A high-rate lignin-based composite hard carbon anode material, its preparation method and application

Abstract

This invention discloses a high-rate lignin-based composite hard carbon anode material, its preparation method, and its applications. The invention uses aniline and pyrrole as guest materials and lignin as the host carbon source. The composite material, after pretreatment of the host material by the guest materials, is prepared into a lignin-based hard carbon material through a one-step high-temperature carbonization process. This invention achieves the construction of high closed-pore volume and large carbon interlayer spacing in the lignin-based hard carbon, providing abundant intercalation and filling sites for sodium ions in the hard carbon layers and closed pores, thereby realizing high specific capacity and high plateau capacity of the hard carbon anode for sodium-ion batteries. The prepared hard carbon anode material exhibits high reversible specific capacity, excellent rate performance, and cycle stability. This method demonstrates the feasibility of modifying the lignin structure using intermolecular forces, realizing the high-value utilization of lignin and facilitating large-scale production.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery anode materials, specifically relating to a high-rate lignin-based composite hard carbon anode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion battery anodes include alloy materials, metal oxides, organic compounds, and carbon materials. Hard carbon in carbon materials consists of bent graphene sheets and sp... 3 Cross-linked structure composition. These graphene sheets are randomly stacked to form numerous closed nanopores, while sp 3 The cross-linked structure is rich in defects, and the closed pores and defects provide abundant storage sites for sodium ions. The sodium storage behavior of hard carbon materials can be divided into three steps: adsorption, intercalation, and filling. The adsorption and intercalation processes provide ramp capacity at potentials from 2.5V to 0.1V, while the filling process provides plateau capacity at potentials from 0.1V to 0.01V. The sodium storage rate performance of hard carbon mainly depends on the width of the carbon interlayer spacing and the degree of defects (Chemistry of Materials 2022, 34, 3489–3500). Larger interlayer spacing and abundant defects ensure faster sodium ion transport kinetics. Therefore, the wider the carbon interlayer spacing of hard carbon materials, the better their rate performance. A paper (Small 2022, 18, 2105303) reported the preparation of hard carbon nanofibers with different carbon interlayer spacings using different carbonization temperatures to study the relationship between interlayer spacing and sodium storage ramp capacity. This study used in-situ XRD and Raman spectroscopy to demonstrate that a larger carbon interlayer spacing is more conducive to sodium ion insertion into the carbon layer for storage and provides ramp capacity. Furthermore, large carbon interlayer spacing can be achieved by adding guest materials to hard carbon precursors to construct carbon layer support structures. Chinese patent application CN111072009A discloses a method for preparing a hard carbon anode for sodium-ion batteries. This patent uses a mixture of swollen heavy organic matter and a crosslinking agent, and crosslinks the two under the catalysis of Lewis acids to prepare a hard carbon material with large carbon interlayer spacing. This method is cumbersome due to the need to add swelling agents, increasing preparation costs, and the fact that many of these agents are flammable and explosive, posing a safety risk in production. Large carbon interlayer spacing can also be achieved through intermolecular forces in the precursor material. An article (Adv. Energy Mater. 2023, 2302055) reports a method for preparing a composite graphite anode material with large carbon interlayer spacing and rich surface defects by crosslinking graphene oxide with polyaniline. This method prepares a composite graphite material with large carbon interlayer spacing and nitrogen-rich edge defects by dispersing aniline monomers on the surface of graphene oxide through polymerization and crosslinking, and is applied to potassium-ion batteries. This composite graphite anode material has a capacity of 491 mAh g / L. -1The platform has high capacity and superior rate performance. However, the article mentions that the structure of polyaniline and graphene oxide not only involves amination bonding reactions but also π-π adsorption. Currently, no research has shown whether π-π adsorption between precursor molecules of hard carbon materials can regulate the structure, thereby enabling the preparation of hard carbon materials with large carbon interlayer spacing through high-temperature carbonization.

[0003] The literature (Resources Chemicals and Materials. 2023, 2, 245-251) prepared a hard carbon anode material via one-step carbonization of corn cob lignin. This hard carbon anode material suffers from a low closed-pore volume, failing to provide a large number of pore-filling active sites, thus limiting its reversible specific capacity (284 mAh g⁻¹). -1 The rate capability is relatively low, resulting in poor rate performance (at 1 Ag). -1 Its current density is 85.8 mAh g. -1 The aforementioned problems restrict the practical application of lignin-based hard carbon. Summary of the Invention

[0004] To overcome the problems of insufficient specific capacity and poor rate performance of lignin-based hard carbon, the primary objective of this invention is to provide a method for preparing high-rate lignin-based composite hard carbon anode materials.

