What Are the Advantages of Lithium ion Pouch Cell Production Line？

Generally, pouch battery can apply for every application, but why cylindrical, prismatic and other cells still exist? These types have both goodness and shortcoming.

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Types pf battery cell

Cylindrical Cell

Cylindrical and prismatic cells are two of the most popular options on the market. Cylindrical lithium cells are easy to manufacture and mechanically stable, making them enduringly popular. They&#;re also very safe, if internal pressure grows too great, most cells are designed to rupture, mitigating safety hazards, and benefit from longevity, an attractive price point, and comparatively low watt-per-hour cost, making them an economical choice. [caption id="attachment_" align="aligncenter" width="493"]

Structure of Cylindrical Cell

Small cylindrical cells are generally used in portable technologies such as laptops and medical devices. Large cylindrical cells are popular for electric vehicles, a growing market largely driven by manufacturer Tesla.

Prismatic Cell

The prismatic lithium cell&#;s key advantages lie in its thin profile, effective use of space; the thin, rectangular shape facilitates better layering and increased flexibility. Unsurprisingly, prismatic cells are typically found in mobile phones, tablets, and other lightweight electronic devices.

Structure of Prismatic Cell

While space efficiency makes prismatic cells highly attractive, several disadvantages exist. Prismatic cells are expensive to design and manufacture, in turn making them more expensive for consumers. They die quicker, as thermal management is less effective, and are relatively sensitive to deformation in high-pressure situations. Other drawbacks include a limited number of standardized sizes and an average higher watt-per-hour price.

Pouch Cell

In , Li-polymer surprised the battery world with a radical new design, the pouch cell. The pouch cell makes the most efficient use of space and achieves a 90 to 95 percent packaging efficiency, the highest among battery packs, advantages of flexible size and safety performance. Eliminating the metal enclosure reduces weight but the cell needs some alternative support in the battery compartment. The pouch pack finds applications in consumer, special, as well as automotive applications.

Grepow Pouch Cell Battery

The soft pack battery is packaged in aluminum plastic film. When a safety problem occurs, the soft pack battery will generally bulge, does not explode like a steel case or an aluminum case. The shell or aluminum shell battery explodes; the weight is light, the weight of the soft pack battery is 40% lighter than the equivalent capacity of the shell lithium battery, 20% lighter than the aluminum shell lithium battery; the internal resistance is small, the internal resistance of the soft pack battery is lighter The battery is small, which can greatly reduce the self-consumption of the battery; the cycle performance is good, the cycle life of the soft pack battery is extended, the attenuation of 100 cycles is 4%~7% less than that of the aluminum shell; the design is flexible, the size can be arbitrary, and the shape can be Thinner, can be customized according to customer needs, develop new battery models. Stacking pouch cell production please view: What is Cell Stacking Technology?

Production Technique

The stacking process is a lithium polymer battery manufacturing process in which a positive electrode, a negative electrode is cut into small pieces and a separator is laminated to form a small cell, and a single cell is stacked in parallel to form a large cell.

The battery cell used stacking technology has the advantages of small internal resistance, long life, high space utilization, and high energy density after group. In terms of battery performance, compared with the winding technology, the lamination stacking technology can increase the energy density of the battery by 5%, increase the cycle life by 10% and reduce the cost by 5% under the same conditions. Battery cell Stacking vs Winding Technology: https://www.grepow.com/blog/winding-and-stacking-of-cells.html

8 Advantages of choosing pouch cell battery

1.The flexibility of the Lithium Battery Pack

The completely assembled battery packs with the BMS built-in as a standard battery module. Modules can be assembled in a parallel configuration for increased capacity, or in a series configuration to increase the voltage. If needed, the BMS can offer an output cable for communication. These battery modules can be charged separately or as a whole battery pack if assembled.

2.Cycle Life

We have tested a cell that was randomly picked off the assembly line. After the accelerated equivalent of more than 4,400 charge cycles of constant cycling, this 10 AH cell still registered about 9 AH. That is a very impressive small drop of storage capacity after 12 years of about 10%.

