Lithium Ion Battery (Li-ion, Lithium Ion Battery): Lithium-ion batteries have the advantages of light weight, large capacity, and no memory effect, so they are widely used - many digital devices use lithium-ion batteries as power sources, despite their price Relatively expensive. Lithium-ion batteries have high energy density, their capacity is 1.5 to 2 times that of nickel-metal hydride batteries of the same weight, and they have a very low self-discharge rate. In addition, lithium-ion batteries have almost no "memory effect" and the advantages of no toxic substances are also important reasons for their wide application. In addition, please note that the outside of the lithium battery is generally marked with English 4.2V lithiumion battery (lithium battery) or 4.2V lithium secondary battery (lithium secondary battery), 4.2V lithiumion rechargeable battery (rechargeable battery), so users must buy batteries. Look at the signs on the exterior of the battery block to prevent mistaking the cadmium-nickel and nickel-hydrogen batteries for lithium batteries because the battery type is not clearly seen.
Lithium battery standard 3.7V or 4.2V are the same. It's just that the manufacturer's label is different. 3.7V refers to the plateau voltage (i.e. typical voltage) at which the battery is discharged during use, while 4.2V refers to the voltage at full charge. Common rechargeable 18650 lithium batteries, the voltage is standard 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 is from 1800mAh to 2600mAh, (18650 power battery capacity) Mostly in 2200~2600mAh), the mainstream capacity even has a standard 3500 or 4000mAh or more.
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, such as as low as 2.8V and 3.2V). Most lithium batteries cannot be discharged with a no-load voltage below 3.2V, otherwise over-discharge will damage the battery (generally, lithium batteries on the market are basically used with a protection board, so over-discharge will also cause the protection board to fail to detect. to the battery so that the battery cannot be charged). 4.2V is the highest limit voltage for battery charging. It is generally believed that charging the no-load voltage of the lithium battery to 4.2V is considered to be fully charged. During the battery charging process, the battery voltage gradually rises from 3.7V to 4.2V, and the lithium battery cannot be charged. Charge the no-load voltage above 4.2V, otherwise it will damage the battery, which is the special place of lithium battery.
The 18650 battery life theory is 1000 cycles of charging. Due to the large capacity per unit density, most of them are used in notebook computer batteries. In addition, because 18650 has very good stability at work, it is widely used in major electronic fields: commonly used for charging work lights, solar energy work Lamp, solar energy storage power supply, high-grade strong light flashlight, portable power supply, wireless data transmitter, electric heating warm clothes, shoes, portable instruments and meters, portable lighting equipment, portable printers, industrial instruments, medical instruments, etc.
18650 means, 18mm in diameter and 65mm in length. The AA battery model is 14500, 14 mm in diameter and 50 mm long. Generally, 18650 batteries are used more in industry, but few in civilian use. The most common ones are laptop batteries and high-end flashlights.
Charge and discharge principle:
The working principle of lithium-ion battery refers to its charging and discharging 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, and it has many micropores. The lithium ions reaching the negative electrode are embedded in the micropores of the carbon layer. The more lithium ions embedded, the higher the charging capacity.
In the same way, when the battery is discharged (that is, the process of using the battery), the lithium ions embedded in the carbon layer of the negative electrode come out and move back to the positive electrode. The more lithium ions that return to the positive electrode, the higher the discharge capacity. What we usually call battery capacity refers to the discharge capacity.
It is not difficult to see that during the charging and discharging process of lithium ion batteries, lithium ions are in a state of motion from positive electrode → negative electrode → positive electrode. If we compare the lithium-ion battery to a rocking chair, the two ends of the rocking chair are the poles of the battery, and the lithium-ion is like an excellent sportsman, running back and forth between the two ends of the rocking chair. So, experts have given lithium-ion batteries another cute name, rocking chair batteries.
Charge and discharge process:
The 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 batteries, 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 it is reduced to a certain value (usually 1/10 of the set current), the charging circuit is cut off, the charging completion indicator light is on, and the charging is completed.
Overcharging and discharging Li-ion batteries can cause permanent damage to the positive and negative electrodes. Overdischarge leads to the collapse of the negative electrode carbon sheet structure, and the collapse will prevent lithium ions from being inserted during the charging process; overcharge causes too many lithium ions to intercalate into the negative electrode carbon structure, and some of the lithium ions can no longer be released.
