Aqueous high-voltage electrolyte and its preparation method, and a supercapacitor

Abstract

This disclosure discloses an aqueous high-voltage electrolyte and its preparation method, as well as a supercapacitor, belonging to the field of supercapacitor technology. The preparation method of the aqueous high-voltage electrolyte includes: adding an electrolyte salt to deionized water and stirring until the electrolyte salt is completely dissolved to obtain a mixed solution; adding a high-voltage additive and a hydrogen-eliminating additive to the mixed solution, and stirring to obtain the aqueous high-voltage electrolyte. This disclosure utilizes the synergistic effect of two additives, which preferentially adsorb at the electrode / electrolyte interface. By adjusting the interfacial double-layer structure, disrupting the hydrogen bond network of water molecules, or forming a protective layer, these additives effectively increase the water decomposition overpotential, thereby achieving a stable widening of the operating voltage window without significantly altering the basic composition and physicochemical properties of the electrolyte.

Description

Technical Field

[0001] This disclosure belongs to the field of supercapacitor technology, specifically relating to an aqueous high-voltage electrolyte and its preparation method, and a supercapacitor. Background Technology

[0002] Supercapacitors, with their high power density, long cycle life, and fast charge / discharge speed, have shown broad application prospects in energy storage, rail transportation, and smart grids. Among them, aqueous supercapacitors, using aqueous solutions as electrolytes, offer significant advantages such as high safety, environmental friendliness, high ionic conductivity, and low cost. However, compared to traditional organic supercapacitors, their energy density remains relatively low, which severely limits their large-scale commercial application.

[0003] Energy density (E) is given by the formula E = 0.5 × CV 2 The voltage is determined by the formula, where C is the specific capacitance and V is the operating voltage window. Therefore, one of the most effective ways to improve energy density is to widen the operating voltage window. The theoretical decomposition voltage of aqueous electrolytes is 1.23 V, but in reality, due to factors such as the catalytic effect of electrode materials, the actual operating voltage of traditional aqueous supercapacitors (such as those using 1 M Na2SO4 or KOH electrolytes) is usually limited to between 1.0 V and 1.2 V. Exceeding this voltage, water molecules in the electrolyte will undergo violent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at the electrode interface, leading to decreased capacitor efficiency, capacity decay, shortened cycle life, and even equipment damage.

[0004] To overcome this bottleneck, existing technologies have proposed the following main solutions:

[0005] 1) "Salt-in-water" electrolyte: By using ultra-high concentrations of lithium salts, sodium salts, etc., the number of free water molecules in the system is reduced, thereby inhibiting the electrochemical decomposition of water and widening the voltage window to 2.5 V or even higher. However, this method has problems such as high salt cost and a significant increase in electrolyte viscosity leading to a decrease in ionic conductivity and rate performance.

[0006] 2) Mixed solvent electrolyte: Water is mixed with organic solvents such as acetonitrile and dimethyl sulfoxide to stabilize the interface by altering the solvation structure and hydrogen bond network. While this method can increase the voltage to some extent, it introduces flammable and toxic organic solvents, violating the original intention of ensuring the safety and environmental friendliness of aqueous electrolytes.

[0007] 3) Electrode surface modification: This involves constructing a protective coating (such as oxides or polymers) on the surface of the electrode material to prevent direct contact between water molecules and the electrode. This method is complex, and the coating may increase internal resistance, affecting capacitance performance.

[0008] 4) Single additive regulation: Some studies have attempted to add a single type of additive (such as organic amines or ionic liquids) to the electrolyte to inhibit water decomposition. However, since it is impossible to simultaneously meet the stability requirements of the positive and negative electrode interfaces, it often only achieves a slight widening of the voltage window and leads to side effects such as a decrease in capacity retention, which cannot meet the requirements of practical applications.

