According to the material type of cathode materials, the classification mainly includes the following three types:

　　a) Transition metal oxide cathode materials, such as LiCoO2, LiMnO2, LiNiO2, LiFeO2, etc., whose general formula is LiMOy (where M is one or more transition metals).

　　b) Polyanionic cathode materials are a series of cathode materials containing tetrahedral or octahedral anion structural units XOmn-, such as LiFe(Co,Mn,Ni,V)PO4, Li2Fe(Mn)SiO4, LiFeAsO4, etc., which are generally The formula is Li-M-XmOn (where M is one or more transition metals, and X is a metal or non-metal that can form polyanions such as Mo, As, P, S, V, Mn, W, etc.).

　　c) Polymer cathode materials, mainly including conductive polymers and organic sulfur compounds. Conductive polymer cathode materials mainly include polyacetylene, polypyrrole, polythiophene, polyaniline and their derivatives. Their electrode reactions as cathode materials for lithium-ion batteries use anions. The reversible doping/dedoping process of A- (such as: ClO4-, BF4-, PF4-, AsF6-, etc.); the main organic sulfur compounds include: polydithiothiadiazole, polydithiodiphenylamine, Trimeric thiocyanate, etc., their electrode reactions as positive electrode materials utilize the oxidation-reduction reaction of sulfur.

　　2.2 Classification of channels according to Li+ embedding and deintercalation

　　According to the channel classification of Li+ intercalation and deintercalation, it can be divided into three categories: one-dimensional tunnel structure cathode materials, such as LiFePO4; two-dimensional layered structure cathode materials, such as LiMO2 (M=Co, Ni, Mn), Li1+XV3O8 and Li2MSiO4 (M=Fe,Mn); three-dimensional framework structure cathode materials, such as LiMn2O4 and Li3V2(PO4)3.

　　3 Latest technological progress of main cathode materials

　　3.1 Lithium cobalt oxide

　　Lithium cobalt oxide was the first cathode material to be commercialized and applied on a large scale. Lithium cobalt oxide is suitable for making small lithium-ion batteries used in digital products, mobile phones, etc. As the functionality of mobile phones increases, more and more power is required. Accordingly, the lithium cobalt oxide cathode materials used have also been technically updated and improved.

　　Lithium cobalt oxide batteries are often used in small mobile devices and have strong power, but the scarcity of cobalt resources cannot be ignored.

　　The replacement of lithium cobalt oxide is marked by compaction density and has obvious differences in physical and chemical properties. The first-generation lithium cobalt oxide is composed of agglomeration of smaller primary particles, while the second-generation lithium cobalt oxide is a single particle with larger particle size. The capacity of the two generations of lithium cobalt oxide is around 160mA·h/g, but the compacted density is very different. The first generation is about 3.6g/cm3, the second generation is more than 4.0g/cm3, and the latest type is more than 4.3g/cm3. . The mass production method of lithium cobalt oxide is through multiple high-temperature solid-phase synthesis. The method of technical improvement is to add doping elements, especially the addition of excess lithium element, which can change the growth characteristics of particles during the high-temperature reaction process, so that The size of a single primary particle increases, which enhances the compactness and surface smoothness of the particles, thereby increasing the compaction density. Other doping elements such as titanium, zirconium, and aluminum can improve the stability of electrochemical performance.

　　3.2 Lithium manganate:

　　As a lithium battery material with a long history of use, lithium manganate has high safety, especially its strong resistance to overcharging, which is a major outstanding advantage. Due to the good structural stability of lithium manganate itself, when designing the battery cell, the amount of positive electrode material does not need to exceed the negative electrode by much. In this way, the number of active lithium ions in the entire system is small. After the negative electrode is full, there will not be too many lithium ions in the positive electrode. Even if an overcharge occurs, a large amount of lithium ions will not be deposited on the negative electrode to form crystals. Therefore, the overcharge resistance of lithium manganate is relatively good among commonly used materials. In addition, the material is cheap and the production process requirements are relatively low. It is an early cathode material that has been widely used.

　　The disadvantages of lithium manganate are poor long-term cycle stability, high temperature cycle stability and storage performance. In the study of synthesis methods and modification of spinel lithium manganate lithium-ion battery cathode materials, typical synthesis methods include melt impregnation method, solid phase reaction method, molten salt method, sol-gel method, Penchini method, etc., and another The focus of the research is modification, including doping modification and surface coating. Doping with low-valent elements Cr, Mg, Li, B, Al, Co, Ga, Ni, etc. can reduce the relative content of Mn3+, reduce its disproportionation and dissolution, and also suppress the Jahn-Teller effect. By coating metal oxides (ZnO, Al2O3, CoO), LiCoO2, phosphates, polymers, etc., the chance of contact between Mn3+ and the electrolyte is reduced.

　　High-temperature cycle and shelf life issues can be improved to a certain extent through modification technology, but all methods will produce a common result, which is a reduction in initial capacity. The initial capacity of the actual synthesized pure spinel lithium manganate can reach 130mA·h /g or above, the capacity of large-scale products produced through modification technology is around 110mA·h/g, or even lower, and some foreign products are controlled at around 105mA·h/g. The technical development of spinel lithium manganate is different from that of lithium cobalt oxide. Lithium cobalt oxide has obvious generation differences. Lithium manganate reflects the coexistence of different technical methods. Different synthesis technologies produce different product morphologies, but the performance advantages are different. It is not obvious that the technological development direction of lithium manganate is to improve high-temperature cycle performance and shelf life.

