An optimization method for improving yield of starch-derived hard carbon

Abstract

The application provides an optimization method for improving the yield of starch-derived carbon, which comprises the following steps: preparing a mixture of polyphosphoric acid and concentrated phosphoric acid, adding corn starch under oil bath condition, continuously heating and stirring to make the mixture fully react, placing the product in a tube furnace filled with inert gas for carbonization treatment, and washing and drying the final product to obtain "coral reef"-shaped bulk body starch-derived hard carbon. In the application, the starch is pretreated with the mixed solution of polyphosphoric acid and phosphoric acid before the carbonization process, so that the starch is dehydrated and crosslinked, and then the carbon yield is improved to 30% in the high-temperature pyrolysis process, and the hard carbon material with "coral reef"-shaped bulk body structure is obtained. The method can not only inhibit the foaming of the starch, but also help to reduce the specific surface area of the starch-derived hard carbon, and greatly enhance the yield of the starch-derived hard carbon. The method has the advantages of low cost, simple operation and large-scale production, and has great potential in the preparation of starch-derived carbon materials and the electrochemical application field.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hard carbon materials, and particularly relates to an optimization method for improving the yield of starch-derived carbon to obtain "coral reef"-like bulk starch-derived hard carbon. BACKGROUND

[0002] Biomass is considered one of the most promising sources for manufacturing functional carbon materials due to its sustainability, low cost, high carbon content, easy accessibility, and diverse molecular structure. Biomass carbon materials have become good negative electrode materials for sodium-ion batteries due to their excellent electrochemical performance, simple preparation method, and wide range of raw material sources. Among various biomass hard carbon precursors (starch, cellulose, sucrose, etc.), starch is an excellent hard carbon precursor due to its low price, abundant source, and absence of impurities, and it presents a granular structure.

[0003] However, starch expands and foams during high-temperature pyrolysis and carbonization, resulting in a decrease in the yield of starch-derived hard carbon. Although traditional preparation methods use prolonged dehydration time or pre-oxidation to inhibit foaming during carbonization, they have obvious disadvantages: long time consumption, high energy consumption, and low yield. Therefore, there is an urgent need to develop a simple and large-scale production preparation strategy to improve the yield of starch-derived hard carbon and inhibit its expansion and foaming under the premise of low energy consumption and high efficiency. SUMMARY

[0004] The present application provides a modification method for corn starch precursors to address the technical problems in the prior art. In the pretreatment, the starch is added to a mixed solution of polyphosphoric acid and concentrated phosphoric acid to gelatinize, dehydrate, and crosslink the starch, thereby achieving yield improvement during high-temperature pyrolysis and obtaining hard carbon materials with "coral reef"-like bulk structure. This method not only inhibits the foaming of starch but also helps to reduce the specific surface area and improve the electrical conductivity. This method is low in cost, simple in operation, and can be produced on a large scale, and has great potential in the preparation of starch-derived carbon materials and their electrochemical applications.

[0005] To achieve the above-mentioned purposes, the present application is implemented by the following technical solutions:

[0006] In one aspect, the present application provides an optimization method for improving the yield of starch-derived hard carbon, comprising the following steps:

[0007] Step 1: preparing a mixture of polyphosphoric acid and concentrated phosphoric acid;

[0008] Step 2: adding corn starch under heating conditions, continuously heating and stirring to complete the reaction, and obtaining black powder-like starch;

[0009] Step 3, the black powdery starch obtained in step 2 is first subjected to pre-carbonization treatment and then carbonization treatment to obtain a hard carbon material final product with a "coral reef" shaped bulk structure.

[0010] Further, the mixing ratio of the polyphosphoric acid and the concentrated phosphoric acid solution in step 1 is 1:3.

[0011] Further, the mass ratio of the corn starch and the polyphosphoric acid / concentrated phosphoric acid mixed solution is 1:2-5:2.

[0012] Further, step 1 specifically comprises: heating the concentrated phosphoric acid to 100-120 DEG C under oil bath condition, and then adding the polyphosphoric acid while stirring.

[0013] Further, after adding the corn starch in step 2, the temperature is continuously heated to 130-150 DEG C, and the puffed corn starch is continuously reacted for 2-4 h under the condition until it is completely reacted into black powdery starch.

[0014] Further, the pre-carbonization treatment specifically comprises: heating to 300-500 DEG C at a heating rate of 2-5 DEG C / min under inert gas protection and continuously for 2-4 h.

[0015] Further, the carbonization treatment specifically comprises: heating to 1000-1500 DEG C at a heating rate of 2-5 DEG C / min under inert gas protection and continuously for 2-4 h.

