Cross-Linked Separator Coating for Heat-Resistant Li-Ion Cells
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Solution Overview
Problem
Existing lithium secondary batteries face challenges with thermal stability and safety due to the deterioration of separators, leading to potential short circuits and risks of overheating or fire, especially in high-capacity and high-output applications.
Innovation Solution
A separator is developed with a coating layer comprising an aqueous cross-linking reactive polyacrylamide-based copolymer and inorganic particles, with a weight ratio of binder to inorganic particles ranging from 1:10 to 1:35 and a thickness of 0.5 μm to 4 μm, enhancing thermal resistance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a thin-film separator is used to increase capacity and current density, then productivity and energy density are improved, but mechanical strength and thermal resistance deteriorate
Solution Approach 1:
The separator is constructed as a composite material consisting of a polyolefin base layer combined with a coating layer containing inorganic particles (such as alumina, silica, or boehmite) dispersed in a binder polymer. This composite structure allows the thin-film separator to maintain mechanical strength and thermal resistance while achieving high capacity and current density, as the inorganic particles provide thermal stability and structural reinforcement without significantly increasing thickness.
2Volume of moving object
If the separator thickness is reduced to improve energy density, then volume efficiency increases, but safety and thermal stability deteriorate
Solution Approach 1:
The separator employs local quality enhancement by applying a functional coating layer only on specific surfaces or regions where thermal and mechanical reinforcement is most needed. The coating layer contains inorganic particles concentrated in areas prone to thermal degradation or mechanical stress, allowing the bulk of the separator to remain thin for high energy density while localized regions provide enhanced safety and thermal stability.
Solution Approach 2:
By incorporating inorganic particles into a coating layer applied on the thin-film separator, the invention creates a composite structure that provides thermal stability and mechanical reinforcement only where required, maintaining overall thinness for high energy density while ensuring safety in critical regions.
3Temperature
If a coating layer is applied to improve thermal resistance, then thermal stability is improved, but manufacturing complexity increases
Solution Approach 1:
The coating layer is formed by controlling parameters such as particle size distribution, binder polymer molecular weight, and coating thickness within specific ranges. By optimizing these parameters, the invention achieves high thermal resistance with a relatively simple single-layer coating structure, avoiding the need for complex multi-layer configurations while maintaining manufacturing feasibility.
Solution Approach 2:
The coating layer is designed with a porous structure having controlled porosity (30-80%) and pore size (0.01-10 μm), allowing electrolyte penetration and ion transport while providing thermal reinforcement. This porous architecture can be formed through simple processes like phase separation or foam formation during coating application, avoiding complex manufacturing steps while achieving the desired thermal resistance.
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 separator provides improved thermal resistance and stability, resulting in enhanced battery safety and lifespan characteristics for lithium secondary batteries.
Implementation Method 1
the polyacrylamide-based copolymer includes at least two cross-linking reactive groups cross-linkable with each other
Implementation Method 2
a coating layer arranged on at least one surface of the porous substrate
Data Source
AI summary
Provided are a separator, a lithium secondary battery employing the same, and a method of preparing the separator. The separator includes: a porous substrate; and a coating layer arranged on at least one surface of the porous substrate, wherein the coating layer includes a binder and inorganic particles, the binder includes an aqueous cross-linking reactive polyacrylamide-based copolymer, and the polyacrylamide-based copolymer includes at least two cross-linking reactive groups cross-linkable with each other, a weight ratio of the binder to the inorganic particles is about 1:10 to about 1:35, and a thickness of the coating layer is greater than 0.5 μm and no greater than 4 μm. The separator has significantly improved thermal resistance characteristics and low resistance, and therefore, a lithium secondary battery with improved battery stability and lifespan characteristics at the same time may be provided.