Brief Introduction of 4680 Cylindrical Cell(Ⅰ)

1. Introduction

The 4680 cylindrical cell is a new generation of cylindrical cell with 46mm diameter and 80mm height launched by Tesla. For batteries, when the energy density increases, the power density will decrease. The diameter of 46mm is the best choice for cylindrical cells that take into account both high energy density and high power density.

Core innovation: large battery cell + full-tab structure + dry battery technology

Performance breakthrough: 4680 cell greatly increases battery power (6 times that of 2170 cell), reduces battery cost (14% compared to 2170 cell). The heat dissipation performance, production efficiency, and charging speed are optimized, and there is room for further improvement in energy density and cycle performance.

2. structural change

The 4680 battery greatly improves battery power, optimizes heat dissipation performance, production efficiency, and charging speed by using a full-tab structure.

What is the tab: The metal conductor that leads the positive and negative electrodes out of the battery is the contact point when the battery is charged and discharged. The larger the tab contact area and the shorter the tab spacing, the higher the battery output power.

Traditional batteries only have two tabs, which are connected to the positive and negative electrodes respectively, while the 4680 battery realizes full-tab structure (cut the tabs directly from the positive/negative electrodes), as a result, the current path is greatly increased, and the distance between the tabs is shortened, thereby greatly increasing the battery power.

Advantages of full-tab：

• Increased output power, 6 times that of 2170 batteries
• Improve safety: The tab area of the 4680 battery is greatly increased, which greatly improves the heat dissipation effect (only 20% of the traditional cylindrical battery), and enhances the thermal stability of the battery.
• Fast charging performance is greatly improved: due to the full-tab structure, electrons are easier to move inside the battery, and the current rate is increased, so the charging and discharging speed is faster.
• Improve production efficiency: Eliminate the process and time of adding tabs on the production line, reducing the possibility of manufacturing defects.

Difficulties in the full-tab process: the process of folding the tabs together, currently there are three types: kneading and pressing tabs, cutting tabs, and multi-tabs:

• The shape of the tabs of kneading and pressing tabs is uncontrolled, and short circuits are prone to occur. The two sections are closed during manufacture, and the penetration of electrolyte is greatly hindered.
• Cutting tabs (Tesla) are obliquely cut into slices and rolled up, which is better than random extrusion and takes up less space, but the surface has a large degree of undulation. The two sections are still closed during manufacturing, and the injection cannot be continuously produced.
• Multi-tabs are difficult to fold neatly, and tab position errors are easily magnified.

In the connection between all tabs and the collector plate or shell, the requirements for laser welding technology are relatively high: from spot welding (traditional two tabs) to surface welding (4680 battery full tabs), the welding process and welding volume have increased , The laser intensity and focal length are not easy to control, and it is easy to cause false welding or over welding. The current battery yield is low (80%).

Advantages of larger size:

• Reduce battery cost: reduce the proportion of the shell to cell capacity, and the number of structural parts and welding is also significantly reduced, which is 14% lower than the cost of 2170.
• Improve capacity density: As the cell size increases, the number cells in the battery pack decreases, the proportion of metal casings decreases, the proportion of positive and negative electrodes increases, and the energy density increases.
• The BMS system is more worry-free: the number of cells in the battery pack is reduced, and the monitoring and status analysis of the batteries are simpler.
• Increased structural strength, perfect combination with CTC technology: 4680 has a larger size and higher structural strength. As a structural battery, it becomes a part of the car structure, which not only provides energy, but also serves as a structural support, saving space and reducing weight (10 %), thus increasing the cruising range (14%).

Disadvantages of larger size:

Increased heat generation: The larger the battery size, the more heat it generates, and the more difficult it is to dissipate heat. Therefore, it is more difficult to control the heat. The greater the power of the battery explosion, it is the biggest bottleneck for battery manufacturers to increase the battery size. And Tesla has made a breakthrough in thermal stability through the full-tab technology.