Aqueous Battery Binder Composition With Stable Storage Viscosity
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Solution Overview
Problem
Aqueous solutions of copolymers of vinyl alcohol and alkali metal neutralized ethylenically unsaturated carboxylic acid or carboxymethyl cellulose or their salts exhibit significant viscosity increases during storage, leading to difficulties in application and uneven adhesive strength in secondary batteries.
Innovation Solution
The copolymers are dissolved under specific conditions to prevent viscosity increases by controlling the viscosity change rate during storage, ensuring the compositions remain stable at room temperature and elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the copolymer or carboxymethyl cellulose is dissolved in water to form an aqueous binder solution, then the binder can be applied to produce electrodes or separators, but the viscosity of the solution significantly increases during storage, making it difficult to apply and causing uneven adhesive strength
Solution Approach 1:
The patent applies parameter changes by controlling the molecular weight of the copolymer of vinyl alcohol and alkali metal neutralized product of ethylenically unsaturated carboxylic acid within a specific range (10,000 to 1,000,000, preferably 50,000 to 500,000) and adjusting the composition ratio between vinyl alcohol units and carboxylic acid units (1:4 to 4:1). These parameter optimizations enable the aqueous binder solution to maintain stable viscosity during storage while remaining applicable for electrode and separator production.
2Loss of time
If the binder solution is stored at room temperature for long periods, then preparation time for battery production is reduced, but the viscosity increases significantly, degrading the binder performance
Solution Approach 1:
The patent implements preliminary action by preparing the aqueous binder solution in advance and storing it at room temperature. Through optimizing the copolymer molecular weight and composition parameters, the binder solution maintains stable viscosity even after long-term storage, enabling manufacturers to prepare binders ahead of time without compromising performance. This eliminates the need for fresh preparation before each use while ensuring consistent adhesive strength.
3Stability of the object's composition
If polyacrylic acid is used as an alternative binder, then viscosity increase during storage is avoided, but the adhesive strength and binding performance may be insufficient for secondary battery applications
Solution Approach 1:
The patent employs composite material strategy by utilizing a copolymer structure combining vinyl alcohol units and alkali metal neutralized carboxylic acid units in specific ratios. This copolymer composition achieves both adequate adhesive strength for secondary battery electrodes and separators and stable viscosity during storage, overcoming the limitations of using single-component polymers like polyacrylic acid.
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: Changerate%=Xa1−Xb1/Xb1×100 is 0 to 10%.