P. Smyrek

Laser annealing of textured thin film cathode material for lithium ion batteries

The material development for advanced lithium ion batteries plays an important role in future mobile applications and energy storage systems. It is assumed that electrode materials made of nano-composited materials will improve battery lifetime and will lead to an enhancement of lithium diffusion and thus improve battery capacity and cyclability. Lithium cobalt oxide (LiCoO2) is commonly used as a cathode material. Thin films of this electrode material were synthesized by non-reactive r.f. magnetron sputtering of LiCoO2 targets on silicon or stainless steel substrates. For the formation of the high temperature phase of LiCoO2 (HT-LiCoO2), which exhibits good electrochemical performance with a specific capacity of 140 mAh/g and high capacity retention, a subsequent annealing treatment is necessary. For this purpose laser annealing of thin film LiCoO2 was investigated in detail and compared to conventional furnace annealing. A high power diode laser system operating at a wavelength of 940 nm with an integrated pyrometer for temperature control was used. Different temperatures (between 200°C and 700°C) for the laser structured and unstructured thin films were applied. The effects of laser treatment on the LiCoO2 thin films studied with Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction to determine their stoichiometry and crystallinity. The development of HT-LiCoO2 and also the formation of a Co3O4 phase were discussed. The electrochemical properties of the manufactured films were investigated via electrochemical cycling against a lithium anode.

Direct laser interference patterning and ultrafast laser-induced micro/nano structuring of current collectors for lithium-ion batteries

Laser-assisted modification of metals, polymers or ceramics yields a precise adjustment of wettability, biocompatibility or tribological properties for a broad range of applications. Due to a specific change of surface topography on micro- and nanometer scale, new functional properties can be achieved. A rather new scientific and technical approach is the laserassisted surface modification and structuring of metallic current collector foils for lithium-ion batteries. Prior to the thick film electrode coating processes, the formation of micro/nano-scaled surface topographies on current collectors can offer better interface adhesion, mechanical anchoring, electrical contact and reduced mechanical stress during cycling. These features in turn impact on the battery performance and the battery life-time. In order to generate the 3D surface architectures on metallic current collectors, two advanced laser processing structuring technologies: direct laser interference patterning (DLIP) and ultrafast laser-induced periodic surface structuring (LIPSS) were applied in this study. After laser structuring via DLIP and LIPSS, composite electrode materials were deposited by tape-casting on the modified current collectors. The electrode film adhesion was characterized by tensile strength measurements. The impact of various surface structures on the improvement of adhesive strength was discussed.

Laser processes and analytics for high power 3D battery materials

Laser processes for cutting, modification and structuring of energy storage materials such as electrodes, separator materials and current collectors have a great potential in order to minimize the fabrication costs and to increase the performance and operational lifetime of high power lithium-ion-batteries applicable for stand-alone electric energy storage devices and electric vehicles. Laser direct patterning of battery materials enable a rather new technical approach in order to adjust 3D surface architectures and porosity of composite electrode materials such as LiCoO2, LiMn2O4, LiFePO4, Li(NiMnCo)O2, and Silicon. The architecture design, the increase of active surface area, and the porosity of electrodes or separator layers can be controlled by laser processes and it was shown that a huge impact on electrolyte wetting, lithium-ion diffusion kinetics, cell life-time and cycling stability can be achieved. In general, the ultrafast laser processing can be used for precise surface texturing of battery materials. Nevertheless, regarding cost-efficient production also nanosecond laser material processing can be successfully applied for selected types of energy storage materials. A new concept for an advanced battery manufacturing including laser materials processing is presented. For developing an optimized 3D architecture for high power composite thick film electrodes electrochemical analytics and post mortem analytics using laser-induced breakdown spectroscopy were performed. Based on mapping of lithium in composite electrodes, an analytical approach for studying chemical degradation in structured and unstructured lithium-ion batteries will be presented.

Surface micro-structuring of intercalation cathode materials for lithium-ion batteries: a study of laser-assisted cone formation

Strong efforts are currently undertaken in order to further improve the electrochemical performance of high energy lithium-ion batteries containing thick composite electrode materials. The properties of these electrode materials such as active surface area, film thickness, and film porosity strongly impact the cell life-time and cycling stability. A rather new approach is to generate hierarchical architectures into cathode materials by laser direct ablation as well as by laserassisted formation of self-organized structures. It could be shown that appropriate surface structures can lead to a significant improvement of lithium-ion diffusion kinetics leading to higher specific capacities at high charging and discharging currents. In this paper, the formation of self-organized conical structures in intercalation materials such as LiCoO2 and LiNi1/3Mn1/3Co1/3O2 is investigated in detail. For this purpose, the cathode materials are exposed to excimer laser radiation with wavelengths of 248 nm and 193 nm leading to cone structures with outer dimensions in the micrometer range. The process of cone formation is investigated using laser ablation inductively coupled plasma mass spectrometry and laser-induced breakdown spectroscopy (LIBS). Cone formation can be initiated for laser fluences up to 3 J/cm2 while selective removal of lithium was observed to be one of the key issues for starting the cone formation process. It could be shown that material re-deposition supports the cone-growth process leading to a low loss of active material. Besides the cone formation process, laser-induced chemical surface modification will be analysed by LIBS.

