Microporous Battery Separator Structure for Heat-Resistant Puncture Strength
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Solution Overview
Problem
Polyolefin-based microporous membranes used as separators in secondary batteries suffer from shrinkage and breakage at high temperatures, compromising their heat resistance and safety.
Innovation Solution
A polyolefin-based microporous membrane with specific molecular weight and melting temperature combinations of polyethylene and polypropylene, along with controlled surface roughness, porosity, and gas permeability, enhancing puncture strength and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyolefin-based microporous membrane is used as a separator to achieve ion permeability and electrical insulation, then the battery safety is improved through hole-closing function, but the membrane shrinks and breaks when heated to high temperatures
Solution Approach 1:
The patent uses a composite structure consisting of a polyolefin base layer providing hole-closing function and a heat-resistant coating layer containing inorganic particles (such as alumina, silica, or boehmite) dispersed in a binder resin. This composite structure allows the separator to maintain both the hole-closing safety function and high-temperature structural integrity, preventing shrinkage and breakage at elevated temperatures while retaining ion permeability
2Reliability
If the membrane porosity is increased to improve ion permeability, then the gas permeability increases, but the puncture strength may be compromised
Solution Approach 1:
The patent applies different properties to different layers: the base layer is designed with optimized porosity (30-40%) and pore size (0.03-0.08 μm) for ion permeability, while the heat-resistant coating layer provides mechanical reinforcement with inorganic particles and binder resin. This local differentiation allows the membrane to achieve high ion permeability in the base layer while the coating layer compensates for strength reduction, maintaining puncture strength above 0.3 N/μm even with increased porosity
3Manufacturing precision
If the surface roughness is reduced to improve membrane uniformity, then the manufacturing precision is improved, but the surface area for ion transport may be reduced
Solution Approach 1:
The patent resolves this contradiction by transitioning from a two-dimensional surface uniformity constraint to a three-dimensional solution: the heat-resistant coating layer with controlled thickness (1-5 μm) and specific surface roughness (0.5-2.0 μm) provides both mechanical reinforcement and sufficient ion transport pathways. The coating layer's porous structure and inorganic particle distribution create additional ion transport channels in the vertical dimension, compensating for the reduced surface area from smoother surfaces while maintaining manufacturing precision
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 improved puncture strength, gas permeability, and thermal stability, ensuring safety and high capacity of secondary batteries by preventing internal short circuits and excessive temperature rise.
Implementation Method 1
a first polyethylene having a weight average molecular weight of 30×104 g/mol to 100×104 g/mol and a melting temperature of 133° C. or higher; and a second polyethylene having a weight average molecular weight of less than 30×104 g/mol and a melting temperature of 126° C. or lower
Implementation Method 2
a gas permeability of 0.8×10−5 Darcy or more, a porosity of 30.0% or more
Data Source
AI summary
A polyolefin-based microporous membrane, a separator for a secondary battery, and manufacturing method thereof are provided. The polyolefin-based microporous membrane has a puncture strength of 0.3 N/μm or more, a gas permeability of 0.8×10−5 Darcy or more, a porosity of 30.0% or more, and a surface roughness of 2.1 μm or less, the surface roughness being obtained by selecting 5 random points on a front surface and 5 random points on a back surface, each random point having an area of 284 μm wide×220 μm long, measuring a maximum height difference (μm, Rmax) which is a difference between the highest surface height and the lowest surface height in the area of each point, and adding an average value of values measured in each of the 5 points on the front surface and an average value of values measured in each of the 5 points on the back surface.