Deformation self-adaptive electrolyte as well as preparation method and application thereof

Abstract

The invention relates to a deformation self-adaptive electrolyte, a preparation method thereof and application of the deformation self-adaptive electrolyte in a water-based rechargeable magnesium metal battery. The electrolyte is in a gel state, and is prepared through ultraviolet initiation by taking water, magnesium salt, an additive and a polymer monomer as raw materials. The gel electrolyte not only has excellent flexibility and can spontaneously adapt to various deformations such as stretching, torsion and load bearing, but also can change the hydrogen bond environment of water molecules through the hydrogen bond interaction of polymer organic functional groups, effectively reduces the activity of water, and improves the water utilization rate. Therefore, the electrochemical stability window of the electrolyte is widened to 3.5 V or above, and the side reaction of a metal magnesium negative electrode is remarkably inhibited. The electrolyte disclosed by the invention is applied to the aqueous rechargeable magnesium metal battery, can effectively reduce polarization voltage, improve magnesium deposition / dissolution reversibility and prolong the cycle life of the battery, can bear various deformation effects and maintain the electrochemical performance of the battery, and has a wide application prospect. The electrolyte preparation method is simple, convenient, efficient and suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium secondary batteries, and in particular relates to a deformation adaptive electrolyte and a preparation method thereof, and application thereof in an aqueous rechargeable magnesium metal battery. Background Art

[0002] In recent years, electrochemical energy storage technologies represented by secondary batteries have developed rapidly. As a new energy storage technology with great potential, magnesium secondary batteries have the advantages of low cost, high volume energy density, low production of dendrites during magnesium deposition, and high safety. In particular, aqueous rechargeable magnesium metal batteries have significant advantages of intrinsic safety, green environmental protection, and low cost compared to non-aqueous rechargeable magnesium metal batteries that use organic electrolytes and require an anhydrous and oxygen-free assembly environment. However, the electrolyte used in aqueous rechargeable magnesium metal batteries faces the problems of narrow electrochemical window and easy corrosion of the metal magnesium negative electrode to produce ion-insulating Mg(OH) due to the presence of a large amount of water as a solvent. 2 The passivation layer increases polarization and thus prevents subsequent electrochemical reactions from occurring. Therefore, developing a new electrolyte system to achieve stable circulation of the magnesium negative electrode is the key to developing aqueous rechargeable magnesium metal batteries!

[0003] Existing studies have shown that salt-in-water electrolytes (ACS Energy Letters 2022, 7, 2657-2666) and water-in-solvent electrolytes (Advanced Energy Materials 2022, 12, 2103352) can effectively limit the solvent water network in aqueous rechargeable magnesium metal batteries, thereby widening the electrochemical window and achieving stable circulation of the magnesium metal negative electrode. However, the above-mentioned electrolyte system is at great risk of electrolyte leakage when subjected to external deformations such as stretching, torsion, and load-bearing, which seriously affects the stable circulation of the magnesium metal negative electrode and the battery life. Therefore, the development of an aqueous rechargeable magnesium metal battery electrolyte with deformation adaptability, a wide electrochemical window, and the ability to achieve stable circulation of the magnesium metal negative electrode is a technical problem that needs to be urgently solved in this field. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention aims to provide a deformation adaptive electrolyte and a preparation method thereof and an application in an aqueous rechargeable magnesium metal battery, so as to solve the technical problem that the existing aqueous rechargeable magnesium metal battery electrolyte system does not have deformation adaptive capability, while meeting the requirements of the aqueous rechargeable magnesium metal battery for a wide electrolyte electrochemical window and the ability to achieve stable circulation of the magnesium metal negative electrode.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A deformation - adaptive electrolyte, characterized in that the electrolyte is in a gel state and uses water, magnesium salt, additive, and polymer monomer as raw materials;

[0007] The magnesium salt is composed of one or more of magnesium chloride, magnesium sulfate, magnesium trifluoromethanesulfonate, magnesium perchlorate, and magnesium bromide, and its content is 5wt% - 20wt%;

[0008] The additive is one of 1 - butyl - 3 - methylimidazolium trifluoromethanesulfonate, 1 - ethyl - 3 - methylimidazolium bromide, N - methylformamide, triethylene glycol, acetonitrile, succinonitrile, and trimethyl phosphate, and its content is 1wt% - 3wt%;

[0009] The polymer monomer is composed of one or two of acrylamide, acrylic acid, and dimethylaminoethyl methacrylate, and its content is 10wt% - 40wt%;

[0010] Except for the above substances, the balance of the electrolyte raw materials is water.

