Microporous Li-Ion Separator Coating for Puncture and Wettability
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Solution Overview
Problem
Lithium-ion secondary battery separators face challenges in achieving balanced strength, wettability with nonaqueous electrolyte solutions, voltage endurance, and cycle characteristics, while also requiring improved puncture depth and gas permeability, which existing microporous films fail to adequately address.
Innovation Solution
A microporous film for lithium-ion secondary batteries is developed, comprising a polyolefin resin as the major component with specific areas of its micropores coated with a different resin, enhancing puncture depth and maintaining gas permeability through a network structure and surface coating with a hydrophobic resin that has a low elastic modulus and specific solubility properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If microporous films are produced by dry methods with high porosity (70-95%), then ion permeability is improved, but strength and puncture resistance deteriorate
Solution Approach 1:
The invention uses composite materials by combining polyolefin resin with elastomer particles to create a microporous film that achieves both high porosity (30-95%) and high strength. The elastomer particles act as reinforcement within the porous structure, allowing the film to maintain mechanical integrity while permitting ion transport.
Solution Approach 2:
The invention applies local quality by distributing elastomer particles throughout the microporous structure to provide localized reinforcement. This allows different regions of the film to have optimized properties - the polyolefin matrix provides porosity for ion transport while the elastomer particles provide localized strength and puncture resistance.
2Reliability
If microporous films are produced by wet methods with extractable matter, then porosity is improved, but manufacturing complexity and environmental impact worsen
Solution Approach 1:
The invention takes out the need for extractable matter and solvent extraction steps by using a dry method where elastomer particles are directly incorporated into the polyolefin matrix during film formation. This eliminates the complex wet processing steps including solvent immersion and extraction, simplifying the manufacturing process while achieving the desired microporous structure.
3Productivity
If separator thickness is reduced to improve battery energy density, then productivity and energy density are improved, but strength and safety deteriorate
Solution Approach 1:
The invention enables production of ultra-thin separators (1-20 μm) with high strength by incorporating elastomer particles into the polyolefin matrix. The elastomer reinforcement allows the film to maintain adequate mechanical strength and puncture resistance even at thicknesses one-tenth of conventional separators, thereby enabling high energy density battery designs.
4Reliability
If porosity is increased to improve ion permeability, then ion transport is improved, but mechanical strength and handling properties worsen
Solution Approach 1:
The invention applies local quality by strategically distributing elastomer particles within the microporous structure to provide localized mechanical reinforcement. This allows the film to maintain high porosity (30-95%) for optimal ion transport while the elastomer particles provide localized strength to prevent film rupture and improve handling properties.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a separator with improved strength, wettability, voltage endurance, and cycle characteristics, along with increased puncture depth and maintained gas permeability, effectively addressing the limitations of existing separators.
Implementation Method 1
Microporous resin films or membranes exhibit electrical insulating properties or ion permeability
Implementation Method 2
at least one area of surfaces of micropores in the microporous film is coated with a resin (B) different from the polyolefin resin (A)
Data Source
AI summary
Problem: The invention provides a separator for a lithium-ion secondary battery exhibiting excellent strength, wettability with nonaqueous electrolyte solutions, voltage endurance and cycle characteristics in lithium-ion secondary batteries, and a method of increasing the puncture depth of the separator.Solution: A separator for a lithium-ion secondary battery is formed of a microporous film comprising a polyolefin resin (A) as a major component, and a resin (B), at least portions of the surfaces of the micropores in the microporous film being coated with resin (B).