Tesla may be the first to take a look at the 18650 battery as a new energy battery for electric cars. When developing batteries for electric vehicles, tesla tested many kinds of batteries and finally targeted the 18650 battery. What are the advantages and disadvantages of the 18650 battery?
First, a brief introduction to the 18650 cylindrical lithium ion is given:
The 18650 refers to the battery shape specification, which is a standard battery model set by SONY in order to save costs. 18 means 18mm in diameter, 65 means 65mm in length, and 0 means cylindrical.
18650 battery originally refers to nickel-metal hydride battery and lithium ion battery, because nickel-metal hydride battery is now used less, so now refers to lithium ion battery.The nominal voltage of a single unit of 18650 lithium ion battery is generally 3.6v or 3.7v.The minimum discharge termination voltage is generally 2.5 ~ 2.75V.The common capacity is 1200 ~ 3300mAh.
The 18650 cylindrical battery is the most mature and stable lithium ion battery widely used in electronic products.Over the years, Japanese manufacturers have accumulated a great deal of experience in the production process of 18650 batteries, which makes the consistency and safety of the 18650 batteries produced reach a very high level.
Cascade lithium-ion batteries, by contrast, are far from mature.Common have square battery, soft pack battery, even the size, size, pole ear position is not uniform.Battery manufacturers have the production process can not meet the conditions, most of the human control, battery consistency is not up to the level of 18650 batteries.If the battery consistency is not up to par, the management of a large number of batteries in series and in parallel will not allow each battery to perform better, and the 18650 cell can solve this problem.
In contrast to the more successful all-electric car, nissan's LEAF, which USES a cascade of lithium-ion batteries.This is because nissan has been cooperating with NEC for many years, and has accumulated profound accumulations in battery technology, and has considerable achievements in quality control.The LEAF's batteries come from AESC, a joint venture between nissan and NEC.
2. Cooling capacity
The battery is thin, has a large surface, and has a good thermal balance and cooling capacity, so the nissan LEAF is bold enough to use a passive thermal management system (essentially, no management), where the heat is carried away by the natural convection of the air.The LEAF went from a single battery to a battery module made up of four single batteries in two and two strings, to a battery pack made up of 48 battery modules in series without any thermal management system such as fans and coolant pipes. On the other hand, the tesla's 18650 battery is relatively small, and the temperature difference inside the battery is not too large during normal charging and discharging. However, the temperature difference of more than 6,000 individual batteries should also be kept within 5 ° c, which is very difficult.The complexity of tesla's thermal management system is greatly increased due to the small capacity of the 18650 battery.That said, the small capacity 18650 battery is not an optimal choice for cooling capacity alone.
3. About security
Because laminated lithium ion batteries are generally encapsulated with aluminum plastic film, which is thin in thickness and poor in mechanical strength. In extreme cases such as car collision, aluminum plastic film is easy to break and lead to safety accidents.That's why nissan is adding an aluminum casing to the four individual modules.
The car 18650 battery is usually steel shell, which is safer. As mentioned above, with the continuous improvement of 18650 battery production technology, the safety is also improving.Tesla has also put a lot of effort into responding to potential safety incidents with its 18650 battery.If the temperature of a single battery is too high, depending on the severity of the anomaly, the module in which the battery is located disconnects the circuit to prevent the accident from spreading.Due to the small monomer capacity, the severity of the accident will be low as long as no spreading occurs.
4. About cost
The 18650 lithium ion battery has the characteristics of large capacity, long life and high safety performance, and is favored by consumers because of its small size, light weight and convenient use. With the development of 18650 battery technology, the consistency and stability of the battery have reached a very high standard.As the first lithium ion battery, the 18650 battery is also the most mature and stable battery in the world, and still occupies a leading position in its application field.
Tesla, on the other hand, USES the 18650 battery, which can be built from previous production lines by manufacturers such as panasonic of Japan.Amid growing competition for the 18650 batteries used in consumer electronics, manufacturers such as panasonic have teamed up with tesla to upgrade their products, revamping old production lines to produce power batteries.Industrial production has a scale effect, when the scale of the production of products reaches an order of magnitude, the cost will be greatly reduced.A new energy vehicle requires thousands of 18650 batteries, so the cost of purchasing a single unit is manageable.
It can be said that using 18650 battery as the power source of car lithium cylindrical battery is the best choice at this stage. As battery technology matures, more new batteries for new energy electric vehicles may emerge.