A high-platform capacity lignin-based hard carbon material, its preparation and application in sodium-ion batteries

Abstract

The application discloses a high-platform-capacity lignin-based hard carbon material and preparation and application thereof in sodium ion batteries. The lignin is rich in oxygen-containing functional groups, which are used for adsorbing zinc ions; the zinc is uniformly dispersed in the lignin molecules in the form of atoms; the generated ZnO agglomeration growth is inhibited through the uniform distribution of the zinc and the three-dimensional network structure of the lignin; the size of the nano ZnO serving as a template is uniform and the nano ZnO can be highly dispersed in the carbon material; the carbon material with high specific surface area and uniform pore structure is prepared; and the open pores are converted into closed pores under high-temperature carbonization, the closed pore capacity of the material is improved, and the prepared lignin-based hard carbon material has an extremely high platform capacity.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a high-platform-capacity lignin-based hard carbon material, its preparation method, and its application in sodium-ion batteries. Background Technology

[0002] Due to increasing demand for lithium resources and the scarcity of natural resources, lithium-ion batteries are in short supply in the market. Sodium ions have similar properties to lithium ions, and sodium has the advantages of abundant resources, wide distribution, and low cost, making sodium-ion batteries the most promising supplement to lithium-ion batteries.

[0003] Negative electrode materials for sodium-ion batteries include alloys, metal oxides, and carbon-based materials. Among these, hard carbon, a type of carbon-based material, stands out due to its high reversible specific capacity (~300 mAh g⁻¹). -1 The balance between low plateau potential and long cycle life makes hard carbon a promising candidate for practical applications in sodium-ion batteries.

[0004] Hard carbon refers to carbon materials that are difficult to graphitize even at high temperatures of 2500℃. It consists of curved graphene sheets and amorphous carbon structures. It is generally believed that the sodium storage mechanism of hard carbon consists of two parts: the capacity in the ramp region above 0.1V comes from the intercalation of sodium ions within the graphite domain and their adsorption on defects, while the capacity in the plateau region below 0.1V comes from the filling of sodium clusters in closed pores. The high plateau capacity (<0.1V) in sodium-ion batteries has significant advantages in improving energy density, fast charge / discharge performance, cycle stability, and optimizing energy storage efficiency.

[0005] Improving the closed-pore volume of hard carbon is key to increasing platform capacity. The template method, by adjusting the size of the template, controls the pore size and distribution within the carbon material, and is an effective way to construct a closed-pore structure. Chinese patent application CN118684227A discloses a method for preparing a negative electrode material for sodium-ion batteries. This patent uses ZnO as an activator, physically mixes it with coal powder, and ball-mills the mixture to obtain a final product. The mixture is then carbonized at high temperature to prepare a ZnO-activated pore-forming lignin-based hard carbon material. The hard carbon material prepared by this method has a capacity of 351 mAh g / g. -1 The high specific capacity. However, during the ball milling process of ZnO and coal powder, oxygen-containing functional groups are easily introduced; at the same time, the directly added nano-ZnO, due to its large size, will significantly etch the carbon material, thereby generating a large specific surface area and leading to an increase in ramp capacity. Meanwhile, the plateau capacity is only 175 mAh g. -1 Upgraded to 210mAh g -1 This is not conducive to increasing the platform's capacity.

[0006] Existing strategies for constructing closed-pore structures often involve two or more cumbersome steps. Furthermore, the removal of hard templates and certain activators requires the use of solvents such as hydrochloric acid, sulfuric acid, and hydrofluoric acid, making it difficult to simultaneously achieve industrial production goals such as low cost, process simplicity, and environmental friendliness. In addition, using metal ions from precursor molecules as template sources easily leads to template particle agglomeration and growth, resulting in excessively large and unevenly distributed template pores. Adding external templates of fixed sizes often involves multiple steps, easily introducing defect sites and increasing unnecessary specific surface area, thus failing to obtain hard carbon materials with high plateau capacity. Therefore, the method of template introduction, its size, and its dispersion degree play a crucial role in controlling the closed-pore structure of hard carbon and obtaining hard carbon materials with high plateau capacity.