[0009] In summary, existing technologies for broadening the voltage window of aqueous supercapacitors all involve significant compromises in performance, cost, or safety. In particular, there is a lack of a technology that can achieve a significantly broadened operating voltage window and stable performance without sacrificing the intrinsic advantages of aqueous electrolytes through a two-dimensional control of "additive synergy and process adaptation optimization." Therefore, developing an aqueous high-voltage electrolyte that is easy to operate, low-cost, highly process-compatible, and can effectively suppress HER and OER reactions through multi-component synergy, along with its preparation method, has become a key technical problem urgently needing to be solved in this field. This is of great significance for promoting the large-scale commercial application of aqueous supercapacitors. Summary of the Invention

[0010] In view of the shortcomings of existing aqueous supercapacitors, such as narrow operating voltage window, low energy density, high cost, poor safety, complex process or unstable performance of existing voltage-widening schemes, this disclosure aims to provide an aqueous high-voltage electrolyte and its preparation method, and a supercapacitor.

[0011] The core solution of this disclosure is to design a two-component synergistic system of "high voltage additive - hydrogen elimination additive" and deeply adapt it to the electrode preparation and electrolyte wetting processes of aqueous supercapacitors. Under the premise of ensuring high safety, high conductivity and low cost of electrolyte, it can achieve a stable widening of the working voltage window, while improving the cycle life and capacity retention of the device.

[0012] The first aspect of this disclosure provides a method for preparing an aqueous high-voltage electrolyte, the method being adapted to the assembly process of an aqueous supercapacitor, comprising the following steps:

[0013] Add the electrolyte salt to deionized water and stir until the electrolyte salt is completely dissolved to obtain a mixed solution;

[0014] A high-voltage additive and a hydrogen elimination additive were added to the mixed solution, and the solution was stirred to obtain an aqueous high-voltage electrolyte.

[0015] The high-voltage additive includes one or more of methyltributyl dibutyl phosphate, diisopropyl ammonium thiophosphate, tetramethyl ammonium phosphate, tetrahexyl hexafluorophosphate, and methyltriethyl dibutyl phosphate.

[0016] Optionally, the electrolyte salt is any one or a mixture of several of sulfates and imines.

[0017] Optionally, the sulfate is selected from one or two of sodium sulfate and lithium sulfate;

[0018] The imine salt is selected from one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0019] Optionally, the sulfate in the mixed solution has a mass fraction of 10-15%;

[0020] The imine salt has a mass fraction of 3-5% in the mixed solution.

[0021] Optionally, the high-voltage additive has a mass fraction of 0.5%-3% in the prepared aqueous high-voltage electrolyte.

[0022] Optionally, the hydrogen-eliminating additive is selected from any of the following structural formulas:

[0023] (I-1);

[0024] (I-2);

[0025] (I-3);

[0026] (I-4).

[0027] Optionally, the hydrogen removal additive has a mass fraction of 0.5%-2% in the prepared aqueous high-voltage electrolyte.

[0028] A second aspect of this disclosure provides an aqueous high-voltage electrolyte, which is prepared by the method of the first aspect described above, and its composition is: deionized water, 10%~15% sulfate, 3%~5% imine salt, 0.5%~3% high-voltage additive, and 0.5%~2% hydrogen removal additive (mass fraction).

[0029] Optionally, the electrolyte disclosed herein has the characteristics of high ionic conductivity, wide voltage window (2.2~2.8 V), and low viscosity, and has good compatibility with carbon-based electrodes and separator materials of aqueous supercapacitors, and can be directly adapted to the existing industrial assembly process of supercapacitors.

[0030] A third aspect of this disclosure provides an aqueous supercapacitor, comprising a positive electrode, a negative electrode, a separator, and the aqueous high-voltage electrolyte described in the second aspect above. Both the positive and negative electrodes are carbon nanotube-based electrodes, and their fabrication process is adapted to the characteristics of the electrolyte. The mass ratio of the electrode active material to the binder is 9:1, and the rolling density is 1.0~1.2 g / cm³. 3These process parameters ensure that the electrode has a suitable pore structure, which facilitates electrolyte wetting and ion transport, while forming a stable interface layer with the additives in the electrolyte. Attached Figure Description

[0031] Figure 1 A flowchart illustrating the preparation method of the aqueous high-voltage electrolyte according to a specific embodiment of this disclosure;

[0032] Figure 2 This is the voltage window curve for Embodiment 4 of this disclosure. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain this disclosure and represent a part of the embodiments of this disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the protection scope of this disclosure.

