Preparation method of modified asphalt-based hard carbon microspheres for negative electrode of sodium-ion battery

Abstract

The invention belongs to the technical field of sodium ion batteries, and relates to a preparation method of modified asphalt-based hard carbon microspheres for a negative electrode of a sodium ion battery. The preparation method comprises the following steps: (S1) oxidizing asphalt powder to obtain oxidized asphalt; (S2) modifying the oxidized asphalt by thienyl silane to obtain thienyl silane modified asphalt; (S3) adding the thienyl silane modified asphalt, thiophene aldehyde, an oxidant and a surfactant into water, and reacting at 40-65 DEG C for 5-8 hours; adding an acidic catalyst, and reacting at 80-95 DEG C for 3-6 hours to obtain modified asphalt microspheres; and (S4) sequentially carrying out low-temperature pre-carbonization and high-temperature carbonization on the modified asphalt microspheres to obtain the modified asphalt-based hard carbon microspheres for the negative electrode of the sodium-ion battery. According to the invention, asphalt is modified to obtain an asphalt-polythiophene precursor with a compact network structure, namely the modified asphalt microspheres, and the hard carbon microspheres formed by segmented carbonization have excellent electrochemical performance when being used as the negative electrode of the sodium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a preparation method of modified asphalt-based hard carbon microspheres for the negative electrode of a sodium-ion battery. Background Art

[0002] In recent years, lithium-ion batteries have become the mainstream energy storage devices due to their excellent electrochemical properties. However, the limited crustal reserves and uneven distribution of lithium resources severely restrict their industrial expansion in China. Sodium-ion batteries, with the advantages of rich resource reserves, wide distribution, and low cost, have gradually become an important direction for new energy storage systems. The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, both storing and releasing energy through the insertion and extraction of ions in the positive and negative electrode materials. However, compared with the + radius of Li Na + has a larger ionic radius and its thermodynamic instability in the graphite negative electrode leads to challenges in the sodium storage capacity, structural stability, and cycle life of the electrode. Therefore, the development of new negative electrode materials suitable for sodium-ion batteries has become the research focus. Hard carbon materials, due to their rich pore structure and high specific surface area, exhibit good sodium storage ability and have become a research hotspot for current sodium-ion battery negative materials. Asphalt, as a widely existing and low-cost by-product of petroleum processing, is an optional raw material for preparing hard carbon materials. However, the hard carbon materials directly carbonized from asphalt have insufficient conductivity and poor rate performance. Therefore, asphalt modification strategies have gradually been applied to high-performance hard carbon negative electrode materials.

[0003] The electrochemical properties of asphalt-based hard carbon are mainly controlled by key parameters such as the graphite layer spacing, pore morphology, degree of heteroatom doping, and defect structure. Research shows that appropriate crosslinking degree of precursor molecules, rich defect content, and appropriate and uniform particle size are beneficial to improving the performance of hard carbon negative electrode materials for sodium-ion batteries. Ji Lichang et al. (J. Mater. Chem. A, 2023, 11, 26727) used coal tar asphalt as the precursor and obtained block-shaped hard carbon negative electrode materials with rich oxygen crosslinked structures and diameters greater than 10 μm by adjusting the temperature and time of the pre-oxidation process. This material has a reversible specific capacity of 276.8 mAh g -1 at a current density of 0.1C (1C = 300 mA g -1 ). Xiong Zhiyong et al. (Journal of Colloid And Interface Science 658(2024)610–616) used asphalt as the precursor and simultaneously introduced N and O elements into asphalt by element doping method. While reducing the particle size of block-shaped hard carbon, hard carbon negative electrode materials with rich defect sites were obtained. This material has a specific capacity at 30 mA g -1A reversible specific capacity of 317 mAh g at a current density. -1 However, the capacities of the above two pitch-based hard carbon materials at a current density of 1 A g -1 are both below 150 mAh g -1 . CN119461333A selects a method combining element doping and pre-oxidation to improve the sodium storage capacity of pitch-based hard carbon. The obtained hard carbon material has a blocky morphology with a diameter of 1-10 μm. CN119330336A discloses a method combining polycondensation and pre-oxidation to increase the cross-linking degree of pitch molecules. The obtained hard carbon material has a blocky structure with different sizes. However, the rate performance and cycle stability of the pitch-based hard carbon materials in the above patent documents still need to be further improved.

