Low-temperature fluorine-containing magnesium-chargeable battery electrolyte, preparation method and application thereof

Abstract

This invention relates to the field of electrochemical technology and discloses a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, comprising a magnesium salt, a main solvent, and a composite additive. The composite additive is a mixed solution of an amine solvent and a fluorinated ether solvent. The concentration of the magnesium salt is 0.1-1.0 mol / L, and the volume ratio of the main solvent to the composite additive is (2-3.3):1. The preparation method includes the following steps: S1: Weigh a certain amount of magnesium salt and dissolve it in the main solvent, stirring for 6-8 hours to form solution A; S2: Slowly add the fluorinated ether solvent to solution A in S1, stirring for 6-8 hours to form solution B; S3: Add the amine solvent to solution B in S2, stirring for 6-8 hours to obtain the low-temperature fluorine-containing rechargeable magnesium battery electrolyte. Its application: The application of a low-temperature fluorine-containing rechargeable magnesium battery electrolyte in rechargeable magnesium batteries. The technical solution of this invention can improve the reversible magnesium deposition and dissolution performance of the electrolyte, and also improve the performance of Mg at low temperatures. 2+ The transport dynamics and ionic conductivity.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, specifically to a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, its preparation method, and its application. Background Technology

[0002] Energy security is the lifeline of a nation. Achieving safe, reliable, and low-cost energy storage technologies is fundamental to achieving energy transition. As one of the countries richest in magnesium resources, my country possesses 70% of the world's magnesium reserves, providing a solid resource guarantee for the development of rechargeable magnesium batteries. Metallic magnesium has a high theoretical specific capacity, while also offering advantages such as high safety and low cost, making magnesium batteries a powerful disruptor in the battery industry.

[0003] With the rapid development of new energy vehicles, the requirements for battery performance are constantly increasing, among which the ability to operate in low-temperature environments has become one of the key indicators for measuring the level of battery technology. Electrolyte, as an important component of rechargeable magnesium batteries, is widely regarded as a key factor limiting the ionic conductivity and stability of magnesium-ion batteries at low temperatures. Because Mg... 2+ Desolvation process and Mg at the electrode-electrolyte interface 2+ Magnesium ion transport is subject to a high energy barrier, resulting in slow transport kinetics. Therefore, the selection of the main solvent and additives in the electrolyte is crucial. Ether-based organic solvents, with their low freezing point, low viscosity, and weak solvation energy, are often used as solvents for low-temperature electrolytes in magnesium-ion batteries. However, weakly solvable ether solvents have poor solubility for magnesium salts, making it difficult to achieve efficient and reversible deposition and dissolution of magnesium. To address the problem of reversible deposition and dissolution of magnesium in magnesium salts using ether solvents, amine solvents with strong solvation capabilities are typically introduced to promote the formation of an effective electrode-electrolyte interface, thereby achieving efficient and reversible deposition and dissolution of magnesium. However, the high viscosity and high desolvation energy resulting from strong solvation capabilities of amine solvents can affect the deposition and dissolution of magnesium at low temperatures. 2+ The transport dynamics lead to a decrease in ionic conductivity. Summary of the Invention

[0004] This invention aims to provide a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, its preparation method, and its applications. This electrolyte can improve the reversible magnesium deposition and dissolution performance at low temperatures, and also enhance the performance of Mg at low temperatures. 2+ The transport dynamics and ionic conductivity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, comprising magnesium salt, main solvent and composite additive, wherein the composite additive is a mixed solution of amine solvent and fluorine-containing ether solvent, the concentration of magnesium salt is 0.1-1.0 mol / L, and the volume ratio of main solvent to composite additive is (2-3.3):1.

[0006] Preferably, the volume ratio of amine solvent to fluorinated ether solvent in the composite additive is (1.6-4):1.

[0007] Preferably, the magnesium salt is any one or a combination of two of magnesium trifluoromethanesulfonate and magnesium bis(trifluoromethanesulfonyl)imide.

[0008] Preferably, the main solvent is any one or a combination of several of ethylene glycol dimethyl ether, tetrahydrofuran, and diethylene glycol dimethyl ether.

[0009] Preferably, the amine solvent is any one or a combination of several of 2-methoxyethylamine, N-methyl-2-methoxyethylamine, 2,2-dimethoxyethylamine, 1-methoxy-2-propaneamine, and 3-propoxyethylamine.

