Negative Electrode Binder Slurry for Lithium-Ion Battery Swelling Control
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Solution Overview
Problem
Lithium ion secondary batteries face issues with swelling of the negative electrode due to charging and discharging, leading to worsened electrical characteristics such as cycle characteristics, and there is a need for improved adherence between the negative electrode mixed material layer and the current collector while maintaining conductivity.
Innovation Solution
A slurry composition for a negative electrode using a first particulate binder with an aliphatic conjugated diene and aromatic vinyl monomer unit, a second particulate binder with a similar structure but higher swelling capacity, and a water-soluble polymer to suppress swelling and enhance electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional binders are used in the slurry composition, then the negative electrode active material can be bound to the current collector, but the negative electrode swells during charging and discharging, worsening cycle characteristics
Solution Approach 1:
The patent applies parameter changes by carefully controlling the glass transition temperature (Tg) of the binder within -50°C to 0°C, and controlling the number average particle size within 150 nm to 280 nm. These specific parameter ranges optimize the binder's mechanical properties to accommodate volume changes during lithium insertion/extraction while maintaining strong adhesion, thereby suppressing electrode swelling and improving cycle characteristics.
Solution Approach 2:
The patent uses composite materials by combining the binder with specific additives including a water-soluble polymer and conductive materials in the slurry composition. This composite approach creates a synergistic effect where the binder provides structural integrity and adhesion, while the water-soluble polymer enhances flexibility and swelling resistance, collectively suppressing electrode deformation during cycling.
2Strength
If the binder strongly binds the negative electrode active material to the current collector, then adherence is improved, but the conductivity of lithium ions in the electrode mixed material layer may be compromised
Solution Approach 1:
The patent applies parameter changes by optimizing the glass transition temperature of the binder within -50°C to 0°C, which balances adhesion strength and ionic conductivity. At this Tg range, the binder maintains sufficient flexibility to allow lithium ion diffusion while providing strong mechanical bonding. Additionally, controlling the number average particle size within 150 nm to 280 nm ensures adequate surface area for adhesion while maintaining porosity for ion transport.
Solution Approach 2:
The patent introduces a water-soluble polymer as an intermediary substance in the slurry composition that mediates between the binder's adhesion function and the conductivity requirement. This additive enhances the overall performance by improving wetting and adhesion while maintaining a porous structure that facilitates lithium ion transport, thus resolving the contradiction between strong bonding and ionic conductivity.
3Shape
If the binder has high swelling capacity to accommodate active material expansion, then swelling is suppressed, but the adherence between the negative electrode mixed material layer and the current collector may be reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the glass transition temperature within -50°C to 0°C and the number average particle size within 150 nm to 280 nm. This specific parameter range creates a binder with optimal mechanical properties that can swell sufficiently to accommodate active material expansion while maintaining strong adhesion to the current collector through enhanced surface area and optimized viscoelastic behavior.
Solution Approach 2:
The patent uses composite materials by formulating a slurry composition that includes the binder combined with a water-soluble polymer and conductive materials. This composite structure allows the binder to provide swelling capacity while the water-soluble polymer enhances adhesion and flexibility, creating a synergistic system that simultaneously achieves swelling suppression and strong adherence.
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 swelling and improves electrical characteristics like cycle and rate characteristics by ensuring strong adherence and conductivity, leading to a more stable and efficient lithium ion secondary battery.
Implementation Method 1
the first particulate binder has a degree of swelling in electrolysis solution of 110% by mass or more to 200% by mass or less, the second particulate binder has a degree of swelling in electrolysis solution of 250% by mass or more to 600% by mass or less
Implementation Method 2
suitably binding particles of the negative electrode active material to each other and the negative electrode active material to the current collector with a binder
Implementation Method 3
guaranteeing conductivity of lithium ions in the electrode mixed material layer (negative electrode mixed material layer) when the negative electrode is immersed in an electrolysis solution
Implementation Method 4
a water soluble polymer
Data Source
AI summary
A slurry composition includes a negative electrode active material, a particulate binder, a water soluble polymer, and water. The particulate binder includes a first particulate binder and a second particulate binder. The first particulate binder includes a copolymer (A) including an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit, has a degree of swelling in electrolysis solution of 110% to 200% by mass, has a glass transition temperature of −30° C. to 60° C., and has a gel content of 70% to 98% by mass. The second particulate binder includes a copolymer (B) including an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit, has a degree of swelling in electrolysis solution of 250% to 600% by mass, and has a gel content of 70% to 98% by mass.