A low-temperature electrolyte for rechargeable magnesium batteries and a preparation method thereof

Abstract

The application provides a rechargeable magnesium battery low-temperature electrolyte and a preparation method thereof. The electrolyte contains anhydrous oxygen-free composite organic solvent, organic magnesium salt, inorganic magnesium salt and composite additive. The preparation method is that the organic magnesium salt, the inorganic magnesium salt and the composite additive are sequentially added into the anhydrous oxygen-free composite organic solvent under room temperature and inert atmosphere, and the electrolyte is obtained by magnetic stirring for 60 h to 72 h. The electrolyte preparation process is simple and easy for large-scale industrial production. The electrolyte does not freeze at a low working environment of-40 DEG C, has high conductivity, can realize reversible deposition-dissolution of magnesium at low temperature, and is suitable for the rechargeable magnesium battery applied in the low-temperature working environment, and has good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rechargeable magnesium batteries, and particularly relates to a rechargeable magnesium battery low-temperature electrolyte and a preparation method thereof. BACKGROUND

[0002] In recent years, rechargeable magnesium batteries are considered as one of the most potential new energy storage technologies for realizing the "double carbon" goal due to the advantages of abundant raw material magnesium reserves, high volume specific capacity and high safety.

[0003] However, it is well known that the low-temperature performance of rechargeable metal (ion) batteries is usually not ideal, which seriously limits their application in low-temperature environments. The electrolyte is considered as the "blood" of the battery and is a key component of the battery, playing an important role in transmitting ions between the positive and negative electrodes of the battery. The poor low-temperature performance of rechargeable metal (ion) batteries is largely related to the lack of electrolytes suitable for low-temperature working environments, because many electrolytes will increase in viscosity, crystallize or solidify at low temperatures, resulting in a sharp decrease in electrolyte conductivity, which cannot normally play the role of transmitting ions, thereby significantly increasing the interfacial impedance between the electrolyte and the electrode, sharply decreasing the battery performance or making the battery unable to work at all.

[0004] Due to the above problems, even for the relatively mature lithium-ion battery technology, improving its low-temperature performance is considered as an urgent problem to be solved. For rechargeable magnesium batteries, a new energy storage technology, there is currently no related report on electrolytes suitable for low-temperature working environments at home and abroad, so it is a long way to go to develop electrolytes that can be used in low-temperature working environments and improve the low-temperature application performance of rechargeable magnesium batteries. SUMMARY

[0005] In view of the above deficiencies in the prior art, the purpose of the present application is to provide a rechargeable magnesium battery low-temperature electrolyte to fill the gap in rechargeable magnesium battery electrolytes that can be used in low-temperature working environments at home and abroad.

[0006] The application also provides a preparation method of the rechargeable magnesium battery low-temperature electrolyte.

[0007] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0008] A rechargeable magnesium battery low-temperature electrolyte, characterized in that it contains anhydrous and oxygen-free composite organic solvent, organic magnesium salt, inorganic magnesium salt and composite additive; and the working environment temperature is allowed to be as low as-40℃.

[0009] Further, the total molar concentration of the organic magnesium salt and the inorganic magnesium salt in the anhydrous and oxygen-free composite organic solvent is 1.6-2.4 mol / L, wherein the amount of substance of the organic magnesium salt is 3-5 times the amount of substance of the inorganic magnesium salt; and the total molar concentration of the composite additive in the composite organic solvent is 0.06-0.1 mol / L.

[0010] The anhydrous and oxygen-free composite organic solvent is composed of tetrahydrofuran and perfluoroalkyl polyoxyethylene ether, and the volume of tetrahydrofuran is 4-9 times the volume of perfluoroalkyl polyoxyethylene ether.

