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Summary of lipo battery 3s pole piece rolling process

This article is an article introducing the rolling of lipo battery 3s pole pieces. The text explains the meaning and purpose of rolling of lithium battery pole pieces. Interested partners and CNHL go to see it together.

1 lipo battery 3s pole piece rolling significance

After the lipo battery 3s pole piece is coated and dried, the peeling strength of the active material and the current collector foil is very low, and it needs to be rolled to enhance the bonding strength of the active material and the foil, in order to prevent the active material and the foil from being in the electrolyte. Soaking, lipo battery 3s peeling off during use. At the same time, pole piece rolling can compress the volume of the cell, improve the energy density of the cell, reduce the porosity between the active material, conductive agent, and binder inside the pole piece, reduce the resistance of the lipo battery 3s, and improve the performance of the lipo battery 3s.
The following article about the lithium battery pole piece has a detailed introduction, and the partners who need it can click to view:
Common 4s lipo battery pole piece defect types and their influence and detection

2 lipo battery 3s pole piece roller press introduction

In order to improve the consistency of the density and thickness of the surface material of the lipo battery 3s pole piece, the positive and negative pole pieces must be rolled after the coating process. This process is called the rolling of the lipo battery 3s pole piece. At present, the domestic and foreign manufacturers of lithium ion lipo battery 3s all use two-roller presses to roll the pole pieces. The two-roller presses are composed of two cast steel compaction rollers, a motor and a drive shaft.

The mainstream model has a roll diameter of 500 mm and a roll body length of 500 mm to 700 mm. The thickness consistency of the pole pieces along the width direction is poor. In order to ensure the accuracy requirements of thickness consistency, the ratio of the length to the diameter of the roll is often small, which eventually leads to a narrower rolling width of the pole piece.
In the field of copper foil, aluminum foil and other foil materials, most of the foil materials are produced by rolling with four-roller rolling machine, the surface precision can reach several microns, and the rolling width can reach more than 1 m. But there is no precedent for the application of a four-roll roll press in pole piece rolling?

Rolling machine rolling process


The complete rolling process is to fix the coated pole piece on the unwinding mechanism, correctly pass the pole piece through the double roll gap, and connect the winding system. After the rolling mode is turned on, the motor drives the upper and lower rollers to rotate at the same time, and the pole piece pulled by the winding mechanism will steadily pass through the rolling gap, and finally be pressed to the required compaction density. The roller press needs to be coated with a thin layer of oil when it is not working to prevent it from rusting. Before use, wipe the oil layer with absolute ethanol, and clean the winding and unwinding mechanism and automatic deviation correction mechanism.


Roller function module

Therefore, an excellent roller press must contain the following functional modules:
1) Roll pressure adjustment and quick response function:
The pressure adjustment between the two rolls of the rolling machine is a necessary condition to improve the compaction density of the active material of the lipo battery 3s pole piece. Due to the influence of intermittent coating, single and double staggering and other factors, the pressure adjustment between the two rolls must respond quickly .

2) Roll gap adjustment and accurate reset function:
The adjustment of the gap between the two rolls of the rolling machine is a necessary condition to obtain the thickness of the lipo battery 3s pole piece. Due to the change of the pole piece coating method and the need of pole piece splicing, the gap between the two rollers needs to be reset accurately after being quickly adjusted.
Tension adjustment and quick response function before and after the pole piece rolling: Adjusting the front and rear tension during the rolling process of the lipo battery 3s pole piece can control the flatness of the lipo battery 3s pole piece. During the rolling process, the rolling line speed often changes instantaneously, and the rapid response of tension control is an important means to prevent belt breakage.

3) The stepless speed regulation of the roll and the synchronization function of the line speed:
The lipo battery 3s pole piece rolling machine must perform stepless speed change on the two rolls during the start and stop process or according to the needs of the process, and at the same time ensure that the line speeds of the two rolls are consistent.

