A high-voltage electrolyte additive and its preparation method and application

Abstract

The present invention discloses a high-voltage electrolyte additive, its preparation method, and application, belonging to the field of energy storage technology. Polyethyleneimine having a branched or hyperbranched structure is modified with 1,3-propane sultone to synthesize a branched zwitterionic polymer (PESB). The high-voltage electrolyte PESB provided by the present invention can be used as an aqueous electrolyte additive to obtain an aqueous electrolyte with low viscosity and high ionic conductivity, and to increase the operating voltage of aqueous energy storage devices. Furthermore, the synthesis method of the high-voltage electrolyte PESB provided by the present invention is simple, low-cost, and environmentally friendly, and has good application prospects as a high-voltage electrolyte additive for electrochemical devices.

Description

Technical Field

[0001] The present invention belongs to the field of energy storage technology, and specifically relates to a high-voltage electrolyte additive and a preparation method and application thereof. Background Art

[0002] Currently, electrochemical energy storage is one of the simplest and most efficient of the various existing energy storage methods. Electrochemical energy storage devices and equipment include secondary batteries, electrochemical supercapacitors, or a combination of the two. Among them, lithium-ion batteries have rapidly developed due to their outstanding advantages, such as long cycle stability, high energy density, and low self-discharge rate. During the charge and discharge process of lithium-ion batteries, lithium ions can reversibly embed and extract from the electrode active material, completing the reversible conversion of electrical energy into chemical energy, and the charge and discharge process does not destroy the crystal structure of the electrode material. Supercapacitors, also known as electrochemical capacitors, are considered excellent candidates for next-generation energy storage systems due to their fast charge and discharge rates, high power density, long cycle life, good safety, and environmental friendliness. The energy storage mechanisms of supercapacitors can be mainly divided into electrochemical double-layer capacitors and pseudocapacitors. The charge storage mechanism of electrochemical double-layer capacitors is the electrostatic interaction at the electrode and electrolyte interface, while pseudocapacitors use fast and reversible Faradaic oxidation-reduction reactions to store charge.

[0003] Electrolytes are key materials for electrochemical energy storage devices, including lithium-ion batteries and supercapacitors, and their performance has a significant impact on the internal resistance, lifespan, and rate performance of the devices. Although currently commonly used organic electrolytes have good salt dissolution capabilities and a high electrochemical stability window, their toxicity and flammability pose serious safety risks to such energy storage devices during use. Aqueous electrolytes have the advantages of low cost and high safety performance, which can eliminate the safety risks brought by organic electrolytes. At the same time, the ionic conductivity of aqueous electrolytes is generally high, which is conducive to the high rate performance of electrochemical energy storage devices. However, the electrochemical stability window of conventional aqueous electrolytes is relatively narrow. Since the energy density of electrochemical devices is proportional to the operating voltage, the energy density of electrochemical devices can be increased by increasing the operating voltage value, which is particularly effective for double-layer supercapacitors. Therefore, one of the keys to increasing the operating voltage of aqueous energy storage devices is to obtain aqueous electrolytes with a wide electrochemical stability window.

[0004] One of the common methods to broaden the electrochemical window of aqueous electrolytes is to prepare an aqueous solution of high-concentration salt, that is, a "salt-in-water" electrolyte. However, the preparation of salt-in-water electrolytes requires the use of a large amount of expensive lithium salts such as lithium trifluorosulfonyl imide, which results in a very high preparation cost of the aqueous electrolyte. In addition, the viscosity of salt-in-water electrolytes is relatively high, and salting out often occurs. In addition, some studies have improved the electrochemical stability window of aqueous electrolytes by adding additives such as small organic molecules or high molecular weight polymers to the electrolyte solution, and utilizing the strong interaction between these additive molecules and water molecules to destroy the hydrogen bond network between water molecules. However, the amount of these additives added is generally very large, which makes the electrolyte system essentially deviate from the aqueous electrolyte system, and also leads to negative problems such as low ionic conductivity and excessive viscosity of the electrolyte.