[0034] As shown in Figure 1, one aspect of this disclosure provides a method S100 for preparing an aqueous high-voltage electrolyte, specifically including the following steps S110~S120:

[0035] S110. Preparation of basic electrolyte: Add electrolyte salt to deionized water according to a preset ratio, and stir for 2-4 hours at 25~35℃ and 300~500 r / min until the electrolyte salt is completely dissolved to obtain a homogeneous mixed solution.

[0036] It should be noted that the stirring parameters in step S110 must be matched with the subsequent electrode wetting process to ensure that the electrolyte salt is fully dissolved and the solution viscosity is appropriate, so as to avoid abnormal electrode interface reaction due to uneven local concentration.

[0037] In step S110, the electrolyte salt is any one or a mixture of several of sulfates and imines.

[0038] In some preferred embodiments, the electrolyte salt is a compound system of sulfate and imine salt. This compound system can form good interfacial compatibility with carbon-based electrode materials. Specifically, the sulfate is selected from one or two of sodium sulfate and lithium sulfate, and its mass fraction in the mixed solution is 10% to 15%. This ratio range can ensure that the electrolyte has a high ionic conductivity, while avoiding the increase in viscosity due to excessive salt concentration, thus meeting the high power requirements of supercapacitors.

[0039] In some preferred embodiments, the sulfate is selected from one or two of sodium sulfate and lithium sulfate; and the mass fraction of the sulfate in the mixed solution is 10-15%.

[0040] In some preferred embodiments, the imine salt is selected from one or both of lithium bisfluorosulfonylimide (LiFSI) and lithium bistrifluoromethanesulfonylimide (LiTFSI), and its mass fraction in the mixed solution is 3% to 5%. The introduction of the imine salt can optimize the solvation structure of the electrolyte, synergistically improve the interfacial stability with subsequent additives, and this ratio range can balance cost and performance, avoiding the cost surge caused by excessive imine salt.

[0041] S120, synergistic additive compound: High voltage additive and hydrogen elimination additive are added sequentially to the above mixed solution, and stirring is continued for 1 to 2 h at 25~35℃ and 300~500 r / min. Then, it is allowed to stand for 0.5~1 h to remove bubbles, and an aqueous high voltage electrolyte is obtained.

[0042] It should be noted that the feeding sequence and stirring parameters in step S120 have been optimized to ensure that the two additives are evenly dispersed and form a stable synergistic system, thus avoiding additive agglomeration that leads to uneven interface modification.

[0043] In some preferred embodiments, the high-voltage additive is a quaternary ammonium phosphate compound selected from one or more of methyltributyldibutylammonium phosphate, diisopropylammonium thiophosphate, tetramethylammonium phosphate, tetrahexylhexafluorophosphate, and methyltriethyldibutylammonium phosphate; its mass fraction in the final aqueous high-voltage electrolyte is 0.5% to 3%. The molecular structure of this type of additive contains both quaternary ammonium cations and phosphate anions, which can form specific interactions with the positive and negative electrodes of the supercapacitor, respectively. Furthermore, the amount of additive is optimized through process control to ensure effective interface modification.

[0044] In step S120, the high-voltage additive is a quaternary ammonium phosphate, whose molecular structure contains both quaternary ammonium cations and phosphate anions. Its mechanism of action lies in the preferential adsorption of quaternary ammonium cations at the negative electrode interface. Specifically, the quaternary ammonium cations preferentially adsorb onto the negatively charged negative electrode surface, forming a "hydrophobic protective layer." This layer significantly inhibits the hydrogen evolution reaction through electrostatic shielding, preventing the cations from approaching the electrode and being reduced to hydrogen gas. This alters the double-layer structure, raises the energy barrier of the hydrogen evolution reaction, and significantly increases the hydrogen evolution overpotential, thus protecting the negative electrode. Secondly, the phosphate anions adsorb at the positive electrode interface to inhibit the oxygen evolution reaction, forming a protective film that prevents water molecules from directly contacting the electrode and inhibiting oxygen evolution. Simultaneously, the phosphate group, being a strong hydrogen bond acceptor, effectively disrupts the hydrogen bond network of water molecules in the electrolyte, reducing water activity. The hydrophobic long chains in the molecule synergistically construct a dense protective layer, thus protecting the positive electrode.

