Multilayer Battery Separator with Silane Crosslinking for Thermal Stability
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Solution Overview
Problem
Current lithium secondary battery separators face challenges in ensuring safety due to insufficient shutdown margin and thermal shrinkage, which can lead to ignition risks during overheating, despite efforts to enhance heat resistance and reliability.
Innovation Solution
A multilayer porous film separator is developed, comprising a resin porous film and a heat-resistant porous layer with heat-resistant particles, where the heat-resistant porous layer has a thickness of 1 to 15 μm and a 180° peel strength of 0.6 N/cm or more, ensuring strong adhesion and improved heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyethylene with low melting point is used as separator material to ensure shutdown effect, then battery safety is improved, but shutdown temperature is too close to thermal runaway temperature, reducing safety margin
Solution Approach 1:
The separator is divided into multiple functional layers: a polyethylene base layer for shutdown function, a silane-crosslinked polyethylene layer for high-temperature dimensional stability, and a heat-resistant porous layer for thermal runout prevention. Each layer addresses specific temperature ranges and safety concerns independently.
Solution Approach 2:
The separator combines multiple materials with complementary properties: polyethylene (low melting point for shutdown), silane-crosslinked polyethylene (high temperature stability), and heat-resistant porous material (dimensional stability at thermal runout temperature). The composite structure integrates the advantages of each material while mitigating their individual limitations.
2Strength
If drawing is performed on the separator film to increase porosity and improve strength, then workability is improved, but crystallinity increases and shutdown temperature rises, reducing safety margin
Solution Approach 1:
The separator undergoes preliminary silane grafting and crosslinking treatments before final assembly. The silane groups are introduced in advance and crosslinked to form a stable network that prevents excessive crystallization during subsequent drawing processes, maintaining low shutdown temperature while achieving required strength.
Solution Approach 2:
The crosslinking degree and porosity parameters are optimized to achieve the desired balance. By controlling the silane crosslinking density and pore structure, the separator maintains mechanical strength for workability while preventing crystallinity-induced shutdown temperature elevation.
3Strength
If drawing is performed on the separator film to ensure strength, then workability is improved, but distortion occurs and shrinkage at high temperature increases, reducing reliability
Solution Approach 1:
Different regions of the separator have different properties: the polyethylene base layer provides shutdown function, the silane-crosslinked layer provides dimensional stability through crosslinked network structure that resists shrinkage, and the heat-resistant porous layer maintains structural integrity at high temperatures. Each layer addresses specific stability requirements locally.
Solution Approach 2:
The silane-crosslinked polyethylene layer is specifically designed to counteract thermal shrinkage. The crosslinked network structure expands or maintains dimensions at high temperatures, compensating for the shrinkage tendency of the polyethylene base layer and preventing overall separator distortion.
4Reliability
If heat resistant porous layer is formed on the separator surface to prevent thermal shrinkage, then reliability is improved, but adhesion between layers may be insufficient, reducing effectiveness
Solution Approach 1:
The silane-crosslinked polyethylene layer acts as an intermediary between the polyethylene base layer and the heat-resistant porous layer. It provides both mechanical anchoring and chemical bonding sites that ensure strong adhesion while maintaining the thermal shrinkage resistance function of the outer heat-resistant layer.
Solution Approach 2:
Physical adhesion is enhanced by chemical crosslinking mechanisms. The silane groups form covalent bonds with the polyethylene base layer, replacing weak physical adhesion with strong chemical bonding. This ensures the heat-resistant porous layer remains firmly attached under thermal and mechanical stress.
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 non-aqueous electrolyte battery with enhanced safety and reliability by preventing thermal shrinkage and maintaining ion permeability, even under high temperatures and mechanical stress, thus reducing the risk of ignition.
Implementation Method 1
a film that has been uniaxially or biaxially drawn so as to increase the porosity and improve the strength... because such a drawn film has an increased crystallinity, as well as an increased shutdown temperature close to the thermal runaway temperature of the battery... distortion occurs in the film due to drawing, and if the film is exposed to a high temperature, the film shrinks due to residual stress
Implementation Method 2
In order to ensure what is called a shutdown effect that causes a resin constituting a separator to melt so as to close the pores at a temperature equal to or less than a temperature at which thermal runaway occurs in the battery
Implementation Method 3
a multilayer porous film having a resin porous film containing a thermoplastic resin as a main component and a heat resistant porous layer containing heat resistant particles as a main component
Data Source
AI summary
A separator for batteries according to the present invention includes a multilayer porous film having a resin porous film containing a thermoplastic resin as a main component and a heat resistant porous layer containing heat resistant particles as a main component, and the heat resistant porous layer has a thickness of 1 to 15 μm, and the 180° peel strength between the resin porous film and the heat resistant porous layer is 0.6 N/cm or more.