Research

Research Unit A (Electrode Materials)

Electrode materials define and limit the amount of energy that can be stored per weight and volume of a battery. Our goal is to identify, synthesize and test new high-capacity post-lithium storage materials and thereby gain an even deeper understanding of their functionality.

Spokespersons

• Dr. Holger Euchner
• Dr. Julia Maibach

Work Package A.1 – Insertion of monovalent ions

A comprehensive approach is taken for the rational design of novel, tailored materials, which are abundant, low-cost, non-toxic, and environmentally benign, and which will enable sodium-ion batteries to play an important role in a sustainable energy future. We perform therefore detailed theoretical and experimental studies, exploring insertion of Na ions into oxidic structures at high potentials and Na storage in hard carbons at low potentials.

Project A.1.1 Insertion of Na ions at high potential

The key challenge addressed by the project is the understanding of the Na-ion insertion in a variety of high potential insertion cathode materials, including inorganic and organic compounds, allowing for the design of new materials for Na-ion storage.
The outcome of this project, i.e., the high-performance materials for Na-ion storage at high potentials, will be used as input for the cell scale-up activities in WP D.1 “Cell Design and Production”.

Responsible PI

• Dr. Margret Wohlfahrt-Mehrens

Project A.1.2 - Na storage in hard carbons - Insertion versus adsorption mechanisms

The main objectives are to develop a detailed understanding of the Na-storage mechanism in hard carbons and to design anode materials with tailored structural and morphological properties and enhanced electrochemical performance (i.e., sloping potential profile, low irreversible capacity, reversible behavior, and fast kinetics). The main target here is the correlation of the structural properties of hard carbons with their electrochemical behavior.

Responsible PI

• Prof. Dr. Helmut Ehrenberg

Project A.1.3 - Intercalation mechanism of alkali metal ions in carbon based anode materials

Understanding and improving carbon based anode materials is of significant importance for lithium and particularly post-lithium ion technology. Especially, the storage mechanism of alkaline metals in non-graphitic carbons that can be obtained from bio waste and is e.g. used in sodium ion batteries, is still largely debated. To elucidate the underlying processes, the storage mechanism of Li, K and Na in different types of carbon based model systems will be investigated by atomistic simulation methods.

Responsible PI

• Dr. Holger Euchner

Project A.1.4 - Structure-resolved simulation of sodium-ion-electrodes

Within this project simulation tools will be developed, which will allow for microstructure resolved investigations of sodium batteries. Connecting these tools with material databases will enable an automatic parameterization and a data driven prediction and optimization of the performance of electrode materials.

Responsible PI

• Dr. Simon Hein

Work Package A.2 – Insertion of Multivalent Ions

Multivalent ions offer higher storage capacities than monovalent ions, because two or more exchanged electrons are involved with the insertion of one single ion. Higher energy densities can be achieved if the active material in the cathode is capable of hosting the multivalent cation at a sufficiently high voltage. In addition, a reasonable rate performance is necessary for practical application. The identification of well-working hosts needs a joint and comprehensive approach of theoretical modeling, synthesis and advanced analytics.

Project A.2.1 Synthesis and evaluation of hosts for multivalent ions

This project is to characterize and understand multivalent-ion insertion based on suitable, structurally and chemically well-defined model systems. The project aims to synthesize model systems for probing ion-electron interactions, to compare Mg-free hosts with Mg-placeholder and Mg-rich compounds and to accomplish the transition from model systems to insertion electrodes.

Responsible PI

• Dr. Margret Wohlfahrt-Mehrens

Project A.2.2 Transport of multivalent ions in host matrices

The ion mobility in a solid host is a peculiar challenge for multivalent ions. The high specific charge of these ions results in stronger interactions with the electronic structure of the host. This behavior is critical for the applicability of such storage concepts. The project aims to comprehensively describe ionic and host-specific parameters, which determine the insertion and extraction of ions, and their interactions with each other and to rationally design ionic pathways with lower energy barriers for ionic transportsynthesize model systems for probing ion-electron interactions, to compare Mg-free hosts with Mg-placeholder and Mg-rich compounds and to accomplish the transition from model systems to insertion electrodes.

