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Challenges Designing and Manufacturing Lithium-Ion Battery Packs Q&A

Epec Engineered Technologies
Written by Epec Engineered Technologies
Posted on May 18, 2023 at 9:14 AM

At the conclusion of our webinar, Challenges Designing and Manufacturing Lithium-Ion Battery Packs, we had several questions submitted to our presenter, Randy Ibrahim, Battery Development Consultant at Epec. We have compiled these questions into a readable format on our blog.

Q&A From Our Live Battery Webinar

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Watch the Recording Below:

Free Ebook Download: Battery Pack Designs with Lithium-Ion Chemistries

Question: Can chemistries other than lithium-ion be used in custom batteries?

Answer: Oh, yeah, absolutely. We've actually done all. We can add fuel gauges to all chemistries. We have that capability. Also, custom electronics, you name it, anything to do with lithium-ion we can do basically, with all chemistries. Also, we can make them any size and shape. In fact, I think one of Epec's products, I wasn't involved with it, but I saw it when I was out at the manufacturing is actually using alkaline cells. You know, those D cells you see at the checkout line at your grocery store. We can weld all those up, and they totally encapsulated them to make them water-resistant. The sky's the limit. We can make anything custom if you have a special need, even that one-time use alkaline cell, we can absolutely do it.

Question: What are the most important factors to consider when choosing a lithium-ion battery cell custom battery pack?

Answer: First thing that comes to mind, we'll be looking at the energy density, because usually, people come to us for lithium-ion specifically and no other chemistries. Usually, it's a portable-type product. And with those, we look at energy density. And usually, customers are looking for something, a huge amount of energy in a very small package, and it's lightweight. And so, we look at those cells. But along with that, we would want to factor in what the discharge rates are. Because in the lithium-ion world, we have basically two cells out there called an energy cell and a power cell. You'll see the power cells in your drill batteries at Home Depot; those are all power cells. They can deliver a lot of current in a short amount of time, and the battery itself doesn't overheat internally. And that's because the structure of a power cell, they're usually lower energy density because they use up extra space in there to have conduits deliver extra current, and without voltage drops within the cell. Energy cells have a lot thinner, current delivery devices built into the cell, so they can pack more chemistry in. They actually run longer, but you can't draw a lot of energy out at a really fast rate.

And then cycle life is sometimes important. You know, maybe a lithium-ion phosphate cell would be considered a little heavier cell, but they can get in 2,000, 3,000 cycles off the cells versus maybe 500, 600 on others.

Obviously, all lithium-ion, we need to wrap paramount safety around it. Lithium-ion phosphate is less so. They're a little more robust in the safety realm. Also really important is temperature because with lithium, you know, in the old days, lithium was ruled out for, like, window blinds because it was too high in temperature. They're getting a little better now, so we can incorporate them in some of the higher-temperature types of applications.

Question: How can thermal management be incorporated into a custom lithium pack?

Answer: A lot of times, a larger enclosure is better because we can dissipate the heat better. We actually sometimes put heat spreaders in a pack if there's too much heat. A lot of times if you have a battery charger built into the battery, we have to pull the heat out. And so, sometimes we'll use a metalized heat spreader, and use a thinner enclosure to dissipate that heat, manage it a little bit better.

Another thing that comes to mind would be Tesla, which uses active cooling where every single cell, they have this liquid that goes around every single cell. I have in my lab 1/16th of a monolith pack. So, all the cells, they prevent thermal gradient, and they do all that by active cooling. They're not relying on the inner cells pulling out heat. And if you didn't use active cooling, those inner cells would get hotter in a Tesla. But since you have this nice, little cooling channel with liquid, the inner cells are the exact same temperatures as the outer cells, and they can preheat on a cold day. So, active cooling, and also active warming is pretty important.

And let's say that you don't have the money, you don't have the budget for this, and you can't sell the product. There again, you can control this thermal, you can manage the thermals by having these temperature sensors and having the product adjust its behavior, so it can get the temperatures under control, throttle back on that processor, and slow down the motor if possible. But sometimes the end product does have some flexibility. And so, the battery can scream out loud to the product, and prevent some of these temperature issues.

Question: What are the less common safety features that should be incorporated in a custom lithium battery?

Answer: I think second-tier, third-tier safeties, you know, a lot of times, they're there, but we don't really discuss them. One that does come to mind would be cell balancing. A lot of people think of that as more of a cycle life feature where if you can keep all the cells balanced. It's, kind of, like an ice cube tray. You fill it with water really quick and you, kind of, wiggle it around, so all the water is at the exact same level. Same thing with cell balancing. If you keep them all balanced, you can get a lot more cycles out of your pack. But a really nice side benefit is, if you incorporate cell balancing, you don't ever let one cell get really, really low, or one really, really high, so they're out of sync with all the other cells. Because if you have that, one, your safety circuits will kick in, the low-side and high-side. The perception to the end user would be, "Wow, O.K., this pack is not good, I'll only get 50% runtime," because you're hitting these limits.

