Coal-based hard carbon negative electrode material and preparation method and application thereof

Abstract

The coal-based hard carbon negative electrode material, a preparation method and application thereof, the preparation method of the coal-based hard carbon negative electrode material comprises the following steps: mixing and heating a coal-based raw material and an explosive agent, performing an explosion reaction, forming a plurality of open pore structures on the surface of the coal-based raw material, and obtaining a negative electrode material precursor; and heating and carbonizing the negative electrode material precursor, closing the open pore structures, forming a closed pore structure, and obtaining the coal-based hard carbon negative electrode material. The pore structure of the coal-based hard carbon negative electrode material is regulated through the explosion method, so that the sodium storage effect and the cycle performance of the coal-based hard carbon negative electrode material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a coal-based hard carbon negative electrode material, a preparation method and application thereof. BACKGROUND

[0002] Sodium-ion batteries have become the first choice to replace lithium-ion batteries due to the abundant resources of sodium and good low-temperature performance. However, the sodium ion radius is larger than that of lithium ion, which makes the graphite negative electrode unable to match the sodium-ion battery system. Hard carbon materials are widely used as negative electrode materials for sodium-ion batteries due to their advantages such as large carbon layer spacing, rich pore structure, adjustable structure, stable chemical properties and low cost.

[0003] Due to the problems of low sodium storage capacity and poor cycle performance of hard carbon materials, it is necessary to regulate the structure of hard carbon materials. At present, external cross-linking agents and pore-forming agents are introduced during the pyrolysis process of hard carbon materials to achieve the purpose of regulating the structure of hard carbon materials. However, the above method has some problems in practical application, such as high price of introducing external cross-linking agents, large amount of cross-linking agent addition, poor uniformity of the product, and complex process flow, which is not conducive to large-scale production. SUMMARY

[0004] In view of this, in order to solve at least one of the above technical problems, the present application provides a preparation method of a coal-based hard carbon negative electrode material.

[0005] In addition, the present application also provides a coal-based hard carbon negative electrode material prepared by the above preparation method, and an electrochemical device using the coal-based hard carbon negative electrode material.

[0006] The present application provides a preparation method of a coal-based hard carbon negative electrode material, which comprises:

[0007] mixing and heating the coal-based raw material with an explosive agent to perform an explosion reaction, so as to form a plurality of open pore structures on the surface of the coal-based raw material, and obtain a negative electrode material precursor; and

[0008] carbonizing the negative electrode material precursor to close the open pore structures, so as to form a closed pore structure, and obtain the coal-based hard carbon negative electrode material.

[0009] In some possible embodiments, the coal-based raw material comprises bituminous coal, and the bituminous coal comprises at least one of long flame coal, gas coal, fat coal, coking coal, lean coal and meager coal.

[0010] In some possible embodiments, in the step of mixing and heating the coal-based raw material with the explosive agent, the temperature of the heating is 600-800°C, and the time of the heating is 1-2h.

[0011] In some possible embodiments, a mass ratio of the coal-based raw material to the explosive agent is 1: (0.1-1).

[0012] In some possible embodiments, in the step of heating and carbonizing the anode material precursor, a temperature of the carbonization is 1300-1500 DEG C, and a time of the carbonization is 2-3 hours.

[0013] In some possible embodiments, the explosive agent comprises a nitrate, and the nitrate comprises at least one of KNO3, Mg(NO3)2, Zn(NO3)2 and Ca(NO3)2.

[0014] In some possible embodiments, before the step of heating and carbonizing the anode material precursor, the preparation method further comprises:

[0015] The coal-based hard carbon anode material precursor is subjected to acid pickling, wherein the acid in the acid pickling comprises at least one of hydrochloric acid, nitric acid and sulfuric acid, a concentration of the acid in the acid pickling is 1-6 mol / L, a solid-liquid ratio of the anode material precursor to the acid in the acid pickling is 1: (3-5 g / mL), a time of the acid pickling is 5-10 hours, and a temperature of the acid pickling is 25-60 DEG C.

[0016] In some possible embodiments, before the step of mixing and heating the coal-based raw material and the explosive agent, the preparation method further comprises:

[0017] The coal-based raw material is subjected to crushing and drying, wherein a temperature of the drying is 60-110 DEG C, and a time of the drying is 24-48 hours.

[0018] The application further provides a coal-based hard carbon anode material, which is prepared by the preparation method.

