Classification and analysis of lithium battery cathode materials

Classification of lithium battery cathode materials Ideal lithium battery cathode materials should be able to hold a large amount of lithium ions, have high ionic conductivity and electronic conductivity, and good stability. Existing anode materials are difficult to meet the above requirements at the same time. Therefore, the development of new anode materials with better electrochemical performance and the modification of existing materials have always been research hotspots in the field of lithium battery anode materials. At present, anode materials can be divided into three types: embedded anode materials, alloy anode materials and conversion anode materials. A. Embedded cathode material The most typical embedded anode material is carbon. According to the degree of graphitization, carbon materials can be divided into soft carbon, hard carbon and graphite. Commonly used soft carbon materials include petroleum coke, needle coke, carbon fiber, carbon microspheres and so on. Hard carbon is difficult to graphitize above 2500°C. The discharge capacity of graphite is 350 mAh/g, and it has a layered structure. The carbon atoms in the same layer are arranged in a hexagonal shape, and van der Waals forces are used between layers. Lithium ions can be inserted between graphite layers to form li-gic. Graphite material has good conductivity, high crystallinity, and stable charging and discharging platform. It is the most commercialized cathode material for lithium batteries. Except for graphite, the lithium storage mechanism of other carbon materials is the same. It should be pointed out that hard carbon materials have a higher discharge capacity than graphite, because in addition to the same embedding mechanism as graphite, there are some micropores or defects in the hard carbon structure, which can be used for Li+ storage and disassembly [15 ]. However, the application of hard carbon as anode material is limited due to low cycle efficiency, large voltage change with capacity, unstable discharge platform. B. Alloy anode materials Alloyed lithium storage materials refer to metals and their alloys, mesophase compounds and complexes capable of alloying with lithium. According to reports, lithium can react with tin, silicon, zinc, aluminum, antimony, germanium, lead, magnesium, calcium, arsenic, bismuth, platinum, silver, gold, cadmium, mercury and other metals at room temperature. The mechanism is alloying and reverse alloying reactions. Generally speaking, the theoretical capacity and charge density of alloy anode materials are much higher than buried anode materials. At the same time, this type of material has a high potential for lithium insertion, and it is difficult to deposit lithium under high-current charging and discharging conditions. Lithium and dendrites will not appear, which will cause short circuits in the battery, which is of great significance for high-power devices. C. Conversion anode materials There are currently as many as 10 types of transition metal materials reported, mainly referring to the oxides and sulfides of transition metal elements such as Co, Ni, Mn, Fe, V, Ti, Mo, W, Cr, Cu, Ru, etc. , Nitride, Phosphate and Fluoride. In the past, people didn't think this material had a future. There is no space for lithium ion insertion and escape in the spatial structure of this material, which does not conform to the traditional lithium ion mosaic mechanism, and the reaction with lithium at room temperature is considered irreversible. It was not until some transition metal oxides were found to have high reversible discharge capability (3 times that of graphite) that this material gradually attracted the attention of researchers. Figure 2 shows the first specific discharge capacity of some converted anode-like materials. Different from the above three cathode materials, lithium titanate Li4Ti5O12 with spinel structure has also received more and more attention. The working voltage of Li4Ti5O12 is 1.5v, which is relatively high compared with general negative electrode materials. Under this voltage, the electrolyte will not decompose. Therefore, lithium titanate is used as a negative electrode material for batteries. In addition, the volume of lithium titanate material does not change much before and after the insertion and removal of lithium ions. It is a zero-strain material with outstanding safety performance and has become a popular candidate material for the next generation of lithium batteries in energy storage power stations. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: Which is better for polymer lithium ion battery or lithium ion battery?