Low-temperature-resistant molecular crowding electrolyte and application thereof in proton pseudocapacitor

Abstract

The invention discloses a low-temperature-resistant molecular crowding electrolyte and an application thereof in a proton pseudocapacitor. The low-temperature-resistant molecular crowding electrolyte comprises a molecular crowding agent, inorganic acid and water. The molecular crowding agent can effectively adjust the hydrogen bond structure and number of water molecules, inhibits freezing of water in a dynamic pathway, and shows excellent ion transport kinetics at low temperature. And when the copper hexacyanoferrate (III) acid electrode material is selected, the maximum capacity of the obtained proton pseudocapacitor at the low temperature of-60 DEG C is 39 mAh g1, and the proton pseudocapacitor can stably circulate for more than 500 times at the temperature of-40 DEG C, so that the proton pseudocapacitor has a good market prospect.

Description

Technical Field

[0001] The invention relates to an electrolyte and application thereof in an electrochemical energy storage device, in particular to a low-temperature resistant molecular crowding electrolyte and application thereof in a proton pseudocapacitor. Background Art

[0002] Proton (H + ) has the lowest ionic mass and smallest ionic radius, and is comparable to larger metal ions (such as Li + 、Na + , K + and Zn 2+ Compared with other cations, H + It has higher specific capacity and faster kinetic behavior, and can migrate quickly through non-diffusion conduction mechanisms even in the bulk phase of electrode materials. Proton pseudocapacitors with protons as load ions break through the power limitations of traditional metal ion batteries and the energy limitations of capacitors, combining the advantages of both. Therefore, they are favored by researchers. Proton pseudocapacitors are a new type of energy storage device that has the advantages of high power, wide temperature range, and high safety. They have broad application prospects in extreme environments such as aerospace.

[0003] At present, proton pseudocapacitors face serious capacity attenuation problems in extreme environments such as ultra-low temperatures, and key mechanisms such as ion transport of components such as electrolytes at low temperatures are unclear. It is urgent to develop widely applicable new ultra-low temperature resistant electrolytes and proton pseudocapacitor design strategies.

[0004] Compared with weak or volatile acids such as acetic acid, phosphoric acid, and hydrochloric acid, sulfuric acid has higher ionic conductivity and a wider electrochemical stability window, so sulfuric acid electrolyte is often used in proton capacitors / batteries. As the solution concentration increases, sulfuric acid is completely ionized to produce SO4 2- The number of H2O increases, forming hydrogen bonds with a large number of water molecules, destroying the hydrogen bond network between water molecules, reducing the activity of water molecules, and significantly reducing the freezing point of the solution. Therefore, concentrated sulfuric acid has a lower freezing point (for example, the freezing point of 4.2MH2SO4 is -74°C) and good ionic conductivity. Proton capacitors / batteries using concentrated sulfuric acid electrolytes usually exhibit good electrochemical properties at low temperatures. However, concentrated acid electrolytes usually cause structural distortion of the electrode surface lattice, corrode the electrodes and current collectors, and cause the capacity of the device to decay, so it is necessary to develop low-temperature resistant dilute acid electrolytes. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a low-temperature resistant molecular crowding electrolyte and its application in a proton pseudocapacitor to solve the corrosion problem of the existing concentrated acid electrolyte system on electrode materials and current collectors. The present invention provides a low-cost, high-safety, environmentally friendly low-temperature molecular crowding electrolyte, which has the advantages of low viscosity and high ionic conductivity at low temperatures, and is applied to low-temperature resistant proton pseudocapacitors through reasonable design.

[0006] In order to solve the problems of the prior art, the technical solution adopted by the present invention is:

[0007] A low-temperature molecular crowding electrolyte is a composite electrolyte composed of an inorganic acid, water and a molecular crowding agent, wherein the inorganic acid is one or more of sulfuric acid, phosphoric acid and hydrochloric acid, and the molecular crowding agent is polyethylene glycol, polyethylene glycol dimethyl ether, polyvinyl alcohol, polypropylene glycol, polyvinyl pyrrolidone, polyacrylamide or dextran.

[0008] Preferably, the volume fraction of the molecular crowding agent is 10 to 90%.

[0009] Preferably, the molecular crowding agent is polyethylene glycol, and the average molecular weight is 300.

[0010] Preferably, the concentration of the inorganic acid is 0.1-0.5 mol / L. A suitable acid concentration can provide sufficient proton concentration to ensure high ion conductivity and reduce corrosion to the electrode.

[0011] Preferably, the inorganic acid is sulfuric acid.

[0012] Preferably, the freezing point of the electrolyte is lower than -80°C.

