For the 18650 batteries as a new energy electric vehicle battery technology line, we may first turn to Tesla. Tesla in the development of electric vehicle battery, tested a lot of types of batteries, but the final target locked in the SC30 18650 Battery, then what are the advantages and disadvantages of 18650 batteries?
First of all, 18650 cylindrical lithium ion batteries to do a brief understanding
18650 is actually the shape of the battery specifications, Japan SONY company was to save costs and set a standard battery model, of which 18 said the diameter of 18mm, 65 said length of 65mm, 0 for the cylindrical battery. SC30 18650 Battery refers to the original nickel-metal hydride batteries and lithium-ion batteries, nickel-metal hydride batteries are now less used, so now refers to the lithium-ion battery. 18650 lithium-ion battery single standard voltage is generally 3.6V or 3.7V, the minimum discharge termination voltage is generally 2.5 ~ 2.75V, common capacity of 1200 ~ 3300mAh.
SC30 18650 Battery is the earliest, most mature, most stable lithium-ion battery, widely used in electronic products. Over the years, the Japanese manufacturers in the SC30 18650 Battery production process has accumulated a lot of experience, making the output of the SC30 18650 Battery consistency, security has reached a very high level.
In contrast, the stacked lithium-ion battery is far from mature, common with a square battery, soft battery, and even size, size, ear and so are not unified, the battery manufacturers have the production process can not meet the conditions , Most of the human-based control, the battery consistency of less than SC30 18650 Battery level. If the battery consistency does not meet the requirements, a large number of battery strings, parallel to the formation of the battery management will not be able to make each battery better performance, and 18650 batteries can solve this problem.
In summary, the SC30 18650 Battery has a small capacity and requires a large number of monomers (Model S has 7104), but the consistency is good; the capacity of the stacked battery can be made large (20 Ah to 60 Ah ), The number of monomers can be reduced, but the consistency is poor. In contrast, it is difficult at this stage to invest a lot of manpower and resources together with the battery supplier to improve the production process of laminated batteries. Therefore, in the development of Roadster and Model S, Tesla's only option is to buy batteries from the market, self-developed battery system. The development of a set of more than 6,000 modules to manage a good battery system and the development of a more than 200 series of poor consistency of the battery system, compared to the former technical difficulty should be lower. Even if the number of single cells increased, but if the performance of these batteries is reliable, it is easy to manage some.
Compared to another very successful pure electric vehicles, Nissan LEAF, which uses a laminated lithium-ion battery. This is because Nissan and NEC for many years, in the battery technology has accumulated very deep, in the quality control has considerable skill. LEAF battery from AESC - Nissan and NEC joint venture.
Compared to the United States, Japan, and other different regions of the car manufacturers in the development of electric vehicles and battery manufacturers of vertical and horizontal is a very interesting thing.
On the cooling capacity
Laminated battery thickness is thin, the surface is large, soaking, cooling capacity are good, so Nissan LEAF very boldly using a passive thermal management system (in fact, is not management!), By the natural convection of the air to take away the heat.
From left to right, LEAF from the monomer, to four single battery two strings and two strings of the battery module, and then by the 48 battery modules in series composed of the battery as shown below:
It can be seen that there is no thermal management system on the battery pack without any fan, coolant piping. Probably this is no strokes have strokes.
In turn, look at Tesla, SC30 18650 Battery head is relatively small, in the normal charge and discharge the internal battery temperature difference will not be too much. However, the temperature difference of more than 6,000 cells should also be kept within 5 ° C, which is a very difficult task. But Tesla did it. How did you do it? What are the advantages of Tesla's battery management system (BMS) compared to other electric vehicles?
As shown above, these pipes are coolant flow path, the flow channel evenly distributed in the middle of the battery module, allowing each cell can be a good contact with the water pipe, so that each battery in the cooling away the heat is almost The same temperature difference can be effectively controlled in a very small range.
To sum up, due to the use of a small capacity of SC30 18650 Battery, Tesla's thermal management system complexity is greatly increased. In other words, if the use of small capacity SC30 18650 Battery from the cooling capacity considerations, is not the best choice.