Separator Technology for Liquid Lithium - Ion Batteries

　　Separators in lithium - ion batteries serve a dual role: preventing short circuits between electrodes and allowing lithium ion passage. They are thin (10–25 μm), porous films (pore size: 100–500 nm, porosity: 30–50%) made of polymers or ceramic - polymer composites. Key separator technologies include:

　　1. Polymeric Separators: The Industry Standard

　　Polyolefin - based separators (polyethylene [PE], polypropylene [PP]) dominate the market due to their balance of cost, mechanical strength, and chemical resistance.

　　Single - Layer PE/PP: PE separators (melting point: ~130°C) offer high ionic conductivity but poor thermal stability. PP separators (melting point: ~160°C) provide better heat resistance but lower conductivity.

　　Multilayer PE/PP Composites: e.g., PP/PE/PP trilayers, where the middle PE layer ensures ionic transport, and the outer PP layers prevent thermal runaway by melting at higher temperatures (shutdown temperature: ~135°C), blocking ion flow.

　　2. Ceramic - Coated Separators: Enhancing Thermal Stability

　　To address the thermal limitations of polyolefins (e.g., shrinkage above 150°C in PE), ceramic coatings (e.g., Al₂O₃, SiO₂, ZrO₂) are applied to the separator surface:

　　Mechanism: The ceramic layer acts as a thermal barrier, maintaining dimensional stability up to 200°C. It also absorbs electrolyte, improving wettability and reducing interfacial resistance.

　　Applications: High - energy - density batteries (e.g., NCM811/graphite systems) and fast - charging batteries, where thermal runaway risks are higher.

　　3. Polymeric Blends and Composite Separators

　　Polyvinylidene Fluoride (PVDF): Offers chemical resistance and higher thermal stability than polyolefins but is more expensive. Often blended with polyolefins or ceramics for niche applications.

　　Electrospun Nanofiber Separators: Ultra - thin (~5 μm) mats with high porosity, enabling faster ion transport. However, their low mechanical strength limits large - scale adoption.

　　4. Key Performance Metrics

　　Ionic Conductivity: Dependent on porosity and electrolyte absorption. Ceramic - coated separators typically have 10–15% higher conductivity than pure polyolefins.

　　Mechanical Strength: Measured by puncture resistance (e.g., PE separators: ~200 N/cm). Ceramic coatings can double this value.

　　Thermal Stability: Assessed via dimensional change at high temperatures. Polyolefin separators may shrink by 10–15% above 150°C, while ceramic - coated variants show <5% shrinkage.

　　5. Challenges and Innovations

　　Thinning for Higher Energy Density: Separators are being thinned from 16 μm to 9 μm or lower, but this increases the risk of punctures. Nanocomposite coatings (e.g., Al₂O₃/PVDF) are being developed to maintain strength at reduced thickness.

　　Solid - State Transition: In semi - solid batteries, separators may be replaced by polymer - electrolyte composites, but liquid electrolytes still require traditional separators for now.

Read recommendations:

Coin Battery LR 754

Which is better, graphene battery or lithium battery

2023 (17th) International Forum on Power Lithium Battery Technology and Industry Development

connector for energy storage battery manufacture

6F22 carbon battery