Magnesium ion-containing water-alcohol mixed electrolyte and application thereof

Abstract

The application discloses a kind of magnesium ion-containing water-alcohol mixed electrolyte and application, the electrolyte includes solvent, magnesium salt and additive, the solvent is the mixed solvent of water, alcohol organic matter, the additive is water-soluble carboxylic acid, the volume molar concentration of the additive is 0.01-2 mol / L.The electrolyte of the application has wide electrochemical stability window and higher ionic conductivity, and the raw material used is safe and easy to obtain, the preparation method is simple, and the cost is low, conducive to large-scale batch production.The electrolyte of the application is applied to magnesium ion-containing secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, in particular to a magnesium ion-containing water-alcohol mixed electrolyte and application thereof. BACKGROUND

[0002] Compared with the intercalation-type negative electrode material used in traditional lithium-ion batteries, direct use of metal negative electrodes can produce higher energy density and faster kinetics. Rechargeable magnesium batteries have broad application prospects due to their low reduction potential (-2.36 V vs. SHE) and theoretical volume capacity (3833 mAh cm-2).

[0003] In the field of rechargeable magnesium batteries, the development of organic electrolytes for rechargeable magnesium batteries has always been an important research topic. Magnesium can undergo reversible reactions in the electrolyte of Grignard reagent. However, Grignard reagent electrolyte exhibits a narrow electrochemical window (≤2.0 V) on alkaline metal current collectors (such as Al, Cu, Ni, stainless steel, etc.) (J. Electrochem. Soc., 2012, 160(2): A351). Organic boron magnesium salt as a solute and aprotic polar configuration with organic ethers can effectively broaden the electrochemical window (CN 102916220 A), but the strong coordination between magnesium ions in organic electrolyte and the solvent and the small ionic conductivity seriously damage their diffusion kinetics, and the cost is high, and the synthesis process is complex. These limitations of organic electrolytes have prompted researchers to develop water magnesium batteries.

[0004] However, the development of aqueous solution magnesium batteries also faces challenges. The first is the narrow electrochemical window of aqueous solution electrolyte. The narrow window limits the choice of positive and negative electrode materials. By using eutectic electrolyte, the electrochemical window of the electrolyte is widened, but the compatibility of magnesium with the electrolyte still needs to be explored (J. Am. Chem. Soc., 2024, 146(0): 7018-7028, Energy Environ. Sci., 2022, 15(3): 1282-1292). Another challenge is the serious passivation and corrosion of the magnesium electrode, especially in traditional aqueous solution electrolytes. In conventional aqueous solution electrolytes, due to the high activity of metallic magnesium, magnesium itself will undergo self-discharge. Even if the electroplating reaction occurs, the newly generated magnesium will quickly react with water molecules to produce hydrogen and Mg(OH)2 or MgO, leading to the formation of a passivation layer, which hinders the transmission of electrons and ions and eventually leads to battery failure.

[0005] In summary, there are many deficiencies in the electrolyte of rechargeable magnesium batteries at present. SUMMARY

[0006] In order to solve the above technical problems, the application provides a magnesium ion water-alcohol mixed electrolyte, which has a wide electrochemical stability window and high ionic conductivity, and raw materials are safe and easy to obtain, the preparation method is simple, the cost is low, and large-scale batch production is facilitated.

[0007] In order to achieve the above object, the technical scheme adopted by the application is as follows:

[0008] The application provides a magnesium ion water-alcohol mixed electrolyte, which comprises a solvent, a magnesium salt and an additive, and the solvent is a mixed solvent of water and alcohol organic matter.

[0009] Preferably, the alcohol organic matter is a binary or multi-alcohol organic matter.

[0010] Preferably, the binary or multi-alcohol organic matter is one or more of ethylene glycol, glycerol and 1,2 butanediol.

[0011] Preferably, the volume ratio of the water and the binary or multi-alcohol organic matter is 10:1-1:4.

[0012] Preferably, the additive is a water-soluble carboxylic acid.

[0013] Preferably, the additive is one or more of lactobionic acid, citric acid and malonic acid.

[0014] Preferably, the volume molar concentration of the additive is 0.01-2 mol / L.

