Analyze the burr in the cutting process of lithium battery

1, the cutting method of lithium battery electrode disc shear has completely different characteristics:

(1) When the electrode is cut, the upper and lower disc knives have a rear angle, similar to the scissors blade, and the blade width is particularly small. The upper and lower disc knives do not have horizontal gaps, but the upper and lower knives touch each other and have lateral pressure.

(2) There is basically a rubber roller on the upper and lower parts of the plate when cutting, which balances the shear force and shear torque generated by the upper and lower knives during cutting to avoid large deformation of the board. The pole cut did not roll up and down.

(3) Polar coating is a composite material composed of particles and has almost no plastic deformation ability. When the internal stress generated by the upper and lower disc knives is greater than the binding force between the coated particles, the coating produces cracks and expands separation.

2, Polar slice cut quality affecting factors

There are many factors that affect the size of the Burr, the morphological characteristics of the cross-section, and the accuracy of the size of the electrode. According to existing theories, It can be summarized as follows: physical and mechanical properties of the electrode, the thickness of the pole, the lateral pressure of the upper and lower pairs of tools, the amount of overlap of the upper and lower pairs of tools, the wear state of the blade, the bite angle, and the accuracy of the disc knife.

(1) Effects of physical and mechanical properties of materials. Generally speaking, the plasticity of the material is good, cracks will appear later when cutting, the depth of the material is cut is large, and the proportion of the resulting section light band is large; The plastic poor material, under the same parameter conditions, is prone to fracture, the proportion of the tear zone of the section will be larger, and the light zone will naturally be smaller.

(2) The effect of up-and-down formation on the lateral pressure of the tool. The cutting tool lateral pressure is one of the key factors affecting the cutting quality in the cutting. When shear, whether the upper and lower cracks of the fracture surface coincide and the stress and strain state of the shear force are closely related to the size of the lateral pressure. The lateral pressure is too small, and the cutting of the electrode may have defects such as incomplete cut sections and falling materials. The pressure is too large, the tool is easier to wear, and the life is shorter.

(3) Effect of up-and-down formation on the amount of overlap of tools. The setting of the amount of overlap is mainly related to the thickness of the electrode, and the reasonable amount of overlap is conducive to the bite of the tool. The influence includes the advantages and disadvantages of the shear quality, the size of the bristle, and the speed of the tool edge wear.

(4) The effect of biting. In disc cutting, the bite angle refers to the angle between the shear section and the center line of the sheared plate. When the angle of bite is increased, the horizontal force generated by the shear force will also increase. If the horizontal partition force is greater than the feed tension of the electrode, the sheet is either slippery or arched in front of the round knife and can not be cut. And the bite angle decreases, the diameter of the blade will increase, and the size of the splitter will also increase accordingly. Therefore, how to balance the bite angle, blade diameter, plate thickness and overlap, must refer to the actual working conditions.

In the pole-cutting process, the lateral pressure and the amount of overlap of the cutter are the main adjustment parameters of the disc cutter, which need to be adjusted in detail according to the properties and thickness of the pole-cutting. In the previous equipment manufacturing and technology, the cutter often lacked accurate numerical parameters, but based on experience according to the batch adjustment. With the Advancement of equipment technology, the technology of tuning knives is also continuously improving and numerical. At present, there is an automatic adjustment device for the side pressure cylinder of the pole splitter tool. When the pole splitter splice splice pressure is set to adjust the side pressure of the tool and control the cutting quality.

3, the main defects of the pole division

The typical morphology of the cut section of the polar film shows that the main particles of the fracture surface coating are separated from each other, and the collection fluid is plastically cut off and torn. When the compaction density of the polar film coating increases and the binding force between the particles increases, some particles of the polar film coating are also cut off. The main defects in polarimetric sectioning include the following:

(1) Thorn

The burrs, especially metal burrs, are extremely harmful to lithium batteries. Larger metal burrs directly puncture the diaphragm, causing short circuits between positive and negative poles. Polar-chip cutting process is the main process of Burr production in lithium ion battery manufacturing process. Figure 3 shows the typical morphology of the metal burr produced by the Polaroid splicing. The Polaroid forms a collection fluid burr at the splicing, which is more than 100 μm in size. The number and size of burrs are controlled by cutting tool angle, lateral pressure of cutting tool and tension adjustment of receiving and releasing coil.

In order to avoid this situation, it is most critical to find the most suitable lateral pressure and tool overlap according to the nature and thickness of the pole. In addition, the edge quality can also be improved by cutting the knife and reversing the tension of the roll.

(2) Waves edge

Discharge and wave-edge defect, wave-edge, existing when the electrode is sectioned. When the wave edge appears, the edge correction jitter will appear when the electrode is cut and wound, which will cause the process accuracy. In addition, the final thickness and morphology of the battery will also have an adverse effect.

Polaroid cut off material and wave edge defects.

(3) Powder Drop

The appearance of powder off the electrode will affect the battery performance. When the positive pole falls off the powder, the battery capacity decreases, and when the negative pole falls off the powder, the negative pole can not wrap the positive pole, which easily causes lithium analysis.

The above quality problems are mainly solved by finding suitable tuning parameters.

(4) Size does not meet the requirements

Polar-chip splitter is based on the battery specifications, through the roller to carry out the cutting of the battery electrode, requiring high accuracy in the size of the splitter. When winding the battery design, the diaphragm must wrap the negative pole to avoid direct contact between the positive and negative poles to form a short circuit, and the negative pole must wrap the positive pole to avoid charging. When the positive lithium ion does not have a negative living material to accept lithium, generally, The size difference between the negative pole and the diaphragm, the negative pole and the positive pole is 2-3 mm, and as the specific energy requirements increase, the size difference continues to decrease. Therefore, the size accuracy of the electrode is becoming more and more high, otherwise the battery will have serious quality problems.

4, the main failure mode of disc cutter

In the process of pole-cutting, the quality of the pole-cutting disc blade directly affects the performance of pole-cutting. The splitter needs to be operated for a long time, so it is important that the splitter blades have good mechanical properties such as hardness, manufacturing process and wear resistance. There is a certain life span in the continuous operation of the disc cutter. In the cutting process, it is necessary to manage the life of the cutter. In general, the main failure method of the disc cutter is tool wear, which includes:

(1) Fatigue failure

There is a lateral pressure on the cutting disc knife, and the upper and lower tools overlap each other on the side of the blade mouth. During the continuous cutting process, the stress on the blade part is large and concentrated, due to frequent extrusion, shear, friction, and cyclic changes. The mechanical load effect, In the blade area, fatigue micro-cracks are likely to occur, and then under the action of cyclic stress, they will extend toward the center along the side of the disc knife. When the crack grows to a certain extent, the stress reaches the limit of the strength of the tool material and causes the tool edge. Local micro-damage.

(2) Adhesion wear

Adhesives with extrusion marks can also be found in the tool wear area. These adhesives are formed by the adhesion of polar fragments to the tool. This is due to the fact that the lateral edge of the disc knife is in contact with the polarizer, and there is a large contact pressure, so that the cut material is partially cold-soldered to the side of the disc knife. These adhesive layers are continuously disassembled and re-formed during the cycle cutting process. The shedding process may cause the hard phase of the tool to fall off and aggravate the wear process. This situation is most easily formed when cutting aluminum foil. Due to the low melting point of aluminum, the cutting chip and the side of the tool are glued together to cause tool wear and shortened life.

(3) Grinding wear

Although the hardness of the shards and chips is lower than the hardness of the tool, they often contain some tiny hard spots with extremely high hardness. The groove pattern can be carved on the surface of the tool. This is abrasive wear.

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