A cellulose-based hard carbon composite material and its preparation method and application

Abstract

The present invention provides a cellulose-based hard carbon composite material, and a preparation method and application thereof. The hard carbon composite material includes an inorganic oxide pore plugger, wherein the inorganic oxide plugs the open pores and converts them into closed pores, and the inorganic oxide is one or more of aluminum oxide, silicon oxide and calcium oxide. The cellulose and the inorganic oxide are uniformly mixed by ball milling and pyrolyzed under an inert atmosphere. The present invention uses cellulose as a carbon source, and has the advantages of a wide source of raw materials, low cost, simple process and environmental friendliness. The obtained hard carbon composite material exhibits structural characteristics such as abundant closed pores, reduced specific surface area and enlarged carbon layer spacing. While providing abundant active sites, it promotes the transmission of sodium ions and exhibits excellent structural stability. At a current density of 0.02 A / g, the first-week reversible capacity reaches 341.9 mAh / g, the first-week coulombic efficiency reaches 82.4%, and the capacity retention rate is 82.0% after 500 cycles at 0.5 A / g.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium battery materials, and in particular relates to a cellulose-based hard carbon composite material and a preparation method and application thereof. Background Art

[0002] In recent years, sodium-ion batteries have rapidly developed in the field of large-scale energy storage due to their advantages such as abundant sodium resources and low cost. This has promoted the exploration of commercially promising anode materials. Among the various reported anode materials, hard carbon has abundant sodium storage sites, low sodium storage potential, and good cycle stability, making it one of the most commercially promising anode materials for sodium-ion batteries. In order to achieve large-scale production and application, it is also necessary to find suitable hard carbon material precursors. Cellulose, as the most abundant natural polymer, has the advantages of wide availability, renewability, and low price. It is a high-quality carbon source for the preparation of hard carbon anode materials.

[0003] The general chemical formula of cellulose is (C6H 10 O5) n , containing rich heteroatoms. During high-temperature pyrolysis, heteroatoms will escape from the system in the form of volatiles. This process will introduce a large number of open pore structures, so the specific surface area and defect content of cellulose-based hard carbon are generally high. When cellulose-based hard carbon is used as the negative electrode of a sodium-ion battery, a large number of open pores and defects enhance the adsorption behavior of sodium ions in the voltage slope region and increase the contact area between the material and the electrolyte, thereby increasing the capacity of the slope region and reducing the first-cycle coulomb efficiency, which is not conducive to the improvement of the battery energy density. In order to effectively solve such problems, it is possible to consider converting open pores into closed pores and designing negative electrode materials with high platform capacity and high first-cycle coulomb efficiency. Currently, commonly used pore conversion strategies include increasing the pyrolysis temperature and deposition (including chemical vapor deposition and atomic layer vapor deposition), but the implementation of these methods requires expensive equipment or complex processing technology, resulting in high overall costs and difficult to meet actual industrial applications. In addition, higher pyrolysis temperatures will also reduce the carbon layer spacing of hard carbon, which is not conducive to the transmission and storage of sodium ions.

[0004] Therefore, developing a simple, low-cost and effective strategy to convert open pores into closed pores is crucial for designing hard carbon anodes with high sodium storage capacity and high first-cycle coulombic efficiency. Summary of the Invention

[0005] In response to the problems existing in the prior art, the first purpose of the present invention is to provide a cellulose-based hard carbon composite material, including an inorganic oxide pore plugger, which plugs open pores and converts them into closed pores. The inorganic oxide is one or more of aluminum oxide, silicon oxide and calcium oxide.

[0006] The specific surface area of ​​the hard carbon composite material is 1-30m2 / g, and the true density is 1.90-2.15g / cm 3 The distance between carbon layers is between 0.375-0.395nm.

[0007] The carbon interlayer spacing of cellulose-based hard carbon composites is 0.001-0.021nm larger than that of cellulose-based hard carbon materials.

[0008] The composite material has a large number of closed-pore structures, a small specific surface area and an enlarged carbon layer spacing, which provides abundant active sites, reduced interfacial resistance and enlarged transmission channels for the storage of sodium ions, ultimately showing excellent sodium storage capacity and first-cycle coulombic efficiency.

[0009] The second object of the present invention is to provide a method for preparing the hard carbon composite material, which is prepared using cellulose as a carbon source and inorganic oxides as pore-blocking materials.

[0010] The cellulose includes one or more of microcrystalline cellulose, α-cellulose and β-cellulose.

[0011] The preparation method of the hard carbon composite material specifically comprises mixing cellulose and an inorganic oxide to form a mixture, mixing the mixture uniformly with a ball mill, and pyrolyzing the mixture at high temperature under an inert atmosphere to obtain the hard carbon composite material.

[0012] The mass ratio of the inorganic oxide in the mixture is 0.1-5wt%.