[0045] In this embodiment, the quaternary ammonium salt cation (negative electrode) and phosphate anion (positive electrode) work together to achieve bidirectional stability of the electrode interface, thereby increasing the decomposition voltage of the electrolyte by suppressing HER and OER.

[0046] In other preferred embodiments, the hydrogen elimination additive includes any of the following structural formulas:

[0047] (I-1:CAS:58556-13-1);

[0048] (I-2:CAS:68082-23-5);

[0049] (I-3:CAS:18032-45-6);

[0050] (I-4: CAS: 144675-84-3), and the mass fraction of this hydrogen removal additive in the prepared aqueous high-voltage electrolyte is 0.5%-2%. This type of additive can form a synergistic effect with high-voltage additives, and its alkenyl and siloxane structures can generate weak interactions with the functional groups on the surface of carbon-based electrodes, improving the interfacial bonding stability and adapting to the preparation process of carbon-based electrodes.

[0051] In step S120, as the positive electrode potential increases, the alkenyl group (-C=C-) in the hydrogen additive undergoes catalytic hydrogenation to generate an ethyl group, directly consuming hydrogen. Simultaneously, the silicon-oxygen bond (-Si-O-Si-) in the hydrogen additive forms a hydrophobic layer, physically preventing water from contacting the electrode.

[0052] The core innovation of this disclosure lies in the three-dimensional synergistic effect of "high-voltage additive - hydrogen elimination additive - preparation / assembly process", the specific mechanism of which is as follows:

[0053] Interfacial regulation effect of high-voltage additives: In the molecular structure of quaternary ammonium phosphate additives, the quaternary ammonium cations (such as tetramethylammonium ions) have strong positive charge and steric hindrance effect, and can preferentially adsorb onto the negatively charged anode surface to form a dense "hydrophobic cation protective layer". This protective layer repels hydrated protons (H3O) through electrostatic shielding effect. + This prevents the phosphate anion from approaching the negative electrode surface and undergoing a reduction reaction, significantly increasing the energy barrier for the hydrogen evolution reaction. At the same time, the phosphate anion has strong hydrogen bond acceptor properties, which can preferentially adsorb onto the positively charged positive electrode surface, disrupting the hydrogen bond network between water molecules, reducing the activity of water, inhibiting the occurrence of the oxygen evolution reaction, and forming an ion-conductive inorganic-organic composite protective film that prevents water molecules from directly contacting the positive electrode.

[0054] Synergistic enhancement effect of hydrogen-free additives: The alkenyl group (-C=C-) in alkenyl siloxane additives can undergo an addition reaction with the trace amount of hydrogen generated by the hydrogen evolution reaction under high potential conditions at the positive electrode, directly consuming the hydrogen and avoiding gas accumulation that could lead to device expansion; at the same time, the silicon-oxygen bonds (-Si-O-Si-) in its molecules can form a flexible hydrophobic layer on the electrode surface through cross-linking reactions, which, together with the protective layer formed by the high-voltage additives, further blocks the contact between water molecules and the electrode, improving interface stability.

[0055] Synergistic adaptation of processes and materials: The controlled stirring temperature, speed and time parameters during the preparation process ensure that the electrolyte salt is fully dissolved and the additives are uniformly dispersed, avoiding uneven interface modification due to excessively high local concentrations; The pore structure and rolling density of the supercapacitor electrode are optimized to ensure that the electrolyte quickly wets the inside of the electrode, allowing the additives to fully contact the electrode surface to form a protective layer, while ensuring rapid ion transport inside the electrode, avoiding a decrease in power density due to increased interfacial impedance.

