Synthesis method and application of 2,3-dicyanohydroquinone derivatives

Abstract

The invention discloses a synthesis method and application of a 2,3-dicyanohydroquinone derivative. The compound uses 2,3-dicyanohydroquinone as the starting material for the reaction, and is subjected to a nucleophilic substitution reaction with a halogenated olefin or an alkyne to obtain the target product. The synthetic raw materials of the synthetic method are cheap and readily available, and the synthetic process is relatively simple. The 2,3-dicyanohydroquinone derivative has an olefin unsaturated alkoxy group and a cyano group on its structural benzene ring. When applied to a lithium-ion battery, a stable SEI film can be effectively formed during charge and discharge. In addition, the cyano group may form a relatively effective protective film on the positive electrode surface during the battery charge and discharge process, covering its active site, thereby reducing the reactivity of the positive electrode to the electrolyte, and reacting with HF acid at high temperature to reduce the damage of HF acid to the electrode surface and the current collector, thereby improving the high and low temperature performance and cycle performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery electrolytes, and in particular to a synthesis method and application of a 2,3-dicyanohydroquinone derivative. Background Art

[0002] Lithium-ion batteries, with their advantages of no memory effect, environmental friendliness, and high energy density, have been widely used in portable electronic devices such as laptops, mobile phones, and cameras, bringing great convenience to people's lives. However, there are still many areas where lithium-ion batteries need improvement, such as battery cycle stability and high- and low-temperature performance, which are important factors restricting the large-scale application of lithium-ion batteries in electric vehicles. The electrolyte is one of the key materials in lithium-ion batteries, directly determining the battery's cycle stability and high- and low-temperature performance. Currently, battery performance is usually improved by changing the composition of the electrolyte.

[0003] To solve the current problem, the present invention applies 2,3-dicyanohydroquinone derivatives as lithium-ion electrolyte additives to lithium-ion batteries. The benzene ring of this structure is connected to an olefin unsaturated alkoxy group and a cyano group, which can effectively form a stable SEI film during charging and discharging. During the charging and discharging process of the battery, the cyano group forms a relatively effective protective film on the surface of the positive electrode, covering its active sites, which can reduce the reactivity of the positive electrode to the electrolyte. It will react with HF acid at high temperature, reducing the damage of HF acid to the electrode surface and the current collector, thereby improving the high and low temperature performance and cycle performance of the battery. Summary of the Invention

[0004] In view of the above problems of the prior art, the present invention aims to provide a method for synthesizing a 2,3-dicyanohydroquinone derivative and its application as an additive in lithium-ion battery electrolyte.

[0005] The technical solutions adopted in the present invention are as follows:

[0006] A derivative with the following structural formula:

[0007]

[0008] Wherein, R1 and R2 are straight-chain or branched olefins or alkynes containing 2 to 6 carbon atoms;

[0009] Preferably, the structural formula of the derivative comprises any one of the following structures:

[0010]

[0011] The above-mentioned 2,3-dicyanohydroquinone derivatives are synthesized as follows:

[0012] Under nitrogen protection, the raw material 2,3-dicyanohydroquinone is reacted with a haloolefin or alkyne to undergo a nucleophilic substitution reaction to obtain a 2,3-dicyanohydroquinone derivative. The reaction is as follows:

[0013]

[0014] Wherein X is a halogen atom;

[0015] Furthermore, the molar ratio of 2,3-dicyanohydroquinone to R1X in the synthesis reaction is 1:1 to 1.2.

[0016] Furthermore, the molar ratio of 2,3-dicyanohydroquinone to R2X in the synthesis reaction is 1:1 to 1.2.

[0017] Furthermore, the reaction temperature in the synthesis reaction is -10°C to 100°C, preferably -5°C to 70°C.

[0018] Furthermore, the synthesis reaction time is 2 to 24 hours, preferably 8 to 16 hours.

