The explosion of a notebook battery is not only related to the production process of the lithium battery cells used in it, but also 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-discharge management of notebook computers will overheat the battery cells, thereby greatly increasing the activity of the cells, and at the same time increasing the probability of explosion and burning.
Lithium battery material composition and performance analysis
First, let's take a look at the material composition of lithium batteries. The performance of lithium ion batteries mainly depends on the structure and performance of the internal materials of the battery used. These battery internal materials include negative electrode materials, electrolytes, separators, and positive electrode materials. Among them, the selection and quality of positive and negative materials directly determine the performance and price of lithium-ion batteries. Therefore, the research on cheap and high-performance positive and negative electrode materials has always been the focus of the development of the lithium-ion battery industry.
The negative electrode material is generally made of carbon material, 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 price. In the current commercial production of lithium-ion batteries, the cost of cathode materials accounts for about 40% of the cost of the entire battery, 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 requires only about 5 grams of positive electrode material, while a lithium-ion power battery for driving a bus may require up to 500 kilograms of positive electrode material.
Although there are many types of cathode materials that can theoretically be used for lithium-ion batteries, the common cathode material is LiCoO2. When charging, the potential applied to the two poles of the battery forces the compounds of the cathode to release lithium ions, and the molecules of the embedded anode are arranged in a lamellar structure. in carbon. During discharge, lithium ions are precipitated from the carbon in the lamellar structure and recombine with the compound of the positive electrode. The movement of lithium ions creates an electrical 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 compound of the positive electrode to release lithium ions, which are embedded in the carbon where the molecules of the negative electrode are arranged in a lamellar structure. During discharge, lithium ions are precipitated from the carbon in the lamellar structure and recombine with the compound of the positive electrode. The movement of lithium ions creates an electrical current. Although the principle is very simple, in actual industrial production, there are many practical problems 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 In addition to maintaining stability, the electrolyte filled between the positive and negative electrodes also needs to have good conductivity and reduce the internal resistance of the battery.
Although the lithium-ion battery has the advantages mentioned above, it has relatively high requirements on the protection circuit. During use, overcharge and overdischarge 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 the 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 starts to determine whether it can be charged. Charging is prohibited if the battery voltage or temperature is outside the manufacturer's allowable range. The allowable charging voltage range is: 2.5V~4.2V per cell.
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 of fast charging; then, according to the fast charging speed recommended by the battery manufacturer, generally 1C, the charger charges the battery with constant current, The battery voltage rises slowly; once the battery voltage reaches the set termination voltage (usually 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 is overtime, switch to the top cut-off charging; when the top cut-off charging, the charger supplements the battery with a very small charging current. After the top end of charging for a period of time, turn off the charging.