High-rate lignin-based composite hard carbon negative electrode material as well as preparation method and application thereof

Abstract

The invention discloses a high-rate lignin-based composite hard carbon negative electrode material as well as a preparation method and application thereof. According to the method, aniline and pyrrole are used as guest materials, lignin is used as a subject carbon source, and the guest materials are used for preparing the lignin-based hard carbon material through one-step high-temperature carbonization on a composite material obtained after the subject material is pretreated. The construction of high closed pore volume and large carbon interlayer spacing in the lignin-based hard carbon is realized, and abundant intercalation and filling sites are provided for sodium ions in a hard carbon layer and closed pores, so that high specific capacity and high platform capacity of the hard carbon negative electrode of the sodium ion battery are realized. And the prepared hard carbon negative electrode material has relatively high reversible specific capacity, excellent rate capability and cycling stability. The method proves the feasibility of modifying the lignin structure by using the intermolecular force, realizes high-value utilization of the lignin, and is beneficial to large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of anode materials for sodium-ion batteries, and particularly relates to a high-rate lignin-based composite hard carbon anode material, a preparation method thereof, and an application thereof. Background Art

[0002] The anodes of sodium-ion batteries include alloy materials, metal oxides, organic compounds, carbon materials, etc. The hard carbon in carbon materials consists of curved graphene sheets and sp 3 cross-linked structures. These graphene sheets are randomly stacked to form numerous closed nanopores. At the same time, the sp 3 cross-linked structures are rich in defects, and the closed pores and defects provide abundant storage sites for sodium ions. The sodium storage behavior of hard carbon materials is divided into three steps: adsorption, intercalation, and filling. Among them, the adsorption and intercalation processes provide ramp capacity at a potential of 2.5 V to 0.1 V, and the filling process provides plateau capacity at a potential of 0.1 V to 0.01 V. The sodium storage rate performance of hard carbon mainly depends on the width of the carbon layer spacing and the degree of defects (Chemistry of Materials 2022, 34, 3489-3500). A large layer spacing and rich defects can ensure faster sodium ion transport kinetics. Therefore, the larger the width of the carbon layer spacing of the hard carbon material, the better its rate performance. The article (Small 2022, 18, 2105303) reported the preparation of hard carbon nanofibers with different carbon layer spacings by using different carbonization temperatures to study the relationship between the layer spacing and the sodium storage ramp capacity. This study used in-situ XRD and Raman tests to prove that the larger the carbon layer spacing, the more beneficial it is for sodium ions to insert into the carbon layer for storage and provide ramp capacity. In addition, a large carbon layer spacing can be achieved by adding guest materials to the hard carbon precursor to construct a carbon layer support structure. Chinese Patent Application CN111072009A discloses a preparation method for a hard carbon anode of a sodium-ion battery. This patent uses a swollen heavy organic matter mixed with a cross-linking agent, and cross-links the two under the catalytic action of a Lewis acid to prepare a hard carbon material with a large carbon layer spacing. This method has cumbersome process steps, requires the addition of a swelling agent to increase the preparation cost, and most of them are flammable and explosive reagents, without production safety. A large carbon layer spacing may also be achieved through the intermolecular force of the precursor material. The article (Adv. Energy Mater. 2023, 2302055) reported a method for preparing a composite graphite anode material with a large carbon layer spacing and rich surface defects by cross-linking graphene oxide and polyaniline. This method polymerizes and cross-links aniline monomers on the surface of graphene oxide to prepare a composite graphite material with a large carbon layer spacing and nitrogen-rich edge defects for application in potassium-ion batteries. This composite graphite anode material has 491 mAh g -1The platform capacity and excellent rate performance. However, the article mentions that there are not only amination bonding reactions in the structures of polyaniline and graphene oxide, but also π-π adsorption. Currently, there is no research indicating whether the π-π adsorption between the precursor molecules of hard carbon materials can regulate the structure and then prepare hard carbon materials with large carbon layer spacing through high-temperature carbonization.

[0003] The literature (Resources Chemicals and Materials. 2023, 2, 245 - 251) prepared a hard carbon anode material by one-step carbonization of corncob lignin. This hard carbon anode material has the disadvantage of low closed pore volume and cannot provide a large number of pore-filling active sites. Therefore, its reversible specific capacity (284 mAh g -1 ) is relatively low, and the rate performance is poor (at a current density of 1 A g -1 , its capacity is 85.8 mAh g -1 ). The above problems restrict the practical application of lignin-based hard carbon. Summary of the Invention

[0004] In order to overcome the problems of insufficient specific capacity and poor rate performance of lignin-based hard carbon, the primary object of the present invention is to provide a preparation method for a high-rate lignin-based composite hard carbon anode material.

