Low-cost all-inorganic rechargeable magnesium battery and electrolyte and preparation method thereof

Abstract

The invention discloses a low-cost all-inorganic rechargeable magnesium battery and an electrolyte and a preparation method thereof. The electrolyte is composed of an electrolyte salt and a non-aqueous solvent, wherein the electrolyte salt is at least one of MgCl2, MgBr2, MgI2, Mg (ClO4) 2, MgSO4, Mg3 (PO4) 2 and Mg (NO3) 2; the non-aqueous solvent is an amine solvent or a mixed solvent composed of the amine solvent and an ether solvent; the amine solvent is prepared from at least one of 2-methoxyethylamine, 3-methoxypropylamine and 1, 3-propane diamine. The inorganic magnesium salt is adopted as the electrolyte salt, the price is low, the preparation method is simple and mild, the problems that organic magnesium salt is high in cost and complex in synthesis process are solved, and great commercial application potential is achieved; meanwhile, the prepared electrolyte solves the problem of large overpotential caused by incompatibility of the electrolyte and a magnesium metal negative electrode, and the magnesium battery adopting the electrolyte has excellent electrochemical performance of the magnesium metal negative electrode.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium metal batteries and their electrolytes, and in particular relates to a low-cost all-inorganic rechargeable magnesium battery and its electrolyte and a preparation method. Background Art

[0002] Rechargeable magnesium battery is a multivalent metal battery with great development potential. Compared with lithium metal battery, magnesium negative electrode has many advantages: its volume energy density is higher than lithium (3833mAh / cc Mg vs. 2046mAh / cc Li); at the same time, magnesium resources are abundant in the earth's crust, and the price of magnesium is much cheaper than lithium; in addition, unlike lithium, magnesium tends to form a smooth plane during the deposition process, and is not easy to form dendrites, and magnesium metal is relatively stable at room temperature and safer. Therefore, magnesium secondary batteries are expected to have significant advantages over lithium secondary batteries in terms of cost and safety.

[0003] However, although the traditional magnesium battery electrolyte (commercial magnesium salt dissolved in commercial organic solvent) has a simple preparation method and a high degree of compatibility with the positive electrode material, this type of traditional magnesium battery electrolyte will react with magnesium metal to form a passivation layer, so there is an incompatibility problem with a large negative electrode overpotential. Ether electrolytes (such as tetrahydrofuran THF, ethylene glycol dimethyl ether DME) are currently widely used as solvents for magnesium battery electrolytes because they are not easy to react with magnesium sheets to form an unfavorable passivation film. However, most inorganic magnesium salts have poor solubility in ether solvents. Therefore, magnesium battery electrolytes based on ether solvents mostly use organic magnesium salts, such as boranes or organic borates. Such organic magnesium salts are expensive, the synthesis process is complex and the repeatability is poor, and it is difficult to meet the actual commercial application standards. The lack of electrolytes with excellent performance, low price and simple preparation process is one of the key factors restricting the development of magnesium secondary batteries. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a low-cost all-inorganic rechargeable magnesium battery and its electrolyte and preparation method, thereby solving the problems in the above-mentioned background technology.

[0005] One of the technical solutions adopted by the present invention to solve its technical problems is: providing a low-cost all-inorganic rechargeable magnesium battery electrolyte, including an electrolyte salt and a non-aqueous solvent; the electrolyte salt is at least one of MgCl2, MgBr2, MgI2, Mg(ClO4)2, MgSO4, Mg3(PO4)2, and Mg(NO3)2; the non-aqueous solvent is an amine solvent or a mixed solvent composed of an amine solvent and an ether solvent; the amine solvent includes but is not limited to one or more of 2-methoxyethylamine, 3-methoxypropylamine, and 1,3-propylenediamine; the ether solvent includes but is not limited to one or more of tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxolane.

[0006] In a preferred embodiment of the present invention, the concentration range of the electrolyte salt in the electrolyte is 0.01 mol / L to the maximum solubility of the electrolyte salt.

[0007] In a preferred embodiment of the present invention, the volume ratio of the amine solvent in the mixed solvent is 20%-99% of the total volume of the mixture of the amine solvent and the ether solvent.

[0008] In a preferred embodiment of the present invention, the water content of the electrolyte is less than 20 ppm.

