When using mobile phones, electric vehicles, or energy storage devices in daily life, we often hear two words:

Overcharging and overdischarging.

Many people know that they can damage batteries, but they do not understand the reasons behind it.

In fact, the stable operation of lithium batteries relies on strict voltage range control. Once it exceeds this range, the internal structure of the battery may undergo irreversible changes.

1. What is overcharging of lithium batteries

The so-called overcharging refers to:

After the battery has reached a fully charged state, it continues to charge.

Under normal circumstances, lithium ions will detach from the positive electrode during charging, migrate through the electrolyte to the negative electrode, and embed into the negative electrode material.

But when the negative electrode is close to saturation, continuing to input lithium ions will result in a situation of "nowhere to place".

At this point, metal lithium may precipitate on the negative electrode surface; Continuous decomposition of electrolyte; The SEI film is constantly damaged and rebuilt; This is the main problem caused by overcharging.

2. Why is overcharging dangerous

Firstly, overcharging accelerates battery aging.

Due to the increase in side reactions, a large amount of active lithium will be consumed, resulting in a decrease in the amount of recyclable lithium, manifested as:

Capacity reduction

Internal resistance increases

Shortened cycle life

Secondly, overcharging may pose safety risks.

When there is severe overcharging, the positive electrode material may undergo structural changes and even release oxygen; At the same time, lithium precipitated from the negative electrode may form a dendritic structure.

If lithium dendrites pierce the diaphragm, it may cause an internal short circuit and lead to uncontrolled heat generation.

3. What is lithium battery over discharge

Overdischarging is the opposite of overcharging.

It refers to:

The battery level is already too low, but it continues to discharge.

During the discharge process, lithium ions will detach from the negative electrode and return to the positive electrode.

When the battery voltage drops to a low state, both the negative and positive electrode materials will undergo adverse changes.

4. What are the impacts of excessive discharge

Firstly, the negative electrode structure may be damaged.

Taking graphite negative electrode as an example, excessive lithium removal will change the material structure and reduce the subsequent lithium storage capacity.

Secondly, copper current collectors may dissolve.

When the battery voltage is too low, the negative electrode potential increases, and the copper foil may oxidize and dissolve to form copper ions.

When recharging, these copper ions may deposit on the negative electrode, forming metallic copper particles and increasing the risk of short circuits.

In addition, excessive discharge can also lead to:

Permanent decrease in battery capacity

Internal resistance increases

Cycle performance deteriorates

5. Why do batteries not easily overcharge or discharge

Modern lithium batteries are typically equipped with a Battery Management System (BMS).

It will monitor in real-time:

voltage

electric current

temperature

State of Charge (SOC)

When the voltage reaches the upper or lower limit, the system will automatically stop charging or discharging.

This is also why regular battery products generally do not easily experience severe overcharging or overdischarging.

6. How to use lithium batteries correctly

To extend battery life, please note:

Avoid long-term charging to 100%

Avoid frequent use until completely out of battery

Avoid high current charging in low-temperature environments

Use legitimate charging equipment

For ordinary users, keeping the battery level within a reasonable range is more beneficial for lifespan than frequently pursuing full and full charging.

In conclusion

The overcharging and overdischarging of lithium batteries are essentially breakthroughs in the working boundary of the battery.

Overcharging can easily lead to lithium deposition and increased side reactions;

Overdischarge may cause structural damage and dissolution of the current collector.

How long a battery can last depends not only on the material itself, but also on the way it is used.

Only by understanding the principles of overcharging and overdischarging can we truly achieve scientific use of electricity and enable lithium batteries to perform for a longer period of time.