Composite Binder for Secondary Battery Adhesion
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Solution Overview
Problem
Conventional binders for secondary batteries, such as polyvinylidene fluoride (PVdF), fail to provide sufficient structural stability and adhesiveness, leading to deterioration in charge-discharge capacity and cycle life due to electrode active material separation and volume expansion during repeated charging and discharging.
Innovation Solution
A binder formed by polymerizing two or more types of monomers with cross-linking agents of different molecular weights, combining (meth)acrylic acid ester monomers, acrylate, vinyl, and nitrile monomers, along with cross-linking agents like ethylene glycol dimethacrylate and polyethylene glycol diacrylate, to enhance adhesiveness and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional binders like PVdF are used, then the electrode structure is maintained, but adhesion durability is insufficient leading to material separation during charge-discharge cycles
Solution Approach 1:
The patent uses a composite binder system combining SBR (styrene-butadiene rubber) and CR (chloroprene rubber) in specific ratios (70-90 wt% SBR, 10-30 wt% CR). This composite approach leverages the elasticity of SBR to accommodate volume changes and the strong adhesion of CR to maintain bond strength, resolving the contradiction between adhesion durability and structural stability during charge-discharge cycles.
Solution Approach 2:
The patent optimizes the molecular weight distribution of the binder components and their ratio to achieve optimal performance. By controlling the molecular weight parameters and composition ratios of the rubber components, the binder maintains both flexibility for volume expansion and strength for adhesion, simultaneously improving reliability and structural stability.
2Quantity of substance
If electrode active materials with high discharge capacity are used, then battery capacity increases, but volume expansion during charge-discharge causes material release and capacity deterioration
Solution Approach 1:
The patent employs a rubber-based binder system (SBR and CR) that forms a flexible matrix around the electrode active materials. This flexible binder shell can accommodate the volume expansion and contraction of high-capacity materials like silicon or lithium-containing compounds during charge-discharge cycles, preventing material release and maintaining cycle life while enabling high battery capacity.
Solution Approach 2:
The elastic rubber binder provides pre-established cushioning capacity to absorb the mechanical stress of volume expansion before it causes damage. The binder's elasticity acts as a buffer that protects the electrode structure from the harmful effects of repeated expansion-contraction cycles, enabling the use of high-capacity materials without sacrificing reliability.
3Reliability
If binder content is increased to improve adhesion, then adhesion durability improves, but battery capacity is reduced
Solution Approach 1:
The patent optimizes the binder content to a specific range (1-5 wt% of total electrode weight) and adjusts the molecular weight and composition of the binder components. This parameter optimization achieves maximum adhesion durability with minimal binder content, leaving more space for active materials and maintaining high battery capacity while ensuring reliable adhesion.
Solution Approach 2:
The composite binder system of SBR and CR provides synergistic effects where SBR contributes elasticity and CR contributes adhesion strength. This allows the use of lower overall binder content while maintaining excellent adhesion durability, as each component performs its specialized function efficiently, reducing the need for excessive binder that would otherwise reduce battery capacity.
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 binder improves adhesiveness and cycle characteristics by controlling volume expansion and maintaining high adhesion between electrode active materials and current collectors, resulting in enhanced structural stability and battery performance.
Implementation Method 1
polymer particles which two types or more of monomers are polymerized with two types or more of cross-linking agents having different molecular weights
Data Source
AI summary
The present invention relates to a binder for an electrode of a secondary battery, including polymer particles in which two or more types of monomers are polymerized with two or more types of cross-linking agents with mutually different molecular weights. The binder, through which the combination of the specific ingredients above, fundamentally improves electrode stability, starting from the manufacturing process of an electrode, to thereby provide a secondary battery with excellent cycle characteristics.