[0019] In addition, the application further provides an electrochemical device, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises a negative electrode material, and the negative electrode material is the coal-based hard carbon anode material.

[0020] Compared with the prior art, the coal-based raw material is mixed and heated with the explosive agent, the surface of the coal-based raw material has an oxygen-containing functional group, and the oxygen-containing functional group reacts with the explosive agent during the heating process, so that the coal-based raw material can be instantaneously decomposed to produce gas and explode, a large number of relatively open pore structures are generated on the surface of the coal-based raw material during the gas escaping process, and the relatively open pore structures are closed by high-temperature carbonization, thereby forming a closed pore structure in which solvent molecules are difficult to enter but sodium ions can freely enter. The closed pore structure is beneficial to the storage of sodium ions and the isolation of electrolyte of the coal-based hard carbon negative electrode material, so that the coal-based hard carbon negative electrode material has high and stable sodium storage effect and good cycle performance. In addition, the preparation method is simple in process and low in cost, and is conducive to large-scale production of the coal-based hard carbon negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A process flow chart of the preparation method of the coal-based hard carbon negative electrode material provided in the embodiments of the present application is shown.

[0022] Figure 2 A structure schematic diagram of the electrochemical device provided in the embodiments of the present application is shown.

[0023] Figure 3 A charge-discharge curve diagram of the battery prepared by the coal-based hard carbon negative electrode material in Embodiment 1 of the present application is shown.

[0024] Figure 4 An X-ray diffraction diagram of the coal-based hard carbon negative electrode material in Embodiment 1 of the present application is shown.

[0025] Figure 5 A nitrogen adsorption isotherm diagram of the coal-based hard carbon negative electrode material in Embodiment 1 of the present application is shown. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, any other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0027] One of the storage mechanisms of sodium ions in the hard carbon negative electrode material is adsorption-pore filling, that is, during the discharging process, the sodium ions are first adsorbed on the surface of the carbon microcrystal, and as the discharging depth increases, the sodium ions continue to fill in the nanometer closed pores formed by the stacking of the carbon microcrystals, so that increasing the closed pore content of the hard carbon negative electrode material is the key to improving the sodium storage capacity.

[0028] Please refer to Figure 1 The preparation method of the coal-based hard carbon negative electrode material provided in the embodiments of the present application specifically includes the following steps:

[0029] Step S1, the coal-based raw material is mixed with the explosive agent and heated to perform an explosion reaction to form a plurality of open pore structures on the surface of the coal-based raw material, to obtain a negative electrode material precursor.

[0030] In the explosion method, the coal-based raw material and the explosive agent are mixed and heated. Due to the large number of oxygen-containing functional groups on the surface of the coal-based raw material, the oxygen-containing functional groups of the coal-based raw material are decomposed to produce gas under the promotion of the explosive agent, and an explosion reaction occurs instantaneously to produce a large amount of gas. A large number of relatively open pore structures are formed on the surface of the coal-based raw material during the escape of the gas, which efficiently creates pores in the coal-based raw material and effectively increases the pore content of the coal-based raw material. A negative electrode material precursor with a large number of open pore structures is obtained.

[0031] Further, the micro-explosion method can be used to generate a small-scale explosion and instant high-pressure gas to initiate the reaction, which has high control precision. The stability and safety of the explosive agent during storage, mixing, and application can be ensured by following strict safety operation procedures. Specialized equipment is used to control and guide the explosion reaction to ensure that the equipment can withstand the instant high pressure, and appropriate protective measures such as pressure relief devices or safety valves are provided to ensure the safety of the process.

[0032] In some embodiments, the coal-based raw material can be crushed before step S1. Crushing the coal-based raw material into smaller particles can increase its surface area and make the mixture of the coal-based raw material and the explosive agent more uniform, increasing the contact probability of the oxygen-containing functional groups and the explosive agent, which helps to improve the completeness and uniformity of the explosion reaction, thereby improving the efficiency of the explosion reaction and increasing the gas production and pore content. The median particle size D50 of the crushed coal-based raw material can be 3 μm to 10 μm, further 3 μm to 5 μm, and exemplarily 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, etc.

[0033] In some embodiments, the coal-based raw material can be dried before step S1 to remove the moisture in the coal-based raw material, which is beneficial to improve the stability and completeness of the explosion reaction. The drying temperature can be 60°C to 110°C, and the drying time can be 24h to 48h.