But the other thing is, let's say something goes wrong with maybe some of your safety circuits, also now these cells constantly excursion to low-side all the time or high-side all the time. That can also have an impact on dendrite growth within the pack, it could be causing some issues with the pack that could affect the separating material, and that could ultimately cause internal shots. So, cell balancing could be considered a safety feature if you stretch it a little bit.

A couple of other things: we encapsulate some batteries. Some really cool stuff on the Epec website that talks about encapsulation, and potting materials, and what have you. One safety feature that's pretty important to put in those types of products will be gas release. All these cells have little ways, but they do vent. They're very controlled. They usually have, like, perforated metal little star patterns. So, instead of just blowing up randomly off the side, it's usually on the top cap [SP], and there'll be a little relief, pressure relief. A lot of cells have it.

And it's important when a cell does vent … that way, there's a nice little channel for gas to leave the pack, even though it's encapsulated, but that's kind of cool stuff. A lot of these cells have built-in CIDs (Current Interrupt Device). So, the secondary protection webinar that I did in 2017 talks a little bit about CIDs. They have built-in safety and are lesser known. The only other thing I can think of is my original RV had a battery disconnect feature. Got old school with this little lever, right, disconnect that. I mean, that's a safety feature.

Other than that, maybe some flame-retardant materials, make sure all materials in your pack have high-temperature ratings. You don't propagate a flame if something were to happen, or they don't catch fire, just because they're a low temperature rated device installation, thermal barriers, fish paper, things like that, make sure those are all rated for high temperatures. That'd be safety features that are lesser known.

Question: How can a company ensure the quality of off-the-shelf batteries is up to their standards?

Answer: Obviously, you don't have any control over off-the-shelf batteries, but there are certain things within your control. I would personally define some sort of quality standard or requirement. I'd communicate, find out who this company is, and go visit them even if they're overseas. Define what your quality requirements and expectations are.

Work with only reputable manufacturers. The other thing is, and we actually did this with a power supply company, request documentation. And it's super-important to verify because they have the UL numbers, everything. We actually looked it up in the UL books, it didn't exist.

Sample. I would also get samples. We do that with a lot of different products. And just don't order it from them. Just make sure you get random samples and do it often. Even after you're purchasing from them, maybe you're down the road, get samples, verify that they still meet the standards that you're looking for, runtime, voltage, everything, whatever is important to you.

Question: Anyone who doesn't get a regulatory mark on a Lithium battery has way too much money. Guaranteed lawsuit if a fire happens.

Answer: I completely agree with you; you make a valid point. As a minimum compliance with UN38.3 transportation testing is required by law. However, regulatory marks and standards dealing with lithium batteries, as it helps ensure the safety of the products incorporating them, are not always required in the United States. Regulatory marks such as UL, CE, TÜV, and other recognized certifications indicate that the batteries have undergone rigorous testing and meet specific safety and performance criteria. I agree. Deep pockets may be needed if companies cut corners and don’t test their products even if in their situation it’s not required by law.

To enforce your point: neglecting to obtain regulatory marks or certifications can indeed lead to potential risks, including safety hazards and legal liabilities. In the event of a battery-related incident, failure to comply with regulatory requirements can significantly increase the likelihood of a lawsuit, especially if it is determined that negligence or non-compliance when required contributed to the incident.

I believe it is essential for manufacturers to prioritize safety and take the necessary steps to comply with relevant standards and regulations, as this helps protect end-users, mitigates risks, and builds trust in the market. Consulting with experts in battery safety, regulatory compliance, and product liability can provide valuable guidance in navigating these matters and avoiding potential legal issues.

Question: Most end-product standards require batteries to meet the appropriate standards.

Answer: Absolutely! When manufacturing products that incorporate batteries, it is essential to ensure compliance with the appropriate standards and regulations. Identifying the relevant regulatory standards specific to the type of product you are manufacturing is critical. These standards could include safety, performance, and environmental requirements for batteries. In the United States, for example, batteries are required to comply with and be tested to the UN38.3 standard which requires meeting UL 1642 for lithium-ion cells or UL 2054 for medical batteries. For batteries marketed globally, it's important to be aware of international standards as well. Examples of international standards for batteries include IEC 62133 for lithium-ion cells and IEC 61960 for nickel-metal hydride (NiMH) cells.

Question: Do you have any recommendations when looking for cells online for in-house manufacturing? Is it as straightforward as Google searching and finding ones that fit your requirements?

Answer: While a Google search can be a starting point, multiple sources should be used, including industry-specific websites, and forums. Working with industry professionals, attending trade shows, or seeking recommendations from trusted contacts can also help you find reliable suppliers and appropriate cells for your manufacturing needs.

Keep in mind that if you are considering the manufacturing of Li-Ion batteries in-house, your shipping department will need to be trained and certified in DOT hazardous shipping regulations to legally ship the product you produce.