[0056] The core solution of this disclosure is to design a two-component synergistic system of "high voltage additive - hydrogen elimination additive" and deeply adapt it to the electrode preparation and electrolyte wetting processes of aqueous supercapacitors. Under the premise of ensuring high safety, high conductivity and low cost of electrolyte, the operating voltage window is stably widened, while improving the cycle life and capacity retention of the device.

[0057] Compared with the prior art, this disclosure has the following significant advantages:

[0058] 1. Significantly widened and stable voltage window: Through the synergistic effect of dual additives, the working voltage window of the aqueous supercapacitor can be widened to 2.2~2.8 V, which is more than double that of the traditional aqueous electrolyte (1.0~1.2 V), and close to the performance of "salt-in-water" electrolyte. Moreover, the voltage stability is excellent, and the capacity retention rate is still more than 83% after 4000 cycles.

[0059] 2. Balancing safety and high conductivity: The electrolyte uses water as the sole solvent, without introducing any flammable or toxic organic solvents, thus retaining the high safety characteristics of aqueous electrolytes; at the same time, the electrolyte salt is at a conventional concentration, and the electrolyte ionic conductivity is >100 mS / cm, far exceeding that of "salt-in-water" electrolytes (<50 mS / cm), ensuring the high power performance of the supercapacitor;

[0060] 3. Low cost and simple process: The electrolyte salts and additives used are all industrially mass-produced products, and the amount used is small (total mass fraction of additives ≤5%). The preparation process does not require high temperature, high pressure or complex purification steps, and can be directly adapted to the existing industrial assembly process of aqueous supercapacitors, making it easy to mass-produce.

[0061] 4. Excellent performance stability: The "rigid and flexible" interface protective layer formed by the synergistic effect of the two additives can simultaneously suppress hydrogen evolution and oxygen evolution reactions at both the positive and negative electrodes, significantly improving the cycle life and capacity retention of the supercapacitor, and solving the problem of unstable performance of existing single additive solutions.

[0062] 5. Strong process compatibility: The electrolyte has good compatibility with various electrode materials such as carbon-based and transition metal oxides, and the type of electrode material can be adjusted according to different application scenarios, thus expanding its application range.

[0063] Another aspect of this disclosure is to provide an aqueous high-voltage electrolyte, which is prepared by the preparation method described above. For details of the preparation process, please refer to the above description and will not be repeated here.

[0064] In this embodiment, the aqueous high-voltage electrolyte is composed of: deionized water, 10%~15% sulfate, 3%~5% imine salt, 0.5%~3% high-voltage additive, and 0.5%~2% hydrogen removal additive.

[0065] The electrolyte of this embodiment has the characteristics of high ionic conductivity, wide voltage window (2.2~2.8 V) and low viscosity, and has good compatibility with carbon-based electrodes and separator materials of aqueous supercapacitors, and can be directly adapted to the existing industrial assembly process of supercapacitors.

[0066] In another aspect of this disclosure, a supercapacitor is proposed, comprising a positive electrode, a negative electrode, a diaphragm, and the aforementioned aqueous high-voltage electrolyte.

[0067] In this embodiment, the supercapacitor is a symmetrical supercapacitor, with both the positive and negative electrodes being carbon nanotube-based electrodes. Its fabrication process is adapted to the electrolyte characteristics: the mass ratio of electrode active material to binder is 9:1, and the rolling density is 1.0~1.2 g / cm³. 3 These process parameters ensure that the electrode has a suitable pore structure, which facilitates electrolyte wetting and ion transport, while forming a stable interface layer with the additives in the electrolyte.

[0068] The preparation method of aqueous high-voltage electrolyte will be further explained below with reference to specific embodiments:

[0069] Example 1

[0070] The electrolyte was prepared using the following method:

[0071] Step 1: Dissolve 13.5% sodium sulfate and 3% lithium bis(trifluoromethanesulfonyl)imide in 100 mL of deionized water and stir for 3 h to completely dissolve them to obtain a mixed solution.

[0072] It should be noted that the contents of sodium sulfate and lithium bis(trifluoromethanesulfonylimide) are percentages by mass relative to the mixed solution.

