Cyclic carbonate for electrolyte, preparation method of cyclic carbonate and electrolyte

Abstract

The invention belongs to the field of electrolyte, and particularly relates to cyclic carbonate for electrolyte and a preparation method thereof and electrolyte, and the preparation method of the cyclic carbonate for electrolyte comprises the following steps: adding a porous carbon nanomaterial as a catalyst and epoxide into a reaction kettle, and introducing CO2 for reaction to obtain the cyclic carbonate. The metal oxide modified nitrogen-doped porous carbon nanomaterial with a high specific surface area is designed and developed to catalyze CO2 and epoxide to synthesize the cyclic carbonate for the electrolyte, the cyclic carbonate for the electrolyte is prepared by catalyzing carbon dioxide under a mild condition, and on the basis of ensuring the high content of the cyclic carbonate, the epoxypropane conversion rate is 99.9%; the reaction time is shortened, the purity of the obtained cyclic carbonate product is 99.9%, and the method is suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the field of electrolytes, and particularly relates to a cyclic carbonate for electrolytes, a preparation method thereof, and an electrolyte. Background Art

[0002] Cyclic carbonates are a class of compounds with important applications in electrolytes. For example, ethylene carbonate (EC) and propylene carbonate (PC), as the core solvents of lithium-ion battery electrolytes, have characteristics such as high dielectric constant, low viscosity, and wide electrochemical window, which can effectively improve the ion conduction rate and battery cycle stability to meet the requirements of different types of batteries. In lithium-ion batteries, the EC-DMC mixed solvent system has good comprehensive performance and can form a stable solid electrolyte interface (SEI) film on the electrode surface, improving the cycle performance and safety performance of the battery.

[0003] Traditional methods for synthesizing cyclic carbonates (such as phosgene method and haloalcohol method) have defects such as highly toxic raw materials, complex process flows, and high energy consumption, and the by-products are seriously polluted, making it difficult to meet the requirements of sustainable development. The addition reaction of carbon dioxide with epoxides to form cyclic carbonates under the action of a catalyst is a common green chemical method, meeting the requirements of sustainable development, with an atom utilization rate of up to 100%, and carbon dioxide has a wide source and low cost. This technology can consume hundreds of thousands of tons of CO2 and simultaneously co-produce high-value-added products, forming a resource recycling system to contribute to the "dual carbon" goal.

[0004] However, it is not easy to activate thermodynamically stable carbon dioxide. Therefore, the catalyst plays an important role in the process of converting carbon dioxide into cyclic carbonates. So far, a variety of CO2 / epoxide cycloaddition catalysts have been developed. Quaternary ammonium salts and phosphonium salts, ionic liquids, transition metal complexes, salen complexes, and alkali metal salts have been widely studied as homogeneous catalysts. Normally, homogeneous catalysts have higher catalytic activity than heterogeneous catalysts, but it is very difficult to separate and purify homogeneous catalysts from the products, which limits their wide application.

[0005] As an efficient heterogeneous catalyst, metal oxides can be easily separated by centrifugation or filtration, which can effectively solve the problem of separating the catalyst from the product and can be reused. The surface of calcined metal oxides usually contains some acidic and basic active centers, which can interact with adsorbed CO2, thereby polarizing CO2 molecules and promoting the addition reaction with epoxides. However, for traditional metal oxide catalysts, due to aggregation, the specific surface area is relatively small, reducing the CO2 adsorption performance. Therefore, it is necessary to develop metal oxide nanoporous materials with high specific surface area and multiple active sites for the preparation of cyclic carbonates from carbon dioxide. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a cyclic carbonate for electrolyte and a preparation method thereof and an electrolyte.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for preparing cyclic carbonate for electrolyte includes the following steps: adding porous carbon nanomaterial as a catalyst and epoxide into a reaction kettle and introducing CO2 for reaction to obtain cyclic carbonate.

[0009] The mass ratio of the added amount of the porous carbon nanomaterial to the epoxide is 6.0-10.0%, preferably 9%.

[0010] The epoxide is one of ethylene oxide and propylene oxide or a mixture thereof.

