Graft Copolymer Binder for High-Temperature Li-Ion Battery Cycle Life
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Solution Overview
Problem
Current lithium ion secondary batteries face challenges in maintaining cycle capacity retention at high temperatures, requiring a binder with improved high-temperature performance for positive electrodes.
Innovation Solution
A graft copolymer composition is developed, featuring a polyvinyl alcohol stem polymer and branch polymers with specific monomer units, such as alkoxypolyethylene glycol (meth)acrylate, which provides a glass transition temperature range of 260K to 365K, enhancing cycle capacity retention at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional binder is used in lithium ion secondary batteries, then the battery can operate, but the cycle capacity retention rate deteriorates at high temperatures
Solution Approach 1:
The invention uses a graft copolymer composed of polyvinyl alcohol as the stem polymer and polyacrylonitrile or polyacrylic acid as branch polymers. This composite structure combines the binding properties of PVA with the oxidation resistance and high-temperature stability of the acrylonitrile/acrylic acid branches, achieving excellent cycle capacity retention at high temperatures while maintaining effective binding functionality.
Solution Approach 2:
The invention optimizes the glass transition temperature of the binder composition to a specific range (260K to 365K) and controls the ratio of polyvinyl alcohol content (C PVA /(C M +C PVA )) to be 0.25 to 0.3. These parameter adjustments ensure the binder maintains appropriate flexibility and binding strength at high operating temperatures, preventing capacity degradation.
2Strength
If the polyvinyl alcohol content is increased to improve binding properties, then binding strength improves, but the glass transition temperature increases excessively
Solution Approach 1:
The invention precisely controls the polyvinyl alcohol content ratio (C PVA /(C M +C PVA )) to be 0.25 to 0.3 and the glass transition temperature to be 260K to 365K. This balanced composition provides sufficient binding strength while preventing excessive glass transition temperature that would occur with higher PVA content alone.
Solution Approach 2:
The graft copolymer structure integrates polyvinyl alcohol with polyacrylonitrile or polyacrylic acid branches, creating a composite material that achieves effective binding properties without requiring excessive PVA content, thereby controlling the glass transition temperature within the optimal range.
Data Source
AI summary
A composition with an excellent cycle capacity retention rate at high temperatures is provided. According to the present invention, a composition comprising a graft copolymer, wherein the graft copolymer has a stem polymer and a plurality of branch polymers, the stem polymer has a polyvinyl alcohol structure, each of a first monomer unit and a second monomer unit is included in at least one of the plurality of branch polymers, the second monomer unit is different from the first monomer unit, a glass transition temperature of the composition is 260K to 365K is provided.