5. Three-dimensional silicon/carbon coreeshell electrode as an anode material for lithium-ion batteries   

Jung Sub Kim, Wilhelm Pfleging, Robert Kohler, Hans Jürgen Seifert, Tae Yong Kim, Dongjin Byun, Hun-Gi Jung, Wonchang Choi, Joong Kee Lee 

Published online: 2014

This study developed periodic 3D Si@C core–shell electrodes for lithium-ion batteries by combining material design and electrode design, because the rate capability of an electrode is strongly influenced by its electronic conductivity, lithium-ion diffusivity, and electrolyte accessibility. The carbon shell allows faster electron transport from the current collector to the active material, providing efficient electron transport along the 3D geometry. Moreover, side reactions between the active material and electrolyte can be minimized. The periodic arrays with void spaces can also accommodate the volume changes during the insertion and extraction of Li-ions. Furthermore, electrolyte accessibility can be increased by the 3D architecture. First, Si nanoparticles were coated with a thin carbon layer by thermal decomposition. The Si@C material was then incorporated into a conventional slurry electrode on a Cu current collector, followed by laser ablation to create periodic 3D channels. The test cells consisted of a working electrode, lithium foil as the counter and reference electrode, and a polypropylene (PP) membrane as the separator. The pristine Si and Si@C particles were investigated by SEM and TEM equipped with EDX. Furthermore, the crystal structure was determined by XRD, while the quality of the carbon coating was investigated by Raman spectroscopy. Galvanostatic charge–discharge cycling tests were performed to analyze the electrochemical properties. Fig. 1 schematically shows the proposed design of the 3D Si@C core–shell electrode for high electrochemical performance. The corresponding data are shown in Fig. 3(b), where a native oxide layer (6.4 wt%) on the Si surface and a C coating with a thickness of 7 nm were observed. These results are in good agreement with the elemental analysis and TEM images. Fig. 4 shows the XRD patterns and Raman spectra of the Si particles before and after carbon coating. Except for the typical diffraction peaks of Si, no other peaks were observed for the Si@C core–shell particles, confirming that the carbon layer was very thin and constituted only a small fraction of the total mass. The relative intensity ratio (ID/IG) of the D-band to the G-band was used to characterize the degree of disorder in the carbon materials. The (ID/IG) ratio of the Si@C core–shell particles was 1.04, as shown in the inset of Fig. 4(b). These results indicate that the thermally decomposed carbon contained a mixture of disordered and ordered carbon structures. Fig. 6(a) shows the voltage profiles for the first and second discharge (lithiation)–charge (delithiation) curves of the pristine Si, Si@C, and 3D Si@C core–shell electrodes. For the Si@C and 3D Si@C core–shell electrodes, a distinct plateau at 1.14 V was observed in the first lithiation profiles, which was attributed to electrolyte decomposition and the formation of the SEI on the electrode surface. Fig. 6(b) and (c) show the discharge capacities of the prepared samples in different potential windows at a constant current density. After an obvious drop in the first cycle, commonly caused by irreversible reactions, the discharge capacity of the Si@C core–shell anode increased during the following several cycles. The 3D Si@C core–shell anode showed slightly better cyclability compared with the Si@C electrode. Fig. 8 shows the SEM images of the Si@C and 3D Si@C core–shell electrodes obtained after lithiation (after the first cycle) and delithiation (after 300 cycles). The results indicate that the structure did not significantly change during the volume changes associated with Li-ion insertion and extraction, and that the empty spaces functioned to relieve mechanical stress and prevent structural failure. Therefore, the unique 3D Si@C core–shell electrode with laser-generated grooves plays an important role in minimizing the deterioration of electrical contact between the active particles and conductive network and in alleviating the physical stress experienced by the Si electrode. 

4. Three-dimensionalization via control of laser-structuring parameters for high energy and high power lithium-ion battery under various operating conditions  

Junsu Parka, Hyeongi Songb, Inseok Jangc, Jaepil Leec, Jeongwook Umc, Seong-guk Baec, Jihun Kimb, Sungho Jeongc, Hyeong-Jin Kimb,

