these batteries have the advantages of wide raw material sources,non-toxicity and harmlessness,and low cost.More and more scholars are paying attention.As one of the significant elements of the battery,the separator mainly separates the positive and negative electrodes of the battery and avoids the short circuit of the battery.At present,commercial lithium battery separators are still mainly based on polyolefin films.However,such separators have poor electrolyte wettability and liquid retention,poor thermal dimensional stability,and are likely to cause battery short circuits or even explosions.In particular,it is difficult to suppress the shuttle effect of lithium-sulfur battery polysulfides.Therefore,the development of new battery separators with high porosity,excellent electrolyte wettability,and high-temperature stability has become a research focus in the field of lithiumsulfur batteries in recent years.Electrospun PMIA nanofiber membranes have become the new type of lithium-sulfur battery separators with the most research potential at present due to their excellent high temperature resistance,high specific surface area and mechanical strength.However,self-discharge is severe due to the low lyophilic and liquid-retaining properties,which seriously hinders its further development.Therefore,in order to improve this kind of problem and better improve the electrochemical performance,this topic mainly works in two aspects:(1)Using high-performance PMIA as the substrate,SiO₂-F co-doped PMIA composite gelation film was prepared by electrostatic spinning technique.The mixture of F-doped PMIA film and SiO₂-F co-doped PMIA film enables the designed functional separator to have an extremely high electrolyte absorption capacity,and retains outstanding heat stability and good shrinkage resistance,and effectively limit the shuttle effect of polysulfides through physical limits and chemisorption.The Li-S battery combined with the designed separator has outstanding initial discharge capacity at 1274.8 mAhg^-1 and excellent cycle stability.At 0.5 C rate,the assembled battery has an excellent capacity retention rate of 814.8 mAhg^-1and a Coulomb efficiency of 98.42% after 600 cycles.(2)Electrospinning technology was used to prepare fluorine-doped PMIA nanofiber membranes containing MOFs.The microstructure was characterized by SEM,XRD,and FTIR.The influence of thermal stability,etc.,was initially tested on the electrochemical performance of batteries assembled with separators containing different proportions of MOFs.The results showthat the prepared aluminum-based MOFs have high purity,and the doped fluorinated PMIA nanofiber membrane has high thermal stability,good lyophilicity and liquid retention.According to preliminary AC impedance test,3 wt% MOFs-doped fluorinated PMIA nanofiber membrane has better electrochemical performance.The lithium-sulfur battery has a small charge transfer resistance and interface resistance,and has a very small Warburg impedance.Li-S battery combined using the designed separator,its PMIA,F-doped PMIA and MOF(3%)-F doped PMIA battery cycle,the initial specific capacity of the assembled battery was 1075.6 mAhg^-1,1093.1mAhg^-1,and 1133.2 mAhg^-1,respectively.The assembled batteries had specific discharge capacities of 520.4 mAhg^-1,613.9 mAhg^-1,and 782.6 mAhg^-1 after 300 cycles.