Types of Lithium Batteries: Lithium Cell Format
Cylindrical lithium cells
As can easily be inferred, cylindrical cells are cylinder-shaped, are the most commonly used and were among the first to be mass-produced. They can have different diameters, the most common being the 1865, where the number 18 indicates the diameter (18 mm) and the number 65 indicates the length (65 mm). There are, however, other formats, such as the 2170 or, again, the one most recently adopted by Tesla, the pioneer of lithium batteries for electric cars, with its 4680 used to power the Tesla Model Y. Apart from a few car manufacturers who have made this choice, cylindrical cells are routinely used in medium-small battery packs, e.g. in micro-mobility (bikes, scooters and motor scooters), portable tools, medical devices, and so on.
Lithium pouch cells
These types of lithium cell are so called because of their bag-like shape. They have a lightweight design and, as they have no inherent robustness, special protections, such as the addition of aluminium frames, must be inserted during production of the module to give them structural robustness. They come in various sizes which can be modified according to the manufacturer’s requirements. These cells are mainly used in smartphones, drones, laptops and the automobile industry.
Prismatic lithium cells
Prismatic lithium cells have a solid rectangular casing made of aluminium or of a very strong plastic material. The internal components are layered. They come in different sizes, with a variety of formats depending on the field of application. Their individual components can reach a high capacity. Due to their structure, prismatic cells are best suited for the production of lithium batteries for the machinery and industrial vehicles industry, or the energy storage sector, all of which normally require medium-high capacities.
The benefits and drawbacks of the various cell types have already been discussed, but few people ever enquire about the lithium-ion battery cell production process and how it works.
Although the many cell types that make up a lithium battery appear very different from one another when viewed from the outside, it is astonishing to learn how similar their interiors actually are. The different types of battery cell production and assembly will now be explored in more detail.
Cylindrical cells are usually produced in standard models in terms of size. One common size is the 18650 type (18 mm diameter, 65 mm height). This type has a total mass of about 45 grams and can support a capacity of about 1.2 to 3 Ah depending on the technology employed.
Pouch cells have a soft construction that requires the use of a support structure with these cells. Additionally, the cell should not be placed near sharp edges. The approximate cell capacity range is 2.5-8 Ah, and the approximate weight is 75-225 g.
Prismatic cells are manufactured with a capacity ranging from several Ah targeted for laptops and cell phones to hundreds of Ah designed for EV applications. The weight range is 0.8-5.2 kg.
Prismatic Cells are the Best Choice for Forklift Batteries
The differences in battery technology today allow customers to choose the best fit for their applications. Thus, lithium prismatic cells are the preferred technology for material handling equipment (MHE):
Hundreds of Ah nominal capacity. The technology provides the best ratio of power and energy per volume unit. This is especially important in the high-capacity, high-current and relatively low voltage batteries used in MHE.
Optimal utilization of available pack space. There are no space cavities between the cells. This allows maximum capacity for the battery pack, and still have enough room to accommodate for required extra weight, sealing, heater, internal charger or other battery upgrades within the battery compartment’s limited area.
Contacts are strong enough for reliable bus-bars connection. This is a hugely important safety factor with high vibration operations, especially in cushion-tire type lift trucks.
Flexible battery weight. LIB pack weight is not a limitation for most of the MHE in terms of its range per one charging (unlike passenger EVs). Forklifts operate mostly near their charging stations and their batteries are often engineered as a counterweight.
Stacking of individual sheets
This solution involves cutting the anode, cathode and separator sheets individually, using a robotic arm for each, and then stacking them on top of each other until the entire lithium cell is created.
The other two construction techniques, however, result in a single sheet that may be rolled onto itself in a variety of ways.
The folding method known as Z-folding sees the anodes and cathodes cut into sheets, while the separator remains continuous. In this case, the anode and cathode sheets are first cut and then inserted into the separator, a continuous roll which keeps the two electrodes separate by means of a Z-folding process.
The rolling process consists of rolling four sheets of material together, first stacked on top of each other (anode sheet + separator + cathode sheet + separator), and then rolled onto a cylindrical or ovoid base to give the typical shape of the prismatic or cylindrical cell case.
As has already been illustrated, the assembly methods may be different, but the battery cell composition remains the same. In the images of the various assembly processes can be seen how the anode has a basic brown colour, as the coating is deposited on a thin layer of copper. Then comes the plastic or ceramic separator, and finally, the cathode, which is grey in colour, since it is deposited on a layer of aluminium.