The Importance of Contaminant-free EV Battery Cell Manufacturing
As global demand for Electric Vehicles (EVs) continues its steep upward trajectory, more attention is turning towards the challenges of expanding regional EV battery supply in order to meet future needs.
Battery performance, reliability and safety plays a critical role in the success of any EV – without its beating heart, no matter how good its design – the vehicle is just an inanimate object. And yet, the performance, or in some cases catastrophic failure of its battery, can literally make or break the success of a vehicle and the car manufacturer’s reputation as they transition more heavily into this sector. To add to this, the huge demand from EV manufacturers is placing unprecedented pressures on suppliers to keep apace, adding further to the pressure for optimising battery production output and minimising waste. Within the complexities of cell manufacturing, be that based on lithium-ion or hydrogen fuel-cell technology, there are many processes where either static or contamination can build-up resulting in wide-reaching detrimental effects on the battery’s performance and safety, not to mention, profitability and market success.
To produce lithium-ion batteries, a number of common process stages are required. If, however, there are any stages where even a trace amount of particulate or ionic contamination becomes embedded into the internal layers of the battery, it can damage the separator film. This poses a serious and significant threat to both production output and battery performance. And, given the complexities of battery manufacture, there are many areas throughout production, where contamination can occur through electro-static attraction.
Neglecting the consequences of static charges and surface contamination during manufacturing can result in a number of serious risks. These range from poor performance, material defects and product recalls to overheating, spontaneous ignition and even explosion with cataclysmic consequences for the manufacturers and consumers. In fact, nearly all cases of EV fires have been linked to the malfunction of their lithium-ion batteries.
Causes and consequences
With high quality, high value and sensitive materials being used in the latest high-performance cell designs, the manufacturing environment is vitally important and must therefore be very carefully controlled to avoid contamination issues. Contaminants can range from metallic and non-metallic particulates as well as water or organic substances, which can reduce critical tolerances in coating processes causing reduced charge density, or damage the separator film resulting in shortages in the circuitry as well as poor wetting of the electrolyte.
Coating roller cleaning
A further contamination risk area in the coating process is the roller itself. Essentially this roller provides an accurate position of the web to maintain a high tolerance coating layer. Contamination on the roller can therefore compromise the accuracy of the coating.
Pre-calendering
Calendering is the common compaction process for lithium-ion battery electrodes. It has a substantial effect on porosity and coating density, poor structure and therefore performance. During pre-calendering, the web and coating layers are compressed together to form the exact required thickness. Cleaning the web prior to this critical phase prevents loose particulates from the drying process being encapsulated into the surface, resulting in coating layer intolerance.
Post slitting
The slitting process can create significant volumes of debris of varying sizes from base and coating materials as well as toxic dust, presenting high contamination risks. Cleaning is therefore imperative to avoid the potential for future electrical shortages and expensive rejects. The use of a web cleaner at this stage ensures particles are removed and filtered from the operating environment, to avoid re-contamination.
Depending on the process and materials, contamination can be bonded or un-bonded requiring careful analysis to select between contact or non-contact cleaning solutions.
Meech’s non-contact system, CyClean-R, incorporates advanced computational fluid dynamics that allow converters to thoroughly clean low-tension webs. Ideal for use in a wide variety of applications, including narrow, mid and wide web, CyClean-R is available as a single-sided and double-sided web cleaner. From its position on the web roller, it delivers optimal, consistent removal of dry, unbonded contamination from any web material (particle removal to 0.5 micron is achievable).
Alternatively RoClean-C is the latest contact web cleaner from Meech that combines dynamic air flow and rotating brush technology. The battery web passes through an ionisation cloud on entrance and exit, while the brushes rotates in the opposite direction to the web for thorough disruption of any challenging contamination particles. Contaminants are drawn into the vacuum chamber. The positive air flow not only disrupts contamination on the web, it also ensures that any contamination left on the brush is also moved to vacuum chamber.
Post cutting/stamping/laser cutting of electrodes
Similar to the post-slitting stage, during electrode cutting, large amounts of particles and debris can contaminate the battery components. To minimise this, cleaning the surface of the substrate will help prevent contaminant build-up and ensure there are no electrical shortage risks.
Cleaning & static control on the separator film
The separator film is extremely sensitive to electrostatic charges created by friction, winding and unwinding throughout the transfer process. Static charges generated on insulative materials such as the separator film attract ambient charged particles adding further to contamination risk problems. More significantly, charges generated can be high and if not carefully controlled, can lead to small sparks, which in turn results in small dendritic burns in the material. While not immediately obvious, these can lead to a loss of insulative properties and create shortages in the battery cell itself. In soak tests or in final vehicle use, these show up as a loss of capacity or even over-heating problems when later installed in a vehicle.
Throughout the separator film transfer process, ionisation bars should be located close to the film where charges can be carefully monitored and managed. To maximise static control and elimination, active ionisers can be tuned to match the material and application to ensure rapid decay times and minimal residual charges, coupled with voltage sensors to respond to varying application speeds or distances. For ultimate protection, the performance of the ionisers and sensors can be monitored in real time, so there is no loss of control on this critical material.
Meech’s Hyperion pulsed DC ionising bars – the 971IPS, 960IPS, 929IPS, and 924IPS provide short, medium and long-distance static elimination respectively, and can be installed quickly and easily onto converter’s lines.
Additionally, Meech’s SmartControl Touch harnesses the power of Industry 4.0 within scaled up battery manufacturing applications by connecting multiple ionisation bars and sensors for advanced monitoring and control. This system offers improved productivity, quality and safety assurance.
Conclusion
With the demand of EVs set to dominate the future of the automotive industry over the next few decades, it is now more important than ever that those in the industry engage and collaborate with the right specialised partners in areas of strategic importance to maximise production efficiencies, maintain competitive advantage and secure ongoing client/customer relationships. This article has identified the potentially catastrophic safety, performance and cost implications of particulate and ionic contamination in EV battery manufacturing. As a result, partnering with specialists in static elimination and both web cleaning and surface contaminant removal is vital to maintaining an optimum manufacturing environment for high yield, high performance output at lowest cost.
Donald Lewis, Business Development Manager, Meech Static Eliminators.
