Analysis of Li-ion Battery Safety Issues

In recent years, the market demand for lithium-ion batteries has increased day by day, and higher requirements have been placed on the energy density and safety of lithium-ion batteries. However, in recent years, safety accidents caused by the burning and explosion of lithium-ion batteries are not uncommon, such as the explosion and fire of the Samsung Galaxy Note 7 battery, the spontaneous combustion of Tesla electric vehicles, and the smoke storm from the lithium battery of the Boeing 737 airliner, which have severely affected consumer confidence. , Causing people to panic and safety concerns about the entire lithium battery industry. The development trend of lithium batteries 01 The development trend of lithium batteries As lithium batteries are more and more widely used in electronic devices and other products, even in satellites, aviation, etc., people’s understanding of lithium batteries is becoming more and more profound. At the same time, Higher requirements are also put forward for the safety of lithium batteries. 02 Problems facing the development of lithium batteries in China Many important raw materials for the development of lithium batteries in my country have to rely on foreign imports, and the raw material industry chain of anode materials is not perfect. Therefore, there is still a long way to go to improve the industrial chain of lithium battery production that belongs to our country. (Future development trend of lithium battery technology) Cause analysis of lithium-ion battery safety problems From external reasons, overcharge, overdischarge, battery short-circuit, thermal shock, needle sticks, etc. will all cause safety problems for lithium-ion batteries. From the analysis of internal reasons, the safety problems of lithium-ion batteries are mainly caused by the following points: 01 negative electrode lithium due to the slow kinetics of intercalation in the negative electrode material, in the case of low temperature overcharge or high current charging, metal lithium will directly precipitate in The surface of the negative electrode may cause lithium dendrites, causing micro short circuits. The highly active metal lithium and the liquid electrolyte directly undergo a reduction reaction, which loses active lithium, increases internal resistance, and affects battery performance. As the cycle continues, lithium dendrites will further increase, and then pierce the diaphragm, causing the battery to short-circuit, leak, and even explode. 02 Oxygen release and structural destruction of cathode materials. When the anode is charged to a higher voltage, it is in a high oxidation state. The oxygen in the crystal lattice easily loses electrons and precipitates in the form of free oxygen. The free oxygen will oxidize with the electrolyte and release a large amount of oxygen. The organic electrolyte with low ignition point is extremely unsafe in the presence of oxygen and the temperature rises, so that the battery is very easy to burn and explode. 03 Electrolyte decomposition and reaction The electrolyte of liquid lithium-ion battery is a mixed solution of lithium salt and organic solvent, among which the commercial lithium salt is lithium hexafluorophosphate. This material is prone to thermal decomposition at high temperatures and will interact with trace amounts of water and organic solvents. Between the thermochemical reaction. The organic solvents of the electrolyte are carbonates. Such solvents have a low boiling point and flash point, and are easy to react with PF5 released by lithium salt at high temperature and are easy to be oxidized. When lithium and oxygen are present, a series of exothermic side reactions will occur, directly affecting the battery performance, and even causing the battery to catch fire and explode. 04 Poor separator uniformity and shrinkage rupture. When lithium dendrites pierce the separator or the separator shrinks and ruptures at high temperatures, it will short-circuit the positive and negative electrodes of the battery. In severe cases, it will cause safety accidents. 05 High temperature failure High temperature can come from external reasons, or from internal short circuits, electrochemical and chemical exothermic reactions, and large current Joule heat. At high temperatures, a series of adverse reactions will occur inside the battery, such as the decomposition of SEI film, the reaction of highly active positive and negative materials with the electrolyte, the self-decomposition of lithium salts, the release of oxygen from the positive electrode, and the reaction of the electrolyte. These reactions are possible Causes heat to run out of control. Both the industry and the academia have taken a variety of improvement measures for the safety of lithium battery technology from materials, electrodes, cells, modules, power management, thermal management, system design and other levels. Although certain progress has been made, there has been no improvement. To achieve the desired effect, its safety issues are still very prominent. Therefore, how to break through this technical bottleneck, meet the needs of high-safety battery technology, and develop non-flammable and explosive lithium batteries is very necessary and urgent.