Swelling limited modified resin-based sodium ion battery hard carbon negative electrode material and preparation method thereof

Abstract

The application discloses a kind of swelling limited modified resin-based sodium ion battery hard carbon negative electrode materials and preparation method thereof.The application includes the following steps: polymer precursor particles are placed in a modified solution containing a modified component for swelling treatment, and free modified components on the surface of the polymer precursor particles are removed;the polymer precursor particles subjected to swelling treatment are vacuum dried, and then heat-cured embedding or self-catalyzed copolymerization is performed to limit and fix the modified components in the resin network, obtaining limited modified resin particles;the limited modified resin particles are subjected to segmented atmosphere carbonization to obtain carbide, and the carbide is vacuum dried and sieved to obtain the swelling limited modified resin-based sodium ion battery hard carbon negative electrode material.The hard carbon negative electrode material of the application has adjustable pore structure, lower open specific surface area, suitable interlayer spacing and stable sodium storage sites, which can improve the initial coulomb efficiency, low potential platform capacity ratio and cycle stability of sodium ion battery.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, specifically to a swelling-confined modified resin-based hard carbon anode material for sodium-ion batteries and its preparation method. Background Technology

[0002] Sodium-ion batteries offer advantages such as abundant sodium resources, low cost, good safety, and suitability for large-scale energy storage. Hard carbon materials, due to their disordered carbon structure, large interlayer spacing, and tunable pore structure, are considered important candidate systems for sodium-ion battery anode materials.

[0003] Resin-based hard carbon precursors are commonly used in the preparation of hard carbon anode materials due to their designable composition, high char residue, and good batch stability. Existing resin-based hard carbon anode materials are typically obtained through direct resin curing, pre-carbonization, and high-temperature carbonization. They can also be modified through mechanical mixing, solution blending, impregnation, or the addition of metal salts, heteroatom sources, or template agents. However, traditional blending or impregnation methods often suffer from uneven distribution of modified components, surface enrichment, migration or agglomeration during carbonization, making it difficult to achieve effective confinement and stable dispersion of modified components within the polymer precursor particles.

[0004] On the other hand, the open specific surface area, closed pore structure, microcrystalline interlayer spacing, defect structure, and heteroatom distribution of hard carbon anode materials all affect the intercalation, adsorption, and pore-filling storage behavior of sodium ions. If the modified components in the polymer precursor cannot be effectively fixed, an uneven pore structure, an increase in open pores, or the aggregation of residual impurities are easily formed during carbonization, which leads to an increase in the initial irreversible capacity, a decrease in the initial coulombic efficiency, and a decline in cycle stability.

[0005] Therefore, it is necessary to provide a new method for modifying resin-based hard carbon precursors, so that the modified components can enter the interior of the precursor particles through the swelling effect of the polymer network, and be fixed by subsequent curing or cross-linking processes. Combined with segmented carbonization in different atmospheres, the hard carbon structure and sodium storage performance can be controlled and adjusted. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a swelling-confined modified resin-based hard carbon anode material for sodium-ion batteries and its preparation method. This invention utilizes the characteristic that polymer precursor particles can swell but do not completely dissolve, allowing the modified components to enter the polymer network along with the swelling medium. Through the removal of surface free components and subsequent curing treatment, the modified components are confined and fixed within the polymer cross-linked network. Finally, a resin-based hard carbon anode material with tunable structure is obtained through segmented carbonization under different atmospheres.

[0007] To achieve the above objectives, the technical solution designed by the present invention is as follows: This invention provides a method for preparing a swelling-confined modified resin-based hard carbon anode material for sodium-ion batteries, comprising the following steps: (1) The polymer precursor particles are placed in a modified solution containing the modified components for swelling treatment, and then the free modified components on the surface of the polymer precursor particles are removed. When the polymer precursor particles are cross-linked phenolic resin particles, the corresponding modification solution is zinc acetylacetone modification solution. When the polymer precursor particles are resorcinol-formaldehyde resin particles, the corresponding modification solution is furfuryl alcohol modification solution. (2) Vacuum drying of the polymer precursor particles after swelling treatment, followed by thermosetting embedding or autocatalytic copolymerization to obtain confined modified resin particles. (3) The confined modified resin particles are carbonized in a segmented atmosphere to obtain carbides. The carbides are then vacuum dried and sieved to obtain the swollen confined modified resin-based sodium-ion battery hard carbon anode material.

[0008] Furthermore, the polymer precursor particles are cross-linked phenolic resin particles; The method for preparing the cross-linked phenolic resin particles is as follows: I. Mix phenol, a 35-40% (w / w) aqueous solution of formaldehyde, and oxalic acid in a mass ratio of 90-95:60-65:0.5-1; II. Under high-purity nitrogen and at a speed of 250-300 r / min, the temperature is increased to 80-90℃ at a rate of 3-5℃ / min, and the temperature is maintained for reflux reaction for 10-12 hours. Ⅲ. After the reflux reaction is completed, vacuum distillation is carried out at 80~85℃ and -0.08~-0.1MPa for 4~6 hours to obtain phenolic prepolymer; IV. After cooling, the phenolic prepolymer is crushed and mixed with hexamethylenetetramine for ball milling. The ball milling speed is 200~220 r / min and the ball milling time is 10~30 min. The mass ratio of phenol to hexamethylenetetramine is 1:0.08~0.12. V. Dry the ball-milled mixture at 110~160℃ for 4~6h, cool it, crush it and sieve it to obtain cross-linked phenolic resin particles with a particle size of 150~250μm. The preparation process of the zinc acetylacetone modified solution is as follows: zinc acetylacetone is dissolved in acetone to obtain a zinc acetylacetone modified solution with a concentration of 0.01~0.02 g / mL. The specific process of step (1) is as follows: cross-linked phenolic resin particles and zinc acetylacetone modified solution are mixed and stirred for 5-6 hours at a mass-volume ratio of 1:5~7 g / mL, wet particles are collected by centrifugation, acetone is added to the wet particles and shaken for 30-35 seconds, and the wet particles are collected by centrifugation after shaking.

