Preparation method and application of metal atom modified folate derivative hard carbon material

Abstract

The application is a preparation method and application of a metal atom modified folate derived hard carbon material. The method uses folate and soluble metal salt as raw materials to prepare a metal atom modified hard carbon material through a hydrothermal-carbonization method; that is, by adjusting the temperature and solvent ratio of the hydrothermal reaction, using the chelation of the carboxyl functional group of folate and metal ions, controlling the content of metal atoms and the microstructure of the product, and based on the catalytic effect of metal atoms, reducing the carbonization temperature, reducing surface defects, improving the interface reaction kinetics, and thus improving the rate performance of the hard carbon. The method is simple, the raw materials are simple, it is environmentally friendly, the process has good repeatability, the product quality is stable, and the rate performance of the hard carbon is: 140 mAh g ‑1 of specific capacity is realized at a current density of 1 A g ‑1 .

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, specifically to a metal single-atom modified folic acid-derived hard carbon material with high rate performance, its preparation method, and its application in sodium-ion batteries. Background Technology

[0002] With the continuous growth of global energy demand and the urgent need for sustainable energy solutions, the research and development of novel electrochemical energy storage devices has become an inevitable trend. Among these, sodium-ion batteries have become a research hotspot due to their abundant resources, low cost, and environmental friendliness, but they still face challenges such as low energy density and poor rate performance. Developing advanced electrode materials is crucial to overcoming the performance bottlenecks of sodium-ion batteries.

[0003] Hard carbon, as a carbon-based anode material, has attracted much attention due to its excellent overall electrochemical performance, wide availability of raw materials, and simple preparation method, showing great promise for application. Hard carbon possesses a unique microstructure, consisting of short-range ordered carbon layers stacked alternately, forming abundant defects and pores, as well as a large interlayer spacing, resulting in a high mAh g⁻¹. -1 The theoretical sodium storage capacity of hard carbon is [not specified]. However, the disordered microstructure and slow interfacial reaction kinetics of hard carbon result in poor rate performance, and the commercial preparation process of hard carbon usually involves high-temperature carbonization (1400~1600℃), which consumes a lot of energy, further hindering the widespread application of hard carbon.

[0004] In the prior art, patent CN117658101A discloses a molybdenum-doped hard carbon anode material for sodium-ion batteries and its preparation method. The hard carbon anode material includes a hard carbon matrix, a molybdenum metal source, and ammonium persulfate. The molybdenum-based dopant phase is combined with the hard carbon precursor via a hydrothermal method. During subsequent high-temperature carbonization, the molybdenum group modulates the microstructure of the hard carbon, increasing the number of active sites and thus improving the reversible capacity of the hard carbon. However, this method of introducing a metal dopant phase into hard carbon has limitations. For example, molybdenum doping requires the additional introduction of a heteroatom precursor (ammonium persulfate), and carbonization requires a relatively high temperature (1200~1500℃). Patent CN117446781A discloses a method for preparing a phosphorus-metal alloy co-doped hard carbon composite material. The method involves ball milling and mixing red phosphorus, a crosslinking agent, and a solid resin, followed by heating and curing at 300-500°C to obtain an intermediate. The intermediate, metal alloy powder, and sodium carboxymethyl cellulose are then mixed uniformly in a certain proportion and carbonized at a high temperature (1200-1500°C). Thanks to the high specific capacity of the metal compound and the pore-forming effect of phosphorus, the specific capacity of the hard carbon is improved. However, this doped material has complex raw materials, a cumbersome preparation process, and high energy consumption.

