Preparation method of hard carbon doped with pre-oxidized heavy organic matter in situ

Abstract

The invention relates to the technical field of sodium ion battery negative electrode materials, and discloses an in-situ doped pre-oxidized heavy organic matter hard carbon preparation method which comprises the following steps: step 1, low-temperature oxidation: obtaining a pre-oxidized carbon material after heat treatment is finished; step 2, element doping: obtaining a hard carbon precursor doped with a sulfur element; step 3, low-temperature curing: obtaining a cured sulfur element doped pre-oxidized heavy organic matter hard carbon precursor; step 4, high-temperature carbonization: obtaining a sulfur element doped pre-oxidized heavy organic matter hard carbon precursor material with a stable structure; the medium-temperature coal pitch is oxidized at low temperature to obtain the pre-oxidized carbon material, then the sulfur element doped material reacts with the medium-temperature coal pitch at low temperature, hydrogen ions of the medium-temperature coal pitch are substituted by sulfur to form relatively stable chemical bonds, and the continuity of the chemical bonds is beneficial to enhancing the stability of the structure; sulfur atom doping not only provides active sites and increases sodium storage capacity, but also expands interlayer spacing and improves rate capability.

Description

Technical Field

[0001] The invention relates to the technical field of negative electrode materials for sodium ion batteries, and in particular to a method for preparing hard carbon by in-situ doping and pre-oxidation of heavy organic matter. Background Art

[0002] Hard carbon refers to carbon that is difficult to graphitize, and is mainly obtained by pyrolysis of high molecular polymers. Depending on the pyrolysis temperature and the precursor material, hard carbon can be mainly divided into high-temperature pyrolytic carbon, low-temperature pyrolytic carbon, resin carbon, heavy organic carbon, biomass carbon and carbon black.

[0003] The sulfur atoms doped in the hard carbon material of the negative electrode of the sodium ion battery are sourced from elemental sulfur. Elemental sulfur is a yellow powder, also known as sulfur. Long-term inhalation of sulfur dust can easily cause fatigue, dizziness, indigestion and other symptoms. Workers should take good protection. Powdered sulfur is stored in a ventilated and dry warehouse. Sulfur powder should not be exposed to moisture during transportation. Handle it with care during loading and unloading to prevent moisture from being exposed to damage to the packaging.

[0004] Heteroatom doping can significantly improve the sodium storage performance of carbon materials, but current related research still has problems such as cumbersome doping process, low heteroatom content, low first coulombic efficiency of materials, unstable cycle performance, etc. Therefore, it is of practical significance to find a suitable carbon source and use a simple doping method to prepare heteroatom-doped carbon materials with high heteroatom content and excellent electrochemical properties so that they can be used in the negative electrode of sodium ion batteries. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter, comprising the following steps:

[0007] Step 1: Low-temperature oxidation: placing the medium-temperature coal tar pitch in an oxygen atmosphere for low-temperature heat treatment, and obtaining a pre-oxidized carbon material after the heat treatment;

[0008] Step 2, element doping: ball-milling and mixing the medium-temperature coal tar pitch and the sulfur-doped material in proportion, stirring evenly to obtain a hard carbon precursor doped with sulfur;

[0009] Step 3, low temperature curing: placing the hard carbon precursor and the pre-oxidized carbon material together in a reaction kettle, and curing at low temperature to obtain a cured sulfur-doped pre-oxidized heavy organic hard carbon precursor;

[0010] Step 4, high temperature carbonization: subjecting the above sulfur-doped pre-oxidized heavy organic hard carbon precursor to high temperature heat treatment in an inert gas atmosphere. After the heat treatment, a sulfur-doped pre-oxidized heavy organic hard carbon precursor material with a stable structure is obtained.

[0011] In one specific embodiment, in step one, the heating method of low temperature heat treatment is: introducing oxygen at a flow rate of 5-400 mL / min into a muffle furnace for temperature sintering, and keeping the temperature at a low temperature of 200-400°C for 1-3h; the heating rate is 1-10°C / min.

[0012] In a specific embodiment, in step 2, the element doping material includes one or more of elemental sulfur, thiourea, poly-2-hydroxymethylthiophene, 3-formaldehyde benzothiophene and sulfuric acid.

[0013] In a specific embodiment, in step 2, the mixing mass ratio of the medium-temperature coal tar pitch and the sulfur-doped material is 1:1-5.