Responsible PI

• Prof. Dr. Helmut Ehrenberg

Project A.2.3 Organic electrodes

Objectives ot this project are to synthesize and characterize functionalized organic electrode materials (Por, Pc, GDY), to elucidate the electrode-electrolyte interaction under idealized conditions and to test porphyrins, phthalocyanines, and graphdiyne as electrode materials for Ca2+- and Al3+-ions.

Responsible PI

• Prof. Dr. Mario Ruben

Project A.2.4 - Anion-dominated redox chemistry for high energy and fast kinetic multivalent rechargeable batteries

Multivalent battery cathode materials always suffer from sluggish kinetics and therefore providing low capacity. In the project, we proposed to activate the anionic redox with multi-electron transfer in the cathode materials, so that the local charge compensation could be easily achieved. With the new concept, high-energy Mg- and Ca battery cathodes with fast cation diffusion are expected to be developed.

Responsible PI

• Dr. Zhenyou Li

Project A.2.5 - Electrospun hierarchical vanadium oxide nanostructures with controllable morphology, porosity and elemental composition as cathode materials for Mg-ion batteries

This project aims at the fabrication of novel electrode materials for Mg ion batteries that feature well-designed and controllable morphology, size, degree of porosity and elemental composition to overcome current limitations in Mg ion batteries including low ionic conductivity, structural and electrochemical stability and electrochemical reversibility. Furthermore, to provide a fundamental understanding of how structure-property-function correlations in this materials class affect the overall electrochemical performance in Mg ion batteries.

Responsible PI

• Dr. Montaha Anjass

Project A.2.4 - CAN - Calcium Alloys aNodes for Ca-ion batteries

Calcium and Calcium-ion batteries are nowadays drawing considerable attentions. Calcium is the fifth most abundant element in the Earth’s crust and it has a very low standard reduction potential, which makes it an ideal candidate as anode material. However, the further development of Calcium and Calcium-ion batteries is hindered by the modest performance of traditional graphite anode and the difficulty of enabling the calcium metal electrode. In this scenario, the primary goal of the project CAN is to pioneer the development and to build a fundamental understanding of new anode materials as well as demonstrating a proof-of-concept Ca-ion battery cell.

Responsible PI

• Dr. Mario Marinaro

Work Package A.3 – Conversion

Conversion reactions are different from insertion and are characterized by chemical reactions in the solid, which lead to a complete reordering of the elements in the electrode. This mechanism promises higher packing densities and increased volumetric capacity of the electroactive ion while offering the potential to use more abundant raw materials. However, due to the reordering of the active electrode material, conversion electrodes typically suffer from (micro-) reversibility issues and from kinetic barriers in the different reaction steps, which lead to efficiency losses. This is a major roadblock for multivalent systems, and any strategy to build suitable electrodes must take into account not only the particular properties of the electrode, but also of the interaction of the electrode with the electrolyte.

Project A.3.1 Reversibility of conversion reactions in sodium ion batteries (SIBs)

The conversion of sodium offers the advantage of higher specific discharge capacities due to the complete reduction of the electroactive species involving several electrons. While several materials have been proposed and developed that sufficiently facilitate this conversion process, there is a severe lack in reversibility. Therefore, within this project we will develop an in-depth comprehension of the Na-ion conversion storage mechanism and design cobalt-free, environmentally friendly, conversion electrode materials for high capacity negative electrodes in aqueous and non-aqueous electrolytes.

Responsible PI

• Prof. Dr. Timo Jacob

Project A.3.2 Overpotentials and irreversible processes in multivalent systems

In this project we will investigate the fundamental processes in multivalent systems, focusing on Mg-, Zn-, Ca- and Al-ion based batteries. The project is to develop an in-depth comprehension of multivalent-ion conversion storage mechanism, to track the origin of overpotentials in conversion systems and to develop strategies to avoid them and to design conversion electrode materials for high capacity positive electrodes.

Responsible PI

• Prof. Dr. Maximilian Fichtner

Work Package A.4 – Transport and Conversion in Anionic Systems

Anionic charge transfer by [OH]− is used in alkaline batteries such as the rechargeable nickel-cadmium and nickel-metal hydride batteries, as well as in zinc-air batteries. Halide batteries based on Cl− and F− and aluminum batteries using [AlCl4]− shuttles are among new and promising alternatives for anionic post-Li systems. Anion transfer is conceptually simple and particularly attractive for high capacity conversion electrodes because only two solid phases (the metal chloride and a metallic phase) are involved in the reversible reaction.

