Phenolic resin asphalt super-crosslinking hard carbon composite material and preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium ion battery hard carbon negative electrode materials, and particularly relates to a phenolic resin asphalt super-crosslinking hard carbon composite active material and a preparation method and application thereof.The preparation method comprises the steps of phenolic resin precursor synthesis, oxidized asphalt precursor synthesis, super-crosslinking reaction and stepped carbonization; the preparation method comprises the following steps: reacting phenol with formaldehyde under the action of a catalyst to obtain a phenolic resin precursor; pre-oxidizing the coated asphalt in an air atmosphere to generate an asphalt precursor; the preparation method comprises the following steps: mixing a phenolic resin precursor with an asphalt precursor, adding an acid catalyst into an organic solvent, and performing reflux heating to form a chemically bonded three-dimensional cross-linked network structure; and sequentially carrying out low-temperature pre-carbonization and high-temperature carbonization in an inert gas atmosphere to obtain a target product, namely the hard carbon composite material. The target product provided by the invention has rich closed pore and multistage through pore structure hard carbon, and the sodium storage capacity of the hard carbon material is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sodium ion battery hard carbon negative electrode material, in particular to a phenolic resin pitch super-crosslinking hard carbon composite active material and its preparation method and application. BACKGROUND

[0002] Sodium ion batteries have become an important supplement to lithium ion batteries in the field of low-speed electric vehicles and large-scale grid energy storage due to the cost advantages of abundant sodium resources, wide distribution, etc. The negative electrode material plays a very important role in improving the energy density of sodium ion batteries. Hard carbon has a typical short-range disorder and long-range ordered graphite crystalline structure, which can accommodate the insertion / extraction of sodium ions, and is an ideal negative electrode material. The main hard carbon precursors on the current market include biomass, phenolic resin and pitch. Biomass has poor batch stability and low yield (±15% capacity fluctuation) due to the influence of production location and season, and the yield is less than 40%; phenolic resin, as a traditional hard carbon precursor, has the advantage of controllable structure, but is expensive and has more surface defects of hard carbon, with low first coulombic efficiency (≤80%); pitch has the advantages of high aromaticity, high carbon content and low price, but due to its high temperature graphitization (ID / IG≤0.8), the specific capacity is low (<100 mAh / g), which cannot meet the commercialization needs of sodium ion batteries. From the perspective of performance and commercialization application, a single precursor or simple mechanical mixing of two precursors cannot effectively control the microstructure (defects, interlayer spacing, closed pores) of hard carbon. SUMMARY

[0003] The present application aims to overcome the shortcomings of the prior art and provides a phenolic resin pitch super-crosslinking hard carbon composite material and its preparation method and application, which can avoid interface separation, inhibit pitch carbonization at high temperature, have high closed pore rate, large interlayer spacing, ideal energy density and rate performance, and realize high reversible capacity, high first efficiency and cycle stability in sodium ion batteries.

[0004] To solve the above technical problems, the present application is implemented as follows: A preparation method of a phenolic resin pitch super-crosslinking hard carbon composite material, characterized in that it comprises the following steps: (1) Synthesis of phenolic resin precursor: phenol and formaldehyde are reacted under the action of a catalyst to obtain a linear or bulk phenolic resin precursor with a molecular weight of 300-5000 g / mol; (2) Synthesis of oxidized pitch precursor: coated pitch is pre-oxidized in an air atmosphere to generate an oxidized pitch precursor containing carboxyl, hydroxyl or carbonyl groups; (3) Super-crosslinking reaction: the phenolic resin precursor obtained in step (1) and the oxidized pitch precursor obtained in step (2) are mixed, an acid catalyst is added in an organic solvent, and reflux heating is performed to form a three-dimensional crosslinking network structure with chemical bonding. (4) Staged carbonization: sequentially performing low-temperature pre-carbonization and high-temperature carbonization under inert gas atmosphere to obtain the target product hard carbon composite material.

[0005] Further, in the step (1), the catalyst is one of sodium hydroxide, ammonia water, triethylamine, ethylenediamine, oxalic acid, sulfuric acid or phosphoric acid.

[0006] Further, in the step (1), the temperature of the phenolic resin precursor is 60-150℃, and the reaction time is 2-8 hours.

