Research On Realizing The Solidification Of Lithium Sulfur Batteries By Optimizing The Interfacial Engineering

Sulfur has been treated as one of the most promising cathode materials for secondary energy storage chemistry,inspired by its high theoretical specific capacity(1675 mAh/g)and high theoretical energy density(2600 Wh/kg)when it is coupled with Li metal anode.In addition,sulfur possesses high reserves in nature,delivering low cost and eco-friendly properties,which have become a cusp in academia and industry.In conventional lithium sulfur(Li-S)batteries,the soluble intermediate products of sulfur during the charge and discharge processes will lead to severe shuttle effect,low Coulombic efficiency and poor cycling stability.Besides,utilizing lithium metal as anode is the prior prerequisite on realizing high energy density of the Li-S batteries.However lithium metal possesses vital defects including unstable nature against organic liquid electrolyte,safety concerns derived from dendrite growth.Till now these dilemmas confronted limited effective solutions.Solid state electrolyte is promising to absolutely solve the problems of lithium metal hence will import new opportunities on development of batteries.Regarding the problems in Li-S batteries and lithium metal,we take the suppression on shuttle effect by single ionic conduction as dominat task,gradually solidify the battery system by importing solid state electrolyte.The solid state electrolyte will improve the performance and safety of Li-S batteries simultaneously,providing new strategies and insights on developing Li-S batteries.The major research topics are summarized as follows:1.Sulfonic groups originated ionic selective and adsorptive dual functional interlayer for lithium sulfur batteries.The sulfonic groups possessing negative charge will realize cationic selection,suppressing the free migration of polysulfide anion.In addition,sulfonic groups will adsorb lithium polysulfide by forming“lithium bond”,fulfilling the dual function on suppressing the free migration of polysulfide and improving the utilization of active sulfur.In conventional liquid electrolyte,utilizing this designed interlayer,after 250 cycles at 0.5 C,the capacity retention can reach 802mAh g^-1.2.Pre-modifying lithium metal anode by solid state electrolyte.Lithium ion conductive solid state electrolyte is one of the promising materials towards lithium metal anode protection.The solid state electrolyte will guarantee the ionic conduction at the anode-electrolyte interface,meanwhile prevent the corrosive parasitic reaction stemmed from soluble polysulfide,organic electrolyte and lithium salts.Herein,we introduced Li₃PS₄ solid state electrolyte by a pre-reaction triggered by P₂S₅/S@THF solution.The electrolyte systems have imported the solid state electrolyte.Cooperating with liquid electrolyte,the electrolyte system exhibits hybrid system,which is a state combining solid state electrolyte with liquid electrolyte.The solid state electrolyte based protective layer will significantly improve the cycling stability and Coulombic efficiency of lithium sulfur batteries.Without any LiNO₃ additives in electrolyte,the Coulombic efficiency of lithium sulfur batteries still remained more than 90%,after200 cycles at 0.3 C,the specific capacity could remain 840 mAh g^-1.3.Garnet solid electrolyte based Li-S battery with modified anodic and cathodic interfaces.Researches have paid great endeavors on suppressing the shuttle effect in liquid electrolyte.Nevertheless,the shuttle effect can't be absolutely eliminated.Hence we utilized dense garnet solid state electrolyte.and good interfacial contact will be realized between Li metal and solid state electrolyte.Liquid electrolyte could be avoided at anodic interfaces.Melted lithium will tightly attached on garnet solid state electrolyte by lithiophilic modification on solid state electrolyte.At cathode side,a tiny amount of liquid electrolyte is added to maintain interfacial wetting.Li₂S/P₂S₅ additives at cathode side will significantly improve the cycling stability.In this section,solid state electrolytes have played important roles in the Li-S batteries.The solid state electrolyte dominates the battery system as“quasi solid state battery”.In the quasi solid state system,the performances of Li-S batteries have been significantly improved,after 500cycles at 1 C,the specific capacity of 805 mAh g^-1 is remained,accompanying with a low decaying rate of 0.0058%per cycle.The existence of solid state electrolyte is validated as key point.4.Highly endurable anode-electrolyte interfaces towards solid state battery.Utilizing the interfacial reaction between Al₄Li₉ and LLZO will form robust SEI with low interfacial impedance of<1?cm².The anode-solid state electrolyte interface can also endure high current density.Cooperating with tiny liquid or polymer at cathode side will contribute to assembling quasi solid state or all solid state battery.This designed electrolyte system could avoid the usage of liquid electrolyte,realizing the solidification of battery.At all solid state mode operated at 60 ^oC,the Li-S batteries have achieved the performance of over 800 mAh g^-1 after 100 cycles,with high Coulombic efficiency of 100%.