Coal-based negative electrode material and preparation method thereof

Abstract

The present invention discloses a coal-based negative electrode material and a preparation method thereof. The method comprises: selecting coal having an inertin content greater than 40% in its macerals as screening coal; deashing the screened coal to obtain deashed coal; and carbonizing the deashed coal to obtain the coal-based negative electrode material. The present invention screens the coal used for preparing the negative electrode material through coal petrological analysis to determine the characteristics of the coal type used for preparing the negative electrode material; deashing the screened coal to reduce the ash content of the deashed coal to less than 0.1%, thereby ultimately preparing the coal-based negative electrode material and achieving efficient utilization of coal.

Description

Technical Field

[0001] The present disclosure relates to the field of carbon materials, and in particular to a coal-based negative electrode material and a preparation method thereof. Background Art

[0002] my country has a large coal consumption and high carbon dioxide emissions. In order to seek efficient utilization of coal in the low-carbon era, the development of coal-based carbon material technology has become a hot topic in the research field of the coal industry.

[0003] CN114789998A discloses a negative electrode material, a preparation method thereof, and a battery. The negative electrode material is prepared by high-temperature treatment, mixed with graphite, and then homogenized under high pressure to prepare a composite powder of the coal-based material and graphene by spraying, which has excellent sodium storage performance.

[0004] CN105185997A discloses a sodium ion secondary battery negative electrode material, its preparation method and use. The material is an amorphous carbon material, which is obtained by high-temperature cracking of coal as the main raw material: coal and a hard carbon precursor are used as raw materials, a solvent is added, and then mechanically mixed, dried, and then cross-linked, cured, and cracked under an inert atmosphere.

[0005] CN113493193A discloses an amorphous carbon material and a preparation method thereof, a sodium ion battery negative electrode and a sodium ion battery. The amorphous carbon material is obtained by purifying coal to reduce the ash content of the coal to less than 10%, and then granulating, extracting and carbonizing the coal to obtain the amorphous carbon material, which is suitable for use in sodium ion batteries.

[0006] Given the complex conditions of coal formation and the diverse types and structural properties that significantly impact the performance of coal-based anode materials, there is currently a lack of efficient technical solutions for using coal to prepare anode materials. For example, CN114789998A and CN105185997A do not select the type of coal used; whereas CN113493193A primarily selects coal based on its macroscopic properties rather than its structural characteristics. For example, clean coal with a volatile matter content of 10-50 wt.%, a caking index of <50, and an ash content of <10 wt.% is selected. The clean coal is then subjected to solvent extraction, followed by carbonization of the residue to prepare the anode material. Furthermore, the ash content in the residue is concentrated, which reduces the quality and performance of the carbon material. Summary of the Invention

[0007] The purpose of the present invention is to provide a coal-based negative electrode material and a preparation method thereof, which can screen out the types of coal suitable for preparing the coal-based negative electrode material from the source, thereby achieving efficient utilization of coal.

[0008] To achieve the above-mentioned object of the invention, the present invention provides a method for preparing a coal-based negative electrode material, comprising the following steps:

[0009] (1) Coal with an inertin content greater than 40% in its macerals is used as screening coal;

[0010] (2) removing ash from the screened coal to obtain removed ash coal;

[0011] (3) Carbonizing the deashed coal to obtain a coal-based negative electrode material.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] First, the present invention screens the coal used to prepare the coal-based negative electrode material through coal petrological analysis, requiring that the inertin content in the screened coal be greater than 40%, thereby determining the characteristics of the coal used to prepare the coal-based negative electrode material;

[0014] Second, the present invention efficiently removes ash from the screened coal that meets the requirements, and the ash content of the removed coal is reduced to less than 0.1%;

[0015] 3. The present invention can screen out coal that is more suitable for preparing coal-based negative electrode materials, and then prepare coal-based negative electrode materials through existing processes to achieve efficient utilization of coal. DETAILED DESCRIPTION

[0016] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0017] Unless otherwise specified, the materials and instruments used in the embodiments of the present invention can be obtained from commercial channels.

