Binder Composition for Secondary Battery Negative Electrode
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Solution Overview
Problem
Secondary batteries face issues with negative electrode swelling during charging and discharging, capacity degradation in extreme temperatures, and reduced adhesion between the current collector and electrode active material, leading to performance and production quality challenges.
Innovation Solution
A binder composition for the negative electrode comprising a particulate binder and a water-soluble polymer with specific ion conductivity and swelling properties, including a crosslinkable monomer unit, fluorine-containing (meth)acrylic acid ester monomer unit, and a reactive surfactant unit, is used to enhance adhesion and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional binders are used to bind electrode active materials to current collector, then adhesion is improved, but negative electrode swelling occurs during charging and discharging
Solution Approach 1:
The patent uses a composite binder system combining styrene-butadiene copolymer particles with carboxymethyl cellulose and sodium polyacrylate. This composite approach creates a network structure where the copolymer provides adhesion strength while the cellulose and polyacrylate components control swelling behavior through their hydrophilic properties and molecular structures, resolving the contradiction between strong bonding and volume stability.
Solution Approach 2:
The patent optimizes specific parameters of the binder composition including the weight ratios of copolymer to hydrophilic polymers (0.95:0.05 to 0.5:0.5), glass transition temperature (-50°C to 0°C), and particle size distribution (0.01-10 μm). These parameter adjustments fine-tune the balance between adhesion strength and swelling resistance, allowing the binder to maintain structural integrity while accommodating volume changes during lithium insertion/extraction.
2Reliability
If electrode structure is modified to improve performance, then capacity is improved, but manufacturing complexity increases
Solution Approach 1:
The patent incorporates functional components directly into the binder formulation before electrode assembly. The styrene-butadiene copolymer is pre-synthesized with controlled glass transition temperature and particle size, and carboxymethyl cellulose and sodium polyacrylate are pre-mixed in optimal ratios. This preliminary preparation of the binder composition simplifies the manufacturing process while ensuring the electrode achieves high capacity and stable performance.
3Strength
If binder composition is optimized for adhesion, then bonding strength is improved, but coating uniformity deteriorates
Solution Approach 1:
The patent employs copolymer particles with specific local structural characteristics - the styrene-butadiene copolymer has a glass transition temperature between -50°C and 0°C, creating regions of controlled flexibility within the binder matrix. The carboxymethyl cellulose and sodium polyacrylate provide localized hydrophilic zones that enhance wetting and uniform distribution. This local quality differentiation allows strong bonding at the electrode-active material interface while maintaining overall coating uniformity.
Solution Approach 2:
The patent controls particle size distribution of the copolymer (0.01-10 μm) and optimizes the molecular weight and degree of substitution of carboxymethyl cellulose and sodium polyacrylate. These parameter adjustments ensure the binder composition has appropriate viscosity and flow characteristics for uniform coating application, while simultaneously providing sufficient bonding strength through optimized molecular structures and interfacial interactions.
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 solution effectively suppresses negative electrode swelling, maintains capacity, and improves adhesion between the current collector and electrode active material, resulting in a stable and high-performance secondary battery with uniform quality.
Implementation Method 1
a swelling degree of the water-soluble polymer to a liquid with a solubility parameter of 8 to 13 (cal/cm3)1/2 is 1.0 to 2.0 times a swelling degree of the particulate binder measured under the same conditions
Implementation Method 2
improves adhesion between the current collector and electrode active material
Data Source
AI summary
A binder composition for a negative electrode of a secondary battery, including a particulate binder, and a water-soluble polymer containing an acidic functional group, wherein the water-soluble polymer has an ion conductivity of 1×10−5 to 1×10−3 S/cm; and a swelling degree of the water-soluble polymer to a liquid with a solubility parameter of 8 to 13 (cal/cm3)1/2 is 1.0 to 2.0 times a swelling degree of the particulate binder measured under the same conditions; and use thereof.