Carbon-molybdenum disulfide composite negative electrode material and preparation method and application thereof

Abstract

The application belongs to the technical field of sodium ion battery carbon negative electrode materials, and particularly relates to a carbon-molybdenum disulfide composite negative electrode material and a preparation method and application thereof, adopts ethylene tar as a carbon source, has the characteristics of sufficient yield and low price, the prepared ethylene tar-based composite carbon material has great significance in restricting the volume expansion of molybdenum disulfide by using carbon. The method has the advantages of simple process and low cost, and has the feasibility of industrial production; the ethylene tar-based composite carbon material has good electrochemical performance in the negative electrode of a sodium ion battery, widens the selection of raw materials for the production of the carbon negative electrode of the sodium ion battery, and lays a foundation for the application of the sodium ion battery in the battery application field.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion battery carbon negative electrode materials, and particularly relates to a carbon-molybdenum disulfide composite negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have been widely used in electrochemical energy storage devices, but due to the low reserves of lithium element, they have been unable to meet the growing energy demand. Sodium ion batteries are considered to be the most promising alternative to lithium ion batteries because of their similar battery assembly technology to lithium ion batteries and the relatively abundant reserves of sodium element in the earth's crust. However, due to the fact that the atomic radius of metallic sodium is much larger than that of metallic lithium, the graphite negative electrode material of traditional lithium ion batteries is not suitable for use in sodium ion batteries. Therefore, there is an urgent need to design a new type of negative electrode material with a larger lattice spacing to achieve a higher sodium ion storage capacity.

[0003] Molybdenum disulfide is considered to be a very promising negative electrode material for sodium ion batteries due to its high capacity and graphene-like layered structure. However, the irreversible conversion reaction during the sodiumization / desodiumization process is a problem that must be overcome before its practical application; and the agglomeration of molybdenum disulfide nanostructures is prone to occur during preparation and use, which reduces the specific surface area of the material, reduces the degree of exposure of active sites, and thus affects the storage and transport of sodium ions, reduces the reversible specific capacity and cycle performance of the battery, and research on how to limit the expansion of molybdenum disulfide as a negative electrode for sodium ion batteries is imminent. SUMMARY

[0004] The purpose of the present application is to provide a carbon-molybdenum disulfide composite negative electrode material and a preparation method and application thereof, so as to overcome the shortcomings of the prior art, use ethylene tar as a carbon source which is abundant in production and low in price, prepare an ethylene tar-based composite carbon material, and use carbon to limit the volume expansion of molybdenum disulfide, which has great significance. The method has a simple process and low cost, and has the feasibility of industrial production.

[0005] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0006] In the first aspect, the present application provides a preparation method of a carbon-molybdenum disulfide composite negative electrode material, comprising the following steps:

[0007] (1) subjecting ethylene tar to vacuum distillation to obtain ethylene tar distillation residue;

[0008] (2) mixing the ethylene tar distillation residue, a molybdenum source and a sulfur source in a solvent to obtain a first solid powder;

[0009] (3) subjecting the first solid powder to carbonization treatment to obtain a second solid powder;

[0010] (4) the second solid powder is subjected to acid treatment, and after water washing, the carbon-molybdenum disulfide composite negative electrode material is obtained.

[0011] In some other embodiments, in step (1), the temperature of the reduced pressure distillation treatment is 300-400℃, the pressure is 0-100pa, and the time is 2-3h.

[0012] In some other embodiments, in step (2), the mass ratio of the molybdenum source to the sulfur source is 1:(1.5-2.5).

[0013] The mass ratio of the ethylene tar distillation residue to the molybdenum source is (1-3):1.

[0014] In some other embodiments, in step (2), the molybdenum source is one of sodium molybdate, ammonium molybdate, magnesium molybdate, and potassium molybdate.

[0015] The sulfur source is one of thiocyanate, ammonium thiocyanate, CH4N2S, ammonium sulfide, sodium sulfide, potassium sulfide, and sodium thiosulfate.