[0010] Preferably, the fluorinated ether solvent is any one or a combination of several of the following: ethyl nonafluorobutyl ether, methyl nonafluorobutyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, perfluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, ethyl 1,1,2,3,3,3-hexafluoropropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether.

[0011] This application also provides another technical solution, a method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, comprising the following steps:

[0012] S1: Weigh a certain amount of magnesium salt and dissolve it in the main solvent, stir for 6-8 hours to form solution A;

[0013] S2: Slowly add a fluorinated ether solvent to solution A in S1 and stir for 6-8 hours to form solution B;

[0014] S3: Add an amine solvent to solution B in S2 and stir for 6-8 hours to obtain a low-temperature fluorine-containing rechargeable magnesium battery electrolyte.

[0015] Preferably, the operations of S1-S3 are all carried out at 25°C in a glove box filled with inert gas, and the water and oxygen content in the box is less than 0.01 ppm.

[0016] Preferably, the process further includes pretreatment of the main solvent, fluorinated ether solvent, and amine solvent; the specific pretreatment process is as follows: mixing the main solvent, fluorinated ether solvent, or amine solvent with metallic sodium, redistilling under an inert atmosphere, and adding a high-temperature activated solvent to the distilled solvent. Type of molecular sieve, sealed and stored under an inert atmosphere.

[0017] The present invention also provides another technical solution: the application of a low-temperature fluorine-containing rechargeable magnesium battery electrolyte in rechargeable magnesium batteries.

[0018] Compared with existing technologies, the beneficial effects of this solution are as follows:

[0019] (1) Due to the poor solubilization ability of ether solvents for magnesium salts, the solubility of magnesium salts in them is relatively low. Compared with ester and nitrile solvents, ether solvents have better compatibility with magnesium anodes, but certain problems still exist. For example, pure ether solvents are difficult to achieve reversible magnesium deposition and dissolution in magnesium salts. To address this, amine solvents with strong solubilization ability can be added, which can not only improve the solubility of magnesium salts but also form N-rich organic components on the electrode surface, which is beneficial to the transport of magnesium ions at the interface. However, the strong solubilization of amine solvents will increase the viscosity of the electrolyte, which is not conducive to the ionic conductivity at low temperatures. Therefore, by adding fluorinated ether solvents, their low melting point and low polarity can be utilized to further promote the generation of inorganic components at the electrode / electrolyte interface through their synergistic reduction effect with anions in magnesium salts, thereby improving the migration ability and ionic conductivity of magnesium ions at low temperatures. Thus, it can be seen that the fluorinated low-temperature rechargeable magnesium battery electrolyte provided by this technical solution can improve the reversible magnesium deposition and dissolution performance of the electrolyte, and at the same time, it can also improve the Mg at low temperatures. 2+ The transport dynamics and ionic conductivity.

[0020] (2) The present invention provides a fluorine-containing low-temperature rechargeable magnesium battery electrolyte. The ionic conductivity of the SS‖SS half-cell using fluorine-containing ether solvent at -20℃ can reach 3.05mS / cm, which is much higher than that of the electrolyte without fluorine ether solvent. This indicates that the fluorine-containing low-temperature rechargeable magnesium battery electrolyte can significantly improve the ionic conductivity of the electrolyte.

[0021] (3) This invention provides a fluorine-containing low-temperature rechargeable magnesium battery electrolyte, which enables magnesium-ion batteries to operate stably at low temperatures. For example, at -20°C, the Mg||Mg symmetric cell operates at 0.5 mA / cm². 2 Cyclic testing was conducted at the specified current density, and the battery could cycle stably for 200 hours without a significant increase in polarization potential. The deposition overpotential was low at 269mV, indicating that the fluorine-containing low-temperature rechargeable magnesium battery electrolyte has excellent compatibility and stability with magnesium.

[0022] (4) This invention provides a fluorine-containing low-temperature rechargeable magnesium battery electrolyte. In a Mg‖SS battery using a fluorine-containing ether solvent at -20°C, the coulombic efficiency of reversible magnesium deposition and dissolution gradually increases, reaching 89.29% in the first cycle and an average coulombic efficiency of 99.76%. In a Mg‖SS battery without a fluorine-containing ether solvent, the coulombic efficiency in the first cycle reaches 77.26%, with an average coulombic efficiency of 99.75%. This indicates that the fluorine-containing ether solvent electrolyte has a significant advantage in first-cycle coulombic efficiency, suggesting that it provides better performance during initial battery use, is more conducive to reversible magnesium deposition and dissolution, or can more quickly form a stable electrode-electrolyte interface.

