Investigation on flame retardant microcapsules based composite phase change material for battery thermal safety

The thermal safety of lithium-ion batteries is confronted significant challenges owing to flammability and localized heat accumulation during operation. To enhance the fire resistance and thermal regulation, a novel flame-retardant composite phase change material (CPCM) by incorporating aluminum hypophosphite microcapsules (AHP@MCA) and ammonium polyphosphate (APP) has been proposed. This CPCM system utilizing polyethylene glycol (PEG2000) as the phase change medium, epoxy resin (ER) as the structural support and expanded graphite (EG) to enhance thermal conductivity. The AHP@MCA microcapsules were fabricated via in-situ polymerization to improve dispersion and thermal stability. The optimized formulation, designated as PEEMA3, demonstrated a thermal conductivity of 1.267 W/(m·K) a latent heat of 101.02 J/g and exceptional shape stability with 99.3 % mass retention at 65 °C. Flame retardancy testing revealed the limiting oxygen index (LOI) of 28.7 % and remarkable 72 % reduction in peak heat release rate (PHRR), attributing to synergistic gas-phase and condensed-phase mechanisms. In battery module tests, PEEMA3 effectively maintained the surface temperature below 47.51 °C during 1C discharge and delayed thermal runaway propagation by 54.8 %. This research can provide the potential prospects of multifunctional CPCMs for safe and efficient energy storage applications.