High-capacity hard carbon material and preparation method and application thereof

Abstract

The invention relates to the technical field of negative electrode materials, and particularly discloses a high-capacity hard carbon material and a preparation method and application thereof. The preparation method comprises the following steps: adding biomass into an acid solution for reaction, adding the obtained pretreated biomass and organic carboxylic acid metal salt into water, carrying out cross-linking esterification reaction and solid-liquid separation at 70-90 DEG C, and drying the obtained solid at 160-200 DEG C to obtain a hard carbon precursor; and heating the hard carbon precursor to 1100-1300 DEG C in a protective atmosphere, and carbonizing to obtain the high-capacity hard carbon material. The esterification structure inhibits ordering of a carbon matrix, bends a carbon layer around pores, realizes wrapping of the pores, and finally converts an internal porous structure into a rich closed-pore structure. The preparation method focuses on a technological means of anion / cation coordinated regulation and control, and coordinated regulation and control of a pore-interface are carried out from the atomic scale, so that a new way is provided for low-cost preparation of a high-capacity and high-first-effect hard carbon material.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials, and in particular to a high-capacity hard carbon material and a preparation method and application thereof. Background Art

[0002] Hard carbon materials, due to their rich, tunable porosity, adjustable interlayer spacing, and significant economic advantages, have become preferred materials for sodium-ion battery anodes. However, biomass hard carbon formed by direct carbonization is primarily composed of partially graphitized crystallites and lacks sufficient closed pores, resulting in limited sodium ion storage. Furthermore, ester-based electrolytes readily undergo solvent decomposition on the hard carbon surface, forming a solid electrolyte interphase (SEI) layer dominated by organic components. This results in poor mechanical properties of the interphase, which cracks with even slight expansion, consuming more electrolyte. Furthermore, sodium ions face significant resistance to passage through this interphase. These two factors limit the capacity of hard carbon (<300 mAh / g) and its low first coulombic efficiency (<80%), significantly impacting the energy density of sodium-ion electrochemical devices and failing to meet the requirements for industrial use. Therefore, optimizing the pore structure and surface chemistry of biomass hard carbon through molecular design is crucial to overcoming this performance bottleneck. Summary of the Invention

[0003] In response to the above problems, the present invention provides a high-capacity hard carbon material, its preparation method and application. Biomass is used as the carbon source, and organic carboxylic acid metal salts are introduced as structure-directing agents. Combined with the pore structure regulation-space confinement process, the obtained high-capacity hard carbon material has a rich closed-pore structure, which effectively improves the capacity and initial efficiency of the hard carbon material.

[0004] In order to solve the above technical problems, the technical solution provided by the present invention is: In a first aspect, the present invention provides a method for preparing a high-capacity hard carbon material, comprising the following steps: S100, adding biomass to an acid solution for reaction to obtain pretreated biomass; S200, adding the pretreated biomass and the organic carboxylic acid metal salt to water, performing a cross-linking esterification reaction at 70° C. to 90° C., separating the solid from the liquid, and drying the obtained solid at 160° C. to 200° C. to obtain a hard carbon precursor; The organic carboxylate metal salt includes at least one of an organic carboxylate zinc salt or an organic carboxylate potassium salt; S300 , heating the hard carbon precursor to 1100° C. to 1300° C. under a protective atmosphere for carbonization to obtain a high-capacity hard carbon material.

[0005] Compared with the prior art, the preparation method of the high-capacity hard carbon material provided by the present invention first pre-treats the biomass with an acid solution to remove impurities in the biomass. The pre-treated biomass is then subjected to a cross-linking esterification reaction with an organic carboxylic acid metal salt at a specific temperature, and the metal cations undergo π-cation coordination with the benzene ring of lignin in the biomass, while the carboxyl group of the organic acid anion forms an ester bond network with the hydroxyl group of the cellulose. Drying is carried out under specific temperature conditions to remove moisture while making the π-cation coordination and the ester bond network tighter. Finally, the hard carbon precursor is carbonized (high-temperature carbonization) at a specific temperature, and the metal cations are reduced to nano-metal atoms and volatilize to expand the pores. At the same time, the ester bond network induces the carbon skeleton to shrink at high temperature, causing the ends of the pores to bend and close.