[0016] The solvent is one of dichloromethane, ethanol, cyclohexane, and acetone.

[0017] In some other embodiments, in step (2), a pore-forming agent is further added.

[0018] The mass ratio of the pore-forming agent to the ethylene tar distillation residue is (1.5-2.5):1.

[0019] The pore-forming agent is one of calcium carbonate, silicon dioxide, and calcium sulfate.

[0020] The particle size of the pore-forming agent is 50-150nm.

[0021] In some other embodiments, in step (3), the carbonization treatment is: under an inert atmosphere, the temperature is 550-650℃, the heating rate is 1-5℃ / min, and the time is 2-5h.

[0022] In some other embodiments, in step (4), the acid treatment is: the solid-liquid ratio of the second solid powder to the acid is 0.01-0.03g / mL, the concentration of the acid is 35-45wt%, and the treatment time is 1-2h.

[0023] The acid is one of HF, HCl, and HNO3.

[0024] In a second aspect, the present application provides a carbon-molybdenum disulfide composite negative electrode material prepared by the preparation method of the carbon-molybdenum disulfide composite negative electrode material in the first aspect.

[0025] In a third aspect, the present application provides application of the carbon-molybdenum disulfide composite negative electrode material in the second aspect in preparation of a sodium ion battery negative electrode material.

[0026] In a fourth aspect, the present application provides a sodium ion battery, comprising a positive electrode, a negative electrode, an electrolyte, a separator and a current collector, wherein the negative electrode is the carbon-molybdenum disulfide composite negative electrode material in the second aspect.

[0027] Reaction mechanism: uniform mixing and distribution of the carbon material and molybdenum disulfide is the key reason for solving the problems of low specific capacity of the carbon material and poor cycle stability of molybdenum disulfide. The presence of carbon can uniformly disperse molybdenum disulfide, avoid the agglomeration of molybdenum disulfide, and when the volume of molybdenum disulfide changes, the carbon material can provide certain support and limitation, so that the expansion is more uniform, and the structural damage caused by local stress concentration is relieved; in addition, the carbon material itself has a certain flexibility, which can provide a buffer space for the volume expansion of molybdenum disulfide in the charging and discharging process, thereby greatly improving the electrochemical performance.

[0028] Advantages of the present application:

[0029] (1) The present application uses ethylene tar as raw material, which has the advantage of low price, and the carbon material has good electrical conductivity. Uniform mixing and compounding of the carbon material and molybdenum disulfide can significantly improve the electron transport capacity of the composite material, reduce the electron transport resistance, and make the electrode reaction more rapid. At the same time, the presence of carbon can change the diffusion path and dynamics of sodium ions in molybdenum disulfide, and reduce the diffusion energy barrier of sodium ions

[0030] (2) During the charging and discharging process of the sodium ion battery, the single molybdenum disulfide will expand and shrink in volume, causing damage and pulverization of the electrode structure, and then affecting the cycle performance of the battery. The carbon material can act as a physical support to limit the volume change of molybdenum disulfide, buffer the expansion stress, and reduce the structural damage of the electrode material. The carbon material and molybdenum disulfide are uniformly dispersed to avoid agglomeration, and when the volume of molybdenum disulfide changes, the carbon material can provide certain support and limitation, so that the expansion is more uniform.

[0031] (3) The carbon-molybdenum disulfide composite negative electrode material prepared by the present application has excellent electrochemical performance, which solves the problems of low specific capacity of the carbon electrode and poor cycle stability of molybdenum disulfide in the sodium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0032] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the description of the exemplary embodiments of the present application and the explanation thereof, explain the present application, and do not constitute an improper limitation of the present application.

