Phenolic resin-based hard carbon sodium ion battery negative electrode material, negative electrode and preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion battery negative electrode materials, in particular to a phenolic resin-based hard carbon sodium ion battery negative electrode material, a negative electrode and a preparation method and application thereof. The crosslinking degree and the main chain rigidity of the phenolic resin are regulated and controlled by regulating the number of benzene rings in side chains of aldehyde molecules, so that the internal space (free volume) of the phenolic resin is influenced, and a rich closed-pore structure is finally formed; then waste gas generated by pyrolysis of phenolic resin is used as a carbon source for chemical vapor deposition, and resin carbon is used as a substrate, so that the pore surface of hard carbon can be effectively sealed, electrolyte permeation is prevented, and open pores in the hard carbon material are converted into closed pore structures to be used as efficient sodium storage sites. Meanwhile, the method also has green sustainability and cycle economy, volatile waste gas generated by pyrolysis is reutilized as a carbon source to be deposited on the surface of resin carbon, the carbon yield is improved, the dynamic performance of the hard carbon material is also improved, and emission of the volatile waste gas is reduced.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, and in particular to a phenolic resin-based hard carbon sodium-ion battery anode material, the anode itself, its preparation method, and its application. Background Technology

[0002] With the rapid development of renewable energy and electric vehicles, lithium-ion batteries face challenges from lithium resource scarcity and rising costs. Sodium-ion batteries, due to the abundance, wide distribution, and low cost of sodium resources, have become a research hotspot in the energy storage field. However, the ionic radius of sodium ions is significantly larger than that of lithium ions, resulting in slow insertion / extraction kinetics and low capacity in traditional graphite anodes, which fails to meet practical needs. Therefore, developing high-performance sodium-ion battery anode materials has become a key technological breakthrough.

[0003] Hard carbon materials, due to their disordered microcrystalline structure and large interlayer spacing, can achieve high sodium storage capacity through mechanisms such as adsorption, intercalation, and pore filling, making them a mainstream candidate material for sodium-ion battery anodes. Hard carbon is composed of curved graphite sheets, exhibiting short-range order and long-range disorder, displaying a disordered layered structure with abundant defects and non-uniform pores. However, because the radius of sodium ions is much larger than that of lithium ions, the performance of ordinary graphite anode materials is not ideal. Hard carbon materials have a larger interlayer spacing than graphite, and hard carbon anodes have a higher sodium ion insertion / extraction capability compared to graphite-based anodes. The ramp capacity at high potentials is widely attributed to Na+. + Adsorption onto the surface and defect sites of hard carbon, the plateau capacity is closely related to the pore structure. Therefore, a deeper understanding of Na... + The storage mechanism facilitates the large-scale production of hard carbon anodes with structural stability and high carbon yield. Phenolic resin (PF) stands out in the market competition due to its well-established industrial base, structural stability, ease of design, high residual carbon rate, and good electrochemical performance. However, phenolic resin-based hard carbon anode materials still suffer from low initial coulombic efficiency and low cycle retention.

[0004] Chinese patent CN 117865115 A discloses a method for preparing a phenolic resin-based hard carbon anode material, comprising the following steps: mixing phenolic resin, curing agent, and alcohol solvent in a mass ratio of (2-20):1:(2-100), stirring evenly, drying to obtain a block, crushing and grinding the block into powder, heating and curing, subjecting the cured semi-finished product to high-temperature treatment, and cooling to obtain the hard carbon anode material. The phenolic resin-based hard carbon anode material prepared by this invention has a carbon yield between 51-61%, a specific capacity between 317-335 mAh / g, and an initial coulombic efficiency between 89-93%.

