When our lithium-ion battery is charging, lithium ions are transferred from the positive electrode inside the battery to the negative electrode of the battery under the action of an external electric field. At the same time, electrons also flow from the positive electrode to the negative electrode through the external circuit, and the current flows from the negative electrode to the positive electrode through the external circuit. The inside of the battery remains electrically neutral. When a lithium ion battery is discharged, lithium ions are transferred from the negative electrode inside the battery to the positive electrode of the battery under the action of an external electric field. At the same time, electrons also flow from the negative electrode to the positive electrode through the external circuit, and the external circuit current flows from the positive electrode to the negative electrode. Reaction mechanisms in lithium-ion batteries include: Embedding reaction, Phase transition mechanism, Reversible chemical bonding mechanism, Conversion reaction mechanism, Surface charge mechanism, Underpotential deposit mechanism, Organic free Radial mechanism, Interfacial Charge Mechanism and other reaction mechanisms.
The general lithium-ion battery is composed of: positive electrode material, negative electrode material, electrolyte and separator. In addition to this, there are: adhesives, conductive carbon black, current collectors, tabs, and other outer packaging materials. Each key component must have the following characteristics:
(1) It is reversible, and the active material that can release lithium reversibly is the positive and negative electrodes. The positive electrode generally requires high redox properties, and the transition metal compound LiMO2: M capable of redox potential is at least one or more of Mn, Co, and Ni. The negative electrode generally needs active materials with low oxidation-reduction potential that can insert and remove lithium, such as graphite, Si, and Sn alloys.
(2) Electrolyte is the transmission medium between the positive and negative electrodes of lithium batteries, and is an important transmission medium for lithium ions to and from the positive and negative electrodes. Generally, it is an organic carbonate solution in which lithium salt is dissolved. Lithium salts mainly include LiPF6, LiClO4 and so on.
(3) The separator is a microporous film with a certain porosity and electrical insulation, such as polyethylene (PE), polypropylene (PP), etc. The main function of the separator is to separate the positive and negative electrodes of the battery to avoid short-circuiting caused by direct contact between the positive and negative electrodes. When the internal temperature of the lithium battery rises above the withstand temperature of the separator due to a short circuit, the commonly used PP/PE will melt and seal the pores, prevent the passage of Li+, and prevent the burning and explosion of the battery from causing greater losses, so the separator is Provides safety for us to use lithium-ion batteries.