Composite hard carbon material for sodium ion battery and preparation method of composite hard carbon material

Abstract

The invention belongs to the technical field of hard carbon sodium ion battery negative electrode materials, and particularly relates to a composite hard carbon material for a sodium ion battery and a preparation method of the composite hard carbon material. The composite hard carbon material contains a sucrose carbon microsphere aggregate with a conductive network; the outer surfaces of the sucrose carbon microspheres are smooth petroleum asphalt soft carbon layers, and bent graphite domains are arranged in the sucrose carbon microspheres. In the co-carbonization process of the sucrose carbon microspheres and the petroleum asphalt, the graphitization process of the hard carbon core is induced, the disorder degree of the whole material is reduced, defect sites are reduced, the synergistic carbonization effect is fully exerted in the carbonization process, and the first-circle coulombic efficiency of the material can be effectively improved by 43-45%.

Description

Technical Field

[0001] The present invention belongs to the technical field of hard carbon sodium ion battery negative electrode materials, and specifically relates to a composite hard carbon material for sodium ion batteries and a preparation method thereof. Background Art

[0002] In recent years, excessive consumption of fossil fuels has triggered a series of global challenges, including a sharp increase in carbon emissions, an intensified greenhouse effect, and an energy security crisis. To address this challenge, promoting the large-scale deployment of renewable energy and accelerating the transition to a low-carbon and clean energy consumption structure has become an international consensus. The development of efficient energy storage technologies is a key component in achieving the efficient utilization of new energy. Since the commercialization of lithium-ion batteries in the 1990s, they have dominated mobile electronic devices and electric vehicles due to their excellent energy density. However, the scarcity of lithium resources in the Earth's crust (reserves are only approximately 0.0065%) and their uneven distribution make it difficult to support the rapid growth of global energy demand. In contrast, sodium resources are abundant (accounting for 2.74% of the elements in the Earth's crust), are low-cost, and are widely distributed, making sodium-ion batteries a highly promising alternative for next-generation energy storage technologies.

[0003] As one of the core components of sodium-ion batteries, the performance of the anode material directly determines its energy density and cycle life. Although graphite anodes have been widely used in lithium-ion batteries, their narrow interlayer spacing (0.335nm) cannot effectively accommodate the large ionic radius of sodium ions (1.02Å), resulting in extremely low sodium storage capacity.

[0004] Hard carbon (also known as "difficult-to-graphitize carbon") is an amorphous carbon material formed by disordered stacking of graphene sheets with a lateral size of about 40Å. Its unique structural characteristics are reflected in two aspects: first, the enlarged (002) crystal plane interlayer spacing (0.37-0.40nm), which provides sufficient space for the insertion / extraction of sodium ions; second, the presence of nanopores and structural defects formed by the random orientation of graphene sheets inside. These characteristics together constitute the rapid transmission channels and adsorption sites of sodium ions, which are the key to determining its electrochemical performance.

[0005] Hard carbon anodes for sodium-ion batteries face three major drawbacks: low first-cycle coulombic efficiency, poor rate / cycling performance, and high cost. Existing technologies achieve this through: ① structural manipulation, expanding the interlayer spacing to 0.38nm, template pore creation, and nitrogen doping to enhance conductivity; and ② pre-sodiumization compensation, such as using sodium benzophenone reagents to achieve near-100% first-cycle efficiency.

[0006] However, these solutions have significant limitations: structural optimization leads to a contradiction between compaction density and capacity, and excessive pore creation exacerbates side reactions; the pre-sodiumization technology reagents are expensive and the process is complex; the mass production process has problems such as expensive equipment (microwave heat treatment), pickling pollution and large batch fluctuations (yield is only 85%).

