Magnesium-sulfur battery electrolyte and preparation method and application thereof

Abstract

The invention relates to the technical field of magnesium-sulfur batteries, and discloses a magnesium-sulfur battery electrolyte as well as a preparation method and application of the magnesium-sulfur battery electrolyte. Particularly, the halogen ions in the lithium salt additive are added, so that the solvation structure of magnesium ions in the electrolyte magnesium salt on a negative electrode interface can be adjusted, the dissolution / deposition overpotential of a magnesium negative electrode is reduced, and the reversibility of magnesium deposition is improved. Due to the improvements, the specific discharge capacity and cycling stability of the magnesium-sulfur battery are remarkably improved, the magnesium-sulfur battery shows excellent electrochemical performance, the ionic conductivity of the electrolyte is 9.08 * 10 <-3 > S / cm, and the discharge capacity is 1,200 mAh / g under the 0.1 C rate discharge condition; and after 100 times of cycles are repeated, no attenuation is generated, and the problems in the prior art are effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnesium-sulfur batteries, in particular to a magnesium-sulfur battery electrolyte and a preparation method and application thereof. BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure and can not constitute the prior art.

[0003] In recent years, rechargeable magnesium-sulfur batteries have been considered as an important development direction for next-generation high-performance energy storage technology due to their high energy density, high safety, and low cost. Compared with traditional lithium-ion batteries, rechargeable magnesium-sulfur batteries have many advantages, such as high volume capacity, low electrode potential, and abundant reserves of magnesium in the earth's crust. However, although rechargeable magnesium-sulfur batteries exhibit many advantages, their practical application still faces many challenges, including low operating voltage, slow kinetics, and poor cycle stability. Electrolyte, as a key component of the battery, plays a crucial role in the overall performance of the battery. Currently, the commonly used electrolyte in magnesium-ion batteries mainly includes nucleophilic electrolyte and non-nucleophilic electrolyte. However, nucleophilic electrolyte is prone to chemical reaction with the electrode, and the magnesium ion deintercalation at room temperature is limited by the high energy barrier at the electrode / electrolyte interface. Although non-nucleophilic electrolyte can improve the deposition-dissolution efficiency of magnesium ions, it still has some problems, such as narrow electrochemical window, short cycle life, etc. In order to solve these problems, researchers have been exploring new electrolyte materials and preparation methods. Among them, boron-based electrolyte has become an important research direction due to its unique chemical properties and electrochemical performance. However, pure boron-based electrolyte still has some limitations in practical application, such as fast cycle decay, low discharge capacity, etc. Therefore, developing a modified boron-based electrolyte preparation method that can improve the mass transfer efficiency of the electrolyte and enhance the performance of the battery is of great significance for promoting the practical application of rechargeable magnesium batteries.

[0004] There are some invention patents on solving the problem of improving the performance of rechargeable magnesium battery electrolyte. For example: CN113363578A discloses a boron-based non-nucleophilic rechargeable magnesium battery electrolyte and its preparation method. The invention uses magnesium salt, organic boric acid and its derivatives, catalyst, water removal agent and anhydrous oxygen-free organic solvent as raw materials to prepare the electrolyte by one-step in-situ synthesis under inert atmosphere. The electrolyte has the characteristics of high conductivity, small overpotential, wide electrochemical window, high magnesium deposition-dissolution efficiency, good compatibility with Mg anode and high-pressure cathode, good cycle stability, etc. However, the invention still uses multiple catalysts and water removal agents in terms of raw material selection, preparation process and cost, which needs to be further optimized to achieve lower cost and improve the electrochemical performance and cycle stability of the electrolyte. CN119419360A proposes a rechargeable magnesium battery magnesium-lithium composite electrolyte and its preparation method and application. The invention introduces lithium salt additives into the organic ether solvent electrolyte containing electrolyte magnesium salt, uses the fast diffusion and migration rate of Li + to improve the kinetic performance of the electrolyte, and uses Cl - to regulate the solvation structure of Mg 2+ at the negative electrode interface, reduce the overpotential of magnesium negative electrode dissolution / deposition, and improve the electrochemical reversibility. However, the invention still needs to be further optimized in terms of the type and concentration of lithium salt additives to improve the kinetic performance of magnesium ions and the selection range of positive electrode materials. SUMMARY

