Sodium-ion battery hard carbon material and preparation method thereof
By subjecting phenolic resin to two-stage heat treatment under ozone atmosphere and compounding phenolic resin with boron phenolic resin, the problem of insufficient electrochemical performance of phenolic resin-based hard carbon anode materials was solved, and high-performance hard carbon materials suitable for sodium-ion batteries were prepared, improving the battery's capacity, energy density and rate performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XINJIANG UNIVERSITY
- Filing Date
- 2026-04-16
- Publication Date
- 2026-07-14
AI Technical Summary
In the existing technology, the electrochemical performance of phenolic resin-based hard carbon anode materials cannot meet the requirements of industrial sodium-ion batteries, especially in terms of capacity, energy density and conductivity.
A two-stage heat treatment method was adopted to perform low-temperature oxidation crosslinking and heated catalytic decomposition of phenolic resin in an ozone atmosphere, forming a closed microporous and short-range graphite domain structure. Combined with the compounding of phenolic resin and boron phenolic resin, the electron cloud distribution of the carbon skeleton was optimized, thereby improving the electrochemical performance of the material.
A hard carbon material with high capacity, high energy density, good conductivity and stable cycle performance was prepared. It is suitable for large-scale production and applied to sodium-ion secondary batteries, which improves the working voltage and energy density of sodium-ion batteries and enhances rate performance and safety.
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Figure CN122380342A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of hard carbon materials technology, and in particular to a hard carbon material for sodium-ion batteries and its preparation method. Background Technology
[0002] As global dependence on fossil fuels gradually decreases and environmental pollution becomes increasingly serious, the development and utilization of new energy sources has become an urgent priority. Against this backdrop, secondary batteries, as key chemical energy storage devices, are playing an increasingly important role. Replacing fossil fuels with electricity as the primary energy source for transportation will significantly reduce greenhouse gas emissions. Furthermore, combining renewable energy sources such as wind, solar, and geothermal energy with advanced power grid systems will greatly improve the efficiency of renewable energy utilization.
[0003] Among various rechargeable battery technologies, sodium-ion batteries have received widespread attention in recent years due to their abundant resources and low cost. Compared to lithium-ion batteries, sodium resources are widely distributed and inexpensive, giving them greater potential for commercial applications. However, developing high-performance electrode materials is crucial for the widespread application of sodium-ion batteries. Currently, significant progress has been made in the research and development of some cathode materials, which basically meet application requirements, but anode materials remain the main bottleneck restricting the practical application of sodium-ion batteries.
[0004] Among the reported sodium-ion battery anode materials, amorphous carbon materials are considered one of the most promising due to their relatively low sodium storage potential, high sodium storage capacity, and good cycle stability. Fossil mineral precursors have significant advantages in preparing amorphous carbon materials: they are inexpensive, abundant in domestic reserves, and have high carbonization yields, making them highly commercially viable. However, amorphous carbon materials obtained after calcination often exhibit high structural order and low porosity, which reduces their capacity at low temperatures, leading to a decrease in the overall battery energy density. Taking phenolic resin-based carbon materials as an example, during the pyrolysis of phenolic resin, the main component, phenolic hydroxyl groups, polymerize and rearrange to form plate-like aromatic fused ring structures, which then stack into plates under the influence of van der Waals forces. As the temperature further increases, the order and density of the carbon material continuously increase, eventually transforming into highly ordered graphite, which is detrimental to sodium ion storage. Researchers often choose to pre-oxidize the precursor, introducing more oxygen-containing functional groups during the pretreatment stage to obtain hard carbon modified by high-temperature calcination, thereby improving the electrochemical performance of hard carbon anode materials. Below are some specific examples:
[0005] CN119430148A discloses a method for preparing hard carbon from pre-oxidized heavy organic materials by in-situ doping, comprising the following steps: (1) Low-temperature oxidation: pre-oxidized carbon material is obtained by low-temperature oxidation of medium-temperature coal tar pitch; (2) Element doping: sulfur element doping material and medium-temperature coal tar pitch are reacted at low temperature to obtain a hard carbon precursor doped with sulfur element; (3) Low-temperature curing: a cured sulfur element doped pre-oxidized heavy organic hard carbon precursor is obtained; (4) High-temperature carbonization: a stable sulfur element doped pre-oxidized heavy organic hard carbon precursor material is obtained.