[0034] In some embodiments, the coal-based raw material can be bituminous coal. Bituminous coal is characterized between high aromatic anthracite and low aromatic lignite, mainly composed of carbon, hydrogen, oxygen, sulfur and a small amount of nitrogen, unlike the ordered microcrystalline structure of anthracite-based hard carbon, bituminous coal has both aromatic units and side chains, which makes the ordered / disordered phase structure of bituminous coal more easily controllable. During the explosion process, more accurate control can be achieved by controlling these structural units. Moreover, bituminous coal also has the advantage of high oxygen content. During the heat treatment process, the more abundant oxygen-containing functional groups on the surface of bituminous coal are decomposed and exploded to generate a large amount of gas, which is beneficial to realize a large amount of pore formation of the coal-based hard carbon negative material precursor compared with other coal-based raw materials. In addition, the high oxygen content of bituminous coal can better control the carbonization process of the material when it is converted into hard carbon, reduce internal stress, and improve the stability and mechanical strength of the coal-based hard carbon negative material.

[0035] In some embodiments, the bituminous coal can include at least one of long flame coal, gas coal, fat coal, coking coal, lean coal, and lean coal. Different types of bituminous coal can be selected for use according to specific application requirements to optimize the performance of the coal-based hard carbon negative material. For example, long flame coal is selected as a bituminous coal raw material, which can utilize the high volatile matter and lower fixed carbon content of long flame coal to promote the explosion reaction and form more pore structures.

[0036] In some embodiments, the explosive agent can include a nitrate salt, which can include at least one of KNO3, Mg(NO3)2, Zn(NO3)2, and Ca(NO3)2. The above-mentioned explosive agent can release a large amount of oxygen at high temperature, effectively improving the explosion reaction intensity during the heat treatment process and promoting the formation of pores of the coal-based raw material.

[0037] In some embodiments, the mass ratio of the coal-based raw material to the explosive agent can be 1:(0.1-1). The mass ratio of the coal-based raw material to the explosive agent can control the intensity and scale of the explosion reaction, and within the above range, the mass ratio is beneficial to optimize the pore structure of the negative material precursor, and form enough pores that can be closed in the subsequent heating and carbonization process. The mass ratio of the coal-based raw material to the explosive agent can be further 1:(0.5-1), for example, 1:0.1, 1:0.2, 1:0.5, 1:0.8, or 1:1, etc.

[0038] In some embodiments, the temperature of the heating in this step can be 600-800°C, further 700-800°C, for example, 600°C, 650°C, 700°C, 750°C, or 800°C; the heating time can be 1-2h, further 1.5-2h, for example, 1h, 1.2h, 1.5h, 1.8h, or 2h, etc. Suitable heating conditions help the explosion reaction to proceed fully, so that the oxygen-containing functional groups of the coal-based raw material can be effectively decomposed to generate the required pore structure.

[0039] Step S2, heating the negative electrode material precursor for carbonization, so that the open pore structure is closed to form a closed pore structure, and a coal-based hard carbon negative electrode material is obtained.

[0040] The high-temperature carbonization of the negative electrode material precursor enables the carbon layers to rearrange to form a more stable amorphous carbon structure. This carbonization process changes the pore structure of the negative electrode material precursor, and the open pore structure in the negative electrode material precursor is closed to form a closed pore structure capable of storing sodium, thereby improving the sodium storage capacity and cycle performance of the coal-based hard carbon negative electrode material. Due to the presence of the closed pore structure, the specific surface area of the coal-based hard carbon negative electrode material is reduced, which can reduce the side reactions between the coal-based hard carbon negative electrode material and the electrolyte, and improve the initial coulombic efficiency of the battery prepared from the coal-based hard carbon negative electrode material.

[0041] In some embodiments, the carbonization temperature can be 1300°C to 1500°C. At the above temperature, sufficient energy is provided for the rearrangement of carbon atoms, and a closed pore structure is obtained. The carbonization temperature can be further 1400°C to 1500°C, and can exemplarily be 1300°C, 1350°C, 1400°C, 1450°C, or 1500°C, etc.

[0042] In some embodiments, the carbonization time can be 2h to 3h. The length of the carbonization time affects the completion degree of the carbonization process. By controlling the carbonization time to be 2h to 3h, the carbon atoms have sufficient time to rearrange to form a stable closed pore structure, and the carbonization process is ensured to be fully carried out. The carbonization time can be further 2.5h to 3h, and can exemplarily be 2h, 2.3h, 2.5h, 2.8h, or 3h, etc.

