1,2,4,5-tetrafluoro-6-vinylbenzene derivatives and synthesis methods and applications thereof

Abstract

The invention discloses a 1,2,4,5-tetrafluoro-6-vinylbenzene derivative and a synthesis method and application thereof. The compound is prepared by using 1,2,3,4,5-pentafluoro-6-vinylbenzene as a starting material for the reaction, and a target product is obtained by a nucleophilic substitution reaction with an alkyl alcohol. The synthetic raw materials of the synthetic method are cheap and readily available, the synthetic process is simple, and the yield and purity are both high. The structure of the 1,2,4,5-tetrafluoro-6-vinylbenzene derivative contains a benzene ring connected to four fluoride ions. When used as an additive in an electrolyte, it helps to form a uniform and stable protective layer on the surface of the positive electrode, and the fluorine-containing protective layer can inhibit the deposition of manganese ions on the surface of the negative electrode during the cycle process and the decomposition of the electrolyte during the high-temperature cycle process, and can inhibit the increase of the DC resistance, thereby improving the charge and discharge performance of the lithium-ion battery at high temperature.

Description

Technical Field

[0001] The invention relates to the field of preparation of battery electrolyte additives, in particular to 1,2,4,5-tetrafluoro-6-vinylbenzene derivatives and synthesis methods thereof and applications in lithium ion battery electrolytes. Background Art

[0002] Lithium-ion batteries have successfully entered our lives. With the progress of society and the improvement of people's material level, people have higher and higher requirements for lithium-ion batteries. Due to the advantages of high safety, strong discharge capacity, long cycle life, and high capacity density, lithium-ion batteries are a very promising battery, especially in the application fields of electric vehicles, smart phones, laptops, etc., which has attracted widespread attention.

[0003] At present, the positive electrode of lithium-ion batteries uses lithium-intercalated transition metal oxides, and the negative electrode material uses lithium-intercalable compounds. During the cycle process, the transition metal ions will dissolve, causing the cations to mix and lead to irreversible phase changes. At the same time, with the consumption of electrolyte, the internal resistance continues to increase. This deterioration will be aggravated at high temperatures, accelerating the loss of battery capacity and the increase of internal impedance, resulting in a faster shortening of the cycle life of lithium-ion batteries. Summary of the invention

[0004] The purpose of the present invention is to provide a 1,2,4,5-tetrafluoro-6-vinylbenzene derivative substance, a synthesis method thereof and a lithium ion battery electrolyte containing the substance in view of the above-mentioned problems of the prior art.

[0005] The technical solution adopted by the present invention is specifically as follows:

[0006] A 1,2,4,5-tetrafluoro-6-vinylbenzene derivative, the structural formula of which is as follows:

[0007]

[0008] Wherein, R1 is H or F, and R2 and R3 are C1-C6 alkyl groups containing hydrogen or multiple halogen atoms (F, Cl, Br, I);

[0009] When 1,2,4,5-tetrafluoro-6-vinylbenzene derivatives are used as additives in electrolytes, a uniform and stable protective layer can be formed on the surface of the positive electrode, and the fluorine-containing protective layer can inhibit the deposition of manganese ions on the surface of the negative electrode during the cycle and the decomposition of the electrolyte during high-temperature cycles, and can inhibit the increase of DC resistance, thereby improving the cycle performance of lithium-ion batteries at high temperatures.

[0010] A method for synthesizing a 1,2,4,5-tetrafluoro-6-vinylbenzene derivative comprises the following steps:

[0011] 1) Under nitrogen protection, take the raw alcohol and organic base or inorganic base for reduction reaction to obtain the intermediate alcohol salt, the reaction is as follows:

[0012]

[0013] 2) Under nitrogen protection, the intermediate obtained in the first step directly reacts with 1,2,3,4,5-pentafluoro-6-vinylbenzene to obtain the target compound. The reaction is as follows:

[0014]

[0015] Furthermore, in step 1), the reaction solvent is an organic solvent such as tetrahydrofuran, acetonitrile, N,N-dimethylformamide, dioxane, ethylene glycol dimethyl ether, acetone, etc.;

[0016] The molar ratio of the alcohol to the base is 1:1-3;

[0017] The acid-base reaction temperature for salt formation is -20°C to 0°C, and the time is 0.5 to 2h;

