Preparation And Characterization Study Of Polyethylene Oxide Based Composite Solid Electrolyte With Garnet-type Nanofibers

Owing to the high energy density and superior safety,all-solid-state lithium ion batteries are regarded as an ideal energy storage solution for electric vehicles and large-scale electrical power grids.Solid state electrolytes are the key component of solid-state batteries,as a part of that,the composite polymer electrolytes(CPEs),which combine the advantages of solid polymer electrolytes(SPEs)and inorganic ceramic electrolytes(ICEs),is one of the most attractive research topics in the field of solid state electrolyte because of its high ionic conductivity and small interfacial resistance at temperature above 60?.However,the relatively low ionic conductivity at room temperature and the formation of lithium dendrites limit their safety and cycling stability,thereby hindering the practical applications of all-solid-state lithium ion batteries using CPEs.To solve the aforementioned issues,a novel concept for composite polymer electrolytes had been applied and studied in this work:Ceramic nanowires instead of particles had been used as fillers in our novel composite solid electrolytes,the garnet-type Li₇La₃Zr₂O₁₂(LLZO)ceramic nanowires were fabricated by electrospinning technique and further optimized by doping with Al and Ta elements.As a result,an electric field of 15?20 k V and an ejection speed of 0.3?0.5 m L·h^-1 were found to be the optimal condition for fabricating the electrospun samples.The Ta doped LLZO nanofibers with stable cubic structure and continuous fiber morphology were achieved by doping with 0.3 mol Ta and calcinating at 700?for 3h.The as-prepared nanowires with an average diameter of266 nm were finally chosen as the filler for this study.The prepared garnet-type LLZTO ceramic nanofibers were filled in the polymer-in-salt matrix to construct a novel CPEs.A variety of lithium ion transmission channels,and the interaction between anion and ceramic nanofibers in the CPEs were explored to optimize lithium ion conduction.Polymer and lithium salt used in this study are polyethylene oxide(PEO)lithium bistrifluoromethane-sulfonimide(Li TFSI),respectively.The novel CPE exhibit an excellent ionic conductivity of 2.13×10^-4 S·cm^-1 at room temperature,a high Li⁺transference number of 0.57 as well as electrochemical stability up to 4.9 V.Using Li Fe PO₄ as the cathode,the assembled all-solid-state lithium metal battery delivers high initial capacity of 125.8 m Ah·g^-1 and a capacity retention of 94.9%after 60 cycles at room temperature.On the other hand,a novel 3D active ceramic framework,which composes a tri-layer structure of network-ceramic-network,was well designed and prepared through electrospinning and sol-gel methods.The ceramic framework was then casted with PEO/salt matrix to obtain the network-ceramic-network composite electrolyte(NCN-CPE).The NCN-CPE exhibits an excellent ionic conductivity of 3.4×10^-4 S·cm^-1 at 40?,a wide electrochemical stability up to5V.The assembled all-solid-state batteries possess high initial capacity of 152.6 m Ah·g^-1 and a capacity retention of 90.0%after 500 cycles at 40?and 0.2 C.