The pros and cons of a modular Li-On battery design

Despite a slight slowing of Battery Electric Vehicles (BEVs) uptake in 2024, by year end, BEVs are still expected to account for more than 736 GWh of global light vehicle battery requirements, equating to 911 GWh. According to analysts at GlobalData, this growth is part of a broader forecast predicting that light vehicle hybrid and EV battery use will rise to over 2,900 GWh annually by 2031, a 9-fold increase from 2021.

When it comes to batteries, modular designs typically have higher costs and mass compared to CTP or CTC designs and can limit customisation due to the defined space requirements of the modular boxes. However, despite these drawbacks, modular Li-ion battery designs offer significant advantages in terms of thermal runaway containment, serviceability and scalability, making them ideal for various applications. Modular battery packs also facilitate mechanical separation, making it easier to recycle or repurpose battery components, a growing trend in the industry.

Thermal Runaway in BEV: A Guide to its Prevention

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Advantages of modular battery pack designs

John Albaugh is Market Development Manager for Electric Vehicles at Elkem Silicones, one of the world’s leading silicone manufacturers. Elkem supplies battery materials and silicone solutions for battery packs. According to Albaugh, there are four primary benefits associated with the design of a modular battery pack.

1. Thermal runaway containment

Albaugh explains that a modular design allows for electrical and physical isolation of individual modules or groups of cells, reducing the risk of short circuits. This compartmentalisation helps to contain thermal runaway events within a single module, preventing propagation to the entire battery pack. Further, modular designs are considered more robust, with improved mechanical integrity, reliability and longevity. The modular approach can provide better protection against impacts, vibrations, and other environmental stresses. For instance, in a collision, piercing or breakage of one compartment would not automatically spread to the next.

Albaugh adds: “In a modular design, you use thermal protection materials between the modules – with battery foam and potting [material] between the cells…materials underneath the lid of the module and sheets of materials between the modules.”

2. Serviceability

Modularity enables easier servicing and maintenance, as individual modules or cells can be repaired or replaced as needed. This improves the overall serviceability and longevity of the battery pack. Additionally, the modular approach enables battery swapping, which is a business model adopted by some OEMs.

“For some OEMs, battery swapping is part of their business model,” says Albaugh. “You drive in like you’re going to get an oil change, but it’s the battery.”

The modular design also enables easier servicing and maintenance for stationary energy storage applications, such as backup power or grid-scale storage. Albaugh emphasises that the serviceability advantages of the modular design are a key benefit, as it allows for more targeted and cost-effective maintenance and repair, extending the useful life of the battery pack.

3. Recyclability and reuse

The modular design facilitates the mechanical separation of materials, making it easier to recycle or repurpose the battery components. Spent modules can be reused in other applications, such as energy storage systems, extending the overall lifecycle of the battery materials.

Albaugh contrasts this with the difficulty of separating materials in designs that use adhesives like polyurethanes: “Their adhesive strengths are so high that you can’t separate them effectively. So, you’re left with using a shredder and then melting them down and reclaiming the ore. As for the polyurethanes, they use isocyanates for raw materials. Those raw materials, before crosslinking, are toxic, and there’s special disposal guidelines.”

Albaugh highlights that silicone-based materials are easier to mechanically separate and have a safer chemical composition, making them more suitable for recycling.

As EV batteries start to flood the market, there will be a need to establish a value chain and market for used battery packs. This will incentivise the upfront design considerations for recyclability and reuse, says Albaugh. If the battery modules have proper fire protection materials integrated, they can be more easily reused in other applications. Otherwise, the modules may need to be reworked or upgraded before being repurposed.

 4. Scalability and flexibility

Modular designs allow for easier scaling of battery capacity. Manufacturers can adjust the number of modules to meet specific energy needs, which is particularly beneficial in electric vehicle applications where energy requirements can vary significantly. This flexibility also enables the battery pack to be customised for different vehicle or application requirements.

Albaugh adds that modular designs can also optimise performance characteristics such as energy density and charging speed.

Challenges for modular battery pack designs

However, modular designs provide certain complications. For example:

Increased costs

The initial development and manufacturing costs of modular battery systems may be higher due to the need for additional components and more sophisticated designs, says Albaugh. Further, the integration of advanced materials and safety features may also drive-up costs, making it an important consideration for manufacturers. While modular designs offer flexibility, they can also introduce complexity into the overall battery management system (BMS). The need to manage multiple modules and ensure proper communication between them can complicate the design and increase the chance of failure if not executed correctly.

Mass

Modular designs typically require more materials, resulting in increased weight compared to CTP or CTC designs. Further, the defined space requirements of the modular boxes can limit the degree of customisation possible, as the modules need to fit within the available space. “There’s a compromise,” notes Albaugh.

How can silicones help?

For Elkem, using silicones is part of the solution to reducing this extra weight, while utilising the unique chemistry of the material. Silicone has been used in manufacturing for over 70 years, often due to its high thermal stability and fire-retardant properties.

“If we talk about specifics, like Elkem’s RTF 3250 [Room Temperature Foam], it’s lightweight, safe and easy to use,” explains Albaugh. “The foam is filled with hollow glass microspheres, which makes the material density less than one gram per cubic centimetre. The raw materials are safe. Basically, when you burn it, it’s fire mitigating. RTF 3250 is also a lightweight filler, so there’s no change in volume as the material cures (and no pressure placed on the components). From this standpoint, it’s easier to use.

“However, because the balloons are glass, they tend to float to the surface, and if left too long would separate. So, we fine-tune the cure chemistry so it can cure at room temperature quickly. If you’re trying to fill very small, less than 1mm spaces, in the nooks and crannies between batteries, it’s much easier to use than a traditional foam.”

Overall, Albaugh says he believes modular battery designs are a developing trend that could see greater uptake and scalability, especially as an emphasis on improving battery component recycling and reuse is likely to emerge in the future. With their inherent fire protection and safety features, Albaugh predicts that modular battery designs will become more widely accepted and valued in the industry. “Nobody questions the value of the seat belt or the airbag,” he says.

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