The influence of overheating on lithium batteries and the ARC safety assessment method for lithium batteries

The influence of overheating on lithium batteries and the ARC safety assessment method for lithium batteries. In recent years, as lithium batteries have been widely used, there have been frequent lithium battery accidents. How to detect the safety of lithium batteries and how to prevent safety accidents of lithium batteries has always been the focus of the industry. Under normal circumstances, lithium batteries produced under current technical conditions are relatively safe. Most safety accidents are caused by the use of lithium batteries not in accordance with safety standards and operating specifications. Lithium batteries do not have too many dangers, but when fully charged In the state, the high heat caused by the rapid release of electric ions is the culprit of the accident. At the same time, the temperature of the lithium battery reflects the thermal state of the battery, which is essentially the heating and heat transfer of the lithium battery. Studying the thermal characteristics of lithium batteries and their calorific value and heat transfer characteristics under different conditions can help us understand the main ways in which the exothermic chemical reactions of lithium batteries occur. Standardize operating standards to prevent safety accidents. Unsafe behaviors Unsafe behaviors of lithium batteries, including battery overcharging and discharging, rapid charging and discharging, short circuits, mechanical abuse conditions, and high temperature thermal shock, can easily trigger dangerous side reactions in the battery and cause the lithium battery to generate heat, which is directly destroyed Positive and negative electrodes on the surface of the passivation film. When the lithium battery is irreversibly damaged, it will force the lithium battery to short-circuit and cause high heat. The state of the lithium battery when the temperature rises sharply. When the temperature of the lithium battery rises to 130°C, the SEI film on the cathode surface is decomposed, and the high-activity lithium carbon anode is exposed to the electrolyte to undergo a violent re-redox reaction, and the heat generated causes the battery to enter High-risk state. When the internal temperature of the battery rises above 200°C, the anode is decomposed by the passivation film on the surface of the positive electrode and oxygen will be precipitated. It will continue to react violently with the electrolyte, generating a lot of heat and forming a higher internal pressure. When the battery temperature reaches above 240°C, the lithium carbon cathode and the binder undergo a strong exothermic reaction. (Picture 1) (Picture 1 The stage reflection of the violent temperature rise of lithium battery) Lithium battery safety assessment instrument In the lithium battery safety research, the calorimeter is the most important instrument. The most commonly used calorimeter is the accelerating calorimeter. Its English name is translated as vacuum rate calorimeter, abbreviated as ARC. ARC is a new type of thermal analysis instrument recommended by the United Nations for the assessment of dangerous goods. It provides the time, temperature and pressure data of the chemical reaction under adiabatic conditions. Based on the adiabatic principle, a larger sample weight can be used, and the sensitivity is high. It can accurately measure the initial thermal decomposition temperature of the sample and the temperature and pressure change curve over time during the adiabatic process, especially the travel scanning calorimetry. It is impossible to give a process in which the thermal decomposition pressure of materials such as the differential thermal analysis method changes slowly. ARC safety assessment method ARC avoids the heat exchange between the tested sample and the environment through accurate temperature tracking, and provides an almost adiabatic environment. It mainly tests and analyzes the exothermic behavior of the tested sample. In addition to testing thermal control, the arc can provide an adiabatic environment. Combining electric arc, DC constant current source and charging and discharging device, it can test the specific heat capacity and adiabatic temperature rise of the battery during charging and discharging. The temperature of the lithium battery has a great influence on the safety of the lithium battery. The use environment itself also has a certain temperature, and the lithium battery will also produce a certain temperature during use. In addition, temperature has a great influence on the chemical reaction inside the lithium battery. Excessive temperature can even damage the service life of lithium batteries. In severe cases, it will cause safety problems for lithium batteries. Disclaimer: The articles published on this site are all from the Internet and do not represent the views of this site. If there is any infringement, please contact to delete WeChat: Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact delete A: The Ministry of Industry and Information Technology said that power batteries need to shift the center of gravity to system safety