[0007] CN116332152A discloses a sodium ion battery core-shell structure bagasse hard carbon-based negative electrode material and its preparation method. This patent adopts the method of first carbonizing the bagasse core into a shape, and then coating it with different carbon materials in different ways to form a core-shell structure. However, carbonizing the core first will cause the hard carbon core to have a disordered structure. Even if it is coated with other carbon materials and then carbonized again, it is only a simple combination of different carbon materials. It will not have much impact on the hard carbon core. Each carbon material independently exerts its own characteristics, and the composite characteristics of the composite carbon material cannot be fully utilized, which has limited improvement in the electrochemical performance of the material. In addition, the carbonization process is complicated and increases energy consumption. Summary of the Invention

[0008] The purpose of the present invention is to provide a composite hard carbon material for sodium ion batteries with high first-cycle coulombic efficiency, high sodium storage capacity and excellent cycle stability, and a preparation method thereof, in order to address the problems of low first-cycle coulombic efficiency, poor rate / cycle performance and high cost faced by the hard carbon negative electrode of sodium ion batteries in the prior art.

[0009] The technical solution of the present invention is: A composite hard carbon material for sodium-ion batteries comprises aggregates of sucrose carbon microspheres with a conductive network. The sucrose carbon microspheres have a smooth, petroleum-asphalt-like soft carbon layer on their outer surface and curved graphite domains within them. Within the aggregates, a conductive network is formed between the microspheres.

[0010] The petroleum pitch soft carbon layer has a higher degree of graphitization, fewer defect sites, a more ordered internal carbon layer arrangement, and a narrower carbon layer distance. During the synergistic carbonization process with sucrose carbon microspheres, it induces and promotes the graphitization process of the sucrose carbon microspheres, reduces the defect sites of the mixed carbon material, promotes carbon layer growth, and reduces the irreversible capacity of the material. While maintaining the capacity, it also enhances its structural stability and effectively improves the first-cycle coulombic efficiency by 43%-45%. At the same time, the different carbon microspheres in the sucrose carbon microsphere aggregates contained in the composite hard carbon material adhere together, not only making the structure more stable, but more importantly, forming a conductive network, further enhancing the material's conductivity.

[0011] In the present invention, the particle size of the sucrose carbon microsphere aggregates of the composite hard carbon material for sodium ion batteries is 4-10 μm.

[0012] In the present invention, the particle size of the sucrose carbon microspheres of the composite hard carbon material for sodium ion batteries is 1-2 μm.

[0013] In the present invention, the average thickness of the petroleum asphalt soft carbon layer on the outer surface of the sucrose carbon microspheres of the composite hard carbon material for sodium ion batteries is 10-15 nm.

[0014] In the present invention, the porosity of the sucrose carbon microspheres of the composite hard carbon material for sodium ion batteries is 0.01 cm 3 / g-0.05cm 3 / g, specific surface area 150m 2 / g-180m 2 / g, pore size is 0.5-5nm.

[0015] In the present invention, the composite hard carbon material for sodium ion batteries has a petroleum asphalt number average molecular weight of sucrose carbon microspheres of 400-5000 g / mol, a softening point of 180-280°C, and a density of 1.02-1.04 g / cm³.

[0016] The aforementioned method for preparing composite hard carbon materials for sodium-ion batteries begins by using sucrose for low-temperature hydrothermal treatment to form a carbon microsphere precursor, before the disordered structure of the microspheres is formed. The precursor is then coated with petroleum asphalt using a liquid-phase coating method, followed by sintering for a synergistic carbonization reaction. This fully exploits the composite synergistic effect of the materials, improving their electrochemical performance and producing a hard carbon anode material for sodium-ion batteries. Combining the two carbonization steps into a single one also reduces energy consumption and process complexity.

[0017] The specific steps are as follows: (1) Preparation of porous sucrose carbon microspheres: Sucrose was weighed and dissolved in deionized water to obtain a sucrose aqueous solution with a concentration of 1-10 wt %.

