With the rapid development of new energy vehicles in recent years, lithium batteries have also been raging. Power batteries have always been an important area of new energy vehicles. Whoever masters the power battery will have a new energy vehicle. Among the power batteries, the most eye-catching is the lithium-ion battery.
Lithium-ion batteries have a high energy density, and their capacity is 1.5 to 2 times that of nickel-hydrogen batteries of the same weight, 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 made them widely used in the field of new energy vehicles.
Today's widely used cylindrical lithium-ion batteries have 18,650 batteries and 21,700 batteries.
The 18650 battery originally referred to the nickel-hydrogen battery and the lithium-ion battery. Since the nickel-hydrogen battery is now less used, it is now referred to as a lithium-ion battery. 18650 is the originator of lithium-ion battery--a standard lithium-ion battery model that Japan SONY Company set in order to save cost. Among them, 18 means diameter 18mm, 65 means length is 65mm, 0 means cylindrical battery. The common 18650 battery has a ternary lithium ion battery and a lithium iron phosphate battery.
Speaking of the 18650 battery, Tesla had to be mentioned. Tesla tested many types of batteries when developing electric vehicle batteries, but finally locked the target at 18650 batteries and used 18650 batteries as new energy electric vehicle batteries. Technical route. It can be said that Tesla is able to have the performance of the traditional fuel car, in addition to the motor technology, but also benefit from Tesla's advanced battery technology. So why did Tesla choose the 18650 battery as its power source?
Before entering the field of new energy vehicles, 18650 batteries have been widely used in electronic products. It is the earliest, most mature and stable lithium-ion battery. After years of experience, Japanese manufacturers have accumulated 18650 batteries in consumer products. Advanced technology is excellently used in the field of automotive batteries. Panasonic is one of the world's largest battery technologies and the largest companies. Compared with other manufacturers, Panasonic has the least defects and large scale, and it is easy to select a consistent battery.
In contrast, other batteries, such as stacked lithium-ion batteries, are far from mature, and many products cannot be unified in size, size, etc., and the production processes possessed by battery manufacturers cannot meet the conditions. In general, the battery's consistency does not reach the level of 18,650 batteries. If the consistency of the battery does not meet the requirements, the management of a large number of battery strings and battery packs formed in parallel will not allow the performance of each battery to be better, and the 18650 battery can solve this problem well.
High security performance
18650 lithium battery has high safety performance, no explosion, no burning; non-toxic, non-polluting, RoHS-certified; and high temperature resistance, discharge efficiency of 100% under 65 degrees.
The 18650 battery is generally packaged in a steel case. In extreme cases such as a collision of a car, the safety accident can be minimized and the safety is higher. In addition, the size of each battery unit of the 18650 is small, and the energy of each unit can be controlled to a small range. Compared with the use of a large-sized battery unit, even if a unit of the battery pack fails, it can be reduced. The impact of the failure.
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 a 18650 lithium battery pack, the 18650 lithium battery pack can break through 5000mah. It has a capacity of 1.5 to 2 times that of a nickel-hydrogen battery of the same weight and has a very low self-discharge rate. The energy density of the 18650 cell is currently able to reach 250Wh/kg, meeting the requirements of Tesla's cruising range.
Low cost, high-cost performance
The 18650 lithium battery has a long service life, and the cycle life can reach more than 500 times in normal use, which is more than twice that of ordinary batteries. The 18650 product has a high level of technology maturity, structural design, manufacturing technology and manufacturing equipment, as well as the proven technology of the 18650 module, which reduces its operating costs and maintenance costs.
At present, the 18650 battery, which has been widely used, has a history of many years. Although it is more mature than other types of battery technology, it still faces problems such as high heat production, complex group formation, and inability to achieve fast charging. In this context, the 21700 cylindrical ternary battery came into being.
On January 4, 2017, Tesla announced that it has started mass production of the new 21700 battery jointly developed with Panasonic, and emphasized that it is the highest energy density and lowest cost battery in the current mass production battery.
The battery 21700 is a model of a cylindrical battery, specifically: 21 - the outer diameter of the cylindrical battery is 21 mm; 700 - the height of the cylindrical battery is 70.0 mm.
This is a new model developed to meet the requirements of electric vehicles for longer mileage and to improve the effective utilization of vehicle battery space. The same material, 21700 compared to the common 18650 cylindrical lithium battery, the capacity can be more than 35%.
The new 21700 has four significant advantages:
(1) The battery cell capacity is increased by 35%. Taking the 21700 battery produced by Tesla as an example, after switching from the 18650 model to the 21700 model, the battery cell capacity can reach 3 to 4.8 Ah, a significant increase of 35%.
(2) The energy density of the battery system is increased by about 20%. According to the data disclosed by Tesla, the energy density of the 18650 battery system used in the early stage was about 250Wh/kg. Later, the energy density of the 21700 battery system produced was about 300Wh/kg. The volumetric energy density of the 21700 battery was higher than the original 18650. Nearly 20%.
(3) The cost of the system is expected to drop by about 9%. From the battery price information disclosed by Tesla, the 21700 battery power lithium battery system is priced at $170/Wh, while the 18650 battery system is priced at $185/Wh. With the 21700 battery on the Model3, only the battery system cost can be reduced by about 9%.
(4) The weight of the system is expected to drop by about 10%. The overall volume of the 21700 is greater than 18650. As the monomer capacity increases, the energy density of the monomer is higher. Therefore, the number of battery cells required under the same energy can be reduced by about 1/3, which will reduce the difficulty of system management and reduce the battery. The number of metal structural parts and electrical accessories used in the package further reduces the weight of the battery. After switching to a new 21700 battery, Samsung SDI found that the system was 10% lighter than current batteries.
Maintaining the high reliability and stable performance of the 18650 battery, the performance of the 21700 battery is greatly improved in all aspects than the 18650. In addition, compared with other battery models, the 21700 is similar to the more mature 18650 battery in terms of battery raw material selection, manufacturing process and technical process, so most of the 18650 and 21700 production lines are compatible.
The pursuit of high specific energy in power batteries has become an irreversible trend, and many battery companies have begun to turn their attention to the layout of 21700 batteries. Some companies' production lines are imported from abroad, but they are assembled on their own, so they can convert 18650 to 21700 at a lower cost.