[0005] Chinese Patent No. 116605864 A discloses a method for preparing phenolic resin-based hard carbon anode materials for sodium-ion batteries. The method uses phenolic resin foaming material as a hard carbon precursor material, and prepares the phenolic resin-based hard carbon anode material for sodium-ion batteries through carbonization, pore adjustment, and carbon deposition, resulting in a phenolic resin-based hard carbon anode material with high capacity and high initial coulombic efficiency. This invention utilizes a method of high-temperature calcination of carbides under inert gas to achieve large-pore shrinkage, thus forming a structural change in the hard carbon material. Summary of the Invention

[0006] The main objective of this invention is to provide a phenolic resin-based hard carbon sodium-ion battery anode material, anode, preparation method, and application thereof to solve the aforementioned technical problems. By purifying and reusing the waste gas generated from the pyrolysis of phenolic resin synthesized from different aldehyde monomers and resorcinol, a rich closed-pore structure is constructed. This strategy is used to prepare a high-capacity, high-efficiency, high-rate, and long-cycle-life hard carbon anode material for sodium-ion batteries with a rich closed-pore structure.

[0007] To achieve the above objectives, the present invention provides a method for preparing a phenolic resin-based hard carbon sodium-ion battery anode material, comprising the following steps: S1: After mixing resorcinol and aldehyde monomers at a molar ratio of 1:0.5-1.2, add an alkaline catalyst, adjust the pH to alkaline, and stir evenly to obtain mixture A; S2: Heat the mixture A to 80℃-120℃ and keep it at that temperature for 2-6 hours. After the phenolic condensation reaction is complete, the suspension B is obtained. S3: Add 0.8-1.2 mol / L dilute hydrochloric acid to suspension B, adjust the pH to neutral, and wash and dry to obtain thermosetting phenolic resin C; S4: Thermosetting phenolic resin C is cured and pre-oxidized at 160℃-200℃ for 6-24h to obtain powder D; S5: Powder D is pyrolyzed. The volatiles produced by pyrolysis are purified by removing CO2, H2O and O2. The purified organic gas is then transferred to the CVD reaction furnace chamber and purified organic gas is introduced for vapor deposition to obtain powder E. S6: The powder E is subjected to high-temperature carbonization under a nitrogen atmosphere and then pulverized to obtain the final product, phenolic resin hard carbon anode material.

[0008] Preferably, the aldehyde monomer is one or more of formaldehyde, benzaldehyde, naphthaldehyde, and anthracene formaldehyde; the alkaline catalyst is a NaOH solution with a concentration of 4-6 mol / L; and the stirring time after adjusting the pH value is 1-3 h.

[0009] Preferably, in step S1, the resorcinol is mixed with the aldehyde monomer using an ethanol solution.

[0010] Preferably, in step S2, the reaction process is monitored by infrared spectroscopy. When the disappearance of the hydroxymethyl peak and the formation of the methylene bridge bond are detected, the reaction is completely ended, and suspension B is obtained.

[0011] Preferably, in step S4, the temperature is increased to 180°C in a muffle furnace at a rate of 2-5°C / min for curing-pre-oxidation, and then held for 6-24 hours to obtain powder D.

[0012] Preferably, in step S5, the CVD equipment sequentially includes a pyrolysis generator, a purification device, and a CVD reaction chamber; wherein, In the pyrolysis generator, argon is used as a carrier gas to extract the volatile waste gas generated by the pyrolysis of phenolic resin. The pyrolysis heating curve is that the temperature is raised to 650-750℃ at a rate of 1-3℃ / min under argon atmosphere and held for 2-4 hours. The purification device includes a molecular sieve for removing CO2, H2O, and O2 gases; The CVD reactor chamber includes a return gas port for depositing purified organic gas vapor onto the surface of the pyrolyzed powder D.

[0013] Preferably, in step S6, the high-temperature carbonization curve is heated to 950-1050℃ at a rate of 4-6℃ / min and held for 1-3 hours, then heated to 1200-1500℃ at a rate of 1.5-2.5℃ / min and held for 1-3 hours; step S6 also includes shaping, classifying, and sieving the product after high-temperature carbonization to obtain D. V 50 refers to phenolic resin hard carbon anode materials for sodium-ion batteries with a thickness of 2.0-8.0 μm and a span of <1.2.

