imren rechargeable batteries 21700 lithium battery pack

Is The 21700 Battery Really Perfect? | IMREN Battery

The heart is the key to a person, and cars also have a "heart". The heart of a fuel car is an internal combustion engine, and the heart of an electric car is a battery. The quality of the "heart" determines the length of the vehicle.

Tesla has been active in the news at home and abroad for a long time since its birth. In the past, Tesla had insufficient capacity and could not be delivered on time. Later, Elon Musk said that he wanted to withdraw from the market in order not to be affected by the listing. All kinds of events have made Tesla hot.

With regard to the Tesla Model 3, many people have paid attention to its price and endurance. Few people have paid attention to its battery. On the contrary, the battery of the Model 3 is the highlight of the car. The Model 3 does not use the same 18650 battery as the model, but uses a better and more advanced 21700 battery.

Tesla launched the 21700 battery to lead the technical direction and to be forced by cost pressure.

In the battery field of electric vehicles, cylindrical lithium battery, soft bag battery and square lithium battery have been maintained. Tesla's 18650 battery and 21700 battery belong to cylindrical lithium battery, which is the earliest commercialized power battery with the highest degree of production automation and the lowest current cost.

According to the information disclosed by Tesla at present, under the existing conditions, the energy density of its 21700 battery system is about 300Wh/kg, which is about 20% higher than the 250Wh/kg of its original 18650 battery system. At the same time, according to the test data of Panasonic's power lithium battery monomer, the volume energy density of its 21700 battery is much higher than that of the 18650 battery monomer. The increase of energy density of single cell is much higher than that of group by 20%.

300Wh/kg should be the lithium ternary battery with the highest energy density among the current pure electric vehicles. The improvement of energy density directly increases the range.

Musk priced this car at $35000 at the beginning of the Model 3 project, aiming to reduce the price of Tesla.

If you still use the same battery system as the models, the cost will exceed, but if you reduce the battery pack on the model 3, the range will not meet the expectation. In the face of this situation, we can only find a battery with lower cost but no reduction in mileage.

Obviously, according to the current situation, Musk is very satisfied with the 21700 battery. First of all, the capacity of the single battery can reach 3~4.8Ah, with an increase of 35%. After grouping, the energy density still increases by 20%. Secondly, the cost of Tesla 18650 battery system is about 171 US dollars/Wh. After switching to 21700, the system cost of battery is about 155 US dollars/Wh, achieving a cost reduction of about 9%.

Tesla cannot start without the 18650 battery, but Musk is not as positive about the 18650 battery as we thought. He once publicly said on social media that the appearance of the 18650 battery is completely a historical accident. It is the standard of early products. Now only 21700 batteries can meet the requirements of electric vehicles for battery performance.

Is the 21700 battery really perfect?

Although the 21700 battery is better than the 18650 battery in terms of endurance and cost, it has defects in terms of battery cycle life.

Compared with the 18650 battery, the 21700 battery increases the physical size of the cylindrical cell. Although this will increase the energy volume, it will also reduce the cycle life and magnification of the cell. If the size is continuously increased, the safety and adaptability of the cell will be reduced, and the potential safety hazard and design difficulty of new energy vehicles will be increased invisibly. It is estimated that the cycle life will be reduced by about 20% for every 10% increase in capacity; The charge-discharge ratio will be reduced by 30-40%, and the cell will have a temperature rise of about 20%. The increase of battery temperature and the reduction of cycle life are fatal defects for electric vehicles.

In theory, compared with the 18650 battery, the 21700 battery has shorter life, longer charging time of the same capacity and lower security. However, if Tesla's BMS is excellent enough, these problems can also be optimized.

Write at the end

From the perspective of the national guidelines on the energy density of power lithium batteries, the energy density of single power battery will exceed 300Wh/kg in 2020, and the energy density of power battery system will reach 260Wh/kg. The current best 18650 battery can not meet this technical requirement, so selecting a better battery becomes the future choice.

The use of 21700 batteries will greatly help the weight, endurance and cost of Tesla electric vehicles. From now on, Tesla Model 3 will have surprises both in terms of endurance and price. These conditions may make it a dark horse.

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