Working Groups

The colossal improvement in performance and cost of lithium-ion batteries (LIBs) have made them the preferred technology for electrical energy storage. Even so, Li-ion batteries achieve high power and energy density, they are unlikely to meet all the performance, cost, and scaling targets required for applications such as electromobility and energy storage systems. The demand to further increase energy density and reduce cost, in addition to the growing concern related to the availability of natural resources, has accelerated the investigation of LIB recycling and the development of so-called “next-generation” batteries.

The working group Recycling and Materials Synthesis develops highly performant and sustainable batteries. Through recycling, materials reprocessing, designing synthesis processes, and material characterization, the multi-skilled working group provides solutions to meet future demands. Various battery types are explored such as solid-state, lithium-air, lithium-sulfur, sodium-ion, and redox flow batteries, along with fuel cells.

Material recovery

Recycling spent LIBs is a complex multi-stage process that involves safe deactivation, dismantling, mechanical processing, thermal treatment, and hydrometallurgy. These integrated processes enable maximized material recovery including the direct recovery of electrode materials. As the first process step, the working groups explore automated dismantling opportunities for different types of battery systems and cells. The mechanical processing includes the comminution of the batteries to maximize the liberation of materials, classification, and sorting processes. Applied thermal treatment options are, among others, vacuum thermal drying, pyrolysis, and roasting. In hydrometallurgy, leaching is performed by applying suitable lixiviants followed by impurities removal, material recovery, and purification. The teams evaluate the performance and viability of the different process routes with respect to product purity, robustness, economic viability, and sustainability.

Material reprocessing

Depending on the type of degradation experienced by the recovered materials, they can be directly reused or need to be reprocessed. Such assessment requires a stepwise characterization to determine the composition, morphology, size, crystallinity, and interfacial properties of the recovered materials. Then, the material can be reintegrated into a battery or necessitates additional post-treatment such as thermal or chemical treatment.

Synthesis

The principal shortcoming of methods used during the material recovery is their need for several purification stages to obtain Battery-grade materials. For this purpose, several downstream operations that require significant consumption of energy and reactants in addition to waste products are carried out. To minimize these processes, the influence of impurities present in the re-synthesized materials is considered and tolerance benchmarks are defined. To guarantee the sustainability of the resources, alternative raw materials from bio-based sources are explored.

Close-loop

Throughout the different recycling stages, digitalized monitoring of energy and material usage, cost, and waste production is conducted to compare the impact of different production systems and to assess their scale-up viability.

Contact:
Kirstin Schneider
kirstin.schneider(at)tu-clausthal.de

Tasks and objectives

The working group "Components" of the Battery LabFactory Braunschweig (BLB) deals with the production of battery cell components and their characterization. It combines the experience of the associated institutes in order to look at process steps and challenges from the material to the electrode from different angles. The goal is cross-institute coordination, joint development of standards at the manufacturing level, and evaluation and standardization of analysis methods.

Component manufacturing

While only anodes and cathodes have to be processed for the production of conventional liquid electrolyte based lithium-ion batteries (LIBs), this also applies to the separators in the case of solid-state batteries (SSBs). Furthermore, due to the particularly moisture-sensitive solid electrolytes, dry room or argon atmospheres are often required. The production steps considered include the processes of dispersing, coating, drying, compacting and cutting, irrespective of the battery system.

The production of electrodes and separators begins with the dispersion of the powdered individual components into the desired solvent. In this production step, a large number of different machines on different scales can already be used, which are operated either in batches or continuously (cf. Figure 1). Common to all these processes is the complex task of dispersing powdered components into a solvent as homogeneously, quickly and efficiently as possible. In addition, dispersion has a decisive influence on the interaction and structure of the components: For example, the formation of carbon black networks determines the electrical contacting of the active material particles and thus the initial capacity of the battery cell.

Dispersion is followed by coating of the suspensions onto a substrate. Comma bar or slot die processes are used, and equipment of different sizes, ranging from film applicators to continuous pilot-scale coating lines (cf. Figure 2), is also available for the various product volumes. While the production of anodes and cathodes involves copper and aluminum for subsequent current conduction, separators for SSBs are coated directly onto the electrode or onto a carrier substrate and then used free-standing.

The applied liquid film is dried in the subsequent step, either discontinuously using the heatable surface of the film applicator or continuously following to the coating equipment using convection, diffusion and infrared drying. The drying process affects not only thickness, width and porosity, but also the distribution of components within the coating through sedimentation, diffusion and buoyancy. The resulting layer properties have an impact on cell performance in several respects: For example, the area weight is decisive for the equal weighting of both electrodes ("balancing").

