The demand for rechargeable batteries, especially lithium-ion-based (LIB) models, is growing rapidly worldwide. According to the World Economic Forum, passenger cars will account for around 60% of global battery demand by 2030. Together with the commercial transportation and energy sectors, a study by Mordor Intelligence assumes that the global market for lithium-ion batteries will grow at an average annual rate of around 20% between 2022 and 2027, reaching a market size of USD 200 billion in 2027. Electric vehicles are expected to account for the majority of demand for lithium-ion batteries. Frost & Sullivan forecasts that between 12 and 15 million electric vehicles will be sold in 2025 - this will require a tenfold increase in global lithium-ion battery capacity compared to 2018.

The LIB manufacturing process is anything but trivial: first, individual cells must be produced and then assembled into battery modules with hundreds of cells. Even the failure of a single cell can necessitate the disassembly of an entire module and the removal of the defective cell(s). Undetected defective cells have even worse consequences, as they can severely affect the output power and performance of the entire module or even pose a hazard. In April 2022, for example, US safety regulators launched an investigation into electric and hybrid vehicle batteries after five automakers issued recalls for potential defects that could cause fires or stall engines. According to the National Highway Traffic Safety Administration, the investigation involved more than 138,000 vehicles with batteries from South Korean manufacturer LG Energy Solution, which are used in vehicles from General Motors, Mercedes-Benz, Hyundai, Stellantis and Volkswagen.

Safer batteries through inspection

As there is still no long-term experience with standardized fault detection and failure analysis equipment to understand the risks in the production of lithium-ion batteries, there is a strong case for strengthening quality controls on all individual cells before and after assembly into modules.

The first visual inspection during the LIB production process takes place during the manufacture of the foils used to produce the electrodes (cathodes and anodes). The quality and consistency of the films and their coatings are crucial for the function and safety of the cells: Foreign particles, unevenness and irregularities that push or rub through the separator foil over time can cause a short circuit, which can lead to catastrophic battery failure. Typically, this inspection is performed after cutting or punching. During these processes, particles can be deposited on the surface before the electrodes are rolled, folded or stacked.

Often it is just a few dark gray defects on a dark gray background that can determine the performance and service life of a battery cell. It is important for manufacturers to detect these defects in the range of 50 µm down to 10 µm. Contact imaging sensors are often used for an initial 'rough' inspection, but for detailed inspection further down the line, companies rely on line scan cameras and highly sensitive TDI (Time Delay & Integration) cameras to provide the resolution and sensitivity required.

More innovative solutions for this task include multi-field TDI cameras, which have the added benefit of simultaneously capturing light from three different spectrums and angles, providing more image data for defect detection and analysis.

The Linea HS 16k multifield TDI camera enables the simultaneous recording of up to three images under different lighting conditions.

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Other types of imaging are used in various phases of battery assembly. For example, high-speed 3D laser profilers measure the shape of three-dimensional objects, such as the uniformity of the welding of a contact tab, the deformation of the tab and its alignment. A poorly welded contact tab can break or cause a temporary loss of contact.

Area scan cameras are mainly used in the packaging of individual cells in larger batteries, where the alignment of hundreds of cells in the housing must be precisely controlled.

A look inside the 'black box'

After assembly, the 'black box' nature of battery modules poses a problem, because how can a module be inspected without looking inside? The Battery Innovation Center (BIC) in Newberry, USA, has addressed this problem and developed a solution with imaging that goes beyond the visual realm. The BIC focuses on the development, testing, validation and commercialization of safe, reliable and lightweight batteries for commercial and military applications. The process includes tests in which the batteries are subjected to a worst-case scenario and even destructive treatment in order to understand any resulting safety issues. To gain as much data as possible from these tests, the BIC uses a high-speed thermal imaging camera from Teledyne Flir to detect details of heat development.