[0007] Therefore, there is a need to develop a preparation method that has no impact on template introduction, uniform template size, high dispersion, low precursor raw material cost, simple process, and is also environmentally friendly. Summary of the Invention

[0008] To address the problems of low plateau capacity ratios in existing hard carbon material preparation methods, and the difficulty in simultaneously achieving important industrialization indicators such as controllable pore structure, low cost, simple preparation route, and environmental friendliness in increasing hard carbon plateau capacity, this invention aims to provide a method for preparing lignin-based hard carbon materials with high plateau capacity. Specifically, this method involves lignin adsorbing zinc salts to generate in-situ zinc templates for pore creation, thereby controlling the closed-pore structure of the hard carbon.

[0009] This invention utilizes the abundant oxygen-containing functional groups of lignin to adsorb zinc ions. Zinc is uniformly dispersed in lignin molecules in an atomic manner. By uniformly distributing zinc and using the three-dimensional network structure of lignin to inhibit the growth of ZnO agglomerates, the nano-ZnO used as a template is ensured to be uniform in size and highly dispersed in the carbon material. This produces a carbon material with high specific surface area and uniform pore structure. Furthermore, the open pores are transformed into closed pore structures under high-temperature carbonization, which improves the closed pore volume of the material and gives the prepared lignin-based hard carbon material an extremely high plateau capacity.

[0010] Another object of the present invention is to provide a high-platform-capacity lignin-based hard carbon material prepared by the above preparation method.

[0011] Another object of the present invention is to provide the above-mentioned high-platform-capacity lignin-based hard carbon material as an anode material for sodium-ion batteries.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] A method for preparing a high-platform-capacity lignin-based hard carbon material includes the following steps:

[0014] (1) Disperse lignin in an aqueous solution of zinc salt, heat and stir, filter, and dry to obtain a lignin-adsorbed zinc salt precursor.

[0015] (2) The precursor is carbonized in one step under an inert gas atmosphere to obtain lignin-based hard carbon material.

[0016] Preferably, in the zinc salt aqueous solution of step (1), the zinc salt is at least one of zinc acetate and zinc gluconate.

[0017] Preferably, the mass concentration of the zinc salt aqueous solution in step (1) is 5-20 g / L; more preferably, it is 10 g / L.

[0018] Preferably, the mass ratio of lignin to zinc salt in step (1) is 12:1 to 4:1; more preferably, it is 6:1.

[0019] Preferably, the heating and stirring temperature in step (1) is 50-100°C and the time is 0.5-24h; more preferably, the heating and stirring temperature is 70°C and the time is 1-16h; the most preferred time is 1-4h.

[0020] Preferably, the mass ratio of lignin to adsorbed zinc salt in step (1) is 30:1 to 10:1; more preferably, it is 17:1 to 10:1; and most preferably, it is 17:1 to 12.5:1.

[0021] Preferably, the heating rate of the one-step carbonization in step (2) is 1 to 30 °C / min, and the flow rate of the inert gas is 2 to 100 mL / min; more preferably, the heating rate of the one-step carbonization is 5 °C / min, and the flow rate of the inert gas is 50 mL / min.

[0022] Preferably, the temperature of the one-step carbonization in step (2) is 1200-1700℃ and the time is 1-4h; more preferably, the temperature of the one-step carbonization is 1200-1600℃ and the time is 4h; most preferably, the temperature of the one-step carbonization is 1400-1600℃.

[0023] Preferably, the inert gas in step (2) is at least one of nitrogen, argon and helium.

[0024] Preferably, the lignin in step (1) is at least one of alkali lignin, enzymatically hydrolyzed lignin, and lignin sulfonate; the enzymatically hydrolyzed lignin is the residue of enzymatically hydrolyzed lignin obtained from the bio-smelting process; the alkali lignin is alkali lignin extracted from black liquor of papermaking; and the lignin sulfonate is lignin sulfonate extracted from pulping liquor of the sulfite process.

[0025] Preferably, the drying temperature in step (1) is 80-100°C and the time is 12-36 hours.

[0026] The high-platform-capacity lignin-based hard carbon material prepared by the above method.

[0027] The above-mentioned high-platform-capacity lignin-based hard carbon material is used in sodium-ion batteries.