When looking for cells online for in-house manufacturing, here are some pointers:

  1. Work with reputable suppliers or distributors that you currently use and trust and check it they have a source that they would trust that specialize in battery cells and have a track record of providing quality products. Established suppliers often have a wide range of options and can offer technical support and documentation.
  2. As mentioned in the presentation:
    • You need to develop battery specifications. Clearly define your requirements and specifications for the cells you need. Consider parameters such as voltage, capacity, energy density, cycle life, operating temperature range, size, weight, and safety features. Having a clear understanding of your requirements will help narrow down your search.
    • Ensure that the selected cells are compatible with your system or device. Consider factors such as mechanical fit, electrical connections, and the required charging and discharging protocols. Understanding the integration aspects will help you avoid any compatibility issues during the manufacturing process.
  3. Look for cells that meet recognized industry standards and certifications, such as ISO, UL, or IEC. These certifications indicate that the cells have undergone testing and meet specific safety and performance criteria. Additionally, check for any relevant product datasheets, technical specifications, or independent test reports provided by the supplier.
  4. Also, check for customer reviews or testimonials about the supplier and the specific cells you are considering. Feedback from other customers can provide insights into the quality, reliability, and performance of the cells and the supplier's services.
  5. Often overlooked are the shipping and logistics. Evaluate the supplier's shipping options, lead times, and any associated costs. If you have specific delivery requirements or time constraints, make sure the supplier can accommodate them.

Question: How do you determine the cycle life for a product roughly?

Answer: Determining the cycle life of a battery involves considering various factors and methodologies. Here's a high-level overview:

  1. Manufacturer Specifications: Start by checking the battery manufacturer's specifications. Many reputable manufacturers provide estimated cycle life values based on standardized testing protocols or empirical data. These specifications can serve as a rough guideline. Unfortunately, they are for low steady-state currents normally to make their cell look good.
  2. Accelerated Aging Tests: Cycle life can be estimated by conducting accelerated aging tests in controlled laboratory conditions. This involves subjecting the battery to repetitive charge and discharge cycles while monitoring its performance and capacity degradation. By tracking the degradation over time, you can estimate the number of cycles the battery can endure before reaching a specified capacity threshold (e.g., 80% of its original capacity). This approach can be costly.
  3. Past Data and Experience: Historical data and real-world experience with similar battery chemistries and applications can offer insights into cycle life. Industry research, technical papers, and case studies may provide valuable information and comparisons. This is less accurate but might meet your needs for a “rough” estimation.
  4. Battery Chemistry and Design: Different battery chemistries have varying inherent cycle life characteristics. Researching the specific chemistry of the battery in question and understanding its typical cycle life performance can provide a rough estimation. Additionally, the battery's design factors such as electrode materials, cell construction, and manufacturing quality can influence its cycle life.
  5. Operational Conditions: The battery's cycle life is drastically affected by factors like discharge rate, depth of discharge (DOD), charging protocols, operating and storage temperatures, and environmental conditions. Considering the specific operating conditions and how they align with the battery's design and specifications can help estimate its cycle life.

It's essential to note that rough estimations are not as accurate as actual testing. Conducting specific tests tailored to battery chemistry, application, and desired performance is the most reliable method for determining cycle life. These tests need to include the real-life discharge and charging profiles and the temperature extremes that the product will experience in the field. Testing products used outdoors can be much more involved than products used indoors mainly due to temperature variables.

Question: Do you see 18650 or 21700 as the future of cylindrical cell formats?

Answer: Both the 18650 and 21700 cylindrical cell formats have their advantages and are widely used in various applications. We specify both form factors depending on the application at hand. The 18650 format has been around for a long time and is commonly found in many consumer electronics devices, electric vehicles, and energy storage systems. It has an established manufacturing infrastructure and a well-developed supply chain.

The 21700 format on the other hand offers several advantages over the 18650, which is why Tesla has pushed for it. Firstly, it has a larger capacity and higher energy density, which translates to increased energy storage within the same form factor. This is particularly important for applications that require higher power and longer runtimes, such as electric vehicles and large-scale energy storage systems.

Additionally, the 21700 format typically exhibits lower internal resistance, allowing for improved power delivery and reduced heat generation during high-current applications. This can enhance the overall efficiency and thermal management of devices utilizing these batteries.

Also, the 21700 format has “gained traction” in the electric vehicle industry (pun intended), with major manufacturers adopting it for their vehicles. This industry support can drive further advancements and economies of scale, potentially “driving” costs down and increasing availability.

However, it's important to consider that the 18650 format still maintains a significant market presence due to its established infrastructure, widespread adoption, and compatibility with existing devices and systems. It remains a reliable choice for many applications. Whether one format will completely replace the other in the future is unlikely. Both formats have their merits and continue to coexist in the market. Factors such as technological advancements, cost considerations, industry preferences, and specific application requirements will play a role in determining their future.

As you know, battery technology is evolving rapidly, and one thing we know for certain is that new formats will emerge in the future, which could potentially surpass both the 18650 and 21700 formats in terms of performance, energy density, and safety.

Topics: Battery Packs

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