[0013] The method for preparing the low-temperature molecular crowded electrolyte comprises the following steps:

[0014] Step 1: At room temperature, mix the molecular crowding agent and water, and stir thoroughly to form a uniform composite solution;

[0015] Step 2: Add the inorganic acid to the composite solution prepared in step 1, and stir thoroughly until the solution becomes clear to form a uniform electrolyte.

[0016] Application of the above-mentioned low-temperature molecular crowded electrolyte in proton pseudocapacitors.

[0017] Preferably, the operating temperature of the proton pseudocapacitor is -60 to 25°C.

[0018] Preferably, when the electrode material of the proton pseudocapacitor is copper hexacyanoferrate (III) electrode material, the maximum capacity of the proton pseudocapacitor at a low temperature of -60°C is 39 mAh g -1, and can stably cycle more than 500 times at -40℃.

[0019] The molecular crowding agent of the present invention forms hydrogen bonds with free water molecules, breaks the original hydrogen bond network between water molecules, effectively reduces the freezing point of the solution, inhibits the freezing of the solution, and has the characteristics of low temperature and high ion conductivity.

[0020] Beneficial effects:

[0021] Compared with the prior art, the present invention provides a low-temperature resistant molecular crowded electrolyte and its application in a proton pseudocapacitor. The molecular crowded electrolyte used can effectively adjust the structure and number of hydrogen bonds of water molecules, inhibit the freezing of water in the kinetic pathway, and exhibit excellent ion transport kinetics at low temperatures. The electrode material achieves excellent rate performance and cycle stability in the low-temperature electrolyte. The obtained electrolyte has important value in the application of low-temperature resistant proton pseudocapacitors.

[0022] In addition, the low-temperature molecular crowded electrolyte of the present invention is low in cost, highly safe, and environmentally friendly, and has the characteristics of high ionic conductivity and low viscosity at low temperatures, and has good market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The infrared spectra of the electrolytes of Example 1 and Comparative Example 1 of the present invention are shown in FIG.

[0024] Figure 2 A schematic diagram showing the change in conductivity of the low-temperature electrolyte provided in Example 1 of the present invention with respect to temperature;

[0025] Figure 3 A charge and discharge curve diagram of the corresponding electrode at different temperatures in the low-temperature electrolyte provided in Example 1 of the present invention;

[0026] Figure 4 This is a cycle performance diagram of the corresponding electrode material in the low-temperature electrolyte provided in Example 1 of the present invention after 500 cycles at -40°C. DETAILED DESCRIPTION

[0027] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0028] A low-temperature molecular crowding electrolyte is a composite electrolyte composed of an inorganic acid, water and a molecular crowding agent. The water and the molecular crowding agent are used as solvents to dissolve and dilute the solute to achieve rapid ion transport at low temperatures. The inorganic acid ionizes to provide protons, which are used in proton pseudocapacitors.

[0029] Among them, molecular crowding agents include polyethylene glycol, polyethylene glycol dimethyl ether, polyvinyl alcohol, polypropylene glycol, polyvinyl pyrrolidone, polyacrylamide, dextran, and the volume fraction of molecular crowding agents is 10-90%. Functional groups (hydroxyl, amino, etc.) in molecular crowding will combine with water molecules to form new hydrogen bond networks, synergistically destroying the hydrogen bond networks of water molecules, thereby inhibiting the coagulation of electrolytes. The volume fraction of molecular crowding agents is important. Low content of crowding agents cannot destroy sufficient hydrogen bond networks between water molecules, and the increase of crowding agent content will also bring about problems such as reduced ion conductivity and increased viscosity.

[0030] The inorganic acid includes one or more of sulfuric acid, phosphoric acid, and hydrochloric acid. Specifically, the concentration of the inorganic acid is 0.1 to 0.5 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, etc. Those skilled in the art can make an adaptive selection within this range according to actual needs. Sulfuric acid and / or phosphoric acid molecules are ionized in water to provide sufficient proton concentration.

[0031] The preparation method of the low-temperature molecular crowded electrolyte comprises:

[0032] Step 1: Mix a certain proportion of polyethylene glycol (average molecular weight of 300) and water at room temperature, for example, the volume fraction of polyethylene glycol is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90%, and stir well to form a uniform composite solution;

[0033] Step 2: Add the inorganic acid to the composite solution prepared in step 1, and stir thoroughly until the solution becomes clear to form a uniform electrolyte.

[0034] Application of the above-mentioned low-temperature molecular crowded electrolyte in proton pseudocapacitors.

