Theory and Modelling
Coarse-grained molecular dynamics simulations of polymeric materials for energy storage applications
Polymers are promising materials for next-generation energy storages. Depending on the application, polymeric materials may either serve as ionically conducting but mechanically stable electrolytes or as active materials if the monomer units can be reversibly oxidized and reduced. To optimize these materials, molecular simulation techniques such as molecular dynamics (MD) simulations offer a powerful tool to gain insights about the underlying processes at the microscopic level. However, due to the large intrinsic relaxation times of polymers as well as the rather long length scales on which e.g. microphases form in electrolytes based on block copolymers, fully atomistic MD simulations become technically challenging. This project therefore envisages to develop and validate coarse-grained models, for instance based on the well-known MARTINI model, to study the formation of relevant structural features and the resulting impact on the transport properties on larger scales. Backmapping to the atomistic scale furthermore allows us to gain insights on e.g. the lithium ion dynamics on smaller scales.
Data-driven and simulation-based understanding of solid states electrolytes
Currently, high-throughput screening (HTS) using machine learning became more popular and most effective approach in different fields of science and technology. With the enhanced computational facility and powerful algorithms now it possible to use screening strategy to down select a pool of candidates based on successive property evaluations. For say, in the case of materials design, the goal of such computational screening is to establish a database for a materials property and to identify the promising candidates prior to the experimental synthesis. Aspuru-Guzik et al. have developed a high-throughput framework to study potential candidate organic molecules for photovoltaics using density functional theory (DFT) and with available experimental data. Similar approach being used for search in various applications including drug discovery, electrolytes, ionic liquids, etc. This data-driven approach enables ML to predict a wide range of properties without the need for fundamental understanding of the chemistry or physics behind it.
In the proposed project, we are interested in HTS of solid-state electrolytes (SSE) for potential applications in energy storage. Unlike liquid electrolytes, SSE is safe, leak proof, non-volatile and possess high power density. Li ion battery is the one of the well-known and highly used SSE-based battery. However, their usage is limited due to the high resistance at the electrode/solid electrolyte interface that hinders the fast charging and discharging capacity. Hence, the search for suitable candidates is highly crucial for advanced energy storage systems. In this perspective, a hierarchical computational scheme for screening multiple properties of a large number of SSE materials is necessary. By using high-throughput quantum chemical predictions of properties, such as electrochemical stability window, conductivity, .... etc . many unpromising candidates will be eliminated and uncover structure−property relationships. Further, molecular dynamic simulation for a specific electrolytes will be carried out to understand the ion transport mechanisms in detail.
In silico development of thermal conduits for battery heat management
As has been shown recently, transition metal dichalcogenide (TMDC) heterostructures are promising candidates for highly thermally insulating materials. They are thus ideally suited for insulting coatings of thermal conduits, which could play a key role in thermal management solutions for batteries. In this project, a series of classical atomistic molecular dynamics simulations will be carried out to theoretically predict the thermal conductivity of TMDC bilayer and trilayer structures made up of different combinations of MX2 (M = Mo, W and X = S, Se, Te) with the aim to find the best insulating material. One possibility is to employ the Green-Kubo method as implemented in the LAMMPS molecular dynamics code to extract the thermal conductivity tensor from the simulations. Thus, one can obtain both in-plane and cross-plane conductivities from the same simulation. To start with, optimized Stillinger-Weber-type interaction potentials from the literature will be used within each monolayer, while existing van der Waals parameters will be employed to describe the interactions between the layers. Density Functional Theory (DFT) calculations with periodic boundary conditions will be carried out to test and, if necessary, refine these interaction potentials. The effects of impurities / defects as well as mechanical strain will also be investigated.
Accelerated, high throughput experimentation-based design and development of advanced functional electrolytes and interfaces for lithium battery applications
The development of novel and advancement of existing electrolytes calls for design of innovative and ultrapure electrolyte components (conducting salts, organic solvents and (multi)-functional additives) supported by theoretical calculations and simulations. The developed and well-established high throughput screening (HTS) approach, comprising systematic and fast, fully automated formulation of liquid electrolytes, cell assembly and preselected physicochemical and electrochemical measurements on an electrolyte and cell level, serves as a filtration effect towards identifying affordable, electrochemically and thermally outperforming lead electrolyte candidates for a specific application in a given cell chemistry. Further comprehensive characterization of lead electrolytes by means of selected electrochemical, analytical, spectral and structural methods provides insight into understanding of main operation and failure mechanisms taking place in a battery comprising nonaqueous aprotic electrolyte|electrode interfaces. Through strong interaction and complementarity, a new degree of integration in the high throughput formulation-characterization-performance evaluation chain will be achieved. On the basis of obtained experimental results and thorough analysis supported by machine learning , novel combinations of electrolyte formulations, either in terms of concentrations or even different components will be proposed facilitating further advancement of tailored functional electrolyte components for maximized performance and safety.
