Aqueous Binder Composition for Secondary Cell Electrodes
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Solution Overview
Problem
Conventional lithium ion secondary battery binders, such as polyvinylidene fluoride using N-methylpyrrolidone, have low binding properties with active materials and require large amounts, leading to reduced capacity and energy density, and are costly due to the use of organic solvents like NMP, which also pose environmental challenges during production.
Innovation Solution
An aqueous binder composition for secondary battery electrodes incorporating a silane coupling agent without ethylenically unsaturated bonds, a resin polymerized from ethylenically unsaturated monomers, and a hydrophilic solvent, optimized to provide high electrolyte resistance and improved binding properties between active materials and current collectors, even in the presence of chain carbonate electrolytes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyvinylidene fluoride (PVDF) binder using N-methylpyrrolidone (NMP) solvent is used, then resistance to swelling of the resin itself to the electrolytic solution is improved, but binding property with active material is low and capacity and energy density are reduced
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by incorporating specific functional groups (carboxyl, hydroxyl, or amine groups with specific content ratios) into the polymer chain. This modifies the binder's interaction properties with active materials, achieving strong binding without requiring large amounts of binder, thus resolving the contradiction between swelling resistance and binding property.
Solution Approach 2:
The invention creates a composite binder structure by combining polyvinylidene fluoride with specific functional monomers containing carboxyl, hydroxyl, or amine groups. This composite approach allows the binder to simultaneously achieve resin swelling resistance from PVDF and strong active material binding from the functional groups, eliminating the need to use large amounts of binder.
2Strength
If N-methylpyrrolidone (NMP) solvent is used in binder, then binding property is improved, but product price increases and working environment maintenance becomes difficult
Solution Approach 1:
The invention replaces the expensive and environmentally problematic NMP solvent with water as the dispersant. This substitution dramatically reduces production costs and eliminates the need for complex NMP recovery and environmental maintenance systems, while the functional groups in the polymer ensure adequate binding properties are maintained.
Solution Approach 2:
The functional groups (carboxyl, hydroxyl, amine) act as intermediaries between the binder polymer and the active materials. These groups provide the necessary binding functionality that would otherwise require NMP, enabling the use of water as a safe and inexpensive dispersant while maintaining strong binding properties.
3Strength
If binder with glass transition temperature of 30°C or less is used, then binding property is improved, but binder swells in electrolytic solution containing chain carbonate
Solution Approach 1:
The invention applies local quality by distributing specific functional groups (carboxyl, hydroxyl, or amine groups) at controlled intervals along the polymer chain, defined by specific content ratios. This localized functional group placement provides swelling resistance at the molecular level while maintaining overall binding strength, preventing the uniform swelling that occurs in conventional low glass transition temperature binders.
Solution Approach 2:
The invention changes the chemical structure parameters by incorporating functional groups with specific content ratios into the polymer chain. This structural modification allows the binder to maintain low glass transition temperature for good binding properties while the functional groups provide cross-linking or interaction points that resist swelling in chain carbonate-containing electrolytic solutions.
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 solution enhances the binding properties and electrolyte resistance of the binder, reducing the likelihood of active material peeling and improving the cycle characteristics and energy density of lithium ion secondary batteries, while being more environmentally friendly and cost-effective.
Implementation Method 1
incorporating a silane coupling agent without ethylenically unsaturated bonds, a resin polymerized from ethylenically unsaturated monomers
Implementation Method 2
a resin polymerized from ethylenically unsaturated monomers
Implementation Method 3
high electrolyte resistance and improved binding properties between active materials and current collectors, even in the presence of chain carbonate electrolytes
Data Source
AI summary
The present invention provides a secondary battery electrode binder that demonstrates excellent performance in regard to active materials binding to each other or to a collector in an aqueous dispersion system, and that has electrolytic solution resistance even when the electrolytic solution composition has a large content of chain carbonate. It is possible to improve cycle characteristics of the charge and discharge at high temperature of this secondary battery. The present invention provides an aqueous binder composition for a secondary battery electrode containing a silane coupling agent without ethylenically unsaturated bonds, a resin which is a polymer of at least one kind of ethylenically unsaturated monomers, and at least one kind of solvent selected from the group consisting of water and a hydrophilic solvent. The amount of silane coupling agent is from 0.5 to 9 parts by mass based on 100 parts by mass of ethylenically unsaturated monomer. The pH of the composition is 2.5 to 8.0.