[0018] In step 2), the reaction solvent is an organic solvent such as tetrahydrofuran, acetonitrile, N,N-dimethylformamide, dioxane, ethylene glycol dimethyl ether, acetone, etc.;

[0019] The molar ratio of 1,2,3,4,5-pentafluoro-6-vinylbenzene to fluoroalcohol is 1:1-2;

[0020] The nucleophilic reaction temperature is from room temperature to reflux reaction, and the time is 1 to 5 hours;

[0021] Furthermore, in step 1), the acid-base reaction does not require any treatment and is directly reacted with 1,2,3,4,5-pentafluoro-6-vinylbenzene, and the reaction solution is directly used in the next step.

[0022] Furthermore, in step 2), after the nucleophilic reaction, the reaction is quenched with saturated ammonium chloride, extracted with an organic solvent, washed with water, dried over anhydrous magnesium sulfate, and purified to obtain the 1,2,4,5-tetrafluoro-6-vinylbenzene derivative.

[0023] A lithium ion battery electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the additive is a 1,2,4,5-tetrafluoro-6-vinylbenzene derivative.

[0024] The above-mentioned lithium ion battery electrolyte, the lithium salt is composed of one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, tris(trifluoromethylsulfonyl)methyl lithium, bis(trifluoromethylsulfonyl)methyl lithium, lithium trifluoromethylsulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, LiAsF6, and LiClO4 mixed in any proportion.

[0025] The above-mentioned lithium ion battery electrolyte has a lithium salt content of 1% to 20% by mass.

[0026] In the above-mentioned lithium ion battery electrolyte, the organic solvent is composed of one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, vinylene carbonate, propylene sulfite, vinyl sulfate, propylene sultone, lithium difluorophosphate and triphenyl phosphite mixed in any proportion.

[0027] The above-mentioned lithium ion battery electrolyte has an additive content of 0.5% to 5% by mass.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The present invention proposes a 1,2,4,5-tetrafluoro-6-vinylbenzene derivative substance, a synthesis method thereof, and a lithium ion battery electrolyte containing the substance. 1,2,3,4,5-pentafluoro-6-vinylbenzene is used as a starting raw material for the reaction, and a target product is obtained by a nucleophilic substitution reaction with a fluorine-containing alkyl alcohol. The synthetic raw materials of the synthetic method are cheap and easy to obtain, the synthetic process is relatively simple, and the yield and purity are very high. When the 1,2,4,5-tetrafluoro-6-vinylbenzene derivative is used as an additive in the electrolyte, it helps to form a uniform and stable protective layer on the surface of the positive electrode, and the fluorine-containing protective layer can inhibit the deposition of manganese ions on the surface of the negative electrode during the cycle and the decomposition of the electrolyte during the high-temperature cycle, and can inhibit the increase of DC resistance, thereby improving the performance of the lithium ion battery in the high-temperature cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the NMR spectrum of 1,2,4,5-tetrafluoro-3-(2,2,2-trifluoroethoxy)-6-vinylbenzene (FSE) in Example 1 of the present invention.

[0031] Figure 2 It is the NMR spectrum of 1,2,4,5-tetrafluoro-3-(2,2,3,3,3-pentafluoropropoxy)-6-vinylbenzene (FSP) in Example 2 of the present invention.

[0032] Figure 3 It is the NMR spectrum of 1,2,4,5-tetrafluoro-3-(3,3,3-trifluoropropoxy)-6-vinylbenzene (FST) in Example 3 of the present invention.

[0033] Figure 4 It is the room temperature charge and discharge curve of the 1,2,4,5-tetrafluoro-3-(2,2,2-trifluoroethoxy)-6-vinylbenzene (FSE) battery in the comparative example and Examples 4-6 of the present invention.

[0034] Figure 5 It is the room temperature charge and discharge curve of the 1,2,4,5-tetrafluoro-3-(2,2,3,3,3-pentafluoropropoxy)-6-vinylbenzene (FSP) battery in the comparative example and Examples 7-9 of the present invention.

[0035] Figure 6 It is the room temperature charge and discharge curve of the 1,2,4,5-tetrafluoro-3-(3,3,3-trifluoropropoxy)-6-vinylbenzene (FST) battery in the comparative example and Examples 10-12 of the present invention.

