Study On Preparation And Properties Of Ge-doped LLTO Solid Electrolyte

Rechargeable Li ion batteries have been one of most promising and attractive electrochemical power sources due to their high energy density and environmental friendliness.Their market has expanded to widespread applications at various fields such as electric devices including digital cameras and mobile phones,electric vehicles and energy storage systems,in which safety issue are crucial.The Li ion secondary batteries possess safety issues are mainly resulted from the use of flammable organic liquid electrolytes.To some extent,the lithium batteries are easily exposed to the risk of explosion or fire.In order to solve the safety problems,it is necessary to develop nonflammable ceramic solid electrolytes for all-solid-state lithium batteries.It is important that the solid electrolytes should have a high ionic conductivity comparable to conventional organic electrolytes as well as sufficient electrochemical stability in a wide operating voltage range.All-solid-state lithium batteries are being considered to be a future energy storage technology in terms of stability,energy and safety compared with conventional liquid-electrolyte-based batteries.Based on these reasons,the main content of this paper is as follows:Li_0.33La_0.56TiO₃?LLTO?perovskites are synthesized by solid state reaction as Li ion conductive electrolytes.The optimum preparation process of Li_0.33La_0.56TiO₃ electrolyte was determined by experimental study.The optimum sintering process is pre-sintering at 800?,the optimum pressing pressure is 30 MPa,and the optimum sintering process is holding for 6 h at 1150?.Under these conditions,Li_0.33La_0.56TiO₃ electrolyte could obtain maximum apparent density and the densest microscopic morphology.The ion conductivity is 1.7×10^-6 S cm^-1,which is three times higher than that at 1000?.After addition of GeO₂,the sinterability and Li ion conductivity are enhanced for the perovskite solid electrolyte.The Li_0.33La_0.56Ti_0.95Ge_0.05O₃ electrolytes exhibit the highest sinterability and Li ion conductivity among the as-prepared Li_0.33La_0.56Ti_1-xGe_xO₃ electrolytes.The Li_0.33La_0.56Ti_0.95Ge_0.05O₃ electrolytes could obtain maximum apparent density which is increased by about 8%than that of LLTO electrolyte.The lithium transference number(t⁺_Li)of Ge-doped LLTO is close to 1,indicating that Ge-LLTO?x=0.5?solid electrolyte is pure ionic conductor.The total conductivity of Li_0.33La_0.56Ti_0.95Ge_0.05O₃ is 1.2×10^-5 S cm^-1,which is one order of magnitude higher than that of the LLTO electrolyte.Moreover,the Ge-LLTO electrolytes are stable in a potential range of 0-10 V vs.Li/Li⁺.And then,we have successfully prepared a flexible PEO₄-LiTFSI-x wt%?0?x?80?Ge-LLTO composite solid electrolyte membrane via solution-casting method.It was found that the as prepared composite electrolytes exhibited enhanced flexibility compared to the electrolytes without PEO and LiTFSI.The highest conductivity is obtained for PEO₄-LiTFSI-40 wt%Ge-LLTO about 4.4×10^-6 S cm^-1,which is one order of magnitude higher than that of the solid polymer electrolyte..The composite solid electrolyte with 40 wt%Ge-LLTO evenly distributed showed a good mechanical property and a good electrochemical stability window of 5.5 V vs.Li/Li⁺at room temperature.Moreover,the PEO₄-LiTFSI-40 wt%Ge-LLTO composite solid electrolyte is pure ionic conductor due to its lithium transference number close to one.The PEO₄-LiTFSI-40 wt%Ge-LLTO composite solid electrolyte membrane displayed excellent thermal stability.