Difluoro (oxalato) borate spiro quaternary ammonium salt electrolyte, preparation method thereof and electrolyte solution

Abstract

The invention provides a difluoro (oxalato) borate spiro quaternary ammonium salt electrolyte, a preparation method thereof and an electrolyte solution. The structural formula of the difluoro (oxalato) borate spiro quaternary ammonium salt electrolyte is as follows: # imgabs 0 # imgabs 1 #, wherein n is 1 or 2. The preparation process comprises the following steps: adding pyrrolidine, alkali and a reaction solvent into a reaction container, dropwise adding 1, 4-dibromobutane into the reaction container, and heating to react; generating an intermediate product spiro quaternary ammonium bromide, and reacting the generated spiro quaternary ammonium bromide with a normal-temperature aqueous solution of lithium difluoro (oxalato) borate to generate the spiro quaternary ammonium salt of the difluoro (oxalato) borate. The electrolyte for the capacitor can be prepared by dissolving the difluoro oxalato borate spiro quaternary ammonium salt in an acetonitrile solvent. The preparation method has the advantages that the corresponding electrolyte has excellent electrochemical stability and a wide voltage window under high voltage. Under the working voltage of 3.2 V, after 10000 times of cycle tests, the capacity retention rate reaches 94.12%, and the coulombic efficiency is close to 100%; wide application prospects and industrialization values are realized.

Description

Technical Field

[0001] The invention belongs to the field of supercapacitors, and in particular relates to a difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte and a preparation method and an electrolyte. Background Art

[0002] Supercapacitors are a new type of energy storage device between traditional capacitors and rechargeable batteries. They have the characteristics of fast charging and discharging of capacitors, and have higher energy density than traditional capacitors. Due to their advantages such as high power density, fast charging and discharging, and long cycle life, they have shown broad application prospects in electric vehicles, renewable energy systems, and portable electronic devices.

[0003] At present, the double-layer supercapacitors widely used in business usually use tetraethylammonium tetrafluoroborate (TEA-BF4) or triethylmethylammonium tetrafluoroborate (TEMA-BF4) as electrolyte salts. The working voltage of these electrolytes can usually only reach 2.7V-2.8V and their solubility is low.

[0004] There are also anionic electrolyte salts containing fluorinated sulfonyl imide (FSI-) and bistrifluorosulfonyl imide (TFSI-). These electrolytes can improve the voltage resistance to a certain extent, but when continuously charged and discharged under high-voltage conditions, these anions are prone to corrosion of the aluminum foil current collector, affecting the long-term stability of the capacitor. In addition, the preparation process of such electrolyte salts is usually complex and costly, which limits the feasibility of their large-scale application.

[0005] To this end, providing an electrolyte salt with a more environmentally friendly and efficient preparation process, high purity, excellent ionic stability and a wide voltage window is of great significance to improving the overall performance of supercapacitors. Summary of the invention

[0006] In view of the problems of narrow working voltage window and complex preparation of electrolytes for supercapacitors in the prior art, the present invention provides a difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte and a preparation method and an electrolyte. The quaternary ammonium salt has a simple synthesis process and good electrochemical stability.

[0007] The technical solution of the present invention is as follows: a difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte, the structural formula of which is as follows: The cation is a bicyclic heterocyclic compound containing a five-membered ring with a nitrogen atom as the only ring heteroatom, wherein n is 1 or 2.

[0008] The present invention also provides a method for preparing the above-mentioned difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte, comprising the following steps: S1, adding pyrrolidine, a base, and a reaction solvent into a reaction container, adding 1,4-dibromobutane dropwise thereto, and heating to react; generating an intermediate product, a spirocyclic quaternary ammonium bromide, and purifying the reaction solution to obtain a pure product of a spirocyclic quaternary ammonium bromide salt; S2. The pure spirocyclic quaternary ammonium bromide salt produced in step S1 is reacted with lithium difluorooxalate borate, with water as solvent, to produce difluorooxalate borate spirocyclic quaternary ammonium salt.

[0009] Furthermore, in step S1, the reaction solvent is any one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, acetonitrile, tetrahydrofuran, and dichloromethane; the base is sodium hydroxide or potassium hydroxide; the reaction temperature is room temperature to 80° C., and the reaction time is 8-10 hours.