[0005] Another objective of this invention is to provide the above-described preparation method for obtaining high-ratio lignin-based composite hard carbon anode materials.

[0006] Another object of the present invention is to provide the application of the above-mentioned high-rate lignin-based composite hard carbon anode material in sodium-ion batteries.

[0007] Simultaneously, lignin-based composite hard carbon, possessing both large interlayer spacing and high closed pore volume, is more conducive to providing more sodium storage active sites and more charge transfer active sites, thereby improving the slope capacity and rate performance of the hard carbon anode. To this end, this invention mixes lignin and aniline / pyrrole in an aqueous sodium hydroxide solution to form a mixture, dissolves ammonium persulfate in an aqueous hydrochloric acid solution to form a solution, and then adds the solution to the mixture to form a water-insoluble lignin-polyaniline / pyrrole composite. This lignin-polyaniline / pyrrole composite, after filtration, washing, and drying, serves as a precursor for lignin-based composite hard carbon, which is then prepared by high-temperature carbonization. By introducing aniline or pyrrole and binding it with the intermolecular forces between lignin molecules, the aniline or pyrrole in the system is polymerized to break the stacked structure of the lignin itself, forming a porous precursor structure. During high-temperature carbonization, with the loss of nitrogen atoms in polyaniline or polypyrrole through bond breaking, the rearrangement of carbon crystallites and the growth of carbon layers lead to the development of abundant nitrogen edge defects, large carbon interlayer spacing, and abundant closed-pore structures in hard carbon. Ultimately, the surface pore structure closes to form the closed-pore structure of hard carbon. The nitrogen-containing guest molecule-controlled lignin aggregate preparation of lignin-based composite hard carbon materials of this invention can be used in electrochemical energy storage fields such as sodium-ion battery anodes.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing a high-rate lignin-based composite hard carbon anode material includes the following steps:

[0010] (1) After mixing and dissolving lignin and nitrogen-containing monomers, an initiator solution is added to carry out a polymerization reaction to obtain a lignin nitrogen-containing polymer complex;

[0011] The nitrogen-containing monomer is at least one of aniline and pyrrole;

[0012] (2) The lignin nitrogen-containing polymer composite was carbonized in an inert gas atmosphere to obtain a lignin-based composite hard carbon material.

[0013] 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 papermaking black liquor; and the lignin sulfonate is lignin sulfonate extracted from sulfite pulping liquor.

[0014] Preferably, the mass ratio of lignin to nitrogen-containing monomer in step (1) is 1:1 to 4:1; more preferably 1:1 to 2:1; and most preferably 1:1 to 1.5:1.

[0015] Preferably, the initiator solution in step (1) is added dropwise to control the reaction rate, wherein the initiator and the nitrogen-containing monomer are of equal mass; the initiator is a persulfate, more preferably ammonium persulfate.

[0016] Preferably, the polymerization reaction in step (1) is carried out at room temperature for 10 to 14 hours; more preferably, it is carried out for 12 hours.

[0017] Preferably, the carbonization temperature in step (2) is 1300-1600℃ and the time is 2±0.5h.

[0018] Preferably, the preparation method of the high-ratio lignin-based composite hard carbon anode material includes the following steps:

[0019] (1) Disperse lignin and nitrogen-containing monomers in an alkaline aqueous solution and mix them evenly to obtain a mixture;

[0020] (2) Add the persulfate initiator to the hydrochloric acid aqueous solution and mix well to obtain the initiator solution;

[0021] (3) The initiator solution is added dropwise to the mixture in step (1) to carry out the polymerization reaction and obtain the lignin nitrogen-containing polymer complex;

[0022] (4) The lignin nitrogen-containing polymer composite was carbonized in an inert gas atmosphere to obtain a lignin-based composite hard carbon material.

[0023] More preferably, the alkali in the alkaline aqueous solution in step (1) is at least one of sodium hydroxide and potassium hydroxide; the concentration of the alkaline aqueous solution is 0.25 to 0.5 mol / L.