[0015] Preferably, the magnesium salt comprises one or more of magnesium chloride, magnesium perchlorate, magnesium trifluoromethanesulfonate and bis(trifluoromethanesulfonylimide) magnesium.

[0016] Preferably, the mass molar concentration of the magnesium salt is 1-5.5 mol / kg.

[0017] The electrolyte is applied to a magnesium ion-containing secondary battery.

[0018] Compared with the prior art, the application has the following beneficial effects:

[0019] (1) The application uses water and alcohol organic matter as the solvent, and the magnesium salt has good solubility in the solvent, and the magnesium ion water-alcohol mixed electrolyte has high ionic conductivity.

[0020] (2) Due to the introduction of the dihydric or polyhydric alcohol organic matter, the dihydric or polyhydric alcohol interacts with the water molecules around the magnesium ions, so that the solvation state of the magnesium ions in the mixed electrolyte changes, effectively broadening the potential window, reducing the water activity, reducing the corrosion and passivation of the magnesium electrode, so that the magnesium negative electrode can be reversibly cycled in the electrolyte, and the cycle capacity and life of the magnesium ion battery can be improved.

[0021] (3) The additive is a water-soluble carboxylic acid, and the negatively charged oxygen atom of the carboxylate group has a certain electrophilicity, which preferentially binds to the negative electrode during the cycle. In addition, the lactose molecules in the solution will be complexed with magnesium, changing the solvation environment of the electrolyte and effectively broadening the potential window. Preferably, such as lactobionic acid has carboxyl and hydroxyl groups, in addition to the carboxylate group, plus the hydroxyl group binds part of the water due to the action of hydrogen bonds, limiting the contact between water and magnesium, thereby alleviating the side reaction.

[0022] (4) The mixed electrolyte of the present application uses readily available raw materials and has a simple and convenient preparation process, low cost, and is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Electrochemical window diagram of the mixed electrolyte prepared for Example 1.

[0024] Figure 2 Electrochemical window diagram of the mixed electrolyte prepared for Example 2.

[0025] Figure 3 Electrochemical window diagram of the mixed electrolyte prepared for Example 3.

[0026] Figure 4 Cycle diagram of the symmetric battery assembled based on the mixed electrolyte prepared in Example 1.

[0027] Figure 5 Cycle diagram of the symmetric battery assembled based on the mixed electrolyte prepared in Example 2.

[0028] Figure 6 Cycle diagram of the symmetric battery assembled based on the mixed electrolyte prepared in Example 3.

[0029] Figure 7 Cyclic voltammogram of the battery assembled based on the mixed electrolyte prepared in Example 2.

[0030] Figure 8 Cycle diagram of the battery assembled based on the mixed electrolyte prepared in Example 2. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be further described below in combination with examples. The examples are used to explain the embodiments of the present application and do not exceed the scope of the subject matter of the present application, and the protection scope of the present application is not limited by the examples.

[0032] Those skilled in the art can make appropriate process, parameter improvement and optimization with reference to the content herein, and when these improvements do not deviate from the spirit and scope of the present application, they are all within the protection scope required by the present application.

[0033] In the following examples, the positive and negative electrodes of the symmetrical battery are both 250 nm thick magnesium sheets, and the electrolyte content is 3.5 ml. After the magnesium / magnesium symmetrical battery is assembled, it is placed at room temperature for 5 minutes, and then tested by constant current test method, with a test current density of 0.1 mA / cm 2 , and a test capacity density of 0.1 mAh / cm 2 .

[0034] The full battery is made of CuHCF as the positive electrode, 250 nm magnesium sheet as the negative electrode, and the electrolyte content is 3.5 ml. After the full battery is assembled, it is placed at room temperature for 5 minutes. The cyclic voltammetry test is used, with a test scanning speed of 1 mV / s and a voltage interval of 1-3 V. The constant rate test method is used for testing, with a rate of 100 mA / g for 5 cycles for activation, and then the rate is increased to 1000 mA / g for testing, with a cycle voltage interval of 1-3 V.

