Briefly describe the production process of lithium battery pole pieces
The meaning of coating.Lithium - Ion Battery Equipment
Slurry coating is the next process after the preparation of the slurry. The important purpose of this process is to uniformly coat the slurry with good stability, good viscosity and good fluidity on the positive and negative electrode current collectors. The pole piece coating is of great significance to the lithium-ion battery pack, which is mainly reflected in the following points:
1. It is of great significance to the capacity of the finished battery
During the coating process, if the thickness of the positive and negative slurry coatings at the front, middle, and rear positions of the pole piece is inconsistent, it will easily cause the battery capacity to be too low or too high, and it is more likely to form lithium precipitation during the battery cycle, affecting the battery. life.
2. It is of great significance to the safety and performance of the battery
5S work should be done before coating to ensure that no particles, sundries, dust, etc. are mixed into the pole piece during the coating process. If the sundries are mixed, it will cause a micro-short circuit inside the battery, and in severe cases, the battery will catch fire and explode. What is more taboo in battery factories is that in a batch of batteries, the difference in capacity and cycle life is large, so during the coating process of the pole piece, it is necessary to ensure that the parameters before and after the pole piece are consistent.
3. It is important for battery life
The large difference before and after slurry coating, the mixing of dust into the pole piece, the uneven thickness of the pole piece on the left and right, etc., are all related to the advantages and disadvantages of the electrochemical performance of the battery.
Second, the coating method
It is understood that the coating equipment is mainly composed of winding and unwinding unit, feeding unit, tension control system, coating machine head, oven and other parts. Coating can be divided into transfer coating and extrusion coating.
1. Transfer coating
The coating roller rotates to drive the slurry, adjust the amount of slurry transfer by adjusting the blade gap, and use the rotation of the back roller or the coating roller to transfer the slurry to the substrate. According to the process requirements, the thickness of the coating layer is controlled to meet the weight requirements. At the same time, the solvent in the slurry spread on the substrate is removed by drying and heating, so that the solid substance is well bonded to the substrate. The advantage is that the viscosity of the slurry is not high, the coating parameters are easy to adjust, and there is no material blocking. The pulp is exposed to air between the rolls, which partially affects the properties of the pulp.
2. Extrusion coating
The feeding system transports the paint to the screw pump, and then the slurry is powered to the extrusion head. The slurry is formed into a liquid film by extrusion and then coated on the moving current collector. After drying, a uniform texture is formed. coating as shown. Its advantages are that the pole piece is very uniform and high precision after coating, the edge of the coating is flat, the operating system is closed, and it is not affected by foreign matter, which is suitable for mass production. The disadvantage is that the equipment has high precision requirements, high maintenance requirements, high slurry viscosity range requirements, and new gaskets should be replaced when changing specifications.
3. Problems that should be paid attention to in coating
point defect
During the coating process, the internal bubbles of the slurry are sprayed on the pole piece, and when dried in the oven, the bubbles burst, forming a white round spot on the pole piece. The active material coating is thin here, and it is most likely to cause micro-short circuit during the charging and discharging process of the battery. When there is foreign matter in the pole piece, the coating film around the particle is a low surface tension area, and the liquid film migrates to the surrounding in a radiating manner, forming point defects. Important measures to prevent such defects are: controlling the operating environment, optimizing slurry agitation, controlling the coating speed, and ensuring that the substrate is clean.
Thick edge defect
During the rolling process of the pole piece, the thick side is subjected to greater pressure, which not only causes the pole piece to have different lateral densities, but also causes the live material particles at the thick side to be crushed. After the pole pieces with thick edge defects are pressed, serious warpage will occur, which will also have a great impact on the subsequent slitting and winding processes.
Slurry coating is the next process after the preparation of the slurry. The important purpose of this process is to uniformly coat the slurry with good stability, good viscosity and good fluidity on the positive and negative electrode current collectors. The pole piece coating is of great significance to the lithium-ion battery pack, which is mainly reflected in the following points:
1. It is of great significance to the capacity of the finished battery
During the coating process, if the thickness of the positive and negative slurry coatings at the front, middle, and rear positions of the pole piece is inconsistent, it will easily cause the battery capacity to be too low or too high, and it is more likely to form lithium precipitation during the battery cycle, affecting the battery. life.
2. It is of great significance to the safety and performance of the battery
5S work should be done before coating to ensure that no particles, sundries, dust, etc. are mixed into the pole piece during the coating process. If the sundries are mixed, it will cause a micro-short circuit inside the battery, and in severe cases, the battery will catch fire and explode. What is more taboo in battery factories is that in a batch of batteries, the difference in capacity and cycle life is large, so during the coating process of the pole piece, it is necessary to ensure that the parameters before and after the pole piece are consistent.
3. It is important for battery life
The large difference before and after slurry coating, the mixing of dust into the pole piece, the uneven thickness of the pole piece on the left and right, etc., are all related to the advantages and disadvantages of the electrochemical performance of the battery.
Second, the coating method
It is understood that the coating equipment is mainly composed of winding and unwinding unit, feeding unit, tension control system, coating machine head, oven and other parts. Coating can be divided into transfer coating and extrusion coating.
1. Transfer coating
The coating roller rotates to drive the slurry, adjust the amount of slurry transfer by adjusting the blade gap, and use the rotation of the back roller or the coating roller to transfer the slurry to the substrate. According to the process requirements, the thickness of the coating layer is controlled to meet the weight requirements. At the same time, the solvent in the slurry spread on the substrate is removed by drying and heating, so that the solid substance is well bonded to the substrate. The advantage is that the viscosity of the slurry is not high, the coating parameters are easy to adjust, and there is no material blocking. The pulp is exposed to air between the rolls, which partially affects the properties of the pulp.
2. Extrusion coating
The feeding system transports the paint to the screw pump, and then the slurry is powered to the extrusion head. The slurry is formed into a liquid film by extrusion and then coated on the moving current collector. After drying, a uniform texture is formed. coating as shown. Its advantages are that the pole piece is very uniform and high precision after coating, the edge of the coating is flat, the operating system is closed, and it is not affected by foreign matter, which is suitable for mass production. The disadvantage is that the equipment has high precision requirements, high maintenance requirements, high slurry viscosity range requirements, and new gaskets should be replaced when changing specifications.
3. Problems that should be paid attention to in coating
point defect
During the coating process, the internal bubbles of the slurry are sprayed on the pole piece, and when dried in the oven, the bubbles burst, forming a white round spot on the pole piece. The active material coating is thin here, and it is most likely to cause micro-short circuit during the charging and discharging process of the battery. When there is foreign matter in the pole piece, the coating film around the particle is a low surface tension area, and the liquid film migrates to the surrounding in a radiating manner, forming point defects. Important measures to prevent such defects are: controlling the operating environment, optimizing slurry agitation, controlling the coating speed, and ensuring that the substrate is clean.
Thick edge defect
During the rolling process of the pole piece, the thick side is subjected to greater pressure, which not only causes the pole piece to have different lateral densities, but also causes the live material particles at the thick side to be crushed. After the pole pieces with thick edge defects are pressed, serious warpage will occur, which will also have a great impact on the subsequent slitting and winding processes.
