Research Of Functional Additives And Composite Separator For Lithium Sulfur Battery

Secondary lithium-sulfur battery is currently known as one of the system with the highest theoretical capacity,which has a huge potential for further development.In this paper,the S@pPAN composite cathodes were prepared by combining sulfur?S?and polyacrylonitrile?PAN?at300?.The special structure of the composite not only inhibits the dissolution of sulfur and polysulfide during the reaction process,but also enhances the thermal stability of this cathode material.However,there still exist some notable drawbacks of the current Li/S@pPAN system:?a?Fast capacity decay of the electrode in the long-term charge/discharge process,with unstable interface layer and poor lithium diffusion coefficient;?b?Lithium dendrites,it can not only pierce the separator,but also cause short circuit problems even explosion;?c?The carbonate electrolytes are volatile and flammable,which is one of the severe safety hazard for lithium-sulfur battery system.In order to solve these problems,the effective functional electrolyte additives and a kind of organic/ceramic composite electrolyte sepeator were used to improve the cycling stability,rate performance and the thermal stability of the lithium-sulfur battery.The detailed contents and achievements are as follows:The effect of TMSB additive on the performance of S@pPAN composite electrode has been investigated.When 1 wt.%TMSB was added into the conventional electrolyte?1 M LiPF₆/EC+DMC?1:1,v/v??,the S@pPAN composite cathode exhibits excellent cycling stability and superior rate performance.The DSC data show that TMSB enhances the thermal stability of the functional electrolyte,and it improves the cycling stability of the S@pPAN composite cathode even at 60?.The EIS and XPS analysis indicates that TMSB participates in the formation of the interfacial layer between S@pPAN electrode and electrolyte.It helps to reduce the interface impedance and greatly increase.The lithium diffusion coefficients increase 3 times in the cathodic reaction and 5 times in anodic process.TFP additive greatly enhances the thermal stability and flame retardant of the conventional electrolyte.When adding 15 wt.%TFP,The S@pPAN electrode exhibits the best cycle performance and rate performance.Even if charging/discharging at a large rate of 2 C,the capacity retention is more than 80%at the 300^th cycle.When discharging at 10 C,TFP-containing battery shows high discharging specific capacity of 1130 mAh g^-1.TFP improves the wettability and compatibility between functional electrolyte,S@pPAN electrode material and the separator.Moreover it enhances the migration and diffusion of lithium ions,and modifies the electrode/electrolyte SEI film.As a result,the battery shows little loss of the active materials and lower interface impedance.PVDF-HFP/Al₂O₃ composite is a type of electrolyte separator with simple preparation method,instead of the traditional PE separator in this paper.This composite electrolyte separator shows many advantages,including the high mechanical strength,low surface energy,good wettability,good electrolyte-retention ability and excellent stability at high temperature.It also exhibits excellent rate performance.