Negative Electrode Binder Distribution for Battery Performance
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face issues with binder migration during the manufacturing process, leading to decreased input and output characteristics due to the segregation of binders on the surface of the negative electrode mixture layer, which inhibits lithium ion penetration and storage/releasing reactions.
Innovation Solution
A nonaqueous electrolyte secondary battery design with a negative electrode mixture layer divided into three regions, where the diene rubber binder is distributed differently in each region, with a higher abundance in the intermediate region to suppress side reactions and an oxidized carbon-carbon double bond in the surface region to allow lithium ion permeation, improving temperature-dependent characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the coating film is dried under mild drying conditions to suppress binder migration, then binder segregation is reduced, but input and output characteristics cannot be improved satisfactorily
Solution Approach 1:
The patent applies local quality by creating distinct regions within the negative electrode mixture layer with different binder characteristics. The first region (near the current collector) has low binder content for efficient electron exchange, the second region (intermediate) has high binder content for suppressing side reactions during storage, and the third region (surface) has oxidized binder for lithium ion permeation. This spatial differentiation of binder properties resolves the contradiction by allowing each region to optimize for its specific function rather than using uniform mild drying conditions throughout.
Solution Approach 2:
The patent employs parameter changes by controlling the oxidation state of the diene rubber binder in different regions. Specifically, the binder in the third region is oxidized to convert the carbon-carbon double bond to a carbonyl group, which changes the chemical properties to allow lithium ion permeation while maintaining binder film integrity. This parameter change (oxidation state) enables the surface region to permit ion transport without requiring severe drying conditions that would cause excessive binder migration.
2Reliability
If binder migration is suppressed by mild drying conditions, then binder distribution remains uniform, but lithium ion penetration and storage/releasing reactions are inhibited
Solution Approach 1:
The patent deliberately creates non-uniform binder distribution through controlled migration, where each region has optimized binder characteristics: the first region has minimal binder for efficient electron exchange between the negative electrode mixture layer and current collector, the second region has abundant binder to suppress side reactions during high-temperature storage, and the third region has oxidized binder that permits lithium ion permeation. This local differentiation resolves the contradiction by making binder non-uniformity functional rather than harmful.
Solution Approach 2:
The patent converts the harmful effect of binder migration into a beneficial feature by controlling and directing the migration process. Instead of preventing binder migration through mild drying, the invention allows controlled migration to occur and then oxidizes the binder in the third region to create a permeable surface layer. The binder migration, which would normally be considered a defect causing performance degradation, is transformed into a mechanism for creating the desired three-region structure with optimized lithium ion penetration and reaction characteristics.
3Reliability
If the diene rubber binder is oxidized on the surface to allow lithium ion permeation, then low-temperature characteristics improve, but the binder film integrity may be compromised
Solution Approach 1:
The patent applies local quality by restricting oxidation to only the third region (surface region) while leaving the binder in the first and second regions unoxidized. This creates a gradient where the surface has oxidized binder for lithium ion permeation and low-temperature performance, while the underlying regions maintain unoxidized binder for structural integrity and side reaction suppression. The localized application of oxidation resolves the contradiction by confining the structural modification to only where it is needed for ion permeation.
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 configuration enhances input and output characteristics by facilitating electron exchange at normal temperatures, suppressing storage deterioration, and maintaining performance over time, while also improving low-temperature performance by allowing lithium ion penetration through the oxidized binder film.
Implementation Method 1
when the solvent is dried, so-called binder migration, that is, a phenomenon in which the binder migrates to a surface side of a coating film may occur
Implementation Method 2
The third region contains the diene rubber binder having an oxidized carbon-carbon double bond
Implementation Method 3
improving low-temperature performance by allowing lithium ion penetration through the oxidized binder film
Implementation Method 4
electrons are easily exchanged between the negative electrode mixture layer and the negative electrode current collector core
Data Source
AI summary
A nonaqueous electrolyte secondary battery includes: a negative electrode current collector core; and a negative electrode mixture layer that is formed on the negative electrode current collector core. The negative electrode mixture layer contains a diene rubber binder. A section of the negative electrode mixture layer in a thickness direction is divided into a first region, a second region, and a third region from a negative electrode current collector core side by trisecting the negative electrode mixture layer in the thickness direction. An abundance of the diene rubber binder in the second region is greater than an abundance of the diene rubber binder in the first region. The third region contains the diene rubber binder having an oxidized carbon-carbon double bond.