Positive Electrode Slurry Kneading for Conductive Network Preservation
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Solution Overview
Problem
Increasing the solid content in the slurry for positive electrode production in nonaqueous electrolyte secondary batteries leads to high viscosity, reducing handling and workability, and excessive dispersion of electrically conductive materials can sever conductivity paths, decreasing battery performance.
Innovation Solution
A method involving two kneading steps: the first with electrically conductive carbon fine particles and a hydrophobic binder in N-methyl-2-pyrrolidone, followed by adding a positive electrode active material and water, with controlled moisture content to form a stable network and efficient conductive paths, allowing high solid content and reduced solvent usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the solid content of the slurry is increased to improve productivity and reduce costs, then productivity and cost efficiency are improved, but slurry viscosity becomes excessively high and handling and workability during coating decrease
Solution Approach 1:
The invention changes the chemical composition parameters of the slurry by introducing a specific surfactant and controlling the ratio of conductive material to binder, thereby reducing viscosity and surface tension to improve handling and workability while maintaining high solid content for productivity
2Ease of operation
If a large amount of energy is applied during kneading to highly disperse the electrically conductive material and lower slurry viscosity, then slurry viscosity is reduced and handling is improved, but the network structure of the electrically conductive material is severed and electrically conductive paths are shortened
Solution Approach 1:
The invention changes the chemical environment by adding surfactant and controlling material ratios, allowing adequate dispersion at lower energy input that preserves the conductive network structure while achieving acceptable viscosity reduction
Solution Approach 2:
The surfactant acts as an intermediary substance that facilitates dispersion of conductive material without requiring excessive mechanical energy, thereby preventing damage to the conductive network while still reducing slurry viscosity
3Ease of operation
If the electrically conductive material is excessively dispersed to lower viscosity, then slurry viscosity decreases and coating becomes easier, but the network structure of the electrically conductive material is severed and electrically conductive paths are shortened
Solution Approach 1:
The invention optimizes the chemical parameters including surfactant concentration and material ratios to enable coating at lower viscosity without excessive dispersion that would damage the conductive network
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 method produces a positive electrode with superior electrical conductivity and durability, reducing resistance and maintaining high productivity while minimizing environmental impact.
Implementation Method 1
a hydrophobic binder that gels when contacted by water
Implementation Method 2
a hydrophobic binder that gels when contacted by water
Data Source
AI summary
Provided is a method for producing a positive electrode for a nonaqueous electrolyte secondary battery having superior electrical conductivity with high productivity. The production method disclosed herein includes the following steps: a first kneading step (S10) for kneading electrically conductive carbon fine particles and a hydrophobic binder that gels when contacted by water, in N-methyl-2-pyrrolidone (NMP); a second kneading step (S20) for adding a positive electrode active material and water to a first kneaded product obtained in the first kneading step followed by additional kneading; and a step (S30) for forming a positive electrode active material layer on the surface of a positive electrode current collector by coating a second kneaded product obtained in the second kneading step on the positive electrode current collector. The first kneaded product contains moisture, and the ratio of the mass of the moisture to the mass of the NMP is 0.002 or less in the first kneaded product, while in the second kneading step (S20), the water is added at a mass ratio of 0.0022 to 0.0115 based on the mass of the NMP.