Project A.4.1: Reversible interaction of Cl-ions with solid electrodes

The work in the project will focus on a selection of materials combinations with high theoretical capacities. The goal is to develop an understanding of the reversible shuttle and incorporation mechanism of the chloride ions at these electrode materials and to develop suitable new liquid electrolytes. In addition, a cell concept shall be developed which will also enable the use of electrolyte-soluble metal chlorides as active materials so that a wider selection of high capacity materials is possible.

Responsible PI

• Prof. Dr. Maximilian Fichtner

Work Package A.5 – Degradation

Electrode degradation processes leading to a loss in overall performance are a major challenge for post-Li systems. Phenomena related to degradation are complex and depend on battery chemistry, design, and actual operation conditions. So far, degradation studies have been focused on lithium ion batteries, to understand the strong relation between structural changes and the electrochemical processes during charge-discharge cycling Such electrode degradation phenomena may be even more severe for ions with larger sizes, e.g., sodium ions, and multivalent ions, which results in an increased insertion barrier and insertion strain, and thus in lower performance. Degradation studies in post-Li batteries are scarce and the origin of degradation is mostly unknown.

Project A.5.1 Studies at post-lithium model electrodes

Aiming at a fundamental understanding of the processes contributing to degradation, we will investigate degradation-induced changes at the electrode surface or in the surface near region with atomic/molecular resolution in a combined experimental and theoretical approach, using chemically and structurally well-defined model electrodes and employing a variety of ex-situ / in-situ techniques for surface characterization as well as quantum chemical modeling based on DFT.

Responsible PI

• Prof. Dr. Axel Groß

Project A.5.2 Studies at realistic post-lithium electrode materials

In this project we will use a combined experimental and theoretical approach to investigate the degradation of realistic post-Li electrodes on a nanoscopic to mesoscopic scale. The complex interplay of chemical and electronic properties of the electrode and of electrolyte components, including mechanical properties shall be solved since also the morphology of the electrode composite can either have a stabilizing or a destabilizing effect on the system. This requires a multi-method experimental approach, including surface and bulk characterization, locally resolved electrochemical measurements as well as mesoscopic theoretical modeling using phase field theory based models.

Responsible PI

• apl. Prof. Dr. Christine Kranz

Research Unit B (Electrolyte)

Electrolytes enable the transport of electrically charged particles (ions) between the two electrodes of a battery. The main objective is the identification, synthesis and testing of new, stable and highly efficient liquid or solid transfer systems for post-lithium-ions.

Spokespersons

• Prof. Dr. Timo Jacob
• Prof. Dr. Carsten Streb

Work Package B.1 – Liquid Electrolytes

Central topic of this WP is the development of liquid electrolytes with high ionic conductivities and chemical and electrochemical stability, combined with low cost and high safety performance, which do not exist so far, and which are a must to ensure the exploitation of post-Li batteries. The ionic mobility is of key importance for the performance of batteries. Typically, in liquid electrolytes both anions and cations are mobile, leading to the establishment of concentration gradients and the occurrence of overvoltage. Thus, new liquid electrolytes exhibiting high ionic conductivity for the electroactive species must be developed, tailored to the needs of post-Li batteries, to maximize energy efficiency and rate capability, but also the cycling stability, which is expected to be much more critical for multivalent than for monovalent ions.

Project B.1.1 Synthesis of non-reactive electrolytes

Main topic of this project is to derive and experimentally implement strategies for designing and synthesizing novel electrolytes specifically tailored for post-Li battery systems which are highly stable over a wide potential range and suitable for applications with respect to their corrosive behavior. Specific problem of these electrolytes is the wide variation in electroactive ion hardness.

Responsible PI

• Prof. Dr. Timo Jacob

Project B.1.2 Mechanisms of ionic transport in liquids

This project focuses on understanding the ion-solvent and ion-ion interactions in liquid electrolytes for post-Li systems and developing a continuum transport theory for mono- and multivalent ions in electrolytes based on atomistic properties. Further objectives are to describe multivalent ion transport in electrolytes by multiscale modeling and to detect multivalent ion mobility in-situ by optical methods.