[0011] Further, the anhydrous and oxygen-free composite organic solvent is prepared by the following method:

[0012] The tetrahydrofuran and perfluoroalkyl polyoxyethylene ether are mixed in proportion and then added to a distillation device, and metallic sodium is added in a proportion of 25 g per liter of organic solvent, and benzophenone is used as an indicator, and the mixture is re-distilled under an inert atmosphere; the distilled solvent is added with high-temperature activated molecular sieves, sealed and stored under an inert atmosphere for standby.

[0013] Further, the organic magnesium salt is bis(trifluoromethanesulfonylimide) magnesium, and the inorganic magnesium salt is magnesium borate.

[0014] The composite additive is composed of a sulfonyl fluoride additive and an ethylenediaminetetraacetate additive, and the amount of substance of the sulfonyl fluoride additive is 2-4 times the amount of substance of the ethylenediaminetetraacetate additive. The sulfonyl fluoride additive is any one of perfluorohexyl sulfonyl fluoride or perfluorobutyl sulfonyl fluoride, and the ethylenediaminetetraacetate additive is any one of disodium ethylenediaminetetraacetate or disodium calcium ethylenediaminetetraacetate.

[0015] The application also provides a preparation method of the low-temperature electrolyte of the rechargeable magnesium battery, which comprises the following steps:

[0016] The anhydrous and oxygen-free composite organic solvent, the organic magnesium salt, the inorganic magnesium salt and the composite additive are prepared according to the above components, the organic magnesium salt, the inorganic magnesium salt and the composite additive are sequentially added to the anhydrous and oxygen-free composite organic solvent, and magnetic stirring is performed for 60-72 h to obtain the electrolyte. The reaction is performed under an inert atmosphere at room temperature, and the content of water and oxygen is less than 0.01 ppm.

[0017] Compared with the prior art, the application has the following beneficial effects:

[0018] 1. The electrolyte comprises anhydrous and oxygen-free composite organic solvent, organic magnesium salt, inorganic magnesium salt and composite additive; the anhydrous and oxygen-free composite organic solvent is composed of tetrahydrofuran and perfluoroalkyl polyoxyethylene ether, which can ensure low freezing point, small viscosity and other characteristics of the solvent, adjust the solvation structure formed by the solvent molecules and magnesium ions, improve the solubility of the magnesium salt and enhance the low-temperature stability of the electrolyte; the magnesium salt is the provider of Mg 2+ in the electrolyte and is a key component for realizing reversible deposition and stripping of magnesium, the organic and inorganic double magnesium salt (bis(trifluoromethanesulfonylimide) magnesium and magnesium borate) without halogen ions is used, which can ensure high concentration and large conductivity of the electrolyte and does not cause corrosion to the negative magnesium metal and the positive current collector material; the composite additive is composed of sulfonyl fluoride additive and ethylenediaminetetraacetate additive, which can help to improve the affinity of the solvent to the electrolyte salt, increase the solubility of the magnesium salt in the solvent, promote the charge transfer between the electrolyte and the electrode interface and improve the low-temperature kinetics.

[0019] 2. The synergistic effect between the components of the electrolyte gives the electrolyte the characteristics of good affinity to the magnesium negative electrode, large conductivity, small overpotential and high magnesium deposition and stripping efficiency at low temperature, especially the electrolyte still has high conductivity and can realize reversible deposition and stripping of magnesium at a working environment as low as-40 DEG C, so it is suitable for application in rechargeable magnesium batteries in low-temperature working environment and has good application prospect.

[0020] 3. The rechargeable magnesium battery low-temperature electrolyte is prepared in situ by one-step stirring at room temperature, the process is simple and easy for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The contact angle test result of the electrolyte prepared in example 1 of the present application on the magnesium negative electrode surface after storage at-20 DEG C for 24 hours.

[0022] Figure 2 The contact angle test result of the electrolyte prepared in example 1 of the present application on the magnesium negative electrode surface after storage at-40 DEG C for 24 hours.

[0023] Figure 3 The magnesium deposition and stripping curve of the electrolyte prepared in example 1 of the present application at-20 DEG C.

