Cyclic carbonate for electrolyte, preparation method thereof, and electrolyte

Abstract

This invention belongs to the field of electrolytes, specifically relating to a cyclic carbonate for electrolytes, its preparation method, and the electrolyte itself. The preparation method of the cyclic carbonate for electrolytes includes the following steps: porous carbon nanomaterials are added as a catalyst and epoxides to a reaction vessel, and CO2 is introduced to react and obtain the cyclic carbonate. This invention designs and develops nitrogen-doped porous carbon nanomaterials modified with high specific surface area metal oxides to catalyze the synthesis of cyclic carbonate for electrolytes from CO2 and epoxides. Under mild conditions, it catalyzes the preparation of cyclic carbonate for electrolytes from carbon dioxide, achieving a 99.9% propylene oxide conversion rate while ensuring a high cyclic carbonate content, shortening the reaction time, and obtaining a cyclic carbonate product with 99.9% purity, suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of electrolytes, specifically relating to a cyclic carbonate for electrolytes, its preparation method, and the electrolyte itself. Background Technology

[0002] Cyclic carbonates are a class of compounds with important applications in electrolytes. For example, ethylene carbonate (EC) and propylene carbonate (PC), as core solvents in lithium-ion battery electrolytes, possess characteristics such as high dielectric constant, low viscosity, and a wide electrochemical window, which can effectively improve ion conductivity and battery cycle stability to meet the needs of different types of batteries. In lithium-ion batteries, the EC-DMC mixed solvent system exhibits excellent overall performance, capable of forming a stable solid electrolyte interphase (SEI) film on the electrode surface, thereby improving the battery's cycle performance and safety.

[0003] Traditional methods for synthesizing cyclic carbonates (such as the phosgene process and haloalcohol process) suffer from drawbacks such as highly toxic raw materials, complex processes, and high energy consumption, and produce serious byproduct pollution, making it difficult to meet the needs of sustainable development. The addition reaction of carbon dioxide with epoxides under the action of a catalyst to produce cyclic carbonates is a common green chemistry method that meets the requirements of sustainable development, achieves 100% atom utilization, and utilizes widely available and inexpensive carbon dioxide. This technology can consume tens of thousands of tons of CO2 while simultaneously producing high-value-added products, forming a resource recycling system and contributing to the "dual carbon" goals (carbon dioxide, carbon dioxide, and carbon sequestration).

[0004] However, activating thermodynamically stable carbon dioxide is not easy. Therefore, catalysts play a crucial role in the conversion of carbon dioxide to cyclic carbonates. To date, various CO2 / epoxide cycloaddition catalysts have been developed. Quaternary ammonium and phosphate salts, ionic liquids, transition metal complexes, Salen complexes, and alkali metal salts have been extensively studied as homogeneous catalysts. Normally, homogeneous catalysts exhibit higher catalytic activity than heterogeneous catalysts, but the separation and purification of homogeneous catalysts from the products is very difficult, limiting their widespread application.

[0005] Metal oxides, as highly efficient heterogeneous catalysts, can be easily separated from products through centrifugation or filtration, and can be reused. The surface of calcined metal oxides typically contains acidic and basic active sites that can interact with adsorbed CO2, polarizing the CO2 molecules and promoting the addition reaction with epoxides. However, traditional metal oxide catalysts suffer from low specific surface area due to aggregation, reducing their CO2 adsorption performance. Therefore, there is a need to develop high specific surface area, multi-active-site metal oxide nanoporous materials for the preparation of cyclic carbonates from carbon dioxide. Summary of the Invention

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

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

[0008] A method for preparing cyclic carbonates for electrolytes includes the following steps: porous carbon nanomaterials are added to a reaction vessel as a catalyst along with epoxides, and CO2 is introduced to react and obtain cyclic carbonates.

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

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

[0011] Specifically, the steps are as follows: 1) Porous carbon nanomaterials as catalysts and epoxides are added to the reactor and stirred thoroughly; 2) Air in the reactor is purged with CO2, then the reactor is connected to a CO2 cylinder with constant output pressure, the reactor is heated and kept at a constant temperature to obtain cyclic carbonates; 3) After the reactor cools to room temperature, the unreacted CO2 is released, the catalyst and cyclic carbonate product are separated, and the catalyst is recovered for continued recycling.