Published online: 22 April 2021

Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery (LIB) electrodes. This paper reports the analysis results of electrode performance, internal resistances, and mass loss of LIB electrode according to laser-structuring parameters, the groove depth and pitch. The rate capability and areal discharge capacity of thick and dense NCM cathodes are analyzed for performance test. The internal resistances are measured by electrochemical impedance spectroscopy (EIS) using both a conventional half-cell and a symmetric cell filled with a non-lithium electrolyte (The Nyquist impedance plot was fitted by Z-fit software to precisely measure the individual internal resistances). For mass loss, laser induced breakdown spectroscopy (LIBS) is employed to examine how lithium-ions diffuse through the grooves, and the data are used to determine the reasonable groove pitch and depth with minimum mass loss. Surface chemistry is also analyzed by X-ray photoelectron spectroscopy (XPS) to investigate chemical changes of electrode materials after laser structuring. A LiNi0.5Co0.2Mn0.3O2 NCM cathode (90 wt% active materials, 5 wt% polyvinylidene fluoride (PVDF) binder, and 5 wt% Super C65 conductive carbon) was prepared for laser structuring as follows. The electrode slurry, consisting of binder solution, active material and conductive carbon, was mixed by ball-milling process and then coated on an aluminum current collector. Considering the XPS results and the previous study, the overall electrical conductivity of the NCM cathode appears to be improved after laser structuring (enhanced C–C peak indicates an improvement in electronic conductivity). The performance results presented in Figure 3 reveal several important characteristics of the laser-structured electrodes. First, the electrode performance can be enhanced even with a small geometric modification to the electrode. Second, the groove pitch and groove depth have optimal values for improving performance. Finally, the effects of groove depth and pitch on performance enhancement depend differently on the electrode operating condition, particularly the current rate. At higher current rates, groove depth is a more important parameter for improving performance. The lithium distribution in the original and laser-structured electrodes was investigated using LIBS mapping. In the original electrode, a high lithium concentration was observed only within a thin layer near the electrode surface. Beyond this surface layer, the lithium concentration decreased drastically with increasing depth, as shown in Figure 5(a). For the laser-structured electrodes shown in Figure 5(b–f), a high lithium concentration was observed not only within a thin layer near the electrode surface but also along the surfaces of the grooves. This distribution indicates that lithium ions can diffuse in two dimensions within the laser-structured electrode.

These results clearly demonstrate that the grooves facilitate lithium-ion diffusion into deeper regions of the electrode by shortening the diffusion pathway. As a result, the laser-structured electrodes exhibit lower ionic resistance. Both the groove pitch and depth affect each type of resistance. In particular, the effects of these parameters operate differently in the electrochemical performance depending on the electrode operating conditions such as the current rates. Thus, at high current rate conditions, to achieve the desired performance enhancement, a deep and dense groove pattern will be suitable to simultaneously reduce the electronic and ionic resistances.

3. Welding of high-entropy alloys and compositionally complex alloys—an overview  

Michael Rhode1,2 & Tim Richter1 & Dirk Schroepfer1 & Anna Maria Manzoni3 & Mike Schneider4 & Guillaume Laplanche4

Published online: 14 April 2021

This paper summarizes the most important results on the welding of HEAs/CAAs and their weld joint properties. HEAs represent a new class of materials which contain more than 5 alloying elements and are defined in this overview as single-phase solid solution. This new material allows overcoming the strength-ductility trade-off issue of the traditional alloys. The paper mentions 4 core effects of HEAs: “High-entropy effect”, “Lattice distortion effect”, “Sluggish diffusion” and “Cocktail effect” and also explains in detail each effect. According to the references cited in this paper, the quality of a weld joint depends on the microstructure of the different welding zones, their corresponding properties, and the structural integrity of the welded joint. However the welding process may influence the material behavior and properties regarding the differences in energy input and the maximum temperature. Therefore it affects the welded joints’s structure and properties, e.g., the size/shape of the weld pool and the HAZ (heat-affected zone), the hardness distribution expressed by hardening or softening, residual stresses, defects, and weld imperfections. Many HEAs/CCAs are complex in their metallurgical behavior because of the formation of secondary phases such as IMCs during welding. It has been reported that welding defects in the FCC CoCrFeMnNi HEA such as cracks or pores can be mostly avoided by welding parameter adjustments. But these investigations have only involved remelted base material or single-layer butt joints and the study using filler metals for welding of HEAs are rare. The authors suggested that the CoCrFeMnNi alloy shows promising weldability for fusion welding techniques including LBW and TIG. The paper also explains the risk of loss of the Mn content due to its high vapor pressure at high energy densities (as provided by LBW), therefore affecting the balance of the elemental concentration. Cited from a research of Nam et al, a large heat input resulted in a so-called “undercut” phenomenon due to the evaporation of elements with high vapor pressures like Mn. For all the heat inputs that were investigated, shrinkage voids were found to form, and the origin was not discussed, but it is obvious that the evaporation of Mn had an influence. Due to the low thermal conductivity of HEA, the heat may accumulate in the welding zone making the process become problematic. Overheating during welding may lead to the precipitation of IMCs that strongly affect the HAZ-properties of the CoCrFeMnNi HEA. The precipitation of the σ phase was reported to reduce the toughness, ductility and increase the hardness and embrittle HEAs. However the PWHT may be performed to dissolve these IMCs but need to be investigated. The weld shrinks upon cooling, due to thermal contraction, at a much faster rate than the base material. This leads to the formation of high tensile residual stresses in the weld while compression residual stresses develop in the base material. The tensile residual stresses in the weld seam promote crack formation and increasing the thermal conductivity can minimize residual stresses and thus reduce the susceptibility to cracking.