[0024] Figure 4 The magnesium deposition and stripping curve of the electrolyte prepared in example 1 of the present application at-40 DEG C. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below in combination with specific examples.

[0026] 1. A rechargeable magnesium battery low-temperature electrolyte and a preparation method thereof

[0027] Example 1

[0028] A rechargeable magnesium battery low-temperature electrolyte is prepared according to the following method:

[0029] First, anhydrous and oxygen-free composite organic solvent is prepared: 90.0 mL of tetrahydrofuran and 10.0 mL of perfluoroalkyl polyoxyethylene ether are mixed uniformly, then added to a distillation device, 2.5 g of metallic sodium is added, benzophenone is used as an indicator, and re-distillation is performed under an inert atmosphere; the distilled solvent is added with high-temperature activated molecular sieves, sealed and stored under an inert atmosphere for standby use.

[0030] Preparation of electrolyte: under an inert atmosphere (water and oxygen content is less than 0.01 ppm) at room temperature, 10 mL of the anhydrous and oxygen-free composite organic solvent prepared by the above method is taken, 3.468 g of bis(trifluoromethanesulfonimide) magnesium, 0.4396 g of magnesium borate, 0.3369 g of perfluoro hexyl sulfonyl fluoride and 0.0672 g of disodium ethylenediaminetetraacetate are sequentially added to the anhydrous and oxygen-free composite organic solvent, and magnetic stirring is performed for 66 h to obtain the electrolyte.

[0031] Examples 2-5

[0032] The raw materials, amount, stirring time, etc. for preparing the rechargeable magnesium battery low-temperature electrolyte are shown in Table 1:

[0033] Table 1

[0034]

[0035]

[0036] The rechargeable magnesium battery low-temperature electrolyte is prepared by the same method as in Example 1, i.e. including:

[0037] First, anhydrous and oxygen-free composite organic solvent is prepared: 90.0 mL of tetrahydrofuran and 10.0 mL of perfluoroalkyl polyoxyethylene ether are mixed uniformly, then added to a distillation device, 2.5 g of metallic sodium is added, benzophenone is used as an indicator, and re-distillation is performed under an inert atmosphere; the distilled solvent is added with high-temperature activated molecular sieves, sealed and stored under an inert atmosphere for standby use.

[0038] Preparation of electrolyte: under an inert atmosphere (water and oxygen content is less than 0.01 ppm) at room temperature, 10 mL of the anhydrous and oxygen-free composite organic solvent prepared by the above method is taken, 3.468 g of bis(trifluoromethanesulfonimide) magnesium, 0.4396 g of magnesium borate, 0.3369 g of perfluoro hexyl sulfonyl fluoride and 0.0672 g of disodium ethylenediaminetetraacetate are sequentially added to the anhydrous and oxygen-free composite organic solvent, and magnetic stirring is performed for 66 h to obtain the electrolyte.

[0039] II. Performance test method of the low-temperature electrolyte of the rechargeable magnesium battery

[0040] a. Affinity test of the low-temperature electrolyte to the magnesium negative electrode

[0041] The affinity of the low-temperature electrolyte to the magnesium negative electrode is characterized by testing the contact angle of the electrolyte on the surface of the magnesium negative electrode after the electrolyte is stored at-20℃ and-40℃ low-temperature environment for 24 hours. The smaller the contact angle, the better the affinity of the electrolyte to the magnesium negative electrode. The contact angle less than 10 degrees is called super-affinity state, indicating that the electrolyte can quickly infiltrate the magnesium negative electrode. The test is completed by using a Germany Dataphysics OCA20 video optical contact angle measuring instrument.

