A method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter

Abstract

The present invention relates to the technical field of anode materials for sodium-ion batteries, and discloses a method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter, which includes the following steps: Step 1, low-temperature oxidation: After heat treatment, a pre-oxidized carbon material is obtained; Step 2, element doping: A hard carbon precursor doped with sulfur elements is obtained; Step 3, low-temperature curing: A cured hard carbon precursor of pre-oxidized heavy organic matter doped with sulfur elements is obtained; Step 4, high-temperature carbonization: A hard carbon precursor material of pre-oxidized heavy organic matter doped with sulfur elements with a stable structure is obtained; In the present invention, medium-temperature coal tar pitch is first low-temperature oxidized to obtain a pre-oxidized carbon material, and then the sulfur element-doped material and medium-temperature coal tar pitch are reacted at low temperature, so that the hydrogen ions in the medium-temperature coal tar pitch are replaced by sulfur to form relatively stable chemical bonds. The continuity of the chemical bonds is beneficial to enhancing the stability of the structure. The doping of sulfur atoms not only provides active sites to increase the sodium storage capacity, but also expands the interlayer spacing to improve the rate performance.

Description

Technical Field

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

[0002] Hard carbon refers to carbon that is difficult to be graphitized, mainly obtained by pyrolyzing high molecular polymers. According to the pyrolysis temperature and different precursor materials, hard carbon can be mainly divided into high-temperature pyrolysis carbon, low-temperature pyrolysis carbon, resin carbon, heavy organic matter carbon, biomass carbon, carbon black, etc.

[0003] In the hard carbon material for the anode of sodium-ion batteries, the doped sulfur atoms use elemental sulfur as the sulfur source. Elemental sulfur is a yellow powder, also known as sulfur. After inhaling sulfur dust for a long time, symptoms such as fatigue, dizziness, and indigestion are likely to occur. Workers should do a good job in protection. Powdered sulfur is stored in a ventilated and dry warehouse. During transportation, sulfur powder must be protected from moisture. When loading and unloading, handle it with care to prevent moisture absorption due to damaged packaging.

[0004] Heteroatom doping can significantly improve the sodium storage performance of carbon materials. However, current related research still has problems such as cumbersome doping process operations, low heteroatom content, low initial Coulomb efficiency of the material, and unstable cycling performance. 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 a high heteroatom content and excellent electrochemical performance for application in the anode of sodium-ion batteries. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing hard carbon by in-situ doping of pre-oxidized heavy organic matter to solve the problems raised in the above background art.

[0006] To achieve the above purpose, the present invention provides the following technical solution: A method for preparing hard carbon by in-situ doping of pre-oxidized heavy organic matter, comprising the following steps:

[0007] Step 1, Low-temperature oxidation: Place medium-temperature coal tar pitch in an oxygen atmosphere for low-temperature heat treatment, and obtain pre-oxidized carbon materials after the heat treatment ends;

[0008] Step 2, Element doping: Ball-mill and mix medium-temperature coal tar pitch and a sulfur element doping material in proportion, and obtain a hard carbon precursor doped with sulfur element after stirring evenly;

[0009] Step 3, Low-temperature curing: Place the above hard carbon precursor and pre-oxidized carbon materials together in a reaction kettle, and obtain a cured hard carbon precursor of pre-oxidized heavy organic matter doped with sulfur element after low-temperature curing;

[0010] Step 4. High-temperature carbonization: Heat-treat the sulfur element-doped pre-oxidized heavy organic matter hard carbon precursor in an inert gas atmosphere. After the heat treatment is completed, a stable structure sulfur element-doped pre-oxidized heavy organic matter hard carbon precursor material is obtained.

[0011] In a specific embodiment, in Step 1, the heating method for low-temperature heat treatment is: Introduce oxygen with a flow rate of 5 - 400 mL / min into a muffle furnace for temperature sintering, keep the temperature at 200 - 400 °C for 1 - 3 h; 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-formylbenzothiophene, and sulfuric acid.

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

[0014] In a specific embodiment, in Step 3, 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 3, the conditions for low-temperature curing are: at a temperature of 150 - 300 °C, keep the time for 1 - 5 h.

