CN115197266B - Method for purifying tri (2-cyanoethyl) phosphate - Google Patents

Abstract

The present invention provides a method for purifying tris(2-cyanoethyl)phosphate, comprising the following steps: firstly, after the crude tris(2-cyanoethyl)phosphate is mixed with alkali solution, an organic solvent is added and mixed again, and an organic phase is separated to obtain an organic phase solution; then, the organic phase solution obtained in the above steps and a stabilizer are subjected to reduced pressure distillation to obtain purified tris(2-cyanoethyl)phosphate. The tris(2-cyanoethyl)phosphate purification process provided by the present invention is simple and feasible, and a nitroxide free radical stabilizer is particularly used to make the product more stable and not easy to decompose or cause other side reactions during the purification process, and the product has a higher purity, meets the electronic grade application requirements, and better broadens the industrial production and application of high-purity tris(2-cyanoethyl)phosphate additives, meets the high-level requirements of lithium ion batteries, and can be used as a high-voltage lithium ion battery electrolyte additive to improve the high temperature performance and cycle performance of the battery.

Description

Method for purifying tris(2-cyanoethyl)phosphate

Technical Field

The invention belongs to the technical field of lithium ion battery electrolyte and relates to a method for purifying tris(2-cyanoethyl)phosphate.

Background Art

Lithium-ion battery is a secondary battery (rechargeable battery) that mainly relies on the movement of lithium ions between the positive electrode and the negative electrode to work. During the charging and discharging process, Li ⁺ is intercalated and deintercalated back and forth between the two electrodes: during charging, Li ⁺ is deintercalated from the positive electrode and embedded in the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; during discharging, the opposite is true. Batteries generally use materials containing lithium elements as electrodes and are the representative of modern high-performance batteries. Lithium-ion batteries usually include positive electrodes, negative electrodes, diaphragms, electrolytes and shells. They have the advantages of high operating voltage, high specific energy, long cycle life, light weight, low self-discharge, no memory effect and high performance-price ratio. They have become the main choice of rechargeable power sources in high-power electric vehicles, artificial satellites, aerospace and other fields, especially in 3C, energy storage, power and other fields. It has been widely used. However, with the development requirements of miniaturization of 3C products and long driving range of new energy vehicles, higher requirements are put forward for the overall performance of lithium-ion batteries, especially in terms of energy density and cycle performance. Under the existing positive and negative electrode systems, increasing the battery charging voltage is the most effective way to increase the battery energy density, but this will bring great challenges to the electrolyte of lithium-ion batteries. Phosphate compounds (such as tris(trimethylsilyl)phosphate, lithium difluorophosphate, lithium difluorobis(oxalatophosphate), etc.) and nitrile compounds (such as adiponitrile, succinonitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, etc.), as common additives for lithium-ion electrolytes, have played a significant role in improving the high voltage performance, high temperature performance and cycle performance of lithium-ion batteries. In particular, cyanophosphate additives have received widespread attention in the industry.

However, for cyanophosphate additives, cyano (-CN) and phosphate groups are both effective structures of cyanophosphate additives. In theory, the higher the proportion of this effective structure, the better the beneficial effect as an additive. However, due to steric hindrance effects and the difficulty in separating organic matter with different degrees of substitution, the purification of cyanophosphate additives has become one of the difficulties in their application. Moreover, additives used in lithium-ion batteries generally have high requirements for purity.

Therefore, as the downstream application industries gradually increase their requirements for the performance of lithium-ion batteries, further developing more purification processes for phosphate compound lithium-ion electrolyte additives and further broadening the depth and breadth of their use has become one of the urgent issues to be solved by many front-line researchers and scientific research companies in this field.

Summary of the invention

In view of this, the present invention provides a method for purifying tris(2-cyanoethyl)phosphate. The purification method provided by the present invention has a simple and feasible purification process, and the purity of the product can reach 99.95%, meeting the requirements of electronic grade applications. The product can be used as an additive for high-voltage lithium-ion battery electrolyte to improve the high temperature performance and cycle performance of the battery.

The present invention provides a method for purifying tris(2-cyanoethyl)phosphate, comprising the following steps:

1) mixing a crude tris(2-cyanoethyl)phosphate product and an alkali solution, adding an organic solvent and mixing again, separating an organic phase to obtain an organic phase solution;

2) The organic phase solution and stabilizer obtained in the above step are subjected to reduced pressure distillation to obtain purified tris(2-cyanoethyl)phosphate.