[0018] The present invention provides a method for preparing a coal-based negative electrode material, comprising the following steps:

[0019] (1) Coal with an inertin content greater than 40% in its macerals is used as screening coal;

[0020] (2) performing ash removal treatment on the screened coal to obtain ash-removed coal;

[0021] (3) Carbonizing the deashed coal to obtain a coal-based negative electrode material.

[0022] In the present invention, the coal macerals in step (1) are the components of coal under a microscope, including vitrinite, inertinite, exinite and mineral group.

[0023] Those skilled in the art will understand that the vitrinite is formed by gelation of plant residues, the inertinite is formed by charring, the exinite is formed by lipid substances in plant remains, and the mineral group is mainly derived from inorganic minerals in coal.

[0024] Furthermore, the inorganic minerals are the main components of coal ash and will be removed during the ash removal process.

[0025] Those skilled in the art will understand that the volatile matter yield of the exinite is the highest, followed by the vitrinite, and the inertinite is the lowest. This is because the chain compounds with low thermal decomposition resistance account for a large proportion of the exinite, while the inertinite is mainly composed of condensed aromatic structures with strong thermal decomposition resistance, and the vitrinite is between the two.

[0026] In the present invention, the calculation method of the inertin content in step (1) is M 惰质组 / (M 镜质组 +M 惰质组 +M 壳质组 );

[0027] Among them, M 惰质组 is the volume content of inertinite in the coal macerals, M 镜质组 is the volume content of vitrinite in the coal macerals, M 壳质组 is the volume content of exinite in the coal macerals.

[0028] In the present invention, the inertinite content is the content of inertinite in the coal macerals without considering the mineral groups in the coal macerals, and the sum of the contents of vitrinite, inertinite and exinite is taken as 100%.

[0029] Furthermore, the content of inertinite, vitrinite and exinite in the coal macerals can be obtained by analysis and detection in accordance with national standards GB / T 16773-2008 (method for preparation of coal rock analysis samples) and GB / T 8899-2013 (method for grouping and mineral determination of coal macerals).

[0030] In the present invention, the screened coal in step (1) is a coal with an inertin content greater than 40%, preferably a coal with an inertin content greater than 50%, more preferably a coal with an inertin content greater than 60%, and most preferably a coal with an inertin content greater than 70%.

[0031] The inventors of the present application have discovered that when the inertin content in coal is greater than 40%, the coal-based negative electrode material prepared after ash removal has excellent performance. This is because the inertin content in the carbonization stage is small, and after carbonization treatment, it is more conducive to the formation of a coal-based negative electrode material with a relatively uniform and stable structure, and the influence of the residual vitrinite and exinite after carbonization is significantly reduced.

[0032] The present invention does not limit the method of removing ash in step (2), which may be a physical method, a chemical method, or a combination of physical and chemical methods in the art.

[0033] In some embodiments, in order to reduce the ash content in the deashed coal as much as possible and reduce the impact of the chemical components in the ash on the product coal-based negative electrode material, the deashing method in step (2) is preferably a chemical method, or a combination of physical and chemical methods.

[0034] Those skilled in the art will understand that among the chemical methods, the hydrofluoric acid method (HF / HCl) has the highest ash removal efficiency. However, hydrofluoric acid is harmful to the human body and the environment, and can corrode equipment materials and factory buildings. Therefore, conventional acids and alkalis can be used instead of hydrofluoric acid.

[0035] Furthermore, the conventional acid and alkali are conventional acids used for coal ash removal, such as hydrochloric acid, sulfuric acid, and nitric acid, and conventional alkalis used for coal ash removal, such as sodium hydroxide and potassium hydroxide.

[0036] In some embodiments, the conventional acid-base method can be used to remove coal ash using a combination of HCl / NaOH, a combination of HNO3 / NaOH, and a combination of H2SO4 / NaOH.

[0037] Those skilled in the art will understand that although the dust removal efficiency of the conventional acid-base method is not as good as that of the hydrofluoric acid method, the conventional acid-base method has obvious advantages in terms of economic and environmental benefits, and under certain conditions, the dust removal effect of the conventional acid-base method can be comparable to that of the hydrofluoric acid method.