[0009] Furthermore, in step I, the formaldehyde aqueous solution has a mass fraction of 37% (w / w), and the mass ratio of phenol, formaldehyde aqueous solution, and oxalic acid is 94.1:64.9:0.94; In step II, the stirring speed is 250 r / min, the heating rate is 5℃ / min, the temperature is raised to 90℃, and the reflux reaction time is 12h. In step III, the temperature of vacuum distillation is 80℃, the vacuum degree of vacuum distillation is -0.08MPa, and the time of vacuum distillation is 6h. In step IV, the mass ratio of phenol to hexamethylenetetramine is 1:0.1; In step V, the drying temperature is 110℃ and the drying time is 4 hours; The concentration of the zinc acetylacetone modified solution is 0.02 g / mL; The mass-to-volume ratio of the cross-linked phenolic resin particles to the zinc acetylacetone modified solution is 1:5 g / mL.

[0010] Furthermore, the polymer precursor particles are resorcinol-formaldehyde resin particles. The preparation process of the resorcinol-formaldehyde resin particles is as follows: ① Mix resorcinol, ammonia water with a mass fraction of 25~28% (w / w), anhydrous ethanol and water, with the mass ratio of ammonia water to resorcinol being 1:13.5~14; ② Under the conditions of 35~45℃ and 300~350r / min, a formaldehyde aqueous solution with a mass fraction of 35~40% (w / w) is added dropwise to the reaction system of step ① and the reaction is carried out for 2~2.5h; the mass ratio of ammonia water to formaldehyde aqueous solution is 1:20~22; ③ Under conditions of 200~220r / min, the temperature is increased to 80~85℃ at a heating rate of 3~5℃ / min for aging reaction for 12~16h. After the reaction is completed, the temperature is cooled, the precipitate is collected by centrifugation, and resin particles are obtained. ④ The resin particles are washed, vacuum dried, pulverized and sieved in sequence to obtain resorcinol-formaldehyde resin particles with a particle size of 5~20μm. The preparation process of the furfuryl alcohol modified solution is as follows: furfuryl alcohol and p-toluenesulfonic acid are dissolved in anhydrous ethanol to obtain the furfuryl alcohol modified solution, wherein the mass ratio of furfuryl alcohol to p-toluenesulfonic acid is 1:0.01~0.02; The specific process of step (1) is as follows: resorcinol-formaldehyde resin particles and furfuryl alcohol modified solution are mixed at a mass-volume ratio of 1:10~12 g / mL, vacuumed to -0.08~-0.1 MPa and maintained for 10~12 min, then high-purity nitrogen is introduced to restore to normal pressure, and the vacuuming and nitrogen filling process is repeated twice. Then, the mixture is stirred at 200~220 r / min for 4~4.5 h. After stirring, the mixture is filtered to obtain separated particles, and the separated particles are washed with anhydrous ethanol to obtain wet particles.

[0011] Furthermore, in step ①, the mass fraction of ammonia is 25% (w / w), and the mass ratio of ammonia to resorcinol is 1:13.775; In step ②, the mass fraction of the formaldehyde aqueous solution is 37% (w / w), and the mass ratio of ammonia water to formaldehyde aqueous solution is 1:20.275; In step ③, the heating rate is 5℃ / min, the temperature is raised to 80℃, and the aging reaction time is 12h. The mass ratio of furfuryl alcohol to p-toluenesulfonic acid is 1:0.02; The mass-to-volume ratio of resorcinol-formaldehyde resin particles to furfuryl alcohol modified solution is 1:10 g / mL, the vacuum degree is -0.08 MPa, the vacuum holding time is 10 min, the stirring speed is 200 r / min, and the stirring time is 4 h.

[0012] Furthermore, in step (2), when the polymer precursor particles are cross-linked phenolic resin particles, they are subjected to thermosetting embedding treatment after vacuum drying. The conditions for thermosetting embedding treatment are: thermosetting at 150~170℃ for 2.5~3.5h under a high-purity nitrogen atmosphere of 100~150mL / min. When the polymer precursor particles are resorcinol-formaldehyde resin particles, they are subjected to autocatalytic copolymerization after vacuum drying. The autocatalytic copolymerization process is as follows: under a high-purity nitrogen atmosphere of 100~150mL / min, the temperature is first held at 80~85℃ for 2~2.5h, and then the temperature is increased to 140~150℃ at a heating rate of 2~2.5℃ / min and held for 4~4.5h. In step (3), the segmented atmosphere carbonization specifically involves: i. Under a high-purity nitrogen atmosphere of 300~350mL / min, heat to 180~200℃ at a heating rate of 2~2.5℃ / min and hold for 2~2.5h; ii. In a mixed gas atmosphere of 300~350mL / min, heat to 500~550℃ at a heating rate of 3~3.5℃ / min and hold for 1.5~2h; iii. Under a high-purity nitrogen or high-purity argon atmosphere of 300-350 mL / min, heat to 1300-1400℃ at a heating rate of 5-5.5℃ / min and hold at that temperature for 2-2.5 hours; iv. Under a high-purity nitrogen or high-purity argon atmosphere of 300~350 mL / min, the carbide is obtained after cooling; When the polymer precursor particles are cross-linked phenolic resin particles, step (3) further includes: adding the carbide to a 1.0~1.5mol / L hydrochloric acid solution, stirring at 60~65℃ and 200~220r / min for 2~2.5h, filtering after stirring to obtain a precipitate, washing until the pH of the precipitate is 6.5~7.0, vacuum drying and sieving the precipitate to obtain a swelling-confined modified resin-based sodium-ion battery hard carbon anode material.

