A hard carbon anode material based on surface modification of strongly polar functional groups and its preparation method

Abstract

This invention discloses a hard carbon anode material based on surface modification with strongly polar functional groups and its preparation method. The material comprises resin-based hard carbon and strongly polar functional groups uniformly loaded on its surface defects; the density of strongly polar functional groups loaded on the surface defects of the resin-based hard carbon is 0.5~3×10⁻⁶. 8 mol / μm 2 The strongly polar functional group is an ester carbonyl or ketone carbonyl. The preparation process of this material is as follows: boron / phosphorus co-doped phenolic resin is carbonized into resin-based hard carbon, which is then thoroughly mixed with raw materials including a modifier containing strongly polar functional groups in an electrode solvent to carry out a grafting loading reaction, obtaining a negative electrode slurry. This slurry is then uniformly coated onto copper foil, and subsequently dried and compacted to obtain the final product. The hard carbon negative electrode material, through surface modification with strongly polar functional groups, passivates the sp2 group on the hard carbon surface. 3 This method overcomes the defects, inhibits irreversible decomposition of the electrolyte, and can induce the formation of an ultrathin SEI film rich in inorganic phase, fundamentally solving the technical problem of irreversible sodium loss.

Description

Technical Field

[0001] This invention relates to a surface-modified hard carbon anode material, specifically to a hard carbon anode material based on surface modification with strong polar functional groups and its preparation method, belonging to the field of battery material technology. Background Technology

[0002] The global trend of energy structure transformation towards renewable energy grids and electric transportation has driven an urgent need for cost-effective and scalable energy storage technologies. Sodium-ion batteries, with their abundance of sodium in the Earth's crust and good compatibility with existing lithium-ion battery manufacturing infrastructure, are becoming an important supplement to lithium-ion battery systems in large-scale energy storage applications. In the development of sodium-ion batteries, the development of high-performance anode materials is crucial. Among them, hard carbon materials, due to their unique turbine layer microstructure, can achieve reversible Na+ anode transfer near zero potential. + Intercalation / deintercalation has become one of the most promising candidates for anode materials. However, the commercial application of hard carbon anodes is still limited by their low first-cycle coulombic efficiency, a key indicator that directly affects the energy density and cost-effectiveness of the battery. This efficiency loss mainly stems from irreversible sodium loss during the solid electrolyte interface formation process, as well as electrolyte decomposition catalyzed by defective carbon surfaces.

[0003] Current research focuses on innovations in electrolyte engineering, surface coating, and pre-sodiumization strategies. However, the influence of binder systems on electrode performance is equally significant. The fluorine-rich nature of traditional polyvinylidene fluoride (PVDF) binders induces the formation of excess NaF crystals in the SEI film. These rigid inorganic phases not only hinder sodium ion transport but also exacerbate electrode polarization. In contrast, aqueous binders such as sodium alginate and carboxymethyl cellulose, through hydrogen bonding, form a surface coating effect that significantly optimizes the interfacial chemical environment and reduces irreversible sodium ion loss. It is important to note that different binders directly affect the types and enrichment levels of functional groups on the surface of hard carbon anodes. However, no direct research has yet demonstrated that modifying the hard carbon surface with binders can directly regulate the SEI film, thereby comprehensively improving the electrochemical performance and engineering applicability of hard carbon anodes. Summary of the Invention

[0004] To address the problems existing in the prior art, the first objective of this invention is to provide a hard carbon anode material based on surface modification with strongly polar functional groups. This hard carbon anode material, through surface modification with strongly polar functional groups, enriches the material surface with sp³ hybrid carbon, oxygen-containing functional groups, and microporous structures. Furthermore, by utilizing the directional dipole interaction between the strongly polar functional groups and the defect sites of hard carbon, multiple chemical bonds, including hydrogen bonds and coordination bonds, are constructed, significantly improving the bonding strength of the hard carbon surface and effectively inhibiting the stripping of active materials during cycling.

