固体电解质Beta-Al2O3的结构与导电性能的关系研究

As energy crisis is increasingly intensified over the world, the rational use and storage issue of the renewable energy is becoming a commonly-concerned focus. Sodium sulfur battery is an emerging energy storage technology that uses sodium and sulfur for electrode materials and beta-Al2O3 ceramics for the electrolyte. It has the advantage of mass energy storage, which makes it the best storage equipment for the renewable energy, such as wind energy and solar energy. Therefore, the storage quality of sodium sulfur battery has important significance to the application prospect of the renewable energy..Beta-Al2O3 solid electrolyte is the key material of the sodium sulfur battery, which strongly affects the prosperity and service life of the battery. The structure and bonding performance of materials is the key factor to determine conductivity, for the element system has many species and complex network structures, and lacks of characterization methods. Many scientific problems need to be solved. This project used the solid, liquid methods to prepare Beta-Al2O3 solid electrolyte materials of different composition and structure and assemble battery to test charge and discharge performance. In this study, solid-state NMR techniques were used, XRD, EIS, and other testing techniques were combined with， to test and analysis structure, chemical composition, atomic coordination, bonding character and conductive characteristics of material under different conditions. Thus, network structure of the atomic model were established, calculation based on the primary principle of quantum mechanics and molecular dynamics were carried out, and studied stability of network structure and structure of high temperature conversion processes from the energy and electronic structure level. On the basis of experimental analysis and theoretical calculations, the relationship between the conductive properties and structural properties were established.This project aims to build structure tests and calculation methods of the Beta-Al2O3 solid electrolyte material from atomic scale analysis to reveal the nature of conductive properties in order to guide optimization design of material's properties.

Beta-Al2O3固体电解质材料是钠硫电池的关键材料之一，材料的结构及键合特性是决定该材料导电性能的关键因素，但是该体系元素种类多、网络结构复杂，而表征手段缺乏，很多科学问题亟待解决。本项目采用固、液相法制备具有不同组成和结构的Beta-Al2O3固体电解质材料，并组装电池进行充放电；引入固体核磁共振技术，探讨测试条件，并结合X射线衍射技术、交流阻抗技术等方法，分析不同制备条件、载荷状态下材料的结构、化学组成、原子配位、成键特性和导电性能；建立网络结构的原子模型，进行基于量子力学的第一性原理和分子动力学原理的计算，从能量和电子结构层面研究该网络结构的稳定性以及该结构高温转化过程；在实验分析和理论计算的基础上，建立该材料导电性能与材料结构特性的关系。本项目旨在建立原子尺度分析Beta-Al2O3固体电解质材料结构的测试技术和计算方法，揭示该材料导电性能的本质，指导该材料的性能优化。

Beta-Al2O3固体电解质是钠硫电池的关键材料之一，材料的结构是决定该材料导电性能的关键因素，但是该体系元素种类多、结构复杂，而表征手段缺乏，很多科学问题亟待解决。本项目针对Beta-Al2O3固体电解质材料的结构与性能的关系展开研究，形成了以下的成果：（1）探明了采用固相反应法、溶液凝胶-低温燃烧法合成Beta-Al2O3固体电解质材料的工艺，制备出具有不同组成和结构的Beta-Al2O3固体电解质材料。（2）建立了Beta-Al2O3固体电解质中铝氧多面体结构的固体核磁共振测试条件，分析了不同体系的铝氧多面体结构，发现在Beta-Al2O3中，铝氧四配位Al(Ⅳ)和六配位Al(Ⅵ)分别位于δ=50ppm和δ=-5ppm附近，稳定剂的添加使得Al(Ⅳ)和Al(Ⅵ)向低场方向偏移，有助于改善Al(Ⅵ)的对称性。（3）首次建立Beta-Al2O3固体电解质中β-Al2O3相、β″-Al2O3相的分子模型，发现合成的beta-Al2O3中，β-Al2O3相化学式为Na2O•8.52Al2O3，六方结构，空间群为P63/mmc，晶胞参数a=5.5941 Å，c=22.5300 Å；β″-Al2O3为Na2O•6.03Al2O3，三方结构，空间群为R3m，晶胞参数为a=5.6017 Å，c= 33.6219Å。且β″相中Na离子迁移过程所需的最大跨距仅为β相的1/3，解释了β″相电导率高于β相的原因。Li的取代使得O-Al(Li)键的键长降低，Na原子占位大大提高从而提高了离子电导率。（4）建立了Beta-Al2O3固体电解质在模拟两电极及三电极的钠硫电池中的研究方法，发现Beta-Al2O3固体电解质在钠硫电池中稳定性较好。利用分子动力学原理探明，Beta-Al2O3固体电解质中Na+的导电机理是典型的离子电导体，其中Na+的迁移数为1.16、扩散系数为3.5×10-5cm2/s。（5）采用基于量子力学的第一性原理发现，费米能级处β"-Al2O3的态密度是β-Al2O3的3倍，β"-Al2O3的赝能隙较β-Al2O3的窄，因此β相体系中形成键的共价性更好，系统更稳定。揭示了Beta-Al2O3固体电解质导电性与结构的关系。