[0011] The present invention also provides a preparation method of the deformation - adaptive electrolyte. Prepare materials according to the above components and ratios. The specific steps include:

[0012] ① Dissolve the magnesium salt and the additive in water, then add the polymer monomer, and fully mix them by magnetic stirring;

[0013] ② Pass nitrogen into the solution obtained in step ① for 20 min to remove dissolved oxygen, and obtain a precursor solution;

[0014] ③ Add a photoinitiator and a cross - linker to the precursor solution obtained in step ②, fully stir and mix them, and then drop them into a mold;

[0015] ④ Irradiate with ultraviolet light to initiate the polymerization of the raw materials in the mold, and thus obtain the deformation - adaptive electrolyte.

[0016] Further, the photoinitiator is 2 - hydroxy - 2 - methylpropiophenone, and the molar ratio of the photoinitiator to the polymer monomer is 1:200 - 1:50.

[0017] Further, the cross - linker is N,Nˊ - methylenebisacrylamide, and the molar ratio of the cross - linker to the polymer monomer is 1:200 - 1:50.

[0018] Further, the wavelength of the ultraviolet light is 280 - 365 nm, the power density is 10 - 20 mW cm -2 , the illumination time is 5 - 30 min, and the sample is 5 cm away from the light source.

[0019] The present invention also provides the application of the deformation - adaptive electrolyte in an aqueous rechargeable magnesium metal battery.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The electrolyte of the present invention is in a gel state and is composed of water, magnesium salt, additive and polymer. The cross-linked network of the polymer endows the electrolyte with excellent flexibility, which can spontaneously adapt to various deformations such as stretching, torsion and load-bearing; and the hydrogen bond interaction of the organic functional groups of the polymer can change the hydrogen bond environment of water molecules in the electrolyte, effectively reducing the water activity, thereby broadening the electrochemical stability window of the electrolyte to more than 3.5V and significantly inhibiting the side reactions of the magnesium metal negative electrode.

[0022] (2) The electrolyte of the present invention not only has the significant advantages of intrinsic safety, environmental friendliness and low cost of aqueous electrolytes, but also avoids the defects of easy leakage and lack of deformation adaptability of aqueous electrolytes. When it is applied to aqueous rechargeable magnesium metal batteries, it can effectively reduce the polarization voltage, improve the reversibility of magnesium deposition / dissolution, extend the cycle life of the battery, and can withstand various deformation effects while maintaining its electrochemical performance, making it suitable for various scenarios.

[0023] (3) The method for preparing the deformation self-adaptive electrolyte of the present invention is simple and efficient, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the infrared spectrogram of the electrolyte prepared in Example 1 of the present invention and its monomer;

[0025] Figure 2 It is the tensile stress-strain curve of the electrolyte prepared in Example 1 of the present invention;

[0026] Figure 3 It is the deformation schematic diagram of the electrolyte prepared in Example 1 of the present invention under different mechanical actions;

[0027] Figure 4 It is the electrochemical stability window of the electrolyte prepared in Example 1 of the present invention;

[0028] Figure 5 It is the polarization curve of the magnesium metal negative electrode in the electrolyte prepared in Example 1;

[0029] Figure 6 It is the constant current charge-discharge curve of the magnesium-magnesium symmetric battery assembled with the electrolyte prepared in Example 1 of the present invention in the original state;

[0030] Figure 7 It is the constant current charge-discharge curve of the magnesium-magnesium symmetric battery assembled with the electrolyte prepared in Example 1 of the present invention after being folded 180°;

[0031] Figure 8 It is the electrochemical stability window of the electrolyte in Comparative Example 1;

[0032] Figure 9 is the polarization curve of the magnesium metal anode in the electrolyte of Comparative Example 1;

[0033] Figure 10 is the constant current charge-discharge curve of the magnesium-magnesium symmetric battery using the electrolyte of Comparative Example 1. Detailed Implementation Modes

[0034] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are only used to illustrate the present invention, rather than to limit the present invention. Any improvement to the method under the premise of the concept of the present invention belongs to the scope of protection required by the present invention.

[0035] Example 1:

[0036] I. Preparation of Deformation Adaptive Electrolyte

[0037] First, weigh magnesium chloride, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, polymer monomer acrylamide, and water in a mass ratio of 5:1:10:34. Dissolve magnesium chloride and 1-butyl-3-methylimidazolium trifluoromethanesulfonate in water, then add acrylamide, and mix them evenly by magnetic stirring. Then, introduce nitrogen for 20 min to remove dissolved oxygen to obtain a precursor solution. Then, add a photoinitiator and a crosslinking agent to the precursor solution according to a molar ratio of 2-hydroxy-2-methylpropiophenone (photoinitiator 1173), N,N′-methylenebisacrylamide (crosslinking agent MBA) to acrylamide of 1:1:100, and stir to dissolve and disperse them evenly to form a mixed solution. Finally, drop the mixed solution into a mold, place it under an ultraviolet light irradiation device (wavelength 365 nm, power density 15 mW cm -2 ), and react for 10 minutes at a distance of 5 cm from the light source to ensure that the polymerization reaction proceeds sufficiently, thereby obtaining a polyacrylamide gel electrolyte.