[0009] The second technical solution adopted by the present invention to solve the technical problem is: to provide a low-cost method for preparing an all-inorganic rechargeable magnesium battery electrolyte, comprising the following steps:

[0010] 1) Weighing an electrolyte salt and drying it in a vacuum oven at 200° C. for 72 hours; the electrolyte salt is at least one of MgCl2, MgBr2, MgI2, Mg(ClO4)2, MgSO4, Mg3(PO4)2, and Mg(NO3)2;

[0011] 2) adding an amine solvent to a 4A molecular sieve for pre-drying; the amine solvent includes but is not limited to one or more of 2-methoxyethylamine, 3-methoxypropylamine, and 1,3-propylenediamine;

[0012] 3) mixing the electrolyte salt with the solvent prepared in step 2), stirring at room temperature for at least 24 hours using a magnetic stirrer until the electrolyte salt is completely dissolved; then adding 4A molecular sieves and drying for 24 hours, repeating the drying process at least three times until the water content is less than 20 ppm using a Karl Fischer water meter, and the electrolyte is prepared.

[0013] The third technical solution adopted by the present invention to solve the technical problem is: to provide a low-cost method for preparing an all-inorganic rechargeable magnesium battery electrolyte, comprising the following steps:

[0014] 1) Weighing an electrolyte salt and drying it in a vacuum oven at 200° C. for 72 hours; the electrolyte salt is at least one of MgCl2, MgBr2, MgI2, Mg(ClO4)2, MgSO4, Mg3(PO4)2, and Mg(NO3)2;

[0015] 2) taking a pre-dried amine solvent and a pre-dried ether solvent in a volume ratio of 20%-99% of the total volume of the amine solvent, mixing them and stirring at room temperature for 24 hours to make them uniformly mixed; the amine solvent includes but is not limited to one or more of 2-methoxyethylamine, 3-methoxypropylamine, and 1,3-propylenediamine; the ether solvent includes but is not limited to one or more of tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxolane;

[0016] 3) mixing the electrolyte salt with the solvent prepared in step 2), stirring at room temperature for at least 24 hours using a magnetic stirrer until the electrolyte salt is completely dissolved; then adding 4A molecular sieves and drying for 24 hours, repeating the drying process at least three times until the water content is less than 20 ppm using a Karl Fischer water meter, and the electrolyte is prepared.

[0017] The fourth technical solution adopted by the present invention to solve its technical problem is: providing a low-cost all-inorganic rechargeable magnesium battery, using the above-mentioned electrolyte, the negative electrode material is a pure metal Mg sheet, and the positive electrode material includes but is not limited to an oxide positive electrode such as MnO2, V2O5, MgMn2O4, a sulfide positive electrode such as S, Mo6S8, or a polyanion positive electrode or an organic positive electrode or one of the modified materials of the above materials.

[0018] Compared with the background technology, this technical solution has the following advantages:

[0019] 1. The magnesium salt in the electrolyte of the present invention only needs to use traditional inorganic magnesium salts: MgCl2, Mg(ClO4)2, MgSO4, Mg3(PO4)2, Mg(NO3)2, which is low in cost and does not require the use of organic magnesium salts with high cost and complex synthesis process. It is helpful to realize the large-scale application of magnesium battery electrolyte and has commercial application potential.

[0020] 2. The present invention uses an amine organic molecular solvent as a single component solvent to dissolve an inorganic magnesium salt or mixes an amine organic molecular solvent with an ether to dissolve an inorganic magnesium salt to prepare an electrolyte. Unlike traditional pure ether solvents, the electrolyte containing an amine solvent has good solubility for the inorganic magnesium salt, and can realize a magnesium battery electrolyte system with an inorganic magnesium salt as an electrolyte.

[0021] 3. Since amine solvents have fast transfer kinetics in the magnesium metal negative electrode, the organic rechargeable magnesium battery using the electrolyte of the present invention can have excellent electrochemical performance and long cycle life. 2+ The solvation structure formed with amine molecules is beneficial to the magnesium dissolution / deposition reaction, and can effectively alleviate the anion and solvent decomposition side reactions, thereby improving the kinetic behavior of magnesium metal anode dissolution / deposition. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the Mg / / Mg symmetric cell diagram of Example 1, with a current density of 0.1 mA / cm -2 , area capacity is 0.1mAh / cm -2 .

[0023] Figure 2A A time-voltage diagram showing a Mg / / SS (stainless steel) half-cell test, Figure 2B Coulombic efficiency plot showing the Mg / / SS half-cell test at a current density of 0.1 mA / cm -2 , area capacity is 0.1mAh / cm -2 .

