A high electrochemical window magnesium ion battery electrolyte, a preparation method and application thereof

Abstract

The application discloses a high-electrochemical-window magnesium ion battery electrolyte, a preparation method and application thereof. The electrolyte comprises an organic solvent, a magnesium salt electrolyte and a quaternary ammonium salt. The organic solvent is one or a mixture of multiple of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and tetrahydrofuran. The magnesium salt electrolyte is one or multiple of Mg(TFSI)2, Mg(OTf)2, MgCl2 and AlCl3, Mg(BH4)2, Mg[B(hfip)4]2 and MgBOR. The general formula of the quaternary ammonium salt is N + (R1R2R3R4); wherein R1, R2, R3 and R4 are selected from one or more of linear or branched carbon number 1-10.

Description

Technical Field

[0001] This invention relates to the field of magnesium-ion battery technology, specifically to a magnesium-ion battery electrolyte with a high electrochemical window, its preparation method, and its application. Background Technology

[0002] Today, portable electronic products and electric vehicles place higher demands on secondary energy storage batteries. In recent years, magnesium-ion batteries have gained popularity due to their high volumetric energy density (3832 mAh / cm³). 3 Magnesium has attracted much attention due to its advantages such as negative redox potential (-2.37V vs. SHE), high abundance in the Earth's crust, and good safety, and is considered a promising candidate for new lithium battery technology. However, due to severe passivation of the magnesium anode and slow diffusion kinetics of the cathode, most rechargeable magnesium batteries have very low power densities (<0.5kW kg⁻¹). -1 0.8mW cm -2 ).

[0003] Electrolyte, as the "blood" of a battery, plays a crucial role in its overall performance. In magnesium-ion batteries, the interfacial layer caused by electrolyte decomposition often hinders the growth of magnesium ions. 2+ Due to diffusion, most simple ionic salts that easily form passivation films (such as Mg(ClO4)2 and Mg(BF4)2) and polar aprotic solvents (such as carbonates and nitriles) are unsuitable as electrolytes for magnesium-ion batteries. In existing magnesium-ion battery electrolyte technologies, nucleophilic electrolytes are compatible with Mg intercalated cathodes, but at room temperature, Mg... 2+ The insertion / extraction is affected by Mg at the electrode / electrolyte interface. 2+ The high energy barrier of desolvation and its low diffusion rate in materials significantly limit its use. Furthermore, nucleophilic components readily react with electrophilic materials, making them unsuitable for organic polymer electrodes and conversion-type cathodes (such as sulfur and iodine). Currently, extensive research has been conducted on non-nucleophilic electrolyte components, among which MgTFSI2, a common electrolyte component, has attracted attention due to its high solubility in ethers, wide electrochemical window, and high conductivity.

[0004] However, electrolytes using only Mg(TFSI)₂ exhibit large overpotentials (>2.0V) and low CE (<50%) even at high temperatures. Mg(TFSI)₂ electrolytes are highly sensitive to impurities, which strongly affect their Mg deposition / dissolution properties. Cl⁻ can be released through Cl⁻. -The complex dynamic interaction with H2O protects the Mg surface from passivation by trace amounts of moisture. Therefore, introducing MgCl2 into the Mg(TFSI)2 electrolyte is an effective strategy for achieving reversible deposition / dissolution and reducing overpotential. Combining Mg(TFSI)2-MgCl2 in DME increases the CE to 80%, achieves an overpotential of 400 mV, and maintains a negative electrode stability limit of 3.5 V. Besides consuming impurities in the water, MgCl2 also contributes to the formation of [Mg...]. x Cl y ] n+ Electroactive materials. The active cations in Mg(TFSI)2-MgCl2 / THF are mainly the Cl- component of the electrolyte. It is noteworthy that the performance of Mg(TFSI)2-based electrolytes is highly dependent on the purity of the Mg salt, which can be improved by introducing reagents other than MgCl2. Existing techniques have also found that by adding trace amounts of Mg(BH4)2 dehydrating agent, the deposition / dissolution overpotential in Mg(TFSI)2 / G4 electrolytes is approximately -0.35V (deposition) and 0V (dissolution), with an initial cycle CE of 84% and a retention of 75% after 500 cycles. Furthermore, a chlorine-free and non-corrosive Mg(TFSI)2-based electrolyte can be prepared using dimethylamine (DMA) as a co-solvent. In symmetrical Mg battery cycling, its polarizability reaches 210 mV after more than 1500 min, comparable to performance in APC electrolytes. When using DMA-THF-G4 as a mixed solvent, the CE increases to 75%, while the CE of the Mg(TFSI)2-G4 electrolyte is only 38%. Existing technologies also include using rPDI as an additive in Mg(TFSI)2-DME electrolyte, which has high air tolerance and can still be assembled into a battery for normal operation after exposure to air, at 1.0 mA / cm 2 It can cycle for 300 hours at a current density of 250mV, with a maximum withstand current density of up to 5mA / cm. 2 However, the electrochemical window is not high, only about 2.0V on copper foil.

