Tag: Defects

Manufacturing defects in silicon-based Li-ion batteries trigger degradation

Manufacturing defects in silicon-based Li-ion batteries trigger degradation

Li-ion batteries are widely used in mobile devices, transportation and energy storage, but they have limitations, including durability and degradation over time. When and why defects and failure appear in commercial batteries is still mostly unknown.

Now scientists from the ESRF, the ILL and the CEA-IRIG, Materials Center Leoben Forschung GmbH and battery manufacturer VARTA Innovation GmbH have used non-destructive X-ray and neutron imaging at the ESRF and ILL, respectively, to determine one of the origins and causes of the degrading mechanism in silicon-based Li-ion batteries.

X-rays and neutrons analysis

The samples were industrially graded batteries that are currently being tested for future commercialisation and that include large amount of silicon. The difference with current batteries lies in the anode, which is often made of state-of-the-art graphite in commercial batteries. In the new batteries, the anode consists of a slurry mix of silicon and graphite composite. “This new anode configuration, with silicon in it, enables manufacturers to introduce a bigger quantity of lithium in the same space, increasing the capacity of the battery”, explains Jakub Drnec, corresponding author of the publication and scientist in charge of ID31.

In order to characterise the new materials and determine their behaviour, the team first used the ILL’s instrument NEXT, as neutrons are an optimal tool to observe the distribution of lithium in the battery. At NeXT, 3D high resolution neutron tomography is coupled with X-ray tomography to image the entire cell. Subsequently they analysed the samples on beamlines BM05 and ID31 at the ESRF in operando conditions, i.e. while they were charged and discharged. In particular, they tracked Li dynamics and the morphology of the composite and how it changed over time using the technique of small angle X-ray scattering (SAXS). They also used X-ray diffraction (XRD) to study the cathode charging and absorption X-ray tomography to investigate the voids created that can lead to mechanical failure.

 “This is a unique multi-modal study where we have combined neutron and X-ray tomography data from the same battery together and got a full picture of what is happening”, explains Drnec. “It shows how vast and comprehensive our research is when we use both X-rays and neutrons”, he adds.

Silicon agglomerations

The results show that the way the slurry of materials is mixed during wet electrode processing is uneven, with large silicon chunks not being mixed with graphite, and this triggers a break of chemistry around the anode. That part of the battery then becomes inactive and the defects can cause mechanical failure in the cell. “What is surprising is that after the first charge of the battery we already observe this phenomenon”, says Drnec.

Read more on ESRF website

Image: Multimodal correlative data and 3D rendering of the cell. Top part: X-ray CT data. Middle part: neutron CT data. Bottom part: Combined NXCT data in false color. A 2D SWAXS CT slice is also shown in the measured position. Right: Integrated graphite intensity. Left: Integrated SAXS intensity. The insert highlights the various components and internal cell damage as observed with NXCT.

Credit: Lübke E. et al, Energy and Environmental Science, 14 May 2024.

A simpler way to inorganic perovskite solar cells

A simpler way to inorganic perovskite solar cells

Inorganic perovskite solar cells made of CsPbI3 are stable over the long term and achieve good efficiencies. A team led by Prof. Antonio Abate has now analysed surfaces and interfaces of CsPbI3 films, produced under different conditions, at BESSY II. The results show that annealing in ambient air does not have an adverse effect on the optoelectronic properties of the semiconductor film, but actually results in fewer defects. This could further simplify the mass production of inorganic perovskite solar cells.

Metal halide perovskites have optoelectronic properties that are ideally suited for photovoltaics and optoelectronics. When they were discovered in 2009, halide perovskites in solar cells achieved an efficiency of 3.9 per cent, which then increased extremely fast. Today, the best perovskite solar cells achieve efficiencies of more than 26 per cent. However, the best perovskite semiconductors contain organic cations such as methylammonium, which cannot tolerate high temperatures and humidity, so their long-term stability is still a challenge. However, methylammonium can be replaced by inorganic cations such as Cesium (Cs). Inorganic halide perovskites with the molecular formula CsPbX3 (where X stands for a halide such as chloride, bromide and iodide) remain stable even at temperatures above 300 °C. CsPbI3 has the best optical properties for photovoltaics (band gap ∼1.7 eV).