[0005] The purpose of the present invention is to solve the above problems: 1. The pure boron-based electrolyte has the problems of fast cycle decay, low discharge capacity and other problems in practical application, which is difficult to meet the actual needs of rechargeable magnesium batteries; 2. The existing boron-based non-nucleophilic rechargeable magnesium battery electrolyte still uses multiple catalysts and water removal agents in terms of raw material selection, preparation process and cost, which needs to be further optimized to achieve lower cost and improve the electrochemical performance and cycle stability of the electrolyte; 3. The current rechargeable magnesium battery electrolyte still needs to be further optimized in terms of the type and concentration of lithium salt additives to improve the kinetic performance of magnesium ions and the selection range of positive electrode materials; 4. In the existing technology, the electrochemical window of the electrolyte is narrow, the cycle life is short, and it is difficult to meet the needs of high-performance rechargeable magnesium batteries; 5. The preparation method of part of the boron-based electrolyte is complex, the cost is high, and it is not conducive to large-scale production and application; etc. The present invention provides a magnesium-sulfur battery electrolyte and its preparation method and application, which has a simple preparation method, low preparation cost, and greatly improves the overall performance of the battery.

[0006] The technical solution of the present invention is as follows: In one aspect, the present invention provides a magnesium-sulfur battery electrolyte comprising a boron-based salt and an additive, wherein the additive is a lithium salt.

[0007] According to a preferred embodiment, the lithium salt is lithium nitrate or lithium chloride.

[0008] According to a preferred embodiment, the lithium salt is lithium chloride.

[0009] According to a preferred embodiment, the additive is added in an amount of 1%-10% by mass ratio to the boron-based salt.

[0010] According to a preferred embodiment, the boron-based salt in step 1 is Mg[B(HFIP)4]2 fluorinated alkoxy borate magnesium.

[0011] Another aspect of the present application provides a preparation method of a magnesium-sulfur battery electrolyte as described above, comprising the following steps: Step 1, synthesis of a boron-based salt; Step 2, prepare a mixed solution according to a ratio of 0.2g-1.8g boron-based salt to 0.5-4 mL diethyl alcohol methyl ether solvent; slowly add an additive powder in an amount of 1%-10% by mass ratio to the boron-based salt to the above solution; more preferably, the additive powder is added in an amount of 1%-7% by mass ratio to the boron-based salt. More preferably, the additive powder is added in an amount of 1%-5% by mass ratio to the boron-based salt.

[0012] Step 3, stir and dissolve the mixed electrolyte under an inert atmosphere. Specifically, stir and dissolve the mixed electrolyte under a nitrogen atmosphere, control the gas pressure to be 0.5-1.5 MPa, the stirring speed to be 300-600 rpm, and the stirring time to be 3-6 hours, to obtain the desired boron-based non-nucleophilic rechargeable magnesium battery electrolyte.

[0013] According to a preferred embodiment, the boron-based salt in step 1 is Mg[B(HFIP)4]2 fluorinated alkoxy borate magnesium.

[0014] Another aspect of the present application provides a magnesium-sulfur battery electrolyte as described above for use as a magnesium-sulfur battery electrolyte.

[0015] Another aspect of the present application provides a magnesium-sulfur battery electrolyte as described above for use in the preparation of a magnesium-sulfur battery.

[0016] Another aspect of the present application provides a magnesium-sulfur battery comprising a battery positive electrode, a battery negative electrode, and an electrolyte, wherein the electrolyte is a magnesium-sulfur battery electrolyte as described above.

