What is the side voltage of soft-pack lithium battery

The side voltage of the soft-pack lithium battery refers to

1. Voltage of the aluminum layer between the positive ear and the aluminum plastic film

2. Voltage of the aluminum layer between the anode ear and the aluminum plastic film

The theory is that, whether positive or negative, they are insulated from the aluminium film, which means their voltage should be zero

In fact: considering the battery materials and its processing process, can produce local damage, lead to local conduction between them (including electronic channel and ion channel), the formation of micro batteries, thus has the potential difference (voltage), the higher the voltage, illustrate the potential risk of the battery, the higher the voltage standard difference between each manufacturer. Most of the industry is below 1.0V.

Soft-pack lithium batteries are just liquid lithium ion batteries covered by a polymer shell. In the structure of the use of aluminum plastic film packaging, in the case of potential safety problems in the case of soft-pack battery will only blow.

Soft pack lithium battery parameters

Nominal voltage: 3.7v

Operating voltage: 2.4~ 4.2v

Nominal capacity: 1250mAh

Standard discharge current: 0.2c

Maximum continuous discharge current: 0.5c

Working temperature: charging: 0 ~ 45 ℃

Discharge: - 20 ~ 60 ℃

Product size: MAX9.5*35*52mm

Finished product resistance: 150 m or less Ω

Over-discharge protection voltage is 2.5 0.05v

Over current value: 2~4A

Understand soft pack lithium battery production process and process flow

Advantages of flexible lithium battery

1. The structure of the flexible battery with good safety performance is packed with aluminum plastic film. In the case of potential safety hazards, the flexible battery will only blow up and crack at most, unlike the explosion of the steel and aluminum cell.

2. Lightweight flexible pack battery is 40% lighter than lithium battery with the same capacity, and 20% lighter than aluminum battery.

3. The capacity of large-capacity soft-pack battery is 10-15% higher than that of steel shell battery of the same size, and 5-10% higher than that of aluminum shell battery.

4. Small soft package of battery internal resistance of the lithium battery internal resistance is small, the current domestic soft package can be done in the internal resistance of battery core minimum below 35 m Ω, greatly reduced since the power consumption of the battery.

5. Design flexible flexible package battery shape can be customized according to customer needs, develop new cell model.

Soft pack lithium battery disadvantages

There are few models of soft-pack cell, which can not meet the market demand.

Developing new models is costly.

Understand soft pack lithium battery production process and process flow

Soft pack lithium battery 8 process full solution

Soft package cell, in fact, is the use of aluminum plastic packaging film as a packaging material cell. Relatively speaking, lithium ion battery packaging is divided into two categories, one is a soft package cell, a metal shell cell. In recent years, due to the special needs of some cells with plastic shell, can also be classified as such.

The difference between the two in addition to the different shell materials, decided that its packaging is also different. Soft package cell is used in thermal packaging, and the metal shell cell is generally used in welding (laser welding). The reason why the flexible package cell can be used for thermal packaging is that it USES aluminum plastic packaging film.

1. Soft-pack cell

The so-called soft package cell, in fact, is the use of aluminum plastic packaging film as a packaging material cell. Relatively speaking, lithium ion battery packaging is divided into two categories, one is a soft package cell, a metal shell cell. In recent years, due to the special needs of some cells with plastic shell, can also be classified as such.

The difference between the two in addition to the different shell materials, decided that its packaging is also different. Soft package cell is used in thermal packaging, and the metal shell cell is generally used in welding (laser welding). The reason why the flexible package cell can be used for thermal packaging is that it USES aluminum plastic packaging film.

2, aluminum packaging film

Understand soft pack lithium battery production process and process flow

The composition of the aluminum plastic packaging film (aluminum plastic film for short) is shown in the figure. From the section, there are three layers: nylon layer, Al layer and PP layer.

Each of the three layers has its own role. First, the nylon layer ensures the shape of the aluminum plastic film, so that the film will not deform before being manufactured into a lithium ion battery.

The Al layer is a layer of metal that prevents water from seeping in. Lithium ion battery is very afraid of water, the general requirements of the water content in the PPM level, so the packaging film must be able to block the infiltration of water and gas. Nylon is not waterproof and cannot protect. At room temperature, Al reacts with oxygen in the air to form a dense oxide film, which prevents water and gas from infiltrating into the cell and protects the cell. Al layer also provides the plasticity of the punching hole when the aluminum plastic film is formed, as shown in point 3.

PP stands for polypropylene, a material that melts at temperatures of more than 100 degrees Celsius and is viscous. Therefore, the thermal packaging of the battery mainly relies on the melting and bonding of PP layer under the action of head heating, and then the head is removed, and the cooling solidifies the bonding.

Aluminum plastic film looks very simple, actually, how to put the three layers of material evenly, firmly together is not so easy. Unfortunately, now the quality of good aluminum plastic film is basically imported from Japan, domestic is not without, but the quality remains to be improved.

3. Aluminum plastic film forming process

Soft package cells can be designed according to customer needs into different sizes, when the shape of the size of the design, it is necessary to open the corresponding mold, the aluminum plastic film forming. The forming process is also called "chong pit" (actually I think it should be "chong pit", but everyone write it like this). As the name suggests, it is to use the forming mold to rush out a pit that can hold coil core on the aluminum plastic film under the condition of heating. See the following figure for details.

Understand soft pack lithium battery production process and process flow

After the aluminum plastic film is punched and cut, it is generally called Pocket bag, as shown in the figure below. Generally, when the cell is relatively thin, single hole is selected to punch (the left of the figure below), and double hole is selected when the cell is relatively thick (the right of the figure below), because the deformation on one side will break through the deformation limit of the aluminum plastic film and cause the rupture.