[0005] In summary, most existing MgTFSI2 electrolyte technologies still suffer from disadvantages such as low deposition and dissolution efficiency, large overpotential, narrow potential window, and high corrosivity to current collectors. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a magnesium-ion battery electrolyte with a high electrochemical window, a preparation method and its application, so as to solve the problems of low deposition and dissolution efficiency, large overpotential, narrow potential window and high corrosivity to current collectors in the existing electrolyte.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A high electrochemical window magnesium-ion battery electrolyte, comprising an organic solvent, a magnesium salt electrolyte, and a quaternary ammonium salt; the organic solvent is one or more mixtures of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and tetrahydrofuran; the magnesium salt electrolyte is one or more of Mg(TFSI)2, Mg(OTf)2, MgCl2, AlCl3, Mg(BH4)2, Mg[B(hfip)4]2, and MgBOR; the quaternary ammonium salt has the general formula N + (R1R2R3R4); where R1, R2, R3, and R4 are selected from one or more straight or branched chains with 1-10 carbon atoms.

[0009] The molar concentration of the magnesium salt in the organic solvent is 0.1 mol / L to 0.5 mol / L; the molar concentration of the quaternary ammonium salt in the organic solvent is 50 mmol / L to 0.5 mol / L.

[0010] Preferably, the quaternary ammonium salt has the following general formula:

[0011]

[0012] Wherein, X- is selected from BH4 - , F-, Cl-, Br - I - One or more of them.

[0013] This invention also provides a method for preparing a magnesium-ion battery electrolyte with a high electrochemical window, comprising the following steps:

[0014] Step 1: Prepare the magnesium salt electrolyte and organic solvent according to claim 1, and mix and stir them;

[0015] Step 2: Add quaternary ammonium salt under stirring conditions and stir for 10h to 30h to obtain the electrolyte.

[0016] Preferably, the preparation method is carried out at room temperature and under conditions of being filled with inert gas; at the same time, the water content and oxygen content in the reaction system are both less than 0.01 ppm.

[0017] Preferably, the organic solvent is pretreated as follows: The molecular sieve was heated to 300℃ and activated for 5 hours, then added to an organic solvent and sealed for storage. The activation process refers to... The molecular sieve was heated to 300°C and held for 5 hours, and then added to an organic solvent while still hot.

[0018] Preferably, the magnesium salt electrolyte is pretreated as follows: the magnesium salt electrolyte is vacuum dried at 60℃~200℃ for 24h and then sealed and stored.

[0019] Preferably, the quaternary ammonium salt is pretreated as follows: the quaternary ammonium salt is vacuum dried at 60℃~100℃ for 24h and then sealed and stored.

[0020] The present invention also provides an application of a high electrochemical window magnesium-ion battery electrolyte, wherein the electrolyte is used in the preparation of rechargeable magnesium-ion batteries.

[0021] The present invention also provides a magnesium-ion battery that can be filled with a magnesium-ion battery electrolyte having a high electrochemical window, the magnesium-ion battery containing the above-mentioned electrolyte.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. In the electrolyte of this invention, the magnesium salt electrolyte is preferably Mg(TFSI)2. This type of magnesium salt has a moderate binding capacity with ether solvents, thereby reducing free ether molecules in the electrolyte and thus reducing the decomposition of ether molecules under high voltage. The anodic oxidation decomposition potential of the electrolyte of this invention on stainless steel is as high as 4.8V (vs. Mg / Mg). 2+ Therefore, it can be matched with a variety of high-voltage cathode materials, enabling magnesium-ion batteries to work stably under high voltage.

