Study On Composite Modification Of Polyvinylidene Fluoride-Hexafluoropropylene Polymer Solid Electrolyte

Solid-state lithium batteries have been widely studied due to their high safety,high energy density,strong endurance,etc.As a key component for solid-state batteries,commonly solid electrolytes play an important role in determining the performance of the battery directly.Polymer solid electrolytes have drawn researchers'attention because of their good flexibility and light weight.However,the low conductivity at room temperature and poor interface stability have limited their commercial applications.In order to solve these issues,the PVDF-HFP-based polymer electrolyte is modified by inorganic materials,which is designed to improve its ionic conductivity,thermodynamic properties and interfacial stability,and ultimately achieve a solid electrolyte with excellent performance.In the experiment of compounding a polymer solid electrolyte with a two-dimensional material graphene oxide?GO?,the mechanical properties and electrochemical properties of the polymer electrolyte after compounding with GO are improved,which are demonstrated by the analysis of structure and properties.The ionic conductivity of the composite solid electrolyte PVDF-HFP/LITFSI/GO is 7.43×10^-5S·cm^-1 at room temperature with GO content of 0.5 wt.%,and the electrochemical stability window is greater than 4.5 V.Moreover,it has an excellent ability to inhibit the growth of lithium dendrites.On the one hand,the PVDF-HFP/LITFSI/GO composite solid electrolyte is assembled with LiFePO₄ electrode in an all-solid-state lithium battery for testing.It was found that the specific capacity was maintained at 133.2mAh·g^-1 after 200 cycles at 0.2 C at 55°C with GO content of 0.5 wt.%.On the other hand,the solid state battery is assembled by interface modification and tested at high temperature and room temperature.Its electrochemical performance is greatly improved compared to all solid state batteries.In the experiment of compounding a polymer solid electrolyte with a three-dimensional garnet ceramic Li_6.5La₃Zr_1.5Ta_0.5O₁₂?LLZTO?powder,garnet LLZTO is prepared by a solid state reaction method.The ceramic disc sintered at 1150°C for 12h has the highest ionic conductivity of 5.68×10^-4 S·cm^-1 at room temperature.After compounding with LLZTO,the system thermodynamic properties,ionic conductivity and interfacial stability are improved.Besides,the optimal composite amount of LLZTO in the system is investigated.The conductivity of PVDF-HFP/LITFSI/LLZTO composite solid electrolyte with LLZTO content of 12.5 wt.%is 8.80×10^-5 S·cm^-1 at room temperature,and the electrochemical stability window was greater than 5 V.On the one hand,the PVDF-HFP/LITFSI/LLZTO composite solid electrolyte is assembled with LiFePO₄ in an all-solid-state lithium battery for high-temperature testing.At the optimum compounding amount,there is 127.7 mAh·g^-1 after 200 cycles at 0.2 C.On the other hand,the assembled solid-state battery by interfacial modification is tested.It was found that no significant attenuation is observed in the specific capacity after a long cycle of 500 cycles at 0.5 C at room temperature.The research of this subject provides a way of thinking and method for the development of solid electrolyte.