Polyolefin Microporous Membrane for Pressure-Stable Battery Separators
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Solution Overview
Problem
Conventional polyolefin microporous membranes used in nonaqueous secondary batteries, such as lithium ion secondary batteries, face challenges in maintaining both high output and cycle characteristics while ensuring safety, particularly under external pressure, as improving ion permeability can lead to deterioration in safety during nail penetration tests.
Innovation Solution
A polyolefin microporous membrane with specific characteristics, including post-compression porosity, crystallinity, basis weight-converted puncture strength, air permeability, and thickness, is developed to enhance the membrane's structural homogeneity and ion permeability, ensuring both high output and safety by maintaining porosity and low air permeability even under pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ion permeability is improved by increasing porosity, then output characteristics are enhanced, but safety deteriorates during nail penetration tests
Solution Approach 1:
The patent applies parameter changes by precisely controlling the porosity of the polyolefin microporous membrane within the range of 30-80% and the basis weight within 1-20 g/m². By optimizing these parameters, the membrane achieves high ion permeability for improved output characteristics while maintaining sufficient mechanical strength and structural integrity to pass safety tests including nail penetration tests. The specific porosity range allows adequate ion transport without creating excessive voids that would compromise safety.
Solution Approach 2:
The patent implements local quality by creating a microporous structure with controlled pore size distribution and spatial arrangement. The membrane possesses different local characteristics: highly porous regions for ion permeability and sufficiently dense regions for mechanical strength. This heterogeneous structure allows the membrane to simultaneously achieve high ion permeability for output enhancement and maintain structural integrity for safety assurance.
2Productivity
If porosity is increased to maintain high output, then ion permeability improves, but mechanical strength deteriorates
Solution Approach 1:
The patent resolves this contradiction through parameter changes by controlling the porosity within 30-80% and basis weight within 1-20 g/m². These optimized parameters ensure that even at high porosity levels, the membrane maintains adequate mechanical strength by preventing excessive void formation and maintaining sufficient polymer matrix continuity to support structural integrity while allowing high ion flux for output.
Solution Approach 2:
The patent employs composite material principles by creating a microporous polyolefin structure that combines dense polymer regions for mechanical strength and porous regions for ion transport. This composite microstructure, achieved through controlled phase separation during membrane formation, allows simultaneous optimization of mechanical properties and ion permeability for high output performance.
3Productivity
If basis weight is reduced to improve ion permeability, then output characteristics enhance, but puncture strength deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the basis weight within the narrow range of 1-20 g/m². This precise control ensures that the membrane is thin enough to provide high ion permeability for improved output characteristics while maintaining sufficient material quantity and structural integrity to achieve adequate puncture strength. The lower bound of 1 g/m² prevents excessive thinness that would compromise strength.
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 membrane achieves high output and excellent cycle characteristics while maintaining safety by reducing electrical resistance and inhibiting increases in resistance, ensuring satisfactory battery performance and safety in nonaqueous secondary batteries.
Implementation Method 1
Polyolefin microporous membranes exhibit excellent electrical insulation and ion permeability
Implementation Method 2
Polyolefin microporous membranes exhibit excellent electrical insulation and ion permeability
Data Source
AI summary
A polyolefin porous film is provided which has a film thickness of 1-30 μm and an air permeability of at most 500 sec/100 cm3, and which has a 30% or higher porosity after compression, measured in a compression test under the conditions in which the temperature is 70° C., the pressure is 8 MPa and the compression time is 3 minutes.