Why is the capacity of iron phosphate lithium ion batteries and ternary lithium ion batteries declining?

Reasons for the capacity degradation of lithium iron phosphate batteries 1. The internal resistance of lithium-ion batteries, especially the inconsistency of the internal resistance of polarization, causes the voltage of individual batteries to change drastically during the charging and discharging process, which leads to drastic changes in the entire battery pack. 2. The inconsistency of the voltage of the single ultra-thin battery will affect the peak shaving ability of the battery and reduce the energy released by the overall lithium iron phosphate battery. 3. Due to the heat release and heat absorption processes of ultra-thin batteries during operation, the battery temperature will continue to change. When overheated, performance degradation and safety hazards will be caused. Facts have proved that the electric vehicle operation and test fires that have occurred in recent years have led to fires Cables are all caused by insufficient over-temperature protection to cause the battery to heat up. The battery types include not only lithium manganate, but also lithium iron phosphate batteries. 4. Capacity is the most serious factor in discreteness. Inconsistent capacity can cause performance problems in two aspects. One is that some lithium iron phosphate batteries will be overcharged and overdischarged, leading to unsafe factors such as combustion and explosion. Because the low-capacity single battery ends work early, the energy of other single cells in the entire ultra-thin battery pack cannot be fully released, which causes the life of the entire lithium iron phosphate battery to decay. 5. 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. 6. Temperature is definitely one of the key factors affecting the life of lithium iron phosphate batteries. Too high or too low temperatures will reduce the active lithium ion content, thereby reducing the life of lithium ion batteries. Reasons for the capacity decay of ternary lithium-ion battery 1. The structure change 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 element will inevitably be oxidized to reach one The high oxidation state is accompanied by the transformation of the 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. With the use of lithium-ion batteries, changes in the graphite structure will also cause the battery capacity to decrease. Liu et al. studied the capacity decay mechanism of LiFePO4/C batteries, which is also applicable to ternary lithium-ion batteries. They found that although the carbon material after cycling maintains the morphology and structure of graphite, the half-height width of its crystal plane becomes larger, resulting in The crystal grain size in the c-axis direction becomes smaller, and the change in the crystal structure causes cracks in the carbon material, which destroys the SEI film on the negative electrode surface and promotes the repair of the SEI film. The excessive growth of the SEI film consumes active lithium, thus causing the irreversible capacity of the battery attenuation. 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 batteries. Regardless of the positive and negative electrode materials and processes used, as the lithium-ion battery is recycled, the electrolyte will decompose and occur between the positive and negative materials. The interface reaction will cause the capacity attenuation. The introduction of Co reduces the cation mixing and occupation and effectively stabilizes the layered structure of the material. The introduction of Mn can reduce the cost and improve the safety and stability of the material. Ternary materials have better electrochemical performance and stability, and have been accepted by mainstream lithium battery manufacturers in the world, and are used in electric vehicles, 3C and other fields. Fourth, the use conditions of lithium-ion batteries must be mentioned is the use of lithium-ion battery environment and conditions damage to its capacity: (1) lithium-ion battery abuse; (2) temperature factors. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.