Compared with the single tab structure of the 2170 battery, the tesla 4680 battery adopts the design of all tabs + current collectors. At the same time, the mainstream solution adopts the new design of drilling the positive pole at the bottom of the shell groove and laser welding the cover plate to seal the shell slot.
Tesla made a "combination punch" around the tesla 4680 battery of "large battery cell + full tab + high nickel and high silicon + CTC", and at the same time achieved:
- Long battery life: Tesla 4680 battery energy density increased by >20%;
- Fast charging: All tabs optimize the thermoelectric performance of the battery, which can withstand high-rate currents above 4C;
- Low cost: Large battery + high energy density dilutes the cost per Wh.
In addition, due to its superior thermal safety performance and uniform internal stress distribution, tesla 4680 battery is more suitable for high-nickel and high-silicon systems than square ones.
Nickel high silicon tesla 4680 battery+CTC solution. In addition, leading battery suppliers such as LG, Panasonic, Samsung, CATL, and EVE also followed up with the deployment of tesla 4680 battery batteries. The tesla 4680 battery is expected to usher in an inflection point driven by Tesla and the head battery factory.
What is tesla 4680 battery
The tesla 4680 battery is a battery with a diameter of 46mm and a height of 80mm. Compared with the previously used 2170 battery, tesla 4680 battery has 5 times the battery capacity, which can increase the cruising range of the corresponding model by 16%, and the output power is 6 times that of the 2170 battery.
Comparison of two current structural schemes of tesla 4680 battery
The end where the negative pole lug is located is facing the bottom of the steel shell groove; the positive pole lug is led out from the open end, and is welded and connected with the positive pole terminal. Pulse laser penetration welding is used to weld the base of the steel shell to the full tab of the negative electrode through the groove.
- Advantages: The structure without negative electrode collector plate does not occupy the space in the height direction of the steel shell, which improves the space utilization rate.
- Disadvantages: When the thickness of the battery wall increases, it is difficult to weld the tabs to the bottom of the shell firmly by penetration welding.
The positive current collecting plate is directly welded to the positive pole, and the positive pole is clamped on the opening at the bottom of the groove of the casing, and an insulating seal is provided there.
The battery cell has a full tab structure, and the two ends are respectively connected to the positive and negative current collectors, the pole is electrically connected to the battery through the positive current collector, and the case is electrically connected to the negative current collector. The cover plate is connected with the notch of the housing, and the explosion-proof line is etched on the cover plate.
Difficulties of tesla 4680 battery
The new structure brings process implementation and consistency challenges, affecting cell yield.
- Coating: The arc-shaped edge of the full tab coating requires higher precision of the equipment (the outer ring is more and more white than the inner ring, and the length of the tab is longer as it reaches the outer ring).
- Tab cutting: The process requirements are higher. If the edges are not aligned, there will be gaps in the tab bonding.
- Laser welding: All lugs are welded to the surface of the collector plate, and the number of solder joints increases (the number of solder joints of tesla 4680 battery is more than five times higher than that of 21700).
- Liquid injection: It is difficult to inject liquid after covering all tabs, which affects continuous production.
Reasons for using high nickel and high silicon
In principle, the tesla 4680 battery cylindrical battery is just a form of packaging, not limited to the material system. However, from the application level, high-Ni and high silicon can give full play to the advantages of tesla 4680 battery large cylinders with better thermal performance and uniform internal stress distribution than square ones.
Since the integration efficiency of cylindrical batteries is lower than that of square batteries, that is to say, to make packs with the same energy density, the energy density of cylindrical cells must be higher than that of square batteries. Therefore, to achieve a higher pack energy density, it is natural to require cylinders with high nickel.
Cylinders are more suitable for high nickel than squares. The core reason is that the square high-nickel is in surface contact, and the single battery is large, the heat generated in the body is not easy to release, and the thermal runaway design is not easy to control.
On the other hand, the chemical properties of iron lithium are stable, and the requirements for heat dissipation and thermal runaway are relatively high. Low, so the square CTP is very suitable for the battery of the iron-lithium system, giving full play to the advantages of the high integration of the square, but the thermal runaway design has a difficult shortcoming.
Tesla 4680 battery+ lithium iron has lost the advantages of tesla 4680 battery in passenger cars, and may be used in two-wheeled vehicles and electric tools in the future. In addition, because the negative electrode will expand after adding silicon, the internal stress distribution of the cylinder is more uniform than that of the square, and the square is easy to cause particle breakage under this scheme, which affects performance and life. Therefore, in order to maximize the energy density of the battery cell, choose a high-silicon solution with high-nickel.
Application of tesla 4680 battery
Silicon-based negative electrode
Silicon-based anode is the next-generation mainstream anode material. The mass production of tesla 4680 battery drives the demand explosion. As an ideal next-generation negative electrode material, the specific capacity of pure silicon is 10 times that of graphite. However, pure silicon expands nearly 3x during the charging process. At present, it is doped with silicon oxide. The current doping content is about 5%, and the tesla 4680 battery is expected to increase to more than 10%.
LiFSi is a new lithium salt suitable for high-nickel high-voltage high-rate batteries. The use of high nickel in tesla 4680 battery leads to reduced thermal stability and high charge and discharge power requires improved conductivity of the electrolyte. As the nickel content increases, the thermal stability of the ternary positive electrode decreases, and the structural stability becomes worse.
The tesla 4680 battery adopts a full tab structure to pursue high magnification performance. High nickel and high rate increase the performance requirements of lithium salt. Lithium bisfluorosulfonyl imide (LiFSi) is a new type of electrolyte solute lithium salt, which has better low-temperature discharge and high-temperature performance retention, longer cycle life, higher rate discharge performance, and higher safety performance.
PVDF is mainly used in the positive electrode and separator in the battery as a binder.
PVDF is coated on the side contacting the negative electrode to increase the viscosity:
- Improve the stability of the silicon carbon negative electrode powder;
- Stick it tighter to increase the energy density;
- Improve the liquid retention. Assuming that the PVDF coating is 1μm, the density of PVDF is 1.8g/cm³, and the consumption of 1GWh is about 20 tons.
If the amount of binder (inactive material) is too high, the energy density and conductivity will be reduced. It is estimated that the total amount of PVDF used in the tesla 4680 battery will increase to about 6% of the mass fraction of the positive electrode material.
Due to the tight arrangement of the tabs, it is difficult to use metal die-cutting for all tabs, and in some schemes, the width of the tabs changes along the length of the pole piece, so laser die-cutting is more suitable. Laser welding equipment benefits from the tesla 4680 battery plan, and the major battery factories in the superimposed industry also plan to have production capacity, which is expected to usher in a rapid increase in volume.
The tesla 4680 battery scheme adds the welding of all tabs + current collectors. Compared with the 21700 battery, the number of solder joints is increased by more than 5 times, and the number of welding equipment is increased by 3 times. The difficulty of the welding process is greatly increased, and the equipment may change from the original pulse laser to the continuous laser, and the value will increase.
With the advantages of high efficiency, price and service, domestic shell production equipment is expected to gradually form a replacement in the stage of substantial expansion of lithium battery structural parts.