[0024] More preferably, the ratio of lignin to alkaline aqueous solution in step (1) is 6g:100-200mL; more preferably, it is 6g:150mL.

[0025] More preferably, the concentration of the hydrochloric acid aqueous solution in step (2) is 0.25 to 0.5 mol / L.

[0026] More preferably, the concentration of the persulfate initiator in step (2) in the hydrochloric acid aqueous solution is 1.5-6 g: 150 mL.

[0027] More preferably, after the polymerization reaction in step (3) is completed, the product mixture is filtered, washed with water and dried, wherein washing refers to rinsing the filtered product with deionized water at least 3 times; the drying temperature is 80-120℃ and the time is 12-24h.

[0028] More preferably, the inert gas in step (4) is at least one of nitrogen, helium and argon.

[0029] More preferably, the flow rate of the inert gas in step (4) is 2 to 100 mL / min; more preferably, it is 30 to 80 mL / min.

[0030] More preferably, the heating rate of carbonization in step (4) is 0.1 to 30 °C / min; more preferably, it is 1 to 5 °C / min.

[0031] This invention provides a high-ratio lignin-based composite hard carbon anode material prepared by the above-described method.

[0032] This invention provides the application of the above-mentioned high-rate lignin-based composite hard carbon anode material in sodium-ion batteries.

[0033] The method described in this invention enables the construction of high closed pore volume and large carbon interlayer spacing in lignin-based composite hard carbon, providing a large ion transport space for sodium ions in the hard carbon interlayer and providing abundant filling sites in the closed pores of hard carbon, thereby achieving high specific capacity, plateau capacity and good rate performance of hard carbon anode for sodium-ion batteries.

[0034] The resulting hard carbon material has a low open pore structure and a specific surface area of ​​less than 10 m². 2 g -1 This hard carbon at 1 mol L -1 A sodium-ion half-cell assembled with NaPF6 / DME electrolyte was tested at a current density of 50 mAg. -1 The capacity is 320-366 mAh g. -1 .

[0035] This invention aims to select a nitrogen-containing, inexpensive guest material to structurally regulate inexpensive lignin aggregates through π-π adsorption, while simultaneously achieving high-temperature pyrolytic fracture of the carbon layers, thereby preparing a hard carbon anode material with high closed-cell volume and large carbon interlayer spacing. The lignin-based composite hard carbon material prepared by regulating lignin aggregates with a nitrogen-containing guest material exhibits excellent electrochemical performance. During high-temperature carbonization, as carbon microcrystals rearrange and carbon layers grow, the carbon layers expand due to the pyrolysis of polyaniline, leading to the closure of micropores. The hard carbon anode prepared by this method not only possesses a large carbon interlayer spacing and abundant closed-cell structure but also exhibits excellent electrochemical performance.

[0036] This invention achieves the construction of high closed-pore volume and large carbon interlayer spacing in lignin-based hard carbon, providing abundant intercalation and filling sites for sodium ions in the hard carbon layers and closed pores, thereby realizing high specific capacity and high plateau capacity of the hard carbon anode for sodium-ion batteries. The prepared hard carbon anode material exhibits high reversible specific capacity, excellent rate performance, and cycle stability. This method demonstrates the feasibility of modifying the lignin structure using intermolecular forces, realizing the high-value utilization of lignin and facilitating large-scale production.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] (1) This invention utilizes lignin, an abundant and inexpensive carbon source, to regulate the structure of lignin aggregates through polyaniline / pyrrole, followed by high-temperature carbonization to prepare hard carbon anode materials, thereby improving the electrochemical performance of lignin-based composite hard carbon. Compared with other methods, lignin does not require further purification or the addition of pore-forming agents, reducing production costs and shortening the preparation process, which is beneficial for commercial production.

[0039] (2) This invention uses aniline / pyrrole as the guest material for hard carbon precursors and uses π-π adsorption to regulate the structure of lignin aggregates. It clarifies that the pathway for regulating the structure of hard carbon precursors is primarily through intermolecular force regulation via π-π adsorption. Compared with other methods, the introduction of aniline / pyrrole not only increases the carbon interlayer spacing of lignin-based composite hard carbon but also generates a large number of porous structures, providing conditions for the formation of closed-pore hard carbon during high-temperature carbonization.