[0014] The present invention also provides a negative electrode material, including a sodium-ion battery negative electrode material prepared by the preparation method described above.

[0015] The present invention also provides a negative electrode, which is prepared using the negative electrode material described above.

[0016] The present invention also provides an application of the sodium-ion battery anode material prepared according to the above preparation method as a sodium-ion battery anode.

[0017] In this invention, the crosslinking degree and main chain rigidity of phenolic resin are controlled by adjusting the number of benzene rings in the side chain of aldehyde molecules, thereby affecting its internal space (free volume) and ultimately forming a rich closed-cell structure.

[0018] Formaldehyde: It has no aromatic ring, contains only one carbonyl group, and exhibits high reactivity. It readily condenses with the ortho / para-hydroxyl groups of resorcinol to form a high-density methylene bridge (-CH2-). The cross-linking network is predominantly short-chain. The introduction of formaldehyde results in a high cross-linking density in the precursor, leading to a high proportion of micropores (<2nm) after carbonization. High-temperature carbonization facilitates the formation of more closed-pore structures. Benzaldehyde: It contains one benzene ring and forms π-π conjugation with the aromatic ring of resorcinol. During condensation, it tends to generate an extended conjugated structure of "aromatic ring-methylene-aromatic ring," resulting in a more complex cross-linking network. The introduction of benzaldehyde promotes the formation of medium-sized (2-50nm) mesopores in the precursor, balancing accelerated ion diffusion with exposure of active sites. Naphthaleneform: It contains two fused benzene rings, with a smaller molecular volume. Larger diameters increase steric hindrance and decrease condensation rate, making it easier to form long-range cross-linked chains of "resorcinol-naphthalene ring". The introduction of naphthaldehyde during aromatic ring polymerization forms a "node-long chain" structure, which easily generates hierarchical porous structure (micropores + mesopores + macropores) after carbonization. The macropores (>50nm) promote rapid electrolyte penetration. Anthracene formaldehyde contains three fused benzene rings, which are more rigid and can inhibit excessive cross-linking during polymerization, retaining more unreacted aromatic ring fragments. The cross-linking network presents a "node-long chain" structure. The introduction of anthracene formaldehyde provides a longer π-conjugated skeleton for carbonization, and graphitization rearrangement is more likely to occur under high-temperature carbonization, which reduces structural defects (such as edge sites and heteroatom vacancies) after carbonization, forming a more ordered layered structure, thereby improving the ion / electron transport efficiency.

[0019] By using the waste gas generated from the pyrolysis of phenolic resin as a carbon source for chemical vapor deposition, and with the resin carbon serving as a substrate, the pore surface of the hard carbon can be effectively sealed, thereby preventing electrolyte permeation and transforming the open pores in the hard carbon material into closed pore structures, serving as efficient sodium storage sites. Simultaneously, this method is also green, sustainable, and circularly economical. The volatile waste gas generated during pyrolysis is reused as a carbon source deposited on the resin carbon surface, improving carbon yield and enhancing the kinetic properties of the hard carbon material while reducing volatile waste gas emissions. Attached Figure Description

[0020] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the preparation process of the sodium-ion battery anode material in this invention.

[0021] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0022] The technical problems solved by the embodiments of the present invention, the technical solutions adopted, and the technical effects achieved will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other equivalent or obvious variations of embodiments obtained by those skilled in the art without creative effort fall within the protection scope of the present invention. The embodiments of the present invention can be embodied in various different ways as defined and covered by the claims.

[0023] It should be noted that many specific details are given in the following description for ease of understanding. However, it is obvious that the present invention may be implemented without these specific details.

[0024] It should be noted that, in the absence of explicit limitations or conflicts, the various embodiments and their technical features in this invention can be combined with each other to form a technical solution.