[0011] Specifically, the method comprises the following steps: 1) adding porous carbon nanomaterial as a catalyst and epoxide into a reactor respectively, stirring and mixing them thoroughly; 2) using CO2 to purge and remove the air in the reactor, then connecting the reactor to a CO2 cylinder with a constant output pressure, then heating the reactor, and keeping the temperature to react to obtain cyclic carbonate; 3) after the reactor is cooled to room temperature, venting the unreacted CO2, separating the catalyst and the cyclic carbonate product, and recovering the catalyst for further recycling.

[0012] The CO2 pressure in step 2) is 0.4-1.2MPa; preferably 0.8MPa; the reaction temperature is 40-120°C; preferably 100°C; the reaction time is 5-10h; preferably 8h.

[0013] The porous carbon nanomaterial is prepared by the following method: S1) adding citric acid to a metal salt aqueous solution to form a citric acid chelate compound viscous gel; the metal salt is cobalt nitrate and / or magnesium nitrate; S2) drying the obtained viscous gel and grinding it into powder; S3) calcining in a N2 atmosphere to obtain a porous carbon nanomaterial.

[0014] In step S1), the metal salt is a mixture of cobalt nitrate and magnesium nitrate. Preferably, the molar ratio of cobalt nitrate to magnesium nitrate is (1-3):(1-3); more preferably 3:1.

[0015] In step S1), the molar ratio of the metal salt to the citric acid is 1:(1-10); after citric acid is added to the metal salt aqueous solution, the mixture reacts at 60-90°C to form a viscous gel; the drying temperature in step S2) is 100-120°C; the drying time is 5-7h; the calcination temperature in step S3) is 400-800°C; the calcination time is 1-5h; preferably, the calcination temperature in step S3) is 500°C and the time is 3h.

[0016] The present invention also includes a cyclic carbonate obtained by the described preparation method.

[0017] The present invention also includes an electrolyte solution comprising the cyclic carbonate.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] By designing and developing a metal oxide-modified nitrogen-doped porous carbon nanomaterial with a high specific surface area and multiple active sites to catalyze the synthesis of cyclic carbonates from CO2, the present invention realizes the efficient and stable conversion of CO2, and can obtain various cyclic carbonates for electrolyte solutions. The product separation is simple, and at the same time, the yield and selectivity of preparing propylene carbonate for electrolyte solutions can both reach 99.9% under mild reaction conditions (100 °C, 0.8 MPa, 6 h).

[0020] The technical solution of this application utilizes the acid-base bifunctional active sites simultaneously possessed by metal oxides to activate epoxides and carbon dioxide molecules for catalytic conversion to prepare cyclic carbonates. At the same time, nitrogen-doped carbon functionalization helps to increase the basic sites to activate CO2 molecules and improve its catalytic performance, realizing the preparation of propylene carbonate for electrolyte solutions under mild reaction conditions (100 °C, 0.8 MPa, 6 h). Description of the Drawings

[0021] Figure 1 Scanning electron microscope (SEM) images of Cat1 (a) in Example 1, Cat2 (b) in Example 2, Cat3 (c) in Example 3, and Cat4 (d) in Example 4;

[0022] Figure 2 X-ray diffraction (XRD) patterns of Cat1-Cat4 obtained in Examples 1-4;

[0023] Figure 3 Transmission electron microscope (TEM) image and elemental distribution map of Cat4 in Example 4;

[0024] Figure 4 Reaction condition optimization diagram for preparing propylene carbonate for electrolyte solutions by catalyzing CO2 and propylene oxide with Cat4 in Example 4;

[0025] Figure 5 Gas chromatogram (diluted with ethyl acetate) of preparing propylene carbonate for electrolyte solutions by catalyzing CO2 and propylene oxide with Cat4 in Example 4. Detailed Embodiments

[0026] In order to enable those skilled in the art of the present technology to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the drawings and the best embodiments.

[0027] Example 1

[0028] A nitrogen-doped porous carbon nanomaterial modified with metal oxide based on high specific surface area, comprising the following steps:

[0029] Dissolve 1.7 g of Co(NO3)2·6H2O in 100 mL of deionized water to form a mixed salt solution. Then, under vigorous mechanical stirring for 10 minutes, introduce 1.1 g of citric acid (molar ratio of metal salt to citric acid 1:1) to form a citric acid chelate compound and stir at 80 °C for 10 h. Dry the obtained viscous gel at 110 °C for 5 h. Finally, grind the resin into fine powder and calcine it in a tube furnace with nitrogen component at 500 °C for 3 h, with a heating rate of 5 °C / min, to obtain a nitrogen-doped porous carbon nanomaterial modified with metal cobalt oxide, namely Cat1.

