A non-aqueous magnesium electrolyte and a preparation method thereof

Abstract

The present invention belongs to the technical field of secondary energy storage batteries, and in particular to a non-aqueous magnesium electrolyte and a preparation method thereof. The non-aqueous magnesium electrolyte is an organic magnesium salt, an amine additive, a strong reducing additive and a non-aqueous organic solvent; wherein the concentration of the organic magnesium salt in the non-aqueous organic solvent is 0.05-5mol / L; the molar ratio of the organic magnesium salt to the amine additive is 1:(0.1-50); the molar ratio of the organic magnesium salt to the strong reducing additive is 1:(0-10); the non-aqueous organic solvent is an ether organic solvent; the organic magnesium salt is bis(trifluoromethanesulfonyl)imide magnesium. The non-aqueous magnesium electrolyte of the present invention has the advantages of higher magnesium deposition / dissolution efficiency, lower deposition overpotential (less than 0.5V), better cycle life, simple preparation and low price. Moreover, the non-aqueous magnesium electrolyte formula can use organic magnesium salts with lower purity, further reducing costs.

Description

Technical Field

[0001] The invention belongs to the technical field of secondary energy storage batteries, and particularly relates to a non-aqueous magnesium electrolyte and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used in social life, such as mobile phones, computers, and electric vehicles. However, the content of lithium metal in the earth's crust is not high, which makes lithium-ion batteries expensive. At the same time, during the charging and discharging process, the generation of lithium dendrites will pierce the diaphragm and cause battery short circuit, causing safety problems. Moreover, the energy density of lithium-ion batteries is not high, and it is increasingly difficult to meet the needs of social development. These problems of lithium-ion batteries have shifted the research focus to new secondary energy storage battery technology.

[0003] As one of the next generation of secondary energy storage battery technologies, rechargeable magnesium batteries have the characteristics of high energy density, high safety performance and low price of magnesium metal. First, the volume energy density of rechargeable magnesium batteries is 3833mAh / cm 3 , much larger than rechargeable lithium batteries (2046mAh / cm 3 ). Secondly, rechargeable magnesium batteries are not prone to dendrites during the charging and discharging process, which greatly reduces safety risks; moreover, the high content of magnesium metal in the earth's crust makes magnesium metal very advantageous in terms of price.

[0004] However, the development of rechargeable magnesium batteries is still in its early stages, and its development is mainly limited by the electrolyte and the positive electrode. For the electrolyte, it needs to meet the following requirements: 1. High magnesium deposition / dissolution efficiency; 2. Low magnesium deposition / dissolution overpotential; 3. Wide voltage window; 4. Non-corrosive (free of chloride ions, etc.); 5. High ionic conductivity; 6. Simple preparation, etc.

[0005] Ether electrolytes based on Mg(TFSI)2 have the advantages of high voltage window, non-corrosiveness and simple preparation, and are considered to be one of the most promising electrolytes for rechargeable magnesium batteries. However, this type of electrolyte has an extremely abnormal magnesium deposition / dissolution overpotential (about –2.0V); moreover, it is very sensitive to impurities, and the performance of reagents produced by different suppliers also varies significantly.

[0006] Therefore, a non-aqueous magnesium electrolyte modified by adding amine additives and strong reducing additives based on Mg(TFSI)2 is now invented. Summary of the invention

[0007] In order to solve the influence of impurities on Mg(TFSI)2 type electrolyte, the present invention provides a non-aqueous magnesium electrolyte and a preparation method thereof.

[0008] To achieve the above purpose, the present invention adopts the following technical solution:

[0009] A non-aqueous magnesium electrolyte, characterized in that the non-aqueous magnesium electrolyte comprises an organic magnesium salt, an amine additive, a strong reducing additive and a non-aqueous organic solvent; wherein the concentration of the organic magnesium salt in the non-aqueous organic solvent is 0.05-5 mol / L; the molar ratio of the organic magnesium salt to the amine additive is 1:(0.1-50); the molar ratio of the organic magnesium salt to the strong reducing additive is 1:(0-10); the non-aqueous organic solvent is an ether organic solvent;

[0010] The organic magnesium salt is magnesium bis(trifluoromethanesulfonyl)imide.