[0005] The second objective of this invention is to provide a method for preparing a hard carbon anode material based on surface modification with strongly polar functional groups. This method uses a functional binder as both a binder and a surface modifier for the hard carbon anode material. The strongly polar functional groups in the functional binder preferentially adsorb onto the hard carbon surface, selectively covering its highly active sites, blocking direct contact between the electrolyte and defects, and simultaneously regulating the PF6⁻ anion decomposition pathway to induce the formation of a dense inorganic SEI film (thickness ≤12nm) mainly composed of NaF and Na₂CO₃. This increases the electrolyte efficiency (ICE) to 85.1%, fundamentally solving the technical problem of irreversible sodium loss caused by the formation of a thick and loose organic-inorganic composite SEI film due to the catalytic decomposition of the electrolyte by highly active defect sites on the hard carbon surface.

[0006] To achieve the above technical objectives, this invention provides a hard carbon anode material based on surface modification of strongly polar functional groups, comprising resin-based hard carbon and strongly polar functional groups uniformly loaded on its surface defects; the density of strongly polar functional groups loaded on the surface defects of the resin-based hard carbon is 0.5~3×10⁻⁶. 8 mol / μm 2 The strongly polar functional group is an ester carbonyl or a ketone carbonyl.

[0007] This invention redesigns the polarity and density distribution of functional groups on the hard carbon surface. By utilizing the directional dipole interaction and hydrogen bonding between polar groups and sp³ hybrid carbon and oxygen-containing functional groups on the hard carbon surface, selective coverage of highly active defect sites on the hard carbon surface, such as dangling bonds and edge carbons, is achieved. It is important to note that the type and density of functional groups must strictly adhere to the above requirements. If the polarity of the functional groups is too low, it will lead to uneven electrolyte penetration, thereby obstructing ion transport pathways and reducing the effective reaction interface, which will also limit the capacity at high rates. If the functional group density is too low, it will result in low hard carbon capacity and make it difficult to induce the formation of a dense SEI.

[0008] As a preferred embodiment, the hard carbon anode material further includes a conductive material, the mass ratio of which to the resin-based hard carbon is (3~5):(12~16).

[0009] As a preferred embodiment, the conductive material is at least one of acetylene black, Super P, and carbon nanotubes.

[0010] As a preferred embodiment, the strongly polar functional group is one of ester carbonyl, ketone carbonyl, and aldehyde groups. The strongly polar functional group used in this invention, by regulating the electrolyte decomposition pathway, can induce PF6 during the initial charge-discharge process. - Anions preferentially decompose in the binder-covered area, generating an inorganic dense SEI film mainly composed of NaF and Na2CO3, which inhibits direct contact between hard carbon and electrolyte, thereby improving its coulombic efficiency.

[0011] As a preferred embodiment, the density of strongly polar functional groups loaded on the surface defects of the resin-based hard carbon is 0.9~2×10⁻⁶. 8 mol / μm 2 .

[0012] The loading of highly polar functional groups must strictly adhere to the above requirements. Insufficient loading leads to insufficient sodium ion adsorption sites and an incomplete SEI film, reducing capacity and cycle life. Excessive loading hinders electron conduction and exacerbates side reactions, impairing rate performance and structural stability. Therefore, a balance must be struck between enhancing sodium ion adsorption and maintaining the conductive network through precise control of the loading.

[0013] This invention also provides a method for preparing a hard carbon anode material based on surface modification with strongly polar functional groups:

[0014] Step S1: Phenolic monomers, aldehyde monomers and boron modifiers are polymerized in a solvent to obtain boron / phosphorus co-doped phenolic resin;

[0015] Step S2: Carbonize the boron / phosphorus co-doped phenolic resin by programmed temperature rise under a protective atmosphere to obtain resin-based hard carbon.

[0016] Step S3: The raw materials, including resin-based hard carbon and modifiers containing strong polar functional groups, are thoroughly mixed in the electrode solvent to carry out a grafting and loading reaction to obtain a negative electrode slurry.

[0017] Step S4: Coat the negative electrode slurry evenly onto the copper foil, and then dry and compact it in sequence to obtain the final product.