[0019] Furthermore, the reaction solvent in the synthesis reaction is an aprotic polar solvent such as N,N-dimethylformamide, acetone, acetonitrile, dimethyl sulfoxide, etc.; the base used in the reaction is an inorganic base such as potassium carbonate, sodium carbonate, sodium bicarbonate, etc., or an organic base such as triethylamine, isopropylamine, diisopropylamine, pyridine, etc.

[0020] Furthermore, the crude product obtained after the reaction is purified by crystallization to obtain the target product 2,3-dicyanohydroquinone derivative.

[0021] A lithium-ion battery electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the additive contains the above-mentioned 2,3-dicyanohydroquinone derivative and fluoroethylene carbonate; the mass percentage of the 2,3-dicyanohydroquinone derivative is 0-1.5wt%, and the mass percentage of the fluoroethylene carbonate is 0-4.0wt%.

[0022] The above-mentioned lithium-ion battery electrolyte, the lithium salt is one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, tris(trifluoromethylsulfonyl)methyllithium, bis(trifluoromethylsulfonyl)methyllithium, lithium trifluoromethylsulfonate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide), LiAsF6, and LiClO4 mixed in any proportion. Preferably, the lithium salt is lithium hexafluorophosphate; the mass percentage of the lithium salt is 12.50%.

[0023] In the above-mentioned lithium-ion battery electrolyte, the organic solvent is 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; preferably, the organic solvent combination is: ethylene carbonate + diethyl carbonate + ethyl methyl carbonate, and the mass percentage of the organic solvent is 82% to 87.5%.

[0024] The present invention provides a synthesis method and application of a 2,3-dicyanohydroquinone derivative. The synthetic raw materials of the synthesis method are inexpensive and readily available, and the synthesis process is relatively simple. The 2,3-dicyanohydroquinone derivative has an olefin unsaturated alkoxy group and a cyano group attached to the benzene ring of the structure. When applied to a lithium-ion battery, it can effectively form a stable SEI film during charging and discharging. During the battery charging and discharging process, the cyano group may form a relatively effective protective film on the positive electrode surface, covering its active sites, which can reduce the reactivity of the positive electrode to the electrolyte. At high temperatures, it reacts with HF acid to reduce HF acid damage to the electrode surface and current collector, thereby improving the high and low temperature performance and cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the H NMR spectrum of 3,6-bis(allyloxy)phthalonitrile in Example 1. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the embodiments, but this does not constitute any limitation to the present invention. Any limited modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0027] In order to explain the technical content of the present invention in detail, further description will be given below in conjunction with the embodiments.

[0028] The 2,3-dicyanohydroquinone derivatives in the embodiments of the present invention have the structure: Wherein R1 and R2 are straight chain or branched olefins or alkynes containing 2 to 6 carbon atoms, and the following specific structures are used as examples in the embodiments:

[0029]

[0030]

[0031] Example 1

[0032] The structural formula of 3,6-bis(allyloxy)phthalonitrile is as follows:

[0033]

[0034] The synthesis steps are as follows:

[0035] To a 250ml three-necked reaction flask, 150ml DMF, 20.0g (124.9mmol) 2,3-dicyanohydroquinone, 34.5g (249.6mmol) potassium carbonate were added, and the atmosphere was replaced with nitrogen three times. After the reaction solution was cooled to -5°C under a nitrogen atmosphere, 31.6g (261.2mmol) allyl bromide was added dropwise. After the addition was complete, the reaction was kept warm for 30 minutes, then heated to 100°C and reacted for 8h. After cooling to room temperature, the reaction solution was slowly poured into 300ml water, filtered, and the filter cake was washed three times with 50ml water and dried to obtain a crude product. The crude product was purified by recrystallization from ethyl acetate to obtain 26.0g (108.2mmol) of the target product with a yield of 86.6%.

[0036] Examples 2-6

[0037] The reaction steps are the same as those in Example 1, except for the specific products and reaction conditions as shown in Table 1.