[0006] Through extensive testing, the present invention discovered that the closed-pore structure is primarily formed by the curved and intertwined graphite domains formed by the carbonization of cellulose. If the temperature of the cross-linking esterification reaction is too high, the organic carboxylate ions in the organic carboxylate metal salt will hydrolyze the biomass, consuming the cellulose on the biomass surface. This will reduce the number of closed pores formed in the hard carbon material and the closed-pore volume, thereby reducing the capacity and initial efficiency of the negative electrode material. If the drying temperature in S200 is too low, the π-cation coordination and ester bond network will not be strengthened. If the drying temperature in S200 is too high, the π-cation coordination and ester bond network will be too tight, making it difficult for the metal ions to be reduced or volatilized during subsequent high-temperature carbonization, and the carbon layers will not be easily reorganized. If the carbonization temperature is too high, the esterification structure (ester bond network) will be severely damaged, thereby losing its barrier effect, resulting in a high degree of graphitization and a significant reduction in the closed-pore structure. Furthermore, if the carbonization temperature is too high, a large amount of metal atoms will evaporate and will not be able to remain on the surface of the carbon matrix.

[0007] Preferably, in S100, the biomass includes at least one of bamboo, walnut shells or sycamore leaves.

[0008] Preferably, in S100, the particle size of the biomass is 180 mesh to 220 mesh.

[0009] Preferably, in S100, the acid solution includes a dilute hydrochloric acid solution with a mass concentration of 8% to 12%.

[0010] Preferably, in S100, the mass volume ratio of the biomass to the acid solution is 1 g:(5-8) mL.

[0011] Preferably, in S100, the reaction temperature is 10° C. to 40° C., and the reaction time is 6 h to 12 h.

[0012] For example, in S100, after the reaction is completed, the steps further include washing and drying to obtain pretreated biomass.

[0013] Preferably, in S200, the organic carboxylate metal salt includes at least one of zinc oxalate, potassium oxalate, zinc acetate or potassium acetate.

[0014] Through a large number of experiments, the present invention found that although other metal cations (such as sodium ions) can also form coordination structures with the benzene rings of lignin, at high temperatures (1100°C~1300°C), the volatility of metallic sodium is poor and the pore-forming effect is poor, resulting in limited storage of sodium ions and a small increase in battery capacity; other anions cannot form an ester bond network with cellulose hydroxyl groups, and thus cannot form a closed-pore structure, which is not conducive to the effective storage of sodium ions.

[0015] Preferably, in S200, the mass volume ratio of the pretreated biomass, the organic carboxylic acid metal salt and water is (10-12) g: (3-5) g: 100 mL.

[0016] Preferably, in S200, the cross-linking esterification reaction time is 4 hours to 6 hours.

[0017] By limiting the conditions of the cross-linking esterification reaction (including the amount of each raw material, reaction temperature and time), the present invention can further control the degree of the cross-linking esterification reaction, thereby effectively controlling the structure of the hard carbon material and maximizing the improvement of the electrochemical performance of the hard carbon material.

[0018] For example, in S200 , after the solid-liquid separation, the process further includes: washing the obtained solid and then drying it.

[0019] Preferably, in S200, the drying includes vacuum drying, and the drying time is 3 hours to 5 hours.

[0020] Preferably, in S300, the protective atmosphere includes a nitrogen atmosphere or an argon atmosphere.

[0021] Preferably, in S300, microwave heating is used to heat the hard carbon precursor to 1100° C. to 1300° C. within 5 seconds to 10 seconds.

[0022] This invention uses microwave heating, capitalizing on the transfer of heat from the interior of the material to the surface. The internal high-temperature field promotes the volatilization of metal atoms, while the surface low-temperature field locks them in place, creating a porous carbon matrix with a metal-rich surface. The retained metal atoms on the surface catalyze the decomposition of electrolyte salts, forming an inorganic-dominated SEI layer. This inorganic-dominated SEI layer is thinner, offering less resistance to sodium ion penetration and better kinetics. Furthermore, the inorganic-dominated SEI layer exhibits superior mechanical properties, preventing cracking of the interface layer even when the electrode expands, thereby reducing excessive electrolyte consumption.