Responsible PI

• Prof. Dr. Arnulf Latz

Project B.1.3 Tailoring electrolytes for optimized interphases

This project focuses on the systematic development of electrolyte additives optimized for the formation of ion-conducting, electron-insulating, and stable interphases on a rational basis. Electrolyte additives supply the building blocks for the interphase formation, and/or increase the concentration of the electroactive ions in the system. The work in this project starts with identifying (electro-)chemical reactions involving additives, which are relevant for the formation and the properties of interphase layers, on model electrodes.

Responsible PI

• Prof. Dr. Arnulf Latz

Project B.1.4 - Coupled electrochemical and calorimetric investigations on liquid and solid electrolytes for the use in Na-ion batteries

Apart from electrochemical properties (ionic conductivity, transference number, etc.) the thermal, chemical and electrochemical stability of electrolytes are crucial prerequisites for their application in for next-generation batteries. Isothermal microcalorimetry (IMC) allows us to detect the heat flow originating from electrolyte decomposition reactions inside of a battery. Within this project, we are going to use a coupled electrochemical and calorimetric characterization method in order to gain a deeper understanding on how chemical, electrochemical and thermal stability of Na-ion conducting electrolytes can be tuned. Therefore, we will investigate the impact of additives and ionic liquids in liquid electrolytes as well as the impact of the chemistry and structure of solid polymer electrolytes for the use in Na-ion batteries.

Responsible PI

• Prof. Dr. Jens Tübke

Project B.1.5 - Influence of additives in carbonate-based electrolytes on the interfaces of Na-ion battery electrodes

It is known from Lithium Ion Batteries (LIB), that additives, solved in the applied liquid electrolyte, show a significant positive impact on the cell performance like cycling stability, accessible electrochemical potential window as well as on safety issues. Of particular importance is the interaction of these additives at the interface between liquid electrolyte and electrode surface. In case of Sodium Ion Battery (SIB), the influence of additives is widely unknown. The aim of this project is the systematic investigation of the influence of various additives in combination with carbonate-based electrolytes and suitable conducting salts on the electrochemical behaviour of SIBs.

Responsible PI

• Prof. Dr. Thomas Hanemann

Project B.1.6 - Sodium ion battery electrolytes based on ionic liquids

Ionic liquids (ILs) are ideal candidates for SIB electrolytes as anion and cation can be tuned independently, and their binding behaviour with the Na⁺ cation can be tuned by molecular chemistry. Here, we will establish a new class of SIB-ILs based on bulky organic cations featuring Na⁺ binding sites, together with (poly)anionic metal-based cluster compounds where Na⁺ coordination can be tuned by structural modification, binding site incorporation and surface polarization tuning. Systematic molecular level studies by experiment and theory will provide the basis for developing next-generation sodium ion transporting ILs with wide potential window, high stability and low environmental impact.

Responsible PI

• Prof. Dr. Carsten Streb

Project B.1.7 - Ionic Liquids and Deep Eutectic Solvents as Electrolytes for Na and Mg Deposition

Sodium and magnesium have the advantage over lithium that under normal conditions dendrites are usually not form during deposition. However, due to their chemical nature, both metals can act as strong reducing agents and can react with the electrolyte in many different ways. Therefore, within this project we are investigating the underlying deposition and dissolution processes on an atomic scale using in-situ electrospectroscopic methods.  Besides ionic liquids we will also study other possible non-aqueous electrolytes to be used in these battery systems.

Responsible PIs

• Prof. Dr. Timo Jacob

Work Package B.2 – Solid Electrolytes as Single-Ion Conductors

Different from liquid systems, solid electrolytes can be tailored to ensure that only the electroactive species is mobile. These single-ion conductors have the advantage to avoid concentration gradients in the electrolyte during charge and discharge, which circumvents the contribution of mass transport to the cell overpotential and improves the utilization of the active electrode materials up to almost 100% even at relatively high charge/discharge currents according to Newman’s simulation, which were confirmed by fundamental transport theories for solid electrolytes. In addition, solid electrolytes offer improved safety: For metal anode batteries, dendrite growth can be avoided by mechanically optimized solid electrolytes, as indicated by the Chazalviel model.

