Core tip: Before entering the field of new energy vehicles, 18650 batteries have been widely used in electronic products, is the earliest, most mature and stable lithium-ion batteries, after years of experience, Japanese manufacturers will 18650 batteries in consumer products accumulated advanced technology is extremely well applied to the field of automotive batteries. Panasonic is one of the world's largest battery technology and scale, compared to other manufacturers, the least defective products, larger scale, but also easy to select from a good consistency of the battery.
With the hot development of new energy vehicles in recent years, lithium batteries have also been on fire. Power battery has always been an important area of new energy vehicles, who has mastered the power battery, who has mastered the new energy vehicles. And in the power battery, the most attention is the lithium-ion battery.
Lithium-ion battery energy density is very high, its capacity is the same weight of nickel-hydrogen batteries 1.5 to 2 times, and has a very low self-discharge rate. In addition, lithium-ion batteries have almost no "memory effect" and do not contain toxic substances, these advantages of lithium-ion batteries have been widely used in the field of new energy vehicles.
Today's more widely used cylindrical lithium-ion batteries are 18650 batteries and 21700 batteries.
18650 battery:
18650 battery originally refers to NiMH and Li-ion batteries, as NiMH batteries are now less used, so now more refers to Li-ion batteries. 18650 is the originator of Li-ion batteries - Japan SONY company in order to save costs and set a standard Li-ion battery model, where 18 means the diameter of 18mm, 65 means the length is 65mm, 0 means the cylindrical battery. Common 18650 batteries are ternary lithium-ion batteries and lithium iron phosphate batteries.
About 18650 battery and 21700 battery concept and its advantages in detail
Speaking of 18650 battery, we have to mention Tesla, Tesla in the electric car battery development, testing many kinds of batteries, but finally locked the target in the 18650 battery, 18650 cells as a new energy electric car battery technology route. It can be said that the reason why Tesla can have no less than the traditional fuel car performance, in addition to the electric motor technology, but also thanks to Tesla's advanced battery technology. So why did Tesla choose 18650 battery as its power source?
Advantages
Mature technology and high consistency
Before entering the field of new energy vehicles, 18650 battery has been widely used in electronic products, is the earliest, most mature and stable lithium-ion battery, after years of experience, Japanese manufacturers will 18650 battery in consumer products accumulated advanced technology is extremely well applied to the field of vehicle batteries. Panasonic is one of the world's largest battery technology and scale, compared to other manufacturers, the least defective products, larger scale, but also easy to select from the good consistency of the battery.
In contrast, other batteries such as laminated lithium-ion batteries are far from mature, and many products cannot even be unified in terms of size and dimensions, and the production processes that battery manufacturers have cannot meet the conditions. In general, the consistency of the battery does not reach the level of 18650 batteries. If the consistency of the battery does not meet the requirements, the management of the battery pack formed by a large number of batteries in series and parallel will not allow each battery to perform better, and 18650 cells can solve this problem very well.
High safety performance
18650 lithium battery has high safety performance, no explosion, no combustion; non-toxic, non-pollution, certified by RoHS trademark; and good high temperature resistance, discharge efficiency up to 100% at 65 degrees.
18650 batteries are generally encapsulated in steel cases, which can better minimize the occurrence of safety accidents in extreme situations such as car collisions, and have higher safety. In addition, the small size of each 18650 battery cell allows the energy of each cell to be controlled in a smaller range, which reduces the impact of failure even if a cell in the battery pack fails compared to using a large size battery cell.
High energy density
The capacity of 18650 lithium battery is generally between 1200mah and 3600mah, while the general battery capacity is only about 800mah, if combined into 18650 lithium battery pack, the 18650 lithium battery pack can exceed 5000mah. its capacity is 1.5 to 2 times of the same weight of NiMH batteries, and has a very low self-discharge rate. The energy density of 18650 cells can reach 250Wh/kg to meet the high range requirements of Tesla.
Low cost, high cost performance
18650 lithium battery has a long service life of more than 500 cycles in normal use, which is more than twice as long as ordinary batteries. 18650 products have a high degree of technical maturity, structural design, manufacturing technology and manufacturing equipment, as well as the technology of 18650 modules are very mature, which makes its operating costs and maintenance costs lower.
The 18650 battery has been widely used for many years and is relatively mature compared to other types of batteries, but it still faces problems such as high heat production, complex group formation, and inability to achieve fast charging. In such a context, 21700 cylindrical ternary batteries came into being.
On January 4, 2017, Tesla announced the start of mass production of the new 21700 battery jointly developed with Panasonic, and stressed that this is the highest energy density and lowest cost of the currently available mass-produced batteries.
21700 battery:
Battery 21700 is a cylindrical battery model, specifically: 21 - refers to the outer diameter of the cylindrical battery is 21mm; 700 - refers to the height of the cylindrical battery is 70.0mm.
This is a new model developed to meet the requirements of electric vehicles for longer range and to improve the effective utilization of vehicle battery space. With the same material, the 21700 can have more than 35% higher capacity compared to the common 18650 cylindrical lithium battery.
The new 21700 has four significant advantages.
About 18650 battery and 21700 battery concept and its advantages in detail
(1) 35% increase in the capacity of the battery monomer. Take Tesla's 21700 battery for example, after switching from 18650 model to 21700 model, the battery capacity can reach 3 to 4.8Ah, a significant increase of 35%.
(2) Battery system energy density increased by about 20 percent. Tesla disclosed data, the early use of 18650 battery system energy density of about 250Wh / kg, and later its production of 21700 battery system energy density of about 300Wh / kg, 21700 battery volume energy density than the original 18650 nearly 20% higher.
(3) The cost of the system is expected to decline by about 9%. From the analysis of the battery price information disclosed by Tesla, the power lithium battery system of 21700 battery is priced at $170 / Wh, while the 18650 battery system is priced at $185 / Wh. After using 21700 battery in Model 3, the cost of the battery system alone can be reduced by about 9%.
(4) The weight of the system is expected to drop by about 10%. 21700 overall volume is larger than 18650, and with the increase in the capacity of a single cell, the energy density of a single cell is higher, so the number of cells required for the same energy can be reduced by about 1/3, which will reduce the difficulty of system management and also reduce the number of metal structural parts and electrical accessories used in the battery pack, which further reduces the weight of the battery. After Samsung SDI switched to a new set of 21700 cells, the system was found to be 10% lighter than the current cells.
Maintaining the high reliability and stable performance of the 18650 type battery, the 21700 battery performance is significantly improved in all aspects over the 18650. In addition, compared to other battery models, the 21700 is similar to the more mature 18650 battery in terms of battery raw material selection, production process and technology flow. Therefore, most of the production lines of 18650 and 21700 can be compatible, and some companies are more prudent to make articles on the production line, and close the production line to 21700 and 18650 compatible.
The pursuit of high specific energy of power batteries has become an irreversible trend, many battery companies began to turn their attention to the layout of 21700 batteries. Some companies import production lines from abroad, but assembly is carried out by themselves, so they can invest less cost to achieve the conversion of 18650 to 21700.