[0030] Example 2

[0031] The difference between Example 2 and Example 1 is only that the mixed salt solution is different. Specifically: Dissolve 1.5 g of Mg(NO3)2·6H2O in 100 mL of deionized water to form a mixed salt solution. Then prepare the catalyst according to the method of Example 1 to obtain a nitrogen-doped porous carbon nanomaterial modified with metal magnesium oxide, namely Cat2.

[0032] Example 3

[0033] The difference between Example 3 and Example 1 is only that the mixed salt solution and the calcination method are different. Specifically: Dissolve 1.7 g of Co(NO3)2·6H2O and 0.5 g of Mg(NO3)2·6H2O (molar ratio 3:1) in 100 mL of deionized water to form a mixed salt solution. Then prepare the catalyst according to the method of Example 1. The difference is that finally, the powder is calcined in a muffle furnace with air component at 500 °C for 3 h, with a heating rate of 5 °C / min, to obtain a cobalt-magnesium metal oxide material, namely Cat3.

[0034] Example 4

[0035] The difference between Example 4 and Example 1 is only that the mixed salt solution is different. Specifically: Dissolve 1.7 g of Co(NO3)2·6H2O and 0.5 g of Mg(NO3)2·6H2O (molar ratio 3:1) in 100 mL of deionized water to form a mixed salt solution. Then prepare the catalyst according to the method of Example 1 to obtain a nitrogen-doped porous carbon nanomaterial modified with cobalt-magnesium metal oxide, namely Cat4.

[0036] Example 5

[0037] Example 5 is only different from Example 1 in that the mixed salt solution is different. Specifically, 0.6 g of Co(NO3)2·6H2O and 0.5 g of Mg(NO3)2·6H2O (molar ratio 1:1) are dissolved in 100 mL of deionized water to form a mixed salt solution. Then, the catalyst is prepared according to the method of Example 1 to obtain a nitrogen-doped porous carbon nanomaterial modified with cobalt-magnesium metal oxide, namely Cat5.

[0038] Example 6

[0039] Example 6 is only different from Example 1 in that the mixed salt solution is different. Specifically, 0.6 g of Co(NO3)2·6H2O and 1.5 g of Mg(NO3)2·6H2O (molar ratio 1:3) are dissolved in 100 mL of deionized water to form a mixed salt solution. Then, the catalyst is prepared according to the method of Example 1 to obtain a nitrogen-doped porous carbon nanomaterial modified with cobalt-magnesium metal oxide, namely Cat6.

[0040] Example 7

[0041] Performance study on the synthesis of cyclic carbonates for electrolytes from carbon dioxide and propylene oxide catalyzed by Cat1 - Cat6: 150 mg of the catalyst and 2 mL of propylene oxide are added to a 25 mL stainless steel autoclave equipped with a magnetic stirrer, and the mixture is stirred and reacted at 0.8 MPa and 100 °C for 6 h. After the reaction, the temperature is lowered in an ice-water bath, and the excess carbon dioxide is slowly released. An appropriate amount of ethyl acetate (internal standard for chromatographic analysis) is added to the reacted liquid, and the solid catalyst is separated by centrifugation. The liquid sample is analyzed by a gas chromatograph (SP-7890P l us / F) equipped with a capillary chromatograph (KB-5) to obtain the yield and selectivity of propylene carbonate as shown in Table 1.

[0042] Table 1. Results of the synthesis of cyclic carbonates from carbon dioxide and propylene oxide catalyzed by Cat1 - Cat6

[0043]

[0044]

[0045] Example 8

[0046] Example 8 is only different from Example 4 in that the calcination temperature is 400 °C and the calcination time is 3 h.

[0047] Example 9

[0048] Example 9 is only different from Example 4 in that the calcination temperature is 600 °C and the calcination time is 3 h.