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

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

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] In the present invention, the medium-temperature coal tar pitch is first low-temperature oxidized to obtain a pre-oxidized carbon material, and then the sulfur element doping material and the medium-temperature coal tar pitch are reacted at low temperature, so that the hydrogen ions in the medium-temperature coal tar pitch are replaced by sulfur to form relatively stable chemical bonds. The continuity of the chemical bonds is beneficial to enhancing the structural stability. The sulfur atom doping not only provides active sites to increase the sodium storage capacity, but also expands the layer spacing to improve the rate performance; the introduction of oxygen functional groups promotes the mutual connection of aromatic carbon fragments, thereby increasing the layer spacing, forming closed pores, and increasing defect sites. This unique microstructure feature helps to balance the plateau capacity and the high-potential capacity. The high-temperature carbonization treatment changes the macropores in the amorphous hard carbon material into micropores, increases the number of closed pores, improves the capacity in the plateau region, and improves the cycle capacity. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of sulfidation - carbonization of hard carbon of in - situ doped pre - oxidized heavy organic matter of the present invention. Detailed Embodiments

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

[0022] Embodiment 1

[0023] A method for preparing hard carbon of in - situ doped pre - oxidized heavy organic matter includes the following steps:

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

[0025] Step 2, element doping: Ball - mill and mix 1 g of medium - temperature coal tar pitch and 1 g of elemental sulfur, and stir evenly to obtain a hard - carbon precursor doped with sulfur element;

[0026] Step 3, low - temperature curing: Place the above - mentioned hard - carbon precursor and pre - oxidized carbon material in a reaction kettle at a mass ratio of 1:1, heat it to 280 °C, and keep it at a constant temperature for 3 h for low - temperature curing. After low - temperature curing, a cured hard - carbon precursor of pre - oxidized heavy organic matter doped with sulfur element is obtained;

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

[0028] Embodiment 2

[0029] A method for preparing hard carbon of in - situ doped pre - oxidized heavy organic matter includes the following steps:

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

[0031] Step 2, element doping: Ball - mill and mix 1 g of medium - temperature coal tar pitch and 1 g of elemental sulfur, and stir evenly to obtain a hard - carbon precursor doped with sulfur element;

[0032] Step 3. Low-temperature curing: Place the above-mentioned hard carbon precursor and pre-carbonized material in a reaction kettle at a mass ratio of 1:1, heat up to 280 °C, keep the temperature constant for 3 h for low-temperature curing. After low-temperature curing, a cured pre-carbonized heavy organic matter hard carbon precursor doped with sulfur element is obtained;

[0033] Step 4. High-temperature carbonization: Under a nitrogen atmosphere, heat the above-mentioned pre-carbonized heavy organic matter hard carbon precursor doped with sulfur element to 800 °C at a heating rate of 5 °C / min, and conduct high-temperature carbonization heat treatment for 2 h. After the heat treatment is completed, a pre-carbonized heavy organic matter hard carbon precursor material with a stable structure doped with sulfur element is obtained.

[0034] Example 3

[0035] A method for preparing hard carbon by in-situ doping of pre-carbonized heavy organic matter, comprising the following steps:

[0036] Step 1. Low-temperature oxidation: Place 2 g of medium-temperature coal tar pitch in a muffle furnace, under an oxygen atmosphere, heat up to 300 °C at a heating rate of 5 °C / min, and conduct low-temperature oxidation heat treatment for 2 h. After the heat treatment is completed, a pre-carbonized material is obtained;

[0037] Step 2. Element doping: Ball-mill and mix 1 g of medium-temperature coal tar pitch and 5 g of elemental sulfur, and stir evenly to obtain a hard carbon precursor doped with sulfur element;

[0038] Step 3. Low-temperature curing: Place the above-mentioned hard carbon precursor and pre-carbonized material in a reaction kettle at a mass ratio of 1:1, heat up to 280 °C, keep the temperature constant for 3 h for low-temperature curing. After low-temperature curing, a cured pre-carbonized heavy organic matter hard carbon precursor doped with sulfur element is obtained;

[0039] Step 4. High-temperature carbonization: Under a nitrogen atmosphere, heat the above-mentioned pre-carbonized heavy organic matter hard carbon precursor doped with sulfur element to 800 °C at a heating rate of 5 °C / min, and conduct high-temperature carbonization heat treatment for 2 h. After the heat treatment is completed, a pre-carbonized heavy organic matter hard carbon precursor material with a stable structure doped with sulfur element is obtained.