Manufacturing of advanced Li(NiMnCo)O2 electrodes for lithium-ion batteries

Lithium-ion batteries require an increase in cell life-time as well as an improvement in cycle stability in order to be used as energy storage systems, e.g. for stationary devices or electric vehicles. Nowadays, several cathode materials such as Li(NiMnCo)O2 (NMC) are under intense investigation to enhanced cell cycling behavior by simultaneously providing reasonable costs. Previous studies have shown that processing of three-dimensional (3D) micro-features in electrodes using nanosecond laser radiation further increases the active surface area and therefore, the lithium-ion diffusion cell kinetics. Within this study, NMC cathodes were prepared by tape-casting and laser-structured using nanosecond laser radiation. Furthermore, laser-induced breakdown spectroscopy (LIBS) was used in a first experimental attempt to analyze the lithium distribution in unstructured NMC cathodes at different state-of-charges (SOC). LIBS will be applied to laser-structured cathodes in order to investigate the lithium distribution at different SOC. The results will be compared to those obtained for unstructured electrodes to examine advantages of 3D micro-structures with respect to lithium-ion diffusion kinetics.

Femtosecond laser patterning of lithium-ion battery separator materials: impact on liquid electrolyte wetting and cell performance

High capacity Li-ion batteries are composed of alternating stacked cathode and anode layers with thin separator membranes in between for preventing internal shorting. Such batteries can suffer from insufficient cell reliability, safety and electrochemical performance due to poor liquid electrolyte wetting properties. Within the electrolyte filling process, homogeneous wetting of cathode, separator and anode layers is strongly requested due to the fact that insufficient electrolyte wetting of battery components can cause limited capacity under challenging operation or even battery failure. The capacity of the battery is known to be limited by the quantity of wetting of the electrode and separator layers. Therefore, laser structuring processes have recently been developed for forming capillary micro-structures into cathode and anode layers leading to improved wetting properties. Additionally, many efforts have been undertaken to enhance the wettability and safety issues of separator layers, e.g. by applying thin coatings to polymeric base materials. In this paper, we present a rather new approach for ultrafast femtosecond laser patterning of surface coated separator layers. Laser patterning allows the formation of micro-vias and micro-channel structures into thin separator membranes. Liquid electrolyte wetting properties were investigated before and after laser treatment. The electrochemical cyclability of batteries with unstructured and laser-structured separators was tested in order to determine an optimal combination with respect to separator material, functional coating and laser-induced surface topography.

Fabrication and characterization of silicon-based 3D electrodes for high-energy lithium-ion batteries

For next generation of high energy lithium-ion batteries, silicon as anode material is of great interest due to its higher specific capacity (3579 mAh/g). However, the volume change during de-/intercalation of lithium-ions can reach values up to 300 % causing particle pulverization, loss of electrical contact and even delimitation of the composite electrode from the current collector. In order to overcome these drawbacks for silicon anodes we are developing new 3D electrode architectures. Laser nano-structuring of the current collectors is developed for improving the electrode adhesion and laser micro-structuring of thick film composite electrodes is applied for generating of freestanding structures. Freestanding structures could be attributed to sustain high volume changes during electrochemical cycling and to improve the capacity retention at high C-rates (> 0.5 C). Thick film composite Si and Si/graphite anode materials with different silicon content were deposited on current collectors by tape-casting. Film adhesion on structured current collectors was investigated by applying the 90° peel-off test. Electrochemical properties of cells with structured and unstructured electrodes were characterized. The impact of 3D electrode architectures regarding cycle stability, capacity retention and cell life-time will be discussed in detail.

Towards Reliable Organs-on-Chips and Humans-on-Chips

The artificial production of complete three-dimensional vascularized functional organs is still a research challenge, although recent advances are opening up new horizons to the treatment of many diseases by combining synthetic and biological materials to produce portions of veins, capillaries, arteries, skin patches and parts of bones and soft organs. Counting with artificially obtained completely functional replicas of human organs will constitute a benchmark for disease management, but there is still a long way to achieve the desired results and produce complete organs in vitro. In the meantime, having at hand simple biomimetic microsystems capable of mimicking the behaviour of complete complex organs, or at least of some of their significant functionalities, constitutes a realistic and very adequate alternative for disease modeling and management, capable of providing even better results than the use of animal models. These simplified replicas of human organ functionalities are being developed in the form of advanced labs-on-chips generically referred to as “organs-on-chips” and are already providing interesting results. This chapter provides an introduction to this emerging area of study and details different examples of organs-on-chips and their development process with the aid of computer-aided design and engineering technologies and with the support of rapid prototyping and rapid tooling resources.

Femtosecond laser modification of Li(NiCoMn)O 2 electrodes for lithium-ion batteries

Ultrafast laser micromachining processes for modification and formation of three-dimensional architectures in cathode materials were developed. The electrochemical properties were investigated applying cell test with current densities in the range of (0.05-28.79) mA/cm2.

Laser in battery manufacturing: impact of intrinsic and artificial electrode porosity on chemical degradation and battery lifetime

The main goal is to develop an optimized three-dimensional (3D) cell design with improved electrochemical properties, which can be correlated to a characteristic lithium distribution along 3D micro-structures at different State-of-Health (SoH). 3D elemental mapping was applied for characterizing the whole electrode as function of SoH. It was demonstrated that fs-laser generated 3D architectures improves the battery performance regarding battery power and lifetime. It was quantitatively shown by laser-induced breakdown spectroscopy that 3D architectures act as attractor for lithium-ions. Furthermore, lateral intrinsic porosity variations were identified to be possible starting points for lithium plating and subsequent cell degradation. Results achieved from post-mortem studies of cells with laser structured electrodes (intrinsic and artificial porosity variation), and unstructured lithium-nickel-manganese-cobalt-oxide electrodes will be presented.