[0035] Preparation of the positive electrode sheet: the active material, conductive agent and binder are mixed in proportion, dropped on the carbon cloth, and then baked in a vacuum oven at 80°C for 12 hours. The active material is CuHCF, the conductive agent is Ketjen black, and the binder is sodium carboxymethyl cellulose, mixed in a mass ratio of active material: conductive agent: binder = 8:1:1.

[0036] Preparation of the negative electrode sheet: the magnesium sheet is soaked in 0.1 M sulfuric acid for 30 seconds to remove the oxide layer, and then washed with ultrapure water and dried for standby use.

[0037] For the ionic conductivity of the electrolyte, it is evaluated by a conductivity meter at room temperature.

[0038] For the mass molar concentration of magnesium salt, a thermal gravimetric analyzer is used for testing, with argon as the protective gas atmosphere, a flow rate of 20 mL / min, a temperature rising speed of 5°C / min, and a test temperature range of room temperature to 200°C. Under normal conditions, water and ethylene glycol are easy to evaporate, and are completely lost at about 200°C, while the decomposition temperature of magnesium perchlorate is 251°C. The mass molar concentration is obtained by comparing the remaining mass and the mass loss.

[0039] A three-electrode system was applied to the electrochemical window test. Among them, the working electrode was a glassy carbon electrode, the counter electrode was a Pt electrode, and the reference electrode was a magnesium sheet. Linear sweep voltammetry test was used for testing, and the test scan speed was 10 mV / s. Example 1

[0040] Preparation of mixed electrolyte:

[0041] (1) Excess Mg(ClO4)2 was dissolved in ultrapure water and completely dissolved at 80°C, and then placed in a 30°C oven to wait for Mg(ClO4)2 to precipitate, to obtain saturated magnesium perchlorate, and the upper clear liquid was used as solution A;

[0042] Mg(ClO4)2 was mixed with ethylene glycol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B;

[0043] (2) The solution A prepared in step (1) was mixed with solution B according to a volume ratio of 1:1 and stirred uniformly to obtain a magnesium ion mixed electrolyte of 5.1 mol / Kg.

[0044] (3) 0.1 mol / L lactobionic acid was added to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte.

[0045] The mixed electrolyte prepared in this example 1 was tested by conductivity meter, and the conductivity at room temperature was 16.92 mS / cm.

[0046] As shown in Figure 1 , the mixed electrolyte prepared in this example 1 has a wide electrochemical window, about 3.6 V.

[0047] As shown in Figure 4 , the magnesium-magnesium symmetric battery shows stable charge-discharge curves, and the cycle life can reach 250 h. Example 2

[0048] Preparation of mixed electrolyte:

[0049] (1) Excess Mg(ClO4)2 was dissolved in ultrapure water and completely dissolved at 80°C, and then placed in a 30°C oven to wait for Mg(ClO4)2 to precipitate, to obtain saturated magnesium perchlorate, and the upper clear liquid was used as solution A;

[0050] Mg(ClO4)2 was mixed with ethylene glycol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B;

[0051] (2) The solution A prepared in step (1) was mixed with solution B according to a volume ratio of 1:1 and stirred uniformly to obtain a magnesium ion mixed electrolyte of 5.1 mol / Kg.

[0052] (3) 0.5 mol / L lactobionic acid was added to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte.

[0053] The mixed electrolyte prepared in Example 2 was tested by a conductivity meter, and the conductivity at room temperature was 12.7 mS / cm.

[0054] As shown in Figure 2 , the mixed electrolyte prepared in Example 2 has a wide electrochemical window of about 4 V.

[0055] As shown in Figure 5 , the magnesium-magnesium symmetric battery shows a stable charge-discharge curve, and the cycle life can reach 300 h.

[0056] As shown in Figure 7 , it can be known through testing that the full battery has a pair of redox peaks near 2 V and 2.7 V, which indicates that the battery has a high discharge platform. At the same time, after 3 scans, there is almost no change in capacity, indicating that the battery has good reversibility.

