Cologne, February 2021 – Vacuum technology is relevant to the quality and safety ofvarious stages in the production of lithium-ion batteries. The vacuum specialists atLeybold have been supporting manufacturers of lithium-ion batteries in their processesand technological challenges for many years and, as such, have been heavily involved inthe development of electric mobility.
Helping shape developments
Electric mobility is the latest trend in a very dynamic market environment. "From the perspectiveof vacuum technology, we have been closely monitoring this evolution for many years," says Dr.Sina Forster, Business Development Manager at Leybold GmbH. “Having an opportunity to helpshape current developments and research is incredibly exciting,” she adds.
In her opinion, one of the main tasks is to determine new vacuum applications and markets fromnew technologies and developments as early as possible. The strategic role of vacuumtechnology is therefore to enable and advance these developments. For example, the design ofthe vacuum environment is a factor that can have a positive influence on processes. Vacuum isoften used during the electrolyte filling stage to ensure that the cell is evenly saturated with theelectrolyte and to lend purity to the filling process.
Lithium-ion batteries as a vacuum application
Leybold studied developments in this area and identified opportunities for vacuum application inthe manufacturing process of lithium-ion batteries. Because there was initially little informationavailable regarding the manufacturing process of lithium-ion components, the company joinedforces with Verband Deutscher Maschinen und Anlagenbau (VDMA) and the Chair ofProduction Engineering of E-Mobility Components at RWTH Aachen University in order toestablish a manufacturing process. In addition to lithium-ion batteries, Leybold has also beenfocusing on developments in fuel cells. Applicable vacuum processes are already emerging,including the coating of the bipolar plates under vacuum. Here, it’s important to observe thetechnological developments over the next few years and, if necessary, to provide supportthrough cooperation.
Vacuum technology is used in various process steps in electrode manufacture as well as inresearch and development. As such, Leybold works closely with machine and plantmanufacturers who supply battery manufacturers with production plants. Additionally, Leyboldcooperates with battery manufacturers as well as with institutions that conduct research tofurther develop battery technologies.
Development increasing in Europe
The majority of production continues to take place in Asia. However, much of the research anddevelopment is shifting to Europe, making the EU (and especially Germany) more important asa research and production location.
Vacuum technology is used in battery cell production as well as in processes such as theapplication of active materials to electrodes. "In general, air is a disturbing factor in manyproduction environments because the millions of particles and gas molecules have a negativeinfluence on this production step, sometimes even making it impossible. When mixing the slurry,particles and air bubbles must be avoided in order to achieve a high-quality product. Mostmixers, therefore, work under vacuum," explains Dr. Sina Forster.
Vacuum improves processes
Vacuum is also essential during the drying stage to remove even the smallest remainingamounts of solvents and moisture. Without vacuum, the drying process would need to becarried out at much higher temperatures and would last much longer. This would have anegative effect on the electrode quality. As soon as electrolytes are incorporated intosubsequent process steps, vacuum takes on a safety aspect, since many of the electrolytesused are highly reactive and inflammable. High-quality vacuum is essential here. On the onehand, it lends purity to the process so that no particles or moisture can enter the cell duringelectrolyte filling and degassing. On the other hand, it provides a low-reaction environmentwithout oxygen or humidity with which the electrolyte could react.
Vacuum technology is relevant to the quality and safety of various stages in the production of lithium-ion batteries.
"The greatest challenge always lies in the gas mixture being pumped. In principle, everythingthat's pumped and processed is also transported by the vacuum pump. In battery production,this affects the solvents and electrolytes which tend to be toxic and can damage the pumps andpossibly the pump oil," says Dr. Sina Forster. "But very warm ambient temperatures and highhumidity are, generally speaking, also circumstances that present us with challenges," sheadds. This is where battery manufacturers are called upon to help, either by ensuring the correctcooling of the pump or by using condensers.
High-quality drying results under vacuum
Opportunities for improvement exist in many areas, as there are still no established processesthat have proven to be efficient. Vacuum drying, for example, is a customer-specific process ofpressure, temperature and process gases (such as nitrogen). In order to achieve high-qualitydrying results through the aid of vacuum drying, industry-related research projects are alreadybeing conducted under the direction of the VDMA.
Leak detection also plays a central role in production from a safety perspective. The cell mustbe 100% leak-proof in order to ensure a long battery life. A valid leak test can only be performedvia a vacuum leak detection system. Even the smallest leaks can be detected with the aid of ahelium leak detector or mass spectrometer. On the other hand, undetected leaks greatly shortenthe battery's service life and/or lead to highly-reactive electrolytes escaping.
Some components of lithium-ion batteries that are treated in a vacuum are toxic. In order toprotect the environment and the vacuum technology from pollutants, the vacuum pump musthave the ability to withstand these gases. Additionally, the toxic materials must be confinedwithin the process and discharged in a correspondingly safe manner.
Dry pumps save time and money
For these toxic gases, dry-running vacuum pumps are used. Oil-sealed vacuum pumps tend tobe unsuitable for these applications, as the pump oil could be damaged or contaminated by thegases. Using dry-compressing pumps, battery manufacturers save time and money since theywould otherwise need to change the pump oil frequently. “ Oil-sealed vacuum pumps haveincreasingly been used in the process of electrolyte filling and degassing, which we are nowreplacing with dry-running vacuum pumps for many of our customers," summarizes Dr. Sina Forster.
Using dry-compressing pumps like Varodry, battery manufacturers save time and money since they would otherwise need to change the pump oil frequently.
In order to ensure sufficient process reliability when handling toxic gases, hermetically-sealedpumps are used, which prevent even the smallest quantities of gas from escaping. This is animportant factor, especially in the case of toxic electrolytes, where occupational safety is alsoimportant.
Faster and more reliable with vacuum technology
Vacuum technology thus plays an important role in drying, electrolyte filling and degassing."Vacuum is essential in all three process steps," underscores Dr. Sina Forster. But upstreamprocess steps, such as mixing with vacuum mixers, stacking with vacuum grippers anddownstream process steps, such as packaging, are also handled more quickly and reliably withvacuum technology.
In the future, the influence of a pure vacuum environment and specifications can be even betterdetermined. With the development of individually-marked electrode sheets which can be tracedthrough the entire production process using lasered QR codes, the influence of individualprocess parameters on battery quality can be accurately traced.
Vacuum ensures the handling of toxic electrolytes
Vacuum technology also plays an important role in terms of safety during battery production and use. For example, the safe handling of toxic electrolytes in the future will continue to be possible only under vacuum conditions. Driving electric cars, we trust in the quality of the battery, which can best be tested and guaranteed under vacuum.
It must be said, however, that processes under vacuum always require more energy than thoseunder atmospheric pressure. However, enormous progress has been made here in recent yearstowards energy-efficient pumps, and today we use highly-economical vacuum pumps in batteryproduction. "This means that we can now dedicate ourselves to the core questions: How can weachieve more throughput, safety and quality in battery production by efficiently designingvacuum systems? And here, too, we'll be making many important advances in the field ofvacuum technology in the coming years," Dr. Sina Forster concludes.
