Polyolefin Separator Film Compressive Modulus and Surface Roughness
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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 in balancing shutdown and meltdown temperatures with mechanical strength and electrical resistance.
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 provides enhanced resistance and adaptability to external forces, ensuring safe operation and maintaining battery characteristics during compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer or laminated polyolefin micro porous film is used as a separator film, then safety is improved by preventing short circuits and enabling pore closing at elevated temperatures, but pressure resistance in the thickness direction deteriorates
Solution Approach 1:
The patent applies composite materials by combining polyolefin resin with inorganic particles (such as alumina, silica, or boehmite) to create a separator film that maintains the pore closing safety function while gaining enhanced mechanical strength and pressure resistance. The inorganic particles form a rigid framework that supports the polyolefin matrix, preventing film collapse under compression while preserving ion transport channels.
Solution Approach 2:
The patent implements local quality by creating regions with different properties within the separator film. The inorganic particles are distributed to provide localized structural support in areas subject to compression, while maintaining the overall porosity and pore closing capability of the polyolefin matrix. This allows different regions of the film to fulfill different functions: safety shutdown and mechanical reinforcement.
2Reliability
If the pore closing starting temperature is set too low, then safety is improved by preventing thermal runaway, but battery performance deteriorates due to impeded ion flow
Solution Approach 1:
The patent applies parameter changes by optimizing the pore closing starting temperature to a specific range (100°C to 150°C) that balances safety and performance. This temperature range is carefully selected to close pores before thermal runaway occurs while maintaining ion flow during normal operating conditions. The inorganic particles also help maintain structural integrity at these temperatures, enabling controlled pore closing without complete film collapse.
3Volume of stationary object
If the separator film is compressed in the thickness direction, then device density is improved, but Gurley value changes significantly affecting ion transport
Solution Approach 1:
The patent applies porous materials by incorporating inorganic particles that maintain open pore structures even under compression. The rigid inorganic framework prevents complete pore collapse, preserving ion transport channels while allowing the film to be compressed for higher device density. The porous structure of the inorganic particle network continues to facilitate electrolyte penetration and ion movement despite reduced thickness.
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 polyolefin micro porous film exhibits excellent durability and resistance to external pressures, maintaining battery performance and safety by balancing shutdown and meltdown temperatures, and reducing changes in Gurley value under pressure, thus ensuring reliable operation in 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 polyolefin micro porous film having excellent pressure resistance in a thickness direction
Data Source
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.