Aqueous Processed Thick-Film Li(Ni0.6_{0.6}Mn0.2_{0.2}Co0.2_{0.2})O2_2 Electrodes with 3D Architectures

The development of high areal energy density electrodes with layered metal oxide cathode materials is currently worldwide a main topic in research and industry. Water-based binders were applied in the presented work for the manufacturing of NMC 622 (Li(Ni0.6Mn0.2Co0.2)O2) cathodes in order to achieve environmental friendly and cost-reduced production, replacing the conventional organic PVDF binder and the toxic and volatile NMP solvent. However, the pH value of aqueous processed cathode slurries increases to over 12 due to the reaction between NMC 622 particles and water, which decreases the specific discharge capacity of the cells and on the other side results in the chemical corrosion of the current collector during casting. In order to avoid the damage of the current collector and protect the cathode material, different acids could be applied during mixing process to adjust the slurry pH value. In addition, the energy density at battery level can be increased with increasing electrode film thickness which corresponds to an enhanced areal capacity. However, capacity fading of thick-film electrodes at C-rates above C/2 is mainly due to a limited lithium-ion diffusion kinetics and crack formation in cathode particles. 3D electrode architectures produced by ultrafast laser ablation are proven to improve the capacity retention at high discharge rates and the electrolyte wettability of electrodes as reported in our previous works. In this work, NMC 622 electrodes with a film thickness of 150 µm (5.8 mAh/cm2) were manufactured with aqueous binders TRD 202A and CMC, and were subsequently laser structured. With increasing film thickness from 70 µm to 150 µm, the mass loading of cathodes increased from 17 mg/cm2 to 36 mg/cm2. The slurry pH values were adjusted between 9 - 10 with citric acid (CA), phosphoric acid (PA), and acetic acid (AC). The dried electrodes were characterized using XPS and SEM. The unstructured and structured electrodes with different thicknesses were afterwards assembled versus lithium in coin cells. Rate capability test and cyclic voltammetry (CV) were performed in order to investigate the electrochemical performance of the electrodes. Cells containing 70 µm cathodes with PA and CA+PA showed about 10 mAh/g higher capacity at C/20 to C/5 compared to cells with PA, while at 1C to 3C cells with CA showed the lowest capacities With increasing electrode film thickness, cells with PA and PA+CA retained 5-10 mAh/g more capacity than cells with CA at C/20 to C/5. The cells with PA maintained about 120 mAh/g discharge capacity at C/2, while cells with PA+CA and CA showed about 80 mAh/g and 45 mAh/g, respectively. In comparison to cells with unstructured electrodes, laser structuring increased the discharge capacity of cells with 70 µm electrodes from 1C to 3C, regardless of the type of added acid. As for cells with thick-film electrodes, the discharge capacity of cells containing structured electrodes with CA+PA increased to 120 mAh/g, which is about 40 mAh/g higher compared to cells with unstructured electrodes. Finally, CV proved that the addition of acids had no effect on the redox reaction of NMC 622

Laser patterning and electrochemical characterization of thick-film cathodes for lithium-ion batteries

Lithium-ion batteries (LIBs) are currently dominating the electrochemical storage sector due to their excellent properties such as high energy density, high power density, and long cycle lifetime. For automotive applications, current research focuses on the merger of two concepts: (i) the “thick film concept” which enables a high energy density due to a reduced amount of inactive materials, and (ii) the “three-dimensional (3D) battery concept”, which provides a high power density with improved interfacial kinetics at mass loadings ≥ 35 mg/cm2. Latter could be realized by applying ultrafast laser patterning of electrodes, which in turn includes an advanced 3D electrode design. Briefly, a rapid and homogeneous electrode wetting with liquid electrolyte can be induced, and besides a high capacity retention during long-term cyclability. Recently, various electrode designs such as line, grid, and hole structures have been reported for cathodes and anodes. However, the mass loss of those electrodes needs to be considered, since the cathode represents about 50 % of the total material costs of LIBs. Thus, the use of electrode structures with a high aspect ratio as well as a significantly reduced material removal is of great importance. In this work, 150 μm thick-film Li(Ni0.6Mn0.2Co0.2)O2 electrodes were manufactured by roll-to-roll tape-casting and subsequently structured with different pattern types using ultrafast laser radiation. Additionally, different designs were applied for laser patterning and the mass loss was minimized down to 7 %. Finally, the cathodes were assembled in half-cells for studying the impact of different laser patterning designs on electrochemical performance