2. Overlap joining of aluminium and copper using laser micro welding with spatial power modulation   

S. Hollatz1 & P. Heinen1 & E. Limpert2 & A. Olowinsky1 & A. Gillner 1,2

Published online: 28 January 2020 

This study contains the results for overlap joints of copper and aluminium using a laser beam welding process with spatial power modulation. In this paper, the challenging in welding of dissimilar materials is mentioned. The reasons are explained by the differing material properties like thermal conductivity as well as the formation of intermetallic phases. It also explain the crack's formation in the process by 2 reasons. Firsly the melting temperature of copper is much higher than the melting point of aluminium. That leads to additional temperature-induced dynamics in the melt pool due to the higher temperature gradient. During cooling, the different solidification can cause tensions in the weld seam that may lead to cracks. Secondly, during cooling, there is the intermetallic phases formation in the weld seam. These phases have a significant higher hardness. The resulting joints can be brittle and tend to crack. In addition, the paper also shows that increasing laser power increases penetration depth, while connection width is mainly affected by oscillation amplitude. The material arrangement strongly affects the process window due to differences in melting point and heat transfer. Higher power also promotes Al–Cu mixing and possible intermetallic phase formation. Beside that, to investigate more about the intermetallic phases, the authors used the EDX of the cross sections. The mechanical properties of the weld seams are investigated by performing tensile tests.

1. Brief History of Early Lithium-Battery Development   

Mogalahalli V. Reddy 1 , Alain Mauger 2, Christian M. Julien 2 , Andrea Paolella 1 and Karim Zaghib 1,*

1) Centre of Excellence in Transportation Electrification and Energy Storage (CETEES), Hydro-Québec, 1806, Lionel-Boulet blvd., Varennes, QC J3X 1S1, Canada; MogalahalliVenkatesh.VenkatashamyReddy@hydro.qc.ca (M.V.R.); paolella.andrea@hydro.qc.ca (A.P.)

2) Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Sorbonne Université, UMR-CNRS 7590, 4 Place Jussieu, 75005 Paris, France; alain.mauger@upmc.fr (A.M.); christian.julien@upmc.fr (C.M.J.)

Published: 17 April 2020 

This study reviews and summarizes the important developments in the history of lithium batteries, especially focusing on lithium-ion batteries. Lithium was discovered in 1817 through the analysis of petalite ore (LiAlSi₄O₁₀) and was quickly recognized as a promising battery anode because of its excellent physical properties: low density, high specific capacity, and low redox potential. In 1958, by examining the solubility of lithium in various non-aqueous electrolytes, Harris observed the formation of a passivation layer that could prevent a direct chemical reaction between lithium and the electrolyte while still allowing ionic transport across it, which led to studies on the stability of lithium-ion batteries. From the 1960s to 1972, different types of primary lithium batteries were introduced to the market. After this period of primary batteries, from the 1970s to 1990, research began to focus on the development of rechargeable (secondary) lithium-ion batteries using the intercalation of lithium in different materials. After several years of research, two potential materials for the cathode were LiFePO₄, which has remarkable thermal stability but low redox potential (3.5 V), and LiCoO₂, which has rather poor stability but belongs to the class of 4 V cathodes. In 1992, the solid-solution concept for Li(NiₓMnᵧCoz)O₂ (NMC) cathodes was proposed, and the material was later commercialized by various companies due to its high energy density; it now shares the market with LiFePO₄. For the anode, lithium metal and lithium alloys were investigated because of their high specific capacity and low redox potential, but dendrite formation and poor cycling stability limited their use. Graphite was later explored as an alternative because Li⁺ can reversibly intercalate and deintercalate between its carbon layers. Electrolyte research focused on non-aqueous electrolytes with good ionic conductivity and stability. The formation of a passivation layer was important because it prevents direct reactions between lithium and the electrolyte while allowing ionic transport. The separator electrically isolates the cathode and anode while allowing Li⁺ transport, and its ionic permeability, stability, and mechanical strength are important for battery safety and performance.