If the layer does not yet have the desired parameters after drying, densification follows using presses or calenders.  By applying a static pressure or a line load, particle and pore structure within the layer are changed. While in conventional LIBs a defined porosity must be set to achieve a balance between electron and ion conduction, in SSBs the aim is to achieve the lowest possible porosity for solid-state conduction of electrons and ions.

Finally, electrodes and separators are cut before cell assembly. This is not only necessary for the production of stackable layers in the construction of pouch cells, but also to specifically exclude defects. Separation is performed mechanically with the aid of punches or related cutting tools, or with the use of a laser. The processes each have advantages and disadvantages depending on the product, but no longer have any influence on the microstructure of the component and thus on its properties.

Analysis and characterization

Precise, systematic and uniform analytical methods are crucial in understanding scientific relationships and optimizing battery cell components. The analytics used can be divided into five categories: Process-related, structural, mechanical, electrical and electrochemical.

Process-related analytics include the tracking of rotational speeds, energy consumption, speeds or forces during the individual production steps in order to obtain an overview of the input variables as well as the general conditions of the "component" system.

Structural analytics include methods that deal with the structure and composition of the components, for example particle size measurement, imaging analyses (SEM, EDX), pore structure analysis or BET measurements. They characterize the structure of the component as-is and provide a basis for mechanical and electrical analytics.

Mechanical analytics characterize the behavior under mechanical stress to meet the dynamic requirements of component manufacturing and operation. This is done by measuring the adhesion of thin films to carrier substrates (adhesion measurement) or the mechanical deformation behavior under pressure (nanoindentation).

Electrical analysis includes the determination of the electrical continuity conductivity or the surface conductivity. The measured electrical resistivity can be used, among other things, to quantify the carbon black networks within the electrode or to evaluate the conductivity of surface coatings on active materials.

The electrochemical properties are usually determined using half and full cells. In addition to measure the ionic conductivity of LIBs and SSBs, liquid electrolytes or solid electrolyte-based separators can also be investigated. Furthermore, properties such as rate capability, cycling stability and specific capacitance can be examined by cycling the cells. Electrochemical measurements take place under defined temperature and pressure in a climatic chamber and using special cell pressing equipment.

Conclusion

Batteries are complex systems whose properties depend significantly on the processes and their influences on the micro- and macrostructures. In order to establish a relationship between the processes and the performance, a detailed and comprehensive view of the individual components is necessary, which will be implemented to the best of our ability within BLB. The “Components” working group will help to find, develop and expand competencies and opportunities within the BLB structure.

Contact:
Christine Oertel
c.oertel(at)tu-braunschweig.de

The working group Cell and System focuses on the development of processes and components to meet the high requirements on safety, cost and performance of state-of-the-art and future batteries. 

Converting/Laser Cutting

The fully automatic separation of the electrodes for the stacking process takes place by means of a remote laser cutting process. Advantages of this method compared with other separating methods are a contactless and therefore wear-free separation of the electrodes as well as the high flexibility of the process. A pyrometer monitors the focus position as well as the cutting parameters of the system during the laser cutting process.

Cell Assembly

During the automated cell assembly, the electrode-separator-composite (ESC) is build using a z-folding process. In the z-folding process, the anodes and cathodes are placed alternately on a stacking table, while the separator is continuously fed and folded around the deposited electrodes. The quality parameters during cell assembly are the deposition accuracy and the reduction of damages caused by mechanical loads during handling. As an alternative to z-folding, the working group investigates the application of winding in the context of cylindrical cells and develops new stacking processes with increased productivity.

Contacting terminals, housing and electrolyte filling

Following the cell assembly, the current conductors of each electrode are connected. This step is realized in the BLB by means of ultrasonic welding and resistance spot welding. The housing of the contacted ESC depends on the cell format and the assembly technology. Winded ESC have a hard cylindrical housing while stacked/z-folded cells have a soft housing of two metal-polymer-composite pouch sheets. After the housing, the cell is filled with electrolyte and sealed. The filling process takes place in a dry room or in an inert atmosphere because the electrolyte is highly sensitive regarding moisture. During the final sealing, the cell is evacuated to improve the homogenous wetting of the electrode. To visualize the influence of filling parameters on the wetting process optical inspections methods, e.g. CT, and electrochemical characterisation methods, e.g. EIS, are used.

Formation, Ageing and Diagnostic

In the process step of formation, the cells are electrically activated by initial cycles of charging and discharging. During these cycles, a cover layer is formed on the basis of chemical reactions between components of the electrolyte and the graphite electrode. This cover layer is called Solid Electrolyte Interphase (SEI). The process parameters chosen in the formation process have an impact on the structure, thickness and composition of the SEI and exert therefore significant influence on the cell characteristics, cycle stability and safety aspects. After the forming process the cells are matured over a determined period of time and under defined ambient conditions. After terminating these last two process steps, the cells are characterized by electrical and electrochemical measurements at different age stages. The working group Diagnosis & Use provides an insight into the applied diagnostic methods.