Project B.2.1: Inorganic and Polymer Solid Electrolytes as Single-Cation Conductors

Key challenge of this project is to increase the room temperature mobility of mono-, di- and trivalent ions in single-ion conducting solid electrolytes by careful design of the matrix including the negative counter-charge – with the constraint that the matrix has to be redox stable against electrode materials. This project aims to develop an in-depth understanding of the effect of aliovalent doping and structural tuning of phosphate glasses on polyvalent cation mobility, to develop concepts for softening lattice dynamics for improved polyvalent ion mobility and to derive design criteria for single-ion conducting polymer electrolytes.

Responsible PI

• Prof. Dr. Jürgen Janek

Project B.2.2 - Solid electrolytes and chloride ion transport in solid phases

In this project we will identify, synthesize and explore Cl- conducting solid electrolytes for use in Cl-ion batteries. Objectives of this project are to identify, synthesize and characterize new inorganic and organic compounds with high conductivity for chloride ions, to describe Cl- ion transport in solid electrolytes in a theoretical model and to identifying suitable combinations of solid electrolyte and electrode materials by compatibility and cell tests.

Responsible PI

• Prof. Dr. Jürgen Janek

Project B.2.3 - Approaches for polymer electrolytes

Aim of this project is the development of novel solid polymer electrolytes for multivalent cations, such as Mg2+ and Al3+. A deeper understanding of the mechanism of multivalent ions in batteries is developed. Therefore the project deals with this challenge by identifying, tuning and developing structural and ionic properties of polymer electrolytes. One such approach involves the use of PEO as an interesting building block within divers polymer architectures to provide mechanical stability, low cost and electrochemical stability. The synthesis and electrochemical characterisation of the polymer electrolytes are accompanied by construction of batteries, performance tests of cells, safety test and life cycle analysis.

Responsible PIs

• Prof. Dr. Patrick Theato

Project B.2.4 - All-solid potassium batteries – a polymer electrolyte approach

Potassium-Ion batteries (PIB or KIB) are based on abundant and cheap materials such as potassium itself, iron or manganese and may qualify as an interesting and economic complementary energy storage system to Li-ion batteries, e.g. as interim storage solution for intermittent energy sources like wind or solar power. Unlike other post-Li battery systems KIB can use the same key components that are used in Li-ion batteries, for instance the same type of graphite anode and electrolyte. Over the course of the next three years, solid polymer electrolytes will be explored for this battery system with the aim to produce safer batteries and to achieve longer battery life as compared to the commonly used liquid (and typically flammable) electrolytes. During this project we investigate how K-ion are transported through polymer films and study the characteristics of all-solid potassium batteries.

Responsible PI

• Dr. Fabian Jeschull

Project B.2.5 -  Synthesis and characterization of Mg2+ and Ca2+ ion-rich anti-perovskites as superionic conductors for multivalent ion batteries

The development of solid electrolytes for post-Li ion batteries requires designing new structures away from that are currently used for lithium ions. Antiperovskites are potential candidates due to their high versatility, tunability and high thermal stability. Their electronic structure can be tuned to be superconductors, semiconductors, or insulators through modifying their intrinsic and/or extrinsic structural defects. The current project is aimed to synthesize and characterize electronically insulating antiperovskites with high ionic conductivity to be used as solid electrolyte for Mg and Ca ion batteries.

Responsible PI

• Dr. Hagar K. Hassan

Research Unit C (Interfaces)

We aim to understand the formation and nature of interfaces that form within a post-Li battery - e.g. at the contact between electrode and liquid or solid electrolyte. Their microstructure and chemical composition have a decisive influence on the interface processes within the battery and thus determine, among other things, its performance and longevity.

Spokespersons

• apl. Prof. Dr. Christine Kranz
• Jun.-Prof. Dr.-Ing. Helge S. Stein

Work Package C.1 – Structure and Stability of Solid-Solid Interfaces

All-solid-state batteries (ASSBs) consist of active materials (AMs) and solid electrolytes (SE) and can therefore comprise three types of interfaces: AM/SE, AM/AM and SE/SE interfaces. Their structure and their thermodynamic stability as well as their kinetics are decisive for the reversible and stable function of ASSBs. However, the understanding of interfacial properties and phenomena is still limited for post-Li systems, and studies typically focus on bulk transport in first examples of sodium and magnesium solid electrolytes. The major focus are interfaces between solid electrolytes and the anode or cathode of potential sodium ASSBs.

