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

Abstract

The invention relates to the technical field of electrochemistry, and discloses a low-temperature fluorine-containing rechargeable magnesium battery electrolyte which comprises magnesium salt, a main solvent and a composite additive, the composite additive is a mixed solution of an amine solvent and a fluorine-containing 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 comprises the following steps: S1, weighing a certain amount of magnesium salt, dissolving the magnesium salt in a main solvent, and stirring for 6-8 hours to form a solution A; s2, slowly adding a fluorine-containing ether solvent into the solution A in the S1, and stirring for 6-8 hours to form a solution B; and S3, adding an amine solvent into the solution B in the S2, and stirring for 6-8 hours to prepare the low-temperature fluorine-containing rechargeable magnesium battery electrolyte, the application is the application of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte in a rechargeable magnesium battery. According to the technical scheme, the reversible magnesium deposition dissolving performance of the electrolyte can be improved, and meanwhile, the transmission dynamics performance and the ionic conductivity of Mg < 2 + > at the low temperature can also be improved.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemistry, and in particular to a low-temperature fluorine-containing rechargeable magnesium battery electrolyte and a preparation method and application thereof. Background Art

[0002] Energy security is the lifeline of a country. Realizing safe, reliable and low-cost energy storage technology is the foundation for achieving energy transformation. As one of the countries with the richest magnesium resources, my country has 70% of the world's magnesium reserves, which provides a solid resource guarantee for the development of rechargeable magnesium batteries. Magnesium metal has a high theoretical specific capacity, and has the advantages of high safety and low cost, making magnesium batteries one of the powerful disruptors in the battery field.

[0003] With the rapid development of new energy vehicles, the requirements for battery performance are constantly rising. Among them, the ability to work in low temperature environments has become one of the key indicators to measure the level of battery technology. As an important component of rechargeable magnesium batteries, electrolyte is widely regarded as a key factor limiting the ionic conductivity and stability of magnesium ion batteries at low temperatures. 2+ Desolvation process and Mg in the electrode-electrolyte interface 2+ There is a high energy barrier for transport, which results in slow kinetics of magnesium ion transport. Therefore, the selection of main solvents and additives in the electrolyte is crucial. Ether organic solvents with low freezing point, low viscosity and weak solvation energy are often used as low-temperature electrolyte solvents for magnesium ion batteries. However, weakly solvated ether solvents have poor solvation ability for magnesium salts, making it difficult to achieve efficient reversible deposition and dissolution of magnesium. In order to solve the problem that ether solvents are difficult to achieve reversible deposition and dissolution of magnesium in magnesium salts, amine solvents with strong solvation ability are usually introduced to promote the formation of an effective electrode and electrolyte interface, thereby achieving effective reversible deposition and dissolution of magnesium. However, the high viscosity and high desolvation energy caused by amine solvents with strong solvation ability will affect Mg at low temperatures. 2+ The transport kinetics of the ions decreases. Summary of the invention

[0004] The present invention is intended to provide a low-temperature fluorine-containing rechargeable magnesium battery electrolyte and a preparation method and application thereof, which can improve the reversible magnesium deposition and dissolution performance of the electrolyte, and at the same time, can also improve the Mg at low temperature. 2+ transport kinetics and ionic conductivity.

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

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

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

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

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

[0010] Preferably, the fluorinated ether solvent is any one of 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, or a combination of several thereof.

[0011] The present 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 operation processes of S1 to S3 are all carried out at 25° C. in a glove box filled with inert gas, and the contents of water and oxygen in the glove box are both lower than 0.01 ppm.

[0016] Preferably, the main solvent, the fluorinated ether solvent and the amine solvent are pretreated; the specific process of the pretreatment is: mixing the main solvent or the fluorinated ether solvent or the amine solvent with metallic sodium, re-distilling under an inert atmosphere, adding a high temperature activated Type molecular sieve, sealed and stored under inert atmosphere.