[0006] CN119240664A discloses a hard carbon material and its preparation method, comprising the following steps: pre-oxidizing a plastic precursor to obtain a pre-oxidized plastic; adding the obtained pre-oxidized plastic to a mixed solution of deionized water and alcohol, and then adding 2,6-pyridine dicarboxylic acid to perform a crosslinking reaction to obtain a plastic-based resin carbon precursor; and carbonizing the obtained plastic-based resin carbon precursor at high temperature to obtain the hard carbon material.
[0007] CN119349553A discloses a high-conductivity hard carbon composite material and its preparation method, comprising the following steps: pre-oxidizing a hard carbon precursor in an air atmosphere to obtain a pre-oxidized precursor; pulverizing the pre-oxidized precursor and pre-carbonizing it in an inert atmosphere to obtain a pre-carbonized precursor; mixing the pre-carbonized precursor with a dispersant, carbon nanotube slurry, binder and solvent and grinding it to obtain black liquor; drying the black liquor and carbonizing it at high temperature in an inert atmosphere to obtain a high-conductivity hard carbon composite material.
[0008] CN119430135A discloses a sodium-ion battery negative electrode hard carbon material and its preparation method, including the following steps: first, co-oxidized raw materials (any one or a mixture of biomass and carbonizable raw materials) are carbonized in an oxygen-containing atmosphere, then mixed with starch to form a mixed raw material, which undergoes a first stage of heat treatment in air, and then undergoes a second stage of heat treatment in a protective atmosphere to obtain a biomass-based composite hard carbon material.
[0009] CN119191268A discloses a hard carbon material and its preparation method, comprising the following steps: (S1) crushing asphalt and heat-treating it under an oxidizing atmosphere to obtain a pre-oxidized precursor; (S2) mixing the pre-oxidized precursor with crosslinking agent I uniformly and performing a first crosslinking under an inert atmosphere and heating conditions to obtain crosslinked precursor I; wherein the crosslinking agent I is a polymer with carboxyl groups in its side chain; (S3) mixing the crosslinked precursor I and crosslinking agent II uniformly and performing a second crosslinking under an inert atmosphere and heating conditions to obtain crosslinked precursor II; wherein the crosslinking agent II is a small molecule aromatic compound containing multiple anhydrides and / or carboxyl groups; (S4) calcining, cooling and grinding the crosslinked precursor II under an inert atmosphere to obtain an amorphous sodium-ion battery anode material.
[0010] Existing technologies utilize ozone as an oxidizing atmosphere, as reported in CN119528112A and CN119160874A. However, there is no research on the oxidation of phenolic resins as carbon precursors under ozone atmospheres. Summary of the Invention
[0011] To address the issue that the electrochemical performance of existing phenolic resin-based hard carbon anode materials cannot meet the demands of industrialized batteries, this invention provides a sodium-ion battery anode material, its preparation method, and its application. Using industrially viable phenolic resin as raw material, a two-stage reaction is carried out under an ozone atmosphere: first, low-temperature heat treatment for oxygen crosslinking polymerization, followed by catalytic decomposition at elevated temperatures. Through the formation of closed micropores and defects in the crosslinked polymerized phenolic resin carbon, which are beneficial for sodium-ion storage, and catalytic cracking promoting the formation of numerous short-range ordered graphite domain structures, a high-capacity, high-energy-density, and high-conductivity carbon material is proposed. This material is low-cost, simple to prepare, has adjustable disorder, high carbon yield, and is suitable for large-scale production. It is then applied as an anode material in sodium-ion secondary batteries.