Project C.1.1.: Interface kinetics and solid electrolyte redox chemistry

Suitable solid electrolytes need to be stable against reduction at the anode and against oxidation at the cathode, both in equilibrium (thermodynamic stability) and under current load. At low and high potentials at anode and cathode, complex heterogeneous interface reactions can lead to the build-up of highly resistive natural interphases. To detect the formation of such phases, the quantitative evaluation of interface kinetics and the analysis of the interface structure under different operation conditions is indispensable.

Responsible PI

• Prof. Dr. Christian Kübel

Work Package C.2 – Structure, Function, and Stability of Solid-Liquid Interfaces

In batteries with liquid electrolytes, the particular structure, function and stability of solid-liquid interfaces is of crucial importance for the performance. They not only control ion and electron transfer, but also (electro-)chemical degradation processes of electrolyte and electrode.

Project C.2.1 Challenges in metal deposition and dissolution

This project aims at a fundamental understanding of the elementary processes responsible for the growth behavior during metal deposition from the atomic scale, on model electrodes, up to the cell level. The insights gained in these studies will then be used to develop electrolytes and/or additives which allow the reversible deposition of the relevant metals without dendrite formation and with minimized degradation. On all levels, experiment and theory will closely interact.

Responsible PI

• Prof. Dr. Rolf Schuster

Project C.2.2 - Towards haloaluminate-free Aluminum batteries

The aim of this project is to push the research frontiers on Aluminum batteries by developing a system based on non-corrosive electrolytes and on tailored interfaces. So far, an indispensable component of Al-based electrolytes is AlCl₃, which provides a very corrosive environment. This represents a serious obstacle to the development of Al-batteries in terms of sustainability, safety and cost. In this project, alternative Aluminum salts will be explored in combination with deep eutectic solvents. On the other side, the Aluminum surface will be tailored by surface modifications in order to facilitate the Aluminum plating and stripping.

Responsible PI

• Dr. Sonia Dsoke

Project C.2.3 - Transient operando studies on electrochemical interfaces in mangesium-based batteries by reflection anisotropy spectroscopy

Magnesium-based batteries are a promising next-generation, post-lithium battery technology. Especially for novel material combinations, however, we often know only very little about the atomistic structure of the electrode-electrolyte interface under operation conditions. In this project, we will use a highly interface-sensitive optical spectroscopy to study electrochemical processes at the interfaces of Mg-battery systems in a time resolved manner to understand them and hereby help to improve their functionality.

Responsible PI

• Dr. Matthias May

Work Package C.3 – Interphases

Due to the intrinsic instability of many electrochemical interfaces, the formation of interphase layers is often observed on battery electrodes. This is an effect of electron transfer and consecutive complex chemical and electrochemical reactions. In fact, the success of the Li-ion battery would not have been possible without the existence of the Solid Electrolyte Interphase (SEI) formed as an interphase between graphite and the liquid electrolyte. For designing stable and safe post-Li batteries, a thorough experimental and theoretical understanding of the structure, function and stability of interphases is necessary.

Project C.3.1 Interphases at carbon-based electrodes

Carbon-based electrodes are currently a first choice for anodes in SIBs. However, their sustained usability will depend to a large extent on the properties of the interphase formed on the interface of the anode. The main objective of the project is therefore to develop new theoretical tools and analytical methods, to obtain a comprehensive picture of structure, local chemical composition and growth mechanisms of interphases.

Responsible PIs

• apl. Prof. Dr. Christine Kranz
• Prof. Dr. Arnulf Latz

Project C.3.2 – Interphases at inorganic electrodes

Inorganic electrodes will be relevant in the form of metal electrodes formed by the electroactive species but also insertion electrodes. Due to the inherent instability of most of the interfaces between electrodes and electrolytes, formation of interphases cannot be avoided also for inorganic electrodes. The interphases which are formed for a certain combination of electrolytes and inorganic electrodes will be crucial for the choice of the proper electrolyte-electrode combination. This project aims to  develop model electrodes for controlled investigation of interphase formations and to understand the interaction of multivalent ions in different electrolytes with inorganic surfaces.