Preferably, the tris(2-cyanoethyl)phosphate has a structure as shown in formula (I):

The tris(2-cyanoethyl)phosphate is an additive for lithium-ion battery electrolyte;

The purified tris(2-cyanoethyl)phosphate is electronic grade tris(2-cyanoethyl)phosphate;

The purity of the purified tris(2-cyanoethyl)phosphate is greater than or equal to 99.9%.

Preferably, the purity of the crude tris(2-cyanoethyl)phosphate is 60% to 97%;

The alkali solution includes one or more of NaOH, LiOH, KOH, Ba(OH) ₂ , Ca(OH) ₂ , Na(CO ₃ ) ₂ and NaHCO ₃ ;

The mass concentration of the alkali solution is 1% to 20%;

The organic solvent includes one or more of dichloromethane, dichloroethane, benzene, ethyl acetate, chloroform, toluene, octane, petroleum ether, tridecane, octacosane, carbon disulfide, carbon tetrachloride, ethane and cyclohexane;

The mass ratio of the alkali solution to the crude tris(2-cyanoethyl)phosphate is (1-10):10;

The mass ratio of the organic solvent to the alkali solution is (2-10):1.

Preferably, the stabilizer comprises a nitroxide free radical stabilizer;

The stabilizer includes one or more of N,N-di-tert-butyl nitroxide free radical stabilizer, tert-amyl-tert-butyl nitroxide free radical stabilizer, 2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer, 1-hydroxy-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer, 1-carbonyl-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer, 4-acetylamino-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer and 4-amino-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer;

The mass ratio of the stabilizer to the crude tris(2-cyanoethyl)phosphate is (0.01-1):100;

The purified tris(2-cyanoethyl)phosphate is tris(2-cyanoethyl)phosphate including a stabilizer;

The mass content of the stabilizer in the purified tris(2-cyanoethyl)phosphate is 20 to 150 ppm.

Preferably, the method for preparing the crude tris(2-cyanoethyl)phosphate comprises the following steps:

1) mixing 3-hydroxypropionitrile and a hydrogen chloride chelating agent to obtain a system solution;

2) adding phosphorus oxychloride organic solution to the system solution obtained in the above step to carry out low-temperature reaction, adding organic metal base under the reaction temperature condition of stage II after the dropwise addition is completed, and continuing the reaction under the temperature condition to obtain tris(2-cyanoethyl)phosphate.

Preferably, the hydrogen chloride chelating agent includes one or more of triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine and pyridine;

The molar ratio of the hydrogen chloride chelating agent to phosphorus oxychloride is (3-6):1;

The molar ratio of 3-hydroxypropionitrile to phosphorus oxychloride is (3-10):1;

The solvent in the phosphorus oxychloride organic solution includes one or more of toluene, n-hexane, petroleum ether, ethyl ether, tert-methyl butyl ether, dichloromethane and dichloroethane;

The temperature of the low temperature reaction is -40 to 10°C;

The volume ratio of the solvent to phosphorus oxychloride is (1-10):1.

Preferably, the method of adding the phosphorus oxychloride organic solution comprises dropwise addition;

The rate of the dripping is 5 to 20 ml/h;

The organic base includes one or more of sodium hydrogen, sodium methoxide, sodium ethoxide, potassium ethoxide, sodium methoxide, potassium tert-butoxide, n-butyl lithium and lithium diisopropylamide;

The molar ratio of the organic base to the phosphorus oxychloride is 1:(10-20);

The temperature of the stage II reaction is 50-100°C;

The continued reaction time is 0.5 to 20 hours.

Preferably, after the continued reaction, a post-treatment step is also included;

The post-treatment step comprises one or more steps of extraction, washing and rotary evaporation;

The extraction comprises organic phase extraction;

The extractant for the extraction includes one or more of toluene, xylene, ether, dichloromethane, ethyl acetate, chloroform, benzene, trichloroethane and dichloroethane.

The present invention also provides the use of tris(2-cyanoethyl)phosphate prepared by the purification method described in any one of the above technical solutions in lithium ion batteries.

Preferably, the lithium-ion battery comprises a high-voltage lithium-ion battery;

The lithium-ion battery is specifically an electrolyte of a lithium-ion battery;

The tris(2-cyanoethyl)phosphate is used as an additive for lithium ion battery electrolyte;

The mass content of the tris(2-cyanoethyl)phosphate in the lithium ion battery electrolyte is 0.1% to 5%.

