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A possible way to increase the energy density in lithium-ion batteries, and, at the same time, reduce the production costs, is to use thicker electrodes. However, transport limitations can occur in thick electrodes, leading to a drawback in performance. A way to mitigate this problem is a more sophisticated microstructure of the electrode, using, e.g., structural gradients. This can, for instance, be achieved by multi-layer casting, i.e., casting and drying of a first layer, and then adding a second layer. An important question is how the interface between the two layers is shaped and how the corresponding microstructure influences the electrochemical performance. In the present paper, two different two-layer cathodes are analyzed and compared to single-layer cathodes of the same thickness. The analysis involved tomographic imaging, a statistical analysis of the 3D microstructure of the active material particle systems with a focus on the interface between the layers, and electrochemical characterization of the active material systems using experimental measurements as well as electrochemical simulations. The analysis showed that at the interface the connectivity of active material particles decreases, which results in higher electric resistivity. This effect is stronger if an intermediate calendering step is performed, i.e., the first layer is calendered before casting the second layer.

Due to improvements on combustion-engines and electric-engines for cars, tyre noise has become the prominent noise source at low and medium speeds. Models exist that simulate the noise produced by a rolling tyre, as do models that auralize different traffic situations from a basic data set. In this paper, an established model for tyre noise (SPERoN) is combined with an auralization tool. The combined model can predict the spectrum of the sound at 7.5 m, as well as reproduce the sound for a given listener position. The auralization uses a methodology where recorded sounds are converted to source signals for engine and tyre/road-interaction. These can be shaped by the spectra estimated in SPERoN and synthesized back into a pass-by signal. Psychoacoustic judgements were used to compare the modelled signals with recorded signals. To see how well the modelled signals match the real recorded signals for perception, two listening-tests were performed. The simulated and recorded signals were rated by pleasantness, loudness, roughness and sharpness using semantic differentials. It was found that responses for simulated and recorded signals correlate for all cases, but rankings could not be reproduced exactly. The model can be further improved to be more applicable for listening tests.

Nowadays, long charging times have become one of the main limitations to a greater worldwide spread of electric vehicles (EV). Enabling high C-rates charging is a promising approach to eliminate this problem and alleviate range anxiety. When a battery is charged at high currents, several factors have to be taken into account. Temperature is certainly a key parameter because when it is too high this can lead to degradation of components (binder, electrolyte, active material, etc), however, when it is too low intercalation kinetics becomes sluggish. Using 3D-printed testing plates (PP3D plates) with Li-reference electrode, we developed a tool for electrochemical investigations of pouch cells. These plates enabled to build a new well-designed 3-electrode pouch cell. This setup allows the identification of the best high C-rate cycling procedure to improve the performance and cycling life of the lithium ion cells. We explored the electrochemical behavior of NMC811 cathodes and graphite anodes, during high discharge C-rates test up to 7 C and charge C-rates up to 2 C. Moreover, the temperature influence on charging performance and longtime cycling stability is investigated. The cells cycled at 25 °C using optimized procedures reached an 80% state of health after more than 1000 cycles., publishedVersion

In traditional Li‐ion batteries, the electrolyte consists of a Li‐conducting salt dissolved in organic solvents at a concentration of 1 mol L−1 (1 M). In this work, we use increased LiPF6 concentrations between 1 and 2.3 M to investigate the influence of the electrolyte salt concentration on the rate capability of ultra‐thick (49.5 mg cm−2) and thin (5.6 mg cm−2) NCM 622 electrodes, respectively. At higher electrolyte salt concentrations than 1 M, thin electrodes suffer from increased polarization, due to a higher viscosity and a reduced ionic conductivity. In contrast, by raising the salt concentration from 1 to 1.9 M the discharge capacity of ultra‐thick electrodes is increased by more than 50 % for current densities above 3 mA cm−2, which significantly improves their rate capability. 3D microstructure resolved simulations revealed that this effect results from the mitigation of Li‐ion depletion in the electrolyte filled pore space of ultra‐thick electrodes.

More than the sum of its parts! Moving from binary to ternary blends of active materials in cathode materials for lithium ion batteries provides a versatile design beyond the properties of the individual components. Synergistic effects improve the rate capability, power, thermal, and chemical stability of the blend. Overall advantageous performance is achieved while economizing 25 % cobalt and nickel of a NMC622 based electrode. The combination of two active materials into one positive electrode of a lithium-ion battery is an uncomplicated and cost-effective way to combine the advantages of different active materials while reducing the disadvantages of each material. In this work, the concept of binary blends is extended to ternary compositions. The combination of three different active materials provides high versatility in designing the properties of an electrode. Therefore, the unique properties of a layered oxide, phospho-olivine, and spinel type material are mixed to design a high-energy cathode with improved environmental friendliness. Four different compositions of blend electrodes are investigated, each with individual benefits. Synergistic effects improved the rate capability, power density, thermal and chemical stability simultaneously. The blend electrode consisting of 75 % NMC, 12.5 % LMFP and LMO provides similar energy and power density as a pure NMC electrode while economizing 25 % cobalt and nickel., publishedVersion

