Understanding Battery Separator Industry Standards and Innovation

Inside the battery the separator stands as both a neglected yet essential component. The separator exists between the positive and negative electrodes to block direct contact that causes short circuits and yet permits ion flow to execute the battery's charging and discharging operations. The "selective permeability" feature functions as the essential controller for battery safety and operational efficiency.

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

The Core Role of the Separator

Prevent short circuits: Electronic insulation within the separator prevents direct contact between positive and negative electrodes which eliminates the risk of overheating and combustion that could lead to explosion through short circuits.

Promote ion transfer: Pore size distribution and porosity within the separator material directly influence lithium ion migration efficiency which in turn determines the battery's charging speed and its overall capacity.

Safety protection mechanism: Polyolefin separators block ion transfer by using their "thermal closure" property when temperatures rise to prevent thermal runaway.

The separator technology used in lead-acid batteries and lithium-ion batteries exhibits both differences and similarities.

Differences: The separators used in lead-acid batteries primarily consist of acid-resistant microporous PVC or glass fiber while lithium battery separators consist mainly of polyolefins (PE/PP) which require resistance to organic electrolytes. Lead-acid battery separators prioritize acid corrosion resistance while lithium battery separators require enhanced thermal stability (such as ceramic coating) and mechanical strength to prevent dendrite penetration.

Commonalities: Separators need to maintain a balance between porosity and mechanical strength to ensure efficient ion conduction while avoiding electrode material penetration. All battery types require chemical stability to prevent electrolyte corrosion and redox reactions throughout their operational life.

Electric vehicle and energy storage system development faces increased battery performance demands because of the fast-paced global energy transition. Advancements in solid-state battery technology require separators to become thinner than 10 micrometers and achieve porosity levels above 40% to enhance lithium ion transmission efficiency. The optimization of pore size distribution in new separators enables high current charging and discharging capabilities while decreasing internal resistance through techniques like gradient pore design. Batteries now operate in wider applications thanks to ceramic composite separators that withstand temperatures up to 300°C and polymer electrolyte separators that work at -30°C.

The technological advancement stems from industry standard updates. The separator's puncture strength has advanced from an initial 1.0N/μm threshold to exceed 2.5N/μm in order to address the dendrite formation problems that occur with high-nickel ternary positive electrodes.

The necessity to control costs creates competition between dry processes which are low cost with poor uniformity and wet processes which deliver excellent performance but consume high energy.

Battery Separator Industry Standards

As the core component of the battery, the battery separator directly affects the energy density, cycle life and safety of the battery.

1. International general standards

The chemical stability, porosity, temperature resistance and mechanical strength of the separator are the basis for ensuring battery performance.

Porosity: Porosity directly affects the wettability of the electrolyte and the ion transfer efficiency. International standards require that the porosity must be between 40% and 60% (lithium-ion batteries), and the test methods include true density method and mercury intrusion method. Among them, the true density method is recommended for composite separators due to its environmental protection and accuracy.

Heat resistance: Polyolefin materials (such as polyethylene and polypropylene) are widely used due to their high-temperature self-closing properties (PE closed-cell temperature is about 130°C, PP rupture temperature is about 160°C) to prevent thermal runaway.

Mechanical strength: Tensile strength and puncture strength must meet specific values (such as UL 2591 requires separator tensile strength ≥100 MPa, puncture strength ≥300 N/mm²).

The core standards for evaluating the safety of lithium battery separators have added the following tests:

Physical properties: including thickness uniformity (±1 μm error), porosity (40%-60%), and pore size distribution (0.01-1 μm).

Thermal properties: dimensional stability (shrinkage at high temperature<5%), closed cell temperature and melting temperature test.

Mechanical tests: tensile strength (longitudinal ≥100 MPa) and puncture strength (≥300 N/mm²).

2. Special standards for lead-acid battery separators

Acid corrosion resistance and oxidation resistance: The electrolyte of lead-acid batteries is sulfuric acid, and the separator needs to remain stable in strong acid and high temperature (70-80°C) environment:

Acid corrosion resistance: Polyethylene (PE) and polyvinyl chloride (PVC) separators are widely used due to their resistance to sulfuric acid corrosion and need to pass the acid solubility test in the standard.

Anti-oxidation technology: The separator needs to withstand the oxidation reaction of the positive active material (PbO₂). Polypropylene (PP) is better than PE in oxidation resistance and is often used in multi-layer composite separators.

Battery Separator Technology Innovation in Materials and Manufacturing Methods

Material innovation: from traditional optimization to composite innovation

Polyethylene (PE) and polypropylene (PP) are the mainstream materials for lithium-ion battery separators. In recent years, they have significantly improved thermal stability and mechanical strength through optimization methods such as molecular chain directional arrangement and crystallinity regulation. For example, the PE separator prepared by the wet process achieves a more uniform pore distribution through synchronous biaxial stretching technology, and its melting point is increased from 130°C to above 160°C, effectively alleviating the problem of thermal shrinkage. The polypropylene separator is optimized through the dry stretching process, and the porosity is increased from 40% to 60%, and the ionic conductivity is increased by 30%.

The new composite material breaks through the performance bottleneck through multi-dimensional synergistic effects: the graphene/polyimide (PI) composite separator combines the high thermal conductivity of graphene and the high temperature resistance of PI, and maintains structural integrity at 200°C, with a thermal shrinkage rate of less than 5%.

The nanocellulose composite membrane has a three-dimensional network structure formed by hydrogen bond self-assembly, with high porosity (more than 80%) and ultra-low resistance (<0.5Ω·cm²). Its directional fiber design increases the ion transmission rate by 50%.

The alumina/PVDF coated separator balances lithium ion selectivity and electrolyte wettability through gradient pore structure design, and the cycle life is extended to more than 2,000 times.

Manufacturing process upgrade: precision and functionalization in parallel

The gradient distribution of separator pores and bionic structure design can be achieved by using fused deposition modeling (FDM) and direct ink writing (DIW) technology. For example, the 3D-printed boron nitride (BN) separator adjusts the electric field distribution through a porous framework, inhibits the growth of zinc dendrites, and enables the capacity retention rate of zinc-ion batteries to reach 84.4% at a current density of 0.5A/g. In addition, the technology can also integrate thermal management functions, such as the printed PVDF-HFP separator still maintains electrochemical stability at high temperatures (120°C).

Electrospun nanofiber coating: The polyaniline (PANI)/carbon nanotube (CNT) composite coating prepared by electrospinning can reduce the water loss rate of lead-acid batteries by 30%, inhibit hydrogen evolution corrosion, and extend the cycle life by 40%.

Ceramic-polymer composite coating: The alumina/PVDF hybrid coating enhances the puncture strength of the separator (>500g/mil) and improves the affinity of the electrolyte through the "hard-soft" synergistic effect, and the liquid absorption rate is increased to 300%.