Lithium Battery Separator Layers for Heat Stability and Anode Adhesion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing lithium battery separators face challenges in maintaining high-temperature safety and adhesive force, particularly at the negative electrode interface, leading to issues like lithium salt precipitation, capacity drop, and thermal runaway.
Innovation Solution
A separator design with a porous substrate, a heat-resistant layer containing specific binders and inorganic particles, and an adhesive layer with a copolymer and fluorine-based polymer, enhancing adhesive force and heat resistance, especially at the negative electrode interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high nickel-based positive electrode active material is used to achieve high capacity and high output, then battery capacity and output are improved, but gas generation increases leading to lithium salt precipitation and potential short-circuits
Solution Approach 1:
The patent introduces an adhesive layer as an intermediary between the separator and the negative electrode. This adhesive layer, comprising a copolymer including a first unit derived from a vinyl aromatic monomer, a second unit derived from an alkyl acrylate, and a third unit derived from a phosphonate-based monomer, acts as a mediator to prevent direct contact between generated gas and the negative electrode interface, thereby suppressing lithium salt precipitation and potential short-circuits while maintaining the benefits of high nickel-based positive electrode materials
Solution Approach 2:
The patent employs composite materials in the adhesive layer by combining multiple polymer units (vinyl aromatic monomer unit, alkyl acrylate unit, and phosphonate-based monomer unit) to create a multi-functional coating. This composite structure provides both adhesive properties to maintain interface integrity and chemical resistance to prevent lithium salt precipitation, enabling the use of high nickel-based positive electrode materials without compromising safety
2Temperature
If the separator is exposed to high temperature environment, then thermal runaway risk increases, but the separator must maintain shape without shrinking to ensure safety
Solution Approach 1:
The patent modifies the thermal parameters of the separator by coating it with an adhesive layer having specific glass transition temperature and swelling degree characteristics. The adhesive layer is designed with a glass transition temperature of 60°C to 90°C and a swelling degree of 600% to 1000%, which changes the thermal response behavior of the separator, enabling it to maintain shape stability at high temperatures while retaining the necessary thermal shutdown function
Solution Approach 2:
The patent applies a thin film adhesive coating on the separator surface. This flexible thin film layer, though thin, provides significant thermal stability and shape maintenance capability. The adhesive layer acts as a protective shell that constrains the separator's thermal shrinkage at high temperatures while allowing the separator to perform its essential functions including ion transport and thermal shutdown
3Reliability
If the adhesive force between separator and negative electrode is increased to prevent lithium salt precipitation, then safety is improved, but the separator may lose its shutdown function at high temperatures
Solution Approach 1:
The patent applies local quality by differentiating the properties of different regions of the separator. The adhesive layer is applied only on specific surfaces of the separator (either one-sided or two-sided coating), providing enhanced adhesive force and lithium salt precipitation prevention at the negative electrode interface, while the bulk separator material retains its original heat-fusible resin composition and shutdown function. This localized modification allows simultaneous achievement of high adhesive force and thermal safety
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 high-temperature cycle-life characteristics and safety by maintaining adhesive force and shape stability, effectively preventing lithium salt precipitation and thermal issues.
Implementation Method 1
the separator should be able to suppress the ignition of the battery with a shutdown function, which is a function of blocking pores by melting the heat-fusible resin and the safety of the battery should be ensured by maintaining its shape without shrinking even at high temperatures
Implementation Method 2
the separator is required to have ultra-high heat resistance and high adhesion to the negative electrode
Data Source
AI summary
Disclosed are a separator for a rechargeable lithium battery, and a rechargeable lithium battery including the same, the separator for a rechargeable lithium battery including a porous substrate; a heat resistant layer on one surface of the porous substrate; and an adhesive layer on the other surface of the porous substrate, wherein the heat resistant layer includes a first binder and inorganic particles, the first binder includes at least one selected from polyacrylate, polyacrylic acid, polyacrylonitrile, polyvinyl alcohol, polysulfonic acid, polyacrylamide, polyamide, polyurea, polyurethane, and a copolymer thereof, the adhesive layer includes a second binder and a third binder, the second binder includes a copolymer including a first unit derived from a vinyl aromatic monomer, a second unit derived from an alkyl acrylate, and a third unit derived from a phosphonate-based monomer, and the third binder includes a fluorine-based polymer.