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

[0018] Compared with the prior art, the beneficial effects of this solution are:

[0019] (1) Since ether solvents have poor solvating ability for magnesium salts, the solubility of magnesium salts in them is relatively low. Compared with ester and nitrile solvents, ether solvents are more compatible with magnesium negative electrodes, but there are still certain problems. For example, pure ether solvents are difficult to achieve reversible magnesium deposition and dissolution in magnesium salts. To this end, amine solvents with strong solvating 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 transmission of magnesium ions at the interface. However, strongly solvating amine solvents will increase the viscosity of the electrolyte, which is not conducive to ionic conductivity at low temperatures. Therefore, by adding fluorinated ether solvents, taking advantage of their low melting point and low polarity characteristics, and relying on their synergistic reduction effect with anions in magnesium salts, the formation of inorganic components in the electrode / electrolyte interface can be further promoted, thereby improving the migration ability and ionic conductivity of magnesium ions at low temperatures; it can be seen that the fluorinated low-temperature rechargeable magnesium battery electrolyte provided by the present 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+ transport kinetics and ionic conductivity.

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

[0021] (3) The present invention provides a fluorine-containing low-temperature rechargeable magnesium battery electrolyte, which can enable the magnesium ion battery to operate stably at low temperatures. At -20°C, the Mg|Mg symmetrical battery has a charge and discharge rate of 0.5 mA / cm 2 The cyclic test was carried out at a current density of 200 hours, and the polarization potential did not increase significantly. The deposition overpotential was as low as 269 mV, indicating that the fluorine-containing low-temperature rechargeable magnesium battery electrolyte has excellent compatibility and stability with magnesium.

[0022] (4) The present invention provides a fluorine-containing low-temperature rechargeable magnesium battery electrolyte. When a Mg‖SS battery containing a fluorine-containing ether solvent is used at -20°C, the coulombic efficiency of the reversible deposition and dissolution of magnesium gradually increases, and the coulombic efficiency of the first cycle reaches 89.29%, and the average coulombic efficiency is 99.76%. For a Mg‖SS battery without a fluorine-containing ether solvent, the coulombic efficiency of the first cycle reaches 77.26%, and the average coulombic efficiency is 99.75%. It can be seen that the electrolyte containing a fluorine-containing ether solvent has a significant advantage in the first cycle coulombic efficiency, indicating that it can provide better performance when the battery is initially used, is more conducive to the reversible deposition and dissolution of magnesium, or can form a stable electrode-electrolyte interface faster.

[0023] (5) The technical solution sets the volume ratio of the main solvent to the composite additive to (2-3.3):1, which can improve the reversible magnesium deposition dissolution performance of the electrolyte on the one hand; on the other hand, it can improve the cycle stability of the electrolyte. If the volume ratio of the main solvent to the composite additive is greater than 3.3:1, the reversible magnesium deposition 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) The present technical solution can remove the moisture in the main solvent, the fluorinated ether solvent and the amine solvent by pretreating the main solvent, the fluorinated ether solvent and the amine solvent. At the same time, the generated sodium ions are insoluble in the organic solvent and are removed by re-distillation. The present technical solution can optimize the ionic conductivity, stabilize the electrode interface and reduce the occurrence of side reactions by removing the moisture in the organic solvent.

[0025] (7) The present 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 easily available, the cost is low, and it is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0029] Figure 4 The low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 of the present invention is 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 in Comparative Example 1 of the present invention is 0.5 mA / cm 2 Coulombic efficiency of reversible magnesium deposition / dissolution at -20 °C under current density;

[0031] Figure 6 The Mg|Mg symmetrical battery assembled with the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 of the present invention is 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 the present invention at -20°C. DETAILED DESCRIPTION

[0033] The following is further described in detail through specific implementation methods:

[0034] Example 1

[0035] A low-temperature fluorine-containing rechargeable magnesium battery electrolyte comprises a magnesium salt, a main solvent and a composite additive, wherein the composite additive is a mixed solution of an amine solvent and a fluorine-containing 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 fluorine-containing ether solvent in the composite additive is (1.6-4):1; in the present 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 fluorine-containing ether solvent in the composite additive is 1.8:1.

[0036] Wherein, the magnesium salt is any one of magnesium trifluoromethanesulfonate and magnesium bis(trifluoromethylsulfonyl)imide or a combination of both; in this embodiment, the magnesium salt is magnesium bis(trifluoromethylsulfonyl)imide;

[0037] The main solvent is any one or a combination 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 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 of 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, or a combination of several thereof; in the present embodiment, the fluorinated ether solvent is methyl nonafluorobutyl ether.

