The Preparation And Properties Of Asymmetric Polymer Electrolytes For Lithium Batteries

Traditional liquid electrolytes for lithium metal batteries（LMBs）have potential safety hazards such as leakage,combustion,and even explosion,which hinder the further application and development of lithium batteries.Therefore,gel electrolytes and solid electrolytes have come into the spotlight.Polymer is a suitable material for the skeleton of gel electrolytes due to its advantages of good flexibility and designability.Among them,poly（vinylidene fluoride-co-hexafluoropropylene）（PVDF-HFP）is often used as the matrix for gel electrolytes due to its high dielectric constant.However,there are no obvious application advantages for gel polymer electrolytes（GPEs）,which used pure PVDF-HFP as matrix due to its low mechanical performance and ionic conductivity.Moreover,there are few studies about solid polymer electrolytes（SPEs）prepared by in-situ polymerization and used PVDF-HFP nanofiber membranes as the supporting skeleton.Therefore,in this work,multifunctional asymmetric GPEs based on PVDF-HFP were prepared by structural design,which can match high-voltage LMBs,avoid the collapse of cathode structure and suppress the growth of lithium dendrites.What’s more,we have conducted a preliminary exploration of in-situ polymerized SPEs based on nanofiber membranes.In this work,PVDF-HFP based asymmetric GPEs doped with barium titanate（BTO）and hexagonal boron nitride nanosheets（h-BNNS）were prepared by electrospinning to match high-voltage LMBs.T his GPE showed excellent electrochemical performance and the Li/Li Ni_0.5Co_0.2Mn_0.3O₂battery assembled with this GPE delivered excellent cycle performance(151 m Ah g^-1at 0.5 C,maintaining 80%capacity after 170 cycles),which was better than pure PVDF-HFP based GPE.Besides,we prepared PVDF-HFP based asymmetric GPEs doped with BTO and polydopamine coated BTO（PDA@BTO）to match high-voltage LMBs,and the layer doped with PDA@BTO was near to lithium metal anode.The encapsulation of BTO by polydopamine not only can avoid the unwanted reaction between Ti⁴⁺and Li metal,but also can improve the interface compatibility between GPEs and electrodes.This GPE exhibited ionic conductivity of 5.36×10^-3S cm^-1.The Li/Li Ni_0.8Co_0.1Mn_0.1O₂battery assembled with this GPE delivered high discharge specific capacity of 197 m Ah g^-1at 0.5 C,and 113 m Ah g^-1at 10 C.In addition,SPEs supported by PVDF-HFP based nanofiber membranes were prepared by in-situ polymerization of 1,3-dioxolane（DOL）.The supporting of nanofiber membranes can improve the mechanical properties of SPEs and the in-situ polymerization can ameliorate the poor interface between SPEs and electrodes.This SPE showed ionic conductivity of 2.2×10^-4S cm^-1.The Li/Li Ni_0.8Co_0.1Mn_0.1O₂battery assembled with this SPE delivered the discharge specific capacity of 154 m Ah g^-1at 1 C,and 81.2%of capacity retention after 200 cycles.