[0012] In step 2), the CO2 pressure is 0.4-1.2 MPa; preferably 0.8 MPa; the reaction temperature is 40-120℃; preferably 100℃; and the reaction time is 5-10 h; preferably 8 h.

[0013] The porous carbon nanomaterials are prepared by the following method: S1) Citric acid is added to an aqueous solution of a metal salt to form a citric acid chelate viscous gel; the metal salt is cobalt nitrate and / or magnesium nitrate; S2) the obtained viscous gel is dried and ground into powder; S3) calcined under N2 atmosphere to obtain porous carbon nanomaterials.

[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, it is 3:1.

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

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

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

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

[0019] This invention utilizes nitrogen-doped porous carbon nanomaterials modified with high specific surface area and multiple active sites, modified with metal oxides, to catalyze the synthesis of cyclic carbonates from CO2, achieving efficient and stable CO2 conversion. This yields a variety of cyclic carbonates suitable for electrolytes, with simple product separation. Furthermore, under mild reaction conditions (100℃, 0.8MPa, 6h), the yield and selectivity of propylene carbonate for electrolytes can reach 99.9%.

[0020] The technical solution of this application utilizes the dual-functional acid-base sites of metal oxides to activate the catalytic conversion of epoxides and carbon dioxide molecules to prepare cyclic carbonates. Simultaneously, nitrogen-doped carbon functionalization helps increase the activation of basic sites for CO2 molecules, improving its catalytic performance and enabling the preparation of propylene carbonate for electrolytes under mild reaction conditions (100℃, 0.8MPa, 6h). Attached Figure Description

[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 The X-ray diffraction (XRD) patterns of Cat1-Cat4 obtained in Examples 1-4 are shown below.

[0023] Figure 3 The image shows a transmission electron microscope (TEM) image and elemental distribution map of Cat4 in Example 4.

[0024] Figure 4 This is a diagram showing the optimized reaction conditions for preparing propylene carbonate electrolyte from CO2 and propylene oxide using Cat4 catalysis in Example 4.

[0025] Figure 5 The gas chromatogram (diluted with ethyl acetate) of propylene carbonate used in the preparation of electrolyte from CO2 and propylene oxide using Cat4 catalysis in Example 4. Detailed Implementation

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

[0027] Example 1

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

[0029] 1.7 g of Co(NO3)2·6H2O was dissolved in 100 mL of deionized water to form a mixed salt solution. Then, under vigorous mechanical stirring for 10 minutes, 1.1 g of citric acid (metal salt to citric acid molar ratio 1:1) was introduced to form a citric acid chelate compound, and the mixture was stirred at 80 °C for 10 h. The resulting viscous gel was dried at 110 °C for 5 h. Finally, the resin was ground into a fine powder and calcined in a tube furnace under nitrogen at 500 °C for 3 h at a heating rate of 5 °C / min to obtain nitrogen-doped porous carbon nanomaterials modified with cobalt oxide, namely Cat1.

[0030] Example 2

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

[0032] Example 3

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

[0034] Example 4

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

[0036] Example 5

[0037] The only difference between Example 5 and Example 1 is the mixed salt solution. Specifically, 0.6 g of Co(NO3)2·6H2O and 0.5 g of Mg(NO3)2·6H2O (molar ratio 1:1) were dissolved in 100 mL of deionized water to form a mixed salt solution. The catalyst was then prepared according to the method of Example 1 to obtain nitrogen-doped porous carbon nanomaterials modified with cobalt-magnesium metal oxides, namely Cat5.

