Modified electrolyte of rechargeable magnesium battery as well as preparation method and application of modified electrolyte

Abstract

The invention provides a modified electrolyte of a rechargeable magnesium battery as well as a preparation method and application of the modified electrolyte. The modified electrolyte comprises a phenoxy magnesium-aluminum halide complex, an organic ether solvent and a lithium salt additive, the lithium salt additive is selected from at least one of lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium bis (fluorosulfonyl) imide and lithium bis (trifluoromethanesulfonyl) imide. The lithium salt additive does not contain chloride ions, corrosion to a current collector is inhibited, and a solvation structure of magnesium ions in the electrolyte is effectively regulated and controlled, so that the lithium salt additive has a wide electrochemical window, high ionic conductivity, low overpotential and high reversibility. The invention further provides a preparation method of the magnesium battery electrolyte, the preparation process is simple, convenient and efficient, raw materials are low in price, and industrial large-scale production is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a modified electrolyte for rechargeable magnesium batteries, its preparation method, and its application. Background Technology

[0002] Rechargeable magnesium batteries have attracted much attention due to their abundant resources, high safety, and large theoretical specific capacity. Magnesium accounts for up to 2.7% of the Earth's crust. Magnesium secondary batteries, using metallic magnesium as the negative electrode, are less prone to dendrite formation during charging and discharging, and magnesium metal possesses a high specific capacity of up to 3833 mAh / cm³. -3 Due to their high volumetric capacity and low standard electrode potential (-2.37 V vs SHE), rechargeable magnesium batteries are considered a promising new electrochemical energy storage system. However, problems such as slow magnesium ion kinetics and poor stability of the magnesium metal anode / electrolyte interface severely restrict the commercialization of rechargeable magnesium batteries.

[0003] Constructing magnesium-lithium composite electrolytes is one effective strategy to solve the above problems. By introducing lithium salt additives, the solvation structure of the electrolyte can be controlled, promoting the formation of a stable negative electrode / electrolyte interface, improving ionic conductivity, enhancing magnesium deposition and dissolution efficiency, and strengthening magnesium ion kinetics. Currently, most magnesium-lithium composite electrolyte systems for magnesium batteries widely studied employ a phenyl Grignard reagent-aluminum trichloride-lithium chloride combination. This modified electrolyte system contains chloride ions (Cl... - This modified electrolyte exhibits strong corrosiveness, severely shortening the lifespan of magnesium batteries, hindering magnesium ion migration, and slowing electrolyte / electrode interface kinetics. Furthermore, its electrochemical window is narrow (<2.75V). Additionally, this modified electrolyte system possesses strong nucleophilicity, making it incompatible with electrophilic magnesium battery cathode materials such as elemental sulfur.

[0004] Therefore, finding a more suitable modified electrolyte for rechargeable magnesium batteries and solving the aforementioned technical problems of existing electrolytes for magnesium secondary batteries is urgent and important, and is also one of the focal points of attention for many leading researchers and R&D companies in the field. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a modified electrolyte for rechargeable magnesium batteries, a method for preparing the modified electrolyte, and its application, which can significantly improve the electrochemical performance of magnesium batteries.

[0006] This invention provides a modified electrolyte for a rechargeable magnesium battery, comprising a phenoxy magnesium aluminum halide complex, an organic ether solvent, and a lithium salt additive.

[0007] The lithium salt additive is selected from at least one of lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethanesulfonylimide.

[0008] Preferably, the concentration of phenoxy magnesium aluminum halide complex in the modified electrolyte is 0.25~1.0 mol / L;

[0009] The concentration of lithium salt additive in the electrolyte is 0.1~1.0 mol / L.

[0010] Preferably, the organic ether solvent is selected from one or more of tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, and tetrahydrofuran.

[0011] Preferably, the phenoxy magnesium aluminum halide complex is prepared by reacting phenoxy magnesium halide with aluminum trichloride.

[0012] Preferably, the molar ratio of magnesium phenoxyhalide to aluminum trichloride is 1 to 3:1.

[0013] Preferably, the magnesium phenoxy halide has the structure shown in Formula I:

[0014] Formula I;

[0015] R is a C1-C3 alkyl group; Y is selected from Cl, Br or I.