[0025] Example 1: S1. Pour resorcinol and benzaldehyde in a 1:1 molar ratio into a beaker and stir well. Slowly add a 5 mol / L NaOH solution (5% of the mass of resorcinol) prepared in advance with deionized water and adjust the pH of the solution to 10 to obtain solution A.

[0026] S2. Place solution A on a graphite heating plate and heat it to 60°C at a rate of 2°C / min at room temperature. Hold the temperature for 2 hours while stirring continuously. Then heat it to 100°C at a rate of 5°C / min and continue the reaction for 4 hours. Monitor the reaction progress by infrared spectroscopy (FTIR). When the hydroxymethyl peak disappears and the methylene bridge bond is formed, the reaction is completely finished, and suspension B is obtained.

[0027] S3, slowly add 1 mol / L HCl to suspension B to remove residual alkali and adjust the pH to 7. Pour into a vacuum filter and rinse repeatedly with deionized water for 1 hour to remove unreacted phenols, aldehydes and salts. Then place the material on the filter screen in a vacuum drying oven and heat to 100℃ to dry for 12 hours to obtain thermosetting phenolic resin C.

[0028] S4. Resin C is placed in a muffle furnace for curing-pre-oxidation treatment. The temperature is increased to 180°C at a rate of 2°C / min under air atmosphere and held for 12 hours before depolymerization treatment to obtain powder D.

[0029] S5, powder D is placed in the CVD chamber under an argon atmosphere for pyrolysis. The temperature is increased to 700℃ at a rate of 2℃ / min and held for 2h. The volatile waste gas generated by pyrolysis is extracted and recovered by using argon as a carrier gas and purified by 3Å molecular sieve and copper-based treatment. The purified gas is then passed into a 700℃ reactor and reacted continuously for 2h for vapor phase deposition treatment to obtain powder E.

[0030] S6, Powder E is placed in a high-temperature carbonization furnace and heated to 1000℃ at a rate of 5℃ / min under a nitrogen atmosphere, and held for 2 hours. Then, the temperature is further increased to 1300℃ at a rate of 2℃ / min and held for 2 hours to obtain powder F. Powder F is then fed into a three-in-one equipment for shaping and grading, controlling D... V The phenolic resin hard carbon anode material for sodium-ion batteries was obtained by passing the material through a 325-mesh sieve with a thickness of 6.0±0.5μm and a span of <1.2.

[0031] Example 2 (replacing benzaldehyde with formaldehyde): The difference between this embodiment and Example 1 is that the resorcinol in S1 with a molar ratio of 1:0.8 and the 37% formaldehyde aqueous solution are poured into a beaker and stirred evenly. Then, a 5 mol / L NaOH solution (5% of the mass of the solute resorcinol) prepared in advance with deionized water is slowly added to adjust the pH of the solution to 10, thus obtaining solution A.

[0032] Example 3 (replacing benzaldehyde with naphthaldehyde): The difference between this embodiment and Example 1 is that first, naphthaldehyde and a small amount of anhydrous ethanol are placed together in an agate grinding dish for grinding and dissolution. Then, resorcinol and naphthaldehyde in a molar ratio of 1:1.2 in S1 are poured into a beaker and stirred evenly. Solution A in S2 is placed on a graphite hot plate and heated to 60°C at a rate of 2°C / min at room temperature. The temperature is maintained for 2 hours with continuous stirring. Then, the temperature is increased to 100°C at a rate of 5°C / min and the reaction is continued for 8 hours. The reaction process is monitored by infrared spectroscopy (FTIR). When the hydroxymethyl peak disappears and a methylene bridge bond is formed, the reaction is completely finished, and suspension B is obtained.

