Battery Separator Copolymer Coating for Heat Shrinkage Resistance
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Solution Overview
Problem
Existing polyolefin-based separators in lithium secondary batteries suffer from severe heat shrinkage at high temperatures and weak mechanical properties, leading to potential battery instability and safety issues.
Innovation Solution
A copolymer composition is developed, comprising 30% to 80% by weight of specific monomer units such as acrylate-based, acrylonitrile-based, vinylamide-based, and acrylamide-based units, and 20% to 70% by weight of vinylpyrrolidone monomer units, combined with a cross-linking agent, to form a slurry composition that is applied to a separator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polyolefin-based films are used as separators, then the manufacturing process is simple and cost-effective, but the separator exhibits severe heat shrinkage at high temperatures and weak mechanical properties
Solution Approach 1:
The patent applies composite materials by combining polyolefin base film with a coating layer containing inorganic particles (alumina, silica, titania) and a specific copolymer binder. This composite structure provides both the manufacturing simplicity of polyolefin and enhanced mechanical strength, with the coating layer contributing tensile strength and dimensional stability while the base film provides ease of manufacture
2Ease of manufacture
If polyolefin-based films are used as separators, then the manufacturing process is simple, but the separator exhibits severe heat shrinkage at high temperatures leading to battery instability
Solution Approach 1:
The composite structure of polyolefin base film coated with inorganic particles and copolymer binder provides heat shrinkage resistance. The inorganic particles (alumina, silica, titania) have high thermal stability and low thermal expansion, while the copolymer binder maintains structural integrity at elevated temperatures, together preventing the heat shrinkage that occurs in pure polyolefin separators
Solution Approach 2:
The patent changes the chemical composition parameters of the coating layer by using a specific copolymer with 30-80 wt% acrylonitrile units and 20-70 wt% vinylpyrrolidone units. This specific compositional parameter range provides optimal heat resistance and adhesion, preventing heat shrinkage while maintaining manufacturing feasibility
3Stability of the object's composition
If a coating layer with inorganic particles and binders is applied to improve stability, then heat shrinkage resistance improves, but adhesion to the base film and uniform coating become critical requirements
Solution Approach 1:
The patent optimizes the compositional parameters of the copolymer binder, specifying 30-80 wt% acrylonitrile units and 20-70 wt% vinylpyrrolidone units. This specific parameter range provides optimal balance between adhesion to polyolefin base film and uniform coating formation, resolving the manufacturing precision challenges
Solution Approach 2:
The coating layer is designed with specific local properties: inorganic particles provide heat shrinkage resistance, while the copolymer binder provides adhesion and coating uniformity. This local differentiation of functions within the composite coating structure allows each component to optimize its specific role
4Reliability
If conventional separators are used, then the basic separation function is provided, but heat resistance is insufficient particularly when wetted with electrolyte solution
Solution Approach 1:
The composite coating layer of inorganic particles and copolymer binder provides enhanced heat resistance while maintaining basic separation function. The inorganic particles (alumina, silica, titania) have high melting points and thermal stability, and the copolymer binder maintains structural integrity at elevated temperatures even when wetted with electrolyte, together providing superior heat resistance
Solution Approach 2:
The patent uses a copolymer binder that can be applied as a relatively thin coating layer, providing cost-effective heat resistance enhancement. The coating layer is designed to be sufficient for heat resistance without excessive thickness that would compromise ion conductivity or increase cost
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 copolymer composition significantly improves the adhesion and heat resistance of the separator, maintaining excellent heat resistance even when wetted with an electrolyte solution, thereby enhancing the lifespan and stability of lithium secondary batteries.
Implementation Method 1
a copolymer including 30% or more to 80% or less by weight of at least one type of monomer unit selected from the group consisting of acrylate-based monomer units, acrylonitrile-based monomer units, vinylamide-based monomer units, and acrylamide-based monomer units and 20% or more to 70% or less by weight of vinylpyrrolidone monomer units
Implementation Method 2
a cross-linking agent
Implementation Method 3
coating one side or both sides of the porous base of the separators with inorganic particles and binders, the inorganic particles can provide the function of avoiding a shrinkage rate of the base
Data Source
AI summary
Proposed is a copolymer composition including a copolymer and a cross-linking agent, in which the copolymer includes 30% or more to 80% or less by weight of at least one type of monomer units selected from the group consisting of acrylate-based monomer units, acrylonitrile-based monomer units, vinylamide-based monomer units, and acrylamide-based monomer units and 20% or more to 70% or less by weight of vinylpyrrolidone monomer units, based on 100% by weight of the copolymer. In addition, a slurry composition, a separator, and a secondary battery that contains the polymer composition are proposed.