[0035] The electrolyte of the present invention is tested in a three-electrode test system to obtain electrochemical data, including the above-mentioned low-temperature molecular crowded electrolyte, electrode, diaphragm, activated carbon membrane and reference electrode; specifically, the electrode, diaphragm, activated carbon membrane and reference electrode are placed in an electrolytic cell mold, and then the molecular crowded electrolyte is slowly added dropwise, and the above-mentioned three-electrode test system is obtained after packaging;

[0036] The preparation method of the electrode material comprises: dissolving K3Fe(CN)6 and anhydrous CuSO4 in water respectively to obtain a first solution; centrifuging the first solution to obtain a precipitate, and then washing and drying the precipitate to obtain a copper hexacyanoferrate (III) Prussian blue analogue. The specific steps are as follows: dissolving 5mmol K3Fe(CN)6 and 10mmol CuSO4 in 50ml water respectively; slowly adding the copper sulfate solution to the K3Fe(CN)6 solution under magnetic stirring, and rapidly stirring for 6h to obtain the first solution; then centrifuging by a centrifuge, and washing the precipitate with deionized water and anhydrous ethanol three times respectively; finally, drying in a vacuum drying oven at 60°C for 12h to obtain an olive green copper hexacyanoferrate (III) Prussian blue analogue. The above-mentioned electrode material, conductive carbon black, polyvinylidene fluoride binder and N-methylpyrrolidone solvent are mixed and ground to obtain a mixed slurry. The mixture is coated on a carbon paper current collector to obtain the electrode.

[0037] It should be pointed out that the specific contents involved in the embodiments of the present application can be found in the description of the above embodiments, and for the sake of brevity, they will not be repeated here.

[0038] For ease of understanding, the technical solution provided in this application is described in detail below in conjunction with specific embodiments.

[0039] Example 1

[0040] A low-temperature molecular crowded electrolyte, specifically composed of a solvent (water), a molecular crowding agent (polyethylene glycol with an average molecular weight of 300), and an electrolyte (sulfuric acid), and a specific preparation method is as follows: 60 mL of polyethylene glycol and 40 mL of deionized water are taken in a measuring cylinder, and rapidly stirred for 1 hour to form a uniform mixed solvent. 1.1 mL of concentrated sulfuric acid is measured in a measuring cylinder, and the concentrated sulfuric acid is slowly added to 50 mL of the above mixed solvent under rapid stirring. After stirring for 10 minutes, the concentrated sulfuric acid is transferred to a 100 mL volumetric flask, and the mixed solvent is continuously added to make up the volume to obtain a low-temperature molecular crowded electrolyte. The volume fraction of polyethylene glycol is 60%, and the concentration of the electrolyte is 0.2 mol / L.

[0041] The infrared spectrum of the low-temperature molecular crowded electrolyte of the present invention is obtained by Fourier transform infrared spectrometer. Figure 1 As shown, at wave numbers 3000 to 3700 cm -1 The hydroxyl characteristic peak between the two groups undergoes a red shift (moves to a lower wave number) due to the addition of polyethylene glycol. The area of ​​the left part of the characteristic peak increases, while the area of ​​the right part decreases accordingly, indicating that the hydrogen bonds between water molecules are destroyed by the molecular crowding agent.

[0042] The ionic conductivity of the electrolyte of the present invention at 25°C, 0°C, -20°C, -40°C, -60°C, and -80°C was obtained by electrochemical impedance spectroscopy. The results are as follows: Figure 2As shown, two platinum electrodes are used as working electrode and counter electrode, and silver / silver chloride is used as reference electrode.

[0043] Figure 2 The conductivity of the low-temperature electrolyte provided by the embodiment of the present invention changes with temperature. It can be seen from the figure that the conductivity of the low-temperature electrolyte decreases with decreasing temperature, and has a conductivity of 248.3 mS cm at 25°C. -1 High ionic conductivity, still maintains 3.02mS·cm at -60℃ -1 The electrical conductivity even exceeds the ionic conductivity of most aqueous electrolytes reported in the literature (such as the electrolyte of ZnSO4 plus H2O and ethylene glycol mentioned in the literature An aqueous hybrid electrolyte for low-temperature zinc-based energy storage devices) at low temperatures.

[0044] Example 2

[0045] The difference from Example 1 is that the volume fraction of polyethylene glycol is 20%.

[0046] Example 3

[0047] The difference from Example 1 is that the volume fraction of polyethylene glycol is 40%.

[0048] Example 4

[0049] The difference from Example 1 is that the volume fraction of polyethylene glycol is 80%.

[0050] Example 5

[0051] The difference from Example 1 is that the electrolyte is phosphoric acid, and the concentration of the electrolyte is 0.5 mol / L.

[0052] Example 6

[0053] The difference from Example 1 is that the molecular crowding agent is polyvinyl alcohol (average molecular weight is 9000) with a volume fraction of 50%.

[0054] Example 7

[0055] The difference from Example 1 is that the molecular crowding agent is polyvinyl pyrrolidone (average molecular weight is 8000) with a volume fraction of 70%.

[0056] Example 8

[0057] The difference from Example 1 is that the molecular crowding agent is polyethylene glycol dimethyl ether (average molecular weight is 1000) and the volume fraction is 60%.

