Among the core components of lithium batteries, the lithium battery separator directly determines the safety boundary and service life of the battery. Currently, the mainstream lithium battery separators on the market are mainly divided into four categories — PE separators, 3-layer polyolefin (PP/PE/PP) separators, non-woven separators, and ceramic-coated separators. The significant differences in processes and structures of different separators lead to great variations in their key performances such as mechanical strength, puncture resistance, and cycle stability.
To accurately compare the actual performance of various separators, the research team comprehensively analyzed the performance advantages and disadvantages of the four types of separators through mechanical strength tests (tensile strength, puncture resistance), battery cycle performance tests, and micro-morphology analysis using Focused Ion Beam Scanning Electron Microscopy (FIB-SEM). This article will present the test results in detail, providing data support for separator selection in scientific research and industrial production, and helping to accurately optimize battery performance.
Experimental Design: Comprehensive Test System to Restore the Real Performance of Separators
To ensure the objectivity and reference value of the test results, the experiment adopted a standardized test plan covering the mechanical properties and battery application performance of the separators. The specific design is as follows:
Test Samples: PE separators, 3-layer polyolefin (PP/PE/PP) separators, non-woven separators, ceramic-coated separators (with PE as the base film and inorganic oxide coating).
Test Equipment: Uniaxial tensile machine (for testing tensile strength), puncture force tester (for testing puncture resistance), battery charge-discharge test cabinet (for testing cycle performance), focused ion beam microscope (for observing micro-morphology).
Test Standards: Tensile strength test refers to ASTM D882—2018 standard; puncture resistance test refers to GB/T 21302—2007 standard; battery cycle test adopts 1C/1C charge-discharge rate, covering room temperature and 55℃ high-temperature environments, with battery capacities including 10Ah, 15Ah, 20Ah and other specifications.
Mechanical Performance PK: Who Can Withstand the Dual Test of Tension and Puncture?
During battery assembly and charge-discharge processes, the lithium battery separator needs to withstand multiple mechanical stresses such as tension, extrusion, and puncture. Once broken, it will directly lead to battery short circuit. Tensile strength and puncture resistance are the core indicators to evaluate the mechanical performance of the lithium battery separator, and the performance of the four types of separators varies significantly.
Tensile Strength: 3-Layer Polyolefin Separator Leads Far Ahead
Tensile strength is directly related to the damage resistance of the separator during battery winding and packaging. In particular, the longitudinal tensile strength needs to reach a high level, while the transverse strength needs to be appropriately controlled (to avoid positive and negative electrode contact caused by excessive transverse shrinkage).
Test Results: With the increase of separator width, the longitudinal tensile strength of all four types of separators shows an upward trend. Among them, the 3-layer polyolefin separator has the best tensile strength performance. When the width is 10mm, the tensile strength reaches 2.6MPa; the PE separator and ceramic-coated separator perform similarly, at a medium level; the non-woven separator has the worst tensile strength, only 0.6MPa when the width is 10mm, less than 1/4 of the 3-layer polyolefin separator.
Core Reason: The 3-layer polyolefin separator integrates the mechanical advantages of different materials through the PP/PE/PP composite structure, combined with the optimized stretching process, forming stronger tensile resistance; while the non-woven separator has a loose fiber structure and uneven pore distribution, resulting in weak mechanical tensile strength.
Puncture Resistance: PE Separator Wins the Championship, Ceramic-Coated Separator Has Obvious Advantages
Sandwiched between the uneven positive and negative electrodes, the lithium battery separator needs to resist puncture by electrode burrs, lithium dendrites, etc. Puncture resistance is the key to ensuring long-term battery safety.
Test Results: With the increase of the puncture head diameter, the puncture resistance of all four types of separators increases. The PE separator has the most excellent puncture resistance. When the puncture head diameter is 3.175mm, the puncture resistance reaches 20N; the ceramic-coated separator provides additional protection due to the surface-coated inorganic oxide coating, with a puncture resistance of 17N, which is better than the 3-layer polyolefin separator; the non-woven separator still ranks the bottom in puncture resistance, only 2.8N, which is difficult to resist puncture risks under complex working conditions.
Core Reason: The PE separator has a dense and uniform microporous structure and strong mechanical stability; the inorganic oxide coating of the ceramic-coated separator has high hardness and dense structure, which can effectively block the intrusion of punctures; while the loose structure of the non-woven separator cannot form an effective puncture-resistant barrier.
Cycle Performance Duel: Performance Persistence Under High Temperature and Long Cycle
The structural stability and ion transmission efficiency of the lithium battery separator directly affect the cycle life of the battery. The experiment focused on comparing the cycle performance of the PE separator and ceramic-coated separator with excellent performance, covering different temperature, capacity, and cycle number scenarios.
Room Temperature Environment: Ceramic-Coated Separator Is Better in Long Cycle
Under room temperature and 1C/1C charge-discharge rate conditions:
When the battery capacity is 10Ah, after 900 cycles, the capacity retention rate of the battery assembled with the ceramic-coated separator reaches 92.1%, and that of the battery assembled with the PE separator is 86.4%;
When the battery capacity is 20Ah, after 1000 long cycles, the capacity retention rate of the battery assembled with the ceramic-coated separator is 67.3%, and that of the battery assembled with the PE separator is only 44.3%.
