Preparation And Electrochemical Properties Of Pvdf-based Composite Solid Electrolyte Modified By Garnet-Type Llsbo

Lithium-ion batteries have been widely used in consumer electronics markets,electric transportation,aerospace,large-scale energy storage and other fields due to their energy storage and conversion functions,meanwhile they are environmentally friendly,convenient and efficient.However,there are some limitations caused by that the liquid electrolyte in the traditional commercial lithium battery is easy to flame and explode,and matches with electrode materials inferiorly.Therefore,solid state electrolyte is selected to replace the liquid electrolyte to obtain the favorite lithium-ion battery with high specific energy,high stability and security.Inorganic electrolyte is considered to own the excellent electrochemical properties,but the contact performance with electrode is unsatisfactory.On the other hand,flexible polymer electrolytes have an undesirably low ionic conductivity.Therefore,it is necessary to develop the new composite solid electrolyte of polymer electrolyte modified by inorganic materials to solve the problem of poor contact between electrolyte and electrode.The composite solid electrolyte has not only the high conductivity of inorganic electrolyte,but also the flexibility of polymer matrix.In this work,the composite electrolyte of polymer modified by garnet-type electrolyte was prepared successfully.In order to improve the ion transport of the interface between inorganic electrolyte and polymer matrix,the surface modification of garnet-type electrolyte was carried out through the metal-organic framework.Moreover,the composite electrolyte of polymer modified by inorganic electrolyte with three-dimensional framework structure was fabricated to optimize the electrochemical performances.The three-dimensional framework structure of inorganic electrolyte was obtained via an ice template method.The main research results are as follows:（1）PVDF-based composite electrolyte membrane with blending PEO was prepared by casting method,in it,garnet-type electrolyte Li_6.25La₃Sn_1.25Bi_0.75O₁₂（LLSBO）were as fillers.The effects of LLSBO on the crystallinity,microstructure and ionic conductivity of polymer were investigated.Experimental results show that LLSBO can reduce the crystallinity of polymer and promote the dehydrofluorination of PVDF.With the content of LLSBO was increased to be 15%,the ionic conductivity of composite electrolyte is arrived to 1.11×10^-4S cm^-1at room temperature,the stability window can reach 4.9 V.Meanwhile the electrolyte membrane possessed a tensile strength of 6.2 MPa,and the elongation of 32%.After 120cycles with 2 C rate at 28^oC,the assembled full battery presented the capacity retention of 81.56%and Coulomb efficiency of 99%.（2）The surface modification of garnet-type LLSBO electrolyte was carried out through the metal-organic framework ZIF-8,and then was added into polymer matrix to prepare composite electrolyte membrane.The effects of ZIF-8 with different contents modified LLSBO on the electrochemical properties of electrolytes were investigated.When the ratio of LLSBO to ZIF-8 was 4:1 and the content of fillers reached 15%,the ionic conductivity of as-prepared electrolyte sample was arrived to 2.25×10^-4S cm^-1at room temperature,the activation energy was 0.318 e V and the transference number reached 0.51.With 0.1 m A/cm²at 28^oC,the battery can cycle 800 h with a polarization voltage less than 60 m V.After 135 stable cycles at 2 C rate,the capacity retention rate of 80.45%and Coulomb efficiency of 99%.（3）Three-dimensional framework structure garnet（LLSBO-Ice）was prepared by ice template method,and filled by polymer to prepare composite electrolyte membrane.The effects of ionic transport performance with different contents of LLSBO-Ice were investigated.When the content of LLSBO-Ice was arrived to 60%,the conductivity reached 1.2×10^-4S cm^-1at room temperature,which is 3.6 times higher than that of the polymer matrix,and 8.5 times higher than the composite electrolyte prepared with same content of particles.The activation energy was 0.249 e V,the stability window can reach 4.95 V,and the migration number was 0.62.At 28^oC,the discharge capacity arrived to 152.49 mAh g^-1at 0.2 C rate.After 75 cycles,the retention reached 88.23%.