Recent Progress in Laser Texturing of Battery Materials: A Review of Tuning Electrochemical Performances, Related Material Development, and Prospects for Large-Scale Manufacturing

Traditional electrode manufacturing for lithium-ion batteries is well established, reliable, and has already reached high processing speeds and improvements in production costs. For modern electric vehicles, however, the need for batteries with high gravimetric and volumetric energy densities at cell level is increasing; and new production concepts are required for this purpose. During the last decade, laser processing of battery materials emerged as a promising processing tool for either improving manufacturing flexibility and product reliability or enhancing battery performances. Laser cutting and welding already reached a high level of maturity and it is obvious that in the near future they will become frequently implemented in battery production lines. This review focuses on laser texturing of electrode materials due to its high potential for significantly enhancing battery performances beyond state-of-the-art. Technical approaches and processing strategies for new electrode architectures and concepts will be presented and discussed with regard to energy and power density requirements. The boost of electrochemical performances due to laser texturing of energy storage materials is currently proven at the laboratory scale. However, promising developments in high-power, ultrafast laser technology may push laser structuring of batteries to the next technical readiness level soon. For demonstration in pilot lines adapted to future cell production, process upscaling regarding footprint area and processing speed are the main issues as well as the economic aspects with regards to CapEx amortisation and the benefits resulting from the next generation battery. This review begins with an introduction of the threedimensional battery and thick film concept, made possible by laser texturing. Laser processing of electrode components, namely current collectors, anodes, and cathodes will be presented. Different types of electrode architectures such as holes, grids, and lines, were generated; their impact on battery performances are illustrated. The usage of high-energy materials, which are on the threshold of commercialization, is highlighted. Battery performance increase is triggered by controlling lithium-ion diffusion kinetics in liquid electrolyte filled porous electrodes. This review concludes with a discussion of various laser parameter tasks for process upscaling in a new type of extreme manufacturing

Upscaling of the Laser Structuring of Lithium-Ion Battery Electrodes - Process Development and Electrochemical Properties As a Function of Design Patterns

Structuring of electrodes for lithium-ion batteries by using ultrashort pulsed laser ablation is a quite promising approach to significantly increase the electrochemical performance of lithium-ion batteries. The main impact of such 3D electrodes is due to shortening of lithium-ion diffusion pathways and improving the electrolyte wetting of composite electrodes The latter is reducing the electrolyte filling process time and saving the need for warm aging in the manufacturing process. The 3D electrode concept, in combination with an increase in electrode layer thickness, facilitates an increase in energy and power density of batteries at the same time. To implement the laser structuring process in industrial cell manufacturing, an adaptation of the ultrafast laser technology to the coating speed has to be established. In the presented study, the use of an ultrashort pulsed laser system of high power up to 300 W and high repetition rate in the MHz regime was evaluated regarding processing speed for patterning of graphite and silicon/graphite anodes. For composite graphite anodes (film thickness > 76 µm) with an areal capacity of about 2.5 – 4.0 mAh/cm2 and a thick-film silicon/graphite anode with 5 wt.% silicon content (film thickness 80 µm, areal capacity 4.3 mAh/cm2) the laser and process parameters and processing speed were evaluated and optimized. Furthermore, different structure patterns including hole, grid and line pattern, were studied regarding upscaling in roll-to-roll processing. The different types of patterns were evaluated with respect to accessible electrochemical properties. Prior to cell assembly and during post-mortem studies, the quality of structured electrodes was examined by profilometry and scanning electron microscopy. Debris formation and a thermal impact to active material and current collector could be avoided. To evaluate the electrochemical properties such as high rate capability, cell impedance, and cell lifetime, coin cells and pouch cells were manufactured. For this purpose, NMC 622 cathodes were prepared as the respective counter-electrodes and a cell balancing in the range of 1.1-1.2 was ensured

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

3D printing of anode architectures for customized lithium-ion batteries

The expansion of renewable energies is increasing the demand for affordable and enhanced energy storage systems. Here, 3D lithium-ion battery concepts represent a promising approach to improve e.g., energy and power density as well as lifetime of batteries. This work explores the potential of the laser induced forward transfer (LIFT) method as a tool for the realization of new types of 3D electrode architectures on structural and compositional level. Using a pulsed nanosecond UV laser, several parameters were examined to determine the variables affecting reliable material and voxel transfer, including laser fluence as a function of donor layer thickness and donor paste-to-substrate distances, as well as the influence of viscosity and solid content of the anode paste. In addition, a 3D anode is produced by combining laser structuring with subsequent localized laser printing with silicon-rich anode paste