[0013] Furthermore, in step (2), the conditions for the thermosetting embedding treatment are: thermosetting at 160°C for 3 hours under a high-purity nitrogen atmosphere of 100 mL / min; The autocatalytic copolymerization process is as follows: under a high-purity nitrogen atmosphere of 100 mL / min, the temperature is first maintained at 80°C for 2 hours, and then the temperature is increased to 140°C at a rate of 2°C / min and maintained for 4 hours.

[0014] Furthermore, in step i, the flow rate of high-purity nitrogen is 300 mL / min, the heating rate is 2℃ / min, the temperature is raised to 200℃, and the holding time is 2h. In step ii, the flow rate of the mixed gas is 300 mL / min, the heating rate is 3℃ / min, the temperature is raised to 550℃, and the holding time is 2h. The mixed gas is a nitrogen-carbon dioxide mixture or a nitrogen-ammonia mixture. In the nitrogen-carbon dioxide mixture, the volume ratio of nitrogen to carbon dioxide is 98:2, and in the nitrogen-ammonia mixture, the volume ratio of nitrogen to ammonia is 99:1. In step iii, the flow rate of high-purity nitrogen or high-purity argon is 300 mL / min, the heating rate is 5℃ / min, the temperature is raised to 1300℃, and the holding time is 2h. In step iv, the flow rate of high-purity nitrogen or high-purity argon is 300 mL / min; The concentration of the hydrochloric acid solution is 1.0 mol / L.

[0015] This invention also provides a swelling-confined modified resin-based sodium-ion battery hard carbon anode material prepared by the aforementioned method, wherein the BET specific surface area of ​​the hard carbon anode material is ≤22.5 m². 2 / g; X-ray diffraction d002 interlayer spacing is 0.37nm~0.38nm.

[0016] The present invention also provides a sodium-ion half-cell, wherein the sodium-ion half-cell comprises the swelling-confined modified resin-based sodium-ion battery hard carbon anode material described above.

[0017] The principle of this invention: 1. In this invention, the polymer precursor particles are in a partially cross-linked state, exhibiting the characteristics of being swollen but not completely dissolved. When placed in a swelling medium (modified solution) containing modified components, solvent molecules enter the polymer network, increasing the intersegment spacing and free volume, thereby allowing the modified components to enter the interior of the polymer precursor particles along with the swelling medium.

[0018] 2. After removing the free modified components from the outer surface of the particles, the polymer network further shrinks or cross-links through thermosetting embedding or autocatalytic copolymerization, confining the modified components inside the particles within the cross-linked polymer network. This process reduces the tendency of the modified components to migrate, precipitate, and aggregate during subsequent carbonization.

[0019] 3. In the segmented carbonization process under different atmospheres, the first stage of drying and curing is mainly used for solvent removal and curing; the second stage of pre-carbonization is used for pre-carbonization and regulation of volatile component release; the third stage of high-temperature carbonization is used for high-temperature carbon skeleton rearrangement and hard carbon structure formation; and the fourth stage of cooling protection is used for inert atmosphere protection and cooling. Confined modified resin particles can influence the evolution of hard carbon structures through template action, catalysis, heteroatom introduction, volatilization pore formation, crosslinking enhancement, residual char rate regulation, or microcrystalline structure regulation. By selecting different modifying components and segmented carbonization atmospheres, the open pores, closed pores, interlayer spacing, defect structure, and surface chemical composition of hard carbon materials can be adjusted, thereby improving sodium ion storage behavior.

[0020] The beneficial effects of this invention are: Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention utilizes the characteristic that polymer precursor particles can swell but not completely dissolve to achieve the penetration of modified components into the interior of the polymer network, which is different from traditional mechanical mixing or ordinary surface impregnation.

[0021] 2. By removing the free modified components on the outer surface and further employing thermosetting embedding or autocatalytic copolymerization, the modified components are confined and fixed in the polymer crosslinking network, which helps to reduce the risk of migration, precipitation or agglomeration of the modified components during carbonization.

[0022] 3. This invention uses segmented carbonization in different atmospheres to ensure that the polymer precursor is in a suitable atmosphere during the drying and curing, pre-carbonization, high-temperature carbonization and cooling protection stages, thereby adjusting the release of volatile components, char residue, pore structure and microcrystalline structure.

[0023] 4. This invention can achieve targeted regulation of the sodium storage performance of hard carbon materials by selecting different modifying components to control the pore structure, microcrystalline structure, heteroatom composition, defect structure, carbon residue rate and surface chemical state.

[0024] 5. The hard carbon anode material obtained by this invention can have a low open specific surface area, suitable interlayer spacing, adjustable pore structure and stable sodium storage active sites, which is beneficial to improving the first coulombic efficiency, reversible capacity, low potential plateau capacity ratio and cycle stability of sodium-ion batteries. Attached Figure Description

[0025] Figure 1 A schematic diagram of the preparation process for a swelling-confined modified resin-based hard carbon anode material for sodium-ion batteries; Figure 2 A schematic diagram of a polymer precursor particle swelling, inhaling modified components, and then being solidified and confined. Figure 3 This is a schematic diagram of the segmented atmosphere carbonization process of the present invention; Figure 4 A schematic diagram comparing the structures of ordinary blends or surface impregnation with the swelling confinement modification of the present invention; Figure 5 A statistical chart of the capacity of a sodium-ion half-cell after 100 cycles; Figure 6 This is a graph showing the initial charge-discharge curve of a sodium-ion half-cell. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can understand it.

