Global electric vehicle (EV) sales are expected to reach 14.5 million units in 2023, according to a forecast by Counterpoint Research. This would represent a 32% increase from the 10.9 million units sold in 2022. The growth in electric car sales is being driven by a number of factors, including government incentives, increasing availability of appealing models at different price points and falling battery prices. The United States is expected to be the largest market for electric cars in 2023, followed by China and Europe. The upward trend in EV sales looks certain to continue and EVs are expected to achieve a market share of 30% or more by 2030, according to a forecast by Deloitte Insights. The trend is not restricted to cars - electric trucks and buses are now a common sight in China.
https://www2.deloitte.com/us/en/insights/focus/future-of-mobility/electric-vehicle-trends-2030.html
Realizing the environmental benefits of EVs depends on the lifetime of the batteries that power them. An EV is only as good and as reliable as its battery. On average electric car batteries weigh 450kg (a Tesla Model S battery weighs 544 kg), and are a structural element of the vehicle, so they cannot be easily swapped out when a fault is discovered. A study in cell.com 'Levelized Cost of Charging Electric Vehicles in the United States' estimates that electric cars have an expected life 15 years and over 250,000 km but that lifetime is largely dependent on the quality of the battery when the car is manufactured.
Why is inline X-ray testing of EV batteries a good idea?
EV battery faults begin when small problems in a battery cell, for example internal shorts, are exacerbated by the flow of current through the cell. Some problems arise when the battery is in use and manufacturers try to catch such faults with continuous battery monitoring. Defects introduced in the manufacturing of the battery cell must be identified before the cell is integrated into a battery and then a vehicle. Identifying faults that could lead to battery fires is important for safety. Battery quality is also important economically because EVs can only be economically viable and confer an environmental benefit if batteries have a long lifetime.
Leakage current is an internal phenomenon in cells. Small shorts within a cell will cause currents, which slowly deplete the charge stored in a cell. Shorts can be caused by foreign particles in a cell or morphological deformation of the interior of the cell.
Different types of battery: Prismatic, Cylindrical and Pouch (left to right)
How is inline X-ray testing conducted?
Inline testing is a process whereby each cell produce in a line is rapidly tested for defects. X-ray imaging is ideal for battery testing because it is non-destructive and can image the interior structure of the cell. X-ray imaging can be 2D or 3D.
X-ray imaging systems target three main challenges during line inspection: electrode position, shape and foreign particles.
3D X-ray imaging uses computed tomography (called CT) to reconstruct a 3D image of the cell. 2D imaging often uses line detectors which acquire an 2D image as the cell is translated across the detector. This can be quick. However, 2D imaging is limited in detecting the electrode alignment. That is where a 3D inspection is required.
3D CT Cylindrical battery cell
3D imaging requires the acquisition of a large number of projection images, typically one per degree, from different angles over an angular range of 180 degrees or more. This is often done by rotating the object being imaged. Inline EV battery CT typically demands that a 3D CT scan of a cell is performed in about 3 seconds, giving a throughput of 20 parts per minute (20 PPM) or more. The 3D reconstructed X-ray image is analysed by AI-based software to classify the cell as good or bad.
For the cylindrical type of battery cell used predominantly by Tesla and the blade type used by BYD, it turns out that 3D CT does a better job than 2D inspection. Companies have therefore been rushing to develop systems capable of acquiring a CT scan of a battery cell in three seconds or less. This is where Spectrum Logic comes in!
Spectrum Logic makes the 2824HS and 2824HR.
Spectrum Logic makes large area, high speed CMOS X-ray detectors such as the 2824HS and 2824HR. The 2824HS can operate at 170 fps in 50% region of interest mode with a 10 gigabit ethernet interface and a pixel pitch of 100 microns. The full active area can be readout at 89 fps. The 2824HR has four times the number of pixels and a smaller pixel pitch of 50 microns. It can be readout at 44 fps in 50% ROI mode with a 10 gigabit ethernet interface. These detectors have proven their ability to function 24/7 in the full-scale commercialization of inline 3D CT inspection of EV battery cells and are the first to do so.