Formula Design for MCA and Aluminum Hypophosphite (AHP) in Separator Coating for Flame Retardancy

Formula Design for MCA and Aluminum Hypophosphite (AHP) in Separator Coating for Flame Retardancy

Based on the user’s specific requirements for flame-retardant separator coatings, the characteristics of Melamine Cyanurate (MCA) and Aluminum Hypophosphite (AHP) are analyzed as follows:

1. Compatibility with Slurry Systems

• MCA:
• Aqueous systems: Requires surface modification (e.g., silane coupling agents or surfactants) to improve dispersibility; otherwise, agglomeration may occur.
• NMP systems: May exhibit slight swelling in polar solvents (recommended: test swelling rate after 7-day immersion).
• AHP:
• Aqueous systems: Good dispersibility, but pH must be controlled (acidic conditions may cause hydrolysis).
• NMP systems: High chemical stability with minimal swelling risk.
  Conclusion: AHP shows better compatibility, while MCA requires modification.

2. Particle Size and Coating Process Adaptability

• MCA:
• Original D50: ~1–2 μm; requires grinding (e.g., sand milling) to reduce particle size, but may damage its layered structure, affecting flame-retardant efficiency.
• Post-grinding uniformity must be verified (SEM observation).
• AHP:
• Original D50: Typically ≤5 μm; grinding to D50 0.5 μm/D90 1 μm is achievable (excessive grinding may cause slurry viscosity spikes).
  Conclusion: MCA has better particle size adaptability with lower process risk.

3. Adhesion and Abrasion Resistance

• MCA:
• Low polarity leads to poor adhesion with PE/PP separator films; requires 5–10% acrylic-based binders (e.g., PVDF-HFP).
• High friction coefficient may necessitate adding 0.5–1% nano-SiO₂ to improve wear resistance.
• AHP:
• Surface hydroxyl groups form hydrogen bonds with the separator, improving adhesion, but 3–5% polyurethane binders are still needed.
• Higher hardness (Mohs ~3) may cause microparticle shedding under prolonged friction (requires cyclic testing).
  Conclusion: AHP offers better overall performance but requires binder optimization.

4. Thermal Stability and Decomposition Properties

• MCA:
• Decomposition temperature: 260–310°C; cannot generate gas at 120–150°C, potentially failing to suppress thermal runaway.
• AHP:
• Decomposition temperature: 280–310°C, also insufficient for low-temperature gas generation.
  Key Issue: Both decompose above the target range (120–150°C). Solutions:
• Introduce low-temperature synergists (e.g., microencapsulated red phosphorus, decomposition range: 150–200°C) or modified ammonium polyphosphate (APP, coated to adjust decomposition to 140–180°C).
• Design an MCA/APP composite (6:4 ratio) to leverage APP’s low-temperature gas generation + MCA’s gas-phase flame inhibition.

5. Electrochemical and Corrosion Resistance

• MCA:
• Electrochemically inert, but residual free melamine (purity ≥99.5% required) may catalyze electrolyte decomposition.
• AHP:
• Acidic impurities (e.g., H₃PO₂) must be minimized (ICP test: metal ions ≤10 ppm) to avoid accelerating LiPF₆ hydrolysis.
  Conclusion: Both require high purity (≥99%), but MCA is easier to purify.

Comprehensive Solution Proposal

1. Primary Flame Retardant Selection:

• Preferred: AHP (balanced dispersibility/adhesion) + low-temperature synergist (e.g., 5% microencapsulated red phosphorus).
• Alternative: Modified MCA (carboxyl-grafted for aqueous dispersion) + APP synergist.

1. Process Optimization:

• Slurry formula: AHP (90%) + polyurethane binder (7%) + wetting agent (BYK-346, 0.5%) + defoamer (2%).
• Grinding parameters: Sand mill with 0.3 mm ZrO₂ beads, 2000 rpm, 2 h (target D90 ≤1 μm).

1. Validation Tests:

• Thermal decomposition: TGA (weight loss <1% at 120°C/2h; gas output at 150°C/30min via GC-MS).
• Electrochemical stability: SEM observation after 30-day immersion in 1M LiPF₆ EC/DMC at 60°C.

Final Recommendation

Neither MCA nor AHP alone meets all requirements. A hybrid system is advised:

• AHP (matrix) + microencapsulated red phosphorus (low-temperature gas generator) + nano-SiO₂ (abrasion resistance).
• Pair with a high-adhesion aqueous resin (e.g., acrylic-epoxy composite emulsion) and optimize surface modification for particle size/dispersion stability.
  Further testing is needed to validate thermal-electrochemical synergy.