Electrolyte additive and preparation method thereof

Abstract

The invention relates to an electrolyte additive and a preparation method thereof, and belongs to the technical field of electrolyte. The preparation method comprises the following steps: by taking allyl-1, 3-sultone as a raw material, carrying out Michael addition reaction on double bonds of the allyl-1, 3-sultone and amino groups of 4-amino-2-(trifluoromethyl) thiophene under the catalytic action of 1, 8-diazabicyclo-undec-7-ene to obtain an intermediate with a tertiary amine structure, and carrying out condensation reaction on the intermediate to obtain an intermediate with a tertiary amine structure; the preparation method comprises the following steps: carrying out a quaternary ammonium salt reaction on a tertiary amine structure of an intermediate and bromine atoms of ethyl bromoacetate to obtain an additive, and compounding the additive and a phosphate additive to obtain the electrolyte additive. Allyl-1, 3-sultone is used for modification, and fluoroalkyl is introduced, so that the intermolecular force is effectively reduced; the dependence of the electrolyte viscosity on the temperature is weakened, and the ionic conductivity of the electrolyte under the low-temperature condition is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytes, and in particular relates to an electrolyte additive and a preparation method thereof. Background Art

[0002] As a representative of high-energy-density secondary batteries, lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and energy storage systems. Their performance optimization is highly dependent on the careful design of the electrolyte formulation. Additives, as key components for regulating the function of the electrolyte, have a decisive influence on the high and low temperature performance, cycle life, and safety of the battery. Sulfonate compounds (such as 1,3-propane sultone (PS), propenyl-1,3-sultone (PST) and its derivatives) have become an important category of additives for improving battery stability due to their unique molecular structure. This type of compound can form a sulfonate-rich interface film at the positive and negative electrode interfaces, effectively inhibiting the redox side reactions of solvent molecules, significantly improving gas production during high-temperature storage, and increasing capacity recovery. However, the solid electrolyte interface film and the positive electrode electrolyte interface film formed by the sulfonate have poor ionic conductivity, which may lead to a continuous increase in the internal resistance of the battery. To address the above technical deficiencies, the present invention provides an electrolyte additive and a method for preparing the same. Summary of the Invention

[0003] The object of the present invention is to provide an electrolyte additive and a preparation method thereof, so as to solve the problems mentioned in the above background technology.

[0004] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing an electrolyte additive comprises the following steps: Step 1: Propylene-1,3-sultone, 4-amino-2-(trifluoromethyl)thiophene, 1,8-diazabicycloundec-7-ene, and N,N-dimethylformamide are mixed in a three-necked flask equipped with a condenser, a thermometer, and a magnetic stirring rotor. After turning on the magnetic stirring, the mixture is reacted at a temperature of 80 to 120° C. for 10 to 16 hours. After the reaction is completed, the reaction solution is rotary evaporated to remove the solvent and then eluted by silica gel column chromatography to obtain an intermediate; Step 2: Mix the intermediate, ethyl bromoacetate, and N,N-dimethylformamide in a three-necked flask equipped with a condenser, a thermometer, and a magnetic stirring rotor. After turning on the magnetic stirring, react at a temperature of 50-110° C. for 8-24 hours. After the reaction is completed, the reaction solution is rotary evaporated to remove the solvent and then eluted by silica gel column chromatography to obtain the first additive. The third step is to compound the prepared first additive and the second additive in any proportion to obtain an electrolyte additive.

[0005] Furthermore, the second additive is a phosphate additive, including at least one of tris(2,2,2-trifluoroethyl) phosphate and tris(1,1,1,2,2,2-hexafluoro-2-propyl) phosphate.

[0006] Furthermore, in the first step, the usage ratio of propenyl-1,3-sultone, 4-amino-2-(trifluoromethyl)thiophene, 1,8-diazabicycloundec-7-ene, and N,N-dimethylformamide is 0.03-0.04 mol: 0.01 mol: 0.004-0.006 mol: 40-60 mL.

[0007] Furthermore, the amount ratio of the intermediate, ethyl bromoacetate, and N,N-dimethylformamide used in the second step is 0.005 mol: 0.006-0.01 mol: 40-60 mL.

[0008] Preferably, the mass ratio of the first additive to the second additive is 1 to 2:1.

[0009] An electrolyte additive is prepared by any of the above preparation steps.