[0017] Compared with the prior art, the present application has the following beneficial effects: 1. A magnesium-sulfur battery electrolyte, taking boron-based salt as base, adding specific lithium salt, especially lithium chloride, into the boron-based salt, the addition of halogen ion in lithium salt additive can adjust the solvation structure of magnesium ion in magnesium salt of electrolyte at the interface of negative electrode, reduce the dissolution / deposition overpotential of magnesium negative electrode, and improve the reversibility of magnesium deposition, significantly improve the performance of electrolyte, the prepared electrolyte has an ionic conductivity of 9.08 x 10 -3 S / cm, the discharge capacity of the assembled button cell is 1200 mAh / g under 0.1C rate discharge condition; after 100 cycles, there is no attenuation, and the electrochemical performance and cycle stability are more excellent than those of the prior art, which provides a new possibility for the practical application of rechargeable magnesium battery; 2. A preparation method of a magnesium-sulfur battery electrolyte, the preparation method is simple in conditions and operation, does not need to use various catalysts and water removal agents, greatly reduces the production cost; at the same time, the battery is simple in preparation, low in cost and high in efficiency; 3. A magnesium-sulfur battery electrolyte, the boron-based electrolyte added with lithium nitrate additive can be cycled more than 50 times at 0.1C without any attenuation, and the discharge capacity is maintained at 1100 mAh / g, which effectively widens the electrochemical window of the electrolyte and improves the cycle life of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Discharge capacity cycle of the boron-based electrolyte added with boron-based lithium chloride additive for Example 1; Figure 2 Discharge capacity cycle of the boron-based electrolyte added with boron-based lithium triflate additive for Example 2; Figure 3 Linear sweep voltammetry for determining the oxidation stability of the lithium chloride-containing electrolyte in different electrodes; Figure 4 Overpotential diagram of the lithium chloride additive electrolyte symmetrical cell at 0.1 mA cm -2 Figure 5 Discharge capacity cycle of the boron-based electrolyte for Comparative Example 1. DETAILED DESCRIPTION

[0019] ​The specific examples listed in the present application are only as examples of the present application, and the present application is not limited to the specific examples described below. Any equivalent modifications and alternatives to the examples described below are also within the scope of the present application for those skilled in the art. Therefore, equivalent transformations and modifications made without departing from the spirit and scope of the present application should be included in the scope of the present application. If no specific conditions are specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If no manufacturer is specified for all reagents or instruments, it is a conventional product that can be purchased on the market. In order to better illustrate the present application, numerous specific details are given in the following specific embodiments. Those skilled in the art should understand that the present application can also be implemented without some specific details. In some embodiments, methods, means, apparatus and steps that are well known to those skilled in the art are not described in detail, in order to highlight the main idea of the present application.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Unless otherwise specified, the units used in the specification are international standard units, and the numerical values and numerical ranges appearing in the present application should be understood to include the systematic errors that are inevitable in industrial production.

[0021] The features and properties of the present application are further described in detail below in conjunction with the examples.

[0022] Example 1 A preparation method of an electrolyte, comprising the following steps: Step 1, take boron-based salt Mg[B(HFIP)4]2; Step 2, prepare a mixed solution according to the proportion of 0.5 g boron-based salt 1 mL diethylene glycol methyl ether solvent; slowly add 0.02 g lithium chloride powder to the above solution; Step 3, the mixed solution of step 2 is stirred and dissolved under inert atmosphere. Specifically, the mixed electrolyte is stirred under nitrogen atmosphere, the gas pressure is controlled at 0.5 MPa, the stirring speed is 300 rpm, and the stirring time is 3 hours, to obtain the required boron-based non-nucleophilic rechargeable magnesium battery electrolyte.

[0023] The prepared electrolyte has an ionic conductivity of 9.08 x 10 -3 S / cm, and the cycle life test result is: under the condition of 0.1C rate discharge, using the electrolyte, the positive electrode material is S / C, the negative electrode material is polished magnesium sheet, and the discharge capacity of the assembled button cell is 1200 mAh / g. Figure 1 Discharge capacity cycle diagram of the battery assembled for the boron-based electrolyte added with lithium chloride additive. Figure 3To determine the oxidative stability of the electrolyte containing lithium chloride in different electrodes using linear sweep voltammetry, the electrolyte remains oxidatively stable up to 3.7 V on copper foil. In addition, it is also compatible with standard stainless steel cells. Figure 4 Polarization curves of lithium chloride additive electrolyte symmetric cells at 0.1 mA cm -2

[0024] Example 2 A method for preparing a rechargeable magnesium-sulfur battery electrolyte, comprising the following steps: Step 1, take boron-based salt Mg[B(HFIP)4]2; Step 2, prepare a mixed solution according to the ratio of 0.5 g boron-based salt to 1 mL diethyldimethyl ether solvent; slowly add 0.086 g lithium triflate powder to the above solution.

[0025] Step 3, stir and dissolve the mixed solution of Step 2 under an inert atmosphere to mix uniformly. Specifically, mix the electrolyte under an argon atmosphere, control the gas pressure at 0.8 MPa, the stirring speed at 350 rpm, and the stirring time at 3 hours to obtain the desired boron-based non-nucleophilic rechargeable magnesium battery electrolyte.