[0004] The foregoing literature discloses methods for oxidative doping or polycondensation of pitch. However, it is difficult for the current technology to fully consume the excessive hydrogen atoms in pitch and condense them into macromolecular substances. As a result, molecular rearrangement and recombination still occur during the subsequent carbonization process, leading to a relatively high graphitization degree of the carbonization product. Therefore, the electrochemical performance is not excellent enough, manifested as low reversible capacity, poor rate performance, poor cycle stability, especially low capacity at a relatively high current density. In addition, the hard carbon materials formed by the above pitch still have a relatively large blocky structure, so the packing density is low, and the economic characteristics of pitch cannot be fully utilized, resulting in the need to improve the industrial application prospects. Summary of the Invention

[0005] In view of the problems of low reversible capacity, poor rate performance, poor cycle stability, especially low capacity at a high current density and low packing density of pitch-based hard carbon in the prior art, the present invention provides a preparation method of modified pitch-based hard carbon microspheres for the negative electrode of a sodium-ion battery. The prepared hard carbon is microspheres with appropriate sizes, rich defect sites and large interlayer spacing, so that the hard carbon has excellent electrochemical performance.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of modified pitch-based hard carbon microspheres for the negative electrode of a sodium-ion battery, comprising the following steps:

[0008] (S1) Oxidize pitch powder to obtain oxidized pitch;

[0009] (S2) Modify the oxidized pitch with thiophenylsilane to obtain thiophenylsilane-modified pitch;

[0010] (S3) Add thiophenylsilane-modified pitch, thiophene aldehyde, oxidant, and surfactant to water, react at 40-65 °C for 5-8 h; then add an acidic catalyst and react at 80-95 °C for 3-6 h to obtain modified pitch microspheres;

[0011] (S4) Under an inert atmosphere, the modified asphalt microspheres are successively subjected to low-temperature pre-carbonization and high-temperature carbonization to obtain modified asphalt-based hard carbon microspheres for the negative electrode of sodium-ion batteries.

[0012] Further, in step (S1), the asphalt powder is at least one of coal tar asphalt, petroleum asphalt, and natural asphalt, with a softening point of 60-120 °C and a particle size of 120-200 mesh.

[0013] The oxidation treatment in step (S1) is a conventional oxidation process, which is a well-known technology to those skilled in the art and is not particularly limited. Its role is to introduce oxygen-containing groups, such as hydroxyl groups, into the asphalt, which is beneficial for the subsequent modification with thiophenylsilane. For example, the oxidant can be selected from at least one of oxygen, ozone, sulfuric acid, nitric acid, potassium permanganate, potassium nitrate, and iron(III) oxide. According to the different oxidants selected, the oxidation methods are different. When oxygen or ozone is selected as the oxidant, a gas-phase oxidation method is adopted, that is, a method of heating and ventilating, such as heating to 250-350 °C and holding for 6-15 h; when sulfuric acid or nitric acid is selected as the oxidant, a liquid-phase oxidation method is adopted, such as soaking the asphalt in 3-5 mol / L nitric acid or sulfuric acid at 40-60 °C for 4-8 h; when potassium permanganate, potassium nitrate, or iron(III) oxide is selected as the oxidant, a solid-phase oxidation method is adopted, such as mixing the asphalt with potassium permanganate in a mass ratio of 1:(0.2-0.4) to form a mixture and then heating to 250-350 °C and holding for 6-15 h.

[0014] Further, in step (S2), the mass ratio of the oxidized asphalt to the thiophenylsilane is 100:(8-15), preferably 100:(12-15).

[0015] Further, in step (S2), the thiophenylsilane is at least one of trimethoxy-2-thiophenesilane and triethoxy-2-thiophenesilane.

[0016] Further, in step (S2), the modification method is as follows: the thiophenylsilane is added to water, the pH is adjusted to 4-6, and a hydrolysis reaction is carried out at 20-30 °C for 20-40 min to obtain a hydrolysis solution; the oxidized asphalt is dispersed in an alcohol aqueous solution to obtain a dispersion; the hydrolysis solution is added to the dispersion, and a stirring reaction is carried out at 50-60 °C for 4-6 h to obtain thiophenylsilane-modified asphalt.