[0073] Step 2: Add Formula I-1 as a hydrogen removal additive to the mixed solution at a dosage of 0.5%, and continue stirring for 1 hour;

[0074] Step 3: Add 0.5% of methyltributyldibutylammonium phosphate high-voltage additive to the mixed solution, continue stirring for 1 hour, and let stand for 0.5 hours to remove bubbles to obtain an aqueous high-voltage electrolyte.

[0075] It should be noted that the content of hydrogen removal additives and high-voltage additives is a percentage of the mass relative to the aqueous high-voltage electrolyte.

[0076] As shown in Table 1, the voltage window is 0-2.3V, and the capacitance retention rate is 89.4% after 4000 cycles.

[0077] Example 2

[0078] This embodiment provides an aqueous high-voltage electrolyte, which differs from Embodiment 1 only in that the amount of high-voltage additive added to the electrolyte is 1%, while the rest is the same as Embodiment 1.

[0079] As shown in Table 1, the voltage window is 0-2.5V, and the capacitance retention rate is 90.5% after 4000 cycles.

[0080] Example 3

[0081] This embodiment provides an aqueous high-voltage electrolyte, which differs from Example 1 only in that the high-voltage functional additive methyltributyl dibutyl phosphate in Example 1 is replaced with methyltriethyl dibutyl phosphate at an addition amount of 1%, while the rest is the same as Example 1.

[0082] As shown in Table 1, the voltage window is 0-2.4V, and the capacitance retention rate is 78.5% after 4000 cycles.

[0083] Example 4

[0084] This embodiment provides an aqueous high-voltage electrolyte, which differs from Example 1 only in that the high-voltage functional additive methyltributyl dibutyl phosphate in Example 1 is replaced with tetramethyl ammonium phosphate, with an addition amount of 1%. Everything else is the same as in Example 1.

[0085] As shown in Table 1, the voltage window is 0-2.8V, and the capacitance retention rate is 90% after 4000 cycles.

[0086] like Figure 2 As shown, the voltage window in Example 4 reaches 2.8V, mainly due to the addition of lithium bis(trifluoromethanesulfonylimide) on the positive electrode side, TFSI -It preferentially undergoes oxidative decomposition on the positive electrode surface before water molecules, forming a CEI film rich in LiF, sulfonates, and other components. This film is dense, stable, and ionicly conductive, effectively preventing water molecules from contacting the positive electrode material, thereby suppressing the oxygen evolution reaction (OER) and significantly increasing the cutoff voltage on the positive electrode side. On the negative electrode side, a "water-deficient" or "shielded" interface layer is formed on the negative electrode surface, which helps suppress the hydrogen evolution reaction (HER). Meanwhile, TFSI... - It may also partially participate in the formation of the negative electrode interface. Simultaneously, the electrolyte contains alkenylsiloxane and tetramethylammonium phosphate. When the positive electrode potential increases, the hydrogenation reaction of the vinyl groups directly consumes hydrogen gas and inhibits the hydrogen evolution reaction due to its hydrophobic properties. Under the influence of an electric field, tetramethylammonium phosphate strongly migrates and adsorbs onto the negatively charged negative electrode surface. Its large spatial structure (four methyl groups) forms a physical barrier layer or "adsorption layer" at the electrode / electrolyte interface. This bidirectional expansion of the stable potentials at both the positive and negative electrodes ultimately increases the operating voltage window of the entire aqueous capacitor.

[0087] Example 5

[0088] The electrolyte was prepared using the following method:

[0089] Step 1: Dissolve 10% lithium sulfate and 3% lithium difluorosulfonylimide in 100 mL of deionized water and stir for 3 h to completely dissolve them to obtain a mixed solution;

[0090] Step 2: Add Formula I-2 as a hydrogen removal additive to the mixed solution at a dosage of 0.5%;

[0091] Step 3: Add 0.5% of the high-voltage additive methyltributyldibutylammonium phosphate to the mixed solution and stir thoroughly to obtain an aqueous high-voltage electrolyte.

[0092] As shown in Table 1, the voltage window is 0-2.3V, and the capacitance retention rate is 86% after 4000 cycles.

