Lignin-based hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention discloses a lignin-based hard carbon negative electrode material as well as a preparation method and application thereof, and belongs to the technical field of sodium ion battery negative electrode materials. The preparation method comprises the following steps: performing hydrothermal reaction on a mixed solution of lignin and biomass molecules, performing in-situ synthesis on a phenol reaction product generated by the lignin and an aldehyde / acid reaction product generated by the biomass molecules to obtain a cross-linked lignin product, and performing high-temperature carbonization to obtain the lignin-based hard carbon material. The cross-linked lignin-based hard carbon has large interlayer spacing, extremely low specific surface area and rich closed-pore structures, is used for sodium ion batteries, has high reversible capacity and excellent rate capability, is beneficial to promoting development of high-energy-density sodium ion batteries, and has the advantages of simple preparation method, low cost, controllable structure and wide application prospect. And large-scale industrial production can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a biomass molecule-crosslinked lignin-based hard carbon negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] Sodium-ion batteries are the most promising battery systems to be commercialized among the secondary batteries under research and have been applied as power sources for electric vehicles. However, current sodium-ion batteries have a relatively low energy density (~120 Wh / kg), and developing high specific capacity negative electrode materials is the key to improving the energy density of sodium-ion batteries.

[0003] Hard carbon is an amorphous carbon material that is difficult to graphitize at high temperatures above 2500 °C. It is composed of stacked distorted graphene sheets, arranged disorderly, with a large interlayer spacing (0.37 - 0.4 nm) and a rich closed nanopore structure. As a negative electrode material for sodium-ion batteries, it can provide abundant storage sites for sodium ions, showing advantages such as high reversible capacity (200 - 400 mAh / g) and long cycle life. Hard carbon is usually prepared by high-temperature carbonization of oxygen-containing organic substances such as biomass and polymers, and the nature of the carbon source is an important factor affecting the microstructure of hard carbon. It is urgent to prepare low-cost and high-performance hard carbon materials by controlling the price of carbon precursors, optimizing carbonization process parameters, and developing technologies for precisely regulating the structure of hard carbon.

[0004] Lignin is the main by-product in the pulp industry and the enzymatic hydrolysis fermentation industry, and it is a low-cost and green sustainable hard carbon precursor. However, lignin contains rich aromatic ring structures, and the severe π-π stacking between its molecules hinders the rearrangement of carbon ring structures during carbonization, resulting in a lack of closed pore structures suitable for sodium ion storage in the directly carbonized lignin-based hard carbon, with low capacity and poor rate performance during sodium ion storage. Therefore, it is necessary to modify and decorate lignin to regulate the closed pore structure of hard carbon.

[0005] Carbon source crosslinking is an effective strategy for regulating the closed pore structure of hard carbon. CN117735522A discloses a hard carbon material, its preparation method, application, and battery. Waste rubber is successively subjected to oxidation and curing with a strong oxidizing reagent, crosslinking and curing with strong acids and bases, and carbonization treatment to obtain a hard carbon material with a controllable closed pore aperture structure. CN117326546B discloses a lignin-phenolic resin-based hard carbon material, its preparation method, and application. Activated lignin and phenolic resin are blended to obtain a crosslinked composite, which is subjected to pre-carbonization and carbonization treatment to obtain a hard carbon material, enriching the number of closed pores in the hard carbon. CN117550585A reports a preparation method and application of a coal tar pitch-based hard carbon material. An acid anhydride substance rich in halogen atoms is crosslinked with coal tar pitch under the drive of a high-temperature thermal field, and the microcrystalline structure and pore structure in the hard carbon are regulated. However, the sodium storage capacity and rate performance of the above hard carbon materials have not been improved significantly. In addition, a large amount of acid-base activators are used in the crosslinking process in the above patents, which is not green; it is necessary to go through the processes of activation, pre-oxidation, and pre-carbonization, and the preparation process is complex.

[0006] In summary, how to feasibly develop a strategy for hard carbon materials with a controllable closed pore structure and excellent sodium storage performance is an urgent problem to be solved currently. Summary of the Invention

[0007] To solve the disadvantages and deficiencies of the prior art, the primary object of the present invention is to provide a preparation method of a biomass molecule-crosslinked lignin-based hard carbon material.