[0024] Figure 3 Shown is the cyclic voltammogram of Mg / / SS with a scan rate of 25 mV / s.

[0025] Figure 4A The charge and discharge curve of Mo6S8 / / Mg full battery is shown. Figure 4B The graph shows the number of cycles of the full battery of the electrolyte used - the discharge capacity. The positive electrode material is Mo6S8 and the current density is 100mA / g. DETAILED DESCRIPTION

[0026] Example 1

[0027] In the electrolyte of the low-cost all-inorganic rechargeable magnesium battery of this embodiment, the electrolyte magnesium salt is selected as MgCl2, and the non-aqueous solvent is a single-component solvent 3-methoxypropylamine, and the concentration is 0.5 mol / L. The electrolyte preparation method is as follows:

[0028] 1) Before use, magnesium salt must be dried in a vacuum oven at 200 degrees Celsius for 72 hours to completely remove the moisture contained therein;

[0029] 2) 3-methoxypropylamine is pre-dried using an ultra-dry solvent and adding 4A molecular sieves;

[0030] 3) Weigh the magnesium salt and transfer it to the bottle, calculate the required amount of electrolyte, and then use a pipette to accurately add a quantitative amount of 3-methoxypropylamine. The configured electrolyte is stirred at room temperature for at least 24 hours using magnetic stirring until the magnesium salt is completely dissolved. Then add 4A molecular sieve and dry for 24 hours. The drying process is repeated at least three times until the water content is less than 20ppm using a Karl Fischer water meter. The electrolyte configuration of this embodiment is complete.

[0031] The electrolyte of this embodiment was used to assemble Mg / / Mg symmetric battery, Mg / / SS semi-symmetric battery, and Mo6S8 / / Mg full battery, and the test results are shown in the attached figure.

[0032] Figure 1 The cycling diagram of the Mg / / Mg symmetric cell using 3-methoxypropylamine as solvent is shown. The test results show that the -2 Under these conditions, the symmetrical battery has an ultra-low overpotential (less than 0.10 V) and can maintain a cycle performance of more than 200 hours, indicating that this type of electrolyte has excellent electrochemical properties of magnesium metal negative electrode.

[0033] Figure 2A The cycling diagram of the Mg / / SS semi-symmetric cell using 3-methoxypropylamine as solvent is shown. The test results show that the -2 Under these conditions, it can undergo a reversible deposition-dissolution cycle, and both the deposition overpotential and the dissolution overpotential are low; Figure 2B The Coulombic efficiency curve of the Mg / / SS semi-symmetric cell using 3-methoxypropylamine as the solvent is shown. The test results show that the Mg / / SS semi-symmetric cell has a coulombic efficiency of 0.1 mA / cm -2 Under the same conditions, the average coulombic efficiency can be maintained at more than 95% for more than 100 cycles. These test results show that this type of electrolyte has excellent electrochemical performance of magnesium metal anode.

[0034] Figure 3 The cyclic voltammogram of Mg / / SS using 3-methoxypropylamine as solvent is shown. The test results show that under the condition of 25mV / s, it has a very low deposition or stripping overpotential, and can undergo reversible deposition and dissolution cycles. Its high response current also indicates its excellent electrochemical reaction kinetics. The test results show that this type of electrolyte has excellent electrochemical performance of magnesium metal anode.

[0035] Figure 4A The charge and discharge curves of the Mo6S8 / / Mg full battery using 3-methoxypropylamine as a solvent are shown. It can be seen that the rechargeable magnesium battery has a higher charge and discharge voltage platform and a higher discharge capacity at a current density of 100 mA / g. Figure 4BThe cycle curve of the Mo6S8 / / Mg full battery using 3-methoxypropylamine as the solvent is shown, and the rechargeable magnesium battery can be stably cycled for more than 100 cycles. These test results show that the electrolyte of this embodiment has excellent electrochemical properties.

[0036] Example 2

[0037] The difference between this embodiment and embodiment 1 is that the magnesium salt is MgCl2, the solvent is single-component 3-methoxypropylamine, and the concentration is 0.3 mol / L.

[0038] Example 3

[0039] The difference between this embodiment and embodiment 1 is that the magnesium salt is MgCl2, the solvent is single-component 2-methoxyethylamine, and the concentration is 0.7 mol / L.

[0040] Example 4

[0041] The difference between this embodiment and embodiment 1 is that the magnesium salt selected is MgCl2, the solvent is single-component 1,3-propylenediamine, and the configuration concentration is 1.0 mol / L.