[0038] Table 1. Product structures, reaction conditions, and yields corresponding to Examples 2-6

[0039]

[0040]

[0041]

[0042] Example 7

[0043] The synthetic product of this embodiment is 3,6-bis((4,4-difluorobut-3-en-1-yl)oxy)phthalonitrile, and its structure is as follows:

[0044]

[0045] The synthesis steps are as follows:

[0046] To a 250ml three-necked reaction flask, 150ml DMF, 20.0g (124.9mmol) 2,3-dicyanohydroquinone, 34.5g (249.6mmol) potassium carbonate were added, and the atmosphere was replaced with nitrogen three times. After the reaction solution was cooled to -10°C under a nitrogen atmosphere, 44.7g (261.6mmol) 4-bromo-1,1-difluorobutene was added dropwise. After the addition was complete, the reaction was kept warm for 30 minutes, then the temperature was raised to 70°C and the reaction was carried out for 24h. After cooling to room temperature, the reaction solution was slowly poured into 300ml water, filtered, and the filter cake was washed three times with 50ml water. After drying, the crude product was obtained. The crude product was purified by crystallization from ethyl acetate to obtain 33.2g (97.6mmol) of the target product with a yield of 78.1%.

[0047] Example 8

[0048] The synthetic product of this embodiment is 3-(allyloxy)-6-(but-3-ene-1-oxy)phthalonitrile, and its structure is as follows:

[0049]

[0050] The synthesis steps are as follows:

[0051] To a 250ml three-necked reaction flask, 150ml DMF, 20.0g (124.9mmol) 2,3-dicyanohydroquinone, 34.5g (249.6mmol) potassium carbonate were added, and the atmosphere was replaced with nitrogen three times. After the reaction solution was cooled to -5°C under a nitrogen atmosphere, 15.1g (124.9mmol) allyl bromide was added dropwise. After the addition was complete, the reaction was kept warm for 2h, and 18.5g (137.4mmol) 4-bromo-1-butene was continued to be added dropwise. The reaction was kept warm for 30 minutes, and then the temperature was slowly raised to 70°C for 16h. After cooling to room temperature, the reaction solution was slowly poured into 300ml water, filtered, and the filter cake was washed three times with 50ml water. After drying, the crude product was obtained. The crude product was purified by crystallization from ethyl acetate to obtain 21.6g (84.9mmol) of the target product with a yield of 68.0%.

[0052] Examples 9-14

[0053] The reaction steps are the same as those in Example 8, except for the differences in the specific synthetic products and reaction conditions as shown in Table 2:

[0054] Table 2. Product structures, reaction conditions, and yields corresponding to Examples 9-14

[0055]

[0056]

[0057]

[0058] The 2,3-dicyanohydroquinone derivatives prepared in each example were subjected to H NMR spectrum test. Figure 1 This is the hydrogen nuclear magnetic spectrum of 3,6-bis(allyloxy)phthalonitrile prepared in Example 1. 1HNMR: δ 4.62 (4H, d, J = 7.5 Hz), 5.30-5.50 (4H, 5.32 (dd, J = 16.5, 1.3 Hz), 5.48 (dd, J = 10.7, 1.3 Hz)), 6.00 (2H, ddt, J = 16.5, 10.7, 7.5 Hz), 7.25 (2H, d, J = 8.5 Hz).

[0059] Application Example 1-17

[0060] The 2,3-dicyanohydroquinone derivatives prepared in the above examples were used as an electrolyte additive to prepare the electrolyte. The electrolyte preparation process is as follows:

[0061] Under closed environmental conditions with a moisture content of ≤10 ppm, the electrolyte is composed of the following components by mass fraction based on the total weight of the electrolyte: 82-87.5 wt% of an organic solvent (ethylene carbonate / ethyl methyl carbonate / diethyl carbonate in a mass ratio of approximately 1:1:1) is mixed evenly, 12.50 wt% of lithium hexafluorophosphate is added and stirred to dissolve, and finally, 0-1.50 wt% of one of the 2,3-dicyanohydroquinone derivatives prepared in Examples 1-14 and 0-4 wt% of fluoroethylene carbonate are added as electrolyte additives and stirred evenly to obtain different lithium ion battery electrolytes.

