Secondary Battery Binder Copolymer Gel for Cycle Stability
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Solution Overview
Problem
Conventional binders for secondary battery electrodes, such as PVdF and SBR, fail to provide sufficient adhesion strength and cycle stability, leading to deterioration in battery performance due to volume expansion and insufficient flexibility, especially when used with active materials like natural graphite or silicon, which results in rapid capacity loss over cycles.
Innovation Solution
A binder comprising a gel with a polymer particle obtained by copolymerizing three or more types of monomers, specifically a mixture of ethylenically unsaturated carbonic acid ester, vinyl, and ethylenically unsaturated carbonic acid monomers, with a swelling index of 1.1 to 5.0 and incorporating a cross-linking agent, to enhance adhesion and maintain structural integrity during charge/discharge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional binders like PVdF are used, then adhesion strength is improved, but cycle stability deteriorates due to insufficient flexibility and volume expansion
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by using copolymers with specific monomer ratios (acrylic acid 1-20 wt%, vinyl monomer 70-95 wt%, other monomers 5-20 wt%) and controls gel content (30-100%) and swelling index (1.05-5.0) to achieve both strong adhesion and flexibility for maintaining cycle stability
Solution Approach 2:
The invention uses composite polymer structures combining multiple monomer units (acrylic acid, vinyl monomers like styrene or acrylonitrile, and other monomers) with cross-linking agents to create a binder that simultaneously provides adhesion strength and elastic flexibility to accommodate volume changes during cycling
2Quantity of substance
If materials with high discharge capacity like silicon or tin are used, then energy density is improved, but volume expansion increases causing separation from electrode material
Solution Approach 1:
The binder acts as a flexible binding matrix that can elastically deform to accommodate the large volume changes of high-capacity materials like silicon and tin during lithiation and delithiation, maintaining continuous electrical contact and preventing particle separation while allowing the active material to expand and contract
Solution Approach 2:
The invention optimizes the binder's physical parameters including gel content (30-100%) and swelling index (1.05-5.0) to create a three-dimensional network structure with appropriate porosity and elasticity that can buffer volume expansion while maintaining structural integrity during repeated charge-discharge cycles
3Strength
If PVdF is used as binder, then adhesion strength is improved, but power capacity deteriorates due to electrolyte absorption and swelling
Solution Approach 1:
The invention changes the chemical composition to use copolymers with controlled gel content (30-100%) and swelling index (1.05-5.0), replacing PVdF with a more chemically resistant binder system that maintains adhesion strength while minimizing electrolyte interaction and swelling, thereby preserving power capacity
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 proposed binder significantly improves adhesion strength and cycle properties, maintaining at least 90% capacity after 50 cycles by controlling volume expansion and ensuring effective lithium ion movement, thereby extending the battery's lifespan and performance.
Implementation Method 1
a swelling index of the binder to an electrolyte is 1.1 to 5.0
Implementation Method 2
a gel comprising a polymer particle obtained by copolymerizing three or more types of monomers
Data Source
AI summary
Provided is a binder for secondary battery electrodes wherein the content of a gel comprising a polymer particle obtained by copolymerizing three or more types of monomers is 50 to 100% by weight and a swelling index of the binder to an electrolyte is 1.1 to 5.0. The binder fundamentally improves electrode stability due to the gel content defined above and increases ionic conductivity due to the swelling index, thus providing secondary batteries with superior cycle properties.