Gel polymer electrolyte for magnesium ion battery and preparation method thereof

Abstract

The present invention discloses a gel polymer electrolyte for magnesium ion batteries and a preparation method thereof, and belongs to the technical field of magnesium ion batteries. The preparation method of the gel polymer electrolyte for magnesium ion batteries of the present invention comprises: reacting cellulose with acrylonitrile to obtain modified cellulose MC; dissolving the modified cellulose MC in an organic solvent to form a uniform and stable MC casting solution, coating the MC casting solution on a glass plate, immersing it in a coagulation bath, and drying to obtain a modified cellulose film after the film is formed and falls off; immersing the modified cellulose film obtained in step S2 in an LX-144 electrolyte for activation, gelation, and preparation of a gel polymer electrolyte. The high-performance gel polymer electrolyte for magnesium ion batteries prepared by the method provided by the present invention has a series of advantages such as high electrical conductivity and excellent electrochemical performance, and can significantly improve the electrochemical performance of magnesium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium ion batteries, and in particular relates to a gel polymer electrolyte for magnesium ion batteries and a preparation method thereof. Background Art

[0002] As people's living standards continue to improve, higher requirements are placed on the safety and energy density of energy devices, especially in the fields of mobile electronic devices, electric vehicles and large-scale energy storage. However, lithium-ion batteries have long been plagued by problems such as lithium resource shortages and safety, and have become even more controversial in recent years. Therefore, the development of new secondary battery chemistries with low cost and high safety is imperative. In the periodic table, magnesium and lithium are in diagonal positions, have similar chemical properties, and are more abundant in the earth's crust, far higher than lithium, so the raw materials of magnesium-ion batteries are cheaper; at the same time, the metal magnesium negative electrode benefits from the 2e - The reaction mechanism has a volumetric capacity of up to 3833 mAh cm -3 , which is much higher than that of metallic lithium (2046 mAh cm -3 ); Magnesium metal has low chemical activity, making the preparation and handling of magnesium metal electrodes in air relatively safe, significantly improving the safety of chemical power sources. Therefore, magnesium-ion batteries are considered a promising alternative to lithium-ion batteries in the future and are attracting widespread attention from scientists.

[0003] However, since the electrolyte composed of magnesium salts and polar aprotic solvents easily forms a non-conductive passivation film on the surface of the magnesium negative electrode, magnesium ions are difficult to migrate, hindering further magnesium deposition / dissolution reactions. Therefore, it is very necessary to find an electrolyte that is compatible with the Mg negative electrode and does not form a passivation layer on the surface of the Mg negative electrode. So far, researchers have only studied the electrolytes that can reversibly deposit / dissolve Mg. 2+ Extensive exploration has been conducted on liquid electrolytes such as Grignard reagent electrolytes, boron electrolytes, and bis(trifluoromethanesulfonyl)magnesium imide electrolytes. The organic solvents used in the above electrolytes are all ether solvents, which are the only solvents proven to not form a passivation film with the magnesium negative electrode.

[0004] Compared with the above-mentioned liquid electrolytes, polymer electrolytes have attracted widespread attention from more and more researchers due to their advantages such as high safety, wide voltage window, and good flexibility. Gel polymer electrolytes combine the advantages of solid electrolytes and liquid electrolytes, making them an electrolyte with great application prospects. In recent years, a number of gel polymer electrolytes for magnesium-ion batteries have been reported, most of which use polyvinylidene fluoride, polyethylene oxide, and polyacrylonitrile as polymer matrices. However, these gel polymer electrolytes do not exhibit good electrochemical performance in magnesium-ion batteries. Therefore, exploring new gel polymer electrolytes is of great significance for achieving stable and long-life magnesium-ion batteries. At the same time, the main source of the above-mentioned polymer electrolyte matrix relies on dwindling fossil fuels, which has disadvantages such as unsustainability and non-biodegradability. As the magnesium-ion battery market gradually expands, it may cause major environmental pollution problems, which is not in line with the current concept of green development.