[0005] Therefore, there is an urgent need to develop new methods for preparing hard carbon materials modified with metal atoms, which can meet the requirements of simple raw materials, high controllability and low carbonization temperature, and further improve the rate performance of hard carbon. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of current technologies by providing a method for preparing and applying folic acid-derived hard carbon materials modified with metal atoms. This method uses only folic acid (containing a nitrogen-containing carbon source) and soluble metal salts as raw materials, and prepares metal-atom-modified hard carbon materials via a hydrothermal-carbonization method. Specifically, by controlling the temperature and solvent ratio of the hydrothermal reaction, the chelation effect between the carboxyl functional groups of folic acid and metal ions is utilized to control the content of metal atoms and the microstructure of the product. Furthermore, based on the catalytic effect of metal atoms, the carbonization temperature is lowered, surface defects are reduced, and interfacial reaction kinetics are improved, thereby enhancing the rate performance of the hard carbon. This invention offers advantages such as simplicity, simple raw materials, environmental friendliness, good process repeatability, and stable product quality. The rate performance of the hard carbon is as follows: 1 A g -1 Achieving 140 mAh g at a current density -1 Specific capacity.

[0007] The technical solution of this invention is as follows:

[0008] A method for preparing a folic acid-derived hard carbon material modified with metal atoms includes the following steps:

[0009] Step 1: Preparation of precursor solution:

[0010] Folic acid and water-soluble metal salts were added to a mixed solvent, then stirred and sonicated to obtain a suspension.

[0011] In the water-soluble metal salt, the metal is iron, cobalt, nickel, copper or zinc, and the salt is a nitrate or chloride; the molar ratio of folic acid powder and water-soluble metal salt is 10:1 to 1:10, preferably 2:1 to 1:1;

[0012] The mixed solvent is ethanol and deionized water, with a volume ratio of ethanol to water of 1~1.5:1~2, preferably ethanol to water ratio of 1:1.

[0013] Add 0.5–2.5 mmol of folic acid to every 60 mL of the mixed solution;

[0014] Step 2, Hydrothermal Treatment:

[0015] The suspension was transferred to a reaction vessel and placed in a forced-air drying oven for hydrothermal treatment at 120-220℃ for 1-4 hours.

[0016] Step 3: Cleaning and Drying

[0017] After the hydrothermal reaction is complete, the precipitate is immersed in deionized water, centrifuged, and then washed. Repeat the "immersion-centrifugation-washing" cycle 2 to 4 times, and then freeze-dry overnight to obtain the intermediate.

[0018] Step 4: High-temperature carbonization:

[0019] The intermediate obtained in step three was placed in a quartz tube furnace under argon protection and carbonized at 800-1100℃ for 1-3 hours. After cooling to room temperature with the furnace, the folic acid-derived hard carbon material FA-M (M represents the type of metal atom) modified with metal atoms was obtained.

[0020] In step two, the preferred hydrothermal temperature is 120℃~180℃.

[0021] In step four, the carbonization temperature is preferably 700~1000℃.

[0022] The metal atom-modified folic acid-derived hard carbon material obtained by the method is used as an active material for the negative electrode in sodium-ion batteries.

[0023] In the sodium-ion battery described above: the positive electrode material is sodium metal, the separator is glass fiber, the electrolyte solute is 1 M sodium hexafluorophosphate (NaPF6), and the electrolyte solvent is dimethyl ethylene glycol (DME).

[0024] The metal single-atom modified hard carbon obtained by the method can be used to make sodium-ion batteries with higher coulombic efficiency and better rate performance.

[0025] The mechanism of this invention is as follows:

[0026] This invention regulates the solubility of folic acid by altering the hydrothermal temperature and improves the rate performance of hard carbon anode materials by adjusting the microstructure of the metal, thereby increasing the graphitization degree, conductivity, and surface active sites. The specific process is as follows:

[0027] The -COOH group in folic acid molecules undergoes hydrolysis in the mixed solution, producing -COO - Negatively charged, it can chelate with positively charged metal ions through electrostatic interactions, promoting further dissolution of folic acid molecules. The dissolved folic acid molecules then form precursors with specific morphologies through self-assembly reactions. By controlling the self-assembly mechanism of folic acid by altering the solvent polarity, hard carbon with a three-dimensional porous structure can be obtained, which is beneficial for improving the wetting of the material with the electrolyte and enhancing the rate performance of the hard carbon. Furthermore, the growth of graphite microregions during metal atom-catalyzed carbonization can lower the carbonization temperature of the material and reduce energy consumption during the preparation process.