[0014] In a specific embodiment, in step three, the mixing mass ratio of the hard carbon precursor and the pre-oxidized carbon material is 1:0.5-1.

[0015] In a specific embodiment, in step three, the low temperature curing condition is: at a temperature of 150-300° C., and a holding time of 1-5 hours.

[0016] In a specific embodiment, in step 4, the inert gas is one or more of nitrogen, argon and helium.

[0017] In one specific embodiment, in step four, the heating method of high temperature heat treatment is: passing an inert gas with a flow rate of 4-450 mL / min into a muffle furnace for temperature sintering, and keeping the high temperature at 700-900°C for 2-5h; the heating rate can be 1-10°C / min.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention firstly oxidizes medium-temperature coal tar pitch at low temperature to obtain a pre-oxidized carbon material, and then reacts the sulfur-doped material and the medium-temperature coal tar pitch at low temperature, so that the hydrogen ions of the medium-temperature coal tar pitch are replaced by sulfur to form relatively stable chemical bonds. The continuity of the chemical bonds is conducive to enhancing the stability of the structure. The sulfur atom doping not only provides active sites to increase the sodium storage capacity, but also expands the interlayer spacing to improve the rate performance. The introduction of oxygen functional groups promotes the mutual connection of aromatic carbon fragments, thereby increasing the interlayer spacing, forming closed pores, and increasing defect sites. This unique microstructural feature helps to balance the plateau capacity and high potential capacity. The high-temperature carbonization treatment converts large pores in the amorphous hard carbon material into small pores, increases the number of closed pores, improves the platform area capacity, and improves the cycle capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the sulfurization-carbonization of hard carbon in situ doped with pre-oxidized heavy organic matter according to the present invention. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0022] Example 1

[0023] A method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter comprises the following steps:

[0024] Step 1, low-temperature oxidation: 2 g of medium-temperature coal tar pitch is placed in a muffle furnace, and in an oxygen atmosphere, the temperature is raised to 300°C at a heating rate of 5°C / min, and a low-temperature oxidation heat treatment is performed for 2 hours. After the heat treatment, a pre-oxidized carbon material is obtained;

[0025] Step 2, element doping: 1g of medium-temperature coal tar pitch and 1g of elemental sulfur are ball-milled and mixed, and stirred evenly to obtain a hard carbon precursor doped with sulfur;

[0026] Step 3, low-temperature curing: placing the hard carbon precursor and the pre-oxidized carbon material in a reaction kettle at a mass ratio of 1:1, heating to 280°C, maintaining the constant temperature for 3 hours, and performing low-temperature curing. After low-temperature curing, a cured sulfur-doped pre-oxidized heavy organic hard carbon precursor is obtained;

[0027] Step 4, high temperature carbonization: The above-mentioned sulfur-doped pre-oxidized heavy organic hard carbon precursor is heated to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere, and subjected to high-temperature carbonization heat treatment for 2 hours. After the heat treatment, a sulfur-doped pre-oxidized heavy organic hard carbon precursor material with a stable structure is obtained.

[0028] Example 2

[0029] A method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter comprises the following steps:

[0030] Step 1, low-temperature oxidation: 2 g of medium-temperature coal tar pitch is placed in a muffle furnace, and in an oxygen atmosphere, the temperature is raised to 250°C at a heating rate of 5°C / min, and a low-temperature oxidation heat treatment is performed for 2 hours. After the heat treatment, a pre-oxidized carbon material is obtained;

[0031] Step 2, element doping: 1g of medium-temperature coal tar pitch and 1g of elemental sulfur are ball-milled and mixed, and stirred evenly to obtain a hard carbon precursor doped with sulfur;

[0032] Step 3, low-temperature curing: placing the hard carbon precursor and the pre-oxidized carbon material in a reaction kettle at a mass ratio of 1:1, heating to 280°C, maintaining the constant temperature for 3 hours, and performing low-temperature curing. After low-temperature curing, a cured sulfur-doped pre-oxidized heavy organic hard carbon precursor is obtained;

[0033] Step 4, high temperature carbonization: The above-mentioned sulfur-doped pre-oxidized heavy organic hard carbon precursor is heated to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere, and subjected to high-temperature carbonization heat treatment for 2 hours. After the heat treatment, a sulfur-doped pre-oxidized heavy organic hard carbon precursor material with a stable structure is obtained.

