Microlayer Battery Separator Structure for Thin High-Strength Cells

The patent employs composite materials by combining multiple polymer layers (polyethylene, polypropylene, polyvinylidene fluoride) with specific additives (silicon dioxide, titanium dioxide, zinc oxide) in a multilayer coextruded structure. Each layer and additive serves specific functions: the polyethylene layer provides shutdown function, polypropylene provides thermal stability, polyvinylidene fluoride enhances mechanical strength, and the metal oxide additives improve puncture resistance and electrochemical stability. This composite approach optimizes the balance between strength and manufacturing complexity.

The patent applies local quality by assigning different properties to different layers of the multilayer separator. The outer layers contain higher concentrations of reinforcing additives (silicon dioxide, titanium dioxide) for enhanced puncture strength, while the inner layers focus on shutdown function and ion conductivity. The microporous structure is strategically designed with varying pore sizes and distributions across different layers to optimize both mechanical strength and separation performance locally.

The patent uses composite materials with high-strength additives (silicon dioxide, titanium dioxide, zinc oxide) dispersed throughout the polymer matrix to compensate for the reduced thickness. These additives form a reinforcing network that maintains puncture strength even when the overall separator thickness is reduced to 15-30 micrometers, enabling high energy density while preserving safety.

The patent employs a controlled microporous structure with optimized pore size distribution and porosity (30-50%) to maintain mechanical integrity at reduced thickness. The porous network provides structural reinforcement through tortuous pathways and interlocking pore walls, preventing catastrophic failure while allowing ion transport, thus enabling thin separators with adequate strength.

The patent segments the additive distribution across different layers of the multilayer structure. Different additives are concentrated in specific layers: silicon dioxide and titanium dioxide are primarily in the outer layers for puncture resistance, while zinc oxide is distributed in the inner layers for thermal stability. This segmentation reduces the precision required for uniform mixing throughout the entire separator, as each layer can be formulated and processed independently with its own optimized additive package.

The use of composite materials with compatible polymer matrices and well-selected additives facilitates easier processing. The selected additives (silicon dioxide, titanium dioxide, zinc oxide) have good compatibility with the polymer phases and can be uniformly dispersed using conventional mixing techniques, reducing the manufacturing precision requirements while still achieving the desired safety and durability enhancements.

The patent segments the manufacturing process into distinct coextrusion stages for different layers, each with optimized formulations. This allows independent optimization of each layer's properties (thickness, additive content, porosity) without requiring complete re-optimization of the entire separator, making it easier to manufacture thin, strong separators with the specified 15-30 micrometer thickness and high puncture strength.

The patent utilizes parameter changes in the coextrusion process, including temperature gradients, pressure control, and cooling rates, to achieve the desired microporous structure and additive distribution. By optimizing parameters such as extrusion temperature (180-220°C), cooling rate (5-20°C/min), and pore-forming agent concentration, the process achieves high-strength thin separators with consistent properties, improving ease of manufacture while meeting the stringent performance requirements.