X-ray tomography to inspect lithium batteries for e-mobility

lithium battery inspection using X-ray tomography

In a fast-changing energy landscape, the growing demand for e-mobility has pushed the electric battery industry to the forefront of innovation... E-mobilité accounts for about half of the market demand for lithium batteries. Worldwide, the battery manufacturing market is growing by more than 15% a year (between 2010 and 2022, sales of electric vehicles increased from 120,000 to more than 10 million), leading to the creation of the famous battery ‘ gigafactories ’ to meet that demand.

Exponentially rising quantities and more efficient battery design have driven manufacturers to adopt more advanced inspection and quality control methods in order to reduce the risk of fire and failure and to guarantee higher quality. And to support these inspections, cmm machines and especially X-ray CT Scanners aka computed tomography have emerged as a tool offering unrivalled capability to examine the internal structure of batteries in depth, analyze materials and detect anomalies on a micro and nano scale.

From battery development to quality control

This growing demand presents both opportunities and challenges for electric battery manufacturers. Increasing production, improving battery quality, boosting battery capacity, making the manufacturing process more eco-friendly and so on - all of this with significant financial implications. This is why manufacturers are increasingly turning to computed tomograpy and its many applications, because unlike any other inspection or measurement technique, CT Scanners allow a non-destructive and immersive inspection of batteries! This is essential because once closed, the battery is sealed and cannot be opened without damaging it.

Battery composition

E-mobility doesn't necessarily mean 100% electric, just as it doesn't just mean electric cars, but a whole ecosystem that has developed over the years, including drones, electric scooters, electric bikes, buses, boats and even aeroplanes! And while the size of the batteries differs, the principle and components remain the same. In the case of lithium batteries (which are currently the most common on the market), there are always lithium-ion cells, an electronic board, a wiring system and a case. To give an idea of scale, an electric bike or EAB requires between 40 and 60 lithium-ion cells to produce a battery. And the battery principle for an electric vehicle is exactly the same, but on a larger scale. Did you know that an electric car requires between 5,000 and 8,000 lithium-ion cells? That's around 130 electrical bikes! That's around 300 kg for a city car and 600 kg for larger models. The battery in a Tesla S 85 kW weighs 540 kg, more than a quarter of the car's weight.

lithium battery inspection by tomography

So how is a cell made up and how does it work?

Most battery cells are made up of the following metals: lithium, cobalt, nickel and manganese. These are metals that are capable of storing large quantities of energy in a ‘compact’ and relatively light format. Once these metals have been harvested, they are melted down and shaped into electrochemical cells. The heart of a lithium-ion battery lies in its individual cells, each made up of three key elements: electrodes, electrolyte and separator. (SCHEMA)

1. Electrodes :

· The anode, where oxidation occurs, receives the ions during charging.

The cathode stores lithium ions when discharging.

2. Electrolyte :

This conducting liquid allows ions to circulate between the electrodes during charging and discharging, creating an electric current. Its composition is often based on a lithium salt dissolved in an organic solvent. -How it works: when the battery is charged, the ions are dissolved in the electrolyte and move towards the anode. When the battery is discharged, the ions pass through the electrolyte from the anode to the cathode.

3. Separator :

A thin membrane made up of small pores to allow lithium ions to pass through, it prevents any contact between the anode and cathode and ensures the safety of the cell. The manufacture of cells, and therefore batteries, is not an easy process, and to avoid any short-circuits, problems or rejects, it has become important for manufacturers to control production and the final product.

Why use X-rays to produce batteries for e-mobility? ?

Given fast-growing demand, resources with a high ecological impact and the industrialisation of processes, battery manufacturers are increasingly monitoring batteries and cells throughout the production chain. With 3 main objectives:

Standardization and reliability: As production increases, the need to ensure the standardization, reproducibility and reliability of batteries is a key issue. Each battery must meet strict performance and safety standards, which requires inspection and quality control at various stages of the process.

Detecting faults: The complexity of analysing lithium-ion batteries comes in particular from their chemical composition and structural integrity, making it more difficult to detect faults. You can't simply open a cell to check that everything is correctly positioned. You need a technology that allows you to see through the materials to identify faults such as internal shorts, inhomogeneities in the active materials and separation problems. This is where X-ray tomography becomes an ideal tool, enabling in-depth non-destructive inspection of internal battery components. This allows defective batteries to be identified at an early stage of production, reducing scrap and the associated costs.