Some chargers are implemented using cheap solutions, which are not good enough in control accuracy, which may easily cause abnormal battery charging or even damage the battery. When buying a charger, try to choose a 18650 lithium-ion battery charger from a big brand. The quality and after-sale service are guaranteed to prolong the service life of the battery. The brand-guaranteed 18650 lithium-ion battery charger has four protections: short circuit protection, overcurrent protection, overvoltage protection, battery reverse polarity protection, etc. Overcharge protection: When the charger overcharges the lithium-ion battery, in order to prevent the internal pressure from rising due to temperature rise, the charging state needs to be terminated. To this end, the protection device needs to monitor the battery voltage, and when it reaches the battery overcharge voltage, it activates the overcharge protection function and stops charging. Over-discharge protection: In order to prevent the over-discharge state of the lithium-ion battery, when the lithium-ion battery voltage is lower than its over-discharge voltage detection point, the over-discharge protection is activated, the discharge is terminated, and the battery is kept in a standby mode with low quiescent current. Overcurrent and short circuit protection: When the discharge current of the lithium-ion battery is too large or a short circuit occurs, the protection device will activate the overcurrent protection function.
The nominal voltage of a single cell is generally: 3.6V or 3.7V
The charging voltage is generally: 4.20V (4.2V-4.3V for lithium cobalt oxide)
The minimum discharge termination voltage is generally: 2.75V, lower than this voltage will easily lead to a serious decrease in battery capacity and even scrapping
Maximum charge termination voltage: 4.20V
Capacity: more than 1000mAh, the conventional capacity is 2200mAh-3200mAh, the highest battery capacity of 18650 is LG, which can achieve 3600mAh, but the price is not low.
Advantages and disadvantages:
1. Large capacity The capacity of 18650 lithium battery is generally between 1200mah and 3600mah, while the general battery capacity is only about 800mah. If combined into a 18650 lithium battery pack, the 18650 lithium battery pack can easily exceed 5000mah.
2. Long service life 18650 lithium battery has a very long service life, and the cycle life can reach more than 500 times in normal use, which is more than twice that of ordinary batteries.
3. High safety performance 18650 lithium battery has high safety performance. In order to prevent battery short circuit, the positive and negative electrodes of 18650 lithium battery are separated. Therefore, the possibility of short-circuiting has been reduced to the extreme. A protection board can be installed to avoid overcharging and overdischarging of the battery, which can also prolong the service life of the battery.
4. High voltage The voltage of 18650 lithium battery is generally 3.6V, 3.8V and 4.2V, which is much higher than the 1.2V voltage of nickel-cadmium and nickel-hydrogen batteries.
5. There is no memory effect. It is not necessary to empty the remaining power before charging, which is convenient to use.
6. Small internal resistance: The internal resistance of the polymer battery is smaller than that of the general liquid battery. The internal resistance of the domestic polymer battery can even be below 35mΩ, which greatly reduces the self-consumption of the battery and prolongs the standby time of the mobile phone. In time, it can fully reach the level in line with international standards. This polymer lithium battery that supports large discharge current is an ideal choice for remote control models, and has become the most promising product to replace NiMH batteries.
7. It can be combined in series or in parallel to form a 18650 lithium battery pack
8. Wide range of use Laptops, walkie-talkies, portable DVDs, instrumentation, audio equipment, model aircraft, toys, video cameras, digital cameras and other electronic equipment.
The biggest disadvantage of the 18650 lithium battery is that its size has been fixed, and it is not very well positioned when installed in some notebooks or some products. Of course, this disadvantage can also be said to be an advantage, which is compared to other lithium batteries such as polymer lithium batteries. This is a disadvantage in terms of customizable and resizable. Compared with some products with specified battery specifications, it has become an advantage.
18650 lithium battery production requires protection circuits to prevent the battery from being overcharged and causing discharge. Of course, this is necessary for lithium batteries, which is also a common drawback of lithium batteries, because the materials used in lithium batteries are basically lithium cobalt oxide materials, and lithium batteries made of lithium cobalt oxide materials cannot be discharged at large currents, and their safety poor.
18650 lithium battery requires high production conditions. Compared with general battery production, 18650 lithium battery has high requirements for production conditions, which undoubtedly increases the production cost.
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