[0017] Even further, the alcohol content in the alcohol aqueous solution is 30-60 wt%, and the alcohol is selected from at least one of methanol and ethanol.

[0018] Further, in step (S3), the mass ratio of the thiophenylsilane-modified asphalt, thiophene aldehyde, oxidant, and surfactant is 100:(10 - 20):(20 - 40):(0.2 - 0.4), preferably 100:(15 - 20):(20 - 40):(0.2 - 0.4). The thiophene groups on the surface of the thiophenylsilane-modified asphalt and thiophene aldehyde undergo chemical oxidative copolymerization under the action of the oxidant, that is, in-situ polymerization to form poly(thiophene) containing aldehyde groups modified on the asphalt surface.

[0019] Further, in step (S3), the thiophene aldehyde is at least one of 3-thiophenecarboxaldehyde, 4-methylthiophene-3-carboxaldehyde, and 3,4-thiophenedicarboxaldehyde, preferably 3,4-thiophenedicarboxaldehyde; the oxidant is at least one of ammonium persulfate and potassium persulfate; the hydrophilic-lipophilic balance value (HLB) of the surfactant is 15 - 18, and it is selected from at least one of polysorbate 80, fatty alcohol polyoxyethylene ether, and poloxamer 188.

[0020] Further, in step (S3), the acidic catalyst is at least one of nitric acid, hydrochloric acid, or boric acid with a concentration of 10 - 15 mol / L, and the dosage ratio of the acidic catalyst to the thiophenylsilane-modified asphalt is (5 - 10) mL:100 g. Under the action of the acidic catalyst, the aldehyde groups in the poly(thiophene) coated on the asphalt surface react with the polycyclic aromatic hydrocarbons in the asphalt to form a macromolecular cross-linked network structure.

[0021] Further, in step (S4), the inert atmosphere is nitrogen and / or argon; the conditions for low-temperature carbonization are: keeping the temperature at 350 - 500 °C for 1 - 3 h; the conditions for high-temperature carbonization are: keeping the temperature at 1100 - 1400 °C for 2 - 5 h. The present invention adopts staged carbon burning. The first low-temperature carbonization can effectively promote the removal of small-molecule substances in the intermediate material, which is beneficial to the formation of a rich pore structure.

[0022] Further, the particle size of the modified asphalt microspheres for the negative electrode of the sodium-ion battery prepared by the present invention is 2 - 5 μm.

[0023] The present invention uses thienylsilane to modify the surface of oxidized asphalt, and the hydrolyzed thienylsilane undergoes a condensation reaction with the surface functional groups of the oxidized asphalt, thereby introducing the thienylsilane into the asphalt in the form of chemical bonds. The thiophene groups on the surface of thiophene silane-modified asphalt can be copolymerized with thiophene aldehyde under the action of an oxidant to form aldehyde-containing polythiophene modified on the asphalt surface by in-situ polymerization. This in-situ polymerization modification of the aldehyde-containing thiophene groups can achieve multiple purposes: first, sulfur atom doping of hard carbon is achieved for the subsequent carbonization stage, thereby increasing the sodium ion storage active sites and thereby increasing the capacity of the sodium ion battery; second, since it is a modified layer formed by in-situ polymerization, the pores of the hard carbon obtained after subsequent segmented carbonization are more uniform; third, the aldehyde groups in the aldehyde-containing polythiophene can then undergo condensation reactions with polycyclic aromatic hydrocarbons in the asphalt under the action of an acidic catalyst, consuming hydrogen atoms to form a macromolecular cross-linked network structure, thereby forming an asphalt-polythiophene complex with a dense network structure; the dense cross-linked structure makes it difficult for molecular rearrangement and recombination to occur during the subsequent carbonization process, thereby obtaining a larger carbon layer spacing, which is beneficial to improving the sodium storage capacity and cycle stability. In addition, since the in-situ polymerization and the condensation reaction of the aldehyde group and the polycyclic aromatic hydrocarbons in the asphalt are all carried out in the liquid phase, under the action of the surfactant and the surface tension of the liquid, the asphalt-polythiophene complex formed is a microsphere particle, and then after segmented carbonization, hard carbon microspheres are formed. The microsphere-shaped hard carbon is conducive to improving the packing density, which is beneficial to the rate performance and cycle performance, and is conducive to large-scale production and application. In summary, after the above modification, modified asphalt-based hard carbon microspheres with excellent electrochemical performance are finally obtained.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention obtains a pitch-polythiophene precursor with a dense network structure by modifying asphalt. The precursor forms hard carbon microspheres with a large carbon layer spacing and abundant active sites after carbonization. The hard carbon microspheres have excellent electrochemical properties when used as negative electrodes for sodium ion batteries, and are characterized by high reversible capacity, good rate performance and cycle stability, and especially high capacity under high current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the SEM image of the modified asphalt-based hard carbon microspheres prepared in Example 1.