[0049] Example 10

[0050] Example 10 is only different from Example 4 in that the calcination temperature is 700 °C and the calcination time is 3 h.

[0051] Example 11

[0052] Example 11 is only different from Example 4 in that the calcination temperature is 800 °C and the calcination time is 3 h.

[0053] The performance study of Examples 1, 8, 9, and 10 for the synthesis of cyclic carbonates from carbon dioxide and propylene oxide was carried out as in Example 7, and the yields and selectivities of propylene carbonate are shown in Table 2.

[0054] Table 2 Results of Examples 4, 8 - 10 for the synthesis of cyclic carbonates from carbon dioxide and propylene oxide

[0055] Catalyst Calcination temperature Yield (%) Selectivity (%) Example 4 500℃ >99 >99 Example 8 400℃ 91 91.7 Example 9 600℃ 93.5 93.8 Example 10 700℃ 93.4 92.6 Example 11 800℃ 92.2 92.8

[0056] Example 12

[0057] Performance study of Cat4 for the synthesis of cyclic carbonates from carbon dioxide and other epoxides:

[0058] It is only different from Example 7 in that propylene oxide is adjusted to other epoxides, the catalyst is Cat4, and other conditions remain unchanged. The conversion rates and selectivities of the cyclic carbonates obtained are shown in Table 3.

[0059] Table 3 Results of Cat4 for the synthesis of cyclic carbonates from carbon dioxide and other epoxides

[0060]

[0061]

[0062] SEM characterization was carried out on Cat1 ( Figure 1 a) in), Cat2 ( Figure 1 b) in), Cat3 ( Figure 1 c) in), and Cat4 ( Figure 1 d) in) of Examples 1 - 4. The results show that Cat4 (d) modified with cobalt - magnesium metal oxides has an obvious pore structure. The strong interaction between cobalt and magnesium leads to the generation of pore structures in the material, increasing the specific surface area of the material, which is consistent with the results in Table 3.

[0063] XRD characterization was carried out on Cat1 - Cat4 of Examples 1 - 4 ( Figure 2 ), and the results show that CoO and MgO nanoparticles were successfully modified in the nitrogen - doped porous carbon materials respectively, and the catalyst structure remained intact.

[0064] For Cat1 - Cat4 in Examples 1 - 4, nitrogen adsorption - desorption tests were carried out at 77K to determine the pore structure parameters, including specific surface area, pore diameter, and pore volume. The results are shown in Table 4.

[0065] Table 4. Pore structure parameters of Cat1 - Cat4 in Examples 1 - 4

[0066] Catalyst <![CDATA[Specific surface area (m 2 / g)]]> Pore diameter (nm) <![CDATA[Pore volume (cm 3 / g)]]> Cat1 119.552 5.158 0.122 Cat2 110.128 4.240 0.107 Cat3 45.254 14.86 0.117 Cat4 179.777 6.517 0.175

[0067] For Cat4 in Example 4, TEM characterization ( Figure 3 ) was carried out. The results showed that a carbon layer with a porous structure could be observed, which was consistent with the results of SEM and Table 3. At the same time, Co, Mg, C, N, and O elements were evenly dispersed in the carbon powder, further proving that CoO and MgO were successfully modified in the nitrogen - doped carbon material, and also proving that nitrogen doping could be successfully achieved by calcining Cat4 at 500 °C.

[0068] For the reaction temperature ( Figure 4 a) in), reaction pressure ( Figure 4 b) in), reaction time ( Figure 4 c) in), and the mass ratio of catalyst to propylene oxide ( Figure 4 d) in) of the reaction of Cat4 in Example 4 for the preparation of cyclic carbonate from carbon dioxide and propylene oxide were optimized. The results showed that under mild conditions (100 °C, 0.8 MPa, 6 h), when the mass ratio of the catalyst addition amount to the epoxide was 9%, the yield and selectivity of propylene carbonate for electrolyte preparation could both reach 99.9%.