[0038] Example 6

[0039] The only difference between Example 6 and Example 1 is the mixed salt solution. Specifically, 0.6 g of Co(NO3)2·6H2O and 1.5 g of Mg(NO3)2·6H2O (molar ratio 1:3) were dissolved in 100 mL of deionized water to form a mixed salt solution. The catalyst was then 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 of cyclic carbonates in the electrolyte for the synthesis of carbon dioxide and propylene oxide using Cat1-Cat6 catalyst: 150 mg of catalyst and 2 mL of propylene oxide were added to a 25 mL stainless steel autoclave equipped with a magnetic stir bar, and the reaction was stirred at 0.8 MPa and 100 °C for 6 h. After the reaction, the mixture was cooled in an ice-water bath to slowly release excess carbon dioxide. An appropriate amount of ethyl acetate (internal standard for chromatographic analysis) was added to the reaction liquid, and the solid catalyst was separated by centrifugation. The liquid sample was analyzed by a gas chromatograph (SP-7890P l us / F) equipped with a capillary chromatograph (KB-5). The yield and selectivity of propylene carbonate are 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] The only difference between Example 8 and Example 4 is that the calcination temperature is 400℃ and the calcination time is 3h.

[0047] Example 9

[0048] The only difference between Example 9 and Example 4 is that the calcination temperature is 600℃ and the calcination time is 3h.

[0049] Example 10

[0050] The only difference between Example 10 and Example 4 is that the calcination temperature is 700℃ and the calcination time is 3h.

[0051] Example 11

[0052] The only difference between Example 11 and Example 4 is that the calcination temperature is 800℃ and the calcination time is 3h.

[0053] Examples 1, 8, 9, and 10 show the performance of catalytic synthesis of cyclic carbonates from carbon dioxide and propylene oxide as in Example 7. The yield and selectivity of propylene carbonate are shown in Table 2.

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

[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 catalyzing the synthesis of cyclic carbonates from carbon dioxide and other epoxides:

[0058] The only difference from Example 7 is that propylene oxide was replaced with other epoxy compounds, the catalyst was Cat4, and other conditions remained unchanged. The conversion and selectivity of the cyclic carbonates are shown in Table 3.

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

[0060]

[0061]

[0062] For Cat1 in Examples 1-4 Figure 1 a) Cat2 Figure 1 (b) Cat3 Figure 1 c) and Cat4 Figure 1 SEM characterization of Cat4(d) showed that the cobalt-magnesium metal oxide modified Cat4(d) has an obvious porous structure. The strong interaction between cobalt and magnesium leads to the formation of a porous structure in the material, which increases the specific surface area of ​​the material, consistent with the results in Table 3.

[0063] XRD characterization was performed on Cat1-Cat4 in Examples 1-4. Figure 2 The results showed that CoO and MgO nanoparticles were successfully modified into nitrogen-doped porous carbon materials, and the catalyst structure remained intact.

[0064] For Cat1-Cat4 in Examples 1-4, nitrogen adsorption-desorption tests were performed at 77K to determine pore structure parameters, including specific surface area, pore diameter, and pore volume, as 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)]]> Aperture (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] TEM characterization of Cat4 in Example 4 ( Figure 3 The results showed that a porous carbon layer could be observed, which is consistent with the results of SEM and Table 3. Meanwhile, Co, Mg, C, N, and O elements were uniformly dispersed in the carbon powder, further demonstrating that CoO and MgO were successfully modified in the nitrogen-doped carbon material. This also proves that nitrogen doping can be successfully achieved by calcining Cat4 at 500℃.

[0068] The reaction temperature for the Cat4-catalyzed preparation of cyclic carbonates from carbon dioxide and propylene oxide in Example 4 ( Figure 4 a) Reaction pressure ( Figure 4 (b) Reaction time ( Figure 4 c) and the mass ratio of catalyst to propylene oxide ( Figure 4 Optimization was carried out in section d), and the results showed that under mild conditions (100℃, 0.8MPa, 6h), the mass ratio of catalyst addition to epoxide was 9%, and the yield and selectivity of propylene carbonate for preparing electrolyte could reach 99.9%.