[0010] Beneficial effects of the present invention: 1) The present invention uses propenyl-1,3-sultone as a raw material, utilizes the double bond of propenyl-1,3-sultone and the amino group of 4-amino-2-(trifluoromethyl)thiophene to undergo Michael addition reaction under the catalysis of 1,8-diazabicycloundec-7-ene to obtain an intermediate having a tertiary amine structure, and then the tertiary amine structure of the intermediate reacts with the bromine atom of ethyl bromoacetate to produce a quaternary ammonium salt reaction to obtain an additive. The additive of the present invention is compounded with a phosphate additive to obtain an electrolyte additive. The present invention modifies propenyl-1,3-sultone and introduces a fluoroalkyl group, thereby effectively reducing intermolecular forces, weakening the temperature dependence of the electrolyte viscosity, and improving the ionic conductivity of the electrolyte under low temperature conditions.

[0011] 2) The present invention modifies propenyl-1,3-sultone and changes the energy level orbit of propenyl-1,3-sultone, thereby effectively optimizing the interfacial stability of the sultone additive and effectively suppressing the cyclic attenuation of the electrolyte. DETAILED DESCRIPTION

[0012] The following will clearly and completely describe the technical solutions of the embodiments of this application in conjunction with the embodiments. Obviously, the embodiments described are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection requested by this application.

[0013] In the description of this application, all numbers disclosed herein are approximate, regardless of whether the word "about" or "approximately" is used. The value of each number may vary by less than 10% or by a reasonable difference considered by a person skilled in the art, such as 1%, 2%, 3%, 4% or 5%.

[0014] The sources of all raw materials in the present invention are not particularly limited and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0015] Example 1 A method for preparing an electrolyte additive comprises the following steps: Step 1: 0.03 mol of propenyl-1,3-sultone, 0.01 mol of 4-amino-2-(trifluoromethyl)thiophene, 0.006 mol of 1,8-diazabicycloundec-7-ene, and 40 mL of N,N-dimethylformamide were mixed in a three-necked flask equipped with a condenser, a thermometer, and a magnetic stirring rotor. After turning on the magnetic stirring, the mixture was reacted at a temperature of 80° C. for 16 hours. After the reaction was completed, the reaction solution was rotary evaporated to remove the solvent and then eluted by silica gel column chromatography to obtain an intermediate; Step 2: 0.005 mol of the intermediate, 0.006 mol of ethyl bromoacetate, and 40 mL of N,N-dimethylformamide were mixed in a three-necked flask equipped with a condenser, a thermometer, and a magnetic stirring rotor. The mixture was stirred at 110° C. for 8 h. After the reaction was completed, the reaction solution was evaporated to remove the solvent and then eluted by silica gel column chromatography to obtain the first additive. The third step is to compound the prepared first additive and the second additive tris(1,1,1,2,2,2-hexafluoro-2-propyl) phosphate in a mass ratio of 1:1 to obtain an electrolyte additive.

[0016] An electrolyte additive is prepared by the above preparation steps.

[0017] Example 2 A method for preparing an electrolyte additive comprises the following steps: Step 1: 0.035 mol of propenyl-1,3-sultone, 0.01 mol of 4-amino-2-(trifluoromethyl)thiophene, 0.005 mol of 1,8-diazabicycloundec-7-ene, and 50 mL of N,N-dimethylformamide were mixed in a three-necked flask equipped with a condenser, a thermometer, and a magnetic stirring rotor. After turning on the magnetic stirring, the mixture was reacted at a temperature of 100° C. for 13 hours. After the reaction, the reaction solution was rotary evaporated to remove the solvent and then eluted by silica gel column chromatography to obtain an intermediate; Step 2: 0.005 mol of the intermediate, 0.008 mol of ethyl bromoacetate, and 50 mL of N,N-dimethylformamide were mixed in a three-necked flask equipped with a condenser, a thermometer, and a magnetic stirring rotor. The mixture was stirred at 80°C for 16 hours. After the reaction, the reaction solution was evaporated to remove the solvent and then eluted by silica gel column chromatography to obtain the first additive. The third step is to compound the prepared first additive and the second additive tris(1,1,1,2,2,2-hexafluoro-2-propyl) phosphate in a mass ratio of 1.5:1 to obtain an electrolyte additive.

[0018] An electrolyte additive is prepared by the above preparation steps.