Composite design for Li – S solid state batteries
Li-S solid state batteries are an ideal option to use earth abundant materials as active materials, while at the same time mitigating detrimental side reactions that stem from liquid electrolytes. However, a careful design of the microstructure and composition of the cathode composite, composed of solid electrolyte, carbon and sulfur, is needed. In this doctoral project a deeper understanding of the underlying reaction and influence of microstructure on the behavior of Li-S solid state batteries needs to be elucidated, with the question of how can better design these composites. Within the scope of the project, you will learn how to synthesize sulfide based superionic conductors, form composite electrodes and measure the underlying transport properties that are then compared via cycling of solid state Li-S batteries.
Design of ion transport in sulfidic solid electrolytes
Sulfidic or thiophosphate based solid ionic conductors currently typically achieve ionic conductivities between 1 and 10 mS/cm. These conductivities are sufficient to study the influences and reactions occurring in solid state batteries, but for high energy density cells much faster ionic transport is needed. In this doctoral project, pertinent materials will be investigated for their structure – transport correlations in order to better understand and push ionic conductivities in materials. Within the scope of the project, you will learn how to synthesize sulfide based superionic conductors, how to analyze their structure and ionic transport.
Development of Aqueous Electrolyte Compounds for Aqueous Lithium Ion Batteries
Aqueous lithium ion batteries (aLiBs) has proven to be safe and environmentally friendly due to their non-flammable and non-toxic compounds. Therefore, they provide an excellent large-scale-solution to store Energy from sustainable sources. However, most aLiBs suffer from dissolution of their electrodes in the electrolyte, H2/O2-evolution during charge processes and side reactions of their electrodes with electrolyte compounds. In this doctoral project, you will learn how to design new electrolyte compounds and how to build aLiBs. Furthermore, you will learn, apply and develop electro- and physico-chemical analysis methods to generate a deeper understanding for ion transport mechanism and internal reaction processes.
Interface design of Ni-rich Cathodes for Lithium Metal Batteries
Layered transition metal oxides, in particular lithium nickel manganese cobalt oxide (NMC) and lithium nickel cobalt aluminum oxide (NCA), are used as state-of-the-art cathode materials in high-energy lithium ion cells. However, these materials suffer from rapid capacity fading for example in the presence of polymer electrolytes. By careful design of the microstructure and interface of the cathode composites towards the polymer electrolyte, challenges such as large charge-transfer resistances and structural changes upon cycling can be mitigated. Within the scope of the project, you will prepare custom-made Ni-rich cathode materials and suitable functional coatings as well as tailored polymer electrolytes, in this way optimizing the operational conditions of application-relevant cell concepts.
Molecular Design of Film-Forming Electrolyte Additives
One reason for poor cycling performance of lithium ion batteries is the loss of active lithium from the anode surface owing to parasitic side reactions during the formation of the solid electrolyte interphase (SEI). This SEI can be improved by the addition of suitable additives to hasten the formation of a thin, stable, but flexible SEI leading lower internal resistance, higher power capability and longer battery lifetime. Taking advantage of our expertise in organic chemistry and catalysis, our group focuses on the molecular design of film-forming additives, extending fundamental understanding of significant substrate parameters towards a systematic approach to electrolyte additive design.
Advancing Formation through Efficient Catalyst Design
Current formation procedures are subject to long duration due to them having to go through several charge/discharge cycles making them cost and time intensive. During formation, solvent or additives undergo a polymerization reaction forming a thin layer on the anode surface in the process. To tackle this challenge, suitable catalysts can be applied promoting the polymerization and therefore improving sustainability, costs and energy efficiency. During this project, the candidate will deepen their understanding towards catalyzed polymerization reactions on the anode surface and learn how to design and synthesize suitable polymerization catalysts contributing to a fundamental understanding of the chemistry inside lithium ion batteries.