[0027] Example 1 Preparation method of swelling-confined modified resin-based sodium-ion battery hard carbon anode material 1 Preparation process as follows Figure 1 As shown, it includes the following steps: 1. Synthesis of cross-linked phenolic resin particles: (1) Add 94.1g of phenol, 64.9g of 37% (w / w) formaldehyde aqueous solution and 0.94g of oxalic acid to a 500mL four-necked glass flask equipped with a mechanical stirrer, reflux condenser, thermometer and nitrogen delivery tube.

[0028] (2) High-purity nitrogen (nitrogen purity ≥ 99.999%) was introduced at a flow rate of 100 mL / min for 20 min to replace the air. After the high-purity nitrogen was introduced, the temperature was raised to 90℃ at a heating rate of 5℃ / min under stirring at 250 r / min, and the temperature was kept at that temperature for reflux reaction for 12 h.

[0029] (3) After the reaction is completed, the reaction system is cooled to 80°C and subjected to vacuum distillation for 6 hours under a vacuum of -0.08 MPa provided by a rotary vane vacuum pump to obtain phenolic prepolymer.

[0030] (4) Cool the obtained phenolic prepolymer to room temperature, and use a pulverizer to intermittently pulverize it 3 times at 10000 r / min, each time for 10s and with an interval of 30s. After passing it through a 20-mesh sieve, add it to a 500mL zirconium ball mill jar with 9.4g hexamethylenetetramine and mix and ball mill it for 10min at 200r / min using a planetary ball mill.

[0031] (5) Spread the ball-milled mixture on a stainless steel tray and treat it at 110°C for 4 hours in a forced-air drying oven to perform partial cross-linking. After cooling, crush it using a high-speed universal pulverizer and collect particles with a particle size of 150~250μm through 60-mesh and 100-mesh standard sieves to obtain cross-linked phenolic resin particles, i.e., polymer precursor particles.

[0032] 2. Swelling-limited modification of zinc acetylacetone: (1) Add 100 mL of acetone and 2.0 g of zinc acetylacetonate monohydrate to a 250 mL jacketed glass reactor, and stir at 25 °C and 300 r / min for 20 min to completely dissolve it, so as to obtain a modified zinc acetylacetonate solution.

[0033] (2) Add 20.0 g of the cross-linked phenolic resin particles prepared in step 1 to the zinc acetylacetone modified solution. Connect the reactor to a circulating constant temperature water bath and maintain it at 25°C. Stir at 150 r / min for 6 h using a paddle mechanical stirrer. This causes the polymer precursor particles to swell and allows the modified components to enter the interior of the polymer precursor particles, such as... Figure 2 As shown.

[0034] (3) After the treatment, centrifuge at 5000 r / min for 10 min using a benchtop centrifuge, discard the supernatant to obtain wet particles; add 20 mL of acetone to the wet particles, shake for 30 s and centrifuge again at 5000 r / min for 5 min to remove free zinc acetylacetone from the outer surface of the particles to obtain wet particles.

[0035] (4) The wet particles were placed in a vacuum drying oven and dried at 50℃ and -0.09MPa for 8h. Then they were transferred to a nitrogen-protected oven and heat-cured at 160℃ for 3h under the condition of continuous introduction of high-purity nitrogen at 100mL / min, so that the phenolic resin could be further crosslinked and zinc acetylacetone could be confined and fixed in the resin network to obtain zinc acetylacetone confined modified resin particles.

[0036] 3. Segmented atmosphere carbonization and post-treatment (e.g.) Figure 3 (as shown) (1) The 10.0g zinc acetylacetone confined modified resin particles prepared in step 2 were evenly spread in an alumina boat with a length of 200mm and a width of 40mm, and placed in the constant temperature zone of a horizontal quartz tube furnace with an inner diameter of 80mm. High-purity nitrogen was introduced at a flow rate of 500mL / min to replace the air for 30min. Then the flow rate of high-purity nitrogen was adjusted to 300mL / min, and the temperature was increased to 200℃ at 2℃ / min and kept at the temperature for 2h (first stage drying and curing).

[0037] (2) Then switch to a nitrogen-carbon dioxide mixture with a volume ratio of 98:2, the total flow rate of the mixture is 300 mL / min, and the temperature is increased to 550℃ at 3℃ / min and kept at 2h (second stage pre-carbonization).

[0038] (3) Then switch to high-purity nitrogen gas at a flow rate of 300 mL / min, and heat to 1300℃ at 5℃ / min and keep warm for 2 hours (third stage high-temperature carbonization).

[0039] (4) After the heat preservation is completed, the mixture is naturally cooled to room temperature under the protection of high-purity nitrogen with a flow rate of 300 mL / min to obtain carbides (fourth stage cooling protection).

[0040] (5) The carbide was added to 200 mL of 1.0 mol / L hydrochloric acid solution and stirred at 200 r / min for 2 h in a constant temperature water bath at 60 °C. After stirring, the mixture was filtered using a Buchner funnel to obtain a precipitate. The precipitate was washed with deionized water by vacuum filtration until the pH of the filtrate was 6.5-7.0. The washed precipitate was dried at 100 °C and -0.09 MPa vacuum for 12 h, and then ground using an agate mortar and passed through a 325 mesh standard sieve to obtain the swelling-confined modified resin-based sodium-ion battery hard carbon anode material 1, namely, zinc acetylacetone swelling-confined modified phenolic resin-based sodium-ion battery hard carbon anode material.

