What are the disadvantages of high-temperature operation of lithium batteries?

Disadvantages of high-temperature operation of lithium batteries (1) When the anode metal of lithium batteries is dissolved at high temperatures, the lithium electrolyte LiPF6 of the lithium battery will be thermally decomposed to form PF5, and the water in the electrolyte will be further hydrolyzed to form HF. High frequency is considered to be an important cause of metal dissolution in the cathode material. The shortcomings of high-temperature operation of lithium batteries Regarding lithium manganate spinel, its high-temperature destruction mechanism is the same as that at room temperature. During the low-voltage discharge process, Mn3﹢ disproportionation reaction produces Mn2﹢ and Mn4﹢, Mn2﹢ dissolves in the electrolyte, Mn+ will still be in the solid phase, in the process of dissolution, the material will still have a spinel structure, and replace it The lithium manganese is gone. Therefore, the formation of disordered lithium-rich phase spinel lithium manganese oxide, the dissolution process can be expressed as: LiMn204→Li[lixmn2-x]04+Mn2+The dissolution of manganese also occurs in the high-pressure area, but the dissolution mechanism is not yet It's totally clear. However, it is generally believed that the chemical unpacking reaction is caused by HF, and LiF is an insoluble by-product, which can be observed on the surface of spinel lithium manganate after failure, while HF is formed due to the presence of a small amount of water in the electrolyte of. With the dissolution of manganese, the change of the material structure and the destruction of the crystal lattice will cause it, on the one hand, it will lead to a reduction in the charging capacity and high-voltage areas, on the other hand, it will lead to an increase in the contact resistance between the active materials and a decrease in the mobility of lithium ions. Eventually lead to battery failure. The manganese ions from the positive electrode will be dispersed on the negative electrode by the electrolyte, and then deposited on the negative electrode, resulting in deterioration of the performance of the negative electrode. At high temperatures, metallic iron also dissolves in lithium iron phosphate materials. However, in the early research on the high-temperature performance of lithium iron phosphate batteries, it was not found that the dissolution of iron and the accelerated decay of the capacity at high temperatures. Years. Ndersson, such as lithium iron phosphate half-cells, has studied the electrochemical performance at different temperatures and the improvement of the temperature environment with the increase of battery charging and discharging capacity, and the specific performance has also improved. Cycle at 40 ℃, the battery shows better than 23c Cycle performance, no obvious side-use is observed. At the same time, after cycling the battery capacity at 60℃ for 20 cycles, the DSC results also show that the lithium iron phosphate material in ordinary electrolyte has good thermal stability. No obvious reaction at ℃. Compare LiFePO4 and LiMn2O. The solubility of the material in the electrolyte at room temperature and high temperature. The results show that the lithium iron phosphate material will also dissolve in the electrolyte at high temperatures, but the solubility is much lower than that of the lithium manganate material. At the same time, the electrolyte and the water in the material will accelerate the dissolution of the material. It was found that the lithium iron phosphate material is a phenomenon of iron dissolution under the 60 ℃ cycle. At the same time, the capacity of the lithium iron phosphate battery due to the iron dissolution at the high temperature cycle/C decays sharply. Through the analysis of the SEM and EDS results, they concluded that the The anode dissolution of the cathode deposited iron and the deterioration of the performance of the cathode, the iron deposit may be the catalytic decomposition of the electrolyte, so the negative impedance is significantly increased, which eventually leads to the degradation of the battery capacity. (2) Destruction of the material structure When lithium ions are repeatedly inserted and released, the volume of the lithium battery material will expand and contract, and long-term volume changes may cause the collapse of the material structure. In the lithium manganate spinel material, as the cycle progresses, the material will have a distortion effect, causing the oxygen octahedron to deviate from the spherical symmetry and deform into a deformed octahedral configuration. When there are defects in the material structure, it will collapse during repeated shrinkage and expansion. When LiMn2O4 is embedded in 3v lithium to become Li1+xMn2O4, Li to octahedral 16c, making Mn3﹢concentration greater than Mn4﹢concentration, thereby reducing the symmetric structure, the cubic system of crystal structure is divided into four quarters. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.