Streaks, pinholes, heavy edges, and periodic variation cannot be diagnosed from appearance alone. Direction, cross-web position, repeat period, and timing are the first evidence.
Defect map
Give the defect coordinates before changing settings
A continuous machine-direction streak often points to a fixed cross-web location in the die, debris, or backing roll. Periodic machine-direction variation is more likely to match pump stroke, roll rotation, or tension. Random pinholes require separation of bubbles, particle cores, and wetting. Cross-web start-stop lines, splice disturbances, and edge defects follow different paths.
Record roll, lot, running length, cross-web position, length, width, repeat interval, and inline image for every defect. A photograph without coordinates cannot be aligned with equipment histories.
| Defect signature | First suspects | First validation |
|---|---|---|
| Continuous streak at fixed cross-web position | Die lip, agglomerate, scratch, backing roll | Inspect the same position and filter residue |
| Equal-spacing periodic variation | Pump stroke, roll, tension | Convert spacing to time and compare frequencies |
| Random pinholes or craters | Bubbles, debris, foil, wetting | Inspect defect core, deaeration, and foil |
Feed system
Feed-system defects often carry a time or frequency signature
Pump pulsation, hose compliance, rising filter pressure, and return control change die-inlet pressure. If variation matches pump stroke, inspect pump type, stroke, damping, and suction before changing die gap. Progressive filter blockage often appears as a slow pressure rise and a trend within one roll.
Bubbles can enter at pump suction, joints, return lines, or low tank level. A properly deaerated slurry can re-entrain air in feeding, so tank level, suction pressure, and pinholes should be reviewed together.
- —A normal mean pressure does not exclude high-frequency pulsation
- —Filter pressure needs roll- and time-based history
- —Separate deaeration from feed-line air ingestion
Die and web
Die, backing roll, tension, and foil jointly set wet-film geometry
Dried material, scratches, or small die-lip deformation create fixed-position streaks; backing-roll runout or debris can produce similar marks. Test die and backing roll separately. Tension and steering variation make coating width, edges, and front-back alignment change over time.
Heavy edges and recession depend on surface tension, rheology recovery, die-edge design, and web speed. Edge correction must be followed through drying, calendering, and slitting for shedding and burr formation.
A defect disappearing after die cleaning proves the location mattered this time; the source of contamination still needs to be found to prevent recurrence.
Diagnostic matrix
Turn appearance into an executable check
The table sets the diagnostic order; it does not assign a root cause from appearance alone. Similar defects can come from different stages and need confirmation by slurry sample, equipment inspection, cross-section, or offline test.
| Symptom | Possible sources | Check first | Adjustment direction |
|---|---|---|---|
| Machine-direction streak | Die, agglomerate, feed, backing roll | Cross-web position, filter residue, lip, backing roll | Clean and isolate, then address filtration or feeding |
| Periodic loading | Pump, tension, roll rotation | Defect period versus equipment frequency | Adjust pump/damping/tension or service rotating part |
| Pinholes and craters | Bubbles, debris, foil, wetting | Defect core, deaeration, pump inlet, foil | Test gas, cleanliness, and surface state separately |
| Heavy or receded edge | Rheology, surface tension, edge design, speed | Wet/dry edge profile and slurry recovery | Coordinate recovery, edge design, and steady-state speed |
Close the loop
Close a defect with affected roll sections and prevention actions
After diagnosis, record root cause, validation, affected running length, disposition, and recovery first-piece. “Parameters adjusted” is not enough to recognize recurrence. Repeated defects should be compared with maintenance, filter life, slurry lot, and environment.
Defect severity must be followed into calendering, slitting, assembly, and cell results. Safety-relevant metal particles, bare foil, and extensive delamination cannot be released because average loading passes.
- —Locate affected material by running length and cross-web position
- —Repeat first-piece approval after recovery
- —Safety defects are not offset by averages
Bibliography
References
- 01Binder migration: Frequently observed yet overlooked phenomena in electrode processing
- 02Advanced electrode processing for lithium-ion battery manufacturing
- 03Impact of Electrode Defects on Battery Cell Performance: A Review
- 04Electrode Manufacturing for Lithium-Ion Batteries—Analysis of Current and Next Generation Processing
- 05Challenges and opportunities for high-quality battery production at scale
Updated: 2026-08-26