[0005] Another object of the present invention is to provide a high-rate lignin-based composite hard carbon anode material prepared by the above preparation method.

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

[0007] The lignin-based composite hard carbon with 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, in the present invention, lignin and aniline / pyrrole are mixed in an aqueous sodium hydroxide solution to form a mixture, and ammonium persulfate is dissolved in an aqueous hydrochloric acid solution to form a solution. Then the solution is added to the mixture to form a water-insoluble lignin-polyaniline / pyrrole composite. The lignin-polyaniline / pyrrole composite is used as the precursor of the lignin-based composite hard carbon after filtration, washing with water, and drying, and the lignin-based composite hard carbon is prepared by high-temperature carbonization. Through the introduction of aniline or pyrrole and the intermolecular force binding between lignin molecules, and then polymerizing aniline or pyrrole in the system to break the stacking structure of lignin itself, a precursor structure with porous surface is formed. During the high-temperature carbonization process, with the bond breaking loss of nitrogen atoms in polyaniline or polypyrrole, the rearrangement of carbon microcrystals and the growth of carbon layers, rich nitrogen edge defects, large carbon layer spacing, and rich closed pore structures in the hard carbon are developed, and finally the surface pore structure is closed to form the closed pore structure of the hard carbon. The preparation method of the nitrogen-containing guest molecule-regulated lignin aggregate to prepare the lignin-based composite hard carbon material of the present invention can be used in electrochemical energy storage fields such as the anode of sodium-ion batteries.

[0008] The object of the present invention is achieved by the following technical solutions:

[0009] A preparation method of a high-rate lignin-based composite hard carbon anode material, comprising the following steps:

[0010] (1) After mixing and dissolving lignin and a nitrogen-containing monomer, an initiator solution is added for polymerization reaction to obtain a lignin-nitrogen-containing polymer composite;

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

[0012] (2) Under an inert gas atmosphere, the lignin-nitrogen-containing polymer composite is carbonized to obtain a lignin-based composite hard carbon material.

[0013] Preferably, the lignin in step (1) is at least one of alkali lignin, enzymatic hydrolysis lignin, and lignin sulfonate. The enzymatic hydrolysis lignin is the residue of enzymatic hydrolysis lignin obtained from the biological smelting process; the alkali lignin is the alkali lignin extracted from paper-making black liquor; the lignin sulfonate is the lignin sulfonate extracted from the pulping liquor by the sulfite method.

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

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

[0016] Preferably, the temperature of the polymerization reaction in step (1) is room temperature, and the time is 10 to 14 hours; more preferably 12 hours.

[0017] Preferably, the temperature of the carbonization in step (2) is 1300 to 1600 °C, and the time is 2 ± 0.5 h.

[0018] Preferably, the method for preparing the high-rate lignin-based composite hard carbon negative electrode material includes the following steps:

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

[0020] (2) Add a persulfate initiator to an aqueous hydrochloric acid solution and mix evenly to obtain an initiator solution.

[0021] (3) Drop the initiator solution into the mixture in step (1) to carry out a polymerization reaction to obtain a lignin nitrogen-containing polymer composite.

[0022] (4) Under an inert gas atmosphere, carbonize the lignin nitrogen-containing polymer composite to obtain a lignin-based composite hard carbon material.

[0023] Further preferably, the base 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] Further preferably, the ratio of lignin to the alkaline aqueous solution in step (1) is 6 g: 100 to 200 mL; more preferably 6 g: 150 mL.

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

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

[0027] Further preferably, after the polymerization reaction in step (3), the product mixture is filtered by suction, washed with water and dried. The water washing means that the suction-filtered product is rinsed with deionized water at least 3 times; the drying temperature is 80 to 120 °C, and the time is 12 to 24 h.

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

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

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

[0031] The present invention provides a high-rate lignin-based composite hard carbon negative electrode material prepared by the above preparation method.

[0032] The present invention provides application of the above-mentioned high-rate lignin-based composite hard carbon negative electrode material in a sodium ion battery.

