Lithium Battery Cells Different packaging Technology

The so-called packaging is to integrate the Lithium battery cells into a standardized module, supporting and protecting the cells. We can understand the battery module as the “coat” of the Lithium battery cells. With this layer of coat, the power battery can better adapt to the unique use scene of the car.

When the car is running, it will encounter bumps, impacts, high temperature, low temperature and other environments. The module is to connect, fix, buffer and improve the insulation effect of the battery cells in the battery pack. At the same time, when a battery pack adopts a module structure, when a battery cell fails, you only need to find the module to which it belongs and replace it to solve the problem, effectively reducing the cost and difficulty of maintenance.

At present, there are mainly three mainstream packaging forms, namely Cylinder, Prismatic and Punch. Among them, the outer packaging of Cylinder and Prismatic batteries is generally hard shell or aluminum shell, while the pouch Lithium battery cells is packed with aluminum-plastic film. We introduce one by one:

Hard shell

Hard shell, as the name suggests, is to wrap the battery with a hard shell such as a steel shell or an aluminum shell, and it is divided into cylinder and prismatic. Generally speaking, the hard shell technology is more mature and the safety is better, but it is not as good as the pouch Lithium battery cells in terms of energy density.

Cylinder batteries

Cylinder batteries are the most familiar type of battery. The advantages of cylindrical batteries are mainly high production efficiency and high degree of standardization. In the field of cylindrical batteries, the main battery manufacturer is Panasonic in Japan, and Tesla is the most widely used among vehicle manufacturers. For example, Tesla’s 18650 battery, 18 means the diameter of the battery is 18mm, 65 means the length of the battery is 65mm, and 0 means a cylinder. The capacity of an 18650 battery is usually around 3000 mAh. The main disadvantage of cylindrical batteries is that the capacity of a single cell is too small, and many Lithium battery cells need to be used together. In order to improve this shortcoming, the industry began to introduce “big cylindrical” batteries, such as 21700 cylindrical batteries, 21 represents the diameter of the battery is 21mm, and 70 represents the length of the battery is 70mm. Compared with 18650, 21700 Lithium battery cells are larger, driving the energy density of the entire battery system to be higher. Above 21700, the industry has called 46800 cylindrical batteries. In short, large cylinders represent the future of cylindrical batteries.

Prismatic battery

Prismatic battery, as the name suggests, is to integrate the Lithium battery cells into a square shell. The geometric principle tells us that the square can be seamlessly connected with each other, so the space utilization rate is higher than that of the cylindrical battery. This packaging technology is conducive to making the internal materials of the battery more tightly wrapped. At the same time, the hard shell is made of high-strength aluminum alloy, so the battery is not easy to expand and is relatively safer. Rectangular batteries are a technology widely used by domestic battery manufacturers. According to data from the CCID Research Institute of the Ministry of Industry and Information Technology, the shipments of prismatic batteries by CATL and BYD accounted for 60% of the domestic market share. For downstream vehicle manufacturers, the versatility of prismatic batteries is also relatively high. Automakers such as Weilai and BMW all use prismatic batteries.

Pouch cell

Pouch Lithium battery cells is the “coat” that wraps the battery core is soft. At present, the material used for the Pouch cell is aluminum-plastic film. Compared with hard shell batteries, it has two obvious advantages. One is light weight. Under the same capacity, soft pack batteries are 20% lighter than aluminum shell batteries. Second, they have high energy density. Punch cell battery has 50% more capacity than the aluminum shell battery. Although it is just an ordinary film, it actually has a high technical threshold. At present, the global aluminum-plastic film industry is mainly controlled by Japanese and Korean manufacturers, and the country mainly relies on imports, which directly leads to the soft pack battery in the domestic market with a lower share.

With the in-depth development of the power battery industry, the disadvantages of the technical path from batteries to modules and then to battery packs have gradually emerged. The biggest disadvantage is the low space utilization rate. The overall space utilization rate of the battery pack is only 40%, and the remaining 60% of the space is occupied by a large number of beams, longitudinal beams and other materials in the module. In order to pursue a higher mileage, it is necessary to place more cells in a limited space. Based on such industry needs, the moduleless architecture CTP technology solution was born.

CTP New Technology Solution

CTP, the English full name is Cell to Pack, that is, from cells to batteries, that is, no module architecture. This is an emerging technical solution in the field of power batteries.

In the past two years, CTP technology has developed rapidly in China. There are currently two mainstream technical solutions, one is the familiar blade battery; the other is a solution that replaces small modules with large modules.

Let’s look at the blade battery first. The CTP design idea is to directly install the Lithium battery cells into the battery pack shell in an array, and directly omit the module step. How does the blade battery directly skip the module? The Lithium battery cells are made into a thin and long shape. In the length direction, the 148 mm of the conventional battery cell becomes 900 mm. The length of nearly 1 meter looks like a blade, so that the blade battery can replace the beam structure. In the thickness direction, stacking technology is adopted, and the stringer structure can be replaced by stacking “blade batteries”, which can finally ensure that the battery pack has sufficient structural strength.

Due to the omission of accessories such as beams, longitudinal beams, and bolts, the space rate is greatly improved, and the space utilization rate inside the battery pack shell is increased from the original 40%-50% to 60%-80%.

The CTP design idea from the small module to the large module is an iterative way to continuously improve the space utilization efficiency of the battery. The design idea is to reorganize the original module structure and remove the side panels of the module. In 2021 and 2022, CTP2.0 and CTP3.0 technologies will be launched successively, among which CTP3.0 is the familiar Kirin battery.

Kirin battery uses a flat tray, removes the longitudinal beams or beams on the box, and uses low-expansion batteries, which cooperate with the battery body to meet structural requirements

The structure is more compact, the number of batteries per unit volume is more, the number of battery pack components is reduced by 40%, and the space utilization rate reaches 72%, which also makes the energy density of Kirin battery reach 255Wh/kg. The cruising range of the vehicle can exceed 1000 kilometers.

Finally, it should be pointed out that the module-less battery also has a relatively obvious disadvantage, that is, the difficulty and cost of subsequent maintenance of new energy vehicles are relatively high. This is easy to understand. If it is a module-based architecture, you only need to find out the problematic module. However, under the module-free architecture, a problem with one battery cell may affect the entire battery pack, so that the difficulty of maintenance has increased geometrically.