[0024] 2. The anions in the electrolyte of this invention help to avoid the formation of a passivation film on the Mg surface. (BH4) - It can remove trace amounts of water and impurities; I - ,Br - Mg can be formed on the Mg surface 2+ A conductive SEI film, which in turn allows Mg 2+ Capable of reversible deposition / dissolution; at 0.1 mA / cm 2 At a current density of up to 98%, the electrolyte of the present invention achieves a deposition and dissolution efficiency of up to 98% on stainless steel, with an overpotential as low as 150mV.

[0025] 3. The quaternary ammonium salt cations used as additives in the electrolyte of this invention exhibit highly stable electrochemical performance regarding the negative reduction potentials of magnesium, sodium, and even lithium. Therefore, they possess high reduction stability on the Mg surface and will not undergo reduction within the battery's operating voltage range. Consequently, the electrolyte of this invention exhibits good stability. Simultaneously, the quaternary ammonium salt cations possess a shielding effect on Mg, utilizing a physical electrostatic field effect rather than chemical reaction products to inhibit the growth of dendritic crystals on the Mg electrode surface and induce Mg… 2+ Uniform deposition extends battery life, achieving a voltage of 0.5 mA / cm². 2 Under a current of 5 mA / cm², the assembled Mg / / Mg symmetric cell can cycle more than 700 times, with a maximum overpotential not exceeding 400 mV; at 5 mA / cm², 2It can also achieve normal deposition / dissolution even under high current density.

[0026] 4. The electrolyte of the present invention can achieve high-voltage cycling by simply adjusting the amount of quaternary ammonium salt additive, without the need to use expensive ionic liquids or other additives, or to add multiple additives and adjust their proportions, thus avoiding disadvantages such as high viscosity and high cost. At the same time, the preparation process of the electrolyte of the present invention is simple and the preparation and synthesis time is short, and the reaction conditions are mild. In addition, no toxic gases are generated during the reaction process, which meets the requirements of green environmental protection, and therefore it is easy to use for large-scale industrial production.

[0027] 5. The electrolyte described in this invention does not use commonly used chlorine-containing compounds and is not corrosive to the current collector and battery casing, thus increasing the battery's working life. Attached Figure Description

[0028] Figure 1 Linear scanning voltammetry diagrams of the electrolyte prepared in Example 1 of this invention on different working electrodes.

[0029] Figure 2 The electrolytes prepared in Example 1 and the comparative example of this invention were tested using stainless steel SS as the working electrode at a speed of 0.1 mA / cm². 2 Capacity-voltage plot of deposition / dissolution at current density.

[0030] Figure 3 The electrolytes prepared in Example 1 and the comparative example of this invention used stainless steel SS as the working electrode and were applied at 0.1 mA / cm². 2 Coulombic efficiency diagram of reversible magnesium deposition / dissolution at current density. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] I. Examples and Comparative Examples

[0033] Example 1:

[0034] A Mg(TFSI)2-based non-nucleophilic rechargeable magnesium battery electrolyte, the specific raw materials and preparation method of which include:

[0035] (1) Solvent pretreatment: Add 3A molecular sieve activated at 300℃ for 5h to organic ether solvent while hot, and store it in a glove box in a sealed container.

[0036] (2) Pretreatment of magnesium salt electrolyte: After vacuum drying at 200℃ for 24h, Mg(TFSI)2 magnesium salt was placed in a glove box for sealed storage.

[0037] (3) Pretreatment of quaternary ammonium salt additives: Tetraethylammonium borohydride (TEABH4) was vacuum dried at 80°C for 24 hours and then sealed and stored in an anhydrous and oxygen-free glove box.

[0038] (4) Preparation of electrolyte: All reactions were carried out under an anhydrous and oxygen-free inert atmosphere. 29.23g of Mg(TFSI)2 (0.5M) was slowly added to 100mL of ethylene glycol dimethyl ether under stirring and stirred for 2h; then 5.8g of tetraethylammonium borohydride (0.4M) was added under stirring and stirred for 24h to obtain the target electrolyte.

[0039] The electrolyte preparation methods for Examples 2-6 are shown in Table 1 below (the pretreatment methods for other reagents are the same as in Example 1):

[0040]

[0041]

[0042] Comparative example:

[0043] A comparative electrolyte for a Mg(TFSI)2-based non-nucleophilic rechargeable magnesium battery, the specific raw materials and preparation method of which include:

[0044] (1) Solvent pretreatment: Add the solvent to the organic ether solvent while it is still hot and heat it at 300°C for 5 hours. Molecular sieves should be stored in a sealed glove box.