[0013] The ball milling speed is 300-500 r / min, the ball milling time is 1-3 hours, and the ball to material ratio is (15-25):1.

[0014] The pyrolysis temperature is 1000-1600° C., the pyrolysis time is 1-3 hours, the pyrolysis atmosphere is nitrogen or argon, and the heating rate is 1-5° C. / min.

[0015] The third object of the present invention is to provide the application of the above-mentioned hard carbon composite material in the negative electrode of sodium ion battery.

[0016] An active negative electrode material for a sodium ion battery is the hard carbon composite material.

[0017] A negative electrode plate for a sodium ion battery comprises a current collector, a conductive agent coated on the current collector, a binder and the hard carbon composite material.

[0018] A sodium ion secondary battery comprises the negative electrode plate of the sodium ion battery.

[0019] The present invention has the following beneficial effects:

[0020] (1) The present invention uses inorganic oxides to block the open pores generated by cellulose during the pyrolysis process, thereby preparing a hard carbon composite material with a rich closed-pore content, which provides a new idea for the design of the closed-pore structure of the hard carbon negative electrode of sodium ion batteries.

[0021] (2) The present invention uses cellulose, which is abundant in nature and widely available, as a carbon source, which not only achieves high-value utilization and conversion of low-value carbon sources, but also reduces process costs.

[0022] (3) Compared with existing technologies such as increasing the pyrolysis temperature or deposition, the present invention prepares a hard carbon composite material with excellent electrochemical properties through simple ball milling mixing and carbonization, which has the advantages of simple preparation process, low operation difficulty, low cost, and environmental friendliness.

[0023] (4) The present invention provides a hard carbon composite material using cellulose as a carbon source and an inorganic oxide as a pore-blocking material. This material can be used as a negative electrode material for sodium ion batteries and has the advantages of large reversible capacity, high first-cycle coulombic efficiency, excellent kinetic performance, and stable structure. At a current density of 0.02 A / g, the first-cycle reversible capacity is 341.9 mAh / g, the first-cycle coulombic efficiency is 82.4%, and the capacity retention rate after 500 cycles at 0.5 A / g is 82.0%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the nitrogen isothermal adsorption-desorption curve of the hard carbon material prepared in Comparative Example 1.

[0025] Figure 2 This is the XRD pattern of the hard carbon material prepared in Comparative Example 1.

[0026] Figure 3 This is the first week charge and discharge curve of the hard carbon material prepared in Comparative Example 1 at 0.02 A / g.

[0027] Figure 4 This is the first week charge and discharge curve of the hard carbon material prepared in Comparative Example 2 at 0.02 A / g.

[0028] Figure 5 This is the nitrogen isothermal adsorption-desorption curve of the composite material prepared in Example 1.

[0029] Figure 6 This is the XRD pattern of the composite material prepared in Example 1.

[0030] Figure 7 This is a charge-discharge curve of the composite material prepared in Example 1 at 0.02 A / g in the first week.

[0031] Figure 8 This is a diagram of the rate performance of the composite material prepared in Example 1.

[0032] Figure 9 This is a graph showing the cycling performance of the composite material prepared in Example 1 at 0.5 A / g.

[0033] Figure 10 This is a charge-discharge curve of the composite material prepared in Example 2 at 0.02 A / g during the first week.

[0034] Figure 11 This is a charge-discharge curve of the composite material prepared in Example 3 at 0.02 A / g in the first week.

[0035] Figure 12 This is a charge-discharge curve of the composite material prepared in Example 4 at 0.02 A / g during the first week.

[0036] Figure 13 This is a charge-discharge curve of the composite material prepared in Example 5 at 0.02 A / g in the first week.

[0037] Figure 14 This is a charge-discharge curve of the composite material prepared in Example 6 at 0.02 A / g in the first week. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below with reference to the embodiments, but the present invention is not limited thereto.

[0039] Comparative Example 1

[0040] A method for preparing a cellulose-based hard carbon negative electrode material for a sodium ion battery comprises the following steps:

[0041] (1) 5 g of microcrystalline cellulose was ball-milled in a planetary ball mill at a speed of 500 r / min, a ball-to-material ratio of 20:1, and a ball-to-material ratio of 1 h.

[0042] (2) 3 g of the ball-milled material was weighed and pyrolyzed to 1200 °C at a heating rate of 5 °C / min under an argon atmosphere, kept at this temperature for 2 h, and then cooled to room temperature to obtain a cellulose-based hard carbon material.

[0043] A small amount of the above cellulose-based hard carbon material was taken for nitrogen isothermal adsorption-desorption, true density and XRD tests. The results are as follows Figure 1 and Figure 2 As shown, the material specific surface area is 64.0m 2 / g, the true density is 2.16g / cm 3 The XRD curve shows the typical characteristics of amorphous carbon. Two broad diffraction peaks are observed near 23° and 43°, corresponding to the (002) and (100) diffraction crystal planes of the carbon material, respectively. The carbon interlayer spacing is calculated to be 0.374 nm.