The present invention provides a method for purifying tris(2-cyanoethyl)phosphate, comprising the following steps: firstly, mixing a crude tris(2-cyanoethyl)phosphate with an alkali solution, then adding an organic solvent and mixing again, separating an organic phase to obtain an organic phase solution; then subjecting the organic phase solution obtained in the above steps and a stabilizer to reduced pressure distillation to obtain purified tris(2-cyanoethyl)phosphate. Compared with the prior art, the present invention aims at the problem that the types of existing lithium ion electrolyte additives need to be further developed, starting from the direction of phosphate compounds, and creatively obtaining a method for purifying tris(2-cyanoethyl)phosphate for cyanophosphate additives with multiple cyano groups (-CN) and phosphate groups due to steric hindrance effects, organic matter with different degrees of substitution is difficult to separate, and the like.

The tris(2-cyanoethyl)phosphate provided by the present invention has a novel structure and a simple and feasible purification process. The present invention particularly uses a nitroxide free radical stabilizer to make the product more stable and less likely to decompose or cause other side reactions during the purification process. At the same time, the product only carries ppm-level stabilizers after distillation and purification. The tris(2-cyanoethyl)phosphate product obtained by the method provided by the present invention has a high purity, meets the requirements of electronic-grade applications, better broadens the industrial production and application of high-purity tris(2-cyanoethyl)phosphate additives, and meets the high-level requirements of lithium-ion batteries. The product can be used as an electrolyte additive for high-voltage lithium-ion batteries to improve the high-temperature performance and cycle performance of the battery.

Experimental results show that the purity of the tris(2-cyanoethyl)phosphate product obtained by the purification method provided by the present invention is ≥99.9%, which meets the requirements of electronic grade application.

DETAILED DESCRIPTION

In order to further understand the present invention, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses analytically pure materials or materials of conventional purity in the field of lithium-ion batteries.

The present invention provides a method for purifying tris(2-cyanoethyl)phosphate, comprising the following steps:

1) mixing a crude tris(2-cyanoethyl)phosphate product and an alkali solution, adding an organic solvent and mixing again, separating an organic phase to obtain an organic phase solution;

2) The organic phase solution and stabilizer obtained in the above step are subjected to reduced pressure distillation to obtain purified tris(2-cyanoethyl)phosphate.

The invention firstly mixes a crude tris(2-cyanoethyl)phosphate product and an alkali solution, then adds an organic solvent and mixes again, and then separates an organic phase to obtain an organic phase solution.

In the present invention, the tris(2-cyanoethyl)phosphate preferably has a structure as shown in formula (I):

In the present invention, the tris(2-cyanoethyl)phosphate is preferably an additive for lithium ion battery electrolyte.

In the present invention, the purified tris(2-cyanoethyl)phosphate is preferably electronic grade tris(2-cyanoethyl)phosphate.

In the present invention, the purity of the purified tris(2-cyanoethyl)phosphate is preferably greater than or equal to 99.9%, greater than or equal to 99.9035%, greater than or equal to 99.9525%. Specifically, the purity of the purified tris(2-cyanoethyl)phosphate is electronic grade purity.

In the present invention, the purity of the crude tris(2-cyanoethyl)phosphate is preferably 60% to 97%, more preferably 65% to 90%, more preferably 70% to 85%, and more preferably 75% to 80%.

In the present invention, the alkali solution preferably includes one or more of NaOH, LiOH, KOH, Ba(OH) ₂ , Ca(OH) ₂ , Na(CO ₃ ) ₂ and NaHCO ₃ , more preferably NaOH, LiOH, KOH, Ba(OH) ₂ , Ca(OH) ₂ , Na(CO ₃ ) ₂ or NaHCO ₃ .

In the present invention, the mass concentration of the alkali solution is preferably 1% to 20%, more preferably 5% to 16%, and more preferably 9% to 12%.

In the present invention, the organic solvent preferably includes one or more of dichloromethane, dichloroethane, benzene, ethyl acetate, chloroform, toluene, octane, petroleum ether, tridecane, octacosane, carbon disulfide, carbon tetrachloride, ethane and cyclohexane, more preferably dichloromethane, dichloroethane, benzene, ethyl acetate, chloroform, toluene, octane, petroleum ether, tridecane, octacosane, carbon disulfide, carbon tetrachloride, ethane or cyclohexane.

In the present invention, the mass ratio of the alkali solution to the crude tris(2-cyanoethyl)phosphate is preferably (1-10):10, more preferably (3-8):10, and more preferably (5-6):10.

In the present invention, the mass ratio of the organic solvent to the alkali solution is preferably (2-10):1, more preferably (3-9):1, more preferably (4-8):1, and more preferably (5-7):1.