[0057] As shown in Figure 8 , the full battery can cycle 600 times at a current density of 1000 mA / g, with a capacity of 22.42 mAh / g. Example 3

[0058] Preparation of mixed electrolyte:

[0059] (1) Excess Mg(ClO4)2 was dissolved in ultrapure water and completely dissolved at 80°C, and then placed in a 30°C oven to wait for Mg(ClO4)2 to precipitate, to obtain saturated magnesium perchlorate. The upper clear liquid was used as solution A;

[0060] Mg(ClO4)2 was mixed with ethylene glycol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B;

[0061] (2) Solution A and solution B prepared in step (1) were mixed in a volume ratio of 1:1 and stirred uniformly to obtain a magnesium ion mixed electrolyte of 5.1 mol / Kg.

[0062] (3) 1 mol / L lactobionic acid was added to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte.

[0063] The mixed electrolyte prepared in Example 3 was tested by a conductivity meter, and the conductivity at room temperature was 6.02 mS / cm.

[0064] As shown in Figure 3As shown, the mixed electrolyte prepared in Example 3 has a wide electrochemical window of approximately 4.1 V.

[0065] like Figure 6 As shown, the magnesium-magnesium symmetric battery exhibits a stable charge-discharge curve and a cycle life of up to 250 hours. Example 4

[0066] Preparation of mixed electrolyte:

[0067] (1) Dissolve excess Mg(ClO4)2 in ultrapure water and completely dissolve it at 80°C. Then place it in an oven at 30°C and wait for Mg(ClO4)2 to precipitate to obtain saturated magnesium perchlorate. Use the supernatant as solution A.

[0068] Mg(ClO4)2 and ethylene glycol were mixed in a 1:1 molar ratio and stirred for 12 h to obtain solution B;

[0069] (2) Mix solution A and solution B prepared in step (1) at a volume ratio of 4:1 and stir evenly to obtain magnesium ion mixed electrolyte.

[0070] (3) Add 0.1 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the required mixed electrolyte. Example 5

[0071] Preparation of mixed electrolyte:

[0072] (1) Dissolve excess Mg(ClO4)2 in ultrapure water and completely dissolve it at 80°C. Then place it in an oven at 30°C and wait for Mg(ClO4)2 to precipitate to obtain saturated magnesium perchlorate. Use the supernatant as solution A.

[0073] (2) Mix the solution A prepared in step (1) with glycerol at a volume ratio of 4:1 and stir until homogeneous to obtain a magnesium ion mixed electrolyte.

[0074] (3) Add 0.1 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the required mixed electrolyte. Example 6

[0075] Preparation of mixed electrolyte:

[0076] (1) Dissolve excess Mg(ClO4)2 in ultrapure water and completely dissolve it at 80°C. Then place it in an oven at 30°C and wait for Mg(ClO4)2 to precipitate to obtain saturated magnesium perchlorate. Use the supernatant as solution A.

[0077] (2) The solution A prepared in step (1) is mixed with 1,2-butanediol in a volume ratio of 4:1 and stirred uniformly to obtain a magnesium ion mixed electrolyte.

[0078] (3) 0.1 mol / L lactobionic acid is added to the magnesium ion mixed electrolyte prepared in step (2) to obtain the required mixed electrolyte. Example 7

[0079] Preparation of the mixed electrolyte:

[0080] (1) Excessive Mg(OTf)2 is dissolved in ultrapure water and completely dissolved at 80°C, and then placed in a 30°C oven to wait for Mg(OTf)2 to precipitate, to obtain saturated Mg(OTf)2, and the supernatant is used as solution A;

[0081] (2) The solution A prepared in step (1) is mixed with ethylene glycol in a volume ratio of 1:1 and stirred uniformly to obtain a magnesium ion mixed electrolyte.

[0082] (3) 0.1 mol / L lactobionic acid is added to the magnesium ion mixed electrolyte prepared in step (2) to obtain the required mixed electrolyte. Example 8

[0083] Preparation of the mixed electrolyte:

[0084] (1) Excessive Mg(TFSI)2 is dissolved in ultrapure water and completely dissolved at 80°C, and then placed in a 30°C oven to wait for Mg(TFSI)2 to precipitate, to obtain saturated (TFSI)2, and the supernatant is used as solution A;

[0085] (2) The solution A prepared in step (1) is mixed with ethylene glycol in a volume ratio of 1:1 and stirred uniformly to obtain a magnesium ion mixed electrolyte.