[0008] The present invention selects industrial lignin as the hard carbon precursor, disperses it with biomass molecules in a solvent. During the hydrothermal process, phenolic reaction products generated by the cracking of lignin and aldehyde / acid reaction products generated by the cracking of biomass molecules are crosslinked in situ. The crosslinked lignin product is subjected to high-temperature carbonization to obtain a hard carbon material. This method can regulate the crosslinking degree of lignin and optimize the structure of hard carbon by changing the dosage, type, and solvent system of biomass molecules.

[0009] Another object of the present invention is to provide a biomass molecule-crosslinked lignin-based hard carbon negative electrode material prepared by the above preparation method.

[0010] Another object of the present invention is to provide the application of the above biomass molecule-crosslinked lignin-based hard carbon negative electrode material in a sodium-ion battery.

[0011] The object of the present invention is achieved by the following technical solutions:

[0012] A preparation method of a biomass molecule-crosslinked lignin-based hard carbon material, comprising the following steps:

[0013] (1) Mix and disperse lignin and biomass molecules in a solvent, and obtain a hard carbon precursor through a hydrothermal reaction;

[0014] (2) Carbonize the hard carbon precursor in an inert gas atmosphere to obtain the hard carbon negative electrode material.

[0015] Preferably, the lignin in step (1) is at least one of alkali lignin, enzymatically hydrolyzed lignin, kraft lignin, lignosulfonate, organosolv lignin, and groundwood lignin.

[0016] More preferably, the lignosulfonate is at least one of sodium lignosulfonate, potassium lignosulfonate, and calcium lignosulfonate.

[0017] Preferably, the biomass molecule in step (1) is at least one of starch, cellulose, sucrose, xylan, maltose, xylose, fructose, dextran, glucose, furfural, p - coumaric acid, and phenol; more preferably, it is at least one of glucose, xylose, starch, cellulose, and furfural.

[0018] Preferably, the mass ratio of the lignin to the biomass molecule in step (1) is 1:10 - 50:1; more preferably, it is 20:1 - 1:1; most preferably, it is 10:1 - 1:1.

[0019] Preferably, the solvent in step (1) is at least one of water, ammonia aqueous solution, ethylenediamine, methanol, ethanol, and dilute sulfuric acid; the pH of the ammonia aqueous solution is 9 - 12; the pH of the dilute sulfuric acid solution is 2 - 5.

[0020] Preferably, the mass ratio of the lignin to the solvent in step (1) is 1:5 - 1:100; more preferably, it is 1:5 - 1:10.

[0021] Preferably, the temperature of the hydrothermal reaction in step (1) is 120 - 250 °C, and the time is 1 - 24 h; more preferably, the temperature of the hydrothermal reaction is 150 - 190 °C, and the time is 2 - 18 h.

[0022] Preferably, the temperature of the carbonization in step (2) is 800 - 2000 °C, and the time is 0.5 - 10 h; more preferably, carbonize at 1000 - 1400 °C for 2 - 8 h; most preferably, carbonize at 1100 - 1400 °C for 2 - 8 h.

[0023] Preferably, the heating rate of the carbonization in step (2) is 2 - 10 °C / min; more preferably, it is 2 - 5 °C / min.

[0024] Preferably, the inert gas in step (2) is at least one of nitrogen, argon, and helium.

[0025] A biomass molecule - crosslinked lignin - based hard carbon negative electrode material prepared by the above - mentioned preparation method.

[0026] Application of the above lignin-based hard carbon anode material cross-linked by biomass molecules in sodium-ion batteries.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] (1) In the present invention, lignin is used as the hard carbon precursor and biomass molecules are used as the cross-linking agent. The two are mixed in a solvent and in-situ cross-linking occurs through a one-step hydrothermal method to obtain a hard carbon precursor complex. The preparation method of this process is simple, and the raw materials used are all biomass-derived materials, which have the characteristics of low cost and sustainability and are easy to realize industrial application.

[0029] (2) The hard carbon material obtained in the present invention has a rich closed pore structure suitable for sodium storage, showing stable sodium storage performance with high capacity and high rate. Description of the Drawings

[0030] Figure 1 XRD patterns of the hard carbon materials prepared in Example 1 and Comparative Examples 1 and 2.

[0031] Figure 2 BET diagrams of the hard carbon materials prepared in Example 1 and Comparative Examples 1 and 2.

[0032] Figure 3 SAXS diagrams of the hard carbon materials prepared in Example 1 and Comparative Examples 1, 2 and 3.