[0028] The high-capacity lignin-based hard carbon material of this invention is used to fabricate the negative electrode of a sodium-ion battery: Lignonin-based hard carbon material (active material), acetylene black conductive agent, and polyvinylidene fluoride (PVDF) binder are weighed in a mass ratio of 8:1:1. PVDF is dissolved in an appropriate amount of 1-methyl-2-pyrrolidone (NMP) and stirred until completely dissolved. Then, the uniformly ground active material and acetylene black are added to the above solution, and stirring is continued to ensure uniform mixing of the slurry. The slurry is then uniformly coated onto a circular copper foil (12 mm in diameter), dried in a vacuum oven at 100°C, and finally flattened on a tablet press with a pressure of 10 MPa to obtain the electrode sheet.

[0029] The prepared electrode sheets, sodium sheets, and separator were assembled into a CR2025 button-type sodium-ion battery in a glove box filled with high-purity argon gas. The electrolyte was a 1 mol / L NaPF6 DME electrolyte. The charge-discharge performance and cycle stability of the sodium-ion battery were tested using a battery testing system.

[0030] The method described in this invention enables the construction of high closed pore volume in lignin-based hard carbon, providing abundant filling sites for sodium ions in the closed pores of hard carbon, thereby achieving a high plateau capacity of hard carbon anode in sodium-ion batteries.

[0031] The high platform capacity lignin-based hard carbon material of this invention has a specific surface area of ​​2-8 m². 2 g -1 It has abundant closed pores, with a pore volume of 0.3–0.5 cm. 3 g -1 The average size of the closed pores is 1–3 nm; sodium-ion half-cells were assembled and tested in 1 mol / L NaPF6 DME electrolyte, and the results were obtained at a current density of 50 mA·g. -1 It exhibits a capacity of 200–300 mAh g. -1 High platform capacity; hard carbon prepared from 153 mg of zinc provides a capacity of up to 358 mAh g. -1 .

[0032] This invention aims to utilize lignin, rich in oxygen-containing functional groups and possessing a three-dimensional network structure, to adsorb zinc ions. Zinc is uniformly dispersed at the atomic level within the lignin molecules. During carbonization, the three-dimensional network structure of lignin inhibits the aggregation and growth of ZnO, generating a highly dispersed ZnO template to etch and create pores in the carbon material, thereby improving the specific surface area and pore structure uniformity of the carbon material. At temperatures above 900℃, ZnO undergoes carbothermic reduction with C, further activating and creating pores in the carbon material. Simultaneously, the ZnO template is self-removed, and the pores are subsequently sealed at high temperatures, thus preparing a hard carbon anode material with high closed-pore volume. This method not only uses environmentally friendly and inexpensive lignin and zinc acetate as precursor materials but also enables one-step calcination preparation of hard carbon materials with high closed-pore volume without the need for additional acid or alkali solutions to remove the template. The hard carbon anode prepared by this method not only possesses a rich closed-pore structure but also exhibits excellent electrochemical performance.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] (1) This invention utilizes lignin, which is abundant, inexpensive and contains abundant oxygen-containing functional groups to provide active sites, as a carbon source. By adsorbing zinc ions to generate templates for pore formation, the open pores are transformed into closed pores at high temperature, thus preparing a hard carbon anode material with small block size, large interlayer spacing and high closed pore volume, thereby improving the electrochemical performance of lignin-based hard carbon.

[0035] (2) The present invention uses the method of lignin adsorbing zinc ions to prepare the precursor. The oxygen-containing functional groups of lignin adsorb and coordinate zinc ions, and zinc is dispersed in lignin molecules at the atomic level. Through the uniform distribution of zinc ions and the in-situ generation of ZnO template, the specific surface area and pore structure uniformity of carbon materials are improved.

[0036] (3) The present invention utilizes the three-dimensional network structure of lignin to effectively inhibit the agglomeration and growth of ZnO, ensuring the high dispersion of nano ZnO in the carbon matrix, and avoiding the agglomeration of ZnO nanoparticles into large-sized particles, which would require excessive etching of carbon materials and result in the formation of large-pore structures that cannot be closed at high temperatures.

