Cylindrical vs Prismatic vs Pouch Cells, Who Is the “King”

To say which type of cell is the “Number One” in the industry, the status of prismatic cells can be described as soaring. In the first quarter of 2022, its share in the global battery market reached 63.6%. From January to August, its share in the electric car market was as high as 92.8%. The ultra-high market share is a direct reflection of its product strength. What advantages does the prismatic cell have, and can it become the leader in the industry? Today, let’s talk about this issue.

Cylindrical vs Prismatic vs Pouch cells

History

From the perspective of history and technology, the cylindrical cell officially entering the commercial market in 1991 was earlier and more mature than the prismatic battery that only appeared in 1995. Why has the prismatic cell become the mainstay of the battery industry? Especially in today’s electric car battery market, it is not an exaggeration to call it “outstanding.” The prismatic cell can achieve today’s brilliant achievements because it has obvious advantages in terms of safety, performance, and customization.

Size

First, let’s talk about the customizable advantages of prismatic cells in shape. The so-called customization refers to mass production and tailoring for individual customers. Each company has its system and standards in the automotive market, and the same is true for the power batteries used in its EV models.

The main internal structure of the prismatic cell includes a shell, a top cover, a positive plate, a negative plate, a diaphragm, and safety components. However, unlike cylindrical cells such as 18650, 2170, and 4680, prismatic cells have no specific length, width, and height restrictions and can be produced in different sizes according to different needs.

Take the blade(Prismatic) cell produced by BYD as an example. Its size was 356mm100mm28mm when it was mass-produced in 2008. In 2013, a blade cell of 420mm109.5mm39mm was made and changed to 960mm*90mm in 2020. *13.5mm.

Prismatic cells do not have a fixed size but can be changed according to the various specific needs of buyers, and products that meet specific needs can be directly designed and produced. We all know that the battery packs of electric vehicles are assembled in the chassis area of the vehicle as flat cuboids, so on the premise of satisfying customization, Prismatic cells can save a lot of assembly time.

Take BYD Han EV as an example. There are about 180 blade cells in its battery pack, so it is only necessary to connect the positive and negative electrodes of these batteries to form a battery pack for an electric car. There are more than 4,000 cylindrical cells in the battery pack of the Tesla Model 3, so it is necessary to connect the positive and negative electrodes of these 4,000 cells in sequence, and the greater the number, the more assembly time will naturally be required.

BYD Blade cell

Space Utilization

There are many advantages of prismatic cells. In terms of shape, its space utilization rate is higher than that of cylindrical cells. The multi-cell cells form a honeycomb structure when the cylindrical cells are arranged next to each other because of the shape. There will be some gaps between these cells and many gaps between thousands of batteries. In the high cost of the land battery pack, although these spaces are wasted, it makes people feel distressed, but due to the shape of the cylindrical cell, there is no good solution.

Relatively speaking, prismatic cells have a reasonable space utilization rate. Even if the cells inside the battery pack must be laid in multiple layers, they can be stacked together tightly without wasting much space. The advantage of high space utilization is very obvious; that is, more batteries can be packed in a limited space, so the energy density of the battery pack will also increase accordingly.

Production Process

In addition to the space utilization rate of the battery pack as a whole, from the manufacturing process perspective, the prismatic cell also has some advantages compared with the space utilization rate of the cylindrical cell in a single cell.

Since the advent of cylindrical and prismatic cells, the production process of a single cell is mainly divided into two methods: winding and stacking. Cylindrical cells can only be made by winding technology, but prismatic cells can choose to use winding or lamination according to needs craft. As the name suggests, the inside of the cell is wound one by one, which is the winding process, and the inside is stacked one by one, which is the lamination process.

In the same space, the stacking process can fill up the entire space according to its characteristics. The winding process will eventually waste a part of the space, so from the theoretical data, the materials used in the cell are the same, and the stacking process The energy density of the battery produced under the next generation will be higher. Perhaps this is one of the reasons why the prismatic cell is so popular and even mentioned in the “White Paper on the Development of High-speed Laminated Cells for Automotive Specifications in China”.

At the same time, for the cell produced under the stacking process, each layer of the cell has a separate tab. The more the number of tabs, the more electrons flow from the positive electrode to the negative electrode, and the cell’s charge and discharge performance is stronger. This is like comparing ten lanes to 2 lanes. During rush hour, the former must have more vehicles in total.

Material Costs

The reason for setting an assumption of “same material” is that the current mainstream EV batteries are mainly divided into two types: lithium iron phosphate(LFP) and nickel cobalt manganese(NCA and NMC), and the cost and energy density of the two are different. In terms of cost, producing NCA batteries requires cobalt (Co), which is more expensive than gold (Au). Lithium iron phosphate batteries do not use cobalt (Co), so the production cost of the former is higher than that of the latter. , and the same is true for the energy density of a single cell.