Most cathode materials for lithium-ion batteries exhibit a low electronic conductivity. Hence, a significant amount of conductive graphitic additives are introduced during electrode production. The mechanical stability and electronic connection of the electrode is enhanced by a mixed phase formed by the carbon and binder materials. However, this mixed phase, the carbon binder domain (CBD), hinders the transport of lithium ions through the electrolyte pore network. Thus, reducing the performance at higher currents. In this work we combine microstructure resolved simulations with impedance measurements on symmetrical cells to identify the influence of the CBD distribution. Microstructures of NMC622 electrodes are obtained through synchrotron X-ray tomography. Resolving the CBD using tomography techniques is challenging. Therefore, three different CBD distributions are incorporated via a structure generator. We present results of microstructure resolved impedance spectroscopy and lithiation simulations, which reproduce the experimental results of impedance spectroscopy and galvanostatic lithiation measurements, thus, providing a link between the spatial CBD distribution, electrode impedance, and half-cell performance. The results demonstrate the significance of the CBD distribution and enable predictive simulations for battery design. The accumulation of CBD at contact points between particles is identified as the most likely configuration in the electrodes under consideration., publishedVersion

© 2017 Elsevier Ltd Due to improvements in combustion-engines and use of electric-engines for cars, tyre noise has become the prominent noise source also at lower speeds. Models exist that simulate the noise produced by a rolling tyre, as do models that auralize different traffic situations from basic data. In this paper, a novel auralization method is introduced, with the purpose to enable synthesis of useful car pass-by sound signals for various situations. The method is based on an established model for tyre noise levels (SPERoN) that is combined with a validated auralization tool (LISTEN). In the LISTEN approach, source signals for tyre–road interaction and propulsion are produced from data based on recorded pass-by sounds. In the combined model, the tyre–road interaction data is shaped by the spectra estimated in SPERoN and synthesized back into a pass-by signal. The combined model is made to agree spectrally with measurements for a receiver at 7.5 m distance. Psychoacoustic judgments were used to compare the modelled signals with recorded signals, and the pass-by sounds for a given listener position showed promising quality and accuracy with respect to perceived pleasantness.

The manufacture of lithium nickel manganese cobalt oxides (NMC) suspensions for cathodes is typically performed with organic solvents like N-methyl-pyrrolidone (NMP) or N-ethyl-2-pyrrolidone (NEP). It is widely known that these substances are caustic and toxic to reproduction. The utilization of water for the preparation of a cathode suspension is less hazardous and saves costs. Unfortunately NMC alkalinizes the water to a very pH value, which leads to a pit corrosion of the aluminum substrate. The development and optimization of water-based NMC suspensions therefore must include investigations on lowering the pH value without deteriorating the electrochemical performance of the material. One option is the addition of amphoteric oxidic additives. This work focusses on Al2O3 and SiO2 as additives and explores their effects on the pH of the suspension and on the substrate corrosion as well as on the electrochemical performance of the NMC-cathode prepared therefrom. Furthermore the impact of the particle sizes of the additives was studied.

When constructing a tyre, it is of importance that improvements and planned changes are not only physically measurable, but that they also can be perceived by a listener. Tyre/road noise becomes a more important focus area, especially with the growing market of electric vehicles. In the design of tyre/road sound, there are three main aims: to reduce the overall sound level, to increase pleasantness and to do so still maintaining the carried information about e.g. driving conditions. To be able to do this, an understanding of how physical changes in a tyre are reflected in the perception of the same tyre is essential. In the present study, the aim is thus to determine if the rolling noise of a tyre can be both differentiated and characterized by its perceptual qualities. The focus is on the perception of the sound outside the car, perceived by, for example, a pedestrian. Listeners have judged different road tyre combinations and their perception in terms of their emotional responses (pleasantness, activation and stress) and their psychoacoustic responses (loudnes s, sharpness, roughness, and pitch). The results confirmed that rolling noise can be perceptually differentiated. Further, it is possible to differentiate between the effects of the street and the effects of the tyre on all emotional and most psychoacoustic parameters. The results suggest that changes to both road surfaces and tyres can affect both emotional and psychoacoustic perceptual qualities.