Responsible PIs

• apl. Prof. Dr. Christine Kranz
• Prof. Dr. Arnulf Latz

Project C.3.3 - Autonomous Interphase Engineering

In this project we will deploy a system capable of autonomous material synthesis, characterization and data mining techniques using artificial intelligence (AI) in experiment evaluation and design. This new paradigm for battery research will greatly accelerate the pace of research towards new and highest-performing battery materials. Several robots will be able to test several thousand materials per day. With the help of algorithms and AI, the quality and information content of the robot's measurements are evaluated autonomously. A central AI decision maker produces predictions and then suggests the optimal follow-up experiment. This method adds to the already extreme acceleration of research and was shown to be capable of an up to 30 times more rapid optimization than traditioned trial and error.

Responsible PI

• Jun.-Prof. Dr.-Ing. Helge S. Stein

Research Unit D (Integration and Sustainable Cell Engineering)

Up-scaling of materials synthesis and cell construction, studies on the production capability of new technical approaches, assessment of cell safety and life cycle analyses of new technologies will pave the way for technology transfer. Central research data management and the development of automated data analysis tools will flank all work in the Cluster, set standards for the handling of research data and enable integrative, cross-research field data analysis, which we hope will lead to new insights in battery research.

Spokespersons

• Dr.-Ing. Janna Hofmann
• Dr. Margret Wohlfahrt-Mehrens

Work Package D.1 – Cell Design and Production

In this WP, electrodes, electrolytes and interfaces from RU A, B and C are combined with other components like separator and housing to obtain full cells. The obtained devices will provide the basis for the realistic evaluation of energy-storage capabilities of post-Li systems. This approach is mainly applied to Na-ion and Mg-ion batteries and can be adapted to the specific demands of other cell chemistries.

Project D.1.1 Engineering electrodes and cell design

This project is dedicated to the definition and realization of specific and optimized electrode and cell designs for promising cell chemistries. The specific objectives are to fabricate hierarchically structured materials and electrodes, to develop of a tool box for microstructure characterization of cell components and to model transport in and mechanics of electrodes as multi-phase systems.

Responsible PI

• Prof. Dr. Helmut Ehrenberg

Project D.1.2 Scale-up of materials and cell producibility

New approaches and fundamental aspects are tested on small-size laboratory cells in the capacity range of a few mAh only. Representative information and comprehensive cell testing requires larger cells with capacities of several Ah. This requires a significant amount of electrode materials, electrolytes, and cell components which are not available yet for post-Li batteries. Scale-up and producibility are serious bottlenecks for bringing basic cell concepts to application and will be addressed comprehensively already in an early stage of development.

Responsible PI

• Prof. Dr. Jürgen Fleischer

Project D.1.3 - Digital twins for electrode microstructure fabrication - investigation of particulate flow and drying process

The electrode microstructure has high impact on the performance and degradation behavior of battery systems. Actively designing the microstructure properties of such electrodes is a key point to solve future challenges concerning capacity and rate capability in post-Li battery systems. In this project we develop a framework to model the formation of hierarchically structured electrodes. Simulation studies with that framework will provide a realistic picture how to design a morphology of hierarchically structured anodes according to the given criteria identified by partner projects in Research Unit (RU) D of Post Lithium Storage Cluster of Excellence (POLIS).

Responsible PI

• Dr. Daniel Schneider

Project D.1.4 - Development of a Na-ion full reference cell within POLIS and practical studies addressing its upscaling and commercialization compared to Li-ion cells

The aim of this project is to scale up full sodium-ion batteries (NIBs) from small research coin-type cells into large industrial-type pouch format (see left Figure). This depicts a more realistic composition of the battery resulting in realistic physical properties such as heat generation, so that degradation and safety features can be investigated under realistic conditions. A new method developed in our lab for electrolyte and gas extraction (see right Figure) from pouch-type cells will be used to study the composition of gas and liquids by HPLC-MS/ UV-Vis (salts/ carbonates) and GC-MS/ FID/ TCD (volatile liquids and gases).