[0045] (2) Pretreatment of magnesium salt electrolyte: After vacuum drying at 200℃ for 24h, Mg(TFSI)2 magnesium salt was placed in a glove box for sealed storage.

[0046] (3) Preparation of electrolyte: All reactions were carried out under an anhydrous and oxygen-free inert atmosphere. 29.23g of Mg(TFSI)2 was slowly added to 100mL of ethylene glycol dimethyl ether with stirring, and stirred for 24h to obtain the comparative electrolyte.

[0047] II. Performance Comparison

[0048] The performance testing method for the electrolyte is as follows (the testing methods are the same for other embodiments).

[0049] a. Magnesium reversible deposition / dissolution and oxidation stability testing

[0050] The magnesium reversible deposition / dissolution coulombic efficiency and oxidative stability of the electrolyte described in this invention were tested using cyclic voltammetry (CV) and linear voltammetry (LSV), respectively, with a Shanghai Chenhua CHI 660 electrochemical workstation as the testing instrument. Testing was conducted using assembled CR2032 coin cells, with the positive electrode current collector made of stainless steel (SS), the negative electrode made of polished magnesium sheet, and the separator made of glass fiber membrane. The assembled cells were allowed to stand at room temperature for at least 4 hours before testing. The CV scan rate was 25 mV / s, and the voltage range was -0.8 V to 2.0 V; the LSV scan range was open-circuit voltage to 6.0 V, with a scan rate of 25 mV / s.

[0051] b. Coulombic efficiency test of magnesium reversible deposition / dissolution performance

[0052] The reversible deposition / dissolution performance and coulombic efficiency of the electrolyte were tested using a constant current charge-discharge (CP) tester from Wuhan Landian. The tests were conducted by assembling CR2032 coin cells. The positive electrode current collector used stainless steel (SS), aluminum foil (Al), and molybdenum foil (Mo), the negative electrode used a polished magnesium sheet, and the separator used a glass fiber membrane. The assembled cells were allowed to stand at room temperature for at least 4 hours before testing. The CP discharge time was 30 minutes, the charging cutoff voltage was 2V, and the current density was 0.1 mA / cm². 2 ~0.5mA / cm 2 .

[0053] c. Polarization performance test

[0054] The polarization performance of the electrolyte was tested using a constant current charge-discharge (CP) tester from Wuhan Landian. Testing was conducted by assembling a CR2032 coin-type Mg / / Mg symmetric battery, with both positive and negative electrodes made of polished magnesium sheets (Mg). The assembled battery was allowed to stand at room temperature for at least 4 hours before testing. The charge-discharge test current was 0.05 mA / cm². 2 ~5mA / cm 2 .

[0055] The results obtained by Example 1 using the above testing method are as follows:

[0056] Using stainless steel SS as the working electrode, the deposition overpotential of the electrolyte is as low as -300mV, and the dissolution overpotential is 180mV, which is relatively low. Figure 1 Electrochemical stability potential of electrolyte on stainless steel, aluminum foil, molybdenum foil, copper foil, nickel foil, and carbon cloth (vs. Mg / Mg). 2+ The voltage ratings are 4.6V, 4.0V, 3.6V, 3.0V, 3.0V, and 3.0V respectively. Figure 2The electrochemical window is relatively high. Stainless steel was used as the working electrode, and the electrolyte was at 0.5 mA / cm². 2 The average deposition / dissolution efficiency after 100 cycles at a given current density is 98%. Figure 3 At 0.5 mA / cm 2 At the current density, the initial polarization potential is as low as 180mV, and the polarization potential after 700 cycles does not exceed 300mV, with no significant increase in overpotential.

[0057] The electrochemical performance of the comparative example and Example 1 is shown in the table below. The electrochemical window on stainless steel (SS) is also relatively high, reaching 4.2V, but its deposition overpotential is as high as -1.68V, dissolution overpotential as high as 1.80V, and the deposition-dissolution efficiency is only about 15.4%. It short-circuits after about 100 cycles, and its electrochemical performance is far lower than that of Example 1. Figure 2 , Figure 3 At different current densities (0.1 mA / cm²), 2 0.5mA / cm 2 1mA / cm 2 The overpotentials of the two examples were compared. The overpotentials in Example 1 were 0.18V, 0.20V, and 0.21mV, respectively; the overpotentials in the comparative examples were 2.01V, 2.20V, and 2.30V, respectively. (At 0.5mA cm⁻¹) -2 At the specified current density, the Mg / / Mg symmetric cell exhibits a cycling overpotential exceeding 2.0V and fails due to a short circuit after less than 200 cycles. Therefore, it is evident that the performance of Example 1 is superior to that of the comparative example in all aspects.

