What are the types and characteristics of lithium batteries?
Lithium manganate, as a kind of lithium battery material with long service history, has high safety, especially strong anti-overcharge ability, which is a prominent advantage. Because of the good structural stability of lithium manganate, the amount of cathode materials need not exceed the negative pole too much in the design of the core. In this way, the number of active lithium ions in the whole system is small, and after the negative electrode is filled, there will not be too many lithium ions in the positive electrode. Even if there is overcharge, there will not be a large number of lithium ion crystallization in the negative deposition. Therefore, the overcharge resistance of lithium manganate is * in common materials.
In addition, the material is cheap, and the production process requirements are relatively low. It is a cathode material which has been widely used earlier.
But it also has obvious defects. The high temperature properties of spinel lithium manganate are not good. Oxygen defect makes the core prone to capacity attenuation at high voltage stage. At the same time, the same capacity attenuation can be caused by recycling at high temperature. The reason lies in the trivalent manganese ion which causes disproportionation effect. The main way to prevent high temperature attenuation is to reduce trivalent manganese.
Lithium manganate, limited by its high temperature performance, is generally not used in high-power or high ambient temperature occasions, such as high-speed passenger cars, plug-in mixing and so on. Lithium manganate is seldom used as power. But for electric buses, city logistics vehicles, etc., lithium manganate can be fully qualified.
Lithium iron phosphate
The advantages of lithium iron phosphate are mainly embodied in its safety and cycle life. The main determinant is the olivine structure of lithium iron phosphate. Such a structure, on the one hand, leads to lower ion diffusion ability of lithium iron phosphate, on the other hand, it also has better high temperature stability and good cycling performance.
Lithium iron phosphate has obvious shortcomings, such as low energy density, poor consistency and poor low temperature performance.
Low energy density is determined by the chemical properties of the material itself. A lithium iron phosphate macromolecule can only accommodate one lithium ion.
Consistency, especially poor batch stability, is not only related to the level of production management, but also to its own chemical properties. Lithium iron phosphate is one of the most difficult cathode materials for lithium batteries. The high difficulty of consistency and uniformity of chemical reaction brings another problem. Iron and iron impurities in lithium iron phosphate materials always exist, which brings potential failure to batteries.
Lithium iron phosphate battery, because of its high safety, is still the main power lithium battery for electric vehicles in China, although the energy density part affects its scope of use. In particular, the use of lithium iron phosphate batteries is mandatory under the state policy for buses involving the safety of a large number of people's lives.
Ternary lithium cathode material, which combines the advantages of LiCoO 2, LiNiO 2 and LiMnO 2, forms a synergistic effect in the same core, takes into account the three requirements of material structure stability, activity and low cost. It is one of the three main cathode materials with energy density* Its low temperature effect is also better than that of lithium iron phosphate battery.
Among the three elements, the higher the content of Ni, the higher the energy density of the core, and the lower the safety of the core. In practical applications, the proportion of the three materials in the core has been changing with time. The pursuit of energy density is getting higher and higher, so the proportion of Ni is getting higher and higher.
The shortcomings of ternary materials are safety. In the process of thermal runaway, the by-products of ternary materials contain a large amount of gas, which greatly improves the risk of accidents and the ability to spread. Secondly, the cyclic life of ternary materials is also a bottleneck, which can not reach the level of lithium iron phosphate at present; *, because of the special microstructure of ternary materials, it is not suitable for high pressure compaction operation, so the popular processing method of increasing energy density is not applicable to it.
The market share of ternary materials is gradually expanding, mainly driven by the pursuit of vehicle mileage. In order to catch up with or even surpass the endurance of fuel vehicles, electric vehicles must be equipped with as much power as possible in a limited space, which makes energy density particularly important. Last year, the state introduced a subsidy policy to stimulate the research and development of high energy density cores. It set a threshold for energy density, and there will be no subsidy if it can't get in. From vehicle factory to pack factory to battery manufacturer, every link must conform to the general trend of improving energy density of products, so ternary lithium batteries have been more and more applied. The improvement of the safety performance of the battery itself and the ability of system monitoring to deal with accidents will also promote the expansion of the ternary lithium battery market.