Lithium-Ion Battery Electrode Binder for Adhesion and Flexibility
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Solution Overview
Problem
The existing methods for forming a porous membrane layer on lithium-ion secondary battery electrodes result in reduced flexibility and adhesion strength, leading to production yield issues and potential overheating due to separator shrinkage during internal short-circuits.
Innovation Solution
An electrode design incorporating an electrode active material layer with a binder that forms a spherical island phase and a porous membrane layer with inorganic filler, where the binder is an unsaturated carboxylic ester-based polymer with a high content of acrylic acid alkyl ester monomer units, enhancing adhesion strength and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an inorganic filler dispersing slurry is applied on an electrode active material layer to form a porous membrane layer, then safety is improved by preventing separator shrinkage, but adhesion strength between collector and active material layer is reduced
Solution Approach 1:
The invention changes the molecular weight parameter of the binder polymer to a specific range (10,000 to 100,000), which optimizes the balance between adhesion strength and flexibility. This parameter adjustment prevents the binder from being too weak (causing adhesion loss) or too rigid (causing flexibility loss), thereby resolving the contradiction between maintaining adhesion strength and preventing separator shrinkage.
Solution Approach 2:
The invention uses a composite binder system comprising both a water-soluble polymer and a carboxymethyl cellulose derivative. This composite material approach allows the binder to exhibit both strong adhesion properties (from the water-soluble polymer) and flexibility (from the carboxymethyl cellulose derivative), thus resolving the contradiction between adhesion strength and flexibility when inorganic filler slurry is applied.
2Reliability
If an inorganic filler dispersing slurry is applied and dried to form a porous membrane layer, then safety is improved, but flexibility of the porous membrane layer is reduced
Solution Approach 1:
The invention adjusts the molecular weight of the binder to a specific range (10,000 to 100,000) and controls the glass transition temperature to be -50°C or lower. These parameter changes ensure the binder remains flexible even after drying and inorganic filler application, preventing the membrane from becoming brittle while maintaining safety improvements.
Solution Approach 2:
The composite binder system combining water-soluble polymer and carboxymethyl cellulose derivative provides both safety enhancement and flexibility retention. The carboxymethyl cellulose derivative specifically contributes to maintaining flexibility and preventing brittleness in the dried porous membrane layer.
3Reliability
If inorganic filler dispersing slurry is applied to improve safety, then separator shrinkage is prevented, but electrode swelling occurs reducing production yield
Solution Approach 1:
The invention optimizes the binder molecular weight to a specific range and controls the glass transition temperature to prevent electrode swelling. These parameter adjustments ensure the electrode maintains its dimensional stability during the inorganic filler application process, thereby preventing production yield reduction while maintaining safety improvements.
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
This design inhibits the permeation of the dispersion medium into the electrode active material layer, improving adhesion strength, flexibility, and preventing electrode swelling, while also enhancing the adhesiveness between the separator and electrode active material layer.
Implementation Method 1
the binder forms a spherical island phase having an average diameter of 0.5 μm or more in a cross-section of a composite membrane including the binder and the thickener
Implementation Method 2
it is possible to obtain an electrode for a lithium-ion secondary battery, able to inhibit reduction in adhesion strength between the collector and the electrode active material layer because this binder can inhibit permeation of the dispersion medium
Implementation Method 3
thus-prepared inorganic filler dispersing slurry is applied on the surface of the electrode active material layer, followed by drying with hot air
Implementation Method 4
apply an inorganic filler dispersing slurry on a surface of an electrode active material layer followed by drying to form a porous membrane layer
Implementation Method 5
improve adhesion strength between a collector and an active material layer after applying and drying an inorganic filler dispersing slurry
Data Source
AI summary
Disclosed is an electrode for a lithium-ion secondary battery which includes a porous membrane layer that is inhibited from decreasing in flexibility. The electrode for lithium-ion secondary battery comprises a current collector and, formed thereon in the following order, an electrode active-material layer comprising an electrode active material, a thickener, and a binder and a porous membrane layer containing an inorganic filler, wherein the binder is one which, when used to form a composite film comprising the binder and the thickener, forms a spherical island phase in a cross section of the composite film, the island phase having an average diameter of 0.5 µm or larger. The binder preferably is an unsaturated carboxylic acid ester polymer having a content of alkyl acrylate monomer units of 85 mass% or higher.