Working principle and characteristics of lithium ion battery

Lithium ion battery refers to a secondary battery composed of two compounds that can reversibly embed and de embed lithium ions as positive and negative electrodes.

When the battery is charged, lithium atoms in the cathode are ionized into lithium ions and electrons, and lithium ions move to the anode to synthesize lithium atoms with electrons. During discharge, lithium atoms are ionized from the inner anode surface of graphite crystal into lithium ions and electrons, and lithium atoms are synthesized at the cathode.

Lithium ion battery is an alternative product of metal lithium battery. The main components of the battery are positive electrode, negative electrode, electrolyte, diaphragm and shell. Among them, the most important positive electrode, negative electrode, electrolyte and diaphragm are also known as the four main materials of lithium battery.

Positive electrode - the carbon electrode that can absorb lithium ions is used. During discharge, lithium becomes lithium ions, separates from the battery anode and reaches the cathode of lithium ion battery.

Negative electrode - the materials shall be embedded lithium compounds with potential as close as possible to lithium potential, such as various carbon materials, including natural graphite, synthetic graphite, carbon fiber, mesophase small ball carbon and metal oxides.

Electrolyte --- a mixed solvent system composed of ethylene carbonate, propylene carbonate and low viscosity diethyl carbonate of LiPF6.

Diaphragm --- polyolefin microporous membranes such as PE, PP or their composite membranes are adopted, especially PP / PE / PP three-layer diaphragm, which not only has low melting point, but also has high puncture resistance and plays a role of thermal insurance.

Shell --- made of steel or aluminum, and the cover assembly has the function of explosion-proof and power-off.

The working principle of lithium-ion battery refers to its charge and discharge principle: when charging the battery, 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, which has many micropores. The lithium ions reaching the negative electrode are embedded into the micropores of the carbon layer. The more lithium ions embedded, the higher the charging capacity.

Similarly, when the battery is discharged (that is, the process of using the battery), the lithium ion embedded in the negative carbon layer comes out and moves back to the positive electrode. The more lithium ions returned to the positive electrode, the higher the discharge capacity. What we usually call battery capacity refers to discharge capacity.

It is not difficult to see that during the charging and discharging process of lithium-ion battery, lithium ions are in a moving state from positive → negative → positive. If we compare the lithium ion battery to a rocking chair, the two ends of the rocking chair are the two poles of the battery, and the lithium ion is like an excellent athlete running back and forth at both ends of the rocking chair. Therefore, experts gave lithium-ion battery a lovely name rocking chair battery.