[0018] The sucrose aqueous solution is stirred at room temperature until completely dissolved, and then subjected to hydrothermal reaction at 160° C.-200° C. for 8-16 hours to obtain black powdery carbon microspheres; the obtained carbon microspheres are washed, filtered, and dried to obtain the sucrose carbon microspheres.

[0019] (2) Asphalt liquid phase coated sucrose carbon microspheres: First, the sucrose carbon microspheres obtained in step (1) and petroleum asphalt are added to an ethanol aqueous solution in a weight ratio of 1:(0.2-1); Then, the mixture is stirred and evaporated to dryness at 40-80° C., and then dried at 70-120° C. for 12-24 hours to obtain petroleum asphalt-coated sucrose carbon microspheres.

[0020] The study found that although petroleum asphalt can induce graphitization well, form a highly conductive network and a stable structure, and improve rate performance and cycle life, if the degree of graphitization is not properly controlled, either the optimization effect will not be significantly improved; or it will lead to a decrease in reversible capacity and coulombic efficiency, which will have a negative impact on the electrochemical performance of the battery.

[0021] To address this technical coupling issue, extensive research has revealed that the delicate relationship between the dosage of sucrose carbon microspheres and petroleum pitch plays a key role in the degree of graphitization. A weight ratio of sucrose carbon microspheres to petroleum pitch of 1:0.2-1 (0.2-1) achieves the ideal degree of graphitization.

[0022] (3) High temperature sintering to prepare composite hard carbon materials: The petroleum asphalt-coated sucrose carbon microspheres obtained in step (2) are ground into powder, placed in a tube furnace and sintered at 1100-1400° C., with a holding time of 1-4 h and a heating rate of 2-7° C. / min; and the composite hard carbon material is obtained.

[0023] The carbon microspheres formed by the hydrothermal treatment of sucrose in step (1) have a large number of nanopores inside and have a large theoretical sodium storage capacity. However, they have a low degree of graphitization and many defects, resulting in a low first-cycle coulombic efficiency and an unstable structure. While the surface is coated with the asphalt soft carbon reinforcement material structure, the high degree of graphitization of the soft carbon is utilized to induce an increase in the degree of graphitization of the sucrose hard carbon, so as to achieve the purpose of improving the first-cycle coulombic efficiency.

[0024] In the present invention, in the method for preparing the composite hard carbon material for sodium ion batteries, the drying temperature in step (1) is 70-120° C. and the drying time is 12-24 hours.

[0025] In the present invention, in the method for preparing a composite hard carbon material for a sodium ion battery, the volume ratio of ethanol to deionized water in the ethanol aqueous solution in step (2) is 1:1.

[0026] The beneficial effects of the present invention are as follows: the composite hard carbon material for sodium ion batteries described in the present invention contains sucrose carbon microsphere aggregates with a conductive network; the outer surface of the sucrose carbon microspheres is a smooth petroleum asphalt soft carbon layer, and the sucrose carbon microspheres have curved graphite domains. In the sucrose carbon microsphere aggregates, a conductive network is formed between the sucrose carbon microspheres. In the process of co-carbonization of sucrose carbon microspheres and petroleum asphalt, the graphitization process of the hard carbon core is induced, the overall disorder of the material is reduced, the defect sites are reduced, and the synergistic carbonization effect is fully utilized in the carbonization process, which can effectively improve the first-cycle coulomb efficiency of the material by 43-45%. At the same time, merging the two-step carbonization into a one-step carbonization can reduce energy consumption and reduce process complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope photograph of the composite hard carbon material for sodium ion batteries prepared in Example 2.

[0028] Figure 2 This is the XRD pattern of the composite hard carbon material for sodium ion batteries prepared in Example 2.

[0029] Figure 3 The Raman spectra of Example 2 and Comparative Example 1 are shown.

[0030] Figure 4 Graph showing the first cycle charge and discharge curves of the composite hard carbon material for sodium ion batteries prepared in Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is described in detail below with reference to the accompanying drawings.