[0043] In some embodiments, the negative electrode material precursor can be subjected to acid washing before step S2. Specifically, the negative electrode material precursor is subjected to acid washing with an acid agent to remove impurities such as explosive agents, and then washed with deionized water to neutralization, and then dried at a certain temperature to remove water.

[0044] In some embodiments, the acid agent can include at least one of hydrochloric acid, nitric acid, and sulfuric acid, etc.

[0045] In some embodiments, the concentration of the acid (i.e., the acid agent) in the acid washing is 1mol / L to 6mol / L, which can effectively remove impurities. The concentration of the acid in the acid washing can be further 3mol / L to 5mol / L, and can exemplarily be 1mol / L, 2mol / L, 3mol / L, 4mol / L, 5mol / L, or 6mol / L, etc.

[0046] In some embodiments, the solid-liquid ratio of the negative electrode material precursor and the acid agent is 1: (3 g / mL~5 g / mL). By controlling the strength and efficiency of the acid washing, effective cleaning of the negative electrode material precursor is ensured, while avoiding excessive corrosion of the negative electrode material precursor. The solid-liquid ratio of the negative electrode material precursor and the acid agent can be further 1: (3 g / mL~4 g / mL), and exemplarily can be 3 g / mL, 3.5 g / mL, 4 g / mL, 4.5 g / mL or 5 g / mL, etc.

[0047] In some embodiments, the acid washing time is 5h~10h, and the acid washing temperature is 25℃~60℃. The appropriate time and temperature can ensure the sufficient removal of impurities, while avoiding damage to the structure of the negative electrode material precursor.

[0048] Compared with the prior art, the preparation method of the coal-based hard carbon negative electrode material provided by the embodiments of the present application has the following beneficial effects:

[0049] 1. The coal-based hard carbon negative electrode material is prepared by explosion method. By mixing and heating the coal-based raw material and the explosive agent to generate explosion reaction, the coal-based raw material is pore-made, and a large number of open pore structures are generated. Subsequently, high-temperature carbonization makes the pores close, forming a large number of closed pore structures, which is beneficial to improve the sodium storage capacity and cycle performance of the coal-based hard carbon negative electrode material. At the same time, due to the existence of a large number of closed pore structures, the specific surface area of the coal-based hard carbon negative electrode material is reduced, the contact between the coal-based hard carbon negative electrode material and the electrolyte is reduced, and the occurrence of side reactions is reduced.

[0050] 2. By further controlling the mass ratio of the coal-based raw material and the explosive agent, the strength and scale of the explosion reaction are adjusted to form micro-explosion, which is beneficial to improve the control accuracy of the explosion reaction and adjust the closed pore structure and specific surface area of the coal-based hard carbon negative electrode material.

[0051] 3. The bituminous coal with high oxygen content is used as the coal-based raw material, which is combined with the explosion method. Not only can the efficiency of the explosion reaction be significantly improved to generate larger and more pores, thereby improving the pore structure of the coal-based hard carbon negative electrode material, but also the carbonization effect can be optimized to improve the stability and mechanical strength of the coal-based hard carbon negative electrode material. In addition, the bituminous coal has aromatic units and side chains, which can more accurately regulate the pore structure through the aromatic units and side chains in the explosion process.

[0052] 4. The preparation method is simple, efficient and low in price, which is beneficial to large-scale production of the coal-based hard carbon negative electrode material and has excellent commercialization prospect.

[0053] The coal-based hard carbon negative electrode material is prepared by the preparation method as described above. Since the coal-based hard carbon negative electrode material has a large number of closed pore structures, the sodium storage capacity and cycle performance of the coal-based hard carbon negative electrode material are greatly improved; and since the coal-based hard carbon negative electrode material has a small specific surface area, the contact area between the coal-based hard carbon negative electrode material and the electrolyte is small, thereby effectively reducing the occurrence of negative electrode interface side reactions.

[0054] Referring to Figure 2 As shown in FIG. 1, the present application also provides an electrochemical device (for example, a battery), which includes a positive electrode sheet 10, a negative electrode sheet 20, a separator film 30, and an electrolyte 40, wherein the negative electrode sheet 20 includes a negative electrode material, and the negative electrode material is the coal-based hard carbon negative electrode material as described above.