[0033] Figure 4 Charge-discharge diagrams of the hard carbon materials prepared in Example 1 and Comparative Examples 1, 2 and 3 as the anode of a sodium-ion battery at the fifth cycle under a current density of 50 mA / g.

[0034] Figure 5 Capacity contribution diagrams of the hard carbon materials prepared in Example 1 and Comparative Examples 1, 2 and 3 as the anode of a sodium-ion battery at the fifth cycle under a current density of 50 mA / g.

[0035] Figure 6 Rate diagrams of the hard carbon materials prepared in Example 1 and Comparative Examples 1, 2 and 3 as the anode of a sodium-ion battery at different current densities.

[0036] Figure 7 Capacity contribution diagrams of the hard carbon materials prepared in Examples 2, 3, 4 and 5 as the anode of a sodium-ion battery at the fifth cycle under a current density of 50 mA / g. Detailed Embodiments

[0037] The present invention will be further described in detail below with reference to the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0038] In the embodiments of the present invention, those not specified with specific conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. The raw materials, reagents, etc. without indicating the manufacturer can be obtained as conventional products through commercial purchase.

[0039] Example 1

[0040] 1) Add alkali lignin and glucose in a mass ratio of 1:1 to an ammonia water solvent (the pH of the ammonia water solvent is 10), and the mass ratio of alkali lignin to the ammonia water solvent is 1:10. After ultrasonic treatment of the obtained mixed liquid for 5 min, hydrothermal treatment is carried out at 180 °C for 12 h to obtain a hard carbon precursor, which is reserved for use;

[0041] 2) Place the hard carbon precursor in a nitrogen atmosphere for carbonization. The carbonization heating rate is 5 °C / min, and it is heated to 1300 °C and kept warm for 2 h to obtain a hard carbon material.

[0042] Example 2

[0043] 1) Add enzymatic hydrolysis lignin and xylose in a mass ratio of 2:1 to water, and the mass ratio of enzymatic hydrolysis lignin to water is 1:5. After ultrasonic treatment of the obtained mixed liquid for 5 min, hydrothermal treatment is carried out at 170 °C for 2 h to obtain a hard carbon precursor, which is reserved for use;

[0044] 2) Place the hard carbon precursor in a nitrogen atmosphere for carbonization. The carbonization heating rate is 2 °C / min, and it is heated to 1200 °C and kept warm for 6 h to obtain a hard carbon material.

[0045] Example 3

[0046] 1) Add organic lignin and starch in a mass ratio of 10:1 to methanol, and the mass ratio of organic lignin to methanol is 1:5. After ultrasonic treatment of the obtained mixed liquid for 5 min, hydrothermal treatment is carried out at 160 °C for 18 h to obtain a hard carbon precursor, which is reserved for use;

[0047] 2) Place the hard carbon precursor in a nitrogen atmosphere for carbonization. The carbonization heating rate is 5 °C / min, and it is heated to 1400 °C and kept warm for 8 h to obtain a hard carbon material.

[0048] Example 4

[0049] 1) Add alkali lignin and cellulose in a mass ratio of 2:1 to a dilute sulfuric acid solution (the pH of the dilute sulfuric acid solution is 2), and the mass ratio of alkali lignin to the dilute sulfuric acid is 1:10. After ultrasonic treatment of the obtained mixed liquid for 5 min, hydrothermal treatment is carried out at 190 °C for 10 h to obtain a hard carbon precursor, which is reserved for use;

[0050] 2) Place the hard carbon precursor in a nitrogen atmosphere for carbonization. The carbonization heating rate is 5 °C / min, and it is heated to 1100 °C and kept warm for 2 h to obtain a hard carbon material.

[0051] Example 5

[0052] 1) Add sulfate lignin and furfural into an ethanol solution (the volume concentration of the ethanol solution is 50%) at a mass ratio of 4:1. The mass ratio of sulfate lignin to ethanol is 1:100. After ultrasonic treatment of the obtained mixed liquid for 5 min, hydrothermal treatment is carried out at 150 °C for 10 h to obtain a hard carbon precursor for standby;

[0053] 2) Place the hard carbon precursor in a nitrogen atmosphere for carbonization. The carbonization heating rate is 5 °C / min. Heat up to 1300 °C and keep the temperature for 2 h to obtain a hard carbon material.

