What are the components of lithium battery electrolyte

Electrolyte is one of the four key materials of lithium-ion batteries. It is called the "blood" of lithium-ion batteries. Its function is to conduct electrons between the positive and negative electrodes in the battery. It is also the lithium-ion battery to obtain the advantages of high voltage and high specific energy. An important guarantee, do you understand the composition of the electrolyte composition of lithium batteries? The following editor will give you a detailed introduction about the components of lithium battery electrolyte and the types of lithium battery electrolyte.

1. What are the electrolyte components of lithium batteries?

Lithium battery electrolyte composition is mainly composed of three parts:

(1) Solvent: cyclic carbonate (PC, EC); chain carbonate (DEC, DMC, EMC); carboxylic acid esters (MF, MA, EA, MA, MP, etc.) (used to dissolve lithium salt) .

(2) Lithium salt: LiPF6, LiClO4, LiBF4, LiAsF6, etc.

(3) Additives: film-forming additives, conductive additives, flame retardant additives, overcharge protection additives, additives to control the content of H2O and HF in the electrolyte, additives to improve low-temperature performance, and multifunctional additives.

The electrolyte used in lithium ion batteries should generally meet the following basic requirements:

a. High ionic conductivity, generally should reach 1x10-3~2x10-2 S/cm.

b. High thermal and chemical stability, no separation occurs in a wide voltage range.

c. A wider electrochemical window keeps the stability of electrochemical performance in a wider voltage range.

d. It has good compatibility with other parts of the battery, such as electrode materials, electrode current collectors and separators.

e. Safe, non-toxic and non-polluting.

2. Types of lithium battery electrolyte

1. Liquid lithium battery electrolyte

The choice of electrolyte has a great influence on the performance of lithium-ion batteries. It must have good chemical stability, especially when it is not easy to decompose at higher potentials and higher temperature environments, and has higher ionic conductivity (>10- 3 S/cm), and it must be inert to the anode and cathode materials and not corrode them.

Due to the high charge and discharge potential of lithium-ion batteries and the chemically active lithium embedded in the anode material, the electrolyte must use organic compounds instead of water. But the ionic conductivity of organic matter is not good, so it is necessary to add a soluble conductive salt in the organic solvent to improve the ionic conductivity.

At present, lithium ion batteries mainly use liquid electrolytes, and their solvents are anhydrous organics such as EC, PC, DMC, DEC, and most of them use mixed solvents, such as EC/DMC and PC/DMC. Conductive salts include LiClO 4, LiPF6, LiBF6, LiAsF6, etc. The order of their conductivity is LiAsF6>LiPF6>LiClO 4>LiBF6. LiClO4 is prone to safety problems such as explosion due to its high oxidability, and is generally limited to experimental research; LiAsF6 has high ionic conductivity, easy purification and good stability, but contains toxic As, and its use is restricted; LiBF6 chemistry And the thermal stability is not good and the conductivity is not high. Although LiPF6 will undergo decomposition reaction, it has high ionic conductivity. Therefore, the current lithium-ion batteries basically use LiPF6. Currently, most of the electrolytes used in commercial lithium-ion batteries use LiPF6 EC/DMC, which has high ionic conductivity and good electrochemical stability.

2. Solid electrolyte

Direct use of metallic lithium as anode material has a very high reversible capacity, its theoretical capacity is as high as 3862mAh·g-1, which is more than ten times that of graphite materials, and the price is relatively low. It is regarded as the most attractive new generation of lithium ion batteries The anode material, but will produce dendritic lithium. Using solid electrolyte as ion conduction can inhibit the growth of dendritic lithium, making it possible for metallic lithium to be used as an anode material. In addition, the use of solid electrolyte can avoid the shortcomings of liquid electrolyte leakage, and the battery can be made into a thinner (only 0.1mm thick), higher energy density, and smaller volume high-energy battery. Destructive experiments show that solid-state lithium-ion batteries have high safety performance. After destructive experiments such as nail penetration, heating (200℃), short-circuit and overcharge (600%), liquid electrolyte lithium-ion batteries will leak and explode. In addition to the slight increase in internal temperature (<20°C), solid-state batteries do not have any other safety issues. The solid polymer electrolyte has the characteristics of good flexibility, film-forming properties, stability, and low cost. It can be used as a separator between positive and negative electrodes and as an electrolyte for transferring ions.

Solid polymer electrolytes can generally be divided into dry solid polymer electrolytes (SPE) and gel polymer electrolytes (GPE). SPE solid polymer electrolyte is mainly based on polyethylene oxide (PEO), but its disadvantage is low ion conductivity, which can only reach 10-40cm at 100°C. In SPE, ion conduction mainly occurs in the amorphous region, and transfers and migrates by the movement of polymer chains. PEO is easy to crystallize due to the high regularity of its molecular chain, and crystallization will reduce the ion conductivity. Therefore, in order to improve the ionic conductivity, one can reduce the crystallinity of the polymer and increase the mobility of the chain, and on the other hand, it can increase the solubility of the conductive salt in the polymer. The use of grafting, block, cross-linking, copolymerization and other means to destroy the crystalline properties of the polymer can significantly improve its ionic conductivity. In addition, the addition of inorganic composite salt can also improve ionic conductivity. Adding a liquid organic solvent with high dielectric constant and low molecular weight such as PC to the solid polymer electrolyte can greatly improve the solubility of the conductive salt. The formed electrolyte is the GPE gel polymer electrolyte, which has a high temperature at room temperature. Ionic conductivity, but in the process of use, it will leak out and become invalid. Gel polymer lithium ion batteries have been commercialized.

The above is the content of the composition of the lithium battery electrolyte and the types of lithium battery electrolytes compiled by the editor for everyone. The role of the lithium battery electrolyte is still relatively large. The lithium battery electrolyte is the carrier of ion transmission in the battery. It is composed of high-purity organic solvent, electrolyte lithium salt, necessary additives and other raw materials. The electrolyte is generally composed of high-purity organic solvent, electrolyte lithium salt (lithium hexafluorophosphate, LiFL6), necessary additives and other raw materials, under certain conditions , Formulated according to a certain proportion.