Lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite materials, preparation methods and applications

Abstract

The present application provides a lignocellulose phenolic resin / doped bamboo-based porous carbon derived hard carbon composite material, a preparation method and application, the lignocellulose phenolic resin / doped bamboo-based porous carbon derived hard carbon composite material takes bamboo-based porous carbon as the core, doped atoms are loaded in the pores and the surface of the bamboo-based porous carbon, and lignocellulose phenolic resin is cracked in situ to form a carbon coating layer.The present application fully plays the advantages of the synergistic effect among lignocellulose phenolic resin, doped atoms and bamboo-based porous carbon, and the structure and properties are complementary, so that the specific surface area of the hard carbon composite material is increased, the conductivity is improved, excellent electrochemical performance is obtained, meanwhile, the lignocellulose modified phenolic resin is coated on the surface of the bamboo-based porous carbon to form a carbon coating layer, the contact of the surface of the bamboo-based porous carbon and the doped atoms with the electrolyte is reduced, the side reaction is reduced, the loss of irreversible capacity is reduced, the first coulombic efficiency is significantly improved, and higher sodium storage specific capacity is obtained.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material, its preparation method, and its application. Background Technology

[0002] Driven by both cost and efficiency concerns in the lithium-ion battery market, the development of novel energy storage battery technologies is receiving increasing attention. Sodium-ion batteries, with their numerous advantages including low cost, cleanliness, environmental friendliness, good low-temperature performance, and safety, are rapidly developing in various fields such as energy storage devices, communication base stations, and low-speed electric vehicles. Currently, the main anode materials for sodium-ion batteries include carbon-based materials, alloy materials, conversion materials, organic materials, and metal oxide materials. Carbon-based materials, with their wide availability and strong sodium storage capacity, have become the mainstream choice for sodium-ion battery anodes.

[0003] Carbon-based materials can be further divided into hard carbon and soft carbon based on whether they become graphitized after high-temperature carbonization. Hard carbon has a disordered internal crystal arrangement, more pores, and can store sodium in the interlayer of graphite sheets, closed micropores, surfaces, and defect sites, resulting in higher capacity. Therefore, hard carbon has become the preferred anode material for sodium-ion batteries, and the selection of hard carbon precursors has become crucial for the industrialization of sodium-ion batteries. Commonly used hard carbon precursors for sodium-ion batteries are mainly divided into three categories: resin-based, pitch-based, and biomass-based. Biomass-based precursors are widely available, inexpensive, environmentally friendly, and possess abundant heteroatoms and unique microstructures, leading to faster industrialization and making them the choice of major manufacturers. However, they still face problems such as low initial coulombic efficiency, low sodium storage capacity, and poor rate performance. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a hard carbon composite material derived from lignocellulose phenolic resin / doped bamboo-based porous carbon, which solves the problems of low initial coulombic efficiency, low sodium storage capacity, and poor rate performance common in existing hard carbon materials. Furthermore, this invention also provides a method for preparing the hard carbon composite material derived from lignocellulose phenolic resin / doped bamboo-based porous carbon. In addition, this invention also provides applications of the hard carbon composite material derived from lignocellulose phenolic resin / doped bamboo-based porous carbon.

[0005] To achieve the above objectives and other related objectives,

[0006] In a first aspect, the present invention provides a hard carbon composite material derived from lignocellulose phenolic resin and doped bamboo-based porous carbon, wherein bamboo-based porous carbon serves as the core, and doped atoms are loaded into the pores and surface of the bamboo-based porous carbon, and lignocellulose phenolic resin is pyrolyzed in situ to form a carbon coating layer.

[0007] Furthermore, the bamboo-based porous carbon is obtained from bamboo-based biomass raw materials through activation treatment.

[0008] Furthermore, the doped atoms include one or more of B, N, and P.

[0009] Furthermore, the raw material containing the doped atoms includes one or more of boron source, nitrogen source, and phosphorus source; the boron source is preferably boric acid, the nitrogen source is preferably urea, and the phosphorus source is preferably sodium dihydrogen phosphate.

[0010] Furthermore, the mass ratio of the doped bamboo-based porous carbon to the lignocellulose phenolic resin is (99-90):(1-10).

[0011] A second aspect of the present invention provides a method for preparing a hard carbon composite material of lignocellulose phenolic resin / doped bamboo-based porous carbon, comprising the following steps:

[0012] (I) Preparation of lignocellulose phenolic resin

[0013] The lignocellulose biomass raw material is first pretreated, and then copolymerized with phenolic and aldehyde compounds under alkaline conditions. After centrifugation and drying, lignocellulose phenolic resin is obtained.

[0014] (II) Preparation of doped bamboo-based porous carbon

[0015] The pretreated bamboo-based biomass raw material was activated to obtain activated bamboo-based porous carbon.

[0016] The activated bamboo-based porous carbon was hydrothermally doped with raw materials containing doped atoms, and then centrifuged and dried to obtain doped bamboo-based porous carbon.

[0017] The doped bamboo-based porous carbon was pre-carbonized under a protective atmosphere, and after cooling, the pre-carbonized material was obtained.

[0018] The pre-carbonized material is crushed and purified by compound acid to obtain the acid-washed purified material;

[0019] The acid-washed purified material is washed with water and then washed with alkali to obtain the alkali-washed purified material.

[0020] (III) Preparation of hard carbon composite materials derived from lignocellulose phenolic resin / doped bamboo-based porous carbon

[0021] The lignocellulose phenolic resin obtained in step (I) is mixed evenly with the alkali-washed purified material obtained in step (II), and after high-temperature segmented carbonization, a lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material is obtained.

[0022] There is no distinction in the order of steps (i) and (ii), and step (ii) may be performed before step (i).

[0023] This invention involves coating doped bamboo-based porous carbon with phenolic resin modified with lignocellulose. During mixing, the resin's adhesive properties are used to uniformly adhere the carbon to the surface of the alkali-washed purified material. In the subsequent high-temperature carbonization process, a layered structure of resin-decomposed carbon is formed, which effectively improves the conductivity and reversible capacity of the doped bamboo-based porous carbon material.

[0024] This invention leverages the synergistic effect of lignocellulose phenolic resin, doped atoms, and bamboo-based porous carbon to fully utilize the advantages of each component. The complementary structure and properties result in a hard carbon composite material that combines the advantages of traditional hard carbon materials with those of nano-doped materials. This leads to increased specific surface area, improved conductivity, and excellent electrochemical performance. Furthermore, the lignocellulose-modified phenolic resin coats the surface of the bamboo-based hard carbon anode material, forming a carbon coating layer. This reduces contact between the bamboo-based porous carbon material surface and impurity atoms with the electrolyte, minimizing side reactions and irreversible capacity loss. The initial coulombic efficiency is significantly improved, resulting in a higher sodium storage capacity.

[0025] In step (i), the lignocellulosic biomass raw material includes at least one of corn stalks, rice straw, reeds, sorghum stalks, rice husks, wood waste, rapeseed shells, and sawdust.

[0026] In step (I), the pretreatment process of the lignocellulose biomass raw material is as follows: the lignocellulose biomass raw material is washed with water and then placed in a drying oven for drying. The drying temperature of the drying oven is 60-120℃ and the drying time is 4-24h.

[0027] In step (I), the copolymerization reaction of lignocellulose biomass raw material with phenolic compounds and aldehyde compounds specifically includes the following steps: adding the pretreated lignocellulose biomass raw material, phenolic compounds and aldehyde compounds into a four-necked flask, then adding an alkaline solution with a concentration of 30-50%, adjusting the pH to 10-14, and reacting at 60-80℃ for 0.5-4 hours.

