Detailed explanation of the reasons for the capacity decline of ternary material lithium-ion battery packs

Ternary lithium-ion battery packs mainly convert chemical energy into electrical energy through the oxidation reaction of internal electrodes. The internal structure of lithium-ion batteries is composed of the positive and negative materials of the battery and the electrolyte. When the battery is repeatedly charged and discharged, The motor inside the battery will cause crystals in the battery body material electrodes, causing the internal conductivity of the battery to decrease, that is, the activity of lithium ions has decreased, which will cause its resistance to increase, and finally affect the lithium ion battery The degradation of capacity, in fact, from the actual environment, affects the degradation of the battery. There are voltages for charging and discharging, and even the power of charging and discharging the battery and the temperature of the environment. At present, new energy vehicle batteries mainly use ternary lithium-ion battery packs, so the biggest point about ternary lithium-ion battery packs is that they are afraid of the high temperature of the environment, which will affect their service life. Of course, This will also affect the energy density. In terms of the power of electric vehicles, battery degradation is mainly due to the fact that the vehicle uses different charging and discharging magnifications to meet different driving conditions during use. The more the charging and discharging magnification is Larger, the faster the battery capacity decays. In fact, it is also important because the change in the structure and properties of the material makes the internal ion diffusion relatively difficult. Regarding the battery, if the internal resistance is inconsistent, the internal current and voltage distribution will be uneven, which will cause a local single battery under-voltage. Taken together, it will affect the life of the power lithium-ion battery pack. There are actually many factors, and of course various factors also influence each other. First of all, if the battery is a lithium iron phosphate battery pack, this situation is relatively normal. Because of the cathode material of the lithium iron phosphate battery, the conductivity itself is a little lower than that of the same type of lithium ion battery. Therefore, when in use, the single-cell lithium iron phosphate battery in the lithium iron phosphate battery pack will inevitably not work consistently. The technology and quality of the lithium-ion battery protection board used in the lithium-ion battery pack is too poor, and the protection parameters set can not be accurately positioned, resulting in the overcharge protection and over-discharge protection of the lithium-ion battery pack are not perfect, so long-term use causes It is also common sense that the performance of lithium-ion battery packs will drop significantly. Of course, there are some reasons that may also cause the performance of lithium-ion battery packs to decline, but the above two are the two most common situations, and the other reasons are not listed here. The current decline of lithium-ion power lithium batteries is also unavoidable. With the continuous improvement of the technology of power lithium batteries, it is very important to solve the related problems of battery capacity decline in order to extend the service life of power lithium batteries. Of course, this is also crucial to the development of electric vehicles. Reasons for the attenuation of the capacity of ternary materials lithium-ion batteries 1. The structure of the positive electrode material. The positive electrode material is an important source of lithium ions. When lithium ions are extracted from the positive electrode, in order to maintain the neutral state of the material, the metal elements will inevitably be oxidized to reach A high oxidation state is accompanied by a change in composition. The transformation of components easily leads to phase transition and changes in bulk structure. The phase transition of the electrode material can cause the change of the lattice parameters and the lattice mismatch. The induced stress caused by this causes the breakage of the crystal grains and initiates the propagation of cracks, causing mechanical damage to the structure of the material, thereby causing the degradation of electrochemical performance. 2. Anode material structure Commonly used anode materials for commercial lithium-ion batteries include carbon materials, lithium titanate, etc. This article uses typical anode graphite for analysis. The decay of the capacity of lithium-ion batteries occurs for the first time in the formation stage, during which SEI is formed on the surface of the negative electrode, consuming part of the lithium ions. 3. The oxidative decomposition and interface reaction of the electrolyte. The nature of the electrolyte significantly affects the specific capacity, life, rate charge and discharge performance, operating temperature range and safety performance of lithium-ion batteries. The electrolyte mainly includes three parts: solvent, electrolyte and additives. The decomposition of the solvent and the decomposition of the electrolyte will cause the loss of battery capacity. The decomposition and side reactions of the electrolyte are important factors for the capacity degradation of lithium-ion battery packs. No matter what kind of positive and negative electrode materials and processes are used, as the lithium-ion battery is recycled, the decomposition of the electrolyte and the interaction with the positive and negative materials Any interfacial reaction that occurs will cause capacity degradation. In addition, high-rate charging and discharging will also cause the capacity loss of lithium-ion battery packs. This is because the positive and negative electrodes will shrink and expand in volume during the charging and discharging process. The greater the charge and discharge current, the greater the contraction and expansion, and the greater the stress. The particles of the positive and negative electrodes are more likely to be broken or peeled off from the current collector during rapid changes in volume, resulting in faster cycle decay. 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