[0032] The petroleum asphalt used in the specific embodiment has a number average molecular weight of 1280 g / mol, a softening point of 250° C., and a density of 1.02 g / cm³. Example 1

[0033] The method for preparing the composite hard carbon material for sodium ion batteries comprises the following specific steps: (1) Preparation of porous sucrose carbon microspheres: Weigh 2 g of sucrose and dissolve it in 60 mL of deionized water to obtain a sucrose aqueous solution with a concentration of 3 wt%.

[0034] The sucrose aqueous solution was placed on a magnetic stirrer, stirred at room temperature until completely dissolved, and then placed in a high-pressure reactor for hydrothermal reaction at 160° C. for 8 hours to obtain black powdery carbon microspheres.

[0035] The obtained carbon microspheres were washed alternately with 100 mL of ethanol / deionized water, filtered, and dried at 70° C. for 12 h to obtain the sucrose carbon microspheres.

[0036] (2) Asphalt liquid phase coated sucrose carbon microspheres: First, the sucrose carbon microspheres obtained in step (1) and petroleum asphalt are added to an ethanol aqueous solution at a weight ratio of 1:0.2; the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:1.

[0037] Then, the mixture was stirred and evaporated to dryness at 40°C, and then dried at 70°C for 12 h to obtain petroleum asphalt-coated sucrose carbon microspheres. (3) High temperature sintering to prepare composite hard carbon materials: The petroleum asphalt-coated sucrose carbon microspheres obtained in step (2) are ground into powder, placed in a tube furnace and sintered at 1100° C. with a holding time of 1 h and a heating rate of 2° C. / min to obtain the composite hard carbon material.

[0038] The composite hard carbon material obtained in this example is used as a negative electrode material for a sodium ion battery, and the obtained first-cycle discharge capacity is 381 mAh / g, and the first-cycle coulombic efficiency is 77%. Example 2

[0039] The method for preparing the composite hard carbon material for sodium ion batteries comprises the following specific steps: (1) Preparation of porous sucrose carbon microspheres: Weigh 4 g of sucrose and dissolve it in 60 mL of deionized water to obtain a 6 wt% sucrose aqueous solution. The sucrose aqueous solution was stirred at room temperature until completely dissolved, and then subjected to hydrothermal reaction at 180°C for 12 h to obtain black powdery carbon microspheres.

[0040] The obtained carbon microspheres were washed alternately with 100 mL of ethanol / deionized water, filtered, and dried at 80° C. for 14 h to obtain the sucrose carbon microspheres; (2) Asphalt liquid phase coated sucrose carbon microspheres: First, the sucrose carbon microspheres obtained in step (1) and petroleum asphalt are added to an ethanol aqueous solution at a weight ratio of 1:0.5; the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:1.

[0041] Then, the mixture was stirred and evaporated to dryness at 60°C, and then dried at 80°C for 14 h to obtain petroleum asphalt-coated sucrose carbon microspheres. (3) High temperature sintering to prepare composite hard carbon materials: The petroleum asphalt-coated sucrose carbon microspheres obtained in step (2) are ground into powder, placed in a tube furnace and sintered at 1200° C. with a holding time of 2 h and a heating rate of 4° C. / min to obtain the composite hard carbon material.

[0042] pass Figure 1 It can be seen that petroleum asphalt is successfully coated on the surface of sucrose microspheres to form a soft carbon layer, and part of the asphalt adheres the carbon microspheres together to form aggregates.

[0043] pass Figure 2 It can be seen that there is a peak at about 23° corresponding to the (002) crystal plane of hard carbon, proving that hard carbon material has been prepared.

[0044] pass Figure 3 It can be seen that the ID / IG value of the Raman spectrum of the composite hard carbon material obtained in this embodiment is 1.150. Compared with the comparative example 1 without asphalt coating (ID / IG value is 1.187), its ID / IG value is reduced, indicating an increase in the order of the material and a decrease in defects.

