Preparation method of MOF-based solid electrolyte membrane for sodium-ion batteries

Abstract

This invention relates to the field of sodium-ion batteries, specifically to a method for preparing a MOF-based solid electrolyte membrane for sodium-ion batteries, comprising the following steps: 1) dissolving a soluble zinc salt in solvent I, then adding 2-methylimidazole to dissolve it, followed by crystallization; the resulting MOF crystals are washed and baked; 2) uniformly dispersing the obtained MOF particles in an ionic liquid solvent; then separating them, resuspending the separated solid precipitate in acetone, and using the resulting suspension as a coating solution; 3) uniformly coating the coating solution onto a pre-cleaned substrate to form a thin film, followed by drying and heat treatment; finally, separating the film from the substrate to obtain the MOF-based solid electrolyte membrane. This invention, through rational design and optimization, improves the overall performance of sodium-ion batteries, providing reliable technical support for the practical application of sodium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and more specifically to a method for preparing a MOF-based solid electrolyte membrane for sodium-ion batteries. Background Technology

[0002] With the increasing global energy demand and the growing severity of environmental problems, the development of clean and sustainable energy storage technologies has become a research hotspot in the field of science and technology. Lithium-ion batteries, with their high energy density and long cycle life, are widely used in portable electronic devices and electric vehicles. However, the limited and uneven distribution of lithium resources poses challenges to large-scale energy storage applications. Therefore, finding alternatives to lithium-ion batteries has become an urgent problem to be solved. Against this backdrop, sodium-ion batteries, due to the abundance, wide distribution, and low cost of sodium resources, have gradually become a research focus.

[0003] The basic principle of sodium-ion batteries is similar to that of lithium-ion batteries, primarily storing and releasing electrical energy through the insertion and extraction of sodium ions. The core components of a sodium-ion battery include the positive electrode material, the negative electrode material, and the electrolyte. However, research on the electrolyte for sodium-ion batteries has lagged behind compared to that of the positive and negative electrode materials. As an indispensable component of sodium-ion batteries, the electrolyte's main function is to conduct sodium ions, while also requiring high ionic conductivity, good electrochemical stability, and a wide voltage window. Currently, sodium-ion batteries mainly use liquid electrolytes. In 2024, a patent (CN118248948A) from Henan Penghui Power Supply Co., Ltd. reported the preparation of a layered oxide / hard carbon system sodium-ion battery using a non-aqueous organic solvent, sodium salt, and additives as the electrolyte. This battery maintained a capacity retention rate of over 91.51% after 200 cycles and over 87.28% after 400 cycles. However, liquid electrolytes have some significant drawbacks, such as flammability, leakage, and poor thermal stability, which seriously affect the safety and lifespan of sodium-ion batteries. Therefore, developing solid-state electrolytes with high safety and high stability has become an important direction in sodium-ion battery research.

[0004] Metal-organic frameworks (MOFs) are a class of porous materials composed of metal ions or metal clusters and organic ligands through coordination bonds. They possess large specific surface areas, abundant pore structures, and tunable chemical functions. Applying MOFs to solid-state electrolytes in sodium-ion batteries can effectively improve sodium-ion conductivity by utilizing their porous structure, while the tunability of their structure also provides possibilities for optimizing electrolyte performance. Yu et al. (ACS Applied Materials & Interfaces, 2021, 13(21): 24662-24669) reported a UiO66 grafted with sodium sulfonate (-SO3Na) groups as an electrolyte, exhibiting a specific surface area of ​​3.6 × 10⁻⁶ at room temperature. -4 The ionic conductivity is measured in S / cm. Since MOF materials themselves have poor electrical conductivity, they often need to be doped or composited with other materials to improve their ionic conductivity. Secondly, MOF materials have relatively weak mechanical properties, requiring structural optimization during preparation to enhance their stability and durability. Furthermore, the preparation methods for MOF-based solid electrolytes require further research to achieve simple and low-cost synthesis processes. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a novel method for preparing MOFs-based solid electrolytes.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing a MOF-based solid electrolyte membrane for sodium-ion batteries, comprising the following steps:

[0007] 1) Dissolve the soluble zinc salt in solvent I, then add 2-methylimidazole to dissolve it and continue stirring for 1 to 2 hours (to promote the formation of MOF crystals by metal ions and organic ligands), and then crystallize.