[0018] In the method provided by this invention, a functional binder is used as both a binder and a surface modifier for the hard carbon anode material. On the one hand, the functional polar functional groups of the binder are used to modify the surface of the hard carbon, thereby controlling the uniform growth of the SEI film on its surface and suppressing interfacial side reactions. On the other hand, by regulating the dissolution-volatilization kinetics of the binder in the solvent, the dried binder forms a three-dimensional interconnected hydrogen bond network. During the charging and discharging process, this network dynamically buffers the volume expansion of the hard carbon particles through the reversible breaking and recombination of hydrogen bonds, while maintaining continuous ion transport channels.

[0019] As a preferred embodiment, the phenolic monomer is at least one of 3-aminophenol, phenol, xylenol, and resorcinol.

[0020] As a preferred embodiment, the aldehyde monomer is formaldehyde and / or furfural.

[0021] As a preferred embodiment, the boron modifier is at least one selected from 3-hydroxyphenylboronic acid, 4-hydroxyphenylboronic acid, neopentyl glycol 4-hydroxyphenylboronic acid, and boric acid.

[0022] As a preferred embodiment, the protective atmosphere is at least one of nitrogen, argon, and helium.

[0023] As a preferred embodiment, the carbonization reaction conditions are as follows: under a protective atmosphere, the temperature is increased from room temperature to 1200-1400℃ at a rate of 2-5℃ / min, and pyrolysis is carried out for 1-3 hours.

[0024] As a preferred embodiment, the modifier containing strongly polar functional groups is at least one of polyvinyl acetate, polydopamine, polysulfonated styrene, polyphosphazene, and polyethylene glycol diacrylate.

[0025] As a preferred embodiment, the electrode solvent is at least one selected from N-methylpyrrolidone, deionized water, tetrahydrofuran, and dimethyl sulfoxide.

[0026] As a preferred embodiment, the grafting loading reaction is carried out under stirring conditions for 8-12 hours.

[0027] As a preferred embodiment, the drying conditions are: vacuum drying at 80~100℃ until the material reaches a constant weight.

[0028] As a preferred embodiment, the compaction conditions are: compaction at 80~120MPa until the material density is 1.2~1.5g / cm³. 3 .

[0029] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows:

[0030] (1) The hard carbon anode material provided by the present invention is made rich in sp³ hybrid carbon, oxygen-containing functional groups and microporous structure by surface modification of strong polar functional groups. The directional dipole interaction between strong polar functional groups and hard carbon defect sites is used to construct multiple chemical bonds of hydrogen bonds and coordination bonds, which greatly improves the bonding strength of the hard carbon surface and effectively inhibits the stripping of active material during cycling.

[0031] (2) In the preparation method provided by the present invention, a functional binder is used as both a binder and a surface modifier for the hard carbon anode material. The strongly polar functional groups in the functional binder are preferentially adsorbed on the surface of the hard carbon, selectively covering its highly active sites, blocking the direct contact between the electrolyte and defects, and simultaneously regulating PF6. - The anion decomposition pathway induces the formation of a dense inorganic SEI film (thickness ≤12nm) mainly composed of NaF and Na2CO3, increasing the ICE to 88.3%. This fundamentally solves the technical problem of irreversible sodium loss caused by the formation of a thick and loose organic-inorganic composite SEI film due to the catalytic decomposition of electrolyte by highly active defect sites on the hard carbon surface.