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

[0041] S1: Weigh a certain amount of magnesium salt and dissolve it in the main solvent, stir it magnetically for 6-8 hours, and the speed of the magnetic stirrer is 400r / min to form a solution A. In this embodiment, 1.7245g Mg(TFSI)2 is weighed and dissolved in 4.5mL ethylene glycol dimethyl ether, and stirred it magnetically for 6 hours, and the speed of the magnetic stirrer is 400r / min to form a solution A;

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

[0043] S3: Add an amine solvent to the B solution 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 was added to the B solution in S2, and 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 operation processes of S1-S3 are all carried out at 25° C. in a glove box filled with inert gas, and the contents of water and oxygen in the box are both lower than 0.01 ppm. In this embodiment, the inert gas is argon.

[0045] The invention also includes pre-treating the main solvent, the fluorinated ether solvent and the amine solvent; the specific process of the pre-treating is: mixing the main solvent or the fluorinated ether solvent or the amine solvent with metallic sodium, re-evaporating under an inert atmosphere, adding a high temperature activated In this embodiment, the specific process of pretreatment is as follows: 50 mL of ethylene glycol dimethyl ether or methyl nonafluorobutyl ether or 2-methoxyethylamine is added to a container, 1.5 g of metallic sodium is added, and redistilled under an argon atmosphere. To the distilled solvent, 350 ° C high temperature activated 15 h is added. The mixture was sealed and stored under argon atmosphere.

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

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

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

[0049] Table 1

[0050]

[0051] Comparative Example 1

[0052] Different from Example 1, in a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, the composite additive contains only 2-methoxyethylamine, does not contain methyl nonafluorobutyl ether, and 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, the amount of Mg(TFSI)2 added in S1 is 1.5784g, and the volume of ethylene glycol dimethyl ether is 4.5mL; the volume of 2-methoxyethylamine in S3 is 0.9mL.

[0053] Comparative Example 2

[0054] Different from Example 1, in a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, the composite additive contains only methyl nonafluorobutyl ether, does not contain 2-methoxyethylamine, and 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, the amount of Mg(TFSI)2 added in S1 is 1.4615 g, and the volume of ethylene glycol dimethyl ether is 4.5 mL; the amount of methyl nonafluorobutyl ether added in S2 is 0.5 mL.

[0055] Comparative Example 3

[0056] Different from Example 1, in a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, the concentration of magnesium bis(trifluoromethylsulfonyl)imide is 0.05 mol / L; in 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] Different from Example 1, in a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, the concentration of magnesium bis(trifluoromethylsulfonyl)imide is 1.2 mol / L; in 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] Different from Example 1, in a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, the volume ratio of 2-methoxyethylamine to methyl nonafluorobutyl ether is 1:1; in a method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, in S2, the amount of methyl nonafluorobutyl ether added is 0.7 ml, and in S3, the amount of 2-methoxyethylamine added is 0.7 ml.

[0061] Comparative Example 6

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

[0063] The electrochemical performance test of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Examples 1-6 and Comparative Examples 1-6:

[0064] The ionic conductivity of the electrolyte and the reversible magnesium deposition and dissolution performance were tested by electrochemical impedance spectroscopy and cyclic voltammetry, respectively. Specifically, a two-electrode system was used, with a magnesium sheet (Φ12 mm) electrode as the reference electrode and counter electrode, and a stainless steel foil (SS, Φ16 mm) electrode as the working electrode, or a stainless steel foil (SS, Φ16 mm) as the counter electrode, reference electrode and working electrode; for the electrochemical impedance spectroscopy, the test frequency was 100000 Hz-0.01 Hz, the applied excitation signal was 5 mV, and the test temperature was -20 ° C; for the cyclic voltammetry, the test potential was -1 V-2 V, the scanning speed was 25 mV / s, the test temperature was -20 ° C, and the test was scanned from the negative direction of the open circuit voltage; in addition, all electrodes were alternately cleaned with ethanol and deionized water for 3 times to remove impurities on the entire electrode surface; the cleaned electrodes were vacuum dried for 12 hours and then placed in a glove box for use.

[0065] The coulombic efficiency and charge-discharge characteristics of magnesium in electrolyte were tested by assembling CR2032 button cells for constant current charge-discharge testing. Specifically, the test was performed in an inert atmosphere glove box, with water and oxygen content less than 0.01ppm; the working electrode was polished stainless steel foil (SS), the counter electrode and reference electrode were polished magnesium sheets, and the diaphragm was GF / A film; after the battery was assembled, it was left to stand at room temperature for 12 hours before testing; the entire test process was performed on the Xinwei charge-discharge test system, with a current density of 0.1mA / cm 2 -1.0mA / cm 2 , time control (discharging for 1 hour); the current density during charging is 0.1mA / cm 2 -1.0mA / cm 2 , using voltage control (charging to 1.2Vvs.MgRE).

