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Lithium battery protection circuit design Views [0] Published: 2017-12-07 11:02:01


With the rapidly increasing lithium-ion rechargeable battery usage in various industries, the battery safety performance is also increasingly prominent, not only requires lithium-ion batteries with excellent charge and discharge performance, but also requires a higher safety performance. The lithium battery in the end why the fire or even explode it, what measures can be avoided and put an end to it?


Material Composition and Performance of Lithium Battery


First of all, let's look at the material composition of lithium batteries, lithium-ion battery performance depends on the structure and performance of the internal materials used in the battery. The internal materials of these batteries include anode materials, electrolytes, separators, and cathode materials. Which positive and negative material selection and quality directly determine the performance and price of lithium-ion battery. Therefore, cheap, high-performance positive and negative materials research has been the focus of lithium-ion battery industry.


Negative electrode material generally use carbon materials, the current development of more mature. The development of cathode materials has become a constraint to further improve the performance of lithium-ion batteries, the price further reduce the important factor. In the current commercial production of lithium-ion batteries, the cost of cathode material accounts for about 40% of the total cost of the battery, the cathode material prices directly determine the price of lithium-ion batteries to reduce the price. This is especially true for lithium-ion batteries. For example, a cell phone with a small lithium-ion battery requires only about 5 grams of cathode material, while driving a bus lithium-ion battery may need up to 500 kg of cathode material.


Although theoretically it can be used as a cathode material for lithium ion batteries, there are many types of cathode materials. The common cathode material mainly consists of LiCoO2. During charging, the potential applied to the two poles of the battery forces the cathode compound to release lithium ions. Of carbon. When discharged, lithium ions are precipitated from the carbon in the sheet structure and recombine with the positive electrode compound. The movement of lithium ions creates a current. This is the principle of lithium battery 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, and the carbon atoms in the negative pole are arranged in the carbon of the layered structure. When discharged, lithium ions are precipitated from the carbon in the sheet structure and recombine with the positive electrode compound. The movement of lithium ions creates a current. Although the principle is very simple, there are actually many practical problems to be considered in actual industrial production: 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 More lithium-ion; filled in between the positive and negative electrolyte, in addition to maintaining stability, but also need to have good conductivity, reducing battery resistance.


Although lithium-ion batteries have all the advantages mentioned above, but it is relatively high protection circuit requirements, should be strictly avoided in the process of over-charging, over-discharge phenomenon, the discharge current should not be too large, in general, the discharge rate Should not be greater than 0.2C. Lithium battery charging process as shown. In a charging cycle, the lithium-ion battery needs to detect the voltage and temperature of the battery before starting charging to determine whether it is rechargeable. Charging is forbidden if battery voltage or temperature is outside the manufacturer's allowable range. Allow to charge the voltage range is: Each battery 2.5V ~ 4.2V.


In the case of a battery under deep discharge, the charger must be precharged to allow the battery to meet the conditions of fast charge. Then, according to the fast charge speed recommended by the battery manufacturer, it is generally 1C, and the charger charges the battery at a constant current. The battery voltage rises slowly; once the battery voltage reaches the set termination voltage (usually 4.1V or 4.2V), constant current charge termination, fast decay charging current, charging into the full charge process; full charge process, the charge current gradually Attenuation, until the charge rate is reduced to C / 10 or below the full time or overtime, turn off the top of the charge; the top end of the charge, the charger with a very small charge current for the battery to recharge energy. Turn off the charge after the top end of the charge for a period of time.


Lithium battery protection circuit design


Due to the chemical characteristics of lithium-ion battery, during normal use, its internal chemical and chemical energy conversion into positive reactions, but under certain conditions, such as its over-charge, over-discharge and over-current will lead to the battery Internal side effects of chemical reactions, the side effects intensified, it will seriously affect the battery performance and service life, and may produce a large number of gases, the internal pressure of the battery quickly increased after the explosion caused by security issues, so all the lithium-ion batteries are required A protection circuit for the battery charge and discharge conditions for effective monitoring, and in some conditions turn off charge and discharge circuits to prevent damage to the battery.


Lithium-ion battery protection circuits include over-charge protection, over-current / short-circuit protection and overdischarge protection, over-charge protection high precision, low protection IC power consumption, high withstand voltage and zero volt chargeability.


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