[0010] Furthermore, in step S2, the reaction temperature is room temperature, the reaction is an instantaneous reaction, and the purity of lithium difluorooxalatoborate is greater than 99%.

[0011] Further, the molar ratio of pyrrolidine, 1,4-dibromobutane, base and lithium difluoro(oxalato)borate is 1.0:(0.95-1.0):(1.2-1.5):(1.05-1.2).

[0012] Furthermore, the method further comprises the step of refining the difluorooxalate borate spirocyclic quaternary ammonium salt: S31, recrystallizing the crude product obtained in step S2 with acetonitrile and isopropanol to improve the purity of the product; S32, mixing the product after recrystallization in step S31 with activated carbon, performing decolorization treatment, and then performing reduced pressure distillation to obtain a refined solid; S33, vacuum drying the solid obtained in step S32 to finally obtain a high-purity difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte.

[0013] Preferably, in step S31, the recrystallization solvent is acetonitrile, the heating temperature of the crystallization process is 80° C., and low-valent isopropanol is added after the crude product is dissolved in acetonitrile to crystallize the product; this step is repeated 1-3 times to ensure the purity of the product.

[0014] Preferably, the activated carbon in step S32 is 100-300 mesh; the added amount is 0.5% of the total mass of the solution; the decolorization treatment temperature is room temperature, and the time is 6-10 hours.

[0015] Preferably, the vacuum drying temperature in step S33 is 50-60° C. and the time is 12-24 hours.

[0016] The present invention also provides an electrolyte prepared from the difluorooxalate borate spirocyclic quaternary ammonium salt, which is prepared by dissolving the difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte in an acetonitrile solvent, and the electrolyte concentration is 1 mol / L.

[0017] The advantages of the present invention are: a new type of ionic liquid electrolyte salt, spiro-(11')-difluoro(oxalate)borate (SBP-DFOB), has been developed. This electrolyte is used in combination with acetonitrile (CN) to form an electrolyte with excellent electrochemical stability and a wide voltage window at high voltage. Compared with traditional electrolytes, the SBP-DFOB / CN system exhibits excellent solvation structure and ionic stability. At an operating voltage of 3.2V, the supercapacitor based on this electrolyte has a capacity retention rate of 94.12% and a coulombic efficiency of nearly 100% after 10,000 cycle tests; it has broad application prospects and industrial value.

[0018] The preparation method of SBP-DFOB is a two-step synthesis with a short route, mild reaction conditions and high product purity. The raw materials used are less toxic and less corrosive to equipment, meeting the requirements of green chemistry. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 H NMR spectrum of spiro-(11')-difluoro(oxalato)borate (SBP-DFOB) electrolyte 1 H NMR spectra; Figure 2 The F-NMR spectrum of spiro-(11')-difluoro(oxalato)borate (SBP-DFOB) electrolyte; Figure 3 The constant current charge and discharge curves of supercapacitors containing SBP-DFOB / AN electrolyte at different voltages at room temperature; Figure 4 The constant current charge and discharge curves of supercapacitors containing SBP-BF4 / AN electrolyte at different voltages at room temperature; Figure 5 This is a comparison chart of the long cycle performance of supercapacitors with two electrolytes, SBP-DFOB / AN and SBP-BF4 / AN, at room temperature, 3.2V working voltage and 5 A / g current density; Wherein, SDF is the abbreviation of SBP-DFOB / AN, which means that spiro-(11')-difluoro(oxalato)borate is dissolved in acetonitrile to prepare an electrolyte with a concentration of 1 mol / L; SBF is the abbreviation of SBP-BF4 / AN, which means that spiroquaternary ammonium tetrafluoroborate is dissolved in acetonitrile to prepare an electrolyte with a concentration of 1 mol / L. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0021] The difluorooxalatoborate spirocyclic quaternary ammonium salt electrolyte provided by the present invention belongs to spiro-(11')-difluoro(oxalato)borate (hereinafter referred to as SBP-DFOB), and the specific structure is as follows: Its cation is a bicyclic heterocyclic compound containing a five-membered ring with a nitrogen atom as the only ring heteroatom. - [B(C2O2)F2] - , [B(C2O4)2] - , [B(C2O2)(CF3)F] - , [B(C2O2)(CH3)F] - Any one of.