3.Reliability

Where one cell fails, another cell takes over. You can replace single faulty units while the rest of the system continues to function flawlessly, increases the reliability of the system. As an example, a 36-volt pack at 10 AH will only require 12 pouch cells welded together. If that same application were to use cylindrical cells, it would require 72 pieces of 1.5 Ah cells welded together. In a series string if any of the 72 cells have a problem the complete pack will fail. Also, 72 cells mean 144 nodes, each node represents one potential fault. So, a cylindrical based pack is not as reliable as an electrically equivalent pouch cell pack which would only have 24 nodes. In addition, the pouch cell welding procedure is much more reliable than welding cylindrical cells.

4.Improved Energy Storage

A pouch cell&#;s energy storage capacity is much greater in a given physical space in comparison to cylindrical cells.

5.Safety

Whenever either pouch cells or cylindrical cells have internal problems, pressure builds and they will swell up. In those infrequent situations, pouch cells merely swell up. Cylindrical cells are traditionally encased in an iron jacket, so that when the pressure builds within a cylindrical cell whose ends are held captive by other batteries or the case, they can literally explode which could result in a dangerous safety hazard.

6.Weight

Typically, pouch cells weigh less than the equivalent prismatic or cylindrical battery. The flat pouch cell energy density is greater than other shaped cells, but its much more difficult of manufacturing stacking pouch cell battery, so this is testing the battery manufacturer's production technique.

7.Uniformity and Consistency

Grepow's entire pouch cell line is manufactured by automatic equipment, then it is manually tested to ensure that the quality of each cell is up to standard, eliminating human error in hand-made cells, and allows every cell to have uniformity and consistency.

8.Included Smart BMS

One of the other benefits of using pouch cells for smaller applications is the fact that Grepow can furnish a BMS (Battery Management System) with the pack to balance the batteries and protect them from over-charging and being over-discharged.

Pouch cell battery apply on different areas

Generally, pouch battery can apply for every applications, it depends on their shape and parameter requirements. It is no doubt that the pouch cell has many benefits than other types of cell, but it's not fit for any applications, at least for now.

Tesla with cylindrical cell

Cylindrical Cell is still the most common type we can see, such as in the automotive industry, Tesla and BYD are still using cylindrical battery. Compared to the pouch or prismatic cells, cylindrical cells like the can be produced more quickly; so more kWh of cell produced per hour due to its configuration - another reason for a lower cost per kWh.

Another advantage of cylindrical cells over the flat cells (e.g. pouch, prismatic) is that its electrodes are wound evenly and tightly and encased in a metal casing. This minimizes electrode material from breaking up from the mechanical vibrations, thermal cycling from charging and discharging, and mechanical expansion of the current conductors inside the cell from thermal cycling. So, with over 7,000 &#; cells&#; in Tesla's small power pack, you'd think the chances of a bad connection in one of the 14,000+ interfaces is pretty high. Not if you weld the cell terminals to each other with connector tabs. Many cells are connected in series to build up the voltage; then these series lines are connected to each other in a parallel fashion to increase amperage. So, if one cell goes bad, its impact on the entire pack is low. However, when large prismatic cells go South, it could mean a significant % of the power pack is in trouble.

Trends of the pouch cell

However, its no doubt that the market trend is the increased utilization of pouch cells, due to their increased form factor flexibility and the ability to produce sleek-looking products. The advantage of low internal resistance is also more attractive, and longer battery life also reduces the extra cost for customers to replace batteries/products. Our clients can use this as a big selling point to attract fresh users, which is perfect fit for 3C products like wearable devices, smartphones, speakers, etc. The advantages of soft pack batteries in terms of safety and energy density have also received increasing attention. From the perspective of new power battery capacity this year, soft pack batteries accounted for 30%. The penetration rate of future soft pack batteries in the field of new energy vehicles will gradually increase. From cost point of view, most of the aluminum-plastic film production areas are imported from Japan and South Korea, the proportion of Chinese-made is less than 10%, which makes it difficult to reduce the manufacturing cost of pouch cell batteries. At present, Japan's aluminum plastic film technology is indeed at the leading level in the world. After obtaining the relevant production line and patent through acquisition, the cost of aluminum plastic film can be reduced by about 20% to 30%, which reduces the cost of the pouch cell battery and meets the demand for more mass production.

