Gold, silver and silver are indeed a good season for recruitment. Not long after we sent out the recruitment article (I clicked on the resume), we welcomed a new colleague in operations.
After the new colleague who was extremely healthy found that everyone did not have the habit of napping at noon, "too rolled" became her mantra.
Please, our company did not go to work until 10 o'clock, where can I sleep at noon.
If you really want to talk about "volumes", you have to be the bosses.
Now, it is nothing new for the bosses of major technology companies to show their faces for their own products.
However, recently, Lucid Motors CEO Peter Rawlinson has raised this standard a lot.
As a former chief engineer of Tesla's Model S, Rawlinson is undoubtedly a manager of the technology flow.
Through a battery technology communication meeting, he fully showed everyone what is called "the soul painting that does not understand technology is not an excellent CEO".
As the world's longest EPA production car, what are the little secrets of Lucid Air's battery pack?
High voltage = high efficiency
Lucid Air Grand Touring is equipped with a 112 kWh battery pack, how much energy is 112 kWh?
Rawlinson gives us a very vivid example.
"We picked up a 100-gram apple from the ground and placed it on a table 1 meter above the ground, a process that consumed 1 joule of energy. And the 112 kWh battery pack, which translates to about 400 million joules, allows us to do 400 million apple picking moves."
How is the 112 kWh parameter determined?
Rawlinson first explained the relationship between energy and power, and introduced us to a very clear and easy-to-understand calculation process.
About 10 years ago, electric cars consumed about 330 Wh of electricity for every mile they traveled, as technology advanced. Today, the power consumed by electric cars traveling 1 mile has dropped to 250 Wh.
If you want an electric car to have a range of 400 miles, you need a 100 kWh battery pack.
We continue to calculate that the 2170 battery used by the Lucid Air has about 17-18 Wh of charge per cell, and it takes about 6000 2170 cells to form a 100 kWh battery pack.
This is the basis for the design of the Lucid Air battery pack, 6600 2170 cells.
But stacking batteries, everyone will, for an electric car with the longest EPA life in the world, of course, there are some different skills.
For example, at this stage, the battery pack voltage of electric vehicles is generally around 400V, and Lucid uses a high voltage of 924V.
As for why, Rawlinson explains to us the theoretical support behind the selection of high-voltage batteries with several very basic physical formulas.
Ohm's Law
Voltage U = Current I × Resistance R ------------
Electrical power calculation formula
Power P = Voltage U × Current I ------------
Bring the formula into the formula, you can get it
P = I^2 × R
This is also the formula for calculating the heat generation of the system resistance.
And this calorific is useless to us, and we hope that the smaller it is, the better.
According to P = I^2 × R, the smaller the current I, the smaller the power P of the amount of heat generated.
The question is, how to reduce the current while keeping the total power of the system unchanged?
As can be seen from P = U × I, when power P remains constant, we increase the voltage U, and the current I decreases.
Taking Lucid Air as an example, Lucid increases the battery pack voltage to twice, the current will become one-half of the original, and the heating power will be reduced to a quarter of the original.
Therefore, high voltage means higher drive efficiency, which is a big reason why Lucid chose high voltage battery packs.
How to build a 924V voltage
The full voltage of a 2170 cell is 4.2V, so how can the 4.2V be boosted to 924V?
First of all, let's introduce a knowledge point of battery string paralleling. The batteries are connected in series to increase the output voltage; the batteries are connected in parallel to increase the output current.
Rawlinson took 3 flashlights of different lengths and voltage levels to illustrate.
These flashlights use a 1.5V No. 1 dry cell as an energy source. Plug 3 dry batteries into the flashlight in series to get a 4.5V voltage flashlight; 4 dry batteries in series to get 6V; 6 dry batteries in series to get 9V.
Similarly, if a 4.2V 2170 cell wants to boost to 924V, it needs to connect 220 2170 cells in series.
But if you connect the battery in series like a flashlight, 220 2170 cells are connected in series end to end, and the length is almost 15 meters. This length is obviously inappropriate to put on a sedan.
In fact, in order to balance the voltage level and current output capability, Lucid divides 6600 2170 cells into 22 groups, and every 300 cells form a battery module.
In a battery module, 300 2170 cells were divided into 10 groups on average. Every 30 cells are connected in parallel with each other to form a "Group".
10 groups in a module are connected in series to get a 42V output voltage.
In order to make the 300 cells "vertical and parallel" to form a battery module, Lucid made two efforts to do this.
One is to make the positive and negative poles of the 2170 battery cell at the same end of the cell.
