Method for preparing high-performance hard carbon by using small organic molecules

Abstract

The invention discloses a method for preparing high-performance hard carbon by using small organic molecules. According to the method, small organic molecules are selected as a carbon source, an acid-base impurity removal process of a biomass carbon source is not needed, the production cost is reduced, and serious environmental pollution is avoided; meanwhile, spherical carbon precursors with different structures can be obtained through precursor design from organic small molecular monomers, and finally, the high-performance spherical hard carbon material is prepared through high-temperature graphitization treatment, so that the aim of accurately regulating and controlling the structure of the hard carbon material is fulfilled.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion batteries and energy storage thereof, and relates to a method for preparing high-performance hard carbon by utilizing small organic molecules. Background Art

[0002] Hard carbon is the preferred negative electrode material for sodium ion batteries. At present, the most common method for preparing hard carbon is to use cheap biomass such as coconut shells, peanut shells, grapefruit peels, tea stems, sawdust and other types of waste biomass as organic carbon sources (such as patents with publication numbers CN113381016A; CN113666356 A; CN113745509A), and then prepare it through acid-base impurity removal-low temperature pre-carbonization-crushing-high temperature carbonization and other methods. The above method seems to have the cost advantage of raw materials, but the impurities naturally present in biomass need to be removed with a large amount of acid or alkali before carbonization, which will result in high costs and serious environmental pollution. At the same time, the natural structure of biomass is not easy to regulate, so the performance of the final hard carbon is subject to the biomass precursor. In addition, the differences in the structural composition of biomass lead to the need for the preparation process to be adjusted and optimized in real time according to the biomass precursor, thereby increasing the difficulty of controlling the hard carbon preparation process. Summary of the invention

[0003] In order to improve the above technical problems, the present invention selects organic small molecules as carbon sources, without the need for acid-base removal of impurities, and simultaneously obtains carbon precursors through the amination reaction of organic amine small molecules and organic halogen small molecules. By selecting different amines and halogens, precise control of the structure of the hard carbon material is achieved, thereby preparing high-performance hard carbon negative electrode materials for sodium ion batteries.

[0004] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0005] A method for preparing hard carbon comprises the following steps:

[0006] 1) reacting an organic amine small molecule with an organic halogen small molecule to obtain a carbon precursor;

[0007] 2) pretreating the carbon precursor obtained in step 1);

[0008] 3) The carbon precursor pretreated in step 2) is subjected to high-temperature graphitization treatment in a non-oxidizing atmosphere to obtain the hard carbon.

[0009] According to an embodiment of the present invention, the reaction molar ratio of the organic amine small molecule to the organic halogen small molecule is 1:0.5-5, exemplified by 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5.

[0010] According to an embodiment of the present invention, the organic amine small molecule is selected from one, two or more of aromatic amines, aliphatic amines, alcohol amines, amides, alicyclic amines, aromatic amines and naphthyl amines, etc. For example, the organic amine small molecule is selected from at least one of octylamine, n-butylamine, ethylenediamine, benzylamine, methyldiethanolamine, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, benzidine and its derivatives, aniline, 3,3-diaminobenzidine, 3,3',5,5'-tetramethylbenzidine, 2-naphthylamine, 3,3'-dimethylbenzidine, 3.3'-dimethyl-4.4'diaminodiphenylmethane, caprolactam, methylcyclohexanediamine, 1,8-diaminonaphthalene and 1,5-naphthalenediamine, etc.

[0011] According to an embodiment of the present invention, the organic halogen small molecule is selected from a linear aliphatic halogen compound or an aromatic organic halogen compound. For example, the linear aliphatic halogen compound is at least one of dichloromethane, chloroform, carbon tetrachloride, dichloroethane, dichloropropane, dibromoethane and dibromopropane, etc.; the aromatic organic halogen compound is at least one of dibromobenzene, dichlorobenzene, tribromobenzene, trichlorobenzene, 1-benzyl-3-bromobenzene, 1-benzyl-2-chlorobenzene, benzyl bromide and benzyl chloride, etc.

[0012] According to an embodiment of the present invention, in step 1), the reaction temperature is 0°C to 200°C, preferably 100°C to 200°C, and exemplarily 150°C; the reaction time is 1 to 48 hours, and exemplarily 24 hours.

[0013] According to an embodiment of the present invention, in step 1), the reaction is carried out in a solvent system. For example, the organic amine small molecule is first dissolved in a solvent, and then mixed with the organic halogen small molecule to obtain a mixed solution. Preferably, the solvent can be a mixed solvent of one or more of water, ethanol, xylene, dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone (NMP) and ethylene glycol.

