Shish-Kebab Polyolefin Separator for Rapid Charging Safety
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Solution Overview
Problem
Existing non-aqueous electrolyte secondary battery separators face challenges in achieving a balance between maintaining safety through effective shutdown and preventing meltdown, while also ensuring high capacity retention rates during rapid charging, due to difficulties in controlling pore structure and material costs associated with high heat-resistant fluorocarbon resins.
Innovation Solution
A biaxially-oriented polyolefin porous film with a shish-kebab structure formed by extended-chain and folded-chain crystals, where the average distances between adjacent crystals are controlled to enhance mechanical strength and ion mobility, combined with a heat-resistant porous film laminated on top to prevent short circuits during high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pore diameter of the separator is increased to improve lithium ion mobility for rapid charging, then the capacity retention rate is improved, but needle-like metal lithium (dendrites) growth is facilitated causing internal short circuits
Solution Approach 1:
The separator employs a dual-layer structure where the first layer (polyolefin porous film) provides shutdown function and the second layer (heat-resistant porous film) provides mechanical strength and dendrite suppression. Each layer has locally optimized properties: the first layer has controlled pore size for ion mobility while the second layer has larger pores and higher strength to prevent dendrite penetration, resolving the contradiction between charging speed and safety.
Solution Approach 2:
The invention combines two different porous films with complementary functions: a polyolefin porous film for shutdown capability and a heat-resistant porous film for mechanical strength and dendrite suppression. This composite structure allows the separator to simultaneously achieve high lithium ion mobility for rapid charging while preventing dendrite-induced short circuits through the synergistic effects of the two materials.
2Productivity
If the porosity of the separator is increased to improve lithium ion mobility, then the capacity retention rate is improved, but the tensile strength and piercing strength are lowered
Solution Approach 1:
The separator is divided into two functional layers: the first layer (polyolefin porous film) with optimized porosity for ion mobility but lower mechanical strength, and the second layer (heat-resistant porous film) with higher mechanical strength to compensate for the reduced strength of the first layer. This segmentation allows each layer to be optimized for its specific function while the combination maintains overall mechanical integrity.
Solution Approach 2:
By combining a polyolefin porous film with a heat-resistant porous film, the separator achieves both high porosity for rapid ion transport and sufficient mechanical strength. The heat-resistant layer acts as a reinforcement that prevents the separator from becoming too weak when the first layer's porosity is increased for rapid charging applications.
3Reliability
If a composite film combining polyolefin porous film with highly heat-resistant layer is used to prevent meltdown, then the safety is improved, but the material cost increases due to fluorocarbon resins
Solution Approach 1:
The invention changes the key parameter of heat resistance by using a heat-resistant porous film with a melting point of 150°C or higher (such as polyphenylene sulfide, polyether ether ketone, or aramid) instead of traditional fluorocarbon resins. This parameter change maintains the meltdown prevention function while significantly reducing material costs and improving ease of manufacture.
Solution Approach 2:
The invention replaces expensive fluorocarbon resins with more economical heat-resistant materials that provide equivalent or superior heat resistance. The use of materials like polyphenylene sulfide, polyether ether ketone, or aramid offers a cost-effective alternative to fluorocarbon-based composite films while maintaining the necessary safety performance.
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 a suitable pore structure for lithium ion mobility, ensuring high capacity retention and improved safety by preventing internal short circuits and maintaining mechanical integrity during rapid charging cycles.
Implementation Method 1
a biaxially-oriented polyolefin porous film with a shish-kebab structure formed by extended-chain and folded-chain crystals, where the average distances between adjacent crystals are controlled to enhance mechanical strength and ion mobility
Implementation Method 2
combined with a heat-resistant porous film laminated on top to prevent short circuits during high temperatures
Implementation Method 3
When the battery temperature increases to a certain temperature, the polyolefin porous film softens to close the pores therein. As a result, the ion conductivity between the electrodes is lost, and the battery reaction is stopped
Data Source
AI summary
Disclosed is a separator for a non-aqueous electrolyte secondary battery, the separator including a biaxially-oriented polyolefin porous film including extended-chain crystals and folded-chain crystals, wherein the extended-chain crystals and the folded-chain crystals form a shish-kebab structure. The average distance between the extended-chain crystals adjacent to each other is 1.5 μm or more and less than 11 μm, and the average distance between the folded-chain crystals adjacent to each other is 0.3 μm or more and less than 0.9 μm. A heat resistant porous film may be laminated on the polyolefin porous film. The heat resistant porous film includes a resin having heat resistance or a melting point higher than a melting point of the polyolefin porous film.