Popularization of electric vehicles (EVs) is an effective solution to promote carbon neutrality, thus combating the climate crisis. Advances in EV batteries and battery management interrelate with government policies and user experiences closely.

 

The types of EVs that use batteries include:

• All-electric vehicles, also known as battery electric vehicles (BEVs), are completely powered by electricity. To recharge, the vehicle can be plugged into a wall outlet or charger.
• Plug-in hybrid electric vehicles (PHEVs) are powered by both electricity and an internal combustion engine (ICE). Unlike older hybrid electric vehicles, PHEVs can be operated on electricity alone. The gas-powered engine is available for longer trips when charging is unavailable or unreliable.
• Hybrid electric vehicles (HEVs), like PHEVs, are powered by electricity and an ICE. However, an HEV cannot be plugged in to charge the battery. Since they cannot operate on electricity alone, they are not nearly as efficient as BEVs and PHEVs.

Besides the machine and drive as well as the auxiliary electronics, the rechargeable battery pack is another most critical component for electric propulsions and await to seek technological breakthroughs continuously

 

Most electric vehicles are powered by lithium-ion batteries and regenerative braking, which slows a vehicle down and generates electricity at the same time.

 

Currently, among all batteries, lithium-ion batteries (LIBs) do not only dominate the battery market of portable electronics but also have a widespread application in the booming market of automotive and stationary energy storage. The reason is that battery technologies before lithium (e.g., lead–acid or nickel based batteries) and battery technologies beyond lithium, so called ‘post-lithium’ technologies, such as sodium-ion batteries (SIBs), mainly suffer from significantly lower energy density and specific energy compared to state-of-the-art LIBs.

 

There are several types of lithium-ion batteries, with lithium nickel manganese cobalt oxide (NMC) and lithium iron phosphate (LFP) batteries being the most common ones used in EVs.

 

Lithium-ion batteries are used in EVs because they:

• Have high energy density:They can store a relatively large amount of electrical energy into a smaller and more lightweight package than other battery technologies.
• Perform well at high temperaturesand can withstand low temperatures without being damaged.
• Have a low self-discharge rate, meaning that the battery holds its energy well even if it’s not used for days or weeks.
• Are able to withstand many charge cycleswhile retaining almost all of their original capacity.

 

Lithium-ion batteries, like all batteries, store energy and convert it to electrical energy when in use. This electricity is produced by the movement of electrons, which are small particles with a negative charge that are found in all atoms. Chemical reactions within the battery move these electrons from one electrode to another. There are two electrodes in a battery: the anode (a negative electrode) and the cathode (a positive electrode). Electrons start off in the anode and then move to the cathode through an electrolyte medium, which can be either liquid or solid. When the battery is in use, the electrons move from the anode electrode to the cathode electrode; when the battery is charging, they move from the cathode to the anode. Another key component of a battery is the separator, a thin, porous membrane that, as the name implies, separates the anode and cathode electrodes while enabling the lithium ions to move from one to the other. It also prevents short circuiting, which happens when an electric current flows down a wrong or unintended path.

 

Production Process of Battery: 

The production of the lithium-ion battery cell consists of three main process

steps: electrode manufacturing, cell assembly and cell finishing.

 

Electrode Manufacturing:

a) Mixing – Quality Features:

• Homogeneity of the slurry
• Particle size
• Purity (amount of foreign objects)
• Viscosity

 

b) Coating – Quality Features:

• Coating thickness accuracy (homogeneity in and across the coating direction)
• Surface quality (blowholes, particles)
• Adhesion between coating and substrate

 

c) Drying – Quality Features:

• Adhesion between coating and substrate
• Residual humidity
• Surface finish (cracks, inclusions, etc.)

 

d) Calendering – Quality Features:

• Defined porosity
• Surface texture
• Adhesion between coating and substrate

 

e) Slitting – Quality Features:

• Edge geometry (cutting burr)
• Thermal (temperature-affected zone) and mechanical stress
• Particle contamination during the cutting process

 

f) Vacuum Drying – Quality Features:

• Surface condition (cracks, etc.)
• Residual moisture content (no residual moisture desired)

 

CELL ASSEMBLY:

a) Separation – Quality Features:

• Cutting edge geometry (e.g. smearing of the active material over the cutting edges)
• Thermal and mechanical stress during the cutting process

 

b) Stacking – Quality Features:

• Positioning accuracy of the anode and cathode sheets
• Damage-free electrode surfaces and edges
• Avoidance of electrostatic charging

 

c) Packaging – Quality Features:

• Low contact resistance as well as low mechanical and thermal stress during the welding process
• Fatigue strength and tightness of the sealing seams

 

d) Electrolyte Filling – Quality Features:

• Dosing and distribution accuracy of the electrolyte in the cell
• No electrolyte residues in the sealing seam
• Tightness of the sealed cell

 

e) Winding – Quality Features:

• Positioning accuracy of anode and cathode foils
• Damage-free electrode surfaces and edges

 

f) Packaging – Quality Features:

• Low contact resistance as well as low mechanical and thermal stress during the welding process
• Insulation against the metallic housing

 

g) Electrolyte Filling – Quality Features:

• Dosing and distribution accuracy of the electrolyte in the cell
• Tightness of the sealed cell
• electrolyte quantity

 

CELL FINISHING:

a) Roll Pressing – Quality Features:

• Optimum formation of the SEI layer during the subsequent formation process
• Electrolyte distribution within the cell
• Capacity of the cell after formation

 

b) Formation – Quality Features:

• Formation of the SEI layer
• Stability of the SEI layer
• Internal resistance of the cell

 

c) Degassing – Quality Features:

• Residual gas inside the cell
• Damage-free cell handling (different characteristics of the gas bubbles)

 

d) Aging – Quality Features:

• Capacity
• Internal resistance
• Self-discharge rate

 

e) EOL Testing – Quality Features:

• Low self-discharge
• Low internal resistance
• Constant capacity

 

With the above information on the steps involved in manufacturing batteries, let us some areas of quality inspection or defect inspection or measurement kind of Machine Vision Inspections that can be applied related to those quality features listed in each step of the production process.