[0014] According to an embodiment of the present invention, step 1) further comprises performing solid-liquid separation on the mixed solution after the reaction to obtain a carbon precursor. For example, the mixed solution is filtered to obtain a carbon precursor.

[0015] According to an embodiment of the present invention, in step 2), the pretreatment temperature is 25-400°C, preferably 100-400°C, and exemplarily 25°C, 50°C, 100°C, 200°C, 300°C, and 400°C; the pretreatment atmosphere is one or a mixed gas of any multiple of oxygen, hydrogen, ammonia, methane, acetylene, water vapor, carbon monoxide, carbon dioxide, sulfur dioxide, argon, air, chlorine and helium; the pretreatment time is 0.5-24h, preferably 2-8h, and exemplarily 0.5h, 1h, 2h, 4h, 6h, 8h, 9h, 12h, and 24h.

[0016] According to an embodiment of the present invention, in step 3), the temperature of the high-temperature graphitization treatment is 400-1600°C, preferably 1000°C-1400°C, and exemplarily 400°C, 600°C, 800°C, 1000°C, 1100°C, 1300°C, 1400°C, and 1600°C; the time of the high-temperature graphitization treatment is 0.5-24h, preferably 1-6h, and exemplarily 1h, 2h, 3h, and 4h.

[0017] According to an embodiment of the present invention, in step 3), the heating rate of the high temperature graphitization treatment is 0.5 to 10 °C / min, exemplarily 5 °C / min.

[0018] According to an embodiment of the present invention, in step 3), the non-oxidizing atmosphere is, for example, one of nitrogen, argon, hydrogen, helium, etc., or a mixed gas of any multiple thereof.

[0019] According to an embodiment of the present invention, the method for preparing hard carbon comprises the following steps:

[0020] Step 1: Synthesis of carbon precursor

[0021] The organic amine small molecules and the organic halogen small molecules are dissolved in a solvent, reacted at a temperature of 0°C to 200°C for 1 to 48 hours, and solid-liquid separation is performed to obtain a carbon precursor.

[0022] Step 2: Pretreatment of carbon precursor: The carbon precursor obtained in step 1 is treated at 25-400° C. for 0.5-24 h;

[0023] Step 3: Graphitization of carbon precursor

[0024] The pretreated sample is graphitized in a non-oxidizing atmosphere at 400-1600° C. for 0.5-24 hours to obtain the hard carbon.

[0025] The present invention also provides a hard carbon material prepared by the above preparation method.

[0026] According to an embodiment of the present invention, the carbon layer spacing of the hard carbon material is 0.350-0.380 nm, exemplified by 0.351 nm, 0.353 nm, 0.355 nm, 0.358 nm, 0.359 nm, 0.371 nm, and 0.377 nm.

[0027] According to an embodiment of the present invention, the S of the hard carbon material D / S G It is 1.40-1.80, and examples are 1.42, 1.44, 1.49, 1.55, 1.71, 1.77, and 1.78.

[0028] The present invention also provides the use of the hard carbon material in a battery, preferably in a sodium ion battery, for example, as a negative electrode material of a sodium ion battery.

[0029] The present invention also provides a sodium ion battery, which contains the hard carbon material.

[0030] Beneficial effects of the present invention:

[0031] The present invention selects organic small molecules as carbon sources, and does not require acid-base impurity removal processes for biomass carbon sources, thereby reducing production costs and avoiding serious environmental pollution. At the same time, carbon precursors of different structures can be obtained from organic small molecule monomers through precursor design, and finally high-performance hard carbon materials are prepared through high-temperature graphitization treatment, achieving the goal of precise regulation of the structure of hard carbon materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the SEM morphology of the hard carbon material prepared in Example 1.

[0033] Figure 2 is the XRD data of the hard carbon material prepared in Example 1.

[0034] Figure 3 This is the Raman spectrum of the hard carbon material obtained in Example 1.

[0035] Figure 4 It is the first cycle charge and discharge curve diagram of the hard carbon material prepared in Example 1 and Example 4.

[0036] Figure 5 It is a rate performance diagram of the hard carbon material obtained in Example 1 and Example 4.

