Transition metal single atom modified hard carbon material, and preparation method and application thereof

Abstract

The application discloses a kind of transition metal single atom modified hard carbon material and its preparation method and application, belong to electrochemical energy storage material technical field.Preparation method includes the following steps: (1) in glucose solution, add transition metal ions to prepare mixed solution;(2) in mixed solution, add yeast to culture;(3) the culture obtained in step (2) is heated to boiling to deactivate yeast, obtain hard carbon precursor;(4) hard carbon precursor is washed, dried;(5) the hard carbon precursor after drying is calcined under inert gas atmosphere, i.e. transition metal single atom modified hard carbon material.The preparation strategy of hard carbon material proposed in the application has universality and high efficiency, which provides a new technical path for developing high-performance, long-life sodium-ion battery negative materials.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials technology, specifically relating to a hard carbon material modified with a single atom of a transition metal, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries (SIBs) have shown broad application prospects in transportation energy and large-scale energy storage due to the abundance of sodium resources (approximately 1350 times that of lithium in the Earth's crust) and low cost. Among the many SIB anode materials, hard carbon is considered one of the most commercially promising anode materials due to its wide availability of raw materials, high sodium storage capacity, and structural stability. Its unique "long-range disorder, short-range order" graphite microcrystalline structure and large interlayer spacing (>0.36 nm) provide a significant advantage for Na+ ions. + It provides an ideal insertion / extraction channel. However, hard carbon anodes still face the challenge of insufficient electrode / electrolyte interface (SEI) film stability during commercialization. Because the Fermi level of hard carbon is higher than the lowest unoccupied molecular orbital (LUMO) level of the electrolyte, electrons readily migrate from the electrode to the electrolyte, triggering electrolyte decomposition and forming the SEI film. Although the SEI film can passivate the electrode surface to some extent, it also increases the Na+ content. + The migration impedance. More importantly, in Na + During repeated insertion / extraction, the SEI film continuously breaks down and reconstructs due to volume changes, constantly consuming active sodium and electrolyte, leading to low initial coulombic efficiency (ICE) and rapid capacity decay during long cycles. Transition metal single-atom materials, due to their high atom utilization and excellent catalytic performance, have been widely used in recent years to regulate the composition and structure of SEI films. Introducing metal single-atom sites into hard carbon materials helps to construct more stable interfacial films. However, existing methods often rely on external nitrogen or phosphorus sources to construct the metal coordination environment, which is prone to metal atom aggregation due to uneven nitrogen and phosphorus distribution, reducing the number of active sites and triggering side reactions. Therefore, developing novel precursors that can achieve highly dispersed metal atoms and controllable coordination structures is of great significance for constructing stable SEI films and realizing long-life sodium-ion batteries. Summary of the Invention

[0003] In view of the above-mentioned prior art, the present invention provides a hard carbon material modified with a transition metal single atom, its preparation method and application, which solves the problem that the introduction of metal single atom sites into hard carbon materials in the prior art relies on external nitrogen or phosphorus sources to construct the metal coordination environment, and is prone to metal atom agglomeration due to uneven distribution of nitrogen and phosphorus, which reduces the number of active sites and triggers side reactions.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a method for preparing a hard carbon material modified with a single atom of a transition metal, comprising the following steps: (1) Add transition metal ions to glucose solution to prepare a mixed solution, wherein the concentration of transition metal ions in the mixed solution is less than 0.01 mM; (2) Add yeast to the mixed solution for culturing; (3) Heat the culture obtained in step (2) to boiling to inactivate the yeast and obtain hard carbon precursor; (4) Wash and dry the hard carbon precursor; (5) The dried hard carbon precursor is calcined in an inert gas atmosphere. The calcination conditions are to raise the temperature to 1200~1500 ℃ and hold for 2~3 h, and then cool to room temperature to obtain hard carbon material modified with transition metal single atom.

