The cathode material of lithium ion batteries is an important part of rechargeable lithium batteries. It not only needs to be used as an electrode material, but also needs to participate in electrochemical reactions. It must have stable safety performance and sustainable charging and discharging. Therefore, we need to consider comprehensively when designing and selecting cathode materials for lithium-ion batteries. The ideal lithium battery cathode material should meet the following conditions:
① Good safety performance: The material is required to have high chemical stability, and it is not easy to have irrelevant reactions with other substances in the battery during normal storage or during charging and discharging, and it also needs to have thermal stability;
②Large capacity: the cathode material is required to have a low relative molecular mass, and a large amount of lithium ions can be inserted into its host structure
③Good charge and discharge high rate performance: high diffusion rate inside and on the surface of the electrode material is required;
④The material itself has high potential: in this way, a large potential difference can be formed with the negative electrode material, resulting in a battery design with high energy density. At the same time, the insertion and extraction of charged ions has little effect on the electrode potential, and the charge and discharge process will not be over Large voltage fluctuations will not adversely affect other electrical systems in the system.
⑤Easy to prepare, environmentally friendly, and inexpensive;
Lithium-ion battery cathode materials are generally lithium-containing transition metal oxides and polyanionic compounds. Because transition metals often have multiple valence states, they can maintain the electrical neutrality of the lithium ion insertion and extraction process; another lithium-intercalation compound has a higher electromotive force than lithium, which can ensure that the battery has an open circuit voltage. Generally speaking, the transition metal oxide is larger than the transition metal sulfide with respect to the potential of lithium.
In transition metal oxides, the order of potential relative to lithium is: 3d transition metal oxide>4d transition metal oxide>5d transition metal oxide; and in 3d transition metal oxide, Co, Ni, Mn are particularly contained. The element is mainly lithium metal oxide.
Commercial lithium battery cathode materials commonly used in daily life generally use lithium-intercalating compounds, such as LiCoO2, with a theoretical specific capacity of 274mA·h·g-1 and an actual specific capacity of about 146mA·h·g-1. Li(NiCoMn)O2 ternary material, its theoretical specific capacity is similar to LiCoO2, but the actual specific capacity is slightly different according to the composition.
The theoretical specific capacity of LiMn2O4 material is 148mA·h·g-1, the actual specific capacity is 115mA·h·g-1; the theoretical specific capacity of LiFePO4 material is 170mA·h·g-1, and the actual specific capacity can reach about 150mA·h·g-1 . At present, the main development idea of cathode materials is to develop various related derivative materials on the basis of LiCoO2, LiMnO2, LiFePO4 and other materials. Among them, the ternary material NCM is widely used.