Contact:
Jan-Aut Deeken
j.deeken(at)tu-braunschweig.de

Maximilian Liedtke
maximilian.liedtke(at)tu-braunschweig.de

The working group Diagnostics & Usage aims to enhance the professional exchange between diagnostics experts from different areas of BLB. We want to enable researchers in need of diagnostics equipment and know-how to carry out their experiments to the highest quality standards. This is done for a number of techniques ranging from material to system level and across a variety of methods such as electrical, thermal, mechanical, or optical approaches.

By combining the competence of all BLB institutes, we aim to gain fundamental knowledge about the production, the fundamentals, and the usage of batteries. This is promoted by the approach of knowledge-driven battery production which will advance the determination of process-structure-property relationships. By collecting, interpreting, and connecting information across the different complexity scales we pursue a broad and fundamental understanding of processes and their interactions. On this basis cell performance, durability, and safety of the batteries can be improved and the development of a cost-efficient and sustainable production is enabled.

Diagnostics

A great number of measurements are performed at the BLB to characterize materials, electrodes, cells and production processes on all kind of levels from the material to the suspension up to the electrode, cell and pack. Establishment of standardized measurement methods, traceability of measurement results to the SI, quantification of measurement uncertainties and assurance of reproducibility are strived at as far as possible. Obviously, each institute has developed specialized competences with respect to measurements in its field of activity. The working group Diagnostics & Usage plays a supporting and intermediary role to identify and establish possible common standards and synergies. One example are the standard procedures for the measurement of impedance spectra and current load that have been defined across institutes.

Furthermore, metrological research with respect to electromobility promotes the development of electrochemical measurement methods for the state of charge (SOC), state of health (SOH), and state of safety (SOS). The experimental techniques employed include electrochemical impedance spectroscopy, non-linear frequency response analysis, material and in-operando cell characterization by means of X-ray spectrometry, and safety tests of battery modules and systems.

Usage

The BLB is a research facility that produces battery cells and keeps improving every step through research. Ultimately, the performance, durability and safety of the final product are the key parameters that need to be optimised. Therefore, analytics of the usage phase are very important and need to be coupled back to the production. Via this loop, every generation of BLB cells keeps improving above the previous generation. The usage phase is characterized by cyclization of batteries under defined current loads and defined environmental conditions. Depending on the way the battery is used, it may age in different ways and thus exert a different behaviour at later stages during its life cycle. Safety tests such as nail penetration or external heating can be used to describe the response of battery systems to misuse. Other non-destructive or destructive techniques in combination with sophisticated analysis supported by numerical simulations will reveal the causes of a change of behaviour, e.g. permanent changes of the anode, cathode or SEI layer. The working group Diagnostics & Usage supports the exchange of researchers from the whole spectrum of BLB’s institutes to help put experimental results into context and broaden the impact of our research.

Contact:
Valerie Mohni
v.mohni(at)tu-braunschweig.de

Batteries, especially lithium-ion, offer a large range of applications, including mobile consumer devices, energy storage systems, and electric vehicles. Although being a well-established technology, the complex processes and parameter interdependencies along the battery process chain are still not fully understood. In this context, the cross-sectional research topic “Digitalization & Simulation” provides the digitalization of battery cell production and recycling to achieve a knowledge-based improvement of quality as well as economic and environmentally sustainable batteries. “Digitalization & Simulation” comprehends data acquisition, storage, and management from material preparation up to formation and recycling. The acquired data is applied in the development and validation of multilevel model-based methods. With that, knowledge-based decision support is achieved, leading to improvements in the product, processes, battery cell production, and recycling.

I. Data acquisition and management

Standardization
In the BLB, data is generated along the process chain by a variety of analytical methods and test routines. It is crucial to define and implement quality control as well as measures to assure data quality and reliability. For that, best practice guidelines for frequently used procedures and processes are developed which allows the creation of a baseline to benchmark different data streams.      

Automated and manual data acquisition

Production and product data are the basis of simulation and data-based approaches as well as further analyses. Within this context, requirements for data acquisition in battery cell production and strategies for automated and manual data acquisition are developed. The automated data acquisition includes sensors, programmable logic controllers (PLCs), machines, technical building services (TBS), and measurement of environmental conditions through weather stations. The manual data acquisition comprehends off-line acquired data from intermediate product analytics, final product analytics, and operational data.