[0037] Figure 6 This is the XRD data of the hard carbon material prepared in Example 7. DETAILED DESCRIPTION

[0038] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0039] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0040] Example 1

[0041] The method for preparing hard carbon comprises the following steps:

[0042] Step 1: Take 1 g of p-phenylenediamine, dissolve it in 30 mL of N-methylpyrrolidone (NMP for short), then add 5 mL of p-dichlorobenzene, use a polytetrafluoroethylene reactor, react at 150 ° C for 24 hours, and filter to obtain a carbon precursor;

[0043] Step 2: Treat the carbon precursor at 200°C for 6 hours in an oxygen atmosphere, then switch to a nitrogen atmosphere, heat it to 1300°C at a heating rate of 5°C / min, keep it warm for 2 hours, and cool the carbonization furnace to room temperature to obtain the hard carbon material.

[0044] The SEM morphology of the hard carbon material prepared in this example is as follows: Figure 1 As shown, it can be seen from the figure that the hard carbon material prepared by the present invention is spherical.

[0045] Figure 2 This is the XRD spectrum of the hard carbon material prepared in this example. The carbon layer spacing calculated according to the Bragg equation is 0.359 nm.

[0046] Figure 3 is the Raman spectrum of the hard carbon material prepared in this example. S is calculated based on the peak area. D / S G =1.55.

[0047] Example 2

[0048] The method for preparing hard carbon comprises the following steps:

[0049] Step 1: Take 1 g of 1,5-naphthalene diamine, dissolve it in 30 mL of N-methylpyrrolidone (NMP for short), then add 5 mL of p-dichlorobenzene, use a polytetrafluoroethylene reactor, react at 150 ° C for 24 hours, and filter to obtain a carbon precursor;

[0050] Step 2: Treat the carbon precursor at 200°C for 6 hours in an oxygen atmosphere, then switch to a nitrogen atmosphere, heat it to 1300°C at a heating rate of 5°C / min, keep it warm for 2 hours, and cool the carbonization furnace to room temperature to obtain a hard carbon material.

[0051] Example 3

[0052] The method for preparing hard carbon comprises the following steps:

[0053] Step 1: Take 0.5 g of benzidine, dissolve it in 30 mL of N-methylpyrrolidone (NMP for short), then add 5 mL of p-dichlorobenzene, use a polytetrafluoroethylene reactor, react at 150 ° C for 24 hours, and filter to obtain a carbon precursor;

[0054] Step 2: Treat the spherical carbon precursor at 200°C for 6 hours in an oxygen atmosphere, then switch to a nitrogen atmosphere, heat it to 1300°C at a heating rate of 5°C / min, keep it warm for 2 hours, and then cool the carbonization furnace to room temperature to obtain a hard carbon material.

[0055] Example 4

[0056] The method for preparing hard carbon comprises the following steps:

[0057] Step 1: Take 1 g of p-phenylenediamine, dissolve it in 30 mL of N-methylpyrrolidone (NMP for short), then add 5 mL of p-dichlorobenzene, use a polytetrafluoroethylene reactor, react at 150 ° C for 24 hours, and filter to obtain a spherical carbon precursor;

[0058] Step 2: Heat the spherical carbon precursor to 1300°C at a heating rate of 5°C / min, keep it warm for 2 hours, and then cool the carbonization furnace to room temperature to obtain a spherical hard carbon material.

[0059] Example 5

[0060] The method for preparing hard carbon comprises the following steps:

[0061] Step 1: Take 1.0 g of p-phenylenediamine, dissolve it in 30 mL of N-methylpyrrolidone (NMP for short), then add 5 mL of p-dichlorobenzene, use a polytetrafluoroethylene reactor, react at 150 ° C for 24 hours, and filter to obtain a carbon precursor;

[0062] Step 2: Heat the carbon precursor in H 2 / Ar mixed gas (H 2 The carbonized carbon was treated at 400 °C for 6 h in a nitrogen atmosphere (5% volume fraction), then switched to a nitrogen atmosphere, heated to 1300 °C at a heating rate of 5 °C / min, kept warm for 2 h, and then the carbonization furnace was cooled to room temperature to obtain a hard carbon material.

[0063] Example 6

[0064] The method for preparing hard carbon comprises the following steps:

[0065] Step 1: Take 1.0 g of p-phenylenediamine, dissolve it in 30 mL of N-methylpyrrolidone (NMP for short), then add 5 mL of p-dichlorobenzene, use a polytetrafluoroethylene reactor, react at 150 ° C for 24 hours, and filter to obtain a carbon precursor;

[0066] Step 2: Treat the carbon precursor at 400°C for 6 hours in a CO atmosphere, then switch to a nitrogen atmosphere, heat it to 1300°C at a heating rate of 5°C / min, keep it warm for 2 hours, and cool the carbonization furnace to room temperature to obtain a hard carbon material.

