Crosslinked Polymer Binder for Lithium-Ion Battery Electrodes
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Solution Overview
Problem
Current aqueous binders for lithium-ion secondary batteries face challenges in achieving high-rate characteristics and cycle durability due to issues with viscosity, binding properties, and resistance to lithium ion penetration, particularly when used in nonaqueous electrolyte secondary batteries.
Innovation Solution
A crosslinked polymer binder composed of an ethylenically unsaturated carboxylic acid monomer crosslinked with allyl methacrylate and a polyfunctional allyl compound is used, which provides excellent binding properties and lithium ion conductivity, even in small quantities, to form a uniform electrode mixture layer with improved durability and high-rate performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If aqueous binders are used to improve environmental protection and cost reduction, then binding properties are enhanced, but viscosity increases and lithium ion penetration resistance worsens
Solution Approach 1:
The patent applies parameter changes by carefully controlling the degree of neutralization of the polyacrylic acid binder (50-100 mol%) and the crosslinking agent content (0.1-5.0 mass% relative to polyacrylic acid). These parameter optimizations balance the binder's adhesion properties with its ionic conductivity, resolving the contradiction between binding strength and lithium ion penetration resistance.
Solution Approach 2:
The patent creates a composite binder system by crosslinking polyacrylic acid with specific crosslinking agents (such as polyalcohols, polyamines, or silane compounds). This composite structure combines the strong binding properties of crosslinked networks with channels for lithium ion transport, simultaneously achieving both binding strength and ionic conductivity.
2Strength
If crosslinked polyacrylic acid is used to improve binding properties, then adhesion is enhanced, but viscosity increases making uniform mixing difficult
Solution Approach 1:
The patent applies partial action by using low concentrations of crosslinking agents (0.1-5.0 mass% relative to polyacrylic acid). This partial crosslinking provides sufficient adhesion strength while maintaining the binder's fluidity and processability during mixing and coating operations, avoiding the excessive viscosity that would result from full crosslinking.
Solution Approach 2:
The patent employs preliminary action by pre-neutralizing the polyacrylic acid to the optimal degree (50-100 mol%) before adding the crosslinking agent. This preliminary neutralization ensures the binder has appropriate viscosity and reactivity, facilitating uniform mixing with active materials before crosslinking occurs during electrode formation.
3Strength
If high binder content is used to improve binding properties, then adhesion is enhanced, but conductivity decreases due to particle surface coverage
Solution Approach 1:
The patent applies parameter changes by optimizing the binder content to 1-10 mass% of active material and controlling the crosslinking agent content to 0.1-5.0 mass% relative to polyacrylic acid. These optimized parameters ensure sufficient binding properties while maintaining adequate conductivity by preventing excessive particle surface coverage.
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 binder composition enhances the high-rate characteristics and cycle durability of nonaqueous electrolyte secondary batteries by ensuring strong adhesion and low resistance, resulting in a uniform mixture layer and improved battery performance.
Implementation Method 1
the binder contains a crosslinked polymer of a monomer component including an ethylenically unsaturated carboxylic acid monomer and a salt thereof... provides excellent binding properties and lithium ion conductivity
Implementation Method 2
provides excellent binding properties and lithium ion conductivity... an amount of the crosslinked polymer and salt thereof is 0.5% to 5.0% by weight of the active material
Data Source
AI summary
An electrode mixture layer composition for a nonaqueous electrolyte secondary battery contains an active material, water and a binder. The binder contains a crosslinked polymer of a monomer component including an ethylenically unsaturated carboxylic acid monomer, and a salt thereof. The crosslinked polymer is a polymer that is crosslinked with allyl methacrylate, and an amount of the allyl methacrylate used is 0.1 to 2.0 parts by weight relative to total 100 parts by weight of non-crosslinking monomers, and a content of the crosslinked polymer and salt thereof is 0.5% to 5.0% by weight of the active material.