[0069] The product synthesized from carbon dioxide and propylene oxide catalyzed by Cat4 in Example 4 was collected. After being diluted several times with ethyl acetate, its purity was directly detected by gas chromatography. The original gas chromatogram is shown in Figure 5 . The results showed that there was no peak of propylene oxide in the product, indicating that propylene oxide was completely converted, proving that the yield reached 99.9%. At the same time, there was only one product, propylene carbonate, in the product and no by - products, proving that the selectivity reached 99.9%. In summary, the purity of the propylene carbonate product synthesized from carbon dioxide and propylene oxide catalyzed by Cat4 > 99%, and its catalytic effect is significantly better than that of other metal oxides in the same application field, making a breakthrough progress in the application effect in this field.

[0070] In summary, the present invention designs and develops a nitrogen-doped porous carbon nanomaterial modified with metal oxide with high specific surface area for catalyzing the synthesis of cyclic carbonates from CO2. The sol-gel method is used to increase the specific surface area, and the metal oxide with both acid-base bifunctional active sites is utilized to activate the epoxide and carbon dioxide molecules for catalytic conversion to prepare cyclic carbonates. At the same time, nitrogen-doped carbon functionalization helps to increase the basic sites to activate CO2 molecules, realizing the efficient and stable conversion of CO2. The product separation is simple, and the yield and selectivity of propylene carbonate for electrolyte preparation can both reach 99.9% under mild conditions (100 °C, 0.8 MPa, 6 h).

[0071] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of cyclic carbonate for electrolyte, characterized in that, The method comprises the following steps: adding porous carbon nanomaterial as a catalyst and epoxide into a reaction kettle and introducing CO2 to react to obtain cyclic carbonate.

2. Use of the metal oxide-modified nitrogen-doped porous carbon nanomaterial according to claim 1, characterized in that The mass ratio of the added amount of the porous carbon nanomaterial to the epoxide is 6.0-10.0%, preferably 9%.

3. The application of the metal oxide-modified nitrogen-doped porous carbon nanomaterial according to claim 1, characterized in that, The epoxide is one of ethylene oxide and propylene oxide or a mixture thereof.

4. The preparation method of the cyclic carbonate for electrolyte according to claim 1, characterized in that, Specifically, the method comprises the following steps: 1) adding porous carbon nanomaterial as a catalyst and epoxide into a reactor respectively, stirring and mixing them thoroughly; 2) using CO2 to purge and remove the air in the reactor, then connecting the reactor to a CO2 cylinder with a constant output pressure, then heating the reactor, and keeping the temperature to react to obtain cyclic carbonate; 3) after the reactor is cooled to room temperature, venting the unreacted CO2, separating the catalyst and the cyclic carbonate product, and recovering the catalyst for further recycling.

5. The preparation method of the cyclic carbonate for electrolyte according to claim 4, characterized in that, The CO2 pressure in step 2) is 0.4-1.2MPa; preferably 0.8MPa; the reaction temperature is 40-120°C; preferably 100°C; the reaction time is 5-10h; preferably 8h.

6. The preparation method of the cyclic carbonate for electrolyte according to claim 4, characterized in that, The porous carbon nanomaterial is prepared by the following method: S1) adding citric acid to a metal salt aqueous solution to form a citric acid chelate compound viscous gel; the metal salt is cobalt nitrate and / or magnesium nitrate; S2) drying the obtained viscous gel and grinding it into powder; S3) calcining in a N2 atmosphere to obtain a porous carbon nanomaterial.

7. The preparation method of the cyclic carbonate for electrolyte according to claim 6, characterized in that, In step S1), the metal salt is a mixture of cobalt nitrate and magnesium nitrate. Preferably, the molar ratio of cobalt nitrate to magnesium nitrate is (1-3):(1-3); more preferably 3:

1.

8. The preparation method of the cyclic carbonate for electrolyte according to claim 6, characterized in that, In step S1), the molar ratio of the metal salt to the citric acid is 1:(1-10); after citric acid is added to the metal salt aqueous solution, the mixture reacts at 60-90°C to form a viscous gel; the drying temperature in step S2) is 100-120°C; the drying time is 5-7h; the calcination temperature in step S3) is 400-800°C; the calcination time is 1-5h; preferably, the calcination temperature in step S3) is 500°C and the time is 3h.

9. A cyclic carbonate obtained by the preparation method according to any one of claims 1 to 8.

10. An electrolyte, characterized in that, Comprising the cyclic carbonate described in claim 9.

Images