Magnesium-containing ion water-alcohol mixed electrolyte and application

Abstract

The invention discloses a magnesium ion-containing water-alcohol mixed electrolyte and application, the electrolyte comprises a solvent, magnesium salt and an additive, the solvent is a mixed solvent of water and alcohol organic matters, the additive is water-soluble carboxylic acid, and the volume molar concentration of the additive is 0.01-2 mol / L. The electrolyte has a wide electrochemical stability window and high ionic conductivity, the adopted raw materials are safe and easy to obtain, the preparation method is simple, the cost is low, and large-scale batch production is facilitated. The electrolyte is applied to a secondary battery containing magnesium ions.

Description

Technical Field

[0001] The invention relates to the field of electrochemical energy storage, and in particular to a water-alcohol mixed electrolyte containing magnesium ions and applications thereof. Background Art

[0002] Compared with the intercalation-type anode materials used in traditional lithium-ion batteries, the direct use of metal anodes 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 volumetric 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 Grignard reagent electrolytes. However, Grignard reagent electrolytes exhibit 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). Electrolytes composed of organic boron magnesium salts as solutes and non-protonic polar configurations such as organic ethers can effectively broaden the electrochemical window (CN 102916220 A), but the strong coordination between magnesium ions and solvents in organic electrolytes and the low ionic conductivity seriously damage their diffusion kinetics, and the cost is high and the synthesis process is complicated. These limitations of organic electrolytes have prompted researchers to develop aqueous magnesium batteries.

[0004] However, the development of aqueous magnesium batteries also faces challenges. The first is the narrow electrochemical window of aqueous electrolytes. Too narrow a window limits the choice of positive and negative electrode materials. The electrochemical window of the electrolyte is broadened by using eutectic electrolytes, but the compatibility of magnesium with the electrolyte remains to be explored (J. Am. Chem. Soc., 2024, 146(0): 7018–7028, Energy Environ. Sci., 2022, 15(3): 1282-1292). Another challenge is the severe passivation and corrosion of magnesium electrodes, especially in traditional aqueous electrolytes. In conventional aqueous electrolytes, magnesium itself will self-discharge due to the high activity of metallic magnesium. Even if an 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 will hinder the transfer of electrons and ions and ultimately lead to battery failure.

[0005] In summary, there are many deficiencies in the electrolyte of rechargeable magnesium batteries. Summary of the invention

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

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The invention provides a water-alcohol mixed electrolyte containing magnesium ions. The electrolyte comprises a solvent, a magnesium salt and an additive. The solvent is a mixed solvent of water and alcohol organic matter.

[0008] Preferably, the alcohol organic compound is a dihydric or polyhydric alcohol organic compound.

[0009] Preferably, the dihydric or polyhydric alcohol organic substance is one or more of ethylene glycol, glycerol and 1,2-butanediol.

[0010] Preferably, the volume ratio of water to dihydric or polyhydric alcohol organic matter is 10:1-1:4.

[0011] Preferably, the additive is a water-soluble carboxylic acid.

[0012] Preferably, the additive is one or more of lactobionic acid, citric acid, and malonic acid.

[0013] Preferably, the molar concentration of the additive is 0.01-2 mol / L.

[0014] Preferably, the magnesium salt comprises one or more of magnesium chloride, magnesium perchlorate, magnesium trifluoromethanesulfonate and magnesium bis(trifluoromethanesulfonyl imide); Preferably, the mass molar concentration of the magnesium salt is 1-5.5 mol / kg.

[0015] The electrolyte is applied to a secondary battery containing magnesium ions.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) Since the present invention uses water and alcohol organic matter as solvents, the magnesium salt can have good solubility in the solvents, and the magnesium ion-containing water-alcohol mixed electrolyte of the present invention has high ion conductivity.

[0017] (2) Due to the introduction of binary or polyol organic matter, the binary or polyol interacts with the water molecules around the magnesium ions, causing the solvation state of the magnesium ions in the mixed electrolyte to change, effectively widening its potential window, reducing the water activity, and alleviating the corrosion and passivation of the magnesium electrode, so that the magnesium negative electrode can be reversibly circulated in the electrolyte, which can improve the cycle capacity and life of the magnesium ion battery.