Safely

Different from fuel vehicles, as long as there are some explosions and spontaneous combustion incidents in EVs, they can be fermented immediately and trigger heated discussions among many netizens. If these models have high potential safety hazards, consumers will naturally not buy them out of the perspective of their safety.

In theory, a battery pack made of prismatic cells is safer than cylindrical cells. Because thousands of cylindrical cells are used to form a battery pack, it is necessary to consider how to solve the problem of heat generated by these thousands of cells during charging and discharging, and also consider the thermal runaway of the battery after the vehicle is crushed and deformed after a collision accident. This is very difficult for the battery management system compared to managing 180 prismatic cells.

At the same time, in terms of heat control, the prismatic cell has a good heat dissipation advantage because of its flat shape. Its shell can directly transfer heat outward, and the cooling system inside the battery pack can absorb the heat and transfer it to the outside to reduce the probability of thermal runaway.

It is worth mentioning that when a lithium-ion battery is overcharged or overdischarged, especially in a low temperature environment, the lithium ions in the front have not been embedded in the negative electrode. Still, the lithium ions in the rear have arrived. The latter will be the same as the already—the electrons reaching the negative electrode form lithium metal, which is the dendrite phenomenon of lithium-ion batteries. If the number of lithium dendrites is too large, it will pierce the separator and cause a short circuit in the battery. Cylindrical and prismatic batteries with hard shells may explode, ignite, or catch fire.

In lay terms, this is like a vehicle driving fast on a highway, and each lane has a nearly saturated number of cars. If the vehicle in front suddenly brakes, the vehicles behind may not brake in time, causing severe traffic accidents—a major accident involving a series of car crashes on the highway.

winston battery

Pouch Cell

Regarding safety, pouch cells have more safety advantages than cylindrical and prismatic cells. Generally speaking, pure electric vehicles equipped with cylindrical cells and prismatic cells may explode and spontaneously ignite under the influence of internal and external environments. Although pouch cells also have fire risks, they are less dangerous than the previous two or an explosion. Because the outermost layer of the cylindrical cell and the prismatic cell has a hard metal shell, the outer layer of the pouch.

Pouch cell is wrapped in an aluminum-plastic film. Its hardness is very soft compared with the former two, so it has The name of “soft pack” is precise because of the thin and soft shell, which is lighter than cylindrical and prismatic cells under the same cell’s capacity.

It is precisely because of the word “soft” that the pouch cell will not quickly explode when it is thermally out of control. Because the definition of an explosion is “a process in which energy is converted from one form to another or several forms accompanied by a strong mechanical effect within a relatively short time and a small space”. If the soft-pack battery suddenly suffers from thermal runaway, the outer soft shell will bulge or burst, and part of the heat will be released as the space expands, so it will not cause an explosion.

The performance of pouch cells in terms of safety is so good, why its share in today’s new energy vehicle market has been declining since 2017, from 15.3% at the beginning to less than 10% today, becoming What about the “brother in the younger brother” located under the prismatic cells and the cylindrical cells?

One may be because the shell of the pouch cell is made of aluminum-plastic film, which means that the cell as a whole cannot be made too thick. If it is too thick, the overall shape will be the same as a shoulder pole break-off. It is also because it can be made narrow enough. To allow a single cell to hold more power, it needs to be stretched and widened. You must know that the battery pack is placed in the chassis area of ​​the vehicle, and its overall length and width are limited. In this way, it is not easy to form a battery pack if it is too long and wide, forming a vicious cycle.

In addition, due to the softness of the pouch cell, when connecting to form a battery pack, it is necessary to install a protective frame on each battery to protect each battery from friction, collision, and backlog. The aluminum-plastic film of the battery pack is deformed or broken. Such a design will not only waste the space inside the battery pack but also increase the overall weight of the battery pack. Perhaps it is precisely because of these reasons that although pouch cells have many advantages, they still have not been able to “be stronger and bigger” in Ev’s industry.

pouch cell

Wrapping Up

In fact, no matter what type of cell it is, it has its advantages and disadvantages. After all, there is no perfect cell that can meet all needs. However, there is an old saying that “the dwarf pulls out the general”, and the prismatic cell has become the “general” by its performance. This can be seen from data such as market share. Will there be an emerging “dark horse” in the battery industry to replace the dominance of prismatic batteries? Everyone must hope that this is an affirmative answer. As for when that day will come, let us wait and see.

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