Cells are one of the most important properties of a battery. You may have of different kinds of cells, such as the primary and the secondary cells. However, there are other types, such as prismatic, cylindrical and pouch cells. We will be talking about these ones in this article.
Understanding the Battery Production Process
Batteries are produced via a couple of industrial processes, and each of these processes are distinct. These industrial processes also outline the kind of battery format that would be produced.
Battery cells are one of the processes and they are the containers or a single unit device that store and convert the chemical energy into electrical energy.
In addition to storing and converting the energy, the battery cells also come in different forms and shapes, such as:
- Prismatic cells
- Pouch cells and;
- Cylindrical cells
Lithium-ion Batteries as the Major Beneficiaries/Applications
It is worthy of noting that the prismatic and pouch cells are commonly used in Lithium-ion batteries. The usage is for these reasons:
a. The Mainstream Adoption
Today, more applications and consumer electronics are produced with Lithium-ion (Li-Ion) batteries. As such, there is a need for battery cells that match the specific energy storage and conversion needs of these applications. The prismatic and pouch cells match those needs.
b. The Need for Few Cells
Lithium-ion batteries often don’t need more cells, and this is due to the higher voltage output per cell than many other battery systems.
Hence, using the prismatic and pouch cells helps to reduce the number of cells required for the batteries to function.
The Lithium-ion Prismatic Cells
We will now talk about one of the most important battery cells used in producing Lithium-ion batteries – the prismatic cells.
The history of prismatic battery cells can be dated back to the early 1990s. Today, these cells pack a punch, in terms of the solutions they offer. For example, they are used to meet the demands for lowered manufacturing costs and reducing the size or footprints of batteries.
The Structure of Prismatic Cells
The presentation or structure of these cells are one of the unique attributes. They are typically enclosed or encased in a casing that is either made of aluminum or steel.
The electrochemical materials are often stacked, sealed or sandwiched into layers before they are encased in a rigid, aluminum alloy or steel casing.
Here are some additional pieces of information to know about the structure of prismatic battery cells:
- A (blue) insulation film is used to cover the exterior or the outside of the can.
- It is common to have the inner part of the battery adopting a winding or laminating process.
- The shape of the prismatic battery cells is relative. On the one hand, it is a bit larger than the cylindrical battery cells are. On the other hand, the shape is minimalized as much as possible to aid the conservation of space, especially as it has to do with the targeted application(s).
- Prismatic cells have what is called the electrode sheets. These comprise of separators, cathodes and anodes.
- The components of the electrode sheets, as mentioned above, can be infused into the cells either by rolling them up or flattening them into the hard-plastic or metallic sheets. It is also possible to stack these components.
- Prismatic battery cells often have a rectangular or flat shape.
The Targeted Applications
The use cases of these cells are one of the reasons why you may want to consider it. The primary use case or application is for smaller electronic devices, such as mobile phones and smartphones.
However, you can use prismatic battery cells for other purposes, such as:
- DIY Lithium-ion battery banks
- Electric Vehicles (EVs) and;
- Hybrid/Electric Vehicles
Design Considerations for Prismatic Battery Cells
The production process of prismatic cells is often straightforward and this is possible because of the simplified structure that comprises the following:
- Negative electrode plate
- Wound or laminated top cover
- Safety components
- Housing
- Insulating parts
- Positive electrode plate and;
- Diaphragm
These battery cells often take a low-profile design, due to the square size of the outer casing. For this reason, you find prismatic cells having an improved volume utilization, especially in the battery packs.
However, taking note of some of the important design requirements is important. Here are some of the things to have in mind:
The Coverage of the Exterior
While it is common to use an insulation film, which is usually blue, outside of the cover; that is not always the case. You may find some prismatic battery cells using plastic covers in the exterior.
The major consideration here is knowing the kind of plastic outer covers to use. For example, the most affordable covers are often lightweight.
The Melting Point
The melting point of prismatic battery cells is also correlated to the plastic cases or covers. In this case, the melting point has to do with the extent that the cases wouldn’t be exposed to damage.
For context, the melting point can range from 150C (for cheaper plastic covers) and up to 200C for the ABS plastic covers.
Aluminum vs. Plastic Covers for Prismatic Battery Cells
When presented with the option of choosing between the plastic and aluminum covers, it is always advised to go for the latter.
The aluminum or hard metal case enclosures are known for the durability and the higher melting points. Ideally, the covers have a melting point of up to 660C.
You also want to choose the aluminum covers for these reasons:
- These covers do not provide fuel, as much as the plastic-like covers do.
- The use of aluminum covers boosts the protection of the outer cases, which act as the second layer of protection for the battery cell. Due to this reason, it is nearly impossible for (excess) oxygen to penetrate or rush into the case.
Navigating the Pointer Corners
Prismatic battery cells have pointer corners, which require an extra bit of caution. Depending on the application or use case, these corners might experience additional stress, in the form of vibrations and shocks.
By being careful around these corners, it is easier to avoid challenges, such as:
- Cell bloating, as caused by insufficient distribution of electrolyte.
- The weakening of the pointed corners, due to the insufficient protection in the cell enclosure.
What are Pouch Cells?
These are sone of the different cells or single unit containers that store and convert chemical energy into electrical energy.