[0008] The obtained MOF crystals were washed and baked (to activate the crystal structure and improve its surface area and porosity) to obtain MOF particles; the baking was carried out at 90-110℃ for 5-7 hours.

[0009] The molar ratio of zinc salt to 2-methylimidazole is 1:1 ± 0.05;

[0010] 2) Add the MOF particles obtained in step 1) to the ionic liquid solvent and stir until the MOF particles are uniformly dispersed; then separate (centrifuge or filter after standing), and resuspend the solid precipitate obtained by separation in acetone. The resulting suspension is used as the coating solution.

[0011] The ionic liquid solvent consists of an ionic liquid and solvent II;

[0012] 3) The coating solution is uniformly coated onto the pre-cleaned substrate to form a thin film (a uniform thin film). Then, it is dried until the acetone in the film evaporates, and then dried at 60-80°C for 10-12 hours (to solidify the MOF structure and the distribution of the ionic liquid). Next, it is treated at 95-105°C for 1.5-2.5 hours. Finally, the film is separated from the substrate to obtain a MOF-based solid electrolyte membrane (approximately 0.1-0.2 mm).

[0013] The invention yields a MOF-based solid electrolyte membrane doped with ionic liquid (IL).

[0014] As an improvement to the preparation method of the MOFs-based solid electrolyte membrane of the present invention: the ionic liquid in step 2) is 1-butyl-3-methylimidazolium chloride;

[0015] In the ionic liquid solvent, the ratio of ionic liquid to solvent II is 10-50 g / 60-100 mL, and solvent II is composed of water and ethanol, with a water to ethanol volume ratio of 2-3:1.

[0016] Each 1g of MOF particles is prepared with an ionic liquid solvent containing 10-50g (preferably 10-30g) of ionic liquid.

[0017] As a further improvement to the preparation method of the MOFs-based solid electrolyte membrane of the present invention: in step 1), the soluble zinc salt is zinc nitrate or zinc acetate.

[0018] As a further improvement to the preparation method of the MOFs-based solid electrolyte membrane of the present invention: in step 1), solvent I is DMF (N,N-dimethylformamide). Generally, 40-80 mL of solvent I is used for every 0.25 mol of soluble zinc salt.

[0019] As a further improvement to the preparation method of the MOFs-based solid electrolyte membrane of the present invention: in step 1),

[0020] The reagents used for crystallization are ethanol or acetone;

[0021] The washing reagent is ethanol or acetone.

[0022] As a further improvement to the preparation method of the MOFs-based solid electrolyte membrane of the present invention: in step 1),

[0023] The MOF crystals are washed, dried (at room temperature to constant weight), and then baked.

[0024] As a further improvement to the preparation method of the MOFs-based solid electrolyte membrane of the present invention: in step 1),

[0025] After baking, the particles are pulverized to obtain MOF particles that can pass through a 100-mesh sieve.

[0026] As a further improvement to the preparation method of the MOFs-based solid electrolyte membrane of the present invention: in step 2), each 1g of MOFs particles is suspended in 15-25ml of acetone.

[0027] As a further improvement to the preparation method of the MOFs-based solid electrolyte membrane of the present invention: in step 3), the substrate is a glass substrate or a silicon substrate;

[0028] The substrate was rinsed in sequence with acetone, isopropanol, and deionized water to obtain a pre-cleaned substrate.

[0029] As a further improvement to the preparation method of the MOFs-based solid electrolyte membrane of the present invention: the coating in step 3) is spin coating, the spin coating speed is set to 400-600 rpm, and the spin coating time is 20-40 seconds.

[0030] This invention aims to provide a novel method for preparing MOFs-based solid electrolytes, which, through rational design and optimization, improves the overall performance of sodium-ion batteries and provides reliable technical support for the practical application of sodium-ion batteries.

