Li2+2xCo1-xGeO4 as positive electrode material

The daily needs and demands of rechargeable batteries continue to grow. Think of the distance electric vehicles (EV) can travel, or how long you can use your mobile phone until the next charge is required. In both cases lithium ion batteries (LIB) are the energy source. To fulfil the requirements, e.g. reaching longer travel distances with EV, novel materials for LIB must be developed. Such a material can be Li2+2xCo1-xGeO4 (0 = x 0.3). This material shows interesting lithium ion conducting properties. Due to the presence of cobalt (Co), this compound can be seen as a novel electrode material for LIB. The objective of this work is to develop different synthesis strategies, to obtain phase pure Li2+2xCo1- xGeO4 (0 = x 0.3) with certain particle sizes and morphologies. These properties shall be investigated withpowder X-raydiffraction, scanning electron microscopy and elementalanalysis. Moreover, the electrochemical behaviour of these materials will be tested. In these studies, the focus will be on determining the operating voltage as well as the capacity of the Li2+2xCo1-xGeO4 (0 = x 0.3) materials. These properties will be evaluated by cyclic voltammetry and galvanostatic measurements. Additionally, the diffusion of the lithium ions in the Li2+2xCo1-xGeO4 compounds during charge and discharge will be investigated. The best materials will be tested in full cells concerning their long life stability. The applicant, Jürgen Schoiber, will perform the proposed project through the support of the Erwin- Schrödinger-Scholarship. In particular, the above mentioned electrochemical characterization techniques shall be learned, providing the applicant with a new set of research skills that complement his existing ones. The research and training will occur at the University of California, Los Angeles (UCLA), Department of Materials Science and Engineering under the direction of Prof. Bruce Dunn. The learned skills will be applied during the returning phase at the University of Salzburg, department of Chemistry and Physics of Materials in the working group of Prof.in Nicola Hüsing.

The aim of this research project was the investigation of energy storage materials for Lithium-Ion (Li-Ion) and Sodium-Ion (Na-Ion) batteries. The focus lied on the development of materials that can be (dis)charged fast and store high amounts of energy. This would combine the advantages of the two most commonly used energy storage devices, capacitors and batteries. Since capacitors can be (dis)charged fast with low energy density, Li/Na-Ion batteries have higher energy densities but cannot be (dis)charged as fast as capacitors. During the abroad phase oft he scholarship materials (Li2+2xCo1-xGeO4) for Li-Ion batteries were prepared and electrochemically tested. At midterm of the project it could be determined, that this material has the theoretical requirements to address the aforementioned needs, but does not show any electrochemical behavior during testing. Therefore, the materials topic changed to Na2+2xFe2-x(SO4)3, which can be used for Na-Ion battery systems. This material class was first described in 2014 and shows the desired characteristics. Hence, the focus was set on the determination of the charge-storage behavior in full detail, and to increase the storage properties. It could be shown, that this material stores the sodium ions similar to a capacitor with energy densities comparable to battery materials. Furthermore it could be proven, that substitution of a certain amout of iron with manganses or copper further increases the storage behavior. The return phase was used to exchange iron with manganese to obtain the material Na2+2xMn2-x(SO4)3 (NMS). It is known from theoretical calculation that this material should have an operating voltage of 4.5 V, while NFS provides 3.7 V. Therefore higher energy densities are expected. The NMS materials were synthesized and electrochemically tested in different setups. It could be proven, that this compound class is electrochemical active, but a fully detailed evaluation of the compound class could not be done.