[0005] To address these issues, biomass-based polymer electrolytes have attracted widespread attention due to their low cost, high thermal stability / excellent mechanical strength, and good electrochemical performance. These have a significant impact on the sustainable development of energy storage systems. However, natural polymer materials contain many polar functional groups on their surfaces, which easily form hydrogen bonds when the materials self-assemble into films, thereby forming a dense biomass film that is not conducive to the transport of magnesium ions. Therefore, the design and preparation of a high-performance bio-based gel polymer electrolyte for magnesium-ion batteries remains a huge challenge. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a gel polymer electrolyte for magnesium ion batteries and a preparation method thereof, wherein the gel polymer electrolyte for magnesium ion batteries has good electrochemical properties.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions.

[0008] A method for preparing a gel polymer electrolyte, comprising:

[0009] Step S1. Preparation of modified cellulose (MC): cellulose is reacted with acrylonitrile to obtain modified cellulose MC;

[0010] Step S2. Preparation of a modified cellulose membrane (MC membrane): Dissolving modified cellulose (MC) in an organic solvent to form a uniform and stable MC casting solution, coating the MC casting solution on a glass plate, immersing the plate in a coagulation bath, and drying the plate after the membrane is formed and removed.

[0011] Step S3. Preparation of gel polymer electrolyte: The modified cellulose membrane obtained in step S2 is immersed in LX-144 electrolyte for activation to obtain a gel polymer electrolyte.

[0012] The step S1. preparing modified cellulose MC comprises:

[0013] The cellulose is swollen with a NaOH / KSCN solution and filtered to obtain a filter cake; the filter cake is reacted with acrylonitrile, and after the reaction is completed, glacial acetic acid is added to neutralize the reaction solution to neutrality, and the filter cake is washed and dried to obtain the product.

[0014] In some embodiments, during step S1. preparing modified cellulose MC, the mass volume ratio of cellulose to acrylonitrile is 2 g:(20-25) ml. The reaction temperature is 35-38°C, and the reaction time is 2-2.5 hours. Washing is performed using alternating ethanol and deionized water, and drying is performed using vacuum drying at 60-70°C.

[0015] In some embodiments, in step S2, the modified cellulose MC is heated during the dissolution process at a temperature of 60-70° C. and stirred to promote dissolution;

[0016] The organic solvent is selected from one or more of dimethylacetamide DMAC and N,N-dimethylformamide DMF;

[0017] The concentration of MC casting solution is 9.5-11wt%;

[0018] The coagulation bath is 95% ethanol solution.

[0019] Furthermore, the thickness of the modified cellulose membrane MC membrane prepared in step S2 is 90-120 μm.

[0020] In some embodiments, the step S3. preparing the gel polymer electrolyte comprises: cutting the modified cellulose membrane into discs of appropriate size, vacuum drying, cooling to room temperature, and then immersing in LX-144 electrolyte for activation for 6 to 12 hours.

[0021] More preferably, step S1 includes:

[0022] (1) 2 g of cellulose was swelled with 5 ml of 1 M NaOH / 6 M KSCN solution for 30-60 min and filtered;

[0023] (2) reacting the filter cake obtained in the above step with acrylonitrile, wherein the amount of acrylonitrile is 20-25 ml, the reaction temperature is set to 35-38° C., and the reaction time is 2-2.5 h;

[0024] (3) After the reaction is completed, the reaction solution is neutralized with glacial acetic acid and filtered to obtain a filter cake. The filter cake is washed with ethanol and deionized water alternately. The filter cake is transferred to a vacuum oven for drying at a temperature of preferably 60-70°C to obtain the MC product.

[0025] More preferably, the preparation of the gel polymer electrolyte in step S3 includes:

[0026] The resulting MC membrane was cut into small discs with a diameter of 19 mm using a cutting machine. The discs were dried in a vacuum oven at 80°C for 24 hours, cooled to room temperature, and placed in a glove box. In the glove box, the discs were activated by immersing them in LX-144 electrolyte for 8 hours before being removed and the residual electrolyte on the surface was gently blotted with filter paper to obtain the gel polymer electrolyte.

[0027] According to a second aspect of the present invention, a gel polymer electrolyte is provided, which is prepared by the above-mentioned preparation method.

[0028] According to a third aspect of the present invention, there is provided use of the gel polymer electrolyte in a magnesium ion battery.