[0058] Example 9

[0059] The difference from Example 9 is that the electrolyte is a mixture of phosphoric acid and sulfuric acid, the concentration of phosphoric acid is 0.1 mol / L, and the concentration of sulfuric acid is 0.5 mol / L.

[0060] Comparative Example 1

[0061] The difference from Example 1 is that the volume fraction of polyethylene glycol is 0%.

[0062] The low-temperature molecular crowded electrolytes of Examples 1-9 and Comparative Example 1 were applied to proton pseudocapacitors. The above electrolytes were tested in a three-electrode test system to obtain electrochemical data, including the above low-temperature molecular crowded electrolytes, electrodes, diaphragms, and reference electrodes; specifically, the electrodes, diaphragms, activated carbon membranes, and reference electrodes were placed in a Swagelok three-way cell, and then the molecular crowded electrolyte of this embodiment was slowly dripped, and the above three-electrode test system was obtained after packaging. Constant current charge and discharge tests and cycle tests were performed at 25°C, -20°C, -40°C, and -60°C.

[0063] Performance Testing:

[0064] (1) Constant current charge and discharge test: The constructed proton pseudocapacitor three-electrode test system was tested using the LAND battery test system, with a potential range of 0.2-1.1 V and a current density of 0.2 A g -1 ,0.5Ag -1 ,1Ag -1 ,2Ag -1 ,5Ag -1 ,8Ag -1 ,10Ag -1 For the tests under different low-temperature environments, the constructed three-electrode test system was first placed in a low-temperature refrigerator set at 25℃, 0℃, -20℃, -40℃, and -60℃ for 3 hours. After 3 hours, the three electrodes inside the refrigerator were connected using electrode test wires and relevant tests were completed.

[0065] (2) Cyclic performance test: voltage range 0.2-1.1V, current density 2A -1 , the number of cycles is 500. The test steps at different temperatures are the same as those of the constant current charge and discharge test.

[0066] According to the above test methods (1) and (2), the electrical properties of the low-temperature molecular crowded electrolytes provided in Examples 1 to 9 and Comparative Example 1 were tested at different temperatures. The test results are shown in Table 1.

[0067] Table 1

[0068]

[0069] As shown in Table 1, the low-temperature molecular crowded electrolyte in Example 1 has excellent specific capacity both at room temperature and at different low-temperature environments.

[0070] The above-mentioned embodiments are only specific implementations of the present invention. For ordinary technicians in this field, several modifications and improvements can be made within the technical scope of the present invention, which are all included in the protection scope of the present invention. The protection scope of the present invention shall be based on the claims.

Claims

1. A low temperature resistant molecular crowding electrolyte, characterized in that: A composite electrolyte composed of an inorganic acid, water and a molecular crowding agent, wherein the inorganic acid is one or more of sulfuric acid, phosphoric acid and hydrochloric acid, and the molecular crowding agent is polyethylene glycol, polyethylene glycol dimethyl ether, polyvinyl alcohol, polypropylene glycol, polyvinyl pyrrolidone, polyacrylamide or dextran.

2. The low temperature resistant molecular crowded electrolyte according to claim 1, characterized in that: The volume fraction of the molecular crowding agent is 10-90%.

3. The low temperature resistant molecular crowding electrolyte according to claims 1 and 2, characterized in that: The molecular crowding agent is polyethylene glycol, and the average molecular weight is 300.

4. The low temperature resistant molecular crowding electrolyte according to claim 1, characterized in that: The concentration of the inorganic acid is 0.1-0.5 mol / L.

5. The low temperature resistant molecular crowding electrolyte according to claim 4, characterized in that: The inorganic acid is sulfuric acid.

6. The low temperature resistant molecular crowded electrolyte according to claim 1, characterized in that: The freezing point of the electrolyte is lower than -80°C.

7. The low temperature resistant and low temperature resistant molecular crowded electrolyte according to claim 1, characterized in that: The method for preparing the low-temperature resistant molecular crowding electrolyte comprises the following steps: Step 1: At room temperature, mix the molecular crowding agent and water, and stir thoroughly to form a uniform composite solution; Step 2: Add the inorganic acid to the composite solution of step 1, and stir thoroughly to obtain a clear solution to form a uniform electrolyte.

8. Use of the low-temperature molecular crowded electrolyte according to claim 1 in a proton pseudocapacitor.

9. The use according to claim 8, characterized in that: The operating temperature of the proton pseudocapacitor is -60 to 25 °C.

10. The use according to claim 7, characterized in that: When the electrode material of the proton pseudocapacitor is copper hexacyanoferrate (III) electrode material, the maximum capacity of the proton pseudocapacitor at a low temperature of -60°C is 39 mAh g −1 , stable cycling at -40 ℃ for more than 500 times.

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