Lithium-ion batteries (LiBs) industrial production requires a large number of skills in many scientific fields. The process starts from the electrodes manufacturing and ends with the battery formation. Electrodes cutting is undoubtedly a crucial step as it could turn out to be one of the bottlenecks for a fast and efficient production. In this paper, we propose a quicker and cheaper method to evaluate the electrical contact resistance between coating and current collector (RContact) by using impedance spectroscopy (EIS) to compare different cutting methods. The results show the existence of a cutting technique—cell performance relationship.

The development of efficient and sustainable low cost manufacturing techniques for the next generation lithium-ion cells with improved energy density is a key technology for industrial success. There is a strong need for further development of energy-efficient, resource and time saving electrode and cell manufacturing processes, which includes the identification of bottleneck factors along the whole production chain and the replacement of environmentally harmful intermediate steps (e.g. replacement of NMP for the cathode processing). One promising approach to increase both energy density of the cell and process efficiency is the reduction of passive materials in the cell by increasing the mass loading of active material on the electrodes. These thicker electrodes, however, suffer from some drawbacks like lower rate capability, lower mechanical flexibility and reduced adhesion to the current collector. In addition, the mixing and coating process parameters have to be adapted to avoid inhomogeneous binder distribution and mechanical disintegration of particles. The electrochemical and mechanical properties of the electrodes are strongly dependent on the 3D microstructure of the electrode (distribution of carbon black, porosity, distribution of the binder network). Both the mixing strategy during slurry preparation as well as the drying conditions during coating have a strong influence on the mechanical and electrochemical properties of the electrodes, which will be discussed in detail in the presentation. Another approach to optimize electrodes with high areal capacity is the preparation of 3D structured electrodes (e.g. gradient electrodes). We studied the addition of various pore forming additives and the preparation of multilayer electrodes via coating with a dual slot die system. On the anode side silicon based materials are quite attractive due to high specific capacity and energy. However, practical use of silicon is still limited to low amounts of silicon < 5wt% in commercial cells. Anodes with higher silicon content suffer from low cycling life due to high volume change and electrode swelling. A promising approach to improve the cycling life of silicon based electrodes is the use of alternative 3D structured current collectors in combination with adapted binder systems. In general, the cell manufacturing of Li-ion batteries requires precision and accuracy and includes a complex process chain with numerous process parameters. Optimized parameters for critical manufacturing steps during cell assembly as drying, slitting, electrolyte filling and formation will be presented and discussed in more detail.

For future Lithium-ion battery applications such as electric vehicles, the battery manufacturing costs and their energy density are key limiting factors that have to be improved, in order to open this technology for a broader market. To address both challenges at once, one promising strategy is to increase the mass loading of state of the art electrodes to extreme values, thus, yielding ultra-thick electrodes. This approach allows to reduce the amount of passive materials in the cell stack in favor of more active material.[1,2] However, an increase in electrode film thickness is usually associated with a variety of drawbacks such as lower rate capability and higher mechanical stress during drying and processing.[3,4] In this contribution, different concepts to overcome these drawbacks are presented and compared. Ultra-thick NMC 622 cathodes with a mass loading of 50 mg/cm2 (≈ 8 mAh/cm2) were prepared and the influence of different manufacturing processing steps (mixing, drying and calendaring) on the electrochemical properties of these electrodes was investigated. Furthermore, the electrode architecture was optimized by pursuing different structuring strategies, in order to improve the Lithium-ion transport. Firstly, the introduction of electrolyte channels by pore-forming agents and electrode perforation is evaluated. Secondly, a multilayer design is explored[5], whereby local porosity and active material particle sizes can be controlled specifically. Finally, the electrolyte concentration was shown to have a significant influence on the electrochemical performance of ultra-thick electrodes and advantageous structures are identified by 3D microstructure resolved simulations based on stochastic structure models, which were calibrated to tomographic image data.[6–8] By application of combined processing and structuring measures, the specific discharge capacity of ultra-thick cathodes at 8 mA/cm2 (≈ 1C) was enhanced by more than 60%. Acknowledgement: The presented work was financially supported by BMBF within projects HighEnergy and PRODUKT under the reference numbers 03XP0073 and 03XP0028. References: [1] H. Abe, M. Kubota, M. Nemoto, Y. Masuda, Y. Tanaka, H. Munakata, K. Kanamura, J. Power Sources 2016, 334, 78–85. [2] H. Zheng, J. Li, X. Song, G. Liu, V. S. Battaglia, Electrochimica Acta 2012, 71, 258–265. [3] M. Singh, J. Kaiser, H. Hahn, J. Electrochem. Soc. 2015, 162, A1196–A1201. [4] L. Ibing, T. Gallasch, P. Schneider, P. Niehoff, A. Hintennach, M. Winter, F. M. Schappacher, J. Power Sources 2019, 423, 183–191. [5] D. Westhoff, T. Danner, S. Hein, R. Scurtu, L. Kremer, A. Hoffmann, A. Hilger, I. Manke, M. Wohlfahrt-Mehrens, A. Latz, et al., Mater. Charact. 2019, 151, 166–174. [6] T. Danner, M. Singh, S. Hein, J. Kaiser, H. Hahn, A. Latz, J. Power Sources 2016, 334, 191–201. [7] D. Westhoff, J. Feinauer, K. Kuchler, T. Mitsch, I. Manke, S. Hein, A. Latz, V. Schmidt, Comput. Mater. Sci. 2017, 126, 453–467. [8] D. Westhoff, I. Manke, V. Schmidt, Comput. Mater. Sci. 2018, 151, 53–64. Figure 1

