Electrolyte is one of the four key materials of lithium-ion batteries (cathode, anode, diaphragm, electrolyte), lithium-ion battery electrolyte is the carrier of the ion transmission in the battery, plays a vital role. Lithium-ion battery electrolyte is generally composed of lithium salt and organic solvents.
The Role of Electrolyte
Electrolyte, the big classification can be in accordance with the liquid electrolyte, solid electrolyte and gel electrolyte; liquid electrolyte, can be divided into organic electrolyte and inorganic electrolyte. Currently the most widely used is liquid organic electrolyte.
The electrolyte overflows inside the battery case, the positive and negative electrodes of the battery and the diaphragm are immersed in it. On the one hand, the electrolyte provides some of the active lithium ions, which are used as conductive ions during charging and discharging. On the other hand, the electrolyte provides ion channels, or carriers, in which the lithium ions can move on their own.
The lithium ion battery electrolyte is the carrier for ion transport in the battery. Between the positive and negative electrodes of lithium-ion batteries play the role of conducting ions, like the positive electrode and the negative electrode of the "love bond" between the lithium-ion battery to obtain high voltage, high specific energy and other advantages of the guarantee.
The Main Components of Lithium-ion Battery Electrolyte
Electrolyte generally consists of high-purity organic solvents, electrolyte lithium salt, the necessary additives and other raw materials, under certain conditions, according to a certain proportion of the preparation. The main components of lithium ion battery electrode solution are the following seven:
1. vinyl carbonate: molecular formula: C3H4O3, translucent colorless liquid (>35 ℃), room temperature for the crystalline solid, is a good solvent for polyacrylonitrile, polyvinyl chloride.
2. Propylene carbonate, colorless and odorless, or light yellow translucent liquid, soluble in water and carbon tetrachloride, miscible with ether, acetone, benzene and so on. This product should be stored in cool, ventilated, dry place, away from ignition sources, according to the general provisions of low-toxicity chemicals storage and transportation.
3. Diethyl carbonate, colorless liquid, slightly odor; vapor pressure 1.33kPa/23.8℃; flash point 25℃ (combustible liquid can volatilize into vapor and run into the air.
4. Dimethyl carbonate, is a non-toxic, environmentally friendly, widely used chemical raw materials; at the same time, it has a higher evaporation temperature and faster evaporation rate.
5. Methyl ethyl carbonate, colorless and translucent liquid, a high-tech, high value-added chemical product emerging in recent years, an excellent solvent for lithium battery electrolyte, this product should be stored in a cool, ventilated, dry place, according to the provisions of the storage and transportation of flammable chemicals.
6. Lithium hexafluorophosphate, white crystal or powder, strong deliquescence; analyzed when exposed to air or heated, lithium hexafluorophosphate is rapidly analyzed in the air due to the action of water vapor when exposed to air or heated, releasing PF5 and sprouting white fumes.
7. Phosphorus pentafluoride is a phosphorus halide compound. Phosphorus pentafluoride is a colorless odorless gas at room temperature and pressure, and it is a strong irritant to skin, eyes and mucous membranes. Phosphorus pentafluoride is used as a catalyst for polymerization reactions.
How does the electrolyte of lithium-ion battery affect the quality of the battery?
In order to determine the effect of electrolytes on lithium-ion batteries, the research team did related tests using LiTFSI and LiFSI, which are two very similar electrolytes, except that LiFSI contains less carbon and fluorine than LiTFSI. They used the equipment in the environmental molecular laboratory to constantly detect the energy of battery charging and discharging, and finally investigated the decomposition of the electrodes.
They found that in lithium-sulfur batteries with LiTFSI as the electrolyte, lithium atoms are bound by sulfur atoms, forming lithium sulfide (LiSx) on the electrode surface. When LiFSI is used as the electrolyte, lithium sulfate (LiSOx) is formed. By calculating the bonding tightness of the two lithium compounds, they found that lithium sulfide is easily broken to release lithium. However, lithium sulfate is difficult to separate, so the oxygen element in lithium sulfate is the culprit.
By combining macroscopic compositional decomposition with simulations, we can see which bonds are prone to breakage and what happens if a chemical bond breaks." Dr. Ji-Guang (Jason) Zhang, who is leading the study at the National Laboratory, said, "This process allows us to identify the behavior of the electrolyte, leading us to design a better electrolyte and improve the cycle life of lithium-sulfur batteries.
What are the Advantages of Lithium Ion Battery Electrolyte Ingredients?
a. High ionic conductivity, which should generally be 1x10-3~2x10-2S/cm.
b. High thermal and chemical stability, in a wide range of voltage does not occur separation;
c. Wide electrochemical window, maintain the stability of electrochemical performance in a wide range of voltages;
d. Good compatibility with other parts of the battery such as electrode materials, electrode collector and diaphragm.
e. Safe, non-toxic, non-polluting.
The above is a specific analysis of the composition of lithium-ion battery electrolyte, most of the electrolyte used in commercial lithium-ion batteries LiPF6 EC/DMC, which has a high ionic conductivity and good electrochemical stability. In general, the role of lithium-ion battery electrolyte is very large, and its development prospects are also very broad.