[0012] To address the aforementioned technical problems, this invention provides a method for preparing hard carbon materials for sodium-ion batteries, comprising the following steps:
[0013] (S1) The phenolic resin is subjected to a two-stage heat treatment in an ozone-containing gas atmosphere: a first stage reaction at 100-110℃ and a second stage reaction at 130-170℃, to obtain the precursor.
[0014] (S2) The precursor is crushed and carbonized at high temperature in an inert gas atmosphere to obtain hard carbon material for sodium-ion batteries.
[0015] Further, in step (S1), the weight-average molecular weight of the phenolic resin is in the range of 2000-5000 g / mol. This moderate molecular length ensures that ozone can uniformly penetrate the interior, resulting in a synergistic reaction of oxidative cross-linking and oxidative decomposition. If the molecular weight is too high, the molecular chains are tightly intertwined, making it difficult for ozone to diffuse into the interior, potentially leading to a defective structure of excessive surface oxidation and insufficient internal oxidation. If the molecular weight is too low, it is difficult to form an effective three-dimensional cross-linked network structure. Therefore, the weight-average molecular weight of the phenolic resin should preferably be within the above-mentioned range.
[0016] Furthermore, in step (S1), the ozone-containing atmosphere is obtained by electrochemically treating air or pure oxygen, which will convert 5-15% of the oxygen into ozone; for example, when air is treated, the resulting ozone-containing atmosphere has an oxygen volume content of 17-20% and an ozone volume content of 1-3.15%; when pure oxygen is treated, the resulting ozone-containing atmosphere has an oxygen volume content of 85-95% and an ozone volume content of 5-15%.
[0017] Furthermore, in step (S1), the first reaction is a low-temperature pre-oxidation, which involves heating to 100-110℃ at a rate of 1-5℃ / min and holding for 1-2 hours; the second reaction is an oxidative pyrolysis reaction, which involves heating to 130-170℃ at a rate of 1-5℃ / min and holding for 1-2 hours.
[0018] Slow heating and short holding times allow for a more complete reaction between polymers and ozone. During slow heating, oxygen and ozone in heteroatom-rich organic compounds come into contact, forming a uniform and disordered cross-linked structure. This facilitates the subsequent pyrolysis of the cross-links into short-range, inter-crosslinked graphite domains during calcination, allowing them to bend and form closed-cell structures conducive to sodium ion storage. Conversely, if the heating rate is too rapid, the cross-linking copolymerization will cause localized areas to directly condense into highly disordered stacked carbon sheets, resulting in a structure unfavorable for sodium ion storage. Ozone typically has higher solubility in solution and stronger oxidative reactivity, enabling oxidative cross-linking and etching of carbon precursors at lower temperatures.
[0019] When phenolic resin is treated with ozone at low temperatures (100-110℃), its rich heteroatom organic compounds can act as pore modifiers, forming a richer pore structure. Firstly, organic compounds rich in functional groups, especially oxygen-containing functional groups, can decompose into small gaseous molecules containing carbon dioxide at high temperatures. Under the high-temperature conditions of pyrolysis, these molecules react with the carbon layer inside the hard carbon precursor, creating pores, defects, and heteroatom groups. This increases the defect rate on the surface of the carbon material and the pore surfaces, facilitating the reversible adsorption and storage of sodium metal clusters, thereby improving the electrochemical performance of the resulting anode material. Further heating to 130-170℃ enhances the oxidizing power of ozone, which has a certain oxidative decomposition ability on hydroxyl groups, especially phenolic hydroxyl groups. This catalyzes the decomposition of hydroxyl groups to form more short-range graphite domains, contributing to improved capacity and rate performance. Simultaneously, the decomposition ability of ozone varies at different temperatures, and the self-crosslinking process of phenolic resin also differs at different temperatures. By controlling the ozone treatment temperature, the pore structure and short-range graphite domains can be precisely controlled.
[0020] Furthermore, the pulverization method in step (S2) includes, but is not limited to, ball milling and mechanical pulverization, preferably ball milling. The process parameters for ball milling are well known in the art. In one specific embodiment of the present invention, uniform mixing is ball milling, and the ball milling process parameters are a ball-to-material ratio of 10-10:1, a rotation speed of 300-600 rpm, and a ball milling time of 2-8 h.
