The working principle of lithium ion battery
Nowadays, lithium-ion batteries are very common. For example, the mobile phones, notebooks, tablets and other devices we use rely on them as power sources, but few people understand the working power of lithium-ion batteries. Let's learn together:
1. Introduction to Lithium Ion Battery
"Lithium ion battery" refers to a secondary battery composed of two compounds that can reversibly insert and extract lithium ions as the positive and negative electrodes. When the battery is charged, the lithium atoms in the cathode ionize into lithium ions and electrons, and the lithium ions move to the anode to synthesize lithium atoms with the electrons. During discharge, lithium atoms are ionized from the anode surface in the graphite crystal into lithium ions and electrons, and lithium atoms are synthesized at the cathode. Therefore, in this battery, lithium will always appear in the form of lithium ion, and will not appear in the form of metallic lithium, so this battery is called a lithium ion battery.
2. Lithium-ion battery structure
Lithium-ion batteries are an alternative to metal lithium batteries that appeared in the past few years. The main components of the battery are positive and negative electrodes, electrolyte, separator and casing.
Main materials: positive electrode, negative electrode, electrolyte, separator
Structure: round, square, laminated, winding
Form: polymer (soft packaging), liquid lithium ion (steel shell)
Positive electrode: A carbon electrode that can store lithium ions is used. During discharge, lithium becomes lithium ions, leaving the anode of the battery to reach the cathode of the lithium ion battery.
Anode: The material is chosen to be as close as possible to the potential of lithium that can be inserted into lithium compounds, such as various carbon materials including natural graphite, synthetic graphite, carbon fiber, mesophase carbon, etc. and metal oxides.
Electrolyte: A mixed solvent system that uses LiPF6 ethylene carbonate, propylene carbonate and low-viscosity diethyl carbonate and other alkyl carbonates.
Diaphragm: The use of polyolefin microporous membranes such as PE, PP or their composite membranes, especially the PP/PE/PP three-layer membrane not only has a low melting point, but also has high puncture resistance, which plays a role in heat insurance.
Shell: It is made of steel or aluminum, and the cover assembly has the function of explosion-proof and power-off.
3. The working principle of lithium ion battery
The working principle of a lithium ion battery refers to its charging and discharging principle. 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. It has many micropores. The lithium ions that reach the negative electrode are embedded in the micropores of the carbon layer. The more lithium ions are inserted, the higher the charging capacity.
Similarly, when the battery is discharged (that is, when we use the battery), the lithium ions embedded in the carbon layer of the negative electrode are released and move 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 the discharge capacity.
During the charging and discharging process of lithium ion batteries, lithium ions are in a state of movement 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 on the two ends of the rocking chair. Therefore, the experts gave the lithium-ion battery a lovely name, rocking chair battery.