[0029] The present invention has the following beneficial effects:

[0030] (1) The high-performance gel polymer electrolyte prepared by the present invention has a polymer matrix made of biomass material, which has the advantages of being biodegradable and environmentally friendly, and can avoid the environmental pollution problems caused by petroleum-based polymer matrices such as polyvinylidene fluoride;

[0031] (2) The high-performance gel polymer electrolyte prepared by the present invention contains cyano groups in the polymer matrix, which can interact with magnesium ions, thereby promoting the rapid transmission of magnesium ions and thus improving ionic conductivity;

[0032] (3) The high-performance gel polymer electrolyte prepared by the present invention has a polymer matrix with rich porosity, which improves the liquid absorption rate of the membrane, increases the content of electrolyte in the gel polymer electrolyte and the transmission speed of ions in the electrolyte, thereby increasing ionic conductivity;

[0033] (4) The high-performance gel polymer electrolyte prepared by the present invention has the advantages of uniform pore distribution and small pore size in the polymer matrix, which can induce the uniform deposition of magnesium ions on the surface of the magnesium negative electrode and slow down the nucleation rate of magnesium dendrites.

[0034] (5) The high-performance gel polymer electrolyte prepared by the present invention has a highly reversible Mg 2+ The excellent deposition / dissolution ability and good compatibility with Mg anode and cathode materials imply that the gel polymer electrolyte has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Surface SEM image of MC membrane.

[0036] Figure 2 The cross-sectional SEM image of the MC membrane.

[0037] Figure 3 Cycling performance diagram of the magnesium ion battery assembled with the gel polymer electrolyte prepared in Example 1, 0.5C, 25°C. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions of the present invention in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0039] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0040] For the purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, percentages or ratios and other numerical values ​​used in this specification and the appended claims are to be understood as being modified in all instances by the term "about." In addition, all ranges disclosed herein are inclusive and independently combinable.

[0041] In the embodiment of the present invention, LX-144 electrolyte was purchased from Duoduo Chemical Reagent, and its composition was 0.4M (MgPhCl)2-AlCl3 / THF.

[0042] Example 1

[0043] A method for preparing a high-performance gel polymer electrolyte for magnesium ion batteries comprises the following steps:

[0044] (a) Preparation of MC

[0045] Weigh 2g of cellulose into a beaker, then add 5ml of a 1M NaOH / 6M KSCN solution. Allow to swell at room temperature for 30 minutes and filter. Transfer the resulting filter cake to a flask, add 20ml of acrylonitrile, and react at 35°C for 2 hours. After the reaction, neutralize with 1M glacial acetic acid until neutral and filter. Wash the product alternately with ethanol and distilled water and dry it in a vacuum at 60°C. This yields the MC product.

[0046] (b) Preparation of MC membrane

[0047] Weigh 1.0 g of MC powder and 10 ml of DMAC into a beaker, heat and stir at 70°C for 6 h to obtain a uniform and stable MC casting solution. Pour the prepared casting solution onto the surface of a glass plate and apply it with a scraper. Then, immerse the glass plate in an ethanol coagulation bath. After soaking for a period of time, take out the film and dry it for later use.

[0048] (c) Preparation of high-performance gel polymer electrolyte for magnesium ion batteries

[0049] The resulting MC film was cut into small discs with a diameter of 19 mm using a cutting machine. The discs were dried in a vacuum oven at 80°C for 24 hours, cooled to room temperature, and placed in a glove box. In the glove box, the discs were activated by immersing them in LX-144 electrolyte for 8 hours before being removed and the residual electrolyte on the surface was gently blotted with filter paper, resulting in a high-performance gel polymer electrolyte for magnesium-ion batteries.

[0050] Example 2

[0051] A method for preparing a high-performance gel polymer electrolyte for magnesium ion batteries comprises the following steps:

[0052] (a) Preparation of MC

[0053] Weigh 2g of cellulose into a beaker, then add 5ml of a 1M NaOH / 6M KSCN solution. Allow to swell at room temperature for 60 minutes and filter. Transfer the resulting filter cake to a flask, add 25ml of acrylonitrile, and react at 38°C for 2.5 hours. After the reaction, neutralize with 1M glacial acetic acid until neutral and filter. Wash the product alternately with ethanol and distilled water and dry it in a vacuum at 70°C. This yields the MC product.

[0054] (b) Preparation of MC membrane

[0055] Weigh 1.1 g of MC powder and 10 ml of DMAC into a beaker, heat and stir at 60°C for 7 h to obtain a uniform and stable MC casting solution; pour the prepared casting solution onto the surface of a glass plate, apply the casting solution on the glass plate with a scraper, and then immerse it in an ethanol coagulation bath. After soaking for a period of time, take out the film and dry it for later use.