[0028] The present invention has the following beneficial effects:

[0029] 1. This invention proposes a method for preparing metal single-atom modified hard carbon, which has the advantages of simple preparation method, simple raw materials, environmental friendliness, good process repeatability, and stable product quality.

[0030] 2. By selecting folic acid containing nitrogen as the carbon source, without the need to introduce additional heteroatom precursors, metal atom-modified hard carbon materials were successfully obtained after hydrothermal carbonization. By changing the ratio of ethanol and water in the solvent, the self-assembly mode of folic acid was controlled, resulting in hard carbon with a three-dimensional network structure. This increased the contact between hard carbon and electrolyte and improved the rate performance of hard carbon.

[0031] 3. Based on the chelation between the carboxyl functional group in folic acid and metal ions, metal atoms exist stably in folic acid. During the subsequent carbonization process, metal atoms catalyze the graphitization process and reduce the carbonization temperature. Thanks to the electronic structure and geometric effects of the coordination configuration of metal atoms and nitrogen, the conductivity of hard carbon is improved, the number of active sites is increased, and the rate performance of hard carbon is improved. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope image of the folic acid-derived hard carbon material FA-Mn modified with metal atoms prepared in Example 3;

[0033] Figure 2 This is an XRD image of the folic acid-derived hard carbon material FA-Mn modified with metal atoms prepared in Example 3;

[0034] Figure 3 This is a Raman image of the folic acid-derived hard carbon material FA-Mn modified with metal atoms prepared in Example 3;

[0035] Figure 4 These are CV images of the folic acid-derived hard carbon material FA-Mn modified with metal atoms obtained in Example 3;

[0036] Figure 5 These are rate performance images of the folic acid-derived hard carbon material FA-Mn modified with metal atoms in Example 3 at different current densities.

[0037] Figure 6 This is a rate performance image of the folic acid-derived hard carbon material FA without metal atom modification in Comparative Example 1 at different current densities. Detailed Implementation

[0038] The present invention will be further described below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in manuals, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified. All raw materials required for the following embodiments are commercially available.

[0039] Example 1

[0040] Step 1: Preparation of precursor solution:

[0041] Disperse 1.25 mmol folic acid and 1.25 mmol zinc nitrate in a 100 ml beaker, add 30 ml ethanol and 30 ml deionized water, stir for 10 min and sonicate to make the suspension evenly dispersed.

[0042] Step 2, Hydrothermal Treatment:

[0043] The uniformly dispersed solution was transferred to a reaction vessel and placed in a forced-air drying oven for hydrothermal carbonization at 140°C for 3 hours.

[0044] Step 3: Cleaning and Drying

[0045] After the hydrothermal reaction is complete, the precipitate is immersed in deionized water, then centrifuged and washed. The "immersion-centrifugation-washing" cycle is repeated three times, followed by freeze-drying overnight to obtain the precursor.

[0046] Step 4: High-temperature carbonization:

[0047] The precursor obtained in step two was placed in an argon-protected quartz tube furnace and heated to 800°C at a heating rate of 5°C / min. The temperature was held for 2 hours and then cooled to room temperature with the furnace to obtain zinc atom modified hard carbon.

[0048] Example 2

[0049] Step 1: Preparation of precursor solution:

[0050] Disperse 1.25 mmol folic acid and 2.5 mmol cobalt nitrate in a 100 ml beaker, add 40 ml ethanol and 20 ml deionized water, stir for 10 min and sonicate to make the suspension evenly dispersed.

[0051] Step 2, Hydrothermal Treatment:

[0052] The uniformly dispersed solution was transferred to a reaction vessel and placed in a forced-air drying oven for hydrothermal carbonization at 140°C for 3 hours.

[0053] Step 3: Cleaning and Drying

[0054] After the hydrothermal reaction is complete, the precipitate is immersed in deionized water and then centrifuged and washed. The centrifugation and washing process is repeated three times, followed by freeze-drying overnight to obtain the precursor.