[0026] The prepared electrolyte has an ionic conductivity of 8.52 x 10 -3 S / cm, and the cycle life test results are as follows: under the condition of 0.1C rate discharge, using the electrolyte, the positive electrode material is S / C, the negative electrode material is a polished magnesium sheet, and the discharge capacity of the assembled button cell is 1100 mAh / g. Figure 2 Discharge capacity cycle diagram of the battery assembled with boron-based electrolyte added with lithium triflate additive.

[0027] Example 3 A method for preparing a rechargeable magnesium-sulfur battery electrolyte, comprising the following steps: Step 1, in a glove box filled with nitrogen atmosphere, synthesize boron-based salt according to the common method for synthesizing boron-based electrolyte.

[0028] Step 2, prepare a mixed solution according to the ratio of 0.5 g boron-based salt to 1 mL diethyldimethyl ether solvent; slowly add 0.044 g lithium nitrate powder to the above solution.

[0029] Step 3, stir and dissolve the mixed solution of Step 2 under an inert atmosphere to mix uniformly. Specifically, mix the electrolyte under a nitrogen atmosphere, control the gas pressure at 0.6 MPa, the stirring speed at 280 rpm, and the stirring time at 3 hours to obtain the desired boron-based non-nucleophilic rechargeable magnesium battery electrolyte.

[0030] The prepared electrolyte has an ionic conductivity of 9.32 x 10​-3 S / cm, the cycle life test results: under the condition of 0.1C rate discharge, using the electrolyte, the positive electrode material is S / C, the negative electrode material is the polished magnesium sheet, the discharge capacity of the button cell assembled is 1100 mAh / g.

[0031] Comparative Example 1 The present comparative example is a pure boron-based electrolyte without adding lithium salt additive, and the battery is assembled according to the assembly method of Example 1, and the discharge capacity and cycle performance are determined.

[0032] The results show that the highest discharge specific capacity of the corresponding boron-based electrolyte without lithium salt is 735 mAh / g. The 50th cycle discharge specific capacity is as shown in Table 1. Figure 5

[0033] The above examples only express the specific embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the protection scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the technical concept of the present application, a number of modifications and improvements can be made, which are within the protection scope of the present application.​

Claims

1. A magnesium-sulfur battery electrolyte, characterized in that: The invention comprises a boron-based salt and an additive, wherein the additive is a lithium salt.

2. A magnesium-sulfur battery electrolyte according to claim 1, characterized in that: The lithium salt is lithium nitrate or lithium chloride.

3. A magnesium-sulfur battery electrolyte according to claim 2, characterized in that: The lithium salt is lithium chloride.

4. The magnesium-sulfur battery electrolyte according to claim 1, characterized in that: The additive is added in an amount of 1% to 10% by mass of the boron-based salt.

5. The magnesium-sulfur battery electrolyte according to claim 1, characterized in that: The boron-based salt may be of the following type: Mg[B(HFIP)4]2 fluorinated magnesium alkoxyborate.

6. The method for preparing a magnesium-sulfur battery electrolyte according to any one of claims 1 to 5, characterized in that: The steps include: Step 1, synthesizing boron-based salt; Step 2: Prepare a mixed solution in the ratio of 0.2g-1.8g of boron salt to 0.5-4mL of diethanol methyl ether solvent; slowly add additive powder in a mass ratio of 1%-10% of the boron salt to the above solution; Step 3: Stir and dissolve the mixed electrolyte under an inert atmosphere. Specifically, the mixed electrolyte is placed under a nitrogen atmosphere at a pressure of 0.5-1.5 MPa, a stirring speed of 300-600 rpm, and a stirring time of 3-6 hours to obtain the desired boron-based non-nucleophilic rechargeable magnesium battery electrolyte.

7. The method for preparing a magnesium-sulfur battery electrolyte according to claim 6, characterized in that: The boron-based salt may be of the following type: Mg[B(HFIP)4]2 fluorinated magnesium alkoxyborate.

8. Use of the magnesium-sulfur battery electrolyte according to any one of claims 1 to 5 as a magnesium-sulfur battery electrolyte.

9. Use of the magnesium-sulfur battery electrolyte according to any one of claims 1 to 5 in the preparation of a magnesium-sulfur battery.

10. A magnesium-sulfur battery comprising a battery positive electrode, a battery negative electrode and an electrolyte, wherein the electrolyte is the magnesium-sulfur battery electrolyte according to any one of claims 1 to 5.

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