Synthesis And Electrochemical Properties Of Organic-Inorganic Composite Solid Electrolytes

All-solid-state lithium battery achieves double safety and performance compared to traditional lithium-ion batteries.The ionic conductivity of new inorganic ceramic solid electrolytes could be equivalent to that of liquid electrolytes at room temperature,but the contact with electrodes is very poor and the interface impedance is very high.The ionic conductivity of PEO-based polymer solid electrolytes is not high at room temperature,but it possesses high interface stability with the electrodes.In this paper,the sulfide solid electrolyte of Li-Argyrodite structure Li6.25PS5.25Cl0.75 and oxide solid electrolyte of perovskite structure Li0.35La0.55TiO3 were added to polyethylene oxide(PEO)-LiTFSI matrix as an inorganic active filler,respectively.A self-supporting flexible composite electrolyte with excellent electrochemical properties was prepared by s simple solution casting method.1.Sulfide solid-state electrolyte Li6.25PS5.25Cl0.75 was prepared by a mechanical ball milling and heat treatment method,and it was added into PEO-LiTFSI polymer matrix as an active filler.The two-phase structure of composite electrolyte was confirmed by XRD and Raman Spectra.The reduction of crystallinity of PEO was proved by the small angle XRD diffraction.The ionic conductivity of the polymer film can be improved to the greatest extent by 1 wt%LPSCL particles.The ionic conductivity of the composite membrane can be increased from 5.62×106 S/cm to 1.24×10-5 S/cm at room temperature,and the electrochemical window of the composite membrane can reach 5.1 V(vs.Li+/Li).However,excessive introduction of sulfide ceramic particles may cause electrochemical instability of the composite electrolyte.The assembled lithium-metal symmetric battery by CPEs-1 remains stable after 600 h cycles at 60℃ and a current density of 0.1 mA/cm2.The specific discharge capacity of LiFePO4/Li all-solid-state battery was 159.1 mAh/g at the first cycle,and 94.34%capacity retention after 50 cycles at current rates of 0.2 C and 60℃.2.A stable porous structure Li0.35La0.55TiO3 was obtained by a solvothermal and heat treatment method,and it was added into the PEO-LiTFSI polymer matrix as an active filler.The XRD spectra confirmed the obvious two-phase structure of the composite membrane and the reduced crystallinity of PEO matrix.The oxide composite electrolyte with a composite ratio of 30 wt%porous LLTO showed the highest ionic conductivity,the ionic conductivity increased from 5.62×10-6 S/cm to 2.17R10-5 S/cm at room temperature,and the oxidation decomposition voltage could reach 5.0 V(vs.Li+/Li).The assembled lithium symmetric battery remains stable after 2000 h cycles at 60℃ and a current density of 0.1 mA/cm2.Besides,XPS test showed that PEO matrix effectively alleviated the reduction of Ti4+ between LLTO ceramic and lithium metal anode.The assembled LiFePO4/CPEs-30%LLTO/Li solid-state batteries had a good cycle stability and reversibility at different current rates.The discharge specific capacity was 155.3 mAh/g at the first cycle,and 98.77%capacity retention after 100 cycles at current rates of 0.1 C and 60℃.