[0031] Existing MOF-based solid electrolyte membranes typically use MOF materials as the main framework, enhancing electrolyte conductivity by introducing polymers or doping with inorganic / organic ions. Compared to existing technologies, this invention introduces ionic liquids (ILs) into MOF-based solid electrolytes, forming a novel MOF-based solid electrolyte membrane. Unlike traditional polymer or sodium salt doping methods, ionic liquids possess high ionic conductivity and chemical stability. Furthermore, unlike traditional electrolytes, ionic liquids exhibit good conductivity over a wide temperature range and are independent of humidity.

[0032] The MOF-based solid electrolyte of the present invention has the following technical advantages:

[0033] 1) MOFs structures provide a large number of ion transport channels, and the doping of ionic liquids enhances the ionic conductivity of the electrolyte.

[0034] 2) The high chemical stability of MOFs materials and the protective effect of ionic liquids enhance the stability of composite films during cycling.

[0035] 3) Ionic liquids typically have lower volatility, which reduces the risk of leakage and improves battery safety compared to traditional liquid electrolytes, and is also environmentally friendly. Detailed Implementation

[0036] The embodiments of the present invention will be described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes.

[0037] Example 1: Preparation method of MOFs-based solid electrolyte membrane

[0038] 1) First, dissolve 0.25 mol of zinc nitrate in 50 mL of LMF (N,N-dimethylformamide). Then, under stirring, add 0.25 mol of 2-methylimidazole and stir thoroughly at room temperature to ensure that the 2-methylimidazole is dissolved evenly. Then, continue stirring at room temperature for about 1 hour to promote the formation of MOF crystals by zinc ions and organic ligands (2-methylimidazole).

[0039] After the reaction was completed, about 100 mL of ethanol was slowly added as a reaction terminator to allow MOF crystals to precipitate and crystallize from the solution.

[0040] After washing the precipitated MOF crystals with ethanol, place them in a ventilated environment or a vacuum drying oven to dry them completely (dry at room temperature to constant weight), thereby removing the small amount of moisture present from air adsorption and solvents such as ethanol.

[0041] The dried MOF crystals were baked in an oven at 100°C for 6 hours to activate the crystal structure and improve its surface area and porosity. The large MOF crystals after baking were crushed and passed through a 100-mesh sieve to obtain MOF particles of uniform size.

[0042] 2) Add 10g of 1-butyl-3-methylimidazolium chloride (as an ionic liquid) to a solvent consisting of 50mL water and 20mL ethanol to obtain an ionic liquid solution;

[0043] Add 1g of the MOF particles prepared in step 1) to the above-mentioned ionic liquid solvent and stir at room temperature for about 1 hour to ensure that the MOF particles are fully dispersed in the ionic liquid solvent. Then, centrifuge at 5000 rpm for 10 minutes (or filter after standing for 4 hours) to separate the solid precipitate (MOF material doped with part of the ionic liquid) and the solvent (water and ethanol). Resuspend the solid precipitate in 20 mL of acetone, and use the resulting suspension as the coating solution.

[0044] 3) Rinse the glass substrate or silicon substrate sequentially with acetone, isopropanol, and deionized water to obtain a pre-cleaned substrate;

[0045] The coating solution was uniformly coated onto a pre-cleaned substrate using a spin coater; the spin coating speed was set to 500 rpm and the spin coating time to 30 seconds to ensure the formation of a uniform film. The coated substrate was then placed in a ventilated environment or on a heated plate to allow the solvent acetone to evaporate slowly (until no more acetone was evaporated), followed by drying at 80°C for 12 hours to solidify the MOF structure and the distribution of the ionic liquid; then, it was placed in an oven at 100°C for 2 hours. Finally, the film was separated from the substrate phase to obtain a MOF-based solid electrolyte membrane (approximately 0.1 mm thick).

[0046] Example 2, compared to Example 1, makes the following changes:

[0047] The amount of ionic liquid (1-butyl-3-methylimidazolium chloride) was changed from 10g to 30g; the rest was the same as in Example 1.

