Secondary Battery Binder Copolymer for Swelling Control
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Solution Overview
Problem
Current binders for secondary batteries, particularly those using silicon-based active materials, face challenges with electrode swelling and flexibility, leading to reduced cycle-life and conductivity issues, while existing aqueous binders either lack effectiveness in suppressing swelling or suffer from handling difficulties.
Innovation Solution
A novel binder composition for secondary batteries incorporating a copolymer unit with a carboxyl group-containing acrylic monomer and an acrylic acid derivative monomer, along with a second copolymer unit featuring a polymer azo initiator residue, such as polyether or polysiloxane, which provides both strength and flexibility, and includes carboxylmethyl cellulose for improved handling and swelling suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high strength resin binder is used to suppress electrode swelling, then the charge and discharge cycle-life is improved, but the flexibility of the electrode deteriorates and handling becomes difficult
Solution Approach 1:
The patent uses a composite binder system combining carboxymethyl cellulose (CMC) with styrene-butadiene rubber (SBR) in a specific weight ratio range (CMC: 1-10 wt%, SBR: 90-90 wt%). This composite approach allows CMC to provide swelling suppression through its hydrophilic nature and SBR to maintain flexibility and handling properties through its elastic characteristics, resolving the contradiction between electrode stability and ease of operation.
2Stability of the object's composition
If an aqueous binder is used for silicon-based active material, then the electrode structure is maintained during swelling, but the binder flexibility is sharply deteriorated and cracks easily generate
Solution Approach 1:
The patent combines carboxymethyl cellulose (CMC) which provides aqueous-based swelling suppression with styrene-butadiene rubber (SBR) which contributes elasticity and flexibility. This composite binder system maintains electrode structure stability during silicon-based active material swelling while preventing crack formation and preserving binder flexibility, overcoming the limitations of using purely aqueous binders.
3Strength
If a polyimide-based binder is used, then the binding strength is improved, but the compatibility with aqueous solvent is poor and handling becomes difficult
Solution Approach 1:
The patent changes the chemical composition parameters of the binder by selecting carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) which are compatible with aqueous solvents, replacing polyimide-based binders. This parameter change maintains adequate binding strength while dramatically improving handling properties in aqueous environments, allowing for easier electrode fabrication and processing.
Data Source
AI summary
The present application relates to a binder for a secondary battery. The binder includes a first copolymer unit including a carboxyl group-containing acrylic monomer and at least one of an acrylic acid derivative monomer and a substituted or unsubstituted styrene and a second copolymer unit including a residue of a polymer azo initiator. A mass ratio of the second copolymer unit relative to a total mass of the first copolymer unit and the second copolymer unit is 10 mass % to 40 mass %.