[0005] Therefore, it is necessary to develop a new type of high-voltage electrolyte additive and aqueous electrolyte system to increase the operating voltage of aqueous energy storage devices and improve existing problems such as low ion conductivity and excessive viscosity. Summary of the Invention

[0006] The present invention aims to provide a high-voltage electrolyte additive, its preparation method and application. By reacting branched polyethyleneimine with 1,3-propane sultone to prepare a zwitterionic polymer electrolyte additive, the additive effectively improves the problems of low ionic conductivity and high viscosity of aqueous electrolytes and increases the operating voltage of energy storage devices.

[0007] In a first aspect, the present invention provides a method for preparing a high-voltage electrolyte additive, comprising the following steps:

[0008] In solvent 1, under heating conditions, branched polyethyleneimine reacts with 1,3-propane sultone to obtain a reaction mixture;

[0009] The reaction mixture is added to a second solvent for precipitation, and the precipitation is dried to obtain the electrolyte additive.

[0010] Optionally, the solvent 1 includes any one of trifluoroethanol and hexafluoroisopropanol.

[0011] Optionally, the second solvent includes any one of tetrahydrofuran, ethanol, acetone, acetonitrile, and dioxane.

[0012] Optionally, the volume ratio of solvent 1 to solvent 2 is 1:10.

[0013] Optionally, the branched polyethyleneimine includes any one of branched polyethyleneimines with a molecular weight of 300, 600, and 900.

[0014] Optionally, when the molecular weight of the branched polyethyleneimine is 600, the structural formula of the prepared electrolyte additive is as shown in Formula I:

[0015]

[0016] Optionally, the heating condition is 30-70° C., and the reaction time is 12-96 hours.

[0017] Optionally, the mass ratio of the branched polyethyleneimine to the 1,3-propane sultone is 1:(1-10).

[0018] In a second aspect, the present invention provides an aqueous electrolyte prepared using a high-voltage electrolyte additive.

[0019] Optionally, the aqueous electrolyte includes the high-voltage electrolyte additive, water, and a soluble salt.

[0020] Optionally, the soluble salt includes at least one of lithium sulfate, lithium hydroxide, lithium nitrate, lithium acetate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, sodium chloride, sodium sulfate, sodium perchlorate, etc.

[0021] Optionally, the mass ratio of the high-voltage electrolyte additive to water is (1-9):(1-9).

[0022] Optionally, the concentration of soluble salts in the aqueous electrolyte is 0.5-21 m(mol / kg).

[0023] Optionally, at 25-30° C., the electrochemical stability window of the aqueous electrolyte is 2.5-3.5V.

[0024] Optionally, at 25-30° C., the ionic conductivity of the aqueous electrolyte is 0.5-10 mS / cm.

[0025] In a third aspect, the present invention provides an application of an aqueous electrolyte in the preparation of an electrochemical energy storage device, characterized in that the application includes an aqueous secondary battery, an aqueous electrochemical supercapacitor, and an aqueous hybrid capacitor.

[0026] The beneficial effects of the present invention include:

[0027] (1) The preparation method of high-voltage electrolyte addition provided by the present invention has low cost, stable output, and good application prospects;

[0028] (2) The high-voltage electrolyte additive provided by the present invention introduces a branched or hyperbranched zwitterionic polymer as an additive into an aqueous electrolyte. Since the polymer molecules with a branched or hyperbranched structure have a compact structure similar to a sphere, a small hydrodynamic radius of gyration, and less molecular chain entanglement, the increase in relative molecular mass has little effect on the viscosity. Moreover, the branched or hyperbranched polyethyleneimine raw material molecules have reactive functional groups, which can be modified to have zwitterionic groups and then added to the electrolyte as an additive to effectively control the viscosity of the electrolyte. The strong interaction between the zwitterionic groups in the polymer added to the electrolyte and the water molecules restrains the movement of the water molecules, destroys the hydrogen bond network between the water molecules, increases the decomposition voltage of the electrolyte, and increases the electrochemical stable voltage window of the aqueous electrolyte, thereby increasing the energy density of the energy storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Cyclic voltammetry curves of a supercapacitor assembled with the 2m-60%-600PESB electrolyte provided in Example 3 of the present invention under different operating voltage windows;

