In 1990, Sony, Japan successfully developed the first generation of lithium-ion batteries.. Due to its comprehensive performance than existing Ni / CD batteries, Ni / M (h) batteries, no memory effect, no environmental pollution, the lithium-ion battery quickly occupied the secondary battery market.
The study of lithium hexafluorosphate (LiPF6) on its core material has always been a hot spot in the industry.. This article will analyze the research status of LiPF6, and look forward to its development prospects.
. 1. Synthesis of LiPF6 synthesis method for lithium hexafluorophosphate is an important gas-solid reaction method, hydrogen fluoride (HF) solvent method, organic solvent method and ion exchange method, etc.
. Industrial, hydrogen fluoride solvent is mainly, organic solvent method. 1.
1 gas-solid reaction method – solid response method is one of the earlier synthesis methods. The method is to react with a porous fluoride (LIF) solid or LIF nanoparticles after hydrogen fluoride (HF), reacting with pentafluoride (PF5) gas under high temperature high pressure conditions, directly producing product LiPF6 solids. The advantage is that the process is simple, easy to operate, and equipment requirements are not high, but it is not used in industrial production.
. The root cause is that it is difficult to mass media, this is an important issue that this method is difficult to overcome..
As the reaction progresses, the LIF solid phase surface gradually covers the relatively dense LiPF6 product, which hinders the PF5 gas to diffuse the internal portion, resulting in the reaction of the reaction, “clamping” phenomenon. Therefore, this method is difficult to make high purity products, and the yield is also low..
Although many people have studied a lot of exploratory research, they still have solved this problem very well.. 1.
2 ion-exchanged hexafluorophosphate sodium, potassium, ammonium, and organic amine salt properties are relatively stable, easy to purify through a variety of methods.. The so-called ion exchange method is a method for producing LiPF6 by ion exchange reaction using these stable hexafluorophosphate high purity and lithium-containing compounds in an organic solvent.
Commonly used lithium salts include lithium bromide, lithium bromide, lithium nitric acid, lithium nitrate, etc. Methyl ester (DMC), etc., rarely use a solvent having a high boiling point to prevent the production of the product from decomposition when the lithium lithium phosphate complex is.
The advantage of the ion exchange method is that the reaction is simple, there is no PF5 in the raw material, and thus the raw material cost is lower than other methods.. Insufficient is to high hexafluorophosphate and lithium, which increasing the purification and cost of raw material purification.
. Further, the hexafluorophosphate conversion as one of the important reactants is not thorough, the product is purified..
Although many people have studied this method, they are still staying in the laboratory stage, and the industrial application is still in time.. 1.
3 The solvent method is the lack of gas-solid reaction method, and people have developed solvent method.. Solvent method has two types of inorganic solvent method and organic solvent method.
1.3.1 Inorganic Solvent Method (1) HF Solvent Law This method is to solute the LIF in anhydrous HF, then pass into a high purity PF5 gas to react, the reaction is removed, and the HF is removed, and the LiPF6 product is separated.
. Since the reaction is carried out in the liquid phase, the method has a fast reaction speed, good mass transfer heat transfer effect, easy to control, high conversion, and high product purity, so far to achieve industrial production. Although this method has high energy consumption, harsh water conditions, and equipment corrosion, the method has improved after the long-term efforts of scientific research and engineering technicians, and this method has improved, and has become a recognized mainstream industrialization method.
. At present, research on this method related issues has been deeply involved in the engineering level. In terms of raw materials selection and processing, process flow, production equipment, product purification, etc.
, research is very active. The focus of the research focuses on both synthetic reactions and purification and purification, and has obtained a large progress, only 40 patents are nearly 40. In terms of synthesis, the focus of research is how to improve gas-liquid transmission, heat transfer effect, to improve the quality of reaction, and improve PF5 conversion.
Typical technical representatives include LIF-HF solution atomization process, microporous aeration process, tubular reactor process, etc.. In purification technology, the individualization characteristics of the research is more obvious, and it is important to expand around specific processes and product characteristics.
. The method currently adopted except for the traditional thermal vacuum drying, there is also a chemical reaction method, microwave radiation drying method, solvent recrystallization, ultrasonic induced crystallization method, etc..
These methods have their excellent disadvantages, and the application places are not the same, but the improvement of product quality of relevant company has a certain use.. (2) SO2 solvent method This method is to react to the liquid SO2 and PF5 gas in anhydrous LIF solution, and the reaction is raised to remove SO2 and PF5, and the LiPF6 crystal is obtained.
. The advantage is that the reaction temperature is moderate, the equipment is not high, and the HF content in the product is low, but the SO2 content is high..
1.3.2 Organic Solvent Law As is well known, LiPF6 is unstable with heat, solid LIPF6 is decomposed, about 130 ¡ã C in solution, and moisture can cause its rapid decomposition.