[0016] This invention provides a method for preparing a modified electrolyte for a rechargeable magnesium battery as described above, comprising the following steps:

[0017] Under an inert atmosphere, lithium salt additives were added to a mixture of phenoxy magnesium aluminum halide complex / organic ether electrolyte and stirred thoroughly to obtain a modified electrolyte for rechargeable magnesium batteries.

[0018] Preferably, the phenoxy magnesium aluminum halide complex / organic ether electrolyte mixture is prepared by the following method:

[0019] A certain amount of AlCl3 was dissolved in an organic ether solvent and stirred thoroughly until a transparent solution was obtained. The resulting solution was then added to a POMgY ether solution and stirred until clear to obtain a mixture of phenoxy magnesium aluminum halide complex / organic ether electrolyte.

[0020] Preferably, the stirring time is 12-24 hours, the stirring speed is 500-1000 rpm, and the stirring temperature is 25-40℃.

[0021] The water and oxygen content in the inert atmosphere is both below 0.1 ppm.

[0022] This invention provides a rechargeable magnesium battery, comprising the modified electrolyte of the rechargeable magnesium battery described in the above technical solution.

[0023] This invention provides a modified electrolyte for a rechargeable magnesium battery, comprising a phenoxy magnesium aluminum halide complex, an organic ether solvent, and a lithium salt additive; the lithium salt additive is selected from at least one of lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethanesulfonylimide. This invention effectively overcomes the problem of slow magnesium ion kinetics by introducing low-cost, chloride-free sulfonylimide / sulfonic acid lithium salt additives of the aforementioned specific types into the non-nucleophilic magnesium electrolyte system: phenoxy magnesium aluminum halide complex, thereby broadening the selection range of cathode materials; the anions in the lithium salt additive can effectively regulate the solvation structure of magnesium ions at the negative electrode interface in the electrolyte magnesium salt, forming a stable electrode / electrolyte interface, which can significantly improve the electrochemical performance of the magnesium battery. Attached Figure Description

[0024] Figure 1 The LSV diagram of the magnesium battery electrolyte prepared in Example 1 of this invention in a Mg||SS asymmetric cell is shown.

[0025] Figure 2 The graph shows the deposition / dissolution coulombic efficiency of the magnesium battery electrolyte prepared in Example 1 of this invention in a Mg||SS asymmetric cell.

[0026] Figure 3 This is a voltage-time curve of the magnesium battery electrolyte prepared in Example 1 of the present invention in a Mg||Mg symmetric cell;

[0027] Figure 4 The image shows the electrochemical impedance spectroscopy of the magnesium battery electrolyte prepared in Example 1 of this invention in an SS||SS symmetric cell.

[0028] Figure 5 The image shows the electrochemical impedance spectroscopy of the magnesium battery electrolyte prepared in Example 2 of this invention in an SS||SS symmetric cell.

[0029] Figure 6 Capacity curves of the Mg-S batteries assembled in Examples 3 and 4 of this invention;

[0030] Figure 7 This is a specific capacity-voltage curve of the high-capacity Mo6S8||Mg full cell assembled in Example 5 of the present invention. Detailed Implementation

[0031] This invention provides a modified electrolyte for a rechargeable magnesium battery, comprising a phenoxy magnesium aluminum halide complex, an organic ether solvent, and a lithium salt additive.

[0032] The lithium salt additive is selected from at least one of lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethanesulfonylimide.

[0033] The modified electrolyte for the rechargeable magnesium battery provided by this invention includes a phenoxy magnesium aluminum halide complex; the concentration of the phenoxy magnesium aluminum halide complex in the modified electrolyte is 0.25~1.0 mol / L, specifically 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, or 1.0 mol / L.

[0034] In this invention, the phenoxymagnesium aluminum halide complex is prepared by reacting magnesium phenoxyhalide with aluminum trichloride. The molar ratio of magnesium phenoxyhalide to aluminum trichloride is 1~3:1, specifically 1:1, 2:1, or 3:1. The magnesium phenoxyhalide in this invention has the structure shown in Formula I:

[0035] Formula I;

[0036] R is a C1-C3 alkyl group; Y is selected from Cl, Br or I.

[0037] In a specific embodiment of the present invention, the phenoxy magnesium halide is 2-tert-butyl-4-methylphenoxy magnesium chloride.

[0038] The modified electrolyte for the rechargeable magnesium battery provided by the present invention includes an organic ether solvent; the organic ether solvent is selected from one or more of tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, and tetrahydrofuran (THF).