The present invention further subject the organic phase solution and the stabilizer obtained in the above steps to reduced pressure distillation to obtain purified tris(2-cyanoethyl)phosphate.

In the present invention, the stabilizer preferably includes a nitroxide free radical stabilizer.

In the present invention, the stabilizer preferably includes N, N-di-tert-butyl nitroxide free radical stabilizer, tert-amyl tert-butyl nitroxide free radical stabilizer, 2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer, 1-hydroxy-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer, 1-carbonyl-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer, 4-acetylamino-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer and 4-amino-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer. One or more of the agents, more preferably N, N-di-tert-butyl nitroxide free radical stabilizer, tert-amyl-tert-butyl nitroxide free radical stabilizer, 2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer, 1-hydroxy-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer, 1-carbonyl-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer, 4-acetylamino-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer or 4-amino-2,2,6,6-tetramethylpiperidine nitroxide free radical stabilizer.

In the present invention, the mass ratio of the stabilizer to the crude tris(2-cyanoethyl)phosphate is preferably (0.01-1):100, more preferably (0.05-0.8):100, more preferably (0.1-0.6):100, and more preferably (0.2-0.4):100.

In the present invention, the purified tris(2-cyanoethyl)phosphate is preferably tris(2-cyanoethyl)phosphate including a stabilizer.

In the present invention, the mass content of the stabilizer in the purified tris(2-cyanoethyl)phosphate is preferably 20 to 150 ppm, more preferably 40 to 130 ppm, and more preferably 60 to 110 ppm.

In the present invention, the method for preparing the crude tris(2-cyanoethyl)phosphate preferably comprises the following steps:

1) mixing 3-hydroxypropionitrile and a hydrogen chloride chelating agent to obtain a system solution;

2) adding phosphorus oxychloride organic solution to the system solution obtained in the above step to carry out low-temperature reaction, adding organic metal base under the reaction temperature condition of stage II after the dropwise addition is completed, and continuing the reaction under the temperature condition to obtain tris(2-cyanoethyl)phosphate.

The invention firstly mixes 3-hydroxypropionitrile and a hydrogen chloride chelating agent to obtain a system solution.

In the present invention, the hydrogen chloride chelating agent preferably includes one or more of triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine and pyridine, more preferably pyridine, triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine or n-butylamine.

In the present invention, the molar ratio of the hydrogen chloride chelating agent to phosphorus oxychloride is preferably (3-6):1, more preferably (3.5-5.5):1, and more preferably (4-5):1.

In the present invention, the molar ratio of 3-hydroxypropionitrile to phosphorus oxychloride is preferably (3-10):1, more preferably (4-9):1, more preferably (5-8):1, and more preferably (6-7):1.

The present invention further adds a phosphorus oxychloride organic solution to the system solution obtained in the above step, performs a low-temperature dropwise reaction, adds an organic metal base under the temperature condition of stage II, and continues the reaction under the temperature condition to obtain tris(2-cyanoethyl)phosphate.

In the present invention, the organic solvent in the phosphorus oxychloride organic solution preferably includes one or more of benzene, toluene, xylene, n-hexane, dichloromethane, dichloroethane, trichloroethane, acetonitrile, ethyl acetate, petroleum ether, ether and tert-methyl butyl ether, more preferably toluene, xylene, ethyl acetate, ether, tert-methyl butyl ether, dichloromethane or dichloroethane.

In the present invention, the temperature of the low-temperature reaction is preferably -40 to 10°C, more preferably -30 to 5°C, and more preferably -20 to 0°C.

In the present invention, the volume ratio of the organic solvent to phosphorus oxychloride is preferably (1-10):1, more preferably (3-8):1, and more preferably (5-6):1.

In the present invention, the method of adding the phosphorus oxychloride organic solution preferably includes dropwise addition.

In the present invention, the dropping rate is preferably 5 to 20 ml/h, more preferably 8 to 17 ml/h, and more preferably 11 to 14 ml/h.

In the present invention, the organic metal base in the organic metal base solution preferably includes one or more of sodium hydrogen, sodium methoxide, sodium ethoxide, potassium ethoxide, sodium methoxide, potassium tert-butoxide, n-butyl lithium and lithium diisopropylamide, and more preferably includes sodium hydrogen, sodium methoxide, sodium ethoxide, potassium ethoxide, sodium methoxide, potassium tert-butoxide, n-butyl lithium or lithium diisopropylamide.

In the present invention, the molar ratio of the organic metal base to the phosphorus oxychloride is 1:(10-20), more preferably 1:(12-18), and more preferably 1:(14-16).

