Synthesis and characterization of solid electrolytes with high lithium ionic conductivity: Investigation of the influence of stoichiometry on crystal structure and ionic conductivity

在可充电锂离子电池中，阳极和阴极之间的离子传输通常是由溶解在有机溶剂中的锂盐来完成的。虽然有机电解质提供了高离子电导率，但其固有的缺点，如毒性和可燃性，伴随着诸如缺乏温度稳定性和损坏时泄漏风险等问题。如果有可能增加无机固体电解质的离子电导率，则可以将液体电解质完全替换为固态电解质。因此，移动应用程序的安全性和市场接受度可以提高。在本项目中，应将具有高离子电导率的固体陶瓷电解质与低电子电导率结合起来进行鉴定。它们将被制备和广泛表征。作为材料系统，讨论了npp的类。一般结构可以写成（M1）[6] (M2)3[8] [L2[6] (X[4] O4) 3]。M1和M2是间隙体，它们部分或全部被锂占据。L和X的位置分别是钛和磷。这项工作的目的是回答以下问题：NZP结构如何受到各种阳离子取代的影响，以及由此产生的锂离子电导率的后果是什么？这要结合实验和理论工作加以明确。此外，这个问题是关于阴离子（PO4）3-结构成分（部分）被（SiO4）4-取代。通过这样做，更多的Li+可以被带到M1或M2位置。这为在一定程度上解耦插入锂的结构特性提供了机会。为了研究nzp基固体电解质的化学成分和晶体结构对Li分布和Li运动的影响，本项目将采用多种方法。作为解决这些突出问题的基本步骤，研究了碱金属离子的扩散行为作为晶体结构和组成的函数。建模（第一性原理计算和原子模拟）和实验（生产相纯，高度致密的材料及其表征，确定li分布和使用中子衍射的扩散路径）相结合，以确定该类NZP化合物作为固体电解质的优缺点。这为优化NZP结构和成分的科学策略奠定了基础。最后，我们应该能够确定nzp基材料在多大程度上适合作为固体电解质。

In rechargeable lithium-ion batteries the ion transport between anode and cathode is usually made by lithium salts that are dissolved in organic solvents. Although the organic electrolyte provides a high ionic conductivity, intrinsic disadvantages such as toxicity and flammability are accompanied with problems such as lack of temperature stability and the risk of leakage in case of damage. If it is possible to increase the ionic conductivity of inorganic solid electrolyte, the liquid electrolyte may entirely be replaced with a solid-state electrolyte. Thereby the safety and thus the market acceptance for mobile applications could be increased.In the present project solid ceramic electrolytes with high ionic conductivity shall be identified in conjunction with low electronic conductivity. They will be prepared and extensively characterized. As material system, the class of NZP is addressed. The general structure can be written as (M1)[6] (M2)3[8] [L2[6] (X[4] O4) 3]. With M1 and M2 being interstitials, who are partially or fully occupied with lithium. The places L and X are occupied by titanium or phosphorus, respectively. The aim of this work is giving answers to the following question: How is the NZP structure influenced by various cation substitutions and what are the consequences resulting therefrom in terms of lithium ion conductivity? This should be clarified with reference to the combination of experimental and theoretical work. Furthermore, this question is with regard to a (partial) substitution of the anionic (PO4)3- structural components by (SiO4)4-. By doing so, more Li+ can be brought to the M1 or M2 places. This opens up the opportunity to decouple the structural properties of the amount of intercalated Li up to a certain degree.To investigate the influence of chemical composition and crystallographic structure of NZP-based solid electrolyte on the Li distribution and Li-motion, there are various methods that will be applied in this project. As a fundamental step towards resolution the outstanding issues the diffusion behavior of the alkali metal ions are investigated as a function of crystal structure and composition. The combination of modeling (first-principles calculations and atomistic simulations) and experiment (producing phase-pure, highly compacted materials and their characterization, determination of Li-distribution and the diffusion paths employing neutron diffraction) are to identify the pros and cons of the class of NZP compounds as solid electrolytes. This creates the basis for a scientific strategy to optimize the NZP structure and composition. Finally, it should be possible to say to what extent NZP-based materials are suitable as solid electrolytes.