[0033] The method described in the present invention realizes the construction of high closed pore volume and large carbon layer spacing in lignin-based composite hard carbon, provides a larger ion transmission space for sodium ions between hard carbon layers, and provides abundant filling sites in the closed pores of hard carbon, thereby realizing high specific capacity, platform capacity and good rate performance of hard carbon negative electrode of sodium ion battery.

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

[0035] The present invention aims to select a low-cost guest material containing nitrogen elements, and use Π-Π adsorption to perform structural regulation on cheap lignin aggregates, while achieving pyrolysis and fracture of the carbon layer at high temperature, so as to prepare a hard carbon negative electrode material with high closed pore volume and large carbon layer spacing. The lignin-based composite hard carbon material prepared by regulating lignin aggregates with nitrogen-containing guest materials, with the rearrangement of carbon microcrystals and the growth of carbon layers during high-temperature carbonization, the carbon layers are opened due to the cracking of polyaniline, and the micropores will be closed. The hard carbon negative electrode prepared by this method not only has a large carbon layer spacing and a rich closed-pore structure, but also has good electrochemical properties.

[0036] The present invention realizes the construction of high closed pore volume and large carbon layer spacing in lignin-based hard carbon, providing abundant intercalation and filling sites for sodium ions in the hard carbon carbon layer and closed pores, thereby realizing high specific capacity and high platform capacity of hard carbon negative electrode of sodium ion battery. The prepared hard carbon negative electrode material has high reversible specific capacity, excellent rate performance and cycle stability. This method proves the feasibility of modifying the structure of lignin by intermolecular forces, realizes the high value utilization of lignin, and is conducive to large-scale production.

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

[0038] (1) The present invention uses lignin with rich sources and low cost as a carbon source, regulates the structure of lignin aggregates through polyaniline / pyrrole, and then prepares a hard carbon anode material by high-temperature carbonization, which improves the electrochemical performance of the lignin-based composite hard carbon. Compared with other methods, lignin does not need to be further purified and no additional pore-forming agent is required, reducing the production cost and shortening the preparation process flow, which is beneficial to commercial production.

[0039] (2) The present invention uses aniline / pyrrole as the guest material of the hard carbon precursor, and regulates the structure of lignin aggregates through Π-Π adsorption, clarifying that the way to regulate the structure of the hard carbon precursor is the intermolecular force regulation mainly based on Π-Π adsorption. Compared with other methods, the introduction of aniline / pyrrole can not only increase the carbon layer spacing of the lignin-based composite hard carbon, but also generate a large number of pore structures, providing conditions for the formation of closed pores in hard carbon during high-temperature carbonization.

[0040] (3) The hard carbon anode prepared by the present invention has the advantages of large carbon layer spacing, high closed pore volume and high degree of defects. The large layer spacing provides a channel for the insertion of sodium ions into the hard carbon anode, and the high closed pore volume provides a large number of active sites for the filling of sodium ions in the hard carbon anode, so that the lignin-based composite hard carbon prepared by regulating lignin aggregates with this nitrogen-containing guest material has a high plateau capacity, reversible specific capacity, excellent rate performance and cycle stability. Description of the Drawings

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

[0042] Figure 2 is the Raman pattern of the lignin-based hard carbon (LPHC-1-1) in Example 1.

[0043] Figure 3 is the first charge-discharge curve of the lignin-based hard carbon (LPHC-1-1) in Example 1 used as the anode of a sodium-ion battery at a current density of 0.05 A / g. -1 Current density.

[0044] Figure 4 is the curve of the specific capacity of the lignin-based hard carbon (LPHC-1-1) in Example 1 used as the anode of a sodium-ion battery changing with the current density.

[0045] Figure 5 is the cycle curve of the lignin-based hard carbon (LPHC-1-1) in Example 1 used as the anode of a sodium-ion battery at a current density of 0.5 A / g. -1 Current density.

[0046] Figure 6 Figure 5 is a graph showing the specific capacity of the lignin-based hard carbon (LPyHC-4-1) in Example 5 as a sodium-ion battery anode varying with the current density.

[0047] Figure 7 Figure 6 is a graph showing the specific capacity of the lignin-based hard carbon (LHC) in Comparative Example 1 as a sodium-ion battery anode varying with the current density. Detailed implementation manners

[0048] The present invention will be further described in detail below in conjunction with examples and drawings, but the implementation manners of the present invention are not limited thereto.