[0055] The electrochemical device 100 prepared by using the coal-based hard carbon negative electrode material as described above has a significantly improved discharge capacity, long cycle stability, and first coulombic efficiency, since the sodium storage capacity and cycle performance of the coal-based hard carbon negative electrode material are improved, and the specific surface area of the coal-based hard carbon negative electrode material is reduced.

[0056] The coal-based hard carbon negative electrode material, the preparation method thereof, and the electrochemical device are further described below through specific examples.

[0057] Example 1

[0058] Step 1: First, pulverize the bituminous coal block into coal powder with a median particle size of 3 μm to 10 μm; then dry the coal powder at 110°C for 24 h; mix the coal powder and the explosive agent in a mortar at a mass ratio of 1:0.2, heat in a tube furnace at 700°C for 2 h to perform an explosion reaction, and obtain a negative electrode material precursor.

[0059] Step 2: Perform acid washing on the negative electrode material precursor to remove impurities, then wash with deionized water until neutral, and dry; finally, heat and carbonize the washed and dried negative electrode material precursor at 1300°C for 3 h to obtain the coal-based hard carbon negative electrode material.

[0060] Comparative Example 1

[0061] The specific process of the preparation process is referred to Example 1, and the difference from Example 1 is that only coal powder is added in Step 1, and no explosive agent is added, and the rest of the preparation method of the coal-based hard carbon negative electrode material is basically the same as that of Example 1, which is not described in detail here.

[0062] Comparative Example 2

[0063] The specific procedure of the preparation process refers to Example 1, and the difference between Example 1 is that the heating time for the explosion reaction in step 1 is 5 h, and the rest of the preparation method of the coal-based hard carbon negative electrode material is basically the same as that of Example 1, which is not described here.

[0064] Comparative Example 3

[0065] The specific procedure of the preparation process refers to Example 1, and the difference between Example 1 is that the heating time for the explosion reaction in step 1 is 5 h, and the rest of the preparation method of the coal-based hard carbon negative electrode material is basically the same as that of Example 1, which is not described here.

[0066] The coal-based hard carbon negative electrode materials obtained in Example 1 and Comparative Examples 1-3 were subjected to the following tests.

[0067] 1. The batteries prepared using the coal-based hard carbon negative electrode materials in Example 1 and Comparative Examples 1-3 were subjected to charge-discharge tests, and the results are shown in Table 1.

[0068] The specific preparation steps of the battery are as follows: the coal-based hard carbon negative electrode material, the binder PVDF, and the conductive agent Super P are uniformly dispersed in N-methyl pyrrolidone (NMP) at a mass ratio of 93.5:5:1.5, stirred for 4 h to form a slurry, coated on an aluminum current collector, and dried in a 80°C oven for 36 h. The negative electrode sheet with a diameter of 12 mm is ready for use. The assembly of the sodium ion battery is carried out in a glove box. Specifically, the button cell is assembled from bottom to top in the order of negative electrode shell, spring, gasket, 1 mm sodium sheet, glass fiber separator (Whatman C), negative electrode sheet, 0.5 mm gasket, and positive electrode shell. The electrolyte is prepared by dissolving 1.5 M NaPF6 in a solvent of volume ratio 1:2:2 of ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). The addition amount of electrolyte is 70 μL on both sides of the separator. Finally, the battery is compacted in a button cell sealing machine to test the charge-discharge curve of the battery.

[0069] The test procedure of the charge-discharge curve is as follows: 0.1C discharge to 0V, then discharge to 0V at small currents of 0.05C and 0.01C, respectively, and finally charge to 1.5V at 0.1C. The nominal specific capacity is set to 300 mAh / g.

[0070]

[0071] As shown in Table 1, the reversible specific capacity of the battery prepared from the coal-based hard carbon negative electrode material in Example 1 is 310 mAh / g, and the first cycle coulombic efficiency is 86%, which is higher than that of Comparative Examples 1-3. This is because the negative electrode material prepared by the explosion method in Example 1 has a large number of closed pore structures, so that the capacity and cycle performance are greatly improved. The capacity and cycle performance of the negative electrode material in Comparative Examples 1-3 are lower than that in Example 1. Among them, Comparative Example 1 does not add an explosive agent, the explosion reaction is not sufficient, and a large number of closed pore structures are not effectively prepared, so the electrical performance is reduced; the electrochemical performance of the negative electrode material in Comparative Examples 2 and 3 is also reduced due to the change of the reaction conditions. The charge-discharge curve of the battery prepared from the coal-based hard carbon negative electrode material in Example 1 is shown in Figure 3 .