4) Pole piece rolling temperature adjustment function:
Adjusting the rolling temperature of the lipo battery 3s pole piece can directly affect the deformation resistance and plastic deformation of the lipo battery 3s pole piece during the rolling process.
About the lithium battery pole piece, its common defects and solutions are introduced below, and the partners who need it can expand the reading:
1300mah 5s battery pole piece coating defects and influencing factors

5) Correction function of roll deformation:
During the rolling process of the lipo battery 3s pole piece or the temperature adjustment process, the two rolls must have axial deflection deformation and radial bulging deformation. Correcting the roll deformation directly affects the thickness uniformity and compaction density uniformity of the lipo battery 3s pole piece .
The intelligent control function of the pole piece rolling process:
With the continuous improvement of the pole piece rolling speed and the degree of automation, closed-loop control and even intelligent control are required for automatic loading and unloading, automatic tape splicing, automatic pressure, automatic gap adjustment, and online monitoring.

6) Roll cleaning and maintenance functions:
During the rolling process of the lipo battery 3s pole piece, it is common for the surface of the two rolls to stick to powder. Keeping the roll surface clean can not only reduce the wear of the roll, but also improve the surface quality of the lipo battery 3s pole piece. The ease of maintenance of the rolling machine is also a very necessary function.

The laboratory usually uses the experimental manual screw press type pole piece mill, by setting the roll gap value so that the rolls are loaded with pressure on the pole piece, without additional pressure device.
Therefore, the actual pressure is generally relatively small, the compaction density of the rolled pole piece is limited, and the maximum roll gap is generally limited by the mechanical device, and generally too thick pole pieces cannot be rolled.
Pole piece rolling
In addition, pole piece rolling is divided into two methods: cold rolling and hot rolling. At present, hot rolling has been widely used in foreign countries for pole piece rolling, while domestic cold rolling is still used. Compared with cold rolling, hot rolling has some advantages.

The following advantages:
(1) Remove the moisture inside the pole piece; reduce the internal stress of the pole piece, because during slitting or die cutting, the release of the internal stress of the pole piece will be reduced.
(2) Reduce the material rebound of the pole piece after rolling; reduce the deformation resistance of the lipo battery 3s pole piece, which is beneficial to improve the liquid absorption of the active material.
(3) Since the material of the pole piece is in a molten state during the heating process: hot rolling can increase the adhesion between the active material and the fluid, reduce the occurrence of powder drop during the charging and discharging cycle, and improve the lipo battery 3s. cycle life
In terms of rolling schedule: it can be divided into one rolling and multiple rolling. The multiple rolling process is relatively complicated, but it can reduce the rebound of the pole piece, and the pole piece has good gloss and high thickness consistency.

3 lipo battery 3s pole piece rolling purpose

The compaction density of the pole piece has an important influence on the electrochemical performance of the lipo battery 3s. Within a certain range, as the compaction density increases, the distance between the active material particles decreases, the contact area increases, and the paths and bridges that are conducive to ion conduction increase. In the macroscopic aspect, the internal resistance of the lipo battery 3s decreases. However, if the compaction density of the pole piece is too high, the contact between the active material particles is too close, and the electronic conductivity increases.

However, the reduction or blockage of lithium ion channels is not conducive to the development of capacity. When discharging, the polarization increases, the voltage decreases, and the capacity decreases. If the compaction density is too small, the particle spacing is large, the lithium ion moving channel is smooth, and the electrolyte absorption capacity is strong, which is conducive to the movement of lithium ions inside the lipo battery 3s, but the contact between particles is not close enough, which is not conducive to the conduction of electrons. When discharging, it is easy to cause an increase in polarization.

The necessity of rolling: After the pole piece is coated and dried, the peeling strength between the active material and the current collector foil is very low. At this time, it needs to be rolled to enhance the bonding strength between the active material and the foil, so as to avoid the need for rolling. Prevent peeling off during immersion in electrolyte and lipo battery 3s use.

The purpose of rolling is as follows:
1) Ensure that the surface of the pole piece is smooth and flat, and prevent the burr on the coating surface from piercing the diaphragm and causing a short circuit;
2) Compact the coating material of the pole piece to reduce the volume of the pole piece to improve the energy density of the lipo battery 3s;
3) Make the contact between the active material and the conductive agent particles more closely, and improve the electronic conductivity;
4) Enhance the bonding strength between the coating material and the current collector, reduce the occurrence of powder drop of the lipo battery 3s pole piece during the cycle, and improve the cycle life and safety performance of the lipo battery 3s.
Well, the above is all the content of today, I hope it will be helpful to you. For more information on lithium batteries, please click below to view:
Staged charging of 1300mah 22.2V 6s lipo battery

 

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