The effect of overheating on lithium batteries and the lithium battery ARC safety assessment method.
In recent years, as lithium batteries have been widely used, lithium battery accidents have occurred frequently along with them. How to test the safety of lithium batteries and how to prevent safety accidents of lithium batteries has been the focus of the industry. Usually, the current technical conditions of the production of lithium batteries have been relatively safe, most of the safety accidents are not in accordance with safety standards and operating specifications for the use of lithium batteries, lithium batteries themselves do not have too many dangers, but when fully charged state, the rapid release of ions resulting in high heat is the culprit of the accident, while the temperature of the lithium battery reflects the thermal state of the battery, the essence of the lithium battery heat generation and heat transfer. The study of the thermal characteristics of lithium batteries and their heat generation and heat transfer characteristics in different states can help us understand the main ways of the occurrence of exothermic chemical reactions of lithium batteries. Standardize the operation standard and prevent the occurrence of safety accidents.
Unsafe behavior
Unsafe behaviors of Li-ion batteries, including battery overcharging and discharging, rapid charging and discharging, short circuit, mechanical abuse conditions and high temperature thermal shock, can easily trigger dangerous side reactions in the battery and make the Li-ion battery generate heat that directly damages the positive and negative electrodes of the passivation film surface. When irreversible damage damage occurs to the lithium battery, it can force the lithium battery to short circuit leading to high heat.
The state of lithium battery when the violent temperature rise occurs
When the temperature of Li-ion battery rises to 130℃, the SEI film on the cathode surface decomposes and the highly active lithium carbon anode is exposed to the electrolyte for violent reoxidation-reduction reaction, and the heat generated causes the battery to enter a high-risk state.
When the internal local temperature of the battery rises above 200℃, oxygen precipitation occurs after the anode is decomposed by the passivation film on the surface of the anode, and continues to react violently with the electrolyte, generating a large amount of heat and forming a higher internal pressure. When the battery temperature reaches above 240°C, the lithium carbon cathode reacts with the binder in a strong exothermic reaction. (Figure I shows)
(Figure I The phase reflection of the violent temperature rise of lithium battery)
Lithium battery safety assessor
Calorimeter is the most important instrument in lithium battery safety research. The most commonly used calorimeter is the accelerated calorimeter, whose English name translates to vacuum rate calorimeter, or ARC for short. ARC is a new type of thermal analysis instrument recommended by the United Nations for the assessment of dangerous goods. It provides time, temperature and pressure data of chemical reactions under adiabatic conditions.
Based on the principle of adiabatic, it can use a larger sample weight, high sensitivity, can accurately measure the initial thermal decomposition temperature of the sample decomposition and the temperature and pressure change curve with time during the adiabatic process, especially the process of slow change of thermal decomposition pressure of materials such as travel scanning calorimetry, which cannot give differential thermal analysis method.
ARC safety assessment method
ARC provides a near adiabatic environment by precise temperature tracking, avoiding heat exchange between the sample under test and the environment, mainly for testing and analyzing the exothermic behavior of the sample under test.
In addition to the test thermal control, the electric arc can provide an adiabatic environment. Combining the arc, DC constant current source and charge/discharge device, the specific heat capacity and adiabatic temperature rise of the battery during charge/discharge can be tested.
The temperature of lithium batteries has a great influence on the safety of lithium batteries. The use of the environment itself is also a certain temperature, and the lithium battery will also generate a certain temperature when in use. In addition, the temperature will have a great impact on the chemical reaction inside the lithium battery. Excessive temperature can even damage the service life of the lithium battery. In serious cases, it will cause the safety of lithium batteries.
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