[0040] Example 4

[0041] A method for preparing hard carbon by in-situ doping of pre-carbonized heavy organic matter, comprising the following steps:

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

[0043] Step 2. Element doping: Grind and mix 1 g of medium-temperature coal tar pitch and 1 g of elemental sulfur, and stir evenly to obtain a hard carbon precursor doped with sulfur element;

[0044] Step 3. Low-temperature curing: Place the above hard carbon precursor and pre-oxidized carbon material in a reaction kettle in a mass ratio of 1:1, heat up to 280 °C, keep the temperature constant for 3 h for low-temperature curing. After low-temperature curing, a cured hard carbon precursor of pre-oxidized heavy organic matter doped with sulfur element is obtained;

[0045] Step 4. High-temperature carbonization: Heat the above hard carbon precursor of pre-oxidized heavy organic matter doped with sulfur element to 800 °C at a heating rate of 5 °C / min in a nitrogen atmosphere, and conduct high-temperature carbonization heat treatment for 2 h. After the heat treatment is completed, a hard carbon precursor material of pre-oxidized heavy organic matter with a stable structure doped with sulfur element is obtained.

[0046] Example 5

[0047] A method for preparing hard carbon by in-situ doping of pre-oxidized heavy organic matter, comprising the following steps:

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

[0049] Step 2. Element doping: Grind and mix 1 g of medium-temperature coal tar pitch and 1 g of elemental sulfur, and stir evenly to obtain a hard carbon precursor doped with sulfur element;

[0050] Step 3. Low-temperature curing: Place the above hard carbon precursor and pre-oxidized carbon material in a reaction kettle in a mass ratio of 1:1, heat up to 280 °C, keep the temperature constant for 2 h for low-temperature curing. After low-temperature curing, a cured hard carbon precursor of pre-oxidized heavy organic matter doped with sulfur element is obtained;

[0051] Step 4. High-temperature carbonization: Heat the above hard carbon precursor of pre-oxidized heavy organic matter doped with sulfur element to 800 °C at a heating rate of 5 °C / min in a nitrogen atmosphere, and conduct high-temperature carbonization heat treatment for 2 h. After the heat treatment is completed, a hard carbon precursor material of pre-oxidized heavy organic matter with a stable structure doped with sulfur element is obtained.

[0052] Example 6

[0053] A method for preparing hard carbon by in-situ doping of pre-oxidized heavy organic matter, comprising the following steps:

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

[0055] Step 2. Element doping: Ball-mill and mix 1 g of medium-temperature coal tar pitch and 1 g of elemental sulfur, and stir evenly to obtain a hard carbon precursor doped with sulfur element;

[0056] Step 3. Low-temperature curing: Place the above hard carbon precursor and pre-oxidized carbon material in a reaction kettle in a mass ratio of 1:1, heat it to 280 °C, and keep it at a constant temperature for 3 h for low-temperature curing. After low-temperature curing, a cured hard carbon precursor of pre-oxidized heavy organic matter doped with sulfur element is obtained;

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

[0058] Example 7

[0059] A method for preparing hard carbon by in-situ doping of pre-oxidized heavy organic matter, comprising the following steps:

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

[0061] Step 2. Element doping: Ball-mill and mix 1 g of medium-temperature coal tar pitch and 1 g of elemental sulfur, and stir evenly to obtain a hard carbon precursor doped with sulfur element;

[0062] Step 3. Low-temperature curing: Place the above hard carbon precursor and pre-oxidized carbon material in a reaction kettle in a mass ratio of 1:1, heat it to 280 °C, and keep it at a constant temperature for 3 h for low-temperature curing. After low-temperature curing, a cured hard carbon precursor of pre-oxidized heavy organic matter doped with sulfur element is obtained;

