Separator Thermal Shrinkage Suppression via Isocyanate Curing
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Solution Overview
Problem
Lithium secondary batteries face safety issues due to thermal shrinking of polyolefin-based separators at high temperatures, leading to potential short circuits and limited heat resistance, which existing inorganic material coatings fail to adequately address.
Innovation Solution
A separator with a porous polymer substrate and an inorganic particle layer, where a binder with hydroxyl and carboxyl groups is cured using an isocyanate-based curing agent, forming a network structure that integrates inorganic particles and suppresses substrate shrinkage, thereby enhancing thermal stability and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyolefin-based porous substrate is used as a separator, then it provides good electrochemical performance, but it shows severe thermal shrinking behavior at temperatures of 100°C or higher, causing short circuits between cathode and anode
Solution Approach 1:
The patent applies composite materials by combining a polyolefin-based porous substrate with an inorganic material coating layer containing alumina particles and binder polymer. This composite structure maintains the electrochemical advantages of the polyolefin substrate while adding thermal stability through the inorganic coating, preventing thermal shrinking at high temperatures and eliminating short circuit risks.
2Temperature
If an inorganic material coating layer is formed on the porous polymer substrate to prevent thermal shrinking, then heat resistance is improved, but the binder polymer used has limited heat resistance with a melting point of approximately 150°C
Solution Approach 1:
The patent changes the key parameter of the binder polymer by selecting polyvinylidene fluoride-hexafluoropropylene with specific compositional ratios (60-90 mol% vinylidene fluoride and 10-40 mol% hexafluoropropylene). This parameter optimization enhances the binder's heat resistance and chemical stability, allowing it to maintain performance at temperatures exceeding 150°C while preserving adhesion to the inorganic particles and substrate.
3Temperature
If a cross-linking structure is used to enhance heat resistance, then thermal stability is improved, but thermal initiators such as AIBN produce radicals that attack the main chain of the binder polymer, limiting heat resistance enhancement
Solution Approach 1:
The patent extracts and eliminates the harmful thermal initiator (AIBN) from the cross-linking process. Instead of using radical-generating initiators that attack the binder polymer chain, the invention employs alternative cross-linking methods or relies on the inherent thermal stability of the optimized polyvinylidene fluoride-hexafluoropropylene binder, thereby achieving heat resistance enhancement without introducing harmful radicals that would degrade the polymer.
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 significantly reduces thermal shrinkage of the separator, improving high-temperature cycle characteristics and preventing short circuits, while maintaining excellent heat resistance and ion conductance, making it suitable for lithium secondary batteries in electric vehicles.
Implementation Method 1
a binder with hydroxyl and carboxyl groups is cured using an isocyanate-based curing agent, forming a network structure
Data Source
AI summary
Disclosed is a separator containing a porous polymer substrate and an inorganic particle layer formed on at least one surface of the porous polymer substrate, and the separator has increased insolubility for an electrolyte and enhanced dimensional stability at high temperatures, therefore, short circuit between a cathode and an anode may be suppressed even when an electrochemical device is overheated, and high temperature cycle characteristics of the electrochemical device are enhanced. In addition, discharge characteristics are improved due to an ion conductance enhancement, since the impregnation of the separator for the electrolyte increases. Therefore, the separator according to the present invention is suited for electrochemical devices that require heat resistance, in particular, for lithium secondary batteries for electric vehicles, since, while the separator according to the present invention has excellent heat resistance, an electrochemical device that includes the separator gives equal performance in electrochemical properties when compared to existing separators.