[0037] (3) This invention uses lignin, which can adsorb zinc ions, as a precursor. The generated ZnO template performs two pore-forming processes on the carbon material. Specifically, during the heating process, the ZnO template etches pores in the carbon material at 600–800℃ and precipitates from the carbon matrix. Above 900℃, ZnO undergoes a reduction reaction with carbon, further activating and forming pores in the carbon material. The two pore-forming processes produce a rich open-pore structure, which is beneficial for increasing the closed pore volume at high temperatures.

[0038] (4) The hard carbon anode prepared by this invention not only increases the closed pore volume, but also has the advantage of large interlayer spacing. The reduction reaction between ZnO nanoparticles and carbon not only provides activation and pore-forming effect for carbon materials, but also increases their interlayer spacing, providing a channel for sodium ions to be inserted into the hard carbon anode. Attached Figure Description

[0039] Figure 1 The image shows the intermediate carbon product of the lignin-based hard carbon from Example 1 at 600°C (AL-Zn-600).

[0040] Figure 2 The image shows the intermediate carbon product of the lignin-based hard carbon from Example 1 at 800°C (AL-Zn-800).

[0041] Figure 3 The image shows the XRD pattern of the lignin-based hard carbon material (HC-Zn-1600) from Example 1.

[0042] Figure 4 Raman diagram of lignin-based hard carbon material (HC-Zn-1600) in Example 1.

[0043] Figure 5 Example 1 uses lignin-based hard carbon material (HC-Zn-1600) as the negative electrode in a sodium-ion battery at 0.05 A·g. -1 The second charge-discharge curve at current density.

[0044] Figure 6 Example 1 shows the curve of the specific capacitance of lignin-based hard carbon material (HC-Zn-1600) used as the negative electrode of a sodium-ion battery as a function of current density.

[0045] Figure 7 Comparison of the electrochemical performance of hard carbon materials (HC-Zn-1600, HCS-Zn-1600 and HCB-Zn-1600) prepared in Example 1, Comparative Example 1 and Comparative Example 2 (different carbon sources).

[0046] Figure 8 Comparative Example 3: Lignin-based hard carbon material (HC-1600) was used as the negative electrode in a sodium-ion battery at 0.05 A·g. -1 The second charge-discharge curve at current density.

[0047] Figure 9 The curve of specific capacitance versus current density for Comparative Example 3, which uses lignin-based hard carbon material (HC-1600) as the negative electrode of a sodium-ion battery.

[0048] Figure 10 Example 1: A lignin-based hard carbon material (HC-Zn-1600) was used as the negative electrode in a sodium-ion battery at 1 A·g-1 Cyclic curves at current density.

[0049] Figure 11 This is a SEM image of the lignin-based hard carbon precursor (AL-Zn) from Example 1.

[0050] Figure 12 The image shows the XRD pattern of the lignin-based hard carbon precursor (AL-Zn) from Example 1. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0052] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0053] Example 1

[0054] (1) Prepare 100 mL of 10 g / L zinc acetate solution, add 6 g of alkali lignin to the zinc acetate solution, and stir in an oil bath at 70 °C for 4 h until uniformly mixed to obtain lignin with an adsorption rate of 8%.

[0055] (2) Filter the suspension in step (1) to obtain lignin after adsorbing zinc ions, which is named AL-Zn.

[0056] (3) Place the AL-Zn obtained in step (2) in a 90℃ oven for 24 hours to obtain the dried AL-Zn precursor.

[0057] (4) The AL-Zn precursor in step (3) was heated to 1600℃ for 4h under a nitrogen atmosphere and a gas flow rate of 50mL / min, and the temperature was increased at a rate of 5℃ / min to obtain in-situ zinc template-assisted preparation of alkali lignin-based hard carbon, named HC-Zn-1600.

[0058] The EDS and XRD of the AL-Zn precursor are as follows: Figure 11 and Figure 12 As shown. Figure 11 It can be observed that zinc is uniformly dispersed in lignin, and no diffraction peaks of ZnO or Zn metal are observed in the XRD pattern of AL-Zn, indicating that after lignin adsorbs zinc salt, zinc is dispersed in lignin molecules in the form of atoms.

