Separator Coating Method for Lithium Battery Safety
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Solution Overview
Problem
Existing methods for manufacturing separators for electrochemical devices, such as lithium secondary batteries, face issues with inorganic particle dispersion in the slurry for forming porous coating layers, leading to poor adhesion and surface protrusions, which can cause safety concerns like thermal runaway and short-circuits.
Innovation Solution
A method involving preliminary and secondary milling of a pre-dispersion with a controlled weight ratio of binder polymers and inorganic particles, applied to a porous polymer substrate, to achieve homogeneous dispersion and improved adhesion, including specific milling times and solvents to prevent particle aggregation and ensure uniform coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If inorganic particles are mixed with binder polymer at once to form slurry, then the coating layer can be formed, but the inorganic particles are not dispersed effectively
Solution Approach 1:
The patent divides the slurry preparation process into two distinct stages: first preparing a pre-dispersion with inorganic particles and first binder polymer, then mixing with second binder polymer solution. This segmentation allows effective dispersion without requiring excessive process complexity.
Solution Approach 2:
The patent performs preliminary dispersion of inorganic particles with the first binder polymer before adding the second binder polymer. This preliminary action ensures particles are well-dispersed before final slurry formation, improving dispersion uniformity.
2Reliability
If excessive amount of inorganic particles is used to improve safety, then thermal runaway resistance increases, but adhesion decreases
Solution Approach 1:
The patent uses a composite binder system with two different binder polymers having distinct functions. The first binder polymer (polyvinylidene fluoride) provides adhesion, while the second binder polymer (carboxymethyl cellulose) allows high inorganic particle content for thermal runaway resistance. This composite approach maintains both adhesion and safety.
Solution Approach 2:
The patent changes the chemical composition parameters of the binder system by introducing a second binder polymer with different properties (carboxymethyl cellulose vs. polyvinylidene fluoride). This parameter change enables the system to accommodate excessive inorganic particles while maintaining adhesion.
3Ease of manufacture
If polyolefin-based porous substrate is used as separator, then manufacturing ease is improved, but heat shrinking occurs at 100°C or higher causing short-circuit
Solution Approach 1:
The patent uses the porous coating layer as an intermediary between the polyolefin substrate and the electrolyte. This coating layer provides thermal stability and prevents heat shrinking at high temperatures, while the polyolefin substrate maintains manufacturing ease. The coating acts as a protective mediator.
Solution Approach 2:
The patent applies a thin porous coating layer (3-10 μm) on the polyolefin substrate. This thin film provides thermal stability without significantly affecting the substrate's manufacturing properties. The flexible thin film prevents heat shrinkage while maintaining ease of manufacture.
4Strength
If binder polymer content is increased to improve adhesion, then adhesion strength increases, but inorganic particle dispersion homogeneity decreases
Solution Approach 1:
The patent segments the binder polymer content into two functional components: first binder polymer (5-20 parts) for adhesion and second binder polymer (80-95 parts) for particle dispersion. This segmentation allows both adhesion strength and dispersion homogeneity to be optimized simultaneously.
Solution Approach 2:
The patent changes the chemical composition parameters by using two different binder polymers with different functions. The first binder polymer provides adhesion, while the second binder polymer ensures homogeneous particle dispersion, allowing both parameters to be optimized.
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 method results in a separator with enhanced dispersibility, adhesion, and surface uniformity, reducing the risk of thermal runaway and improving the safety and performance of electrochemical devices by preventing short-circuits and maintaining mechanical properties.
Implementation Method 1
conducting a preliminary milling of the pre-dispersion; mixing the pre-dispersion with the binder polymer solution and carrying out a secondary milling
Data Source
AI summary
A method for manufacturing a separator, including the steps of: (S1) preparing a pre-dispersion including inorganic particles dispersed in a pre-dispersion solvent and a first binder polymer dissolved in the pre-dispersion solvent; (S2) conducting a preliminary milling of the pre-dispersion; (S3) preparing a binder polymer solution including a second binder polymer dissolved in a binder polymer solution solvent; (S4) mixing the pre-dispersion with the binder polymer solution and carrying out a secondary milling to obtain a slurry for forming a porous coating layer; and (S5) applying the slurry to at least one surface of a porous polymer substrate, followed by drying, is disclosed. A separator obtained by the method and an electrochemical device including the same are also disclosed. According to the present disclosure, it is possible to provide a separator having a uniform surface and showing improved adhesion.