Preparation Of Multifunctional Polymer Electrolyte And Its Performance In Lithium-sulfur Batteries

Currently lithium ion battery is the most widely used secondary battery in the world,but the development of lithium battery has encountered a bottleneck due to the limitation of its own energy density(120-180 Wh/kg).Lithium sulfur battery has entered the field of vision by its high energy density and high specific capacity.Among them,the theoretical energy density of positive sulfur can reach 2600 Wh/kg,and it is rich and environmentally friendly.Therefore,the development of lithium sulfur battery has become a hot spot.Firstly,PAN is modified with ammonium polyphosphate(APP)of different mass fractions by electrospinning,and APP/PAN(APAN)electrolyte is prepared.The flame retardant performance of APAN electrolyte is good,and APAN has certain inhibition effect of poly sulfide.When the APAN content of APP is 20 wt%,the performance is the best.The room temperature ionic conductivity of APAN electrolyte is above 1×10-3 S/cm,and the electrochemical window is relatively high.Besides,in order to further improve the performance of APAN electrolyte,functional layers of carbon nanotubes(CNTs)are added to increase the physical capture site and further inhibit the shuttle of polysulfide,thus enabling the battery to have excellent cycling stability.At the current density of 0.5C,the capacity of CNTs-20%APAN electrolyte remains above 50%of the initial capacity after 200 cycles.Meanwhile,the carbon layer conductive network constructed by CNTs stimulates the capacity release of the lithium sulfur battery,so that it has a higher initial capacity.Secondly,solid electrolyte is the future development trend,but its low room temperature conductivity inhibits its industrial application.At present,little work has been done to quantitatively or qualitatively analyze the influence of residual solvents on the batteries.In lithium-sulphur batteries,long chains of polysulphides are dissolved in organic electrolytes,making the"shuttle" more obvious.In this paper,the preparation of PVDF-CTFE(PCF)electrolyte by volatile liquid electrolyte at room temperature,to find the the performance influence of lithium sulfur batteries about the quantitative study of electrolyte content in electrolyte.The result shows that as the volatilization time increased electrolyte content gradually decreased,cell cycle stability enhancement when the volatile time within 20 min.20 min volatile PCF electrolytes use in sulfur lithium batteries,under the current density of 0.2 C and worke at room temperature when cycle after 100 laps,capacity remain at a rate of 77%.Finally,in order to maintain the stability of lithium metal anode,keep away from the battery safety problem and to prevent the lithium dendrite from puncturing the diaphragm.In this paper,by adding lithium fluoride(LiF)to the PCF electrolyte,the PCF-LiF electrolyte with structure of A/B layer is prepared.The A layer is composed of pure PCF electrolyte and serves as structural support.The functional layer B is composed of LiF modifies PCF electrolyte and actes on the lithium metal negative electrode,protecting the SEI membrane and promoting the uniform deposition of lithium metal.When this electrolyte is applied to lithium sulfur battery,it is found that with the increase of LiF content,the cycle stability and multiplier performance of the battery are better.This structure electrolyte has high electrochemical decomposition voltage and high ionic conductivity.