This design is actually mentioned in the previous article on the interpretation of Tesla's patent, and interested partners can click here to jump to view. The advantage of this is also obvious, all the cells only need to be placed vertically upwards, and the string parallel between the cells can be completed through the positive and negative busbar connectors.
The second is battery connection technology.
When referring to these connectors, Peter mentions a very fashionable word, "one-piece die casting". Yes, these connectors are manufactured by all-in-one die-casting technology.
At the same time, Rawlinson also explained in great detail why aluminum was chosen as the material for the connector. The main function of the connector is to conduct electricity, the smaller the resistance of the connector, the lower the heat, the higher the efficiency. From this point of view, we should choose the metal with the lowest resistance - silver. But the price of silver is too expensive, combining cost and conductivity factors, copper has become the first choice. But copper is heavier.
Combining the three factors of conductivity, cost and weight, aluminum has become the best choice for connector materials.
When soldering the battery cells to the busbar connectors, Lucid also has his own careful thoughts.
In order to ensure safety, the industry's usual practice is to weld the positive and negative electrodes of the battery cell to the busbar connector with a fuse. If a single cell is short-circuited, the fuse will instantly fuse, disconnecting the cell from the battery module, thereby ensuring the safety of the battery module.
But Lucid found that for a single cell, using two fuses was completely unnecessary. First, as long as one of the positive and negative poles of the battery is disconnected, the connection between the cell and the battery module is disconnected; second, the fuse is compared with the ordinary connection material, and the fuse has a larger resistance and lower efficiency.
Therefore, Lucid chose to use fuse welding on the positive side of the battery and thicker ordinary conductors on the negative electrode.
After talking about a single battery module, and then connecting the 22 battery modules in series, we get a 924V output voltage.
At this point, to summarize, Lucid used a 220 series, 30 parallel connection method to form 6600 2170 cells into a 112 kWh, 924V battery pack.
Different cooling scheme
Rawlinson mentioned that the commonly used battery module cooling scheme in the industry is to set the cooling line between the cells, but Lucid believes that this cooling method is extremely inefficient, for the following two reasons.
1. Cell heat problem
The battery cell emits heat in all directions when working, but the heat conduction efficiency is not the same in different directions. Lucid found that the heat of the battery cell is much more efficient in the longitudinal direction than in the lateral direction.
As a result, the heat dissipated by the operation of the battery cell will accumulate at the bottom of the cell.
2. Efficiency issues
The cooling line arranged between the cells, first, the contact area between the cooling line and the battery is not as large as in the ideal state, in fact, the contact area between them is not continuous, but intermittent.
Second, the cooling line will occupy the space of the battery module, and the most direct consequence is that in the same volume of the battery module, the number of cells that can be accommodated will be reduced, thereby reducing the energy density of the battery module.
Based on the above two points, Lucid has adopted a completely different cooling scheme from Tesla. Lucid eliminated the cooling line between the cells and instead installed a cooling plate at the bottom of the battery module.
The benefits of this design are as follows:
1. Efficient heat dissipation
As mentioned earlier, the heat of the battery will eventually accumulate at the bottom of the cell, and it is undoubtedly the most efficient to take away the heat directly from the bottom of the cell. Secondly, the bottom of the battery cell is a plane, and the contact surface of the heat dissipation plate is also a plane, so that the two planes can be easily and closely contacted together, which further improves the efficiency of heat dissipation.
2. Increase energy density
There is no heat dissipation line barrier between the cells, and the cells and the cells can be arranged at a tighter distance. That is, the energy density of the battery module will be higher.
3. Easy to manufacture
The cooling plate is a combination of two pieces of stamped aluminum. Stamping is a production process that is very conducive to large-scale mass production. This means that this cooling plate has a lower cost, lower production difficulty, better consistency and reliability.
Because Peter Rawlinson was once the chief engineer of Tesla Model S, because Lucid Air and Tesla Model S have so many similarities in technical structure, I was once told that Lucid Air was just a shelled Tesla Model S.
But in fact, by understanding the technical details, Lucid actually has his own soul.
From the battery pack alone, we can feel that Lucid implements the energy-saving and efficient design concept from the top down.
This may also be one of the mysteries of Lucid Air's first EPA endurance.
The Lucid Air is a good car, but the biggest obstacle it is now challenging Tesla is the lack of production.
According to the previous 2021 financial report released by Lucid, due to supply chain problems such as chips, Lucid's 2022 production expectations have been reduced by 40%, and the annual output in 2022 is only enough to meet half of the current scheduled orders in Lucid's hands.
This also means that the Lucid Air that Teacher Chang has in mind should not be able to buy this year.
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(Please remember to pay attention to our video number, a large wave of new car official announcements)