Dual-Layer Separator Coating for Heat Shrinkage and Assembly Stability
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Solution Overview
Problem
Lithium secondary battery separators made from polyolefin materials exhibit severe heat shrinkage at high temperatures, leading to safety issues like internal short-circuits and processing difficulties during battery assembly.
Innovation Solution
A separator design featuring a porous polymer substrate with a first organic/inorganic composite porous layer on one surface and a second organic/inorganic composite porous layer on the other, using inorganic particles with varying diameters and binder polymers to ensure high-temperature safety and assembly processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyolefin separator is used, then insulation property is provided, but heat shrinkage occurs at high temperature causing safety problems
Solution Approach 1:
The patent applies composite materials by combining polyolefin base material with inorganic particles (such as alumina, silica, or boehmite) and binder polymers to form a coated layer on the separator surface. This composite structure maintains the insulation properties of polyolefin while the inorganic particles provide thermal stability and prevent heat shrinkage at high temperatures, directly resolving the contradiction between reliability and heat resistance.
Solution Approach 2:
The patent changes the physical and chemical parameters of the separator surface by coating it with a composite layer containing inorganic particles with specific size distributions (bimodal or multimodal distribution). This parameter change modifies the surface properties to resist thermal contraction while maintaining the bulk material's insulation characteristics, thus preventing heat shrinkage without compromising reliability.
2Object-affected harmful factors
If inorganic particles with binder polymer are coated on polyolefin separator, then heat shrinkage is reduced, but meandering and wrinkling occur during assembly
Solution Approach 1:
The patent applies local quality by creating a coated layer with specific local properties on the separator surface. The coating contains inorganic particles and binder polymer in controlled proportions, forming a layer with optimized local mechanical properties that prevents both heat shrinkage and assembly defects like meandering and wrinkling, while maintaining the overall separator flexibility needed for manufacturing.
Solution Approach 2:
The patent utilizes porous materials by employing a coated layer with controlled porosity that allows ion transport while providing mechanical stability. The porous structure of the inorganic particle-binder composite maintains ion conductivity pathways, preventing assembly issues while the rigid inorganic framework prevents heat-induced deformation, thus resolving the contradiction between heat resistance and assembly processability.
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 solution provides improved thermal safety and assembly processability by minimizing heat shrinkage and preventing issues like wrinkling or meandering during battery assembly, while maintaining mechanical properties and ion conductivity.
Implementation Method 1
the polyolefin separator shows a severe heat shrinking behavior under a high temperature condition due to its material property
Implementation Method 2
high ion conductivity for increasing lithium-ion permeability based on high porosity
Implementation Method 3
a mixture of fine inorganic particles with a binder polymer, coated on at least one surface of the porous substrate
Data Source
AI summary
A separator for an electrochemical device, including: a porous polymer substrate having a first surface and a second surface opposite the first surface; a first organic/inorganic composite porous layer on the first surface of the porous polymer substrate where the first organic/inorganic composite porous layer includes first inorganic particles and a first binder polymer; and a second organic/inorganic composite porous layer on the second surface of the porous polymer substrate where the second organic/inorganic composite porous layer includes the first inorganic particles, second inorganic particles and a second binder polymer. The first inorganic particles have an average particle diameter of 1 nm to 100 nm, and the second inorganic particles have an average particle diameter larger than the average particle diameter of the first inorganic particles. The separator shows improved high-temperature safety and assembling processability.