The explosion mechanism of lithium batteries

There are many reasons for the explosion of lithium batteries, but the important reason is that the high temperature and high pressure inside the battery are directly related to heat generation factors. There are many heat-generating factors inside the battery. If the heat generation rate inside the lithium battery is greater than the heat loss rate, the reaction temperature in the system will continue to rise, which may result in two extreme situations: (1) The temperature of the reacting substance reaches its limit. Fire occurs at the ignition temperature; (2) Since the lithium battery is a closed system, as the internal temperature of the system increases, the reaction speed increases, and the vapor pressure of the reactants rises sharply. At the same time, the analysis of active materials will produce a certain amount of gas in the reaction of active materials and electrolyte. As a result, in the absence of safety valve protection or safety valve failure, the internal pressure of the battery will rise sharply and cause the battery to explode. The common types of explosions are as follows: 2.1. Thermal shock explosion Take the LCO battery as an example. Put it in an environment of 165°C and keep it for 45 minutes to explode. The diaphragm dissolves (the melting point of PE is 125°C, and the melting point of PP is 155° C) The voltage drops rapidly to 0V and the surface temperature of the battery rises above 200°C. The explosion of the battery is caused by a large amount of heat and gas due to the analysis of the solvent, the analysis of LiCoO2, and the reaction between LiCoO2 and the electrolyte. 2.2. Overcharge explosion The voltage-temperature mode of overcharged lithium batteries has three forms: (1) When the charging voltage exceeds 4.5V, a large amount of lithium ions overflow from the positive electrode. If the negative electrode’s ability to insert lithium is very poor, lithium ions will deposit on the surface of the negative electrode to form dendrites to short-circuit the battery, and the battery’s safety is clearly reduced; (2) If the negative electrode’s ability to insert lithium is relatively strong, as lithium ions move from the positive electrode The overflowing solvent is oxidized (much higher than the reaction rate under normal conditions), and a large amount of heat appears to increase the temperature of the battery, and then the reaction between the solvent and the negative electrode simultaneously emits more heat. If the charging current is very low, the thermal stability of the battery is good, and the heat generation rate and the heat dissipation rate are balanced. The product of the electrolyte analysis increases the internal resistance of the battery, or the diaphragm is closed. The voltage increases first and remains constant after burning, and the heat will not run out ; (3) If the charging current is large, the stability of the battery is still very poor, and the voltage and temperature rise rapidly, the battery will catch fire and explode. For example, when a lithium battery is charged to 160% of the standard power, the heat increases sharply, which may be caused by a large amount of heat in the analysis of the electrolyte and the analysis reaction of the positive electrode. If a heat sink is added to the battery to balance the heat release, the battery The explosion will be on alert. 2.3. Short-circuit explosion is divided into external short-circuit and internal short-circuit: straight contact between the positive and negative ears; burrs, diaphragm wrinkles and dust during assembly can cause internal short-circuits, and short-circuits may also cause battery explosion. When the battery is short-circuited, a large amount of heat appears when the current passes through the battery, which heats the battery, and the thermal analysis temperature increases the battery temperature and causes the battery to explode. The biggest difference from heating is that the rate of heat generation is slower, and each reaction proceeds in sequence. In a short-circuit state, the thermal analysis reaction of the positive electrode may occur before the negative electrode reacts with the solvent. 2.4. Acupuncture in other situations: The principle of lithium battery explosion caused by acupuncture is roughly the same as that of a short circuit. When the acupuncture speed is very fast, a lot of heat will appear at the acupuncture site, which will increase the internal temperature of the battery to the temperature of the thermal analysis of the positive electrode. Cause the battery to explode. Impact: When a lithium battery is impacted, the over-voltage loss on the electrode will cause heat to cause the solvent to react with the negative electrode. The heat released will further heat the battery to thermally analyze the positive electrode, causing the battery to explode. Overdischarge: When the lithium battery is overdischarged to 1.0-2.0V, part of the electrolyte will be reduced to release a small amount of heat. After the voltage reached 0.7V, the metal copper began to deposit on the positive electrode, the internal short circuit of the battery, the voltage quickly dropped to 0V, and the lithium battery became a Cu negative electrode. The Cu positive battery bladder surface temperature increased unclearly without danger. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: What are the key processing techniques for lithium batteries