Crosslinked Binder Separator for Lithium Battery Thermal Stability
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in achieving high energy density and thermal stability due to limitations in the separator materials, which affect the battery's cycle-life characteristics and safety, particularly during overheating and explosion scenarios.
Innovation Solution
A separator for rechargeable lithium batteries is developed, comprising a substrate with a heat-resistant porous layer formed by a crosslinked binder and a non-crosslinked binder in specific weight ratios, including multi-functional urethane-based compounds and vinylidenefluoride-based polymers, along with a filler, to enhance mechanical strength, wettability, and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional separator material is used, then the battery can be manufactured with standard materials, but the thermal stability and heat resistance are insufficient leading to safety issues during overheating
Solution Approach 1:
The separator is constructed as a composite material consisting of a polyolefin substrate combined with a heat-resistant porous layer containing crosslinked binder and inorganic filler particles. This composite structure provides both the functional properties of the substrate and the thermal stability of the heat-resistant layer, preventing thermal shrinkage during overheating while maintaining separator performance.
Solution Approach 2:
The patent modifies the physical and chemical parameters of the separator by introducing a crosslinked binder system with specific crosslinking density and a heat-resistant porous layer with controlled composition and thickness. These parameter changes enhance the thermal properties of the separator, enabling it to maintain dimensional stability at elevated temperatures up to 200°C or higher.
2Temperature
If the separator structure is enhanced for better heat resistance, then thermal stability improves, but the mechanical strength and wettability may be compromised
Solution Approach 1:
The heat-resistant porous layer is applied locally on the substrate surface rather than throughout the entire separator structure. This localized approach provides heat resistance where it is most needed (at the interface with electrodes and electrolyte) while preserving the mechanical integrity of the bulk substrate material.
Solution Approach 2:
The heat-resistant porous layer contains inorganic filler particles distributed within a crosslinked binder matrix, creating a porous structure that maintains ion permeability and electrolyte wettability while providing thermal stability. The porosity allows the layer to function as a heat-resistant coating without blocking lithium ion transport.
3Reliability
If a crosslinked binder with high crosslinking density is used, then heat resistance improves, but the cycle-life characteristics and ion permeability may deteriorate
Solution Approach 1:
The patent employs partial crosslinking rather than complete crosslinking of the binder, achieving sufficient heat resistance without excessive crosslinking density. The crosslinking degree is controlled to provide thermal stability while maintaining adequate flexibility and ion permeability for long-term battery cycling performance.
Solution Approach 2:
The porous structure of the heat-resistant layer with controlled porosity and interconnected pores allows lithium ion transport while the crosslinked binder provides thermal stability. The pore structure ensures that even with crosslinking, ion permeability is maintained at levels sufficient for good cycle-life characteristics.
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 improves the battery's thermal stability, cycle-life characteristics, and safety by reducing thermal shrinkage, preventing short-circuits, and maintaining high energy density, even under extreme conditions like overheating and explosion.
Implementation Method 1
the crosslinked binder has a cross-linked structure of at least one crosslinkable compound
Implementation Method 2
improves the battery's thermal stability, cycle-life characteristics, and safety by reducing thermal shrinkage
Implementation Method 3
the separator plays a role of electrically insulating the positive and negative electrodes, and may include micropores through which lithium ions move
Implementation Method 4
the at least one crosslinkable compound including a multi-functional urethane-based compound
Data Source
AI summary
A separator for a rechargeable lithium battery and a rechargeable lithium battery including the same, the separator including a substrate, and a heat-resistant porous layer on at least one side of the substrate, the heat-resistant porous layer including a crosslinked binder and a non-crosslinked binder, wherein the crosslinked binder has a cross-linked structure of at least one crosslinkable compound, the at least one crosslinkable compound including a multi-functional urethane-based compound, and the crosslinked binder and the non-crosslinked binder are included in a weight ratio of about 3:7 to about 8:2.