Design,Preparation And Research On The Comprehensive Properties Of Polymer Electrolytes With High Safety And High Performance

With low flash point,strong volatility and inflammable,the carbonate organic solvent has led to frequent safety accidents of liquid lithium-ion batteries.Reducing the proportion of organic solvents and gradually achieving solid-state electrolyte is the main development direction of lithium-ion batteries.Due to the fast ions diffusion kinetics,inorganic solid electrolytes（ISEs）displays high lithium ion conductivity(～10^-3 S cm^-1),which is instrumental in preserving the electrochemical property and safety of LIBs.However,the poor mechanical properties and weak interface wettability of electrode/electrolyte inhibits the practical application of ISEs.In contrast,with favorable mechanical properties,high toughness and excellent electrode/electrolyte interface wettability,gel（quasi-solid）/full solid-state polymer electrolytes presents more advantages than ISEs in large-scale application.However,the improvements of energy density and security for polymer batteries are still plagued by the poor lithium ion conductivity(～10^-5 S cm^-1)and low oxidation stability.Based on this,three polymer electrolytes are synthesized in this work,and the relevant mechanisms about lithium ion transport are innovatively investigated:（1）Preparation and properties of fumarate nitrile based flame-retardant gel polymer electrolyte.Succinonitrile（SN）is ideally suited for application as a flame-retardant additive due to the merits of excellent thermal stability and high dielectric constant.However,the severe parasitic reactions with Li anode restrict the extensive application of SN.Herein,an in-situ polymerized gel electrolyte consisting of fumaronitrile（FN）,methyl methacrylate（MMA）and ethoxylated trimethylolpropane triacrylate（ETPTA）is prepared.FN segment is fixed in polymer chains and shows the similar molecular structure with SN after polymerization,therefore the flame retardant effect is achieved and the parasitic reaction with Li anode is suppressed.Li/FGPE/Li symmetrical cell exhibits a great performance with the maximum voltage of about 11m V after 7850 h.（2）Research on perfluorinated solvent based gel polymer electrolyte and lithium ion conduction mechanism.On the basis of work（1）,the liquid phase component（named as FLE）is prepared by dissolving lithium difluoroxalate borate（LiDFOB）in vinyl fluoride carbonate（FEC）solvent,and a new high-performance flame retardant gel polymer electrolyte（F-GPE）is in-situ polymerized with MMA,triethylene glycol dimethacrylate（TEGDMA）and ETPTA.The polymer segments are extended with the swelling of FEC,then an electron delocalization interface layer is generated between FEC liquid state and polymer ingredients,which works as an electron-rich“Milky Way”and facilitates the rapid transfer of Li ions by lowering the diffusional barrier dramatically,resulting in a high conductivity of 2.47×10^-4S cm^-1.Remarkably,FEC ingredient provides high flame-retardancy and make F-GPE remains stable under ignition and puncture tests.（3）Research on polyacrylate based SPEs and mechanism of lithium ion conduction.The combination of polymer electrolyte and high nickel cathode has been realized in F-GPE fabricated in work（2）,while in order to further improve the safety performance,it is necessary to construct FSPEs.Polyacrylate is deemed as a promising matrix for next generation FSPEs.However,the further improvement of ionic conductivity within the polyacrylate system has been restricted by perplexing ions migration mechanism,which originates from the long branched chaine structure.Herein,a novel polyacrylate based SPE（named as PV-SPE）is synthesized by in-situ thermal polymerization of poly（ethylene glycol methyl ether methacrylate）（PEGMEMA）and vinylene carbonate（VC）.According to the results of molecular dynamic simulation（MD）,with lower binding energy,VC forms the fast migaration route of Li ions,while PEGMEMA displays high binding energy towards Li ions acts as a"pump",which forms a unique channel with alternating binding energys,so as to provide additional power for ion migration.Noteworthily,owing to the unique pump structure of PV-SPE,the LFP/PV-SPE/Li battery displays favorable electrochemical stability during ultra-long cycling（about 2000 cycles）at 60℃and 1C(1C=170 m A g^-1)without degenerate interface and obvious lithium dendrites.