[0054] Comparative Example 1

[0055] 1) Add alkali lignin into an ammonia water solvent (the mass ratio of alkali lignin to ammonia water solvent is 1:10, and the pH of the ammonia water solvent is 10). After ultrasonic treatment of the obtained mixed liquid for 5 min, hydrothermal treatment is carried out at 180 °C for 12 h to obtain a hard carbon precursor for standby;

[0056] 2) Place the hard carbon precursor in a nitrogen atmosphere for carbonization. The carbonization heating rate is 5 °C / min. Heat up to 1300 °C and keep the temperature for 2 h to obtain a hard carbon material.

[0057] Comparative Example 2

[0058] 1) Add glucose into an ammonia water solvent (the mass ratio of glucose to ammonia water solvent is 1:10, and the pH of the ammonia water solvent is 10). After ultrasonic treatment of the obtained mixed liquid for 5 min, hydrothermal treatment is carried out at 180 °C for 12 h to obtain a hard carbon precursor for standby;

[0059] 2) Place the hard carbon precursor in a nitrogen atmosphere for carbonization. The carbonization heating rate is 5 °C / min. Heat up to 1300 °C and keep the temperature for 2 h to obtain a hard carbon material.

[0060] Comparative Example 3

[0061] 1) Add alkali lignin and glucose into an ammonia water solvent (the pH of the ammonia water solvent is 9) at a mass ratio of 1:15. The mass ratio of alkali lignin to ammonia water solvent is 1:10. After ultrasonic treatment of the obtained mixed liquid for 5 min, hydrothermal treatment is carried out at 180 °C for 12 h to obtain a hard carbon precursor for standby;

[0062] 2) Place the hard carbon precursor in a nitrogen atmosphere for carbonization. The carbonization heating rate is 5 °C / min. Heat up to 1300 °C and keep the temperature for 2 h to obtain a hard carbon material.

[0063] The specific preparation method of the negative electrode material and the sodium ion battery includes the following steps:

[0064] The hard carbon material was dried in a vacuum drying oven at 70 °C for 8 h. The hard carbon material, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 8:1:1, stirred evenly, coated on a copper foil, and dried in a vacuum drying oven at 70 °C for 8 h to obtain the electrode sheet. Battery assembly was carried out in a glove box under argon protection, and the electrolyte was a 1 mol / L NaPF 6 ethylene glycol dimethyl ether solution, and the sodium metal sheet was used as the counter electrode.

[0065] Figure 1 is the XRD pattern of the hard carbon materials prepared in Example 1 and Comparative Examples 1 and 2. Compared with the hard carbon materials of Comparative Examples 1 and 2, the hard carbon in Example 1 has a larger interlayer spacing (d = 0.40 nm), which can ensure the smooth transmission of large-size sodium ions.

[0066] Figure 2 is the BET pattern of the hard carbon materials prepared in Example 1 and Comparative Examples 1 and 2. According to Figure 2 it can be seen that all hard carbon materials have a small specific surface area, indicating the existence of a very small amount of open pore structure.

[0067] Figure 3 is the SAXS pattern of the hard carbon materials prepared in Example 1 and Comparative Examples 1 and 2. As Figure 3 shown, the hard carbon in Example 1 has a more obvious hump at indicating that the hard carbon in Example 1 has a richer closed pore structure.

[0068] Table 1 presents the specific surface area, open pore volume, closed pore diameter, and closed pore volume of the hard carbon materials obtained in the examples and comparative examples, and the specific parameters are given in Table 1. In the hard carbon of Example 1, the specific surface area and open pore volume decreased, while the closed pore volume increased and the closed pore diameter decreased, which indicates that part of the open pore structure in the hard carbon was converted into a closed pore structure, and the closed pore aperture was regulated, increasing the active sites for reversible sodium storage and facilitating the improvement of the reversible sodium storage capacity.

[0069] Table 1 is a comparison table of the specific surface area and open pore volume obtained by nitrogen adsorption and desorption of the carbon materials obtained in Examples 1-5 and Comparative Examples 1-3, as well as the closed pore diameter and closed pore volume obtained by SAXS testing.