Get in touch with Grepow

Pouch cells are the first choice for many manufacturers because of their high energy density, great power performances and other design advantages. While they are widely used in electric vehicles, automotive OEMs have strong opinions about whether they should be used.

On the one side, General Motors believes that the pouch cell is the winner, claiming they offer high production speed, easy maintenance, and better recycling capabilities. 

If you are looking for more details, kindly visit Qingtao.

On the other side, Elon Musk made an equally strong statement, saying Tesla will never use pouch cells due to the high risks related to thermal runaways. He made this statement days after GM announced a recall for all Chevy Bolts ever made.

It&#;s important to note, however, that the recall was due to manufacturing defects that could have been avoided with better processes, and not an inherent flaw in pouch cells.

In the end, lithium-ion battery manufacturers are constantly looking for ways to increase the efficiency and reliability of their processes while reducing manufacturing costs. The performance and service life of pouch cells largely depend on processing technique. 

In this article, we will look at some of the most recent breakthroughs that can improve pouch cell assembly.

What is a Pouch Cell?

A pouch cell is a soft battery design where most of the cell components are enclosed in an aluminum-coated plastic film. Only two tabs stick out, each welded to current collectors in the pouch. These highly conductive tabs carry out the positive and negative connector tabs and allow to get the electric energy out of the pouch cell. 

Inside the pouch, the cell components are arranged in repeated stacks of multiple layers. Each stack contains three layers of solid sheets, two layers of active material, and a liquid electrolyte. When the battery charges or discharges, the ions travel between the cathode and the anode through the liquid electrolyte.  

Source: A review of current collectors for li-ion batteries

Each element has a specific role:

• Current collectors: Highly conductive materials (copper and aluminum) that carry out the negative or positive electrical current through external tabs.
• Active material: A coating applied on each current collector that causes the electrode reaction. It is also called the electrode.
• Anode: The combination of the negative current collector and the active material.
• Cathode: The combination of the positive current collector and the active material.
• Separator: A membrane that prevents electrical contact between the anode and the cathode (and hence short circuits) but lets the ions (i.e., electrically charged atoms) pass through.

How Are Pouch Cells Made?

To ensure the optimal quality and safety of their batteries, pouch cell manufacturers go through a set of precise steps. The procedure can vary depending on the pouch cell manufacturer, but it is essentially the same principles. Here&#;s an overview of what these steps look like.

1. Preparing the electrode sheets

Electrode sheets contain the following ingredients: 

• Binding agent/solvent: Brings together all the ingredients to obtain a homogeneous paste. Examples include polyvinylidene fluoride and N-Methyl-2 pyrrolidone.
• Active material: Produces electrical energy during discharges. Examples include lithium-metal oxide for the cathode and graphite for the anode.
• Conductive material: Increases electrical conductivity. Examples include carbon black and graphite.

These ingredients are mixed under vacuum to prevent air bubbles from getting whipped into the paste as well as moisture from contaminating the lithium oxide and electrolyte. When the paste is homogeneous, it is moved to a machine called the coater where it is poured onto a sheet of a highly conductive metal foil (the &#;current collector&#; in the final assembly). This coater machine then scrapes off excess paste and dries the remaining paste.

Once dried, the semi-shaped electrode is placed into a rolling press to be compressed at high pressure. The goal of this operation is to achieve the right porosity and thickness for the final electrode sheet. The higher the porosity, the better the electron flow, which increases the cells&#; performance.

At this point, the sheet can be cut into the desired shape and size, leaving a conductive tip at the top for the tab.

2. Assembling the pouch cell

With the electrode sheets prepared, the pouch cell is assembled in a controlled environment to prevent moisture from damaging the battery cell components.

The first step in the assembly consists in welding a metal strip to the current collector. This strip will later be used to fix the terminals. It is traditionally welded using ultrasonic bonding, but laser welding is gaining in popularity.