[0040] (3) The hard carbon anode prepared by this invention has the advantages of large carbon interlayer spacing, high closed pore volume and high defect degree. The large interlayer spacing provides a channel for sodium ions to be inserted into the hard carbon anode, and the high closed pore volume provides a large number of active sites for sodium ions to fill the hard carbon anode. Thus, the lignin-based composite hard carbon prepared by this nitrogen-containing guest material through the regulation of lignin aggregates has high plateau capacity, reversible specific capacity, excellent rate performance and cycle stability. Attached Figure Description

[0041] Figure 1 This is the XRD pattern of lignin-based hard carbon (LPHC-1-1) from Example 1.

[0042] Figure 2 This is a Raman diagram of lignin-based hard carbon (LPHC-1-1) from Example 1.

[0043] Figure 3 Example 1 uses lignin-based hard carbon (LPHC-1-1) as the negative electrode in a sodium-ion battery at 0.05 Ag. -1 The first charge-discharge curve at current density.

[0044] Figure 4 Example 1 shows the curve of the specific capacity of lignin-based hard carbon (LPHC-1-1) used as the negative electrode of a sodium-ion battery as a function of current density.

[0045] Figure 5 Example 1 uses lignin-based hard carbon (LPHC-1-1) as the negative electrode in a sodium-ion battery at 0.5 Ag. -1 Cyclic curves at current density.

[0046] Figure 6 Example 5 shows the curve of specific capacity versus current density when lignin-based hard carbon (LPyHC-4-1) is used as the negative electrode of a sodium-ion battery.

[0047] Figure 7 This is a graph showing the specific capacity of lignin-based hard carbon (LHC) used as the negative electrode in a sodium-ion battery as a function of current density, as in Comparative Example 1. Detailed Implementation

[0048] 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.

[0049] 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.

[0050] Example 1

[0051] (1) Prepare 150 mL of 0.5 mol L -1 A sodium hydroxide solution with a molar concentration of 6 g alkali lignin and 6 g aniline were added to the sodium hydroxide solution and stirred at 25°C for 1 hour until uniformly mixed.

[0052] (2) Prepare 150 mL of 0.5 mol L -1 To prepare a hydrochloric acid solution with a molar concentration, add 6g of ammonium persulfate to the hydrochloric acid solution and stir at 25°C for 10 minutes until clear.

[0053] (3) Slowly add the solution from step (2) to the mixed solution from step (1) and stir at 25°C for 12 hours.

[0054] (4) The mixed solution in step (3) is added to a Buchner funnel for filtration and the filter is washed with deionized water to obtain the lignin polyaniline complex, which is named AL\PANI-1-1.

[0055] (5) The lignin-polyaniline composite obtained in step (4) was heated to 1300℃ for 2h under a nitrogen atmosphere and a gas flow rate of 50mL / min at a heating rate of 3℃ / min to obtain a lignin-based composite hard carbon material, named LPHC-1-1.

[0056] X-ray diffraction (XRD) and Raman spectroscopy (Raman) patterns of the LPHC-1-1 hard carbon anode are shown below. Figure 1 and Figure 2 As shown, Figure 1Two broad peaks appear near 21.5° and 44°, corresponding to the (002) and (100) crystal planes of the carbon material. Calculations show that the interlayer spacing of LPHC-1-1 is 0.396 nm, the La value of the carbon material is 3.79 nm, and the Lc value is 0.97 nm. The ID / IG value is calculated to be 0.97. This indicates that LPHC-1-1 possesses a relatively disordered carbon layer structure and a large interlayer spacing, which is beneficial for sodium ion intercalation.

[0057] LPHC-1-1, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 8:1:1. After thorough mixing, the mixture was coated onto copper foil, dried, and rolled before being cut into circular electrode sheets with a diameter of 12 mm. The prepared electrode sheet was used as the working electrode, and a sodium metal sheet was used as the counter electrode. 1 mol L... -1 Sodium-ion half-cells were assembled using NaPF6 (with DME as the solvent) as the electrolyte to test the sodium-ion storage performance of LPHC-1-1, where DME is ethylene glycol dimethyl ether.

