-What is the relationship between voltage and charge of 18650 lithium-ion batteries?

What is the relationship between voltage and charge of 18650 lithium-ion batteries?
author:enerbyte source:本站 click86 Release date: 2024-01-22 10:49:41
abstract:
18650 is a standardized lithium-ion battery model established by Japanese company SONY, the pioneer of lithium-ion batteries, in order to save costs. 18 represents a diameter of 18mm, 65 represents a length of 65mm, and 0 represents a cylindrical battery. The common 18650 ba...

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18650 is a standardized lithium-ion battery model established by Japanese company SONY, the pioneer of lithium-ion batteries, in order to save costs. 18 represents a diameter of 18mm, 65 represents a length of 65mm, and 0 represents a cylindrical battery.

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

The uses of 18650 lithium batteries

The theoretical lifespan of 18650 batteries is 1000 cycles of charging. Due to the large capacity per unit density, most of the 18650 is used for laptop batteries. In addition, due to its excellent stability performance in work, it is widely used in various electronic fields: commonly used in high-end strong light flashlights, portable power supplies, wireless data transmitters, electric heating and warm clothing, shoes, portable instruments and meters, portable lighting equipment, portable printers, industrial instruments, medical instruments, etc.

The relationship between voltage and charge of lithium batteries

An analysis of the correspondence between the open circuit voltage and battery capacity of lithium-ion batteries is presented in a table as follows: the percentage represents the remaining capacity of the battery, and the right side represents 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 useful characteristic for measuring electricity, which is that during discharge, the battery voltage gradually decreases with the passage of electricity, and there is a considerable slope. This provides us with another approximate way of measuring electricity. The method of measuring battery voltage is similar to the principle that measuring the height of the water surface in a water tank can roughly estimate the remaining water volume. But in reality, the voltage of the battery is much more complex than measuring the height of the calm water surface inside the water tank.

There are several instabilities in using voltage to estimate the remaining capacity of a battery:

1. The voltage value of the same battery varies with the magnitude of the discharge current under the same remaining capacity.

The larger the discharge current, the lower the voltage. In the absence of current, the voltage is highest.

2. The impact of environmental temperature on battery voltage, the lower the temperature, the lower the voltage of a battery of the same capacity.

3. The impact of cycling on the battery discharge platform,

As the cycle progresses, the discharge platform of lithium-ion batteries tends to deteriorate. The discharge platform is lowered. So the capacity represented by the same voltage also changes accordingly.

4. Different manufacturers and capacities of lithium-ion batteries have slight differences in their discharge platforms.

5. There are significant differences in the discharge platform of lithium-ion batteries with different types of electrode materials. The discharge platforms of cobalt lithium and manganese lithium are completely different.

All of these can cause voltage fluctuations and voltage differences, making the battery capacity display unstable

When measuring the battery capacity on a mobile phone using voltage, it is impossible for the phone to be in a low current standby state all the time. The temporary loss of high current, such as turning on backlight, playing ringtones, and especially passing through, can cause the battery voltage to quickly decrease. At this point, the displayed capacity of the phone will decrease more than the actual capacity. After the high current is removed, the voltage of the battery will rise. This will lead to an unreasonable phenomenon where the display of phone capacity actually increases.

Table of battery voltage versus battery capacity:

Having said so much, here is a standard table of voltage versus remaining battery capacity (left side) and a table of high current constant current discharge versus battery voltage versus capacity (right side)

100% - -4.20V 100% - -4.20V

90% -4.06V 90% -3.97V

80% -3.98V 80% -3.87V

70% - --3.92V70% - --3.79V ▲

60% --3.87V60% --3.73V

50% -3.82V 50% -3.68V

40% --3.79V ▲ 40% --3.65V

30% --3.77V 30% --3.62V

20% --3.74V20% --3.58V

10% -3.68V10% -3.51V

5% - -3.45V 5% - -3.42V

0% -3.00V0% -3.00V

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