[0007] Further, in the step (2), the softening points of the coated bitumen are 260, 160 and 80℃ respectively, the pre-oxidation temperature is 150-350, and the pre-oxidation time is 1-8h.

[0008] Further, in the step (3), the mass ratio of the phenolic resin precursor to the oxidized bitumen precursor is 1-19:1.

[0009] Further, in the step (3), the acid catalyst is an organic acid, a protonic acid or a Lewis acid; and the organic solvent is ethanol, trichloromethane, dichloromethane, N,N-dimethylformamide or petroleum ether.

[0010] Further, in the step (3), the acid catalyst is added in an amount of 3-20% of the total mass of the raw materials; the cross-linking reaction temperature is 50-180℃, and the reaction time is 2-24h.

[0011] Further, in the step (4), the low-temperature carbonization is performed under nitrogen, argon or helium atmosphere, with the temperature raised to 300-800℃ at a rate of 1-5℃ / min, and the temperature is maintained for 1-8 hours; the high-temperature carbonization is performed with the temperature raised to 1000-1800℃ at a rate of 1-5℃ / min, and the temperature is maintained for 1-8 hours, to obtain the target product hard carbon composite material.

[0012] The hard carbon composite material prepared by the above phenolic resin bitumen super-cross-linked hard carbon composite material preparation method has a closed pore volume ≥0.10 cm 3 / g; the interlayer spacing is 0.42nm ≥d 002 ≥0.38nm; the specific surface area is ≤10m 2 / g; and the reversible capacity is ≥300mAh / g when discharged at a current of 0.1C rate.

[0013] A sodium ion battery comprises a negative electrode of the above hard carbon composite material, and a positive electrode of Prussian blue or layered oxide.

[0014] The phenolic resin is a macromolecular organic polymer with a specific molecular structure, and has the advantages of easy control of synthesis process and controllable structure. The linear thermoplastic phenolic resin and the thermosetting phenolic resin with body phase cross-linking can be prepared by changing the synthesis conditions. The high, medium and low temperature coated bitumen containing different oxygen-containing functional groups is synthesized by changing the pre-oxidation conditions. Under the action of a specific acidic catalyst, the oxygen-containing bitumen is chemically bonded on the phenolic resin through the cross-linking reaction of the oxygen-containing functional groups, the phenolic resin is cross-linked with the bitumen, the rigid skeleton network of the phenolic resin is used as the rigid skeleton of the whole system, and the bitumen component is 'anchored' or chemically bonded on the rigid skeleton network. On the one hand, the surface defects of the phenolic resin-based hard carbon can be optimized, and on the other hand, the graphitization tendency of the bitumen high-temperature carbonization can be inhibited, so that the phenolic resin bitumen super-cross-linked hard carbon has appropriate interlayer spacing and rich closed pore structure, which can effectively improve the low-pressure area platform capacity, thereby realizing the improvement of the electrochemical performance of the sodium ion battery hard carbon negative electrode material.

[0015] Compared with the prior art, the present application has the beneficial effects that the structure is designed from the molecular level, the phenolic resin and the oxidized bitumen are effectively cross-linked through chemical bonding, and the problems of single precursor or mechanical mixing cannot synergistically control the closed pore structure and interlayer spacing of the hard carbon, and the mechanical mixing interface is not strong, and the material stability is poor, etc. The specific surface area, interlayer spacing and pore structure of the synthesized phenolic resin bitumen super-cross-linked hard carbon meet the structure requirements of high-performance hard carbon materials, the higher low-pressure platform capacity and good conductivity can further improve the energy density and rate performance, and provide strong support for the future commercialization of the sodium ion battery hard carbon negative electrode material. The present application chemically anchors the oxygen-containing functional group bitumen in the phenolic resin network through the acid catalytic cross-linking reaction, on the one hand, the rigid skeleton of the phenolic resin is used to inhibit the high-temperature flow of the bitumen, and on the other hand, the present application adopts directional regulation of the hard carbon microstructure, realizes the molecular-level cross-linking of the phenolic resin and the bitumen through chemical bonding instead of physical mixing, avoids interface separation, and overcomes the problems of poor batch stability of biomass raw materials, many surface defects of the phenolic resin-based hard carbon / low initial efficiency, easy graphitization of the bitumen-based hard carbon / insufficient specific capacity, etc. Through the encapsulation of the bitumen pyrolysis gas, rich closed pores are formed, and finally the hard carbon material with high closed pore volume ≥0.10 cm 3 / g, large interlayer spacing (d 002 ≥0.38 nm) is obtained, so that it realizes high reversible capacity (≥300 mAh / g), high initial efficiency (≥85%) and excellent cycle stability in the sodium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is the XRD spectrum of the phenolic resin bitumen super-cross-linked hard carbon of Example 1.