[0058] Figure 3 LPHC-1-1 is used as the negative electrode in sodium-ion batteries at 0.05Ag. -1 The first charge-discharge curve at the current density. At 0.05Ag -1 At a current density of 500 mAh g, the discharge specific capacity of LPHC-1-1 in the first cycle is 500 mAh g. -1 The charging capacity is 355mAh g. -1 Its first-round Coulomb efficiency was 72%.

[0059] Figure 4 The graph shows the specific capacity of LPHC-1-1 used as the anode in a sodium-ion battery as a function of current density. (0.05Ag) -1 At a current density of 355 mAh g, LPHC-1-1 has a capacity of 355 mAh g. -1 The charging specific capacity is at 5Ag -1 At a current density, it has 216 mAh g -1 The specific capacity indicates that LPHC-1-1 exhibits excellent rate performance when used as the anode in sodium-ion batteries.

[0060] Figure 5 LPHC-1-1 is used as the negative electrode in sodium-ion batteries at 0.5Ag. -1 Cyclic performance diagram at current density. At 0.5 Ag -1 At the specified current density, LPHC-1-1 retains 91% of its capacity after 2000 cycles; this indicates that LPHC-1-1 exhibits excellent cycle stability when used as a negative electrode in sodium-ion batteries.

[0061] Example 2

[0062] (1) Prepare 150 mL of 0.5 mol L -1 A sodium hydroxide solution with a molar concentration of 6 g alkali lignin and 4 g aniline were added to the sodium hydroxide solution and stirred at 25 °C for 1 h until uniformly mixed.

[0063] (2) Prepare 150 mL of 0.5 mol L -1 To prepare a hydrochloric acid solution with a molar concentration, add 4g of ammonium persulfate to the hydrochloric acid solution and stir at 25°C for 10 minutes until clear.

[0064] (3) Slowly add the solution from step (2) to the mixed solution from step (1) and stir at 25°C for 12 hours.

[0065] (4) The mixed solution in step (3) is added to a Buchner funnel for filtration and the filter is washed with deionized water to obtain the lignin polyaniline complex, which is named AL\PANI-3-2.

[0066] (5) The lignin-polyaniline composite obtained in step (4) was heated to 1300℃ for 2h under a nitrogen atmosphere and a gas flow rate of 50mL / min at a heating rate of 3℃ / min to obtain a lignin-based composite hard carbon material, named LPHC-3-2.

[0067] Example 3

[0068] (1) Prepare 150 mL of 0.5 mol L -1 A sodium hydroxide solution with a molar concentration of 6 g alkali lignin and 3 g aniline were added to the sodium hydroxide solution and stirred at 25 °C for 1 h until uniformly mixed.

[0069] (2) Prepare 150 mL of 0.5 mol L -1 To prepare a hydrochloric acid solution with a molar concentration, add 3g of ammonium persulfate to the hydrochloric acid solution and stir at 25°C for 10 minutes until clear.

[0070] (3) Slowly add the solution from step (2) to the mixed solution from step (1) and stir at 25°C for 12 hours.

[0071] (4) The mixed solution in step (3) is added to a Buchner funnel for filtration and the filter is washed with deionized water to obtain the lignin polyaniline complex, which is named AL\PANI-2-1.

[0072] (5) The lignin-polyaniline composite obtained in step (4) was heated to 1300℃ for 2h under a nitrogen atmosphere and a gas flow rate of 50mL / min at a heating rate of 3℃ / min to obtain a lignin-based composite hard carbon material, named LPHC-2-1.

[0073] Example 4

[0074] (1) Prepare 150 mL of 0.5 mol L -1 To prepare a sodium hydroxide solution with a molar concentration, add 6g of alkali lignin and 1.5g of aniline to the sodium hydroxide solution and stir at 25°C for 1 hour until uniformly mixed.

[0075] (2) Prepare 150 mL of 0.5 mol L -1 To prepare a hydrochloric acid solution with a molar concentration, add 1.5 g of ammonium persulfate to the hydrochloric acid solution and stir at 25°C for 10 minutes until clear.

[0076] (3) Slowly add the solution from step (2) to the mixed solution from step (1) and stir at 25°C for 12 hours.

[0077] (4) The mixed solution in step (3) is added to a Buchner funnel for filtration and the filter is washed with deionized water to obtain the lignin polyaniline complex, which is named AL\PANI-4-1.