 

1. Coating: Linescan vision inspection is used to check for defects such as scratches, dents, dints, craters, bubbles, inclusions and holes on electrode sheets. , surface inspection combined with gauging width and edge profiles helps to build up an inspection profile for the continuous coated product.

 

2. During vacuum drying, a separator and electrode are brought together in cell construction. Cathode and anode cells are wrapped, rolled, or stacked together. The folded cells have lead tabs attached to them. When the cells have been loaded with electrolytes, vacuum-sealed, and dried, the procedure is complete. This process is monitored by vision inspection for anomalies and out of tolerance product. Critical to quality (CTQ) parameters are assessed in real-time.

 

3. Battery module defect detection. Each battery module will generally contain a number of cells (typically twelves). The modules are joined together and a cooling fluid pipe is attached. Checks for verification for module integrity, assembly characteristics and component verification are all completed using machine vision.

 

4. Stacking alignment and height. As modules and battery slices are built up into a complete battery pack, vision sensors measure the profile of the slice displacement and positioning to provide accurate feedback control for precision stacking.

 

5. Tab inspection. The tabs on the edge of each slice and subsequent modules are checked for debris, chips and cracks. Any small burr, edge deviation or dent can cause issues for the final assembled battery unit.

 

6. Connector Inspection. The main entry and exit to the battery module is via a high-voltage connector. The battery is charged through this connection, and electricity is delivered to the electric motor. Inspection of the main characteristics of the connector assembly are critical to provide a final check for edge deviations, male/female connector profiles and no cracks or dents in the connector profile.

 

7. Automated cosmetic inspection for inclusions, surface debris, scratches, dents and dints ensures that the lithium-ion cells are checked prior to becoming an EV battery.

 

8. Code reading. Codes on the battery modules need to be read for traceability and to track each element through the production process.

 

9. Final assembly verification. The final battery pack is checked for completeness to specification, all necessary assembly parts are available and verification of optical character recognition of codes for full traceability.

 

TELEDYNE DALSA and INSPECTION:

Quality Assurance for Lithium-ion Battery Production While lithium-ion battery production may be conceptually simple with coated electrode stacked sheets and an electrolyte solvent, the actual process is fairly complicated and sensitive. The thickness of the coatings on the electrodes can have a significant effect on a battery’s performance or even its stability. Line scan cameras powered with machine learning algorithms can help automate and streamline the quality assurance stage of lithium-ion battery manufacturing. A line scan camera is a camera that can be mounted on a factory production line to monitor the production of materials as they are moved through the manufacturing process. Line scan cameras are well-suited to inspection of electrode sheets, since the sheets are run at high speeds from big spools through the coating and stacking process. Laser profiling from inspection cameras can cover the whole manufacturing process of lithium-ion batteries. The cameras can measure the thickness of the electrode sheets and coating, look for surface defects on the sheets such as dents, scratches or bent edges, measure the dimensions of the battery casing for cylindrical or pouch batteries, and monitor the quality of the weld of the external terminal on the batteries.

The main challenges in many of the electrode inspection tasks is the speed of the

process and the need to identify ever smaller defects. The camera must be able to keep up with the production speed of the machines and therefore have a high line rate while providing enough sensitivity to allow the use of short exposure times and have enough pixels to cover as wide a field of view (FOV) as possible. Linea 8K and 16K line scan cameras with Camera Link interface are a popular choice in that industry. For slower lines and processes our Linea GigE cameras dominate, but also Linea 4K and Genie Nano 2MP area scan cameras are used for various inspection tasks during the production of lithium-ion batteries.

 

In addition to the various inspection tasks associated with the electrode manufacturing process, such as post-coating, post-calendaring and post-slitting and -separation inspection, other machine vision solutions can contribute to economic processes, e. g. laminating, winding, housing insertion and welding, sealing, grading and finally packaging processes. With a broad portfolio of machine vision components including the necessary frame grabbers, interfaces and software solutions, Teledyne Dalsa is well equipped to enable powerful inspection solutions for lithium-ion battery production.

 

Teledyne DALSA has introduced AxCIS – a fully integrated line scan imaging module which combines sensors, lenses, and lights all-in-one. This Contact Image Sensor (CIS) is easy-to-use and offers a lower system cost for many demanding machine vision applications as well as superior signal-to-noise ratio and a Camera Link HS SFP+ fiberoptic interface. AxCIS can fit anywhere in your system, even with limited vertical clearance and it’s easy to install, with no complex alignment or calibration required and a single 24v power supply.

 

We Online Solutions (Imaging) Pvt. Ltd., Chennai India can provide suitable solutions through components like Cameras and Frame grabbers  from Teledyne DALSA, Lenses from Schneider-Kreuznach  and Filters from Midopt towards the EV battery Inspection.

 

 

Note: Above Blog is written with contents taken from different web sites of manufacturers, Magazines, Research papers that are open to public. Any content found objectionable, wrong info or not to be used by us – can be informed to us at [email protected] and we can correct or remove the content based on the genuineness of the mail received.