Messi Biology said, lithium-ion battery cathode material is a layer structure, lithium ions between the oxygen ion and metal ion layer, in the lithium ion de-embedding and embedding process to form the entire process of charging and discharging, a classical cathode material improvement method is to use other cations, such as trivalent aluminum ions, two-valent magnesium ions to replace the lithium ion part of the occupancy, after the lithium ion de-embedding These inert cations still play the role of supporting the structure, so doping is mainly an improvement method to improve stability at the structural level.
Another method is called cladding, before there is no cladding, the positive material and electrolyte will be in direct contact, because in the charging phase, the positive material surface will exist at high valence, this high valence cation will form irreversible SEI layer at the interface with the organic solvent of electrolyte or electrolyte R&D side reaction, leading to increased impedance, loss of active lithium ions and capacity decay.
If an inert oxide layer, such as the common aluminum oxide, zirconium oxide or magnesium oxide, is wrapped around the surface of the cathode, the direct contact between the cathode material and the electrolyte can be isolated, reducing the rise in interfacial impedance. The simplest one is called dry coating, which is more popular in low and medium nickel materials, using some inert oxides, such as alumina, magnesium oxide, zirconium oxide and cathode material, and then low temperature sintering treatment, between 300℃ and 500℃, can get a discontinuous coating structure on the surface. The effect of this coating is not particularly good and does not achieve complete coating.