[0028] Furthermore, the phenolic compounds include phenol, and the aldehyde compounds include formaldehyde.

[0029] Furthermore, the mass of the phenolic compounds is 1 to 3 times the mass of the lignocellulosic biomass raw material, and the mass of the aldehyde compounds is 4 to 6 times the mass of the lignocellulosic biomass raw material.

[0030] Furthermore, the solid-liquid mass ratio in the copolymerization reaction is 1:3 to 10.

[0031] Furthermore, after the copolymerization reaction is completed, the product is washed and centrifuged multiple times with deionized water, and then placed in a vacuum drying oven for drying at a temperature of 60–120°C for 2–24 hours.

[0032] Phenolic resin is a widely used adhesive, but it suffers from drawbacks such as high viscosity, insufficient cross-linking, formaldehyde release, high raw material costs, and non-renewability, leading to poor performance of composite materials formed with other materials. Therefore, this invention uses lignocellulose modified into phenolic resin. This is primarily because lignin, as the most abundant renewable phenolic compound in nature, possesses active groups such as phenolic hydroxyl, alcoholic hydroxyl, and aldehyde groups similar in structure to phenolic resin. Thus, lignin can be directly used as a raw material to produce lignin-based phenolic resin, which improves the adhesive properties and reduces the amount of phenol used and formaldehyde release. By activating and modifying the lignin molecular structure, the content of hydroxymethyl, phenolic hydroxyl, and alcoholic hydroxyl groups on the lignin molecule is increased. Due to its electronic induction effect, the number of activation sites in the lignin molecular structure increases, resulting in higher activity. This improves the polymerization degree between lignin and phenolic resin, thereby increasing the bonding strength of the lignin-based phenolic resin adhesive and making it more uniform and dense when used as a carbon coating layer.

[0033] In step (ii), the bamboo-based biomass raw material includes at least one of spotted bamboo, moso bamboo, purple bamboo, and bamboo powder.

[0034] This invention uses bamboo-based biomass raw materials as the core of hard carbon composite materials, mainly because bamboo-based biomass raw materials contain a large amount of cellulose. During pulverization, the particle size of the cellulose in the bamboo-based biomass carbonized material decreases, disrupting the crystalline structure of the cellulose and increasing the specific surface area, thus increasing the Na content. + The storage provides more reactive sites, ultimately improving sodium storage capacity and rate performance.

[0035] In step (ii), the pretreatment process of the bamboo-based biomass raw material is as follows: the bamboo-based biomass raw material is washed with water and then placed in a drying oven for drying. The drying temperature of the drying oven is 60-120℃ and the drying time is 4-24h.

[0036] In step (ii), the activation process is as follows: an activator with a concentration of 30-50% is added to the pretreated bamboo-based biomass raw material, and the activation reaction is carried out by stirring at room temperature for 8-24 hours.

[0037] Furthermore, the activator includes at least one of KOH and NaOH solutions, preferably a KOH solution.

[0038] Furthermore, the mass ratio of the activator to the pretreated bamboo-based biomass raw material is 2 to 5:1.

[0039] Furthermore, after the activation reaction is complete, the mixture is centrifuged and then placed in a drying oven for drying at a temperature of 60–120°C for 4–24 hours.

[0040] Because of Na + The large radius leads to slow kinetics. This invention increases porosity by activating bamboo-based biomass raw materials to form a porous carbon structure, which is beneficial for increasing diffusion channels and shortening the transport distance of ions and electrons, thereby improving Na+. + The diffusion rate is increased; furthermore, increasing porosity helps increase the contact area between the porous carbon of bamboo-based biomass and the electrolyte and electrode surfaces, allowing the electrolyte to fully penetrate and thus increasing the effective reaction area; simultaneously, activation can increase the specific surface area of ​​bamboo-based biomass raw materials, which is Na + The storage provides more reactive sites, ultimately improving sodium storage capacity and rate performance.

[0041] In step (ii), the hydrothermal doping process is as follows: after the activated bamboo-based porous carbon, boron source, nitrogen source and phosphorus source are stirred evenly, they are added together to a high-pressure reactor and hydrothermally reacted at 120-180℃ for 12-48h. After the reaction is completed, the mixture is washed with deionized water and ethanol, centrifuged and placed in a vacuum drying oven, and dried under vacuum conditions at 60-120℃ for 2-24h.

[0042] Furthermore, the boron source is boric acid, the nitrogen source is urea, and the phosphorus source is sodium dihydrogen phosphate; the boric acid, urea, and sodium dihydrogen phosphate each account for 10-50% of the mass of the activated bamboo-based porous carbon.

[0043] This invention introduces B, N, P heteroatoms and the cation Na into the surface or pores of bamboo-based porous carbon. + This provides more active sites and induces a disordered carbon structure, optimizing the interlayer spacing and surface wettability of the material. Furthermore, co-doping with multiple atoms can produce synergistic effects, improving the electrochemical performance of the material. The mesopores and micropores in bamboo-based porous carbon can generate numerous defects; the micropores are used for Na... + In terms of storage, mesopores are mainly used to increase the specific surface area of ​​the reaction, reduce the interfacial resistance, and improve the ion transport efficiency; the doping of atoms and the porous carbon structure synergistically improve the sodium storage performance and enhance the capacity and rate performance of hard carbon materials.

[0044] In step (ii), the protective atmosphere for pre-carbonization includes at least one of nitrogen, argon, and helium.

[0045] The pre-carbonization conditions are as follows: heating rate of 2-10℃ / min, pre-carbonization temperature of 500-800℃, and holding time of 1-3h; the pre-carbonization is carried out in a tube furnace.

[0046] Furthermore, the particle size of the pre-carbonized material after pulverization is controlled to be 3–17 μm.

[0047] In step (ii), the composite acid purification process is as follows: the pre-carbonized material is first crushed, then deionized water is added to the crushed pre-carbonized material, stirred and sonicated at room temperature, then composite acid is added and reacted at 60-100℃ for 4-12 hours, and the acid-washed purified material is obtained by centrifugation.

[0048] Furthermore, the stirring time at room temperature is 8–24 h, the ultrasonic frequency is 40–60 kHz, and the ultrasonic time is 10–30 min.

[0049] Furthermore, the composite acid is a mixed solution of an inorganic acid and a chelating agent. The inorganic acid includes at least two of hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid, and sulfuric acid; the chelating agent is a small-molecule organic acid, including at least one of citric acid, acetic acid, and oxalic acid.

[0050] Furthermore, the solid-liquid mass ratio in the composite acid purification process is 1:2 to 5.5.

[0051] In step (ii), the alkaline washing process is as follows: an alkaline solution with a molar concentration of 1–3 mol / L is added to the acid-washed purified material, and the reaction is carried out at 60–100°C for 4–12 h; after the reaction, the material is centrifuged, placed in a drying oven, and dried at 60–120°C for 4–24 h to obtain the alkaline-washed purified material. The alkaline solution includes at least one of KOH, NaOH, NaHCO3, and KHCO3; the solid-liquid mass ratio of the acid-washed purified material to the alkaline solution is 1:3–5.

[0052] In step (iii), the mass ratio of the doped bamboo-based porous carbon to the lignocellulose phenolic resin is (99-90):(1-10).