[0022] The preparation method of SBP-DFOB is as follows: S1. Pyrrolidine, a base and a reaction solvent are added to a reaction container, 1,4-dibromobutane is added dropwise thereto, and the reaction is heated to react; an intermediate product, spirocyclic quaternary ammonium bromide (SBP-Br), is generated, and the reaction solution is purified to obtain a pure product of spirocyclic quaternary ammonium bromide (SBP-Br) salt; S2. The SBP-Br generated in step S1 is reacted with lithium difluoro(oxalate)borate (LiDFOB) in water as solvent to generate spiro-(11')-difluoro(oxalate)borate (SBP-DFOB) electrolyte.

[0023] In step S1, the reaction solvent is any one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, acetonitrile, tetrahydrofuran, and dichloromethane; the base is sodium hydroxide or potassium hydroxide; the reaction temperature is room temperature to 80° C., and the reaction time is 8-10 hours.

[0024] In step S2, the reaction temperature is room temperature, the reaction is instantaneous, and the lithium difluoro(oxalate)borate is LiDFOB with a purity greater than 99%. The preparation method is a two-step synthesis with a short route, mild reaction conditions, high product purity, and a total yield of SBP-DFOB of more than 90%.

[0025] The molar ratio of pyrrolidine, 1,4-dibromobutane, base and lithium difluoro(oxalato)borate is 1.0:(0.95-1.0):(1.2-1.5):(1.05-1.2).

[0026] For the spiro-(11')-difluoro(oxalate)borate (SBP-DFOB) electrolyte generated in step S2, the present invention also provides a purification step thereof: S31, recrystallizing the crude product obtained in step S2 with acetonitrile and isopropanol to improve the purity of the product; S32, mixing the product after recrystallization in step S31 with activated carbon, performing decolorization treatment, and then performing reduced pressure distillation to obtain a refined solid; S33, vacuum drying the solid obtained in step S32 to finally obtain a high-purity SBP-DFOB electrolyte.

[0027] Preferably, the recrystallization solvent in step S31 is acetonitrile, and the heating temperature during the crystallization process is 80° C. After the crude product is dissolved in acetonitrile, low-valent isopropanol is added to crystallize the product; this step is repeated 1-3 times to ensure the purity of the product.

[0028] In step S32, the activated carbon is 100-300 mesh; the added amount is 0.5% of the total mass of the solution; the decolorization treatment temperature is room temperature, and the time is 6-10 hours.

[0029] In step S33, the vacuum drying temperature is 50-60° C. and the time is 12-24 hours.

[0030] The obtained SBP-DFOB was tested by nuclear magnetic resonance hydrogen spectrum and fluorine spectrum, such as Figure 1 , 2 As shown, Figure 1 middle 1 H NMR (DMSO-d6) δ: 3.30~3.35 (m, 8H), 1.90~1.95 (m, 8H), the area ratio of the two hydrogens is 1:1, which is consistent with the number of H environments of the spirocyclic quaternary ammonium SBP and corresponds to the SBP-DFOB cationic target product. Figure 2 Spiro-(11')-difluoro(oxalato)borate anion NMR fluorine spectrum, Figure 2 The results showed that there was only one environment of F, 19F-NMR (CDCl3) δ: -134.50, which confirmed the successful synthesis of SBP-DFOB.

[0031] To further illustrate the SBP-DFOB test effect of the present invention, the following examples are provided for specific description.

[0032] Example 1 Preparation and purification of SBP-DFOB: S1. Add 10.0 g (0.12 mol) of pyrrolidine, 9.6 g (0.24 mol) of sodium hydroxide and an appropriate amount of acetonitrile to a dry reaction bottle, use an ice-water bath to maintain the temperature at 0-5°C, under this condition, add 33.5 g (0.12 mol) of 1,4-dibromobutane dropwise therein, and after the addition is completed, slowly heat to 80-82°C, stir and react for 8 hours; after the reaction is completed, recrystallize the generated spirocyclic quaternary ammonium bromide (SBP-Br) with DMF to obtain a crude product; S2, mixing the SBP-Br obtained in step S1 with 29.2 g (0.12 mol) of LiDFOB in an appropriate amount of aqueous solution to generate spiro-(11')-difluoro(oxalato)borate (SBP-DFOB) electrolyte, and filtering to obtain a solid crude product; S3, the solid crude product obtained in step S2 is recrystallized, the solid crude product is dissolved in acetonitrile at 80° C., and then an equal volume of isopropanol is added to promote crystallization of the product. This process is repeated 2-3 times to improve the purity.