[0049] In the examples of the present invention, those not specified under specific conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. Raw materials, reagents, etc. without indicating the manufacturer can all be obtained as conventional products through commercial purchase.

[0050] Example 1

[0051] (1) Prepare 150 mL of a 0.5 mol / L -1 sodium hydroxide solution, add 6 g of alkali lignin and 6 g of aniline to the sodium hydroxide solution, and stir at 25 °C for 1 h until uniformly mixed.

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

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

[0054] (4) Filter the mixed solution in step (3) through a Buchner funnel, and wash the filter residue with deionized water to obtain a lignin-polyaniline composite, named AL\PANI-1-1.

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

[0056] The X-ray diffraction (XRD) and Raman graphs of the LPHC-1-1 hard carbon anode are as Figure 1 and Figure 2 shown, Figure 1Two broad peaks appear near 21.5° and 44°, corresponding to the (002) and (100) crystal planes of the carbon material. After calculation, the interlayer spacing of LPHC-1-1 is 0.396 nm, the La value of the carbon material is 3.79 nm, the Lc value is 0.97 nm, and the ID / IG value calculated by fitting is 0.97. This indicates that LPHC-1-1 has a relatively disordered carbon layer structure and a large interlayer spacing, which is beneficial to the intercalation of sodium ions.

[0057] LPHC-1-1, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 8:1:1. After stirring evenly, it was coated on a copper foil. After drying and rolling, it was cut into a circular electrode sheet with a diameter of 12 mm for use. The prepared electrode sheet was used as the working electrode, a sodium metal sheet was used as the counter electrode, and 1 mol L -1 NaPF6 (using DME as the solvent) was used as the electrolyte to assemble a sodium-ion half-cell to test the sodium-ion storage performance of LPHC-1-1, where DME is ethylene glycol dimethyl ether.

[0058] Figure 3 For LPHC-1-1 used as the negative electrode of a sodium-ion battery, the first-cycle charge-discharge curve at a current density of 0.05 Ag -1 At a current density of 0.05 Ag -1 The discharge specific capacity of LPHC-1-1 in the first cycle was 500 mAh g -1 The charge specific capacity was 355 mAh g -1 and its first-cycle Coulombic efficiency was 72%.

[0059] Figure 4 For LPHC-1-1 used as the negative electrode of a sodium-ion battery, the curve of specific capacity changing with current density. At a current density of 0.05 Ag -1 The charge specific capacity of LPHC-1-1 was 355 mAh g -1 At a current density of 5 Ag -1 The specific capacity was 216 mAh g -1 This indicates that LPHC-1-1 has excellent rate performance when applied as the negative electrode of a sodium-ion battery.

[0060] Figure 5 This is the cycle performance graph of LPHC-1-1 used as the negative electrode of a sodium-ion battery at a current density of 0.5 Ag -1 At a current density of 0.5 Ag -1 After 2000 cycles, LPHC-1-1 had a capacity retention rate of 91%; this indicates that LPHC-1-1 has excellent cycle stability when applied as the negative electrode of a sodium-ion battery.

[0061] Example 2

[0062] (1) Prepare 150 mL of 0.5 mol / L -1 sodium hydroxide solution, add 6 g of alkali lignin and 4 g of aniline to the sodium hydroxide solution, and stir at 25 °C for 1 h until evenly mixed.

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

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

[0065] (4) Perform suction filtration on the mixed solution in step (3) by adding it to a Buchner funnel, and wash the filter residue with deionized water to obtain a lignin-polyaniline composite, named AL\PANI-3-2.

[0066] (5) Under a nitrogen atmosphere with a gas flow rate of 50 mL / min, heat the lignin-polyaniline composite obtained in step (4) to 1300 °C at a heating rate of 3 °C / min for pyrolytic carbonization for 2 h 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 sodium hydroxide solution, add 6 g of alkali lignin and 3 g of aniline to the sodium hydroxide solution, and stir at 25 °C for 1 h until evenly mixed.

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

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

[0071] (4) Perform suction filtration on the mixed solution in step (3) by adding it to a Buchner funnel, and wash the filter residue with deionized water to obtain a lignin-polyaniline composite, named AL\PANI-2-1.

[0072] (5) Under a nitrogen atmosphere with a gas flow rate of 50 mL / min, heat the lignin-polyaniline composite obtained in step (4) to 1300 °C at a heating rate of 3 °C / min for pyrolytic carbonization for 2 h 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 sodium hydroxide solution. Add 6 g of alkali lignin and 1.5 g of aniline to the sodium hydroxide solution, and stir at 25 °C for 1 h until evenly mixed.

