Composite Latex Binder for Lithium Battery Adhesion and Resistance
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Solution Overview
Problem
Lithium secondary batteries face issues with electrode material separation and capacity degradation due to volume expansion during charge/discharge cycles, requiring a binder with excellent adhesivity and low resistance to maintain structural stability and performance.
Innovation Solution
A binder composition comprising composite latex with conjugated diene and acrylic copolymer latex particles, optimized in pH and particle size to enhance adhesivity and reduce resistance, is developed, including specific monomers and preparation methods to control particle diameter and prevent agglomeration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a binder is used to maintain structural stability and prevent separation of electrode active materials during charge/discharge cycles, then adhesivity is improved, but resistance increases
Solution Approach 1:
The patent adjusts the pH of the composite latex to 7 or less, which optimizes the balance between adhesivity and resistance. This parameter change modifies the chemical properties of the binder to reduce its resistance contribution while maintaining its binding function.
Solution Approach 2:
The patent uses a composite latex comprising conjugated diene latex particles and acrylic copolymer latex particles in independent phases. This composite structure combines the adhesive properties of conjugated diene with the resistance-reducing characteristics of acrylic copolymer, achieving both low resistance and high adhesivity simultaneously.
2Quantity of substance
If high discharge capacity materials such as silicon, tin or silicon-tin alloys are used in combination with natural graphite, then discharge capacity is improved, but volume expansion increases causing separation of negative electrode material
Solution Approach 1:
The elastic polymer binder forms a flexible binding network around electrode active materials that can accommodate volume expansion during lithiation. This flexible binding structure prevents separation of electrode materials while maintaining structural integrity, enabling the use of high-capacity materials like silicon and tin alloys.
Solution Approach 2:
The binder composition is designed to provide preemptive structural support that cushions against the volume expansion forces generated by high-capacity electrode materials during charging. This beforehand cushioning prevents material separation before it can occur.
3Strength
If the binder acts as resistance to provide binding strength, then adhesivity is improved, but ionic conductivity is reduced
Solution Approach 1:
The composite latex combines conjugated diene latex particles (providing binding strength) with acrylic copolymer latex particles (providing low resistance). This composite material achieves both strong adhesion and good ionic conductivity by distributing different functions across different phases.
Solution Approach 2:
The patent optimizes the pH parameter of the composite latex to 7 or less, which reduces the resistance contribution of the binder while maintaining its binding strength. This parameter optimization allows the binder to provide necessary adhesion with minimal impact on ionic conductivity.
Data Source
AI summary
Disclosed is a binder composition for secondary batteries including composite latex comprising conjugated diene latex particles (A) and copolymer latex particles (B), each present in an independent phase, wherein the composite latex has a pH of 7 or less.