Tab Related Defects in Li-ion Pouch Cell Manufacturing

Tabs are the metal strips that carry current from the electrodes inside a pouch cell to the outside circuit. The positive and negative tabs are usually made from different conductive materials, commonly aluminium for the positive and nickel or nickel-plated copper for the negative, and each carries a strip of sealant film where it passes through the pouch seal.

Original EngineerX process map: the 11 main steps of pouch cell manufacturing in the order used on this site; the highlighted step is the subject of this article.

In the line, tabs are welded to the electrode foils, travel with the jelly roll into the pouch, and then pass through auto-packing steps such as positioning, tab-distance inspection, insulation checks and sealing. A tab defect can therefore start early and show itself late.

Why this stage matters

The tab area is where electrical connection and pouch sealing meet. A tab that is crooked, dirty or damaged can disturb both. The result may be a short circuit, a leak at the seal, higher resistance, or a cell that cannot be welded into a module.

Electrical short circuits between the positive and negative tabs.
Increased internal resistance and heating at the joint.
Poor connection in the module or pack.
Leakage or weak sealing around the tab region.
Reduced reliability and possible safety risk.

How tabs are handled in the process

Tab strips are cut and fitted with sealant film, and welded to the electrode foil stack. Weld quality is checked at that stage.
The jelly roll is inserted in the formed pouch pocket with the tabs pointing out toward the sealing area.
A positioning unit aligns the tabs relative to the pouch centreline and to each other.
A camera or gauge measures the tab spacing, protrusion height and angle.
Insulation between the tabs and the laminate metal layer is verified as the plan requires.
The sealing bars close on the tab area. Tab condition, position and sealant film decide whether this seal is good.
Final CCD and electrical checks confirm tab position and the absence of shorts.

Key process parameters

Limits for tab position, spacing and height come from the cell drawing and the cell maker's specification. Typical values depend on cell design, materials and equipment supplier and are not universal.

Parameter	What it controls	How it is checked
Tab position relative to centreline	Alignment of positive and negative tabs in the pouch	CCD measurement or fixture check
Tab angle (skew)	Squareness of the tab to the seal	Vision measurement of the angle
Tab-to-tab distance	Electrical clearance and module connection	CCD or calibrated gauge
Tab protrusion height	Amount of tab outside the seal, and seal pressure on the tab	Gauge or camera
Sealant film position	Whether the film covers the seal zone fully	Visual check and cross-section on samples
Tab surface condition	Contact, corrosion and sealing quality	Visual inspection, cleanliness check
Insulation resistance	Electrical isolation between tab and laminate	Insulation or Hi-Pot tester

Typical defects, causes and corrective actions

Defect	Typical causes	How it is detected	Corrective action
1. Tab misalignment (away from the pouch centreline)	Positioning unit out of adjustment, jelly roll offset in the pocket	CCD tab-position measurement	Re-set the positioning unit and check jelly roll placement
2. Tab skew (angular deviation)	Tab picked up crooked, loose clamp, roll rotated	Angle measurement by vision system	Fix the clamp, adjust the pick-up and insertion alignment
3. Tab distance out of specification	Spacing error at welding or insertion, shift during handling	Tab-distance check by CCD or gauge	Adjust welding or insertion tooling, re-check after each changeover
4. Tab folding or bending	Handling contact, jelly roll insertion force, tooling	Visual and CCD inspection	Smooth the guide surfaces, reduce insertion force, train handlers
5. Tab surface damage	Rough tooling, scratches in transfer, falling cells	Visual inspection under light	Replace damaged contact parts, use protective covers
6. Tab burr formation	Blunt or misaligned tab cutting tool	Microscope or profile check, burr height measurement on samples	Sharpen or replace the cutting tool, reset clearance
7. Tab contamination	Dust, metal particles, oil or process residue	Visual check, tape or wipe test where defined	Clean the area, change wipes and gloves, improve cleanliness
8. End tape / green tape defect	Wrong tape length, poor adhesion, loose layers on winding	Visual check of the roll end, and a gentle hold test for loose layers	Correct tape application settings and surface condition, check tape lot
9. Tab height variation	Inconsistent tab cut or positioning, shift in the clamp	Height gauge or camera	Reset the cut length and positioning stop, re-verify with a sample
10. Tab position shift during JR insertion	Pocket mismatch, insertion speed, loose jelly roll	Dimension check after insertion, comparison with pre-insertion data	Adjust insertion speed and guiding, tighten the jelly roll
11. Tab cracking or fracture	Excessive bending, repeated stress, work hardening	Visual check, bend-test or continuity check on suspect samples	Remove the cell, reduce bending in handling, review tab material and fold method
12. Tab short circuit risk	Tabs too close, missing or shifted insulation, burrs	Short-circuit and insulation tests, CCD distance	Hold the lot, correct spacing and insulation, quarantine suspect cells

Quality checks and measurements

High-resolution CCD checks of tab position, angle, spacing and protrusion height on every cell where possible.
Insulation and short-circuit electrical tests after sealing.
Periodic burr measurement on tab cutting tooling.
Cross-section or peel tests of the tab seal on samples, as set in the quality plan.
Calibration of cameras, gauges and testers, and use of a master cell for daily verification.
Tracking of tab-defect counts by machine, shift and lot.

Safety and handling notes

Tab edges and burrs are sharp. Wear cut-resistant gloves where the instruction requires them, and do not run bare fingers along the edge.
Cells with exposed tabs can short if the tabs touch metal. Use insulated tools, non-conductive trays and keep tabs separated.
Work with open jelly rolls and sealing in the controlled dry room according to the dry-room rules: clean garments, no loose items, and proper entry procedure.
Keep hands clear of sealing bars and positioning units, and use lockout and tagout before adjusting or cleaning machines.
A bent, cracked or shorted tab can overheat. Isolate such cells and place them in the designated container.

Interview questions

Q1. What is the function of a tab?
It conducts current between the internal electrodes and the external circuit.

Q2. Why is the tab area sensitive for sealing?
The pouch seal must close around a metal tab, so the sealant film, tab surface and position must all be correct.

Q3. What is tab skew?
It is the angular deviation of a tab from its intended orientation, which can affect spacing and stress during sealing.

Q4. Why can tab burrs cause a short circuit?
A sharp burr can pierce or damage the separator, creating a conductive path between anode and cathode.

Q5. What is the end tape used for?
It secures the outer end of the wound layers so that the jelly roll stays stable during handling.

Q6. How is tab distance verified?
By a CCD system or gauge compared with the drawing limits.

FAQs

FAQ 1. Are positive and negative tabs made of the same metal?
Usually not. Aluminium is commonly used for the positive tab and nickel or nickel-plated copper for the negative.

FAQ 2. Can a slightly bent tab be straightened by hand?
Only if the work instruction allows it. Repeated bending can crack the tab, so the safe rule is to follow the approved rework method or reject the cell.

FAQ 3. Which defect is the most serious?
A short-circuit risk is the most serious since it can lead to safety events, but cracks and sealing problems at the tab also matter.