[0042] b. Magnesium deposition-dissolution reversibility test at low temperature

[0043] The magnesium deposition-dissolution reversibility test of the electrolyte at low temperature is realized by using the cyclic voltammetry technology of the Autolab PGSTAT302N electrochemical workstation. The test is performed by assembling a CR2032 button cell, which is assembled in an inert atmosphere glove box with water and oxygen content less than 0.01 ppm. The working electrode is a clean stainless steel (SS) foil, the counter electrode is a clean magnesium sheet (also as a reference electrode), the separator is a GF / A membrane, and the electrolyte is assembled into a CR2032 button cell. The cyclic voltammetry potential range is-1.0-2.5V, the scan rate is 25mV / s, and the test temperature is controlled at-20℃ and-40℃, respectively.

[0044] c. Conductivity test of the electrolyte at low temperature

[0045] The conductivity of the electrolyte is obtained by analyzing the electrochemical impedance spectrum. The electrochemical impedance spectrum test is completed on the Autolab PGSTAT302N electrochemical workstation. The test is performed by assembling a CR2032 button cell, which is assembled in an inert atmosphere glove box with water and oxygen content less than 0.01 ppm. The working electrode and the counter electrode (also as a reference electrode) are both clean stainless steel (SS) foils, and the separator is a GF / A membrane, and the electrolyte is assembled into a CR2032 button cell. The excitation signal applied during the test is 5mV, the test frequency range is 10 5 Hz-0.01Hz, and the test temperature is controlled at-20℃ and-40℃, respectively. The bulk resistance R s (Ω) of the electrolyte is obtained from the impedance spectrum measured at different temperatures, and then the conductivity (σ, S / cm) of the electrolyte is obtained by the following definition formula of the conductivity:

[0046] σ=l / SR s

[0047] In the formula, l is the thickness of the electrolyte, cm; S is the contact area of the electrolyte and the electrode, cm2 .

[0048] d. Reversible deposition-stripping coulombic efficiency test of magnesium at low temperature

[0049] The reversible deposition-stripping coulombic efficiency of magnesium in electrolyte was tested by assembling CR2032 button cell. The assembly was carried out in an inert atmosphere glove box, with water and oxygen content less than 0.01 ppm. The working electrode was a clean stainless steel (SS) foil, the counter electrode was a clean magnesium sheet (also as reference electrode), the separator was a GF / A membrane, and the CR2032 button cell was assembled with the self-made electrolyte. After the cell was assembled, it was measured after standing at -20°C and -40°C for 24 hours, respectively. The whole test process was carried out on a Wuhan Land charge-discharge test system. During discharging (1 hour), the deposition reaction of magnesium occurred on the working electrode, and the current density was 0.1-0.5 mAcm -2 ; during charging, the stripping reaction of magnesium deposited on the working electrode occurred, and the current density was 0.1-0.5 mAcm -2 , and voltage control was used (charged to 0.8 V vs. Mg RE).

[0050] The low-temperature performance of the electrolyte prepared in Example 1 was tested by the above method, and the test results were as follows: the contact angles of the electrolyte on the surface of the magnesium negative electrode were 3.3° Figure 1 and 6.1° Figure 2 after being stored at -20°C and -40°C for 24 hours, respectively, both of which were super-philic states, indicating that the low-temperature electrolyte could quickly wet the magnesium negative electrode; the magnesium deposition-stripping overpotential of the electrolyte at -20°C and -40°C was 178 mV Figure 3 and 204 mV Figure 4 , respectively; the conductivity of the electrolyte at -20°C and -40°C was 2.62 mS·cm -1 and 1.14 mS·cm -1 , respectively; the magnesium reversible deposition-stripping (on the stainless steel current collector) coulombic efficiency of the electrolyte at -20°C and -40°C was maintained at 96% and 92% after 100 cycles, respectively; the above performance test results showed that the electrolyte of the application had the characteristics of good affinity with the magnesium negative electrode at low temperature, high conductivity, small overpotential, and high magnesium deposition-stripping efficiency.