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

[0064] Experimental example

[0065] The sulfur element-doped pre-oxidized heavy organic matter hard carbon precursor materials prepared in the above Examples 1-7 are used as the negative electrode materials of sodium-ion batteries, and the specific capacity and cycle number of the negative electrode materials of the sodium-ion batteries are tested;

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

[0067] Table 1

[0068]

[0069]

[0070] The button batteries are tested for constant current charge and discharge at a current density of 500 mA / g, the voltage range is 0-2V, and the cycle is 100 times. The button half-cells of the sulfur element-doped pre-oxidized hard carbon materials prepared in Examples 1-7 all have good cycle retention rates (greater than 90%), showing excellent cycle stability. The specific values are shown in Table 2 (the capacity retention rate of the button half-cells of the electrode materials prepared in Examples 1-7 after 100 cycles).

[0071] Table 2

[0072] Current density 500 mA / g Retention capacity ratio of 100 cycles (%) 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 of pre-oxidized heavy organic matter. The hard carbon material is used as the negative electrode material of a sodium-ion battery, such as Figure 1As shown, first, mesophase pitch is used as a precursor for low-temperature oxidation to obtain a pre-oxidized carbon material. Then, mesophase pitch is used as a precursor, and elemental sulfur is used as a sulfur source dopant. The reaction between sulfur and pitch at low temperature first occurs at the α-H hydrogen of the benzene ring side chain. As the temperature rises, β-H and γ-H will also be substituted by sulfur, and a small amount of hydrogen on the aromatic ring will be substituted by sulfur. When the reaction temperature rises above 240 °C, sulfur can directly react with the aromatic ring of pitch to form asphaltene. The pre-oxidation process can introduce oxygen functional groups into the pitch structure to promote extensive cross-linking formation. The pitch 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 also prevent the degree of graphitization without using a cross-linking agent, further controlling the cost. During the low-temperature reaction process, part of the sulfur element forms chemical bonds with pitch to generate sulfurized pitch. In high-temperature carbonization, this relatively stable structure with pre-formed chemical bonds can prevent part of the sulfur from sublimating and directly flowing away without reaction. High-temperature carbonization causes macropores to become micropores due to the shrinkage of the carbonaceous structure, increasing the number of closed pores, improving the sodium-ion battery platform capacity, and enhancing the cycling performance.

[0074] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter, characterized in that, It includes the following steps: Step 1, low-temperature oxidation: Place medium-temperature coal tar pitch in an oxygen atmosphere for low-temperature heat treatment, and obtain a pre-oxidized carbon material after the heat treatment ends; Step 2, element doping: Ball-mill and mix medium-temperature coal tar pitch and a sulfur element doping material in proportion. The mixing mass ratio of medium-temperature coal tar pitch and the sulfur element doping material is 1:1 - 5. The sulfur element doping material includes one or both of elemental sulfur and thiourea. After stirring evenly, a sulfur element-doped hard carbon precursor is obtained; Step 3, low-temperature curing: Place the above-mentioned hard carbon precursor and the pre-oxidized carbon material together in a reaction kettle. The mixing mass ratio of the hard carbon precursor and the pre-oxidized carbon material is 1:0.5 - 1. After low-temperature curing, the conditions for low-temperature curing are: at a temperature of 150 - 300 °C, keep for 1 - 5 h to obtain a cured sulfur element-doped pre-oxidized heavy organic matter hard carbon precursor; Step 4, high-temperature carbonization: Conduct high-temperature heat treatment on the above-mentioned sulfur element-doped pre-oxidized heavy organic matter hard carbon precursor in an inert gas atmosphere. After the heat treatment ends, a stable structure sulfur element-doped pre-oxidized heavy organic matter hard carbon precursor material is obtained.

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

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

4. A method for preparing hard carbon by in-situ doping and pre-oxidizing heavy organic matter according to claim 1, characterized in that: In Step 4, the heating method for high-temperature heat treatment is: Pass an inert gas with a flow rate of 4 - 450 mL / min in a muffle furnace for temperature sintering, keep at a high temperature of 700 - 900 °C for 2 - 5 h; The heating rate is 1 - 10 °C / min.

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