[0041] Example 2 Preparation method of swelling-confined modified resin-based sodium-ion battery hard carbon anode material 2 1. Synthesis of resorcinol-formaldehyde resin particles: (1) Add 500 mL of deionized water, 200 mL of anhydrous ethanol, 55.1 g of resorcinol and 4.0 g of 25% (w / w) ammonia to a 2 L four-necked glass flask equipped with a mechanical stirrer, a constant pressure dropping funnel, a reflux condenser and a thermometer, and mix well.

[0042] (2) Under stirring conditions of 35℃ and 300r / min, 81.1g of 37% (w / w) formaldehyde aqueous solution was added dropwise to the reaction system of step (1) through a constant pressure dropping funnel and the addition was completed within 20min; after the addition was completed, the reaction was continued at 35℃ and 300r / min for 2h.

[0043] (3) Then, under the condition of 200 r / min, the temperature was increased to 80℃ at a heating rate of 5℃ / min for 12h for aging reaction. After the reaction was completed and cooled to room temperature, the precipitate, i.e. resin particles, was collected by centrifuging at 6000 r / min for 10min using a benchtop high-speed centrifuge.

[0044] (4) Wash the resin particles three times with 300 mL of deionized water, and then wash them three times again with 300 mL of anhydrous ethanol. Centrifuge at 6000 r / min for 10 min each time. Place the washed particles in a vacuum drying oven and dry them at 60℃ and -0.09 MPa for 12 h. Then pulverize and sieve to obtain resorcinol-formaldehyde resin particles with a particle size of 5~20 μm, which are polymer precursor particles.

[0045] 2. Swelling confinement modification of furfuryl alcohol: (1) Add 200 mL of anhydrous ethanol, 10.0 g of furfuryl alcohol and 0.20 g of p-toluenesulfonic acid monohydrate to a 500 mL vacuum impregnation tank, and stir with a magnetic stirrer at 400 r / min for 15 min to form a homogeneous furfuryl alcohol modified solution.

[0046] (2) Add 20.0g of resorcinol-formaldehyde resin particles prepared in step 1 to furfuryl alcohol modified solution, evacuate the impregnation tank to -0.08MPa and maintain it for 10min, and then introduce high-purity nitrogen to restore it to normal pressure (0.1MPa). (3) Repeat step (2) twice for vacuuming and nitrogen filling. Place the impregnation tank in a 30°C constant temperature water bath and mechanically stir at 200 r / min for 4 h to allow furfuryl alcohol to enter the resin network. Filter using a Buchner funnel to obtain separated particles. Quickly wash the separated particles with 20 mL of anhydrous ethanol for 30 s to obtain wet particles.

[0047] (4) The wet particles were placed in a vacuum drying oven and dried at 50℃ and -0.09MPa for 6 hours; then placed in a nitrogen-protected oven and kept at 80℃ for 2 hours under the condition of continuous introduction of high-purity nitrogen at 100mL / min, and then heated to 140℃ at 2℃ / min and kept at 140℃ for 4 hours, so that furfuryl alcohol would undergo autocatalytic copolymerization and be confined and fixed inside the resin network, thus obtaining furfuryl alcohol confined modified resin particles, such as Figure 2 As shown.

[0048] 3. Segmented atmosphere carbonization and post-treatment: (1) The 10.0g furfuryl alcohol confined modified resin particles prepared in step 2 were evenly spread in an alumina boat with a length of 200mm and a width of 40mm, and placed in the constant temperature zone of a horizontal quartz tube furnace with an inner diameter of 80mm. High-purity nitrogen was introduced at a flow rate of 500mL / min to replace the air for 30min. Then the flow rate of high-purity nitrogen was adjusted to 300mL / min, and the temperature was raised to 180℃ at 2℃ / min and kept at the temperature for 2h (first stage drying and curing).

[0049] (2) Then switch to a nitrogen-ammonia mixture with a nitrogen-ammonia volume ratio of 99:1. The total flow rate of the mixture is 300 mL / min. The temperature is increased to 500℃ at 3℃ / min and held for 1.5 h (second stage pre-carbonization).

[0050] (3) Then switch to high-purity argon (argon purity ≥ 99.999%), with a flow rate of 300 mL / min, and heat to 1400℃ at 5℃ / min and keep warm for 2 hours (third stage high-temperature carbonization).

[0051] (4) After the heat preservation is completed, the mixture is naturally cooled to room temperature under the protection of high-purity argon gas flow rate of 300 mL / min to obtain carbides (fourth stage cooling protection).

[0052] (5) The carbide was ground using an agate mortar and passed through a 325-mesh standard sieve, and then dried at 100°C and -0.09MPa vacuum for 6 hours to obtain the swelling-confined modified resin-based sodium-ion battery hard carbon anode material 2, namely furfuryl alcohol swelling-confined modified resorcinol-formaldehyde resin-based sodium-ion battery hard carbon material.

[0053] Comparative Example 1 Preparation method of unmodified resin-based hard carbon material D1 (without swelling confinement modification) 1. Synthesis of cross-linked phenolic resin particles: Same as step 1 in Example 1.

[0054] 2. The cross-linked phenolic resin particles were transferred to a nitrogen-protected oven and heat-cured at 160°C for 3 hours under the condition of continuous introduction of high-purity nitrogen at 100 mL / min to obtain unmodified resin particles.

[0055] 3. Segmented atmosphere carbonization and post-treatment: Same as step 3 in Example 1. Unmodified resin-based hard carbon material D1 is obtained.

[0056] Comparative Example 2 Preparation method of blended modified hard carbon material D2 (ordinary blending modification) 1. Synthesis of cross-linked phenolic resin particles: Same as step 1 in Example 1.

