Thin Battery Separator Structure for Piercing and Heat Resistance
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Solution Overview
Problem
The challenge is to enhance the safety performance of electrochemical devices, such as secondary batteries, by reducing the risk of internal short circuits and thermal runaway while maintaining high energy density, which is hindered by the thinness of separators that lack sufficient strength and heat resistance.
Innovation Solution
A separator with a base film having a tensile energy per unit thickness of ≥1.8 J/10 μm and elongation of ≥150% in both machine and transverse directions, made from a polyethylene-based polymer with a heat-resistant layer, is developed. This film is produced through a process involving stretching and heat-setting, providing improved piercing resistance and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the separator is reduced to increase energy density, then the weight and volume of the secondary battery are reduced, but the risk of internal short circuits increases and safety performance deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the tensile energy per unit thickness to ≥1.8 J/10 μm and elongation to ≥150% in both MD and TD directions. These parameter specifications ensure that even at reduced thickness (2-40 μm), the separator maintains sufficient mechanical strength and toughness to prevent piercing by foreign particles while retaining high energy density benefits
Solution Approach 2:
The separator is constructed as a composite structure with a base film providing mechanical strength and a heat-resistant layer containing inorganic particles (such as alumina, silica, or boehmite) dispersed in a heat-resistant polymer matrix. This composite structure enhances both piercing resistance and heat resistance, allowing thin separators to maintain safety performance
2Quantity of substance
If the thickness of the separator is reduced to increase energy density, then the weight and volume of the secondary battery are reduced, but the mechanical strength and piercing resistance decrease
Solution Approach 1:
The patent specifies minimum tensile energy per unit thickness of ≥1.8 J/10 μm and minimum elongation of ≥150% to ensure adequate piercing resistance. These parameter thresholds are engineered to prevent the separator from being pierced by foreign particles during battery assembly and operation, even when the separator thickness is reduced to 2-40 μm
Solution Approach 2:
The heat-resistant layer contains inorganic particles (alumina, silica, boehmite) with high compressive strength and stiffness, dispersed in a heat-resistant polymer matrix. This composite structure provides enhanced mechanical strength and piercing resistance to the thin separator, compensating for the reduced thickness
3Quantity of substance
If the thickness of the separator is reduced to increase energy density, then the weight and volume of the secondary battery are reduced, but the heat resistance and shrinkage control deteriorate
Solution Approach 1:
The heat-resistant layer is composed of inorganic particles (alumina, silica, boehmite) that are thermally stable and maintain structural integrity at high temperatures, dispersed in a heat-resistant polymer matrix such as polypropylene or polyethylene. This composite structure prevents excessive shrinkage and maintains separator dimensions under thermal stress, even when the overall separator thickness is reduced
Solution Approach 2:
The patent specifies that the heat-resistant layer should have a thickness of 1-10 μm and contain inorganic particles with a volume fraction of 50-90%. These parameter specifications ensure adequate heat resistance and shrinkage control while minimizing the additional thickness added to the separator
4Reliability
If the tensile energy per unit thickness is increased to improve piercing resistance, then the safety performance is improved, but the manufacturing complexity and process control difficulty increase
Solution Approach 1:
The patent specifies a minimum tensile energy per unit thickness of ≥1.8 J/10 μm and minimum elongation of ≥150%, providing clear parameter targets for manufacturing. These parameter specifications guide the selection of base film materials and processing conditions, simplifying quality control while ensuring adequate piercing resistance
Solution Approach 2:
The heat-resistant layer is applied to the base film before the separator is installed in the battery. This preliminary action ensures that the mechanical strength and heat resistance properties are established before the separator undergoes any in-situ processing or assembly operations, simplifying the overall manufacturing process
Data Source
AI summary
The present application provides a separator and a preparation method thereof, an electrochemical device, an electrochemical apparatus and a powered device. The separator comprises a base film, the base film has a tensile energy per unit thickness of ≥1.8 J/10 μm in both MD direction and TD direction, and an elongation of ≥150% in both MD direction and TD direction, and the thickness of the base film is 2 μm˜40 μm.