More things you don't know about the 18650 batteries

18650 batteries are widely used in notebook computers, walkie talkies, portable DVDs, instruments and meters, audio equipment, aircraft models, toys, video cameras, digital cameras and other electronic equipment.

18650 is a standard lithium-ion battery model set by Sony Company of Japan, the originator of lithium-ion battery, in order to save cost, in which 18 represents 18mm in diameter, 65 represents 65mm in length, and 0 represents cylindrical battery.

The common 18650 batteries are divided into lithium ion batteries and lithium iron phosphate batteries. The nominal voltage of lithium ion battery is 3.7V, the charging cut-off voltage is 4.2V, the nominal voltage of lithium iron phosphate battery is 3.2V, the charging cut-off voltage is 3.6V, the capacity is usually 1200mah-3350mah, and the common capacity is 2200mah-2600mah.

Lithium ion battery: lithium ion battery has the advantages of light weight, large capacity and no memory effect, so it has been widely used - many digital devices use lithium ion battery as power supply, although its price is relatively expensive. The energy density of lithium-ion battery is very high, its capacity is 1.5 ~ 2 times that of Ni MH battery with the same weight, and has a very low self discharge rate. In addition, lithium-ion battery has almost no "memory effect" and no toxic substances, which is also an important reason for its wide application. In addition, please note that the lithium battery is generally marked with 4.2 V lithium ion battery or 4.2 V lithium secondary battery and 4.2 V lithium ion rechargeable battery in English. Therefore, users must see the signs on the surface of the battery block when purchasing the battery to prevent cadmium, nickel Nickel hydrogen battery is mistaken for lithium battery.

Lithium battery standard 3.7V or 4.2V are the same. It's just that the manufacturer's labels are different. 3.7V refers to the platform voltage (i.e. typical voltage) discharged during the use of the battery, while 4.2V refers to the voltage when the battery is fully charged. Common rechargeable 18650 lithium batteries have a standard voltage of 3.6 or 3.7V, and 4.2V when fully charged, which has little to do with the power (capacity). The mainstream capacity of 18650 batteries ranges from 1800mAh to 2600mAH (the capacity of 18650 power batteries is mostly 2200 ~ 2600mAH), The mainstream capacity even has the standard of 3500 or 4000 MAH or more (remind everyone that domestic cells with a nominal capacity of more than 3350 MAH on the market may be fake, and the maximum capacity produced in China is 3350 MAH at present).

It is generally believed that when the no-load voltage of the lithium battery is below 3.0V, it is considered that the power is exhausted (the specific value depends on the threshold value of the battery protection board, for example, as low as 2.8V and 3.2V). Most lithium batteries cannot be discharged with no-load voltage below 3.2V, otherwise excessive discharge will damage the battery (generally, lithium batteries in the market are basically used with protective plates, so excessive discharge will also lead to the failure of the protective plates to detect the battery, so the battery cannot be charged). 4.2V is the maximum limit voltage for battery charging. It is generally considered that charging the no-load voltage of lithium battery to 4.2V is full. During battery charging, the battery voltage gradually rises from 3.7V to 4.2V. Lithium battery charging cannot charge the no-load voltage above 4.2V, otherwise it will damage the battery. This is the special place of lithium battery.

18650 battery life theory is 1000 cycles of charging. Due to the large capacity per unit density, most of the 18650 batteries are used in notebook computers. In addition, because of its excellent stability in work, it is widely used in various electronic fields: high-end strong light flashlight, portable power supply, wireless data transmitter, electric heating warm clothes, shoes, portable instruments and meters, portable lighting equipment, portable printers and industrial instruments, Medical instruments, etc.

18650 means 18 mm in diameter and 65 mm in length. The model of No. 5 battery is 14500, with a diameter of 14 mm and a length of 50 mm. Generally, 18650 batteries are used more in industry and less in civil use. Common batteries are used more in notebook batteries and high-grade flashlight.

18650 is only the size and model of the battery. According to the type of battery, it can be divided into 18650 of lithium ion, 18650 of lithium iron phosphate, 18650 of nickel hydrogen (very rare). The common 18650 is lithium ion.

The working principle of lithium ion battery refers to its charge discharge principle. When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The carbon as the negative electrode has a layered structure, which has many micropores. The lithium ions reaching the negative electrode are embedded into the micropores of the carbon layer. The more lithium ions embedded, the higher the charging capacity.

Similarly, when the battery is discharged (that is, the process of using the battery), the lithium ion embedded in the negative carbon layer comes out and moves back to the positive electrode. The more lithium ions returned to the positive electrode, the higher the discharge capacity. What we usually call battery capacity refers to discharge capacity.

It is not difficult to see that during the charging and discharging process of lithium-ion battery, lithium ions are in a moving state from positive → negative → positive. If we compare the lithium ion battery to a rocking chair, the two ends of the rocking chair are the two poles of the battery, and the lithium ion is like an excellent athlete running back and forth at both ends of the rocking chair. Therefore, experts gave lithium-ion battery a lovely name rocking chair battery.

Lithium battery charging control is divided into two stages. The first stage is constant current charging. When the battery voltage is lower than 4.2V, the charger will charge with constant current. The second stage is the constant voltage charging stage. When the battery voltage reaches 4.2V, due to the characteristics of lithium battery, if the voltage is higher, it will be damaged. The charger will fix the voltage at 4.2V, and the charging current will gradually decrease. When the current decreases to a certain value (generally when 1 / 10 of the current is set), cut off the charging circuit, the charging completion indicator light will be on, and the charging is completed.

Excessive charge and discharge of lithium-ion battery will cause permanent damage to the positive and negative electrodes. Excessive discharge leads to the collapse of the carbon sheet structure of the negative electrode, which will lead to the inability of lithium ion insertion during charging; Overcharge makes too many lithium ions embedded in the negative carbon structure, resulting in some lithium ions can no longer be released.

Some chargers use cheap schemes, which are not good enough in control accuracy, which is easy to cause abnormal battery charging and even damage the battery. When choosing a charger, try to choose a large brand 18650 lithium-ion battery charger with guaranteed quality and after-sales service to prolong the service life of the battery. The 18650 lithium ion battery charger guaranteed by the brand has four protection functions: short circuit protection, overcurrent protection, overvoltage protection, battery reverse connection protection, etc. Overcharge protection: when the charger overcharges the lithium-ion battery, it is necessary to terminate the charging state in order to prevent the rise of internal pressure caused by temperature rise. Therefore, the protection device needs to monitor the battery voltage. When it reaches the battery overcharge voltage, it will activate the overcharge protection function and stop charging. Over discharge protection: in order to prevent the over discharge state of lithium-ion battery, when the voltage of lithium-ion battery is lower than its over discharge voltage detection point, activate the over discharge protection, stop the discharge, and keep the battery in the standby mode of low quiescent current. Overcurrent and short circuit protection: when the discharge current of lithium ion battery is too large or short circuit occurs, the protection device will activate the overcurrent protection function