Graft Copolymer Binder for Lithium-Ion Battery Negative Electrodes
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Solution Overview
Problem
Conventional binders for negative electrodes in lithium-ion secondary batteries exhibit poor binding properties with metal foils and are prone to decomposition during charge and discharge cycles, leading to a decrease in battery capacity due to peeling off of active materials.
Innovation Solution
A binder composition is developed by graft copolymerizing (meth)acrylonitrile with polyvinyl alcohol, resulting in a graft copolymer with specific molecular weight and composition ratios, which enhances binding properties and reduction resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional binders (fluorine-based resin, styrene-butadiene copolymer, acrylic copolymer) are used for negative electrode, then the binder can be easily manufactured and applied, but the binding property with metal foil is poor and the binder decomposes during charge-discharge cycles
Solution Approach 1:
The invention uses a graft copolymer composed of polyvinyl alcohol and polyacrylonitrile as a composite material. The polyvinyl alcohol component provides good binding properties with metal foil, while the polyacrylonitrile component provides high reduction resistance. By combining these two polymers into a single graft copolymer structure, the binder simultaneously achieves both strong adhesion and resistance to decomposition during charge-discharge cycles, resolving the contradiction between binding property and compositional stability.
Solution Approach 2:
The invention changes the chemical composition parameters of the binder by creating a graft copolymer with specific composition ratios (polyvinyl alcohol 10-90 mass%, polyacrylonitrile 90-10 mass%). This parameter change transforms the binder from conventional single-polymer structures to a copolymer structure with optimized compositional parameters, enabling simultaneous achievement of good binding properties and high reduction resistance without decomposition.
2Strength
If the binder has strong binding property with metal foil, then the negative electrode maintains good adhesion, but the binder decomposes during repeated charge and discharge
Solution Approach 1:
The graft copolymer binder combines polyvinyl alcohol (providing strong adhesion to metal foil) with polyacrylonitrile (providing high reduction resistance and cycle durability). This composite structure allows the binder to maintain strong binding strength during repeated charge-discharge cycles while resisting decomposition, thus simultaneously achieving both strong adhesion and long duration of action.
Solution Approach 2:
The graft copolymer structure distributes different functional properties to different parts of the polymer chain. The polyvinyl alcohol segments provide local strong adhesion to metal foil, while the polyacrylonitrile segments provide local reduction resistance. This local differentiation of quality within the single binder material enables simultaneous achievement of strong binding and long cycle life.
3Reliability
If polyvinyl alcohol with high degree of polymerization is used, then the binding property is improved, but the solubility and processability decrease
Solution Approach 1:
The graft copolymer combines polyvinyl alcohol chains with polyacrylonitrile side chains. This composite structure modifies the physical properties of polyvinyl alcohol, improving solubility and processability while maintaining the strong binding properties provided by the polyvinyl alcohol backbone. The graft copolymerization introduces functional groups that enhance solubility without sacrificing adhesion strength.
Solution Approach 2:
The invention optimizes the degree of polymerization of polyvinyl alcohol within a specific range (300-3000) and controls the graft copolymer composition (polyvinyl alcohol 10-90 mass%, polyacrylonitrile 90-10 mass%). These parameter changes balance the binding property (which improves with higher polymerization degree) against solubility and processability (which decrease with higher polymerization degree), achieving an optimal compromise for manufacturing.
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 new binder composition improves the cycle characteristics and rate capabilities of lithium-ion secondary batteries by maintaining strong adhesion with active materials and metal foils, reducing peeling and enhancing overall battery performance.
Implementation Method 1
a polymer obtained by graft copolymerizing a monomer containing (meth)acrylonitrile as a main component with polyvinyl alcohol
Data Source
AI summary
Provided is a binder composition for negative electrode that has good binding property with an active material and a metal foil and is superior in reduction resistance. A binder composition for negative electrode comprising a graft copolymer obtained by graft copolymerizing, with polyvinyl alcohol, a monomer containing (meth)acrylonitrile as a main component, wherein the polyvinyl alcohol has an average degree of polymerization of 300 to 3000; the polyvinyl alcohol has a saponification degree of 70 to 100 mol %; the graft copolymer has a polyvinyl alcohol amount of 10 to 90 mass %; and the graft copolymer has a poly(meth)acrylonitrile amount of 90 to 10 mass %.