[0005] The beneficial effects of the above technical solution adopted in this invention are: (1) Preparation of transition metal modified hard carbon materials by biological template method: During the cultivation process, the transition metal ions in the culture solution are adsorbed by the functional groups such as -OH and -COOH on the surface of yeast. After high-temperature calcination, the metal ions are converted into metal atoms and modified into hard carbon structure to improve the cycle stability of sodium ion battery. If transition metal ions are added after yeast culture, the negative charge groups on the surface of yeast have reached the equilibrium state, and the metal ions cannot be adsorbed. The transition metal ions are difficult to remain in the yeast and cannot participate in the subsequent preparation of hard carbon materials. (2) Preparation of transition metal single-atom modified hard carbon materials: By controlling the concentration of transition metal ions in the solution and combining the nitrogen and phosphorus coordination environment provided by the yeast itself, the metal can be realized in the form of single atoms (such as MN) under appropriate concentration conditions. x -C or MP x -C) exists stably in the carbon framework, avoiding the formation of metal clusters. This type of metal single atom can effectively regulate the composition and evolution behavior of the SEI film. (3) Excellent long-term cycling stability: The hard carbon material anode modified with transition metal single atoms obtained by the preparation retains 95% of its capacity after 1500 cycles at a current density of 1 C; after 10000 cycles at a high rate of 5 C, it still retains 80% of its initial capacity, corresponding to a capacity decay rate of only about 0.002% per cycle.

[0006] Based on the above technical solution, the present invention can be further improved as follows.

[0007] Furthermore, the concentration of the glucose solution is 0.04~0.06 g / mL.

[0008] Furthermore, the transition metal ions are iron, cobalt, nickel, copper, manganese, or zinc ions.

[0009] Furthermore, the ratio of yeast to glucose solution is 4-5 g : 100 mL, and the culture time after adding yeast is 24 h; to inactivate yeast, the culture is heated to boiling and kept for 1 h.

[0010] Furthermore, the hard carbon precursor was washed three times each with deionized water and anhydrous ethanol; then freeze-dried for 8 hours.

[0011] Furthermore, the inert gas is argon, with a flow rate of 50 mL / min.

[0012] Furthermore, the calcination conditions are as follows: the temperature is increased to 1400 ℃ at a rate of 3 ℃ / min and held for 2 h, then the temperature is decreased to 500 ℃ at a rate of 4 ℃ / min, and finally cooled to room temperature.

[0013] Furthermore, the hard carbon material prepared by the above-mentioned method for preparing hard carbon materials modified with single atoms of transition metals is also described.

[0014] Furthermore, the above-mentioned hard carbon materials are used in the preparation of sodium-ion batteries.

[0015] Furthermore, hard carbon materials are used as anode materials in sodium-ion batteries.

[0016] The beneficial effects of the present invention are as follows: The present invention specifically relates to a hard carbon material modified with transition metal single atoms constructed by microbial template method, its preparation method and its application in sodium-ion battery negative electrode. (1) This preparation method uses yeast as biological matrix, and utilizes the characteristics of its surface negatively charged functional groups (-COOH, -OH, etc.) to adsorb transition metal ions in solution; combined with the nitrogen and phosphorus elements rich in yeast itself, it can provide a coordination environment; during the cultivation process, metal ions are efficiently adsorbed and atomically dispersed, and then after a step of high-temperature carbonization, an in-situ hard carbon material with MN is formed. x -C or MP x (2) The biotemplate in this invention is suitable for a variety of transition metal ions. The concentration of transition metal ions can be controlled during the cultivation stage. It is also easy to prepare biomass hard carbon materials with different concentrations of single-atom loading modification, including Fe, Co, Ni, Cu, Mn, Zn and other elements. (3) The transition metal single atom introduced in this invention has catalytic properties and can regulate the SEI membrane composition during the cycle. (4) When this transition metal single-atom modified hard carbon material is used as the anode of sodium-ion battery, it exhibits high initial coulombic efficiency (86.7%) and excellent long-term cycling stability at 1 C (1 C = 300 mA g). -1After 1500 cycles at a low C rate, the capacity retention rate is 95%, with almost no significant capacity decay; after 10000 cycles at a high C rate, the capacity decay per cycle is only 0.002%. The preparation method provided by this invention is simple to operate and the experimental results are reliable. By utilizing the characteristics of biological materials, a hard carbon material modified with a single atom of transition metal with excellent performance is prepared. This invention has universality and high efficiency, providing a new technical path for the development of high-performance, long-life sodium-ion battery anode materials, and promoting the research and development progress of high-performance sodium-ion battery anode materials. Attached Figure Description