In the present invention, the temperature of the stage II reaction is preferably 50-100°C, more preferably 60-80°C, and more preferably 65-78°C.

In the present invention, the continued reaction time is preferably 0.5 to 20 hours, more preferably 8 to 17 hours, and more preferably 11 to 15 hours.

In the present invention, after the continued reaction, a post-treatment step is preferably included.

In the present invention, the post-treatment step preferably includes one or more steps of extraction, washing and rotary evaporation, more preferably multiple steps of extraction, washing and rotary evaporation.

In the present invention, the extraction preferably comprises organic phase extraction.

In the present invention, the extractant for extraction preferably includes one or more of xylene, toluene, n-hexane, dichloromethane, ethyl acetate, chloroform, benzene, trichloroethane and dichloroethane, and more preferably dichloromethane, n-hexane, chloroform, xylene, ethyl acetate, ether, benzene or dichloroethane.

In the present invention, the organic phase preferably includes one or more of dichloromethane, ethylene dichloride, benzene, toluene, octane, petroleum ether, tridecane, octacosane, carbon disulfide, carbon tetrachloride, ethane and cyclohexane, more preferably dichloromethane, ethylene dichloride, benzene, toluene, octane, petroleum ether, tridecane, octacosane, carbon disulfide, carbon tetrachloride, ethane or cyclohexane.

The present invention is to complete and refine the overall preparation process, better ensure the structure of tris(2-cyanoethyl)phosphate, and improve the purity and yield of the product. The preparation method of the tris(2-cyanoethyl)phosphate can specifically be the following steps:

1) Add 3-hydroxypropionitrile and a hydrogen chloride chelating agent mixture into a three-necked flask;

2) adding a mixed solution of phosphorus oxychloride and an organic diluent solvent dropwise to step 1) under low temperature conditions;

3) The mixed solution after the reaction in step 2) is heated to 50-100° C., a certain proportion of an organic metal base is added, and the reaction is continued for 0.5 to 20 hours;

4) filtering and extracting the product after the reaction in step 3), and distilling the tri(2-cyanoethyl)phosphate mixture under reduced pressure to obtain a crude tri(2-cyanoethyl)phosphate product;

5) The crude product of step 4) was added to ice water to dissolve, and then an organic solvent was added and stirred thoroughly, and then the organic phase was separated using a separatory funnel (the product tris(2-cyanoethyl)phosphate compound was extracted into the organic phase), and the organic phase was washed with ice water for 3 to 4 times, and the organic solvent was removed by rotary evaporation to obtain pure tris(2-cyanoethyl)phosphate.

The present invention is to complete and refine the overall purification process, better improve the purity of the tris(2-cyanoethyl)phosphate product, and reduce the impurity content. The purification method of the tris(2-cyanoethyl)phosphate can preferably be the following steps:

1) adding the crude product into alkaline water to dissolve, then adding an organic solvent and stirring thoroughly, and separating the organic phase with a separatory funnel (the product tris(2-cyanoethyl)phosphate compound is extracted into the organic phase);

2) Add an appropriate amount of stabilizer to the separated organic phase solution and perform reduced pressure distillation to obtain a high-purity product.

Specifically, the alkaline water in step 1) is one or a mixture of two or more selected from the following substances: NaOH, LiOH, KOH, Ba(OH) ₂ , Ca(OH) ₂ , Na(CO ₃ ) ₂ , NaHCO ₃ , etc., and its concentration is 1% to 20%, preferably 1% to 10%.

Specifically, the organic solvent is one or a mixture of two or more selected from the following substances: at least one of dichloromethane, dichloroethane, benzene, ethyl acetate, chloroform, toluene, octane, petroleum ether, tridecane, octacosane, carbon disulfide, carbon tetrachloride, ethane, and cyclohexane as the extractant, and the ratio of the organic solvent to alkaline water is preferably 2:1 to 10:1, preferably 3:1 to 5:1.

Specifically, the nitroxide free radical stabilizer is N,N-di-tert-butyl nitroxide free radical, tert-amyl-tert-butyl nitroxide free radical, 2,2,6,6-tetramethylpiperidine nitroxide free radical (TEMPO), 1-hydroxy-2,2,6,6-tetramethylpiperidine nitroxide free radical (OH-TEMPO), 1-carbonyl-2,2,6,6-tetramethylpiperidine nitroxide free radical (OXO-TEMPO), 4-acetylamino-2,2,6,6-tetramethylpiperidine nitroxide free radical, 4-amino-2,2,6,6-tetramethylpiperidine nitroxide free radical, etc., which can be a certain compound or a mixture thereof; and its addition amount is 0.01 to 1%.