[0057] 2. Add 20.0g of cross-linked phenolic resin particles and 2.0g of zinc acetylacetone monohydrate to a 500mL zirconia ball mill jar and dry mix at 100r / min for 10min. Then transfer to a nitrogen-protected oven and heat-cur at 160℃ for 3h under continuous high-purity nitrogen flow at 100mL / min to obtain the blended modified resin particles. This step does not use a swelling medium, nor does it involve swelling aspiration or surface washing.

[0058] 3. Segmented atmosphere carbonization and post-treatment: Same as step 3 in Example 1. The resulting blended modified hard carbon material D2 is obtained. This comparative example illustrates that in the absence of swelling absorption and confined distribution, the modified components are mainly located on the particle surface, resulting in an increase in open specific surface area.

[0059] Comparative Example 3 Preparation method of hard carbon material D3 by single inert atmosphere carbonization (single inert atmosphere carbonization) 1. Synthesis of cross-linked phenolic resin particles: Same as step 1 in Example 1.

[0060] 2. Swelling confinement modification of zinc acetylacetonate: Same as step 2 in Example 1.

[0061] 3. The zinc acetylacetone confined modified resin particles were subjected to conventional pre-carbonization and high-temperature carbonization under nitrogen or argon atmosphere throughout the process. Specifically, high-purity nitrogen was used throughout the process at a flow rate of 300 mL / min. The temperature was increased to 200°C at a rate of 2°C / min and held for 2 hours. The temperature was then increased to 550°C at a rate of 3°C / min and held for 2 hours. Finally, the temperature was increased to 1300°C at a rate of 5°C / min and held for 2 hours. After the holding period, the temperature was naturally cooled to room temperature under the protection of high-purity nitrogen at a flow rate of 300 mL / min to obtain the carbide. Subsequent steps were the same as step 3 in Example 1.

[0062] A single inert atmosphere carbonized hard carbon material D3 was obtained. This comparative example is used to illustrate the effect of segmented carbonization under different atmospheres on pore structure and electrochemical performance.

[0063] Performance Test 1 1. The swelling-confined modified resin-based sodium-ion battery hard carbon anode materials 1-2 of Examples 1-2 and hard carbon materials D1-D3 of Comparative Examples 1-3 were subjected to thermogravimetric analysis under high-purity nitrogen protection. The temperature was increased from room temperature to 800℃ at a rate of 10℃ / min and held for 30min. The residual carbon rate of the corresponding carbonization precursor of each hard carbon material at 800℃ was measured. The BET specific surface area was determined by nitrogen adsorption at 77K. X-ray diffraction was performed using Cu Kα rays, and the d002 interlayer spacing was calculated from the (002) peak. Raman spectroscopy was performed using a 532nm laser, and the integral intensity ratio ID / IG of the D peak and G peak was calculated. The results are shown in Table 1.

[0064] Table 1. Corresponding precursor char residue and hard carbon structural parameters As shown in Table 1, Examples 1 and 2, while maintaining a low open specific surface area, exhibited a high residual carbon rate, a large d002 interlayer spacing, and a moderate degree of defects. Comparative Example 3, although having a lower BET specific surface area, also had smaller d002 and ID / IG ratios, indicating that a single inert atmosphere failed to create suitable interlayer spacing and sodium storage defect sites.

[0065] 2. The structures of the cross-linked phenolic resin particles obtained after different modification treatments in Comparative Example 2 and Example 1 were analyzed, and the results are as follows: Figure 4 As shown, the cross-linked phenolic resin particles of Example 1 allow the modified components to be uniformly distributed inside the resin through swelling confinement. After carbonization, the surface open pores can be reduced, and suitable interlayer spacing and defect structure can be formed.

[0066] Example 3 Preparation method of sodium-ion half-cell 1 The swelling-confined modified resin-based sodium-ion battery hard carbon anode material 1 from Example 1, the conductive agent Super P, and the binder sodium carboxymethyl cellulose were mixed in a mass ratio of 8:1:1 to form a powder. Deionized water was added to form a uniform slurry with a deionized water to powder mass ratio of 10:1. The slurry was coated onto the surface of a copper foil current collector, and after drying, rolling, and stamping, a 10mm circular anode sheet was obtained with an electrode loading of 1.0~1.2 mg / cm². 2 .

[0067] In this embodiment, the sodium-ion half-cell 1 was prepared in an inert atmosphere glove box, using the circular negative electrode sheet prepared above as the working electrode, a d12mm metallic sodium sheet as the counter electrode and reference electrode, a glass fiber separator and a 1.0mol / L sodium hexafluorophosphate electrolyte, and a CR2016 button cell casing.

[0068] Example 4 Preparation method of sodium-ion half-cell 2 The sodium-ion half-cell 2 in this embodiment is the same as that in embodiment 3, except that the negative electrode material in this embodiment is the swelling-confined modified resin-based sodium-ion battery hard carbon negative electrode material 2 of embodiment 2.

[0069] Comparative Example 4 Preparation method of sodium-ion half-cell D1 The sodium-ion half-cell D1 in this comparative example is the same as that in Example 3, except that the negative electrode material in this comparative example is the unmodified resin-based hard carbon material D1 of Comparative Example 1.

[0070] Comparative Example 5 Preparation method of sodium-ion half-cell D2 The sodium-ion half-cell D2 in this comparative example is the same as that in Example 3, except that the negative electrode material in this comparative example is the blended modified hard carbon material D2 of Comparative Example 2.

[0071] Comparative Example 6 Preparation method of sodium-ion half-cell D3 The sodium-ion half-cell D3 in this comparative example is the same as that in Example 3, except that the negative electrode material in this comparative example is the single inert atmosphere carbonized hard carbon material D3 of Comparative Example 3.