[0059] Heating the AL-Zn precursor to 600℃ and 800℃ yielded intermediate carbon products of HC-Zn, named AL-Zn-600 and AL-Zn-800, respectively. Scanning tunneling microscopy (SEM) images of AL-Zn-600 and AL-Zn-800 are shown below. Figure 1 and Figure 2 As shown. Figure 1 It can be observed that at 600℃, ZnO begins to etch pores in the carbon layer and gradually precipitates from the carbon matrix. At this time, the average size of ZnO is about 100nm. Figure 2 It can be seen that when the temperature rises to 800℃, the ZnO template further etches the carbon layer to create pores, which disperses the carbon material. The average size of ZnO is about 110nm, and there is no obvious agglomeration growth, thus avoiding the formation of open pores that are difficult to close due to excessive etching of the carbon material.

[0060] X-ray diffraction (XRD) and Raman spectroscopy (Raman) patterns of HC-Zn-1600 hard carbon anode are shown below. Figure 3 and Figure 4 As shown, Figure 3 Two broad peaks appear near 23.9° and 43.6°, corresponding to the (002) and (100) crystal planes of the carbon material. The interlayer spacing of HC-Zn-1600 was calculated to be 0.372 nm using Bragg's equation fitting, while the La value of the carbon material was 5.45 nm and the Lc value was 1.08 nm. The Ic of the carbon material was calculated using fitting. D / I G The value is 1.75. This indicates that HC-Zn-1600 has a disordered carbon layer structure and a large interlayer spacing, which is conducive to the transport of sodium ions.

[0061] The prepared sodium-ion battery electrode sheet was used as the working electrode, the sodium metal sheet was used as the counter electrode, and 1 mol / L NaPF6 (DME as solvent) was used as the electrolyte to assemble a sodium-ion half cell. The sodium-ion storage performance of HC-Zn-1600 was tested. DME is ethylene glycol dimethyl ether.

[0062] Figure 5 HC-Zn-1600 was used as the negative electrode in a sodium-ion battery at 0.05 A·g -1 The second charge-discharge curve at the current density. At 0.05 A·g -1 At a current density of [value missing], HC-Zn-1600 achieves a plateau capacity of up to 271 mAh·g in the second cycle. -1 The platform's capacity accounts for 75.7%.

[0063] Figure 6 The graph shows the specific capacitance of HC-Zn-1600 as a negative electrode in a sodium-ion battery, as a function of current density. (At 0.05 A·g) -1At a current density, HC-Zn-1600 has 358 mAh·g -1 The specific capacity is at 5 A·g -1 At a current density, it has 87 mAh·g -1 The specific capacity indicates that HC-Zn-1600 exhibits good rate performance when used as the negative electrode in sodium-ion batteries.

[0064] Figure 10 HC-Zn-1600 is used as the negative electrode in sodium-ion batteries, at 1 A·g -1 The graph shows the cycling performance at the specified current density. At this current density, HC-Zn-1600 retains 82% of its capacity after 2000 cycles. This indicates that HC-Zn-1600 exhibits excellent cycling stability when used as a negative electrode in sodium-ion batteries.

[0065] Example 2

[0066] (1) Prepare 100 mL of 10 g / L zinc acetate solution, add 6 g of alkali lignin to the zinc acetate solution, and stir in an oil bath at 70 °C for 1 h until uniformly mixed to obtain lignin with an adsorption rate of 6%.

[0067] (2) Filter the suspension in step (1) to obtain lignin after adsorbing zinc ions, which is named AL-Zn6.

[0068] (3) Place the AL-Zn6 obtained in step (2) in a 90℃ oven for 24 hours to obtain the dried AL-Zn6 precursor.

[0069] (4) The AL-Zn6 precursor in step (3) was heated to 1600℃ for 4h under a nitrogen atmosphere and a gas flow rate of 50mL / min, and the temperature was increased at a rate of 5℃ / min to obtain in-situ zinc template-assisted preparation of alkali lignin-based hard carbon, named HC-Zn6-1600.

[0070] Example 3

[0071] (1) Prepare 100 mL of 10 g / L zinc acetate solution, add 6 g of alkali lignin to the zinc acetate solution, and stir in an oil bath at 70 °C for 16 h until uniformly mixed to obtain lignin with an adsorption rate of 10%.