[0069] The product synthesized from carbon dioxide and propylene oxide using Cat4 catalysis in Example 4 was collected, diluted several times with ethyl acetate, and its purity was directly determined by gas chromatography. The original gas chromatogram is shown below. Figure 5 The results showed that no propylene oxide peak was observed in the product, indicating complete conversion of propylene oxide and demonstrating a yield of 99.9%. Furthermore, only propylene carbonate was produced, with no byproducts, demonstrating a selectivity of 99.9%. In summary, the propylene carbonate product synthesized from carbon dioxide and propylene oxide using Cat4 catalysis has a purity >99%, and its catalytic effect is significantly superior to other metal oxides in the same application field, representing a breakthrough in its application.

[0070] In summary, this invention designs and develops nitrogen-doped porous carbon nanomaterials modified with high specific surface area metal oxides to catalyze the synthesis of cyclic carbonates from CO2. The specific surface area is increased via a sol-gel method, and the acid-base bifunctional active sites of the metal oxides are utilized to activate the catalytic conversion of epoxides and carbon dioxide molecules to prepare cyclic carbonates. Simultaneously, nitrogen-doped carbon functionalization helps increase the basic sites for activating CO2 molecules, achieving efficient and stable CO2 conversion. Product separation is simple, and under mild conditions (100℃, 0.8MPa, 6h), the yield and selectivity of propylene carbonate for electrolyte preparation can both reach 99.9%.

[0071] 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 method for preparing a cyclic carbonate for electrolytes, characterized in that, The process includes the following steps: porous carbon nanomaterials are added to a reaction vessel as a catalyst along with epoxides, and CO2 is introduced to react and obtain cyclic carbonates; The porous carbon nanomaterials are prepared in the following manner: S1) Citric acid is added to an aqueous solution of a metal salt to form a viscous gel of citric acid chelate compound; the metal salt is a mixture of cobalt nitrate and magnesium nitrate, with a molar ratio of cobalt nitrate to magnesium nitrate of (1-3):(1-3); the molar ratio of the metal salt to citric acid is 1:(1-10); after adding citric acid to the aqueous solution of the metal salt, a viscous gel is formed by reacting at 60-90℃. S2) The obtained viscous gel is dried and then ground into powder; the drying temperature is 100-120℃; the drying time is 5-7h; S3) Calcination under N2 atmosphere yields porous carbon nanomaterials; calcination temperature is 400-800℃; calcination time is 1-5h.

2. The method for preparing cyclic carbonate for electrolyte according to claim 1, characterized in that, The mass ratio of the porous carbon nanomaterial to the epoxide is 6.0-10.0%.

3. The method for preparing cyclic carbonates for electrolytes according to claim 1, characterized in that, The mass ratio of the porous carbon nanomaterial to the epoxide is 9%.

4. The method for preparing cyclic carbonate for electrolyte according to claim 1, characterized in that, The epoxide is one or a mixture of ethylene oxide and propylene oxide.

5. The method for preparing cyclic carbonate for electrolyte according to claim 1, characterized in that, The molar ratio of cobalt nitrate to magnesium nitrate is 3:

1.

6. The method for preparing cyclic carbonate for electrolyte according to claim 1, characterized in that, In step S3), the calcination temperature is 500℃ and the time is 3h.

7. The method for preparing cyclic carbonate for electrolyte according to claim 1, characterized in that, Specifically, the steps are as follows: 1) Porous carbon nanomaterials as catalysts and epoxides are added to the reactor and stirred thoroughly; 2) Air in the reactor is purged with CO2, then the reactor is connected to a CO2 cylinder with constant output pressure, the reactor is heated and kept at a constant temperature to obtain cyclic carbonates; 3) After the reactor cools to room temperature, the unreacted CO2 is released, the catalyst and cyclic carbonate product are separated, and the catalyst is recovered for continued recycling.

8. The method for preparing cyclic carbonate for electrolyte according to claim 7, characterized in that, In step 2), the CO2 pressure is 0.4-1.2 MPa; the reaction temperature is 40-120℃; and the reaction time is 5-10 h.

9. The method for preparing cyclic carbonate for electrolyte according to claim 7, characterized in that, Step 2) CO2 pressure is 0.8 MPa; reaction temperature is 100℃; reaction time is 8 h.

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