Selection And Research On Additives Of Lithium Sulfur Batteries

Lithium sulfur batteries has become research hot spot in advanced energy storage for its high specific capacity and low cost.Research on lithium sulfur batteries are facing with problems such as heavy passivation of cathodes,high reactivity of anodes and shuttle phenomenon,which result in lowered coulombic efficiency and bad cyclic performance.This work mainly focuses on optimization of electrolytes for lithium sulfur batteries.On one hand,in order to reduce cathode passivation and elevate high current density,selection was made between several kinds of organic solvents and additives to determine suitable ones.On the other hand,a few methods of supressing shuttle mechanism was explored,including using additive to increase electrolyte viscosity,employing additive to form solid-electrolyte interface?SEI?film on the anode,and trying functional solid electrolye separator to effectively separate cathode and anode.According to analysis and selection of solvents and additives,DOL is better than DME in protecting Li anode.It is appropriate for DOL to pair with organic solvents which are capable of solvating a series of reduction products ranging from polysulfides to Li₂S.Adding SL to electrolytes is generally benefit for improving discharging performance?including circumstances of higher sulfur loading of cathodes and higher discharging rates?of high current density.4-8 vol.%SL added is best for alleviating cathode passivation,raising low plateau voltage and elevating cyclic performance of high sulfur loading cathodes.SL-modified electrolytes are capable of partly dissolve lithium sulfides on surface of cathode carbon matrix,which is effective in reducing cathode passivation which appear during middle and late stage of discharging.In order to suppress shuttle mechanism,when applying high viscosity SL as additive,SL:DOL=5:5 lead to slower capacity fading and stabler cyclic performance.But using SL and raising viscosity to suppress shuttle mechanism can hardly carry out long-run steady performance.When using fluoroether additive,efficiency of lithium sulfur batteries goes up but stability of Li symmetry cell decreases after current density rise to 0.2 mA cm^-2.When using Li₂S-P₂S₅ additive,polarization during cycling becomes heavier,and low plateau disappears.More effective and systematic investigation should focus on lectrolyte additives in future.Using ceramic film is beneficial for suppressing capacity fading.Specific capacity decreases from1000 mAh g^-1 to 900 mAh g^-1 after 20 cycles,and coulombic efficiency stays at 100%,indicating that shuttle phenomenon is successfully inhibited.More study is needed on dealing polarization caused by many factors.