[0017] Figure 1 Transmission electron microscopy (TEM) image of the hard carbon material obtained in Example 1 (a) and Cu element loading of the hard carbon materials prepared in Examples 1 and Comparative Examples 1-3 (b). Figure 2 X-ray diffraction (XRD) patterns of the hard carbon materials prepared in Example 1 and Comparative Examples 1-3. Figure 3 High-resolution transmission electron microscopy (STEM) is used to visualize the hard carbon material prepared in Example 1. Figure 4 High-resolution TEM images of the interface regions of the hard carbon materials prepared in Comparative Example 1(a) and Example 1(b). Detailed Implementation

[0018] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0019] Example 1 A hard carbon material modified with low concentration of Cu metal element, the preparation method of which includes the following steps: (1) Dissolve 5 g of glucose in 100 mL of deionized water and stir magnetically for 10 min until completely dissolved; (2) Add 10 μL of 0.1 M Cu(NO3)2 solution to the above solution, so that the Cu concentration in the solution is... 2+ The concentration was 0.01 mM; (3) Add 4 g of active yeast to the solution obtained in step (2) and incubate for 24 h; (4) Heat the culture obtained in step (3) to boiling for 1 h to inactivate the yeast; (5) After the reaction system obtained in step (4) is naturally cooled to room temperature, centrifuge (3500 rpm, 3 min) to collect the precipitate, which is the hard carbon precursor; then wash the hard carbon precursor three times each with deionized water and anhydrous ethanol. (6) Transfer the washed hard carbon precursor to a freeze dryer and dry for 8 h; (7) The dried hard carbon precursor was transferred to a graphite ceramic boat and then to the reaction zone of a tube furnace. Under an argon atmosphere (flow rate of 50 mL / min), the temperature was increased to 1400 °C at a rate of 3 °C / min and held for 2 h. Then the temperature was decreased to 500 °C at a rate of 4 °C / min and finally cooled to room temperature with the furnace to obtain a hard carbon material modified with low concentration of Cu metal elements with disordered graphite microcrystalline structure.

[0020] Example 2 A hard carbon material modified with a lower concentration of Cu metal element is prepared in a method different from that in Example 1, step (2) involves adding 10 μL of a 0.01 M Cu(NO3)2 solution to the solution, so that the Cu concentration in the solution is lower than that in Example 1. 2+ The concentration was 0.001 mM; the remaining steps were the same as in Example 1, to obtain a hard carbon material modified with a lower concentration of Cu metal element with a disordered graphite microcrystalline structure.

[0021] Example 3 A low-concentration Fe metal element modified hard carbon material is prepared in a method different from that in Example 1, in step (2), 10 μL of a 0.1 M Fe(NO3)3 solution is added to the solution, so that the Fe concentration in the solution is reduced. 3+ The concentration was 0.01 mM, and the remaining steps were the same as in Example 1, to obtain a hard carbon material modified with low concentration of Fe metal element with disordered graphite microcrystalline structure.

[0022] Example 4 A low-concentration Ni-modified hard carbon material is prepared in a method different from that in Example 1, step (2) involves adding 10 μL of a 0.1 M Ni(NO3)2 solution to the solution, thereby increasing the Ni concentration in the solution. 2+ The concentration was 0.01 mM, and the remaining steps were the same as in Example 1, to obtain a low-concentration Ni metal element modified hard carbon material with a disordered graphite microcrystalline structure.

[0023] Example 5 A low-concentration Co-modified hard carbon material is prepared in a method different from that in Example 1, step (2) involves adding 10 μL of a 0.1 M Co(NO3)2 solution to the solution, thereby increasing the Co concentration in the solution. 2+ The concentration was 0.01 mM, and the remaining steps were the same as in Example 1, to obtain a low-concentration Co metal element modified hard carbon material with a disordered graphite microcrystalline structure.