[0039] The modified electrolyte for a rechargeable magnesium battery provided by this invention includes a lithium salt additive; the lithium salt additive is selected from at least one of lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethanesulfonylimide. The concentration of the lithium salt additive in the electrolyte is 0.1~1.0 mol / L, specifically 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1.0 mol / L.

[0040] This invention synthesizes a novel modified electrolyte by adding the above-mentioned chloride-free lithium salt additives to a solution of non-nucleophilic phenoxy magnesium aluminum halide complexes, which inhibits corrosion of the current collector and significantly improves the diffusion kinetics of ions.

[0041] This invention provides a method for preparing a modified electrolyte for a rechargeable magnesium battery as described above, comprising the following steps:

[0042] Under an inert atmosphere, lithium salt additives were added to a mixture of phenoxy magnesium aluminum halide complex / organic ether electrolyte and stirred thoroughly to obtain a modified electrolyte for rechargeable magnesium batteries.

[0043] In the inert atmosphere used in this invention, the content of both water and oxygen is less than 0.1 ppm.

[0044] The phenoxy magnesium aluminum halide complex / organic ether electrolyte mixture described in this invention is prepared by the following method:

[0045] A certain amount of AlCl3 was dissolved in an organic ether solvent and stirred thoroughly until a transparent solution was obtained. The resulting solution was then added to a POMgY ether solution and stirred until clear to obtain a mixture of phenoxy magnesium aluminum halide complex / organic ether electrolyte.

[0046] In this invention, AlCl3 is dispersed in an organic ether solvent; POMgY is also pre-spread in an organic ether solvent; the stirring time in this invention is 12-24 hours, the stirring speed is 500-1000 rpm, and the stirring temperature is 25-40℃.

[0047] This invention provides a rechargeable magnesium battery, comprising the modified electrolyte of the rechargeable magnesium battery described in the above technical solution. The rechargeable magnesium battery is preferably a Mg||Mo6S8 battery.

[0048] The beneficial effects of this invention are as follows:

[0049] (1) The present invention uses sulfonylimide / sulfonic acid lithium salts without chloride ions as electrolyte additives to synthesize a novel modified electrolyte in a solution of non-nucleophilic phenoxy magnesium aluminum halide complexes, which inhibits the corrosion of the current collector and significantly improves the diffusion kinetics of ions.

[0050] (2) The modified electrolyte provided by this invention effectively regulates the solvation structure of magnesium ions by introducing commercially available lithium salts, promotes the formation of an SEI layer that can conduct magnesium ions, thereby broadening the electrochemical stability window (oxidation stability voltage 3.6V), achieving high reversibility (first-cycle coulombic efficiency of magnesium deposition / dissolution reaches 94.7%), and improving ionic conductivity (2.71 mS cm⁻¹). -1 ), reducing the overpotential (136mV);

[0051] (3) The modified electrolyte provided by the present invention has low raw material price and simple preparation process. It only needs to be reacted under normal temperature conditions, which is conducive to large-scale industrial production.

[0052] (4) The modified electrolyte provided by this invention is applied to a high-capacity Mg||Mo6S8 battery, achieving a first-cycle coulombic efficiency of 100% and a capacity of 117 mAh g. -1 It can be perfectly matched with sulfur cathode material in Mg-S batteries, exhibiting excellent electrochemical performance.

[0053] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a modified electrolyte for a rechargeable magnesium battery, its preparation method, and its application. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0054] Example 1

[0055] This embodiment provides a method for preparing a magnesium battery electrolyte, the steps of which are as follows:

[0056] In an argon glove box, weigh 0.1333 g of AlCl3 and measure 2 mL of THF. Dissolve the AlCl3 in THF and stir until a clear solution is obtained. Then add it dropwise to a 1 mol / L 2-tert-butyl-4-methylphenoxymagnesium chloride / THF solution and stir until clear to obtain a 2-tert-butyl-4-methylphenoxymagnesium aluminum chloride complex / THF electrolyte. Subsequently, add lithium trifluoromethanesulfonate (LiOTf) and stir thoroughly to obtain a magnesium metal battery modified electrolyte (PMC-LiOTf).

[0057] Taking the modified electrolyte (PMC-LiOTf) prepared above as an example, a coin cell (CR2032) was assembled using PMC-LiOTf, a magnesium sheet as the counter / reference electrode, a stainless steel foil as the working electrode, and a glass fiber separator. Linear sweep voltammetry was then performed at a scan rate of 1 mV / s. -1 ( Figure 1 ).