[0032] (3) In the technical solution provided by the present invention, a three-dimensional dynamic hydrogen bond network is formed through the self-assembly effect induced by solvent evaporation during the drying process of the binder. This network can be reversibly broken and reassembled during charging and discharging, which not only buffers the volume expansion of hard carbon particles, but also maintains continuous ion transport channels, and combines polar groups to Na + The preferential adsorption significantly reduces charge transfer impedance; tests showed that the resulting electrode maintained a charge transfer impedance of 332.5 mAh g after 100 cycles at 0.05 A / g. -1 The reversible capacity reaches 328.6 mAhg at a high rate of 1A / g. -1 . Attached Figure Description

[0033] Figure 1 This is an initial scanning electron microscope image of the hard carbon material obtained in Example 1 of the present invention;

[0034] Figure 2 This is a scanning electron microscope (SEM) image of the hard carbon material obtained in Example 1 of the present invention after 100 cycles; wherein, Figure 2 (a) is a scanning electron microscope image with a resolution of 10 μm. Figure 2 (b) is a scanning electron microscope image with a resolution of 5 μm;

[0035] Figure 3 This is a high-resolution transmission electron microscope image of the hard carbon material obtained in Example 1 of the present invention after 10 cycles;

[0036] Figure 4 This is a test diagram of the contact angle between the hard carbon material obtained in Example 1 of the present invention and the electrolyte;

[0037] Figure 5 These are Raman spectroscopy results of the hard carbon materials obtained in Example 1 and Comparative Examples 1-3 of this invention.

[0038] Figure 6 The first charge-discharge curve of the hard carbon material obtained in Example 1 of this invention at a current density of 0.05 A / g is shown.

[0039] Figure 7 The graph shows the performance of the hard carbon material obtained in Example 1 of this invention after 100 cycles at a current density of 0.05 A / g.

[0040] Figure 8 This is a rate performance diagram of the hard carbon material obtained in Example 1 of the present invention. Detailed Implementation

[0041] To make the technical solutions and advantages of the present invention clearer and more prominent, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are only a part of the present invention, and not all of the embodiments. All raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods. Among them: polyvinyl acetate, CAS No.: 9003-20-7, 25g, purchased from Aladdin Biochemical Technology Co., Ltd.; polyvinylidene fluoride, CAS No.: 24937-79-9, 100g, purchased from Zhengzhou Jinghong New Energy Technology Co., Ltd.; sodium carboxymethyl cellulose, CAS No.: 9004-32-4, 50g, purchased from Maclean Biochemical Technology Co., Ltd.; sodium alginate, CAS No.: 9005-38-3, 500g, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0042] Example 1

[0043] This embodiment provides a hard carbon anode material based on surface modification of strongly polar functional groups, which is composed of a conductive agent, resin-based hard carbon, and strongly polar functional groups uniformly loaded on its surface defects; the strongly polar functional group is ester carbonyl; the density of ester carbonyl groups loaded on the surface defects of the resin-based hard carbon is 2.21 ± 0.1 × 10⁻⁶. 8 mol / μm 2 .

[0044] The preparation process of the above-mentioned hard carbon anode material is as follows:

[0045] (1) 3-aminophenol, formaldehyde and 4-hydroxyphenylboronic acid were polymerized in a solvent at a mass ratio of 2.23:1.5:0.24 to obtain boron / phosphorus co-doped phenolic resin;

[0046] (2) Boron / phosphorus co-doped phenolic resin was heated to 1300℃ at 5℃ / min under nitrogen atmosphere and pyrolyzed for 2 h to obtain resin-based hard carbon.

[0047] (3) Grind the resin-based hard carbon, ester-containing carbonyl modifier and conductive agent thoroughly in a mortar until uniform, and then mechanically stir and mix them in N-methylpyrrolidone for 10 hours to carry out the grafting loading reaction to obtain the negative electrode slurry.

[0048] (4) The obtained negative electrode slurry was uniformly coated onto copper foil to a thickness of 16 μm, and then vacuum dried at 90 °C for 12 h, controlling the compaction density to be 1.3 g / cm³. 3 .

[0049] To simplify the operation and more accurately explain the modification effect of strongly polar functional groups on resin-based hard carbon and the resulting technical effects, the aforementioned ester-containing carbonyl modifier is simplified to polyvinyl acetate. It should be noted that this invention uses polyvinyl acetate as a functional binder, and simultaneously as a binder and surface modifier for hard carbon anode materials. On the one hand, its ester carbonyl groups are used to modify the surface of hard carbon, thereby controlling the uniform growth of its surface SEI film and suppressing interfacial side reactions. On the other hand, by regulating the dissolution-volatilization kinetics of the binder in the solvent, the dried binder forms a three-dimensional interconnected hydrogen bond network. During charging and discharging, this network dynamically buffers the volume expansion of hard carbon particles through the reversible breaking and recombination of hydrogen bonds, while maintaining continuous ion transport channels.