Laser Additive Manufacturing for the Realization of New Material Concepts

In additive manufacturing processes, components are built up in layers from liquids, powders, wires or foils using chemical or physical processes. Direct energy deposition (DED) or powder bed fusion (PBF) can be used as additive manufacturing processes in which metal powder or wires are used to print dense metal layers on substrates or on freeform surfaces of existing components [1]. Metal powder (pure elements, element mixtures, master alloys) or metal wires are melted at high speed and instantaneously deposited in layers on respective metallic substrates. In case of the so-called laser cladding [2], this technology is generally used for applying coatings or for tool repairs. Compared to subtractive processes, additive processes save time and resources, as the material is only added where it is needed. Established steels, nickel-based alloys or titanium alloys are typically used. However, it is also possible to obtain completely new materials by in-situ alloying of powder mixtures or to create material gradients by changing the powder mixture composition during the build-up [3]. High entropy alloys (HEAs) represent a new research field for future applications. These are formed from a large number of elements, all of which are present in similarly strong concentrations e.g., alloys consisting of zirconium, niobium, hafnium, tantalum or tungsten [4]. The alloys formed can generally be single-phase as well as multi-phase mixed crystals. HEAs can often combine high strength and very good ductility. In-situ alloying offers the unique possibility of fast material screening for the future production of new metallic components with outstanding mechanical properties at high temperatures. For a long time, the manufacture of refractory alloys was limited to vacuum arc remelting because of their high melting points. With laser-based methods, these metals are locally melted by the focused laser beam and deposited additively. In addition to material development, additive manufacturing offers great design freedom in component design, which can be used, for example, for the development of load-optimized designs based on the bionic principle [5]. To add up to the versatility of additive manufacturing, laser post-processes can be used to modify the resulting surfaces of parts produced with such technology [6-9]. The different types of laser sources commercially available assure their suitability in a wide range of applications, with continuous wave (cw) lasers being often used for reduction of surface roughness, while pulsed lasers being applied in the modification of surface functionalities and to enhance the geometry accuracy. Even with the prospect of being able to replace certain steps of the additive manufacturing process chain, adopting laser post-processes as an additional step can also be proved beneficial when specific characteristics are required in localized areas of the final built components

3D Printing of Silicon-Based Anodes for Lithium-Ion Batteries

In order to meet the target for the next generation lithium-ion batteries, electrochemical performance such as energy and power density must be increased significantly at the same time. Optimized electrode architectures including 3D battery concepts and advanced materials are in development to achieve this goal. The use of silicon-graphite composite electrodes instead of graphite anodes is currently investigated. This is due to the fact that silicon can provide almost one order of magnitude higher specific energy density (3579 mAh/g) in comparison to natural graphite (330 - 372 mAh/g). However, during lithiation, i.e., lithium silicide formation, a volume expansion of about 300 % can take place, while during lithium intercalation in graphite about 10 % volume expansion can be observed. A huge volume expansion leads to a tremendous mechanical degradation of the anode resulting in a drop in capacity, and a limited battery lifetime. In the presented study, laser induced forward transfer (LIFT) is applied as printing technology to develop sophisticated graphite and graphite-silicon electrode architectures with advanced electrochemical performances. LIFT was performed using a pulsed nanosecond UV laser with a repetition rate of up to 30 kHz and a maximal power of 10 W. To enable an accurate printing process during LIFT, the properties and compositions of the active material inks as well as the laser and process parameters have to be optimized. The printing process in combination with laser structuring provides a high flexibility regarding the final electrode design. In the presented study, the formation of multi-layer electrodes with spatial variation in electrode composition is achieved. As active materials silicon nanoparticles (SNPs) and various types of graphite, i.e., natural graphite, mesocarbon microbeads (MCMB), and artificial flake-like graphite with an average particle diameter of 1 µm up to 15 µm are utilized. The geometry and thickness of each printed layer is adapted with regard to an optimized electrochemical performance and cell lifetime. A single layer thickness of 5 µm up to 20 µm was achieved, while areal capacities of multi-layer anodes reaches values of 2 to 4 mAh/cm². In addition to the applied active materials and architecture concepts, different solvent and binder systems are investigated with regard to process scalability and an improved environmental compatibility. The printed electrodes are electrochemically characterized by rate capability measurements at C-rates of up to 5C. A correlation between capacity retention and electrode architecture is achieved. The results are discussed in terms of upscaling and impact on the next generation anode material

High repetition ultrafast laser ablation of graphite and silicon/graphite composite electrodes for lithium-ion batteries

Laser structuring can be applied to composite electrodes of lithium-ion cells to enhance wetting and to facilitate the usage of thick-film electrodes by reducing the lithium-ion diffusion overpotential and the tortuosity of the electrodes or the usage of electrodes containing silicon, where additional porosity is required to compensate the volume expansion during lithium de-/insertion. To integrate the additional laser processing step in the well-established electrode manufacturing route, the laser processing speed must be significantly increased to match with the belt speed, which is dependent on the electrode thickness and the type of manufacturing route. Upscaling can be realized by increasing the average laser power, laser intensity, and/or laser repetition rate. Here, an ultrashort pulsed laser source with an average power of 300 W and a pulse duration of 600 fs was applied. For the first time, the presented research provides detailed laser ablation processing data for thick-film composite anodes associated with high repetition rates ranging from 4.9 to 48.8 MHz. The patterning results are compared depending on the widths, depths, aspect ratios, the total appearance regarding debris and cracks, and the volume ablation rate. In high repetition rate laser patterning, the subsequent laser pulses interact with the material vapor plasma generated by the previous laser pulses, resulting in lower ablation depths and higher ablation widths. The increase in laser peak intensity leads to higher achievable ablation depths. Processing strategies are identified for two different ablation scenarios focusing on the pouch cells of a Volkswagen ID.3 and the Tesla 4680 cell