Main role of negative active materials for lithium ion batteries1. Effect of negative electrode active substance on the safety of lithium ion battery
The negative electrode active material of the lithium-ion battery is mainly a carbon material, i.e., in the carbon negative electrode, thereby replacing the lithium negative electrode, so that the deposition and dissolution of lithium in the negative surface during the charge and discharge process become lithium in carbon particles embedding and extraction , Reduced the possibility of lithium branch formation, greatly improves the safety of the battery, but this does not mean that there is no safety problem using the carbon negative pole.
It affects the safety factors of lithium-ion batteries in the following aspects:
(1) Effects of different types of carbon materials on battery safety
Previous studies have shown that the carbon negative electrode and the electrolytic solution in the state are released with the electrolyte as the temperature is increased. Under the same charge and discharging conditions, the exothermic rate of the electrolyte and the apholithoxal graphite reaction is much larger than the reaction rate of MCMB, carbon fibers, coke carbon, and the like with the ankolithium. Hard carbon material, soft carbon material, the carbon layer spacing of graphite materials is from 0.38 nm, 0.34 ~ 0.35 nm, 0.335 nm, and after lithium embedded, the layer pitch is about 0.371 nm. The layer spacing of the graphite material is the smallest, and its insertion and disengagement process in the lithium ion is maximized, and the diffusion speed of lithium ions in such carbon layers is also slower, and when the large current charges, the polarization is large, the resistance is large, and the battery is polarized. The safety is poor, and the hard carbon material is reversed. However, some people believe that the degree of graphite can reduce the activation energy of lithium ion diffusion, which is conducive to the diffusion of lithium ions, and the hard carbon material is in a large amount of voids, and its performance is close to metal lithium negative electrode, Security is not good.
(2) Effect of particle size on battery safety performance
Most of the particles in the electrode are in contact, so the small particulate carbon negative electrical resistance is larger than the large particle carbon negative electrode, but due to the large radius, the expansion contraction changes during the charge and discharge process, according to this, the size particles are pressed It is necessary to match the negative electrode to achieve the expansion of the contact area between the particles, reduce the electrode impedance, increase the electrode capacity, and reduce the possibility of active metal lithium precipitation.
(3) Effect of SEI film on battery safety performance
The SEI film of the battery is formed from a solvent molecule, a lithium salt anion, and an impurity molecule in the charge and discharge process. The quality of the formation of the SEI film directly affects the charge and discharge performance and safety of the lithium-ion battery. According to relevant reports: the surface of the carbon material is weakly oxidized, or the reduction, doping, surface-modified carbon material, and using spherical or fibrous carbon materials It will help the Quality of SEI membrane.
2, the effect of negative electrode active substance on cycle performance of lithium ion battery
The physical chemical structure properties of the negative electrode active material have decisive effect on lithium ions, and the structure of the active material is small when using an active material that is easily defilled, and the structure of the active material is small, and this small change is reversible, so there is It is conducive to extending the life of the charge and discharge.
The crystallinity of carbon in the negative electrode of the lithium ion battery can affect the Li + diffusion coefficient of the negative electrode, and the diffusion dynamics of lithium ion is embedded and the deinterlaxing process determines the rateability of the lithium ion battery, so the crystallinity of carbon is microstructure. The degree of influence of cycle performance under different charge and discharge rates is also different. When the graphitized MCF is a negative electrode, since its structure is radial and high graphitization, it is conducive to Li + rapid spread and rapid embedding. Highly crystallized graphite has a high degree of orientation and laminar structure, and a thick carbon layer, Li + insertion is strong, which has an effect of high current charge and discharge cycle properties; odorless and thin carbon The layer, Li + is fast, the fast charge ability is strong, and the volume expansion caused by lithium embedding is much smaller than graphite, so the replacement rate of the charge and discharge cycle is small, and aging is resistant to aging. LicoO2 / graphite of the lithium ion battery When a large current (≥1C) charge is charged in a large amount of organic electrolyte, it is found that the capacity attenuation is faster. The main reason is that when the ≥1c is charged, the graphite layer spacing changes. The powder is expanded, and the organic solvent is easy to decompose with Li + common insertion layers and solvents, and the anatomical cells actually see a more severe pollination and peeling of the negative electrode coating, so that the cycle performance is deteriorated. The MCMB prepared by the heat treatment temperature has a mixed layer structure (non-clear layer structure), wherein the insertion of Li + is easier, the structure is small, so the cycle life performance is excellent in natural graphite. The Beijing colored hospital uses a method of composite graphite in graphite surface of a layer of organic polymer pyrolysis carbon, reducing the organic solvent common insertion reaction, thereby improving charging and discharging cycle performance.
When the lithium ion battery is overcharged, the lithium ion is reduced to the surface of the negative electrode. From the mechanism of micropore, the newly deposited lithium is covered with the surface of the negative electrode, blocking lithium embedded, due to the nature of lithium, easy to react with the electrolyte, resulting in low discharge efficiency and capacity loss. Fast charge, excessive current density, severe polarization, and lithium deposition more obvious. In the solvent, such as Lico3, LIF or other side reactive products, metal lithium in the negative electrode deposition is faster, which in turn affects the cycle performance and safety of the battery. Recommend: LiFePO4 Battery Manufacturer Energy storage battery Manufacturer Integrated machine energy storage battery series Manufacturer Lead lithium battery Manufacturer Outdoor Backup Battery Manufacturer Portable outdoor power supply Manufacturer Power battery Manufacturer Powerwall LiFePO4 Battery Manufacturer Battery rack Manufacturers Telecom LiFePO4 Battery Manufacturer Wall mounted battery storage Manufacturer China Lifepo4 Battery