[0072] Performance Test 2 The performance of sodium-ion half-cells 1-2 from Examples 3-4 and sodium-ion half-cells D1-D3 from Comparative Examples 4-6 were tested at a temperature of 25°C, a voltage range of 0-2V, and a current density of 30mA / g. The capacity statistics after 100 cycles are shown in the figure below. Figure 5 As shown, the initial charge-discharge curve is as follows: Figure 6 As shown in Table 2, the first discharge specific capacity, first coulombic efficiency, and low potential plateau capacity ratio were calculated based on the charge-discharge curves.

[0073] Table 2 Sodium storage performance of hard carbon anode materials Depend on Figure 5 , Figure 6 As shown in Table 2, Examples 1 and 2 exhibit better initial reversible specific capacity, initial coulombic efficiency, low-potential plateau capacity ratio, and cycle retention rate than their respective comparative examples. Although Comparative Example 2 has a higher initial discharge specific capacity, it generates more irreversible interfacial reactions due to its larger open specific surface area, resulting in a lower initial coulombic efficiency. Comparative Example 3 has a lower open specific surface area, but insufficient suitable interlayer spacing and defect sites lead to a lower reversible specific capacity and low-potential plateau capacity ratio.

[0074] All other parts not described in detail are existing technologies. Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a swelling-confined modified resin-based hard carbon anode material for sodium-ion batteries, characterized in that: Includes the following steps: (1) The polymer precursor particles are placed in a modified solution containing the modified components for swelling treatment, and then the free modified components on the surface of the polymer precursor particles are removed. When the polymer precursor particles are cross-linked phenolic resin particles, the corresponding modification solution is zinc acetylacetone modification solution. When the polymer precursor particles are resorcinol-formaldehyde resin particles, the corresponding modification solution is furfuryl alcohol modification solution. (2) Vacuum drying of the polymer precursor particles after swelling treatment, followed by thermosetting embedding or autocatalytic copolymerization to obtain confined modified resin particles. (3) The confined modified resin particles are carbonized in a segmented atmosphere to obtain carbides. The carbides are then vacuum dried and sieved to obtain the swollen confined modified resin-based sodium-ion battery hard carbon anode material.

2. The preparation method according to claim 1, characterized in that: The polymer precursor particles are cross-linked phenolic resin particles. The method for preparing the cross-linked phenolic resin particles is as follows: I. Mix phenol, a 35-40% (w / w) aqueous solution of formaldehyde, and oxalic acid in a mass ratio of 90-95:60-65:0.5-1; II. Under high-purity nitrogen and at a speed of 250-300 r / min, the temperature is increased to 80-90℃ at a rate of 3-5℃ / min, and the temperature is maintained for reflux reaction for 10-12 hours. Ⅲ. After the reflux reaction is completed, vacuum distillation is carried out at 80~85℃ and -0.08~-0.1MPa for 4~6 hours to obtain phenolic prepolymer; IV. After cooling, the phenolic prepolymer is crushed and mixed with hexamethylenetetramine for ball milling. The ball milling speed is 200~220 r / min and the ball milling time is 10~30 min. The mass ratio of phenol to hexamethylenetetramine is 1:0.08~0.

12. V. Dry the ball-milled mixture at 110~160℃ for 4~6h, cool it, crush it and sieve it to obtain cross-linked phenolic resin particles with a particle size of 150~250μm. The preparation process of the zinc acetylacetone modified solution is as follows: zinc acetylacetone is dissolved in acetone to obtain a zinc acetylacetone modified solution with a concentration of 0.01~0.02 g / mL. The specific process of step (1) is as follows: cross-linked phenolic resin particles and zinc acetylacetone modified solution are mixed and stirred for 5-6 hours at a mass-volume ratio of 1:5~7 g / mL, wet particles are collected by centrifugation, acetone is added to the wet particles and shaken for 30-35 seconds, and the wet particles are collected by centrifugation after shaking.

3. The preparation method according to claim 2, characterized in that: In step I, the mass fraction of the formaldehyde aqueous solution is 37% (w / w), and the mass ratio of phenol, formaldehyde aqueous solution and oxalic acid is 94.1:64.9:0.

94. In step II, the stirring speed is 250 r / min, the heating rate is 5℃ / min, the temperature is raised to 90℃, and the reflux reaction time is 12h. In step III, the temperature of vacuum distillation is 80℃, the vacuum degree of vacuum distillation is -0.08MPa, and the time of vacuum distillation is 6h. In step IV, the mass ratio of phenol to hexamethylenetetramine is 1:0.1; In step V, the drying temperature is 110℃ and the drying time is 4 hours; The concentration of the zinc acetylacetone modified solution is 0.02 g / mL; The mass-to-volume ratio of the cross-linked phenolic resin particles to the zinc acetylacetone modified solution is 1:5 g / mL.

4. The preparation method according to claim 1, characterized in that: The polymer precursor particles are resorcinol-formaldehyde resin particles. The preparation process of the resorcinol-formaldehyde resin particles is as follows: ① Mix resorcinol, ammonia water with a mass fraction of 25~28% (w / w), anhydrous ethanol and water, with the mass ratio of ammonia water to resorcinol being 1:13.5~14; ② Under the conditions of 35~45℃ and 300~350r / min, a formaldehyde aqueous solution with a mass fraction of 35~40% (w / w) is added dropwise to the reaction system of step ① and the reaction is carried out for 2~2.5h; the mass ratio of ammonia water to formaldehyde aqueous solution is 1:20~22; ③ Under conditions of 200~220r / min, the temperature is increased to 80~85℃ at a heating rate of 3~5℃ / min for aging reaction for 12~16h. After the reaction is completed, the temperature is cooled, the precipitate is collected by centrifugation, and resin particles are obtained. ④ The resin particles are washed, vacuum dried, pulverized and sieved in sequence to obtain resorcinol-formaldehyde resin particles with a particle size of 5~20μm. The preparation process of the furfuryl alcohol modified solution is as follows: furfuryl alcohol and p-toluenesulfonic acid are dissolved in anhydrous ethanol to obtain the furfuryl alcohol modified solution, wherein the mass ratio of furfuryl alcohol to p-toluenesulfonic acid is 1:0.01~0.02; The specific process of step (1) is as follows: resorcinol-formaldehyde resin particles and furfuryl alcohol modified solution are mixed at a mass-volume ratio of 1:10~12 g / mL, vacuumed to -0.08~-0.1 MPa and maintained for 10~12 min, then high-purity nitrogen is introduced to restore to normal pressure, and the vacuuming and nitrogen filling process is repeated twice. Then, the mixture is stirred at 200~220 r / min for 4~4.5 h. After stirring, the mixture is filtered to obtain separated particles, and the separated particles are washed with anhydrous ethanol to obtain wet particles.