[0072] (2) Filter the suspension in step (1) to obtain lignin after adsorbing zinc ions, which is named AL-Zn10.

[0073] (3) Place the AL-Zn10 obtained in step (2) in a 90℃ oven for 24 hours to obtain the dried AL-Zn10 precursor.

[0074] (4) The AL-Zn10 precursor in step (3) was heated to 1600℃ for 4h under a nitrogen atmosphere and a gas flow rate of 50mL / min, and the temperature was increased at a rate of 5℃ / min to obtain in-situ zinc template-assisted preparation of alkali lignin-based hard carbon, named HC-Zn10-1600.

[0075] Example 4

[0076] (1) Prepare 100 mL of 10 g / L zinc acetate solution, add 6 g of alkali lignin to the zinc acetate solution, and stir in an oil bath at 70 °C for 4 h until uniformly mixed to obtain lignin with an adsorption rate of 8%.

[0077] (2) Filter the suspension in step (1) to obtain lignin after adsorbing zinc ions, which is named AL-Zn.

[0078] (3) Place the AL-Zn obtained in step (2) in a 90℃ oven for 24 hours to obtain the dried AL-Zn precursor.

[0079] (4) The AL-Zn precursor in step (3) was heated to 1400℃ and carbonized for 4h in a nitrogen atmosphere at a gas flow rate of 50mL / min and a heating rate of 5℃ / min to obtain alkali lignin-based hard carbon prepared by in-situ zinc template, named HC-Zn-1400.

[0080] Example 5

[0081] (1) Prepare 100 mL of 10 g / L zinc acetate solution, add 6 g of alkali lignin to the zinc acetate solution, and stir in an oil bath at 70 °C for 4 h until uniformly mixed to obtain lignin with an adsorption rate of 8%.

[0082] (2) Filter the suspension in step (1) to obtain lignin after adsorbing zinc ions, which is named AL-Zn.

[0083] (3) Place the AL-Zn obtained in step (2) in a 90℃ oven for 24 hours to obtain the dried AL-Zn precursor.

[0084] (4) The AL-Zn precursor in step (3) was heated to 1200℃ and carbonized for 4h in a nitrogen atmosphere at a gas flow rate of 50mL / min and a heating rate of 5℃ / min to obtain alkali lignin-based hard carbon prepared by in-situ zinc template, named HC-Zn-1200.

[0085] Example 6

[0086] The difference between this embodiment and Embodiment 1 is that the template source is zinc gluconate, and alkali lignin-based hard carbon is prepared and named HC-ZnGlu-1600.

[0087] (1) Prepare 100mL of 10g / L zinc gluconate solution, add 6g of alkali lignin to the zinc gluconate solution, and stir in an oil bath at 70℃ for 4h until uniformly mixed.

[0088] (2) Filter the suspension in step (1) to obtain lignin after adsorbing zinc ions, which is named AL-ZnGlu.

[0089] (3) Place the AL-ZnGlu obtained in step (2) in a 90℃ oven for 24 hours to obtain the dried AL-ZnGlu precursor.

[0090] (4) The AL-ZnGlu precursor in step (3) was heated to 1600℃ for 4h under a nitrogen atmosphere and a gas flow rate of 50mL / min, and the temperature was increased at a rate of 5℃ / min to obtain in-situ zinc template-assisted preparation of alkali lignin-based hard carbon, named HC-ZnGlu-1600.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is that the carbon source is starch, and starch-based hard carbon is prepared and named HCS-Zn-1600.

[0093] (1) Prepare 100mL of 10g / L zinc acetate solution, add 6g of starch to the zinc acetate solution, and stir in an oil bath at 70℃ for 4h until uniformly mixed.

[0094] (2) Filter the suspension in step (1) to obtain starch after adsorbing zinc ions, which is named St-Zn.

[0095] (3) Place the St-Zn obtained in step (2) in a 90℃ oven for 24 hours to obtain the dried St-Zn precursor.