[0078] (5) The lignin-polyaniline composite obtained in step (4) was heated to 1300℃ for 2h under a nitrogen atmosphere and a gas flow rate of 50mL / min at a heating rate of 3℃ / min to obtain a lignin-based composite hard carbon material, named LPHC-4-1.

[0079] Example 5

[0080] (1) Prepare 150 mL of 0.5 mol L -1 A sodium hydroxide solution with a molar concentration of 6 g alkali lignin and 6 g pyrrole were added to the sodium hydroxide solution and stirred at 25°C for 1 hour until uniformly mixed.

[0081] (2) Prepare 150 mL of 0.5 mol L -1 To prepare a hydrochloric acid solution with a molar concentration, add 6g of ammonium persulfate to the hydrochloric acid solution and stir at 25°C for 10 minutes until clear.

[0082] (3) Slowly add the solution from step (2) to the mixed solution from step (1) and stir at 25°C for 12 hours.

[0083] (4) The mixed solution in step (3) is added to a Buchner funnel for filtration and the filter is washed with deionized water to obtain the lignin polypyrrole complex, which is named AL\PPy-1-1.

[0084] (5) The lignin-polyaniline composite obtained in step (4) was heated to 1300℃ for 2h under a nitrogen atmosphere and a gas flow rate of 50mL / min at a heating rate of 3℃ / min to obtain a lignin-based composite hard carbon material, named LPyHC-1-1.

[0085] Example 6

[0086] (1) Prepare 150 mL of 0.5 mol L -1 A sodium hydroxide solution with a molar concentration of 6 g alkali lignin and 3 g pyrrole were added to the sodium hydroxide solution and stirred at 25°C for 1 hour until uniformly mixed.

[0087] (2) Prepare 150 mL of 0.5 mol L -1 To prepare a hydrochloric acid solution with a molar concentration, add 3g of ammonium persulfate to the hydrochloric acid solution and stir at 25°C for 10 minutes until clear.

[0088] (3) Slowly add the solution from step (2) to the mixed solution from step (1) and stir at 25°C for 12 hours.

[0089] (4) The mixed solution in step (3) is added to a Buchner funnel for filtration and the filter is washed with deionized water to obtain the lignin polypyrrole complex, which is named AL\PPy-2-1.

[0090] (5) The lignin-polyaniline composite obtained in step (4) was heated to 1300℃ for 2h under a nitrogen atmosphere and a gas flow rate of 50mL / min at a heating rate of 3℃ / min to obtain a lignin-based composite hard carbon material, named LPyHC-2-1.

[0091] Example 7

[0092] (1) Prepare 150 mL of 0.5 mol L -1 To prepare a sodium hydroxide solution with a molar concentration, add 6g of alkali lignin and 1.5g of pyrrole to the sodium hydroxide solution and stir at 25°C for 1 hour until uniformly mixed.

[0093] (2) Prepare 150 mL of 0.5 mol L -1 To prepare a hydrochloric acid solution with a molar concentration, add 1.5 g of ammonium persulfate to the hydrochloric acid solution and stir at 25°C for 10 minutes until clear.

[0094] (3) Slowly add the solution from step (2) to the mixed solution from step (1) and stir at 25°C for 12 hours.

[0095] (4) The mixed solution in step (3) is added to a Buchner funnel for filtration and the filter is washed with deionized water to obtain the lignin polypyrrole complex, which is named AL\PPy-4-1.

[0096] (5) The lignin-polyaniline composite obtained in step (4) was heated to 1300℃ for 2h under a nitrogen atmosphere and a gas flow rate of 50mL / min at a heating rate of 3℃ / min to obtain a lignin-based composite hard carbon material, named LPyHC-4-1.

[0097] Figure 6 The graph shows the specific capacity of LPyHC-4-1 as a sodium-ion battery anode, as a function of current density. (0.05Ag) -1 At a current density of 355 mAh g, LPyHC-4-1 has a capacity of 355 mAh g. -1 The charging specific capacity is at 5Ag -1 At a current density, it has 216 mAh g -1 The specific capacity indicates that LPyHC-4-1 exhibits excellent rate performance when used as the anode in sodium-ion batteries.

[0098] Comparative Example 1

[0099] This comparative example is hard carbon prepared by direct carbonization of lignin.