[0024] Example 6 A low-concentration Mn metal element modified hard carbon material is prepared in a method different from that in Example 1, in step (2), 10 μL of a 0.1 M Mn(NO3)2 solution is added to the solution, so that the Mn concentration in the solution is reduced. 2+ The concentration was 0.01 mM, and the remaining steps were the same as in Example 1, to obtain a hard carbon material modified with low concentration of Mn metal element with disordered graphite microcrystalline structure.

[0025] Example 7 A hard carbon material modified with low concentration of Zn metal element is prepared in a method different from that in Example 1, in step (2), 10 μL of a 0.1 M Zn(NO3)2 solution is added to the solution, so that the concentration of Zn in the solution is reduced. + The concentration was 0.01 mM, and the remaining steps were the same as in Example 1, to obtain a hard carbon material modified with low concentration of Zn metal element with disordered graphite microcrystalline structure.

[0026] Comparative Example 1 A spherical hard carbon material, the preparation method of which includes the following steps: (1) Dissolve 5 g of glucose in 100 mL of deionized water and stir magnetically for 10 min until completely dissolved; (2) Add 4 g of active yeast to the above solution and incubate for 24 h; (3) Heat the culture obtained in step (2) to boiling for 1 h to inactivate the yeast; (4) After the reaction system obtained in step (3) is naturally cooled to room temperature, centrifuge (3500 rpm, 3 min) to collect the precipitate, which is the hard carbon precursor; then wash the hard carbon precursor three times each with deionized water and anhydrous ethanol. (5) Transfer the washed hard carbon precursor to a freeze dryer and dry for 8 h; (6) The dried hard carbon precursor was transferred to a graphite ceramic boat and then to the reaction zone of a tube furnace. Under an argon atmosphere (flow rate of 50 mL / min), the temperature was increased to 1400 °C at a rate of 3 °C / min and held for 2 h. Then the temperature was decreased to 500 °C at a rate of 4 °C / min and finally cooled to room temperature with the furnace to obtain a hard carbon material with a disordered graphite microcrystalline structure.

[0027] Comparative Example 2 A medium-concentration Cu-modified hard carbon material is prepared in a method different from that in Example 1, step (2) involves adding 100 μL of a 0.1 M Cu(NO3)2 solution to the solution, thereby increasing the Cu concentration in the solution. 2+ With a concentration of 0.1 mM, the remaining steps are the same as in Example 1, to obtain a hard carbon material modified with a medium concentration of Cu metal element with a disordered graphite microcrystalline structure.

[0028] Comparative Example 3 A high-concentration Cu metal element modified hard carbon material is prepared in a method different from that in Example 1, step (2) involves adding 1000 μL of a 0.1 M Cu(NO3)2 solution to the solution, so that the Cu concentration in the solution increases. 2+ The concentration was 1 mM, and the remaining steps were the same as in Example 1, to obtain a high-concentration Cu metal element modified hard carbon material with a disordered graphite microcrystalline structure.

[0029] Experimental Example 1 Structural analysis of hard carbon materials: The morphology of the material prepared in Example 1 was characterized using transmission electron microscopy (TEM). The results showed that the material exhibited a typical spherical structure. Figure 1 a) This morphology originates from the morphological characteristics of yeast itself, indicating that the morphology was effectively preserved during the carbonization process. Further elemental analysis of the hard carbon materials prepared in Example 1 and Comparative Examples 1-3 was performed using energy-dispersive X-ray spectroscopy (EDS). Figure 1 b), it was found that with the increase of Cu in the yeast culture medium 2+ As the concentration increases, the Cu content in the hard carbon material increases accordingly, confirming that yeast can effectively adsorb or take up Cu from the solution during the culture stage. 2+ It is then stably modified into the hard carbon structure during subsequent heat treatment.