Analysis and Characterization
Advancing Electrophoretic NMR Investigations of Ion Drift Velocities
Classical physicochemical methods to study ion transport in electrolytes are for example impedance spectroscopy, diffusion NMR or electrochemical Li transference measurements. However, they lack the possibility to characterize correlations of different ion species, which often hamper efficient ion transport. In this field, electrophoretic NMR is a unique tool to study ion mobilities in an electric field and in particular mutual influences of the ionic species. Since electrophoretic experiments in concentrated electrolytes suffer from various artefacts, this project will focus on the development of specific probe and electrode geometries, which will finally allow artefact-free determination of ion mobilities in concentrated, viscous electrolytes such as ionic liquids.
Degradation Investigations of Next Generation Battery Electrolytes
For lithium ion battery electrolyte aging, manifold studies and mechanisms can be found in literature with regard to potential hazards and implications for the lifetime of a battery. However, for next generation batteries, only few to none studies are available so far despite the availability of these chemistries for some time. With the help of chromatography-based analytical methods first insights into the processes of these electrolytes and possible degradation mechanisms will be investigated.
Development and Application of Surface-based Methods for the Analysis of Solid State Batteries
Due to the nature of solid state batteries, surface methods with the ability to sputter through the desired sample area are needed. Plasma-based method like glow discharge or laser ablation can therefore be of great importance for lateral and depth profiling of these materials. Focus of this topic is the development of appropriate methods for the analysis for solid state batteries.
Evaluation of Film-Forming Electrolyte Additives at Cell Level
Following the tremendous increase in demand of lithium ion batteries, there is a pressing need to improved energy density, safety and cost, while ensuring a high lifetime. These can be promoted by the addition of small quantities of electrolyte additives which may have a significant impact on cell performance. Evaluation of the physical and chemical properties of these additives can lead to an improved fundamental understanding of stability, suitability of different electrode materials and contribute to a safer, better, and also more sustainable lithium (ion) battery. During this project, the candidate will learn how to analyze newly synthesized electrolyte additives in battery cells in a close, synergistic cooperation of organic and physical chemists.
Liquid Electrolytes in Porous Battery Materials
While the transport properties of liquid battery electrolytes are well investigated in bulk, the influence of interfaces and their implications on ion transport are less established, but essential for battery operation. The project will employ physicochemical studies of ionic liquid- and organic solvent-based electrolytes in various nanoporous materials, such as porous electrodes as well as well-defined model materials. The goal is to understand the interaction of electrolyte components with interfaces and the influence of geometrical restrictions on ion transport. Ion dynamics and transport will be mainly characterized by NMR diffusion and spin relaxation measurements. Beneficial influences of defined interfaces and pore geometries on ion clustering are expected to promote Li+ ion transport.
Lithium metal-ionic liquid interface characterization using operando vibrational spectroscopy
The full integration of lithium metal anodes as a promising alternative to graphite is halted due to the poor cycle life and safety issues regarding the lithium dendrite formation. Mixed electrolyte systems of ionic liquids are considered a key solution to these problems and proved to improve the performance of lithium metal anodes. These electrolyte systems take benefit of ionic liquids high conductivity, wide electrochemical stability window, and stable interfacial chemistry. However, the interfacial properties and performance of the ionic liquid systems can vary significantly depending on their chemical, structural, and charge properties. In this project, operando vibrational spectroscopy characterization techniques are employed to provide molecular-level chemical and structural properties (e.g. adsorption, configuration, and solvation of ions) of ionic liquids at the electrode-electrolyte interface.
Single vs. blended vs. multifunctional electrolyte additives for targeted application(s): how do they work and why are they effective?
Current, straightforward approaches for the optimization of existing functional electrolytes often lead to solutions where specific properties can only be improved at the expense of other relevant ones, implying that current liquid electrolytes are already close to their optimum performance and that major gains can only be achieved with substantially altered formulations. One of the effective solutions refers to the application of functional electrolyte additives, added in small amounts to the electrolyte formulation to attain the demanded properties. Although different electrolyte additives have found their application in advancing the electrolyte performance, not much is understood about their role and effectiveness. This work comprises design, tailored synthesis and comprehensive physicochemical, electrochemical, analytical and structural study of targeted molecules as single, bifunctional or combined additives for advanced LIB electrolytes (on electrolyte and battery cell level) and compares their effectiveness highlighted by the structure-property-reactivity-performance-safety relationship. In addition, this approach enables to further tailor the vital properties of (multi)-functional electrolyte additives for targeted application.