[0058] A coin cell (CR2032) was assembled using PMC-LiOTf, with a magnesium sheet as the counter / reference electrode, stainless steel foil as the working electrode, and glass fiber as the separator. Magnesium deposition / dissolution cycle efficiency was tested at a current density of 0.1 mA·cm⁻¹. -2 The discharge time is 1 hour, and the charging cut-off voltage is 1.2V. Figure 2 ).

[0059] A symmetrical cell (CR2032) was assembled using PMC-LiOTf, with a magnesium sheet as the working / counter electrode and glass fiber as the separator. Polarization performance was tested at a current density of 0.5 mA cm⁻¹. -2 Time control 1 hour ( Figure 3 ).

[0060] The ionic conductivity of the modified electrolyte was tested using EIS; stainless steel foil was used as the reference electrode / working electrode / counter electrode, the test voltage was 5mV, and the frequency range was 1MHz-0.01Hz. Figure 4 ).

[0061] like Figure 1 , Figure 2 As shown, the PMC-LiOTf modified electrolyte exhibits excellent oxidative stability with an electrochemical window of up to 3.6V (vs. Mg / Mg²⁺), and achieves efficient magnesium deposition / dissolution with a first-cycle coulombic efficiency of up to 94.7% and an average coulombic efficiency of approximately 99% after 100 cycles.

[0062] like Figure 3 As shown, at a current density of 0.5 mA cm⁻¹ -2 After 150 hours of cycling, the polarization potential remained stable, and the overpotential was extremely low at 136 mV, indicating that the PMC-LiOTf modified electrolyte exhibits excellent stability for magnesium. Figure 4 As shown, the ionic conductivity of the PMC-LiOTf modified electrolyte is 2.71 mS / cm. -1 The high ionic conductivity reflects the high Mg content. 2+ The migration rate is fast.

[0063] Example 2

[0064] In an argon glove box, weigh 0.1333 g of AlCl3 and measure 2 mL of THF. Dissolve the AlCl3 in THF and stir until a clear solution is obtained. Then add the solution dropwise to a 1 mol / L 2-tert-butyl-4-methylphenoxymagnesium chloride / THF solution and stir until clear to obtain the unmodified electrolyte (PMC).

[0065] The ionic conductivity of the unmodified electrolyte prepared above was tested using EIS, with stainless steel foil as the reference electrode / working electrode / counter electrode. The test voltage was 5mV, and the frequency range was 1MHz-0.01Hz. Figure 5 ).like Figure 5 As shown, the ionic conductivity of the unmodified electrolyte (PMC) is 0.76 mS / cm. -1 The ionic conductivity is much lower than that of the modified electrolyte (PMC-LiOTf) (2.71 mS / cm). -1 This demonstrates that sulfonic acid lithium salt additives are more conducive to Mg 2+ Rapid migration.

[0066] Example 3

[0067] Using the PMC-LiOTf modified electrolyte prepared in Example 1, a battery was assembled with magnesium sheet as the negative electrode, sulfur / carbon composite material as the positive electrode, and glass fiber as the separator. Constant current charge-discharge tests were conducted, with a current density of 0.1 C.

[0068] Example 4

[0069] Using the unmodified PMC electrolyte prepared in Example 2, a battery was assembled with magnesium sheet as the negative electrode, sulfur / carbon composite material as the positive electrode, and glass fiber as the separator. Constant current charge-discharge tests were conducted with a current density of 0.1 C.

[0070] like Figure 6 As shown, the Mg-S battery using the modified electrolyte PMC-LiOTf maintained a specific capacity of 1001 mAh g after 100 cycles at 0.1C. -1 The modified electrolyte PMC exhibited excellent cycle stability. In contrast, the Mg-S battery using the unmodified electrolyte PMC showed a continuous increase in specific capacity during cycling at 0.1C and experienced a short circuit after 89 cycles, fully demonstrating that the modified electrolyte significantly improves the electrochemical performance of Mg-S batteries.

[0071] Example 5

[0072] Using the PMC-LiOTf modified electrolyte prepared in Example 1, with a high loading of Mo6S8 as the positive electrode (4.54 mg / cm³), -2 A full cell was assembled using magnesium sheets as the negative electrode and glass fiber as the separator, and constant current charge-discharge tests were conducted. The voltage range was 0.2-2.2V and the current density was 0.1C.