Specifically, the reduced pressure distillation temperature in step 3) is 100° C. to 250° C., preferably 150° C. to 200° C., and the vacuum pressure is 0.01 MPa to 0.1 MPa.

The present invention proposes a method for purifying the compound of the above embodiment. According to an embodiment of the present invention, the method comprises: adding a crude product to alkaline water to dissolve, adding an organic solvent to fully stir, and separating an organic phase with a separatory funnel, adding a nitroxide free radical stabilizer to the separated organic phase solution, and performing reduced pressure distillation to obtain a high-purity product.

According to an embodiment of the present invention, in order to obtain the compound of the above embodiment, alkaline water can be added to the crude product to prevent the synthesized product from being hydrolyzed in water, which can further improve the purity of the product compound.

According to an embodiment of the present invention, in order to obtain the compound of the above embodiment, a nitroxide free radical stabilizer is selected to be added to solve the problem. The reduced pressure distillation method thereof causes the product to polymerize under high temperature conditions, affecting the product quality and improving the product purity.

According to an embodiment of the present invention, in order to obtain the compound of the above embodiment, alkaline water is selected to be one or a mixture of two or more selected from the following substances: NaOH, LiOH, KOH, Ba(OH) ₂ , Ca(OH) ₂ , Na(CO ₃ ) ₂ , NaHCO ₃ , etc., and its concentration is 1%-20%, preferably 1% to 10%, to prevent product hydrolysis and further improve the purity of the product compound.

According to an embodiment of the present invention, in order to obtain a compound with high purity in the above embodiment, an organic solvent is used for extraction. Specifically, at least one of dichloromethane, dichloroethane, benzene, ethyl acetate, chloroform, toluene, octane, petroleum ether, tridecane, octacosane, carbon disulfide, carbon tetrachloride, ethane, and cyclohexane can be used as an extractant, and the obtained product is purified by the organic phase to obtain high-purity tris(2-cyanoethyl)phosphate.

According to an embodiment of the present invention, in order to obtain the high-purity compound of the above embodiment, a low-pressure and low-temperature reduced-pressure distillation method is selected, the temperature is 100°C to 250°C, preferably 150°C to 200°C, and the vacuum pressure is 0.01MPa to 0.1MPa.

The present invention provides the use of tris(2-cyanoethyl)phosphate prepared by the purification method described in any one of the above technical solutions in lithium ion batteries.

In the present invention, the lithium ion battery preferably includes a high voltage lithium ion battery.

In the present invention, the lithium ion battery is preferably an electrolyte of a lithium ion battery.

In the present invention, the tris(2-cyanoethyl)phosphate is preferably used as an additive for lithium ion battery electrolyte.

In the present invention, the mass content of the tris(2-cyanoethyl)phosphate in the lithium ion battery electrolyte is preferably 0.1% to 5%, more preferably 0.5% to 4%, and more preferably 1% to 3%.

The above steps of the present invention provide a method for purifying tris(2-cyanoethyl)phosphate. The tris(2-cyanoethyl)phosphate provided by the present invention has a novel structure and a simple and feasible purification process. The present invention particularly uses a nitroxide free radical stabilizer to make the product more stable and less likely to decompose or cause other side reactions during the purification process. At the same time, the product only carries ppm-level stabilizers after distillation and purification. The tris(2-cyanoethyl)phosphate product obtained by the method provided by the present invention has a high purity, meets the requirements of electronic-grade applications, better broadens the industrial production and application of high-purity tris(2-cyanoethyl)phosphate additives, and meets the high-level requirements of lithium-ion batteries. The product can be used as an electrolyte additive for high-voltage lithium-ion batteries to improve the high-temperature performance and cycle performance of the battery.

Experimental results show that the purity of the tris(2-cyanoethyl)phosphate product obtained by the purification method provided by the present invention can reach 99.95%, meeting the requirements of electronic grade applications.

In order to further illustrate the present invention, a method for purifying tris(2-cyanoethyl)phosphate provided by the present invention is described in detail below in conjunction with examples. However, it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following examples.

The reagents used in the following examples of the present invention are all commercially available products.