[0093] Example 6

[0094] The electrolyte was prepared using the following method:

[0095] Step 1: Dissolve 10% lithium sulfate and 5% lithium difluorosulfonylimide in 100 mL of deionized water and stir for 3 hours until completely dissolved to obtain a mixed solution.

[0096] Step 2: Add Formula I-3 as a hydrogen removal additive to the mixed solution at a dosage of 0.5%;

[0097] Step 3: Add 0.5% of the high-voltage additive methyltributyldibutylammonium phosphate to the mixed solution and stir thoroughly to obtain an aqueous high-voltage electrolyte.

[0098] As shown in Table 1, the voltage window is 0-2.2V, and the capacitance retention rate is 84% ​​after 4000 cycles.

[0099] Example 7

[0100] The electrolyte was prepared using the following method:

[0101] Step 1: Dissolve 10% lithium sulfate and 5% lithium difluorosulfonylimide in 100 mL of deionized water and stir for 3 hours until completely dissolved to obtain a mixed solution.

[0102] Step 2: Add Formula I-4 as a hydrogen removal additive to the mixed solution at a dosage of 0.5%;

[0103] Step 3: Add 0.5% of the high-voltage additive methyltributyldibutylammonium phosphate to the mixed solution and stir thoroughly to obtain an aqueous high-voltage electrolyte.

[0104] As shown in Table 1, the voltage window is 0-2.4V, and the capacitance retention rate is 86% after 4000 cycles.

[0105] Example 8

[0106] The electrolyte was prepared using the following method:

[0107] Step 1: Dissolve 10% lithium sulfate and 5% lithium difluorosulfonylimide in 100 mL of deionized water and stir for 3 hours until completely dissolved to obtain a mixed solution.

[0108] Step 2: Add Formula I-4 as a hydrogen removal additive to the mixed solution at a dosage of 1%;

[0109] Step 3: Add 0.5% of the high-voltage additive methyltributyldibutylammonium phosphate to the mixed solution and stir thoroughly to obtain an aqueous high-voltage electrolyte.

[0110] As shown in Table 1, the voltage window is 0-2.4V, and the capacitance retention rate is 88% after 4000 cycles.

[0111] Example 9

[0112] The electrolyte was prepared using the following method:

[0113] Step 1: Dissolve 10% lithium sulfate and 5% lithium difluorosulfonylimide in 100 mL of deionized water and stir for 3 hours until completely dissolved to obtain a mixed solution.

[0114] Step 2: Add Formula I-4 as a hydrogen removal additive to the mixed solution at a dosage of 2%;

[0115] Step 3: Add 0.5% of the high-voltage additive methyltributyldibutylammonium phosphate to the mixed solution and stir thoroughly to obtain an aqueous high-voltage electrolyte.

[0116] As shown in Table 1, the voltage window is 0-2.4V, and the capacitance retention rate is 86% after 4000 cycles.

[0117] Example 10

[0118] The electrolyte was prepared using the following method:

[0119] Step 1: Dissolve 10% lithium sulfate and 5% lithium difluorosulfonylimide in 100 mL of deionized water and stir for 3 hours until completely dissolved to obtain a mixed solution.

[0120] Step 2: Add Formula I-4 as a hydrogen removal additive to the mixed solution at a dosage of 0.5%;

[0121] Step 3: Add 2% of the high-voltage additive methyltributyldibutylammonium phosphate to the mixed solution and stir thoroughly to obtain an aqueous high-voltage electrolyte.

[0122] As shown in Table 1, the voltage window is 0-2.6V, and the capacitance retention rate is 84% ​​after 4000 cycles.

[0123] Example 11

[0124] The electrolyte was prepared using the following method:

[0125] Step 1: Dissolve 10% lithium sulfate and 5% lithium difluorosulfonylimide in 100 mL of deionized water and stir for 3 hours until completely dissolved to obtain a mixed solution.

[0126] Step 2: Add Formula I-4 as a hydrogen removal additive to the mixed solution at a dosage of 0.5%;

[0127] Step 3: Add 3% of the high-voltage additive methyltributyldibutylammonium phosphate to the mixed solution and stir thoroughly to obtain an aqueous high-voltage electrolyte.