[0075] (2) Prepare 150 mL of 0.5 mol / L -1 hydrochloric acid solution. 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 in step (2) to the mixed solution in step (1), and stir at 25 °C for 12 h.

[0077] (4) Filter the mixed solution in step (3) through a Buchner funnel, and wash the filter cake with deionized water to obtain a lignin-polyaniline composite, named AL\PANI-4-1.

[0078] (5) Pyrolyze and carbonize the lignin-polyaniline composite obtained in step (4) at a heating rate of 3 °C / min to 1300 °C for 2 h in a nitrogen atmosphere with a gas flow rate of 50 mL / 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 sodium hydroxide solution. Add 6 g of alkali lignin and 6 g of pyrrole to the sodium hydroxide solution, and stir at 25 °C for 1 h until evenly mixed.

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

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

[0083] (4) Filter the mixed solution in step (3) through a Buchner funnel, and wash the filter cake with deionized water to obtain a lignin-polypyrrole composite, named AL\PPy-1-1.

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

[0085] Example 6

[0086] (1) Prepare 150 mL of a 0.5 mol / L -1 sodium hydroxide solution, add 6 g of alkali lignin and 3 g of pyrrole to the sodium hydroxide solution, and stir at 25 °C for 1 h until evenly mixed.

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

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

[0089] (4) The mixed solution in step (3) was filtered by suction in a Buchner funnel, and the filter residue was washed with deionized water to obtain a lignin-polypyrrole composite named AL\PPy-2-1.

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

[0091] Example 7

[0092] (1) Prepare 150 mL of a 0.5 mol / L -1 sodium hydroxide solution, add 6 g of alkali lignin and 1.5 g of pyrrole to the sodium hydroxide solution, and stir at 25 °C for 1 h until evenly mixed.

[0093] (2) Prepare 150 mL of a 0.5 mol / L -1 hydrochloric acid solution, 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 in step (2) to the mixed solution in step (1), and stir at 25 °C for 12 h.

[0095] (4) Filter the mixed solution in step (3) by adding it to a Buchner funnel and wash the filter cake with deionized water to obtain the lignin polypyrrole composite, named AL\PPy-4-1.

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

[0097] Figure 6 The graph shows the variation of the specific capacity of LPyHC-4-1 as a negative electrode for sodium-ion batteries with the current density. At a current density of 0.05 Ag -1 , LPyHC-4-1 has a charging specific capacity of 355 mAh g -1 . At a current density of 5 Ag -1 , it has a specific capacity of 216 mAh g -1 . This indicates that LPyHC-4-1 has excellent rate performance when applied as a negative electrode for sodium-ion batteries.

[0098] Comparative Example 1

[0099] This comparative example is a hard carbon prepared by directly carbonizing lignin.

[0100] (1) Name the alkali lignin as AL. Heat 6 g of alkali lignin to 1300 °C at a heating rate of 3 °C / min for 2 h in a nitrogen atmosphere with a gas flow rate of 50 mL / min to obtain the lignin-based hard carbon, named LHC.

[0101] Mix LHC, conductive carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, stir evenly, coat it on a copper foil, and after drying and rolling, cut it into a circular electrode sheet with a diameter of 12 mm for use. Use the prepared electrode sheet as the working electrode, a sodium metal sheet as the counter electrode, and 1 mol L -1 NaPF6 (DME as the solvent) as the electrolyte to assemble a sodium-ion half-cell and test the sodium storage performance of LHC, where DME is ethylene glycol dimethyl ether.

[0102] Figure 7 The graph shows the variation of the specific capacity of LHC as a negative electrode for sodium-ion batteries with the current density. At a current density of 0.05 Ag -1 , LHC has a specific capacity of 288 mAh g -1 . At a current density of 5 Ag -1 , it has a specific capacity of 60 mAh g -1Specific capacity. It shows that when lignin structure modification is carried out without the participation of aniline or pyrrole, 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 carbon layer spacing is difficult to open, resulting in a decrease in reversible specific capacity and rate performance. The difference in specific capacity between LHC and LPHC-1-1 is mainly the plateau capacity, indicating that polyaniline or polypyrrole, as the guest material, stacks with lignin molecules to form a large number of pore structures on the lignin precursor. A large number of pore structures contribute to the formation of 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 directly carbonizing polyaniline.