[0030] Figure 2 Cyclic voltammetry curves of a supercapacitor assembled with the 2m-70%-600PESB electrolyte provided in Example 4 of the present invention under different operating voltage windows;

[0031] Figure 3 Cyclic voltammetry curves of a supercapacitor assembled with the 2m-60%-600PEI electrolyte provided in Comparative Example 1 of the present invention under different operating voltage windows;

[0032] Figure 4 The constant current charge-discharge curve of the supercapacitor assembled with the 2m-60%-600PESB electrolyte provided in Example 3 of the present invention in the 2.3V voltage window;

[0033] Figure 5 The constant current charge-discharge curve of the supercapacitor assembled with the 2m-70%-600PESB electrolyte provided in Example 4 of the present invention in the 2.5V voltage window;

[0034] Figure 6 The curve of the change of specific capacitance of the supercapacitor assembled with the 2m-60%-600PESB electrolyte provided in Example 3 of the present invention as a function of current density;

[0035] Figure 7 Energy density and power density curves of the supercapacitor assembled with the 2m-60%-600PESB electrolyte provided in Example 3 of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described through the following examples with reference to the accompanying drawings.

[0037] In a first aspect, an embodiment of the present invention provides a method for preparing a high-voltage electrolyte additive, comprising the following steps:

[0038] In solvent 1, under heating conditions, branched polyethyleneimine reacts with 1,3-propane sultone to obtain a reaction mixture;

[0039] The reaction mixture is added to a second solvent for precipitation, and the precipitation is dried to obtain the electrolyte additive.

[0040] In some embodiments, the first solvent includes any one of trifluoroethanol and hexafluoroisopropanol.

[0041] In some embodiments, the second solvent includes any one of tetrahydrofuran, ethanol, acetone, acetonitrile, and dioxane.

[0042] In some embodiments, the volume ratio of solvent 1 to solvent 2 is 1:10.

[0043] In some embodiments, the branched polyethyleneimine comprises any one of branched polyethyleneimines with a molecular weight of 300, 600, and 900.

[0044] In some embodiments, when the molecular weight of the branched polyethyleneimine is 600, the electrolyte additive structure is as shown in Formula I:

[0045]

[0046] In some embodiments, the heating condition is 30-70° C., and the reaction time is 12-96 hours.

[0047] In some embodiments, the mass ratio of the branched polyethyleneimine to the 1,3-propane sultone is 1:(1-10).

[0048] In a second aspect, embodiments of the present invention provide an aqueous electrolyte prepared using a high-voltage electrolyte additive.

[0049] In some embodiments, the aqueous electrolyte includes the high-voltage electrolyte additive, water, and a soluble salt.

[0050] In some embodiments, the soluble salt includes at least one of lithium sulfate, lithium hydroxide, lithium nitrate, lithium acetate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, sodium chloride, sodium sulfate, sodium perchlorate, etc.

[0051] Specifically, the mass ratio of the high-voltage electrolyte additive to water is (1-9):(1-9).

[0052] In some embodiments, the concentration of soluble salts in the aqueous electrolyte is 0.5-21 m(mol / kg).

[0053] In some embodiments, at 25-30° C., the electrochemical stability window of the aqueous electrolyte is 2.5-3.5V.

[0054] In some embodiments, at 25-30° C., the ionic conductivity of the aqueous electrolyte is 0.5-10 mS / cm.

[0055] In a third aspect, an embodiment of the present invention provides an application of an aqueous electrolyte in the preparation of an electrochemical energy storage device, characterized in that the application includes an aqueous secondary battery, an aqueous electrochemical supercapacitor, and an aqueous hybrid capacitor.

[0056] Example 1

[0057] Embodiment 1 of the present invention provides a method for preparing a high-voltage electrolyte additive, comprising the following steps:

[0058] 3 g of branched polyethyleneimine (PEI) with a relative molecular mass of 600 was placed in a round-bottom flask, 25 mL of trifluoroethanol was added, and 12.3 g of 1,3-propane sultone was added dropwise to the round-bottom flask; the mixture was heated to 40°C in an oil bath and stirred for 72 hours to prepare a reaction mixture;

[0059] The reaction mixture was added dropwise to 250 mL of tetrahydrofuran through a dropping funnel. After the addition was complete, the white precipitate in the tetrahydrofuran was taken out and dried in a vacuum drying oven at 60° C. for 12 h to obtain a branched zwitterionic polymer additive, namely, high-voltage electrolyte additive 600PESB, having the structural formula shown in Formula I.