[0027] Figure 2 This is a high-resolution TEM image of the modified asphalt-based hard carbon microspheres prepared in Example 1.

[0028] Figure 3 The modified asphalt-based hard carbon microspheres in Example 1 are 0.1Ag -1 Charge and discharge curves under current density.

[0029] Figure 4 Battery capacity retention performance graph of the modified asphalt-based hard carbon microspheres prepared in Example 1 at different current densities.

[0030] Figure 5 For the modified asphalt-based hard carbon microspheres prepared in Example 1 at 1 A / g -1 Battery capacity retention performance graph after 200 cycles at the current density. Detailed implementation manners

[0031] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. The following examples facilitate a better understanding of the present invention, but do not limit the present invention. The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0032] The coal tar pitch was purchased from Xinjiang Xuandong Energy Co., Ltd., with a softening point of about 80 °C and a particle size of about 200 mesh.

[0033] Example 1

[0034] (S1) Place the coal tar pitch in a muffle furnace, heat it in air, raise the temperature to 300 °C at a rate of 5 °C / min, hold for 12 h, and cool to room temperature to obtain oxidized asphalt;

[0035] (S2) Disperse 16 g of trimethoxy-2-thiophene silane in 80 mL of pure water, adjust the pH to 4.5, and carry out a hydrolysis reaction at 25 °C for 30 min to obtain a hydrolysis solution; disperse 200 g of oxidized asphalt in 2000 mL of an ethanol aqueous solution (ethanol content is 40 wt%), to obtain a dispersion; then add the hydrolysis solution to the dispersion solution, react at 55 °C with stirring at 100 rpm for 5 h, then filter by suction, wash with pure water until the filtrate is colorless, and dry in an oven at 65 °C for 24 h to obtain thiophene-based silane modified asphalt;

[0036] (S3) Disperse 100 g of thiophene-based silane modified asphalt in 1000 mL of pure water, heat to 55 °C and stir for 2 h, then add 10 g of 3,4-thiophene dicarboxaldehyde, 20 g of ammonium persulfate, 0.2 g of polysorbate 80, adjust the pH to 5.0, and react at 55 °C with stirring for 5 h; then add 8 mL of 12 mol / L hydrochloric acid and react at 90 °C for 4 h to obtain a mixed turbid liquid; then centrifuge the mixed turbid liquid, wash with pure water 3 times, and dry in an oven at 85 °C for 24 h to obtain modified asphalt microspheres;

[0037] (S4) Place the modified asphalt microspheres in a carbonization furnace, heat them to 450 °C at a rate of 5 °C / min under a nitrogen atmosphere and hold for 2 h, then heat them to 1200 °C at a rate of 8 °C / min and hold for 3 h, and cool to room temperature to obtain modified asphalt-based hard carbon microspheres for sodium ion batteries.