[0042] Example 5

[0043] The difference between this embodiment and embodiment 1 is that the magnesium salt is Mg(ClO4)2, the non-aqueous solvent is a two-component solvent, which is a mixture of 3-methoxypropylamine and DME in a volume ratio of 1:4, wherein both 3-methoxypropylamine and DME are ultra-dry solvents and 4A molecular sieves are added for pre-drying, and stirred at room temperature for 24 hours to make them uniformly mixed. The electrolyte concentration is configured to be 0.5 mol / L.

[0044] Example 6

[0045] The difference between this embodiment and embodiment 1 is that the magnesium salt is MgSO4, the two-component solvent is 3-methoxypropylamine and THF mixed in a volume ratio of 1:4, and the concentration is 0.5 mol / L.

[0046] Example 7

[0047] The difference between this embodiment and embodiment 1 is that the magnesium salt selected is Mg3(PO4)2, the solvent is single-component 3-methoxypropylamine, and the configuration concentration is 0.5 mol / L.

[0048] Example 8

[0049] The difference between this embodiment and embodiment 1 is that the magnesium salt selected is Mg(NO3)2, the solvent is single-component 3-methoxypropylamine, and the concentration is 0.5 mol / L.

[0050] Example 9

[0051] The difference between this embodiment and embodiment 1 is that the magnesium salt selected is Mg(NO3)2, the solvent is single-component 2-methoxyethylamine, and the concentration is 1.0 mol / L.

[0052] Example 10

[0053] The difference between this embodiment and embodiment 1 is that the magnesium salt selected is MgCl2, the two-component solvent is 3-methoxypropylamine and DME mixed in a volume ratio of 1:4, and the configuration concentration is 0.5 mol / L.

[0054] Embodiment 11

[0055] The difference between this embodiment and embodiment 1 is that the magnesium salt selected is MgCl2, the two-component solvent is 3-methoxypropylamine and THF mixed in a volume ratio of 1:4, and the concentration is 0.5 mol / L.

[0056] Example 12

[0057] The difference between this embodiment and embodiment 1 is that the magnesium salt selected is MgCl2, the two-component solvent is 3-methoxypropylamine and THF mixed in a volume ratio of 2:3, and the concentration is 0.5 mol / L.

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 1 is that the magnesium salt selected is MgCl2, the solvent is single-component DME, and the concentration is 0.1 mol / L.

[0060] Comparative Example 2

[0061] The difference between this comparative example and Example 1 is that the magnesium salt selected is MgCl2, the solvent is single-component DME, and the configuration concentration is 0.2 mol / L.

[0062] Comparative Example 3

[0063] The difference between this comparative example and Example 1 is that the magnesium salt selected is MgCl2, the solvent is single-component DME, and the configuration concentration is 0.3 mol / L.

[0064] Comparative Example 4

[0065] The difference between this comparative example and Example 1 is that the magnesium salt selected is MgCl2, the solvent is single-component DME, and the configuration concentration is 0.5 mol / L.

[0066] Comparative Example 5

[0067] The difference between this comparative example and Example 1 is that the magnesium salt selected is MgCl2, the solvent is single-component DME, and the configuration concentration is 1.0 mol / L.

[0068] Comparative Example 6

[0069] The difference between this comparative example and Example 1 is that the magnesium salt selected is Mg(ClO4)2, the solvent is single-component DME, and the configuration concentration is 0.1 mol / L.

[0070] Comparative Example 7

[0071] The difference between this comparative example and Example 1 is that the magnesium salt selected is Mg(ClO4)2, the solvent is single-component DME, and the configuration concentration is 0.5 mol / L.

[0072] Comparative Example 8

[0073] The difference between this comparative example and Example 1 is that the magnesium salt selected is MgCl2, the solvent is single-component THF, and the configuration concentration is 0.1 mol / L.

[0074] Comparative Example 9

[0075] The difference between this comparative example and Example 1 is that the magnesium salt selected is MgCl2, the solvent is single-component THF, and the concentration is 0.2 mol / L.

[0076] Comparative Example 10

[0077] The difference between this comparative example and Example 1 is that the magnesium salt selected is MgCl2, the solvent is single-component THF, and the concentration is 0.3 mol / L.

