Preparation Of Modified Separator Coating Based On Ketjen Black And Its Application In Lithium Sulfur Batteries

Lithium sulfur batteries,as a new type of secondary battery,has many advantages such as high theoretical specific capacity,abundant active material sulfur reserves,and environmental friendliness.It is expected to alleviate the increasingly serious energy and environmental problems in China,and is the focus and hot field of research at home and abroad.However,the practicality of lithium sulfur batteries still faces problems such as low cathode redox reaction activity,polysulfides shuttle effect,and lithium anode dendrite growth.With regard to the above mentioned problems,this paper takes the modification of the lithium sulfur batteries separator as an entry point,with a view to optimizing the electrochemical performance of the lithium sulfur batteries by designing and preparing a modified coating based on Ketjen Black,and developing a practical lithium sulfur batteries separator modification technology.The main research contents and results are as follows:?1?Ketjen Black?KB?-triphenylphosphine?TPS?multifunctional modified coating was prepared on the surface of the lithium sulfur batteries separator.The coating has a sponge-like structure and can be obtained by the spontaneous reaction between TPP and Li₂S₆ in the KB-triphenylphosphine?TPP?coating.The results show that the coating can significantly improve the electrochemical redox reaction activity of lithium sulfur batteries,the batteries charge-discharge rate performance and cycle stability.When the active material sulfur density is 3.6 mg cm^-2,the charge-discharge rate from 0.1 C to 2 C,the lithium sulfur batteries discharge capacity retention rate increased from 16.1%of the pristine separator polyethylene?PE?to 66.6%of the modified separator?KB-TPS/PE?.At 1C,the capacity decay rate of the modified separator is only 0.045%per cycle.The improvement of the electrochemical performance of lithium sulfur batteries is closely related to modified coatings having higher electronic and Li ion conductivity and effectively inhibiting the"shuttle effect"of polysulfides.?2?Polyvinylidene fluoride?PVDF?-polymethyl methacrylate?PMMA?-KB composite modified coating was prepared on the surface of the lithium sulfur batteries separator.The coating has a uniform pore network structure,which can be prepared by the method of solvent dimethylacetamide?DMAc?and deionized water exchange during the crystallization shrinking process of PVDF when it meets water.At the same time,the crystallinity of PVDF can be adjusted by regulating the content of PMMA to change the size of the porosity.The research results show that the coating has good mechanical properties and improves the electrochemical performance of the battery.Compared with the pristine separator?PE?,the modified separator?PVDF-PMMA-KB/PE?has stronger heat resistance and puncture resistance.When the active material sulfur density is 3.5mg cm^-2,the charge-discharge rate from 0.1 C to 2 C lithium sulfur batteries discharge capacity retention rate increases from 20.2%of the pristine separator to 67.3%of the modified separator,the capacity decay rate of the modified separator per cycle at 1 C is 0.067%.The improvement of the performance of the lithium sulfur batteries is related to the higher conductivity of the functional layer,the functional layer of PVDF pore network structure around 30 nm,inhibiting the shuttle of soluble polysulfides in the electrolyte to the anode,improving the utilization rate of the active material.