Lithium Ion Battery manufacturing : Cutting Technology. Guideline to improve your process.

Lithium Ion battery manufacturing foreseen many cutting process, usually there are three different cutting process:

• Slitting: in electrode manufacturing
• Notching: in first phase of cell assembly area
• Electrode cutting or singulation: in the middle of cell assembly area

Usually the first cutting process is in electrode manufacturing, called slitting. Slitting is the cutting process which split the electrode master coil after calendering process into multiple coil with a specific dimension (width) accordingly to the lithium ion battery cell design.

Moving to Lithium Ion cell assembly process, there are two different cutting process:

• Notching
• Electrode singulation

Electrode cutting in Lithium ion battery manufacturing is the most common process for prismatic cell and new cylindrical tabless cell design. The purpose of electrode notching is to create a cutting profile on electrode in order to remove barefoil and obtain tabs which will be welded later on with current collectors.

Here below you can find an example of electrode notching in lithium ion battery manufacturing:

• Tabless cylindrical cell: common laser notching pattern.

• Prismatic cell (metal can and pouch): common laser / mechanical notching pattern:

Usually in both case we are in roll to roll scenario:

• For Lithium Ion tabless cylindrical cell the incoming electrodes are in reels. After unwinding process the electrodes pass through a laser notching module where the aliminum (for cathode) and copper (for anode) are cutted by a laser beam in order to obtain what is called “flag”. Then the electrodes and separators move to winding head which creare a wound element: Jelly Roll
• For lithium Ion prismatic cell the process is leteraly roll to roll since the input material is a electrode reel. After unwinding process the electrode pass through a notching area which could be a mechanical notching tool or a laser cutting system. In this case not just the metal bare foil but even the coated foil is removed by the notching / cutting system. After the cutting unit, the material move to rewinding area to obtain as output a electrode reel.

The third cutting process in lithium ion battery manufacturing is the singulation. The electrode singulation is the process which singulate the electrodes from continuous web material to single sheet electrodes. Then these electrode sheets can be laminated together with separators and stacked or move into a magazines and then placed on Z-Folding machine in order to obtained the final cell.

In lithium ion Battery manufacturing each cutting process have some common requirements: Accuracy, High cutting rate, Cutting line quality.

• Accuracy: each cutting system must provide high accuracy as cutting pattern. The geometries resulting from cutting process must be compliant to design specification which usually required tollerance of +/-0,15mm with Cpk >1,33.
• High cutting rate: especially for lithium ion battery mass production environment the production rate is one of the main KPI. Each cutting process must satisfy the production rate requirements in term of cuts/minutes for mechanical notching tools or mm of cutted material/min for laser cutting tools. Currently, the cutting units represent the bottle neck for most of the mass production equipment in term of production rate.
• Cutting line quality: to avoid cutting burss and particles from lithium ion battery manufacturing cutting process . The cutting line have to be clean and no particles should remain on electrodes. Particles and cutting burrs can create failure in lithium ion battery cell in downstream process.

Here below you can see the main failure of cutting process:

• Burrs: electrode cutting burrs are resulting of not good cutting process. For mechanical notching could be a warning: you notching tool working life is close to the end and need a resharpening process. In case of laser cutting process, your parameters are totally wrong. Why you have to avoid the curring burrs? The burrs, in the final lithium ion cell can pinch the separator and go through it, this can create a short circuit situation which results in a failure. The are many theories regarding the maximum cutting burrs entity, one of them says “the cutting burrs dimension cannot exceed the half of separator thickness”.

• Decoating: decoating defect in lithium ion battery manufacturing is a common failure in cutting process. It show areas without coating active material and this is a result of too much power in laser cutting application or debrits in mechanical notching tools. Sometimes the decoating defect is much more visible in all electrodes where the active material have poor adhesion with metal foil substrate. Initially this was one of the main defects in electrodes with water based binder. It represent a defect which affect negatevily the capacity of final cell (less active material) but can be a problem in term of particles since the missing active material on barefoil, means potential particles close to the cutting linea area.

• Particles: can be active material of metal particles. Especially in cutting laser application, particles can be a result of spatters. Usually all cutting systems foreseen a suction device which remove particles with vacuum.

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