[0038] In some embodiments, the ash content of the deashed coal in step (2) can be reduced to 0.5%, preferably less than 0.2%, and more preferably less than 0.1%.

[0039] Those skilled in the art will understand that coal-based negative electrode materials made from deashed coal with low ash content can effectively avoid the charge / discharge inert elements in the ash acting as invalid components leading to reduced battery performance, as well as harmful elements in the ash (such as Fe) interacting with the positive and negative electrodes and the electrolyte, increasing the risk of battery use and reducing battery life.

[0040] In some embodiments, the ash-removed coal may be ground before carbonization to a particle size of D 50 =1-100 μm, preferably 2-50 μm, more preferably 3-25 μm.

[0041] The inventors of the present application have found that a preferred particle size can improve the capacity and first coulombic efficiency (first efficiency) of the coal-based negative electrode material.

[0042] Furthermore, the grinding process only needs to ensure that the particle size D of the coal-based negative electrode material is 50 The timing of the grinding process is not limited as long as the requirements are met. For example, the grinding process can also be performed after the carbonization in step (3), and the particle size requirement remains unchanged.

[0043] In some embodiments, in step (3), the carbonization temperature is 600-2200° C., and the carbonization time is 0.1-50 h;

[0044] Preferably, the carbonization temperature is 700-2100° C., and the carbonization time is 0.5-40 h;

[0045] More preferably, the carbonization temperature is 900-1600° C., and the carbonization time is 1-20 h.

[0046] Those skilled in the art will understand that by adjusting carbonization conditions such as temperature and time, the performance of the negative electrode material can be optimized, such as the capacity and first coulombic efficiency (first efficiency) of the negative electrode material.

[0047] Furthermore, the carbonization is carried out under the protection of an inert gas (such as nitrogen).

[0048] The second aspect of the present invention provides a coal-based negative electrode material prepared by the above preparation method.

[0049] In order to better understand the technical solution of the present invention, the present invention is described in detail below with reference to specific embodiments.

[0050] (1) Coal petrology analysis

[0051] Coal petrology analysis was performed on selected coals according to the national standards GB / T 16773-2008 (methods for sample preparation for coal petrography) and GB / T8899-2013 (methods for maceral grouping and mineralogical determination of coal). When calculating the vitrinite, inertinite, and exinite contents in the coal, the mineral groups in the macerals were not considered, and the sum of the contents of the vitrinite, inertinite, and exinite was taken as 100% of the total.

[0052] That is, the calculation method of inertin content is M 惰质组 / (M 镜质组 +M 惰质组 +M 壳质组 ),

[0053] Among them, M 惰质组 is the volume content of inertinite in the coal macerals, M 镜质组 is the volume content of vitrinite in the coal macerals, M 壳质组 is the volume content of exinite in the coal macerals.

[0054] (2) Particle size (D 50 )

[0055] Particle size D 50The particle size was measured using a Malvern Mastersizer 2000 laser particle size analyzer manufactured by Malvern Instruments Ltd., UK.

[0056] (3) Battery performance

[0057] The charge and discharge capacity (capacity) and first coulomb efficiency (first efficiency) of the battery were tested by using a battery test system CT2001A battery tester of Wuhan Blue Electric Electronics Co., Ltd., with a current of 0.1C (1C = 300mAh / g) and a voltage of 0-3V.

[0058] In some embodiments, the coal samples AF are coal samples selected from different coal mines and coal seams, and are used for coal petrological analysis and preparation of coal-based negative electrode materials after ash removal.

[0059] Example 1

[0060] The preparation of coal-based negative electrode materials includes the following steps:

[0061] (1) Coal petrology analysis

[0062] Coal petrological analysis of coal sample A (excluding 3.0% of the mineral group in the microscopic components) showed that the vitrinite content was 58.6%, the inertinite content was 41.4%, and the exinite content was 0%.

