Water-Soluble Electrode Binder for Crack-Resistant Battery Electrodes
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Solution Overview
Problem
Existing binders for nonaqueous secondary batteries, such as those using carboxymethyl cellulose and sodium acrylate-N-vinylacetamide copolymers, face issues with insufficient bonding between active materials and current collectors, leading to peeling and cracking problems, and high internal resistance, which affect the battery's capacity and cycle life.
Innovation Solution
A water-soluble electrode binder comprising a resin component and polyoxyethylene alkyl ether as a surfactant, with a surface free energy of 70 mJ/m² or less, and a dipole component of 26 mJ/m² or less, formed from copolymers of ethylenically unsaturated bonds and dispersants like carboxymethyl cellulose, to enhance bonding and reduce cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a polyvinylidene fluoride (PVDF) binder using N-methyl-2-pyrrolidone (NMP) as a solvent is used, then the binder provides binding properties between active materials and current collector, but a large amount of binder is required which reduces battery capacity and NMP is expensive increasing manufacturing cost
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by using a copolymer of (meth)acrylic acid and (meth)acrylate instead of PVDF, and changes the solvent from NMP to water, achieving both reduced binder quantity and maintained binding properties
Solution Approach 2:
The invention uses a composite binder system comprising a copolymer of (meth)acrylic acid and (meth)acrylate combined with carboxymethyl cellulose, creating a composite material that achieves superior binding properties with less binder content
2Ease of operation
If the sodium acrylate-N-vinylacetamide copolymer binder is used, then the binder is water-soluble and easier to handle, but cracks are generated frequently in electrodes having large film thickness
Solution Approach 1:
The invention creates a composite binder system combining a copolymer of (meth)acrylic acid and (meth)acrylate with carboxymethyl cellulose, where the copolymer provides water solubility and the carboxymethyl cellulose enhances crack resistance in thick electrodes
Solution Approach 2:
The invention optimizes the local properties of different parts of the binder system: the copolymer component provides water solubility for easy handling, while the carboxymethyl cellulose component provides structural integrity and crack resistance in thick electrode regions
3Stability of the object's composition
If carboxymethyl cellulose is used as a thickener in combination with water-dispersible binder, then the slurry viscosity is improved, but the slurry preparation process becomes complicated
Solution Approach 1:
The invention merges the binder and thickener functions into a single integrated system by using a copolymer of (meth)acrylic acid and (meth)acrylate that provides both binding and viscosity control, eliminating the need for separate carboxymethyl cellulose addition and simplifying the preparation process
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 achieves a high peeling strength, reduces internal resistance, and improves discharge capacity retention, resulting in a battery with fewer cracks and better cycle characteristics.
Implementation Method 1
a surface free energy γB at 23°C is 70 mJ/m2 or less, and a dipole component γp is 26 mJ/m2 or less
Implementation Method 2
comprising a resin component (B1) and polyoxyethylene alkyl ether as a surfactant (B2)
Implementation Method 3
The binder serves to bond the active material to each other and bond the active material to the current collector
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention provides an electrode binder for a nonaqueous secondary battery, which can obtain a secondary battery which has an electrode active material layer having few cracks and a high peeling strength to a current collector, and which has a low internal resistance and a good cycle characteristic; and a nonaqueous secondary battery electrode. The electrode binder for a nonaqueous secondary battery contains a resin component and is water-soluble. The surface free energy γB at 23°C is 70 mJ/m2 or less, and the dipole component γpB of the surface free energy is 26 mJ/m2 or less.