　　3.3 Lithium iron phosphate

　　The advantages of lithium iron phosphate are mainly reflected in safety and cycle life. The main determining factor comes from the olivine structure of lithium iron phosphate. This structure, on the one hand, results in lower ion diffusion capacity of lithium iron phosphate, on the other hand, it also gives it better high-temperature stability and good cycle performance. The positive electrode material is rich in iron and very cheap, so the cost is relatively low.

　　Lithium iron phosphate was once the favorite of urban bus systems that did not pay special attention to battery size, but its status has shifted as the subsidy trend changes.

　　Lithium iron phosphate has some disadvantages that are difficult to overcome. Consistency is one of the difficulties that needs to be overcome in the production of lithium iron phosphate materials and batteries. From the perspective of material preparation, the synthesis reaction of lithium iron phosphate is a complex multi-phase reaction, including solid phase phosphate, iron oxide and lithium Salts, as well as precursors of added carbon and reducing gas phases. In this complex reaction process, it is difficult to ensure the consistency of the reaction.

　　Poor conductivity and low ion diffusion coefficient are another difficulty that needs to be overcome, which can be improved through modification methods. The modification methods of lithium iron phosphate include adding conductive agents and preparing nano-sized particles to improve conductivity and lithium ions. Diffusion properties, substitution by coating and doping elements to improve crystallization stability and increase conductivity. The purpose of adding conductive substances is to improve the electronic conductivity of FePO4 after delithiation, such as the introduction of conductive agent carbon black, copper or silver particles with good dispersion properties. Nanoscale particles can reduce the distance that lithium ions have to move in and out of the particles, thereby improving electrical conductivity. However, nanoparticles and the incorporation of some conductive additives will bring certain hidden dangers to safety and have a negative impact on the safety advantages of lithium iron phosphate. The method of surface coating with inorganic oxides is also one of the means to improve structural stability and increase the conductivity of materials. Surface coating of LiFePO4 grains with inorganic substances (such as ZnO or ZrO2) can not only improve cycle life, but also It can improve discharge capacity and rate discharge performance. After the iron atom position or the lithium atom position is replaced with magnesium, titanium, manganese, zirconium, and zinc, the crystallinity of LiFePO4 is improved to a certain extent.

　　Low-temperature performance is another difficulty that lithium iron phosphate batteries need to overcome. Even nanonization and carbon coating have not solved this problem. In actual applications of lithium iron phosphate batteries, auxiliary heating is often used on the outer layer of the battery.

　　At present, the specific energy of a new generation of lithium iron phosphate battery cells can reach 175Wh/kg, and the group can meet the requirements of 150Wh/kg for commercial vehicles. If research and development continues under current conditions, it is achievable to achieve the goal of 180Wh/kg for lithium iron phosphate battery packs by 2020, and there is still greater room for development.

　　3.4 Ternary lithium

　　The ternary lithium cathode material combines the advantages of LiCoO2, LiNiO2 and LiMnO2 to form a synergistic effect within the same battery cell, taking into account the three requirements of material structure stability, activity and lower cost. It is one of the three main The one with the highest energy density among cathode materials. Its low temperature effect is also significantly better than that of lithium iron phosphate batteries. Among the three elements, increasing the content of Ni can obtain higher capacity, increasing the content of Co can obtain a higher voltage platform and improve cycle stability, and increasing the content of Mn can improve safety performance. Therefore, it requires a very sophisticated BMS battery management system to ensure that the battery temperature is within a safe range. Once a fault such as a short circuit occurs, the power supply can be cut off immediately to ensure safety. In actual applications, the proportional relationship between the three materials in the battery core has been changing over time. People's pursuit of energy density is getting higher and higher, so the proportion of Ni is also getting higher and higher. The improvement of the safety performance of the battery itself and the improvement of system monitoring and accident handling capabilities will also promote the expansion of the ternary lithium battery market.

　　Ternary batteries have high energy density, affordable price, and excellent overall performance. They have become the battery type used by most new energy vehicles at present.

　　In recent years, micron-sized primary single crystal particles similar to lithium cobalt oxide have been synthesized from ternary materials by using new precursor preparation processes and three-dimensional free sintering technology. This preparation process overcomes the difficulty in filtration and washing of the precursor caused by the easy oxidation of divalent manganese ions in alkaline solutions when generating hydroxide precipitation. The prepared micron-level primary single-crystal particle compound has a more complete crystal structure, higher compaction density and excellent electrode processing performance, and its electrode compaction density can be as high as 3.85g/cm3.

　　The shortcomings of ternary cathode materials such as mixed arrangement of lithium and nickel and residual lithium on the surface cannot be ignored. In response to the above problems, future work should focus on element doping to improve its structural stability. At the same time, it can also be Surface coating treatment inhibits the occurrence of interface side reactions, thereby improving the electrochemical performance of the ternary cathode material.

Read recommendations:

Coin Battery CR 2032

Detailed breakdown of ternary lithium batteries.18650 rechargeable battery lithium 3.7v 3500mah

Lithium battery charging process.no. 7 alkaline battery

522749 lipo battery

CR2032 button cell