Leitungs- und Diffusionseigenschaften Alkali-Ionen-leitender NASICON-Materialien für den Einsatz in Festkörperbatterien

• Conduction and diffusion properties of Alkaline-ion conducting NASICON materials for the application in solid state batteries

Roßbach, Andreas; Martin, Manfred (Thesis advisor); Eichel, Rüdiger-A. (Thesis advisor)

Aachen : RWTH Aachen University (2021, 2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

Materials with NASICON structure are a promising class of Solid-State ionic conductors for application in electrochemical storage. The crystal structure enables high stability and flexibility and a wide range of compositions. An analysis of literature data of lithium ion conducting NASICON materials revealed the highest ionic conductivities for compositions of the formula Li1+xMx(III)Ti2-x(PO4)3 with 0.3 ≤ x ≤ 0.5 and hexagonal R¯3c structure. In addition, the great influence of microstructure and phase chemistry on conductivity was shown. Li1+xMx(III)Ti2-x(PO4)3(M(III)= Al, Cr, Fe; 0.5 ≤ x ≤ 2.0) was prepared using two current synthesis routes and the samples were characterized in terms of density, stoichiometry and phase chemistry. The focus of the work is on investigations of the conductivity of the polycrystalline material using electrochemical impedance spectroscopy. The scalable synthesis routes allow comparable material quality to previously known methods, which are categorically limited to laboratory scale or not cost effective on a large scale. Additionally, the question of possibly increased oxygen mobility in NASICON was investigated. For this purpose, 18O oxygen exchange experiments followed by depth profiling by secondary ion mass spectrometry were performed on Li1.5Al0.5Ti1.5(PO4)3 and Na3.4Zr2(PO4)0.6(SiO4)2.4. This revealed new, material-specific challenges with regard to the chosen method. The results allow a first classification and show no unusually high oxygen mobility in the dedicated alkali ionic conductors.