Example 1

(1) Add 0.4 mol of anhydrous 3-hydroxypropionitrile and 0.3 mol of a mixed solution of triethylamine into a three-necked flask, and control the reaction temperature to be below 0° C.;

(2) Mix 15.33 g of 0.1 mol of phosphorus oxychloride and 100 ml of xylene and place in a constant pressure dropping funnel;

(3) adding the mixed solution of step (2) dropwise to the mixed solution of step (1), with the dropping rate controlled at 10 ml/h;

(4) After the dropwise addition was completed, the temperature was raised to 60°C, and 0.68 g of sodium ethoxide was added, and the reaction was continued for 5 h;

(5) adding 100 ml of xylene to the solution after the reaction for extraction, filtering out pyridine hydrochloride and distilling the filtrate under reduced pressure to obtain a crude product;

(6) Add 100 g of 60% pure tris(2-cyanoethyl)phosphate into a three-necked flask, add 30 g of 1% NaOH aqueous solution and 90 g of dichloromethane solution, stir for 30 min, place in a separatory funnel and let stand for 1 h before separation;

(7) Add 0.1 g of nitroxyl piperidinol to the separated solution, and purify it in a vacuum distillation apparatus at a temperature of 180° C. and a pressure of −0.095 MPa to obtain 92.5 g of a sample.

The product purity was measured by gas chromatography to be 99.9035%, and the nitrogen oxide free radical piperidinol was 112 ppm.

Example 2

(1) Add 50 g of 70% pure tris(2-cyanoethyl)phosphate to a three-necked flask, add 20 g of 1% NaOH aqueous solution and 80 g of dichloromethane solution, stir for 30 min, place in a separatory funnel and let stand for 1 h before separation;

(2) Add 0.025 g of nitroxyl piperidinol to the separated solution, and purify it in a vacuum distillation apparatus at a temperature of 190° C. and a pressure of -0.085 MPa to obtain 42.5 g of a sample.

The product purity was measured by gas chromatography to be 99.9216%, and the content of nitroxyl piperidinol was 18 ppm.

Example 3

(1) Add 100 g of 80% pure tris(2-cyanoethyl)phosphate into a three-necked flask, add 20 g of 5% NaOH aqueous solution and 100 g of dichloromethane solution, stir for 30 min, place in a separatory funnel and let stand for 1 h before separation;

(2) Add 0.01 g of nitroxyl piperidinol to the separated solution, and purify it in a vacuum distillation apparatus at a temperature of 200° C. and a pressure of -0.08 MPa to obtain 92.5 g of a sample.

The purity of the product was measured by gas chromatography to be 99.9525%, and the content of nitroxyl piperidinol was 21 ppm.

Comparative Example 1

(1) Add 100 g of 60% pure tris(2-cyanoethyl)phosphate into a three-necked flask, add 30 g of 1% NaOH aqueous solution and 90 g of dichloromethane solution, stir for 30 min, place in a separatory funnel and let stand for 1 h before separation;

(2) The separated solution was purified in a vacuum distillation apparatus at a temperature of 150°C and a pressure of -0.095 MPa to obtain 89.7 g of sample.

The purity of the product was measured by gas chromatography and was 49.587%.

Comparative Example 2

1) Add 50g of 70% pure tris(2-cyanoethyl)phosphate into a three-necked flask, add 20g of 1% NaOH aqueous solution and 80g of dichloromethane solution, stir for 30min, place in a separatory funnel and let stand for 1h before separation;

2) The separated solution was purified in a vacuum distillation apparatus at a temperature of 180°C and a pressure of -0.085 MPa to obtain 45.2 g of sample.

The purity of the product was measured by gas chromatography and was 55.893%.

See Table 1, which shows the physical property data of tris(2-cyanoethyl)phosphate prepared in the examples and comparative examples of the present invention.

Table 1

purity Viscosity color Example 1 99.9035% 120mpas Light yellow Example 2 99.9216% 130mpas Light yellow Example 3 99.9525% 100mpas Light yellow Comparative Example 1 49.587% 2100mpas yellow Comparative Example 2 55.893% 1800mpas yellow

The above is a detailed introduction to a method for purifying tris(2-cyanoethyl)phosphate provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enables any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the textual expression of the claims, or if they include equivalent structural elements that are not substantially different from the textual expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims (10)

