A solid-state electrode coating R2R line is a continuous process that applies sulfide-based solid electrolyte onto a current collector using a slot-die method. Domestic electrode-process equipment maker CIS has built a continuous sulfide-based solid electrolyte pilot line at its Daegu Plant 3, with an annual production capacity of 2–5 tons. Compared to wet slurry, sulfide electrolyte is highly moisture-sensitive, requiring simultaneous management of roll-surface contact time and tension deviation. This is where a mechanical contradiction arises: lowering tension increases weaving, while raising tension increases the risk of web breakage and electrolyte powder shedding. Within how many newtons must tension deviation be controlled to satisfy the coating thickness tolerance?
Kinematic Analysis
The tension roll system consists of a tension-transfer path across three sections: the unwinder, the coating section, and the rewinder. The tension difference across each section is determined by the sum of roller inertia and bearing friction torque. The dancer roll just before the coating section is a buffering element that absorbs tension fluctuations, with its spring constant and dancer travel governing response speed. From a load-path perspective, deflection of the dancer roll shaft directly translates into tension deviation, making shaft stiffness a top-level design variable for coating thickness uniformity.
Calculation/Formula Verification
In the relationship between web tension $T$ (N) and roller radius $r$ (mm), the drive torque is as follows.
$$M = T \times r \times 10^{-3}$$
Here $M$ is in N·m. Applying a web width of 500mm, target tension of 80N, and tension-roll radius of 50mm (estimated: typical specification for a pilot-scale R2R line, on-site measurement and reconfirmation required) gives $M = 80 \times 0.05 = 4$N·m. This value must be reverified by converting it to the instantaneous tensile stress the web experiences immediately after coating. Safety factor is applied twofold: a first factor of 4.0 or higher against web breaking strength, and a second factor of 2.5 or higher against coating-layer peel strength. If both criteria cannot be satisfied simultaneously, the design must shift toward lowering tension and increasing dancer roll response speed to correct weaving.
Shop-notes
For the tension roll surface, ceramic coating is considered as the primary option over hard chrome plating to prevent sulfide powder adhesion. Ceramic coating requires securing at least 0.05mm of post-machining grinding allowance to meet roundness tolerance, so the grinding allowance must be separately marked on the machining drawing (machinability note). A non-contact air-turn roll was considered as an alternative but not adopted. The reason it was not adopted is that the burden of maintaining line cleanliness under dust scattering is greater than with a contact-type roll. Tension-roll drive motor capacity requires on-site measurement and reconfirmation.
Design Reflection Checklist
- Has the tension deviation control value been calculated and dual safety-factor verification completed?
- Has the dancer roll spring constant been measured on-site?
- Has the tension roll surface treatment’s grinding allowance been reflected in the drawing?
- Has the drive motor capacity been reconfirmed on-site?
One-Line Summary
For a sulfide-based solid-state electrode coating R2R line, tension deviation control is a design variable that takes precedence over coating thickness tolerance.