[0023] (5) By setting the volume ratio of the main solvent to the composite additive to (2-3.3):1, this technical solution can improve the reversible magnesium deposition and dissolution performance of the electrolyte on the one hand, and improve the cycle stability of the electrolyte on the other hand. If the volume ratio of the main solvent to the composite additive is greater than 3.3:1, the reversible magnesium deposition and dissolution performance of the electrolyte will deteriorate. If the volume ratio of the main solvent to the composite additive is less than 2:1, the cycle stability of the electrolyte will deteriorate.

[0024] (6) This technical solution can remove water from the main solvent, fluorinated ether solvent and amine solvent by pretreatment. At the same time, the generated sodium ions are insoluble in organic solvents and are removed by redistillation. This technical solution can optimize ionic conductivity, stabilize electrode interface and reduce side reactions by removing water from organic solvents.

[0025] (7) This invention provides a method for preparing a fluorine-containing low-temperature rechargeable magnesium battery electrolyte, which is prepared by mixing and stirring a simple magnesium salt, a main solvent and a composite additive at room temperature. The preparation method is simple, the raw materials are readily available, the cost is low, and it is conducive to large-scale production. Attached Figure Description

[0026] Figure 1 The electrochemical impedance curve of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 of this invention at -20°C;

[0027] Figure 2 The electrochemical impedance curve of the low-temperature rechargeable magnesium battery electrolyte prepared in Comparative Example 1 of this invention at -20°C;

[0028] Figure 3 Cyclic voltammetry curve of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 of this invention at -20°C;

[0029] Figure 4 The low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 of this invention is at 0.5 mA / cm2 Coulombic efficiency of reversible magnesium deposition / dissolution at -20°C under current density;

[0030] Figure 5 The low-temperature rechargeable magnesium battery electrolyte prepared for Comparative Example 1 of this invention is at 0.5 mA / cm 2 Coulombic efficiency of reversible magnesium deposition / dissolution at -20°C under current density;

[0031] Figure 6 The Mg|Mg symmetric battery assembled with the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 of this invention operates at 0.5 mA / cm². 2 Polarization performance curve at -20℃ under current density;

[0032] Figure 7 The cyclic voltammetry curve of the low-temperature rechargeable magnesium battery electrolyte prepared in Comparative Example 2 of this invention at -20°C. Detailed Implementation

[0033] The following detailed description illustrates the specific implementation method:

[0034] Example 1

[0035] A low-temperature fluorine-containing rechargeable magnesium battery electrolyte includes a magnesium salt, a main solvent, and a composite additive. The composite additive is a mixed solution of an amine solvent and a fluorinated ether solvent. The concentration of the magnesium salt is 0.1-1.0 mol / L, the volume ratio of the main solvent to the composite additive is (2-3.3):1, and the volume ratio of the amine solvent to the fluorinated ether solvent in the composite additive is (1.6-4):1. In this embodiment, the concentration of the magnesium salt is 0.5 mol / L, the volume ratio of the main solvent to the composite additive is 4.5:1.4, and the volume ratio of the amine solvent to the fluorinated ether solvent in the composite additive is 1.8:1.

[0036] The magnesium salt is any one or a combination of two of magnesium trifluoromethanesulfonate and magnesium bis(trifluoromethanesulfonyl)imide; in this embodiment, the magnesium salt is magnesium bis(trifluoromethanesulfonyl)imide.

[0037] The main solvent is any one or a combination of several of ethylene glycol dimethyl ether, tetrahydrofuran, and diethylene glycol dimethyl ether; in this embodiment, the main solvent is ethylene glycol dimethyl ether.

[0038] The amine solvent is any one or a combination of several of 2-methoxyethylamine, N-methyl-2-methoxyethylamine, 2,2-dimethoxyethylamine, 1-methoxy-2-propylamine, and 3-propoxyethylamine; in this embodiment, the amine solvent is 2-methoxyethylamine.

[0039] The fluorinated ether solvent is any one or a combination of several of the following: ethyl nonafluorobutyl ether, methyl nonafluorobutyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, perfluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, ethyl 1,1,2,3,3,3-hexafluoropropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether; in this embodiment, the fluorinated ether solvent is methyl nonafluorobutyl ether.