[0034] Example 3

[0035] A method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter comprises the following steps:

[0036] Step 1, low-temperature oxidation: 2 g of medium-temperature coal tar pitch is placed in a muffle furnace, and in an oxygen atmosphere, the temperature is raised to 300°C at a heating rate of 5°C / min, and a low-temperature oxidation heat treatment is performed for 2 hours. After the heat treatment, a pre-oxidized carbon material is obtained;

[0037] Step 2, element doping: 1g of medium-temperature coal tar pitch and 5g of elemental sulfur are ball-milled and mixed, and stirred evenly to obtain a hard carbon precursor doped with sulfur;

[0038] Step 3, low-temperature curing: placing the hard carbon precursor and the pre-oxidized carbon material in a reaction kettle at a mass ratio of 1:1, heating to 280°C, maintaining the constant temperature for 3 hours, and performing low-temperature curing. After low-temperature curing, a cured sulfur-doped pre-oxidized heavy organic hard carbon precursor is obtained;

[0039] Step 4, high temperature carbonization: The above-mentioned sulfur-doped pre-oxidized heavy organic hard carbon precursor is heated to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere, and subjected to high-temperature carbonization heat treatment for 2 hours. After the heat treatment, a sulfur-doped pre-oxidized heavy organic hard carbon precursor material with a stable structure is obtained.

[0040] Example 4

[0041] A method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter comprises the following steps:

[0042] Step 1, low-temperature oxidation: Place 1 g of medium-temperature coal tar pitch in a muffle furnace, heat it to 300°C at a heating rate of 5°C / min in an oxygen atmosphere, and perform low-temperature oxidation heat treatment for 2 hours. After the heat treatment, a pre-oxidized carbon material is obtained;

[0043] Step 2, element doping: 1g of medium-temperature coal tar pitch and 1g of elemental sulfur are ball-milled and mixed, and stirred evenly to obtain a hard carbon precursor doped with sulfur;

[0044] Step 3, low-temperature curing: placing the hard carbon precursor and the pre-oxidized carbon material in a reaction kettle at a mass ratio of 1:1, heating to 280°C, maintaining the constant temperature for 3 hours, and performing low-temperature curing. After low-temperature curing, a cured sulfur-doped pre-oxidized heavy organic hard carbon precursor is obtained;

[0045] Step 4, high temperature carbonization: The above-mentioned sulfur-doped pre-oxidized heavy organic hard carbon precursor is heated to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere, and subjected to high-temperature carbonization heat treatment for 2 hours. After the heat treatment, a sulfur-doped pre-oxidized heavy organic hard carbon precursor material with a stable structure is obtained.

[0046] Example 5

[0047] A method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter comprises the following steps:

[0048] Step 1, low-temperature oxidation: 2 g of medium-temperature coal tar pitch is placed in a muffle furnace, and in an oxygen atmosphere, the temperature is raised to 300°C at a heating rate of 5°C / min, and a low-temperature oxidation heat treatment is performed for 2 hours. After the heat treatment, a pre-oxidized carbon material is obtained;

[0049] Step 2, element doping: 1g of medium-temperature coal tar pitch and 1g of elemental sulfur are ball-milled and mixed, and stirred evenly to obtain a hard carbon precursor doped with sulfur;

[0050] Step 3, low-temperature curing: placing the hard carbon precursor and the pre-oxidized carbon material in a reaction kettle at a mass ratio of 1:1, heating to 280°C, maintaining the constant temperature for 2 hours, and performing low-temperature curing. After low-temperature curing, a cured sulfur-doped pre-oxidized heavy organic hard carbon precursor is obtained;

[0051] Step 4, high temperature carbonization: The above-mentioned sulfur-doped pre-oxidized heavy organic hard carbon precursor is heated to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere, and subjected to high-temperature carbonization heat treatment for 2 hours. After the heat treatment, a sulfur-doped pre-oxidized heavy organic hard carbon precursor material with a stable structure is obtained.

