Graft Copolymer Positive Electrode Binder for High-Temperature Stability
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Solution Overview
Problem
There is a need for a composition that balances the suppression of battery performance degradation, high-temperature storage properties, and DC resistance in lithium ion secondary batteries, which existing binders fail to achieve effectively.
Innovation Solution
A graft copolymer composition is developed, comprising a stem polymer with a polyvinyl alcohol structure and a branch polymer with (meth)acrylonitrile or (meth)acrylic acid monomer units, with a gel fraction of 30% or more, along with a crosslinked portion and a free polymer, to create a binder that enhances the stability and performance of positive electrodes in secondary batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional binders are used for positive electrodes, then ease of manufacture is maintained, but battery performance degradation is not sufficiently suppressed and high-temperature storage properties deteriorate
Solution Approach 1:
The invention uses a graft copolymer comprising polyvinyl alcohol as the stem polymer and (meth)acrylonitrile/(meth)acrylic acid as the branch polymer, creating a composite material that combines the advantages of both polymer systems to achieve superior battery performance while maintaining ease of manufacture
Solution Approach 2:
The invention specifies precise parameter ranges including gel fraction (30-80%), (meth)acrylonitrile content (10-50 mass%), and (meth)acrylic acid content (5-20 mass%) to optimize the balance between performance degradation suppression and manufacturing ease
2Productivity
If high-capacity electrode materials are used to increase energy density, then productivity and energy density improve, but battery performance degradation accelerates and DC resistance increases
Solution Approach 1:
The invention optimizes the gel fraction parameter to 30-80% and controls the molecular weight and composition of the graft copolymer to achieve the optimal balance between enabling high-capacity electrodes and suppressing performance degradation
Solution Approach 2:
The binder composition is designed to provide sufficient performance for high-capacity electrodes during the operational lifetime of the battery, using cost-effective polyvinyl alcohol and common monomers that do not require expensive specialized materials
3Strength
If binders with high crosslinking density are used to improve mechanical strength, then strength and durability improve, but DC resistance increases and high-temperature storage properties deteriorate
Solution Approach 1:
The invention precisely controls the crosslinking degree by limiting (meth)acrylic acid content to 5-20 mass% and gel fraction to 30-80%, preventing excessive crosslinking that would increase DC resistance while maintaining sufficient mechanical strength
Solution Approach 2:
The graft copolymer structure provides localized crosslinking at the branch points while maintaining flexibility in the stem polymer regions, creating non-uniform local properties that balance strength and conductivity requirements
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 composition effectively suppresses battery performance degradation, maintains high-temperature storage properties, and reduces DC resistance, resulting in improved battery performance and longevity.
Implementation Method 1
a graft copolymer having a stem polymer and a branch polymer; the stem polymer contains a polyvinyl alcohol structure; the branch polymer contains a first monomer unit containing a (meth)acrylonitrile monomer unit and/or a (meth)acrylic acid monomer
Implementation Method 2
the composition further comprises a free polymer; the free polymer does not have a covalent bond with the graft copolymer; the graft copolymer further includes a crosslinked portion derived from a crosslinking agent
Data Source
AI summary
A composition including a graft copolymer, wherein the graft copolymer has a stem polymer and a branch polymer; the stem polymer contains a polyvinyl alcohol structure, the branch polymer contains a first monomer unit containing a (meth)acrylonitrile monomer unit and/or a (meth)acrylic acid monomer; the composition has a gel fraction of 30% or more; the gel fraction is represented by following formula: the gel fraction %=A×100/1; A g is an insoluble content left on a filter pater when 1 g of the composition is added to 300 ml of dimethyl sulfoxide to obtain a mixture and the mixture is stirred at 60° C. for 15 hours and then filtered through the filter paper, which is a No. 5C filter paper as specified in JIS P 380.