Aqueous Copolymer Binder Composition for Secondary Battery Storage Stability
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Solution Overview
Problem
The viscosity of aqueous solutions of copolymers of vinyl alcohol and alkali metal neutralized ethylenically unsaturated carboxylic acid or carboxymethyl cellulose used as binders for secondary batteries significantly increases during storage, leading to application difficulties and uneven adhesive strength.
Innovation Solution
The copolymer is dissolved under specific conditions to maintain a viscosity change rate of 0-10% when stored at room temperature, preventing significant viscosity increases by adjusting the composition's viscosity before and after storage, ensuring stable application as a binder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the copolymer is dissolved in water to form an aqueous binder solution, then the binder can be applied to electrodes or separators, but the viscosity significantly increases during storage, making application difficult and causing uneven adhesive strength
Solution Approach 1:
The patent applies parameter changes by controlling the molecular weight of the copolymer within a specific range (10,000 to 1,000,000) and adjusting the ratio of vinyl alcohol to alkali metal neutralized ethylenically unsaturated carboxylic acid monomers. By optimizing these parameters, the binder solution maintains stable viscosity during storage while remaining applicable to electrodes and separators.
2Duration of action of stationary object
If the binder solution is stored at room temperature for long periods, then it is ready for use when needed, but the viscosity increases significantly, leading to deficiencies in adhesive strength
Solution Approach 1:
The patent controls the molecular weight and compositional ratio of the copolymer to prevent excessive viscosity increase during long-term storage. This allows the binder solution to be stored at room temperature for extended periods while maintaining reliable adhesive strength for electrode and separator applications.
3Strength
If conventional binders are used, then they provide adequate adhesive strength initially, but viscosity increases during storage, requiring preparation at the time of use rather than advance storage
Solution Approach 1:
The patent optimizes the molecular weight and monomer ratio parameters of the copolymer to achieve a balance between initial adhesive strength and viscosity stability during storage. This enables advance preparation and storage of binder solutions without requiring same-day preparation, reducing time loss while maintaining adequate adhesive strength.
Data Source
AI summary
The present invention provides a method that enables the use of an aqueous solution of a copolymer of vinyl alcohol and an alkali metal neutralized product of ethylenically unsaturated carboxylic acid or carboxymethyl cellulose or a salt thereof, as a binder for secondary batteries, without causing a significant viscosity increase even if stored in the state of an aqueous solution. More specifically, the present invention provides a composition in the form of an aqueous solution containing a copolymer of vinyl alcohol and an alkali metal neutralized product of ethylenically unsaturated carboxylic acid and/or carboxymethyl cellulose or a salt thereof, wherein when the viscosity of the composition after being diluted with water (25° C. or less) to a viscosity of 200±100 mPa·s at room temperature (25° C.) and being adjusted to a temperature of 25° C. is defined as Xa1 (Pa·s), and the viscosity of the composition after being placed in an airtight container and being allowed to stand at 95° C. for 8 hours is defined as Xb1 (Pa·s), the change rate obtained by the following formula:Change rate (%)=(Xa1−Xb1)/Xb1×100is 0 to 10%.