Lithium battery safety assessment and test methods. This year, lithium batteries have frequent safety accidents in electric vehicle power batteries. How to evaluate and test the safety of lithium batteries, better prevention of lithium battery safety accidents has been the industry A point of concern.
The temperature of the lithium battery shows the thermal state of the battery, the essence of which is the result of heat generation and heat transfer of the lithium battery. Studying the thermal characteristics of the lithium battery, and its heat generation and heat transfer characteristics under different conditions, It allows us to recognize the main way of exothermic chemical reactions inside lithium batteries.
Unsafe behavior
The unsafe behavior of lithium batteries, including overcharge and overdischarge, rapid charge and discharge, short circuit, mechanical abuse conditions and high temperature thermal shock, can easily trigger dangerous side reactions inside the battery to generate heat, directly destroying the negative and positive surfaces. Passivation film.
When the cell temperature rises to 130 °C, the SEI film on the surface of the negative electrode decomposes, causing the high-activity lithium carbon anode to be exposed to the electrolyte to undergo a vigorous redox reaction, and the heat generated causes the battery to enter a high-risk state.
When the internal temperature of the battery rises above 200 °C, the passivation film on the surface of the positive electrode decomposes and generates oxygen, and continues to react violently with the electrolyte to generate a large amount of heat and form a high internal pressure. When the battery temperature reaches 240 °C or higher , also accompanied by a strong exothermic reaction of the lithium carbon anode with the binder.
Lithium battery safety evaluation instrument
In the research of lithium battery safety, calorimeter is the most important instrument. The most commonly used calorimeter is accelerometer, the English name is accelerating rate calorimeter, ARC. ARC is recommended by the United Nations for dangerous goods evaluation. A new thermal analysis instrument that provides time-temperature-pressure data for chemical reactions under adiabatic conditions.
ARC is designed based on adiabatic principle, can use a large sample volume, high sensitivity, can accurately measure the initial temperature of thermal decomposition of the sample, temperature and pressure change curve with time during adiabatic decomposition, especially can give differential scanning calorimetry And the differential pressure analysis method can not give the material slowly change the pressure during thermal decomposition.
ARC safety assessment method
Through accurate temperature tracking, ARC avoids the heat exchange between the sample and the environment, which can provide an environment of near-insulation. It mainly tests and analyzes the exothermic behavior of the sample to be tested.
In addition to testing thermal runaway, ARC can provide the characteristics of adiabatic environment. ARC can be combined with DC constant current source and charge and discharge equipment to test the specific heat capacity of the battery and the adiabatic temperature rise of the charge and discharge process.
The temperature problem of the lithium battery has a great influence on the safety of the lithium battery. The environment used also has a certain temperature, and the lithium battery also generates temperature when it is used. What is important is that the temperature will be inside the lithium battery. The chemical reaction has a large impact, and the temperature is too high, which may even damage the service life of the lithium battery. In severe cases, the safety of the lithium battery may be caused.