The Impact of Structural Pattern Types on the Electrochemical Performance of Ultra-Thick NMC 622 Electrodes for Lithium-Ion Batteries

An increase in the energy density on the cell level while maintaining a high power density can be realized by combining thick-film electrodes and the 3D battery concept. The effect of laser structuring using different pattern types on the electrochemical performance was studied. For this purpose, LiNi0.6Mn0.2Co0.2O2 (NMC 622) thick-film cathodes were prepared with a PVDF binder and were afterward structured using ultrafast laser ablation. Eight different pattern types were realized, which are lines, grids, holes, hexagonal structures, and their respective combinations. In addition, the mass loss caused by laser ablation was kept the same regardless of the pattern type. The laser-structured electrodes were assembled in coin cells and subsequently electrochemically characterized. It was found that when discharging the cells for durations of less than 2 h, a significant, positive impact of laser patterning on the electrochemical cell performance was observed. For example, when discharging was performed for one hour, cells containing laser-patterned electrodes with different structure types exhibited a specific capacity increase of up to 70 mAh/g in contrast to the reference ones. Although cells with a hole-patterned electrode exhibited a minimum capacity increase in the rate capability analysis, the combination of holes with lines, grids, or hexagons led to further capacity increases. In addition, long-term cycle analyses demonstrated the benefits of laser patterning on the cell lifetime, while cyclic voltammetry highlighted an increase in the Li-ion diffusion kinetics in cells containing hexagonal-patterned electrodes

Electrochemical Performance of Thick-Film Li(Ni0.6_{0.6}Mn0.2_{0.2}Co0.2_{0.2})O2_{2} Cathode with Hierarchic Structures and Laser Ablation

The electrochemical performance of lithium-ion batteries is directly influenced by type of active material as well as its morphology. In order to evaluate the impact of particle morphology in thick-films electrodes, Li(Ni0.6Mn0.2Co0.2)O2 (NMC 622) cathodes with bi-layer structure consisted of two different particle sizes were manufactured and electrochemically characterized in coin cells design. The hierarchical thick-film electrodes were generated by multiple casting using NMC 622 (TA) with small particle size of 6.7 µm and NMC 622 (BA) with large particle size of 12.8 µm. Besides, reference electrodes with one type of active material as well as with two type of materials established during mixing process (BT) are manufactured. The total film thickness of all hierarchical composite electrodes were kept constant at 150 µm, while the thicknesses of TA and BA are set at 1:2, 1:1 ,and 2:1. Meanwhile, three kinds of thin-film cathodes with 70 µm are applied to represent the state-of-the-art approach. Subsequently, ultrafast laser ablation was ap-plied to generate groove structures inside the electrodes. The results demonstrate that cells with thin-film or thick-film cathode only containing TA, cells with bilayer electrode containing TBA 1:2, and cells with laser structured electrodes show higher capacity at C/2 to 5C, respectively

Ultrafast laser ablation of aqueous processed thick-film Li(Ni0.6_{0.6}Mn0.2_{0.2}Co0.2_{0.2})O2_{O2} cathodes with 3D architectures for lithium-ion batteries