[0033] After decolorization with activated carbon, the product was dissolved in acetonitrile, activated carbon (0.5% of the total mass of the solution) was added, and stirred at room temperature for 2-6 hours. After that, the activated carbon was removed by filtration, and the acetonitrile was removed by vacuum distillation. The decolorized product was vacuum dried in a drying oven for 12 hours, and the drying temperature was controlled at 50-60°C. Spiro-(11')-difluoro(oxalic acid)borate (SBP-DFOB) with a purity of up to 99.9% was obtained, and the final product yield was about 90%.

[0034] Application of supercapacitors with SBP-DFOB electrolyte at room temperature and high pressure The synthesized SBP-DFOB was dissolved in acetonitrile solvent to prepare an electrolyte solution (SBP-DFOB / AN) with a concentration of 1 mol / L. Molecular sieves were added to the electrolyte solution for dehydration and the solution was allowed to stand for 7 days to ensure that the water content was ≤10 ppm.

[0035] Assembling symmetrical supercapacitors: Weigh the corresponding mass of activated carbon powder (YP-50F), conductive carbon black (Super P), and binder (PTFE) in a mass ratio of 82:10:8, add an appropriate amount of alcohol, mix thoroughly, ensure that the materials are evenly dispersed, and mix to a plasticine-like state. Then roll the mixed slurry onto a rolled aluminum foil and dry it. The rolled aluminum foil is cut into pole pieces with a diameter of 18 mm, vacuum dried at 120°C for 12 hours, and weigh the pole pieces after cooling. The average mass of the pole pieces is about 4-5 mg.

[0036] In the glove box, two electrodes of approximately equal mass are grouped together, and the electrode, diaphragm, electrode, flat gasket, and spring sheet are added to the negative electrode shell with a rubber ring in sequence. After the assembled electrode structure is laid flat, the prepared SBP-DFOB / AN electrolyte is added. Finally, the positive electrode shell is covered and packaged with a sealing machine to assemble into an R2430 button capacitor. The capacitor containing the SBP-DFOB / AN electrolyte is subjected to constant current charge and discharge and high voltage stability long cycle tests at different voltages.

[0037] Comparative Example 1 The same concentration of spiro quaternary ammonium tetrafluoroborate (SBP-BF4) electrolyte was prepared. The preparation method was similar to that in Example 1, except that LiDFOB in step S2 was replaced with lithium tetrafluoroborate (LiBF4) to prepare the SBP-BF4 electrolyte.

[0038] Application of supercapacitors with SBP-BF4 electrolyte at room temperature and high pressure Dissolve SBP-BF4 in acetonitrile to prepare a 1 mol / L electrolyte (SBP-BF4 / AN), add molecular sieves for water removal, and let stand for 7 days to ensure that the water content is ≤10ppm.

[0039] The process of assembling a symmetrical supercapacitor is based on the assembly process of Example 1. In a glove box, two pole pieces of approximately equal mass are divided into a group, and pole pieces, diaphragms, pole pieces, flat gaskets, and spring sheets are added to the negative electrode shell with a rubber ring in sequence. After the assembled electrode structure is laid flat, the prepared SBP-BF4 / AN electrolyte is added. Finally, the positive electrode shell is covered, packaged with a sealing machine, and assembled into an R2430 button capacitor. The capacitor containing the SBP-BF4 / AN electrolyte is subjected to constant current charge and discharge and high voltage stability long cycle tests at different voltages.

[0040] Figure 3 , Figure 4 The following are the comparison diagrams of supercapacitors based on SBP-DFOB / AN and SBP-BF4 / AN electrolytes at different voltages at room temperature, where the charge and discharge current density is 0.5 A / g. Figure 4 It can be seen that with the increase of voltage, the symmetry and linearity of the charge and discharge curve of SBP-BF4 / AN become worse and worse. When the voltage exceeds 2.5V, the curve begins to deform. When the voltage is 3V, the curve deformation is very serious, indicating that SBP-BF4 / AN cannot withstand the actual working voltage exceeding 2.5V. On the contrary, Figure 3 The charge and discharge curves of SBP-DFOB / AN maintain a typical triangular shape. When the voltage is less than 3.3 V, the change of potential with time shows an approximately linear relationship, indicating that the SBP-DFOB / AN-based double-layer capacitor has excellent electrochemical reversibility and stability.