[0048] Example 3: The following changes are made compared to Example 1:

[0049] The amount of ionic liquid (1-butyl-3-methylimidazolium chloride) was changed from 10g to 50g; the rest was the same as in Example 1.

[0050] Example 4: The following changes are made compared to Example 1:

[0051] Change "drying at 80°C for 12 hours" in step 3) to "drying at 60°C for 10 hours"; the rest is the same as in Example 1.

[0052] Example 5: The “zinc nitrate” in Example 1 was replaced with “zinc acetate”, while the amount remained unchanged at 0.25 mol. The rest was the same as in Example 1.

[0053] Comparative Example 1, compared to Example 1, is modified as follows:

[0054] Replace "ionic liquid (1-butyl-3-methylimidazolium chloride)" with "ethanol", keep the amount unchanged at 10g; the rest is the same as in Example 1.

[0055] Comparative Example 2, compared to Example 1, made the following changes:

[0056] The amount of ionic liquid (1-butyl-3-methylimidazolium chloride) was changed from 10g to 1g; the rest was the same as in Example 1.

[0057] Comparative Example 3, compared to Example 1, made the following changes:

[0058] The ionic liquid was changed from "1-butyl-3-methylimidazolium chloride" to "1-ethyl-3-methylimidazolium chloride", while the amount remained unchanged at 10g; the rest was the same as in Example 1.

[0059] Comparative Example 4-1, with the following changes made compared to Example 1:

[0060] Change "80℃ treatment for 12 hours + 100℃ treatment for 2 hours" to "80℃ treatment for 16 hours"; the rest is the same as in Example 1.

[0061] Comparative Example 4-2, the following changes were made compared to Example 1:

[0062] Change "80℃ treatment for 12 hours + 100℃ treatment for 2 hours" to "100℃ treatment for 14 hours"; the rest is the same as in Example 1.

[0063] Comparative Example 5, compared to Example 1, is modified as follows:

[0064] Replace "zinc nitrate" with "copper nitrate", keep the amount the same at 0.25 mol, and the rest is the same as in Example 1.

[0065] Experiment 1: The electrolyte membranes obtained from all the above examples and comparative examples were used in sodium-ion batteries. The sodium-ion battery assembly was set up according to steps four and five of Example 1 of the invention CN117174988A, "A method for preparing lithium / sodium-ion battery material and its application in lithium / sodium-ion batteries", and the electrolyte in step four was replaced with the MOFs-based solid electrolyte membrane obtained in the above examples of the present invention.

[0066] The electrochemical workstation was set to electrochemical impedance spectroscopy (EIS) mode, with the EIS measurement frequency range set to 1 Hz to 1 MHz. A small AC voltage of 10 mV was applied to ensure measurement accuracy while avoiding damage to the electrolyte membrane. Impedance data were acquired at room temperature, and the charge transfer resistance (R) was calculated, which reflects the resistance to ionic conductivity.

[0067] Formula for calculating ionic conductivity:

[0068] Where L is the thickness of the electrolyte membrane (approximately 0.1 mm in Example 1), R is the membrane resistance (obtained from EIS data), and A is the contact area between the cathode / anode and the membrane (2 cm²). 2 ).

[0069] The results are shown in Table 1 below.

[0070] Experiment 2, Stability Test:

[0071] The battery assembled in Experiment 1 was connected to the electrochemical workstation at 0.1 mA / cm. 2A 100-cycle charge-discharge test was conducted at a current density of 0.01 to 2.5V, with the charging voltage range set between 0 and 2.0V. Data such as current, voltage, and charge were recorded for each cycle, and the capacity retention rate was calculated.

[0072] Capacity retention rate = Discharge capacity at 100th cycle / Initial capacity × 100%.