[0011] The concentration of the organic magnesium salt in the non-aqueous organic solvent is preferably 0.05-0.4 mol / L; the molar ratio of the organic magnesium salt to the amine additive is preferably 1:(1-10); and the molar ratio of the organic magnesium salt to the strong reducing additive is preferably 1:(0-1).

[0012] The amine additive is one or more of tri(dimethylamino)phosphine, bis(dimethylamino)ethyl ether, N-butyldiethanolamine, N-benzyl-N-ethylaniline, N-(2-cyanoethyl)-N-ethylaniline, alachlor oxalamic acid, oxaloamine, tri(dimethylaminopropyl)amine, N-(isopropylimino)isopropylamine, 4-bromo-4'-(diphenylamino)biphenyl, 5-bromo-2-(dimethylamino)pyrimidine and 4-bromotriphenylamine;

[0013] Wherein, when the amine additive is 4-bromo-4'-(diphenylamino)biphenyl, 5-bromo-2-(dimethylamino)pyrimidine and / or 4-bromotriphenylamine, the amount of the strong reducing agent added is 0.

[0014] When other amines are used as amine additives, the molar ratio of the organic magnesium salt to the strong reducing additive is 1:(0.1-1).

[0015] The strong reducing additive is one or more of dibutyl magnesium, tributyl aluminum, methyl magnesium chloride, methyl magnesium bromide, vinyl magnesium chloride, benzyl magnesium chloride, phenyl magnesium bromide, and p-tolyl magnesium bromide;

[0016] The ether organic solvent is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and tetrahydrofuran.

[0017] The amine additive is preferably tris(dimethylamino)phosphine and / or bis(dimethylamino)ethyl ether;

[0018] The strong reducing additive is preferably dibutyl magnesium and / or triisobutyl aluminum;

[0019] The ether organic solvent is preferably diethylene glycol dimethyl ether.

[0020] A method for preparing the non-aqueous magnesium electrolyte is as follows: organic magnesium salts, amines and strong reducing additives are added to a non-aqueous ether organic solvent according to the above proportions, and magnetic stirring is performed until they are completely dissolved to obtain the non-aqueous magnesium electrolyte.

[0021] A secondary energy storage magnesium battery contains the non-aqueous magnesium electrolyte; the negative electrode is metal magnesium; the positive electrode is Mo6S8, MnO2, V2O5, S, CuS, CuSe and Cu3Se2.

[0022] In the above technical solution of the present invention, magnesium bis(trifluoromethanesulfonyl)imide is dissolved in an ether non-aqueous electrolyte as a blank sample, and its electrochemical performance is improved by adding amine additives and strong reducing additives. Since there is no hydrogen atom connected to the nitrogen atom in the tertiary amine additive, the dissociation of hydrogen atoms will not occur, and thus strong negative electricity will not be displayed. In addition, the steric hindrance of the tertiary amine structure is large, so the tertiary amine will not coordinate with the magnesium ion, but will coordinate with small molecules, namely water molecules, to prevent the water molecules from coordinating with the magnesium ions, and prevent the water molecules from migrating with the magnesium ions to the electrode surface to react and passivate the electrode. The addition of additives such as strong reducing properties will eliminate free water in the electrolyte, further reducing the toxicity of water molecules to the battery performance; at the same time, the strong reducing properties of the strong reducing properties are used to eliminate other free radical impurities in the electrolyte and the oxide passivation layer on the electrode surface. The present invention achieves efficient magnesium deposition / dissolution performance through the synergistic effect of amine additives and Grignard reagent additives.