[0021] Further, in step (S2), the inert atmosphere is argon and / or argon gas; the calcination is carried out by heating to 1200-1800 ℃ at a heating rate of 5-10 ℃ / min and calcining for 2-5 hours.
[0022] The hard carbon material obtained by this invention has an irregular block morphology and structural features of curved graphite microcrystals of different sizes and closed pores. This invention uses phenolic resin as a precursor raw material, which is inexpensive and readily available. After low-temperature ozone oxidation and cross-linking, a porous structure and short-range graphite domains are formed in situ. After cooling to room temperature, a hard carbon material with high capacity, high rate and long cycle life for sodium-ion batteries can be obtained.
[0023] Therefore, in a preferred embodiment of the present invention, step (S1) in the above preparation method is modified as follows: phenolic resin and boron phenolic resin are mixed evenly, and the resulting mixture is subjected to a two-stage heat treatment in an ozone-containing gas atmosphere: successively low-temperature pre-oxidation and heated catalytic reaction to obtain the precursor.
[0024] The inventors discovered that using a blend of phenolic resin and boron-phenolic resin as the carbon source, followed by oxidation under an ozone atmosphere, further improves the electrochemical performance of hard carbon materials. The inventors speculate that this is likely because boron atoms themselves are electron-deficient Lewis acid sites. During the ozone oxidation stage, these uniformly distributed boron sites can efficiently catalyze the decomposition of ozone molecules, achieving uniform catalytic oxidation throughout the system. The uniformly dispersed boron sites, together with the surface oxygen functional groups introduced by ozone oxidation, form a synergistic doping effect: electron-deficient boron atoms and electron-rich oxygen atoms synergistically optimize the electron cloud distribution of the carbon framework, improving the overall electronic conductivity of hard carbon. The inventors also found that adding boric acid or borate esters to the phenolic resin during low-temperature ozone oxidation does not significantly improve the electrochemical performance of hard carbon materials.
[0025] Furthermore, boron phenolic resin (FB resin) is a phenolic monomer. During the condensation reaction of the aldehyde monomer, a certain amount of boric acid is added to obtain the resin. The mass content of boron in the boron phenolic resin is 0.7-1.3 wt%, preferably 0.8-1.1 wt%. The mass percentage of boron phenolic resin in the mixture is 10-15 wt%. There are no particular limitations on the method of uniform mixing, such as ball milling.
[0026] Secondly, the present invention provides a sodium-ion battery hard carbon material prepared by the above-described preparation method.
[0027] Thirdly, the present invention provides a negative electrode sheet for a sodium-ion battery, comprising: a current collector, a binder coated on the current collector, and a sodium-ion battery hard carbon material prepared by the above preparation method.
[0028] Fourthly, the present invention provides a sodium-ion secondary battery, wherein the negative electrode is a negative electrode sheet, or the negative electrode comprises the sodium-ion battery hard carbon material prepared by the above preparation method.
[0029] This invention provides a sodium-ion battery anode material based on carbon materials and phenolic resin, its preparation method, and its application. Using industrially available phenolic resin and abundant, inexpensive asphalt / coal resources as raw materials, and ozone as a catalyst, it achieves both high capacity and high rate capability. It proposes an amorphous carbon material that is low-cost, simple to prepare, has adjustable disorder, high carbon yield, and is suitable for large-scale production, and applies it as an anode material in sodium-ion secondary batteries. Sodium-ion secondary batteries using this invention's anode material exhibit high operating voltage and energy density, excellent rate performance, stable cycle performance, and good safety performance. They can be used not only as power sources for mobile devices and electric vehicles, but also as energy storage devices for renewable energy generation, smart grid peak shaving, distributed power stations, backup power supplies, or communication base stations. Attached Figure Description
[0030] Figure 1 These are the infrared spectra of the low-temperature oxidative crosslinking modified phenolic resin obtained in Example 1 (S1) and Comparative Example 1 (S1), and the unmodified phenolic resin.