Understand soft pack lithium battery production process and process flow

Sometimes, according to the design requirements, a small hole will be punched in the position of the air bag to expand the volume of the air bag.

4. Top and side sealing process

At last we get to the point. , the top and side sealing process is the first packaging process of soft package lithium ion cell. Top and side sealing actually includes two procedures, top sealing and side sealing. First of all, the winding core should be put into the well-developed pit, and then the packaging film should be folded in half along the dotted line, as shown in the figure below.

Understand soft pack lithium battery production process and process flow

The following diagram shows several positions that need to be encapsulated after the aluminum plastic film is loaded into the core, including top sealing area, side sealing area, first sealing area and second sealing area. The following are introduced respectively.

Understand soft pack lithium battery production process and process flow

After putting the coil core into the pit, the entire aluminum plastic film can be put into the jig for top and side sealing in the top and side sealing machine. The top side sealing machine looks like this:

Understand soft pack lithium battery production process and process flow

The top and side sealing machine of this model in the picture has four clamps. The left station is the top sealing and the right station is the side sealing. The two pieces of the yellow metal is on the head, there are a head, encapsulation when two head with a certain temperature (generally at about 180 ℃), closed when the pressure on the aluminum composite membrane, aluminum-plastic film layers of PP melt then stick together, thus encapsulation to OK.

There is not much to say about the side seal (side voltage is too far to talk about), mainly about the top seal, the schematic diagram of the top seal area is shown below. The top seal is to seal the polar ear, the polar ear is metal (positive aluminum, negative nickel), how to package with PP together? This is done by a small part of the polar ear, called the polar ear glue. I am not very clear about the specific structure of ear glue, and I hope someone who knows better can supplement it. I only know that it also has the cost of PP, which means it can melt and bond when heated. The encapsulation at the polar ear is shown in the circle section below. When packaging, the PP in polar ear glue and the PP layer of aluminum plastic film melt and bond, forming an effective packaging structure.

Understand soft pack lithium battery production process and process flow

5. Liquid injection and presealing procedures

After the top and side sealing of the flexible package cell, X-ray should be done to check the parallelism of its coil core, and then it will be dewatered in the drying room. In the drying room static for some time, it entered the injection and pre-sealing process.

Understand soft pack lithium battery production process and process flow

According to the above introduction, after the top side seal of the battery cell is completed, there is only an opening on the side of the air bag, which is used for liquid injection. After the injection is completed, a pre-sealing of the side of the air bag, also known as a letter, should be carried out immediately. After a packet is completed, the cell is theoretically completely isolated from the external environment. The packaging principle of a letter is the same as that of the top and side seals.

6, static, into, fixture shaping process

After the injection and the first letter are completed, the cell needs to be statically placed. According to different processes, it can be divided into high temperature statically placed and normal temperature statically placed. The purpose of statically placed is to let the injected electrolyte fully infiltrate the electrode sheet. Then the cell can be turned into.

Understand soft pack lithium battery production process and process flow

Above is the soft package battery into the cabinet, in fact, is a charge and discharge device, I looked for a long time did not find a picture with a battery, you think about the battery clip on the above screen is OK. In essence, it is the first charge of the cell, but it will not reach the highest voltage and the charging current is very small.

The purpose of the conversion is to form a stable SEI film on the electrode surface, which is equivalent to the process of "activating" the cell. During this process, a certain amount of gas is produced, which is why an air bag is reserved for the aluminum film. Some factory processes will use fixture forming, that is, the battery cell is clamped in the fixture (sometimes it is easy to use glass plate, and then steel clamp) and then the cabinet forming, so that the generated gas will be fully squeezed into the side of the air bag, at the same time the electrode interface after forming is better.

Some cells, especially the thick ones, may be deformed due to the large internal stress. So some factories will set up a baking process after baking, called jigs baking.

7. Second sealing process

We just said that there's going to be gas, so we're going to pump it out and then we're going to do a second encapsulation. Here, some companies have two processes: Degassing (exhaust) and two seals, and the process of cutting air bags at the back. Here, I will call them two seals in a general way.

Understand soft pack lithium battery production process and process flow

In the second seal, the airbag is first punctured with a guillotine knife and vacuumed so that the air in the airbag and a small part of the electrolyte can be extracted. Then immediately two sealing head in the two sealing area for packaging, to ensure the air tightness of the cell. Finally, the encapsulation of the battery to cut off the air bag, a soft package on the basic shape of the battery. The second seal is the final packaging process of the lithium ion battery, and the principle is the same as the previous thermal packaging, which will not be repeated.

8. Subsequent procedures

Because the main question is about packaging, the latter is not much to do with packaging, so two after the process I said together.

After two seals cut the air bag needs to carry on the cutting edge and the folding edge, is one side and two seals the edge to the suitable width, then folds, guarantees the cell width does not exceed bid. After the folding of the cell can be on the sub-capacity cabinet for the capacity, in fact, is the capacity test, see the capacity of the cell has not reached the minimum value of the provisions. In principle, all the cell factory before the need to do capacitance testing, to ensure that the capacity of unqualified cells will not be sent to the hands of customers. However, when the production of cells is large, some companies will do part of the capacitance, to determine the statistical probability of the batch of cell capacity qualified rate.

After the capacity, the qualified capacity of the cell will enter the process, including inspection appearance, paste yellow glue, side voltage detection, pole ear welding and so on, according to customer demand to increase or decrease a number of processes. Finally, OQC inspection, and then packaging shipment.

The page contains the contents of the machine translation.