[0055] Step 4: High-temperature carbonization:

[0056] The precursor obtained in step two is placed in an argon-protected quartz tube furnace and heated to 800°C at a heating rate of 5°C / min, and held for 2 h to obtain cobalt-modified hard carbon.

[0057] Example 3

[0058] Step 1: Preparation of precursor solution:

[0059] Disperse 1.25 mmol folic acid and 1.25 mmol manganese chloride in a 100 ml beaker, add 30 ml ethanol and 30 ml deionized water, stir for 10 min and sonicate to make the suspension evenly dispersed.

[0060] Step 2, Hydrothermal Treatment:

[0061] The uniformly dispersed solution was transferred to a reaction vessel and placed in a forced-air drying oven for hydrothermal carbonization at 140°C for 3 hours.

[0062] Step 3: Cleaning and Drying

[0063] After the hydrothermal reaction is complete, the precipitate is immersed in deionized water and then centrifuged and washed. The centrifugation and washing process is repeated three times, followed by freeze-drying overnight to obtain the precursor.

[0064] Step 4: High-temperature carbonization:

[0065] The precursor obtained in step two is placed in an argon-protected quartz tube furnace and heated to 1000℃ at a heating rate of 5℃ / min, and held for 2 h to obtain manganese atom modified hard carbon.

[0066] Figure 1 Scanning electron microscope image of FA-Mn, a folic acid-derived hard carbon material modified with metal atoms, showing a three-dimensional network structure.

[0067] Figure 2 XRD of FA-Mn, a folic acid-derived hard carbon material modified with metal atoms, is shown. The material is amorphous hard carbon.

[0068] Figure 3 Raman image of FA-Mn, a folic acid-derived hard carbon material modified with metal atoms, showing an intensity ratio of I for the D peak to the G peak. D / I G =0.95, indicating a high degree of graphitization;

[0069] Figure 4 The CV image of FA-Mn, a folic acid-derived hard carbon material modified with metal atoms, shows that the oxidation and reduction peaks have similar shapes, indicating that the sodium storage reaction is reversible and that the redox peaks are close to each other, suggesting a fast reaction kinetic.

[0070] Figure 5 Rate performance images of FA-Mn, a folic acid-derived hard carbon material modified with metal atoms, at different current densities.

[0071] Example 4

[0072] Step 1: Preparation of precursor solution:

[0073] Disperse 1.25 mmol folic acid and 1.25 mmol manganese nitrate in a 100 ml beaker, add 30 ml ethanol and 30 ml deionized water, stir for 10 min and sonicate to make the suspension evenly dispersed.

[0074] Step 2, Hydrothermal Treatment:

[0075] The uniformly dispersed solution was transferred to a reaction vessel and placed in a forced-air drying oven for hydrothermal carbonization at 120°C for 2 hours.

[0076] Step 3: Cleaning and Drying

[0077] After the hydrothermal reaction is complete, the precipitate is immersed in deionized water and then centrifuged and washed. The centrifugation and washing process is repeated three times, followed by freeze-drying overnight to obtain the precursor.

[0078] Step 4: High-temperature carbonization:

[0079] The precursor obtained in step two is placed in an argon-protected quartz tube furnace and heated to 1100℃ at a heating rate of 5℃ / min, and held for 2 h to obtain manganese atom modified hard carbon.

[0080] Comparative Example 1

[0081] Step 1: Preparation of precursor solution:

[0082] Disperse 1.25 mmol of folic acid in a 100 ml beaker, add 30 ml of ethanol and 30 ml of deionized water, stir for 10 min and sonicate to make the suspension evenly dispersed.

[0083] Step 2, Hydrothermal Treatment:

[0084] The uniformly dispersed solution was transferred to a reaction vessel and placed in a forced-air drying oven for hydrothermal carbonization at 140°C for 3 hours.

[0085] Step 3: Cleaning and Drying

[0086] After the hydrothermal reaction is complete, the precipitate is immersed in deionized water and then centrifuged and washed. The centrifugation and washing process is repeated three times, followed by freeze-drying overnight to obtain the precursor.