[0016] Further, in step 3, the products after the pre-carbonization treatment and the carbonization treatment are respectively subjected to washing, filtering and drying treatment, wherein the drying treatment specifically adopts a forced air drying machine, the temperature is 60-100 DEG C, and the time is 8-12 h.

[0017] The application further provides a starch-derived bulk structure hard carbon material prepared by the above method.

[0018] The application further provides an application of the starch-derived bulk structure hard carbon material as a sodium ion battery negative electrode material.

[0019] Compared with the prior art, the application has the beneficial effects that:

[0020] 1. The application first prepares a mixed solution of polyphosphoric acid and concentrated phosphoric acid, and uses the strong water absorption of the polyphosphoric acid to pretreat the starch. The starch is gelatinized, dehydrogenated and crosslinked, and a large amount of hydrogen and oxygen is removed in the pretreatment process, thereby reducing the loss of carbon atoms in the carbonization process, and further greatly improving the yield of the starch-derived hard carbon to 30%.

[0021] 2. Compared with existing traditional methods of extending dehydration time or pre-oxidation, the optimized method of starch precursor of the present invention has a simpler process preparation method, which is suitable for large-scale continuous industrial production. The high-yield hard carbon material with a coral reef-like bulk structure prepared has advantages such as higher initial coulombic efficiency and plateau capacity when used as a negative electrode material for sodium-ion batteries.

[0022] 3. The present invention uses inexpensive and readily available industrial products as raw materials in its preparation process, and has the advantages of simple synthesis process, strong controllability, low cost, wide availability of raw materials and mass production.

[0023] 4. The high-yield hard carbon material with a coral reef-like bulk structure prepared by the process of this invention has a small specific surface area, good conductivity, good cycle stability, high initial coulombic efficiency and plateau capacity, and can be widely used in new energy devices. Attached Figure Description

[0024] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0025] Figure 1 SEM image of the "coral reef" shaped bulk hard carbon prepared in Example 1;

[0026] Figure 2 SEM image of the starch-based hard carbon prepared for comparison.

[0027] Figure 3 Nitrogen adsorption-desorption curves of starch-based hard carbon prepared for comparison and "coral reef" shaped bulk hard carbon prepared in Example 1.

[0028] Figure 4 Pore ​​size distribution diagrams of starch-based hard carbon prepared as a comparative example and "coral reef"-shaped bulk hard carbon prepared in Example 1.

[0029] Figure 5 Sodium-ion half-cells assembled from bulk hard carbon prepared using starch-based hard carbon as a comparative example, at 0.05 A g. -1 Charge-discharge curves at current density;

[0030] Figure 6 The sodium-ion half-cell assembled from the "coral reef"-shaped bulk hard carbon prepared in Example 1 has a performance of 0.05 Ag. -1 Charge-discharge curves at current density;

[0031] Figure 7Electrochemical impedance spectrograms of sodium ion half-batteries assembled with the "coral reef"-like bulk hard carbon prepared in Example 1 and the starch-based hard carbon prepared in Comparative Example. DETAILED DESCRIPTION

[0032] Exemplary embodiments of the present application will be described in detail with reference to the drawings. Although exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0033] The present application proposes an optimization method for improving the yield of starch-derived carbon. Through this method, the yield of starch-derived hard carbon can be improved to 30%, and an ultra-high specific surface area mesoporous carbon preparation method can be provided. The method mainly involves pretreating corn starch with a mixed solution of polyphosphoric acid and concentrated phosphoric acid, then placing it in a tube furnace filled with inert gas for sufficient reaction. After the reaction is completed, the reaction product is washed with a large amount of deionized water, and then dried to obtain a high-yield coral reef-like bulk hard carbon material.

[0034] The following will be described in detail through several specific examples and comparative examples.

[0035] Example 1

[0036] An optimization method for improving the yield of starch-derived carbon is carried out according to the following steps:

[0037] Step 1: A mixed solution of polyphosphoric acid and 85% concentrated phosphoric acid is prepared in a volume ratio of 1:3, and is heated and stirred under oil bath conditions at a temperature of 120°C.

[0038] Step 2: Corn starch is quickly added to the beaker in step 1 to allow it to react fully with the mixed solution, and a total of 300g of corn starch is added.

[0039] Step 3: The oil bath temperature in step 2 is increased to 150°C, and after heating and stirring for 10 minutes, corn starch is continuously added until a total of 500g of starch is added, with a mass ratio of starch to polyphosphoric acid / concentrated phosphoric acid mixed solution of 5:2. The reaction is continued under this condition for 30 minutes, and the gelatinized starch in the beaker swells.