[0063] (2) Coal ash removal

[0064] Coal sample A was deashed using a conventional acid-base method (HCl / NaOH). The ash content of the deashed coal was 0.07%. The specific steps were as follows:

[0065] 400 g of coal sample A, 700 g of sodium hydroxide and 400 ml of water were mixed, kneaded and reacted at 150 ° C for 3 h, and then cooled with water and filtered and washed to obtain alkaline deashed coal;

[0066] According to the acid-coal ratio of 1:1 (volume / weight ratio of concentrated hydrochloric acid to alkaline deashed coal), diluted hydrochloric acid with a concentration of 10 wt.% was added to the alkaline deashed coal, stirred and reacted at 60°C for 0.5h, then filtered, washed and dried to obtain deashed coal.

[0067] (3) Preparation of coal-based negative electrode materials

[0068] The deashed coal was ground using a drum ball mill to obtain D 50 =7μm deashing coal particles;

[0069] Under nitrogen protection, the ash-removed coal particles were carbonized in a horizontal carbonization furnace at 1200°C for 3 hours to obtain coal-based negative electrode materials.

[0070] (4) Performance testing

[0071] Coal-based negative electrode materials are used as the main raw materials to prepare negative electrode sheets, and sodium-ion batteries are assembled to test capacity and initial efficiency.

[0072] Example 2

[0073] The difference from Example 1 is that the object of coal petrological analysis in step (1) is coal sample B (excluding the 5.1% mineral group in the microscopic components), which has a vitrinite content of 46.9%, an inertinite content of 50.0%, and an exinite content of 3.1%;

[0074] The ash content of the deashed coal in step (2) is 0.08%.

[0075] Example 3

[0076] The difference from Example 1 is that the object of coal petrological analysis in step (1) is coal sample C (excluding 2.3% of the mineral group in the microscopic components), whose vitrinite content is 38.3%, the inertinite content is 56.4%, and the exinite content is 5.3%.

[0077] The ash content of the deashed coal in step (2) is 0.07%.

[0078] Example 4

[0079] The difference from Example 1 is that the object of coal petrological analysis in step (1) is coal sample D (excluding 1.8% of the mineral group in the microscopic components), which has a vitrinite content of 36.3%, an inertinite content of 62.8%, and an exinite content of 0.9%;

[0080] The ash content of the deashed coal in step (2) is 0.06%.

[0081] Example 5

[0082] The difference from Example 1 is that the object of coal petrological analysis in step (1) is coal sample E (excluding the 2.1% mineral group in the microscopic components), which has a vitrinite content of 29.2%, an inertinite content of 70.2%, and an exinite content of 0.6%;

[0083] The ash content of the deashed coal in step (2) is 0.05%.

[0084] Example 6

[0085] The difference from Example 5 is that step (2) adopts conventional acid-base method (HNO3 / NaOH) for deashing, and concentrated hydrochloric acid is replaced by concentrated nitric acid; the ash content of the deashed coal is 0.05%.

[0086] The particle size D of the ball milling treatment in step (3)50 5μm.

[0087] Example 7

[0088] The difference from Example 5 is that in step (2), conventional acid-base method (H2SO4 / NaOH) is used for deashing, and concentrated hydrochloric acid is replaced by concentrated sulfuric acid. The ash content of the deashed coal is 0.35%.

[0089] The particle size D of the ball milling treatment in step (3) 50 5μm.

[0090] Example 8

[0091] The difference from Example 5 is that step (2) uses hydrofluoric acid method (HF / HCl) to remove ash, and the ash content of the removed coal is 0.06%. The specific steps are:

[0092] Take 400g of coal sample E, add 1000ml of 4% hydrofluoric acid, react at room temperature for 1h, and then filter. Add 1000ml of 5% hydrochloric acid to the filter cake, react at 60℃ for 1h, and then filter. Wash and dry the filter cake to obtain deashed coal.

[0093] The particle size D of the ball milling treatment in step (3) 50 5μm.

[0094] Example 9

[0095] The difference from Example 5 is that the particle size D of the ball milling process in step (3) is 50 The carbonization conditions are 900℃ and 16h.

[0096] Example 10

[0097] The difference from Example 5 is that the particle size D of the ball milling process in step (3) is 50 The carbonization conditions are 1600℃ and 1h.