[0033] Example 4 (replacing benzaldehyde with anthracene formaldehyde): The difference between this embodiment and Example 1 is that anthracene formaldehyde and a small amount of anhydrous ethanol are first ground and dissolved together in an agate grinding dish. Then, resorcinol and anthracene formaldehyde in a molar ratio of 1:1.2 in S1 are poured into a beaker and stirred evenly. Solution A in S2 is placed on a graphite hot plate and heated to 60°C at a rate of 2°C / min at room temperature. The temperature is maintained for 2 hours with continuous stirring. Then, the temperature is increased to 100°C at a rate of 5°C / min and the reaction is continued for 8 hours. The reaction process is monitored by infrared spectroscopy (FTIR). The reaction is considered to be completely ended when the hydroxymethyl peak disappears and a methylene bridge bond is formed, resulting in suspension B.

[0034] Example 5 (replacing benzaldehyde with a mixture of benzaldehyde, naphthaldehyde, and anthracene formaldehyde): The difference between this embodiment and Example 1 is that firstly, naphthaldehyde and anthracene formaldehyde are ground and dissolved separately with a small amount of anhydrous ethanol in an agate grinding dish. Then, resorcinol, benzaldehyde, naphthaldehyde, and anthracene formaldehyde in the molar ratio of 1:0.4:0.4:0.4 in S1 are poured into a beaker and stirred evenly. Solution A in S2 is placed on a graphite hot plate and heated to 60°C at a rate of 2°C / min at room temperature, kept at the temperature for 2 hours with continuous stirring, and then heated to 100°C at a rate of 5°C / min. After reacting for 8 hours, the reaction process is monitored by infrared spectroscopy (FTIR). The reaction is considered complete when the hydroxymethyl peak disappears and a methylene bridge bond is formed, resulting in suspension B.

[0035] Example 6 (Reducing curing-pre-oxidation time): The difference between this embodiment and embodiment 1 is that material C in S4 is placed in a muffle furnace for curing-pre-oxidation treatment, heated to 180°C at a rate of 2°C / min in air atmosphere and held for 6 hours before depolymerization treatment to obtain powder D.

[0036] Example 7 (Increasing CVD vapor deposition time): The difference between this embodiment and Embodiment 1 is that powder D is pyrolyzed in an argon atmosphere within a CVD chamber. The temperature is increased to 700℃ at a rate of 2℃ / min and held for 2 hours. The volatile waste gas generated by pyrolysis is extracted and recovered using argon as a carrier gas and purified by 3Å molecular sieve and copper-based treatment. The purified gas is then passed into a 700℃ reactor and reacted continuously for 4 hours for vapor phase deposition treatment to obtain powder E.

[0037] Example 8 (Increasing the carbonization temperature): The difference between this embodiment and embodiment 1 is that powder E in S6 is placed in a high-temperature carbonization furnace, heated to 1000°C at a rate of 5°C / min under a nitrogen atmosphere and held for 2 hours, and then heated to 1500°C at a rate of 2°C / min and held for 2 hours to obtain powder F.

[0038] Example 9 (Reducing Particle Size): The difference between this embodiment and embodiment 1 is that the powder F in S6 is fed into a three-in-one device for shaping and grading, and the control of D... V Phenolic resin hard carbon anode material for sodium-ion batteries was obtained by passing 50 at 2.3 μm through a 325-mesh sieve.

[0039] Comparative Example 1 (Pyrolysis waste gas is not purified and is passed into CVD) The difference between this comparative example and Example 1 is that powder D in S5 was pyrolyzed in an argon atmosphere inside a CVD chamber. The temperature was increased to 700°C at a rate of 2°C / min and held for 2 hours. The volatile waste gas generated by pyrolysis was not purified and was directly introduced into a reactor at 700°C for continuous reaction for 2 hours to obtain powder E. Everything else was the same.

[0040] Comparative Example 2 (CVD vapor deposition without pyrolysis waste gas): The difference between this comparative example and Example 1 is that step S5 is omitted. Powder D is placed directly in a high-temperature carbonization furnace and heated to 1000°C at a rate of 2°C / min under a nitrogen atmosphere and held for 2 hours. Then, it is heated to 1300°C at a rate of 2°C / min and held for 2 hours to obtain powder F. Everything else is the same.