[0023] Through a large number of experiments, the present invention found that if the heating rate slows down, the time for the internal heat of the hard carbon precursor to be transferred to the surface will be prolonged, the surface temperature of the hard carbon precursor will increase significantly, the locking ability of the surface metal atoms will be weakened, and the SEI layer dominated by inorganic substances cannot be formed, which will have an adverse effect on the capacity, first effect and other properties of the hard carbon material.

[0024] Preferably, in S300, the carbonization time is 2 hours to 4 hours.

[0025] In a second aspect, the present invention provides a high-capacity hard carbon material prepared by the high-capacity hard carbon material preparation method.

[0026] In a third aspect, the present invention provides a negative electrode material comprising the high-capacity hard carbon material.

[0027] In a fourth aspect, the present invention provides an application of the negative electrode material in a sodium ion battery or a potassium ion battery.

[0028] The present invention has the following beneficial effects: The present invention uses organic carboxylic acid metal salts to react with natural biomass. Vacuum drying can not only quickly remove moisture, but the high temperature provided by drying can also promote the π-cation coordination and ester bond network to be closer. In addition, the esterification structure inhibits the ordering of the carbon matrix, bends the carbon layer around the pores, achieves the wrapping of the pores, and ultimately transforms the internal porous structure into a rich closed-pore structure. The present invention focuses on the process means of coordinated regulation of anions / cations, and coordinates the pore-interface at the atomic scale, providing a new way for the low-cost preparation of high-capacity, high-first-effect hard carbon materials.

[0029] The high-capacity hard carbon material provided by the present invention has a rich closed-pore structure. Using the high-capacity hard carbon material as the raw material for the negative electrode material, the prepared sodium ion battery has a capacity of more than 360 mAh / g and an initial efficiency of more than 93%, and has excellent electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a TEM image of the high-capacity hard carbon material in Example 1 of the present invention; Figure 2 This is a TEM image of the high-capacity hard carbon material in Example 2 of the present invention; Figure 3 This is a TEM image of the hard carbon material in Comparative Example 1 of the present invention; Figure 4 This is a TEM image of the hard carbon material in Comparative Example 2 of the present invention; In the figure, the circled area represents a closed-cell structure. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0032] In the embodiments of the present invention, deionized water is used. Water without manufacturer indication is commercially available.

[0033] Example 1 This embodiment provides a method for preparing a high-capacity hard carbon material, comprising the following steps: S100, 10 g of biomass (walnut shells) was crushed, passed through a 200-mesh sieve, and added to 60 mL of a 10% dilute hydrochloric acid solution. The mixture was stirred and reacted at room temperature for 8 h, and then washed and dried to obtain pretreated biomass.

[0034] S200, 12 g of pretreated biomass and 3 g of organic carboxylic acid metal salt (zinc acetate) were added to 100 mL of water, and a cross-linking esterification reaction was carried out at 90°C. After keeping warm for 4 hours, the solid-liquid separation was carried out, and the obtained solid was washed and vacuum dried at 180°C for 4 hours to obtain a hard carbon precursor.

[0035] S300, in a nitrogen atmosphere, using microwave heating to heat the hard carbon precursor to 1100° C. within 6 seconds for carbonization, keeping the temperature for 3 hours, and then cooling to room temperature to obtain a high-capacity hard carbon material.

[0036] The high-capacity hard carbon material prepared in this example was tested by transmission electron microscopy. Figure 1 As shown in the figure, it can be seen that the high-capacity hard carbon material prepared in this embodiment has a large number of closed pores and a large closed pore volume.

[0037] Example 2 This embodiment provides a method for preparing a high-capacity hard carbon material, comprising the following steps: S100, 10 g of biomass (sycamore leaves) was crushed, passed through a 220-mesh sieve, and added to 70 mL of a 10% dilute hydrochloric acid solution. The mixture was stirred and reacted at room temperature for 10 h, washed, and dried to obtain pretreated biomass.