[0017] Figure 2 It is the charge-discharge curve of the phenolic resin bitumen super-cross-linked hard carbon of Example 2.

[0018] Figure 3 Transmission electron microscope image of the phenolic resin asphalt super-crosslinked hard carbon of Example 3.

[0019] Figure 4 Nitrogen adsorption desorption and pore distribution curve of the phenolic resin asphalt super-crosslinked hard carbon of Example 3. DETAILED DESCRIPTION

[0020] In order to better illustrate the purpose, technical scheme and advantages of the present application, the technical scheme of the present application will be described in detail below. The following examples facilitate better understanding of the present application, but do not limit the present application. The experimental methods in the following examples are conventional methods, unless otherwise specified.

[0021] Example 1 S1. Phenol and formaldehyde solution (37%) were fed in a molar ratio of 1:1.5, NaOH was used as a catalyst, and the amount of NaOH added was 1 wt% (based on phenol). First, phenol was added to a three-necked flask and heated to 60°C in a water bath to melt it, then NaOH was added and stirred for 10 min to mix it evenly with the phenol. After thorough mixing, the temperature was continued to be raised, and when the water bath reached 85°C, formaldehyde solution was added. The reaction was carried out for 2 h, and after the reaction was completed, the reaction product was treated by vacuum distillation and dehydration using a rotary evaporator to synthesize a phenolic resin precursor.

[0022] S2. 1 g of high-temperature coated asphalt powder with a softening point of 260°C was evenly spread in a corundum boat, and heated to 320°C at a rate of 5°C / min in an air atmosphere, and kept at this temperature for 2 h to prepare an asphalt precursor containing oxygen-containing functional groups.

[0023] S3. The phenolic resin obtained in step S1 was dissolved in ethanol, and the asphalt precursor containing oxygen-containing functional groups obtained in step S2 was added to the solution. The mass ratio of phenolic resin to oxidized asphalt was 12:1. After stirring until uniform, 8 wt.% of p-toluenesulfonic acid was added, and the temperature was raised to 160°C in an oil bath under reflux heating and stirring. After 5 h of reaction, the solvent was evaporated and the temperature was allowed to cool to room temperature naturally to obtain a phenolic resin asphalt super-crosslinked precursor.

[0024] S4. The phenolic resin asphalt super-crosslinked precursor sample obtained in step S3 was ground into powder and placed in a corundum boat, which was then placed in a tube furnace. The temperature was raised to 380°C at a rate of 3°C / min under a nitrogen atmosphere, and kept at this temperature for 3 h. The sample was then naturally cooled to room temperature to obtain a pre-carbonized sample.

[0025] S5. The sample obtained in step S4 was placed in a high-temperature tube furnace and calcined. The atmosphere was nitrogen, the heating rate was 2°C / min, the temperature was raised to 1400°C, and the sample was kept at this temperature for 2 h. The sample was then naturally cooled to room temperature to obtain the final hard carbon material.

[0026] Example 2 S1. Phenol and formaldehyde solution (37%) were fed in a ratio of 1 : 1.5 (molar ratio), and triethylamine was used as a catalyst. The amount of triethylamine added was 2 wt.% (based on the amount of phenol). First, the phenol was added to a three-necked flask and heated to 60 °C in a water bath to melt it. Then, triethylamine was added and stirred for 10 min to mix it with the phenol. After mixing, the temperature was increased, and when the water bath reached 75 °C, the formaldehyde solution was added. The reaction was carried out for 3 h. After the reaction was completed, the reaction product was dehydrated by vacuum distillation using a rotary evaporator to obtain a phenol-formaldehyde resin precursor.

[0027] S2. 1 g of a medium-temperature coating pitch powder with a softening point of 160 °C was uniformly spread in a corundum boat. The boat was heated to 280 °C at a rate of 2 °C / min in an air atmosphere and held at this temperature for 3 h to obtain an asphalt precursor containing oxygen-containing functional groups.