[0053] In step (iii), the doped bamboo-based porous carbon and lignocellulose phenolic resin are first mixed in a mixer for 10-30 minutes. After the mixture is homogeneous, it is subjected to high-temperature segmented carbonization under a protective atmosphere. After cooling, the iron is removed and the mixture is passed through a 200-400 mesh sieve to obtain a hard carbon composite material derived from lignocellulose phenolic resin / doped bamboo-based porous carbon.

[0054] Furthermore, the conditions for the high-temperature segmented carbonization are as follows:

[0055] The first stage is low-temperature carbonization, with a temperature of 800-1000℃, a heating rate of 4-6℃ / min, and a holding time of 1-2h.

[0056] The second stage involves high-temperature carbonization at a temperature of 1200–1400℃, a heating rate of 1–2℃ / min, and a holding time of 1–2h.

[0057] The third stage of cooling involves cooling to 800–1100℃ at a rate of 3–5℃ / min, followed by natural cooling with protective gas to 25–30℃.

[0058] During the first stage of low-temperature carbonization, pyrolysis occurs, rapidly releasing a large number of organic molecules, which is conducive to the formation of a rich porous structure. During the second stage of high-temperature carbonization, the degree of graphitization can be improved while maintaining a large interlayer spacing, which is conducive to the insertion and extraction of sodium ions in the material, thereby improving the initial coulombic efficiency and reversible capacity. However, the heating rate in the high-temperature stage should not be too fast, otherwise it will easily cause insufficient volatilization of small molecules and an increase in specific surface area. Therefore, the heating rate is controlled at 1 to 2 °C / min. During the third stage of cooling, the cooling rate should be controlled at 3 to 5 °C / min and decreased slowly, otherwise internal cracks will appear and the performance will be reduced.

[0059] The protective atmosphere includes at least one of nitrogen, argon, and helium.

[0060] In a third aspect, the present invention provides a negative electrode sheet, wherein the negative electrode sheet uses the above-mentioned lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material as the active material of the battery negative electrode material.

[0061] In a fourth aspect, the present invention provides a battery, the battery being a sodium-ion battery, the sodium-ion battery comprising a negative electrode, a positive electrode, a separator, and an electrolyte, wherein the negative electrode comprises the aforementioned negative electrode sheet.

[0062] Furthermore, under a charge-discharge test at a current density of 0.1C, the sodium-ion battery exhibited an initial charge specific capacity greater than 360.7 Ah / g, an initial discharge specific capacity greater than 395.9 Ah / g, and an initial efficiency greater than 94%. Under charge-discharge tests at different rates, the sodium-ion battery maintained a capacity retention rate of greater than 93.1% at 4C / 0.1C.

[0063] As described above, the lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material, its preparation method, and its application of the present invention have the following beneficial effects: The present invention fully utilizes the advantages of each of the three through the synergistic effect among lignocellulose phenolic resin, doped atoms, and bamboo-based porous carbon, complementing each other in structure and properties, thereby increasing the specific surface area and improving the conductivity of the hard carbon composite material, resulting in excellent electrochemical performance. At the same time, the lignocellulose-modified phenolic resin coats the surface of the bamboo-based porous carbon to form a carbon coating layer, reducing the contact between the surface of the bamboo-based porous carbon and the doped atoms and the electrolyte, reducing side reactions, reducing irreversible capacity loss, significantly improving the initial coulombic efficiency, and obtaining a higher sodium storage specific capacity. Attached Figure Description

[0064] Figure 1This is a comparison chart of the charge-discharge curves of Embodiment 1 and Comparative Example 1 of the present invention under 0.1C conditions. Detailed Implementation

[0065] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0066] Example 1

[0067] A method for preparing a lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material includes the following steps:

[0068] S1. Rinse the corn stalks with water, then dry them in a drying oven at 80℃ for 12 hours. After drying, take 30g of corn stalks, 30g of phenol, and 120g of formaldehyde and add them to a four-necked flask. Then add a 40% NaOH solution to adjust the pH to 12 and react at 60℃ for 4 hours. The solid-liquid mass ratio in the mixed solution is 1:3. After the reaction is complete, wash the mixture several times with deionized water, centrifuge, and then place it in a vacuum drying oven at 100℃ for 12 hours to obtain lignocellulose phenolic resin.

[0069] S2. Rinse the bamboo with water and then dry it in a drying oven at 80℃ for 12 hours. After drying, add a 30% KOH solution to the dried bamboo-based biomass and stir at room temperature for 12 hours to carry out the activation reaction. The mass ratio of KOH solution to dried bamboo-based biomass is 3:1. After the reaction is completed, centrifuge and then put it in a drying oven to dry at 80℃ for 12 hours to obtain activated bamboo-based porous carbon.

[0070] S3. Take 20g of activated bamboo-based porous carbon, 2g of boric acid, 2g of urea and 2g of sodium dihydrogen phosphate into a beaker, stir well and then add them together into a 100mL high-pressure reactor. Perform hydrothermal reaction at 160℃ for 24h. After the hydrothermal reaction is complete, wash with deionized water and ethanol, centrifuge and filter, and then place in a vacuum drying oven to dry under vacuum at 80℃ for 12h to obtain doped bamboo-based porous carbon.

[0071] S4. Place the activated bamboo-based porous carbon material into a tube furnace and heat it to 600°C at a rate of 5°C / min under an argon atmosphere. Hold the temperature for 2 hours for pre-carbonization. After cooling to room temperature, the pre-carbonized material is obtained.

[0072] S5. Crush the pre-carbonized material, and the particle size D after crushing. 50The particle size was controlled at around 10 μm. Then, 28 g of deionized water was added to 14 g of pulverized material and stirred until homogeneous. The mixture was then placed in an ultrasonic cleaner and ultrasonicated at 60 kHz for 20 minutes. After ultrasonication, a compound acid was added, and the mixture was purified at 80°C for 8 hours. The solid-liquid mass ratio was 1:4, where the compound acid consisted of 12 g hydrochloric acid, 10 g hydrofluoric acid, and 6 g citric acid. After purification, the mixture was washed several times with deionized water until the filtrate was nearly neutral. After centrifugation, the acid-washed purified material was obtained.

[0073] S6. Add a 2 mol / L NaOH solution to the acid-washed purified material, react at 80℃ for 12 h, then centrifuge and dry in a drying oven at 80℃ for 12 h to obtain the alkali-washed purified material, wherein the solid-liquid mass ratio is 1:3.

[0074] S7. The alkali-washed purified raw material and lignocellulose phenolic resin were mixed at a mass ratio of 95:5. After mixing for 20 minutes, the mixture was placed in a tube furnace for high-temperature segmented carbonization. Under an argon atmosphere, the temperature was first raised to 800℃ at a heating rate of 5℃ / min and held for 1 hour. Then, the temperature was raised to 1300℃ at a heating rate of 2℃ / min and held for 1 hour. Finally, the temperature was lowered to 800℃ at a cooling rate of 4℃ / min and then naturally cooled to 30℃. After removing iron, the mixture was passed through a 325-mesh sieve to obtain a hard carbon composite material derived from lignocellulose phenolic resin / doped bamboo-based porous carbon.

[0075] The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material prepared above was used to prepare sodium-ion batteries.

[0076] Weigh out 0.2g of CMC, 0.4g of SP, 9.2g of lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material, and 0.5g of SBR (40% solid content) according to the mass ratio of 2.0%:4.0%:92.0%:2.0%. Add an appropriate amount of deionized water and stir for 8 hours until a uniform slurry is formed. Use a four-sided coating apparatus to uniformly coat the slurry onto the surface of copper foil. Dry in a 105℃ forced-air drying oven for 2 hours. Cut the Cu foil with active material into circular negative electrode sheets and transfer them to a glove box for later use.