[0056] (c) Preparation of high-performance gel polymer electrolyte for magnesium ion batteries

[0057] The resulting MC film was cut into small discs with a diameter of 19 mm using a cutting machine. The discs were dried in a vacuum oven at 80°C for 24 hours, cooled to room temperature, and placed in a glove box. In the glove box, the discs were activated by immersing them in LX-144 electrolyte for 8 hours before being removed and the residual electrolyte on the surface was gently blotted with filter paper, resulting in a high-performance gel polymer electrolyte for magnesium-ion batteries.

[0058] Example 3

[0059] A method for preparing a high-performance gel polymer electrolyte for magnesium ion batteries comprises the following steps:

[0060] (a) Preparation of MC

[0061] Weigh 2g of cellulose into a beaker, then add 5ml of a 1M NaOH / 6M KSCN solution. Allow to swell at room temperature for 50 minutes and filter. Transfer the resulting filter cake to a flask, add 23ml of acrylonitrile, and react at 36°C for 2 hours. After the reaction, neutralize with 1M glacial acetic acid until neutral and filter. Wash the product alternately with ethanol and distilled water and dry it in a vacuum at 65°C. This yields the MC product.

[0062] (b) Preparation of MC membrane

[0063] 1.05 g of MC powder and 10 ml of DMAC were weighed and added to a beaker. The mixture was heated and stirred at 65°C for 6.5 h to obtain a uniform and stable MC casting solution. The casting solution was poured onto the surface of a glass plate and smeared on the glass plate with a scraper. The glass plate was then immersed in an ethanol coagulation bath. After soaking for a period of time, the film was taken out and dried for later use.

[0064] (c) Preparation of high-performance gel polymer electrolyte for magnesium ion batteries

[0065] The resulting MC membrane was cut into small discs with a diameter of 19 mm using a cutting machine. The discs were dried in a vacuum oven at 80°C for 24 hours, cooled to room temperature, and placed in a glove box. In the glove box, the discs were activated by immersing them in LX-144 electrolyte for 8 hours before being removed and the residual electrolyte on the surface was gently blotted with filter paper, resulting in a high-performance gel polymer electrolyte for magnesium-ion batteries.

[0066] Example 4

[0067] A method for preparing a high-performance gel polymer electrolyte for magnesium ion batteries comprises the following steps:

[0068] (a) Preparation of MC

[0069] Weigh 2g of cellulose into a beaker, then add 5ml of a 1M NaOH / 6M KSCN solution. Allow to swell at room temperature for 50 minutes and filter. Transfer the resulting filter cake to a flask, add 20ml of acrylonitrile, and react at 35°C for 2.5 hours. After the reaction, neutralize with 1M glacial acetic acid until neutral and filter. Wash the product alternately with ethanol and distilled water and dry it in a vacuum at 60°C. This yields the MC product.

[0070] (b) Preparation of MC membrane

[0071] 1.03 g of MC powder and 10 ml of DMAC were weighed and added to a beaker. The mixture was heated and stirred at 60°C for 7 h to obtain a uniform and stable MC casting solution. The casting solution was poured onto the surface of a glass plate and smeared on the glass plate with a scraper. The glass plate was then immersed in an ethanol coagulation bath. After soaking for a period of time, the film was taken out and dried for later use.

[0072] (c) Preparation of high-performance gel polymer electrolyte for magnesium ion batteries

[0073] The resulting MC membrane was cut into small discs with a diameter of 19 mm using a cutting machine. The discs were dried in a vacuum oven at 80°C for 24 hours, cooled to room temperature, and placed in a glove box. In the glove box, the discs were activated by immersing them in LX-144 electrolyte for 8 hours before being removed and the residual electrolyte on the surface was gently blotted with filter paper, resulting in a high-performance gel polymer electrolyte for magnesium-ion batteries.

[0074] The gel polymer electrolytes prepared in Examples 1-4 were assembled into Mo6S8 / / Mg magnesium ion batteries, and performance tests were performed.