[0058] Table 2

[0059] Electrochemical window / V(SS) 4.6 Electrochemical window / V(SS) 4.2 Deposition dissolution efficiency / % (SS) 97.6 Deposition dissolution efficiency / % (SS) 16 <![CDATA[Overpotential / V (0.1 mA cm -2 )]]> 0.15 <![CDATA[Overpotential / V (0.1 mA cm -2 )]]> 2.0 <![CDATA[Overpotential / V (0.5mA cm -2 )]]> 0.18 <![CDATA[Overpotential / V (0.5 mA cm -2 )]]> 2.2 <![CDATA[Overpotential / V (2 mA cm -2 )]]> 0.21 <![CDATA[Overpotential / V (2 mA cm -2 )]]> 2.3

[0060] The above electrochemical performance test results show that the electrolyte of the present invention has the significant advantage of a wide electrochemical window, and at the same time, it has high magnesium deposition-dissolution efficiency, low overpotential, good cycle stability, and can work at high current density.

[0061] Finally, Examples 2-6 were tested for electrochemical performance using the same method as Example 1, and the results are shown in Table 3 below. Clearly, the electrolyte of the present invention exhibits properties such as a wide electrochemical window, high deposition / dissolution efficiency, and low overpotential.

[0062] Table 3

[0063] 2 4.5 95 0.20 3 4.4 98 0.15 4 4.2 97 0.20 5 3.8 94 0.30 6 3.5 92 0.35

[0064] In summary, this invention addresses the problem that existing magnesium-ion battery electrolytes cannot be used at high voltages by adjusting the concentration ratio of quaternary ammonium salt additives to achieve a high-voltage-resistant Mg(TFSI)2-based electrolyte. This electrolyte has a wide electrochemical window, high deposition / dissolution efficiency, low overpotential, and is simple and inexpensive to prepare. Furthermore, this electrolyte does not contain corrosive ions, will not corrode the current collector or battery casing, and is beneficial to battery life. In conclusion, this electrolyte has excellent commercial prospects.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A magnesium-ion battery electrolyte with a high electrochemical window, characterized in that, The electrolyte is composed of an organic solvent, a magnesium salt electrolyte, and a quaternary ammonium salt; the organic solvent is diethylene glycol dimethyl ether; the magnesium salt electrolyte is Mg(TFSI)2; the quaternary ammonium salt is tetraethylammonium borohydride; the molar concentration of the magnesium salt in the organic solvent is 0.5 mol / L; and the molar concentration of the quaternary ammonium salt in the organic solvent is 0.4 mol / L.

2. The electrolyte according to claim 1, characterized in that, The preparation method of the electrolyte includes the following steps: Step 1: Prepare the magnesium salt electrolyte and organic solvent according to claim 1, and mix and stir them; Step 2: Add the quaternary ammonium salt tetraethylborohydride under stirring conditions, and stir for 10h~30h to obtain the electrolyte.

3. The electrolyte according to claim 2, characterized in that, The preparation method is carried out at room temperature and under conditions of inert gas filling; at the same time, the water content and oxygen content in the reaction system are both less than 0.01 ppm.

4. The electrolyte according to claim 2, characterized in that, The organic solvent is pretreated as follows: After heating the 3Å molecular sieve to 300℃ and activating it for 5 hours, it was added to an organic solvent and then sealed for storage.

5. The electrolyte according to claim 2, characterized in that, The magnesium salt electrolyte is pretreated as follows: The magnesium salt electrolyte was vacuum dried at 60℃~200℃ for 24 hours and then sealed for storage.

6. The electrolyte according to claim 2, characterized in that, The quaternary ammonium salt was pretreated as follows: The quaternary ammonium salt was vacuum dried at 60℃~100℃ for 24 hours and then sealed for storage.

7. An application of a high electrochemical window magnesium-ion battery electrolyte, characterized in that, The use of the electrolyte according to any one of claims 1 to 6 in the preparation of a rechargeable magnesium-ion battery.

8. A magnesium-ion battery with a magnesium-ion battery electrolyte having a high electrochemical window, characterized in that, The magnesium-ion battery contains the electrolyte as described in any one of claims 1 to 6.

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