[0028] S3. The phenol-formaldehyde resin obtained in step S1 was dissolved in N,N- dimethylformamide, and the asphalt precursor containing oxygen-containing functional groups obtained in step S2 was added to the solution. The mass ratio of the phenol-formaldehyde resin to the oxidized asphalt was 9:1. After stirring until uniform, 5 wt.% of sulfuric acid was added. The solution was heated and stirred in an oil bath until the temperature reached 120 °C. After 6 h of reaction, the solvent was evaporated, and the mixture was naturally cooled to room temperature to obtain a phenol-formaldehyde resin-asphalt supercrosslinked precursor.

[0029] S4. The phenol-formaldehyde resin-asphalt supercrosslinked precursor obtained in step S3 was ground into powder and placed in a corundum boat. The boat was placed in a tube furnace and heated to 450 °C at a rate of 2 °C / min in a nitrogen atmosphere. The temperature was held at 450 °C for 4 h, and the sample was naturally cooled to room temperature to obtain a pre-carbonized sample.

[0030] S5. The sample obtained in step S4 was calcined in a high-temperature tube furnace in a nitrogen atmosphere at a rate of 1 °C / min. The temperature was increased to 1300 °C, and the sample was held at this temperature for 3 h. The sample was naturally cooled to room temperature to obtain the final hard carbon material.

[0031] Example 3 S1. Phenol and formaldehyde solution (37%) were fed in a ratio of 1 : 0.8 (molar ratio), and oxalic acid was used as a catalyst. The amount of oxalic acid added was 2 wt.% (based on the amount of phenol). First, the phenol was added to a three-necked flask and heated to 60 °C in a water bath to melt it. Then, oxalic acid was added and stirred for 10 min to mix it with the phenol. After mixing, the temperature was increased, and when the water bath reached 75 °C, the formaldehyde solution was added. The reaction was carried out for 2 h. Then, the temperature was increased to 80 °C, and the reaction was continued for 2 h at 80 °C. Finally, the temperature was increased to 85 °C, and the reaction was continued for 2 h. After the reaction was completed, the phenol-formaldehyde resin solution was transferred to a rotary evaporator, and the water was removed by vacuum distillation to obtain a phenol-formaldehyde resin precursor.

[0032] S2. Evenly spread 1 g of low-temperature coated asphalt powder with a softening point of 80°C in a corundum boat, heat it to 260°C at a rate of 1°C / min in an air atmosphere, and keep it warm for 1 hour to prepare an asphalt precursor containing oxygen-containing functional groups.

[0033] S3. Dissolve the phenolic resin obtained in step S1 in a dichloromethane solution, and then add the asphalt precursor containing oxygen-containing functional groups obtained in step S2 to the solution. The mass ratio of phenolic resin to oxidized asphalt is 7:1. Stir until uniform, and add 10 wt.% of aluminum chloride. Reflux and stir in an oil bath to raise the temperature to 100°C. After reacting for 3 hours, evaporate the solvent and naturally cool to room temperature to obtain a phenolic resin asphalt super-crosslinked precursor.

[0034] S4. Grind the phenolic resin asphalt super-crosslinked precursor sample obtained in step S3 into powder and put it into a corundum boat, then place it in a tube furnace, raise the temperature to 500°C at 5°C / min under argon atmosphere, keep it warm for 2h, and naturally cool it to room temperature to obtain a pre-carbonized sample.

[0035] S5. The sample prepared in step S4 was placed in a high-temperature tube furnace and calcined with argon as the atmosphere. The temperature was increased at a rate of 2°C / min to 1500°C, kept at this temperature for 1 hour, and naturally cooled to room temperature to obtain the final hard carbon material.

[0036] Experimental part: The hard carbon materials prepared in Examples 1, 2, and 3 were respectively prepared into sodium ion battery negative electrodes and relevant performance tests were performed.

[0037] The hard carbon materials prepared in Examples 1, 2, and 3, along with conductive carbon black and polyvinylidene fluoride (PVDF) binder, were precisely weighed and mixed in a mass ratio of 8:1:1. The mixture was dissolved in nitrogen-methylpyrrolidone (NMP). The resulting slurry was evenly coated onto copper foil and vacuum-dried at 100°C for 12 hours before removal. LIR2032 button cells were assembled in a high-purity argon glove box using a sodium metal sheet as the counter electrode, a glass fiber separator, and NaClO₄ (EC:DEC = 1:1) as the electrolyte. Electrochemical sodium storage performance was tested at room temperature over a voltage range of 0-2.5 V, with a plateau region of 0-0.1 V.