[0030] X-ray diffraction (XRD) analysis of the crystal structures of Examples 1 and Comparative Examples 1-3 showed that all carbon materials exhibited typical (002) and (100) broad diffraction peaks of hard carbon. Figure 2 It is noteworthy that in Comparative Examples 2 and 3, distinct diffraction peaks appear at 31.2°, 36.0°, 38.9°, 44.9°, and 46.2°, consistent with the Cu3P standard card, indicating that in medium-to-high Cu... 2+ Under certain concentration conditions, Cu tends to form phosphide crystal phases rather than single-atom morphology. Furthermore, at high Cu concentrations... 2+ In Comparative Example 3, a significant graphitization characteristic peak appeared at approximately 26°, indicating that Cu exhibited a catalytic graphitization effect under these conditions, promoting the ordering of the graphite lattice in the carbon material. These results, conversely, confirm that by appropriately reducing the Cu concentration... 2+ At certain concentrations, the phosphorus coordination environment provided by yeast helps stabilize the single-atom structure of Cu.

[0031] To further verify the existence of the single-atom structure, the hard carbon material prepared in Example 1 was characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Figure 3 The results show that at low Cu...2+ Under the specified concentration conditions, Cu exists in an atomically dispersed form in the hard carbon carrier, directly confirming that Example 1 successfully constructed Cu single-atom modified hard carbon.

[0032] Example 8 Fabrication of button cells: The hard carbon anode materials prepared in Examples 1-7 and Comparative Examples 1-3 were assembled into CR2032 coin cells, and their electrochemical performance was tested.

[0033] The specific process is as follows: First, hard carbon material, conductive agent Super P, and binder sodium alginate are mixed in a mass ratio of 8:1:1, with deionized water added as a solvent. The mixture is thoroughly stirred to form a uniform slurry, which is then coated onto the surface of conductive copper foil using a doctor blade method. Subsequently, the electrode is placed in a forced-air drying oven at 60 ℃ for 6 h, and then transferred to a vacuum oven at 100 ℃ for 12 h to completely remove the solvent. The dried electrode is then cut into 10 mm diameter discs using a tablet pressing and punching machine, with the active material loading controlled at approximately 1.0~1.5 mg / cm³. -2 The battery components were assembled sequentially in an argon-filled glove box (with O2 and H2O contents both below 0.01 ppm): negative electrode shell, sodium sheet, electrolyte (1 M NaPF6 / Diglyme), glass fiber separator, hard carbon electrode, gasket, spring sheet, and positive electrode shell, and finally packaged into a 2032 type coin cell.

[0034] Experiment Example 2 Electrochemical performance testing: The CR2032 coin cell assembled in Example 8 was subjected to electrochemical performance (rate and cycle) testing on the Newway test channel. The test conditions were as follows: voltage window of 0.01~2.0 V (vs. Na). + / Na), current density is defined as 1C = 300 mA g -1 The test results are summarized in Tables 1 and 2.

[0035] Table 1. Summary of the electrochemical performance of batteries assembled from the hard carbon materials prepared in Examples 1-3 and Comparative Example 1

[0036] Compared to Comparative Examples 1-3, Example 1 exhibited a higher reversible specific capacity at 0.1 C rate and a capacity as high as 280.1 mAh g⁻¹ at 1 C rate. -1(Table 1). This performance advantage may be attributed to the successful introduction of transition metal single atoms in Example 1, which induced optimization of the hard carbon microstructure and effectively promoted the storage and transport of sodium ions. Regarding long-term cycling stability, Examples 1, Comparative Examples 2 and 3 all exhibited good capacity retention (all above 88%) after 1500 cycles at 1 C, indicating that the introduction of appropriate metal elements helps improve the cycling performance of hard carbon materials. Example 1 was particularly outstanding, achieving a capacity retention of 95.3%, significantly better than the other groups. This result further supports the key role of transition metal single atoms in regulating the electrode / electrolyte interface, which may effectively suppress interfacial side reactions and capacity decay during cycling by promoting the formation of a more stable and uniform SEI film. To further verify the effect of Cu single atoms on electrochemical performance, we prepared hard carbon with a lower concentration of Cu single atoms (Example 2). The higher capacity retention exhibited in Example 2 further demonstrates the beneficial effect of Cu single atoms on the performance of hard carbon.

