The soft-packed batteries we have seen so far are all batteries that use
aluminum-plastic film as packaging material. Broadly speaking, lithium-ion
soft-packed batteries are divided into two categories. One type uses
aluminum-plastic film as packaging. Batteries, the other type is metal-cased
batteries, and metal-packaged batteries include steel shells, aluminum shells,
etc.
1. Soft-packed batteries
The soft-packed batteries we have seen so far are all batteries that use
aluminum-plastic film as packaging material. Broadly speaking, lithium-ion
soft-packed batteries are divided into two categories. One type uses
aluminum-plastic film as packaging. Batteries, the other type is metal-cased
batteries, and metal-packaged batteries include steel shells, aluminum shells,
etc.
Different outer packaging materials determine the use of different
packaging methods. Polymer soft-packed batteries use thermal packaging, while
metal-packed batteries use welding methods.
2. Packaging soft film-aluminum plastic film
The aluminum-plastic composite film can be roughly divided into three
layers - the inner layer is an adhesive layer, mostly made of polyethylene or
polypropylene, which plays a sealing and bonding role; the middle layer is
aluminum foil, which can prevent the penetration of water vapor from the outside
of the battery and prevent internal damage. Leakage of electrolyte; the outer
layer is a protective layer, which is mostly made of polyester or nylon
materials with high melting points. It has strong mechanical properties,
prevents damage to the battery from external forces, and plays a role in
protecting the battery.
The research and development of high-quality aluminum-plastic composite
films is the key to the successful development of liquid flexible packaging
lithium-ion batteries, a high-tech product. As the outer shell of liquid
flexible packaging lithium-ion batteries, the aluminum-plastic composite film is
no longer just a simple outer packaging of the battery, but also an
indispensable and important component of liquid flexible packaging lithium-ion
batteries.
If the importance of this flexible packaging material is not fully
understood, it will be detrimental to the design and development of flexible
packaging batteries. It plays such an important role in the development of
liquid flexible packaging lithium-ion batteries, which shows that the product
has high technical content and is qualitatively different from ordinary
composite packaging materials in terms of design, manufacturing and
application.
Domestic and foreign manufacturers are working hard to continuously improve
their products, and the production technology of aluminum-plastic composite
films is also under continuous research and development.
3. Aluminum plastic film stamping forming process
Soft-packed batteries can be designed into different sizes according to
customer needs. After the outer dimensions are designed, corresponding molds
need to be opened to stamp the aluminum-plastic film. The forming process is
also called pit punching, which uses a forming mold to punch out a pit on the
aluminum-plastic film that can be used to roll the core.
After the aluminum plastic film is punched, it is cut and formed, generally
called a pocket bag. Generally, when the battery core is thin, you choose to
punch a single pit. When the battery core is thick, you choose to punch a double
pit. When punching the double pit, it will be due to the deformation of one
side. The assembly breaks through the deformation limit of the aluminum-plastic
film and causes rupture.
Sometimes, according to design requirements, a small pit will be made on
one side of the pit to expand the volume of the air bag.
4. Packaging side sealing and top sealing process
The packaging process includes two processes: top sealing and side sealing.
First, place the rolled core into the punched pit, and then fold the unpunched
side in half along the punched pit.
After the aluminum-plastic film is loaded into the roll core, the locations
that need to be sealed include the top sealing area, side sealing area, first
sealing area, and second sealing area.
After placing the roll core into the aluminum-plastic film, the
aluminum-plastic film can be placed in the clamp and sealed in the top sealing
and side sealing machines.
The top seal is to seal the tabs. The tabs are made of metal (positive
aluminum, negative nickel). How can they be packaged together with PP? This is
accomplished by a small component on the lug - the lug glue.
I'm not very clear about the specific structure of the ear glue, so I hope
someone knowledgeable can add to it. I only know that it also has the cost of
PP, which means it can melt and bond when heated. The package at the tab
position is shown in the circle in the figure below.
During packaging, the PP in the tab glue and the PP layer of the
aluminum-plastic film melt and bond to form an effective packaging
structure.
5. Liquid injection and pre-sealing process
After the soft-packed battery core is sealed on the top side, it needs to
be x-rayed to check the parallelism of the core, and then it goes into the
drying room to remove moisture. After standing in the drying room for a certain
period of time, the liquid injection and pre-sealing process begins.
After the battery core is sealed on the top side, there is only an opening
on the side of the air bag, which is used for liquid injection. After the liquid
injection is completed, the air bag side needs to be pre-sealed immediately,
also called a seal.
After one seal is completed, the inside of the cell is completely isolated
from the external environment.
6. Resting, forming, and fixture shaping
After the liquid injection and sealing are completed, the battery core
needs to be left to rest. Depending on the production process, it is divided
into high-temperature resting and room-temperature resting. The purpose of
resting is to allow the injected electrolyte to fully infiltrate the cell, and
then You can use it to make it into a chemical.
The formation process is the first charge of the battery cell, but it will
not charge to the highest voltage, and the charging current is also very small.
The purpose of formation is to form a stable SEI film on the electrode surface,
which is also equivalent to a process of activating the battery core.
A certain amount of gas will be produced during this process, which is why
an air bag is reserved.
Some factories will use fixtures to form cells, put the cells in the
fixtures and then put them on the forming cabinet. The gas generated in this way
will be fully squeezed into the air bag, and the electrode interface after
formation will be better.
After the formation is completed, some cells, especially thick cells, will
deform to a certain extent due to large internal stress. Therefore, some
factories will set up a shaping process after formation, also called fixture
baking.
7. Second sealing process
During the second sealing, the air bag is first punctured with a guillotine
and vacuumed at the same time, so that the gas and part of the electrolyte in
the air bag will be extracted. Then immediately carry out the second sealing to
ensure the airtightness of the battery core. Finally, cut off the air bag, and a
soft-packed battery core is basically formed.
8. Subsequent processes
After cutting the air bag for the second seal, you need to trim and fold
the edges to ensure that the width of the battery core does not exceed the
standard. The folded batteries will enter the capacity classification cabinet
for capacity classification, which is actually a capacity test.
After the capacity division is completed, cells with qualified capacity
will enter subsequent processes, including appearance inspection, yellow glue
application, edge voltage detection, tab transfer welding, etc. Several
processes can be added or deleted according to customer needs, and finally OQC
inspection is performed. Then package and ship.
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