[0044] The cellulose-based hard carbon prepared above was used as the negative electrode active material for the preparation of sodium ion batteries. The active material, carbon nanotubes (CNTs), and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 8:1:1 to prepare a slurry. After mixing evenly, the slurry was coated on a copper foil, and then the coated electrode sheet was placed in a vacuum oven at 100°C and dried for 12 hours. The electrode sheet was then cut into 12mm electrode sheets, and the mass loading of the active material was about 1.5mg / cm 2 . CR2032 button cells were assembled in a glove box, with metallic sodium as the counter electrode, a glass fiber membrane (Whatman, GF / F) as the separator, and a 1 mol / L electrolyte solution of NaPF6 as the solute and a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio of 1:1) as the solvent. The button cells were then subjected to constant current charge and discharge tests on a blue battery test system with a voltage range of 0.01-3 V. The test results are shown in Figure 2. Figure 3 As shown, the cellulose-based hard carbon has a first-week reversible capacity of 294.5 mAh / g and a first-week coulombic efficiency of 76.0% at a current density of 0.02 A / g.

[0045] Comparative Example 2

[0046] Cellulose was replaced with α-cellulose, and the rest of the preparation process and experimental conditions were the same as those in Comparative Example 1.

[0047] The nitrogen isothermal adsorption-desorption test method, battery assembly process and electrochemical test method are the same as those in Comparative Example 1. The specific surface area of ​​the cellulose-based hard carbon provided in this comparative example is 55.2 m 2 / g, the sodium storage performance test results are as follows Figure 4 As shown, at a current density of 0.02 A / g, the material has a first-week reversible capacity of 277.6 mAh / g and a first-week coulombic efficiency of 77.8%.

[0048] Example 1

[0049] A method for preparing a sodium ion battery hard carbon composite material comprises the following steps:

[0050] (1) Select microcrystalline cellulose as the carbon source and alumina as the inorganic oxide. Based on the mass ratio of the oxide being 3 wt %, 4.85 g of the carbon source and 0.15 g of the oxide were weighed respectively.

[0051] (2) The weighed carbon source and oxide were mixed evenly using a planetary ball mill. The ball milling speed was 500 r / min, the ball milling time was 1 h, and the ball-to-material ratio was 20:1.

[0052] (3) 3 g of the ball-milled material was weighed and pyrolyzed to 1200 °C at a heating rate of 5 °C / min under an argon atmosphere, kept at this temperature for 2 h, and then cooled to room temperature to obtain a hard carbon composite material.

[0053] A small amount of the above hard carbon composite material was taken for nitrogen isothermal adsorption-desorption, true density and XRD tests. Figure 5 As shown in the figure, compared with comparative example 1, after the introduction of alumina, the specific surface area of ​​the material increased from 64.0m 2 / g decreased to 4.9m 2 / g, while the true density value is 2.16g / cm 3 Reduced to 2.03g / cm 3 , indicating that alumina successfully blocked the open pores and converted them into closed pores. Figure 6 The XRD curve of the hard carbon showed the characteristic peak of alumina, proving the successful introduction of alumina. The (002) peak shifted to a low angle, and the carbon layer spacing was measured to be 0.384 nm, indicating that alumina expanded the carbon layer spacing of the hard carbon.

[0054] The battery assembly process and electrochemical test method are the same as those in Comparative Example 1. The first week charge and discharge results are as follows Figure 7 As shown, the hard carbon composite material provided in this embodiment has a first-week reversible capacity of 341.9 mAh / g and a first-week coulombic efficiency of 82.4% at a current density of 0.02 A / g. The conversion of a large number of open pores to closed pores reduces the contact area between the negative electrode material and the electrolyte, reduces the irreversible defective sodium storage sites, and provides abundant closed-pore sodium storage sites in the low-voltage platform area, thereby increasing the reversible capacity and first-week coulombic efficiency of the hard carbon composite material. The rate performance of the material was evaluated at different current densities (0.02-1 A / g), and the results are shown in FIG. Figure 8 The negative electrode material provided in this embodiment provides reversible capacities of 341.9, 307.1, 244.1, 155.9, 100.8, and 67.9 mAh / g at 0.02, 0.05, 0.1, 0.2, 0.5, and 1 A / g, respectively. The excellent rate performance can be attributed to the synergistic effect of larger interlayer diffusion channels, abundant closed-pore active sites, and lower interfacial resistance. Figure 9 This is the cycling performance diagram of the material at 0.5 A / g. The capacity retention rate is 82.0% after 500 cycles, and the structural stability is good.