[0031] Figure 2 The images show the XRD patterns of the hard carbon materials obtained in Examples 1, 2, 3 and Comparative Example 2.
[0032] Figure 3 This is a high-resolution transmission electron microscope (HRTEM) image of the hard carbon material obtained in Example 1.
[0033] Figure 4 This is a high-resolution transmission electron microscope (HRTEM) image of the hard carbon material obtained in Comparative Example 1.
[0034] Figure 5 These are the charge-discharge curves of the hard carbon materials obtained in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation
[0035] The amorphous carbon anode material for sodium-ion batteries containing hydroxyl precursors described in this invention will be further described below with reference to specific embodiments and accompanying drawings. However, it should be understood that the scope of protection of this invention is not limited to the following embodiments.
[0036] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.
[0037] The phenolic resins were purchased from Henan Hengyuan New Materials Co., Ltd., and were thermosetting phenolic resins with molecular weights of approximately 2000 g / mol and 4000 g / mol. The boron-phenolic resins were purchased from Greenlink Chemical Technology Co., Ltd., with a weight-average molecular weight of approximately 2600 g / mol and a boron content of 0.83 wt%.
[0038] Example 1
[0039] (S1) Weigh 1 kg of phenolic resin powder (weight average molecular weight 2000 g / mol) and place it in a tube furnace. Under an ozone atmosphere (obtained by treating air with an ozone generator, oxygen content 18.9 vol%, ozone content 2.1 vol%), heat at a rate of 2℃ / min, heat to 110℃ and hold for 1 h, then heat to 170℃ at a rate of 2℃ / min and hold for 1 h. After cooling, take out the sample, which is low-temperature oxidative crosslinking modified phenolic resin, place it in a ball mill jar, control the ball-to-material ratio to 10:1, set the ball mill speed to 500 rpm, and use forward and reverse rotation mode. Ball mill for 2 h to obtain the precursor.
[0040] (S2) Grind the precursor, sieve it through a 200-mesh sieve, place it in a high-temperature tube furnace, heat it to 1300 ℃ at a rate of 10 ℃ / min under an argon atmosphere, hold it at that temperature for 4 h, and cool it to room temperature to obtain the hard carbon material, which is called O3HC.
[0041] Comparative Example 1
[0042] The other operating steps are the same as in Example 1, except that in step (S1), the ozone atmosphere is replaced with air to obtain a hard carbon material, which is called O2HC.
[0043] Comparative Example 2
[0044] The hard carbon material obtained by calcining phenolic resin at 1300 °C and holding it at that temperature for 4 hours is called HC.
[0045] Figure 1 These are the infrared spectra of the low-temperature oxidative crosslinking modified phenolic resin obtained in Example 1 and Comparative Example 1 (S1), and the unmodified phenolic resin. It can be seen that after low-temperature ozone treatment, the content of phenolic hydroxyl groups in the low-temperature oxidative crosslinking modified phenolic resin of Example 1 is significantly reduced. This indicates that ozone can promote the oxidative crosslinking of phenolic resin under low-temperature conditions, and at appropriate temperatures, it can also etch and catalyze the phenolic resin, helping it to form a richer porous structure and a large number of short-range graphite domains during high-temperature calcination. In contrast, the change in the phenolic hydroxyl content in the low-temperature oxidative crosslinking modified phenolic resin of Comparative Example 1 is not significant, indicating that air oxidation has a much weaker effect on the crosslinking and etching of phenolic resin than ozone.
[0046] Example 2
[0047] The other operating steps are the same as in Example 1, except that in step (S1), the low-temperature oxidation step is changed to: under an ozone atmosphere, the temperature is increased at a rate of 2 °C / min, and after reaching 100 °C, it is held for 1 hour. Then, the temperature is increased at a rate of 2 °C / min to 150 °C and held for 1 hour. After cooling, the sample is taken out as a low-temperature oxidized crosslinked modified phenolic resin.