[0087] Step 4: High-temperature carbonization:

[0088] The precursor obtained in step two is placed in an argon-protected quartz tube furnace and heated to 1000°C at a heating rate of 5°C / min, and held for 2 hours to obtain hard carbon.

[0089] Assemble the battery:

[0090] Take 70 mg of hard carbon (the products prepared in each example and comparative example respectively), add 20 mg of super P, 10 mg of PVDF, and then add 800 μL of NMP. Stir for 10 min to obtain a slurry, coat it on the surface of copper foil, and dry it at 100 °C for 12 h to obtain the negative electrode.

[0091] The electrolyte solvent is ethylene glycol dimethyl ether, and the solute is 1 M sodium hexafluorophosphate;

[0092] The positive electrode is a sodium tablet;

[0093] A button cell is assembled using the above-mentioned negative electrode, electrolyte, and sodium sheet.

[0094] test:

[0095] Rate performance testing: Discharge to 0.01 V at 0.5 C, then charge to 2 V at 0.5 C, cycle five times; discharge to 0.01 V at 1 C, then charge to 2 V at 1 C, cycle five times; discharge to 0.01 V at 2 C, then charge to 2 V at 2 C, cycle five times; discharge to 0.01 V at 5 C, then charge to 2 V at 5 C, cycle five times; discharge to 0.01 V at 10 C, then charge to 2 V at 10 C, cycle five times (1 C = 100 mA g). -1 The charging specific capacity under different current densities is taken as its rate performance.

[0096] The measured results are shown in the table below (current density is 1 A g). -1 ):

[0097]

[0098] The comparative example is folic acid-derived hard carbon material without metal atom modification, at 1 A g -1 At current densities, the specific capacity is only 100 mAh g. -1Compared to folic acid-derived hard carbon materials modified with metal atoms, its rate performance is inferior. This indicates that metal atoms optimize the microstructure of hard carbon materials and improve their rate performance.

[0099] Figure 1 The SEM image of the hard carbon in Case 3 clearly shows that the prepared hard carbon has a three-dimensional porous network structure.

[0100] Figure 5 The rate performance diagram of the manganese-modified folic acid-derived hard carbon prepared in Case 3 shows that the hard carbon maintains a high specific capacity even at high current densities, even at 1 A g. -1 At a current density of [value missing], the reversible capacity can still reach 140 mAh g. -1 This indicates its outstanding rate capability.

[0101] 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.

[0102] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing a metal atom-modified folate-derived hard carbon material, characterized by, The method comprises the following steps: Step one, preparation of precursor solution: Folic acid and water-soluble metal salt are added to the mixed solvent, followed by stirring and ultrasonic treatment to obtain a suspension; Among the water-soluble metal salt, the metal is iron, cobalt, nickel, copper or zinc, and the salt is nitrate or chloride; the molar ratio of folic acid to water-soluble metal salt is 2:1 to 1:1; The mixed solvent is ethanol and deionized water, and the volume ratio of ethanol to water is 1:1; 0.5-2.5 mmol of folic acid is added per 60 mL of mixed solution; Step two, hydrothermal treatment: The suspension is transferred to a reaction kettle and subjected to hydrothermal treatment at 120-220°C for 1-4 hours; Step three, cleaning and drying After the hydrothermal reaction, the precipitate is immersed in deionized water, centrifuged, and then washed; the "immersion-centrifugation-washing" cycle is repeated 2-4 times, followed by freeze-drying overnight to obtain the intermediate; Step four, high-temperature carbonization: The intermediate obtained in step three is carbonized at 800-1100°C for 1-3 hours under argon, and then cooled to room temperature, to obtain a metal atom-modified folic acid derivative hard carbon material.

2. Use of the metal atom-modified hard carbon material derived from folic acid according to claim 1, characterized in that, Active material for use as a negative electrode in a sodium ion battery.

3. Use according to claim 2, characterized in that In the sodium ion battery: the positive electrode material is sodium metal, the separator is glass fiber, the electrolyte solute is 1 M sodium hexafluorophosphate NaPF6, and the electrolyte solvent is ethylene glycol dimethyl ether DME.

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