[0086] (3) 0.1 mol / L lactobionic acid is added to the magnesium ion mixed electrolyte prepared in step (2) to obtain the required mixed electrolyte. Example 9

[0087] Preparation of the mixed electrolyte:

[0088] (1) Excessive MgCl2 is dissolved in ultrapure water and completely dissolved at 80°C, and then placed in a 30°C oven to wait for MgCl2 to precipitate, to obtain saturated magnesium perchlorate, and the supernatant is used as solution A;

[0089] MgCl2 is mixed with glycerol in a molar ratio of 1:14 and stirred for 12 h to obtain solution B;

[0090] (2) The solution A prepared in step (1) is mixed with solution B in a volume ratio of 9:1 and stirred uniformly to obtain a magnesium ion mixed electrolyte.

[0091] (3) 0.1 mol / L of lactobionic acid is added to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte. Example 10

[0092] Preparation of the mixed electrolyte:

[0093] (1) Excess Mg(ClO4)2 is dissolved in ultrapure water and completely dissolved at 80°C, and then placed in a 30°C oven to wait for Mg(ClO4)2 to precipitate, to obtain saturated magnesium perchlorate, and the supernatant is used as solution A;

[0094] Mg(ClO4)2 is mixed with ethylene glycol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B;

[0095] (2) The solution A prepared in step (1) is mixed with solution B in a volume ratio of 1:1 and stirred uniformly to obtain a magnesium ion mixed electrolyte of 5.1 mol / Kg.

[0096] (3) 0.1 mol / L of citric acid is added to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte. Example 11

[0097] Preparation of the mixed electrolyte:

[0098] (1) Excess Mg(ClO4)2 is dissolved in ultrapure water and completely dissolved at 80°C, and then placed in a 30°C oven to wait for Mg(ClO4)2 to precipitate, to obtain saturated magnesium perchlorate, and the supernatant is used as solution A;

[0099] Mg(ClO4)2 is mixed with ethylene glycol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B;

[0100] (2) The solution A prepared in step (1) is mixed with solution B in a volume ratio of 1:1 and stirred uniformly to obtain a magnesium ion mixed electrolyte of 5.1 mol / Kg.

[0101] (3) 0.1 mol / L of malonic acid is added to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte.

[0102] Some results of Examples 4-11 are summarized in Table 1

[0103] Table 1 Ion conductivity, electrochemical window and cycle life of Examples 4-11

[0104] Example Ionic conductivity (mS / cm) Electrochemical window (V) Magnesium-magnesium symmetric cell cycle life (h) 4 29.5 3.85 98 5 20.3 3.90 122 6 38.7 3.88 84 7 8.15 3.2 130 8 9.10 3.1 140 9 43.5 3.05 105 10 28.9 4.2 101 11 26 3.8 98

Claims

1. A magnesium ion-containing aqueous-alcoholic electrolyte, said electrolyte comprising a solvent, a magnesium salt and an additive, characterized in that: The solvent is a mixed solvent of water and alcohol organic matter, and the additive is one or both of lactobionic acid and citric acid.

2. The electrolyte according to claim 1, characterized in that: The alcohol organic matter is a binary or polyhydric alcohol organic matter.

3. The electrolyte of claim 2, wherein: The binary or polyhydric alcohol organic matter is one or more of ethylene glycol, glycerol and 1,2-butanediol.

4. The electrolyte of claim 2, wherein: The volume ratio of the water and the binary or polyhydric alcohol organic matter is 10:1-1:

4.

5. The electrolyte of claim 1, wherein: The volume molar concentration of the additive is 0.01-2 mol / L.

6. The electrolyte of claim 1, wherein: The magnesium salt includes one or more of magnesium chloride, magnesium perchlorate, magnesium trifluoromethanesulfonate and bis(trifluoromethanesulfonylimide) magnesium.

7. The electrolyte of claim 6, wherein: The mass molar concentration of the magnesium salt is 1-5.5 mol / kg.

8. Use of an electrolyte according to any one of claims 1 to 7, characterized in that: The electrolyte is applied to a secondary battery with a magnesium metal negative electrode containing magnesium ions.

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