[0038] II. Characterization and Testing Methods

[0039] 1. Infrared Spectroscopy Characterization

[0040] Analyze the structural information of the raw materials and the electrolyte of the present invention by infrared spectroscopy, and the measurement range is 400 - 4000 cm -1 .

[0041] 2. Tensile Property Measurement

[0042] The tensile property is tested at room temperature using an electronic universal testing machine. Prepare dumbbell-shaped electrolytes, clamp them on the testing machine fixture for testing, and set the tensile speed to 100 mm / min. The tensile strain is defined as the ratio of the length at tensile fracture to the initial length.

[0043] 3. Conductivity Measurement

[0044] The ionic conductivity σ (S cm -1 ) of the electrolyte of the present invention was measured by electrochemical impedance spectroscopy. According to calculation, where L (cm) is the thickness of the electrolyte, S (cm 2 ) is the contact area between the electrode and the electrolyte, and R (Ω) is the bulk resistance of the gel (obtained by electrochemical impedance spectroscopy). When testing, the AC amplitude was set to 5 mV, and the measurement range was 10 5 Hz to 0.1 Hz.

[0045] 4. Measurement of the electrochemical stability window

[0046] The electrochemical stability window was measured by linear sweep voltammetry (LSV) on a Shanghai Chenhua CHI 660e electrochemical workstation. The measurement was carried out through a three-electrode system. A three-electrode system was assembled with a glassy carbon electrode as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum wire as the counter electrode. The scanning rate was 1 mV / s, and the potential range between the current densities of ±0.1 mA cm -2 was taken as the electrochemical stability window of the electrolyte.

[0047] 5. Measurement of the corrosion current density

[0048] The natural corrosion current density of the magnesium metal negative electrode in the electrolyte was measured by a steady-state polarization curve. The test was carried out on a Shanghai Chenhua CHI 660e electrochemical workstation. A symmetrical cell was assembled for testing, with a clean magnesium foil as the working electrode and the counter electrode. The test range was the open-circuit potential ±300 mV, and the scanning rate was 1 mV / s. The natural corrosion current density of the magnesium foil in the electrolyte was obtained by extrapolating the polarization curve.

[0049] 6. Test of magnesium deposition / dissolution performance

[0050] The magnesium deposition / dissolution performance was detected by constant current charge-discharge testing. The test was carried out on a Neware charge-discharge test system. A symmetrical cell was assembled with a magnesium metal foil as the working electrode and the counter electrode, and constant current charge-discharge testing was carried out under the condition of 0.05 mA cm -2 to determine the polarization voltage and cycle life of magnesium deposition / dissolution.

[0051] 7. Test of the performance of the full cell

[0052] A full cell was assembled with a magnesium metal foil as the negative electrode, CuHCF as the positive electrode active material, and the electrolyte. After being placed for 24 h, performance testing was carried out. The constant current charge-discharge testing was carried out on a Neware charge-discharge test system, and the current was constant at 0.05 A g -1 .

[0053] III. Characterization and test results

[0054] The electrolyte prepared in Example 1 was tested using the above test method, and the test results are as follows:

[0055] The electrolyte and its monomer were characterized by infrared spectroscopy. As Figure 1 shown, compared with the raw material monomers of the polymer gel electrolyte of the present invention, the characteristic absorption peak of the unsaturated hydrocarbon group in acrylamide (CH 2 =CH-CO-NH 2 ) was transformed into the absorption peak of the saturated hydrocarbon group, indicating the successful polymerization of acrylamide.

[0056] The tensile properties of the electrolyte were measured. It can be seen from Figure 2 that the maximum elongation at break of the electrolyte of the present invention is 730%, and the elastic modulus is 0.01 MPa. Further, Figure 3 it shows that the electrolyte of the present invention can withstand stretching, torsion, and load-bearing conditions without breaking, indicating its excellent flexibility.

[0057] The ionic conductivity of the electrolyte was measured. It can be seen from Table 4 that its conductivity is about 10.78 mS cm -1 . Further, it can be seen from Figure 4 that its electrochemical stability window is as high as 3.53 V; it can be seen from Figure 5 that the electrolyte can reduce the natural corrosion current density (i corr ) of magnesium to 2.868×10 -5 A cm -2 .

[0058] The electrolyte was assembled into a magnesium-magnesium symmetric battery for testing. Figure 6 It shows that during the constant current charge and discharge process of 330 hours, the polarization voltage remains within 0.3 V; it can be seen from Figure 7 that after folding the symmetric battery by 180° and testing, it can still maintain a high cycle life of 300 h, indicating that the electrolyte of the present invention endows the battery with excellent deformation adaptability. Further, when assembled with the CuHCF positive electrode material into a full battery, the capacity at 0.05 A g -1 is 120 mAh g -1 , demonstrating the successful application of the electrolyte of the present invention in aqueous rechargeable magnesium metal batteries.

