Failure analysis of lithium-ion battery cells and the concept of lithium-ion battery electrolyte

As the charging voltage increases, the (003) peak of the positive electrode material NCM begins to shift to a low angle. At this time, the (003) crystal plane spacing of NCM increases, that is, the c-axis becomes larger, and reaches the lowest when the voltage reaches 4.0V. Then, the (110) peak shifts to a high angle with the increase in voltage, and there is no rebound trend in the middle, indicating that the (110) crystal plane spacing decreases, corresponding to The a-axis keeps getting smaller. When the voltage is greater than 4.4V, the peak-to-peak intensity of 003 becomes lower and begins to broaden, indicating that the crystal structure begins to deform seriously at this time, and the atoms in the unit cell cannot be arranged well, reaching the material's limit withstand voltage. In addition, the structural stability and phase change process of the material during charging and discharging have an important influence on its electrochemical performance, especially the cycle stability. Through the analysis, the change graph of the unit cell parameters during the charging and discharging process can be obtained, so as to evaluate the volume expansion of the lithium ion battery caused by different cathode materials, and provide feasible data and analysis methods for the safety research and material selection of the lithium ion battery. During the use of lithium-ion batteries, battery life is often reduced or even failed due to overcharge, overdischarge, short circuit, high temperature and other reasons. Therefore, XRD technology is used to conduct thermal failure analysis of lithium-ion batteries, such as XRD analysis from burning residues, to preliminarily determine the cause of the failure. Malvern PANalytical’s unique high-performance hard-ray detection technology (GaliplX3D matrix detector with 100% working efficiency) can be used on the Empyrean diffraction platform to use hard-ray XRD for the original soft-pack structure lithium-ion batteries and commercial finished lithium-ion batteries. The charge-discharge diffraction experiment provides a new and important non-destructive analysis method for the failure analysis and process control of the full battery structure. Lithium-ion battery electrolyte concept The electrolyte is an ionic conductor used for conduction between the positive and negative electrodes of the battery. During the charging and discharging process, lithium ions are transferred back and forth between the positive and negative electrodes. The electrolyte has a relatively large impact on the battery's charge and discharge performance (high and low rate), life (cyclic storage), and temperature application range. Suitable solvents require high dielectric constant and low viscosity. Commonly used are alkyl carbonates such as PC, EC, etc., which have strong polarity, high dielectric constant, but high viscosity, high intermolecular power, and lithium ions move in it. The speed is slow. Linear esters, such as DMC (dimethyl carbonate) and DEC (diethyl carbonate), have low viscosity but low dielectric constant. Therefore, in order to obtain solutions with high ionic conductivity, they are generally used PC+DEC, EC+DMC and other mixed solvents. Electrolytes used in lithium-ion batteries should generally meet the following basic requirements: a. High ionic conductivity, generally should reach 1×10-3~2×10-2S/cm; b. High thermal and chemical stability , No separation occurs in a wide voltage range; c. A wide electrochemical window, to maintain the stability of electrochemical performance in a wide voltage range; d. With other parts of the battery such as electrode materials, electrode current collectors and separators It has good compatibility; e. It is safe, non-toxic and non-polluting. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: How to improve the electrolyte infiltration effect of lithium-ion batteries?