Tracking & Tracing

Each individual process along the battery cell process chain produces an intermediate product whose quality is characterized by the interactions between process parameters, product structure, and production conditions. Therefore, tracking and tracing is mandatory to provide an understanding of the interdependencies between processes as well as intermediate and final products. For that, strategies and technologies are developed to track an object and its corresponding acquired production data as well as to trace this object throughout its life cycle.

Data management

Data management comprehends the storage, structuring, and maintenance of acquired data. Therefore, it is a mandatory element of digitalization strategies and the basis for models and further analyses. Based on the challenges and requirements of battery cell production and policies (e.g. battery passport), concepts for data management from production up to recycling based on new technologies (e.g. blockchain) are developed and implemented in the BLB.

II. Multilevel model-based methods

Model-based methods are developed in the BLB to digitally reproduce complex systems and investigate parameter interdependencies from molecule up to process chain levels. Moreover, these methods are an economic and timely efficient alternative to experimental investigations when studying new scenarios (e.g. materials and processes). This allows, for example, the optimization of battery performance from both a material or process chain perspective, considering their influence on the desired final product properties.               

III. Decision-support and visualization

Data acquisition and management as well as multilevel model-based methods aim to increase product and process quality. Decision-support and visualization focus on presenting the gained insights to improve battery cell production and recycling. As an example, recommendations to achieve higher quality as well as economic and environmentally sustainable production are displayed based on the results of methods to identify critical parameters considering product, process, and process chain.

Contact:
Aleksandra Naumann
al.naumann(at)iwf.ing.tu-bs.de

James Fitz
james.fitz(at)tu-braunschweig.de

Batteries are a key component for the transition to a sustainable energy and transport system. They enable electric cars to drive without tailpipe emissions and serve as buffers to compensate for the volatility in renewable energy production. Moreover, the supply chains and the factory system are important from an economic perspective when it comes to producing safe and affordable high-quality batteries. Therefore, the security of the supply of raw materials and the resilience and flexible adaptation of battery production to changing situations are increasingly important. Despite the considerable benefits related to the use phase of batteries, there are significant environmental and social impacts related to their downstream and upstream phases, such as production.
The research group "Circular Factory Systems and Supply Chains" develops methods and tools to assess and improve the sustainability of current and future battery technologies and to design flexible, transparent, and efficient factory systems and supply chains. Research activities comprise the planning and control of production systems, methods and tools for life cycle sustainability assessment, and decision support for stakeholders in the battery system.

Production planning and control

A battery production system comprises various connected production processes that need to be managed effectively to ensure a high battery quality. Different production methods, converging and diverging material streams, and uncertainties regarding the cause-effect relationships in the production process cause a high complexity in the production of batteries. In order to cope with this complexity, various production planning and control methods are being developed that serve quality management and promote energy and resource efficient production. For example, the improvement of the control methods of the dry room as part of the technical building system (TBS) can lead to higher quality and lower cost and impacts.

Simulations of the production systems are used as a cost-effective solution allowing to compare the impact of different scenarios without affecting the real systems. Typical optimization goals are the improvement of energy efficiency and product quality, decreasing raw material usage, and decreasing scrap and production waste. Further, simulation is used to assess and improve the flexibility of the factory regarding external influences.

Life cycle sustainability assessment

A holistic sustainability assessment covers the entire life cycle from the extraction of battery raw materials through the production to recycling of batteries and analyzes a diverse set of environmental, economic, and social sustainability indicators. To this end, systematic methods such as life cycle assessment (LCA), life cycle costing (LCC), and social life cycle assessment (SLCA) are employed. This enables the identification of sustainability hotspots and supports the systematic improvement of production and recycling processes. The results are further used for political decision support towards sustainable battery supply chains. Current research at BLB in this field addresses the data collection and management for life cycle sustainability assessment, the modeling of battery supply chains, and the development of integrated computational life cycle engineering methods. For primary and secondary supply chains, tracking and tracing methods for material and product tracking are developed to be able to support, i.e., the reliability of the LCA data.

Holistic decision support

In order to derive recommendations for action for different stakeholders in the complex system of circular battery production, operations research and system engineering methods are used at the BLB. These methods are combined with the results of BLB's working groups to provide operational, tactical, and strategic decisions for the design and operation of circular factories and closed-loop supply chains. Examples include site and capacity building planning in circular networks, designing resilient closed-loop supply chains, designing flexible and adaptable circular factories, or optimizing production processes.

Contact:
Edith Uhlig
edith.uhlig(at)tu-braunschweig.de

Jan-Linus Popien
j.popien(at)aip-pl.tu-braunschweig.de