[0037] TEM interface analysis was performed on the samples of Example 1 and Comparative Example 1 after cyclic testing. Figure 4 The results showed that, compared with the unmodified Comparative Example 1, the SEI film formed by Example 1 with Cu single-atom modification was thinner and more uniformly distributed, indicating that the metal single-atom sites can effectively regulate the composition and structure of the SEI film, thereby improving the interfacial stability of the hard carbon anode during long-term cycling.

[0038] Table 2. Summary of the electrochemical performance of batteries assembled from the hard carbon materials prepared in Examples 4-8

[0039] Building upon the successful construction of Cu single-atom modified hard carbon materials in Example 1, this invention further extends the method to other transition metal systems, systematically preparing biomass hard carbon materials loaded with Fe, Ni, Co, Mn, and Zn single atoms respectively (corresponding to Examples 3-7). Electrochemical tests show that all hard carbons modified with transition metal single atoms exhibit high reversible specific capacity at 0.1 C rate, demonstrating the broad applicability of the preparation method of this invention to different metal elements. More notably, after approximately 120 cycles at a 1 C current density, these materials all exhibit excellent capacity retention (all above 96%), indicating that different transition metal single atoms can effectively improve the cycling stability of hard carbon electrodes. This result further confirms that the strategy of constructing metal single-atom modified hard carbon materials based on yeast biotemplates has good universality, and the obtained materials show significant application potential in high-capacity, long-cycle sodium-ion batteries.

[0040] In summary, the precise construction of metal single-atom structures in biomass hard carbon can not only improve the electrochemical performance of the material, but also provide a new material strategy and technical path for the development of long-life and high-stability sodium-ion batteries.

[0041] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for preparing a hard carbon material modified with a single atom of a transition metal, characterized in that, Includes the following steps: (1) A mixed solution is prepared by adding transition metal ions to a glucose solution, wherein the concentration of transition metal ions in the mixed solution is less than 0.01 mM; (2) Add yeast to the mixed solution for culturing; (3) Heat the culture obtained in step (2) to boiling to inactivate the yeast and obtain hard carbon precursor; (4) The hard carbon precursor is washed and dried; (5) The dried hard carbon precursor is calcined in an inert gas atmosphere. The calcination conditions are to raise the temperature to 1200~1500℃ and hold for 2~3 h, and then cool to room temperature to obtain the hard carbon material modified with a single atom of transition metal.

2. The method for preparing hard carbon material modified with a single transition metal atom according to claim 1, characterized in that: The concentration of the glucose solution is 0.04~0.06 g / mL.

3. The method for preparing hard carbon materials modified with transition metal single atoms according to claim 1, characterized in that: The transition metal ions are iron, cobalt, nickel, copper, manganese, or zinc ions.

4. The method for preparing hard carbon material modified with a single transition metal atom according to claim 1, characterized in that: The ratio of yeast to glucose solution is 4-5 g: 100 mL, and the culture time after adding yeast is 24 h; to inactivate yeast, the culture is heated to boiling and kept for 1 h.

5. The method for preparing hard carbon material modified with a single transition metal atom according to claim 1, characterized in that: The hard carbon precursor was washed three times with deionized water and anhydrous ethanol, and then freeze-dried for 8 hours.

6. The method for preparing hard carbon material modified with a single transition metal atom according to claim 1, characterized in that: The inert gas is argon, and the flow rate is 50 mL / min.

7. The method for preparing hard carbon material modified with a single transition metal atom according to claim 1, characterized in that, The calcination conditions were as follows: the temperature was increased to 1400 ℃ at a rate of 3 ℃ / min and held for 2 h, then decreased to 500 ℃ at a rate of 4 ℃ / min, and finally cooled to room temperature.

8. The hard carbon material prepared by the method for preparing hard carbon material modified with a single atom of transition metal according to any one of claims 1 to 7.

9. The application of the hard carbon material according to claim 8 in the preparation of sodium-ion batteries.

10. The application according to claim 9, characterized in that: The hard carbon material is used as the negative electrode material in sodium-ion batteries.

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