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Non-Destructive Evaluation Technologies Making Batteries Safer and More Efficient

Above image: Foreign particles in cell (image created in VGSTUDIO MAX courtesy of Waygate Technologies)

With motorists across the world shifting to hybrid or electric vehicles (EVs) in increasing numbers, the demand for the batteries that power them has skyrocketed. Yet the battery supply chain is in a difficult period of uncertainty. Some larger automotive and battery manufacturers are building their own gigafactories or forming joint ventures to address supply issues. But there remain two significant obstacles: increased costs of procuring key raw materials, such as lithium, and ongoing problems relating to battery reliability and safety.

The rapid growth of the EV market dictates that battery manufacturers scale up for mass production. A recent article by McKinsey reports that demand for EVs is expected to grow by around 30%, nearing 4,500 gigawatt-hours (GWh) a year globally by 2030, and the battery value chain is expected to increase by as much as ten times between 2020 and 2030 to reach annual revenue as high as $410 billion. It is estimated that 90% of the demand will come from mobility applications, most notably EVs.

The upcoming EURO-7 standard stipulates that batteries must retain at least 70% of their capacity eight years after manufacture. The U.S. and China are pushing for even stricter norms that call for 80% battery life after 10 years.

These standards establish clear directives for the battery manufacturers: they need to prioritize quality assurance to reduce the number of faulty batteries and limit the waste of raw materials, which not only raises the cost of production but also has a detrimental effect on the environment.

Performance is Key for EV Batteries

Lithium-ion batteries—the most common cells used in electric and hybrid cars—produce current when lithium ions move from the anode to the cathode. Colder temperatures can slow this process down and restrict battery performance, which can result in a dramatic loss in driving range. When a battery is delivering peak output in hot weather, latent defects in the battery can cause catastrophic failure.

Thermal management systems are extremely important to maintain optimal battery performance and prevent damage under a wide range of driving conditions. Yet such systems cannot mitigate problems when cells already contain physical and electrochemical defects.

Non-Destructive Testing Has Become a Necessity

Battery quality and integrity are of particular concern for all battery manufacturers because they directly affect safety—no more so than in the case of passenger-carrying EVs. Ensuring battery quality as production volumes increase presents a challenge that can result in huge financial losses if not approached with due consideration. If you’re making several cells a minute, a 10% defect rate can equate to several hundred thousand dollars in waste a day.

CT defect analyses support early defect analysis in vertically integrated battery manufacturing process

Contamination of the battery during manufacture can be a major cause of a number of defects. The identification of particles and assessment of particle size is an important contributor, especially for the active material (cathode). Similarly, delamination can reduce the capacity and maximum power of battery cells, while insufficient anode overhang leads to lithium plating at the separator and can affect the life of the battery, in addition to creating safety concerns. The ability to assess battery quality using non-destructive testing is vital for manufacturers who are looking to increase production capacity while keeping waste to a minimum.

Unlike simple mechanical parts, the manufacturing process of batteries has an impact on their final chemical and mechanical structure as well as the composition of the battery. However, opening finished batteries for testing is impractical since it makes them unusable. To overcome these issues, non-destructive testing (NDT) techniques are an efficient solution to minimise product waste, reduce costs, and improve battery reliability and safety.

One increasingly applied NDT technology is industrial computed tomography (CT), which has proven to be a powerful ally for battery quality inspection and root-cause analysis.

Urgent Problems Have Driven Huge Software Advances

Only a few years ago, rudimentary 2D inspection of batteries was common but only called upon to validate and add insight for a known problem. Today, advanced analysis software such as Hexagon’s VGSTUDIO MAX has taken a pivotal role in integrating, cleaning, processing, and visualising 3D datasets.

CT scan analysis in VGSTUDIO MAX identifies the anode overhang caused during the battery cell manufacturing process

Up until recently, and speaking from my own experience, it’s been difficult for even an experienced CT expert to interpret features from a 3D-scan-derived image onscreen, let alone for quality assurance engineers to automate the measurement and quantisation of defects and their importance. But now, finely tuned algorithms, markup and machine learning have risen to the challenge and are making routine CT-based quality assurance possible and fully empowering non-destructive evaluation (NDE) to become routine and reliable.

Visualisation of the internal geometry of batteries using 3D CT-data reconstruction and analysis software enables intelligent identification of features based on size, shape, and other characteristics—so the user can quickly spot issues like foreign particles that are otherwise impossible to find. These visualisations also enable accurate measurements and statistical analyses of quality-critical features such as porosity, or the size of particles suspended in fluid, that not only allow for insights into the material behaviour within the parts, but can be used to feed valuable real-world measurements back into software simulations that inform research and development efforts. Identifying and correcting problems as early as possible during production has ripple effects throughout a product’s lifecycle.

Furthermore, comprehensive data gathered throughout the lifetime and performance of batteries can be used to understand the performance of their components in service. This provides OEMs with the ability to analyse and evaluate battery performance and quality criteria on a larger scale and keep waste to a minimum.

Quality assurance is not the only important result here. There is also an opportunity to improve battery sustainability, by optimising the utilisation of lithium and other materials. Sustainability and quality are not mutually exclusive: one can complement the other when NDT and data analysis are applied to improve design and manufacturing processes.

The Need For Non-Destructive Evaluation

Because batteries are the most critical component in an EV—as well as the most expensive—manufacturers must ensure that those batteries do not fail. Putting NDE findings into action allows the engineering of quality metrics directly into product design. Inline testing using NDE can be undertaken at various stages of production, complementing other vital quality control and assessment practices before parts are assembled. Such techniques are the only way to achieve solid test coverage (up to 100%).

Using NDE creates a vast amount of information and results that will enable designers and engineers to draw conclusions about the real material behaviour within parts, thereby further accelerating R&D and manufacturing-process maturity. Using industrial CT data intelligently to address quality and sustainability can facilitate smart manufacturing processes. The technology is now available to optimize EV-battery manufacturing quality and lifetime performance—and promote even wider acceptance of more environmentally friendly vehicles on roads everywhere.

Author: Daniela Handl – General Manager Volume Graphics at Hexagon Manufacturing Intelligence

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