[0050] Example 2

[0051] This embodiment is exactly the same as Embodiment 1, except that the density of ester carbonyl groups loaded on the surface defects of the resin-based hard carbon is 1.96 ± 0.1 × 10⁻⁶. 8 mol / μm 2 .

[0052] Example 3

[0053] This embodiment is exactly the same as Embodiment 1, except that the density of ester carbonyl groups loaded on the surface defects of the resin-based hard carbon is 0.93 ± 0.1 × 10⁻⁶. 8 mol / μm 2 .

[0054] Example 4

[0055] This embodiment is exactly the same as Embodiment 1, except that polyvinyl acetate is replaced with polyvinylpyrrolidone.

[0056] Comparative Example 1

[0057] This comparative example is exactly the same as Example 1, except that polyvinyl acetate is replaced with polyvinylidene fluoride.

[0058] Comparative Example 2

[0059] This comparative example is exactly the same as Example 1, except that polyvinyl acetate is replaced with sodium carboxymethyl cellulose.

[0060] Comparative Example 3

[0061] This comparative example is exactly the same as Example 1, except that polyvinyl acetate is replaced with sodium alginate.

[0062] Furthermore, the present invention assembles sodium-ion half-cells using the hard carbon anode materials obtained in Examples 1-3 and Comparative Examples 1-3 in an argon-filled glove box, using NaPF6 dissolved in ethylene glycol dimethyl ether as the electrolyte, glass fiber as the separator, and the battery casing kit model is CR2032.

[0063] pass Figures 1-5 As can be seen, the PVAC binder used in Embodiment 1 of the present invention is uniformly distributed on the electrode surface, effectively bonding the hard carbon and conductive agent. The resulting battery maintains its complete electrode structure after 100 cycles, exhibiting good mechanical stability. Figure 3 The SEI film induced by surface modification with strongly polar functional groups exhibits uniformity and ultrathinness, and the electrode has a small contact angle, which is more conducive to electrolyte wetting and penetration; furthermore, through Figure 5 It is known that the material surface contains a large number of specific ester carbonyl structures, proving that the surface modification of this highly polar energy group was successful, providing favorable conditions for sodium ion transport.

[0064] Electrochemical performance was tested using the Blue Battery Testing System. Constant current charge-discharge tests were performed at current densities of 0.05 A / g and 1 A / g, with a voltage window of 0.01–2 V. 0.05 A / g is designated as I, and 1 A / g as II. Specific capacity is expressed in mAh / g. The test results are shown in the table below. Figures 6-8 As shown:

[0065]

[0066] Through Table 1 and Figures 6-8 It can be seen that the initial coulombic efficiency and rate performance of the hard carbon materials obtained in Examples 1-3 of this invention increase with the increase of the density of ester carbonyl groups loaded on the surface defects of the resin-based hard carbon. Among them, Example 1 shows a significant increase in all indicators compared with Comparative Example 1, with a 9.4% increase in capacity after 1000 cycles and a 22.4% increase in initial coulombic efficiency, proving that surface modification with strong polar functional groups can effectively improve the overall performance of the battery. This phenomenon is due to the directional dipole interaction between the strong polar functional groups and the defect sites of hard carbon, which constructs multiple chemical bonds such as hydrogen bonds and coordination bonds, greatly improving the bonding strength of the hard carbon surface, and the carbonyl oxygen atoms and Na + Weak coordination is formed to construct localized high Na+ on the hard carbon surface. + The concentration field lowers the intercalation energy barrier, and the long-chain flexibility and moderate cross-linking structure of PVAC can dynamically adapt to the changes in sodium storage volume of hard carbon. Furthermore, the modifiers used in Examples 1-3 of this invention also serve as binders for the materials. They are not only non-toxic and easily degradable, but also cost only 3-5% of fluorinated binders, which greatly reduces production costs and makes them suitable for industrial production.