[0018] (3) The additive is a water-soluble carboxylic acid. The negatively charged oxygen atom of the carboxylate group has a certain electrophilicity and preferentially binds to the negative electrode during the cycle. In addition, the lactic acid sugar molecules in the solution will form a complex with magnesium, changing the solvation environment in the electrolyte and effectively widening its potential window. Preferably, lactobionic acid has carboxyl and hydroxyl groups. In addition to the carboxylate group, the hydroxyl group also binds part of the water due to the action of hydrogen bonds, limiting the contact between water and magnesium, thereby alleviating side reactions.

[0019] (4) The mixed electrolyte of the present invention 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 THE DRAWINGS

[0020] Figure 1 This is the electrochemical window diagram of the mixed electrolyte prepared in Example 1.

[0021] Figure 2 This is the electrochemical window diagram of the mixed electrolyte prepared in Example 2.

[0022] Figure 3 This is the electrochemical window diagram of the mixed electrolyte prepared in Example 3.

[0023] Figure 4 : This is a cycle diagram of a symmetrical battery assembled based on the mixed electrolyte prepared in Example 1.

[0024] Figure 5 This is a cycle diagram of a symmetrical battery assembled based on the mixed electrolyte prepared in Example 2.

[0025] Figure 6 This is a cycle diagram of a symmetrical battery assembled based on the mixed electrolyte prepared in Example 3.

[0026] Figure 7 The cyclic voltammogram of the battery assembled based on the mixed electrolyte prepared in Example 2.

[0027] Figure 8 This is a cycle diagram of a battery assembled based on the mixed electrolyte prepared in Example 2. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be further described below in conjunction with examples. The examples are used to explain the implementation scheme of the present invention and do not exceed the scope of the subject matter of the present invention. The protection scope of the present invention is not limited by the examples.

[0029] Those skilled in the art can refer to the contents of this article to make appropriate process and parameter improvements and optimizations. When these improvements do not depart from the spirit and scope of the invention, they are within the scope of protection required by the invention.

[0030] 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 left to stand at room temperature for 5 minutes and then tested using a constant current test method with a test current density of 0.1 mA / cm 2 , the test capacity density is 0.1 mAh / cm 2 .

[0031] The full battery is composed 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 left to stand at room temperature for 5 minutes. Cyclic voltammetry is used for testing, with a scan rate of 1 mV / s and a voltage range of 1-3 V. The constant rate test method is used for testing, with 5 cycles at a rate of 100 mA / g for activation, and then the rate is increased to 1000 mA / g for testing, with a cycle voltage range of 1-3 V.

[0032] Preparation of positive electrode sheet: Active material, conductive agent and binder are mixed in proportion, dripped on carbon cloth, and then baked in a vacuum oven at 80°C for 12 h. The active material is CuHCF, the conductive agent is Ketjen black, and the binder is sodium carboxymethyl cellulose, and the mass ratio is active material: conductive agent: binder = 8:1:1.

[0033] Preparation of negative electrode sheet: Soak the magnesium sheet in 0.1 M sulfuric acid for 30 s to remove the oxide layer, then wash with ultrapure water and dry for later use.

[0034] The ionic conductivity of the electrolyte was evaluated using a conductivity meter at room temperature.

[0035] The mass molar concentration of magnesium salt was tested by thermogravimetric analyzer, with argon as the protective gas atmosphere, a flow rate of 20 mL / min, a heating rate of 5 ℃ / min, and a test temperature range of room temperature to 200 ℃. Under normal conditions, water and ethylene glycol are easy to evaporate and completely lost at around 200 ℃, while the decomposition temperature of magnesium perchlorate is 251 ℃. The result was obtained by comparing the remaining mass and the lost mass.

[0036] The three-electrode system was used for the electrochemical window test. The working electrode was a glassy carbon electrode, the counter electrode was a Pt electrode, and the reference electrode was a magnesium sheet. The linear sweep voltammetry method was used for the test, and the test scan rate was 10 mV / s. Example 1

[0037] Preparation of mixed electrolyte: (1) Excess Mg(ClO 4 ) 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C to wait for M Mg(ClO 4 )2 Precipitate to obtain saturated magnesium perchlorate, and use the supernatant as solution A; Mg(ClO 4 ) 2 mixed with ethylene glycol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B; (2) Solution A and solution B prepared in step (1) were mixed in a volume ratio of 1:1 and stirred to obtain a 5.1 mol / kg magnesium ion mixed electrolyte.