[0038] S200, 11 g of pretreated biomass and 4 g of organic carboxylic acid metal salt (zinc oxalate) were added to 100 mL of water, and a cross-linking esterification reaction was carried out at 80°C. After keeping warm for 5 hours, the solid-liquid separation was carried out, and the obtained solid was washed and vacuum dried at 190°C for 4 hours to obtain a hard carbon precursor.

[0039] S300, in a nitrogen atmosphere, using microwave heating to heat the hard carbon precursor to 1200° C. within 7 seconds for carbonization, keeping the temperature for 3 hours, and then cooling to room temperature to obtain a high-capacity hard carbon material.

[0040] The high-capacity hard carbon material prepared in this example was tested by transmission electron microscopy. Figure 2 As shown in the figure, it can be seen that the high-capacity hard carbon material prepared in this embodiment has a large number of closed pores and a large closed pore volume.

[0041] Example 3 This embodiment provides a method for preparing a high-capacity hard carbon material, comprising the following steps: S100, 10 g of biomass (sycamore leaves) was crushed, passed through a 180-mesh sieve, and added to 80 mL of 8% dilute hydrochloric acid solution. The mixture was stirred and reacted at room temperature for 12 h, washed, and dried to obtain pretreated biomass.

[0042] S200, 10 g of pretreated biomass and 4 g of organic carboxylic acid metal salt (potassium acetate) were added to 100 mL of water, and a cross-linking esterification reaction was carried out at 70°C. After keeping warm for 6 hours, the solid-liquid separation was carried out, and the obtained solid was washed and vacuum dried at 200°C for 3.5 hours to obtain a hard carbon precursor.

[0043] S300, in an argon atmosphere, using microwave heating to heat the hard carbon precursor to 1100° C. within 5 seconds for carbonization, keeping the temperature for 4 hours, and then cooling to room temperature to obtain a high-capacity hard carbon material.

[0044] Example 4 This embodiment provides a method for preparing a high-capacity hard carbon material, comprising the following steps: S100, 10 g of biomass (bamboo) was crushed, passed through a 200-mesh sieve, and added to 50 mL of a 12% dilute hydrochloric acid solution. The mixture was stirred and reacted at room temperature for 6 h, and then washed and dried to obtain pretreated biomass.

[0045] S200, 12 g of pretreated biomass and 5 g of organic carboxylic acid metal salt (potassium oxalate) were added to 100 mL of water, and a cross-linking esterification reaction was carried out at 80°C. After keeping warm for 5 hours, the solid-liquid separation was carried out, and the obtained solid was washed and vacuum dried at 165°C for 5 hours to obtain a hard carbon precursor.

[0046] S300, in a nitrogen atmosphere, using microwave heating to heat the hard carbon precursor to 1300° C. within 10 seconds for carbonization, keeping the temperature for 2 hours, and then cooling to room temperature to obtain a high-capacity hard carbon material.

[0047] Example 5 This embodiment provides a method for preparing a high-capacity hard carbon material, which is similar to Example 2, except that: in S300, microwave heating is replaced by resistance wire heating, and the hard carbon precursor is heated to 1300°C within 1 minute. The remaining conditions are the same as those in Example 2 and will not be repeated here.

[0048] Comparative Example 1 This comparative example provides a method for preparing a hard carbon material, which is similar to Example 2, except that in S200, the temperature of the cross-linking esterification reaction is replaced with 100° C. The remaining conditions are the same as those in Example 2 and will not be repeated here.

[0049] The hard carbon material prepared in this comparative example was tested by transmission electron microscopy, and the results were as follows: Figure 3 As can be seen from the figure, the hard carbon material prepared in this comparative example has fewer closed pores and a smaller closed pore volume.

[0050] Comparative Example 2 This comparative example provides a method for preparing a hard carbon material, which is similar to Example 2, except that in S200, the vacuum drying temperature is replaced with 150° C. The remaining conditions are the same as those in Example 2 and will not be repeated here.