[0041] Figure 5 This is a comparison of the long cycle performance of supercapacitors based on SBP-DFOB / AN and SBP-BF4 / AN electrolytes at room temperature and high voltage (3.2V), with a current density of 5A / g. Figure 5 It can be seen that although the efficiency of supercapacitors of the two electrolytes has remained at around 99%, the supercapacitor based on the SBP-DFOB / AN electrolyte performs significantly better than the supercapacitor based on the SBP-BF4 / AN electrolyte during long cycles. The 10,000th cycle of constant current charge and discharge testing of the supercapacitor showed that the capacity retention rates of the supercapacitors assembled with the SBP-DFOB / AN and SBP-BF4 / AN electrolytes were 94.12% and 52.89%, respectively. At this time, the performance of the supercapacitor based on the SBP-DFOB / AN electrolyte is still significantly better than that of the supercapacitor based on the SBP-BF4 / AN electrolyte.

[0042] Therefore, the spiro-(11')-difluoro(oxalate)borate electrolyte of the present invention, as a supercapacitor electrolyte, has high conductivity, high withstand voltage and excellent electrochemical stability; it exhibits a wide voltage window and high energy density, and shows excellent electrochemical performance at a high voltage of 3.2V.

[0043] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte, characterized in that: The structural formula is as follows: The cation is a bicyclic heterocyclic compound containing a five-membered ring with a nitrogen atom as the only ring heteroatom; wherein n is 1 or 2.

2. A method for preparing a difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte, characterized in that: The method for preparing the difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte according to claim 1 comprises the following steps: S1, adding pyrrolidine, a base, and a reaction solvent into a reaction container, adding 1,4-dibromobutane dropwise thereto, and heating to react; generating an intermediate product, a spirocyclic quaternary ammonium bromide, and purifying the reaction solution to obtain a pure product of a spirocyclic quaternary ammonium bromide salt; S2. The pure spirocyclic quaternary ammonium bromide salt produced in step S1 is reacted with lithium difluorooxalate borate, with water as solvent, to produce difluorooxalate borate spirocyclic quaternary ammonium salt.

3. The method for preparing the difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte according to claim 2, characterized in that: In step S1, the reaction solvent is any one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, acetonitrile, tetrahydrofuran, and dichloromethane; the base is sodium hydroxide or potassium hydroxide; the reaction temperature is room temperature to 80° C., and the reaction time is 8-10 hours.

4. The method for preparing the difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte according to claim 2, characterized in that: In step S2, the reaction temperature is room temperature, the reaction is instantaneous, and the purity of lithium difluorooxalatoborate is greater than 99%.

5. The method for preparing the difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte according to claim 2, characterized in that: The molar ratio of pyrrolidine, 1,4-dibromobutane, base and lithium difluoro(oxalato)borate is 1.0:(0.95-1.0):(1.2-1.5):(1.05-1.2).

6. The method for preparing the difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte according to any one of claims 2 to 5, characterized in that: The invention also includes the steps of refining difluorooxalate borate spirocyclic quaternary ammonium salt: S31, recrystallizing the crude product obtained in step S2 with acetonitrile and isopropanol to improve the purity of the product; S32, mixing the product after recrystallization in step S31 with activated carbon, performing decolorization treatment, and then performing reduced pressure distillation to obtain a refined solid; S33, vacuum drying the solid obtained in step S32 to finally obtain a high-purity difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte.

7. The method for preparing the difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte according to claim 6, characterized in that: In step S31, the recrystallization solvent is acetonitrile, and the heating temperature of the crystallization process is 80° C. After the crude product is dissolved in acetonitrile, low-valent isopropanol is added to crystallize the product; this step is repeated 1-3 times to ensure the purity of the product.

8. The method for preparing the difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte according to claim 6, characterized in that: In step S32, the activated carbon is 100-300 mesh; the added amount is 0.5% of the total mass of the solution; the decolorization treatment temperature is room temperature, and the time is 6-10 hours.

9. The method for preparing the difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte according to claim 6, characterized in that: In step S33, the vacuum drying temperature is 50-60° C. and the time is 12-24 hours.

10. A difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte, characterized in that: The electrolyte is prepared by dissolving the difluorooxalate borate spirocyclic quaternary ammonium salt electrolyte in claim 1 in an acetonitrile solvent, and the electrolyte concentration is 1 mol / L.

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