Overcoming Challenges in Prismatic Battery Assembly and Testing

14 Jul.,2025

 

Overcoming Challenges in Prismatic Battery Assembly and Testing

As battery manufacturing grows, companies are working to improve the many formats in which we need electricity to be stored. For example, charging electric vehicles (EVs) faster, helping battery energy storage systems (BESS) last longer, and making portable devices more reliable. One of the form factors for batteries in this solution set is prismatic cells. These robust powerhouses are changing the way battery manufacturers think about energy storage and consumption. But why are prismatic cells becoming the go-to choice for large battery applications?  

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Characterized by their flat, rectangular shape and rigid casing, prismatic cells provide high energy density and power output. Unlike cylindrical cells, which are small and round, and pouch cells, which have a flexible, flat design, prismatic cells offer durability and efficiency due to their rigid casing.  

Prismatic batteries are ideal for high-demand applications such as EVs and energy storage systems. Their larger size and higher energy capacity make them well-suited for products requiring substantial power.  

Challenges of Prismatic Battery Assembly 

Prismatic battery assembly comes with several challenges, including:

  • Manufacturing Complexity: Due to the precision required to assemble a prismatic battery electrode layer, it can be more complex and costly than assembling other cell types.
  • Swelling Problems: Like pouch cells, prismatic cells swell over time. If manufacturers don’t take proper countermeasures with compression, swelling can lead to the deterioration of the battery’s structural integrity.
  • Energy Density Limitations: While the rigid casing of prismatic cells provides structural integrity, it can lead to greater density loss compared to other form factors.

Prismatic batteries are a compelling choice for applications that need to optimize efficiency and space. Still, due to their rectangular shape, manufacturing companies must carefully engineer and test prismatic cells to maximize their advantages, as module misalignment can lead to defects and a loss in efficiency. 

The Prismatic Battery Assembly and Testing Process 

Incoming Cell Validation

It’s crucial to ensure battery cells’ quality and reliability before they are assembled into modules or packs. Skipping or rushing through the testing process can lead to downstream challenges and safety issues with the product, including thermal runaway events. Incoming cell validation for prismatic cells involves a series of thorough tests to verify the cells’ electrical and physical properties.  

Key tests include:  

  • Open Circuit Voltage (OCV) 
  • AC/DC Internal Resistance (IR) 
  • Electrochemical Impedance Spectroscopy (EIS) 
  • Cell Self Discharge 
  • Isolation Voltage

Based on these tests, cells are sorted and categorized, ensuring that only the highest quality cells proceed to assembly. 

Electrical Array Formation  

The electrical array formation process for prismatic cell assembly involves several critical steps to ensure the module’s performance and mitigate swelling, which can occur from a buildup of heat or gas. Initially, cells are built up into an electrical array using busbars, which connect them and form the module. This step helps achieve the desired voltage and amperage needed for the prismatic module. A cooling plate manages the heat generated during operation, and the dispensed thermal interface material (TIM) ensures efficient heat transfer. 

Final Assembly & Testing 

With the cooling plate in place, the entire assembly undergoes rigorous validation tests to confirm the integrity of the electrical connections and overall performance of the prismatic battery. These tests include DC internal resistance (DCIR) and high potential (Hi-Pot) tests, which verify the electrical performance and safety of the cells. 

Testing is often found in the latter stages of prismatic module assembly. Modules are made into a battery pack by stacking them in series or parallel based on the manufacturer’s desired voltage, capacity, or power density. The final pack then undergoes end-of-line tests to ensure the battery fulfills the manufacturer’s specifications. 

The Future of Prismatic Batteries: Cells to Packs 

In some battery lines, manufacturers may merge the module and pack steps to save time, reduce weight, and optimize costs. Prismatic cells are particularly advantageous for cell-to-pack (CTP) applications due to their rectangular shape and rigid casing.  

The design lets manufacturers bypass the traditional module assembly step, directly integrating the cells into a battery pack. By eliminating the need for modules, CTP reduces the number of components, simplifies assembly steps, and enhances the battery pack’s overall energy density. This approach not only optimizes space, but also improves thermal management, contributing to the final product’s reliability. 

Building Prismatic Battery Assembly & Testing Lines 

Prismatic cells represent a significant advancement in battery technology, offering a unique combination of high energy density, durability, and efficient space utilization. Their rigid, rectangular design makes them ideal for high-demand applications such as EVs and BESS. Despite production challenges, including meticulous alignment in module assembly and the risk of swelling, an experienced battery assembly and testing partner can guide manufacturers through each step of the process.  

Battery Assembly Machines Selection Guide: Types, Features ...