[0051] The hard carbon material prepared in this comparative example was tested by transmission electron microscopy, and the results were as follows: Figure 4 As can be seen from the figure, the hard carbon material prepared in this comparative example has fewer closed pores and a smaller closed pore volume.

[0052] Comparative Example 3 This comparative example provides a method for preparing a hard carbon material, which is similar to Example 2, except that in S200, the vacuum drying temperature is replaced with 215° C. The remaining conditions are the same as those in Example 2 and will not be repeated here.

[0053] Comparative Example 4 This comparative example provides a method for preparing a hard carbon material, which is similar to Example 2, except that in S300, the carbonization temperature is replaced with 1400° C. The remaining conditions are the same as those in Example 2 and will not be repeated here.

[0054] Comparative Example 5 This comparative example provides a method for preparing a hard carbon material, which is similar to Example 2, except that in S200, zinc oxalate is replaced with sodium oxalate of equal mass. The remaining conditions are the same as those in Example 2 and will not be repeated here.

[0055] Comparative Example 6 This comparative example provides a method for preparing a hard carbon material, which is similar to Example 2, except that in S200, zinc oxalate is replaced with zinc sulfate of equal mass. The remaining conditions are the same as those in Example 2 and will not be repeated here.

[0056] Comparative Example 7 This comparative example provides a method for preparing a hard carbon material, which is similar to Example 2, except that the addition of zinc oxalate is omitted in S200. The remaining conditions are the same as those in Example 2 and will not be repeated here.

[0057] Application Examples This application example provides a sodium ion half-cell made from the hard carbon materials of Examples 1 to 5 and Comparative Examples 1 to 7, respectively. The preparation method thereof comprises the following steps: S100, grinding the hard carbon material with acetylene black and sodium alginate, wherein the mass ratio of the hard carbon material, acetylene black and sodium alginate is 8:1:1, adding water and mixing evenly to obtain a mixed slurry with a solid content of 85%.

[0058] S200: Coat the mixed slurry on the surface of the copper foil with a coating amount of 2.5g / cm 2 After vacuum drying at 80°C for 12 h, the obtained coating material was cut into small discs with a diameter of 12 mm to obtain negative electrode sheets.

[0059] S300, assemble the negative electrode sheet into a battery, use the sodium metal sheet as the counter electrode, use glass fiber as the separator, and use the electrolyte as a mixture of EC (ethylene carbonate) and DEC (diethyl carbonate) containing 1 mol / L NaPF6 (the volume ratio of EC and DEC is 1:1) to obtain a sodium ion half-cell.

[0060] Verification test The closed pore volume of the hard carbon materials of Examples 1 to 5 and Comparative Examples 1 to 7 was tested, and the test results are shown in Table 1. First, the true density of each hard carbon material was tested to obtain the true density value ρ ture ; Then according to the formula V=1 / ρ ture -1 / 2.26 to calculate the closed pore volume, where 2.26 is the true density of graphite.

[0061] The sodium ion half-cells prepared in the application example were placed on a Land CT2001A battery test system for electrochemical performance testing. The test results are shown in Table 1. The test temperature was 25°C, the test electrochemical window was 0V~2.5V, and the test current density was 30mA / g.

[0062] Table 1 Performance test results of hard carbon materials of Examples and Comparative Examples

[0063] As can be seen from the table, compared with the examples, the temperature of the cross-linking esterification reaction in Comparative Example 1 is too high. At this time, the oxalate anions hydrolyze the biomass, and the cellulose on the surface of the biomass is completely consumed, resulting in a significant reduction in the closed-pore volume, thereby reducing the capacity and first efficiency.

[0064] Compared with the embodiment, the vacuum drying temperature of comparative example 2 is too low, and the effect of strengthening the π-cation coordination and ester bond network cannot be achieved; the vacuum drying temperature of comparative example 3 is too high, the π-cation coordination and ester bond network are too tight, and the metal ions are not easily reduced or volatilized during subsequent high-temperature carbonization, and the carbon layer is not easy to reorganize, resulting in a smaller closed-pore volume, and a significant reduction in capacity and initial efficiency.