[0077] The assembly of the simulated battery was carried out in an Ar atmosphere glove box. The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon electrode prepared above was used as the negative electrode, and a 1.0 mol / L commercial electrolyte was used. The commercial electrolyte was prepared by adding NaPF6 to a volume ratio of EC:DMC=1:1. Na metal sheet was used as the counter electrode. The CR2032 coin cell was assembled, and then charge and discharge tests were carried out at a current density of 0.1C and at different rates.

[0078] Example 2

[0079] A method for preparing a lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material includes the following steps:

[0080] S1. Rinse the corn stalks with water, then dry them in a drying oven at 80℃ for 12 hours. After drying, take 30g of corn stalks, 90g of phenol, and 180g of formaldehyde and add them to a four-necked flask. Then add a 50% NaOH solution to adjust the pH to 12 and react at 80℃ for 2 hours. The solid-liquid mass ratio in the mixed solution is 1:5. After the reaction is complete, wash the mixture multiple times with deionized water, centrifuge, and then place it in a vacuum drying oven at 100℃ for 12 hours to obtain lignocellulose phenolic resin.

[0081] S2. Rinse the bamboo with water and then dry it in a drying oven at 80℃ for 12 hours. After drying, add a 30% KOH solution to the dried bamboo-based biomass and stir at room temperature for 12 hours to carry out the activation reaction. The mass ratio of KOH solution to dried bamboo-based biomass is 3:1. After the reaction is completed, centrifuge and then put it in a drying oven to dry at 80℃ for 12 hours to obtain activated bamboo-based porous carbon.

[0082] S3. Take 20g of activated bamboo-based porous carbon, 2g of boric acid, 2g of urea and 2g of sodium dihydrogen phosphate into a beaker, stir evenly and then add them together into a 100mL high-pressure reactor. Perform hydrothermal reaction at 160℃ for 24h. After the hydrothermal reaction is complete, wash with deionized water and ethanol, centrifuge and filter, and then place in a vacuum drying oven to dry under vacuum at 80℃ for 12h to obtain doped bamboo-based porous carbon material.

[0083] S4. Place the activated bamboo-based porous carbon material into a tube furnace and heat it to 600°C at a rate of 5°C / min under an argon atmosphere. Hold the temperature for 2 hours for pre-carbonization. After cooling to room temperature, the pre-carbonized material is obtained.

[0084] S5. Crush the pre-carbonized material, and the particle size D after crushing. 50 The particle size was controlled at around 10 μm. Then, 28 g of deionized water was added to 14 g of pulverized material and stirred until homogeneous. The mixture was then placed in an ultrasonic cleaner and ultrasonicated at 60 kHz for 20 minutes. After ultrasonication, a compound acid was added, and the mixture was purified at 80°C for 8 hours. The solid-liquid mass ratio was 1:4, where the compound acid consisted of 12 g hydrochloric acid, 10 g hydrofluoric acid, and 6 g citric acid. After purification, the mixture was washed several times with deionized water until the filtrate was nearly neutral. After centrifugation, the acid-washed purified material was obtained.

[0085] S6. Add a 2 mol / L NaOH solution to the acid-washed purified material, react at 80℃ for 12 h, then centrifuge and dry in a drying oven at 80℃ for 12 h to obtain the alkali-washed purified material, wherein the solid-liquid mass ratio is 1:3.

[0086] S7. The alkali-washed purified raw material and lignocellulose phenolic resin were mixed at a mass ratio of 95:5. After mixing for 20 minutes, the mixture was placed in a tube furnace for high-temperature segmented carbonization. Under an argon atmosphere, the temperature was first raised to 800℃ at a heating rate of 5℃ / min and held for 1 hour. Then, the temperature was raised to 1300℃ at a heating rate of 2℃ / min and held for 1 hour. Finally, the temperature was lowered to 800℃ at a cooling rate of 4℃ / min and then naturally cooled to 30℃. After removing iron, the mixture was passed through a 325-mesh sieve to obtain a hard carbon composite material derived from lignocellulose phenolic resin / doped bamboo-based porous carbon.

[0087] The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material prepared above was used to prepare sodium-ion batteries.

[0088] Weigh out 0.2g of CMC, 0.4g of SP, 9.2g of lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite anode material, and 0.5g of SBR (40% solid content) according to a mass ratio of 2.0%:4.0%:92.0%:2.0%. Add an appropriate amount of deionized water and stir for 8 hours until a uniform slurry is formed. Use a four-sided coating apparatus to evenly coat the slurry onto the surface of copper foil. Dry in a 105℃ forced-air drying oven for 2 hours. Cut the Cu foil with active material into circular anode sheets and transfer them to a glove box for later use.

[0089] The assembly of the simulated battery was carried out in an Ar atmosphere glove box. The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon electrode prepared above was used as the negative electrode, and a 1.0 mol / L commercial electrolyte was used. The commercial electrolyte was prepared by adding NaPF6 to a volume ratio of EC:DMC=1:1. Na metal sheet was used as the counter electrode. The CR2032 coin cell was assembled, and then charge and discharge tests were carried out at a current density of 0.1C and at different rates.

[0090] Example 3

[0091] A method for preparing a lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material includes the following steps:

[0092] S1. Rinse the corn stalks with water, then dry them in a drying oven at 80℃ for 12 hours. After drying, take 30g of corn stalks, 30g of phenol, and 120g of formaldehyde and add them to a four-necked flask. Then add a 40% NaOH solution to adjust the pH to 12 and react at 60℃ for 2 hours. The solid-liquid mass ratio in the mixed solution is 1:3. After the reaction is complete, wash the mixture several times with deionized water, centrifuge, and then place it in a vacuum drying oven at 100℃ for 12 hours to obtain lignocellulose phenolic resin.

[0093] S2. Rinse the bamboo with water and then dry it in a drying oven at 80℃ for 12 hours. After drying, add a 50% KOH solution to the dried bamboo-based biomass and stir at room temperature for 24 hours to carry out the activation reaction. The mass ratio of KOH solution to dried bamboo-based biomass is 5:1. After the reaction is completed, centrifuge and then put it in a drying oven to dry at 80℃ for 12 hours to obtain activated bamboo-based porous carbon.

[0094] S3. Take 20g of activated bamboo-based porous carbon material, 2g of boric acid, 2g of urea and 2g of sodium dihydrogen phosphate into a beaker, stir evenly and then add them together into a 100mL high-pressure reactor. Perform hydrothermal reaction at 160℃ for 24h. After the hydrothermal reaction is complete, wash with deionized water and ethanol, centrifuge and filter, and then place in a vacuum drying oven to dry under vacuum at 80℃ for 12h to obtain doped bamboo-based porous carbon material.

[0095] S4. Place the activated bamboo-based porous carbon material into a tube furnace and heat it to 600°C at a rate of 5°C / min under an argon atmosphere. Hold the temperature for 2 hours for pre-carbonization. After cooling to room temperature, the pre-carbonized material is obtained.