[0040] Step 4: The swollen starch in step 3 is continuously reacted under this condition for 2h until it is completely reacted and becomes black powder-like starch.

[0041] Step 5: The black powdery starch obtained in step 4 was transferred into a tube furnace filled with inert gas, and heated to 300°C at a heating rate of 5°C / min for pre-carbonization, with a holding time of 2h. The intermediate product was obtained, and after the intermediate product was cooled to room temperature with the furnace body, it was taken out and washed with a large amount of deionized water, filtered, dried, and then transferred into a tube furnace filled with inert gas, and heated to 1100°C at a heating rate of 2°C / min for carbonization, with a holding time of 2h. The product was obtained, and after the product was cooled to room temperature with the furnace body, it was taken out, to obtain high-yield "coral reef"-shaped bulk hard carbon.

[0042] The drying in step 5 was a blast drying machine, with a temperature of 100°C. The time was 12h.

[0043] The high-yield "coral reef"-shaped bulk hard carbon obtained in step 5 was subjected to basic structural characterization; then the obtained "coral reef"-shaped bulk hard carbon material was used as the negative electrode of a sodium-ion battery, with a sodium sheet as the counter electrode, to assemble a sodium-ion battery, and the performance of the battery was tested.

[0044] Example 2

[0045] Step 1: A mixed solution of polyphosphoric acid and 85% concentrated phosphoric acid was prepared in a volume ratio of 1:3, and heated and stirred under oil bath conditions, with a temperature of 115°C.

[0046] Step 2: Corn starch was quickly added to the beaker of step 1 to fully react with the mixed solution, a total of 100g of corn starch was added, with a mass ratio of starch to polyphosphoric acid / concentrated phosphoric acid mixed solution of 1:2.

[0047] Step 3: The oil bath temperature in step 2 was increased to 130°C, and the reaction was continued under this condition for 30min, and the gelatinized starch in the beaker swelled.

[0048] Step 4: The swollen starch in step 3 was continued to react for 4h under this condition, until it was completely reacted into black powdery starch.

[0049] Step 5: The black powdery starch obtained in step 4 was transferred into a tube furnace filled with inert gas, and heated to 300°C at a heating rate of 5°C / min for pre-carbonization, with a holding time of 2h. The intermediate product was obtained, and after the intermediate product was cooled to room temperature with the furnace body, it was taken out and washed with a large amount of deionized water, filtered, dried, and then transferred into a tube furnace filled with inert gas, and heated to 1100°C at a heating rate of 2°C / min for carbonization, with a holding time of 2h. The product was obtained, and after the product was cooled to room temperature with the furnace body, it was taken out, to obtain high-yield "coral reef"-shaped bulk hard carbon.

[0050] The drying in step 5 was a blast drying machine, with a temperature of 100°C. The time was 12h.

[0051] Example 3

[0052] Step 1: A mixed solution of polyphosphoric acid and 85% concentrated phosphoric acid was prepared with a volume ratio of 1:3, and heated and stirred under oil bath conditions at a temperature of 100°C.

[0053] Step 2: Corn starch was quickly added to the beaker of Step 1 to fully react with the mixed solution, a total of 150 g of corn starch was added, and the mass ratio of starch to polyphosphoric acid / concentrated phosphoric acid mixed solution was 3:2.

[0054] Step 3: The oil bath temperature in Step 2 was increased to 140°C, and the reaction was continued under this condition for 30 min, and the gelatinized starch in the beaker swelled.

[0055] Step 4: The swollen starch in Step 3 was continued to react under this condition for 3 h until it was completely reacted to become black powdery starch.

[0056] Step 5: The black powdery starch obtained in Step 4 was used as a precursor and transferred to a tube furnace filled with inert gas, heated to 500°C at a heating rate of 5°C / min for pre-carbonization, and the holding time was 4 h to obtain an intermediate product. After the intermediate product was cooled to room temperature with the furnace body, it was taken out and washed with a large amount of deionized water, filtered, dried, and then transferred to a tube furnace filled with inert gas, heated to 1000°C at a heating rate of 4°C / min for carbonization, and the holding time was 4 h to obtain a product. After the product was cooled to room temperature with the furnace body, it was taken out to obtain a high-yield "coral reef"-like large block of hard carbon.

[0057] The drying in Step 5 was a blast drying machine, the temperature was 60°C, and the time was 8 h.