[0036] Figure 7 It is a 45 degree cycle diagram of the 1,2,4,5-tetrafluoro-3-(2,2,2-trifluoroethoxy)-6-vinylbenzene (FSE) battery in the comparative example and Examples 4-6 of the present invention.

[0037] Figure 8 It is a 45 degree cycle diagram of the 1,2,4,5-tetrafluoro-3-(2,2,3,3,3-pentafluoropropoxy)-6-vinylbenzene (FSP) battery in the comparative example and Examples 7-9 of the present invention.

[0038] Fig. 9 It is a 45 degree cycle diagram of the 1,2,4,5-tetrafluoro-3-(3,3,3-trifluoropropoxy)-6-vinylbenzene (FST) battery in the comparative example and Examples 10-12 of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with the embodiments, but it does not constitute any limitation to the present invention. Any limited number of modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0040] In order to explain the technical content of the present invention in detail, further description is given below in conjunction with the implementation modes.

[0041] The 1,2,4,5-tetrafluoro-6-vinylbenzene derivative of the present invention has the following structural formula:

[0042]

[0043] Wherein, R1 is H or F, and R2 and R3 are C1-C6 alkyl groups containing hydrogen or multiple halogen atoms (F, Cl, Br, I);

[0044] Example 1

[0045] The synthesis method of 1,2,4,5-tetrafluoro-3-(2,2,2-trifluoroethoxy)-6-vinylbenzene comprises the following steps:

[0046] Step 1: Weigh 9.72 g of trifluoroethanol and add it to 150 ml of tetrahydrofuran. Cool the mixture to below -10°C in an ice-salt bath. Add 3.50 g of sodium hydride in batches under nitrogen protection. Keep warm and stir the mixture for 30 minutes. Use the mixture directly in the next step without further treatment.

[0047] Step 2: Add 17.02 g of pentafluorostyrene to the above reaction solution. After the addition is completed, heat it to reflux and continue the reaction for 3 to 4 hours. After the reaction is completed, quench it with a saturated ammonium chloride solution, extract it three times with dichloromethane, dry the organic phase with anhydrous magnesium sulfate, and concentrate it under reduced pressure to obtain a crude product. After purification, the crude product is 22 g of 1,2,4,5-tetrafluoro-3-(2,2,2-trifluoroethoxy)-6-vinylbenzene finished product, with a yield of 91.6%.

[0048] Example 2

[0049] The synthesis method of 1,2,4,5-tetrafluoro-3-(2,2,3,3,3-pentafluoropropoxy)-6-vinylbenzene comprises the following steps:

[0050] Step 1: Weigh 13.97 g of 2,2,3,3,3-pentafluoropropanol and add it to 150 ml of tetrahydrofuran. Cool it to below -10°C in an ice-salt bath. Add 2.92 g of sodium hydride in batches under nitrogen protection. Keep warm and stir the reaction for 30 minutes. Use it directly in the next step without treatment.

[0051] Step 2: Add 15.03 g of pentafluorostyrene to the above reaction solution. After the addition is completed, heat it to reflux and continue the reaction for 3 to 4 hours. After the reaction is completed, quench it with a saturated ammonium chloride solution, extract it three times with dichloromethane, dry the organic phase with anhydrous magnesium sulfate, and concentrate it under reduced pressure to obtain a crude product. After purification, the crude product can obtain 22.30 g of 1,2,4,5-tetrafluoro-3-(2,2,3,3,3-pentafluoropropoxy)-6-vinylbenzene with a yield of 89.0%.

[0052] Example 3

[0053] The synthesis method of 1,2,4,5-tetrafluoro-3-(3,3,3-trifluoropropoxy)-6-vinylbenzene comprises the following steps:

[0054] Step 1: Weigh 14.58 g of trifluoropropanol and add it to 150 ml of tetrahydrofuran. Cool it to below -10°C in an ice-salt bath. Add 3.15 g of sodium hydride in batches under nitrogen protection. Keep warm and stir the reaction for 30 minutes. Use it directly in the next step without treatment.

