Study Of Low Concentration Salt Triggered In-situ Solid State Gel Electrolyte For Li-S Batteries

Lithium-ion battery has been widely concerned and applied since its successful commercialization.It has become the main powerful source of portable devices that gradually occupies the market of new energy tram and energy storage power station.With the rapidly development of new energy industry in recent years,the current lithium-ion battery can not meet the demand in energy density,safety performance and other aspects.It is urgent to develop the next generation battery technology with higher energy density and higher safety.Li-S batteries with a theoretical energy density of 2600 Wh/kg and a wide range of sulfur resources and low cost are considered as one of the most promising next-generation battery technologies and have attracted extensive attention in recent years.It’s often used in lithium sulfur batteries 1,3-dioxolane（DOL）and ethylene glycol dimethyl ether（DME）liquid electrolyte,the battery charge/discharge process are the more intermediate sulfur ions（LPS）can be dissolved in the electrolyte,shuttle to the lithium cathode,resulting in battery performance attenuation,it is the important reason of lithium sulfur batteries to the application.DOL in-situ ring-opening reaction was initiated by lithium salt to realized in-situ polymerization of liquid electrolyte into gel electrolyte,which effectively solved the LPS shuttle effect during the battery cycle and improved the cycle stability of Li-S battery.But the high concentration of lithium salts required as initiators increases the cost of lithium-sulfur batteries with this new electrolyte system,According to the above key problem,this paper developed a low concentration of salt gel electrolyte in-situ polymerization technology,inside the battery has realized the gel/preparation of solid composite polymer electrolyte,obtained the good electrolyte/electrode contact interface,and solve the problem of LPS shuttle,effectively promoted lithium sulfur batteries circulation performance,specific research contents include:（1）Across the electrode to explore different gel composite electrolyte system,inside the battery was studied by means of in situ gelation of liquid electrolyte,namely in lithium metal surface modification with ether after ethylenediamine lithium base electrolyte have negative state gel electrolyte through crosslinking reaction,the positive side of BF₃initiator induced by Lewis acid cyclic ether solvent base ring opening polymerization preparation of gel electrolyte.This scheme mainly solved the problem of poor compatibility between organic lithium amine/ether based solvent crosslinked gel electrolyte and sulfur anode,and the strong corrosion of lithium metal anode by Lewis acid initiator.（2）A two-phase composite electrolyte was proposed,in which DOL polymerization was initiated at low salt concentration and DME kept the liquid phase in the mixed solvent to maintain the dissolution and reduction of polysulfide and realize the coexistence of gel-liquid phase.Based on the gel electrolyte,the stable cycle of the lithium metal symmetric battery is more than 1400 hours,the lithium deposition/stripping overpotential is only 0.1V,the ionic migration number of the composite electrolyte is 0.75,and the conductivity is 3.09×10^-3S/cm.Based on the electrolyte,a lithium sulfur battery was constructed,which achieved a stable cycle of 200 cycles and a capacity retention rate of68%.These results indicate that the complex electrolyte can effectively block LPS shuttle and improve the cycle life.（3）In order to further improve ion migration number and electrolyte stability of in-situ solid gel electrolyte,in-situ gel/solid composite electrolyte was prepared.A sulfide solid electrolyte,lithium,germanium,phosphorus and sulfur（LGPS）,was combined with DOL in situ gel.In situ solid-state strategy,on the one hand,inorganic solid particles were effectively confined to the lithium anode side,and at the same time,good interface contact between solid composite electrolyte and electrode was achieved.The specific capacity of the lithium-sulfur battery based on the composite electrolyte remains at 750 m Ah/g after200 cycles,which significantly improves the cycling performance of the battery.The results show that the strategy of in situ gel electrolyte can effectively improve the performance of lithium-sulfur battery,and provide a new idea for the industrial application of lithium-sulfur battery.