Why Do Prismatic Batteries Adopt Mylar Film Instead of Alternative Materials?
Mylar film serves as an irreplaceable solution for insulating and protecting jelly rolls inside prismatic batteries. This article analyzes its core strengths including insulation and anti-corrosion performance (preventing lithium intercalation into aluminum shells), a low thermal shrinkage rate of only 0.5%, puncture resistance against electrode burrs, and great compatibility with automatic wrapping processes.
1. Insulation Protection and Anti-Corrosion (Core Function)
Insulation Performance
Boasting excellent electrical insulation, Mylar film effectively separates the negative electrode jelly roll from the metal aluminum shell. It blocks direct contact between the two components, thus avoiding electrochemical corrosion. Without this barrier, lithium ions would intercalate into the aluminum shell to form aluminum-lithium alloys, further triggering electrolyte leakage or internal short circuits.
2. Mechanical Strength and Thermal Stability
High Temperature Resistance
Mylar film features an ultra-low shrinkage rate under high-temperature conditions (e.g., heat generated during battery charging and discharging), vastly outperforming polyolefin separators. PE and PP separators tend to shrink severely above 100°C, while Mylar film withstands internal thermal stress inside the cell and prevents short circuits caused by separator melting during thermal runaway.
Puncture Resistance
With outstanding toughness, Mylar film resists punctures from electrode burrs and mechanical scratches generated during manufacturing, significantly lowering the risk of internal short circuits.
3. Process Compatibility and Cost Efficiency
Flexible Processing
Mylar film can tightly wrap jelly rolls via thermal welding or adhesive lamination, fully compatible with mass automatic production equipment such as automatic wrapping machines.
Controllable Costs
PET Mylar film costs less than special composite materials (e.g., ceramic fiber insulation brackets). Unlike bottom plastic bracket designs, it also eliminates the need for complex structural development.
4. Comparative Drawbacks of Alternative Materials
Polyolefin Separators (PE/PP): Low-cost yet inadequate in insulation and thermal stability, incapable of independently fulfilling shell insulation requirements.
Insulating Adhesive Tapes: Partial pasting cannot achieve full wrapping; tape edges tend to lift off, resulting in insulation failure.
Ceramic-Coated Separators: Designed only to boost the heat resistance of separators themselves, unable to replace Mylar film for shell insulation.
5. Quality Control and Safety Assurance
Automated Inspection
CCD visual inspection systems enable real-time monitoring of Mylar film dimensions and thermal welding positions, with a dimensional tolerance of ±1 mm for welded areas to guarantee uniform wrapping quality.
6. Conclusion
Mylar film stands out as the optimal all-round material for prismatic batteries with balanced advantages in insulation protection, thermal stability, mechanical robustness and cost efficiency. It is irreplaceable for preventing aluminum shell corrosion and securing battery safety. All alternative materials fail to meet the stringent insulation requirements between jelly rolls and aluminum shells for prismatic cells, restricted by functional limitations, high costs or poor process adaptability.