. Therefore, in terms of the reaction system of LIF, PF5 as raw materials, the organic solvent method can be said to a regression of the LIPF6 synthesis technology attribute..
At present, the organic solvent is an important ether, ester, pyridine, and acetonitrile (CH3CN), etc.. (1) The starting point of ether and ester solvent method and ester solvent method, most is based on directly obtaining a lithium ion battery electrolyte.
LIF and PF5 generate LIPF6 reactions, more advantageous in thermodynamics, focusing on solving dynamics. Low chain alkyl ether (such as methyl ether, ether, methyl ether, etc.), cyclic ether (such as tetrahydrofuran, 1,3-dioxane, 2-methyl tetrahydrofuran, etc.
) and a low alkyl ester (eg, EC, Dec, DMC, etc.) can dissolve LiPF6, and some organic matter, such as carbonate, etc. are one of the solvents in the lithium-ion battery.
. With solvent-based solubility, the reaction interface can be continuously updated, thereby maintaining a high reaction rate and a high LIF conversion, and the product can be directly used for lithium ion battery electrolyte. Therefore, use these substances and mixtures of mixture, is a reasonable inevitable choice for solvent method.
. The method is usually made to the LIF-organic solvent suspension, then control the PF5 gas access amount, after the reaction, the excess of the excess PF5 is removed, the product is a lithium ion battery electrolyte..
The advantage of this method is that the reaction is easy to control, the yield is high, and the operation is relatively safe. The equipment is not high; the disadvantage is that the PF5 easy and organic solvent has a sub-reaction to increase the impurities, product color deepening. Further, solvents such as LiPF6 and ethers are usually present in the form of a complex, and it is difficult to isolate LiPF6 crystals in the form of a complex, which also limits the application of LiPF6 in other electrolyte systems.
. (2) Acetonitrile solvent method acetonitrile solvent method is typically made to the LIF-CH3CN suspension, then pass into the PF5 gas, after the reaction is completed, the inert gas is replaced, and the acetonitrile can be removed and the acetonitrile can obtain a high purity LIPF6 product..
The advantage of this method is that the reaction speed is fast, the conditions are mild, and the process is simple, and the high purity of LiPF6 [14-15] is made, and the energy consumption is low, the equipment is small, but the method still cannot prevent the use of PF5, and acetonitrile is toxic.. Acetonitrile solvent method is one of the hotspots of the current theoretical workers and engineering technicians.
The research is important in two aspects: First, start from the synthetic route or process process to reduce product costs; the second is to improve the effect of reactivity to improve product quality. High purity PF5 manufacturing is difficult, high price, directly affecting LIPF6 product cost. In response to this problem, the industry has conducted a lot of research and has made a certain progress.
. For example, a method of obtaining high purity water-free PF5 gas using anhydrous orthophosphate, calcium fluoride and sulfur oxide, has obtained a national patent, and the LIPF6 made by it can be purified after simple refining..
Another method of producing high pure PF5 gas in organic solvent and organic tin flu fluoride in an organic solvent is also caused by a relatively inexpensive five-halide.. It is said that the PF5 made by this method can be used directly in synthesis.
Its highlight advantage is that the price expensive PF5 is greatly reduced by using relatively inexpensive penthahahaminated phosphorus. Second, since fluorine-halogen exchange is carried out in an organic solvent, so there is no HCl overflow, thereby solving the phosphorus When the raw material, the impurity chloride ion affects the quality of the product quality. In addition, the process is simple, the reaction conditions are gentle, and the fluorinaid is easy to purify, and the equipment and environmental requirements are also low.
. 2. Lithium-lithium phosphate technology research and development trend, LiPF6 synthesis technology is more mature, but its technical diffusion is significantly accelerated, and presents a new trend.
. From the technical level, developing new phosphorus sources is one of the trends in the development of hydrogen fluoride solvent method..
Such as Japan’s State, Senfield Chemical and many domestic research units are currently committed to the choice and preparation of phosphorusources, trying to make breakthroughs from raw materials or process methods; in addition to process devices, purification technology, this technology is dominated Energy saving, environmental protection, efficient direction, such as domestic multi-fluoro, Tianjin Chemical Design Institute, Central South University, etc. have many patents. The development of organic solvent method is also increasingly active, such as Japanese central nitrate, Germany’s metal shares, etc.
, has been systematic in synthesis process, product purification, etc.. Another payable new trend is that some companies and research units at home and abroad have started to develop low-cost inorganic lithium salts and hexafluoride synthesis hexafluorophosphate technology, while how effective repeatedly uses valuable substances in used waste batteries.
One of the new hotspots. Reference: Yanglin.Cause of the status and development trend of lithium lithium-ion battery electrolyte hexafluorophosphate [J] .
Journal of Jiaozuo University, 2018,32 (01): 98-100.