Design Of Novel Cyclic Phosphate Esters And Their Applications In Flame Retardant Liquid Electrolytes

In recent years,with the gradual popularity of new energy vehicles,the safety of on-board batteries has been widely concerned by the whole society.The safety problems of lithium-ion batteries are mainly caused by battery thermal runaway.A series of uncontrollable exothermic reactions will be triggered inside the batteries after the thermal runaway of batteries,making the internal temperature of the batteries continue to rise,and the electrolyte,separator,electrode and pouch of the batteries will be violently burned or even exploded.Therefore,it is necessary to design proper flameretardant structures to stop the battery combustion and explosion.Starting from the safety design of electrolytes,two kinds of cosolvents of flame retardant electrolyte was prepared by using two kinds of organic cyclic phosphate ester intermediates through one step fluorinated reaction,and jointly developed a new type of flame retardant electrolyte with lithium salt(Li TFSI),ethylene carbonate(EC)and dimethyl carbonate(DMC),respectively.The flame retardancy and electrochemical properties of fluorinated cyclic phosphate ester based electrolyte were studied.Specific research contents are as follows:1.A new type of flame retardant co-solvent trifluoroethoxyspirocyclic phosphate(SPTE)was synthesized by the reaction of spirocyclic pentaerythritol bisphosphorate disphosphoryl chloride(SPDPC)and trifluoroethanol,and then a flame retardant electrolyte based on SPTE was developed.The experimental results showed that the self-extinguishing time(SET)of 1 mol/L Li TFSI/(SPTE:EC:DMC=16.7:33.3:50.0)(SPTE123)electrolyte was 12.00 s/g,which reached the standard of flame retardant electrolyte.The ionic conductivity of SPTE123 electrolyte was1.014 m S/cm,and the electrochemical oxidation window voltage was 4.2V.SPTE123 electrolyte could make LFP‖Li half cell cycle stably 100 times at 0.5C charging and discharging rate,and improved the rate performance and cycle stability of graphite‖Li half cell.2.A novel flame retardant co-solvent 5,5-Dimethyl-2-(trifluoroethoxy)-1,3,2-dioxaphospholactyl phosphate(DPTE)was synthesized by the reaction of 2,2-Dimethyl-1,3-propanediol phosphoryl chloride(DPPC)with trifluoroethanol,and then a DPTE-based flame retardant electrolyte was developed.The experimental results showed that the SET of 1 mol/L Li TFSI/(DPTE:EC:DMC=25:25:50)(DPTE112)electrolyte was 13.75 s/g,which reached the standard of flame retardant electrolyte.The ionic conductivity of DPTE112 electrolyte was 1.072 m S/cm,and the electrochemical oxidation window voltage was 4.6V.DPTE112 electrolyte could make LFP‖Li half cell at 0.5C charge and discharge rate stable cycle 100 times still had 119 m Ah/g discharge specific capacity,and made graphite‖Li half cell stable cycle 80 times at 0.5C charge and discharge rate,with 344 m Ah/g discharge specific capacity,electrochemical performance was excellent;By analyzing the surface of the recycled graphite,the reason of enhancing the electrochemical performance of the electrolyte with DPTE was explained.