During the charging and discharging process of lithium-ion power batteries, the positive electrode material not only provides the lithium required for the reciprocating insertion and extraction of the positive and negative lithium intercalation compounds, but also bears the burden of forming a solid electrolyte (electrolyte) interface film (SEI film) on the surface of the negative electrode material. Of lithium. The current cathode materials mainly include lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium iron phosphate and nickel cobalt manganese three-element materials.
Lithium cobalt oxide (LiCoO2) is a layered rock salt structure cathode material. Although it has shortcomings such as scarce resources and poor thermal stability, it is still the main source of small lithium ion secondary batteries due to its stable electrochemical performance and high reliability of production processes. Applied cathode material. The synthesis methods of lithium cobalt oxide (LiCoO2) mainly include solid-phase reaction method, sol-gel method, hydrothermal method, precipitation method and so on. There are significant differences in physical and electrochemical properties of lithium cobalt oxide (LiCoO2) materials synthesized by different methods. At present, commercial lithium cobalt oxide (LiCoO2) materials are mainly synthesized by high-temperature solid-phase reaction.
Lithium nickel oxide (LiNiO2) is similar in structure to lithium cobalt oxide (LiNiO2), with higher theoretical capacity, low price, large reserves and no pollution to the environment, but its internal structure leads to very harsh preparation conditions and relatively low cycle capacity attenuation Fast, its practical process has been relatively slow. The use of a small amount of other metal ions to replace part of the nickel to stabilize its structure is one of the directions for improving the performance of the material in recent years, mainly doped with elements such as cobalt (Co), magnesium (Mg) and aluminum (Al). The synthesis method of lithium nickelate (LiNiO2) is mainly a high-temperature solid-phase reaction method.
Lithium manganate (LiMn2O4) is a positive electrode material with a spinel structure. It is cheap and pollution-free, but its capacity decays severely at high temperatures, and the structure of manganese acid (LiMn2O4) is unstable during charging and discharging, due to the occurrence of Jahn-Teller The effect leads to a certain limit in the scope of application. The traditional synthesis methods of lithium manganate (LiMn2O4) mainly include solid-phase reaction method and liquid-phase reaction method. At present, some people use microwave heating method, pulsed laser deposition method, plasma lift chemical vapor deposition method and radio frequency magnetron jet method to prepare lithium manganate (LiMn2O4).
Lithium iron phosphate (LiFePO4) is an olivine-shaped cathode material that belongs to the orthorhombic system. It has a high theoretical capacity, good thermal stability, and excellent charge-discharge cycle performance at room temperature. Therefore, it has good performance in specific fields. Application prospects. However, due to the low energy density, low ionic conductivity and low electronic conductivity of the current materials, poor rate performance, poor low-temperature performance, and complex synthesis, etc., the material is used in power-type lithium-ion batteries, and a lot of work needs to be done. At present, the synthesis methods of lithium iron phosphate (LiFePO4) mainly include high-temperature solid-phase synthesis, microwave sintering, and sol-gel.
Nickel cobalt manganese ternary material (LiNixCo1-2xMnxO2) has excellent charge-discharge cycle stability and better safety performance, so it becomes another positive electrode material that can replace lithium cobaltate. Among them, the product with x=1/3 has the best comprehensive electrochemical performance, and it is also the most studied and the fastest-developing material. At present, the nickel diamond manganese ternary material (LiNixCo1-2xMnxO2) mainly realizes the mixing of Ni, Co, and Mn ions in the liquid phase, and then uses the precipitation method to prepare the reactants before the high temperature reaction. In addition, carbonic acid can also be used The salt precipitation method is used to synthesize the material.
At present, the mainstream cathode materials are lithium cobalt oxide, lithium manganate, ternary materials (lithium nickel manganese oxide) and lithium iron phosphate. Among them, the most mature and widely used lithium-ion battery cathode material is lithium cobalt oxide. However, due to its high cost and safety problems as a power battery, the research and development of power-type lithium-ion batteries in various countries focuses on manganese Lithium oxide, ternary materials and lithium iron phosphate: Lithium manganate technology is relatively mature, but its shortcomings are the short life of single cells and poor high temperature resistance; ternary materials are modifications of existing materials, and more attention is paid to the process Parameters: Lithium iron phosphate is favored because of its long cycle life, excellent safety performance, better high temperature performance, and extremely low price, but it also has poor electrical conductivity, poor low temperature resistance, poor rate performance, It is difficult to control the consistency of material batches and other shortcomings.