[0048] Example 3
[0049] The other operating steps are the same as in Example 1, except that in step (S1), the low-temperature oxidation step is changed to: under an ozone atmosphere, the temperature is increased at a rate of 2 °C / min, and after reaching 100 °C, it is held for 1 hour. Then, the temperature is increased at a rate of 2 °C / min to 130 °C and held for 1 hour. After cooling, the sample is taken out as a low-temperature oxidized crosslinked modified phenolic resin.
[0050] Figure 2 The XRD patterns of the hard carbon materials obtained in Examples 1, 2, 3 and Comparative Example 2 show that the amorphous carbon anode with sodium ions after cross-linking activation by ozone low-temperature treatment has increased amorphousness compared to the carbon material obtained by direct calcination. The modified carbon material has a larger interlayer spacing and lower crystallinity, indicating that the average packing degree of graphite domains has decreased. The short-range ordered graphite domains are more conducive to forming a closed microporous structure when they cross-link with each other, thereby effectively storing sodium ion clusters in the low-pressure plateau region.
[0051] Figure 3 This is a high-resolution transmission electron microscope (HRTEM) image of the hard carbon material obtained in Example 1. Figure 4 This is a high-resolution transmission electron microscope (TEM) image of the hard carbon material obtained in Comparative Example 1. It can be seen that the modified material possesses bent, closed local graphite domains, and it also forms a large number of closed-pore structures. This is closely related to the improved capacity in the low-pressure plateau region. The formation of closed pores provides favorable conditions for the precipitation of sodium metal clusters within the hard carbon, without affecting the diffusion of sodium ions in the anode material. Furthermore, high-temperature calcination reduces the formation of oxygen-containing functional groups and defects on the surface by the activator, eliminating its influence on the material's coulombic efficiency. This structure is completely different from the carbon material obtained by direct calcination of phenolic resin. Simultaneously, the hard carbon sample treated with ozone at low temperature has richer pores, which will lead to a higher plateau capacity.
[0052] Comparative Example 3
[0053] The other operating steps are the same as in Example 1, except that in step (S1), the low-temperature oxidation step is changed to: heating at a rate of 2 °C / min in an ozone atmosphere, heating to 170 °C and holding for 3 hours, and then cooling to remove the sample, which is a low-temperature oxidized crosslinked modified phenolic resin. That is, compared with Example 1, the low-temperature oxidation in Comparative Example 3 is carried out at 170 °C throughout, instead of first holding at 110 °C for 1 hour and then heating to 170 °C for 1 hour as in Example 1.
[0054] Example 4
[0055] The other operating steps are the same as in Example 1, except that in step (S1), the weight-average molecular weight of the phenolic resin is 4000 g / mol.
[0056] Example 5
[0057] The other operating steps are the same as in Example 1, except that step (S1) is changed to:
[0058] (S1) Weigh 0.9 kg of phenolic resin powder (weight average molecular weight 2000 g / mol) and 0.1 kg of boron phenolic resin and ball mill them together. Place the resulting mixture in a tube furnace and heat it at a rate of 2 ℃ / min under an ozone atmosphere. After heating to 110 ℃, hold it for 1 h. Then heat it to 170 ℃ at a rate of 2 ℃ / min and hold it for 1 h. After cooling, take out the sample, which is a low-temperature oxidative crosslinking modified phenolic resin, place it in a ball mill jar, control the ball-to-material ratio to be 10:1, set the ball mill speed to 500 rpm, and use forward and reverse rotation mode. Ball mill for 2 h to obtain the precursor.
[0059] Example 6
[0060] The other operating steps are the same as in Example 1, except that step (S1) is changed to:
[0061] (S1) Weigh 0.85 kg of phenolic resin powder (weight average molecular weight 2000 g / mol) and 0.15 kg of boron phenolic resin and ball mill them together. Place the resulting mixture in a tube furnace and heat it at a rate of 2 ℃ / min under an ozone atmosphere. After heating to 110 ℃, hold it for 1 h. Then heat it to 170 ℃ at a rate of 2 ℃ / min and hold it for 1 h. After cooling, take out the sample, which is a low-temperature oxidative crosslinking modified phenolic resin, place it in a ball mill jar, control the ball-to-material ratio to be 10:1, set the ball mill speed to 500 rpm, and use forward and reverse rotation mode. Ball mill for 2 h to obtain the precursor.
