What is the working principle of lithium-ion battery
Jul 28, 2018

What is the working principle of lithium-ion battery?

Lithium-ion batteries use a carbon material as the negative electrode and a lithium-containing compound as the positive electrode. No lithium metal exists, only lithium ions. This is a lithium ion battery. A lithium ion battery is a general term for a battery in which a lithium ion intercalation compound is used as a positive electrode material. The charging and discharging process of a lithium ion battery is a process of intercalating and deintercalating lithium ions. In the process of intercalation and deintercalation of lithium ions, it is accompanied by embedding and deintercalation of equivalent electrons with lithium ions (commonly, the positive electrode is represented by embedding or deintercalation, and the negative electrode is represented by insertion or deintercalation). During charge and discharge, lithium ions are intercalated/deintercalated and inserted/deintercalated between the positive and negative electrodes, and are aptly referred to as "rocking chair batteries".

When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The carbon as the negative electrode has a layered structure, and it has many micropores. The lithium ions reaching the negative electrode are embedded in the micropores of the carbon layer, and the more lithium ions are embedded, the higher the charging capacity. Similarly, when the battery is discharged (ie, the process we use the battery), the lithium ions embedded in the carbon layer of the negative electrode come out and move back to the positive electrode. The more lithium ions return to the positive electrode, the higher the discharge capacity.

Generally, the charging current of the lithium battery is set between 0.2C and 1C. The larger the current, the faster the charging and the greater the heat of the battery. Moreover, excessive current charging, the capacity is not full, because the electrochemical reaction inside the battery takes time. Just like pouring beer, if it is too fast, it will produce bubbles, but it will not be full.

Use (discharge) precautions

For batteries, normal use is the process of discharging. Need to pay attention to the discharge of lithium battery:

First, the discharge current should not be too large. Excessive current causes heat inside the battery, which may cause permanent damage. On the mobile phone, this is no problem, you can not consider it.

As can be seen from the image on the right, the larger the battery discharge current, the smaller the discharge capacity and the faster the voltage drop.

Second, you must never over discharge! Lithium battery internal storage of electrical energy is achieved by a reversible chemical change of electrochemistry. Excessive discharge will cause irreversible reaction of this chemical change, so lithium battery is most afraid of overdischarge, once the discharge voltage is lower than 2.7V, May cause the battery to be scrapped. Fortunately, the inside of the mobile phone battery has been installed with a protection circuit, the voltage is not low enough to damage the battery, the protection circuit will work, stop discharging.






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