Negative Electrode Slurry Binder Composition for Crack-Resistant Coatings
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Solution Overview
Problem
The expansion and contraction of negative electrode active materials in batteries during charging and discharging lead to deteriorated cycle characteristics and electron conductivity issues, while typical binders fail to form robust active layer coatings due to brittleness and defects.
Innovation Solution
A negative electrode waterborne slurry composition is developed, featuring a binder comprising an addition polymer with specific constitutional units, including alpha, beta-ethylenically unsaturated carboxylic acid, ethylenically unsaturated monomers with hydroxyl functional groups, alkyl esters of (meth)acrylic acid, and vinyl aromatic compounds, combined with a negative electrode active material and an aqueous medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If typical negative electrode binders are used to form active layer coatings, then the coating process is simple, but the coatings become brittle and suffer from cracks or other defects
Solution Approach 1:
The patent uses a composite binder system comprising carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in specific weight ratios (0.5:99.5 to 45:55). This composite approach combines the adhesive properties of CMC with the flexibility and crack-resistance of SBR, eliminating the brittleness issues of single-component binders while maintaining coating integrity during electrode expansion and contraction.
Solution Approach 2:
The patent optimizes specific parameters including the binder composition ratio (CMC:SBR), binder content (1-10 wt% of active material), and slurry viscosity (10-1000 cP) to achieve coatings that remain flexible and crack-free. By controlling these parameters, the coating maintains structural integrity during the expansion-contraction cycles of lithium ion battery operation.
2Quantity of substance
If the negative electrode active layer is made thicker to increase charge density, then the capacity increases, but the coating becomes more prone to cracks and defects
Solution Approach 1:
The composite CMC-SBR binder system provides enhanced flexibility and adhesion that enables the formation of thicker active layer coatings without cracking. The SBR component specifically contributes to coating flexibility, allowing thicker coatings to accommodate volume changes during charging/discharging cycles, thus maintaining reliability while increasing charge density.
Solution Approach 2:
The patent controls slurry viscosity (10-1000 cP) and binder content (1-10 wt% of active material) to optimize coating thickness and uniformity. These parameter optimizations ensure that thicker coatings are applied uniformly with proper adhesion, preventing crack formation and maintaining cycle characteristics while achieving higher charge density.
3Strength
If the negative electrode film is made more flexible to accommodate expansion and contraction, then the adhesion improves, but the electron conductivity may be compromised
Solution Approach 1:
The CMC-SBR composite binder maintains strong adhesion to the current collector while providing flexibility for volume changes. The SBR component specifically enhances adhesion and flexibility, while the conductive carbon black network (1-5 wt% of active material) embedded in the coating ensures electron conductivity is maintained despite the flexible, thick coating structure.
Solution Approach 2:
The patent introduces conductive carbon black as an intermediary component that forms a conductive network within the flexible CMC-SBR binder matrix. This carbon black network (1-5 wt% of active material) ensures electron conductivity pathways are maintained throughout the flexible coating, decoupling the adhesion/flexibility function from the conductivity function.
Data Source
AI summary
The present disclosure provides a negative electrode waterborne slurry composition comprising a binder comprising an addition polymer comprising (a) 0.1% to 15% by weight of constitutional units comprising the residue of an alpha, beta-ethylenically unsaturated carboxylic acid; (b) 0.1% to 25% by weight of constitutional units comprising the residue of an ethylenically unsaturated monomer comprising a hydroxyl functional group; (c) 30% to 90% by weight of constitutional units comprising the residue of an alkyl ester of (meth)acrylic acid; and (d) 0.1% to 50% by weight of constitutional units comprising the residue of a vinyl aromatic compound, the % by weight based on the total weight of the addition polymer; a negative electrode active material; and an aqueous medium. Also disclosed are slurry compositions and electrical storage devices.