[0040] A method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte includes the following steps:

[0041] S1: Weigh a certain amount of magnesium salt and dissolve it in the main solvent. Stir magnetically for 6-8 hours at a speed of 400 r / min to form solution A. In this example, weigh 1.7245 g of Mg(TFSI)2 and dissolve it in 4.5 mL of ethylene glycol dimethyl ether. Stir magnetically for 6 hours at a speed of 400 r / min to form solution A.

[0042] S2: Slowly add a fluorinated ether solvent to solution A in S1, and stir magnetically for 6-8 hours at a speed of 400 r / min to form solution B. In this embodiment, 0.5 mL of methyl nonafluorobutyl ether is slowly added to solution A in S1, and the mixture is stirred magnetically for 6 hours at a speed of 400 r / min to form solution B.

[0043] S3: Add an amine solvent to solution B in S2, and stir magnetically for 6-8 hours at a speed of 400 r / min to obtain a low-temperature fluorine-containing rechargeable magnesium battery electrolyte. In this embodiment, 0.9 mL of 2-methoxyethylamine is added to solution B in S2, and the mixture is stirred magnetically for 6 hours at a speed of 400 r / min to obtain a low-temperature fluorine-containing rechargeable magnesium battery electrolyte.

[0044] The operations of S1-S3 are all carried out at 25°C in a glove box filled with inert gas. The water and oxygen content in the box is less than 0.01 ppm. In this embodiment, the inert gas is argon.

[0045] This also includes pretreatment of the main solvent, fluorinated ether solvents, and amine solvents; the specific pretreatment process is as follows: the main solvent, fluorinated ether solvent, or amine solvent is mixed with metallic sodium, redistilled under an inert atmosphere, and high-temperature activated solvent is added to the distilled solvent. The molecular sieve was sealed and stored under an inert atmosphere. In this embodiment, the specific pretreatment process was as follows: 50 mL of ethylene glycol dimethyl ether, methyl nonafluorobutyl ether, or 2-methoxyethylamine was added to a container, along with 1.5 g of metallic sodium. The mixture was redistilled under an argon atmosphere, and the solvent that had been activated at 350°C for 15 hours was added to the distilled solvent. The molecular sieve was sealed and stored under an argon atmosphere.

[0046] The prepared low-temperature fluorine-containing rechargeable magnesium battery electrolyte can be used in rechargeable magnesium batteries.

[0047] Examples 1-6 prepared various low-temperature fluorine-containing rechargeable magnesium battery electrolytes according to the electrolyte preparation raw materials and their amounts shown in Table 1, and according to the preparation method of Example 1.

[0048] The raw materials and amounts used for preparing the electrolytes in Examples 1-6 are shown in Table 1.

[0049] Table 1

[0050]

[0051] Comparative Example 1

[0052] Unlike Example 1, a low-temperature fluorine-containing rechargeable magnesium battery electrolyte contains only 2-methoxyethylamine as a composite additive and does not contain methyl nonafluorobutyl ether. The volume ratio of ethylene glycol dimethyl ether to 2-methoxyethylamine is 5:1. A method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte does not include S2. In S1, the amount of Mg(TFSI)2 added is 1.5784 g, and the volume of ethylene glycol dimethyl ether is 4.5 mL. In S3, the volume of 2-methoxyethylamine is 0.9 mL.

[0053] Comparative Example 2

[0054] Unlike Example 1, a low-temperature fluorine-containing rechargeable magnesium battery electrolyte contains only methyl nonafluorobutyl ether as a composite additive and does not contain 2-methoxyethylamine. The volume ratio of ethylene glycol dimethyl ether to methyl nonafluorobutyl ether is 9:1. A method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte does not include S3. In S1, the amount of Mg(TFSI)2 added is 1.4615g, and the volume of ethylene glycol dimethyl ether is 4.5mL. In S2, the amount of methyl nonafluorobutyl ether added is 0.5mL.

[0055] Comparative Example 3

[0056] Unlike Example 1, a low-temperature fluorine-containing rechargeable magnesium battery electrolyte has a magnesium bis(trifluoromethanesulfonyl)imide concentration of 0.05 mol / L; a method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, in S1, 0.1725 g of Mg(TFSI)2 is weighed.

