Microporous Polyolefin Battery Separator Multilayer Design
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Solution Overview
Problem
Conventional methods for manufacturing microporous polyolefin films for battery separators fail to simultaneously achieve high strength, permeability, uniform quality, and thermal stability, leading to potential safety issues such as explosions due to overheating.
Innovation Solution
A multilayer film is created by separately manufacturing polyethylene and polypropylene or heat-resistant filler layers, then combining them to form a film with micropores and macropores, respectively, through stretching and cracking processes, without using a diluent, to enhance thermal stability and permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polyethylene is used to achieve low shutdown temperature, then thermal response speed is improved, but thermal stability deteriorates due to low melt fracture temperature
Solution Approach 1:
The separator is divided into multiple functional layers: a polyethylene layer (providing low shutdown temperature of 100-130°C) and a heat-resistant layer containing polypropylene and inorganic filler (providing high melt fracture temperature of 160-200°C). Each layer performs its specific thermal function independently, resolving the contradiction between rapid thermal response and thermal stability.
Solution Approach 2:
The heat-resistant layer is formed as a composite material combining polypropylene (providing structural integrity at high temperature) with inorganic filler such as alumina, silica, or boehmite (providing thermal stability and high melt fracture temperature). This composite structure achieves both the required shutdown temperature and thermal stability.
2Reliability
If inorganic material is added to improve thermal stability, then thermal stability is improved, but mixing uniformity deteriorates leading to pinholes and poor film properties
Solution Approach 1:
The inorganic filler is concentrated in the heat-resistant layer rather than being dispersed throughout the entire separator structure. This segmentation allows for optimized mixing conditions specific to the heat-resistant layer formulation, improving mixing uniformity while maintaining thermal stability.
Solution Approach 2:
Polypropylene acts as an intermediary matrix material that facilitates uniform dispersion of inorganic filler particles. The polypropylene-inorganic filler composite structure promotes homogeneous mixing while maintaining the thermal stability benefits of the inorganic material.
3Strength
If micropores are formed through wet process to achieve high strength and uniform quality, then strength and quality uniformity are improved, but thermal stability deteriorates due to lack of heat-resistant components
Solution Approach 1:
The separator structure is segmented into distinct functional zones: the polyethylene layer (formed by wet process with diluent extraction) provides high strength and uniform micropore structure, while the separate heat-resistant layer containing polypropylene and inorganic filler provides thermal stability. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
The heat-resistant layer is formulated as a composite material system combining polypropylene matrix with dispersed inorganic filler particles (alumina, silica, boehmite, etc.). This composite structure provides both the mechanical properties needed for film integrity and the thermal stability required to prevent melt fracture at elevated temperatures.
4Reliability
If polypropylene is blended with polyethylene to improve thermal stability, then thermal stability is improved, but shutdown temperature increases reducing safety response speed
Solution Approach 1:
Instead of blending polypropylene with polyethylene in a single layer, the structure is segmented into separate layers: a polyethylene layer that maintains the low shutdown temperature (100-130°C) for rapid safety response, and a separate heat-resistant layer containing polypropylene (20-70 wt%) and inorganic filler that provides thermal stability without affecting the shutdown temperature of the polyethylene 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 resulting film exhibits low shutdown temperature, high melt fracture temperature, high strength, and improved thermal stability, suitable for high-capacity and high-power secondary batteries with enhanced safety features.
Implementation Method 1
melting and mixing mixture that comprises 20-50 weight % of polyethylene having a melting temperature of 125° C. or higher and 80-50 weight % of a diluent
Implementation Method 2
melting and mixing mixture
Implementation Method 3
forming a film by stretching the multi-layered sheet
Implementation Method 4
extracting the diluent from the film
Implementation Method 5
heat setting the film
Implementation Method 6
melting and mixing mixture that comprises 20-70 weight % of polypropylene having a melting temperature of 160° C. or higher and 80-30 weight % of a heat-resistant filler having a melting temperature of 170° C. or higher
Implementation Method 7
melting and mixing mixture
Data Source
AI summary
The present invention relates to a multi-layered microporous polyolefin film for a battery separator and a method for preparing the same. The microporous multi-layered film of the present invention has a characteristics to have both the low shutdown temperature conferred by the polyethylene and the high melt fracture temperature conferred by the polypropylene and heat-resistant filler. In addition, it has the high strength and stability conferred by the micropores prepared under wet process and the high permeability and high strength conferred by the macropores prepared under dry process. Therefore, this multi-layered film can be used effectively to manufacture a secondary battery with high capacity and high power.