The soft-packed battery is actually a battery that uses aluminum-plastic film as a packaging material. Relatively speaking, the packaging of lithium-ion batteries is divided into two categories, one is a soft-packed battery core, and the other is a metal-clad battery core. The metal casing core includes steel and aluminum shells, cylinders and squares, and the like.
hium-ion batteries is divided into two categories, one is a soft-packed battery core, and the other is a metal-clad battery core. The metal casing core includes steel and aluminum shells, cylinders and squares, and the like.
The packaging material and structure of the soft pack battery have a series of advantages, for example, the safety performance is good, and the soft pack battery is packaged in aluminum plastic film structure. When a safety problem occurs, the soft pack battery generally blows up, instead of Explosion like steel shell or aluminum shell battery; light weight, soft pack battery weight is 40% lighter than steel shell lithium battery of the same capacity, 20% lighter than aluminum shell lithium battery; internal resistance is small, internal resistance of soft pack battery Compared with the lithium battery, it can greatly reduce the self-consumption of the battery; the cycle performance is good, the cycle life of the soft pack battery is longer, and the 100-cycle attenuation is 4% to 7% less than the aluminum shell; the design is flexible and the shape can be changed freely. The shape can be thinner and can be customized according to customer's needs to develop new battery models.
The proportion of soft packs in the field of power batteries has exceeded square and cylindrical. According to statistics, the output of domestic square, cylindrical and soft-packed lithium batteries in 2015 was 17GWh, 10.1GWh and 19.8GWh, respectively, accounting for 36.4% and 21.5% respectively. 42.3%.
With the introduction of new subsidies for new energy vehicles, the system's energy density has become an important indicator. The ternary soft pack battery capacity is 10~15% higher than that of the same size steel shell lithium battery, 5~10% higher than the aluminum shell battery, and the weight is lighter than the steel shell battery and the aluminum shell battery of the same capacity specification, therefore, Subsidizing the New Deal is more beneficial to the ternary soft pack battery. In view of the advantages of soft pack batteries, industry experts predict that with the development of battery routes, the penetration rate of soft pack batteries in the new energy vehicle market will continue to increase, and the proportion of soft pack batteries in various types of batteries is expected to exceed 50%.
The materials used in the casing determine the way they are packaged. The soft case has an aluminum plastic film and needs to be packaged by heat; the metal case is generally sealed by laser welding. The aluminum plastic film generally has three layers. The nylon layer ensures the shape of the aluminum plastic film, reduces the damage to the outer casing, and ensures that the film does not deform before the lithium ion battery is manufactured, preventing the penetration of air, especially oxygen, and maintaining the battery core. The internal environment ensures that the packaging foil has good deformation ability. The Al layer is composed of a layer of metal Al, which functions to prevent water from penetrating, and maintains the environment inside the cell with a certain thickness strength to prevent external damage to the cell. Lithium-ion batteries are very afraid of water. Generally, the water content of the pole pieces is at the PPM level, so the packaging film must be able to block the infiltration of moisture. Nylon is not waterproof and does not provide protection. Metal Al reacts with oxygen in the air at room temperature to form a dense oxide film, which prevents moisture from penetrating and protects the inside of the cell. The Al layer also provides the plasticity of the crater when the aluminum film is formed. PP is an abbreviation for polypropylene, which is characterized by melting at a temperature of more than one hundred degrees Celsius and is viscous. Therefore, the thermal packaging of the battery mainly relies on the PP layer being melted and bonded under the action of the heating of the head, and then the head is removed, and the temperature is solidified and bonded, and the PP is not dissolved and swelled by the organic solvent in the battery core, thereby effectively preventing The internal electrolyte or the like is in contact with the Al layer to prevent the Al layer from being corroded.
The aluminum plastic film looks very simple. Actually, how to combine the three layers of materials evenly and firmly is not so easy. It is a pity that the quality aluminum film is basically imported from Japan, and the quality of domestic products needs to be improved.
The same process is the same as the general battery process, and will not be described here. Pole forming methods usually use die cutting, and the ear is laser cut or die cut. In the form of pole pieces, the laminated piece generally adopts a zigzag type pole piece and a wound type pole piece, and the piece of the pole piece after cutting is put into a core by stacking and pasting, and put into a punched aluminum plastic film. In the pit, let's talk about the pit.