Responsible PI

• Dr. Anna Smith

Project D.1.5 - Development of filament materials for fused filament fabrication (FFF) 3D printing of all-solid state sodium-ion batteries (ASSSIB)

The overall goal of this project is to develop a 3D printing process as manufacturing technology for post-lithium all-solid-state sodium ion batteries (ASSSIBs) and to evaluate and optimize these processes in battery performance. The goal is to gain understanding in printing material development and thermally post processing, to increase the thickness of the electrode layers without worsening the cell performance in production of sodium ion batteries followed by safety analysis. This includes the complete process chain of preparing and characterizing of the printing materials, up to the electrochemical investigation of the electrochemical cells and the feasibility for upscaling.

Responsible PI

• Dr. Ijaz Mohsin

Work Package D.2 – Safety and Sustainability

The development of safe cells is of utmost importance for a breakthrough of the electrification of transport and for stationary storage and therefore for a critical selection criterion for batteries. Another, increasingly important selection criterion is the sustainability of new technologies as well as their general congruency with societal requirements.

Project D.2.1 Safer Batteries

Thermal and detailed safety studies on the small-scale cell level are necessary prior to a scale-up of cells in order to achieve in-depth understanding of the underlying reaction mechanisms and heat conduction processes, which are at the moment not known for post-Li cells. Thus, the scale-up in WP D.1 will be accompanied by both thermal investigations and safety tests in different calorimeter types and by using IR thermography. Thermal stability data will be acquired from anodes, cathodes and electrolytes for post-Li batteries.

Responsible PI

• Prof. Dr. Hans Jürgen Seifert

Project D.2.2 Sustainability

The complex interactions of various actor interests regarding the economic, environmental and social stamping of technology make decisions in early stages of technology development challenging. A strong need for sustainability assessment arises, entailing multiple and often conflicting dimensions as environmental impacts or economic performance as well as quantification of these to provide a broader base for technology design and identification of potential benefits of technology.

Responsible PI

• Prof. Dr. Armin Grunwald

Work Package D.3 – Correlators

In order to develop components of post-Li batteries with improved properties, a systematic approach using well-defined guidelines is needed. However, research on batteries, in particular post-Li batteries, is characterized by a multitude of important facts and results that often appear to be unconnected. Hence, it is our particular goal to identify and introduce so-called correlators in electrochemical storage. Correlators are defined as relations between fundamental properties that can be directly linked to observable physical or technical properties. Once identified, they enable effective screening of candidates for improving a desired property because only the particular descriptor needs to be optimized.

Project D.3.1 Identification and rationalization of correlators

The very existence of correlators means that a special relationship between a limited number of materials parameters and specific properties exists. Thus, correlators can in principle be directly derived from a rational scientific reasoning. However, the underlying relationship is sometimes not directly obvious so that the identification of correlators may require a statistical approach. In both cases, a deeper analysis of this particular relationship will result in an improved fundamental understanding of the underlying principles governing the performance of a material, process or device, such as a structure-property relationship.

Responsible PI

• Prof. Dr. Axel Groß

Work Package D.4 – Advanced integrated data analysis

Nowadays, new materials for batteries are to be developed within fast processing routes relying on versatile methods. Within the cluster, a huge amount of data, including results from experimental analysis as well as simulations from diverse modeling approaches ranging from atomistic, Monte Carlo, and phase-field, over continuum to production and system modeling, will be produced. Therefore, it is indispensable to establish a suitable infrastructure to enable the processing of large data volumes from simulations and experiments and to create data structure for transferring information between different research units and scientific approaches

Project D.4.1 Sustainable infrastructure for fast data processing and data analysis

This project addresses data management procedures following two main streams of integrated computational materials engineering. First, experimental data shall be integrated with theoretical data covering the whole simulation chain from the atomic to the continuum and production level, based on the concept of Bayesian inference using Kalman filtering. The exchange of data between experimentalists and theoreticians will be instrumental in identifying correlators which, combined with a comprehensive interpretation, will facilitate the transfer and interpretation of information needed to improve post-Li battery systems. Second, concepts to establish an efficient parameter transfer between multiscale approaches pursued in the individual RUs of the Cluster will be addressed, and suitable data processing pipelines will be developed.

Responsible PI

• Prof. Dr. Britta Nestler