[0078] Table 1 Comparison of coulombic efficiency of Examples 1-12 and Comparative Examples 1-10

[0079]

[0080]

[0081] As can be seen from Table 1, when the electrolyte in the embodiment contains the key component of an amine organic solvent, reversible deposition and dissolution of magnesium metal can be performed, and high coulomb efficiency (>95%) and low overpotential (<0.10V) are maintained; when ethers such as DME and THF are used as pure solvents without amine solvents, reversible deposition and dissolution cycles cannot be performed due to the large overpotential, and the coulomb efficiency is 0.0% and the overpotential is greater than 0.6 V. This shows that the electrolyte of the present invention has excellent electrochemical properties and can realize a magnesium battery electrolyte system using an inorganic magnesium salt as an electrolyte.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-cost all-inorganic rechargeable magnesium battery electrolyte, Features: It includes an electrolyte salt and a non-aqueous solvent; the electrolyte salt is MgCl 2 MgBr 2 MgI 2 Mg(ClO 4 ) 2 MgSO 4 Mg 3 (PO 4 ) 2 Mg(NO 3 ) 2 at least one of; the non-aqueous solvent is an amine solvent or a mixed solvent consisting of an amine solvent and an ether solvent; the amine solvent includes but is not limited to one or more of 2-methoxyethylamine, 3-methoxypropylamine, and 1,3-propylenediamine; the ether solvent includes but is not limited to one or more of tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxolane.

2. A low-cost all-inorganic rechargeable magnesium battery electrolyte according to claim 1, Features: The concentration of the electrolyte salt in the electrolyte solution ranges from 0.01 mol / L to the maximum solubility of the electrolyte salt.

3. A low-cost all-inorganic rechargeable magnesium battery electrolyte according to claim 1, Features: The amine solvent in the mixed solvent accounts for 20%-99% of the total volume of the amine solvent and the ether solvent.

4. A low-cost all-inorganic rechargeable magnesium battery electrolyte according to claim 1, Features: The water content of the electrolyte is less than 20 ppm.

5. A method for preparing a low-cost all-inorganic rechargeable magnesium battery electrolyte. Features: The steps include: 1) Weigh the electrolyte salt and dry it in a vacuum oven at 200°C for 72 hours; the electrolyte salt is MgCl 2 MgBr 2 MgI 2 Mg(ClO 4 ) 2 MgSO 4 Mg 3 (PO 4 ) 2 Mg(NO 3 ) 2 At least one of; 2) adding an amine solvent to a 4A molecular sieve for pre-drying; the amine solvent comprises one or more of 2-methoxyethylamine, 3-methoxypropylamine, and 1,3-propylenediamine; 3) mixing the electrolyte salt with the solvent prepared in step 2), stirring at room temperature for at least 24 hours using a magnetic stirrer until the electrolyte salt is completely dissolved; then adding 4A molecular sieves and drying for 24 hours, repeating the drying process at least three times until the water content is less than 20 ppm using a Karl Fischer water meter, and the electrolyte is prepared.

6. A method for preparing a low-cost all-inorganic rechargeable magnesium battery electrolyte, Features: The steps include: 1) Weigh the electrolyte salt and dry it in a vacuum oven at 200°C for 72 hours; the electrolyte salt is MgCl 2 MgBr 2 MgI 2 Mg(ClO 4 ) 2 MgSO 4 Mg 3 (PO 4 ) 2 Mg(NO 3 ) 2 At least one of; 2) taking a pre-dried amine solvent and a pre-dried ether solvent in a volume ratio of 20%-99% of the total volume of the amine solvent and mixing them at room temperature for 24 hours to make them uniformly mixed; the amine solvent includes one or more of 2-methoxyethylamine, 3-methoxypropylamine, and 1,3-propylenediamine; the ether solvent includes one or more of tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxolane; 3) mixing the electrolyte salt with the solvent prepared in step 2), stirring at room temperature for at least 24 hours using a magnetic stirrer until the electrolyte salt is completely dissolved; then adding 4A molecular sieves and drying for 24 hours, repeating the drying process at least three times until the water content is less than 20 ppm using a Karl Fischer water meter, and the electrolyte is prepared.

7. A low-cost all-inorganic rechargeable magnesium battery, Features: A low-cost all-inorganic rechargeable magnesium battery electrolyte is used as described in any one of claims 1 to 4.

8. A low-cost all-inorganic rechargeable magnesium battery according to claim 7, Features: The negative electrode material is pure metal Mg sheet, and the positive electrode material includes MnO 2 、V 2 O 5 MgMn 2 O 4 , S, Mo 6 S 8 .

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