Flame Retardant Analysis and Recommendations for Battery Separator Coatings

Flame Retardant Analysis and Recommendations for Battery Separator Coatings

The customer produces battery separators, and the separator surface can be coated with a layer, typically alumina (Al₂O₃) with a small amount of binder. They now seek alternative flame retardants to replace alumina, with the following requirements:

• Effective flame retardancy at 140°C (e.g., decomposing to release inert gases).
• Electrochemical stability and compatibility with battery components.

Recommended Flame Retardants and Analysis

1. Phosphorus-Nitrogen Synergistic Flame Retardants (e.g., Modified Ammonium Polyphosphate (APP) + Melamine)

Mechanism:

• Acid source (APP) and gas source (melamine) synergize to release NH₃ and N₂, diluting oxygen and forming a char layer to block flames.
  Advantages:
• Phosphorus-nitrogen synergy can lower decomposition temperature (adjustable to ~140°C via nano-sizing or formulation).
• N₂ is an inert gas; NH₃ impact on electrolyte (LiPF₆) needs evaluation.
  Considerations:
• Verify APP stability in electrolytes (avoid hydrolysis into phosphoric acid and NH₃). Silica coating may improve stability.
• Electrochemical compatibility testing (e.g., cyclic voltammetry) is required.

2. Nitrogen-Based Flame Retardants (e.g., Azo Compound Systems)

Candidate: Azodicarbonamide (ADCA) with activators (e.g., ZnO).
Mechanism:

• Decomposition temperature adjustable to 140–150°C, releasing N₂ and CO₂.
  Advantages:
• N₂ is an ideal inert gas, harmless to batteries.
  Considerations:
• Control byproducts (e.g., CO, NH₃).
• Microencapsulation can precisely tune decomposition temperature.

3. Carbonate/Acid Thermal Reaction Systems (e.g., Microencapsulated NaHCO₃ + Acid Source)

Mechanism:

• Microcapsules rupture at 140°C, triggering a reaction between NaHCO₃ and organic acid (e.g., citric acid) to release CO₂.
  Advantages:
• CO₂ is inert and safe; reaction temperature is controllable.
  Considerations:
• Sodium ions may interfere with Li⁺ transport; consider lithium salts (e.g., LiHCO₃) or immobilizing Na⁺ in the coating.
• Optimize encapsulation for room-temperature stability.

Other Potential Options

• Metal-Organic Frameworks (MOFs): e.g., ZIF-8 decomposes at high temperatures to release gas; screen for MOFs with matching decomposition temperatures.
• Zirconium Phosphate (ZrP): Forms a barrier layer upon thermal decomposition, but may require nano-sizing to lower decomposition temperature.

Experimental Recommendations

1. Thermogravimetric Analysis (TGA): Determine decomposition temperature and gas release properties.
2. Electrochemical Testing: Assess impact on ionic conductivity, interfacial impedance, and cycling performance.
3. Flame Retardancy Testing: e.g., vertical burning test, thermal shrinkage measurement (at 140°C).

Conclusion

The modified phosphorus-nitrogen synergistic flame retardant (e.g., coated APP + melamine) is recommended first due to its balanced flame retardancy and tunable decomposition temperature. If NH₃ must be avoided, azo compound systems or microencapsulated CO₂-release systems are viable alternatives. A phased experimental validation is advised to ensure electrochemical stability and process feasibility.

Let me know if you’d like any refinements! Contact by email: lucy@taifeng-fr.com