These cell packs were introduced the battery market just a few years after the debut of the prismatic cells. Launched in 1995, pouch cells are the Lithium-ion batteries with a layer of polymer shell.
Also called the polymer cells, the pouch cells came into the market with a new design. Despite having a similar construction as the prismatic cells, they have some unique features, such as:
- Having flexible electrolytes that make the production simpler.
- Pouch cells have the conductive foil tabs welded to the electrode. Once this is done, these tabs are sealed to the cells’ pouch and they carry both the negative and positive terminals to the outside.
- When compared to the other battery cells, the pouch cells have a higher hand. This is because of the compact profile size, which despite the smaller profile, has a higher efficiency and excellent power delivery.
The Layers of Pouch Cells
The layers used in these cells is based on the packaging materials, which are broadly divided into three (3) layers.
These layers are the:
- Outer Barrier: this serves as the outer or exterior protective layer of the pouch cells. It is commonly made of PET or nylon BOPA.
- Middle Barrier: this refers to the layer positioned at the middle of the cells. The middle barrier or layer is made of aluminum foil. This is also called the intermediate layer or permeable layer.
- Inner Layer: last but not least is the inner layer, which doubles as the multifunctional layer of the pouch cells.
Lightweight Design
If you are in the market for battery cells that are optimizable, then you need to go for the pouch cells. These cells have a lightweight design, which is because of these factors:
- Pouch cells are 20% lighter than the aluminum-shell Lithium-ion batteries, especially, the ones that use a similar capacity.
- These cells weigh 40% less than the batteries using steel-shells.
Besides the lightweight design, pouch cells can also offer up to 90% space-economy, making them ideal for use with space-centric applications.
Typical Applications of Pouch Cells
Polymer or pouch cells are often used with portable and high-end technology applications. They are also used with the automotive, consumer and military applications.
Examples of the applications are:
- Drones
- Mobile and smart phones and;
- Portable energy stations.
Here are some of the classifications of the pouch cells, based on the applications or use cases:
- Larger-Format Pouch Cells: these are used in the following applications: Hybrid vehicles, Energy Storage Systems (ESS) and Electric Vehicles (EVs).
- Curved Pouch Cells: these polymer cells are commonly used in the medical device and wearable consumer electronics applications.
Design Iteration for the Pouch Cells
The pouch cell advantages include lightweight design, high reliability, and a simplified structure that supports the expansion of the battery capacity and the energy density.
However, it requires some technicalities to get everything right. Here are some of the major design considerations:
- Suitable Use Cases: it is always ideal to use the polymer/pouch battery cells in the environments or applications that are relatively stable. These working environments also ought to ensure the service life of the battery packs and the stability of the structure.
- No Standardized Packs: due to the fact that polymer cells don’t have a standardized size or shape, it creates an opening for the manufacturers to define the structure. Thus, each manufacturer is allowed to build the cells for specific applications – and in the design they wish.
The Differences between Prismatic and Pouch Cells
The prismatic cell construction is often compared to the pouch battery cells. In this section, we point out some of the clear differences between prismatic and pouch battery cells.
a. Durability Concerns
When it comes to the service life, you can always choose the prismatic batter cells over the pouch cells. Unlike the polymer cells that are prone to damages caused by humidity or higher temperatures; the prismatic cells stand up to those.
b. Shape and Customizations
There is no doubt that the pouch cells have a similar prismatic cell construction. While the two have rectangular shapes, the design of the pouch/polymer cells can be further customized, as per the manufacturer’s design specifications.
c. The Cost-Factor
How expensive are the battery cells? Factors that influence the final costs include but are not limited to the types of materials required, the costs of these materials and the simplicity of the designs.
Pouch or polymer cells are cost-intensive, due to the complicated and manufacturer-centric customization options. Hence, you will spend more to get the pouch cells designed than having the prismatic battery cells manufactured.
d. The Flexibility of the Packaging Materials
The more flexible a battery cells’ packaging is, the higher the customization and utilization options. In that case, you should go for the pouch cells, due to the use of polymer-coated aluminum foil casings or conductive foil tabs.
e. Performance
The performances of battery cells are often correlated to the applications. On the one hand, we have the prismatic cells, which are ideal for the electric automobiles, such as EVs, as well as Energy Storage Systems (ESS).
On the other hand, we have the pouch cells, which are ideal for key consumer electronics, such as ultra-thin laptops, smartphones and drones.
You can also compare the two along the lines of energy management. While the prismatic battery cells are often susceptible to thermal-management issues, the pouch cells are less likely to explode.
f. Cell Capacity
This is a rather tricky comparison due to the fact that it has to do with the battery cells’ voltage capacities.
On the one hand, the pouch cells are favored to accept more voltage capacities, due to the ability to handle more voltages, as a result of the management of higher voltages within a specific period.
On the other hand, the prismatic battery cells can also handle voltages, due to the stacking of the layers. This way, they get to handle more voltages, because they have a larger capacity.
Wrapping Up
The core differences between the prismatic and pouch battery cells are the performance, cost, durability, packaging materials, shapes, weight and overall costs.
Finally, you can always narrow down the options by looking at the individual applications of the cells and taking note of the likely end-results.