Thermal imaging allows engineers to see what is happening outside the battery when it is damaged, what is happening inside and how the heat is developing. The researchers have also looked at different types of X-ray diffraction for in-situ analysis, including X-ray and ultrasound imaging. This allows the physical structure and materials of the battery to be analyzed and provides clues to physico-chemical reactions related to the operation and degrading performance of a battery. Although a CT analysis cannot provide any information about the electrochemistry within the cell, it can certainly reveal the mechanical inner workings. Overheating of the cell due to a self-reinforcing, heat-producing process and a resulting fire can have mechanical causes, but electrochemical processes can also leave mechanical traces.

While some of the required information can be captured with fast 2D X-ray systems, the visible information is limited when using this technology. With 3D X-ray imaging, it is possible to obtain a complete picture of critical aspects of a battery cell and module, while time-lapse tomography shows processes and changes in an in-service battery as it ages in four dimensions.
Industrial computed tomography is increasingly being used to detect defects and internal changes during the battery life cycle. However, it can be difficult to recognize the meaningful structures: As the materials have a very similar density and are often quite thin, this often results in a low-contrast grayscale image. Software tools for the analysis and visualization of CT data offer advanced functions that enable a more informed view with the help of artificial intelligence.

With the Z-Trak2 model family, Teledyne Dalsa offers economical solutions for 3D inline inspection at high speeds.

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Dynamic neutron radiography has proven to be another promising option for non-destructive testing. It provides researchers with real-time data on the inner workings of a system. Compared to X-rays, this technology offers some useful advantages as neutrons interact differently with elements: Firstly, lithium and the liquid electrolyte in batteries are extremely sensitive, and neutron methods have a lower risk of unwanted reactions. Secondly, the high visibility of neutrons from lighter elements such as hydrogen and lithium allows direct observation of important battery processes such as lithium diffusion, electrolyte consumption and gas formation. Researchers are currently working on improving neutron imaging to match the spatial and temporal resolution of today's CT scans. This imaging technology can help to better address the challenges of the current and next generation of batteries in terms of chemical processes.

Last but not least, some researchers have turned to electron microscopy for a more in-depth analysis of the non-structural conditions within a battery. It can be used to visualize the electrochemical reactions within a battery. As with neutron microscopy, resolution is still a challenge, but very rapid progress is being made.

The future of battery cell production

From a research and development perspective, LIB technology appears to be largely mature. The optimization of product and production remains an important goal. This optimization is a driver for promising steps towards new chemical processes to make batteries more cost-effective and environmentally friendly in the future.

Cobalt, for example, is one of the most important metals in lithium-ion batteries, as it increases the service life and energy density of the batteries. Cobalt is also one of the most expensive materials in a battery. Although battery prices have fallen by 89% between 2010 and 2021, they still account for around 30% of the total cost of an electric vehicle, according to a study by BloombergNEF. With electric vehicle sales rising rapidly worldwide, demand for battery raw materials such as cobalt is expected to soon outstrip supply. Solutions that eliminate the need for cobalt, and even lithium, are therefore becoming increasingly attractive. Some of these solutions rely more heavily on nickel, which brings its own challenges. For example, Indonesia, which controls a quarter of the world's nickel supply, significantly reduced its nickel exports in early 2020. The uncertainties of the pandemic and the global financial markets led to a fall in the price of nickel. This development prompted some companies that actually wanted to invest in increasing their nickel production to hold back their investments. The nickel price rose sharply again at the beginning of 2022.

The author: Gerard White is Senior Business Development Manager at Teledyne Dalsa in Krailling.

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In the future, new technologies are expected to be introduced that will overcome one of the fundamental disadvantages of current LIBs: the liquid, fluorine-containing and highly flammable electrolyte in a battery. This ingredient is a major challenge for the handling, storage and recycling of battery cells. New energy storage technologies based on less scarce materials such as magnesium are promising. Batteries made from magnesium metal could have a higher energy density, greater stability and lower costs than today's lithium-ion cells. Another promising direction is the development of solid-state batteries, which are much more stable but do not (yet) offer competitive performance.