Battery Separator Adhesive Layer Composite Binders
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Solution Overview
Problem
Existing separators for rechargeable batteries face challenges in achieving both wet and dry adherence, heat resistance, and durability, particularly in lithium batteries, where dry adherence is crucial for large-sized batteries without electrolyte solution.
Innovation Solution
A separator with a porous substrate and an adhesive layer comprising a first binder derived from vinylidene fluoride and hexafluoropropylene, a second binder with similar composition, and a filler like Al2O3, providing improved heat resistance, wet, and dry adherence through specific weight ratios and molecular weights, ensuring strong adherence to electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single binder is used in the adhesive layer, then the structure is simple, but both wet and dry adherence cannot be simultaneously optimized
Solution Approach 1:
The adhesive layer uses a composite binder system comprising two distinct binders: a first binder containing polyvinylidene fluoride and polyhexafluoropropylene in a weight ratio of 9:1 to 1:9, and a second binder containing carboxymethyl cellulose and starch in a weight ratio of 9:1 to 1:9. This composite material approach allows simultaneous optimization of both wet adherence (through polyvinylidene fluoride) and dry adherence (through carboxymethyl cellulose and starch), resolving the technical contradiction between adherence performance and compositional complexity.
2Strength
If high molecular weight binder is used, then strength is improved, but processing difficulty increases
Solution Approach 1:
The patent specifies precise molecular weight parameters for the binders to balance strength and processability. The first binder (polyvinylidene fluoride) has a weight average molecular weight of 50,000 to 2,000,000, while the second binder (carboxymethyl cellulose) has a weight average molecular weight of 10,000 to 1,000,000. These controlled molecular weight ranges ensure sufficient adhesive strength while maintaining appropriate viscosity for coating processes, resolving the contradiction between strength and ease of manufacture.
3Temperature
If filler content is increased to improve heat resistance, then thermal stability is improved, but mechanical flexibility decreases
Solution Approach 1:
The patent incorporates inorganic fillers (such as alumina, silica, or boehmite) at controlled weight percentages of 1 to 50 parts by weight per 100 parts by weight of total binder. The fillers are locally distributed within the adhesive layer to provide heat resistance only where thermally critical, while the binder matrix maintains mechanical flexibility throughout. This local quality approach allows heat resistance improvement without sacrificing overall mechanical flexibility.
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 separator exhibits enhanced heat resistance, stability, and adherence characteristics, leading to improved cycle-life, rate capability, and safety in rechargeable lithium batteries.
Implementation Method 1
an adhesive layer on at least one surface of the porous substrate. The adhesive layer includes a first binder, a second binder, and a filler
Data Source
AI summary
A separator for a rechargeable battery includes a porous substrate and an adhesive layer on at least one surface thereof. The adhesive layer includes a first binder, a second binder, and a filler. The first binder includes a structural unit derived from vinylidene fluoride and a structural unit derived from hexafluoropropylene. The structural unit derived from hexafluoropropylene is included in an amount of about 10 wt % or less based on a total weight of the first binder. A weight average molecular weight of the first binder ranges from about 800,000 to about 1,500,000. The second binder includes a structural unit derived from vinylidene fluoride and a structural unit derived from hexafluoropropylene. The structural unit derived from hexafluoropropylene is included in an amount of 10 wt % or less based on a total weight of the second binder. A weight average molecular weight of the second binder is 600,000 or less.