[0055] Step 2: Add 13.12 g of pentafluorostyrene to the above reaction solution. After the addition is completed, heat it to reflux and continue the reaction for 3 to 4 hours. After the reaction is completed, quench it with a saturated ammonium chloride solution, extract it three times with dichloromethane, dry the organic phase with anhydrous magnesium sulfate, and concentrate it under reduced pressure to obtain a crude product. After purification, the crude product can obtain 16.56 g of 1,2,4,5-tetrafluoro-3-(3,3,3-trifluoropropoxy)-6-vinylbenzene with a yield of 85.0%.

[0056] Electrolyte preparation part

[0057] Under closed environmental conditions with a water content of ≤10ppm, the electrolyte is composed of the following components by mass fraction based on the total weight of the electrolyte: an organic solvent (ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a mass ratio of 1:1:1) is evenly mixed, 12.50wt% of lithium hexafluorophosphate is added and stirred to dissolve, and then 0-5wt% of the additive of the present invention is added and stirred to obtain a lithium ion battery electrolyte.

[0058] The above method was used to obtain Examples 4-12, wherein the additive in the electrolyte of Example 4-6 was 1,2,4,5-tetrafluoro-3-(2,2,2-trifluoroethoxy)-6-vinylbenzene, code-named FSE; the additive in the electrolyte of Examples 7-9 was 1,2,4,5-tetrafluoro-3-(2,2,3,3,3-pentafluoropropoxy)-6-vinylbenzene, code-named FSP; the additive in the electrolyte of Examples 10-12 was 1,2,4,5-tetrafluoro-3-(3,3,3-trifluoropropoxy)-6-vinylbenzene, code-named FST, and the additive mass fraction of 0wt% (blank group) was used as a comparative example.

[0059] The composition ratios of the embodiments and comparative examples are shown in Table 1 below.

[0060]

[0061] Test Section

[0062] The prepared electrolyte was injected into the same batch of soft-pack batteries for testing. The soft-pack batteries used ternary 523 as the positive electrode material, and the positive electrode plate formula was NCM523:SP:PVDF=96:2:2. Artificial graphite S360 was used as the negative electrode, and the negative electrode plate formula was S360:SP:CMC2200:LA136D=95.5:1:0.5:2. 20-micron thick PP was used as the separator. The cells were assembled and the electrochemical performance was tested after the injection was completed.

[0063] Figure 4-6The 1C charge and discharge test of the batteries of the comparative example and embodiments 4-12 at room temperature of 25 degrees is shown. It can be seen that there is not much difference in the charge and discharge capacity of the batteries of the comparative example and the embodiment, indicating that the application of the three additives in the battery will not have a side effect on the battery charge and discharge process, and adding a small amount of additives will have a certain promoting effect on the battery capacity. From Table 2, it can be seen that the maximum capacity of the battery can be exerted when the content of FSE, FSP and FST additives is 0.5%.

[0064] Figure 7-9 This is a 1C cycle test experiment of the batteries of the comparative example and Examples 4-12 at a high temperature of 45 degrees. It can be seen that the specific capacity of the battery containing the blank electrolyte after 100 cycles of high-temperature cycling is 134mAh / g, accounting for 80% of the initial capacity, and the capacity decay is 20%; the maximum specific capacity of the battery containing the FSE additive after 100 cycles of high-temperature cycling is 157mAh / g, accounting for 93% of the initial capacity, and the capacity decay is 7%. At this time, the FSE addition amount is 0.5%; the maximum specific capacity of the battery containing the FSP additive after 100 cycles of high-temperature cycling is 156mAh / g, accounting for 92.5% of the initial capacity, and the capacity decay is 7.5%. At this time, the FSP addition amount is 1.0%; the maximum specific capacity of the battery containing the FST additive after 100 cycles of high-temperature cycling is 160mAh / g, accounting for 94% of the initial capacity, and the capacity decay is 6%. At this time, the FST addition amount is 0.5%; the capacity decay of the battery containing the additive after high-temperature cycling is more than 10% less than that of the blank additive, so FSE, FSP and FST can be applied to the battery as additives to improve the high-temperature cycle performance.