[0057] Comparative Example 4

[0058] Unlike Example 1, a low-temperature fluorine-containing rechargeable magnesium battery electrolyte has a magnesium bis(trifluoromethanesulfonyl)imide concentration of 1.2 mol / L; a method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, in S1, 4.1404 g of Mg(TFSI)2 is weighed.

[0059] Comparative Example 5

[0060] Unlike Example 1, a low-temperature fluorine-containing rechargeable magnesium battery electrolyte has a volume ratio of 2-methoxyethylamine to methylnonafluorobutyl ether of 1:1; a method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte includes S2, in which 0.7 ml of methylnonafluorobutyl ether is added, and in S3, 0.7 ml of 2-methoxyethylamine is added.

[0061] Comparative Example 6

[0062] Unlike Example 1, a low-temperature fluorine-containing rechargeable magnesium battery electrolyte has a volume ratio of 2-methoxyethylamine to methylnonafluorobutyl ether of 6:1; a method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, wherein in S2, the amount of methylnonafluorobutyl ether added is 0.2 ml, and in S3, the amount of 2-methoxyethylamine added is 1.2 ml.

[0063] Electrochemical performance tests of the low-temperature fluorine-containing rechargeable magnesium battery electrolytes prepared in Examples 1-6 and Comparative Examples 1-6:

[0064] The ionic conductivity and reversible magnesium deposition dissolution performance of the electrolyte were obtained by electrochemical impedance spectroscopy and cyclic voltammetry, respectively. Specifically, a two-electrode system was used, with a magnesium sheet (Φ12mm) electrode as the reference and counter electrode, and a stainless steel foil (SS, Φ16mm) electrode as the working electrode, or a stainless steel foil (SS, Φ16mm) electrode as the counter, reference, and working electrode. For electrochemical impedance spectroscopy, the test frequency was 100,000 Hz–0.01 Hz, the applied excitation signal was 5 mV, and the test temperature was -20℃. For cyclic voltammetry, the test potential was -1V–2V, the scan rate was 25 mV / s, the test temperature was -20℃, and the scan was performed from the negative direction of the open-circuit voltage. In addition, all electrodes were alternately cleaned three times with ethanol and deionized water to remove impurities from the entire electrode surface. After vacuum drying for 12 hours, the cleaned electrodes were placed in a glove box for later use.

[0065] The coulombic efficiency and charge-discharge characteristics of magnesium in electrolyte were investigated using constant current charge-discharge tests on assembled CR2032 coin cells. Specifically, assembly was performed in an inert atmosphere glove box with water and oxygen content both less than 0.01 ppm; the working electrode was polished stainless steel foil (SS), while the counter and reference electrodes were polished magnesium sheets, and the separator was a GF / A membrane; after assembly, the cells were allowed to stand at room temperature for 12 hours before testing; the entire testing process was conducted on a Newway charge-discharge testing system, with a discharge current density of 0.1 mA / cm². 2 -1.0mA / cm 2 Time-controlled discharge (1 hour); charging current density is 0.1 mA / cm². 2 -1.0mA / cm 2 Voltage control is employed (charging to 1.2V vs. MgRE).

[0066] (1) Electrolyte conductivity test at low temperature

[0067] The conductivity of the electrolyte was obtained by analyzing electrochemical impedance spectroscopy (EIS). EIS measurements were performed on a Chi660e electrochemical workstation. CR2032 coin cells were assembled and tested in an inert atmosphere glove box (water and oxygen content both less than 0.01 ppm). Stainless steel foil (SS, Φ16 mm) was used as the counter electrode, reference electrode, and working electrode, and a GF / A membrane was used as the separator. CR2032 coin cells were assembled together with the low-temperature fluorine-containing rechargeable magnesium battery electrolytes prepared in Example 1 and Comparative Example 1, respectively. The applied excitation signal was 5 mV, the test frequency range was 100000 Hz to 0.01 Hz, and the test temperature was controlled at -20 °C. The bulk resistance Rs (Ω) of the electrolyte was obtained from the impedance spectra, and the conductivity was calculated using the following formula:

[0068] σ=l / SRs

[0069] In the formula, σ is the conductivity of the electrolyte (S / cm);

[0070] l represents the electrolyte thickness (mm);

[0071] S is the contact area between the electrolyte and the electrode (cm²). 2 );

[0072] Rs is the bulk resistance of the electrolyte (Ω);

[0073] The test results of Example 1 and Comparative Example 1 are as follows: Figure 1 , Figure 2As shown, and calculated using the formula σ = l / SRs, the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 has an ionic conductivity of 3.05 mS / cm at -20℃; the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Comparative Example 1 has an ionic conductivity of 1.62 mS / cm at -20℃. This indicates that the combination of fluorinated ether solvents and amine solvents can significantly improve the conductivity of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte.