[0059] Examples 2-7:

[0060] Examples 2-7 are the same as Example 1 in terms of the electrolyte preparation steps and performance test methods, but the compositions and dosages of various substances and the preparation conditions are different. Therefore, the performance test results are different. Specifically, please refer to Tables 1-4 respectively.

[0061] Table 1. Dosages of magnesium salts and additives in each example

[0062]

[0063] Table 2. Composition of polymer monomers, initiators, and crosslinking agents in each example

[0064]

[0065] Table 3. Photopolymerization conditions in each example

[0066]

[0067] Table 4. Performance test results of each example

[0068]

[0069]

[0070] Comparative Example 1

[0071] Comparative Example 1 is an aqueous magnesium chloride electrolyte with the same concentration as in Example 1. It does not have deformation self-adaptive ability; the electrochemical stability window of this electrolyte is only 2.67 V ( Figure 8 ); the corrosion current density of the magnesium metal negative electrode is as high as 5.916×10 -4 A cm -2 ( Figure 9 ), about 20 times the corrosion rate in Example 1; the polarization voltage of the magnesium-magnesium symmetric battery assembled with this electrolyte exceeded 0.5 V ( Figure 10 ) after only less than 20 h of cycling and could not be applied to full cells.

[0072] In summary, by comparing the results of the above examples and comparative examples, it can be concluded that the deformation self-adaptive electrolyte of the present invention not only has excellent flexibility and can spontaneously adapt to various deformations such as stretching, torsion, and load-bearing, but also the hydrogen bond interaction of its polymer organic functional groups can change the hydrogen bond environment of water molecules, effectively reducing the water activity, thereby broadening the electrochemical stability window of the electrolyte to more than 3.5 V and significantly inhibiting the side reactions of the magnesium metal negative electrode.

[0073] When the deformation self-adaptive electrolyte of the present invention is applied to aqueous rechargeable magnesium metal batteries, it can effectively reduce the polarization voltage, improve the reversibility of magnesium deposition / dissolution, extend the cycle life of the battery, and can withstand various deformation effects while maintaining its electrochemical performance, showing broad application prospects. The preparation method of the present invention is simple and efficient and suitable for large-scale production.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the purpose and scope of the present technical solutions shall be covered within the scope of the claims of the present invention.

Claims

1. A deformation adaptive electrolyte, characterized in that: The electrolyte is in a gel state and is made of water, magnesium salt, additives and polymer monomers; The magnesium salt is one or more of magnesium chloride, magnesium sulfate, magnesium trifluoromethanesulfonate, magnesium perchlorate, and magnesium bromide, and its content is 5 wt% to 20 wt%; The additive is one of 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium bromide, N-methylformamide, triethylene glycol, acetonitrile, succinonitrile, and trimethyl phosphate, and the content thereof is 1 wt% to 3 wt%; The polymer monomer is one or two of acrylamide, acrylic acid, and dimethylaminoethyl methacrylate, and the content thereof is 10 wt% to 40 wt%; The electrolyte raw material, in addition to the above substances, has water as the balance.

2. A method for preparing a deformation adaptive electrolyte, characterized in that: The ingredients and proportions are prepared according to claim 1, and the specific steps include: ① Dissolve the magnesium salt and additives in water, then add the polymer monomer and mix them thoroughly by magnetic stirring; ② Passing nitrogen gas into the solution obtained in step ① for 20 min to remove dissolved oxygen to obtain a precursor solution; ③ Add a photoinitiator and a crosslinking agent to the precursor solution obtained in step ②, stir and mix thoroughly, and then drop into the mold; ④Ultraviolet light irradiation triggers the polymerization of raw materials in the mold to obtain a deformation adaptive electrolyte.

3. The method for preparing the deformation adaptive electrolyte according to claim 2, characterized in that: The photoinitiator is 2-hydroxy-2-methylpropiophenone, and the molar ratio of the photoinitiator to the polymer monomer is 1:200-1:

50.

4. The method for preparing the deformation adaptive electrolyte according to claim 2, characterized in that: The crosslinking agent is N,N'-methylenebisacrylamide, and the molar ratio of the crosslinking agent to the polymer monomer is 1:200-1:

50.

5. The method for preparing the shape-adaptive electrolyte according to claim 2, characterized in that: The wavelength of the ultraviolet light is 280-365 nm, and the power density is 10-20 mW cm -2 The illumination time was 5~30 min and the sample was 5 cm away from the light source.

6. Application of a deformation adaptive electrolyte in an aqueous rechargeable magnesium metal battery, characterized in that: The electrolyte obtained by any preparation method according to claims 2-5 is applied to aqueous rechargeable magnesium metal batteries.

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