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What is the relationship between voltage and capacity of 18650 li-ion battery?

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

The common 18650 battery is 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.


18650 lithium battery applications

The 18650 battery life theory is cyclic charging 1000 times. Due to the large capacity per unit density, most of them are 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 is often used in high-end glare flashlights. Power, wireless data transmitters, electric warm clothing and shoes, portable instrumentation, portable lighting equipment, portable printers, industrial equipment, medical equipment, etc.


Lithium battery voltage and power relationship

Analysis of the correspondence between the open circuit voltage of the lithium ion battery and the battery capacity, first give a table: as follows, the percentage is the remaining capacity of the battery, and the right side is the open circuit voltage (OCV) of the corresponding battery.

100%----4.20V

90%-----4.06V

80%-----3.98V

70%-----3.92V

60%-----3.87V

50%-----3.82V

40%-----3.79V

30%-----3.77V

20%-----3.74V

10%-----3.68V

5%------3.45V

0%------3.00V

However, lithium-ion batteries have a characteristic that is useful for electricity metering. When discharging, the battery voltage gradually decreases with the passage of electricity, and has a considerable slope. This provides us with another approximate method of electricity metering. The method of taking the battery voltage is like measuring the water level in the water tank to estimate the amount of water remaining. But in reality the battery voltage is much more complicated than the calm water level measurement inside the tank.

 

18650 lithium-ion battery



Using voltage to estimate the remaining capacity of the battery has the following instabilities:

1. The same battery, in the case of the same remaining capacity, the voltage value changes due to the magnitude of the discharge current. The higher the discharge current, the lower the voltage. In the absence of current, the voltage is highest.

2. The effect of ambient temperature on the battery voltage. The lower the temperature, the lower the battery voltage of the same capacity.

3. The effect of the cycle on the battery discharge platform, as the cycle progresses, the discharge platform of the lithium ion battery tends to deteriorate. The discharge platform is lowered. Therefore, the capacity represented by the same voltage also changes accordingly.

4. Different manufacturers, different capacity lithium-ion batteries, the discharge platform is slightly different.

5. Lithium-ion batteries of different types of electrode materials have large differences in discharge platforms. The discharge platforms of cobalt lithium and manganese lithium are completely different.



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