[0055] Example 2

[0056] The mass proportion of the oxide was changed to 2 wt %, and the rest of the preparation process and experimental conditions were the same as those in Example 1.

[0057] The nitrogen isothermal adsorption-desorption test method, battery assembly process and electrochemical test method are the same as those in Comparative Example 1. The specific surface area of ​​the hard carbon composite material provided in this embodiment is 21.6 m 2 / g, the sodium storage performance test results are as follows Figure 10 As shown, at a current density of 0.02 A / g, the material has a first-week reversible capacity of 314.2 mAh / g and a first-week coulombic efficiency of 79.2%.

[0058] Example 3

[0059] The pyrolysis temperature was changed to 1300° C., and the rest of the preparation process and experimental conditions were the same as those in Example 1.

[0060] The nitrogen isothermal adsorption-desorption test method, battery assembly process and electrochemical test method are the same as those in Comparative Example 1. The specific surface area of ​​the hard carbon composite material provided in this embodiment is 2.6 m 2 / g, the sodium storage performance test results are as follows Figure 11 As shown, at a current density of 0.02 A / g, the material has a first-week reversible capacity of 339.9 mAh / g and a first-week coulombic efficiency of 84.8%.

[0061] Example 4

[0062] The inorganic oxide was replaced with silicon oxide, and the rest of the preparation process and experimental conditions were the same as those in Example 1.

[0063] The nitrogen isothermal adsorption-desorption test method, battery assembly process and electrochemical test method are the same as those in Comparative Example 1. The specific surface area of ​​the hard carbon composite material provided in this embodiment is 19.3 m 2 / g, the sodium storage performance test results are as follows Figure 12 As shown, at a current density of 0.02 A / g, the material has a first-week reversible capacity of 306.7 mAh / g and a first-week coulombic efficiency of 78.6%.

[0064] Example 5

[0065] The inorganic oxide was replaced with silicon oxide, and the mass proportion of the oxide was changed to 4 wt %. The rest of the preparation process and experimental conditions were the same as those in Example 1.

[0066] The nitrogen isothermal adsorption-desorption test method, battery assembly process and electrochemical test method are the same as those in Comparative Example 1. The specific surface area of ​​the hard carbon composite material provided in this embodiment is 8.9 m 2 / g, the sodium storage performance test results are as follows Figure 13 As shown, at a current density of 0.02 A / g, the material has a first-week reversible capacity of 347.2 mAh / g and a first-week coulombic efficiency of 83.9%.

[0067] Example 6

[0068] Cellulose was replaced with α-cellulose, and the rest of the preparation process and experimental conditions were the same as those in Example 1.

[0069] The nitrogen isothermal adsorption-desorption test method, battery assembly process and electrochemical test method are the same as those in Comparative Example 1. The specific surface area of ​​the hard carbon composite material provided in this embodiment is 17.7 m 2 / g, the sodium storage performance test results are as follows Figure 14 As shown, at a current density of 0.02 A / g, the material has a first-week reversible capacity of 324.2 mAh / g and a first-week coulombic efficiency of 83.6%.

Claims

1. A cellulose-based hard carbon composite material, characterized in that: The hard carbon composite material comprises an inorganic oxide pore plugger, wherein the inorganic oxide plugs the open pores and converts them into closed pores, and the inorganic oxide is one or more of aluminum oxide, silicon oxide and calcium oxide; the specific surface area of ​​the hard carbon composite material is 1-30 m 2 / g, true density is 1.90-2.15 g / cm 3 , the carbon layer spacing is 0.375-0.395 nm.

2. A method for preparing the hard carbon composite material according to claim 1, characterized in that: It is prepared with cellulose as carbon source and inorganic oxides as pore blocking materials.

3. The method for preparing a hard carbon composite material according to claim 2, wherein: The cellulose includes one or more of microcrystalline cellulose, α-cellulose and β-cellulose.

4. The method for preparing a hard carbon composite material according to claim 2, wherein: The method comprises the steps of mixing cellulose and inorganic oxides to form a mixture, uniformly mixing the mixture by using a ball mill, and pyrolyzing the mixture at high temperature under an inert atmosphere to obtain a hard carbon composite material.

5. The method for preparing a hard carbon composite material according to claim 4, wherein: The mass ratio of the inorganic oxide in the mixture is 0.1-5 wt%.

6. The method for preparing a hard carbon composite material according to claim 4, wherein: The ball milling speed is 300-500 r / min, and the ball milling time is 1-3 h.

7. The method for preparing a hard carbon composite material according to claim 4, wherein: The pyrolysis temperature is 1000-1600° C., and the pyrolysis time is 1-3 h.

8. Use of the hard carbon composite material according to claim 1 in a negative electrode of a sodium ion battery.

Images