[0128] As shown in Table 1, the voltage window is 0-2.7V, and the capacitance retention rate is 83% after 4000 cycles.

[0129] Comparative Example 1

[0130] The electrolyte was prepared using the following method:

[0131] Step 1: Dissolve 10% lithium sulfate and 3% lithium difluorosulfonylimide in 100 mL of deionized water and stir for 3 h to completely dissolve them to obtain a mixed solution;

[0132] Step 2: Add Formula I-1 as a hydrogen removal additive to the mixed solution at a dosage of 0.5%, stir thoroughly, and obtain the electrolyte.

[0133] As shown in Table 1, the voltage window is 0-1.7V, and the capacitance retention rate is 75% after 4000 cycles.

[0134] Comparative Example 2

[0135] The electrolyte was prepared using the following method:

[0136] Step 1: Dissolve 10% lithium sulfate and 3% lithium difluorosulfonylimide in 100 mL of deionized water and stir for 3 hours until completely dissolved to obtain the basic electrolyte.

[0137] As shown in Table 1, the voltage window is 0-1.6V, and the capacitance retention rate is 68% after 4000 cycles.

[0138] In summary, based on the results of each embodiment, it can be seen that the voltage window and capacity retention of the supercapacitors in Comparative Example 1 and Comparative Example 2 without the addition of high-voltage functional additives are relatively low. However, in Examples 1-11, the addition of high-voltage additives significantly increases the electrochemical window, widening it from 1.6V to about 2.8V. In particular, the voltage window of Example 4 reaches 2.8V, which is close to the performance of the "salt-in-water" electrolyte. In addition, the capacity retention of the assembled supercapacitor is also further improved.

[0139] Table 1 Test results for each embodiment and comparative example

[0140]

[0141] This disclosure proposes an aqueous high-voltage electrolyte and its preparation method, as well as a supercapacitor, which has the following advantages over the prior art: This disclosure utilizes the synergistic effect of two additives, which can preferentially adsorb at the electrode / electrolyte interface. By adjusting the interface double layer structure, disrupting the hydrogen bond network of water molecules, or forming a protective layer, the decomposition overpotential of water is effectively increased, thereby achieving a stable widening of the working voltage window without significantly changing the basic composition and physicochemical properties of the electrolyte.

[0142] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A method for preparing an aqueous high-voltage electrolyte, characterized in that, include: Add the electrolyte salt to deionized water and stir until the electrolyte salt is completely dissolved to obtain a mixed solution; A high-voltage additive and a hydrogen elimination additive were added to the mixed solution, and the solution was stirred to obtain an aqueous high-voltage electrolyte. The high-voltage additive includes one or more of methyltributyl dibutyl phosphate, diisopropyl ammonium thiophosphate, tetramethyl ammonium phosphate, tetrahexyl hexafluorophosphate, and methyltriethyl dibutyl phosphate. The hydrogen elimination additive is selected from any of the following structural formulas: （I-1）； （I-2）； （I-3）； （I-4）。 2. The preparation method according to claim 1, characterized in that, The electrolyte salt is any one or a mixture of several of sulfates and imines.

3. The preparation method according to claim 2, characterized in that, The sulfate is selected from one or two of sodium sulfate and lithium sulfate; The imine salt is selected from one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

4. The preparation method according to claim 2, characterized in that, The sulfate has a mass fraction of 10-15% in the mixed solution; The imine salt has a mass fraction of 3-5% in the mixed solution.

5. The preparation method according to claim 1, characterized in that, The high-voltage additive has a mass fraction of 0.5%-3% in the prepared aqueous high-voltage electrolyte.

6. The preparation method according to claim 1, characterized in that, The hydrogen-eliminating additive has a mass fraction of 0.5%-2% in the prepared aqueous high-voltage electrolyte.

7. A water-based high-voltage electrolyte, characterized in that, The aqueous high-voltage electrolyte is prepared by the preparation method described in any one of claims 1 to 6.

8. A supercapacitor, characterized in that, The supercapacitor includes the aqueous high-voltage electrolyte as described in claim 7.

Images