[0041] The test methods for various performance parameters of the hard carbon anode materials obtained in Examples 1-9 and Comparative Examples 1-2 are as follows: 1. The hard carbon anode materials from Examples 1-9 and Comparative Examples 1-2 were used as anode active materials, and were mixed uniformly with PVDF (dissolved in N-methylpyrrolidone) and conductive carbon black at a mass ratio of 90:5:5. The mixture was coated into an electrode film, dried in a vacuum drying oven at 120°C for 12 hours, and then rolled and punched to obtain hard carbon anode sheets. Using a sodium metal sheet as the counter electrode and 1 mol / L NaPF6 (EC-DEC = 1:1) as the electrolyte, the obtained hard carbon anode sheets were assembled into 2430 button cells in a glove box. The initial coulombic efficiency, rate performance, and cycle performance were tested, and the results are shown in Table 1.

[0042] 2. SAXS Method Testing: The storage ring electron energy of the hard carbon sample was tested using the SAXS method to be 2.2 GeV. The average beam current was 60 mA. A long slit collimation system was used, and the incident X-ray wavelength was 0.154 nm. The scattering intensity was detected using the imaging plate method. Data processing was performed using a self-developed program. The scattering intensity was corrected for blank and sample absorption. The average aperture D... SAXS The result is a weighted average of the pore sizes. The pore distribution and specific surface area of ​​the hard carbon samples were also measured using a physical adsorption analyzer (Micrometrics ASAP2000). The test results are shown in Table 2.

[0043] 3. Initial coulombic efficiency test: First, discharge at a rate of 0.1C (nominal specific capacity set to 300mAh / g) to 0.005V, let stand for 10 minutes, and then charge at a rate of 0.1C to 2.00V to test the initial coulombic efficiency of the hard carbon.

[0044] 4. Rate performance test: After the material completes the first charge and discharge test, it is discharged at constant current and constant voltage (2C / 0.2C) to 0.005V, left to stand for 10 minutes, and then charged at constant current (2C / 0.2C) to 2.00V. The capacity at different rates is calculated.

[0045] 5. Cyclic performance test: After the material completes the first charge and discharge test, it is discharged at constant current and constant voltage (1C) to 0.005V, charged at constant current (1C) to 2.00V, and cycled for 500 cycles. The capacity retention rate at the 500th cycle is calculated.

[0046] 6. Small-angle X-ray scattering (SAXS) method for calculating pore size distribution uses the Shell-Rose method, which assumes that the pores in the sample are formed by the accumulation of spherical scatterers and that the pore distribution is continuous, which can be described by the McLaurent distribution function. The distribution function includes several undetermined parameters. The average pore size is determined by fitting the assumed function to experimental data. E is the pore interface thickness. The interface between the pore cavity and the actual material will produce a certain thickness of voids, which consists of some three-dimensional amorphous carbon layers and functional groups.

[0047] Table 1. Powder properties and electrochemical performance of anode materials Table 2 Pore structure parameters of negative electrode materials As shown in the data from Examples 1-5, as the number of aromatic rings in the aldehyde side groups of formaldehyde, benzaldehyde, naphthalene, and anthracene formaldehyde increases, their precursor structures also change from short-chain crosslinking (formaldehyde) to long-range conjugated crosslinking (anthracite formaldehyde). This strengthens the three-dimensional structure of the carbon layer framework and facilitates carbon layer rearrangement, forming a more ordered layered structure. The crosslinking network of large-sized aromatic rings (naphthalene, anthracene) enhances the three-dimensional framework strength of hard carbon, and the compressive strength also increases accordingly, thereby suppressing volume expansion during cycling and improving cycle life. Due to the increase in the number of aromatic rings, the steric hindrance also increases, resulting in a decrease in the crosslinking density of the precursor, but retaining more unreacted aromatic ring fragments. After carbonization, structural defects (such as edge sites and heteroatom vacancies) are reduced, thereby reducing irreversible capacity and improving the first coulombic efficiency. Formaldehyde acts as... The polymer resin formed by the precursor reactants has a high crosslinking density. After carbonization, it forms a large number of microporous structures, which helps to form a large number of sodium clusters inside the pores, providing sodium storage sites. The extended conjugated structure of benzaldehyde promotes the formation of mesopores after carbonization, shortens the ion / electron migration path and helps ion / electron diffusion. Naphthalenealdehyde forms a "node-long chain" structure during polymerization. After carbonization, it is easy to generate hierarchical pores (micropores + mesopores + macropores), which balances factors such as sodium storage capacity, ion / electron migration rate, material specific surface area and active sites, and improves kinetic and electrochemical performance. An appropriate number of benzene rings after crosslinking and carbonization can balance the number and spatial position of curved carbon layers and long and straight carbon layer structures, which can provide a sufficient growth environment for closed-pore structures to store more sodium ions, thereby affecting the platform capacity.