The soft-packed battery core can be designed into different sizes according to the customer's requirements. When the external dimensions are designed, it is necessary to open the corresponding mold to shape the aluminum plastic film. The forming process is also called punching. As the name suggests, it is a case where a molding die is used to heat a pit on the aluminum film that can accommodate the core, as shown in the following figure:
After the aluminum film is punched and cut, it is generally called the Pocket bag, as shown in the figure below. Under normal circumstances, when the battery core is thin, choose to punch a single pit (the left picture below), when the battery core is thick, choose to double the pit (bottom right), the deformation of the aluminum plastic film is too large to break through the aluminum plastic film. The deformation limit can cause cracking. Sometimes a hole is punched in the air bag area, and an air bag is added. The air bag can be increased as needed. The air bag function is mainly used to collect the gas during the formation process.
Put the folded core into the punched pit and fold it along the yellow line above, as shown below:
The core is placed in the pit and needs to be packaged after several steps. As shown in the following figure, we will introduce them in order:
After placing the core in the pit, the entire aluminum film can be placed in the fixture and the top and side seals are placed in the top side sealer. When encapsulating, the two heads have a certain temperature (generally around 180 °C), and when pressed, they are pressed on the aluminum plastic film, and the PP layer of the aluminum plastic film is melted and then bonded together. Here, let's talk about the top seal. The schematic view of the top seal area is shown below. The top seal is to seal the ear, which is done by a small part of the ear, the ear gel. The polar ear gel melts and bonds when heated. The package in the polar ear is shown in the circle below. During packaging, the PP in the ear gel melts and bonds with the PP layer of the aluminum plastic film to form an effective package structure.
After the top and side seals of the soft pack, X-ray is required to check the alignment of the core, and then the moisture is removed into the drying room. After standing in the drying room for a certain period of time, it enters the injection and a process. (Some factories will add the coating process in the injection process to avoid corrosion of the aluminum plastic film.) Through the above introduction, we know that the battery is in After the top seal and the side seal are completed, only one opening on the side of the air bag is left. This opening is used for liquid injection. After the injection is completed, the pre-sealing of the airbag is required immediately, also called a letter. After a package is completed, the inside of the cell is completely isolated from the external environment. The principle of a package is the same as that of the top side seal, so I won't go into details here. The process is as shown below:
在注液与一封完成后，首先需要将电芯进行静置，根据工艺的不同会分为高温静置与常温静置，静置的目的是让注入的电解液充分浸润极片。然后电芯就可以拿去做化成。化成的主要作用是激活电池，形成SEI膜，具体可看我的历史文章，里面有关于化成工序的详细解释。化成中，由于软包电池的特性，有些厂家会对电池进行整形化成，即采用夹具对电池进行固定化成。
因为化成过程中会产生气体，根据不同材料产气量不同，故而有根据需求增加气囊，扩大容纳气体的体积，二封时我们要将气体抽出然后再进行第二次封装。在这里有些公司成为两个工序：Degassing(排气)与二封，还有后面一个剪气袋加折边的工序，还有一些公司因电池大，产气量大，有预degas，化成，degas，二封工艺。我们就常规的二封，给大家解释，如下图：
In the second seal, the air bag is first pierced by a file, and a vacuum is applied, so that the gas in the air bag and a small portion of the electrolyte are extracted. Then immediately two seals are sealed in the second zone to ensure the airtightness of the battery. Finally, the packaged battery core is cut into the air bag. After the two air bags are cut, the trimming and folding are required. The edges and the two edges are cut to the appropriate width, and then folded to ensure the battery core. The width is not exceeded, so a soft-packed battery is basically formed.
After the battery core is folded, it is placed on the sub-container to carry out the volume separation. The specific capacity is divided. I can see my previous article. After the volume is divided, the qualified batteries will enter the post-process, including inspection of appearance, weight, glue, voltage detection, internal resistance detection, Hi-pot detection, polar ear transfer welding and so on. After the end, it was PACK, and a soft pack battery began to enter the new energy battlefield.
