Lithium cells: differences, uses and how to choose the best ones

Today, lithium cells have become one of the most important components in the world of technology and energy. Their high energy density, long life and fast charging capability have positioned them as a leading choice in a wide range of applications, from electronic devices to electric vehicles.

However, as the demand for lithium cells increases, so does the variety of options available on the market. Understanding the differences between them and knowing how to choose the best ones for each case becomes essential.

In this article, we explore lithium cells, their differences, uses and how to choose the best ones.

Most common lithium cell types

Cells take different physical forms, which determine the structure and design, which in turn affects the electrical and mechanical characteristics of lithium batteries.

The main formats are: cylindrical, sheet or prismatic.

Cylindrical cells

Very similar to household knobs, cylindrical cells have a precisely cylindrical shape. The 18650 cell, with a diameter of 18 mm and a height of 65 mm, is one of the most common and widely used formats in the battery industry.

Advantages of cylindrical cells

Cylindrical lithium-ion cells offer several advantages, the most important of which include:

• Durable housingCylindrical cells are designed with a rugged metal casing, usually made of stainless steel. This housing provides robust protection for the internal components of the cell, making them more durable and able to withstand adverse conditions such as shock, vibration and high temperatures. This is especially important in applications where mechanical strength and additional protection are required.

• Flexibility in cell chemistryCylindrical cells allow the option of changing the internal chemistry of the cell while maintaining the same containment mechanism. This means that manufacturers can adjust the cell chemistry to improve performance, capacity or safety, without the need to completely redesign the case or containment system. This provides flexibility and adaptability to different requirements and advances in lithium battery technology.

• Wide availabilityLithium-ion cylindrical cells, especially standard formats such as the 18650 cell, are widely available on the market. This makes them easy to access and purchase for use in a variety of applications, from portable electronic devices to electric vehicles. The widespread availability of these cylindrical cells contributes to their popularity and ease of integration into various systems and products.

Cylindrical cells

Disadvantages of cylindrical cells.

It is true that cylindrical lithium-ion cells also have some disadvantages. Some of these are listed here:

• Low capacity of individual cellsCylindrical lithium-ion cells have a relatively low individual capacity compared to other lithium cell formats. For example, the most common cylindrical cells, such as the 18650, reach a maximum capacity of around 3Ah. This can limit the amount of energy stored in each cell and require the use of multiple cells in series or parallel to achieve the desired capacity.

• Assembly by weldingIn the construction of battery packs using cylindrical cells, individual cells are assembled in series and in parallel by soldering. This involves a more complex and costly process compared to other connection methods, such as prismatic cells that can be connected by flexible connectors or laser welding. In addition, soldering makes it difficult to replace individual cells in case of failure, as replacement of the entire module is usually required.

• Decreased security of the packageThe series and parallel nature of many cylindrical cells in a battery pack can result in a decrease in the safety of the system as a whole. If an individual cell fails, it can affect the performance and stability of the entire pack. In addition, the lack of individual cell replacement can lead to a higher safety risk, as complete module replacement is required in the event of a cell failure.

Most lithium-ion battery assemblers place several cells in parallel to achieve the desired capacity: for example, to achieve a capacity of 200 Ah using 2.5 Ah cells, 80 cells must be placed in parallel, all of these cells connected in parallel.
If an internal problem causes one of these short circuits to occur, it will not only absorb its own energy but will have to dissipate all the energy of the 80 cylindrical cells in parallel. This could result in very high heat in the module, with disastrous effects such as a fire.
To prevent this, major manufacturers such as Tesla use sophisticated production processes that allow cells to be connected in parallel by a kind of fuse. If a cell short-circuits, the "fuse" burns out and the safety of the battery pack is not compromised.

Unfortunately, none of the lithium-ion battery manufacturers in the industrial market have this type of technology. As a consequence of these negative aspects, we avoid this type of cells at NCPOWER.

Laminated cells, what are they and their advantages and disadvantages?

Laminated or pouch cells are a type of lithium cell that differs from cylindrical cells in their format and construction. Instead of having a cylindrical metal casing, these cells are composed of a flexible sheet that acts as the container and separator for the internal components.

In laminated cells, the active components, such as the cathode, anode and electrolyte, are placed between two layers of flexible material, usually laminated polymers such as polyester or polyolefin polymer. These flexible layers seal the components and prevent leakage or unwanted reactions. Additional sealing layers are used to protect the cell from moisture and external air.