[0038] (3) Add 0.1 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte.

[0039] The mixed electrolyte prepared in Example 1 was tested by a conductivity meter, and the conductivity at room temperature was 16.92 mS / cm.

[0040] like Figure 1 As shown, the mixed electrolyte prepared in Example 1 has a wide electrochemical window of about 3.6 V.

[0041] like Figure 4 As shown, the magnesium-magnesium symmetric battery exhibits a stable charge and discharge curve and a cycle life of up to 250 h. Example 2

[0042] Preparation of mixed electrolyte: (1) Excess Mg(ClO 4 ) 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C and wait for Mg(ClO 4 ) 2 Precipitate to obtain saturated magnesium perchlorate, and use the supernatant as solution A; Mg(ClO 4 ) 2 mixed with ethylene glycol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B; (2) Solution A and solution B prepared in step (1) were mixed in a volume ratio of 1:1 and stirred to obtain a 5.1 mol / kg magnesium ion mixed electrolyte.

[0043] (3) Add 0.5 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte.

[0044] The mixed electrolyte prepared in Example 2 was tested by a conductivity meter, and the conductivity at room temperature was 12.7 mS / cm.

[0045] like Figure 2As shown, the mixed electrolyte prepared in Example 2 has a wide electrochemical window of about 4 V.

[0046] like Figure 5 As shown, the magnesium-magnesium symmetric battery exhibits a stable charge and discharge curve and a cycle life of up to 300 h.

[0047] like Figure 7 As shown in the figure, after testing, it can be known that the full battery has a pair of redox peaks near 2 V and 2.7 V, which shows 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.

[0048] like Figure 8 As shown, 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

[0049] Preparation of mixed electrolyte: (1) Excess Mg(ClO 4 ) 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C and wait for Mg(ClO 4 ) 2 Precipitate to obtain saturated magnesium perchlorate, and use the supernatant as solution A; Mg(ClO 4 ) 2 mixed with ethylene glycol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B; (2) Solution A and solution B prepared in step (1) were mixed in a volume ratio of 1:1 and stirred to obtain a 5.1 mol / kg magnesium ion mixed electrolyte.

[0050] (3) Add 1 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte.

[0051] The mixed electrolyte prepared in Example 3 was tested by a conductivity meter, and the conductivity at room temperature was 6.02 mS / cm.

[0052] like Figure 3 As shown, the mixed electrolyte prepared in Example 3 has a wide electrochemical window of about 4.1 V.

[0053] like Figure 6 As shown, the magnesium-magnesium symmetric battery exhibits a stable charge and discharge curve and a cycle life of up to 250 h. Example 4

[0054] Preparation of mixed electrolyte: (1) Excess Mg(ClO 4 ) 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C and wait for Mg(ClO 4 ) 2 Precipitate to obtain saturated magnesium perchlorate, and use the supernatant as solution A; Mg(ClO 4 ) 2 mixed with ethylene glycol at a molar ratio of 1:1 and stirred for 12 h to obtain solution B; (2) The solution A and solution B prepared in step (1) are mixed in a volume ratio of 4:1 and stirred evenly to obtain a magnesium ion mixed electrolyte.

[0055] (3) Add 0.1 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte. Example 5

[0056] Preparation of mixed electrolyte: (1) Excess Mg(ClO 4 ) 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C and wait for Mg(ClO 4 ) 2 Precipitate to obtain saturated magnesium perchlorate, and use the supernatant as solution A; (2) The solution A prepared in step (1) and glycerol are mixed in a volume ratio of 4:1 and stirred evenly to obtain a magnesium ion mixed electrolyte.

[0057] (3) Add 0.1 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte. Example 6

[0058] Preparation of mixed electrolyte: (1) Excess Mg(ClO 4 ) 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C and wait for Mg(ClO 4 ) 2 Precipitate to obtain saturated magnesium perchlorate, and use the supernatant as solution A; (2) The solution A prepared in step (1) and 1,2-butanediol are mixed in a volume ratio of 4:1 and stirred evenly to obtain a magnesium ion mixed electrolyte.

