At Zephware Technologies, we specialize in advanced lithium-ion energy systems, including LFP prismatic cell compression — a key factor that ensures safety, long cycle life, and consistent performance in modern battery packs.
While electrical design and BMS calibration often take center stage, the mechanical packaging of cells plays a silent but vital role in ensuring cycle life, safety, and performance consistency. In this post, we’ll explore why LFP prismatic cells need compression, what issues it solves, and how good mechanical design achieves it.
Why Do LFP Prismatic Cells Need Compression?
Unlike cylindrical cells (which are inherently self-contained), prismatic LFP cells use a stacked electrode structure sealed in an aluminium laminated pouch or soft aluminum can.
During charge and discharge cycles, the electrodes undergo slight expansion and contraction due to lithium-ion intercalation.
This causes:
- Swelling (thickness increase) of a few tenths of a millimeter per cell.
- Over hundreds of cycles, cumulative mechanical stress on seals.
- Potential loss of contact pressure between electrodes and current collectors.
Without proper compression, this gradual swelling leads to electrochemical and structural degradation — directly impacting performance.
Problems Solved by Proper Compression
1. Prevents Cell Swelling and Delamination
Compression restricts the natural tendency of LFP cells to swell during cycling, maintaining the internal stack pressure. This keeps the electrodes firmly in contact and ensures uniform current distribution, reducing internal resistance.
2. Maintains Contact Pressure and Conductivity
In soft-packed LFP cells, current collectors rely on intimate contact. Compression prevents micro-separation that could lead to localized heating and efficiency loss.
3. Improves Cycle Life and Capacity Retention
Controlled mechanical compression mitigates stress on internal layers, allowing the pack to maintain consistent thickness and capacity across thousands of charge-discharge cycles.
4. Prevents Gas Formation and Seal Fatigue
In poorly constrained packs, minor swelling can open micro-gaps at the seals, accelerating electrolyte decomposition and gas buildup.
Compression reduces this by maintaining constant clamping force across the stack.
5. Enhances Thermal Stability
Tight cell stacking ensures better thermal conduction between cells and the cooling interface — essential for stable operation under high load or temperature extremes.
Design Features for Compressing LFP Prismatic Packs
Different manufacturers use various clamping techniques depending on module size, cost, and serviceability.
Below are the most common and effective compression methods used for LFP prismatic cell modules:
1. Aluminium End Plates with Tie Rods and Nuts
A traditional and widely used method.
Two aluminium or stainless-steel end plates are placed on either side of the cell stack and compressed using threaded tie rods with torque-controlled nuts.
Use Case: Medium-to-large modules (100–300 Ah cells).
Advantages: Precise torque adjustment, high rigidity, easy disassembly.
2. Aluminium Plates with Metal Straps
Here, instead of tie rods, high-tensile steel or aluminium straps are wrapped around the pack and tensioned using a strap-tightening tool.
Use Case: Compact or space-constrained wall-mounted modules.
Advantages: Compact, no protruding rods, quick assembly for automated lines.
3. Bolted Side Frame Assembly
The cell stack is housed within a rectangular aluminium extrusion frame. End plates bolt directly to the frame, providing both structural rigidity and compression.
Use Case: Premium residential or EV modules where aesthetics matter.
Advantages: Clean industrial look, easy integration into larger enclosures.
4. Spring-Loaded or Elastic Compression System
Compression is applied using Belleville washers or wave springs between bolts and endplates.
This maintains consistent pressure even if cells expand or relax over time.
Use Case: High-performance energy storage or mobility applications.
Advantages: Self-adjusting, ideal for long cycle-life packs.
5. Integrated Extruded Aluminium Casing
In this approach, the cell stack slides into a precision-machined or extruded aluminium casing with internal ribs that apply uniform pressure.
Use Case: Modular industrial battery packs or sealed outdoor units.
Advantages: Simplified assembly, strong structural enclosure, excellent thermal conductivity.
Design Considerations at Zephware Technologies
At Zephware, our design process focuses on modularity, manufacturability, and reliability.
We validate each battery module under controlled compression load (typically 250–350 kgf) before assembly.
We would be also able to help in design and develop compression jig and frame designed to:
- Ensure uniform pressure across cell faces.
- Maintain long-term dimensional stability under thermal cycling.
- Support both LFP and NMC prismatic modules interchangeably.
This not only improves cell health but also simplifies after-sales service and scalability.
Conclusion
Compression isn’t just a mechanical afterthought — it’s an essential part of electrochemical stability in LFP prismatic battery packs.
By maintaining consistent pressure, a well-engineered pack avoids swelling, capacity fade, and seal failures — all while enhancing thermal performance and cycle life.
At Zephware Technologies, we integrate mechanical, electrical, and thermal design into a cohesive system — ensuring our LFP battery packs deliver durability, safety, and performance from day one.
Contact Us:
For advanced battery system design and consultation, visit https://zephware.com
Email us at karan@zephware.com
Linkedin: https://www.linkedin.com/company/zephware
