According to statistics, the global demand for lithium-ion batteries has reached 1.3 billion, and with the continuous expansion of application fields, the data is increasing year by year. Because of this, with the rapid surge of lithium ion battery consumption in various industries, the safety performance of the battery is also increasingly prominent, not only requires lithium ion batteries with excellent charging and discharging performance, but also requires higher safety performance. Then why do lithium batteries catch fire or even explode? What measures can be taken to avoid and eliminate them?
Analysis of material composition and performance of 01 lithium battery
First of all, let‘s understand the material composition of lithium battery. The performance of lithium ion battery mainly depends on the structure and performance of the materials inside the battery. The internal materials of these batteries include anode material, electrolyte, diaphragm and positive material. The choice and quality of anode and cathode materials directly determine the performance and price of lithium-ion batteries. Therefore, the research of cheap, high-performance positive and negative electrode materials has been the focus of the development of lithium ion battery industry.
The anode material is generally carbon material, which is mature at present. However, the development of cathode materials has become an important factor restricting the further improvement of lithium-ion battery performance and price. In the current commercial production of lithium-ion batteries, the cost of cathode material accounts for about 40% of the entire battery cost, and the price of cathode material directly determines the price reduction of lithium-ion batteries. This is especially true for lithium-ion power batteries. A small lithium-ion battery for a mobile phone, for example, requires only about five grams of cathode material. A lithium-ion battery to power a bus might require up to 500 kilograms of cathode material.
Although there are many types of material that could theoretically be used as a cathode for lithium-ion batteries, the common cathode material is LiCoO2. When charging, the electric potential applied to the two poles of the battery forces the cathode compound to release lithium ions and become embedded in the lamellar carbon where the negative molecules are arranged. When discharged, the lithium ions precipitate out of the lamellar carbon and recombine with the positive compound. The movement of lithium ions creates an electric current. That‘s how lithium batteries work.
02 Lithium battery charge and discharge management design
Although the principle is very simple, but in the actual industrial production, there are many more practical problems to consider: the material of the positive electrode needs additives to maintain the activity of multiple charging, the material of the negative electrode needs to be designed at the molecular structure level to accommodate more lithium ions; The electrolyte filled between the positive and negative electrodes, in addition to maintaining stability, needs to have good conductivity and reduce the internal resistance of the battery.
Although lithium ion battery has the above advantages, but it has high requirements for the protection circuit, in the process of use should strictly avoid the phenomenon of over charging, over discharge, discharge current should not be too large, generally speaking, discharge rate should not be greater than 0.2C. Within a charging cycle, lithium-ion batteries need to check the battery voltage and temperature before charging to determine whether they can be charged. If the battery voltage or temperature exceeds the manufacturer‘s permissible range, do not charge it. The charging voltage ranges from 2.5V to 4.2V for each battery.
When the battery is in deep discharge, the charger must be required to have a precharge process, so that the battery can meet the conditions of fast charging; Then, according to the fast charging speed recommended by the battery manufacturer, usually 1C, the charger charges the battery at constant current, and the battery voltage rises slowly. Once the battery voltage reaches the set termination voltage (generally 4.1V or 4.2V), the constant current charging terminates, the charging current rapidly attenuates, and the charging enters the full charging process; In the process of full charging, the charging current gradually attenuates until the charging rate is reduced to below C/10 or the full charging time is timeout, and the top cut-off charging; At the top end, the charger replenishes the battery with a very small charging current. After a period of time, turn off the charge.