1. A method for purifying tris(2-cyanoethyl)phosphate, characterized in that it comprises the following steps: 1) After the crude tris(2-cyanoethyl)phosphate is mixed with an alkali solution, an organic solvent is added and mixed again, and the organic phase is separated to obtain an organic phase solution; The alkali solution is one or more of NaOH, LiOH, KOH, Ba(OH) ₂ , Ca(OH) ₂ , Na(CO ₃ ) ₂ and NaHCO ₃ ; The mass concentration of the alkali solution is 1% to 20%; 2) The organic phase solution and the stabilizer obtained in the above step are subjected to reduced pressure distillation to obtain purified tris(2-cyanoethyl)phosphate; The stabilizer is one or more of 2,2,6,6-tetramethylpiperidine nitroxide free radical, 4-hydroxy-2,2,6,6-tetramethylpiperidine nitroxide free radical, 4-carbonyl-2,2,6,6-tetramethylpiperidine nitroxide free radical, 4-acetylamino-2,2,6,6-tetramethylpiperidine nitroxide free radical and 4-amino-2,2,6,6-tetramethylpiperidine nitroxide free radical; The preparation method of the crude tris(2-cyanoethyl)phosphate comprises the following steps: 1) Mixing 3-hydroxypropionitrile and a hydrogen chloride chelating agent to obtain a system solution; The hydrogen chloride chelating agent is selected from one or more of triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine and pyridine; 2) adding phosphorus oxychloride organic solution to the system solution obtained in the above step to carry out low-temperature reaction, adding organic metal base at a temperature of 50-100° C. after the dropwise addition is completed, and continuing the reaction at this temperature to obtain tris(2-cyanoethyl)phosphate; The temperature of the low temperature reaction is -40~10°C; The organic metal base is one or more of sodium hydrogen, sodium methoxide, sodium ethoxide, potassium ethoxide, potassium tert-butoxide, n-butyl lithium and lithium diisopropylamide. 2. The method for purifying tris(2-cyanoethyl)phosphate according to claim 1, wherein the tris(2-cyanoethyl)phosphate has a structure as shown in formula (I): (I); The tris(2-cyanoethyl)phosphate is an additive for lithium-ion battery electrolyte; The purity of the purified tris(2-cyanoethyl)phosphate is greater than or equal to 99.9%. 3. The method for purifying tris(2-cyanoethyl)phosphate according to claim 1, wherein the purity of the crude tris(2-cyanoethyl)phosphate is 60% to 97%. 4. The method for purifying tris(2-cyanoethyl)phosphate according to claim 1, wherein the organic solvent is one or more of dichloromethane, ethylene dichloride, benzene, ethyl acetate, chloroform, toluene, octane, petroleum ether, tridecane, octacosane, carbon disulfide, carbon tetrachloride, ethane and cyclohexane. 5. The method for purifying tris(2-cyanoethyl)phosphate according to claim 1, characterized in that the mass ratio of the alkali solution to the crude tris(2-cyanoethyl)phosphate is (1-10):10; The mass ratio of the organic solvent to the alkali solution is (2-10):1. 6. The method for purifying tris(2-cyanoethyl)phosphate according to claim 1, characterized in that the mass ratio of the stabilizer to the crude tris(2-cyanoethyl)phosphate is (0.01-1):100; The purified tris(2-cyanoethyl)phosphate is tris(2-cyanoethyl)phosphate including a stabilizer; The mass content of the stabilizer in the purified tris(2-cyanoethyl)phosphate is 20-150 ppm. 7. The method for purifying tris(2-cyanoethyl)phosphate according to claim 1, characterized in that in the method for preparing the crude tris(2-cyanoethyl)phosphate, the molar ratio of the hydrogen chloride chelating agent to phosphorus oxychloride is (3-6):1; The molar ratio of 3-hydroxypropionitrile to phosphorus oxychloride is (3-10):1; The solvent in the phosphorus oxychloride organic solution is one or more of toluene, n-hexane, petroleum ether, ethyl ether, tert-methyl butyl ether, dichloromethane and dichloroethane. 8. The method for purifying tris(2-cyanoethyl)phosphate according to claim 7, characterized in that, in the phosphorus oxychloride organic solution, the volume ratio of the solvent to phosphorus oxychloride is (1-10):1. 9. The method for purifying tris(2-cyanoethyl)phosphate according to claim 1, characterized in that in the method for preparing the crude tris(2-cyanoethyl)phosphate, the method for adding the phosphorus oxychloride organic solution is selected from the group consisting of dropwise addition; The rate of the dropwise addition is 5-20 ml/h; The molar ratio of the organic metal base to the phosphorus oxychloride is 1:(10-20); The continued reaction time is 0.5 to 20 hours. 10. The method for purifying tris(2-cyanoethyl)phosphate according to claim 1, characterized in that in the method for preparing the crude tris(2-cyanoethyl)phosphate, after the continued reaction, a post-treatment step is further included; The post-treatment step comprises one or more steps of extraction, washing and rotary evaporation; The extraction is organic phase extraction; The extractant for the extraction is one or more of toluene, xylene, ether, dichloromethane, ethyl acetate, chloroform, benzene, trichloroethane and dichloroethane.