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

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

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

[0108] (4) Filter the mixed solution in step (3) through a Buchner funnel, wash the filter residue with deionized water to obtain polyaniline, named PANI.

[0109] (5) Pyrolytically carbonize polyaniline in a nitrogen atmosphere with a gas flow rate of 50 mL / min at a heating rate of 3 °C / min to 1300 °C for 2 h to obtain polyaniline-based hard carbon, named PAHC.

[0110] Comparative Example 3

[0111] This comparative example is hard carbon prepared by directly carbonizing polypyrrole.

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

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

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

[0115] (4) Filter the mixed solution in step (3) by adding it to a Buchner funnel, and wash the filter cake with deionized water to obtain polypyrrole, named Ppy.

[0116] (5) Pyrolytically carbonize polypyrrole at a heating rate of 3 °C / min to 1300 °C for 2 h in a nitrogen atmosphere with a gas flow rate of 50 mL / min to obtain polypyrrole-based hard carbon, named PyHC.

[0117] Comparative Example 4

[0118] In this comparative example, hard carbon was prepared by directly carbonizing a ground mixture of lignin and polyaniline of equal mass.

[0119] (1) Prepare 150 mL of 0.5 mol / L -1 sodium hydroxide solution, add 6 g of aniline to the sodium hydroxide solution, and stir at 25 °C for 1 h until evenly mixed.

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

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

[0122] (4) Filter the mixed solution in step (3) by adding it to a Buchner funnel, and wash the filter cake with deionized water to obtain polyaniline, named PANI.

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

[0124] (6) Pyrolytically carbonize AL / PANI-G at a heating rate of 3 °C / min to 1300 °C for 2 h in a nitrogen atmosphere with a gas flow rate of 50 mL / min to obtain polyaniline-based hard carbon, named LPHC-G.

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

[0126] Comparison of the interlayer spacing, stabilized discharge specific capacity, and discharge plateau capacity of the hard carbon samples prepared in the examples and comparative examples (the data after stabilization are the charge-discharge data of the fifth cycle)

[0127]

[0128] The above embodiments are preferred embodiments of the present invention. However, the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a high-rate lignin-based composite hard carbon anode material, characterized in that, It includes the following steps: (1) After mixing and dissolving lignin and a nitrogen-containing monomer, an initiator solution is added for a polymerization reaction to obtain a lignin nitrogen-containing polymer composite; (2) Under an inert gas atmosphere, the lignin nitrogen-containing polymer composite is carbonized to obtain a lignin-based composite hard carbon material.

2. The preparation method according to claim 1, characterized in that, The lignin in step (1) is at least one of alkali lignin, enzymatically hydrolyzed lignin, and lignin sulfonate; And / or, the nitrogen-containing monomer in step (1) is at least one of aniline and pyrrole; And / or, the mass ratio of the lignin and the nitrogen-containing monomer in step (1) is 1:1 to 4:

1.

3. The preparation method according to claim 1, wherein The initiator in the initiator solution in step (1) is persulfate; And / or, the mass of the initiator is equal to that of the nitrogen-containing monomer.

4. The preparation method according to claim 1, characterized in that, The temperature of the polymerization reaction in step (1) is room temperature, and the time is 10 to 14 hours.

5. The preparation method according to claim 1, wherein The temperature of the carbonization in step (2) is 1300 to 1600 °C, and the time is 2 ± 0.5 h.

6. According to the preparation method described in any one of claims 1 to 5, characterized in that, It includes the following steps: S1. Disperse lignin and a nitrogen-containing monomer in an alkaline aqueous solution, mix evenly to obtain a mixture; S2. Add a persulfate initiator to a hydrochloric acid aqueous solution and mix evenly to obtain an initiator solution; S3. Drop the initiator solution into the mixture in step S1 for a polymerization reaction to obtain a lignin nitrogen-containing polymer composite; S4. Under an inert gas atmosphere, carbonize the lignin nitrogen-containing polymer composite to obtain a lignin-based composite hard carbon material.

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

8. The preparation method according to claim 6, characterized in that, The inert gas 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 of the carbonization in S4 is 0.1 to 30 °C / min.

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

10. Application of the high-rate lignin-based composite hard carbon anode material according to claim 9 in a sodium-ion battery.

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