[0066] (1) Conductivity test of electrolyte at low temperature

[0067] The conductivity of the electrolyte is obtained by analyzing the electrochemical impedance spectroscopy. The electrochemical impedance spectroscopy test was completed on the Chi660e electrochemical workstation. The test was carried out by assembling CR2032 button cells in an inert atmosphere glove box (water and oxygen content are both less than 0.01ppm). Stainless steel foil (SS, Φ16mm) was used as the counter electrode, reference electrode and working electrode, and the diaphragm was made of GF / A membrane, which was assembled into CR2032 button cells together with the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 and Comparative Example 1. The excitation signal added during the test was 5mV, the test frequency range was 100000Hz~0.01Hz, and the test temperature was controlled at -20℃. The electrolyte bulk resistance Rs (Ω) was obtained from the impedance spectrum, and the conductivity was calculated by the following formula:

[0068] σ=l / SRs

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

[0070] l is the thickness of the electrolyte (mm);

[0071] S is the contact area between electrolyte and electrode (cm 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 by the formula σ=l / SRs, the ionic conductivity of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 is 3.05mS / cm at -20°C; the ionic conductivity of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Comparative Example 1 is 1.62mS / cm at -20°C. It can be seen that the compounding of fluorine-containing ether solvents and amine solvents can significantly improve the conductivity of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte.

[0074] (2) Cyclic voltammetry at -20°C

[0075] The above test method was used to test the reversible magnesium deposition and dissolution performance of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 and Comparative Example 2 at -20°C on a stainless steel working electrode. The test results were as follows: Figure 3 , Figure 7 As shown in the results, with stainless steel SS as the working electrode, at -20°C, the first cycle dissolution current density of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 is 3.98 mA / cm 2 The results show that the electrolyte can reversibly deposit and dissolve magnesium at -20°C; while the electrolyte in Comparative Example 2 that does not contain an amine solvent cannot achieve reversible deposition and dissolution of magnesium.

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

[0077] The coulombic efficiency test of the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in the above-mentioned embodiment 1 and comparative example 1 was carried out on a stainless steel working electrode at -20°C using the above-mentioned test method. The test results are as follows: Figure 4 , Figure 5 As shown, the results show that the coulombic efficiency of magnesium reversible deposition and dissolution in the low-temperature fluorine-containing rechargeable magnesium battery electrolyte (Mg||SS battery) prepared in Example 1 gradually increases, and the coulombic efficiency of the first cycle reaches 89.29%, and the average coulombic efficiency after 1000 stable cycles is 99.76%; the low-temperature rechargeable magnesium battery electrolyte prepared in Comparative Example 1 has a coulombic efficiency of 77.26% in the first cycle, and the average coulombic efficiency after 1000 stable cycles is 99.75%. It can be seen that the electrolyte prepared in Example 1 has a significant advantage in the first cycle coulombic efficiency, indicating that it can provide better performance when the battery is initially used, is more conducive to the reversible deposition and dissolution of magnesium, or can form a stable electrode-electrolyte interface faster.

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

[0079] The above test method was used to test the polarization performance of the symmetrical battery Mg|Mg assembled with the low-temperature fluorine-containing rechargeable magnesium battery electrolyte prepared in Example 1 at -20°C. The test results are as follows: Figure 6As shown, the results show that at a current density of 0.5 mA / cm 2 When the battery was stably cycled for 200 hours, the polarization potential did not increase significantly, and the deposition overpotential was as low as 269mV. The results show that the electrolyte has 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 the above Examples 1-6 and Comparative Examples 1-6 was tested at -20°C using the above electrochemical impedance test, cyclic voltammetry test and constant current charge and discharge test methods. 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°C.

[0083] Table 2

[0084]

[0085]

[0086] It can be seen from Table 2 above that the low-temperature fluorine-containing rechargeable magnesium battery electrolytes prepared in Examples 1 to 6 have higher ionic conductivity and higher CV dissolution current density than those in Comparative Examples 1 to 6. In an environment of -20°C, these electrolytes exhibit good electrochemical properties and can work stably under low temperature conditions.