Energy density is one of the key challenges in the development of advanced lithium ion batteries for many applications. To address this issue, a considerable number of studies have been conducted on high capacity cathode materials1–3. Another approach, covered in this contribution, is reducing the amount of passive material in the cell via increasing the mass loading of the electrodes4,5. These ultra-thick electrodes, however, suffer from certain drawbacks like a low rate capability4–7, reduced adhesion and flexibility or crack formation8. Numerous investigations on the development of electrodes for lithium ion batteries have been performed using preparation techniques typical for lab scale. In common studies, the electrochemical and mechanical properties of an electrode are attributed to mass loading, porosity and the distribution of passive materials in the binder-network9. This study considers manufacturing procedures for NMC cathodes highly relevant to industrial production. A strong influence of the manufacturing process especially on the morphology and electrochemical performance of ultra-thick electrodes was observed. As an example, ultra-thick electrodes with an areal capacity of 8 mAhcm-2 were prepared in pilot scale, yielding a significantly higher capacity than state of the art cathodes7,10. It is demonstrated that the mixing strategy used for slurry preparation significantly alters the distribution of materials and the morphology of the electrode, consequently also influencing adhesion strength and flexibility. These properties are likewise strongly affected by the applied drying procedure. By an optimized mixing and drying procedure, crack-free, ultra-thick electrodes were obtained even in pilot scale. These electrodes, manufactured by the optimized process, show significantly higher flexibility, which is very important for roll-to-roll processing. Scanning electron microscopy revealed the strong effect of the manufacturing process on the morphology of the material distribution within the electrode composite. Electrochemical measurements and impedance spectroscopy furthermore showed the decisive influence of electrode morphology on rate capability and Li+ transport properties. As a result, only by applying an improved mixing process, the areal discharge capacity of ultra-thick cathodes at 1 C was increased by more than 50% compared to a common procedure. Figure 1

Long life, efficient and safe high energy storage systems are the key components for new car concepts (hybrid and full electric cars) as well as for intermediate storage of renewable energy sources. However, present lithium ion technology does not fulfil completely the requirements in terms of energy density, wide operation temperature, long life behaviour and safety even under abuse conditions. In the last twenty years the improvement of energy density of portable lithium ion batteries has mainly been achieved by optimization of electrode microstructure and cell design and not by introducing new electrode materials. The life time and safety of the cells depend strongly on both cell chemistry and proper cell design. Most life time and safety studies focus either on the stability of single components like positive or negative materials from half cell measurements or on performance or safety tests of complete batteries. However, for a better understanding of aging mechanisms and safety issues it is important to analyse the full range from components up to battery level and especially the contribution of negative and positive electrode and their interactions in the complete cell under various operation conditions. We studied the aging behaviour of different complete cells (pouch or 18650) with various cell chemistries by monitoring the voltage profile of the individual electrodes with a reference electrode. The results clearly demonstrate that cycling life and safety are strongly influenced by a proper adjustment of the electrode microstructure and kinetics of the negative and positive electrode. Abuse tests, accelerating rate calorimetry (ARC) and differential scanning calorimetry (DSC) techniques were combined to study potential safety hazards. Gas chromatography (GC) provides powerful information about the chemical decomposition of electrolyte and of interactions within the battery. This combination of methods leads to a detailed description of life-time and safety-relevant processes at different temperatures and rates. The results clearly demonstrate that the safety behaviour of the cells changes with prolonged cycling and capacity fading. Based on the analytical results the microstructure for both electrodes anode and cathode has been optimized in order to minimize aging effects. On the cathode side blend electrodes of different sorts of materials and particle sizes can be used to optimize reversible capacity, rate capability, long term behaviour. For example LFP/NCM blend electrodes combine high mass loading (higher energy density) with excellent cycling life and improved safety. It has been demonstrated that a pouch cell containing synthetic graphite as negative and a NMC/LFP (3:1) blend as positive gives > 96% of initial capacity after 5760 cycles charged and discharged with 1 C rate between 3 – 4.2 V. The presentation will summarize various strategies to improve the cycling stability for high energy and high voltage lithium ion batteries with various materials combinations.

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