Introduction of lithium battery discharge depth

The discharge depth of a lithium battery refers to the ratio of the discharge amount of the lithium battery to the total stored power (nominal capacity). The smaller the number, the lighter the discharge, for example, the depth of discharge is 80%, which means that the discharge is 20% of the remaining capacity. The effect of the depth of discharge on the battery is: the deeper the depth of discharge, the easier the battery life is shortened; the other aspect is the performance on the discharge curve, the more the discharge goes deeper, the more unstable the voltage and current.

The depth of discharge is closely related to voltage and current. It can be said that it is expressed in voltage and acts on current.

Under the same discharge system, the smaller the voltage value, the deeper the discharge depth goes. In practice, the termination voltage value is usually used to control the depth of discharge. The specific working process is completed by protecting the IC. When the lithium battery is likely to be over-discharged, the lithium battery voltage is lower than the IC over-discharge voltage detection point of 2.75. V (some settings are 3.0V). At this time, the discharge protection function is activated, and the MOSFET turns from ON to OFF to turn off the discharge, thereby completing the control of the discharge depth of the lithium battery.

In the discharge depth comparison table between the 3.0V (termination voltage) and 4.2V (open circuit voltage) of the lithium battery, the reverse relationship between the current and the depth of discharge is shown: the larger the current, the shallower the depth of discharge. When the battery is reduced to the same voltage, the lithium battery discharged at 0.05C has a charge of 65.6% at 3.9V, and if it is used for 0.5C discharge, the lithium battery has a charge of 74.9% at 3.9V. Comparison: The small current discharge is more thorough, the smaller the current, the longer the working time, the less the charge is at the same voltage. In short, any discussion on the discharge of lithium batteries should consider the discharge system, the key is the current.

As can be seen from the beginning of this article, when using the electric appliance to issue a "low battery" prompt, it is best to replenish the power in time, instead of waiting for it to automatically shut down. Because the result may cause the lithium battery to be deeply discharged, thereby passing the over-discharge form, causes structural damage to the lithium battery and affects battery life.

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