Copolymer Binder Wet Modulus for Silicon Anode Adhesion
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Solution Overview
Problem
Secondary batteries, particularly lithium secondary batteries, face challenges with electrode exfoliation due to insufficient adhesion between active materials and the current collector, leading to reduced cycle life and capacity, especially with materials like silicon that experience significant volume changes during charge and discharge.
Innovation Solution
A copolymer binder with a wet modulus of 0.02 MPa or more, composed of units derived from vinyl-based, conjugated diene-based, (meth)acrylic acid ester-based, and water-soluble polymers, is used to enhance adhesion and maintain mechanical properties even after electrolyte solution impregnation, thereby improving the life performance of secondary batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an excessive amount of binder is used to improve adhesion between active material and electrode collector, then adhesion is improved, but capacity and conductivity of the electrode are reduced
Solution Approach 1:
The invention changes the physical and chemical parameters of the binder by introducing a specific copolymer structure with hydrophilic functional groups and controlling the wet modulus to be 0.02 MPa or more. This parameter optimization allows the binder to achieve strong adhesion while maintaining electrode capacity and conductivity, resolving the contradiction between adhesion strength and active material content.
2Strength
If an excessive amount of binder is used to improve adhesion, then adhesion is improved, but conductivity of the electrode is reduced
Solution Approach 1:
The invention optimizes the binder's wet modulus parameter to 0.02 MPa or more and introduces hydrophilic functional groups, which changes the binder's interaction with electrolyte and its mechanical properties in the wet state. This allows achieving adequate adhesion with minimal binder content, thereby preserving electrode conductivity.
3Reliability
If insufficient adhesion is present, then electrode exfoliation occurs during drying and pressing, but using more binder to prevent exfoliation reduces capacity
Solution Approach 1:
The invention uses a copolymer binder composed of multiple monomer units including vinyl-based, conjugated diene-based, and water-soluble polymer units, creating a composite material with optimized properties. This composite structure provides superior adhesion performance per unit mass, preventing electrode exfoliation while minimizing the amount of binder needed and preserving capacity.
4Quantity of substance
If silicon or tin materials are used to increase discharge capacity, then capacity is improved, but volume change occurs due to reaction with lithium causing exfoliation
Solution Approach 1:
The invention changes the mechanical properties of the binder by controlling the wet modulus to be 0.02 MPa or more and introducing hydrophilic functional groups. This optimized binder can accommodate the volume changes of silicon or tin active materials during lithium insertion and extraction, maintaining adhesion and preventing exfoliation while allowing the use of high-capacity materials.
5Strength
If the binder does not maintain mechanical properties after electrolyte solution impregnation, then adhesion deteriorates, but using a binder with high wet modulus may reduce flexibility
Solution Approach 1:
The invention optimizes the wet modulus parameter to be 0.02 MPa or more, which is a specific threshold that balances mechanical strength and flexibility. The copolymer structure with hydrophilic functional groups ensures the binder maintains adequate mechanical properties after electrolyte impregnation while retaining enough flexibility to accommodate electrode volume changes during cycling.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The copolymer binder with a high wet modulus effectively suppresses swelling from electrolyte solutions, ensuring improved adhesion and mechanical properties, which enhances the life characteristics and capacity retention of secondary batteries, especially those using silicon-based negative electrode active materials.
Implementation Method 1
a copolymer binder having a wet modulus of 0.02 MPa or more... effectively suppresses swelling from electrolyte solutions
Implementation Method 2
a unit derived from a water-soluble polymer... exhibits improved adhesion, but also maintains high mechanical properties even after electrolyte solution impregnation
Data Source
AI summary
A binder composition for a secondary battery which includes a copolymer binder including at least one unit selected from (A) a unit derived from a vinyl-based monomer, (B) a unit derived from a conjugated diene-based monomer or a conjugated diene-based polymer, (C) a unit derived from a (meth)acrylic acid ester-based monomer, and (D) a unit derived from a water-soluble polymer, wherein the copolymer binder has a wet modulus of 0.02 MPa or more, and a negative electrode for a lithium secondary battery and a lithium secondary battery which include the same.