Date: 2024-10-11 hits: 118
Electrolyte is one of the four key materials (positive electrode, negative electrode, separator, electrolyte) in lithium-ion batteries. It is the "blood" of lithium-ion batteries and plays a role in conducting electrons between the positive and negative electrodes. It is the guarantee for lithium-ion batteries to obtain high voltage, high specific energy, and other advantages. Electrolyte accounts for about 15% of the battery's mass and 30% of its volume. The electrolyte determines the working mechanism of lithium batteries and has a significant impact on various indicators such as cycle efficiency and lifespan, temperature characteristics, safety performance, and rate performance.
Film-forming additive
Types of additives: ethylene carbonate (EC), propylene carbonate (PC), gas substituted ethylene carbonate (FEC), etc.
Main function: During the first charge and discharge process of the battery, film-forming additives can form a stable solid electrolyte interface (SEI) film on the negative electrode surface. SEI film can effectively prevent direct contact between electrolyte and negative electrode material, reduce side reactions, and improve the cycling stability of the battery.
Flame retardant additive
Additive types: Trimethyl phosphate (TMP), Hexavalent ethyl phosphate (FEP), Pentavalent propyl phosphate (FPP), etc
Main function: Lithium ion batteries are prone to thermal runaway under high temperature or overcharging conditions, leading to fire or explosion. Flame retardant additives can reduce the tendency of electrolyte combustion, improve the thermal stability and safety of batteries.
High voltage additive
Types of additives: Ethylene sulfate (VEC), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), etc.
Main function: Under high voltage conditions, the electrolyte is prone to decomposition, which affects the lifespan of the battery. High voltage additives can improve the stability of electrolytes, reduce decomposition products, and enhance the high-voltage performance and cycle life of batteries.
Overcharge protection additive
Types of additives: p-benzonitrile (PTMN), p-dimethylbenzoic acid (DMTB), etc.
Main function: When the battery is overcharged, this type of additive can quickly react to form an insulating film that hinders electronic conduction, preventing the battery from continuing to overcharge and providing overcharge protection to enhance the safety of the battery.
Conductive additive
Types of additives: Ethylene carbonate (EC), gas substituted ethylene carbonate (FEC), lithium gas sulfonate (LiFSI), etc.
Main function: Conductive additives can improve the ion conductivity of the electrolyte, reduce the internal resistance of the battery, and enhance the rate performance and low-temperature performance of the battery.
Lithium deposition inhibitor
Additive types: Ethylene Carbonate (EC), Gaseous Ethylene Carbonate (FEC), Trifluoroacetate (TFAE), etc
Main function: During fast charging and high rate discharge, lithium metal is prone to precipitate on the negative electrode surface, forming lithium dendrites, leading to short circuits and safety hazards. Lithium deposition inhibitors can form a protective film on the negative electrode surface, inhibiting the formation of lithium dendrites and improving the safety and lifespan of batteries.
Industrial structure chain
There are various types of additives, and different lithium-ion battery manufacturers have different requirements for the use and performance of the battery. The raw materials used to prepare the additives and the emphasis on their ratios also vary. The additive industry chain mainly includes upstream raw materials, including ethylene carbonate, fluorinated ethylene carbonate, cyclic compounds, lithium bis (fluorosulfonyl) imide, etc; Midstream production and manufacturing include finished products such as film-forming additives and flame retardant additives; Downstream is the application of terminal products, including liquid electrolyte, gel electrolyte and solid electrolyte.
New additive raw materials
As the nickel content in the ternary material increases, the thermal decomposition temperature decreases and the amount of heat released increases, resulting in the decomposition of lithium hexafluorophosphate into lithium gasification and phosphorus pentafluoride. On the other hand, as the nickel content increases, the content of lithium hydroxide and lithium carbonate on the electrode also increases. Lithium nitride reacts with lithium hexafluorophosphate to produce hydrogen acid, causing severe gas swelling in the battery and having a significant impact on soft pack batteries.
Lithium bis (fluorosulfonyl) imide (LFSI), as a new raw material in lithium battery electrolytes, can effectively improve battery cycling and high and low temperature performance, suppress the production of hydrofluoric acid, slow down the decomposition of lithium hexafluorophosphate, increase battery safety, and extend battery life. It is the best material as a solute, but its price is high and it is currently only used as an additive mixed with LiPF6.
Common lithium salt additive products
At present, high nickel ternary lithium batteries have disadvantages such as poor thermal stability and strong water absorption. Some additives can reduce electrode surface activity and improve interface compatibility. For example, LODFB can improve high and low temperature performance and slightly increase the specific capacity of lithium batteries. LIFS, as a new type of lithium salt, can also be used as a new additive. In addition, various additives such as LBOB and TMSP can significantly improve the performance indicators of lithium batteries. Additives have become one of the main ways to differentiate electrolytes, and the increase in product added value brought about by differentiation is one of the core competitiveness of electrolyte manufacturers.
Global market demand
VC (ethylene carbonate), FEC (vaporized ethylene carbonate), and PS (propylene sulfite) are the three main types of electrolyte additives, accounting for about 5% of the electrolyte's mass. According to GGI data, the current electrolyte additive VC continues to be in short supply, and the shortage of VC in the market has become a bottleneck for electrolyte production. Environmental protection and long-term investment have delayed supply expansion, and the demand for iron and lithium has rebounded, exacerbating the tight supply and demand situation of VC.
New lithium salts are the future direction
Lithium hexafluorophosphate is a commonly used lithium salt in lithium batteries, but it also has disadvantages such as poor thermal stability and easy decomposition when exposed to water during use. Lithium hydrogen sulfide imide (LFSI) has high thermal stability, hydrolysis resistance, and high conductivity. When added as an additive to lithium hexafluorophosphate electrolyte, it can inhibit the generation of hydrogen fluoride in the electrolyte, block the slow and continuous decomposition of lithium hexafluorophosphate, and significantly improve the chemical stability of the electrolyte; On the other hand, by improving the conductivity of the electrolyte and utilizing its unique SEI film-forming ability, not only does it enhance the battery's cycling ability, but it also effectively improves the battery's low-temperature discharge performance and capacity retention after high and low temperature storage. At the same time, it also has the effect of suppressing expansion,
At present, lithium bis (sulfonyl) imide (LIFSI) has the conditions for industrial production. Whether as an additive or as a core solute, it is the best alternative to lithium hexafluorophosphate