Transport limitations in composite electrodes in solid state batteries
Solid state batteries need composites of active material and the fast-conducting solid ionic conductors. However, the influence of composite formation, ion percolation, composite tortuosity and microstructure on the transport (electronic or ionic) are unknown. In this doctoral project a deeper understanding of how limited transport is in composite electrodes needs to be elucidated, with the question of how can composites be designed to overcome transport limitations in solid state batteries. Within the scope of the project, you will learn how to synthesize sulfide based superionic conductors, form composite electrodes and measure the underlying transport properties that are then compared via solid state battery cycling.
Recycling, Sustainability and Life Cycle Analysis
Analysis, toxicity and environmental impact of new battery materials
The development of new innovative materials for the improvement of existing battery cells and the development of new cells for future applications are the main goals of BACCARA. During the development of new materials safety aspects including the toxicity to humans and animals as well as environment aspects play a major role.
The protection of consumers from undesirable, toxicologically questionable compounds is one main focus at the Institute of Food Chemistry. For this purpose, several in vitro test systems are routinely used to determine cytotoxicity, genotoxicity and mutagenicity. Furthermore, the uptake of food toxicants or environmental chemicals into the human body and the human metabolism is studied based on high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS).
Within BACCARA, the established toxicity test systems will be used and adapted for a high-throughput screening to test new materials which are provided by the synthetic groups within the BACCARA consortium. The goal is to identify new, innovative materials which show on the one hand optimal technical properties and on the other hand also low toxicity. Furthermore, in collaboration with the group of Prof. Melanie Esselen we are planning to establish also new test systems to study the environmental compatibility of new battery materials. The focus of these ecotoxicological investigations is on the different endpoints of mortality, growth inhibition and mutagenicity.
Hazard characterization of selected battery materials in cell models
The growing interest in battery systems addresses the questions on alternative materials or on the improvement of existing battery cells. One goal of BACCARA is to enhance battery technology with the use of non-hazardous materials. Nevertheless, batteries should provide low toxic properties but also retain a good performance and shelf life.
The specific adverse outcome pathways (AOP) and mode of action (MoA) of materials as well as the relative amounts present, are key factors to assess risks to humans and environment. The understanding of biological systems and the various ways that potential toxicants can interfere with them to cause adverse effects are focused in the Institute of Food Chemistry.
Cellular test systems e.g. tumor or primary cell lines to determine cytotoxic as well as genotoxic and mutagenic events are well established. Analyses tools such as high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) or high-resolution mass spectrometry (ToF/MS, Orbitrap) are used in the field of toxicokinetic. In collaboration with the group of Prof. Hans-Ulrich Humpf, we are planning to establish also new test systems to study the environmental compatibility of new battery materials. The focus of these ecotoxicological investigations is on the different endpoints of mortality, growth inhibition and mutagenicity.
Major roles of the BACCARA doctoral student will include: (1) cell culture experiments, (2) in vitro cytotoxicity, genotoxicity and mutagenicity studies, (3) investigations of potential endocrine effects, (4) cellular uptake and metabolism, (5) presentation of data at professional meetings, and (6) data publication in peer-reviewed journals.
Experience with basic lab technique is required. Expertise with cell biology, molecular cellular toxicology and/or ecotoxicology is an advantage. The candidates will have an outstanding master or equivalent degree in (environmental) toxicology, food chemistry, biochemistry or related discipline.
Possible Dangers in Handling and Storing of Lithium Ion Batteries from Production to Recycling
The widespread use of lithium-ion batteries (LIBs) in a multitude of industrial and private applications has led to the need for recycling and reutilization of their constituent components. However, due to their high voltage, high amounts of stored energy and a large variety of reactive components, lithium-ion batteries can present a specific and significant hazard potential. This is of particular importance during recycling because nearly every safety precaution of a battery system and battery cell needs to be bypassed. However, similar potential hazards can be found during production. The focus is on the chemical-based potential hazards with regard to the storage and handling of the cells. Therefore, potential hazardous volatile compounds and particles will be investigated.