[0038] Example 2

[0039] The rest is the same as in Example 1, except that: in step (S3), the amount of 3,4-thiophenedicarboxaldehyde is 15 g, and the amount of ammonium persulfate is 30 g. The corresponding reaction conditions are adjusted as follows:

[0040] (S1) is the same as in Example 1;

[0041] (S2) is the same as in Example 1;

[0042] (S3) Disperse 100 g of thiophene-based silane modified asphalt in 1000 mL of pure water, heat to 55 °C and stir for 2 h, then add 15 g of 3,4-thiophenedicarboxaldehyde, 30 g of ammonium persulfate, and 0.3 g of polysorbate 80, adjust the pH to 5.0, and react at 40 °C for 8 h with stirring; then add 8 mL of 12 mol / L hydrochloric acid and react at 80 °C for 6 h to obtain a mixed turbid solution; then centrifuge the mixed turbid solution, wash it 3 times with pure water, and dry it in an oven at 90 °C for 24 h to obtain modified asphalt microspheres;

[0043] (S4) is the same as in Example 1.

[0044] Example 3

[0045] The rest is the same as in Example 1, except that: in step (S3), the amount of 3,4-thiophenedicarboxaldehyde is 20 g, and the amount of ammonium persulfate is 40 g. The corresponding reaction conditions are adjusted as follows:

[0046] (S1) is the same as in Example 1;

[0047] (S2) is the same as in Example 1;

[0048] (S3) Disperse 100 g of thiophene-based silane modified asphalt in 1000 mL of pure water, heat to 55 °C and stir for 2 h, then add 20 g of 3,4-thiophenedicarboxaldehyde, 40 g of ammonium persulfate, and 0.4 g of polysorbate 80, adjust the pH to 5.0, and react at 65 °C for 7 h with stirring; then add 8 mL of 12 mol / L hydrochloric acid and react at 95 °C for 3 h to obtain a mixed turbid solution; then centrifuge the mixed turbid solution, wash it 3 times with pure water, and dry it in an oven at 90 °C for 24 h to obtain modified asphalt microspheres;

[0049] (S4) is the same as in Example 1.

[0050] Example 4

[0051] The rest is the same as in Example 1, except that 3-thiophenecarboxaldehyde is used instead of 3,4-thiophenedicarboxaldehyde in step (S3).

[0052] Example 5

[0053] The rest is the same as in Example 1, except that: in step (S2), the amount of trimethoxy-2-thiophene silane used is 24 g.

[0054] Example 6

[0055] The rest is the same as in Example 1, except that: in step (S2), triethoxy-2-thiophene silane is used to replace trimethoxy-2-thiophene silane, and the amount of triethoxy-2-thiophene silane used is 30 g.

[0056] Comparative Example 1

[0057] The rest is the same as in Example 1, except that: in step (S3), thiophene is used to replace 3,4-thiophene dialdehyde.

[0058] Comparative Example 2

[0059] The rest is the same as in Example 1, except that: step (S2) is omitted, there is no in-situ polymerization in step (S3), and glutaraldehyde is used to directly crosslink the oxidized asphalt instead of 3,4-dialdehyde thiophene. Specifically:

[0060] (S1) is the same as in Example 1;

[0061] (S2) is omitted;

[0062] (S3) Disperse 100 g of oxidized asphalt in 1000 mL of pure water, heat to 55 °C and stir for 2 h, then add 10 g of glutaraldehyde and 0.2 g of polysorbate 80, and then add 8 mL of 12 mol / L hydrochloric acid and react at 90 °C for 4 h to obtain a mixed turbid liquid; then centrifuge the mixed turbid liquid, wash it 3 times with pure water, and dry it in an oven at 90 °C for 24 h to obtain modified asphalt microspheres;

[0063] (S4) is the same as in Example 1.

[0064] Comparative Example 3

[0065] The rest is the same as in Example 1, except that: step (S2) is omitted, specifically:

[0066] (S1) is the same as in Example 1;

[0067] (S2) is omitted;

[0068] (S3) Disperse 100 g of oxidized asphalt in 1000 mL of pure water, heat to 55 °C and stir for 2 h, then add 10 g of 3,4-dialdehyde thiophene, 20 g of ammonium persulfate, and 0.2 g of polysorbate 80, adjust the pH to 5.0, and react at 55 °C for 6 h with stirring; then add 10 mL of 1 mol / L hydrochloric acid and react at 90 °C for 4 h to obtain a mixed turbid solution; then centrifuge the mixed turbid solution, wash it 3 times with pure water, and dry it in an oven at 90 °C for 24 h to obtain modified asphalt microspheres;

[0069] (S4) The same as Example 1.