[0100] (1) Alkali lignin was named AL. 6g of alkali lignin was pyrolyzed and carbonized at 1300℃ for 2h under a nitrogen atmosphere and a gas flow rate of 50mL / min at a heating rate of 3℃ / min to obtain lignin-based hard carbon, which was named LHC.

[0101] LHC, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 8:1:1. After thorough mixing, the mixture was coated onto copper foil, dried, and rolled before being cut into circular electrode sheets with a diameter of 12 mm. The prepared electrode sheet was used as the working electrode, and a sodium metal sheet was used as the counter electrode. 1 mol L... -1 Sodium-ion half-cells were assembled using NaPF6 (with DME as the solvent) as the electrolyte to test the sodium-ion storage performance of the LHC. DME is ethylene glycol dimethyl ether.

[0102] Figure 7 The graph shows the specific capacity of an LHC battery used as the anode in a sodium-ion battery as a function of current density. (0.05 Ag) -1 At a current density of 288 mAh g, the LHC has a capacity of 288 mAh g. -1 The specific capacity at 5Ag -1 At a current density of 60 mAh g -1The specific capacity indicates that without aniline or pyrrole involved in lignin structure modification, the benzene ring stacking structure of lignin itself is difficult to open. After high-temperature carbonization, the closed-pore structure of its hard carbon is less and the interlayer spacing of carbon layers is difficult to open, resulting in a decrease in reversible specific capacity and rate performance. Among them, the specific capacity difference between LHC and LPHC-1-1 is mainly the plateau capacity, indicating that polyaniline or polypyrrole, as guest materials, stacks with lignin molecules, forming a large number of porous structures on the lignin precursor. The large number of porous structures helps to form closed pores during high-temperature carbonization, thereby increasing the plateau capacity and specific capacity of lignin-based hard carbon.

[0103] Comparative Example 2

[0104] This comparative example is hard carbon prepared by direct carbonization of polyaniline.

[0105] (1) Prepare 150 mL of 0.5 mol L -1 To prepare a sodium hydroxide solution with a molar concentration, add 6g of aniline to the sodium hydroxide solution and stir at 25°C for 1 hour until uniformly mixed.

[0106] (2) Prepare 150 mL of 0.5 mol L -1 To prepare a hydrochloric acid solution with a molar concentration, add 6g of ammonium persulfate to the hydrochloric acid solution and stir at 25°C for 10 minutes until clear.

[0107] (3) Add the solution from step (2) to the solution from step (1) and stir at 25°C for 12 hours.

[0108] (4) The mixed solution in step (3) is added to a Buchner funnel for filtration and the filter is washed with deionized water to obtain polyaniline, which is named PANI.

[0109] (5) Polyaniline was pyrolyzed and carbonized at 1300℃ for 2 hours under a nitrogen atmosphere and a gas flow rate of 50 mL / min at a heating rate of 3℃ / min to obtain polyaniline-based hard carbon, which was named PAHC.

[0110] Comparative Example 3

[0111] This comparative example is hard carbon prepared by direct carbonization of polypyrrole.

[0112] (1) Prepare 150 mL of 0.5 mol L -1 To prepare a sodium hydroxide solution with a molar concentration, add 6g of pyrrole to the sodium hydroxide solution and stir at 25°C for 1 hour until uniformly mixed.

[0113] (2) Prepare 150 mL of 0.5 mol L -1 To prepare a hydrochloric acid solution with a molar concentration, add 6g of ammonium persulfate to the hydrochloric acid solution and stir at 25°C for 10 minutes until clear.

[0114] (3) Add the solution from step (2) to the solution from step (1) and stir at 25°C for 12 hours.

[0115] (4) The mixed solution in step (3) is added to a Buchner funnel for filtration and the filter is washed with deionized water to obtain polypyrrole, which is named Ppy.

[0116] (5) Polypyrrole was pyrolyzed and carbonized at 1300℃ for 2 hours under a nitrogen atmosphere and a gas flow rate of 50 mL / min at a heating rate of 3℃ / min to obtain polypyrrole-based hard carbon, named PyHC.

[0117] Comparative Example 4

[0118] This comparative example is hard carbon prepared by directly carbonizing lignin and polyaniline after grinding and mixing them in equal masses.

[0119] (1) Prepare 150 mL of 0.5 mol L -1 To prepare a sodium hydroxide solution with a molar concentration, add 6g of aniline to the sodium hydroxide solution and stir at 25°C for 1 hour until uniformly mixed.