[0038] The specific surface area, pore structure and interlayer spacing parameters of the hard carbon samples of Examples 1, 2 and 3 are shown in Table 1 .

[0039] Finally, it should be noted that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. It should be noted that various modifications and variations are readily apparent to those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a phenolic resin pitch super-crosslinked hard carbon composite material, characterized in that: The following steps are involved: (1) Synthesis of phenolic resin precursor: reacting phenol and formaldehyde in the presence of a catalyst to obtain a linear or bulk phenolic resin precursor with a molecular weight of 300 to 5000 g / mol; (2) Synthesis of oxidized asphalt precursor: pre-oxidizing the coated asphalt in air atmosphere to generate an oxidized asphalt precursor containing carboxyl, hydroxyl or carbonyl groups; (3) Hypercrosslinking reaction: mixing the phenolic resin precursor obtained in step (1) with the oxidized asphalt precursor obtained in step (2), adding an acid catalyst in an organic solvent, and reflux heating to form a chemically bonded three-dimensional crosslinked network structure; (4) Step carbonization: Low-temperature pre-carbonization and high-temperature carbonization are carried out in sequence under an inert gas atmosphere to obtain the target product, a hard carbon composite material.

2. The method for preparing a phenolic resin pitch super-crosslinked hard carbon composite material according to claim 1, characterized in that: In the step (1), the catalyst is one of sodium hydroxide, ammonia water, triethylamine, ethylenediamine, oxalic acid, sulfuric acid or phosphoric acid.

3. The method for preparing a phenolic resin pitch super-crosslinked hard carbon composite material according to claim 2, characterized in that: In the step (1), the temperature of the phenolic resin precursor is 60 to 150° C., and the reaction time is 2 to 8 hours.

4. The method for preparing a phenolic resin pitch super-crosslinked hard carbon composite material according to claim 3, characterized in that: In the step (2), the softening points of the coated asphalt are 260, 160, and 80°C, respectively; the pre-oxidation temperature is 150-350°C; and the pre-oxidation time is 1-8 hours.

5. The method for preparing a phenolic resin pitch super-crosslinked hard carbon composite material according to claim 4, characterized in that: In the step (3), the mass ratio of the phenolic resin precursor to the oxidized asphalt precursor is 1 to 19:

1.

6. The method for preparing a phenolic resin pitch super-crosslinked hard carbon composite material according to claim 5, characterized in that: In step (3), the acid catalyst is an organic acid, a protonic acid or a Lewis acid; and the organic solvent is ethanol, chloroform, dichloromethane, N,N-dimethylformamide or petroleum ether.

7. The method for preparing a phenolic resin pitch super-crosslinked hard carbon composite material according to claim 6, characterized in that: In the step (3), the amount of the acid catalyst added is 3 to 20% of the total mass of the raw materials; the cross-linking reaction temperature is 50 to 180° C., and the reaction time is 2 to 24 hours.

8. The method for preparing a phenolic resin pitch super-crosslinked hard carbon composite material according to claim 6, characterized in that: In the step (4), low-temperature carbonization: in a nitrogen, argon or helium atmosphere, the temperature is raised to 300-800°C at 1-5°C / min and kept warm for 1-8 hours; high-temperature carbonization: the temperature is raised to 1000-1800°C at 1-5°C / min and kept warm for 1-8 hours to obtain the target product, a hard carbon composite material.

9. A hard carbon composite material obtained by the method for preparing a phenolic resin pitch super-crosslinked hard carbon composite material according to any one of claims 1 to 8, characterized in that: Closed pore volume ≥ 0.10 cm 3 / g; interlayer spacing 0.42nm≥d 002 ≥0.38nm; specific surface area ≤10m 2 / g; when discharged at a current rate of 0.1C, the reversible capacity is ≥300mAh / g.

10. A sodium ion battery, characterized in that: A negative electrode comprising the hard carbon composite material according to claim 9, wherein the positive electrode is Prussian blue or a layered oxide.

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