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Lithium Battery Capacity And Discharge Platform

- Sep 04, 2018 -

Nowadays, many people who pay attention to the discharge of lithium batteries have the experience that when the lithium battery is discharged from the full voltage of 4.2V to 3.7V, the time is very long, but once it passes 3.7V, the discharge is very fast, yes, indeed. such.


Let me talk about the discharge platform of the battery, which means that the voltage of the battery changes when the fully charged lithium battery is discharged.


The battery has a constant current discharge, and the battery voltage has to go through three processes, namely, falling, stabilizing, and then falling. In these three processes, the stable period is the longest. The longer the stabilization time, the higher the discharge platform of the battery. The level of the discharge platform is closely related to the battery manufacturing process. It is because the market positioning of each lithium battery manufacturer is different, the technical process is different, the discharge platform controlled by it is different, and the quality is very different.


Generally, a 18650 lithium battery with a full voltage of 4.2V, when discharged with a current of 1C to 3.7V, put for 60 minutes, then we say that the battery capacity is 2200mAh, during this time according to the characteristics of the rechargeable battery Make a picture below to better understand the relationship between battery capacity and voltage and current time and discharge platform:


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Schematic diagram of lithium battery capacity and discharge platform


Capacity (C) = discharge current × battery discharge platform time


For a 18650 lithium battery with a capacity of 2200mAh, 1C discharges to 3.7V for 1 hour.


Capacity (C) = 2200 mA × 1 hour = 2200 mAh


Then the problem comes. For a better lithium battery, the voltage will drop very quickly after 3.7V when we do the product test, so the power will be discharged in a short time.


On the contrary, when the battery is discharged from 4.2V to 3.7V, the voltage drops rapidly, and after 3.7V, the voltage drops slowly. The battery is not good in performance and the general capacity is very low. The discharge platform of a good lithium battery is 3.7V.


In general, under constant voltage conditions, when the charge is 4.2V, the current is less than 0.01C, the battery is stopped, and then left for 10 minutes. At any rate of discharge current, when discharged to 3.7V, the battery is discharged. A length of time is an important indicator of how good or bad a battery is.


However, do not blindly pursue high platforms. Sometimes the platform voltage is high and the capacity is reduced. Because the platform voltage is different under different magnification conditions, the problem of the platform should be considered from many sources. It is a good battery if it has a high capacity and a long duration of the specified voltage.