How to set up a safe lithium battery protection circuit

　　Why do lithium batteries catch fire or even explode? Are there any measures to avoid and stop them?

　　According to statistics, the global demand for lithium-ion batteries has reached 1.3 billion, and with the continuous expansion of application fields, this data is increasing year by year. Because of this, with the rapid increase in the use of lithium-ion batteries in various industries, the safety performance of batteries has become increasingly prominent. Not only are lithium-ion batteries required to have excellent charging and discharging performance, but also higher safety performance. So why did the lithium battery catch fire or even explode? Are there any measures to avoid and stop it? 　　 The explosion of laptop batteries is not only related to the production process of the lithium battery cells used in it, but also to the battery protection board and laptop encapsulated in the battery. The charging and discharging management circuit and the heat dissipation design of the notebook are related. The unreasonable heat dissipation design and charge-discharge management of the notebook computer will cause the battery cell to overheat, thereby greatly increasing the activity of the cell, and increasing the probability of explosion and combustion.　　 Lithium battery material composition and performance analysis 　　 First of all, let's understand the material composition of lithium batteries. The performance of lithium ion batteries mainly depends on the structure and performance of the internal materials used in the battery. The internal materials of these batteries include negative electrode materials, electrolytes, separators, and positive electrode materials. Among them, the choice and quality of positive and negative materials directly determine the performance and price of lithium-ion batteries. Therefore, the research of cheap, high-performance positive and negative materials has always been the focus of the development of the lithium-ion battery industry.　　 Carbon materials are generally used as anode materials, and the current development is relatively mature. The development of cathode materials has become an important factor restricting the further improvement of lithium-ion battery performance and the further reduction of prices. In the current commercial production of lithium-ion batteries, the cost of the cathode material accounts for about 40% of the entire battery cost, and the decrease in the price of the cathode material directly determines the decrease in the price of the lithium-ion battery. This is especially true for lithium-ion power batteries. For example, a small lithium-ion battery used in a mobile phone only needs about 5 grams of positive electrode material, while a lithium-ion power battery used to drive a bus may require up to 500 kilograms of positive electrode material. Although theoretically there are many types of positive electrode materials that can be used as lithium-ion batteries, the main component of common positive electrode materials is LiCoO2. When charging, the electric potential applied to the two poles of the battery forces the compound of the positive electrode to release lithium ions, and the molecules of the negative electrode are arranged in a layered structure. In the carbon. During discharge, lithium ions are precipitated from the carbon of the sheet structure and recombine with the compound of the positive electrode. The movement of lithium ions generates an electric current. This is how the lithium battery works.　　Lithium battery charge and discharge management design　　When the lithium battery is charged, the electric potential applied to the two poles of the battery forces the compound of the positive electrode to release lithium ions, which are embedded in the carbon in which the molecules of the negative electrode are arranged in a sheet structure. During discharge, lithium ions are precipitated from the carbon of the sheet structure and recombine with the compound of the positive electrode. The movement of lithium ions generates an electric current. Although the principle is very simple, in actual industrial production, there are many practical issues that need to be considered: the material of the positive electrode needs additives to maintain the activity of multiple charging and discharging, and the material of the negative electrode needs to be designed at the molecular structure level to accommodate more More lithium ions; the electrolyte filled between the positive and negative electrodes, in addition to maintaining stability, also needs to have good conductivity to reduce the internal resistance of the battery. Although lithium-ion batteries have all the advantages mentioned above, they have relatively high requirements for protection circuits. Overcharge and overdischarge should be strictly avoided during use, and the discharge current should not be too large. Generally speaking, the discharge rate It should not be greater than 0.2C. The charging process of the lithium battery is shown in the figure. In a charging cycle, the lithium-ion battery needs to detect the battery's voltage and temperature before charging to determine whether it is rechargeable. If the battery voltage or temperature exceeds the manufacturer's allowable range, charging is prohibited. The allowable charging voltage range is: 2.5V~4.2V per battery. When the battery is in deep discharge, the charger must be required to have a pre-charging process to make the battery meet the conditions for fast charging; then, according to the fast charging speed recommended by the battery manufacturer, which is generally 1C, the charger will charge the battery with constant current. The battery voltage rises slowly; once the battery voltage reaches the set termination voltage (generally 4.1V or 4.2V), the constant current charging is terminated, the charging current decays rapidly, and the charging enters the full charging process; during the full charging process, the charging current gradually Attenuate until the charging rate drops below C/10 or when the full charge time expires, it will switch to the top end of charging; when the top end of charging, the charger will replenish energy for the battery with a very small charging current. After charging for a while at the top end, turn off charging.