Production in glove boxes

Perovskite semiconductors are produced by spin coating or printing from a solution onto a substrate and are typically processed in glove boxes under a controlled atmosphere: There, the solvent is evaporated by heating, after which a thin layer of perovskite crystallizes. This ‘controlled environment’ significantly increases the cost and complexity of production.

…or ambient conditions

In fact, CsPbI3 layers can also be annealed under ambient conditions without loss or even with an increase in efficiency of up to 19.8 per cent, which is even better than samples annealed under controlled conditions.

What happens at the interfaces?

“We investigated the interfaces between CsPbI3 and the adjacent material in detail using a range of methods, from scanning electron microscopy to photoluminescence techniques and photoemission spectroscopy at BESSY II,” says Dr. Zafar Iqbal, first author and postdoctoral researcher in Antonio Abate’s team.

Read mpre on HZB website

Image: Under the scanning electron microscope, the CsPbI3 layer (large blocks in the upper part of the image) on the FTO substrate looks almost exactly the same after annealing in ambient air as after annealing under controlled conditions.

Credit: HZB

Listening for Defects as They Happen

Listening for Defects as They Happen

Thanks to experiments at the Swiss Light Source SLS, a Swiss research team have resolved a long-standing debate surrounding laser additive manufacturing processes with a pioneering approach to defect detection.

The progression of laser additive manufacturing — which involves 3D printing of metallic objects using powders and lasers — has often been hindered by unexpected defects. Traditional monitoring methods, such as thermal imaging and machine learning algorithms, have shown significant limitations. They often either overlook defects or misinterpret them, making precision manufacturing elusive and barring the technique from essential industries like aeronautics and automotive manufacturing. But what if it were possible to detect defects in real time based on the differences in the sound the printer makes during a flawless print and one with irregularities? Up until now, the prospect of detecting these defects this way was deemed unreliable. However, a research team from EPFL, Paul Scherrer Institute PSI and the Swiss Federal Laboratories for Materials Science and Technology (Empa) have successfully challenged this assumption.

Roland Logé, head of the Laboratory of Thermomechanical Metallurgy at EPFL who led the study, stated, “There’s been an ongoing debate regarding the viability and effectiveness of acoustic monitoring for laser-based additive manufacturing. Our research not only confirms its relevance but also underscores its advantage over traditional methods.”

This research is of paramount importance to the industrial sector as it introduces a groundbreaking, yet cost-effective solution to monitor and improve the quality of products made through Laser Powder Bed Fusion (LPBF). Lead researcher, Milad Hamidi Nasab, remarked, “The synergy of synchrotron X-ray imaging with acoustic recording provides real-time insight into the LPBF process, facilitating the detection of defects that could jeopardize product integrity.” In an era where industries continuously strive for efficiency, precision, and waste reduction, these innovations not only result in significant cost savings but also boost the dependability and security of manufactured products.

LPBF is a cutting-edge method that’s reshaping metal manufacturing. Essentially, it uses a high-intensity laser to meticulously melt minuscule metal powders, creating layer upon layer to produce detailed 3D metallic constructs. Think of LPBF as the metallic version of a conventional 3D printer, but with an added degree of sophistication. Rather than melted plastic, it employs a fine layer of microscopic metal powder, which can vary in size from the thickness of a human hair to a fine grain of salt (15–100 μm). The laser moves across this layer, melting specific patterns based on a digital blueprint. This technique enables the crafting of bespoke, complex parts like lattice structures or distinct geometries, with minimal excess. Nevertheless, this promising method isn’t devoid of challenges.

When the laser interacts with the metal powder, creating what is known as a melt pool, it fluctuates between liquid, vapor, and solid phases. Occasionally, due to variables such as the laser’s angle or the presence of specific geometrical attributes of the powder or of the part, the process might falter. These instances, termed “inter-regime instabilities”, can sometimes prompt shifts between two melting methods, known as “conduction” and “keyhole” regimes. During unstable keyhole regimes, when the molten powder pool delves deeper than intended, it can create pockets of porosity, culminating in structural flaws in the end product. To facilitate the measurement of the width and depth of the melt pool in X-ray images, the Image Analysis Hub of the Center for Imaging developed an approach that makes it easier to visualize small changes associated with the liquid metal and a tool for annotating the melt pool geometry.

Read more on PSI website

Image: By studying 3D metal printing in action simultaneously with X-rays imaging at the TOMCAT beamline and acoustic measurements, the research team could learn which sounds corresponded to defects in printing.

Credit:EFPL / Titouan Veuillet