[0059] (3) Add 0.1 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte. Example 7

[0060] Preparation of mixed electrolyte: (1) Excess Mg(OTf) 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C to wait for Mg(OTf) 2 Precipitate to obtain saturated Mg(OTf) 2 , the supernatant was taken as solution A; (2) The solution A prepared in step (1) and ethylene glycol are mixed in a volume ratio of 1:1 and stirred evenly to obtain a magnesium ion mixed electrolyte.

[0061] (3) Add 0.1 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte. Example 8

[0062] Preparation of mixed electrolyte: (1) Excess Mg(TFSI) 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C to wait for Mg(TFSI) 2 Precipitate to obtain saturated (TFSI) 2 , the supernatant was taken as solution A; (2) The solution A prepared in step (1) and ethylene glycol are mixed in a volume ratio of 1:1 and stirred evenly to obtain a magnesium ion mixed electrolyte.

[0063] (3) Add 0.1 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte. Example 9

[0064] Preparation of mixed electrolyte: (1) Excess MgCl 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C to wait for MgCl 2 Precipitate to obtain saturated magnesium perchlorate, and use the supernatant as solution A; MgCl 2 mixed with glycerol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B; (2) The solution A and solution B prepared in step (1) are mixed in a volume ratio of 9:1 and stirred evenly to obtain a magnesium ion mixed electrolyte.

[0065] (3) Add 0.1 mol / L lactobionic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte. Example 10

[0066] Preparation of mixed electrolyte: (1) Excess Mg(ClO 4 ) 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C and wait for Mg(ClO 4 ) 2 Precipitate to obtain saturated magnesium perchlorate, and use the supernatant as solution A; Mg(ClO 4 ) 2 mixed with ethylene glycol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B; (2) Solution A and solution B prepared in step (1) were mixed in a volume ratio of 1:1 and stirred to obtain a 5.1 mol / kg magnesium ion mixed electrolyte.

[0067] (3) Add 0.1 mol / L citric acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte. Embodiment 11

[0068] Preparation of mixed electrolyte: (1) Excess Mg(ClO 4 ) 2 Dissolve in ultrapure water and completely dissolve at 80°C, then place in an oven at 30°C and wait for Mg(ClO 4 ) 2 Precipitate to obtain saturated magnesium perchlorate, and use the supernatant as solution A; Mg(ClO 4 ) 2 mixed with ethylene glycol at a molar ratio of 1:14 and stirred for 12 h to obtain solution B; (2) Solution A and solution B prepared in step (1) were mixed in a volume ratio of 1:1 and stirred to obtain a 5.1 mol / kg magnesium ion mixed electrolyte.

[0069] (3) Add 0.1 mol / L malonic acid to the magnesium ion mixed electrolyte prepared in step (2) to obtain the desired mixed electrolyte.

[0070] Some results of Examples 4-11 are summarized in Table 1 Table 1 shows the ionic conductivity, electrochemical window and cycle life of Examples 4-11 Example Ionic conductivity (mS / cm) Electrochemical Window (V) Cycle life of magnesium-magnesium symmetric battery (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 water-alcohol mixed electrolyte, the 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.

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

3. The electrolyte according to claim 2, characterized in that: The dihydric or polyhydric alcohol organic substance is one or more of ethylene glycol, glycerol and 1,2-butanediol.

4. The electrolyte according to claim 2, characterized in that: The volume ratio of water to dihydric or polyhydric alcohol organic matter is 10:1-1:

4.

5. The electrolyte according to claim 1, characterized in that: The additive is a water-soluble carboxylic acid.

6. The electrolyte according to claim 5, characterized in that: The additive is one or more of lactobionic acid, citric acid and malonic acid.

7. The electrolyte according to claim 6, characterized in that: The volume molar concentration of the additive is 0.01-2 mol / L.

8. The electrolyte according to claim 1, characterized in that: The magnesium salt includes one or more of magnesium chloride, magnesium perchlorate, magnesium trifluoromethanesulfonate and magnesium bis(trifluoromethanesulfonyl imide).

9. The electrolyte according to claim 8, characterized in that: The mass molar concentration of the magnesium salt is 1-5.5 mol / kg.

10. An application of the electrolyte according to any one of claims 1 to 9, characterized in that: The electrolyte is applied to a secondary battery containing magnesium ions.

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