[0075] The Mo6S8 positive electrode sheet is prepared by mixing the active material Mo6S8, super-P, and PVDF in a mass ratio of 8:1:1, and adding an appropriate amount of the organic solvent N-methylpyrrolidone to obtain a uniform and fluid slurry. The slurry is then applied to the current collector using an automatic coating machine. Finally, the coated current collector is placed in a drying oven at 70°C for 48 hours to obtain the active material electrode sheet for the experiment.

[0076] Before using the magnesium negative electrode, the oxide layer on the surface of the magnesium sheet needs to be removed with sandpaper.

[0077] Charge and discharge cycle performance: Charge and discharge cycle test was carried out at 25℃ and 0.5C, with the voltage test range of 0.2-1.7V.

[0078] The charge and discharge cycle test was carried out at 50℃ and 1.0C, and the voltage test range was 0.2-1.7V.

[0079] The test results are shown in Table 1.

[0080] Table 1 Performance test results

[0081]

[0082] It can be seen that the high-performance gel polymer electrolyte for magnesium ion batteries prepared by the present invention has the advantages of high electrical conductivity and good compatibility with positive and negative electrodes, and can significantly improve the cycle performance of magnesium ion batteries.

[0083] Figure 1 Surface SEM image of MC membrane. Figure 2 The cross-sectional SEM image of the MC membrane. Figure 1 and Figure 2 It can be seen that the MC membrane prepared by this method has rich porosity, which improves the liquid absorption rate of the membrane, increases the content of electrolyte in the gel polymer electrolyte and the transmission speed of ions in the electrolyte, thereby increasing the ionic conductivity.

[0084] Figure 3 Cycling performance diagram of magnesium ion battery assembled with gel polymer electrolyte prepared in Example 1, 0.5C, 25℃ Figure 3 It can be seen that the high-performance gel polymer electrolyte prepared by the present invention has good compatibility with Mg negative electrode and positive electrode materials, which means that the gel polymer electrolyte has good application prospects.

[0085] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a gel polymer electrolyte for a magnesium ion battery, characterized in that: include: Step S1. Preparation of modified cellulose MC: cellulose is reacted with acrylonitrile to obtain modified cellulose MC; Step S2. Preparation of modified cellulose membrane: Dissolving modified cellulose MC in an organic solvent to form a uniform and stable MC casting solution, coating the MC casting solution on a glass plate, immersing it in a coagulation bath, and drying the modified cellulose membrane after the membrane is formed and removed. The modified cellulose MC is heated during the dissolution process at a temperature of 60-70°C and stirred to promote dissolution; the organic solvent is selected from one or more of dimethylacetamide (DMAC) and N,N-dimethylformamide (DMF); the concentration of the MC casting solution is 9.5-11 wt%; the coagulation bath is a 95% ethanol solution; the thickness of the modified cellulose MC film is 90-120 μm; Step S3. Preparation of gel polymer electrolyte: The modified cellulose membrane obtained in step S2 is immersed in LX-144 electrolyte for activation to obtain a gel polymer electrolyte.

2. The preparation method according to claim 1, characterized in that The step S1. preparing modified cellulose MC comprises: The cellulose is swollen with a NaOH / KSCN solution and filtered to obtain a filter cake; the filter cake is reacted with acrylonitrile, and after the reaction is completed, glacial acetic acid is added to neutralize the reaction solution to neutrality, filtered, and the filter cake is washed and dried.

3. The preparation method according to claim 2, characterized in that During the preparation of modified cellulose MC, the mass volume ratio of cellulose to acrylonitrile is 2 g: (20-25) ml.

4. The preparation method according to claim 2, characterized in that During the preparation of modified cellulose MC, the reaction temperature is 35-38° C. and the reaction time is 2-2.5 h.

5. The preparation method according to claim 2, characterized in that During the preparation of modified cellulose MC, ethanol and deionized water were used for washing alternately.

6. The preparation method according to claim 1, characterized in that During the preparation of modified cellulose MC, vacuum drying at 60-70°C is adopted for drying.

7. The preparation method according to any one of claims 1 to 6, characterized in that The step S3. preparing the gel polymer electrolyte comprises: cutting the modified cellulose membrane into discs of suitable size, vacuum drying, cooling to room temperature, and then immersing in LX-144 electrolyte for activation for 6 to 12 hours.

8. A gel polymer electrolyte for magnesium ion batteries, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the gel polymer electrolyte for magnesium ion batteries according to claim 8 in magnesium ion batteries.

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