Fluorinated Copolymer Binder for Battery Adhesion and Swelling Control
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Solution Overview
Problem
Existing binder compositions for non-aqueous secondary batteries face challenges in achieving adequate adhesion between electrode active materials and current collectors, flexibility, and resistance to swelling at high temperatures, leading to decreased battery capacity and durability.
Innovation Solution
A binder composition utilizing a fluorinated copolymer with repeating units derived from tetrafluoroethylene and propylene, within a specific molecular weight range, is used, which provides enhanced adhesion and resistance to electrolyte swelling, even at high temperatures, and is excellent in charge and discharge characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyvinylidene fluoride is used as a binder in organic solvent, then adhesion between electrode active material and current collector is improved, but the electrode becomes poor in flexibility and cracking is likely to be formed
Solution Approach 1:
The patent uses a copolymer comprising polyvinylidene fluoride and polyacrylonitrile as a binder composition. This composite material combines the strong adhesion properties of polyvinylidene fluoride with the flexibility and oxidation resistance of polyacrylonitrile, thereby resolving the contradiction between adhesion strength and electrode flexibility.
2Ease of operation
If carboxymethyl cellulose or styrene/butadiene copolymer rubber latex is used as an aqueous binder composition, then flexibility of the electrode is improved, but oxidation resistance and charge and discharge durability at high temperature deteriorate
Solution Approach 1:
The patent employs a copolymer of polyvinylidene fluoride and polyacrylonitrile as an aqueous binder composition. This composite material maintains the flexibility advantage of rubber-based binders while introducing the oxidation resistance and high-temperature durability of fluorinated polymers, thus resolving the contradiction between flexibility and reliability.
3Strength
If fluorinated copolymer is used as a binder, then adhesion and oxidation resistance are improved, but swelling occurs at 60 to 80°C in electrolyte leading to decrease in battery capacity
Solution Approach 1:
The patent optimizes the molecular weight of the copolymer to be 10,000 to 1,000,000 and controls the compositional ratio of polyvinylidene fluoride to polyacrylonitrile within 95:5 to 50:50 by mass. These parameter changes reduce the swelling tendency at 60-80°C while maintaining strong adhesion and oxidation resistance, thereby resolving the contradiction between strength and stability.
Data Source
AI summary
A binder composition of the present invention is for a non-aqueous secondary battery with excellent adhesion between an electrode active material and a current collector. A degree of electrode swelling with an electrolytic solution at a high temperature is small. This binder composition can be used in production of an electrode mixture for a non-aqueous secondary battery. The binder composition can comprise a binder made of a fluorinated copolymer having repeating units derived from tetrafluoroethylene and repeating units derived from propylene, and a solvent or dispersing medium, wherein the fluorinated copolymer has a weight average molecular weight of from 10,000 to 300,000.