Aquasols produced by exploding copper wires represent complex systems in which identifying individual colloidal components poses challenges due to broad and multimodal size distributions and varying shares among oxidation states. To evaluate the reproducibility of copper wire explosion, the size distribution of metallic and oxidized colloidal components within the 10–300 nm diameter range was assessed. Classification of each individual particle into bins according to size and chemical composition was accomplished by reconstructing the recorded optical extinction spectra of three sols produced under identical conditions as the weighted sum of the extinction spectra of individual copper and copper-oxide particles, computed using Mie theory. Our spectrophotometry-based component analysis revealed differences in particle number concentrations of the mainly oxidized nanoparticles, corresponding to deviations observed in the ultraviolet portion of the extinction spectra. Notable uniformity was observed, however, in the number of metallic fine particles, consistent with agreement in spectral features in the visible range. Regarding mass concentration, practically no differences were observed among the three samples, with nano-to-fine ratios of copper particles agreeing within 0.45%. Despite the complex processes during explosion leading to limited reproducibility in the ratio of different copper oxidation states, very good reproducibility (54.2 ± 0.7%) was found when comparing the total copper content of the samples to the mass of the exploded copper wire.

Wire explosion is a technically straightforward green method for nanoparticle production; however, the determination of polydisperse and multimodal particle size distribution and thereby the assessment of the efficiency of the process pose serious challenges. Fitting extinction spectra derived from the Mie theory to the measured extinction spectra of colloidal solutions produced by the explosion of copper wires of 70 μm diameter and 20 mm length by discharging a capacitor of 435 nF charged to voltages ranging from 4 to 12 kV in an aqueous environment allows for determining the size distribution of the particles in the 10–300 nm diameter range and provides information on their oxidation state as well. In underwater wire explosion of copper, the vast majority of the nanoparticles transforms into copper oxides already during the process. The size distribution remains bimodal throughout the whole charging voltage range investigated. The nanoparticles follow a lognormal size distribution with a mode at 30 nm, while the fine particle population extending from 100 to 300 nm in diameter is dominated by rather normally distributed copper droplets with modes at 160–170 nm. The energy injected into the wire controls the individual concentration of both the fine and nanoparticles with the modes and ranges remaining hardly affected. The number concentration of the nanoparticles increases monotonically with the energy, spanning more than one order of magnitude. The throughput assessed by the total mass of the nanoparticles divided by the total mass of all species identified in the sol within the 0–300 nm diameter range increases monotonically from 1% at 4 kV up to 41% at 12 kV, revealing that wire explosion can be optimized for efficient nanoparticle production.

The growing prominence of the electric vehicle industry, fueled by environmental concerns, has demanded innovation in various aspects of battery technologies with special emphasis on increasing the efficiency of both electric storage and its retrieval. An unexplored area of this is to identify the possibilities and limits of laser soldering. Here, we reveal the effects of surface pretreatment conditions and the amount of filler, along with the laser power and irradiation time on the characteristics of laser-soldered joints, by simultaneously evaluating the electrical and mechanical behavior of laser-soldered nickel-plated steel sheets (Hilumin®). By describing the morphological characteristics of the resolidified solder and the electrical and mechanical properties of the joints, we identify three, characteristically different morphological appearances and highlight the optimal one, where uniform and mostly void-free solder can be produced. Furthermore, we report a correlation between the threshold of upper sheet melting (either expressed as laser power or irradiation time) and joint deterioration in terms of the electrical and mechanical properties of the joint. We conclude that laser soldering can create joints with outstanding electrical conductance and adequate mechanical stability that meets the critical specifications of battery joining technologies when the surface pretreatment condition and processing parameters are properly optimized.