[0074] (2) Cyclic voltammetry test at -20℃

[0075] The reversible magnesium deposition and dissolution performance of the low-temperature fluorine-containing rechargeable magnesium battery electrolytes prepared in Example 1 and Comparative Example 2 at -20°C was tested on a stainless steel working electrode using the above test method. The test results are as follows: Figure 3 , Figure 7 As shown, the results indicate that, using stainless steel SS as the working electrode, the dissolution current density of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 at -20℃ is 3.98 mA / cm² in the first cycle. 2 The results showed that the electrolyte could reversibly deposit and dissolve magnesium at -20℃; while the electrolyte in Comparative Example 2, which did not contain amine solvents, could not achieve reversible deposition and dissolution of magnesium.

[0076] (3) Coulomb efficiency test at -20℃

[0077] The coulombic efficiency of the low-temperature fluorine-containing rechargeable magnesium battery electrolytes prepared in Example 1 and Comparative Example 1 at -20°C was tested on a stainless steel working electrode using the above-described test method. The test results are as follows: Figure 4 , Figure 5 As shown, the results indicate that the coulombic efficiency of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte (Mg‖SS battery) prepared in Example 1 gradually increases, reaching 89.29% in the first cycle and an average coulombic efficiency of 99.76% after 1000 stable cycles. In contrast, the low-temperature rechargeable magnesium battery electrolyte prepared in Comparative Example 1 achieves a coulombic efficiency of 77.26% in the first cycle and an average coulombic efficiency of 99.75% after 1000 stable cycles. Therefore, the electrolyte prepared in Example 1 exhibits a significant advantage in first-cycle coulombic efficiency, indicating that it provides better performance during initial battery use, is more conducive to reversible magnesium deposition and dissolution, or can more quickly form a stable electrode-electrolyte interface.

[0078] (4) Polarization performance test at -20℃

[0079] The polarization performance of the symmetrical Mg‖Mg battery assembled with the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 was tested at -20℃ using the above test method. The test results are as follows: Figure 6As shown, the results indicate that at a current density of 0.5 mA / cm², 2 The battery cycled stably for 200 hours without a significant increase in polarization potential, and the deposition overpotential remained low at 269 mV. These results indicate that the electrolyte exhibits excellent compatibility and stability with magnesium.

[0080] (5) Electrochemical performance test at -20℃

[0081] The electrochemical performance of the low-temperature fluorine-containing rechargeable magnesium battery electrolytes prepared in Examples 1-6 and Comparative Examples 1-6 was tested at -20°C using the electrochemical impedance spectroscopy, cyclic voltammetry, and constant current charge-discharge test methods described above. The results are shown in Table 2.

[0082] Table 2 shows the electrochemical performance test results of the low-temperature fluorine-containing rechargeable magnesium battery electrolytes prepared in Examples 1-6 and Comparative Examples 1-6 at -20℃.

[0083] Table 2

[0084]

[0085]

[0086] As shown in Table 2 above, the low-temperature fluorine-containing rechargeable magnesium battery electrolytes prepared in Examples 1-6 exhibit higher ionic conductivity and higher CV dissolution current density compared to Comparative Examples 1-6. These electrolytes demonstrate excellent electrochemical performance at -20°C and can operate stably under low-temperature conditions.

[0087] By comparing Example 1 and Comparative Example 1, the addition of a fluorinated ether solvent significantly improves the ionic conductivity of the battery electrolyte, and its ionic conductivity is much higher than that of the electrolyte without a fluorinated ether solvent. The average coulombic efficiency of the electrolysis in Comparative Example 1 is comparable to that in Example 1, but... Figure 4 and Figure 5 As shown, the electrolyte prepared in Example 1 has a significant advantage in first-cycle coulombic efficiency, indicating that it can provide better performance during the initial use of the battery, is more conducive to the reversible deposition and dissolution of magnesium, or can form a stable electrode-electrolyte interface more quickly; the dissolution current density of the electrolyte in Example 1 is higher than that of the electrolyte in Comparative Example 1, and the electrolyte containing fluorinated ether solvent can improve the reversible magnesium deposition and dissolution performance of the electrolyte.

