battery cell stack illustration

Comparison between Alumina-coated and Boehmite-coated Separators

Author: Woody Wu at power9tech.cn

battery cell stack illustration

Alumina and Boehmite are examples of ceramic coating materials used on separators. These can be applied on one side or both sides of the separator.

Ceramic-Coated Separators

Ceramic-coated separators consist of a base film (PP/PE) with a surface layer of heat-resistant inorganic ceramic particles (e.g., Al₂O₃, SiO₂, Mg(OH)₂), bonded tightly to the substrate through specialized processing.

  • Combined Properties: Integrates the flexibility of organic materials with the thermal stability of inorganic ceramics, enhancing high-temperature resistance, thermal shrinkage resistance, and puncture strength for improved battery safety.
  • Thermal Runaway Mitigation: The ceramic composite layer addresses thermal shrinkage issues in PP/PE separators, reducing risks of combustion or explosion caused by thermal runaway.
  • Cost-Effective Coatings: Alumina (Al₂O₃) and boehmite (AlOOH) are widely adopted due to their affordability and performance balance.

Alumina (Al₂O₃) Coating

Alumina, or aluminium oxide (Al2O3), is a widely used, hard-wearing technical ceramic known for its high hardness, wear resistance, and excellent electrical and thermal properties. As a ceramic coating on battery separators there are a number of advantages and disadvantages:

Advantages

  1. High-Temperature Stability: Maintains structural integrity at 180°C.
  2. Acid Resistance: Neutralizes free HF in the electrolyte, improving safety and durability.
  3. Performance Enhancement: Forms solid solutions in lithium batteries to boost rate capability and cycle life.
  4. Wettability: Improves electrolyte absorption and retention.

Disadvantages

  1. Cost: Alumina is generally more expensive than boehmite. 
  2. Hardness: Alumina is harder than boehmite, which can lead to increased wear during the coating process. 

Boehmite (AlO(OH)) Coating

Boehmite (AlOOH) is an aluminium oxide hydroxide, the small particle size and the unique structure of oxide hydroxide make it appropriate for use in various industries.

Advantages

  1. Low Abrasiveness: Reduces equipment wear and foreign particle risks during cutting and coating.
  2. Low Density: Provides 25% more coating area per unit mass compared to high-purity Al₂O₃.
  3. Smooth Coating: Offers higher flatness and lower internal resistance.
  4. Eco-Friendly: Lower energy consumption and environmental impact during production.
  5. Cost Efficiency: Simplified manufacturing process reduces production costs.

Disadvantages

  1. Thermal Runaway: Some studies suggest that boehmite coatings may pose a safety hazard in commercial applications due to the increased risk of thermal runaway and battery explosion. 
  2. Potential Contamination: Lower-grade alumina or boehmite may pose a contamination risk and heightened safety hazard. 

Author: Woody Wu at power9tech.cn

References

  1. The Use of Ceramics in Lithium Battery Separators, dln energy
  2. Gaurav Sharma, Yi Jin and Y. S. Lin, Lithium Ion Batteries with Alumina Separator for Improved Safety, 2017 J. Electrochem. Soc. 164 A1184
  3. Dhrupad Parikh, Charl J. Jafta, Bishnu Thapaliya, Jaswinder Sharma, Harry M. Meyer III, Chris Silkowski, Jianlin L, Al2O3/TiO2 Coated Separators: Roll-to-roll processing and implications for improved battery safety and performance, OSTI.gov

See also: Separator, Shutdown Separators, Selecting a Battery Cell Separator

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