[0051] Similarly, the electrolytes prepared in Examples 2-5 were tested by the above method, and the results are shown in Table 2.

[0052] Table 2

[0053]

[0054] It can be seen that the electrolyte has the characteristics of good affinity with magnesium negative electrode at low temperature, high conductivity, small overpotential and high magnesium deposition-dissolution efficiency.

[0055] In conclusion, the prepared rechargeable magnesium battery electrolyte has the characteristics of good affinity with magnesium negative electrode at low temperature, high conductivity, small overpotential and high magnesium deposition-dissolution efficiency through the synergistic effect of the components, and in particular, the electrolyte still has high conductivity and can realize reversible magnesium deposition-dissolution in a working environment as low as-40 DEG C, so it is suitable for rechargeable magnesium batteries working in low temperature environment and has good application prospect.

[0056] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application but not to limit the technical solutions, and those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the technical solutions, which should be covered in the scope of claims of the present application.

Claims

1. A low-temperature electrolyte for a rechargeable magnesium battery, characterized in that, Contains anhydrous and oxygen-free composite organic solvents, organic magnesium salts, inorganic magnesium salts, and composite additives; allows operating ambient temperatures as low as −40℃; The anhydrous and oxygen-free composite organic solvent is composed of tetrahydrofuran and perfluoroalkyl polyoxyethylene ether, with the volume of tetrahydrofuran being 4 to 9 times that of perfluoroalkyl polyoxyethylene ether. The anhydrous and oxygen-free composite organic solvent is prepared by the following method: tetrahydrofuran and perfluoroalkyl polyoxyethylene ether are mixed evenly in a specific ratio, then added to a distillation apparatus. Sodium metal is added at a ratio of 25g per liter of organic solvent. Benzophenone is used as an indicator, and the mixture is redistilled under an inert atmosphere. A molecular sieve activated at high temperature is added to the distilled solvent, which is then sealed and stored under an inert atmosphere for later use. The composite additive consists of sulfonyl fluoride additives and ethylenediaminetetraacetic acid salt additives, wherein the amount of sulfonyl fluoride additives is 2 to 4 times the amount of ethylenediaminetetraacetic acid salt additives.

2. The low-temperature electrolyte for a rechargeable magnesium battery according to claim 1, characterized in that, The total molar concentration of the organic and inorganic magnesium salts in the anhydrous and oxygen-free composite organic solvent is 1.6~2.4 mol / L, wherein the amount of the organic magnesium salt is 3~5 times the amount of the inorganic magnesium salt; the total molar concentration of the composite additive in the composite organic solvent is 0.06~0.1 mol / L.

3. The low-temperature electrolyte for a rechargeable magnesium battery according to claim 1, characterized in that, The organic magnesium salt is bis(trifluoromethanesulfonylimide) magnesium, and the inorganic magnesium salt is magnesium borate.

4. The low-temperature electrolyte for a rechargeable magnesium battery according to claim 1, characterized in that, The sulfonyl fluoride additive is any one of perfluorohexyl sulfonyl fluoride or perfluorobutyl sulfonyl fluoride, and the ethylenediaminetetraacetic acid salt additive is any one of disodium ethylenediaminetetraacetate or calcium disodium ethylenediaminetetraacetate.

5. A method for preparing a low-temperature electrolyte for a rechargeable magnesium battery, characterized in that, Includes the following steps: According to the components of claim 2, take anhydrous and oxygen-free composite organic solvent, organic magnesium salt, inorganic magnesium salt, and composite additive, add the organic magnesium salt, inorganic magnesium salt, and composite additive to the anhydrous and oxygen-free composite organic solvent in sequence, and stir magnetically for 60 h to 72 h to obtain the electrolyte.

6. The method for preparing the low-temperature electrolyte for a rechargeable magnesium battery according to claim 5, characterized in that, The reaction was carried out at room temperature under an inert atmosphere, with both water and oxygen content below 0.01 ppm.

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