[0073] Table 1. Application effects of different solid electrolyte films in sodium-ion batteries

[0074] Experiment 1 (Ionic conductivity S / cm) Experiment 2 (Capacity Retention Rate %) Example 1 <![CDATA[3.5×10 -3 ]]> 95％ Example 2 <![CDATA[4.2×10 -3 ]]> 92％ Example 3 <![CDATA[2.8×10 -3 ]]> 90％ Example 4 <![CDATA[3.1×10 -3 ]]> 93％ Example 5 <![CDATA[3.8×10 -3 ]]> 89％ Comparative Example 1 <![CDATA[1.2×10 -4 ]]> 70％ Comparative Example 2 <![CDATA[1.5×10 -4 ]]> 65％ Comparative Example 3 <![CDATA[1.0×10 -4 ]]> 72％ Comparative Example 4-1 <![CDATA[2.0×10 -4 ]]> 60％ Comparative Example 4-2 <![CDATA[2.1×10 -4 ]]> 62％ Comparative Example 5 <![CDATA[1.8×10 -4 ]]> 68％

[0075] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a MOF-based solid electrolyte membrane for sodium-ion batteries, characterized in that... Includes the following steps: 1) Dissolve the soluble zinc salt in solvent I, then add 2-methylimidazole to dissolve it, and continue stirring for 1-2 hours, then crystallize. The obtained MOF crystals were washed and baked to obtain MOF particles; the baking was carried out at 90~110℃ for 5~7 h. The molar ratio of zinc salt to 2-methylimidazole is 1:1 ± 0.05; 2) Add the MOF particles obtained in step 1) to the ionic liquid solvent and stir until the MOF particles are uniformly dispersed; then separate them and resuspend the solid precipitate obtained from the separation in acetone. The resulting suspension is used as the coating solution. The ionic liquid solvent is composed of an ionic liquid and solvent II, wherein the ionic liquid is 1-butyl-3-methylimidazolium chloride; Each 1 g of MOF particles is prepared with an ionic liquid solvent containing 10-50 g of ionic liquid. 3) The coating solution is uniformly coated on the pre-cleaned substrate to form a thin film. Then, it is dried until the acetone in the film is evaporated, and then dried at 60~80℃ for 10~12 h. Next, it is treated at 95~105℃ for 1.5~2.5 h. Finally, the film is separated from the substrate to obtain a MOF-based solid electrolyte membrane.

2. The method for preparing MOFs-based solid electrolyte membrane according to claim 1, characterized in that: In the ionic liquid solvent, the ratio of ionic liquid to solvent II is 10~50g / 60~100mL, and solvent II is composed of water and ethanol, with a water to ethanol volume ratio of 2~3:

1.

3. The method for preparing MOFs-based solid electrolyte membrane according to claim 2, characterized in that... In step 1), the soluble zinc salt is zinc nitrate or zinc acetate.

4. The method for preparing MOFs-based solid electrolyte membrane according to claim 3, characterized in that... In step 1): Solvent I is DMF.

5. The method for preparing MOFs-based solid electrolyte membrane according to claim 4, characterized in that... In step 1): The reagents used for crystallization are ethanol or acetone; The washing reagent is ethanol or acetone.

6. The method for preparing MOFs-based solid electrolyte membrane according to claim 5, characterized in that... In step 1): After being washed and dried, the MOF crystals are then baked.

7. The method for preparing MOFs-based solid electrolyte membrane according to claim 6, characterized in that... In step 1): After baking, the particles are pulverized to obtain MOF particles that can pass through a 100-mesh sieve.

8. The method for preparing MOFs-based solid electrolyte membranes according to any one of claims 1 to 7, characterized in that... In step 2), each 1g of MOF particles is suspended in 15-25ml of acetone.

9. The method for preparing MOFs-based solid electrolyte membranes according to any one of claims 1 to 7, characterized in that... In step 3), the substrate is a glass substrate or a silicon substrate; The substrate was rinsed in sequence with acetone, isopropanol, and deionized water to obtain a pre-cleaned substrate.

10. The method for preparing MOFs-based solid electrolyte membrane according to claim 9, characterized in that: The coating in step 3) is spin coating, with the spin coating speed set to 400~600 rpm and the spin coating time to 20~40 seconds.