[0067] Example 7

[0068] The method for preparing hard carbon comprises the following steps:

[0069] Step 1: Take 1 g of p-phenylenediamine, dissolve it in 30 mL of N-methylpyrrolidone (NMP for short), then add 5 mL of p-dichlorobenzene, use a polytetrafluoroethylene reactor, react at 150 ° C for 24 hours, and filter to obtain a carbon precursor;

[0070] Step 2: Treat the carbon precursor at 200°C for 9 hours in an oxygen atmosphere, then switch to a nitrogen atmosphere, heat it to 1300°C at a heating rate of 5°C / min, keep it warm for 2 hours, and cool the carbonization furnace to room temperature to obtain the hard carbon material.

[0071] Figure 6 This is the XRD spectrum of the hard carbon material prepared in this example. The carbon layer spacing calculated according to the Bragg equation is 0.377 nm.

[0072] Comparative Example 1

[0073] The method for preparing hard carbon comprises the following steps:

[0074] Step 1: Take 1.0 g of p-phenylenediamine, dissolve it in 30 mL of N-methylpyrrolidone (NMP for short), use a polytetrafluoroethylene reactor, react at 150° C. for 24 hours, and filter to obtain no carbon precursor.

[0075] Table 1 Structural parameters of hard carbon materials obtained in Examples 1-7 and Comparative Example 1

[0076]

[0077]

[0078] It can be seen from Table 1 that the structure of the final hard carbon can be controlled by selecting the type of organic amine molecules, the pretreatment atmosphere, the pretreatment time, etc. However, in Comparative Example 1, no organic halogen small molecules were added, and the hard carbon solid target product could not be obtained after the reaction.

[0079] Test Example 1

[0080] The half-cell test was conducted using a standard CR2032 button cell. The battery slurry was mixed with active material (the hard carbon material prepared above), KT-black and polyvinylidene fluoride (PVDF) binder in a weight ratio of 8:1:1, using N-methylpyrrolidone as solvent (NMP), aluminum foil as current collector, and the pole piece loading was 1 mg / cm 2 The half-cell was assembled in a glove box filled with Ar, with a sodium metal sheet as the counter electrode and glass fiber as the separator; the electrolyte: the solute was 1.0M NaPF 6(sodium hexafluorophosphate), the solvent is DME (dimethyl ether). All button cells were left at room temperature for 24 h before electrochemical testing. Constant current charging / discharging was performed on a Newell battery tester (voltage range: 0-2.5 V).

[0081] Figure 4 The first cycle charge and discharge curves of the hard carbon materials prepared in Example 1 and Example 4. It can be seen from the figure that the slope area of ​​the first cycle discharge curve is basically completely overlapped, but the platform area of ​​Example 1 is longer than that of Example 4. At the same time, the first cycle coulomb efficiency of the battery assembled from the hard carbon material prepared in Example 1 is 80.2%, which is also much higher than the first cycle coulomb efficiency of the battery assembled from the hard carbon material prepared in Example 4, which is 67.61%. The SD area of ​​the hard carbon material obtained in Example 4 without oxygen atmosphere pretreatment is higher, resulting in more defects in the prepared hard carbon material, and more defects will produce more irreversible capacity loss, thus resulting in a lower reversible capacity of Example 4. This shows that the platform capacity of the battery assembled from the hard carbon material obtained after oxygen atmosphere pretreatment is improved, and the first coulomb efficiency is also improved.

[0082] Figure 5 This is a rate performance diagram of a battery assembled from the hard carbon materials prepared in Example 1 and Example 4. It can be seen from the diagram that the rate performance of the battery assembled from the hard carbon material obtained after pretreatment in an oxygen atmosphere is better.

[0083] Table 2 Electrochemical performance of batteries assembled from 1-7 hard carbon materials obtained in Example

[0084] Example First cycle coulomb efficiency (%) Reversible discharge capacity (mAh / g) Rate performance (12.8A / g) 1 80(25mA / g) 360(25mA / g) 143 2 81(25mA / g) 366(25mA / g) 145 3 80(25mA / g) 366(25mA / g) 150 4 68(25mA / g) 225(25mA / g) 75 5 83(25mA / g) 349(25mA / g) 137 6 77(25mA / g) 270(25mA / g) 77 7 66.8(25mA / g) 291(25mA / g) 65

[0085] It can be seen from Table 2 that a larger carbon layer spacing can accommodate more sodium ions, thus having a higher capacity; fewer defects can result in a higher first coulombic efficiency and a higher reversible capacity; and more graphite microcrystalline regions have better rate performance.

