Preparation And Performance Optimization Of Flexible Composite Electrolyte Membranes For Solid-state Lithium Batteries

Solid-state lithium battery is a new type of energy storage device,which uses solid electrolyte instead of organic electrolyte.It is expected to solve the two key problems of low energy density and poor safety of traditional lithium ion battery.Compared with the ceramic electrolyte and the polymer electrolyte,the organic-inorganic composite electrolyte has better electrochemical performances and can form good contact with electrodes.It is a kind of solid electrolyte with excellent electrochemical performances,good mechanical properties,simple preparation method,low production cost and easy to be commercialized.To develop and use the high-performance organic-inorganic composite electrolyte has become an inevitable development trend to break through the energy density bottleneck and improve safety of lithium batteries.In order to meet the requirements of high energy density,the high voltage cathode and the lithium metal anode can be used.For the electrolyte,high conductivity,wide electrochemical stability window,stability of opposite-side electrode,thin thickness and good resistance to lithium dendrite are required.In this paper,organic-inorganic composite solid electrolyte with different composition was prepared by using different polymer matrix and inorganic fillers with different structure.The electrochemical performance of the composite electrolyte and the cycling performance of solid-state battery were discussed.The work contents and main conclusions are as follows:(1)LLTO fibers were prepared by electrospinning,and PAN-LLTO composite electrolytes with different inorganic contents were prepared by using polyacrylonitrile(PAN)matrix.The electrochemical performances of the composite electrolyte were tested,and the Li Ni_0.6Co_0.2Mn_0.2O₂/PAN-LLTO/Li cell was assembled to test the cycling performance at room temperature.The results showed that the ionic conductivity of the composite electrolyte varies with the content of LLTO.The composite electrolyte with 10%mass fraction of LLTO had the highest conductivity,which was 2.6×10^-4 S cm^-1 at room temperature.And the electrochemical stability window increased with the increase of the weight of LLTO.However,the PAN based composite electrolyte showed instability to lithium.The initial discharge specific capacity of Li Ni_0.6Co_0.2Mn_0.2O₂/PAN-LLTO/Li battery was as high as 170 m Ah g^-1,while the capacity decaying rapidly in the cycle,which was mainly caused by the instability between the PAN-LLTO and lithium metal.(2)LLZTO inorganic particles were prepared by high temperature solid phase method.The PEO-LLZTO composite electrolytes with different inorganic contents were prepared by using polyethylene oxide(PEO)as the matrix.The stability of the composite electrolytes against lithium was tested,and the PEO-40LLZTO composite electrolyte with good resistance to lithium dendrite was obtained.The PAN-10LLZTO composite electrolyte with high-voltage resistance as well as high ionic conductivity and the PEO-40LLZTO composite electrolyte with good resistance to lithium dendrite were selected to prepare the composite electrolyte with double layer structure by simple pressurization and superposition.The double layer electrolyte with good ionic conductivity of 1.7×10^-4 S cm^-1at room temperature was used to assemble the Li Ni_0.6Co_0.2Mn_0.2O₂/PEO-LLZTO-PAN-LLTO/Li cell.Compared with the monolayer PAN-10LLTO electrolyte,the performance of the battery is improved obviously.The coulomb efficiency was maintained at about 99%,and the specific discharge capacity of the battery remained at 133 m Ah g^-1 after 100 cycles.