The ideal lithium battery pack
anode material should be able to hold a large amount of Li+, have high ionic conductivity and electronic conductivity, and good stability. Existing negative electrode materials are difficult to meet the above requirements at the same time, and have disadvantages such as low initial charge and discharge efficiency and poor high-current charge and discharge performance. 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 ion battery anode materials. The current research on anode materials can be divided into the following three types: embedded anode materials, alloyed anode materials and conversion anode materials. Embedded anode material: The most typical embedded anode material is carbon material. According to the difference in the degree of graphitization of materials, carbon materials can generally be divided into soft carbon, hard carbon and graphite. Common soft carbon materials include petroleum coke, needle coke, carbon fiber and carbon microspheres; hard carbon is also difficult to graphitize above 2500°C. Graphite has a discharge capacity of 3500mA·h/g and has a layered structure. The carbon atoms in the same layer are arranged in a regular hexagon, and the layers are combined by van der Waals forces. Lithium ions can be inserted between graphite layers to form lithium-graphite intercalation compound (Li-GIC). Graphite materials have good electrical conductivity, high crystallinity, and a stable charging and discharging platform. It is currently the most commercialized negative electrode material for lithium-ion batteries. In addition to 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. This is because, in addition to the same embedding mechanism as graphite, there are also some micropores or defects in the hard carbon structure that can be used for Li+ storage and intercalation. However, due to low cycle efficiency, large voltage changes with capacity, and lack of a stable discharge platform, the application of hard carbon as a negative electrode material has been restricted. Alloyed anode materials: Alloyed lithium storage materials refer to metals and their alloys, mesophase compounds and composites that can undergo alloying reactions with lithium. According to reports, lithium can react with many metals at room temperature (such as Sn, Si, Zn, Al, Sb, Ge, Pb, Mg, Ca, As, Bi, Pt, Ag, Au, Cd, Hg, etc.), and its charge and discharge The essence of the mechanism is the reaction of alloying and inverse alloying. Generally speaking, the theoretical specific capacity and charge density of alloyed anode materials are much higher than that of embedded anode materials. At the same time, this type of material has a high lithium insertion potential, and it is difficult to deposit lithium in the case of high current charging and discharging, and it will not produce lithium dendrites to cause battery short circuits, which is of great significance for high-power devices. Conversion type anode materials: There are dozens of conversion type anode materials reported so far, mainly referring to the oxides of transition metal elements such as Co, Ni, Mn, Fe, V, Ti, Mo, W, Cr, Cu, Ru , Sulfide, nitride, phosphide and fluoride. This type of material was not favored in the past. There is no place for lithium ion insertion and extraction in the spatial structure of this type of material, which does not conform to the traditional lithium ion insertion and removal mechanism, and the reaction with lithium at room temperature was considered irreversible. . It was not until several transition metal oxides were found to have very high reversible discharge capacity (3 times that of graphite) that this material gradually attracted the attention of researchers. Figure 2 shows the first discharge specific capacity of some conversion anode materials. u003cpu003eu003c/pu003eu003cpu003eDifferent from the above three types of anode materials, spinel structure lithium titanate Li4Ti50O12 has also received more and more attention. The operating voltage of Li4Ti5O12 is 1.5V, which is higher than that of general negative electrode materials. Under this voltage, the electrolyte will not decompose. Therefore, lithium titanate is used as the negative electrode material of the battery, and SEI film will not form on the surface of the material during the cycle. High charging and discharging efficiency. In addition, before and after the insertion and extraction of lithium ions, the lithium titanate material hardly changes in volume and is a zero-strain material. It has outstanding safety and has become a popular candidate for lithium-ion batteries for the next generation of energy storage power stations. Material.u003c/pu003eu003c/pu003e
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