Crosslinked Battery Separator Coating Against Heat Shrinkage
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Solution Overview
Problem
Conventional separators for lithium secondary batteries exhibit heat shrinking behavior due to their material properties, leading to potential short-circuits between the cathode and anode, and existing porous coating layers with binder polymers also suffer from heat shrinking issues, compromising safety and adhesion to electrodes.
Innovation Solution
A separator with a crosslinked porous coating layer formed by urethane crosslinking between inorganic particles and a crosslinkable binder polymer, which includes polyvinylidene fluoride-based monomers with acrylate and isocyanate groups, is used, providing enhanced heat resistance and adhesion to electrodes without additional crosslinking steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous coating layer with binder polymer is formed on the porous polymer substrate, then adhesion to electrodes is improved, but heat shrinking occurs in the porous coating layer
Solution Approach 1:
The patent changes the chemical structure of the binder polymer by introducing crosslinkable functional groups (isocyanate groups) that react with hydroxyl groups on inorganic particles to form crosslinked structures. This parameter change in molecular structure transforms the linear polymer chains into a three-dimensional network, eliminating heat shrinking while preserving adhesion properties.
Solution Approach 2:
The patent creates a composite porous coating layer combining inorganic particles (alumina, silica, or boehmite with hydroxyl groups) and crosslinkable binder polymer (polyvinylidene fluoride-based polymer with grafted isocyanate groups). This composite structure provides both adhesion to electrodes and resistance to heat shrinking through the crosslinked network formed between inorganic and organic components.
2Ease of manufacture
If conventional polyolefin-based porous polymer substrate is used as separator, then manufacturing is simple, but severe heat shrinking behavior occurs at 100°C or higher
Solution Approach 1:
The patent modifies the thermal properties of the separator by forming a crosslinked porous coating layer on the polyolefin substrate. The crosslinking reaction between isocyanate groups in the binder polymer and hydroxyl groups on inorganic particles creates a thermally stable network that prevents the severe heat shrinking behavior of conventional polyolefin substrates at temperatures of 100°C or higher.
Solution Approach 2:
The patent develops a composite structure consisting of a polyolefin porous polymer substrate combined with a porous coating layer containing crosslinked inorganic particles and binder polymer. This composite design maintains the manufacturing simplicity of polyolefin substrates while adding heat resistance through the crosslinked coating layer that acts as a thermal stabilizer.
3Object-affected harmful factors
If crosslinkable binder polymer is used in porous coating layer, then heat resistance is improved, but additional crosslinking steps are required
Solution Approach 1:
The patent merges the coating formation process with the crosslinking process by designing a binder polymer that undergoes crosslinking during the normal battery manufacturing process. The isocyanate groups in the polyvinylidene fluoride-based binder polymer react with hydroxyl groups on inorganic particles during battery assembly and initial charging cycles, eliminating the need for separate crosslinking steps while achieving heat resistance.
Solution Approach 2:
The patent enables the porous coating layer to self-crosslink through the chemical reaction between isocyanate groups in the binder polymer and hydroxyl groups on inorganic particles under the conditions present during battery manufacturing and initial operation. This self-service crosslinking mechanism eliminates the need for external crosslinking equipment or additional processing steps, simplifying the overall manufacturing process while achieving the desired heat 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 crosslinked separator achieves improved heat resistance and maintains strong adhesion to electrodes, preventing heat-induced short-circuits and ensuring safety, while the urethane crosslinking process integrates seamlessly into the battery manufacturing without additional processing steps.
Implementation Method 1
a crosslinkable binder polymer crosslinked through urethane crosslinking
Data Source
AI summary
A separator for a lithium secondary battery, including: a porous polymer substrate; and a crosslinked porous coating layer on at least one surface of the porous polymer substrate. The crosslinked porous coating layer includes inorganic particles and a crosslinkable binder polymer crosslinked through urethane crosslinking. The separator has improved heat resistance as compared to the conventional separators and maintains adhesion to an electrode. A lithium secondary battery including the separator is also disclosed.