February-March 2016_Chongqing Terui Battery Materials Co., Ltd._R&D, production and sales of battery cathode materials

Lithium-ion batteries are widely used in consumer electronics, electric vehicles and energy storage due to their high specific energy and power density, long cycle life, and environmental friendliness. As the power source of new energy vehicles, lithium-ion batteries still have many problems in practical applications. For example, the energy density is significantly reduced under low temperature conditions, and the cycle life is also affected accordingly, which also severely limits the large-scale use of lithium-ion batteries. At present, researchers are still arguing about the important factors that cause the poor low-temperature performance of lithium-ion batteries, but the reasons are as follows: 1. The viscosity of the electrolyte increases at low temperatures and the conductivity decreases; 2. The membrane impedance and charge transfer impedance of the electrolyte/electrode interface increase; 3. The migration rate of lithium ions in the body of the active material is reduced. As a result, the electrode polarization is increased at low temperatures and the charge and discharge capacity is reduced. In addition, during low-temperature charging, especially during low-temperature high-rate charging, lithium metal precipitation and deposition will occur in the negative electrode. The deposited metal lithium is easy to irreversibly react with the electrolyte and consumes a large amount of electrolyte. At the same time, the thickness of the SEI film is further increased, resulting in The impedance of the negative electrode surface film of the battery is further increased, and the polarization of the battery is increased again, which will greatly destroy the low-temperature performance, cycle life and safety performance of the battery. This article reviews the research progress of low-temperature performance of lithium-ion batteries, and systematically analyzes the important limiting factors of low-temperature performance of lithium-ion batteries. From the three aspects of positive electrode, electrolyte and negative electrode, the modification methods that researchers have used to improve the low-temperature performance of the battery in recent years are discussed. 1. Cathode material The cathode material is one of the key materials for the manufacture of lithium-ion batteries, and its performance directly affects the various indicators of the battery, and the structure of the material has an important impact on the low-temperature performance of the lithium-ion battery. LiFepO4 with olivine structure has the advantages of high discharge specific capacity, stable discharge platform, stable structure, excellent cycle performance, and abundant raw materials. It is the mainstream cathode material for lithium-ion power lithium batteries. However, lithium iron phosphate belongs to the pnma space group, p occupies the tetrahedral position, the transition metal M occupies the octahedral position, and the Li atom forms a migration channel along the [010] axis in a one-dimensional direction. This one-dimensional ion channel causes the lithium ion only The orderly extraction or insertion in a single way seriously affects the diffusion ability of lithium ions in the material. Especially at low temperatures, the diffusion of lithium ions in the body is further hindered, resulting in an increase in impedance, resulting in more serious polarization and poor low-temperature performance. Nickel-cobalt-manganese-based LiNixCoyMn1-x-yO2 is a new type of solid solution material developed in recent years, which has a single-phase layered structure of α-NaFeO2 similar to LiCoO2. The material has important advantages such as high reversible specific capacity, good cycle stability, and moderate cost. It has also been successfully applied in the field of power lithium batteries, and its application scale has been rapidly developed. However, there are some problems that need to be solved urgently, such as low electronic conductivity and poor stability of large rates, especially as the nickel content increases, the high and low temperature performance of the material deteriorates. The lithium-rich manganese-based layered cathode material has a higher discharge specific capacity and is expected to become the next generation of lithium-ion battery cathode materials. However, there are many problems in the practical application of lithium-rich manganese bases: the first time the irreversible capacity is high, and the layered structure is easily transformed into the spinel structure during the charge and discharge process, which makes the Li+ diffusion channel blocked by the migrated transition metal ions. It causes serious capacity degradation, and poor ion and electronic conductivity, resulting in poor rate performance and low temperature performance. The mainstream ways to improve the ion diffusion performance of cathode materials at low temperatures are: 1. The method of surface coating the active material bo

February-March 2016

February-March 2016

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