[0065] Compared with the embodiment, the carbonization temperature of comparative example 4 is too high, the esterification structure is severely damaged and cannot play a barrier role, the degree of graphitization is high, and the closed-pore structure is greatly reduced; at the same time, a large amount of metal atoms are volatilized and cannot stay on the surface of the carbon matrix, and thus the SEI layer dominated by inorganic matter cannot be formed. The interface layer is thicker and the mechanical properties are poor.

[0066] Compared with Example 7 and Comparative Example 5, Comparative Example 5 uses sodium oxalate as a structure-directing agent. At high temperatures, the volatility of metallic sodium in the coordination structure formed by sodium ions and the benzene rings of lignin is poor, and the pore-forming effect is poor, resulting in limited storage of sodium ions in the sodium ion half-cell and little improvement in the battery capacity.

[0067] Compared with Example 1 and Comparative Example 7, Comparative Example 6 uses zinc sulfate as a structure-directing agent. Sulfate ions cannot form an ester bond network with cellulose hydroxyl groups, and thus cannot form a closed-pore structure, which is not conducive to the effective storage of sodium ions.

[0068] Compared with Examples 1 to 4, Example 5 replaces the rapid microwave heating method with resistance wire heating, which slows down the heating rate, prolongs the time for the internal heat of the hard carbon precursor to be transferred to the surface, increases the surface temperature of the hard carbon precursor, weakens the locking ability of the surface metal atoms, and cannot form an SEI layer dominated by inorganic substances, thereby adversely affecting the capacity, first effect and other properties of the hard carbon material.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a high-capacity hard carbon material, characterized in that: The following steps are involved: S100, adding biomass to an acid solution for reaction to obtain pretreated biomass; S200, adding the pretreated biomass and the organic carboxylic acid metal salt to water, performing a cross-linking esterification reaction at 70° C. to 90° C., separating the solid from the liquid, and drying the obtained solid at 160° C. to 200° C. to obtain a hard carbon precursor; The organic carboxylate metal salt includes at least one of an organic carboxylate zinc salt or an organic carboxylate potassium salt; S300 , heating the hard carbon precursor to 1100° C. to 1300° C. under a protective atmosphere for carbonization to obtain a high-capacity hard carbon material.

2. The method for preparing a high-capacity hard carbon material according to claim 1, wherein: In S100, the biomass includes at least one of bamboo, walnut shells or sycamore leaves.

3. The method for preparing a high-capacity hard carbon material according to claim 1, wherein: In S100, the mass volume ratio of the biomass to the acid solution is 1 g: (5-8) mL; In S100, the reaction temperature is 10°C to 40°C, and the reaction time is 6h to 12h.

4. The method for preparing a high-capacity hard carbon material according to claim 1, wherein: In S200, the organic carboxylic acid metal salt includes at least one of zinc oxalate, potassium oxalate, zinc acetate or potassium acetate.

5. The method for preparing a high-capacity hard carbon material according to any one of claims 1 to 4, wherein: In S200, the mass volume ratio of the pretreated biomass, the organic carboxylic acid metal salt and water is (10-12) g: (3-5) g: 100 mL.

6. The method for preparing a high-capacity hard carbon material according to claim 1, wherein: In S200, the cross-linking esterification reaction time is 4h~6h; In S200, the drying includes vacuum drying, and the drying time is 3 hours to 5 hours.

7. The method for preparing a high-capacity hard carbon material according to claim 1, wherein: In S300, the hard carbon precursor is heated to 1100° C. to 1300° C. within 5 to 10 seconds by microwave heating. In S300, the carbonization time is 2 hours to 4 hours.

8. A high-capacity hard carbon material, characterized in that The high-capacity hard carbon material is prepared by the preparation method of any one of claims 1 to 7.

9. A negative electrode material, characterized in that The high-capacity hard carbon material according to claim 8 is included.

10. Use of the negative electrode material according to claim 9 in a sodium ion battery or a potassium ion battery.

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