[0072] 2. The coal-based hard carbon negative electrode material in Example 1 was subjected to X-ray diffraction test (XRD).

[0073] The XRD results of the coal-based hard carbon negative electrode material in Example 1 are shown in Figure 4 , and the results show that the coal-based hard carbon negative electrode material obtained in Example 1 has a disordered structure, which is beneficial to the insertion and extraction of sodium ions.

[0074] 3. The coal-based hard carbon negative electrode material in Example 1 was subjected to specific surface area test.

[0075] The specific surface area test method is as follows: 500 mg of the coal-based hard carbon negative electrode material in Example 1 is weighed and loaded into a sample tube, and the N2 adsorption and desorption amount of the sample is measured at different pressure points at 77 K by N2 adsorption and desorption, to obtain the adsorption and desorption isotherm. The specific surface area is calculated from the adsorption and desorption isotherm by computer processing data, and the results are shown in Table 2.

[0076]

[0077] The specific surface area test results of the coal-based hard carbon negative electrode material in Example 1 are shown in Figure 5 , and according to Table 2 and Figure 5 , the specific surface area of the coal-based hard carbon negative electrode material obtained in Example 1 is 0.6 m 2 / g, which is smaller than that of Comparative Examples 1-3. The coal-based hard carbon negative electrode material in Example 1 has a smaller specific surface area, which is beneficial to reducing the side reaction between the electrolyte and the coal-based hard carbon negative electrode material and improving the first cycle coulombic efficiency of the prepared battery.

[0078] It is understood that the above embodiments are only exemplary for illustrating the principles of the present application, and the present application is not limited thereto. Various modifications and improvements can be made by those skilled in the art without departing from the spirit and scope of the present application, and these modifications and improvements are also considered as the protection scope of the present application.

Claims

1. A method for preparing a coal-based hard carbon negative electrode material, characterized in that, The preparation method comprises the following steps: After the coal-based raw material is crushed and dried, the coal-based raw material is mixed with an explosive agent and heated to perform an explosion reaction, so as to form a plurality of open pore structures on the surface of the coal-based raw material, thereby obtaining a negative electrode material precursor, wherein the coal-based raw material comprises bituminous coal, the explosive agent comprises a nitrate salt, the nitrate salt comprises at least one of Mg(NO3)2, Zn(NO3)2 and Ca(NO3)2, the heating temperature is 600-800 DEG C, and the heating time is 1-2 hours; and The negative electrode material precursor is subjected to acid pickling, and the acid-pickled negative electrode material precursor is heated and carbonized to close the open pore structures, so as to form a closed pore structure, thereby obtaining the coal-based hard carbon negative electrode material.

2. The method of claim 1, wherein the coal-based hard carbon negative electrode material is prepared by the steps of: The bituminous coal comprises at least one of long flame coal, gas coal, fat coal, coking coal, lean coal and meager coal. ​ 3. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The mass ratio of the coal-based raw material to the explosive agent is 1: (0.1-1).

4. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, In the step of heating and carbonizing the negative electrode material precursor, the carbonization temperature is 1300-1500 DEG C, and the carbonization time is 2-3 hours.

5. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The acid in the acid pickling comprises at least one of hydrochloric acid, nitric acid and sulfuric acid, the concentration of the acid in the acid pickling is 1-6 mol / L, the solid-liquid ratio of the negative electrode material precursor to the acid in the acid pickling is 1: (3-5 g / mL), the acid pickling time is 5-10 hours, and the acid pickling temperature is 25-60 DEG C.

6. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The drying temperature is 60-110 DEG C, and the drying time is 24-48 hours.

7. A coal-based hard carbon negative electrode material, characterized in that, The coal-based hard carbon negative electrode material is prepared by the preparation method of the coal-based hard carbon negative electrode material according to any one of claims 1-6.

8. An electrochemical device, characterized by, The electrochemical device comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises a negative electrode material, and the negative electrode material is the coal-based hard carbon negative electrode material according to claim 7. The electrochemical device comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises a negative electrode material, and the negative electrode material is the coal-based hard carbon negative electrode material according to claim 7.

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