[0086] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing hard carbon, It is characterized in that The method comprises the following steps: 1) reacting an organic amine small molecule with an organic halogen small molecule to obtain a carbon precursor; 2) pretreating the precursor obtained in step 1); 3) The carbon precursor pretreated in step 2) is subjected to high-temperature graphitization treatment in a non-oxidizing atmosphere to obtain the hard carbon.

2. The preparation method according to claim 1, It is characterized in that The reaction molar ratio of the organic amine small molecule to the organic halogen small molecule is 1:0.5-5.

3. The preparation method according to claim 1 or 2, It is characterized in that The organic amine small molecules are selected from one, two or more of aromatic amines, fats, alcohol amines, amides, alicyclic amines, aromatic amines and naphthyl amines. For example, the organic amine is selected from at least one of octylamine, n-butylamine, ethylenediamine, benzylamine, methyldiethanolamine, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, benzidine and its derivatives, 3,3-diaminobenzidine, 3,3',5,5'-tetramethylbenzidine, 2-naphthylamine, 3,3'-dimethylbenzidine, 3.3'-dimethyl-4.4'diaminodiphenylmethane, caprolactam, methylcyclohexanediamine, 1,8-diaminonaphthalene and 1,5-naphthalenediamine.

4. The preparation method according to any one of claims 1 to 3, It is characterized in that The organic halogen small molecules are selected from linear aliphatic halogen compounds or aromatic organic halogen compounds. For example, the straight-chain aliphatic halogen compound is at least one of dichloromethane, chloroform, carbon tetrachloride, dichloroethane, dichloropropane, dibromoethane and dibromopropane; For example, the aromatic organic halogenated compound is at least one of dibromobenzene, dichlorobenzene, tribromobenzene, trichlorobenzene, 1-benzyl-3-bromobenzene, 1-benzyl-2-chlorobenzene, benzyl bromide and benzyl chloride.

5. The preparation method according to any one of claims 1 to 4, It is characterized in that In step 1), the reaction temperature is 0°C to 200°C, preferably 100 to 200°C; the reaction time is 1 to 48 hours. Preferably, in step 2), the pretreatment temperature is 25 to 400° C., preferably 100 to 400° C.; the pretreatment atmosphere is one or a mixture of any multiple of oxygen, hydrogen, ammonia, methane, acetylene, water vapor, carbon monoxide, carbon dioxide, sulfur dioxide, argon, air, chlorine and helium; the pretreatment time is 0.5 to 24 hours, preferably 2 to 8 hours. Preferably, in step 3), the temperature of the high temperature graphitization treatment is 400-1600° C., preferably 1000° C.-1400° C.; the time of the high temperature graphitization treatment is 0.5-24 h, preferably 1-6 h. Preferably, in step 3), the heating rate of the high temperature graphitization treatment is 0.5 to 10 / min. Preferably, in step 3), the non-oxidizing atmosphere is, for example, one or a mixed gas of any multiple of nitrogen, argon, hydrogen, helium, etc.

6. The preparation method according to any one of claims 1 to 5, It is characterized in that The steps include: Step 1: Synthesis of carbon precursor The organic amine small molecules and the organic halogen small molecules are dissolved in a solvent, reacted at a temperature of 0°C to 200°C for 1 to 48 hours, and solid-liquid separation is performed to obtain a carbon precursor. Step 2: Pretreatment of carbon precursor: The carbon precursor obtained in step 1 is treated at 25-400° C. for 0.5-24 h; Step 3: Graphitization of carbon precursor The pretreated sample is graphitized at 400-1600° C. in a non-oxidizing atmosphere for 0.5-24 hours to obtain the hard carbon.

7. The hard carbon material prepared by the preparation method according to any one of claims 1 to 6.

8. The hard carbon material according to claim 7, It is characterized in that The carbon layer spacing of the hard carbon material is 0.350-0.380 nm. Preferably, the S of the hard carbon material D / S G It is 1.40~1.

80.

9. Use of the hard carbon material according to claim 7 in a battery, preferably in a sodium ion battery, for example, as a negative electrode material of a sodium ion battery.

10. A sodium ion battery comprising a hard carbon material prepared by the preparation method according to any one of claims 1 to 6.

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