[0052] Example 6

[0053] A method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter comprises the following steps:

[0054] Step 1, low-temperature oxidation: 2 g of medium-temperature coal tar pitch is placed in a muffle furnace, and in an oxygen atmosphere, the temperature is raised to 300°C at a heating rate of 5°C / min, and a low-temperature oxidation heat treatment is performed for 2 hours. After the heat treatment, a pre-oxidized carbon material is obtained;

[0055] Step 2, element doping: 1g of medium-temperature coal tar pitch and 1g of elemental sulfur are ball-milled and mixed, and stirred evenly to obtain a hard carbon precursor doped with sulfur;

[0056] Step 3, low-temperature curing: placing the hard carbon precursor and the pre-oxidized carbon material in a reaction kettle at a mass ratio of 1:1, heating to 280°C, maintaining the constant temperature for 3 hours, and performing low-temperature curing. After low-temperature curing, a cured sulfur-doped pre-oxidized heavy organic hard carbon precursor is obtained;

[0057] Step 4, high temperature carbonization: The above-mentioned sulfur-doped pre-oxidized heavy organic hard carbon precursor is heated to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere, and subjected to high-temperature carbonization heat treatment for 2 hours. After the heat treatment, a sulfur-doped pre-oxidized heavy organic hard carbon precursor material with a stable structure is obtained.

[0058] Example 7

[0059] A method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter comprises the following steps:

[0060] Step 1, low-temperature oxidation: 2 g of medium-temperature coal tar pitch is placed in a muffle furnace, and in an oxygen atmosphere, the temperature is raised to 300°C at a heating rate of 5°C / min, and a low-temperature oxidation heat treatment is performed for 2 hours. After the heat treatment, a pre-oxidized carbon material is obtained;

[0061] Step 2, element doping: 1g of medium-temperature coal tar pitch and 1g of elemental sulfur are ball-milled and mixed, and stirred evenly to obtain a hard carbon precursor doped with sulfur;

[0062] Step 3, low-temperature curing: placing the hard carbon precursor and the pre-oxidized carbon material in a reaction kettle at a mass ratio of 1:1, heating to 280°C, maintaining the constant temperature for 3 hours, and performing low-temperature curing. After low-temperature curing, a cured sulfur-doped pre-oxidized heavy organic hard carbon precursor is obtained;

[0063] Step 4, high temperature carbonization: The above-mentioned sulfur-doped pre-oxidized heavy organic hard carbon precursor is heated to 800°C at a heating rate of 2.5°C / min under a nitrogen atmosphere, and subjected to high-temperature carbonization heat treatment for 2 hours. After the heat treatment, a sulfur-doped pre-oxidized heavy organic hard carbon precursor material with a stable structure is obtained.

[0064] Experimental example

[0065] The sulfur-doped pre-oxidized heavy organic hard carbon precursor material prepared in Examples 1-7 above is used as a negative electrode material for a sodium ion battery, and the gram capacity and cycle number of the negative electrode material for the sodium ion battery are tested;

[0066] The test method is: using the sulfur-doped pre-oxidized heavy organic hard carbon precursor material in Examples 1-7 as the negative electrode, the metal sodium sheet as the positive electrode, and 1.0 mol / L NaPF6 / EC (ethylene carbonate) + DMC (dimethyl carbonate) + FEC (fluoroethylene carbonate) (EC, DMC and FEC volume ratio 4.5:4.5:1) as the electrolyte, assemble into CR2032 button batteries in an argon glove box. The LAND battery test system is used to test constant current charge and discharge in the 0-2V voltage window. The test conditions and results are as follows:

[0067] Table 1

[0068]

[0069]

[0070] The button cell was subjected to constant current charge and discharge test at a current density of 500 mA / g, a voltage range of 0-2 V, and 100 cycles. The button half-cells of sulfur-doped pre-oxidized hard carbon materials prepared in Examples 1-7 all had good cycle retention rates (greater than 90%), showing excellent cycle stability. Specific values ​​are shown in Table 2 (Capacity retention rates of button half-cells of electrode materials prepared in Examples 1-7 after 100 cycles.)

