Effect of pressure on transport properties of granular lithium ion conductors

TP的核心问题是合成新的非晶含锂固体和研究锂在高压-高温处理下迁移率的变化。该项目的主要目标是通过实验确定输运性质与以下参数之间的关系：-组成和结构类型-有序状态-压实度-锂的局部环境。在第一个阶段，我们重点研究了Li2O-Al2O3-SiO2体系中非晶态化合物的合成、压实和表征。用阻抗谱和核磁共振测定锂迁移率。按照这种方法，我们想要研究在压力/温度处理非晶粉末时，在选定的体系中，组成、结构状态和粒度对锂的原位输运的影响。我们选择了两个模型体系，分别代表更多的离子（例如，LiTaO3和LiNbO3）和更多的共价材料（例如，LiFePO4或LiMgPO4，后者的优点是Mg具有单一氧化态）。该项目的目的是分离颗粒单相体系中体积扩散和晶界扩散对锂输运的影响，并研究这些输运性质在压实过程中的变化。为此，我们希望应用在项目一期开发的新型活塞缸装置。该方法允许在温度和压力的作用下直接测量压实过程中的阻抗谱和体积变化。在控制湿度和氧分压的环境中，粉末可以在开始压缩之前在运行温度下进行预调节。我们特别期望H2O对压实动力学有重大影响，进而影响锂的迁移率。微观分析和光谱方法将对压实后的结构和拓扑变化提供见解。核磁共振测量，如果可能的话，机械松弛光谱将提供关于锂在起始材料和实验后样品中的迁移率的信息。

A central issue of TP is the synthesis of new amorphous Li-bearing solids and the investigation of the change in lithium mobility upon high pressure - high temperature treatment. A primary goal of the project is to determine experimentally the relationships between transport properties and the following parameters: - composition and structure type - state of ordering - degree of compaction - local environment of lithium In the first period we have focussed on the synthesis, compaction and characterization of amorphous compounds in the system Li2O-Al2O3-SiO2. Lithium mobility was determined using impedance spectroscopy and NMR. Following this approach we want to study the influence of composition structural state and particle size on the transport of lithium for selected systems in situ during pressure/temperature treatment of amorphous powders. We choose two model systems representing more ionic (e.g., LiTaO3 und LiNbO3) and more covalent materials (e.g., LiFePO4 or LiMgPO4, the latter one has the advantage that Mg has a single oxidation state), respectively. The aim of the project is to separate effects of volume and grain boundary diffusion on Li-transport in granular single phase systems and to investigate the change of theses transport properties during compaction. For doing so, we want to apply the new piston cylinder apparatus which was developed during the first period of the project. The method allows direct measurement of impedance spectra and volume changes during compaction in function of temperature and pressure. Using an atmosphere with controlled humidity and oxygen partial pressure, the powders can be pre-conditioned at run temperature before starting compression. We expect in particular that H2O has major impact on compaction kinetics and in turn on lithium mobility. Microanalytical and spectroscopic methods will give insights to structural and topological modifications upon compaction. NMR measurements and, if possible, mechanical relaxation spectroscopy will provide information about lithium mobility in starting materials and post-experimental samples.