Detailed explanation of the impact of materials on the safety of lithium-ion power lithium-ion batteries

Generally speaking, the thermal stability of battery materials is an important factor in the safety of lithium-ion power lithium-ion batteries. This is closely related to the thermal activity of the battery material. When the temperature of the battery rises, many exothermic reactions occur inside the battery. If the heat generated exceeds the heat dissipation, a thermal overflow will occur. The important exothermic reactions between lithium battery materials include: SEI film analysis; electrolyte analysis; positive electrode analysis; the reaction between the negative electrode and the electrolyte; the reaction between the negative electrode and the binder; in addition, due to the resistance of the battery, a small amount is also present during use Heat. 3.2.1 Cathode materials Lithium battery cathode materials have always been the key to limiting the development of lithium batteries. Compared with the negative electrode material, the positive electrode material has low energy density and power density, and it is also an important reason for the safety of lithium batteries. The structure of the positive and negative electrode materials has a decisive influence on the insertion and extraction of lithium ions, thus affecting the cycle life of the battery. Using active materials that are easy to deintercalate, the structure of the active material changes small and reversible during charge and discharge cycles, which is beneficial to prolong the life of the battery. Under the conditions of abuse of lithium batteries, as the internal temperature of the battery rises, the positive electrode undergoes active material analysis and electrolyte oxidation. These two reactions will generate a lot of heat, which will lead to a further increase in battery temperature. The delithiation state has very different effects on the lattice transformation of the active material, the analysis temperature and the thermal stability of the battery. Finding positive materials with better thermal stability is the key to lithium-ion power lithium-ion batteries. Layered LiCoO2, LiNiO2, spinel LiMn2O4 and olivine LiFePO4 are currently more researched cathode materials. LiCoO2 has moderate thermal stability and excellent electrochemical performance. However, due to the limitation of cobalt resources, the use of LiCoO2 in lithium-ion power lithium-ion batteries is restricted; although LiNiO2 has a high capacity, it is difficult to synthesize and has poor cycle performance and is not suitable As the cathode material of lithium-ion power lithium-ion batteries; LiMn2O4 has good thermal stability, abundant resources, and low price, which is suitable as the cathode material of lithium-ion power lithium-ion batteries; LiFePO4 has abundant synthetic raw materials, low cost, and no pollution to the environment. It also has higher specific capacity, effective utilization, suitable voltage and better cycle performance, and it is one of the promising lithium ion cathode materials. 3.2.2 Anode material The negative electrode material used in the early days is metal lithium, and the battery assembled with metal lithium as the negative electrode is prone to lithium dendrites during multiple charging and discharging processes. The lithium dendrites will pierce the diaphragm and cause the battery to short circuit and leak. There was even an explosion. The use of lithium intercalation compounds guards against the appearance of lithium dendrites, thereby greatly improving the safety of lithium batteries. At present, there are three types of carbon with more use value and prospects in lithium ion secondary batteries: one is highly graphitized carbon, the other is soft carbon and hard carbon, and the third is carbon nanomaterials. Currently, most of the negative electrode materials used in lithium batteries use graphite, and the theoretically appropriate specific capacity of graphite is only 372mAh/g, and the volumetric specific capacity is only 800mAh/cm3. Although the currently developed medical pyrolytic carbon has a specific capacity of 700 mAh/g, its volume specific capacity is still very limited. Due to the need for high power, metal and metal compound jealous materials with high energy density have attracted widespread attention, and the research needs to develop into small particles (nano-level), single-phase to multi-phase, and doped inactive materials. During the cycle of metal and alloy negative electrodes, the volume will change greatly and the cycle life is short. In order to extend the life, the metallurgical approximation method is used to develop and control the composition and microstructure (nano-level) and surface solution technology of alloy materials. Research statement: As the temperature increases, the carbon negative electrode in the lithium-intercalated state will first have an exothermic reaction with the electrolyte. Under the same charging and discharging conditions, the heat release rate of the reaction between electrolyte and lithium-intercalated artificial graphite is much greater than that of lithium-intercalated MCMB, carbon fiber, coke, etc. The carbon layer spacing of hard carbon materials, soft carbon materials, and graphite materials are about 0.38nm, 0.34~0.35nm, and 0.335nm, respectively. When lithium is embedded in the carbon layer, the layer spacing is about 0.371nm. Graphite materials have the smallest interlayer spacing and the largest deformation during the insertion and extraction of lithium batteries. The diffusion speed of lithium ions in this type of carbon layer is also slow. When charging and discharging with high currents, the polarization and resistance are large, and the battery The safety of hard carbon materials is the opposite. However, it is also believed that the newly added degree of graphitization can reduce the activation performance of lithium ion diffusion and facilitate the diffusion of lithium ions. However, due to the large number of cavities in hard carbon materials, the performance of hard carbon materials is close to that of lithium metal anodes when charged and discharged at high current , Security is not good. In the exploration of new materials, lithiated transition metal nitrides and transition metal phosphorus compounds are good examples. Further research on these materials may inject new vitality into the development of lithium ion battery anode materials. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: What are the advantages of lithium batteries for UPS backup power supply?