Production optimisation: Battery testing using X-ray computed tomography not only helps to guarantee the quality of the batteries produced, but also to optimize production processes. By quickly and accurately identifying defects or variations in materials or the production line, manufacturers can adjust their manufacturing processes to minimize waste and improve efficiency for greater performance.

‘As the electric battery industry evolves, the need for careful and accurate inspection to ensure product performance, safety and durability is a key issue for manufacturers, especially when you consider that up to 30% of batteries can go to waste.X-ray tomography provides a microscopic view inside batteries.At RX Solutions, we are proud to be part of the Upcell alliance and to be able to support European manufacturers in the qualification of their batteries, whether by installing a tomograph directly on their premises or by providing our inspection services" – [Roland Le Floc’h – product manager RX Solutions]

X-ray tomography enables precise inspection of the internal components of batteries, ensuring the structural integrity and correct operation of each cell, which are vital to the reliability of systems in electric vehicles.

X-ray tomography for mobility - Inspection of a lithium-electric battery

Thanks to non-destructive inspection of batteries and cells, it is possible to see in depth and down to nano scale the smallest defect that could reduce the performance and life of the battery or in a less favourable scenario, damage the battery, the vehicle and/or the surrounding area.

inspection batterie lithium par tomographie rayons X

Precise measurement of anode overhang and bend radius. For optimized performance and lifetime..

The aim is to avoid lithium plating, delamination or cracks in the active material if the overhang is too great. For this reason, the cell's anode is longer than the cathode, but its dimensions must be kept within very tight limits to avoid malfunctions and safety concerns such as short circuits. By carefully controlling and optimizing the overshoot, it is possible to improve the efficiency, capacity, cycle stability and overall performance of batteries.

Checking the quality of porous separators

The purpose of a battery separator is to ensure safety by preventing short circuits that would occur if the anode and cathode came into contact. The separator must retain the material while allowing ions to pass from the anode to the cathode when the battery is charging and in the opposite direction when the battery is discharging.

Lithium cell computed tomography

Live X-ray radioscopy of lithium cell

Calculation and analysis of overhang on lithium cells

Lithium cell computed tomography

Live X-ray radioscopy of lithium cell

Calculation and analysis of overhang on lithium cells

Material delamination detection

Delamination can reduce a battery's performance, as well as its lifespan. This problem can occur both during the manufacturing cycle and later in the life of the cell. During the multiple charge and discharge cycles that the battery undergoes, the electrodes are constantly deforming, creating a vacuum and thus delamination. The dark spaces represent the various delaminations of this cell.

Foreign particles

Foreign particles, often copper or aluminium, can be inserted into the cells of a battery at many points in the production chain, most often during the electrode cutting process. This is why it is important to check the size, quantity and position of these particles to determine whether their presence is critical to the battery's life cycle.

Inspection of welds/brazed seams, irregularities in cell layers or structure

In order to prevent any leakage or flammable reaction due to exposure to air and water, it is important to check the quality of the welds both inside and outside the battery to ensure that the cell is waterproof. As all the current flows through the solder joints, non-homogeneous solder joints will create electrical resistance between the components, which will degrade the quality of the cell and the battery.

In a nutshell, the rise of e-mobility means innovation and continuous improvement in the design and manufacture of electric batteries. By offering non-destructive, in-depth inspection of batteries, X-ray computed tomographycan guarantee the performance, safety and durability of batteries and cells. Being able to inspect the structural integrity of batteries offers numerous advantages and new prospects:

- Improved standardization and reliability of batteries
- Accurate detection of internal defects
- Optimization of production processes
- Reduction in scrap and costs
- Better understanding of internal phenomena for more effective R&D

As a French manufacturer of state-of-the-art tomographs, we at RX Solutions are proud to contribute to this evolution in the e-mobility sector, by providing accurate tools for the inspection of electric batteries. Our commitment to the battery market is reflected in our membership of the Upcell Alliance. Upcell Alliance is a not-for-profit association that aims to create a unique European ecosystem of players in the battery manufacturing equipment and machinery industry. The aim is to position Europe as a leader in this field, as more and more batteries are produced in Europe every year.