[0087] By comparing Example 1 with Comparative Example 1, it is found that the addition of fluorinated ether solvents can significantly improve the ionic conductivity of the battery electrolyte, and its ionic conductivity is much greater than that of the electrolyte without fluorinated ether solvents; the average coulombic efficiency of the electrolysis of Comparative Example 1 is equivalent to that of Example 1, but Figure 4 and Figure 5 As shown, the electrolyte prepared in Example 1 has a significant advantage in the first-cycle coulomb efficiency, indicating that it can provide better performance when the battery is initially used, is more conducive to the reversible deposition and dissolution of magnesium, or can form a stable electrode-electrolyte interface faster; the first-cycle dissolution current density of the electrolyte of Example 1 is higher than that of the electrolyte of Comparative Example 1, and the electrolyte containing fluorinated ether solvents can improve the reversible magnesium deposition and dissolution performance of the electrolyte.

[0088] By comparing Example 1 with Comparative Example 2, it can be seen that the electrolyte of Comparative Example 2 without adding an amine solvent cannot achieve reversible deposition and dissolution of magnesium, and its ion conductivity is lower than that of the electrolyte prepared in Example 1.

[0089] By comparing Example 1 with Comparative Example 3, the magnesium salt concentration of the electrolyte prepared in Comparative Example 3 is reduced, the reaction rate of the electrolyte is reduced, and its ionic conductivity, average coulomb efficiency, and CV first cycle dissolution current density are all lower than those of the electrolyte prepared in Example 1.

[0090] By comparing Example 1 with Comparative Example 4, the magnesium salt concentration of the electrolyte prepared in Comparative Example 4 is increased, the viscosity of the electrolyte is increased, and its ionic conductivity, average coulomb efficiency, and CV first cycle dissolution current density are all lower than those of the electrolyte prepared in Example 1.

[0091] By comparing Example 1 with Comparative Example 5, in the electrolyte of Comparative Example 5, the volume ratio of 2-methoxyethylamine to methyl nonafluorobutyl ether is less than (1.6-4):1, that is, the amount of methyl nonafluorobutyl ether increases and the amount of 2-methoxyethylamine decreases. It can be seen from the data in Table 2 that the ionic conductivity, average coulomb 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, in the electrolyte of Comparative Example 6, the volume ratio of 2-methoxyethylamine to methyl nonafluorobutyl ether is greater than (1.6-4):1, that is, the amount of 2-methoxyethylamine increases and the amount of methyl nonafluorobutyl ether decreases. It can be seen from the data in Table 2 that 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 is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records 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: The invention comprises 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 and composite additive is (2-3.3):

1.

2. A low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 1, characterized in that: The volume ratio of the amine solvent to the fluorinated ether solvent in the composite additive is (1.6-4):

1.

3. A low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 2, characterized in that: The magnesium salt is any one of magnesium trifluoromethanesulfonate and magnesium bis(trifluoromethylsulfonyl)imide or a combination of both.

4. A low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 3, characterized in that: The main solvent is any one of ethylene glycol dimethyl ether, tetrahydrofuran and diethylene glycol dimethyl ether or a combination of several of them.

5. A low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 4, characterized in that: The amine solvent is any one of 2-methoxyethylamine, N-methyl-2-methoxyethylamine, 2,2-dimethoxyethylamine, 1-methoxy-2-propylamine, and 3-propoxyethylamine, or a combination of several of them.

6. A low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 5, characterized in that: The fluorinated ether solvent is any one of 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, or a combination of several thereof.

7. A method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte, characterized in that: The following steps are involved: S1: Weigh a certain amount of magnesium salt and dissolve it in the main solvent, stir for 6-8 hours to form solution A; 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.

8. The method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 7, characterized in that: The operation processes of S1-S3 were all carried out at 25°C in a glove box filled with inert gas, and the water and oxygen contents in the box were both less than 0.01 ppm.

9. The method for preparing a low-temperature fluorine-containing rechargeable magnesium battery electrolyte according to claim 8, characterized in that: The invention also includes pre-treating the main solvent, the fluorinated ether solvent and the amine solvent; the specific process of the pre-treating is: mixing the main solvent or the fluorinated ether solvent or the amine solvent with metallic sodium, re-evaporating under an inert atmosphere, adding a high temperature activated Type molecular sieve, sealed and stored under inert atmosphere.

10. 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 to 6 is used in a rechargeable magnesium battery.

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