Advantages of the bag cells

Laminated or pouch lithium cells offer certain positive aspects to their technology. Some of these are:

• High energy densityBag cells have a high energy density, which means they can store a large amount of energy in a relatively small size. This is especially important in applications where long battery life or high power is required, such as in electric vehicles or portable electronic devices.

• Low housing costCompared to cylindrical cells, pouch cells typically have a lower housing cost. This is because the manufacturing process of pouch cells is less complex and uses less expensive materials compared to the metal casings of cylindrical cells. As a result, pouch cells can offer a more economical solution for energy storage.

• Range of available capacityIn the market, there are a variety of pouch cells available with different capacities. They range from a few hundred mAh (milliampere-hours) to around 20 Ah, although manufacturers exceeding this threshold are less common. This gives designers and manufacturers a range of options to suit different power requirements and application size.

Example of stock exchange cells

Disadvantages of the bag cells

Laminated or pouch lithium cells have some negative aspects associated with their fragility and limitations in terms of packaging and capacity. 

Some of these aspects are detailed below:

• Fragility of the casingThe casing of bag cells is more susceptible to damage and breakage compared to cylindrical cells, as it is composed of flexible materials. Even slight pressure, such as the use of a fingernail, can irreversibly damage the casing. This can be problematic in environments where the battery is exposed to impacts or adverse conditions.

• Limitations in the packaging systemPackaging of bag cells requires careful design to avoid any stress or deformation of the individual cells. Vibrations, crushing or deformation can compromise the integrity of the cells and affect their performance and lifetime. In addition, due to the flexible nature of pouch cells, it can be complicated, or even impossible, to develop customised modules for specific applications.

• Medium-low capacity: Bag cells tend to have a medium-low capacity compared to other lithium cell formats. This means that several cells in parallel would be required to achieve sufficient capacity in industrial applications. However, this may affect the safety of the battery pack and increase the complexity of the load balancing and management system.

• Difficulty in individual cell replacementAs with the cylindrical cells, the bag cells are also connected in series or in parallel by soldering. This makes it virtually impossible to replace an individual cell without having to replace the entire module. This can be costly and lead to downtime in the event of a cell failure.

Prismatic cells

Another common format among lithium battery cells is the prismatic type. They are mainly characterised by a solid casing and soldered terminals.

Advantages of prismatic cells

Prismatic cells offer several important advantages compared to other lithium cell formats. Some of these advantages are detailed below:

• Durable housingPrismatic cells have a robust and durable casing, making them suitable for the production of customised battery packs. Their robustness allows them to withstand harsh conditions and minimises the need for costly and complicated mechanical stress studies and tests.

• High capacity of individual elementsPrismatic cells can achieve high capacities in individual cells, up to 300 Ah in a single cell. This high capacity is especially valuable in the creation of large capacity batteries, such as in the industrial market, avoiding the need to use multiple cells in parallel. This not only simplifies design and assembly, but also significantly improves the safety of the entire battery pack.

• Screw postsPrismatic cells often have screw posts on their terminals, which makes them easier to assemble and allows for more convenient element replacement, even on site. This reduces complexity and maintenance time in the event of a cell failure, as it can be replaced without having to disassemble the entire battery pack.

These advantages make prismatic cells an attractive option for a variety of applications, especially those requiring high capacity and customised assembly. However, it is also important to consider the limitations and challenges associated with this cell format.

Disadvantages of prismatic cells

One of the disadvantages of prismatic lithium cells is that their high energy density may be slightly lower compared to other cell formats, such as cylindrical cells. This is partly due to the type of containment box used in prismatic cells.

The solid and robust housing of prismatic cells, while offering advantages in terms of durability and ease of assembly, can take up additional space compared to cylindrical cells, which can affect the overall energy density of the battery. This means that a slightly larger volume is required to store the same amount of energy compared to cylindrical cells of similar dimensions.

However, it is important to note that prismatic cells are still capable of providing significant levels of energy and capacity, and are widely used in a variety of applications. The choice of the appropriate cell format will depend on the specific needs of the application, considering factors such as required capacity, available space, battery pack design and other technical and performance requirements.

Example of prismatic cells

Which are the best for electric vehicles?

NCPOWER has chosen prismatic cells  for its batteries precisely because of their great advantages. These cells offer a good energy density to power density ratio, making them suitable for applications requiring high capacities and sustained energy delivery.

They enable us to achieve high quality performance in both electric vehicle applications. Learn more about our  leading lithium technology in Spain.