[0096] S5. Crush the pre-carbonized material, and the particle size D after crushing. 50 The particle size was controlled at around 10 μm. Then, 28 g of deionized water was added to 14 g of pulverized material and stirred until homogeneous. The mixture was then placed in an ultrasonic cleaner and ultrasonicated at 60 kHz for 20 minutes. After ultrasonication, a compound acid was added, and the mixture was purified at 80°C for 8 hours. The solid-liquid mass ratio was 1:4, where the compound acid consisted of 12 g hydrochloric acid, 10 g hydrofluoric acid, and 6 g citric acid. After purification, the mixture was washed several times with deionized water until the filtrate was nearly neutral. After centrifugation, the acid-washed purified material was obtained.

[0097] S6. Add a 2 mol / L NaOH solution to the acid-washed purified material, react at 80℃ for 12 h, then centrifuge and dry in a drying oven at 80℃ for 12 h to obtain the alkali-washed purified material, wherein the solid-liquid mass ratio is 1:3.

[0098] S7. The alkali-washed purified raw material and lignocellulose phenolic resin were mixed at a mass ratio of 95:5. After mixing for 20 minutes, the mixture was placed in a tube furnace for high-temperature segmented carbonization. Under an argon atmosphere, the temperature was first raised to 800℃ at a heating rate of 5℃ / min and held for 1 hour. Then, the temperature was raised to 1300℃ at a heating rate of 2℃ / min and held for 1 hour. Finally, the temperature was lowered to 800℃ at a cooling rate of 4℃ / min and then naturally cooled to 30℃. After removing iron, the mixture was passed through a 325-mesh sieve to obtain a hard carbon composite material derived from lignocellulose phenolic resin / doped bamboo-based porous carbon.

[0099] The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material prepared above was used in sodium-ion batteries.

[0100] Weigh out 0.2g of CMC, 0.4g of SP, 9.2g of lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite anode material, and 0.5g of SBR (40% solid content) according to a mass ratio of 2.0%:4.0%:92.0%:2.0%. Add an appropriate amount of deionized water and stir for 8 hours until a uniform slurry is formed. Use a four-sided coating apparatus to evenly coat the slurry onto the surface of copper foil. Dry in a 105℃ forced-air drying oven for 2 hours. Cut the Cu foil with active material into circular anode sheets and transfer them to a glove box for later use.

[0101] The assembly of the simulated battery was carried out in an Ar atmosphere glove box. The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon electrode prepared above was used as the negative electrode, and a 1.0 mol / L commercial electrolyte was used. The commercial electrolyte was prepared by adding NaPF6 to a volume ratio of EC:DMC=1:1. Na metal sheet was used as the counter electrode. The CR2032 coin cell was assembled, and then charge and discharge tests were carried out at a current density of 0.1C and at different rates.

[0102] Example 4

[0103] A method for preparing a lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material includes the following steps:

[0104] S1. Rinse the corn stalks with water, then dry them in a drying oven at 80℃ for 12 hours. After drying, take 30g of corn stalks, 30g of phenol, and 120g of formaldehyde and add them to a four-necked flask. Then add a 40% NaOH solution to adjust the pH to 12 and react at 60℃ for 2 hours. The solid-liquid mass ratio in the mixed solution is 1:3. After the reaction is complete, wash the mixture several times with deionized water, centrifuge, and then place it in a vacuum drying oven at 100℃ for 12 hours to obtain lignocellulose phenolic resin.

[0105] S2. Rinse the bamboo with water and then dry it in a drying oven at 80℃ for 12 hours. After drying, add a 30% KOH solution to the dried bamboo-based biomass and stir at room temperature for 12 hours to carry out the activation reaction. The mass ratio of KOH solution to dried bamboo-based biomass is 3:1. After the reaction is completed, centrifuge and then put it in a drying oven to dry at 80℃ for 12 hours to obtain activated bamboo-based porous carbon.

[0106] S3. Take 20g of activated bamboo-based porous carbon, 10g of boric acid, 10g of urea and 10g of sodium dihydrogen phosphate into a beaker, stir evenly and then add them together into a 100mL high-pressure reactor. Perform hydrothermal reaction at 180℃ for 48h. After the hydrothermal reaction is complete, wash with deionized water and ethanol, centrifuge and filter, and then place in a vacuum drying oven to dry under vacuum at 80℃ for 12h to obtain doped bamboo-based porous carbon material.

[0107] S4. Place the activated bamboo-based porous carbon material into a tube furnace and heat it to 600°C at a rate of 5°C / min under an argon atmosphere. Hold the temperature for 2 hours for pre-carbonization. After cooling to room temperature, the pre-carbonized material is obtained.

[0108] S5. Crush the pre-carbonized material, and the particle size D after crushing. 50 The particle size was controlled at around 10 μm. Then, 28 g of deionized water was added to 14 g of pulverized material and stirred until homogeneous. The mixture was then placed in an ultrasonic cleaner and ultrasonicated at 60 kHz for 20 minutes. After ultrasonication, a compound acid was added, and the mixture was purified at 80°C for 8 hours. The solid-liquid mass ratio was 1:4, where the compound acid consisted of 12 g hydrochloric acid, 10 g hydrofluoric acid, and 6 g citric acid. After purification, the mixture was washed several times with deionized water until the filtrate was nearly neutral. After centrifugation, the acid-washed purified material was obtained.

[0109] S6. Add a 2 mol / L NaOH solution to the acid-washed purified material, react at 80℃ for 12 h, then centrifuge and dry in a drying oven at 80℃ for 12 h to obtain the alkali-washed purified material, wherein the solid-liquid mass ratio is 1:3.

[0110] S7. The alkali-washed purified raw material and lignocellulose phenolic resin were mixed at a mass ratio of 95:5. After mixing for 20 minutes, the mixture was placed in a tube furnace for high-temperature segmented carbonization. Under an argon atmosphere, the temperature was first raised to 800℃ at a heating rate of 5℃ / min and held for 1 hour. Then, the temperature was raised to 1300℃ at a heating rate of 2℃ / min and held for 1 hour. Finally, the temperature was lowered to 800℃ at a cooling rate of 4℃ / min and then naturally cooled to 30℃. After removing iron, the mixture was passed through a 325-mesh sieve to obtain a hard carbon composite material derived from lignocellulose phenolic resin / doped bamboo-based porous carbon.

[0111] The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material prepared above was used in sodium-ion batteries.

[0112] Weigh out 0.2g of CMC, 0.4g of SP, 9.2g of lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite anode material, and 0.5g of SBR (40% solid content) according to a mass ratio of 2.0%:4.0%:92.0%:2.0%. Add an appropriate amount of deionized water and stir for 8 hours until a uniform slurry is formed. Use a four-sided coating apparatus to evenly coat the slurry onto the surface of copper foil. Dry in a 105℃ forced-air drying oven for 2 hours. Cut the Cu foil with active material into circular anode sheets and transfer them to a glove box for later use.

[0113] The assembly of the simulated battery was carried out in an Ar atmosphere glove box. The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon electrode prepared above was used as the negative electrode, and a 1.0 mol / L commercial electrolyte was used. The commercial electrolyte was prepared by adding NaPF6 to a volume ratio of EC:DMC=1:1. Na metal sheet was used as the counter electrode. The CR2032 coin cell was assembled, and then charge and discharge tests were carried out at a current density of 0.1C and at different rates.

[0114] Example 5

[0115] A method for preparing a lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material includes the following steps:

[0116] S1. Rinse the corn stalks with water, then dry them in a drying oven at 80℃ for 12 hours. After drying, take 30g of corn stalks, 30g of phenol, and 120g of formaldehyde and add them to a four-necked flask. Then add a 40% NaOH solution to adjust the pH to 12 and react at 60℃ for 2 hours. The solid-liquid mass ratio in the mixed solution is 1:3. After the reaction is complete, wash the mixture several times with deionized water, centrifuge, and then place it in a vacuum drying oven at 100℃ for 12 hours to obtain lignocellulose phenolic resin.

