Battery Separator Crosslinking for Heat Resistance and Uniformity
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Solution Overview
Problem
Current methods for manufacturing lithium secondary battery separators fail to achieve a balance between mechanical properties and heat resistance while also being economically feasible and productive, often resulting in safety issues due to thermal runaway and non-uniform physical properties.
Innovation Solution
A method involving the extrusion and stretching of a composition containing crosslinkable polyolefin with a silane-based compound and a non-crosslinkable polyolefin, followed by application of a crosslinking catalyst and extraction solvent, and subsequent crosslinking using heat and steam to improve heat resistance and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a silane-modified polyolefin is used to manufacture a crosslinking separator, then heat resistance is improved, but the physical properties (thickness, air permeability, puncture strength) become extremely inferior to commercial standards
Solution Approach 1:
The patent changes the molecular weight parameter of the polyolefin from conventional ranges to ultra-high molecular weight (50,000 or more), which fundamentally alters the material properties to achieve both heat resistance and acceptable physical properties
Solution Approach 2:
The patent creates a composite material system by mixing ultra-high molecular weight polyethylene with silane-modified polyolefin, combining the advantages of both materials to achieve balanced heat resistance and physical properties
2Temperature
If ultra high molecular weight polyethylene is mixed with silane-modified polyolefin, then heat resistance is improved, but dispersibility becomes poor leading to non-uniform physical properties
Solution Approach 1:
The patent specifies precise molecular weight parameters (50,000 or more) and mixing ratios to optimize the dispersibility and uniformity of the ultra-high molecular weight polyethylene with silane-modified polyolefin
Solution Approach 2:
The patent employs specific mixing processes and molecular weight matching to achieve homogeneous distribution of components, ensuring uniform physical properties throughout the separator
3Reliability
If alkoxy group-containing vinyl silane is grafted to diluent during reactive extrusion, then crosslinking capability is achieved, but the diluent cannot be recycled and unreacted silane elutes during extrusion
Solution Approach 1:
The patent replaces the conventional recyclable diluent with a sacrificial pore-forming agent that is intentionally designed to be removed after serving its purpose, eliminating the problems of recycling and elution
Solution Approach 2:
The patent extracts/removes the pore-forming agent after it has served its function in creating porosity and facilitating crosslinking, leaving behind a separator with the desired properties without the problematic residual chemicals
4Productivity
If an in-line process is used to apply crosslinking catalyst and perform crosslinking, then productivity is improved, but the steps and equipment remain independent and separate limiting further improvement
Solution Approach 1:
The patent combines the crosslinking catalyst application step and the crosslinking reaction step into a single integrated process, eliminating the independence and separation of steps while achieving high productivity
Solution Approach 2:
The patent designs a multi-functional process where the same equipment and conditions serve both to apply the crosslinking catalyst and to facilitate the crosslinking reaction, reducing the number of independent steps
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
This approach significantly reduces the time required for crosslinking, enhances productivity, and achieves balanced mechanical and heat-resistant properties, improving the reliability and reproducibility of the separators while maintaining economic feasibility.
Implementation Method 1
crosslinking the crosslinkable polyolefin while removing the extraction solvent remaining on the base film by applying heat and steam to the base film
Implementation Method 2
removing the extraction solvent remaining on the base film by applying heat and steam to the base film
Implementation Method 3
applying heat and steam to the base film
Data Source
AI summary
The present invention provides a method of manufacturing a separator, which includes: (a) manufacturing a base film by extruding and stretching a composition that includes a crosslinkable polyolefin in which a silane-based compound is grafted to a first polyolefin, a non-crosslinkable polyolefin consisting of a second polyolefin, and a pore-forming agent; (b) applying a crosslinking catalyst to the surface of the base film while extracting the pore-forming agent from the base film by applying a solution including the crosslinking catalyst and an extraction solvent to the base film; and (c) crosslinking the crosslinkable polyolefin while removing the extraction solvent remaining on the base film by applying heat and steam to the base film.