22 Years' Battery Customization

How to set up a safe lithium battery protection circuit

Jun 28, 2019   Pageview:1012

According to statistics, the global demand for lithium-ion batteries has reached 1.3 billion, and this data is increasing year by year as the application field continues to expand. For this reason, with the rapid increase in the consumption of lithium-ion batteries in various industries, the safety performance of batteries has become increasingly prominent, requiring not only lithium-ion batteries with excellent charging and discharging performance, but also higher safety performance. Why is there a fire or even an explosion? What measures can be taken to avoid and eliminate it?

 

The explosion of the laptop battery is not only related to the production process of the lithium battery cell used therein, 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 cells, thereby greatly increasing the activity of the battery cells and increasing the probability of explosion and burning.

 

Analysis of the composition and performance of lithium battery materials

 

First, let's take a look at the material composition of lithium batteries. The performance of lithium-ion batteries depends mainly on the structure and properties of the materials inside the batteries used. These battery internal materials include a negative electrode material, an electrolyte, a separator, a positive electrode material, and the like. The choice and quality of the positive and negative materials directly determine the performance and price of the lithium ion battery. Therefore, the research of low-cost, high-performance positive and negative materials has always been the focus of the development of the lithium-ion battery industry.

 

The anode material is generally made of carbon material, and the current development is relatively mature. The development of cathode materials has become an important factor that restricts the performance of lithium-ion batteries and further reduces the price. In the current commercial production of lithium-ion batteries, the cost of the cathode material accounts for about 40% of the total battery cost. The reduction in the price of the cathode material directly determines the price of the lithium-ion battery, especially for lithium-ion batteries. For example, a small lithium-ion battery for a mobile phone requires only about 5 grams of positive electrode material, and a lithium-ion battery that drives a bus may require a positive electrode material of up to 500 grams.

 

Although theoretically it can be used as a cathode material for lithium ion batteries, the main component of the common cathode material is LiCoO2. When charging, the potential applied to the poles of the battery forces the cathode compound to release lithium ions, and the embedded anode molecules are arranged in a sheet structure. In the carbon. At the time of discharge, 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 produces a current. This is the principle of working lithium batteries.

 

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, and is embedded in the carbon in which the negative electrode molecules are arranged in a sheet structure. At the time of discharge, 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 produces a current. Although the principle is very simple, in practical industrial production, there are many practical problems 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 electrical conductivity, reducing the internal resistance of the battery.

 

Although lithium-ion batteries have all the advantages mentioned above, they have higher requirements on the protection circuit. In the process of use, excessive charging and over-discharge should be strictly avoided, and the discharge current should not be too large. Generally speaking, The discharge rate should not be greater than 0.2 degrees Celsius. The charging process of the lithium battery is shown in the figure. During a charging cycle, the lithium-ion battery needs to detect the voltage and temperature of the battery before charging begins to determine whether it is chargeable. Charging is prohibited if the battery voltage or temperature is outside the range allowed by the manufacturer. The voltage range that allows charging is: 2.5 v ~ 4.2 v per cell.

 

In the case of 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 1 C, the charger performs constant current charging on the battery. The battery voltage rises slowly. Once the battery voltage reaches the set termination voltage (typically 4.1 v or 4.2 v), the constant current charge is terminated, the charging current is rapidly attenuated, and the charging enters a full charge process. During the full charge process, the charging current is charged. Gradually decay until the charge rate drops below C / 10 or when the full charge time expires, turn to the top cut-off charge; when the top cuts off the charge, the charger replenishes the battery with a very small charge current. After the top end is turned off for a while, the charging is turned off.

 

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