Shape of battery cell - What can we know from the shape?

The battery cell of a lithium-ion battery is the core unit for storing and providing electrical energy in a lithium ion battery pack. Each battery cell stores and releases electrical energy through electrochemical reactions. And the battery cell is the core part responsible for storing electrical energy in rechargeable batteries, and the quality of the battery cell directly determines the overall performance and quality of the rechargeable battery.

This article will tell some information based on the shape of battery cell, from the most common shape, pros and cons to the challenge in each of the shape of battery cell in order to help you know better about battery.

The most common shape of battery cell

According to the packaging form, lithium batteries can be divided into three forms: cylindrical, prismatic and pouch cell. The packaging form refers to the packaging structure of a single lithium battery, and different packaging forms correspond to different manufacturing processes, as well as different forms of battery precision structural components.

At present, the packaging technology route for lithium batteries mainly includes three forms: cylindrical, prismatic, and pouch cell.

Pros and cons of shape of battery cell

Cylindrical cell

Cylindrical batteries are usually packaged in cylindrical steel shells, and bare cells are made using winding technology. Cylindrical batteries are one of the best practices for lithium batteries and are also standardized and universal products. As early as 1992, Japanese company SONY developed the 18650 battery. At present, cylindrical batteries can be divided into models such as 14650, 18650, 21700, 32650, 4680, etc., which are named after the size of the battery.

18650 is the most mature technology, while 21700 is a new type of battery that Tesla has been promoting in recent years (with products from Lishen and Bick in China). Due to its geometric shape of battery cell, the gap between cylindrical batteries is large, which facilitates air circulation and improves heat dissipation efficiency. There are relatively more cylindrical battery cells, which require higher requirements for thermal management systems.

Cylindrical batteries have good consistency, high production efficiency, and strong system level heat dissipation capabilities. After size upgrades, they can improve to some extent the problems of low single cell energy density, multiple battery cells required for modules, poor lifespan, and complex management. However, overall, its low energy density and low grouping efficiency of products are still significant disadvantages.

Prismatic cell

The production of bare cells is usually carried out using winding or cell stacking processes, with prismatic aluminum or steel shells as packaging materials. prismatic batteries have the advantages of high grouping efficiency, large individual capacity, and simple structure. The size and volume are fixed, and the shape of battery cell is not easily changed, which may limit the battery design of some devices. In addition, prismatic batteries have low consistency and are difficult to dissipate heat.

Due to the larger size of prismatic batteries compared to cylindrical batteries, fewer cells are required to achieve the same amount of energy. This means that for the same volume, using prismatic batteries requires fewer electrical connections to be welded, reducing the number of required structural components and improving volume utilization.

Pouch cell

Pouch batteries, due to their use of stacking manufacturing methods, have a thinner volume and the highest energy density (packaged with aluminum-plastic film that is lighter in weight than aluminum shells). They are considered a powerful tool for solving range and safety anxiety, and can also provide a good connection for transitioning to solid-state batteries.

When considering the overall layout of the vehicle, there is more room for imagination in shape and more variation, not limited to rectangles. They can be assembled into small battery packs and placed under the trunk, or made into a T-shaped layout pouch batteries have the advantages of high individual energy density, good electrochemical performance, high safety, flexible design, variable shape of battery cell, strong adaptability, and high energy density. But its product consistency requirements are higher, grouping efficiency is relatively low, and cost is relatively high.

The challenge of shape of battery cell

Cylindrical cell

With the rapid expansion of the electric vehicle market and consumers' increasingly stringent requirements for range, vehicle manufacturers have posed unprecedented challenges to the comprehensive performance of power lithium batteries.

In terms of energy density, battery high energy density means that vehicles can achieve longer range with the same volume or weight of battery cells. The reduction of manufacturing costs helps to promote the popularization of electric vehicles, making them more affordable for more consumers. The extension of cycle life is directly related to the service life and long-term cost of battery cells, reducing the trouble and cost of frequent replacement of battery cells. The improvement of additional product attributes such as safety and low-temperature performance can also enhance the overall competitiveness of electric vehicles.

In the current situation where significant breakthroughs have not been made in the field of raw materials, appropriately increasing the volume of cylindrical cells to obtain more cell capacity has become a promising and feasible exploration direction.

Prismatic cell

In the past few years, the performance of prismatic batteries has been rapidly improved with the support of the domestic industrial chain. CATL Kirin Battery adopts CTP technology to improve the grouping of prismatic cells from the physical structure level, thereby enhancing the energy density and safety performance of the battery pack. These improvements filled the performance gap between prismatic cells and cylindrical batteries, ultimately leading to the rise of prismatic shell cells in the power battery market.

In terms of production technology, there are two different process paths for prismatic battery cells: winding and stacking. Due to the customized production of prismatic lithium battery cells based on product size, this directly leads to a variety of prismatic battery cell models on the market, with thousands of types available. However, the excessive diversification of models has also led to a series of problems, the most prominent of which is the difficulty in achieving unified standardization of processes. In the application scenarios of ordinary electronic products, the use of prismatic cells generally does not cause significant obstacles.

But for industrial equipment products that require multiple battery cells to be connected in series or parallel, the situation is completely different. Due to the high requirements for consistency and production process stability of battery cells in industrial equipment, standardized production of cylindrical lithium battery cells is more advantageous in such scenarios.

Pouch cell

Nowadays, the development trend of batteries has made pouch batteries unpopular for a long time. Even theoretically, compared to prismatic and cylindrical batteries that use hard shell packaging, pouch batteries are less likely to explode when subjected to thermal runaway. However, in reality, the most significant factor affecting the entire automotive battery system is the consistency of individual battery cells, which is precisely one of the disadvantages of pouch batteries and leads to frequent safety accidents in electric vehicles equipped with pouch batteries.

But these problems are not insurmountable. To address the issue of high costs, we can continuously expand production scale, achieve economies of scale, and gradually reduce unit costs. For the problem of leakage, it can be effectively solved by improving the quality of aluminum-plastic film, such as developing new aluminum-plastic film materials, optimizing the production process of aluminum-plastic film, etc., in order to improve the overall reliability and stability of pouch lithium batteries and further expand their application scope.

Conclusion

Shape of battery cell like cylindrical, prismatic, and pouch pack are all showing a rapid development trend in the current lithium battery market. The key to their flourishing development lies in their precise positioning in specific application fields and unique advantages.