[0062] Example 7
[0063] The other operating steps are the same as in Example 1, except that step (S1) is changed to:
[0064] (S1) Weigh 0.8 kg of phenolic resin powder (weight average molecular weight 2000 g / mol) and 0.2 kg of boron phenolic resin and ball mill them together. Place the resulting mixture in a tube furnace and heat it at a rate of 2 ℃ / min under an ozone atmosphere. After heating to 110 ℃, hold it for 1 h. Then heat it to 170 ℃ at a rate of 2 ℃ / min and hold it for 1 h. After cooling, take out the sample, which is a low-temperature oxidative crosslinking modified phenolic resin, place it in a ball mill jar, control the ball-to-material ratio to be 10:1, set the ball mill speed to 500 rpm, and use forward and reverse rotation mode. Ball mill for 2 h to obtain the precursor.
[0065] Application examples Electrochemical performance testing
[0066] The hard carbon material, conductive additive SP, and binder CMC / SBR obtained in the above examples and comparative examples were mixed at a weight ratio of 93:3:4, dissolved in water, and stirred to obtain a uniform slurry. The slurry was then uniformly coated onto carbon-coated aluminum foil using a 50 μm scraper, dried, and sliced to obtain the negative electrode sheet.
[0067] The dried negative electrode sheet was assembled into a coin cell with a sodium metal negative electrode, a carboxylic acid cellulose separator, and an EC / DMC / EMC / 1M NaPF6 electrolyte. The cell was then placed on the LAND test platform for testing, and the first cycle curve was shown in Table 1.
[0068] Figure 5 The hard carbon materials of Examples 1, 1, and 2 were subjected to the above conditions at 50 mA g. -1 The charge / discharge curves.
[0069] The electrochemical performance of the negative electrode materials obtained in the above embodiments and comparative examples is listed in Table 1 below:
[0070] Table 1 Electrochemical performance data
[0071]
[0072] The test results of the half-cells in Table 1 for each embodiment show that the sodium storage capacity and rate performance of the amorphous carbon anode obtained by low-temperature ozone oxidation crosslinking and etching of the phenolic resin-based precursor are significantly improved. (50 mA g) -1 The first charge specific capacity at the current density is approximately 300 mA g. -1 200 mA g -1 The specific capacity during the first charge cycle is 240 mAh g at the given current density. -1 The preferred embodiment described above can achieve 260 mAh g. -1 The above; while Comparative Example 1, oxidized by oxygen, was at 200 mA g. -1The specific capacity at current density is only 172 mAh / g, indicating poor rate performance. The inventors believe that oxidation under oxygen conditions primarily destroys the methylene groups in the cross-linked chains of phenolic resin, while retaining more aromatic rings. Ozone, however, attacks the phenolic hydroxyl groups, leading to deep degradation of the phenolic resin skeleton and near-disappearance of aromaticity and oxygen-containing bridges. The infrared spectrum shows a significant drop in the C=C skeleton peak and near-disappearance of the aromatic CH peak, indicating the breakage of phenolic hydroxyl groups and ether bonds. Aromatic rings open to generate aliphatic oxygen-containing small molecules (carboxylic acids, aldehydes, ketones, etc.), resulting in severe degradation of the resin skeleton. These small molecule fragments volatilize or decompose at high temperatures, leaving behind active carbon atoms or free radicals. Because the original aromatic structure is destroyed, carbonization is no longer constrained by the original cross-linked network, allowing residual carbon atoms to migrate and rearrange more easily, forming long-range ordered graphite domains (similar to catalytic graphitization or vapor-deposited graphite), significantly improving the rate performance of phenolic resin-based hard carbon. It is worth noting that the ozone oxidation temperature needs to be properly controlled to obtain the optimal carbon layer structure and the maximum specific capacity and rate performance. Examples 5-7 are hard carbon materials obtained by low-temperature ozone oxidation of a mixture of phenolic resin and boron-modified phenolic resin, which further improves the electrochemical performance.
