Positive Electrode Plate with Differential PVDF Molecular Weight
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face issues with nonuniform widths of the positive electrode active material layer and protective layer, leading to potential short circuits due to the same weight average molecular weight of polyvinylidene fluoride used in both layers, which affects the stability and reliability of the battery.
Innovation Solution
Increasing the weight average molecular weight of polyvinylidene fluoride in the protective layer slurry compared to the positive electrode active material layer slurry ensures uniform application and width stability, with the protective layer containing inorganic oxide and a conductive agent for enhanced insulation and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the same weight average molecular weight of polyvinylidene fluoride is used in both the positive electrode active material layer and protective layer, then the manufacturing process is simplified, but the widths of the two layers become nonuniform leading to potential short circuits
Solution Approach 1:
The patent applies parameter changes by specifying different weight average molecular weights for polyvinylidene fluoride in the positive electrode active material layer (100,000-350,000) versus the protective layer (350,000-1,300,000). This molecular weight differentiation controls the viscosity and flow characteristics of each layer during manufacturing, ensuring uniform width while maintaining process feasibility.
Solution Approach 2:
The patent implements local quality by assigning different material properties (molecular weight ranges) to different regions (layers) of the electrode structure. The positive electrode active material layer uses lower molecular weight polyvinylidene fluoride for optimal electrochemical performance, while the protective layer uses higher molecular weight for dimensional stability and uniform width control.
2Reliability
If the weight average molecular weight of polyvinylidene fluoride in the protective layer is increased, then the width uniformity and reliability are improved, but the manufacturing complexity increases due to different molecular weight requirements
Solution Approach 1:
The patent resolves this contradiction by establishing specific molecular weight ranges that balance reliability and complexity. The protective layer requires weight average molecular weight of 350,000-1,300,000, which provides sufficient viscosity control for uniform width while remaining within commercially available polymer specifications, avoiding excessive manufacturing complexity.
Solution Approach 2:
The patent effectively uses composite material principles by combining polyvinylidene fluoride with different molecular weights in different layers, creating a multi-layer composite structure where each layer's specific molecular weight composition optimizes both reliability and manufacturability without requiring overly complex material systems.
3Manufacturing precision
If different weight average molecular weights of polyvinylidene fluoride are used in the positive electrode active material layer and protective layer, then the layer width uniformity is improved, but the material selection and processing complexity increases
Solution Approach 1:
The patent applies parameter changes by defining specific molecular weight ranges for polyvinylidene fluoride in each layer. The positive electrode active material layer uses 100,000-350,000 while the protective layer uses 350,000-1,300,000. These ranges are selected to provide clear differentiation for manufacturing control while remaining within commercially available polymer specifications.
Solution Approach 2:
The patent implements local quality by assigning different molecular weight characteristics to different functional layers. The positive electrode active material layer uses lower molecular weight for electrochemical activity, while the protective layer uses higher molecular weight for dimensional stability, with each local region optimized for its specific function.
Data Source
AI summary
A positive electrode plate for a nonaqueous electrolyte secondary battery, the positive electrode plate including: a positive electrode substrate; a positive electrode active material layer formed on the positive electrode substrate; and a positive electrode substrate exposed portion on which the positive electrode active material layer is not formed, the positive electrode substrate exposed portion having a region that is adjacent to the positive electrode active material layer and has a protective layer formed thereon, the positive electrode active material layer and the protective layer containing polyvinylidene fluoride, and the weight average molecular weight Mw of the polyvinylidene fluoride contained in the protective layer being larger than the weight average molecular weight Mw of the polyvinylidene fluoride contained in the positive electrode active material layer. Thus, a high reliable nonaqueous electrolyte secondary battery where the widths of the positive electrode material and the protective layers are stable can be provided.