Lithium-ion batteries have dominated the field of electrochemical energy storage for years due to their high energy density. Recently, with the rapid development of E-mobility, the quest for high power and high energy batteries with reduced production costs has aroused great interest and is still a huge challenge. The energy density at battery level can be increased by using electrodes with thicknesses > 150 μm. However, capacity fade of thick-film electrodes at C-rates > C/2 is observed. To compensate the capacity loss, 3D architectures with a high aspect ratio are produced using ultrafast laser ablation. In addition, aqueous processing of cathodes using water-based binders can achieve environmentally friendly production and cost reduction by replacing the conventional organic PVDF binder and the toxic and volatile NMP solvent. However, the pH value of aqueous processed cathode slurries increases to 12 due to the reaction between active material and water, which decreases the specific capacity of the cells and on the other side results in chemical corrosion of the current collector during casting. In order to determine the optimal pH range and avoid the damage of the current collector, slurries with pH values ranging from 8 to 12 are manufactured. In this work, thick-film Li(Ni0.6Mn0.2Co0.2)O2 electrodes are manufactured with aqueous binders and acid adjustment, and are subsequently structured using ultrafast laser ablation. This combination is beneficial to achieve green production, low cost, high power, and high energy application of lithium-ion batteries

Ultrafast laser ablation of aqueous processed thick-film Li(Ni0.6_{0.6}Mn0.2_{0.2}Co0.2_{0.2})O2_{O2} cathodes with 3D architectures for lithium-ion batteries

Lithium-ion batteries have dominated the field of electrochemical energy storage for years due to their high energy density. Recently, with the rapid development of E-mobility, the quest for high power and high energy batteries with reduced production costs has aroused great interest and is still a huge challenge. The energy density at battery level can be increased by using electrodes with thicknesses > 150 μm. However, capacity fade of thick-film electrodes at C-rates > C/2 is observed. To compensate the capacity loss, 3D architectures with a high aspect ratio are produced using ultrafast laser ablation. In addition, aqueous processing of cathodes using water-based binders can achieve environmentally friendly production and cost reduction by replacing the conventional organic PVDF binder and the toxic and volatile NMP solvent. However, the pH value of aqueous processed cathode slurries increases to 12 due to the reaction between active material and water, which decreases the specific capacity of the cells and on the other side results in chemical corrosion of the current collector during casting. In order to determine the optimal pH range and avoid the damage of the current collector, slurries with pH values ranging from 8 to 12 are manufactured. In this work, thick-film Li(Ni0.6Mn0.2Co0.2)O2 electrodes are manufactured with aqueous binders and acid adjustment, and are subsequently structured using ultrafast laser ablation. This combination is beneficial to achieve green production, low cost, high power, and high energy application of lithium-ion batteries

(Invited) 3D Electrode Architectures for High Power and High Energy Lithium-Ion Battery Operation - Recent Approaches and Process Upscaling

During the next decades, combustion driven cars will be completely replaced by electrical vehicles (EVs) and it seems quite obvious that liquid electrolyte lithium-ion batteries (LIBs) will be the dominating energy storage system for the next at least 5 to 10 years. As a consequence, in Europe numerous Gigafactories have recently been planned with this state of technology. However, the current lithium-ion battery technology suffers so far from some restrictions like the inability to combine high power and high energy operations at the same time. This limitation is mainly attributed to the cathode architecture and respective mass loading. In addition, the further demand for a significantly enhanced fast charging mainly requires an optimization of the anode design flanked by a high areal capacity. Advanced 3D electrode architectures based on a thick film electrode concept seem to be the most promising approach to overcome the current limitations in battery performances. However, respective technology innovations need to provide a high compatibility grade to existing manufacturing routes in order to enable the required integration in existing and planned factories. For so-called "generation 3" materials, i.e., nickel-rich lithium nickel manganese cobalt oxide (NMC) cathode and silicon-based anode materials, structuring technologies using cutting edge ultrafast high power lasers, are being developed in order to manufacture 3D electrode architectures with high areal capacity. Multibeam laser processing using diffractive optical elements and dual scanner approaches were established in order to enable high processing speeds in roll-to-roll electrode handling systems. The technology readiness level (TRL 6) is demonstrated for pouch cells geometries. For water-based NMC 622 and silicon-graphite composites the laser structuring process was developed. Different structures including hole, grid, and line patterns, were studied regarding their impact on electrochemical performances such as high-rate capability and cell lifetime. Lithium concentration profiles of unstructured and structured electrodes were studied post mortem using laser-induced breakdown spectroscopy (LIBS) in order to evaluate lithium intercalation/deintercalation efficiencies and detect possible cell degradation processes. In comparison to unstructured electrodes, 3D electrodes could hereby always be identified as superior: unstructured thick film electrodes show a significant drop in capacity retention for high power operation and tend to form hot spots acting as starting point for cell failure. The upscaling process is flanked by a further improvement of electrode design. For this purpose very recently laser induced forward transfer (LIFT) is applied as printing technology to draw new concepts for sophisticated model electrode architectures with advanced electrochemical performances. Finally, the micro-/nano-scaled texturing of current collectors and separator material is discussed as further possible approaches for boosting the electrochemical performances of LIB pouch cells