[0073] This invention utilizes the oxidative crosslinking and etching effects of ozone to increase the crosslinking degree of the precursor. Simultaneously, the release of gas molecules during pyrolysis increases the porosity of the carbon material while causing the long polymer chains to break. During high-temperature carbonization, local graphite domains can close to form closed pores, and a large number of short-range graphite domains are formed, significantly improving the electrochemical performance of sodium-ion batteries. This is because its effect on phenolic resins is far stronger than ordinary oxidation: ozone can directly attack and destroy the stable aromatic ring framework (C=C) and oxygen-containing bridges, leading to deep degradation of the resin and the generation of aliphatic oxygen-containing small molecules such as carboxylic acids, aldehydes, and ketones. These small molecules volatilize during subsequent high-temperature carbonization, leaving numerous micropores and defects within the material. Simultaneously, the remaining carbon atoms, freed from the constraints of the original crosslinking network, can migrate and rearrange, forming closed-pore structures and short-range graphite domains conducive to sodium ion storage. Etching describes this destructive, pore-forming, and pathway-altering strong oxidizing effect, rather than merely surface modification.
Claims
1. A method for preparing a hard carbon material for sodium-ion batteries, characterized in that, Includes the following steps: (S1) The phenolic resin is subjected to a two-stage heat treatment in an ozone-containing gas atmosphere: a first stage reaction at 100-110℃ and a second stage reaction at 130-170℃, to obtain the precursor. (S2) The precursor is crushed and carbonized at high temperature in an inert gas atmosphere to obtain hard carbon material for sodium-ion batteries.
2. The preparation method according to claim 1, characterized in that, In step (S1), the weight-average molecular weight of the phenolic resin is in the range of 2000-5000 g / mol.
3. The preparation method according to claim 1, characterized in that, In step (S1), the ozone-containing atmosphere is obtained by electrochemically treating air or pure oxygen; when air is treated, the resulting ozone-containing atmosphere has an oxygen volume content of 17-20% and an ozone volume content of 1-3.15%; when pure oxygen is treated, the resulting ozone-containing atmosphere has an oxygen volume content of 85-95% and an ozone volume content of 5-15%.
4. The preparation method according to claim 1, characterized in that, In step (S1), the first reaction is low-temperature pre-oxidation, which involves heating to 100-110℃ at a rate of 1-5℃ / min and holding for 1-2 hours; the second reaction is oxidative pyrolysis, which involves heating to 130-170℃ at a rate of 1-5℃ / min and holding for 1-2 hours.
5. The preparation method according to claim 1, characterized in that, In step (S2), the inert atmosphere is argon and / or argon gas; the calcination is carried out by heating to 1200-1800 ℃ at a heating rate of 5-10 ℃ / min and calcining for 2-5 hours.
6. The preparation method according to claim 1, characterized in that, Step (S1) is changed to: phenolic resin and boron phenolic resin are mixed evenly, and the resulting mixture is subjected to a two-stage heat treatment in an ozone-containing gas atmosphere: low-temperature pre-oxidation and heated catalytic reaction in sequence to obtain the precursor.
7. The preparation method according to claim 6, characterized in that, The mass content of boron phenolic resin is 0.7-1.3 wt%, preferably 0.8-1.1 wt%; further, the mass percentage of boron phenolic resin in the mixture is 10-15 wt%.
8. The sodium-ion battery hard carbon material prepared by the preparation method according to any one of claims 1-7.
9. A negative electrode sheet for a sodium-ion battery, comprising: The current collector, the binder coated on the current collector, and the hard carbon material prepared by the preparation method according to any one of claims 1-7.
10. A sodium-ion secondary battery, wherein the negative electrode is the negative electrode sheet as described in claim 9, or the negative electrode comprises a hard carbon material prepared by any one of claims 1-7.