What is the composition and working principle of lithium ion battery? Next, the composition and working principle of lithium ion battery are introduced.
The current commercial lithium ion battery is mainly composed of four parts: positive electrode, negative electrode, electrolyte and separator. For the positive electrode, a reduction reaction occurs during discharge, and transition metal oxides, such as lithium borate, lithium manganate, and lithium iron phosphate, are more commonly used. For the negative electrode, an oxidation reaction occurs during discharge, and carbon materials such as graphite, coke, and pitch mesophase carbon microspheres are mostly used. The electrolyte of a lithium ion battery acts as a pure ionic conductor, usually an organic carbonate solution in which lithium salt (such as LiPF6) is dissolved. The porous polymer is placed between the positive and negative electrodes as a separator to provide electronic isolation between the positive and negative electrodes to prevent direct contact between the positive and negative electrodes and cause the battery to short-circuit.
Lithium-ion battery is actually a kind of lithium-ion concentration difference battery. When charging, Li+ is extracted from the positive electrode and inserted into the negative electrode through the electrolyte. The negative electrode is in a lithium-rich state. At the same time, the compensation charge of electrons is supplied from the external circuit to the carbon negative electrode to ensure The balance of charge. When discharging, the opposite is true. Li+ is extracted from the negative electrode and inserted into the positive electrode material through the electrolyte, and the positive electrode is in a lithium-rich state. The working principle of lithium ion battery is shown in Figure 1.
The chemical expression of lithium ion battery is:
(+) LiCo02｜Electrolyte｜Graphite (-)
During the charging and discharging process, the following electrochemical reaction is charged.
The total reaction of lithium battery:
Positive reaction of lithium battery:
Lithium battery negative reaction:
Figure 1-1 illustrates the charging and discharging principle of a typical lithium-ion battery (taking graphite as the negative electrode and lithium sulphate as the positive electrode as an example). During the charging process, lithium sulphate loses electrons, lithium ions escape from the lithium sulphate crystal lattice, and the ions Co3+ are oxidized to Co4+, and the lithium ions extracted from the positive electrode are powered by the electric field. The transport of ions is inserted into the layered structure of the graphite negative electrode through the diaphragm. At this time, the electrons obtained by the lithium ions are reduced to metallic lithium atoms and graphite to form LiC6. Compound. During the discharge, LiC6. The compound loses electrons, and lithium ions are extracted from the graphite layer. Driven by the electric field, the electrolyte transports the ions and is embedded in the lithium sulphate positive electrode through the diaphragm. At this time, the lithium sulphate gains electrons, and the lithium ions are inserted into the LiCoO2 lattice. , The ion Co4+ is reduced to Co3+. Under normal charge and discharge conditions, the insertion and extraction of lithium ions between the layers of the layered carbon material and the transition metal oxide generally only cause the change of the layer spacing without causing the destruction of the crystal structure, which is accompanied by the progress of the charge and discharge. , The chemical structure of the positive and negative electrode materials remain basically unchanged, so lithium-ion batteries are often called rocking chair battery.