Polyolefin Micro Porous Film Separator for Battery
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Solution Overview
Problem
Power-storage devices, such as lithium-ion batteries, require a separator film with excellent durability in the thickness direction to manage expansion and contraction while maintaining safety and thermal stability, as existing films face challenges with pore closing temperatures, mechanical strength, and uniform electrolyte distribution.
Innovation Solution
A polyolefin micro porous film with a compressive elastic modulus of 95 MPa to 150 MPa, specific Gurley value changes under pressure, and a surface roughness of 0.01 µm to 0.30 µm, which is produced through a process involving web forming, lamination, and stretching to achieve enhanced mechanical strength and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer or laminated polyolefin micro porous film is used as a separator film to achieve pore closing function for safety, then the danger of ignition due to excessive temperature rise can be prevented, but the flow of ions may be impeded by slight temperature rise when pore closing starting temperature is too low
Solution Approach 1:
The patent optimizes the pore closing starting temperature to be 120°C to 150°C, which is a specific parameter range that balances safety and ion flow. This parameter change ensures that the separator film only closes pores at temperatures high enough to prevent ignition while remaining below temperatures that would impede normal ion flow during battery operation.
2Strength
If the polyolefin micro porous film is compressed in the thickness direction to improve durability and manage expansion and contraction, then the mechanical strength and thermal stability are improved, but the pore structure may be deformed and the Gurley value may change
Solution Approach 1:
The patent applies a preliminary compression treatment to the polyolefin micro porous film before it is installed in the battery. This preliminary action pre-adjusts the pore structure and mechanical properties, ensuring that the film has optimal durability and dimensional stability while maintaining appropriate pore characteristics for ion flow. The compression is controlled to achieve the desired balance between strength and pore structure preservation.
3Volume of moving object
If the separator film is made thinner to reduce battery size and improve energy density, then the volume and weight are reduced, but the mechanical strength and pressure resistance in the thickness direction are decreased
Solution Approach 1:
The patent uses a composite structure consisting of a polyolefin micro porous film combined with a heat-resistant porous layer containing inorganic particles. This composite material approach allows the separator film to be made thinner while maintaining adequate mechanical strength and pressure resistance. The inorganic particles in the heat-resistant layer provide structural support and thermal stability, compensating for the reduced thickness of the polyolefin layer.
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 film exhibits excellent durability and resistance to compression, maintaining battery characteristics and safety by effectively managing pressure and thermal shrinkage, reducing the risk of internal short circuits and improving the reliability of power-storage devices.
Implementation Method 1
when the internal temperature of the device rises to a predetermined temperature or higher due to an abnormal current or the like, pores of the porous film are blocked and become closed to increase electrical resistance so as not to allow ions to flow between both electrodes
Implementation Method 2
a power-storage device which uses a restraint member to limit expansion and contraction from the outside of the device or includes a process of compressing the device
Implementation Method 3
a method of forming pores can be roughly classified into a wet method and a dry method... a dry method (see Patent Documents 1 and 2)... a method of forming pores using cleavage at the time of stretching
Data Source
Figure 1~2
AI summary
A polyolefin micro porous film includes at least one of polyethylene and polypropylene, in which the compressive elastic modulus is 95 MPa or more and 150 MPa or less, the surface roughness (Ra) of a film surface is measured for a front surface and a rear surface, and the average value (Ra(ave)) thereof is 0.01 µm to 0.30 µm.