[0117] S2. Rinse the bamboo with water and then dry it in a drying oven at 80℃ for 12 hours. After drying, add a 30% KOH solution to the dried bamboo-based biomass and stir at room temperature for 12 hours to carry out the activation reaction. The mass ratio of KOH solution to dried bamboo-based biomass is 3:1. After the reaction is completed, centrifuge and then put it in a drying oven to dry at 80℃ for 12 hours to obtain activated bamboo-based porous carbon.

[0118] S3. Take 20g of activated bamboo-based porous carbon, 2g of boric acid, 2g of urea and 2g of sodium dihydrogen phosphate into a beaker, stir evenly and then add them together into a 100mL high-pressure reactor. Perform hydrothermal reaction at 160℃ for 24h. After the hydrothermal reaction is complete, wash with deionized water and ethanol, centrifuge and filter, and then place in a vacuum drying oven to dry under vacuum at 80℃ for 12h to obtain doped bamboo-based porous carbon material.

[0119] S4. Place the activated bamboo-based porous carbon material into a tube furnace and heat it to 600°C at a rate of 5°C / min under an argon atmosphere. Hold the temperature for 2 hours for pre-carbonization. After cooling to room temperature, the pre-carbonized material is obtained.

[0120] S5. Crush the pre-carbonized material to a particle size (D50) of approximately 10 μm. Add 28 g of deionized water to 14 g of the crushed material and stir until homogeneous. Place the mixture in an ultrasonic cleaner and sonicate at 60 kHz for 20 minutes. After sonication, add a compound acid and purify at 80°C for 8 hours. The solid-liquid mass ratio is 1:4. The compound acid consists of 12 g hydrochloric acid, 10 g hydrofluoric acid, and 6 g citric acid. After purification, wash the mixture multiple times with deionized water until the filtrate is nearly neutral. Centrifuge to obtain the acid-washed purified material.

[0121] S6. Add a 2 mol / L NaOH solution to the acid-washed purified material, react at 80℃ for 12 h, then centrifuge and dry in a drying oven at 80℃ for 12 h to obtain the alkali-washed purified material, wherein the solid-liquid mass ratio is 1:3.

[0122] S7. The alkali-washed purified raw material and lignin-based phenolic resin are mixed at a mass ratio of 95:5. After mixing for 20 minutes, the mixture is placed in a tube furnace for high-temperature segmented carbonization. Under an argon atmosphere, the temperature is first raised to 800℃ at a heating rate of 5℃ / min and held for 2 hours. Then, the temperature is raised to 1300℃ at a heating rate of 2℃ / min and held for 2 hours. Finally, the temperature is lowered to 800℃ at a cooling rate of 4℃ / min and then naturally cooled to 30℃. After removing iron, the mixture is passed through a 325-mesh sieve to obtain a hard carbon composite material derived from lignin-cellulose phenolic resin / doped bamboo-based porous carbon.

[0123] The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material prepared above was used in sodium-ion batteries.

[0124] Weigh out 0.2g of CMC, 0.4g of SP, 9.2g of lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite anode material, and 0.5g of SBR (40% solid content) according to a mass ratio of 2.0%:4.0%:92.0%:2.0%. Add an appropriate amount of deionized water and stir for 8 hours until a uniform slurry is formed. Use a four-sided coating apparatus to evenly coat the slurry onto the surface of copper foil. Dry in a 105℃ forced-air drying oven for 2 hours. Cut the Cu foil with active material into circular anode sheets and transfer them to a glove box for later use.

[0125] The assembly of the simulated battery was carried out in an Ar atmosphere glove box. The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon electrode prepared above was used as the negative electrode, and a 1.0 mol / L commercial electrolyte was used. The commercial electrolyte was prepared by adding NaPF6 to a volume ratio of EC:DMC=1:1. Na metal sheet was used as the counter electrode. The CR2032 coin cell was assembled, and then charge and discharge tests were carried out at a current density of 0.1C and at different rates.

[0126] Example 6

[0127] A method for preparing a lignocellulose phenolic resin / doped bamboo-based porous carbon hard carbon composite material includes the following steps:

[0128] S1. Rinse the corn stalks with water, then dry them in a drying oven at 80℃ for 12 hours. After drying, take 30g of corn stalks, 30g of phenol, and 120g of formaldehyde and add them to a four-necked flask. Then add a 40% NaOH solution to adjust the pH to 12 and react at 60℃ for 2 hours. The solid-liquid mass ratio in the mixed solution is 1:3. After the reaction is complete, wash the mixture several times with deionized water, centrifuge, and then place it in a vacuum drying oven at 100℃ for 12 hours to obtain lignocellulose phenolic resin.

[0129] S2. Rinse the bamboo with water and then dry it in a drying oven at 80℃ for 12 hours. After drying, add a 30% KOH solution to the dried bamboo-based biomass and stir at room temperature for 12 hours to carry out the activation reaction. The mass ratio of KOH solution to dried bamboo-based biomass is 3:1. After the reaction is completed, centrifuge and then put it in a drying oven to dry at 80℃ for 12 hours to obtain activated bamboo-based porous carbon.

[0130] S3. Take 20g of activated bamboo-based porous carbon, 2g of boric acid, 2g of urea and 2g of sodium dihydrogen phosphate into a beaker, stir evenly and then add them together into a 100mL high-pressure reactor. Perform hydrothermal reaction at 160℃ for 24h. After the hydrothermal reaction is complete, wash with deionized water and ethanol, centrifuge and filter, and then place in a vacuum drying oven to dry under vacuum at 80℃ for 12h to obtain doped bamboo-based porous carbon material.

[0131] S4. Place the activated bamboo-based porous carbon material into a tube furnace and heat it to 600°C at a rate of 5°C / min under an argon atmosphere. Hold the temperature for 2 hours for pre-carbonization. After cooling to room temperature, the pre-carbonized material is obtained.

[0132] S5. Crush the pre-carbonized material, and the particle size D after crushing. 50The particle size was controlled at around 10 μm. Then, 28 g of deionized water was added to 14 g of pulverized material and stirred until homogeneous. The mixture was then placed in an ultrasonic cleaner and ultrasonicated at 60 kHz for 20 minutes. After ultrasonication, a compound acid was added, and the mixture was purified at 80°C for 8 hours. The solid-liquid mass ratio was 1:4, where the compound acid consisted of 12 g hydrochloric acid, 10 g hydrofluoric acid, and 6 g citric acid. After purification, the mixture was washed several times with deionized water until the filtrate was nearly neutral. After centrifugation, the acid-washed purified material was obtained.

[0133] S6. Add a 2 mol / L NaOH solution to the acid-washed purified material, react at 80℃ for 12 h, then centrifuge and dry in a drying oven at 80℃ for 12 h to obtain the alkali-washed purified material, wherein the solid-liquid mass ratio is 1:3.