[0070] Comparative Example 4

[0071] The rest is the same as in Example 1, except that in step (S4), pre-carbonization is not carried out, that is, one-step carbonization, specifically:

[0072] (S1) The same as Example 1;

[0073] (S2) The same as Example 1;

[0074] (S3) The same as Example 1;

[0075] (S4) Place the modified asphalt microspheres in a carbonization furnace, heat up to 950 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for 5 h, and cool to room temperature to obtain modified asphalt-based hard carbon microspheres for sodium-ion batteries.

[0076] Testing and Analysis

[0077] 1. Structure Analysis

[0078] The SEM image of the modified asphalt-based hard carbon microspheres prepared in Example 1 is as Figure 1 shown. It can be seen from Figure 1 that the synthesized modified asphalt-based hard carbon is spherical with uniform size, and the particle size is in the range of 2 - 5 μm. The microsphere structure is relatively stable, enabling the material to have good structural stability during the cycling process, which is beneficial to the improvement of the cycling performance of sodium-ion batteries. At the same time, the microsphere structure can also improve the packing density of the negative electrode material.

[0079] The high-resolution TEM image of the modified asphalt-based hard carbon microspheres prepared in Example 1 is as Figure 2 shown. It can be seen from Figure 2 that the prepared hard carbon material has a pseudo-graphite structure with short-range order and long-range disorder. The formation of this microscopic structure is due to the fact that the modified asphalt is an asphalt-polythiophene complex with a dense network structure. The fewer hydrogen atoms and the higher dense network structure can effectively reduce the π-π stacking effect between asphalt molecules, thereby inhibiting the excessive migration and rearrangement of carbon atoms during the carbonization process, and thus obtaining a relatively disordered graphite microcrystalline structure.

[0080] 2. Electrochemical Performance Test

[0081] The pitch-based hard carbon microspheres prepared in the examples and comparative examples were used as the negative electrode in a sodium-ion battery, and then their electrochemical performance was tested. The specific steps were as follows:

[0082] a) Fabrication of the negative electrode sheet: The pitch-based hard carbon microspheres prepared in the examples and comparative examples were respectively mixed with the conductive additive Super P and the binder PVDF in a weight ratio of 90:5:5, and then the solvent N-methylpyrrolidone (NMP) was added. After stirring, a uniform slurry was obtained. Then, the slurry was evenly coated on a carbon-coated copper foil using a 75-μm doctor blade, and then vacuum-dried at 80 °C for 8 h in a vacuum oven to form a sheet. Subsequently, the dried sheet was cut into small circular pieces with a diameter of 10 mm, which were the negative electrode sheets;

[0083] b) Assembly of the sodium-ion battery: The prepared negative electrode sheet was assembled with a sodium metal negative electrode to form a sodium-ion battery. The electrolyte used was 1 M sodium hexafluorophosphate (NaPF6) dissolved in dimethyl carbonate:ethylene carbonate:ethyl methyl carbonate (DMC:EC:EMC), and the separator was a porous glass fiber separator (whatman, GF / D). A button cell (CR2032) was assembled in an argon glove box with a water and oxygen value below 0.1 ppm;

[0084] c) Electrochemical performance test. The assembled button cell was subjected to an electrochemical performance test on a NEWARE BTS-4000 battery test system at a constant temperature of 25 °C. The charge-discharge curve of the modified pitch-based hard carbon microspheres in Example 1 at a current density of 0.1 Ag -1 is shown in the figure, and the battery capacity retention performance diagram of the modified pitch-based hard carbon microspheres prepared in Example 1 at different current densities is as Figure 4 , and the battery capacity retention performance diagram of the modified pitch-based hard carbon microspheres prepared in Example 1 at a current density of 1 Ag -1 after 100 cycles is as Figure 5 shown. The specific test results are shown in Table 1.

