Bilayer Negative Electrode Coating for High-Rate Drying Adhesion
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Solution Overview
Problem
The challenge in manufacturing lithium secondary batteries is to enhance the adhesion between the active material layer and the current collector while maintaining a high drying rate, as increased drying rates lead to binder migration and degradation of adhesion, and increasing binder content results in undesirable resistance.
Innovation Solution
A method involving a bilayer structure for the negative electrode, where the slurry for the lower layer and upper layer are coated simultaneously and dried together, with a controlled binder ratio and drying rate to inhibit binder migration, ensuring improved adhesion and resistance characteristics without significantly increasing the binder content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the drying rate is increased to enhance productivity, then the processing speed improves, but the binder migrates to the surface causing degradation of adhesion between the active material layer and current collector
Solution Approach 1:
The patent applies local quality by creating a bilayer structure with different binder contents in different regions. The lower layer (near current collector) has higher binder content (1.5-5.0 wt%) to ensure adhesion, while the upper layer has lower binder content (0.5-2.0 wt%) to prevent surface degradation. This spatial differentiation of binder concentration resolves the contradiction by providing high adhesion at the interface while maintaining low surface binder content even during high-rate drying.
2Reliability
If the binder content is increased to prevent adhesion degradation, then the adhesion between active material layer and current collector improves, but the resistance of the secondary battery increases undesirably
Solution Approach 1:
The patent uses local quality to concentrate binder only where needed for adhesion (lower layer near current collector with 1.5-5.0 wt% binder), while keeping binder content low in the upper layer (0.5-2.0 wt%). This prevents excessive binder from increasing overall resistance, as the binder is strategically placed only at the interface where adhesion is critical, rather than uniformly distributed throughout the active material layer.
Solution Approach 2:
The patent segments the active material layer into two distinct layers with different binder concentrations. The lower layer contains higher binder content for adhesion, while the upper layer contains lower binder content to minimize resistance. This segmentation allows the system to achieve good adhesion without the penalty of uniformly high binder content throughout the entire active material layer.
3Productivity
If multiple coating devices are provided to meet mass production demand, then the production capacity increases, but the investment cost increases significantly
Solution Approach 1:
The patent merges the coating and drying operations by coating both layers simultaneously and drying them together in a single processing step. This integration allows the system to produce bilayer electrodes with controlled binder distribution using one coating device rather than requiring multiple devices or sequential processing, thereby increasing production capacity without proportionally increasing investment 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
This approach results in enhanced interfacial adhesion between the current collector and the active material layer, preventing material separation and achieving excellent resistance characteristics in lithium secondary batteries.
Implementation Method 1
drying the coated slurry for a lower layer and slurry for an upper layer at the same time to form an active material layer
Data Source
AI summary
Disclosed is a method for manufacturing a negative electrode, including the steps of: preparing a slurry for a lower layer containing a first active material, a first binder and a first dispersion medium, and a slurry for an upper layer containing a second active material, a second binder and a second dispersion medium; coating the slurry for a lower layer on one surface of a negative electrode current collector, and coating the slurry for an upper layer on the slurry for a lower layer at the same time or with a predetermined time interval; and drying the coated slurry for a lower layer and slurry for an upper layer at the same time to form an active material layer, wherein A is 103-300 and B is 1.1-3.5 in the following formula:A=B/(drying rate)B=(wt % of the first binder in the solid content of the slurry for a lower layer)/(wt % of the second binder in the solid content of the slurry for an upper layer)Drying rate=(total content of the dispersion medium per unit area of the active material layer)/(drying time)(g/(cm2×min)).