[0019] Example 3 A method for preparing an electrolyte additive comprises the following steps: Step 1: 0.04 mol of propenyl-1,3-sultone, 0.01 mol of 4-amino-2-(trifluoromethyl)thiophene, 0.004 mol of 1,8-diazabicycloundec-7-ene, and 60 mL of N,N-dimethylformamide were mixed in a three-necked flask equipped with a condenser, a thermometer, and a magnetic stirring rotor. After turning on the magnetic stirring, the mixture was reacted at a temperature of 120° C. for 10 hours. After the reaction was completed, the reaction solution was rotary evaporated to remove the solvent and then eluted by silica gel column chromatography to obtain an intermediate; Step 2: 0.005 mol of the intermediate, 0.01 mol of ethyl bromoacetate, and 60 mL of N,N-dimethylformamide were mixed in a three-necked flask equipped with a condenser, a thermometer, and a magnetic stirring rotor. The mixture was stirred at 50°C for 24 hours. After the reaction, the reaction solution was evaporated to remove the solvent and then eluted by silica gel column chromatography to obtain the first additive. The third step is to compound the prepared first additive and the second additive tris(2,2,2-trifluoroethyl) phosphate in a mass ratio of 2:1 to obtain an electrolyte additive.

[0020] An electrolyte additive is prepared by the above preparation steps.

[0021] Comparative Example 1 The difference between this comparative example and Example 1 is that the first additive is not prepared, but propenyl-1,3-sultone and the second additive are directly compounded to obtain the electrolyte additive.

[0022] A method for preparing an electrolyte additive comprises the following steps: The electrolyte additive is obtained by compounding propenyl-1,3-sultone and a second additive, tris(1,1,1,2,2,2-hexafluoro-2-propyl) phosphate, in a mass ratio of 1:1.

[0023] An electrolyte additive is prepared by the above preparation steps.

[0024] Experimental Example 1 The electrolyte additives in Examples 1 to 3 and Comparative Example 1 were added to a solvent (the solvent was a mixture of diethyl carbonate and ethylene carbonate in a mass ratio of 1:1) at a mass fraction to obtain an electrolyte. Lithium manganese oxide was used as the positive electrode active material and graphite was used as the negative electrode to assemble a battery. The high-temperature cycle capacity retention rate (45°C, 500 cycles) and the low-temperature cycle capacity retention rate (-10°C, 50 cycles) of the assembled battery were tested. The test results are shown in Table 1: Table 1

[0025] The above embodiments are intended only to facilitate understanding of the methods and core concepts of the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, but is intended to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an electrolyte additive, characterized in that: The following steps are involved: An intermediate is obtained by a Michael addition reaction between propenyl-1,3-sultone and 4-amino-2-(trifluoromethyl)thiophene, and the intermediate is then reacted with ethyl bromoacetate to produce a quaternary ammonium salt to obtain a first additive. The first additive is compounded with a second additive to obtain an electrolyte additive.

2. The method for preparing an electrolyte additive according to claim 1, characterized in that: The conditions for the Michael addition reaction of propenyl-1,3-sultone with 4-amino-2-(trifluoromethyl)thiophene are: Propylene-1,3-sultone, 4-amino-2-(trifluoromethyl)thiophene, 1,8-diazabicycloundec-7-ene and N,N-dimethylformamide are mixed and the temperature is controlled at 80-120° C. to react.

3. The method for preparing an electrolyte additive according to claim 1, characterized in that: The conditions for the reaction of the intermediate with ethyl bromoacetate to form a quaternary ammonium salt are: The intermediate, ethyl bromoacetate and N,N-dimethylformamide are mixed and the temperature is controlled at 50-110° C. to carry out the reaction.

4. The method for preparing an electrolyte additive according to claim 1, characterized in that: The Michael addition reaction takes 10 to 16 hours.

5. The method for preparing an electrolyte additive according to claim 1, characterized in that: The time for the quaternary ammonium salt reaction to occur is 8 to 24 hours.

6. The method for preparing an electrolyte additive according to claim 1, characterized in that: The second additive is a phosphate additive.

7. The method for preparing an electrolyte additive according to claim 1, characterized in that: The mass ratio of the first additive to the second additive is 1 to 2:

1.

8. The method for preparing an electrolyte additive according to claim 1, characterized in that: The usage ratio of propenyl-1,3-sultone to 4-amino-2-(trifluoromethyl)thiophene is 0.03-0.04 mol:0.01 mol.

9. The method for preparing an electrolyte additive according to claim 1, characterized in that: The usage ratio of the intermediate and ethyl bromoacetate is 0.005 mol: 0.006-0.01 mol.

10. An electrolyte additive, characterized in that The electrolyte additive is prepared by the preparation method according to any one of claims 1 to 9.

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