The Principle of Lithium ion Battery--Simple Introduction

The Principle of Lithium ion Battery

1. Cathode: LiCoO2/LiMn2O/NMC/LiFePO4 + Conductive Agent + Adhesive (PVDF) + Current Collector (Aluminum Foil)

2. Anode: Graphite + Conductive Agent + Thickener (CMC) + Binder (SBR) + Current Collector (Copper Foil)

3. Working Principle

3.1 Charging process

A power supply charges the battery. At this time, the electron e on the cathode electrode runs from the external circuit to the anode electrode, and the cathode lithium ion Li+ "jumps" into the electrolyte from the cathode electrode, "crawling over" the curved hole on the diaphragm, " "Swim" reaches the anode and combines with the electronics that have long since ran.

The reaction that takes place on the cathode electrode is:

The reaction that takes place on the anode electrode is:

3.2 Battery discharge process

The discharge has a constant current discharge and a constant resistance discharge. The constant current discharge is actually a variable resistor that can change with the voltage change in the external circuit. The essence of the constant resistance discharge is to add a resistor to the cathode and anode electrodes of the battery to allow electrons to pass. From this, it can be seen that the battery does not discharge as long as the electrons on the anode electrode cannot travel from the anode electrode to the cathode electrode. Both electrons and Li+ act simultaneously, with the same direction but different paths. When discharging, electrons travel from the anode electrode through the electron conductor to the cathode electrode, and lithium ion Li+“jumps”into the electrolyte from the anode electrode,“crawling”over the diaphragm. The small hole, "swim" reaches the cathode, combined with the electrons that have long since ran.

3.3 Charge and discharge characteristics

The cathode electrode of the battery adopts LiCoO2, LiNiO2 and LiMn2O2. LiCoO2 is a crystal form with stable layer structure. However, when x Li ions are removed from LiCoO2, the structure may change, but whether it changes depends on x. size.

It is found through research that when x > 0.5, the structure of Li1-xCoO2 is extremely unstable, and crystal collapse occurs. The external appearance is the overwhelming end of the cell. Therefore, the cell should control the value of x in Li1-xCoO2 by limiting the charging voltage during use. Generally, the charging voltage is not more than 4.2V, then x is less than 0.5, and the crystal form of Li1-xCoO2 is still stable.

The anode electrode C6 itself has its own characteristics. After the first formation, Li in the cathode electrode LiCoO2 is charged into the anode electrode C6, and Li returns to the cathode electrode LiCoO2 when discharged, but a part of Li must remain in the center of the anode electrode C6 after the formation. In order to ensure the normal embedding of the next charge and discharge Li, otherwise the voltage of the cell is very short, in order to ensure that a part of Li remains in the anode C6, generally by limiting the discharge lower limit voltage: safe charging upper limit voltage≤4.2V, discharge lower limit Voltage≥2.5V.

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