[0085] Table 1 Electrochemical Performance Test

[0086]

[0087] As can be seen from the data in Table 1, the sodium-ion battery assembled with the modified hard carbon microspheres prepared in the examples of the present invention as the negative electrode material has excellent electrochemical performance. Its charge specific capacity at a current density of 0.1 Ag -1 is all above 350 mAh / g, and at 1 Ag -1The charge specific capacity at a high current density is also as high as over 240 mAh / g, and the cycle stability is relatively good. In Comparative Example 1, both the specific capacity and the cycle stability are poor. In Comparative Example 2, although the cycle stability is acceptable, the specific capacity is low. In Comparative Example 3, both the specific capacity and the cycle stability are lower than those of the Example. In Comparative Example 4, although the cycle stability is acceptable, the specific capacity is also on the low side.

Claims

1. A preparation method of modified pitch-based hard carbon microspheres for the negative electrode of a sodium-ion battery, characterized in that, It includes the following steps: (S1) Oxidize the asphalt powder to obtain oxidized asphalt; (S2) Modify the oxidized asphalt with thiophenylsilane to obtain thiophenylsilane-modified asphalt; (S3) Add the thiophenylsilane-modified asphalt, thiophene aldehyde, oxidant, and surfactant into water, react at 40 - 65 °C for 5 - 8 h; then add an acidic catalyst and react at 80 - 95 °C for 3 - 6 h to obtain modified asphalt microspheres; (S4) Under an inert atmosphere, subject the modified asphalt microspheres to low-temperature pre-carbonization and high-temperature carbonization in sequence to obtain modified asphalt-based hard carbon microspheres for the negative electrode of a sodium-ion battery.

2. The preparation method according to claim 1, wherein In step (S1), the asphalt powder is at least one of coal tar asphalt, petroleum asphalt, and natural asphalt, with a softening point of 60 - 120 °C and a particle size of 120 - 200 mesh.

3. The preparation method according to claim 1, wherein In step (S2), the mass ratio of the oxidized asphalt to thiophenylsilane is 100:(8 - 15), preferably 100:(12 - 15).

4. The preparation method according to claim 1, characterized in that, In step (S2), the thiophenylsilane is at least one of trimethoxy-2-thiophenylsilane and triethoxy-2-thiophenylsilane.

5. The preparation method according to claim 1, wherein In step (S2), the modification method is as follows: Add thiophenylsilane into water, adjust the pH to 4 - 6, and carry out a hydrolysis reaction at 20 - 30 °C for 20 - 40 min to obtain a hydrolysis solution; Disperse the oxidized asphalt in an alcohol aqueous solution to obtain a dispersion; Add the hydrolysis solution into the dispersion, and carry out a stirring reaction at 50 - 60 °C for 4 - 6 h to obtain thiophenylsilane-modified asphalt.

6. The preparation method according to claim 1, characterized in that, In step (S3), the mass ratio of the thiophenylsilane-modified asphalt, thiophene aldehyde, oxidant, and surfactant is 100:(10 - 20):(20 - 40):(0.2 - 0.4), preferably 100:(15 - 20):(20 - 40):(0.2 - 0.4).

7. The preparation method according to claim 1, wherein In step (S3), the thiophene aldehyde is at least one of 3-thiophenecarboxaldehyde, 4-methylthiophene-3-carboxaldehyde, and 3,4-thiophenedicarboxaldehyde, preferably 3,4-thiophenedicarboxaldehyde; The oxidant is at least one of ammonium persulfate and potassium persulfate; The hydrophilic-lipophilic balance value (HLB) of the surfactant is 15 - 18, and it is selected from at least one of polysorbate 80, fatty alcohol polyoxyethylene ether, and poloxamer 188.

8. The preparation method according to claim 1, characterized in that, In step (S3), the acidic catalyst is at least one of nitric acid, hydrochloric acid, or boric acid with a concentration of 10 - 15 mol / L, and its dosage ratio to the thiophenylsilane-modified asphalt is (5 - 10) mL:100 g.

9. The preparation method according to claim 1, characterized in that, In step (S4), the inert atmosphere is nitrogen and / or argon; The conditions for low-temperature carbonization are: Keep warm at 350 - 500 °C for 1 - 3 h; The conditions for high-temperature carbonization are: Keep warm at 1100 - 1400 °C for 2 - 5 h.

10. The preparation method according to any one of claims 1-9, characterized in that, The particle size of the obtained modified asphalt-based hard carbon microspheres for the negative electrode of a sodium-ion battery is 2 - 5 μm.

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