Using a stacking machine, the separator is placed between the electrodes, forming a stack that is inserted in the pouch. The sides of the pouch are joined together with a method called heat sealing, leaving one side open. An electrolyte filling system is then used to add the liquid electrolyte into the cell.

Then, the cell is sealed using a vacuum sealing machine, and the pouch cell assembly is complete. The pouch will protect and hold together the components.

At this point, the assembled cell is ready for the final step called &#;formation&#;.  The formation step is key to the cell finishing process. During formation, a critical solid-electrolyte-interphase (SEI) layer is formed by passing current through the cell or charging the cell for the first time.

Pouch Cell Limitations in Battery Pack Assembly

To assemble pouch cells into battery modules and packs, some limitations must be addressed early in the battery design. Here are the most important ones.

Easy Access to the Tabs When Making Connections

Having easy access to the tabs is essential to make electrical connections with the rest of the battery components. This must be planned for in the mechanical design. 

For example, the choice of the welding method used to make the connections can cause mechanical limitations. Ultrasonic bonding requires more free space near the tabs than laser welding which can be done from a distance and without contact.

Related article: Laser welding applications for batteries.

Mechanical Damage Due to Swelling

Pouch cells can gain up to 10% in volume after over 500 charge cycles due to a phenomenon known as swelling (which is when gases are generated during charges and discharges). When multiple pouches start swelling, the gain in volume adds up, causing pressure on the cell components such as the welds.

To prevent damages caused by changes in volume, the mechanical design needs to manage the pressure applied on the cells. For example, some battery designs include springs to create an opposing pressure on the pouches, preventing them from gaining too much volume.

The additional design complexity required to counter-balance this mechanical deformation reduces the pouch cell&#;s intrinsic energy and power density advantage.

Volumetric Energy Diminished by Heat Transfer Plates

Heat management for pouch cells presents unique challenges. With cylindrical cells and prismatic cells, heat can be extracted on the pack&#;s sides. But with pouches, heat needs to be extracted in between cells.

To do this, heat transfer plates (made of aluminum) are inserted in between each pouch to transfer heat to the sides of the pack where cold plates are located. Other designs directly include the cold plates between the pouches.

The addition of transfer plates creates a challenge to optimize the battery pack&#;s volumetric energy. Pouch cells are known for their very dense volumetric energy, which means that they use less space than other types of cells. But in a battery pack where there are over a hundred pouch cells, this advantage is somewhat neglected by the addition of heat transfer plates.

New Methods for Pouch Cell Assembly

Although pouch cells present challenges and limitations, new technologies can help mitigate or overcome these issues. Here are some of the most promising technologies for the pouch cell battery industry.

Laser Cleaning Battery Tabs Before Ultrasonic Bonding

Ultrasonic bonding is a well-established technology in battery production lines. For pouch cells, the process is used to weld battery tabs to current collectors inside the pouch and make connections with busbars, motor winding terminals, and other inductors.

Before performing ultrasonic bonding, surfaces to be joined must be perfectly clean to guarantee the quality of the electrical contact and the weld strength. The best method to clean battery materials is laser cleaning. This process removes coatings and contaminants like varnish, oxide, epoxy, and oil with high precision and repeatability.

Laser Welding Alternative to Ultrasonic Bonding

Laser welding is an innovative method that is increasingly used to replace ultrasonic bonding in pouch cell production lines. One of its advantages is that surfaces to be welded can be cleaned and welded in a single operation. This is because the laser process can also vaporize contaminants, neglecting the damage they could cause to the welds.

With ultrasonic bonding, contaminants affect weld quality because the heat generated between the joined surfaces is so low that the surfaces can actually be welded to the contaminants. By replacing ultrasonic bonding with laser welding, battery manufacturers simplify their production process by effectively removing an extra step.

Laser Technology in Assembly Lines

With the rapid growth of EVs all over the world, battery manufacturers are working hard to optimize their processes and the efficiency of their assembly lines. Laser technology is one of the key technologies that can help battery manufacturers meet their production and quality requirements as well as their green goals.

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