Date: 2025-08-18 hits: 102
In lithium battery electrode processing, tab margins are an unavoidable process design. Simply put, the tab area on the electrode is not coated with slurry, leaving a blank area to facilitate subsequent tab welding. However, if the size of this blank area is not properly controlled, will it cause breakage during the roller pressing process? The answer is: excessive blank area increases the risk of breakage. Let's briefly explain.
A. The Correlation between Tab Margins and Rolling Breakage
First, let's clarify a premise: Tab margins are a necessary process design, but if they are excessive, they can indeed become a cause of roller breaking.
The core of the roller pressing process is to compact the electrode sheet to the designed thickness through the compression of upper and lower rollers, with the goal of increasing energy density and improving electrode performance. Under normal circumstances, the coating area (the area with slurry) is much thicker than the blank area (the copper or aluminum foil substrate alone), and the pressure distribution between the two areas during pressing is inherently different. When the blank area is too wide, this difference is magnified. The coated area, supported by the slurry, deforms uniformly under pressure. However, the substrate in the blank area is more susceptible to localized stress concentration under the same linear pressure.
B. The underlying cause of excessive blanking causing tape breakage
(I) Imbalanced Mechanical Distribution
During the electrode sheet rolling process, the pressure applied by the rollers is transmitted along the width. The electrode slurry layer in the coated area has the ability to disperse pressure, while the substrate in the blank area must independently bear the external load. When the blank width exceeds the reasonable range, the effective load-bearing area of the substrate material increases significantly. Without the buffering effect of the slurry layer, it is highly susceptible to plastic deformation under cyclic extrusion stress. Particularly at the interface between the blank and coated areas, stress concentration areas formed by the thickness gradient lead to a sudden change in the localized pressure distribution. This stress concentration effect is similar to the failure mechanism of materials in repeated bending fatigue tests.
(II) Substrate Fatigue Accumulation
The copper and aluminum foils commonly used in lithium battery production are typically 5-12μm thick and are extremely thin and flexible metal materials. Some manufacturers also perform a secondary rolling process. When the tab area's blank width is too large, the substrate in this area undergoes two independent rolling operations during the rolling process. Each rolling process causes a slight plastic deformation of the substrate. According to metal fatigue theory, this cumulative plastic deformation will lead to the proliferation of internal dislocations and grain distortion, significantly reducing the substrate's tensile strength and fatigue life. When the blank width exceeds the material's fatigue limit, even under normal process tension, the substrate may experience sudden fracture due to fatigue crack propagation.
(III) Equipment Parameter Adaptation Issues
The pressure control systems of most roller-pressing equipment are set based on the overall width, making it difficult to adjust them specifically for the localized blank areas. When the blank area is too wide, the equipment's preset pressure parameters can cause "over-compression" of the blank area. The pressure required for the coating area may be too high for the blank area, causing the substrate to be thinned and even microcracks to form. These microcracks will rapidly expand under subsequent tension and eventually cause the ribbon to break.
C. Practical Solutions to Preventing Wire Breakage
(1) Optimizing Blank Size Design
Set the blank width based on the substrate's characteristics and create a rounded transition at the edges of the blank area to reduce stress concentration.
(2) Adjusting Rolling Parameters in Sections
If zoned pressure control equipment is used in the secondary rolling process, the line pressure in the blank area can be reduced by 20%-30%. Traditional equipment can be adjusted by "reducing pressure and increasing times," for example, changing from two rolls to three, with a 15% pressure reduction each time, to achieve a balance between compacting the coating area and protecting the blank area.
(3) Strengthening Substrate Quality Control
Select annealed, high-ductility foils and conduct tension testing before production to eliminate defective batches. Ensure smooth edges in the margin area during coating to avoid jagged, irregular edges that can cause stress concentration.
D. Summary
Excessive margins in the tab area do increase the risk of tape breakage during rolling, but this is not a causal relationship; rather, it results from the interaction of process parameters and material properties.
