Tina Nestler

Enhancing lithium-ion conductivity in NASICON glass-ceramics by adding yttria

We demonstrate that the ionic conductivity of Li1+xAlxGe2−x(PO4)3 glass-ceramic electrolytes can be tailored by adding Y2O3 to Li2O–Al2O3–GeO2–P2O5 melts. We found that the addition of 5 vol% Y2O3 causes noticeable changes in further glass crystallization process as the key parameters (glass crystallization temperature, viscosity and others) are affected. Small-angle neutron scattering data suggest that Y-containing glasses are suddenly crystallized upon heat treatment producing uniform Li1+xAlxGe2−x(PO4)3 ceramics. Due to the lower resistance of intergrain interfaces, such samples demonstrate a specific ionic conductivity of 0.5 mS cm−1, which is nearly 5 times higher in comparison to Y-free ceramics, prepared under similar conditions. We speculate that such an effect is caused primarily by better intergrain contact in Y-containing ceramics, along with better ionic transport in the grain bulk as evidenced by 7Li NMR.

Cathodes - Technological review

Lithium cobalt oxide (LiCoO2) was already used in the first commercialized Li-ion battery by SONY in 1990. Still, it is the most frequently used cathode material nowadays. However, LiCoO2 is intrinsically unstable in the charged state, especially at elevated temperatures and in the overcharged state causing volume changes and transport limitation for high power batteries. In this paper, some technological aspects with large impact on cell performance from the cathode material point of view will be reviewed. At first it will be focused on the degradation processes and life-time mechanisms of the cathode material LiCoO2. Electrochemical and structural results on commercial Li-ion batteries recorded during the cycling will be discussed. Thereafter, advanced nanomaterials for new cathode materials will be presented.

Separators and electrolytes for rechargeable batteries: Fundamentals and perspectives

Abstract Separators and electrolytes provide electronic blockage and ion permeability between the electrodes in electrochemical cells. Nowadays, their performance and cost is often even more crucial to the commercial use of common and future electrochemical cells than the chosen electrode materials. Hence, at the present, many efforts are directed towards finding safe and reliable solid electrolytes or liquid electrolyte/separator combinations. With this comprehensive review, the reader is provided with recent approaches on this field and the fundamental knowledge that can be helpful to understand and push forward the developments of new electrolytes for rechargeable batteries. After presenting different types of separators as well as the main hurdles that are associated with them, this work focuses on promising material classes and concepts for next-generation batteries. First, chemical and crystallographic concepts and models for the description and improvement of the ionic conductivity of bulk and composite solid electrolytes are outlined. To demonstrate recent perspectives, research highlights have been included in this work: magnesium borohydride-based complexes for solid-state Mg batteries as well as all-in-one rechargeable SrTiO3 single-crystal energy storage. Furthermore, ionic liquids pose a promising safe alternative for future battery cells. An overview on their basic principles and use is given, demonstrating their applicability for Li-ion systems as well as for so-called post-Li chemistries, such as Mg- and Al-ion batteries.

Computational analysis and identification of battery materials

Abstract Crystallography is a powerful descriptor of the atomic structure of solid-state matter and can be applied to analyse the phenomena present in functional materials. Especially for ion diffusion – one of the main processes found in electrochemical energy storage materials – crystallography can describe and evaluate the elementary steps for the hopping of mobile species from one crystallographic site to another. By translating this knowledge into parameters and search for similar numbers in other materials, promising compounds for future energy storage materials can be identified. Large crystal structure databases like the ICSD, CSD, and PCD have accumulated millions of measured crystal structures and thus represent valuable sources for future data mining and big-data approaches. In this work we want to present, on the one hand, crystallographic approaches based on geometric and crystal-chemical descriptors that can be easily applied to very large databases. On the other hand, we want to show methodologies based on ab initio and electronic modelling which can simulate the structure features more realistically, incorporating also dynamic processes. Their theoretical background, applicability, and selected examples are presented.

Assessment of potential Al ion conductors from large crystallographic databases

The possibility to store electrical energy enables not only mobile electronics and electric cars, but will be of paramount importance for the advancing penetration of renewables in the energy grid. Due to the capricious nature of sustainable energy carriers, in times of high production, energy will be stored for times of low or no production in order to balance out offer and demand. Li and Pb strongly dominate the battery market at the moment but the search for new chemistries and technologies for a diversification of applications will become increasingly important in the future. Aluminium offers a substantially higher abundancy, even higher theoretical energy densities, and may profit from its technological maturity. It is therefore a highlypromising candidate for post-Li chemistries.

Energy Storage in crystalline Materials based on multivalent Ions

Energy conversion and storage has become the main challenge to satisfy the growing demand for renewable energy solutions as well as mobile applications. Nowadays, several technologies exist for the conversion of electric energy into e. g. heat, light and motion or vice versa. Among a large variety of storage concepts, the conversion of electrical in chemical energy is of great relevance in particular for location-independent use. Main factors that still limit the use of electrochemical cells are the volumetric and gravimetric energy density, cyclability as well as safety. The concept for a new thin-film rechargeable battery that possibly improves these properties is presented. In contrast to the widespread lithium-ion technology, the discussed battery is based on the redox reaction of multivalent Al-ions and their migration through solid electrolytes. The ion conduction and insertion processes in the crystalline materials of the suggested cell are discussed under a crystallographic point of view to identify suitable electrode and separator materials. A multilayer-stack of all-solid-state batteries is synthesized by pulsed laser deposition and investigated in situ, i. e. during charge and discharge, by X-ray reflection and diffraction methods. The correlation between crystal structure, morphology and electrical performance is investigated in order to characterize the ion diffusion and insertion process.

Categorization of electrochemical storage materials en route to new concepts

Because of their broad range of applications, electrochemical energy storage devices are the subject of a growing field of science and technology. Their unique features of high practical energy and power densities and low prices allow mobile and stationary applications. A large variety of electrochemical systems has been tailored for specific applications: Lithium-ion batteries for example have been optimized for mobile applications ranging from mobile phones to electric vehicles. On the other hand, sodium-sulphur accumulators – among others – have been developed for stationary applications to account for the capricious nature of renewable energies. Chemistry, physics and materials science have led to the optimization of existing cell-chemistries and the development of new concepts such as all-liquid or all-solid state batteries as well as high-energy density metal-air batteries. The aim of the BMBF (Federal Ministry of Education and Research, Germany)-financed project “CryPhysConcept” is to develop new concepts for electrochemical energy storage applying a crystallographic approach. First, a categorization of the main solid components of batteries based on their underlying working principles is suggested. Second, an algorithm for the identification of suitable new materials and material combinations, based on economical, ecological and material properties as well as crystallographic parameters, is presented. Based on these results, new concepts using multi-valent metal ions are proposed. Theoretical as well as experimental results including an iron-ion approach are presented.