[0058] Comparative Example

[0059] The corn starch was transferred to a tube furnace filled with inert gas, heated to 1100°C at a heating rate of 2°C / min, and the holding time was 2 h to obtain a product. After the product was cooled to room temperature with the furnace body, it was taken out to obtain pure starch-based hard carbon.

[0060] The high-yield "coral reef"-like large block of hard carbon prepared in Example 1 was compared with the pure starch-based hard carbon prepared in the comparative example. Figure 1 The SEM image of the high-yield "coral reef"-like large block of hard carbon prepared in Example 1 showed that the material as a whole presented an irregular "coral reef"-like large block structure. Figure 2 The SEM image of the starch-based hard carbon of the comparative example showed that the hard carbon was a large sheet structure.

[0061] Figure 3The nitrogen adsorption-desorption curves of the starch-based hard carbon prepared for the comparative example and the "coral reef"-like bulk hard carbon prepared in Example 1 show that the specific surface area of the high-yield "coral reef"-like bulk hard carbon is significantly reduced. Figure 4 The pore size distribution diagram of the starch-based hard carbon prepared for the comparative example and the "coral reef"-like bulk hard carbon prepared in Example 1 shows that the "coral reef"-like bulk hard carbon has fewer macroporous structures, which is beneficial to the reduction of defects and the reduction of specific surface area.

[0062] Figure 5 The charge-discharge curves of the sodium ion half-batteries assembled by the pure starch hard carbon prepared for the comparative example at a current density of 0.05 Ag -1 The charge-discharge curves of the sodium ion half-batteries assembled by the pure starch hard carbon prepared for the comparative example at a current density of 0.05 Ag Figure 6 The charge-discharge curves of the sodium ion half-batteries assembled by the "coral reef"-like bulk hard carbon of Example 1 at a current density of 0.05 Ag -1 The charge-discharge curves of the sodium ion half-batteries assembled by the "coral reef"-like bulk hard carbon of Example 1 at a current density of 0.05 Ag

[0063] Figure 7 The electrochemical impedance spectrograms of the sodium ion half-batteries assembled by the pure starch hard carbon prepared for the comparative example and the high-yield "coral reef"-like bulk hard carbon prepared in Example 1 show that the electrochemical impedance of the high-yield "coral reef"-like bulk hard carbon is lower, indicating that it has better conductivity.

[0064] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. An optimization method for improving the yield of starch-derived hard carbon, characterized by, The method comprises the following steps: Step 1, preparing a mixture of polyphosphoric acid and concentrated phosphoric acid, wherein the volume ratio of polyphosphoric acid to concentrated phosphoric acid is 1:3; Step 2, adding corn starch under heating conditions, wherein the mass ratio of corn starch to polyphosphoric acid / concentrated phosphoric acid mixed solution is 1:2-5:2, and the mixture is continuously heated and stirred to completely react, thereby obtaining black powder-like starch; Step 3, the black powder-like starch obtained in step 2 is used as a precursor to be pre-carbonized and then carbonized, thereby obtaining a hard carbon material final product with a "coral reef"-like bulk structure.

2. The optimized method of increasing the yield of hard carbon derived from starch according to claim 1, characterized in that, In step 1, the concentrated phosphoric acid is heated to 100-120°C under oil bath conditions, and then polyphosphoric acid is added while stirring.

3. The optimized method of increasing the yield of hard carbon derived from starch according to claim 1, characterized in that, In step 2, after the corn starch is added, the temperature is continuously heated to 130-150°C, and the puffed corn starch continues to react under the conditions for 2-4h until it completely reacts into black powder-like starch.

4. The optimized method of increasing the yield of hard carbon derived from starch according to claim 1, characterized in that, The pre-carbonization treatment is specifically as follows: under the protection of inert gas, heating to 300-500°C at a heating rate of 2-5°C / min and maintaining for 2-4h.

5. The optimized method of increasing the yield of hard carbon derived from starch according to claim 1, wherein, The carbonization treatment is specifically as follows: under the protection of inert gas, heating to 1000-1500°C at a heating rate of 2-5°C / min and maintaining for 2-4h.

6. The optimized method of increasing the yield of hard carbon derived from starch according to claim 1, wherein, In step 3, the products after pre-carbonization treatment and carbonization treatment are respectively washed, filtered and dried, wherein the drying treatment is specifically performed by using a blast drying machine at a temperature of 60-100°C for 8-12h.

7. A starch-derived bulk bulk structure hard carbon material, characterized in that, The method is prepared by any one of claims 1-6.

8. Use of a starch-derived bulk massive structured hard carbon material according to claim 7, characterized in that, As a negative electrode material for sodium ion batteries.

Images