[0065] Table 2. Comparative Example and Example Battery Discharge Capacity Data at Room Temperature

[0066]

[0067] Table 3. Internal resistance data before and after high temperature cycles for comparative examples and various embodiments

[0068]

[0069] Table 3 is the battery internal resistance data of the comparative examples and the batteries of each embodiment before and after high-temperature cycling. It can be seen that the internal resistance of the battery containing blank electrolyte increases from 29.1mΩ to 153.7mΩ before and after cycling, and the increase in internal resistance is 124.6mΩ; the minimum increase in internal resistance of the battery containing TSE additive before and after cycling is 106.8mΩ, and the amount of TSE added is 0.5% at this time; the minimum increase in internal resistance of the battery containing TSP additive before and after cycling is 105mΩ, and the amount of TSP added is 1% at this time; the minimum increase in internal resistance of the battery containing TST additive before and after cycling is 100.3mΩ, and the amount of TST added is 0.5% at this time; when FSE, FSP and FST are added to the battery as additives, the DC internal resistance of the battery can be reduced and the electrochemical performance of the battery can be improved.

[0070] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: It comprises a lithium salt, an organic solvent and an additive, wherein the additive is one or more 1,2,4,5-tetrafluoro-6-vinylbenzene derivatives of FSE, FSP and FST structures; The mass percentage of the additive in the lithium ion battery electrolyte is 0.5% to 5%.

2. The lithium ion battery electrolyte according to claim 1, characterized in that: The lithium salt is composed of one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, tris(trifluoromethylsulfonyl)methyllithium, bis(trifluoromethylsulfonyl)methyllithium, lithium trifluoromethylsulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, LiAsF6, and LiClO4 mixed in any proportion.

3. The lithium ion battery electrolyte according to claim 1, characterized in that The mass percentage of lithium salt in the lithium ion battery electrolyte is 1% to 20%.

4. The lithium ion battery electrolyte according to claim 1, characterized in that: The organic solvent is composed of one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, vinylene carbonate, propylene sulfite, vinyl sulfate, propylene sultone, lithium difluorophosphate and triphenyl phosphite mixed in any proportion.

5. The lithium ion battery electrolyte according to claim 1, characterized in that: The synthesis method of the 1,2,4,5-tetrafluoro-6-vinylbenzene derivative comprises the following steps: 1) Under nitrogen protection, take the raw alcohol and base to carry out acid-base reaction to obtain the intermediate alcohol salt, the reaction is as follows: Wherein, the base is sodium hydride, M + is the cation corresponding to the base; 2) Under nitrogen protection, the intermediate alkoxide obtained in step 1) is directly subjected to a nucleophilic reaction with 1,2,3,4,5-pentafluoro-6-vinylbenzene to obtain the target compound 1,2,4,5-tetrafluoro-6-vinylbenzene derivative, and the reaction is as follows: R1, R2, and R3 in steps 1) and 2) have the same meaning, the target compound 1,2,4,5-tetrafluoro-6-vinylbenzene derivative has a FSE, FSP or FST structure, and R1, R2, and R3 in the target compound 1,2,4,5-tetrafluoro-6-vinylbenzene derivative correspond to the groups of the FSE, FSP or FST structure.

6. The lithium ion battery electrolyte according to claim 5, characterized in that: In step 1), the reaction solvent of the acid-base reaction is one or more of tetrahydrofuran, acetonitrile, N,N-dimethylformamide, dioxane, ethylene glycol dimethyl ether, and acetone; The molar ratio of the alcohol to the base is 1:1-3; The reaction temperature of the acid-base reaction is -20°C to 0°C, and the reaction time is 0.5 to 2 hours.

7. The lithium ion battery electrolyte according to claim 5, characterized in that: In step 2), the solvent for the nucleophilic reaction is one or more of tetrahydrofuran, acetonitrile, N,N-dimethylformamide, dioxane, ethylene glycol dimethyl ether, and acetone; The molar ratio of the 1,2,3,4,5-pentafluoro-6-vinylbenzene to the alcohol in step 1) is 1:1-2; The nucleophilic reaction is a reflux reaction, and the time is 1 to 5 hours.

8. The lithium ion battery electrolyte according to claim 5, characterized in that: In step 2), after the nucleophilic reaction, post-treatment is required, and the post-treatment includes: quenching with saturated ammonium chloride, extracting with an organic solvent, washing with water, drying with anhydrous magnesium sulfate, and purifying to obtain the target compound 1,2,4,5-tetrafluoro-6-vinylbenzene derivative.

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