[0067] It should be noted that the above data is intended to compare the effects of surface modification of strongly polar functional groups on battery performance, and should not be considered as the optimal solution of this method. When those skilled in the art apply the technical solution of this invention to ion batteries of other systems, the performance of the batteries will be different, but it is certain that they will all have a significant performance improvement over the original batteries.

Claims

1. A hard carbon anode material based on surface modification of strongly polar functional groups, characterized in that: It includes resin-based hard carbon and strongly polar functional groups uniformly loaded on its surface defects; the density of strongly polar functional groups loaded on the surface defects of the resin-based hard carbon is 0.5~3×10⁻⁶. 8 mol / μm 2 The strongly polar functional group is an ester carbonyl or a ketone carbonyl. The preparation process of the hard carbon anode material is as follows: Step S1: Phenolic monomers, aldehyde monomers and boron modifiers are polymerized in a solvent to obtain boron / phosphorus co-doped phenolic resin; Step S2: Carbonize the boron / phosphorus co-doped phenolic resin by programmed temperature rise under a protective atmosphere to obtain resin-based hard carbon. Step S3: The raw materials, including resin-based hard carbon and modifiers containing strong polar functional groups, are thoroughly mixed in the electrode solvent to carry out a grafting and loading reaction to obtain a negative electrode slurry. Step S4: Coat the negative electrode slurry evenly onto the copper foil, and then dry and compact it in sequence to obtain the final product.

2. The hard carbon anode material based on surface modification of strongly polar functional groups according to claim 1, characterized in that: The hard carbon anode material also includes a conductive material, the mass ratio of which to the resin-based hard carbon is (3~5):(12~16).

3. The hard carbon anode material based on surface modification of strongly polar functional groups according to claim 2, characterized in that: The conductive material is at least one of acetylene black, Super P, and carbon nanotubes.

4. The hard carbon anode material based on surface modification of strongly polar functional groups according to claim 1, characterized in that: The density of strongly polar functional groups loaded on the surface defects of the resin-based hard carbon is 0.9~2×10⁻⁶. 8 mol / μm 2 .

5. The hard carbon anode material based on surface modification of strongly polar functional groups according to claim 1, characterized in that: The phenolic monomer is at least one of 3-aminophenol, phenol, xylenol, and resorcinol; the aldehyde monomer is formaldehyde and / or furfural; and the boron modifier is at least one of 3-hydroxyphenylboronic acid, 4-hydroxyphenylboronic acid, neopentyl glycol 4-hydroxyphenylboronic acid, and boric acid.

6. The hard carbon anode material based on surface modification of strongly polar functional groups according to claim 1, characterized in that: The protective atmosphere is at least one of nitrogen, argon and helium.

7. A hard carbon anode material based on surface modification of strongly polar functional groups according to claim 1 or 6, characterized in that: The carbonization reaction conditions are as follows: under a protective atmosphere, the temperature is increased from room temperature to 1200-1400℃ at a rate of 2-5℃ / min, and pyrolysis is carried out for 1-3 hours.

8. The hard carbon anode material based on surface modification of strongly polar functional groups according to claim 1, characterized in that: The modifier containing strong polar functional groups is at least one of polyvinyl acetate, polydopamine, polysulfonated styrene, polyphosphazene, and polyethylene glycol diacrylate; the electrode solvent is at least one of N-methylpyrrolidone, deionized water, tetrahydrofuran, and dimethyl sulfoxide; the grafting loading reaction is carried out under stirring for 8-12 hours.

9. The hard carbon anode material based on surface modification of strongly polar functional groups according to claim 1, characterized in that: The drying conditions are: vacuum drying at 80~100℃ until the material reaches constant weight; the compaction conditions are: compaction at 80~120MPa until the material density is 1.2~1.5g / cm³. 3 .

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