Multilayer Battery Separator Thermal Shutdown Mechanism

The patent utilizes the phase transition property of polyethylene material in the separator. When temperature reaches the melting point of polyethylene (approximately 165°C), the separator undergoes phase transition from solid to molten state, automatically closing the pores and shutting down ion transport. This thermal shutdown mechanism prevents heat accumulation and potential explosion without requiring additional active cooling systems.

The battery separator acts as an intermediary component between the positive and negative electrodes. It mediates the thermal management by absorbing and dissipating heat through its thermal conduction properties while simultaneously providing a physical barrier that prevents direct contact between electrodes. The separator's porous structure also allows controlled ion transport, balancing electrical function with thermal safety.

The patent employs a porous polyethylene separator with specifically controlled pore structure. The porous design allows efficient ion transport through the separator under normal operating conditions, maintaining high productivity. When thermal runaway occurs, the pores automatically close due to melting, providing passive thermal shutdown protection. This dual-function porous structure simultaneously achieves both ion transport efficiency and thermal safety without requiring active control systems.

The patent optimizes key parameters of the separator including pore size distribution, porosity (typically 30-80%), and thickness (typically 15-50 μm). By adjusting these parameters, the separator can be tuned to provide optimal ion transport efficiency at operating temperatures while ensuring adequate thermal shutdown capability. The polyethylene crystallinity and molecular weight are also controlled to achieve the desired melting point and mechanical properties.