Lithium Battery Separator Coating with Swellable Surface Adhesion
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Solution Overview
Problem
Olefin-based substrates used in rechargeable lithium batteries suffer from rapid heat shrinkage and insufficient adhesive force at high temperatures, leading to weakened adhesion between the separator and negative electrode, which deteriorates the battery's high-temperature charging and discharging characteristics.
Innovation Solution
A separator with a heat-resistant adhesive layer containing inorganic particles, a heat-resistant binder, and a swellable adhesive binder, composed of vinyl aromatic monomer, alkyl acrylate, and phosphonate-based monomer units, is used to enhance adhesive force and heat resistance, allowing for improved performance under low-temperature and low-pressure conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a coating layer including a mixture of inorganic material particles and a binder is formed on the olefin-based substrate to improve heat resistance, then heat resistance is improved, but the adhesive force on the surface portion of the coating layer is weakened due to density differences causing binder distribution mainly in the lower portion
Solution Approach 1:
The patent introduces a swellable adhesive binder that undergoes parameter change by swelling when it contacts the electrolyte solution. This swelling action changes the volume and distribution state of the adhesive binder, enabling it to migrate from the lower portion to the surface portion of the coating layer, thereby resolving the adhesive force weakness caused by initial density-based segregation
Solution Approach 2:
The adhesive binder performs self-service by automatically swelling and redistributing itself within the coating layer structure. This self-driven mechanism eliminates the need for external intervention to achieve uniform or surface-preferential distribution, and the binder autonomously corrects its position to enhance surface adhesion
2Ease of operation
If olefin-based substrates are used as separators to achieve desired flexibility, then flexibility is improved, but rapid heat shrinkage occurs at high temperatures and adhesive force becomes insufficient
Solution Approach 1:
The patent creates a composite structure by forming a coating layer containing inorganic material particles and adhesive binders on the olefin-based substrate. This composite coating layer combines the flexibility of the polymer substrate with the thermal stability of inorganic particles and the adhesive properties of the binder system, thereby achieving both flexibility and high-temperature reliability
Solution Approach 2:
The adhesive binder acts as an intermediary between the olefin-based substrate and the inorganic material particles. It mediates the interaction between these components, providing strong adhesion to the substrate while anchoring the inorganic particles, thus transferring the thermal stability benefit to the overall separator structure without compromising substrate flexibility
3Ease of manufacture
If the adhesive force between separator and negative electrode is weakened due to binder distribution and lithium salt precipitation at high temperatures, then manufacturing simplicity is maintained, but high-temperature charging and discharging characteristics are deteriorated
Solution Approach 1:
The swellable adhesive binder undergoes parameter change through swelling upon contact with electrolyte solution, transforming from a potentially segregated state to a uniformly distributed or surface-enriched state. This dynamic parameter change ensures strong adhesion under high-temperature operating conditions while maintaining simple coating layer formation during manufacturing
Solution Approach 2:
The coating layer is pre-formed during manufacturing with the adhesive binder distributed in a way that may not yet be optimal for adhesion. The preliminary action of coating is simplified, and the actual adhesion enhancement occurs later when the binder swells in situ during battery operation, separating the manufacturing simplicity from the operational performance
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 maintains strong adhesion and heat resistance, enhancing the high-temperature charge/discharge and storage characteristics of rechargeable lithium batteries, even under manufacturing conditions that do not involve high pressure or temperature.
Implementation Method 1
a swellable adhesive binder, wherein, when measuring the separator with an FT-IR (Fourier Transform Infrared Spectrometer) in ATR (Attenuated Total Internal Reflectance) mode, the swellable adhesive binder distributed from about 7% to about 12% of the thickness from a surface portion of the heat resistant adhesive layer is detected
Data Source
AI summary
Disclosed are a separator for a rechargeable lithium battery and a rechargeable lithium battery including the separator. The separator includes a substrate, and a heat resistant adhesive layer on one surface of the substrate. The heat resistant adhesive layer includes inorganic particles, a heat resistant binder, and a swellable adhesive binder. The swellable adhesive binder includes a first structural unit derived from a vinyl aromatic monomer, a second structural unit derived from an alkyl acrylate, and a third structural unit derived from a phosphonate-based monomer, and the swellable adhesive binder is distributed in the surface of the heat-resistant adhesive layer to 40% to 60% of the total thickness of the heat resistant adhesive layer.