[0134] S7. The alkali-washed purified raw material and lignocellulose phenolic resin were mixed at a mass ratio of 95:5. After mixing for 20 minutes, the mixture was placed in a tube furnace for high-temperature segmented carbonization. Under an argon atmosphere, the temperature was first raised to 800℃ at a heating rate of 4℃ / min and held for 1 hour. Then, the temperature was raised to 1300℃ at a heating rate of 1℃ / min and held for 1 hour. Finally, the temperature was lowered to 800℃ at a cooling rate of 3℃ / min and then naturally cooled to 30℃. After removing iron, the mixture was passed through a 325-mesh sieve to obtain a hard carbon composite material derived from lignocellulose phenolic resin / doped bamboo-based porous carbon.

[0135] The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material prepared above was used in sodium-ion batteries.

[0136] Weigh out 0.2g of CMC, 0.4g of SP, 9.2g of lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite anode material, and 0.5g of SBR (40% solid content) according to a mass ratio of 2.0%:4.0%:92.0%:2.0%. Add an appropriate amount of deionized water and stir for 8 hours until a uniform slurry is formed. Use a four-sided coating apparatus to evenly coat the slurry onto the surface of copper foil. Dry in a 105℃ forced-air drying oven for 2 hours. Cut the Cu foil with active material into circular anode sheets and transfer them to a glove box for later use.

[0137] The assembly of the simulated battery was carried out in an Ar atmosphere glove box. The lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon electrode prepared above was used as the negative electrode, and a 1.0 mol / L commercial electrolyte was used. The commercial electrolyte was prepared by adding NaPF6 to a volume ratio of EC:DMC=1:1. Na metal sheet was used as the counter electrode. The CR2032 coin cell was assembled, and then charge and discharge tests were carried out at a current density of 0.1C and at different rates.

[0138] Comparative Example 1

[0139] A method for preparing a hard carbon composite material, which differs from Example 1 in that: S2 does not contain KOH solution activation, while the rest of the steps are the same as in Example 1, and the obtained battery material is tested using the same method as in Example 1.

[0140] Comparative Example 2

[0141] A method for preparing a hard carbon composite material, which differs from Example 1 in that: S3 does not contain hydrothermal doping, while the rest of the steps are the same as those in Example 1, and the battery material obtained is tested using the same method as in Example 1.

[0142] Comparative Example 3

[0143] A method for preparing a hard carbon composite material, which differs from Example 1 in that steps S1 and S7 are omitted, while the rest are consistent with the steps in Example 1, and the battery material obtained is tested using the same method as in Example 1.

[0144] Comparative Example 4

[0145] A method for preparing a wood-hard carbon composite material differs from Example 1 in that the lignin-based phenolic resin in steps S1 and S7 is replaced with conventional phenolic resin, while the rest of the steps are the same as in Example 1, and the obtained battery material is tested using the same method as in Example 1.

[0146] Comparative Example 5

[0147] A method for preparing a hard carbon composite material differs from Example 1 in that the high-temperature segmented carbonization in step S7 is changed to: heating from room temperature to 1300℃ at a heating rate of 5℃ / min under an argon atmosphere and holding for 1 hour, and then naturally cooling to room temperature. The rest of the steps are the same as those in Example 1, and the obtained battery material is tested using the same method as in Example 1.

[0148] The 11 hard carbon composite materials prepared in Examples 1-6 and Comparative Examples 1-5 were assembled into sodium-ion coin cells for electrochemical performance testing. The test results are shown in Table 1.

[0149] Table 1 Electrochemical performance of sodium-ion batteries

[0150]

[0151] According to the test results of Examples 1-6 in Table 1, the present invention uses bamboo-based biomass raw materials that are activated with alkaline solution, hydrothermally doped, pre-carbonized, acid-washed, and then alkali-washed to obtain doped bamboo-based porous carbon. This carbon is then coated and modified with activated and modified lignocellulose phenolic resin, and finally prepared by high-temperature segmental carbonization. The resulting lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material exhibits high sodium storage capacity, initial coulombic efficiency, and rate performance. Compared with Example 1, Example 2 has increased amounts of phenol and formaldehyde, higher NaOH solution concentration, and higher copolymerization temperature, resulting in a more complete copolymerization reaction. Therefore, the obtained lignocellulose phenolic resin has stronger adhesiveness and more uniform coating, leading to higher capacity and initial efficiency of the sodium-ion battery. Compared with Example 1, Example 3 has increased KOH solution concentration and longer stirring time, resulting in more complete activation, forming more porous structures, which is more conducive to the subsequent insertion of heteroatoms, thus leading to higher sodium storage capacity and rate performance. Compared to Example 1, Example 4 increased the amounts of boric acid, urea, and sodium dihydrogen phosphate, raised the reaction temperature, and prolonged the reaction time, providing more active sites and thus improving the capacity and rate performance of the sodium-ion battery material. Compared to Example 1, Examples 5 and 6 showed that Example 5 extended the holding time for the three stages of high-temperature carbonization, while Example 6 reduced the heating rate for the three stages of high-temperature carbonization, resulting in more complete molecular volatilization, the formation of more porous structures, and increased graphitization. This facilitates the insertion and extraction of sodium ions into the material, thereby improving the initial coulombic efficiency and sodium storage capacity.

[0152] According to Table 1, compared with Examples 1-6, the bamboo-based biomass pretreated material in Comparative Example 1 was not activated with KOH solution and did not form a bamboo-based porous carbon structure. Therefore, it could not provide more pores to accommodate B, N, P heteroatoms and Na cations. + Furthermore, because it lacks a porous carbon structure, it contains fewer micropores and mesopores, resulting in a reduced specific surface area and active sites, which is detrimental to Na+ storage and ultimately leads to poor sodium storage capacity and rate performance of sodium batteries.

[0153] According to Table 1, compared with Examples 1-6, the activated biomass material in Comparative Example 2 was not subjected to hydrothermal doping, and no B, N, P heteroatoms or Na cations were introduced. + The lack of hydrothermal doping or KOH solution activation prevents the formation of synergistic effects between atomic doping and porous carbon structures, thus reducing the conductivity and ion transport capacity of sodium-ion batteries, resulting in poor capacity and rate performance.

[0154] According to Table 1, compared with Examples 1-6, Comparative Examples 3 and 4 did not have phenolic resin coating. In Comparative Example 4, the lignin-based phenolic resin was replaced with conventional phenolic resin, which resulted in poor adhesiveness. When used as a coating layer, it could not be uniformly and densely attached to the surface of the carbonized material. In the later stage of segmented carbonization, it could not form a uniform layered structure of resin cracking carbon coating, which led to a decrease in capacity, initial coulombic efficiency and rate performance.

[0155] According to Table 1, compared with Examples 1-6, Comparative Example 5 changed high-temperature segmented carbonization to high-temperature carbonization, which resulted in insufficient release of organic molecules and was not conducive to the formation of a rich porous structure. It also could not improve the degree of graphitization and expand the interlayer spacing, which was not conducive to the insertion and extraction of sodium ions in the material, thus leading to a decrease in capacity, first coulombic efficiency and rate performance.