[0096] (4) The St-Zn precursor in step (3) was heated to 1600℃ for 4h under a nitrogen atmosphere and a gas flow rate of 50mL / min, and the temperature was increased at a rate of 5℃ / min to obtain in-situ zinc template-assisted preparation of alkali lignin-based hard carbon, named HCS-Zn-1600.

[0097] Comparative Example 2

[0098] The difference between this comparative example and Example 1 is that the carbon source is bamboo powder, and bamboo powder-based hard carbon is prepared and named HCB-Zn-1600.

[0099] (1) Prepare 100mL of 10g / L zinc acetate solution, add 6g of bamboo powder to the zinc acetate solution, and stir in an oil bath at 70℃ for 4h until uniformly mixed.

[0100] (2) Filter the suspension in step (1) to obtain bamboo powder after adsorbing zinc ions, which is named Ba-Zn.

[0101] (3) Place the Ba-Zn obtained in step (2) in a 90℃ oven for 24 hours to obtain the dried Ba-Zn precursor.

[0102] (4) The Ba-Zn precursor in step (3) was heated to 1600℃ for 4h under a nitrogen atmosphere and a gas flow rate of 50mL / min, and the temperature was increased at a rate of 5℃ / min to obtain in-situ zinc template-assisted preparation of alkali lignin-based hard carbon, named HCB-Zn-1600.

[0103] Comparative Example 3

[0104] This comparative example demonstrates the preparation of hard carbon by direct carbonization of lignin.

[0105] (1) Add 6g of alkali lignin to 100mL of aqueous solution and stir in an oil bath at 70℃ for 4h until uniformly mixed.

[0106] (2) Filter the suspension in step (1) to obtain alkali lignin material.

[0107] (3) Place the alkali lignin obtained in step (2) in a 90℃ oven for 24 hours to obtain dried alkali lignin.

[0108] (4) The alkali lignin from step (3) was pyrolyzed and carbonized at 1600℃ for 4 hours under a nitrogen atmosphere and a gas flow rate of 50 mL / min, with a heating rate of 5℃ / min, to obtain alkali lignin-based hard carbon, named HC-1600.

[0109] Sodium-ion battery electrode sheets prepared using HC-1600 were used as working electrodes, sodium metal sheets were used as counter electrodes, and 1 mol / L NaPF6 (DME as solvent) was used as electrolyte to assemble sodium-ion half-cells. The electrochemical performance of HC-1600 was then tested.

[0110] Figure 8 The hard carbon material HC-1600 prepared for Comparative Example 3 was used as the negative electrode in a sodium-ion battery at 0.05 A·g -1 The second charge-discharge curve at the current density. At 0.05 A·g -1 At a current density of [value missing], the plateau capacity of HC-1600 in the second cycle is only 230 mAh·g. -1 .

[0111] Figure 9 The graph shows the specific capacity of Comparative Example 3, used as the negative electrode in a sodium-ion battery, as a function of current density. (0.05 A·g) -1At a current density, HC-1600 has a capacity of 306 mAh·g -1 The specific capacity is at 5 A·g -1 At a current density, it has 46 mAh·g -1 Specific capacity.

[0112] Figure 5 and Figure 8 This indicates that the reversible capacity of lignin-based hard carbon obtained by direct carbonization decreases in the absence of zinc salt as a template agent. The difference in specific capacity between HC-1600 and HC-Zn-1600 is mainly due to plateau capacity, suggesting that lignin adsorbing zinc salt as a template agent can create a large number of pores on the lignin precursor during carbonization. This abundant porosity facilitates the formation of closed pores during high-temperature carbonization, thereby increasing the plateau capacity and specific capacity of the lignin-based hard carbon.

[0113] Comparative Example 4

[0114] (1) Add 6g of alkali lignin to 100mL of aqueous solution and stir in an oil bath at 70℃ for 4h until uniformly mixed.

[0115] (2) Filter the suspension in step (1) to obtain alkali lignin material.

[0116] (3) Place the alkali lignin obtained in step (2) in a 90℃ oven for 24 hours to obtain dried alkali lignin.

[0117] (4) The alkali lignin from step (3) was heated to 1400℃ for 4 hours under a nitrogen atmosphere and a gas flow rate of 50 mL / min, to obtain alkali lignin-based hard carbon, named HC-1400.

