Battery Separator Materials: How to Choose the Best Solution for Your Application?

The Core Role and Selection Criteria of Separators

As the "safety guard" of lithium-ion batteries, the core function of separators is to physically isolate the positive and negative electrodes to prevent short circuits, while realizing ion transmission channels through microporous structures, which directly affects the capacity, cycle life and safety of the battery. The ideal separator needs to balance the following characteristics:

Ultra-thin and high mechanical strength: prevent lithium dendrite puncture (such as power batteries require puncture resistance ≥ 500 MPa).

High thermal stability: ceramic separators can maintain structural stability at 200°C to avoid thermal runaway.

High porosity (40%-60%) and uniform pore size: reduce internal resistance and improve ionic conductivity (traditional polyolefin porosity is only ~40%, and new nanofiber composite materials can reach 70%).

Chemical stability: resistance to electrolyte corrosion (such as polyimide materials perform well in strong acid/alkali environments).

Battery Separators Products List

• PTFE Battery Separator
• PE Battery Separator
• PP Battery Separator
• PP/PE/PP Trilayers Battery Separator
• Ceramic Coated Separator (PE Base Film)
• Ceramic Coated Separator (PP Base Film)
• Cellulose Separator
• PVDF Coated Separator
• Glass Fiber Battery Separator

Classification and Characteristics of Common Separator Materials

Polyolefin separators (PE/PP)

The commercial market is dominated by polyolefin separators (polyethylene PE and polypropylene PP) because they combine high chemical stability with low cost. PE separators show high porosity of 35% and excellent lithium ion transmission efficiency but melt at 130°C which blocks current flow to enhance safety while PP separators demonstrate superior mechanical strength and high temperature resistance with a melting point of 160°C and maintain better dimensional stability. For performance optimization power batteries typically utilize a three-layer composite structure (PP/PE/PP) which combines PE's low-temperature closed-cell properties and PP's high-temperature support to prevent thermal runaway.

PE lacks high temperature resistance which leads to shrinkage and micro-short circuits but PP shows strong heat resistance alongside low porosity that restricts ion transmission. Single-layer PE or PP materials fail to achieve high power needs and must undergo performance improvements through modification methods like ceramic or PVDF coating.

Ceramic coating separator

The addition of nano-alumina and boehmite coatings to polyolefin-based membranes creates ceramic coating separators that deliver improved thermal stability for temperatures above 200°C and enhanced mechanical strength while minimizing thermal shrinkage. Al₂O₃ coating strengthens the separator's puncture resistance against lithium dendrite penetration and makes it appropriate for high-energy-density ternary lithium batteries.

Electric vehicles mainly use ceramic coating separators because they operate in safety-critical applications. The application of ceramic coatings helps prevent thermal runaway while increasing the operational lifespan of batteries. The high cost of this material being approximately 30% more expensive than standard polyolefin separators limits its application to high-end power batteries.

PVDF separator

PVDF (polyvinylidene fluoride) shows outstanding chemical stability while maintaining strong electrolyte affinity because its β-crystal structure enhances electrolyte wettability and decreases battery internal resistance. A PVDF coating is applied to polyolefin membranes like wet PE to improve electrode-separator adhesion while preventing electrode shedding.

PVDF's poor thermal conductivity helps to reduce the risk of short circuits at high temperatures.

Lithium-ion batteries in consumer electronics and electric vehicles make extensive use of this material particularly for soft-pack batteries that utilize aluminum-plastic films. PVDF exhibits high crystallinity and large interfacial resistance which requires modification through blending methods or hydrophilic group surface grafting to improve performance.

Non-woven separator

Non-woven separators utilize glass fiber or synthetic fiber to achieve over 70% porosity while maintaining low cost and simple production methods. PVDF non-woven fabrics stand out because of their great affinity with electrolytes yet their non-uniform pore size distribution creates the risk of micro-short circuits.

Non-woven separators achieve improved thermal stability and mechanical strength through the incorporation of inorganic particles like SiO₂ or the application of organic coatings such as PVDF-HFP. The SiO₂/PVDF-HFP composite separators demonstrate a shrinkage rate under 5% when exposed to high temperatures and their ionic conductivity surpasses that of conventional PE separators. Current applications of this separator type mainly span the cost-conscious sectors like energy storage batteries.

Comparison of Performance of Various Types of Separators

Application Scenarios and Selection Guide for Battery Separators

As one of the core components of lithium-ion batteries, the performance of battery separators directly affects the safety, energy density and life of the battery. Different application scenarios have significantly different requirements for separators, and comprehensive selection is required based on factors such as cost, thermal stability, and mechanical strength. The following is a separator selection guide and technical analysis for major application scenarios:

1. Portable electronic products (such as mobile phones and laptops)

Recommended separator type: polyolefin separator (PE/PP)

Reasons for selection:

Low cost and mature process: The preparation technology of polyolefin (PE/PP) separators is mature, the price of raw materials is low, and it is suitable for large-scale production, occupying the mainstream of the 3C battery market.

Basic performance meets the needs: PE separators are prepared by wet process, with uniform pores and good electrolyte wettability; PP separators have better high temperature resistance and can reduce costs through dry process.

Lightweight and adaptability: The thickness of a single-layer PE or PP separator can be controlled at 10-25μm, which is suitable for the stringent requirements of small batteries for space and weight.

Limitations: Polyolefin separators have a high thermal shrinkage rate at high temperatures, and there is a risk of micro-short circuits in long-term use. They need to be modified by coating (such as PVDF) to improve local performance.

2. Electric vehicles (power batteries)

Recommended separator types: ceramic coated separators or PVDF composite separators

Reasons for selection:

High safety: Ceramic coatings (alumina, boehmite, etc.) can significantly improve the high temperature resistance of separators (>200°C), inhibit thermal shrinkage, and reduce the risk of thermal runaway. PVDF coatings enhance antioxidant capacity and reduce electrolyte decomposition.

High mechanical strength requirements: Power batteries need to withstand frequent charging and discharging and vibration. Ceramic coatings can improve the puncture resistance of separators (>300gf) to prevent short circuits caused by puncture of the pole piece.

Adaptation to high energy density systems: Thin PE base films (such as 12-16μm) are coated with ceramic layers to improve safety and avoid energy density loss.

Technology trends: Inorganic-organic composite coatings (such as ceramics + PVDF) have become the mainstream solution, taking into account both high temperature resistance and electrolyte affinity.

3. Energy storage system (grid level)

Recommended separator type: non-woven separator or composite separator

Reasons for selection:

Balance between long life and cost: non-woven separators (such as glass fiber, aramid fiber) have high porosity (>60%), good liquid retention, and can extend cycle life; composite separators (such as polyolefin + ceramic) can reduce costs through modification while improving thermal stability.

High temperature resistance and safety: Energy storage systems often need to operate in high temperature environments. Ceramic coated separators can suppress thermal runaway, while the high porosity structure of non-woven separators is conducive to heat dissipation.

Adaptable to large-scale applications: Dry single-pulled PP separators are low in cost and suitable for energy storage scenarios with low energy density requirements, and the process is environmentally friendly.

Challenges and improvements: Non-woven separators need to solve the problem of pore size uniformity, and composite separators need to optimize the coating process to reduce costs.