According to statistics, the global demand for lithium-ion batteries has reached 1.3 billion, and with the continuous expansion of application fields, this figure is increasing year by year. For this reason, with the rapid increase in the use of lithium-ion batteries in various industries, the safety performance of batteries has become increasingly prominent. Lithium-ion batteries are not only required to have excellent charging and discharging performance, but also require higher safety performance. So why did the lithium battery catch fire or even explode? Are there any measures to avoid and eliminate it?
The explosion of the notebook battery is not only related to the production process of the lithium battery cells used in it, but also related to the battery protection board packaged in the battery, the charge and discharge management circuit of the notebook computer, and the heat dissipation design of the notebook. The unreasonable heat dissipation design and charge and discharge management of the notebook computer will overheat the battery cell, thereby greatly increasing the activity of the cell and increasing the chance 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. These battery internal materials include negative electrode materials, electrolytes, separators, and positive electrode materials. Among them, the selection and quality of positive and negative electrode materials directly determine the performance and price of lithium-ion batteries. Therefore, research on low-cost, high-performance positive and negative electrode materials has always been the focus of the development of the lithium-ion battery industry.see more:eve lifepo4
Carbon materials are generally used as negative electrode 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 further reduction in price. In the current commercial production of lithium-ion batteries, the cost of cathode materials accounts for about 40% of the entire battery cost, and the reduction in the price of cathode materials directly determines the reduction in the price of lithium-ion batteries. This is especially true for lithium-ion power batteries. For example, a small lithium-ion battery for a mobile phone only needs about 5 grams of positive electrode materials, while a lithium-ion power battery for driving a bus may require up to 500 kilograms of positive electrode materials.
Although theoretically there are many types of positive electrode materials for lithium-ion batteries, the main component of the common positive electrode material is LiCoO2. When charging, the potential applied to the two electrodes of the battery forces the positive electrode compound to release lithium ions, and the embedded negative electrode molecules are arranged in a sheet structure. in the carbon. When discharging, lithium ions are precipitated from the carbon of the sheet structure and recombined with the compound of the positive electrode. The movement of lithium ions creates an electric current. This is how lithium batteries work.
Lithium battery charge and discharge management design
When the lithium battery is charged, the potential applied to the two poles of the battery forces the positive electrode compound to release lithium ions, which are embedded in the carbon in which the negative electrode molecules are arranged in a sheet structure. When discharging, lithium ions are precipitated from the carbon of the sheet structure and recombined with the compound of the positive electrode. The movement of lithium ions creates an electric current. Although the principle is very simple, in actual industrial production, there are much more practical issues to be considered: the material of the positive electrode needs additives to maintain the activity of multiple charge and discharge, 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 and reduce the internal resistance of the battery.see more:Lithium Ion Battery Pack Manufacturers
Although lithium-ion batteries have the advantages mentioned above, they have relatively high requirements for protection circuits. During use, overcharging and overdischarging should be strictly avoided, and the discharge current should not be too large. Generally speaking, the discharge rate Should not be greater than 0.2C. The charging process of lithium battery is shown in the figure. In a charging cycle, the lithium-ion battery needs to detect the voltage and temperature of the battery before charging to determine whether it can be charged. Do not charge if the battery voltage or temperature is outside the range allowed by the manufacturer. The voltage range allowed for charging is: 2.5V~4.2V per battery.
When the battery is in deep discharge, the charger must have a pre-charging process to make the battery meet the conditions of fast charging; then, according to the fast charging speed recommended by the battery manufacturer, generally 1C, the charger will charge the battery with a constant current. The battery voltage rises slowly; once the battery voltage reaches the set end 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 Attenuation, until the charging rate drops below C/10 or the full charging time is overtime, it will switch to the top cut-off charging; when the top cut-off charging, the charger will replenish energy for the battery with a very small charging current. After the top end of charging for a period of time, turn off the charging.