[0045] pass Figure 4 It can be seen that the first-cycle Coulomb efficiency is increased from 51% to 94% compared with the uncoated control.

[0046] The composite hard carbon material obtained in this example is used as a negative electrode material for a sodium ion battery, and the obtained first-cycle discharge capacity is 362 mAh / g, and the first-cycle coulombic efficiency is 94.3%. Example 3

[0047] The method for preparing the composite hard carbon material for sodium ion batteries comprises the following specific steps: (1) Preparation of porous sucrose carbon microspheres: Weigh 6 g of sucrose and dissolve it in 60 mL of deionized water to obtain a 9 wt% sucrose aqueous solution. The sucrose aqueous solution was stirred at room temperature until completely dissolved, and then subjected to hydrothermal reaction at 180°C for 12 h to obtain black powdery carbon microspheres.

[0048] The obtained carbon microspheres were washed alternately with 100 mL of ethanol / deionized water, filtered, and dried at 100° C. for 14 h to obtain the sucrose carbon microspheres; (2) Asphalt liquid phase coated sucrose carbon microspheres: First, the sucrose carbon microspheres obtained in step (1) and petroleum asphalt are added to an ethanol aqueous solution at a weight ratio of 1:0.8; the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:1.

[0049] Then, the mixture was stirred and evaporated to dryness at 80° C., and then dried at 100° C. for 14 h to obtain petroleum asphalt-coated sucrose carbon microspheres.

[0050] (3) High temperature sintering to prepare composite hard carbon materials: The petroleum asphalt-coated sucrose carbon microspheres obtained in step (2) are ground into powder, placed in a tube furnace and sintered at 1300° C. with a holding time of 3 h and a heating rate of 6° C. / min to obtain the composite hard carbon material.

[0051] The composite hard carbon material obtained in this example is used as a negative electrode material for a sodium ion battery, and the obtained first-cycle discharge capacity is 356 mAh / g, and the first-cycle coulombic efficiency is 90%. Comparative Example 1

[0052] Compared with Example 2, the material of this comparative example is sucrose carbon microspheres not coated with asphalt.

[0053] The preparation method of the hard carbon material comprises the following specific steps: (1) Preparation of porous sucrose carbon microspheres: Weigh 4 g of sucrose and dissolve it in 60 mL of deionized water to obtain a 6 wt% sucrose aqueous solution. The sucrose aqueous solution was stirred at room temperature until completely dissolved, and then subjected to hydrothermal reaction at 180°C for 12 h to obtain black powdery carbon microspheres.

[0054] The obtained carbon microspheres were washed alternately with 100 mL of ethanol / deionized water, filtered, and dried at 80° C. for 14 h to obtain the sucrose carbon microspheres.

[0055] (2) High temperature sintering to prepare hard carbon materials: The sucrose carbon microspheres obtained in step (1) are ground into powder, placed in a tube furnace and sintered at 1200° C. with a holding time of 2 h and a heating rate of 4° C. / min to obtain the composite hard carbon material.

[0056] The hard carbon material obtained in this comparative example is used as a negative electrode material in a sodium ion battery, and the obtained first-cycle discharge capacity is 413 mAh / g, and the first-cycle coulombic efficiency is 51%. Comparative Example 2

[0057] The difference from Example 2 is that in step (2), the weight ratio of sucrose carbon microspheres to petroleum asphalt is 1:0.1.

[0058] The rest is the same as Example 2.

[0059] The composite hard carbon material obtained in this comparative example is used as a negative electrode material for a sodium ion battery, and the obtained first-cycle discharge capacity is 402 mAh / g, and the first-cycle coulombic efficiency is 65.2%. Comparative Example 3

[0060] The difference from Example 2 is that in step (2), the weight ratio of sucrose carbon microspheres to petroleum asphalt is 1:1.2.

[0061] The rest is the same as Example 2.

