Custom Lithium ion Battery Pack

What is difference between a notebook 3-cell lithium-ion battery and a 6-cell lithium-ion battery?

Jan 11, 2019   Pageview:16

The laptop's 3-cell lithium battery is a battery pack consisting of three 18650 lithium-ion batteries connected in series. The 6-cell lithium-ion battery is a battery pack consisting of six 18650 lithium-ion batteries connected in series and in parallel, which capacity is much larger than the 3-cell battery pack.


18650 is the originator of lithium-ion battery--a standard lithium-ion battery model that Japan SONY Company set in order to save cost. Among them, 18 means diameter 18mm, 65 means length is 65mm, 0 means cylindrical battery.


The common 18650 battery divided into a lithium ion battery and a lithium-iron phosphate battery. The lithium-ion battery voltage is 3.7V, the charge cut-off voltage is 4.2v, the lithium-iron phosphate battery has a nominal voltage of 3.2V, the charge cut-off voltage is 3.6v, the capacity is usually 1200mAh-3350mAh, and the common capacity is 2200mAh-2600mAh. .


Lithium-ion battery (Li-ion, Lithium-Ion Battery): Lithium-ion batteries have the advantages of lightweight, large capacity, and no memory effect, so they are widely used. Many digital devices use lithium-ion batteries as power supplies, even though their prices are relatively high. Said to be more expensive. Lithium-ion batteries have a high energy density, and their capacity is 1.5 to 2 times that of nickel-hydrogen batteries of the same weight, and has a very low self-discharge rate. In addition, the lithium-ion battery has almost no "memory effect" and does not contain toxic substances, which is also an important reason for its wide application. In addition, please note that the outside of the lithium battery is generally marked with English 4.2Vlithiumionbattery (lithium battery) or 4.2Vlithiumsecondarybattery (lithium secondary battery), 4.2Vlithiumionrechargeablebattery (rechargeable lithium battery), so users must see the appearance of the battery block when purchasing the battery. Prevent cadmium nickel and nickel hydride batteries from being mistaken for lithium batteries because they do not see the battery type [1].


18650 lithium-ion battery


18650 lithium-ion battery


Lithium batteries are the same as 3.7V or 4.2V. It is just that the manufacturer's label is different. 3.7V refers to the platform voltage (ie, typical voltage) that discharged during battery use, while 4.2 volts refers to the voltage at full charge. Common rechargeable 18650 lithium battery, the voltage is 3.6 or 3.7v standard, 4.2v when fully charged, this has little to do with the power (capacity), the mainstream capacity of 18650 battery from 1800mAh to 2600mAh, (18650 power battery capacity) More than 2200 ~ 2600mAh), the mainstream capacity even has the standard 3500 or 4000mAh or more.


It generally believed that the lithium batteries no-load voltage is below 3.0V and it considered that the power used up. (The specific value needs to look at the threshold of the battery protection board, such as low to 2.8V and 3.2V). Most lithium battery discharges cannot put the no-load voltage below 3.2V, otherwise excessive discharge will damage the battery (usually the lithium battery on the market is basically used with a protective plate, so over-discharge will also cause the protection board to detect To the battery, it is impossible to charge the battery). 4.2V is the highest limit voltage for battery charging. It considered that charging the lithium batteries no-load voltage to 4.2V considered to full of electricity. During battery charging, the battery voltage gradually rises to 4.2V at 3.7V, and the lithium battery cannot charged. Charge the no-load voltage to 4.2V or higher, otherwise it will damage the battery. This is the special place for lithium batteries.


The 18650-battery life theory is cyclic charging 1000 times. Due to the large capacity per unit density, most of them used in laptop batteries. In addition, the stability of the 18650 is very good at work. It is widely used in various electronic fields: it often used in high-end glare flashlights. Power, wireless data transmitters, electric heating clothing, shoes, portable instrumentation, portable lighting equipment, portable printers, industrial instruments, medical instruments, etc. [1].


The 18650 means 18 mm in diameter and 65 mm in length. The model number of the No. 5 battery is 14,500, 14 mm in diameter and 50 mm in length. Generally, 18650 batteries used in the industry, and there are few civilians. The common ones used in laptop batteries and high-end flashlights.


The 18650 is just the size of the battery. It can divided according to the type of battery. 18650 for lithium ion, 18650 for lithium iron phosphate, 18650 for nickel hydrogen (rare), and the common 18650 is lithium ion.


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 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 microspores. The lithium ions reaching the negative electrode are embedded in the microspores of the carbon layer, and the more lithium ions are embedded, the higher the charging capacity.


Similarly, when the battery is discharged (ie, the process we use 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 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 the lithium ion battery, the lithium ion is in a state of motion from the positive electrode to the negative electrode to the positive electrode. 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 sportsman, running back and forth at both ends of the rocking chair. Therefore, the experts gave the lithium-ion battery a cute name rocking chair battery.


Charge and discharge process


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


Excessive charging and discharging of lithium-ion batteries can cause permanent damage to the positive and negative electrodes. Over-discharge leads to collapse of the negative carbon sheet structure, and collapse can cause lithium ions to inserted during charging; excessive charging causes excessive lithium ions to be embedded in the negative carbon structure, and some of the lithium ions can no longer be released.


Some chargers are using cheap solutions, which control accuracy is not good and may cause abnormal battery charging and even damage the battery. When purchasing a charger, try to choose brand of 18650 lithium-ion battery charger, which have quality, after-sales guarantee and could extend the battery life. The brand-assured 18650 lithium-ion battery charger has four protections: short circuit protection, over current protection, over voltage protection, and battery reverse connection protection. Overcharge protection: When charger overcharges Li-ion battery, it is necessary to terminate charging state in order to prevent internal pressure from rising due to temperature rise. The protection device needs to monitor the battery voltage. When it reaches battery overcharge voltage, it activates overcharge protection function and stops charging. Over-discharge protection: In order to prevent over-discharge of lithium-ion battery, when lithium-ion battery voltage is lower than its detection point of over-discharge voltage, over-discharge protection activated, discharge stopped, and battery kept in a standby mode with low quiescent current. Overcurrent and short circuit protection: When discharge current of lithium ion battery is too large or a short circuit occurs, the protection device activates overcurrent protection function


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