Electrode Slitting in Lithium-Ion Pouch Cell Manufacturing

Electrode slitting is the step where a wide, coated and calendered electrode roll, called the mother roll, is cut lengthwise into several narrow strips called daughter rolls. Each strip has the width that the final cell design needs, and each is wound on its own core.

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.

Slitting sits between calendering and the assembly stage (winding or stacking). Everything before it works on a wide web to be productive; everything after it needs exact electrode sizes. Slitting is the bridge, and it is also the first place where the coated material is cut, so it is where metal burrs and loose coating dust can first be created.

Why this stage matters

The cut edge of an electrode is the weakest point of the whole sheet. A rough edge can shed coating particles, and a sharp metal burr on the foil can be long enough to press toward the thin separator. During winding or stacking this can lead to an internal short circuit that may appear only after the cell is formed or even after it has been in use.

Width accuracy is equally important. In a pouch cell the anode must be slightly wider than the cathode so that the cathode is fully covered. If the strip width wanders, the overlap changes from cell to cell, which affects capacity and safety margin. Good slitting therefore protects both quality and yield in the later stages.

How the process works

Check the job card for the electrode type, target strip widths, number of cuts and edge-trim allowance.
Fit the correct knife set and spacers. Cathode and anode foils behave differently, so the set-up is often not the same for both.
Load the mother roll on the unwind shaft and thread the web through guide rollers, the knives and the rewind shafts.
Start at low speed and set the web tension. The unwind and rewind tension should be balanced so that the web runs straight without stretching.
Cut a short trial length and take a sample for width and edge inspection before releasing the run.
Run at production speed while sensors, cameras or operators monitor the edges and the strip position.
Rewind the strips onto separate cores, remove the edge trim into a scrap container, and label each daughter roll with lot, width and position on the mother roll.
Seal the finished rolls in protective packing and move them to the dry store or to the drying step if the plant requires a pre-assembly bake.

Key process parameters

Parameter	What it controls	How it is checked
Strip width	Electrode overlap and fit inside the pouch	Calibrated optical gauge or vision system; sample at start, middle and end of the roll
Knife condition and sharpness	Burr height and coating chipping	Edge inspection under magnification and a planned knife-change schedule
Knife overlap and clearance	Shear quality of the cut	Set-up sheet and verification with feeler gauges or the supplier method
Web tension	Straight running, wrinkles, stretching	Tension sensor readout and observation of the web path
Line speed	Cut quality and dust generation	Machine recipe and review of edge quality at each speed change
Rewind alignment	Telescoping and edge damage on the roll	Visual check of roll side face

The correct numerical values, such as width tolerance, depend on cell design, materials and equipment supplier. Tolerances are usually in the range of a fraction of a millimetre, but the actual limit comes from the cell maker's specification.

Typical defects, causes and corrective actions

Burr formation

A raised metal lip on the foil edge. Causes are dull knives, wrong clearance or overlap, and foreign material between the knives. Corrective action: replace or regrind the knives, reset the clearance, and add burr measurement to the routine check.

Jagged or rough edges

The edge looks uneven or torn. Causes are knife wear, vibration, or too high a speed for the coating hardness. Corrective action: reduce speed, check knife mounting and bearings, and confirm the knives are the right type for the material.

Width variation

The strip width drifts along the roll. Causes are web wander, uneven tension and loose knife positions. Corrective action: recheck guides and tension control, tighten the knife holders and compare with a gauge.

Coating chipping and edge cracking

Pieces of coating break off at the cut, or small cracks run inward. Causes include overly brittle coating after heavy calendering, poor adhesion, or a damaged knife. Corrective action: review adhesion and calendering with the process team, and inspect the knife edge.

Particle generation

Fine dust is released into the air and settles on the web. Causes are cutting friction and loose coating at the edge. Corrective action: use dust extraction near the knives, clean the machine often and wipe the web path.

Quality checks and measurements

First-piece approval: width, edge appearance and visible dust are checked before the run is released.
In-process width monitoring with a scanner or camera, or regular manual sampling.
Burr and edge inspection with a microscope or a suitable optical tool, at a frequency set by the control plan.
Visual check for scratches, wrinkles, bare spots and contamination on the rewound rolls.
Recording of knife usage, such as metres cut, so that blades are changed before they become dull.
Labelling for traceability so that any later defect can be traced to a mother roll and slitting lane.

Safety and handling notes

Knives and rewinding shafts are a cut and entanglement hazard. Use lockout and tagout before changing knives, clearing a jam or cleaning inside guards.
Never reach into moving rollers or nip points. Keep long hair, loose clothing and jewellery away from the machine.
Electrode dust can irritate the eyes, nose and throat. Use extraction, masks and eye protection as per the plant procedure.
Edge trim and dust are scrap that contain battery materials and must go into marked containers for approved disposal.
Store daughter rolls in the controlled humidity area specified by the plant. Electrodes pick up moisture and need to be kept protected before assembly.
Keep the area clean: metal particles on the floor or on gloves can end up inside a cell.

Interview questions

Q1. What is the difference between a mother roll and a daughter roll?
The mother roll is the wide coated roll. Daughter rolls are the narrow strips cut from it.

Q2. Why is a burr dangerous?
It can press toward or through the separator and cause an internal short circuit.

Q3. Why must tension be controlled?
Too high a tension stretches the foil or cracks the coating, too low gives wrinkles and wandering.

Q4. How do you know when to change knives?
By edge and burr inspection results and by the knife-life record set in the control plan.

Q5. Why are anode and cathode strips cut to different widths?
The anode is made slightly wider so that it fully covers the cathode and reduces lithium plating risk at the edge.

Q6. What is edge trim?
It is the narrow strip at the sides of the web that is removed and discarded to leave clean, uniform edges.

FAQs

Is slitting done before or after calendering?

In the flow described here, slitting comes after coating, drying and calendering. Some plants arrange extra steps, so the exact order follows the plant's process plan.

Can laser be used instead of knives?

Some lines use laser cutting for certain steps. Rotary knife slitting remains common for wide webs, and the choice depends on the equipment supplier and the cell design.

Does slitting create dust?

Yes, some dust is unavoidable. That is why extraction, cleaning and filtration are part of a good slitting station.