[0062] Application Comparative Example 1-2

[0063] The electrolyte prepared in the comparative example was not added with the 2,3-dicyanohydroquinone derivative of the present invention.

[0064] The components and contents of the electrolytes configured for each application example are shown in Table 3 below:

[0065] Table 3. Electrolyte components and contents corresponding to Examples 15-31 and Comparative Examples 1-2

[0066]

[0067]

[0068] Battery cell preparation

[0069] The battery cell adopts a lithium cobalt oxide graphite system, with the positive electrode formula: lithium cobalt oxide LC109RH:SP:PVDF=96.5:2:1.5; the negative electrode formula: artificial graphite S360:SP:CMC2200:LA136D=96.5:1:0.5:2; the separator adopts a 20μm thick PE separator, the negative electrode current collector adopts a 10μm copper foil, and the positive electrode current collector adopts a 14μm aluminum foil. The designed battery nominal capacity is 1050mAh, and the positive and negative electrode N / P ratio is controlled at 1.08.

[0070] Test section

[0071] The electrolytes prepared in Comparative Examples 1-2 and Application Examples 1-17 were injected into the batteries prepared above, corresponding to battery numbers 1#-19#, respectively. The battery cycle performance, high and low temperature discharge performance, and high temperature storage performance were tested. The test results are shown in Table 4.

[0072] The high temperature storage test steps are as follows: at 25 ° C, charge with a current of 0.33C, constant current and constant voltage until the limit voltage reaches 4.4V, and end the charging when the cut-off current drops to 0.02C. Then discharge with a current of 0.33C and constant current until the cut-off voltage reaches 3.0V and end the discharge. This is the initial capacity; charge with a current of 0.33C, constant current and constant voltage until the limit voltage reaches 4.4V, and end the charging when the cut-off current drops to 0.02C. After the end, measure and record the voltage and internal resistance of the battery cell; place the sample in an open circuit at 60±2 ° C for 7 days; take out the sample and place it at room temperature for 5 hours to observe the appearance of the sample. Observe, measure and record the voltage and internal resistance of the sample; at 25℃, discharge at a constant current of 0.33C to a cut-off voltage of 3.0V, and record the discharge capacity; charge at a constant current and constant voltage of 0.33C until the limit voltage reaches 4.4V, and end the charging when the cut-off current drops to 0.02C; discharge at a constant current of 0.33C to a cut-off voltage of 3.0V, and end the discharge. The test ends after 3 cycles, and the highest discharge capacity is recorded. The internal resistance change rate before and after high-temperature storage, the capacity retention rate after high-temperature storage, and the capacity retention rate after capacity recovery are calculated by the following formulas.

[0073] Internal resistance change rate = ((internal resistance value after high-temperature storage at full charge - internal resistance value before high-temperature storage at full charge) / internal resistance value before high-temperature storage at full charge) * 100%

[0074] Capacity retention after high temperature storage = (discharge capacity after high temperature storage / initial capacity) * 100%

[0075] Capacity retention rate after capacity recovery = (maximum capacity within 3 weeks after high-temperature storage and discharge / initial capacity) * 100%

[0076] High and low temperature discharge test steps: At 25°C, charge at a current of 0.33C, constant current and constant voltage until the limit voltage reaches 4.4V, and end the charging when the cut-off current drops to 0.02C; discharge at a current of 0.33C, constant current at 25°C until the cut-off voltage reaches 3.0V, and end the discharge. This is the initial capacity; after charging at 25°C, discharge at -20°C and 55°C to 3.0V according to the above steps, and record the discharge capacity. Calculate the capacity retention rate at -20°C and 55°C using the following formula:

[0077] -20℃ discharge capacity retention rate = (-20℃ discharge capacity / initial capacity)*100%

[0078] 55℃ discharge capacity retention rate = (55℃ discharge capacity / initial capacity)*100%

[0079] Cycle test steps: Place the battery cell in the Xinwei test cabinet and charge at 1C current, constant current and constant voltage at 25℃ until the limit voltage reaches 4.4V. Charging ends when the cut-off current drops to 0.02C; discharge at 1C current, constant current until the cut-off voltage reaches 3.0V, and the discharge ends. This is the initial capacity; follow the above steps to charge and discharge at 25℃ for 400 cycles. After the end, record the discharge capacity of each week and calculate the capacity retention rate using the following formula:

[0080] Capacity retention rate = (discharge capacity per week / initial capacity) * 100%

[0081] Table 4. Test data of batteries 1-19# under different conditions (wherein the electrolytes used in batteries 1#-19# correspond to the electrolytes configured in comparative examples 1-2 and application examples 1-17, respectively)

[0082]

[0083]

[0084] As can be seen from the above table, when the 3,6-bis(allyloxy)phthalonitrile prepared in Example 1 is used as a lithium ion electrolyte additive in a battery, the overall performance of the battery is the best when the additives are 4.0 wt % fluoroethylene carbonate and 0.5 wt % 3,6-bis(allyloxy)phthalonitrile, respectively.

[0085] On the basis of the above, by further optimizing the mass content of solvents, additives and lithium salts that make up the electrolyte, the newly synthesized additives are applied to lithium cobalt oxide batteries using the above electrolyte ratio. It is found that the addition of 2,3-dicyanohydroquinone derivatives can greatly improve the high and low temperature performance and cycle performance of lithium-ion batteries.

[0086] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications derived therefrom remain within the scope of protection of the present invention.

Claims

1. A 2,3-dicyanohydroquinone derivative, characterized in that: The structural formula is represented by the following general formula: Among them, R 1， R2 is a straight chain, branched chain alkene or alkyne of 2 to 6 carbon atoms; the structural formula is any one of the following structures: 、 、 、 、 、 、 、 、 、 、 、 ,or .

2. A method for synthesizing a 2,3-dicyanohydroquinone derivative according to claim 1, characterized in that: The following steps are involved: Under nitrogen protection, 2,3-dicyanohydroquinone reacts with halogenated olefins or alkynes to undergo nucleophilic substitution reaction to obtain 2,3-dicyanohydroquinone derivatives. The reaction is as follows: Wherein X is a halogen atom.

3. The method for synthesizing the 2,3-dicyanohydroquinone derivative according to claim 2, characterized in that: The molar ratio of 2,3-dicyanohydroquinone to R1X in the synthesis reaction is 1:1 to 1.2; The molar ratio of 2,3-dicyanohydroquinone to R2X in the synthesis reaction is 1:1-1.

2.

4. The method for synthesizing 2,3-dicyanohydroquinone derivatives according to claim 2, characterized in that: The reaction temperature in the synthesis reaction is -10°C~100°C.

5. The method for synthesizing 2,3-dicyanohydroquinone derivatives according to claim 2, characterized in that: The synthesis reaction time is 2~24h.

6. The method for synthesizing 2,3-dicyanohydroquinone derivatives according to claim 2, characterized in that: The reaction solvent in the synthesis reaction is N,N-dimethylformamide, acetone, acetonitrile, or dimethyl sulfoxide among aprotic polar solvents; the base used in the reaction is potassium carbonate, sodium carbonate, or sodium bicarbonate among inorganic bases, or triethylamine, isopropylamine, diisopropylamine, or pyridine among organic bases.

7. The method for synthesizing a 2,3-dicyanohydroquinone derivative according to claim 2, characterized in that: The crude product obtained after the synthesis reaction is crystallized and purified to obtain the target product, namely the 2,3-dicyanohydroquinone derivative.

8. A lithium ion battery electrolyte, characterized in that: The invention comprises a lithium salt, an organic solvent and an additive, wherein the additive composition comprises the 2,3-dicyanohydroquinone derivative and fluoroethylene carbonate according to claim 1; the mass percentage of the 2,3-dicyanohydroquinone derivative is 0-1.5wt%, and the mass percentage of the fluoroethylene carbonate is 0-4.0wt%.

9. The lithium-ion battery electrolyte according to claim 8, characterized in that The mass percentage of the lithium salt is 12.50%, and the mass percentage of the organic solvent is 82% to 87.5%.

Images