[0048] As shown in the data from Example 6, the incomplete reaction of phenolic resin during the curing-pre-oxidation stage resulted in an incomplete cross-linking network in the internal structure. The uncross-linked linear molecular chains were prone to sliding, leading to "weak areas" inside the material, which affected the stability of the material structure and thus the cycle stability of the anode material. The uncross-linked molecular chains did not decompose completely during carbonization, resulting in a disordered pore distribution and reduced ion transport efficiency. The incompletely cross-linked structure could not form a short-range ordered carbon layer structure during high-temperature carbonization, increasing the material defect density and decreasing electronic conductivity. The residual hydroxymethyl or methylene groups generated local defects (such as edge sites and heteroatom vacancies) during carbonization, increasing irreversible capacity loss and thus affecting the initial coulombic efficiency.

[0049] As can be seen from the data in Example 7, as the pyrolysis waste gas is deposited in the vapor phase onto the surface of the resin carbon in CVD, it effectively seals the pore inlets, thereby preventing electrolyte permeation, reducing irreversible capacity loss, and changing the open-pore structure in the hard carbon into closed pores as efficient sodium storage sites. Furthermore, as the deposition time increases, more pore inlets are sealed and transformed into closed-pore structures, resulting in a decrease in specific surface area, thereby improving the capacity and first-time efficiency of the anode material.

[0050] As can be seen from the data in Example 8, as the carbonization temperature increases, the carbon layers rearrange, the carbon layer structure develops towards short-range order, the carbon layer spacing decreases, the pore interface thickness increases, the closed pore volume decreases, and the specific surface area decreases. This can reduce the occurrence of irreversible reactions, thereby reducing the sodium ions consumed during charging and discharging, and improving the first coulombic efficiency of the material.

[0051] As shown by the data from Example 9, small-particle hard carbon has a shorter ion diffusion path, which is beneficial for rapid ion transport and diffusion, and helps to improve the kinetics of electrochemical reactions. The small particle size also increases the specific surface area, thereby increasing the number of active sites and thus improving the rate performance of the hard carbon anode. At the same time, the narrower particle size distribution helps to improve the consistency of the material, which is beneficial for subsequent slurry preparation and improves the processing performance of the material.

[0052] As can be seen from the data of Comparative Example 1 and Example 1, when pyrolysis waste gas is directly introduced into CVD without purification treatment, the presence of gases such as O2, CO2, and H2O will corrode and oxidize the surface of carbon materials, thereby affecting the specific surface area, active sites, and pore structure distribution of the hard carbon anode, and consequently affecting the capacity and first efficiency of the anode material.

[0053] As can be seen from the data of Comparative Example 2 and Example 1, since the original pyrolytic carbon does not undergo vapor deposition coating treatment, it has a rich open-pore structure, which increases the specific surface area. The electrolyte will enter the pores to form an SEI film, resulting in an increase in irreversible capacity and a reduction in first-efficiency. Furthermore, the large number of open-pore structures cannot effectively provide sodium cluster storage sites, thereby reducing the capacity of the anode material.