[0070] Table 1

[0071]

[0072]

[0073] Figure 4Charge-discharge curves of the hard carbon materials prepared in Example 1 and Comparative Examples 1, 2, and 3 as anodes for sodium-ion batteries at the fifth cycle under a current density of 50 mA / g. Compared with the hard carbon anodes of Comparative Examples 1 and 2, the discharge capacity of the hard carbon anode of Example 1 is significantly improved, reaching 392 mAh / g.

[0074] Figure 5 Capacity contribution diagrams of the hard carbon materials prepared in Example 1 and Comparative Examples 1, 2, and 3 as anodes for sodium-ion batteries at the fifth cycle under a current density of 50 mA / g. Compared with the hard carbon anodes of Comparative Examples 1, 2, and 3, the discharge capacity of the hard carbon anode of Example 1 is mainly provided by the plateau capacity, which is related to the abundant closed pores with suitable sizes for sodium storage.

[0075] Figure 6 Rate performance diagrams of the hard carbon materials prepared in Example 1 and Comparative Examples 1, 2, and 3 as anodes for sodium-ion batteries at different current densities. The hard carbon anode has excellent rate performance and can still maintain 65% of the initial capacity at a high current density of 5 A / g.

[0076] Figure 7 Capacity contribution diagrams of the hard carbon materials prepared in Examples 2, 3, 4, and 5 as anodes for sodium-ion batteries at the fifth cycle under a current density of 50 mA / g.

[0077] 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 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 method for preparing a biomass molecular cross-linked lignin-based hard carbon material, characterized in that: The following steps are involved: (1) Mixing lignin and biomass molecules and dispersing them in a solvent to obtain a hard carbon precursor through a hydrothermal reaction; (2) Carbonizing the hard carbon precursor in an inert gas atmosphere to obtain a hard carbon negative electrode material.

2. The method for preparing a biomass molecule cross-linked lignin-based hard carbon material according to claim 1, characterized in that: The biomass molecule in step (1) is at least one of starch, cellulose, sucrose, xylan, maltose, xylose, fructose, dextran, glucose, furfural, p-coumaric acid, and phenol; And / or, the mass ratio of lignin to biomass molecules in step (1) is 1:10 to 50:1 and / or, the lignin in step (1) is at least one of alkali lignin, enzymatic lignin, kraft lignin, lignin sulfonate, organic lignin and groundwood lignin; And / or, the lignin sulfonate is at least one of sodium lignin sulfonate, potassium lignin sulfonate and calcium lignin sulfonate.

3. The method for preparing a biomass molecule cross-linked lignin-based hard carbon material according to claim 1 or 2, characterized in that: The biomass molecule in step (1) is at least one of glucose, xylose, starch, cellulose and furfural; And / or, the mass ratio of the lignin to the biomass molecules in step (1) is 20:1 to 1:

1.

4. The method for preparing a biomass molecule cross-linked lignin-based hard carbon material according to claim 1 or 2, characterized in that: The temperature of the hydrothermal reaction in step (1) is 120 to 250° C. and the time is 1 to 24 hours.

5. The method for preparing a biomass molecule cross-linked lignin-based hard carbon material according to claim 4, characterized in that: The temperature of the hydrothermal reaction in step (1) is 150-190° C. and the time is 2-18 hours.

6. The method for preparing a biomass molecule cross-linked lignin-based hard carbon material according to claim 1 or 2, characterized in that: The carbonization temperature in step (2) is 800-2000° C. and the time is 0.5-10 h; And / or, the heating rate of the carbonization in step (2) is 2 to 10°C / min; And / or, the inert gas in step (2) is at least one of nitrogen, argon and helium.

7. The method for preparing a biomass molecule cross-linked lignin-based hard carbon material according to claim 6, characterized in that: The carbonization temperature in step (2) is 1000-1400° C. and the time is 2-8 hours; And / or, the heating rate of the carbonization in step (2) is 2 to 5°C / min.

8. The method for preparing a biomass molecule cross-linked lignin-based hard carbon material according to claim 1, characterized in that: The solvent in step (1) is at least one of water, aqueous ammonia solution, ethylenediamine, methanol, ethanol and dilute sulfuric acid; the pH of the aqueous ammonia solution is 9 to 12; the pH of the dilute sulfuric acid solution is 2 to 5; And / or, the mass ratio of lignin to solvent in step (1) is 1:5 to 1:

100.

9. A biomass molecule cross-linked lignin-based hard carbon material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the biomass molecule cross-linked lignin-based hard carbon material according to claim 9 in sodium ion batteries.

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