Lithium-ion batteries are sensitive to bad handling. When we charge the battery below the margin defined by the manufacturer, fire, explosion and other dangerous situations may occur.
During normal use, lithium-ion batteries undergo a positive chemical reaction in which electrical energy and chemical energy are converted into each other. However, under certain conditions, such as overcharging, overdischarging, or overcurrent operation, it is easy to cause chemical side reactions inside the battery; when the side reactions intensify, they will seriously affect the performance and service life of the battery, and may produce a large amount of gas, causing the pressure inside the battery to increase rapidly, and then explode and catch fire, leading to safety problems.
After 30 years of industrial development, lithium-ion battery products have made great progress in safety technology, effectively controlling the occurrence of side reactions in the battery and ensuring the safety of the battery. However, as lithium-ion batteries are used more and more widely and their energy density is getting higher and higher, there have been frequent explosions and injuries or product recalls due to safety hazards in recent years.
The materials used in lithium-ion battery cells include: positive electrode active materials, negative electrode active materials, separators, electrolytes and shells, etc. The selection of materials and the matching of the system they form determine the safety performance of the battery cells. When selecting positive and negative electrode active materials and separator materials, manufacturers did not conduct certain assessments on the characteristics and matching of the raw materials, resulting in inherent deficiencies in the safety of the battery cells.
The raw materials of battery cells are not strictly inspected and the production environment is poor, resulting in impurities mixed in during production, which is not only detrimental to the capacity of the battery, but also has a great impact on the safety of the battery. In addition, if too much water is mixed into the electrolyte, side reactions may occur, increasing the internal pressure of the battery and affecting safety. Due to the limitations of the production process, during the production process of the battery cells, the products cannot achieve good consistency. For example, problems such as poor flatness of the electrode matrix, shedding of electrode active materials, mixing of other impurities in the active materials, loose welding of the pole ears, unstable welding temperature, burrs on the edges of the pole pieces, and no use of insulating tape in key parts may have an adverse effect on the safety of the battery cells.
Modern battery chargers can manage dangerous situations and refuse to operate when illegal situations occur. However, this fact does not mean that all cells are bad. In most cases, we can replace exhausted cells and extend the life of the equipment. Figure 1 shows the circuit used to test the battery pack.
Figure 1 An LED indicates the health of a battery based on its voltage.
When the supply voltage is below 2.6V, no current drives the base of the transistor. LED 1 turns on and LED 2 turns off. When the voltage exceeds 2.6V, the transistor begins to short LED 1, turning it off and lighting LED 2. This condition indicates that the battery is below the allowed charge limit. Voltage margin depends largely on the type or color of LED selected. A standard red LED has a forward voltage of 1.7V; a green LED, about 2.1 or 2.2V. The circuit in this design uses a red LED, which has a forward voltage of about 1.6V and a current of 2 mA. Other LEDs may require simple redesigns, mainly the need to use Schottky diodes instead of the 1N4148 in this circuit. Even white or blue LEDs with a forward voltage of 3V or more may be suitable for some applications.
A low-value resistor will increase the brightness of the LED, but it will also increase the supply current. Table 1 shows how this indicator provides three operating states. Although this simple device consumes very little current, we cannot expect long battery life if we use the device as a display, especially when it is stored. While a fully charged 32-Ahr battery will fail in about a year, an empty battery of the same size but with slightly more than the allowable charge margin will fail in a day or two.
We can build a range of indicators in one test module. By connecting to the measure/balance port of the package, we can easily check the entire package with one view. Adding a Zener diode in series to the LED also makes this circuit a simple indicator of higher voltage levels.
Simple and practical detection circuit
It is recommended to add a resistor between be and so as to detect the critical voltage of the battery more accurately.
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Published on 2024-7-5 10:55
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