[0073] like Figure 7 As shown, the prepared high-loading Mg||Mo6S8 battery achieved a 100% coulombic efficiency in its first cycle at 0.1C, realizing perfect reversible insertion / extraction of magnesium ions, and exhibited a high initial specific capacity (117 mAh g). -1 After 10 cycles, there was no significant capacity decay, and the coulombic efficiency remained almost 100%, demonstrating excellent electrochemical performance.

[0074] As can be seen from the above embodiments, the present invention provides a modified electrolyte for a rechargeable magnesium battery, comprising a phenoxy magnesium aluminum halide complex, an organic ether solvent, and a lithium salt additive; the lithium salt additive is selected from at least one of lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethanesulfonylimide. The present invention effectively overcomes the problem of slow magnesium ion kinetics by introducing low-cost, chloride-free sulfonylimide / sulfonic acid lithium salt additives of the above-mentioned specific types into the non-nucleophilic magnesium electrolyte system: phenoxy magnesium aluminum halide complex, thereby broadening the selection range of cathode materials; the anions in the lithium salt additives can effectively regulate the solvation structure of magnesium ions at the negative electrode interface in the electrolyte magnesium salt, forming a stable electrode / electrolyte interface, which can significantly improve the electrochemical performance of the magnesium battery. The above-mentioned types of lithium salt additives used in the present invention are chloride-free, inhibiting corrosion of the current collector and effectively controlling the solvation structure of magnesium ions in the electrolyte, thus exhibiting a wide electrochemical window, high ionic conductivity, low overpotential, and high reversibility. This invention also provides a method for preparing magnesium battery electrolyte, which is simple and efficient, uses inexpensive raw materials, and is conducive to large-scale industrial production.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A modified electrolyte for a rechargeable magnesium battery, comprising a phenoxy magnesium aluminum halide complex, an organic ether solvent, and a lithium salt additive; The lithium salt additive is selected from at least one of lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethanesulfonylimide.

2. The modified electrolyte for a rechargeable magnesium battery according to claim 1, characterized in that, The concentration of phenoxy magnesium aluminum halide complex in the modified electrolyte is 0.25~1.0 mol / L; The concentration of lithium salt additive in the electrolyte is 0.1~1.0 mol / L.

3. The modified electrolyte for a rechargeable magnesium battery according to claim 1, characterized in that, The organic ether solvent is selected from one or more of tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, and tetrahydrofuran.

4. The modified electrolyte for a rechargeable magnesium battery according to claim 1, characterized in that, The phenoxy magnesium aluminum halide complex is prepared by the reaction of phenoxy magnesium halide and aluminum trichloride.

5. The modified electrolyte for a rechargeable magnesium battery according to claim 4, characterized in that, The molar ratio of magnesium phenoxyhalide to aluminum trichloride is 1~3:

1.

6. The modified electrolyte for a rechargeable magnesium battery according to claim 4, characterized in that, The phenoxy magnesium halide has the structure shown in Formula I: Formula I; R is a C1-C3 alkyl group; Y is selected from Cl, Br or I.

7. A method for preparing a modified electrolyte for a rechargeable magnesium battery according to any one of claims 1 to 6, comprising the following steps: Under an inert atmosphere, lithium salt additives were added to a mixture of phenoxy magnesium aluminum halide complex / organic ether electrolyte and stirred thoroughly to obtain a modified electrolyte for rechargeable magnesium batteries.

8. The preparation method according to claim 7, characterized in that, The phenoxy magnesium aluminum halide complex / organic ether electrolyte mixture was prepared by the following method: A certain amount of AlCl3 was dissolved in an organic ether solvent and stirred thoroughly until a transparent solution was obtained. The resulting solution was then added to a POMgY ether solution and stirred until clear to obtain a mixture of phenoxy magnesium aluminum halide complex / organic ether electrolyte.

9. The preparation method according to claim 7, characterized in that, The stirring time is 12~24h, the stirring speed is 500~1000rpm, and the stirring temperature is 25~40℃; The water and oxygen content in the inert atmosphere is both below 0.1 ppm.

10. A rechargeable magnesium battery, comprising the modified electrolyte of the rechargeable magnesium battery according to any one of claims 1 to 6.

Images