[0118] Comparative Example 5

[0119] (1) Add 6g of alkali lignin to 100mL of aqueous solution and stir in an oil bath at 70℃ for 4h until uniformly mixed.

[0120] (2) Filter the suspension in step (1) to obtain alkali lignin material.

[0121] (3) Place the alkali lignin obtained in step (2) in a 90℃ oven for 24 hours to obtain dried alkali lignin.

[0122] (4) The alkali lignin from step (3) was pyrolyzed and carbonized at 1200℃ for 4 hours under a nitrogen atmosphere and a gas flow rate of 50 mL / min, with a heating rate of 5℃ / min, to obtain alkali lignin-based hard carbon, named HC-1200.

[0123] Comparative Example 6

[0124] The difference between this comparative example and Example 1 is that: alkali lignin and zinc acetate are physically mixed in a solid phase to prepare alkali lignin-based hard carbon, named HC-Zn-1600-S.

[0125] (1) Mix 6g of alkali lignin with 1g of zinc acetate in a solid phase and grind for 1 hour until uniformly mixed.

[0126] (2) The mixture in step (1) was heated to 1600℃ for 4h under a nitrogen atmosphere and a gas flow rate of 50mL / min, and the temperature was increased at a rate of 5℃ / min to obtain alkali lignin-based hard carbon, named HC-Zn-1600-S.

[0127] The reversible capacity and test current density in Table 1 are 50 mA·g. -1 The specific surface area was obtained by fitting nitrogen adsorption and desorption data using the BET model of the material, and the diameter and volume of the closed pores were obtained by fitting the SAXS test results.

[0128] Table 1 shows the interlayer spacing, specific surface area, closed pore diameter, closed pore volume, plateau capacity, and specific capacity (test current density 50 mA·g) of the hard carbon samples prepared by the above embodiments and comparative examples. -1 A comparison of ).

[0129] Table 1

[0130]

[0131] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-platform-capacity lignin-based hard carbon material, characterized in that, Includes the following steps: (1) Disperse lignin in an aqueous solution of zinc salt, heat and stir at 50-100℃ for 0.5-24h, filter, and dry to obtain a lignin-adsorbed zinc salt precursor; (2) The precursor is carbonized in one step under an inert gas atmosphere to obtain lignin-based hard carbon material; The mass ratio of lignin to adsorbed zinc salt in step (1) is 30:1 to 10:1; In step (1), the zinc salt in the aqueous solution is at least one of zinc acetate and zinc gluconate; The carbonization temperature in step (2) is 1200-1700℃, and the time is 1-4h.

2. The method for preparing a high-platform-capacity lignin-based hard carbon material according to claim 1, characterized in that, The mass ratio of lignin to zinc salt in step (1) is 12:1 to 4:

1.

3. The method for preparing a high-platform-capacity lignin-based hard carbon material according to claim 2, characterized in that, The mass ratio of lignin to adsorbed zinc salt in step (1) is 17:1 to 10:1; The heating and stirring time in step (1) is 1 to 16 hours.

4. The method for preparing a high-platform-capacity lignin-based hard carbon material according to claim 1, characterized in that, The heating rate of the one-step carbonization in step (2) is 1 to 30 °C / min, and the flow rate of the inert gas is 2 to 100 mL / min.

5. The method for preparing a high-platform-capacity lignin-based hard carbon material according to claim 4, characterized in that, The carbonization temperature in step (2) is 1200-1600℃.

6. The method for preparing a high-platform-capacity lignin-based hard carbon material according to claim 1, characterized in that, The lignin mentioned in step (1) is at least one of alkali lignin, enzymatic hydrolyzed lignin, and lignin sulfonate; The mass concentration of the zinc salt aqueous solution in step (1) is 5-20 g / L.

7. The method for preparing a high-platform-capacity lignin-based hard carbon material according to claim 1, characterized in that, The inert gas in step (2) is at least one of nitrogen, argon and helium; The drying temperature in step (1) is 90°C and the time is 24 hours.

8. A high-platform-capacity lignin-based hard carbon material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the high platform capacity lignin-based hard carbon material as described in claim 8 in sodium-ion batteries.

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