[0054] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for preparing a phenolic resin-based hard carbon sodium-ion battery anode material, characterized in that, The method comprises the steps of: S1: mixing resorcinol and aldehyde monomers in a molar ratio of 1:0.5-1.2, adding an alkaline catalyst, adjusting the pH value to alkaline, and stirring uniformly to obtain a mixed solution A; S2: heating the mixed solution A to 80-120℃, and keeping the temperature for 2-6h to complete the phenolic aldehyde condensation reaction to obtain a suspension B; S3: adding 0.8-1.2mol / L dilute hydrochloric acid to the suspension B, adjusting the pH value to neutral, and washing and drying to obtain a thermosetting phenolic aldehyde resin C; S4: curing and pre-oxidizing the thermosetting phenolic aldehyde resin C at 160-200℃ for 6-24h to obtain a powder D; S5: pyrolyzing the powder D, removing CO2, H2O and O2 from the volatile matter generated by pyrolysis by a purification device to obtain purified organic gas, transferring the solid product after pyrolysis to a CVD reaction furnace cavity, and introducing the purified organic gas for vapor deposition to obtain a powder E; S6: performing high-temperature carbonization treatment on the powder E in a nitrogen atmosphere, and crushing to obtain a final product, i.e., a phenolic aldehyde resin hard carbon negative electrode material.

2. The production method according to claim 1, characterized by, The aldehyde monomer is one or more of formaldehyde, benzaldehyde, naphthaldehyde and anthracene formaldehyde; the alkaline catalyst is a NaOH solution with a concentration of 4-6mol / L; and the stirring time after adjusting the pH value is 1-3h.

3. The preparation method according to claim 2, characterized in that, In the step S1, the resorcinol and the aldehyde monomers are mixed by an ethanol solution.

4. The method of claim 1, wherein, In the step S2, the reaction progress is monitored by infrared spectroscopy, and the reaction is completed when the hydroxymethyl peak disappears and the methylene bridge is formed, to obtain the suspension B.

5. The preparation method according to claim 1, characterized in that, In the step S4, the curing and pre-oxidation is performed in a muffle furnace at a rate of 2-5℃ / min to 180℃, and the temperature is kept for 6-24h to obtain the powder D.

6. The method of claim 1, wherein, In the step S5, the CVD equipment comprises a pyrolysis generator, a purification device and a CVD reaction furnace cavity in sequence; in the pyrolysis generator, argon is used as a carrier gas to extract the volatile waste gas generated by pyrolysis of the phenolic aldehyde resin, and the pyrolysis temperature curve is that the temperature is raised to 650-750℃ at a rate of 1-3℃ / min under an argon atmosphere, and the temperature is kept for 2-4h; the purification device comprises a molecular sieve for removing CO2, H2O and O2; and the CVD reaction furnace cavity comprises a gas return port for vapor deposition of the purified organic gas on the surface of the powder D after pyrolysis. The sodium ion battery negative electrode material prepared by the preparation method of any one of claims 1-7. The negative electrode material is prepared by the preparation method of claim 7.

10. Use of the sodium ion battery negative electrode material prepared by the preparation method of any one of claims 1-7 as a sodium ion battery negative electrode.

7. The preparation method according to claim 1, characterized in that, In the step S6, the high-temperature carbonization curve is heated to 950-1050℃ at a rate of 4-6℃ / min for 1-3h, and then heated to 1200-1500℃ at a rate of 1.5-2.5℃ / min for 1-3h; the step S6 also includes shaping, grading and sieving treatment on the product after high-temperature carbonization, to obtain D V 50 is a phenolic resin hard carbon negative electrode material for sodium ion batteries with 2.0-8.0μm, span <1.

2.

8. A negative electrode material, characterized by, ​ 9. A negative electrode characterized by comprising: ​ ​

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