Acoustic calculation in low frequency sonopheresis based on bubble dynamics

As a type of transdermal permeability enhancement, low frequency sonophoresis (LFS) has been studied for more than twenty years. The acoustic pressure in LFS is a crucial ultrasonic parameter to improve the permeability, but it is difficult to measure in the drug donor because of its small size and narrow shape. In this paper, an acoustic-piezoelectric coupling model is established based on bubble dynamics, which can be utilized to calculate the acoustic pressure distributions in LFS using a commercial finite element software called COMSOL multiphysics. The calculated results of acoustic pressure are in accordance with the measured values, so this model has great potential for theoretical analyses in acoustic fields of LFS. Calculated and experimental results show that the maximum acoustic pressure is under the transducer’s head, and the value dropped as away from the head due to the acoustic attenuation caused by cavitation; the transducer head should be closer to the skin to obtain larger acoustic pressure on the skin. Therefore, this model can be used to simulate and analyze the characteristics of acoustic fields, as a theoretical tool for the structural design of the ultrasonic transducer applied in LFS

Targeting new ways for large-scale, high-speed surface functionalization using direct laser interference patterning in a roll-to-roll process

Direct Laser Interference Patterning (DLIP) is used to texture current collector foils in a roll-to-roll process using a high-power picosecond pulsed laser system operating at either fundamental wavelength of 1064 nm or 2nd harmonic of 532 nm. The raw beam having a diameter of 3 mm @ 1/e$^2$ is shaped into an elongated top-hat intensity profile using a diffractive so-called FBS®-L element and cylindrical telescopes. The shaped beam is split into its diffraction orders, where the two first orders are parallelized and guided into a galvanometer scanner. The deflected beams inside the scan head are recombined with an F-theta objective on the working position generating the interference pattern. The DLIP spot has a line-like interference pattern with about 15 μm spatial period. Laser fluences of up to 8 J cm$^{−2}$ were achieved using a maximum pulse energy of 0.6 mJ. Furthermore, an in-house built roll-to-roll machine was developed. Using this setup, aluminum and copper foil of 20 μm and 9 μm thickness, respectively, could be processed. Subsequently to current collector structuring coating of composite electrode material took place. In case of lithium nickel manganese cobalt oxide (NMC 622) cathode deposited onto textured aluminum current collector, an increased specific discharge capacity could be achieved at a C-rate of 1 °C. For the silicon/graphite anode material deposited onto textured copper current collector, an improved rate capability at all C-rates between C/10 and 5 °C was achieved. The rate capability was increased up to 100% compared to reference material. At C-rates between C/2 and 2 °C, the specific discharge capacity was increased to 200 mAh g$^{−1}$, while the reference electrodes with untextured current collector foils provided a specific discharge capacity of 100 mAh g$^{−1}$, showing the potential of the DLIP technology for cost-effective production of battery cells with increased cycle lifetime