[0071] Table 2

[0072] Current density 500mA / g 100 cycles capacity retention rate (%) Example 1 99.6 Example 2 99.4 Example 3 99.1 Example 4 94.7 Example 5 96.3 Example 6 94.2 Example 7 94.6

[0073] In summary, the present application proposes a method for preparing hard carbon by in-situ doping with pre-oxidized heavy organic matter, and the hard carbon material is used as a negative electrode material for sodium ion batteries, such as Figure 1As shown in the figure, medium-temperature coal tar pitch is first used as a precursor for low-temperature oxidation to obtain pre-oxidized carbon material, and then medium-temperature coal tar pitch is used as a precursor and elemental sulfur is used as a sulfur source dopant. The reaction between sulfur and asphalt at low temperature first occurs at the α-H hydrogen of the benzene ring side chain. As the temperature increases, β-H and γ-H will also be replaced by sulfur, and a small amount of hydrogen on the aromatic ring will be replaced by sulfur. When the reaction temperature rises to above 240°C, sulfur can directly react with the aromatic ring of asphalt to form asphaltene. The pre-oxidation process can introduce oxygen functional groups into the asphalt structure to promote the formation of extensive cross-linking. The asphalt is oxidized by air to form a cross-linked state. After carbonization, the interlayer spacing is larger, which is more conducive to sodium storage. At the same time, it can prevent the degree of graphitization, and no cross-linking agent is needed, which further controls the cost. During the low-temperature reaction, part of the elemental sulfur forms a chemical bond with the asphalt to form sulfide asphalt. In high-temperature carbonization, this relatively stable structure that forms chemical bonds in advance can prevent part of the sulfur from being lost directly after sublimation without reaction. High-temperature carbonization causes the large pores to become small pores due to the shrinkage of the carbon structure, increasing the number of closed pores, improving the platform capacity of the sodium-ion battery and improving the cycle performance.

[0074] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing hard carbon by in-situ doping and pre-oxidation of heavy organic matter, characterized in that: The following steps are involved: Step 1: Low-temperature oxidation: placing the medium-temperature coal tar pitch in an oxygen atmosphere for low-temperature heat treatment, and obtaining a pre-oxidized carbon material after the heat treatment; Step 2, element doping: ball-milling and mixing the medium-temperature coal tar pitch and the sulfur-doped material in proportion, stirring evenly to obtain a hard carbon precursor doped with sulfur; Step 3, low temperature curing: placing the hard carbon precursor and the pre-oxidized carbon material together in a reaction kettle, and curing at low temperature to obtain a cured sulfur-doped pre-oxidized heavy organic hard carbon precursor; Step 4, high temperature carbonization: subjecting the above sulfur-doped pre-oxidized heavy organic hard carbon precursor to high temperature heat treatment in an inert gas atmosphere. After the heat treatment, a sulfur-doped pre-oxidized heavy organic hard carbon precursor material with a stable structure is obtained.

2. The method for preparing hard carbon by in-situ doping and pre-oxidation of heavy organic matter according to claim 1, characterized in that: In step 1, the heating method of low temperature heat treatment is: introducing oxygen at a flow rate of 5-400 mL / min into a muffle furnace for temperature sintering, and keeping the temperature at a low temperature of 200-400° C. for 1-3 hours; The heating rate is 1-10℃ / min.

3. The method for preparing hard carbon by in-situ doping and pre-oxidation of heavy organic matter according to claim 1, characterized in that: In step 2, the element doping material includes one or more of elemental sulfur, thiourea, poly-2-hydroxymethylthiophene, 3-formaldehyde benzothiophene and sulfuric acid.

4. The method for preparing hard carbon by in-situ doping and pre-oxidation of heavy organic matter according to claim 1, characterized in that: In step 2, the mixing mass ratio of the medium-temperature coal tar pitch and the sulfur-doped material is 1:1-5.

5. The method for preparing hard carbon by in-situ doping and pre-oxidation of heavy organic matter according to claim 1, characterized in that: In step three, the mixing mass ratio of the hard carbon precursor and the pre-oxidized carbon material is 1:0.5-1.

6. The method for preparing hard carbon by in-situ doping and pre-oxidation of heavy organic matter according to claim 1, characterized in that: In step three, the low temperature curing conditions are: at a temperature of 150-300° C., and a holding time of 1-5 hours.

7. The method for preparing hard carbon by in-situ doping and pre-oxidation of heavy organic matter according to claim 1, characterized in that: In step 4, the inert gas is one or more of nitrogen, argon and helium.

8. The method for preparing hard carbon by in-situ doping and pre-oxidation of heavy organic matter according to claim 1, characterized in that: In step 4, the heating method of high temperature heat treatment is: passing an inert gas with a flow rate of 4-450 mL / min into a muffle furnace for temperature sintering, and keeping the high temperature at 700-900° C. for 2-5 hours; The heating rate can be 1-10°C / min.

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