Preparation And Performance Optimization Of Organic-inorganic Composite Solid Electrolyte Membran

Solid-state lithium batteries are considered to be one of the most promising energy storage devices due to their high energy density and high safety.As the critical component of the solid-state battery,solid-state electrolytes（SSEs）are the key to develop the solid batteries.Among SSEs,composite polymer solid electrolytes（CPEs）combine the advantages of inorganic electrolytes and polymer electrolytes,which show a high ionic conductivity,wide electrochemical,low price and simple preparation process.In this paper,we have prepared different organic-inorganic composite solid electrolytes by combining SiO₂ fillers with different morphologies and polyethylene oxide（PEO）matrix.The three-dimensional SiO₂ frameworks in developing CPEs with excellent electrochemical,mechanical properties and high ionic conductivity.The specific works are shown below:（1）The diameter of SiO₂particles is 300 nm,which are prepared by the sol-gel method.The composite membranes with SiO₂ mass fraction of 10%are prepared by the solution casting method.The ionic conductivity of the electrolyte with PEO and SiO₂particles is5.28×10^-5 S cm^-1 with thickness of 50μm at 30°C and the electrolyte achieved an area specific resistance of 94.7Ωcm² with the electrochemical stability window of 4.5 V.However,the specific surface energy of SiO₂ particles is large,and shows agglomeration in PEO.Due to the uneven distribution of SiO₂ particles in PEO,the tensile strength of the composite the electrolytes are nearly 0.4 MPa,which cannot effectively suppress lithium dendrites in the long term.In addition,the thermal stability of the electrolytes is tested when the thermal stability test is performed,a short circuit of battery assembled with the composite membrane is observed at 140°C.（2）The membranes of SiO₂ fibers with controllable thickness are prepared by electrostatic spinning as the backbone of PEO based electrolyte,and get the composite electrolyte with superb mechanical strength.The conductivity of the electrolytes is9.32×10^-5 S cm^-1 with thickness of 27μm at 30°C,and the electrolytes achieved an area specific resistance of 29Ωcm².The electrochemical stability window of the electrolytes is4.8 V.Meanwhile,the three-dimensional configuration can homogenize the electric field,which is conducive to the uniform transport of lithium ions and effectively avoid the growth of lithium dendrites.Moreover,the mechanical strength of the membrane of SiO₂ fibers is3.7 MPa,and the mechanical strength of the electrolyte could reach 7.4 MPa.Due to three-dimensional configuration of the membrane,the battery with the electrolyte not appear short circuit after heating to 400℃.（3）The electrochemical performance of solid-state battery with PEO/SiO₂ particles and PEO/SiO₂ fibers as electrolytes are investigated respectively.Cycling at a current density of 0.1 m A cm^-2,Li/PEO/SiO₂ Particle/Li shows a short circuit at the 120 h,and Li/PEO/SiO₂ Fiber/Li can cycle stably for 1000 hours.Meanwhile,the galvanostatic charge and discharge cycles were assessed at 0.1 C,Li/PEO/SiO₂ Particle/Li Fe O₄ only delivered an initial specific capacity of 135 m Ah g^-1,with a coulombic efficiency of 92.2%,and it suffered rapid capacity fading and increasing polarization within 20 cycles.And Li/PEO/SiO₂ Fiber/Li Fe O₄ shows its initial specific capacity is 167.9 m Ah g^-1,it suffered3.28%capacity degradation and exhibited little polarization after 100 cycles.