5. The preparation method according to claim 4, characterized in that: In step ①, the mass fraction of ammonia is 25% (w / w), and the mass ratio of ammonia to resorcinol is 1:13.

775. In step ②, the mass fraction of the formaldehyde aqueous solution is 37% (w / w), and the mass ratio of ammonia water to formaldehyde aqueous solution is 1:20.275; In step ③, the heating rate is 5℃ / min, the temperature is raised to 80℃, and the aging reaction time is 12h. The mass ratio of furfuryl alcohol to p-toluenesulfonic acid is 1:0.02; The mass-to-volume ratio of resorcinol-formaldehyde resin particles to furfuryl alcohol modified solution is 1:10 g / mL, the vacuum degree is -0.08 MPa, the vacuum holding time is 10 min, the stirring speed is 200 r / min, and the stirring time is 4 h.

6. The preparation method according to claim 1, characterized in that: In step (2), when the polymer precursor particles are cross-linked phenolic resin particles, they are vacuum dried and then subjected to thermosetting embedding treatment. The conditions for thermosetting embedding treatment are: 100~150mL / min high-purity nitrogen atmosphere, 150~170℃ for 2.5~3.5h. When the polymer precursor particles are resorcinol-formaldehyde resin particles, they are subjected to autocatalytic copolymerization after vacuum drying. The autocatalytic copolymerization process is as follows: under a high-purity nitrogen atmosphere of 100~150mL / min, the temperature is first held at 80~85℃ for 2~2.5h, and then the temperature is increased to 140~150℃ at a heating rate of 2~2.5℃ / min and held for 4~4.5h. In step (3), the segmented atmosphere carbonization specifically involves: i. Under a high-purity nitrogen atmosphere of 300~350mL / min, heat to 180~200℃ at a heating rate of 2~2.5℃ / min and hold for 2~2.5h; ii. In a mixed gas atmosphere of 300~350mL / min, heat to 500~550℃ at a heating rate of 3~3.5℃ / min and hold for 1.5~2h; iii. Under a high-purity nitrogen or high-purity argon atmosphere of 300-350 mL / min, heat to 1300-1400℃ at a heating rate of 5-5.5℃ / min and hold at that temperature for 2-2.5 hours; iv. Under a high-purity nitrogen or high-purity argon atmosphere of 300~350 mL / min, the carbide is obtained after cooling; When the polymer precursor particles are cross-linked phenolic resin particles, step (3) further includes: adding the carbide to a 1.0~1.5mol / L hydrochloric acid solution, stirring at 60~65℃ and 200~220r / min for 2~2.5h, filtering after stirring to obtain a precipitate, washing until the pH of the precipitate is 6.5~7.0, vacuum drying and sieving the precipitate to obtain a swelling-confined modified resin-based sodium-ion battery hard carbon anode material.

7. The preparation method according to claim 6, characterized in that: In step (2), the conditions for thermosetting embedding treatment are: thermosetting at 160°C for 3 hours under a high-purity nitrogen atmosphere of 100 mL / min; The autocatalytic copolymerization process is as follows: under a high-purity nitrogen atmosphere of 100 mL / min, the temperature is first maintained at 80°C for 2 hours, and then the temperature is increased to 140°C at a rate of 2°C / min and maintained for 4 hours.

8. The preparation method according to claim 6, characterized in that: In step i, the flow rate of high-purity nitrogen is 300 mL / min, the heating rate is 2℃ / min, the temperature is raised to 200℃, and the holding time is 2h. In step ii, the flow rate of the mixed gas is 300 mL / min, the heating rate is 3℃ / min, the temperature is raised to 550℃, and the holding time is 2h. The mixed gas is a nitrogen-carbon dioxide mixture or a nitrogen-ammonia mixture. In the nitrogen-carbon dioxide mixture, the volume ratio of nitrogen to carbon dioxide is 98:2, and in the nitrogen-ammonia mixture, the volume ratio of nitrogen to ammonia is 99:

1. In step iii, the flow rate of high-purity nitrogen or high-purity argon is 300 mL / min, the heating rate is 5℃ / min, the temperature is raised to 1300℃, and the holding time is 2h. In step iv, the flow rate of high-purity nitrogen or high-purity argon is 300 mL / min; The concentration of the hydrochloric acid solution is 1.0 mol / L.

9. A swelling-confined modified resin-based sodium-ion battery hard carbon anode material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The BET specific surface area of ​​the hard carbon anode material is ≤22.5m². 2 / g; X-ray diffraction d002 interlayer spacing is 0.37nm~0.38nm.

10. A sodium-ion half-cell, characterized in that: The sodium-ion half-cell comprises the swelling-confined modified resin-based sodium-ion battery hard carbon anode material as described in claim 9.

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