Battery Separator Coating With Metal Hydroxide Dispersion and Adhesion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing secondary battery separators face challenges in maintaining adhesion force to the electrode while ensuring a uniform coating layer, particularly when using metal hydroxides for improved flame retardancy, as they suffer from poor dispersibility and reduced adhesion due to phase separation issues.
Innovation Solution
A separator for secondary batteries is developed with a coating layer comprising a polyolefin-based substrate, a metal hydroxide inorganic material, a dispersant (tannic acid), and a mixed solvent containing an alcohol, which enhances dispersibility and adhesion force through vapor-induced phase separation, ensuring a uniform coating layer and improved electrode bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If silane-modified polyethylene crosslinking reaction is promoted in the extruder using a crosslinking catalyst master batch, then crosslinking reaction efficiency is improved, but resin aggregates are generated and homogeneity of physical properties deteriorates
Solution Approach 1:
The crosslinking process is divided into two separate stages: first, silane grafting occurs during extrusion to modify the polyethylene; second, the actual crosslinking reaction occurs after membrane formation through moisture exposure or heat treatment. This segmentation prevents resin aggregation during extrusion while achieving the desired crosslinked structure in the final product, thereby maintaining both production efficiency and membrane homogeneity.
Solution Approach 2:
The silane modification is performed as a preliminary action during the extrusion process, preparing the polyethylene for subsequent crosslinking without completing the full crosslinking reaction at that stage. This preliminary grafting allows the resin to remain processable during membrane formation, while the crosslinking structure develops later to provide the required thermal and mechanical properties without causing aggregation issues.
2Quantity of substance
If membrane thickness is reduced to achieve smaller battery cell sizes, then energy density is improved, but membrane rupture resistance at high temperature deteriorates
Solution Approach 1:
The separator is constructed as a composite material combining polyethylene base resin with silane-modified crosslinked structures. This composite approach creates a three-dimensional network within the thin membrane that significantly enhances mechanical strength and thermal stability. The crosslinked gel fraction (30-80%) provides structural reinforcement that compensates for the reduced thickness, enabling membranes of 15 µm or less to maintain rupture temperatures above 200°C while achieving high energy density.
Solution Approach 2:
The crosslinked gel structure is distributed throughout the membrane matrix to provide localized reinforcement. This creates regions of enhanced strength and thermal resistance within the thin membrane structure, allowing the overall membrane to maintain integrity at high temperatures despite reduced thickness. The gel fraction acts as a distributed reinforcement network that prevents catastrophic failure.
3Temperature
If crosslinking reaction is enhanced to improve heat resistance, then membrane rupture temperature is improved, but radical generation increases causing electrolyte decomposition
Solution Approach 1:
The crosslinking chemistry is changed from conventional peroxide-based systems to silane-based moisture-curing or condensation crosslinking. This parameter change in the chemical reaction mechanism achieves the desired crosslinked network structure and high membrane rupture temperature (above 200°C) while significantly reducing harmful radical generation. The silane crosslinking proceeds through hydrolysis and condensation reactions that are less prone to generating free radicals compared to peroxide decomposition.
Solution Approach 2:
The silane crosslinking system utilizes controlled oxidation or moisture-induced hydrolysis rather than strong peroxide oxidants. This alternative chemical pathway accelerates the crosslinking process while minimizing harmful side reactions. The moisture-curing mechanism or controlled hydrolysis of silane groups provides a gentler crosslinking route that achieves high thermal stability without the excessive radical generation associated with traditional peroxide crosslinking systems.
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 results in a separator with enhanced adhesion force to the electrode, preventing disintegration and improving safety by maintaining a uniform coating layer, thus enhancing the stability and performance of secondary batteries.
Implementation Method 1
it has gradually come to light by experimentation that high-temperature membrane rupture properties can be exhibited by constructing silane crosslinked sections (a gel structure) in a polyolefin separator
Implementation Method 2
when a dispersant is used in the process, crosslinked sections are dispersed uniformly, and resin aggregates are prevented from forming
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3
AI summary
Disclosed herein is a separator for a secondary battery comprising a porous separator substrate including a polyolefin-based material and a coating layer coated on at least one surface of the separator substrate, the separator for a secondary battery having a uniform coating layer and improved adhesion force, wherein the coating layer is a dry form of a slurry comprising a binder, an inorganic material, a mixed solvent including at least two solvents, and a dispersant, the inorganic material being a metal hydroxide and the dispersant being a compound including 10 to 30 hydroxy groups in one molecule.