Preparation,Properties And Conducting Mechanism Of Several Solid Ionic Conductor Materials

Solid-state ionic conductors have attracted more and more attention due to their potential applications as electrolytes in solid-state batteries.For example,solid-state lithium ion conductors,solid-state oxygen ion conductors and solid-state proton conductors can be applied to all-solid-state lithium batteries and solid oxide fuel cells,respectively.In this paper,traditional solid phase method and new design strategy are used to explore high performance ionic conductor electrolytes.It mainly focuses on the following three material systems for detailed research:（1）LiNbWO₆-based material:A series ofβ-Li Nb_1-xTa_xWO₆（0≤x≤0.1）materials were synthesized by quenching under ambient air conditions.The AC impedance test results show that lithium ion conductivity dominates in this hexagonal Li Nb WO₆ material.The variable temperature X-ray diffraction revealed a partial hexagonal to tetragonal phase transition in the660-800°C range,resulting in enhanced ionic conduction behavior in this temperature range.The two dimensional and three dimensional lithium ion migration paths ofα-Li Nb WO₆andβ-Li Nb WO₆ were revealed by bond-valency-based method for the first time.（2）LaNbO₄-based materials:A series of La Nb_1-2xGa_xMo_xO_4-0.5x（0≤x≤0.3）and La Nb_1-2xGa_xW_xO_4-0.5x（0≤x≤0.2）materials were prepared by traditional solid phase method.Their phases,structures and electrical properties were studied in depth.For La Nb_1-2xGa_xMo_xO_4-0.5x,when x=0.2,the monocline phase is completely transformed into tetragonal phase,and the conductivity increases with the increase of doping amount.Through the analysis of AC impedance and DC measurements,it was found that the conductivity of samples under wet nitrogen is slightly higher than that under dry nitrogen when the temperature was below 550°C,indicating that the sample had weak proton conduction behavior.For La Nb_1-2xGa_xW_xO_4-0.5xmaterials,XRD data shown that the samples of 0≤x≤0.15 were monoclinic phase.While for the composition of x=0.2,impurities was observed and without phase transformation.The electrical property studies shown that there was no apparent proton conduction in these samples,and the conductivities does not change with the doping amount.the highest conductivity of the La Nb_0.8Ga_0.1W_0.1O_3.95 material reached 2.07×10^-3 S/cm at 900°C.（3）A₃Yb₂Ge₃O₁₂-based material:A series of garnet Sr₃Yb₂Ge₃O₁₂（SYG）and Ca₃Yb₂Ge₃O₁₂（CYG）-based materials were synthesized by high temperature solid phase method.For SYG,the solution limit of La doped at the Sr-site and Ga doped at the Ge-site is x=0.05.When the doping degree was 10%,some pure phases were obtained by element doping at the Ca、Yb-site of CYG,and there were impurities for the Ge-site dopings.Through the analysis of the electrical properties of the above series single phase materials,it was found that the conductivities of some samples were greatly improved,but all of them are dominated by electron conduction.