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，正负极之间的离子传输通常是由溶解在有机溶剂中的锂盐实现的。尽管有机电解液具有较高的离子导电性，但其毒性和易燃性等固有缺点也伴随着温度稳定性不足和损坏时的泄漏风险等问题。如果有可能提高无机固体电解质的离子导电性，液体电解质可以完全被固体电解质取代。因此，移动应用的安全性和市场接受度可以提高。在本项目中，高离子导电性和低电子导电性的固体陶瓷电解质将被识别出来。他们将做好准备，并进行广泛的表征。作为物质系统，对NZP的分类进行了论述。一般结构可以写为(M1)[6](M2)3[8][L2[6](X[4]O4)3]。其中M1和M2为间隙，部分或全部被锂占据。L和X分别被钛和磷占据。这项工作的目的是回答以下问题：不同的阳离子取代对NZP的结构有何影响？由此产生的锂离子电导率是什么？这一点，要结合实验和理论工作加以澄清。此外，这个问题是关于(SiO4)4-取代阴离子(PO4)3-结构组分的(部分)。这样做，可以把更多的Li+带到M1或M2的地方。为了研究NZP基固体电解质的化学成分和晶体结构对锂的分布和运动的影响，本项目将采用多种方法。作为解决悬而未决的问题的基本步骤，碱金属离子的扩散行为作为晶体结构和组成的函数被研究。将模拟(第一性原理计算和原子模拟)和实验(制备相纯、高度致密的材料及其表征、Li分布的确定和利用中子衍射的扩散路径)相结合，以确定NZP化合物作为固体电解质的利弊。这为优化NZP结构和成分的科学战略奠定了基础。最后，应该可以说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.