Preparation Of Polyethylene Oxide Based Composite Electrolyte Membrane And Study On Its Performance Of All Solid State Lithium Battery

All solid state lithium batteries are considered as next-generation battery candidates due to their safety and high energy density.However,solid electrolytes are not good enough to match the performance of traditional liquid electrolytes.It is a difficult problem to improve the transmission efficiency of lithium ions and realize higher ionic conductivity.In the composite solid electrolyte,lithium ions can be transported through the interior of the active inorganic filler,the polymer chain,and the inorganic/polymer interface.In addition,the ion transport mechanism of the composite solid electrolyte largely depends on the type,structure and morphology of the active inorganic filler.Therefore,polyepoxy-ethylene alkyl composite electrolytes containing perovskite type and garnet type inorganic fillers were prepared respectively.It is expected to have both organic and inorganic electrolyte characteristics to achieve the effect of complementary advantages.In this paper,one-dimensional inorganic nanomaterials were prepared by electrospinning technology and high-temperature calcination,and the effect of filler morphology on ionic conductivity of polyethylene oxide based composite solid electrolyte was studied.The influence of the transport path of lithium ions inside the crystal on the electrochemical performance of the composite electrolyte was investigated by in situ blending.Specific research contents and results are as follows:In order to investigate the effect of packing morphology on ion migration path,perovskite-type Li_0.33La_0.557Ti O₃ nanofibers and nanoparticles（LLTO NFs/NPs）were prepared and mixed with PEO-Li TFSI by solution casting method to prepare composite solid electrolyte films.One-dimensional LLTO nanofibers form a three-dimensional nanoskeleton in polyethylene oxide to provide a continuous transport path for lithium ions.When the mass fraction of inorganic LLTO NFs was 15%,the ionic conductivity of the composite solid electrolyte reached a peak of 4.40×10^-4 S/cm（60℃）,the electrochemical window was increased to 5.16 V,and the number of lithium ion migration was up to 0.38.The symmetrical lithium battery had a smaller polarization voltage in the lithium plating/stripping cycle at 0.2m A/cm² current density.At 0.5 C,the discharge specific capacity retention rate was 99.5%after 130 cycles.The lithium ion pathway inside garnet Li₇La₃Zr₂O₁₂（LLZO NFs）crystal was studied by in situ internal doping of In³⁺.More stable cubic phase LILZO NFs was obtained when the mole ratio of doping is 0.2.By replacing Li⁺with In³⁺with large ion radius,the lithium vacancy and the transport path of lithium ions in the crystal are increased successfully,and the ionic conductivity of the composite solid electrolyte is nearly doubled to 9.39×10^-4 S/cm at 60℃.Symmetric lithium battery could cycle 230 h stably at 0.5 m A/cm² current density.All solid state lithium battery had a long cycle life at 0.5 C（60℃）charge and discharge,initial discharge specific capacity of 140 m Ah/g,400 cycles after the capacity retention rate of 80%（109 m Ah/g）,2000 cycles still had 99.75%coulomb efficiency.In summary,this study modified the active inorganic filler in the composite electrolyte.By designing a three-dimensional lithium ion transport network and optimizing the concentration of lithium vacancy in the crystal,the agglomeration of inorganic fillers could be reduced,the transport path of lithium ions could be increased,the ionic conductivity and electrochemical performance of the composite electrolyte could be improved.It provided a new design idea for the preparation of simple,safe,stable and high ionic conductivity solid electrolyte,which had certain theoretical guiding significance and practical application value.