Then, why is Musk eager to change the battery specifications of Tesla products, and why does 2 1700 battery "fall out of favor" in such a short time and become an abandoned child in Musk's eyes? All this has to start from two aspects: battery thermal management and cost.
Spontaneous combustion, spontaneous combustion or spontaneous combustion
Tesla's news has never lacked the topic of spontaneous combustion. Tesla seems to be an unstable factor both at home and abroad, on the road and in the underground garage. Which Tesla model is produced by 12-14? S is the most famous.
In fact, Tesla was recently accused of spontaneous combustion. According to some data, the Model has been mass-produced as early as 20 12 years. S, Tesla has known that there is a problem with battery heat dissipation, which may even lead to fire, and today, eight years later, this problem has not been solved! This evidence came from Tesla's internal mail, which caused a great sensation in North America after being exposed. Shortly after the email was exposed, Tesla's share price fell sharply. Two months after this incident, Musk announced that Tesla would use the 4680 battery.
The email shows that Tesla has commissioned three companies to test and investigate the battery cooling configuration, and the results all show Model? There is a problem with the end connection fittings of the S cooling system. Tesla's battery cooling system is realized by adding an external coolant pipe to the battery. However, the end joint of the pipe is made of aluminum, which is low in strength and easy to wear, resulting in leakage of coolant, short circuit of automobile battery and fire, or leaving flammable residues inside the battery.
Public opinion pointed out that Tesla deliberately concealed the safety of battery packs and let immature models? The forced listing of S eventually led to spontaneous combustion in many parts of the world.
In response to this result, Tesla officials have not yet expressed their views, but many Model? S users have started to complain. They believe that the products they buy have objective defects. Although there will be no 100% problem, who can guarantee that bad luck will not happen to them? Models? The 18650 battery equipped with S has poor temperature control performance and the possibility of series combustion, which is the main reason for many car owners to worry.
Because the battery pack composed of 18650 cells is small, in order to ensure the compactness of the battery pack, the gap between the cells is relatively small, which leads to the difficulty in arranging heat conducting materials and increases the cost of BWS "battery management system". After all, it is very troublesome to balance the voltages of so many batteries.
After 2 1700 battery was adopted by Tesla, this shortcoming was effectively improved. Under the same capacity, not only the number of batteries is reduced, but also the gap between batteries is larger, and heat conducting materials can be better arranged between batteries to balance the heat of the whole battery pack. However, the 2 1700 battery also has some defects: the 2 1700 battery pack does not shrink in size, and the flat heat dissipation scheme cannot be realized. Because the 2 1700 battery pack is still a little short, it is still arranged in a two-layer stacked manner in Tesla's battery pack, which is still flawed from the point of view of thermal management. In addition, due to the limitation of single battery capacity, the charging power of 2 1700 cannot be further broken, which is also one of the factors restricting the energy replenishment rate of electric vehicles.
Therefore, considering the cost and performance of all aspects, Tesla adopted a higher 4680 battery cell, realizing a single-layer layout, making it possible for a single-layer flat plate to dissipate heat.
The principle of flat heat dissipation of battery pack is to fix the copper anode material of lithium battery directly on the bottom plate. Because copper is a good heat conducting material, the heat of each battery can be conducted to the bottom plate, which plays a role in balancing the battery temperature and cooling. Single-layer flat layout can greatly reduce the use of heat conductive materials for battery packs, which is very attractive in cost.
The size and structure of the 4680 battery pack are more compact than before.
Vehicle performance improvement
After the cooling mode is changed, Tesla can pack the battery more tightly, and the volume of the battery pack can also be significantly reduced. This is an advantage because the mass will be more concentrated in the center of the vehicle, which reduces the moment of inertia and improves the handling of the vehicle. Although the electric car has a low center of gravity because the battery is arranged on the floor, it does not mean that it is conducive to maneuverability. The ideal center of gravity distribution of a car must be to concentrate the weight in the middle of the car, and too many battery packs make the weight scattered under the whole car, which is not conducive to the dynamic transformation of the chassis of the car. This time Tesla will shrink the battery pack, which can effectively improve the short board of electric vehicles.
In addition, because the single battery becomes larger, the anode and cathode can bear a larger voltage difference, and the charging power of the battery is much higher than before. The advantages are shorter charging time and lower temperature rise during charging.
The new 4680 electrodeless battery is at 10%? The initial internal resistance at SOC is 3 mOhms, 80%? The SOC gradually drops to 2 milliohms. The resistance of 2 170 battery is 23/20/20 mOhms. We can see that the resistance of the battery is reduced to about 10%. In contrast, the technology marked by Tesla in the patent application can be reduced by 5-20 times.
Comparison of charging power and time between 2 1700 and 4680 batteries
Cheshu review
Through technical analysis, it can be seen that Tesla frequently changed the battery specifications in order to improve the defects in the products. In contrast, the Tesla products you buy now are not perfect.
In addition, the innovation of Tesla battery mainly comes from the innovation of peripheral non-core structure, for example, by increasing the size of battery monomer and relatively reducing the proportion of shell. The real improvement of energy density must and can only be achieved through material innovation. The innovation of production technology can reduce the cost, but it has little effect on the energy density. The innovation of anode and cathode materials will bring a leap in the performance of lithium battery electrochemical system, but it needs long-term scientific research and accumulation.
This article comes from car home, the author of the car manufacturer, and does not represent car home's position.