[0023] The advantages of the present invention are:

[0024] The non-aqueous magnesium electrolyte of the present invention comprises components such as an organic magnesium salt, an amine additive, a strong reducing additive and a non-aqueous organic solvent; compared with a blank sample electrolyte (without additives), the non-aqueous magnesium electrolyte has the advantages of higher magnesium deposition / dissolution efficiency, lower deposition overpotential (less than 0.5V), better cycle life, simple preparation and low price. Moreover, the non-aqueous magnesium electrolyte formula can use an organic magnesium salt with lower purity, further reducing the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The constant current charge and discharge curve of the blank magnesium electrolyte (0.1mol / L magnesium bis(trifluoromethanesulfonyl)imide / diethylene glycol dimethyl ether, no additives). The experimental results show that the magnesium deposition overpotential of this electrolyte is very large, about 2.0V. There is almost no charging capacity, that is, the coulomb efficiency is extremely low. And a short circuit occurred within a few hours. The above analysis shows that this electrolyte cannot carry out normal magnesium deposition / dissolution.

[0026] Figure 2The constant current charge-discharge curve of the non-aqueous magnesium electrolyte (0.1 mol / L bis(trifluoromethanesulfonyl)imide magnesium / diethylene glycol dimethyl ether and tri(dimethylamino)phosphine additive) provided in Example 1 of the present invention. The experimental results show that the electrolyte can operate stably at a low overpotential after the activation process.

[0027] Figure 3 The cyclic voltammetry curve of the non-aqueous magnesium electrolyte (0.1 mol / L bis(trifluoromethanesulfonyl)imide magnesium / diethylene glycol dimethyl ether and tri(dimethylamino)phosphine additive) provided in Example 1 of the present invention. The experimental results show that there are reduction peaks and oxidation peaks in the cyclic voltammetry curve of the electrolyte, indicating that it can deposit / dissolve magnesium, which is consistent with the constant current charge and discharge test results.

[0028] Figure 4 The constant current charge-discharge curve of the non-aqueous magnesium electrolyte (0.1 mol / L bis(trifluoromethanesulfonyl)imide magnesium / diethylene glycol dimethyl ether and bis(dimethylaminoethyl)ether additive) provided in Example 2 of the present invention. The experimental results show that the electrolyte has a lower magnesium deposition / dissolution overpotential and can operate stably for a long time. DETAILED DESCRIPTION

[0029] The following examples are further descriptions of the present invention, but the present invention is not limited to the following examples.

[0030] Example 1

[0031] In an argon atmosphere glove box, use a pipette to transfer 1 mL of diethylene glycol dimethyl ether to a 5 mL glass vial, then add 0.03 mL of tri(dimethylamino)phosphine, add a magnetic stirrer for 1 h to prepare a mixed solvent. Weigh 0.058 g of magnesium bis(trifluoromethanesulfonyl)imide, add it to the mixed solvent, continue magnetic stirring for 1 h, and obtain a non-aqueous magnesium electrolyte after stirring.

[0032] A CR2032 button cell was assembled with magnesium foil as the negative electrode, the non-aqueous electrolyte as the electrolyte, and copper foil as the positive electrode. Constant current charge and discharge tests were performed using the LAND battery test system (see Figure 2 ), the test current density is 0.1mAh / cm 2 The test procedure is to discharge for 1h, charge to 2.0V, and repeat the charge and discharge. Cyclic voltammetry test is performed using an electrochemical workstation (see Figure 3 ), and further studied the magnesium deposition / dissolution performance at a scan rate of 25mV / s. The test results show that the non-aqueous electrolyte can work stably at low deposition potentials.

[0033] Example 2

[0034] In an argon atmosphere glove box, use a pipette to transfer 1 mL of diethylene glycol dimethyl ether to a 5 mL glass vial, then add 0.12 mL of bis(dimethylaminoethyl)ether, add a magnetic stirrer for 1 h to prepare a mixed solvent. Weigh 0.058 g of magnesium bis(trifluoromethanesulfonyl)imide, add it to the mixed solvent, continue magnetic stirring for 1 h, and obtain a non-aqueous magnesium electrolyte after stirring.