[0060]

[0061] Example 2

[0062] Example 2 of the present invention provides a method for preparing a high-voltage electrolyte additive. The difference from Example 1 is that branched PEI with a relative molecular mass of 300 is used for preparation, and other conditions and steps remain the same to obtain a high-voltage electrolyte additive 300PESB.

[0063] Example 3

[0064] Embodiment 3 of the present invention provides a method for preparing an aqueous electrolyte, comprising the following steps:

[0065] 2.8 g (0.01 mol) of lithium bis(trifluoromethanesulfonyl)imide electrolyte was dissolved in 2 g of deionized water, and 3 g of the high-voltage electrolyte additive 600PESB prepared in Example 1 was added; the mass ratio of water to additive was 4:6, and the electrolyte concentration was 2 m, to prepare an aqueous electrolyte 2 m-60%-600PESB.

[0066] Example 4

[0067] Example 4 of the present invention provides a method for preparing an aqueous electrolyte, which differs from Example 3 in that the mass ratio of water to additive is 3:7, and other conditions and steps remain the same, to prepare an aqueous electrolyte 2m-70%-600PESB.

[0068] Example 5

[0069] Example 5 of the present invention provides a method for preparing an aqueous electrolyte, which differs from Example 3 in that the mass ratio of water to additive is 5:5, and other conditions and steps remain the same, to prepare an aqueous electrolyte 2m-50%-600PESB.

[0070] Example 6

[0071] Example 6 of the present invention provides a method for preparing an aqueous electrolyte. The difference from Example 3 is that the high-voltage electrolyte additive 300PESB prepared in Example 2 is used to prepare the aqueous electrolyte; other conditions and steps remain the same to prepare an aqueous electrolyte 2m-60%-300PESB.

[0072] Example 7

[0073] Example 7 of the present invention provides a method for preparing an aqueous electrolyte. The difference from Example 3 is that the high-voltage electrolyte additive 300PESB prepared in Example 2 is used to prepare the aqueous electrolyte; the mass ratio of water to additive is 3:7; other conditions and steps remain the same, and the aqueous electrolyte 2m-70%-300PESB is prepared.

[0074] Comparative Example 1

[0075] Comparative Example 1 of the present invention provides a method for preparing an aqueous electrolyte, which is different from Example 3 in that 600PEI is used as an additive to prepare an aqueous electrolyte 2m-60%-600PEI.

[0076] Performance Verification

[0077] 1. Determination of ionic conductivity of aqueous electrolyte

[0078] The ionic conductivity of the aqueous electrolyte was tested using electrochemical impedance spectroscopy. The test results of Examples 3-7 and Comparative Example 1 are shown in Table 1.

[0079] Table 1 Ionic conductivity test results

[0080]

[0081] Referring to Table 1, the ionic conductivity of the aqueous electrolytes prepared in Examples 3-7 of the present invention using PESB branched zwitterionic polymer as an electrolyte additive is higher than that of Comparative Example 1, demonstrating that the present invention can significantly improve the ionic conductivity of the aqueous electrolyte by using PESB as an additive.

[0082] 2. Performance testing of supercapacitors assembled with aqueous electrolytes

[0083] The aqueous electrolytes prepared in Example 3, Example 4, and Comparative Example 1 were respectively assembled into aqueous supercapacitors to compare their high-voltage performance, including the following steps:

[0084] Activated carbon (AC), acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 were dispersed in N-methylpyrrolidone (NMP) to prepare a uniform dispersion slurry;

[0085] The dispersion slurry was coated on titanium foil and dried in vacuum at 80 °C for 12 h to obtain an AC electrode. The loading amount of AC active material on the electrode was about 2.5 mg / cm 2 ;

