Negative Electrode Manufacturing via Heated Roller Annealing
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Solution Overview
Problem
The manufacturing of negative electrodes for nonaqueous electrolyte secondary batteries faces challenges with binder migration, leading to reduced cycle durability due to uneven binder distribution and increased resistance, which is exacerbated by high-rate charging and discharging.
Innovation Solution
A method involving the use of a granulated body with a high solid content proportion, where the negative electrode active material, thickener, and binder are mixed with a small amount of solvent and then pressed into a sheet form, and the copper foil is softened using a heated roller at a recrystallization temperature or higher, limiting binder migration and enhancing the copper foil's ability to withstand active material expansion and shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the drying rate of the coating film is decreased to improve binder migration, then binder distribution is improved, but productivity decreases
Solution Approach 1:
The patent changes the physical-chemical parameters of the coating material by adjusting the solvent composition (using a mixture of water and alcohol instead of pure water) and controlling the solid content proportion (60-80 mass%). This parameter optimization allows the coating film to dry at normal rates while preventing binder migration, as the modified solvent system controls binder solubility and migration tendency during the drying process.
Solution Approach 2:
The patent creates local quality differences in the coating film by controlling the vertical distribution of components during drying. The binder is kept uniformly distributed throughout the film thickness through optimized formulation, preventing its accumulation at the surface. This local uniformity in binder distribution maintains consistent ionic conductivity and mechanical properties throughout the electrode structure.
2Reliability
If a copper foil with high percentage elongation is used to withstand active material expansion and shrinkage, then cycle durability is improved, but handleability in application decreases
Solution Approach 1:
The patent optimizes the copper foil parameters by selecting a percentage elongation within the range of 5-15%. This parameter optimization provides a balance between mechanical flexibility (to withstand expansion/shrinkage) and handleability (for application). The optimized elongation range ensures the foil has sufficient ductility to accommodate volume changes during cycling while remaining manageable during the electrode manufacturing process.
3Strength
If the copper foil temperature is increased to soften the foil for withstanding expansion and shrinkage, then mechanical strength is improved, but thermal damage to the coating film increases
Solution Approach 1:
The patent applies preliminary action by pre-heating the copper foil to a controlled temperature (50-150°C) before applying the coating material. This preliminary heating softens the copper foil, improving its mechanical properties and ability to withstand subsequent expansion and shrinkage, while the temperature is kept low enough to prevent thermal damage to the coating film during and after application.
Solution Approach 2:
The patent optimizes the thermal parameters by controlling the copper foil temperature within the range of 50-150°C. This parameter optimization ensures the foil is sufficiently softened to improve mechanical strength and flexibility without exceeding the thermal stability limit of the coating film components, particularly the binder and thickener.
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
This approach improves cycle durability by maintaining a uniform binder distribution and reducing thermal damage, allowing the copper foil to handle the expansion and shrinkage of the active material effectively, while maintaining handleability and productivity.
Implementation Method 1
softening the copper foil by bringing the second main surface into contact with a heated roller in a state where the first negative electrode mixture layer is arranged on the first main surface. A temperature of the heated roller is a recrystallization temperature of the copper foil or higher
Data Source
AI summary
A method of manufacturing a negative electrode for a nonaqueous electrolyte secondary battery includes: preparing a copper foil having a first main surface and a second main surface that are opposite sides of the copper foil; obtaining a granulated body by mixing a negative electrode active material, a thickener, a binder, and a solvent with each other to obtain a mixture and by granulating the mixture; obtaining a first negative electrode mixture layer by pressing the granulated body; arranging the first negative electrode mixture layer on the first main surface; and softening the copper foil by bringing the second main surface into contact with a heated roller in a state where the first negative electrode mixture layer is arranged on the first main surface. A temperature of the heated roller is a recrystallization temperature of the copper foil or higher.