Types of Battery Assembly Machines

1. Cell Assembly Machines

Cell assembly machines are designed to assemble individual battery cells. They handle tasks such as stacking electrode layers, inserting separators, and sealing the cell. These machines are crucial in the production of lithium-ion batteries, where precision is essential to ensure the cells' performance and safety.

2. Module Assembly Machines

Lithium battery module assembly machines focus on the assembly of battery modules, which are groups of cells connected in series or parallel. These machines often involve processes like welding, gluing, and stacking to create the desired configuration. Module assembly is a critical step in constructing battery packs for various applications.

3. Pack Assembly Machines

Pack assembly machines are responsible for the final assembly of battery packs. These machines integrate the modules into a complete battery pack, including the necessary wiring, thermal management components, and enclosure. The efficiency and accuracy of lithium battery pack assembly machines directly impact the overall quality and performance of the battery pack.

Li-ion Battery Production Process

1. Mixing

Active materials, conductive auxiliary agents, polymer binders, and organic solvents are mixed together to form an electrode slurry.

2 .Coating, Drying, and Calendering

The electrode slurry is coated to copper and aluminum foil, dried, and calendared.

3. Slitting

The electrode sheets are slit to each battery size.

4. Winding or Stacking

A separator is inserted between the anode and cathode electrode sheets, and the electrode sheets are wound or stacked together.

5. Tab Welding

The tabs of the layered electrode sheets are welded together, and collectors are welded to the tabs.

6. Terminal Welding

The covers and collectors are welded together.

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7. Assembly

8. Case Closing

The covers and cases are welded together.

9. Before Filling

10. Electroyte Filling

Electrolyte is filled via the electrolyte port.

11. After Filling

The electrolyte port is closed.

12. Pre-charging

Following electrolyte fill, a charging current is fed to the cells for the first time.

13. Charging and Discharging

The cells are repeatedly charged and discharged.

14. Aging

The cells are stored for a certain period of time.

15. Pre-shipment inspection

Quality is tested prior to shipment.

Product-Specific Machine Types

Battery assembly machines come in various types, each designed for specific battery products. These include machines tailored for alkaline, nickel-metal hydride (NiMH), and nickel-cadmium (NiCad) batteries. Additionally, there are specialized machines for lithium-ion, lead-acid, and zinc air cells.

1. Alkaline Batteries:

   - Alkaline batteries are widely used and employ a reaction between zinc and manganese dioxide to generate power. They are the predominant type of batteries manufactured in the US.

2. Nickel-Metal Hydride (NiMH) Batteries:

   - NiMH batteries are rechargeable and utilize a hydrogen-absorbing alloy for the negative electrode. Compared to nickel-cadmium batteries, they have similar energy density (by volume) but tend to exhibit higher self-discharge.

3. Nickel-Cadmium (NiCad) Batteries:

   - NiCad batteries are rechargeable and use nickel oxide hydroxide and metallic cadmium as electrodes. They are available in sealed or vented types.

4. Lithium-Ion Batteries:

   - Lithium-ion batteries are rechargeable and employ lithium as the migrating ion during discharge and charging. They are commonly found in consumer electronics, especially portable devices.

5. Lead-Acid Batteries:

   - Lead-acid batteries, the oldest rechargeable type, have relatively low energy density but maintain a high power-to-weight ratio. They are frequently used as car batteries and to power smaller electric motors.

6. Zinc Air Batteries and Cells:

   - Zinc air batteries operate by oxidizing zinc with oxygen from the air. They offer high energy densities and are cost-effective to produce. Applications range from hearing aids to electric cars, depending on size requirements.

These specialized battery assembly machines cater to the distinct manufacturing processes and components associated with each type of battery.

Function-Specific Machine Types

Some specific machines associated with battery assemblers are cell winders and tab welders.

- Cell winders are capable of winding round or prismatic cells 3-12 parts per minute. It is flexible enough to handle up to 5 tabs per cell at varied distances. Tension controls, web speeds, separator cut lengths, and pack roller pressure are adjustable to optimize cell design parameters.

- Tab welders serve the purpose of attaching tabs to cells. In their automatic configurations, these machines are capable of affixing multiple tabs to each cell at varying distances. This design allows for the utilization of thinner substrates, creating additional space within the cell for active materials. The equipment typically features adjustable parameters such as tension controls, the number and placement of tabs, and web speeds, offering flexibility for optimization in the manufacturing process.

Applications

Battery assembly machines are used to create batteries in the aerospace, automotive, consumer electronics, and medical technology industries, among others

Conclusion

In conclusion, selecting the right battery assembly machines is a critical decision for industries involved in battery manufacturing. Understanding the types, features, and applications of these machines is essential for making informed choices that align with production goals and industry requirements.

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