This article mainly explains the structure of TESLA 4680 full-tab battery cells & advantages, process difficulties, prons & cons of larger size

1. Introduction

1.1. Definition

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

1.2. Core innovation

Large battery cell + full-tab + dry battery technology

1.3. Performance breakthrough

The 4680 battery has greatly increased battery power (6 times that of 2170 batteries), reduced battery costs (14% of 2170 batteries), optimized heat dissipation performance, production efficiency, and charging speed, and there is room for further improvement in energy density and cycle performance.

2. Structural changes

2.1. Full tabs

The 4680 battery has greatly increased battery power, optimized heat dissipation performance, production efficiency, and charging speed through changes in the tab structure.

2.1.1. Full Tab Structure

Tab: A metal conductor that leads the positive and negative electrodes from the battery cell. It is the contact point when the battery is charged and discharged. During battery operation, electrons flow from the positive tab to the negative tab. The flow path is proportional to the internal resistance of the battery, and the flow width is inversely proportional to the internal resistance of the battery. The internal power loss of the battery is proportional to the square of the internal resistance. Therefore, the larger the tab contact area, the shorter the tab spacing, and the higher the battery output power.

Traditional batteries have only two tabs, connecting the positive and negative electrodes respectively, while the 4680 battery has a full tab (cutting the tabs directly from the positive/negative electrodes), which greatly increases the current path and shortens the tab spacing, thereby greatly increasing the battery power.

2.1.2. Advantages of full tabs

• Increased output power: The battery current path becomes wider, and the internal resistance is greatly reduced, and the internal loss is reduced accordingly, thereby greatly increasing the battery power (6 times that of 2170 batteries).
• Improve safety: Unlike sheet batteries, cylindrical batteries mostly dissipate heat in the axial direction, and heat is dissipated from the tabs. Traditional cylindrical batteries such as 2170 have only two tabs, and the heat transfer channel is narrow, so the heat dissipation effect is not good. The tab area of 4680 batteries is greatly increased, and the heat transfer channel is wide, which greatly improves the heat dissipation effect (only 20% of traditional cylindrical batteries) and enhances the thermal stability of the battery.
• Greatly improved fast charging performance: 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 to the production line, save equipment space, and reduce the possibility of manufacturing defects.

2.1.3. Difficulties in the full-tab process

1. Tab collection problem in the production of full-tab: The common understanding is the process of folding the tabs together. Currently, there are three types: kneaded tabs, cut tabs, and multi-tabs:

• The tab shape of kneaded tabs is uncontrolled, which is prone to short circuit. The two sections are closed during manufacturing, and the electrolyte penetration is greatly hindered;
• The cut tabs (Tesla) are cut into pieces and rolled up, which is better than irregular extrusion. It occupies less space, but the surface undulation is larger. The two sections are still closed during manufacturing, and the injection cannot be continuously produced;
• Multi-tabs are difficult to fold neatly, and the tab position error is easily magnified in the outer circle.

2. The connection between the full tab and the collector plate or shell requires high laser welding technology: 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 weld through and burn into the battery cell or no welding. The current battery yield is low (80%).

2.1.4. Opportunities brought by full tabs

From the pulse laser spot welding of the previous 2170 battery to the current 4680 battery line or laser dot matrix, the laser welding process has been improved, and it may change from the original pulse laser to continuous laser, and the overall cost has increased.

2.2. Large battery cell

2.2.1. Performance

The 4680 battery has an improvement in diameter and height compared with the previous 2170 battery, with the diameter changing from 21mm to 46mm and the height changing from 70mm to 80mm. The thickness of the battery cell has increased, the curvature has decreased, and the hollow part has become larger.

2.2.2. Advantages of larger size

• Reduce battery cost: reduce the proportion of shell in unit battery capacity, and significantly reduce the number of structural parts and welding (the cost is reduced by 14% compared with 2170 battery).
• Improve capacity density: as the battery size increases, the number of batteries in the battery pack decreases, the proportion of metal shell decreases, the proportion of positive and negative materials increases, and the energy density increases.
• BMS system is more worry-free: the number of batteries in the battery pack is reduced, and the monitoring and status analysis of the battery are simpler.
• Increased structural strength, perfect combination with CTC technology: 4680 is larger in size and has higher structural strength. As a structural battery, it becomes part of the vehicle structure, providing energy and supporting the structure, saving space and reducing weight (10%), thus increasing the cruising range (14%).

2.2.3. Disadvantages of larger size

Increase in heat generation: The larger the battery size, the more heat it generates and the harder it is to dissipate heat. Therefore, it is more difficult to control heat and the more powerful the battery explosion is. This is the biggest bottleneck for battery manufacturers to increase battery size. Tesla has made a breakthrough in thermal stability through full-ear technology.

2.2.4. Actual performance

As the battery size increases, the number of batteries in the battery pack decreases, the proportion of metal shells decreases, the proportion of positive and negative materials increases, and the energy density increases. Compared with 2170 batteries, 4680 batteries have increased energy by 5 times. The current increase in range (16%) mainly comes from CTC technology (14%). With the continuous upgrading of the material system, there is room for further improvement in battery energy density.

CTC means Cell to Chasiss

3. Dry battery technology

The dry electrode process completely skips the step of adding solution, omitting complicated coating and drying processes, greatly simplifying the production process: the active positive and negative electrode particles are mixed with polytetrafluoroethylene (PTFE) to make them fibrous, and the powder is directly rolled into a thin film and pressed onto aluminum foil or copper foil to prepare positive and negative electrode sheets.