[0098] Comparative Example

[0099] The difference from Example 1 is that the object of coal petrological analysis in step (1) is coal sample F, whose vitrinite content is 65.9%, inertinite content is 34.1%, and exinite content is 0%.

[0100] Test Case

[0101] The coal-based negative electrode material obtained in the embodiment and the comparative example was mixed evenly with the conductive carbon black Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 92:3:5, and the solvent N-methylpyrrolidone (NMP) was added to stir into a negative electrode slurry, evenly coated on aluminum foil, and dried to obtain a negative electrode sheet. The negative electrode sheet was punched into a sheet with a diameter of 12 mm, transferred to an MBraun2000 glove box (Ar atmosphere), and assembled into a button cell with a metal sodium sheet as a reference electrode. The charge and discharge capacity (capacity) and the first coulomb efficiency (first effect) of the button cell were tested, and the test results are shown in Tables 1 and 2.

[0102] Table 1:

[0103]

[0104]

[0105] Table 2:

[0106]

[0107] As shown in Table 1, after deducting the mineral group, the higher the inert group content in the coal, the higher the capacity and initial efficiency of the coal-based anode material prepared after ash removal, that is, the better the performance. When the inert group content exceeds 40%, the capacity and initial efficiency of the coal-based anode material are significantly improved. When the inert group content exceeds 70%, the resulting coal-based anode material has a capacity greater than 300 mAh / g and an initial efficiency greater than 90%.

[0108] It can be seen from Examples 5-8 in Table 2 that the screened coal provided by the present invention is deashed using different chemical methods. When the ash content in the deashed coal is relatively high, the capacity and first efficiency of the prepared coal-based negative electrode material are low. When the ash content in the coal is reduced to below 0.1%, the capacity and first efficiency of the negative electrode material can be significantly improved. It can be seen from Examples 9 and 10 that carbonization at higher or lower temperatures within the range specified by the present invention, as well as ball milling with a particle size that is too large or too small, will reduce the capacity and first efficiency of the negative electrode material.

Claims

1. A method for preparing a coal-based negative electrode material, characterized in that: The steps include: (1) Coal with an inertin content greater than 40% in its macerals is considered screening coal; (2) removing ash from the screened coal to obtain removed ash coal; (3) carbonizing the deashed coal to obtain a coal-based negative electrode material; The coal macerals in step (1) are the components of coal under a microscope, including vitrinite, inertinite, exinite and mineral group; The inertin content in step (1) is given by the formula M 惰质组 / (M 镜质组 +M 惰质组 +M 壳质组 ) calculation, where M 惰质组 is the volume content of inertinite in the coal macerals, M 镜质组 is the volume content of vitrinite in the coal macerals, M 壳质组 is the volume content of exinite in the maceral components of coal; The ash content of the deashed coal in step (2) is less than 0.1%.

2. The method for preparing a coal-based negative electrode material according to claim 1, characterized in that: The coal screened in step (1) is coal having an inertinite volume content greater than 50%.

3. The method for preparing a coal-based negative electrode material according to claim 2, characterized in that: The coal screened in step (1) is coal having an inertinite volume content greater than 60%.

4. The method for preparing a coal-based negative electrode material according to claim 3, characterized in that: The coal screened in step (1) is coal having an inertinite volume content greater than 70%.

5. The method for preparing a coal-based negative electrode material according to claim 1, wherein: The ash removal method in step (2) is chemical ash removal or a combination of physical and chemical ash removal.

6. The method for preparing a coal-based negative electrode material according to claim 1, wherein: The carbonization temperature in step (3) is 900-1600° C., and the carbonization time is 1-20 h.

7. The method for preparing a coal-based negative electrode material according to claim 1 or 6, characterized in that: In the step (3), the ash-removed coal is ground before the carbonization or after the carbonization.

8. A coal-based negative electrode material prepared by the method according to any one of claims 1 to 7.

9. The coal-based negative electrode material according to claim 8, characterized in that The particle size D of the coal-based negative electrode material 50 1-100 μm.

10. The coal-based negative electrode material according to claim 9, characterized in that The particle size D of the coal-based negative electrode material 50 3-25 μm.

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