Core Advantages: The inorganic oxide coating of the ceramic-coated separator is closely combined with the base film. The gaps on the coating surface are conducive to the uniform intercalation and deintercalation of lithium ions, while improving the liquid absorption and moisture retention of the electrolyte, optimizing the internal current distribution of the battery, thereby extending the cycle life.
High Temperature Environment (55℃): Ceramic-Coated Separator Has Crushing Stability
In a high-temperature environment, the risk of thermal shrinkage of the lithium battery separator increases, which is a more severe test for battery cycle performance:
When the battery capacity is 10Ah, after 300 cycles, the capacity retention rate of the battery assembled with the ceramic-coated separator is 76.5%, and that of the battery assembled with the PE separator is 68.9%;
When the battery capacity is 15Ah, after 300 cycles, the capacity retention rate of the battery assembled with the ceramic-coated separator reaches 83.9%, and that of the battery assembled with the PE separator is only 69.5%.
Core Reason: The inorganic oxide coating of the ceramic-coated separator can play a supporting role at high temperatures, effectively inhibiting the thermal shrinkage of the base film, avoiding short circuits caused by positive and negative electrode contact, and maintaining the stability of ion transmission channels. In contrast, the PE separator is prone to thermal shrinkage at high temperatures, leading to rapid attenuation of cycle performance.
Micro-Morphology Revealed: Performance Code of Ceramic-Coated Separators
To explore the source of the performance advantages of ceramic-coated separators, the research team analyzed their micro-morphology through Focused Ion Beam Scanning Electron Microscopy (FIB-SEM):
PE Base Film Structure: The surface of the base film presents an obvious three-dimensional fibrous structure, indicating that it is prepared by a wet process. This structure provides a basic channel for ion transmission;
Coating Bonding State: Inorganic oxide particles are uniformly distributed on the surface of the PE base film, with uniform coating thickness and tight bonding with the base film, without shedding, cracking, or other phenomena, ensuring mechanical stability;
Coating Pore Structure: There are cavities of varying sizes between oxide particles. These pores can not only improve the liquid absorption and moisture retention capacity of the electrolyte but also optimize the transmission path of lithium ions, improve the uniformity of current distribution, and lay a structural foundation for the improvement of cycle performance.
Core Conclusion: Selection Guide for Four Types of Separators
Through comprehensive testing and analysis, the performance advantages and disadvantages and applicable scenarios of the four types of lithium battery separators have been clearly presented, providing a clear reference for selection in scientific research and production:
Separator TypeCore AdvantagesPerformance ShortcomingsApplicable Scenarios3-Layer Polyolefin SeparatorHigh tensile strength, stable structureMedium puncture resistance, general high-temperature cycle performanceMid-to-low-end power batteries and digital batteries with high requirements for mechanical strengthPE SeparatorExcellent puncture resistance, good room-temperature cycle performance, controllable costProne to thermal shrinkage at high temperatures, general long-cycle stabilityDigital batteries and energy storage batteries used at room temperature and sensitive to costCeramic-Coated SeparatorGood high-temperature cycle stability, long cycle life, high puncture resistanceMedium tensile strength, slightly higher cost than PE separatorsHigh-performance power batteries, high-temperature working condition batteries, long-life energy storage batteriesNon-Woven SeparatorGood wettability, high porosityExtremely poor tensile strength and puncture resistance, poor cycle performanceLow-end disposable batteries with extremely low requirements for safety and service life
Conclusion
The four types of mainstream lithium battery separators show distinct differentiated characteristics in mechanical performance and cycle performance: the 3-layer polyolefin separator has outstanding tensile strength, the PE separator has excellent puncture resistance, the ceramic-coated separator performs best under high temperature and long cycle, and the non-woven separator is difficult to adapt to high-performance scenarios due to weak mechanical performance.
With the trend of lithium batteries developing towards high energy density, long service life, and high safety, the ceramic-coated separator, with its comprehensive performance advantages, has become the preferred choice for high-performance power batteries and energy storage batteries; the PE separator and 3-layer polyolefin separator still occupy an important position in mid-to-low-end scenarios due to their cost advantages; the application range of non-woven separators will further shrink. In the future, the research and development direction of lithium battery separators will focus on the optimization of ceramic coatings (such as reducing costs and improving the bonding force with the base film), the improvement of the puncture resistance of 3-layer polyolefin separators, and the development of new composite structures, to achieve comprehensive improvement of mechanical performance and cycle performance.
For more in-depth research on separator materials and test technologies, you can refer to the research published by the Journal of Power Sources. Our previous articles on polyolefin lithium battery separators and PGZ composite separators further elaborate on the development of separator materials and processes. For detailed industry standards and test methods, refer to the report released by the Institute of Electrical and Electronics Engineers (IEEE).