Copolymer-Polyrotaxane Electrode Binder for Battery Cycle Life
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Solution Overview
Problem
Conventional binders for non-aqueous secondary batteries fail to maintain sufficient binding between electrode active materials and current collectors due to insufficient toughness, leading to decreased discharge capacity and cycle life.
Innovation Solution
A binder composition comprising a copolymer and polyrotaxane, where the copolymer is derived from specific monomers with ethylenically unsaturated bonds and a carboxy group, and the polyrotaxane has a cyclic molecule with a chain molecule and stopper groups, allowing for improved adhesion and flexibility to accommodate electrode expansion and contraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional binders are used in non-aqueous secondary batteries, then the electrode structure is simple and easy to manufacture, but the binding strength between electrode active materials and current collectors is insufficient, leading to poor cycle characteristics
Solution Approach 1:
The invention uses a composite binder system comprising polyrotaxane and copolymer in specific weight ratios (0.1-50 parts polyrotaxane per 100 parts copolymer). The polyrotaxane provides toughness and flexibility to accommodate electrode expansion/contraction, while the copolymer ensures adhesion to the current collector. This composite approach resolves the contradiction by achieving superior binding strength through material composition rather than structural complexity.
Solution Approach 2:
The invention optimizes the glass transition temperature (Tg) of the binder composition by controlling the copolymer composition (monomer (a1) and monomer (a2) ratios) and polyrotaxane content. By adjusting these parameters, the binder maintains appropriate flexibility and adhesion properties across different temperature conditions, thereby improving binding strength without requiring complex multi-component systems.
2Strength
If the binder composition is optimized for adhesion, then binding strength improves, but the flexibility to accommodate electrode expansion and contraction decreases
Solution Approach 1:
The polyrotaxane component introduces molecular-level flexibility through its unique structure of cyclic molecules threaded on a linear polymer chain with stopper groups. This allows the binder to dynamically adapt to electrode volume changes during charging/discharging cycles while maintaining strong adhesion. The copolymer provides the adhesive function, creating a division of labor that resolves the adhesion-flexibility contradiction.
Solution Approach 2:
The polyrotaxane structure enables dynamic response to mechanical stress: the cyclic molecules can move along the linear chain and the stopper groups prevent irreversible deformation. This dynamic behavior allows the binder to flexibly accommodate electrode expansion and contraction while maintaining binding strength, directly resolving the contradiction between adhesion and adaptability.
Data Source
Figure 1~2
AI summary
The binder composition for a non-aqueous secondary battery includes a copolymer and a polyrotaxane, the copolymer having a first structural unit derived from a monomer (a1) and a second structural unit derived from a monomer (a2), the monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, the monomer (a2) is a compound having a carboxy group and having only one ethylenically unsaturated bond, and the polyrotaxane has a cyclic molecule having a cyclic skeleton and a chain molecule that penetrates an opening of the cyclic molecule and has stopper groups at both ends.