[0086] A symmetrical capacitor was assembled using AC electrodes as the positive and negative electrodes, the diaphragm was a Whatman glass fiber diaphragm, and the aqueous electrolytes were the aqueous electrolytes prepared in Example 3, Example 4, and Comparative Example 1, respectively;

[0087] The working voltage of three aqueous supercapacitors was detected by cyclic voltammetry, and the cyclic voltammetry curves were obtained. Figure 1-3 As shown;

[0088] The constant current charge-discharge curves of the supercapacitors prepared with the aqueous electrolytes of Example 3 and Example 4 were tested by the constant current charge-discharge method. The results are as follows: Figure 4 、 Figure 5 As shown;

[0089] See also Figure 1-3 In Examples 3 and 4, the working voltage of the supercapacitors assembled with the aqueous electrolyte containing 600 PESB of high-voltage electrolyte additive can reach 2.5 V, while in Comparative Example 1, which uses PEI alone as an additive, the working voltage of the supercapacitor assembled is less than 2 V.

[0090] See also Figure 4 、 Figure 5The constant current charge-discharge curves of the supercapacitor assembled with the aqueous electrolyte 2m-60%-600PESB in Example 3 at operating voltages of 2.3V and 2.5V respectively show nearly symmetrical isosceles triangle profiles, indicating typical double-layer capacitance behavior;

[0091] See also Figure 6 、 Figure 7 By calculating the constant current charge and discharge curve, the current density and specific capacitance relationship curves and the power density and energy density relationship curves of the supercapacitor assembled with the aqueous electrolyte 2m-60%-600PESB in Example 3 were obtained respectively. It can be seen that the assembled supercapacitor has very good rate performance and high energy density.

[0092] In summary, the addition of PESB significantly increases the operating voltage of the supercapacitor. This is because the branched zwitterionic polymer PESB, when added as an additive to the aqueous electrolyte, can destroy the hydrogen bond network between water molecules through strong interaction with water, thereby increasing the decomposition voltage of water molecules and thus increasing the operating voltage of the electrolyte in the device. Therefore, the aqueous electrolyte prepared from the high-voltage electrolyte provided by the present invention can increase the operating voltage of the supercapacitor.

[0093] While the embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations of these embodiments are possible. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as set forth in the claims. Furthermore, the invention described herein is susceptible to other embodiments and may be practiced or implemented in a variety of ways.

Claims

1. Use of an aqueous electrolyte in the preparation of an electrochemical energy storage device, characterized in that: The applications include aqueous secondary batteries, aqueous electrochemical supercapacitors, and aqueous hybrid capacitors; the aqueous electrolyte includes a high-voltage electrolyte additive, water, and a soluble salt; and the preparation method of the high-voltage electrolyte additive comprises the following steps: In solvent 1, under heating conditions, branched polyethyleneimine reacts with 1,3-propane sultone to obtain a reaction mixture; The reaction mixture is added to a second solvent for precipitation, and the precipitate is dried to obtain the high-voltage electrolyte additive.

2. The use according to claim 1, characterized in that The first solvent includes any one of trifluoroethanol and hexafluoroisopropanol; the second solvent includes any one of tetrahydrofuran, ethanol, acetone, acetonitrile, and dioxane.

3. The use according to claim 1, characterized in that The mass ratio of the branched polyethyleneimine to the 1,3-propane sultone is 1:(1-10).

4. The use according to claim 1, characterized in that The branched polyethyleneimine includes any one of a branched polyethyleneimine with a molecular weight of 300 and a branched polyethyleneimine with a molecular weight of 600; When the molecular weight of the branched polyethyleneimine is 600, the structural formula of the high-voltage electrolyte additive prepared is as shown in Formula I:

5. The use according to claim 1, characterized in that The soluble salt includes at least one of lithium sulfate, lithium hydroxide, lithium nitrate, lithium acetate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), sodium chloride, sodium sulfate, and sodium perchlorate.

6. The use according to claim 1, characterized in that The mass ratio of the high-voltage electrolyte additive to water is (1-9):(1-9).

7. The use according to claim 1, characterized in that The concentration of soluble salt in the aqueous electrolyte is 0.5-21 mol / kg.

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