[0120] (2) Prepare 150 mL of 0.5 mol L -1 To prepare a hydrochloric acid solution with a molar concentration, add 6g of ammonium persulfate to the hydrochloric acid solution and stir at 25°C for 10 minutes until clear.

[0121] (3) Add the solution from step (2) to the solution from step (1) and stir at 25°C for 12 hours.

[0122] (4) The mixed solution in step (3) is added to a Buchner funnel for filtration and the filter is washed with deionized water to obtain polyaniline, which is named PANI.

[0123] (5) Grind and mix the polyaniline from step (4) with an equal mass of alkali lignin to obtain a lignin-polyaniline mixture, named AL / PANI-G.

[0124] (6) AL / PANI-G was pyrolyzed and carbonized at 1300℃ for 2h under a nitrogen atmosphere and a gas flow rate of 50mL / min at a heating rate of 3℃ / min to obtain polyaniline-based hard carbon, which was named LPHC-G.

[0125] The test current density for the reversible capacity in Table 1 is 50 mA / g. The specific surface area was obtained by fitting nitrogen adsorption-desorption data using the BET model. The diameter and volume of the closed pore were obtained by fitting the SAXS test results.

[0126] Table 1 compares the interlayer spacing, stabilized discharge specific capacity, and discharge plateau capacity of the hard carbon samples prepared in the examples and comparative examples (stabilized data are from the fifth charge-discharge cycle).

[0127]

[0128] 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-rate lignin-based composite hard carbon anode material for sodium-ion batteries, characterized in that, Includes the following steps: (1) After mixing and dissolving lignin and nitrogen-containing monomers, an initiator solution is added to carry out a polymerization reaction to obtain a lignin nitrogen-containing polymer complex; (2) Under an inert gas atmosphere, the lignin nitrogen-containing polymer composite is carbonized to obtain a lignin-based composite hard carbon material; The lignin in step (1) is at least one of alkali lignin and enzymatically hydrolyzed lignin; The nitrogen-containing monomer in step (1) is pyrrole; In step (1), the initiator and the nitrogen-containing monomer are of equal mass; The mass ratio of lignin to nitrogen-containing monomers in step (1) is 1:1 to 4:1; The carbonization temperature in step (2) is 1300-1600 °C and the time is 2 ± 0.5 h.

2. The preparation method according to claim 1, characterized in that, The lignin mentioned in step (1) is alkali lignin.

3. The preparation method according to claim 1, characterized in that, The initiator in the initiator solution in step (1) is persulfate.

4. The preparation method according to claim 1, characterized in that, The polymerization reaction in step (1) is carried out at room temperature for 10 to 14 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Disperse lignin and nitrogen-containing monomers in an alkaline aqueous solution, mix thoroughly to obtain a mixture; S2. Add the persulfate initiator to the hydrochloric acid aqueous solution and mix well to obtain the initiator solution; S3. The initiator solution is added dropwise to the mixture in step S1 to carry out the polymerization reaction and obtain the lignin nitrogen-containing polymer complex; S4. Under an inert gas atmosphere, the lignin-containing nitrogen polymer composite is carbonized to obtain a lignin-based composite hard carbon material.

6. The preparation method according to claim 5, characterized in that, The alkali in the alkaline aqueous solution described in S1 is at least one of sodium hydroxide and potassium hydroxide; And / or, the concentration of the alkaline aqueous solution is 0.25–0.5 mol / L; And / or, the ratio of the lignin to the alkaline aqueous solution is 6 g: 100-200 mL; And / or, the concentration of the hydrochloric acid aqueous solution described in S2 is 0.25–0.5 mol / L; And / or, the concentration of the persulfate initiator in the hydrochloric acid aqueous solution is 1.5–6 g: 150 mL.

7. The preparation method according to claim 5, characterized in that, The inert gas mentioned in S4 is at least one of nitrogen, helium, and argon; And / or, the flow rate of the inert gas in S4 is 2 to 100 mL / min; And / or, the heating rate for carbonization described in S4 is 0.1 to 30 °C / min.

8. A high-rate lignin-based composite hard carbon anode material for sodium-ion batteries prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the high-rate lignin-based composite hard carbon anode material for sodium-ion batteries as described in claim 8 in sodium-ion batteries.

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