[0035] A CR2032 button cell was assembled with magnesium foil as the negative electrode, the non-aqueous electrolyte as the electrolyte, and copper foil as the positive electrode. Constant current charge and discharge tests were performed using the LAND battery test system (see Figure 4 ), the test current density is 0.1mAh / cm 2 The test procedure is to discharge for 1h, charge to 2.0V, and repeat the charge and discharge. Cyclic voltammetry test was performed using an electrochemical workstation to further study the magnesium deposition / dissolution performance, with a scan rate of 25mV / s. The test results show that the non-aqueous electrolyte can work stably at a low deposition potential.

[0036] Example 3

[0037] In a glove box with an argon atmosphere, 1 mL of diethylene glycol dimethyl ether was transferred to a 5 mL glass vial using a pipette, and then 0.058 g of magnesium bis(trifluoromethanesulfonyl)imide was weighed and added to the solvent, and magnetic stirring was performed for 1 h. After stirring, 25 μL of 1 mol / L dibutyl magnesium / tetrahydrofuran solution was added, and magnetic stirring was continued for 1 h. After stirring, 0.03 mL of tri(dimethylamino)phosphine was added, and magnetic stirring was performed for 1 h using a magnet. After stirring, a non-aqueous magnesium electrolyte was obtained.

[0038] A CR2032 button battery was assembled with magnesium foil as the negative electrode, the non-aqueous electrolyte as the electrolyte, and copper foil as the positive electrode. The constant current charge and discharge test was performed using the LAND battery test system, and the test current density was 0.1 mAh / cm 2 The test procedure is to discharge for 1h, charge to 2.0V, and repeat the charge and discharge. Cyclic voltammetry test was performed using an electrochemical workstation to further study the magnesium deposition / dissolution performance, with a scan rate of 25mV / s. The test results show that the non-aqueous electrolyte can work stably at a low deposition potential.

[0039] Example 4

[0040] In a glove box with an argon atmosphere, 1 mL of diethylene glycol dimethyl ether was transferred to a 5 mL glass vial using a pipette, and then 0.058 g of magnesium bis(trifluoromethanesulfonyl)imide was weighed and added to the solvent, and magnetic stirring was performed for 1 h. After stirring, 25 μL of 1 mol / L 1 mol / L triisobutylaluminum / toluene solution was added, and magnetic stirring was continued for 1 h. After stirring, 0.12 mL of bis(dimethylamino)ethyl ether was added, and magnetic stirring was performed for 1 h using a magnetic son. After stirring, a non-aqueous magnesium electrolyte was obtained.

[0041] A CR2032 button battery was assembled with magnesium foil as the negative electrode, the non-aqueous electrolyte as the electrolyte, and copper foil as the positive electrode. The constant current charge and discharge test was performed using the LAND battery test system, and the test current density was 0.1 mAh / cm 2 The test procedure is to discharge for 1h, charge to 2.0V, and repeat the charge and discharge. Cyclic voltammetry test was performed using an electrochemical workstation to further study the magnesium deposition / dissolution performance, with a scan rate of 25mV / s. The test results show that the non-aqueous electrolyte can work stably at a low deposition potential.

Claims

1. A non-aqueous magnesium electrolyte, characterized in that: It is composed of 1 mL of diethylene glycol dimethyl ether, 0.03 mL of tris(dimethylamino)phosphine, and 0.058 g of bis(trifluoromethanesulfonyl)imide magnesium.

2. The nonaqueous magnesium electrolyte according to claim 1, characterized in that: The 0.03 mL of tris(dimethylamino)phosphine was replaced by 0.12 mL of bis(dimethylamino)ethyl ether.

3. The nonaqueous magnesium electrolyte according to claim 1, characterized in that: Also included was 25 μL of a 1 mol / L dibutylmagnesium / tetrahydrofuran solution.

4. The nonaqueous magnesium electrolyte according to claim 2, characterized in that: Also included was 25 μL of a 1 mol / L triisobutylaluminum / toluene solution.

5. A secondary energy storage magnesium battery, characterized in that: A non-aqueous magnesium electrolyte comprising any one of claims 1 to 4; a negative electrode being metallic magnesium; and a positive electrode being Mo6S8, MnO2, V2O5, S, CuS, CuSe and Cu3Se2.

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