[0156] In summary, this invention leverages the synergistic effect of lignocellulose phenolic resin, doped atoms, and bamboo-based porous carbon, fully utilizing the advantages of each component. Their complementary structure and properties result in an increased specific surface area and improved conductivity in the hard carbon composite material, leading to excellent electrochemical performance. Simultaneously, the lignocellulose-modified phenolic resin coating on the bamboo-based porous carbon surface forms a carbon coating layer, reducing contact between the bamboo-based porous carbon surface and doped atoms with the electrolyte, minimizing side reactions and irreversible capacity loss, and significantly improving the initial coulombic efficiency, thus achieving a higher sodium storage specific capacity. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0157] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a lignocellulosic phenolic resin / doped bamboo-based porous carbon derived hard carbon composite material, characterized in that, The bamboo-based porous carbon is taken as a core, B, N and P co-doped atoms are loaded in the pores and on the surface of the bamboo-based porous carbon, and an outer layer is formed by in-situ cracking of lignocellulose phenolic resin to form a carbon coating layer; The preparation method comprises the following steps: (1) preparing lignocellulose phenolic resin The lignocellulose biomass raw material is pretreated, and then copolymerization is carried out with a phenolic compound and an aldehyde compound under alkaline conditions, and after centrifugation and drying, the lignocellulose phenolic resin is obtained; (2) preparing doped bamboo-based porous carbon The pretreated bamboo-based biomass raw material is activated to obtain activated bamboo-based porous carbon; The activated bamboo-based porous carbon is hydrothermally doped with a boron source, a nitrogen source and a phosphorus source, and after centrifugation and drying, the doped bamboo-based porous carbon is obtained; wherein the boron source is boric acid, the nitrogen source is urea, and the phosphorus source is sodium dihydrogen phosphate, and the boric acid, urea and sodium dihydrogen phosphate each account for 10-50% of the mass of the activated bamboo-based porous carbon; The doped bamboo-based porous carbon is pre-carbonized under a protective atmosphere, and after cooling, pre-carbonized material is obtained; wherein the pre-carbonization conditions are: a heating rate of 2-10℃ / min, a pre-carbonization temperature of 500-800℃, and a constant temperature time of 1-3h; The pre-carbonized material is crushed and purified by a composite acid to obtain acid-washed purified material; the composite acid is a mixed solution of inorganic acid and chelating agent, the inorganic acid includes at least two of hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid and sulfuric acid; the chelating agent includes at least one of citric acid, acetic acid and oxalic acid; the solid-liquid mass ratio in the composite acid purification process is 1:2-5.5; After the acid-washed purified material is washed with water, an alkali solution with a molar concentration of 1-3mol / L is added to the acid-washed purified material, and the reaction is carried out at 60-100℃ for 4-12h; after the reaction is completed, centrifugation and drying are carried out to obtain alkali-washed purified material; (3) preparing lignocellulose phenolic resin / doped bamboo-based porous carbon derived hard carbon composite material The lignocellulose phenolic resin obtained in step (1) and the alkali-washed purified material obtained in step (2) are mixed uniformly at a mass ratio of (1-10):(99-90), and after high-temperature staged carbonization, the lignocellulose phenolic resin / doped bamboo-based porous carbon derived hard carbon composite material is obtained; The high-temperature staged carbonization conditions are as follows: First-stage low-temperature carbonization, temperature 800-1000℃, heating rate 4-6℃ / min, constant temperature time 1-2h; Second-stage high-temperature carbonization, temperature 1200-1400℃, heating rate 1-2℃ / min, constant temperature time 1-2h; Third-stage cooling, cooling to 800-1100℃, cooling rate 3-5℃ / min, and natural cooling to 25-30℃ with protective gas.

2. The method for preparing a lignocellulosic phenolic resin / doped bamboo-based porous carbon derived hard carbon composite material according to claim 1, characterized in that, In step (1), at least one of the following features (1) to (7) is included: (1) The lignocellulose biomass raw material includes at least one of corn straw, straw, reed, sorghum stem, rice husk, wood waste, rapeseed hull and sawdust; (2) the pretreatment process of the lignocellulosic biomass raw material is that the lignocellulosic biomass raw material is cleaned with water and then dried in a drying box, the drying temperature of the drying box is 60-120 DEG C, and the drying time is 4-24 h; (3) the copolymerization reaction specifically comprises the following steps: the pretreated lignocellulosic biomass raw material, phenolic compound and aldehyde compound are added into a four-necked flask respectively, then an alkali solution with a concentration of 30-50% is added, the pH is adjusted to 10-14, and reaction is carried out at 60-80 DEG C for 0.5-4 h; (4) the phenolic compound comprises phenol, and the aldehyde compound comprises formaldehyde; (5) the mass of the phenolic compound is 1-3 times the mass of the lignocellulosic biomass raw material, and the mass of the aldehyde compound is 4-6 times the mass of the lignocellulosic biomass raw material; (6) the solid-liquid mass ratio in the copolymerization reaction is 1:3-10; (7) after the copolymerization reaction is completed, the product is washed with deionized water multiple times, centrifuged, and then dried in a vacuum drying box, the drying temperature is 60-120 DEG C, and the drying time is 2-24 h.

3. The method for preparing the lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material according to claim 1, characterized in that, In step (two), at least one of the following features (8) to (11) is included: (8) the bamboo-based biomass raw material comprises at least one of Dendrocalamopsis oldhami, Phyllostachys edulis, Phyllostachys nigra and bamboo powder; (9) the pretreatment process of the bamboo-based biomass raw material is that the bamboo-based biomass raw material is cleaned with water and then dried in a drying box, the drying temperature of the drying box is 60-120 DEG C, and the drying time is 4-24 h; (10) the activation process is that an activator with a concentration of 30-50% is added into the pretreated bamboo-based biomass raw material, stirring is carried out at normal temperature for 8-24 h for activation reaction; the activator comprises at least one of KOH and NaOH solution; the mass ratio of the activator to the pretreated bamboo-based biomass raw material is 2-5:1; (11) after the activation reaction is completed, centrifugation is carried out, and then drying is carried out in a drying box, the drying temperature is 60-120 DEG C, and the drying time is 4-24 h.

4. The method for preparing the lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material according to claim 1, characterized in that, In step (two), at least one of the following features (12) to (13) is included: (12) the hydrothermal doping process is that the activated bamboo-based porous carbon, boron source, nitrogen source and phosphorus source are stirred uniformly and then added into a high-pressure reaction kettle, and hydrothermal reaction is carried out at 120-180 DEG C for 12-48 h; (13) after the hydrothermal reaction is completed, washing is carried out with deionized water and ethanol, centrifugation is carried out, and then drying is carried out in a vacuum drying box at 60-120 DEG C under vacuum condition for 2-24 h.

5. The method for preparing the lignocellulose phenolic resin / doped bamboo-based porous carbon-derived hard carbon composite material according to claim 1, characterized in that, In step (two), at least one of the following features (14) to (17) is included: (14) the particle size of the crushed pre-carbonization material is controlled to be 3-17 um; (15) the composite acid purification process is that the pre-carbonization material is crushed first, then deionized water is added into the crushed pre-carbonization material, stirring and ultrasonic treatment are carried out at room temperature, a composite acid is added, reaction is carried out at 60-100 DEG C for 4-12 h, and acid-washing purified material is obtained through centrifugation; (16) The stirring time at room temperature is 8-24 h, the ultrasonic frequency is 40-60 KHz, and the ultrasonic time is 10-30 min; (17) The alkali solution comprises at least one of KOH, NaOH, NaHCO3 and KHCO3; and the solid-liquid mass ratio of the acid-washing purified material to the alkali solution is 1:3-5.

6. A negative electrode sheet characterized by comprising: The negative pole piece adopts the hard carbon composite material prepared by the preparation method of the lignocellulose phenolic resin / doped bamboo-based porous carbon derived hard carbon composite material, and the hard carbon composite material is used as an active substance of a battery negative pole material.

7. A battery, which is a sodium-ion battery, comprising a negative electrode, a positive electrode, a separator, an electrolyte, characterized in that, The negative pole comprises the negative pole piece of claim 6.

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