[0088] By comparing Example 1 with Comparative Example 2, the electrolyte of Comparative Example 2 without the addition of amine solvents could not achieve reversible deposition and dissolution of magnesium, and its ionic conductivity was lower than that of the electrolyte prepared in Example 1.

[0089] By comparing Example 1 with Comparative Example 3, the electrolyte prepared in Comparative Example 3 has a lower magnesium salt concentration, a lower reaction rate, and lower ionic conductivity, average coulombic efficiency, and CV first-cycle dissolution current density than the electrolyte prepared in Example 1.

[0090] By comparing Example 1 with Comparative Example 4, the electrolyte prepared in Comparative Example 4 had a higher magnesium salt concentration and a higher viscosity, and its ionic conductivity, average coulombic efficiency, and CV first-cycle dissolution current density were all lower than those of the electrolyte prepared in Example 1.

[0091] By comparing Example 1 with Comparative Example 5, the volume ratio of 2-methoxyethylamine to methylnonafluorobutyl ether in the electrolyte of Comparative Example 5 is less than (1.6-4):1, that is, the amount of methylnonafluorobutyl ether increases and the amount of 2-methoxyethylamine decreases. As can be seen from the data in Table 2, the ionic conductivity, average coulombic efficiency and CV first-cycle dissolution current density of Comparative Example 5 are all lower than those of the electrolyte prepared in Example 1.

[0092] By comparing Example 1 with Comparative Example 6, the volume ratio of 2-methoxyethylamine to methylnonafluorobutyl ether in the electrolyte of Comparative Example 6 is greater than (1.6-4):1, that is, the amount of 2-methoxyethylamine increases and the amount of methylnonafluorobutyl ether decreases. As can be seen from the data in Table 2, the ionic conductivity and average coulombic efficiency of Comparative Example 6 are lower than those of the electrolyte prepared in Example 1.

[0093] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A low-temperature fluorine-containing rechargeable magnesium battery electrolyte, characterized in that: It includes magnesium salt, main solvent and composite additive. The composite additive is a mixed solution of amine solvent and fluorinated ether solvent. The concentration of magnesium salt is 0.1-1.0 mol / L. The volume ratio of main solvent to composite additive is (2-3.3):

1. The volume ratio of amine solvents to fluorinated ether solvents in the composite additive is (1.6-4):1; The magnesium salt is any one or a combination of two of magnesium trifluoromethanesulfonate and magnesium bis(trifluoromethanesulfonyl)imide; the main solvent is an ether solvent.

2. The low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 1, characterized in that: The main solvent is any one or a combination of several of ethylene glycol dimethyl ether, tetrahydrofuran, and diethylene glycol dimethyl ether.

3. The low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 2, characterized in that: The amine solvent is any one or a combination of several of 2-methoxyethylamine, N-methyl-2-methoxyethylamine, 2,2-dimethoxyethylamine, 1-methoxy-2-propaneamine, and 3-propoxyethylamine.

4. The low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 3, characterized in that: Fluorinated ether solvents are any one or a combination of several of the following: ethyl nonafluorobutyl ether, methyl nonafluorobutyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, perfluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, ethyl 1,1,2,3,3,3-hexafluoropropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether.

5. A method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, characterized in that: Includes the following steps: S1: Weigh a certain amount of magnesium salt and dissolve it in the main solvent. Stir for 6-8 hours to form solution A, wherein the main solvent is an ether solvent. S2: Slowly add a fluorinated ether solvent to solution A in S1 and stir for 6-8 hours to form solution B; S3: Add an amine solvent to solution B in S2 and stir for 6-8 hours to obtain a low-temperature fluorine-containing rechargeable magnesium battery electrolyte.

6. The method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 5, characterized in that: The operations of S1-S3 were all carried out at 25°C in a glove box filled with inert gas, with the water and oxygen content in the box both below 0.01 ppm.

7. The method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 6, characterized in that: It also includes pretreatment of the main solvent, fluorinated ether solvent and amine solvent; the specific process of pretreatment is as follows: the main solvent or fluorinated ether solvent or amine solvent is mixed with metallic sodium, redistilled under an inert atmosphere, 4Å molecular sieve activated at high temperature is added to the distilled solvent, sealed and stored under an inert atmosphere.

8. An application of a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, characterized in that: The low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to any one of claims 1-4 is used in rechargeable magnesium batteries.

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