[0062] The composite hard carbon material obtained in this comparative example is used as a negative electrode material in a sodium ion battery, and the obtained first-cycle discharge capacity is 320.5 mAh / g, and the first-cycle coulombic efficiency is 62%. Comparative Example 4

[0063] The difference from Example 2 is that the asphalt in step (2) is coal asphalt.

[0064] The rest is the same as Example 2.

[0065] The coal tar pitch has a number average molecular weight of 935 g / mol, a softening point of 120°C, and a density of 0.98 g / cm³.

[0066] After testing, it was found that the electrochemical performance of sodium ion batteries using this material as the negative electrode fluctuated greatly. Comparative Example 5

[0067] The difference from Example 2 is that glucose is used in step (1).

[0068] The rest is the same as Example 2.

[0069] The composite hard carbon material obtained in this comparative example is used as a negative electrode material in a sodium ion battery, and the obtained first-cycle discharge capacity is 334 mAh / g, and the first-cycle coulombic efficiency is 74%.

Claims

1. A composite hard carbon material for sodium ion batteries, characterized in that: The composite hard carbon material contains sucrose carbon microsphere aggregates with a conductive network; the outer surface of the sucrose carbon microspheres is a smooth petroleum asphalt soft carbon layer, and the sucrose carbon microspheres have curved graphite domains inside.

2. The composite hard carbon material for sodium ion batteries according to claim 1, characterized in that The particle size of the sucrose carbon microsphere aggregates is 4-10 μm.

3. The composite hard carbon material for sodium ion batteries according to claim 1, characterized in that The particle size of the sucrose carbon microspheres is 1-2 μm.

4. The composite hard carbon material for sodium ion batteries according to claim 1, characterized in that The average thickness of the petroleum asphalt soft carbon layer is 10-15nm.

5. The composite hard carbon material for sodium ion batteries according to claim 1, characterized in that The porosity of the sucrose carbon microspheres is in the range of 0.01 cm 3 / g-0.05cm 3 / g, specific surface area 150m 2 / g-180m 2 / g, pore size is 0.5-5nm.

6. The composite hard carbon material for sodium ion batteries according to claim 1, characterized in that The sucrose carbon microsphere petroleum asphalt has a number average molecular weight of 400-5000 g / mol, a softening point of 180-280° C., and a density of 1.02-1.04 g / cm³.

7. A method for preparing a composite hard carbon material for sodium ion batteries according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Preparation of porous sucrose carbon microspheres: Weigh sucrose and dissolve it in deionized water to obtain a sucrose aqueous solution with a concentration of 1-10 wt%; The sucrose aqueous solution was stirred at room temperature until completely dissolved, and then subjected to hydrothermal reaction at 160-200°C for 8-16 hours to obtain black powdery carbon microspheres; The obtained carbon microspheres are washed, filtered, and dried to obtain the sucrose carbon microspheres; (2) Asphalt liquid phase coated sucrose carbon microspheres: First, the sucrose carbon microspheres obtained in step (1) and petroleum asphalt are added to an ethanol aqueous solution in a weight ratio of 1:(0.2-1); Then, the mixture is stirred and evaporated to dryness at 40-80°C, and then dried at 70-120°C for 12-24 hours to obtain petroleum asphalt-coated sucrose carbon microspheres; (3) High temperature sintering to prepare composite hard carbon materials: The petroleum asphalt-coated sucrose carbon microspheres obtained in step (2) are ground into powder, placed in a tube furnace and sintered at 1100-1400° C., with a holding time of 1-4 h and a heating rate of 2-7° C. / min; and the composite hard carbon material is obtained.

8. The method for preparing a composite hard carbon material for sodium ion batteries according to claim 7, characterized in that: The drying temperature in step (1) is 70-120° C., and the drying time is 12-24 hours.

9. The method for preparing a composite hard carbon material for sodium ion batteries according to claim 7, characterized in that: The volume ratio of ethanol to deionized water in the ethanol-water solution in step (2) is 1:1.

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