[0033] Figure 1is a process flow chart of a treatment process in the embodiment of the present application;

[0034] Figure 2 is an infrared spectrum of a raw material ethylene tar distillation residue in the embodiment of the present application;

[0035] Figure 3 is a SEM image and a TEM image of a sample in Example 1 of the present application;

[0036] Figure 4 is a Mapping image of a sample in Example 1 of the present application;

[0037] Figure 5 is a SEM image and a TEM image of a sample in Example 2 of the present application;

[0038] Figure 6 is a Mapping image of a sample in Example 2 of the present application;

[0039] Figure 7 is an XRD image of Examples 1 and 2 of the present application;

[0040] Figure 8 is a Raman spectrum of Examples 1 and 2 and Comparative Examples 1 and 2 of the present application;

[0041] Figure 9 is a N2adsorption-desorption curve of Examples 1 and 2 of the present application;

[0042] Figure 10 is a specific surface area graph of Examples 1 and 2 and Comparative Examples 1 and 2 of the present application;

[0043] Figure 11 is a cycle performance graph of Examples 1 and 2 and Comparative Examples 1 and 2 of the present application at a current density of 0.5 A g-1; -1

[0044] Figure 12 is an AC impedance graph of Examples 1 and 2 of the present application. DETAILED DESCRIPTION

[0045] In order to make the technical problems and technical solutions to be solved in the present application more clear, the following will be described in detail in combination with the drawings and specific embodiments. Unless otherwise defined, all the professional terms used in the following have the same meaning as commonly understood by those skilled in the art. The professional terms used in the present text are only for the purpose of detailed description of the specific embodiments and are not intended to limit the protection scope of the present application.

[0046] Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment, etc. used in the present application can be purchased from the market or can be prepared by the existing methods.

[0047] ​I. Preparation of negative electrode material

[0048] The present application provides a process flow chart of the preparation method of carbon-molybdenum disulfide composite negative electrode material as shown in Figure 1 The following will be described in detail in combination with specific embodiments.

[0049] Example 1

[0050] A preparation method of a sodium ion battery carbon-molybdenum disulfide composite negative electrode material, comprising the following steps:

[0051] Step (1): Perform vacuum distillation treatment on ethylene tar (SINOPEC Qingdao Refining and Chemical Co., Ltd.) at 350℃, the distillation pressure is close to vacuum, and maintain for 3h to obtain ethylene tar distillation residue, and use a ball mill to grind the ethylene tar distillation residue into ethylene tar distillation residue solid powder with uniform size.

[0052] Step (2): Dissolve 3g of ethylene tar distillation residue in organic reagent CH2Cl2 under normal temperature and pressure and magnetic stirring, then add 3g of Na2MoO4 and 6g of CH4N2S, mix thoroughly, and then evaporate CH2Cl2 completely to obtain brown-black block solid, which is ground into powder state.

[0053] Step (3): Put the ground brown-black powder into a porcelain boat, then place it in a tube furnace filled with Ar atmosphere for high-temperature carbonization, the carbonization temperature is 600℃, the carbonization time is 3h, the carbonization heating rate is 5℃ / min, and after carbonization, cool it to room temperature naturally, then take it out and grind it into powder.

[0054] Step (4): Put the powder prepared in step (3) into a 250ml polytetrafluoroethylene container, add 40wt% concentrated HF (solid-liquid ratio 0.02g / mL), wash thoroughly, then perform water washing by suction filtration to obtain the negative electrode material.

[0055] Step (5): In an argon-filled glove box (H2O<0.01ppm and O2<0.01ppm), assemble the prepared negative electrode material into a sodium ion battery (CR2032 type button cell), and the specific assembly process is as follows:

[0056] The negative electrode material, Ketjen black and polyvinylidene fluoride (PVDF) were mixed and ground in a ratio of 8:1:1, then dissolved in N-methyl pyrrolidone (NMP) and stirred for 2 hours to obtain a black viscous slurry containing active substances. Copper foil was used as the current collector, and the slurry was uniformly coated on the surface of the copper foil using an SQZ type four-side preparation device. The coated copper foil was placed in a vacuum drying oven and dried at 120°C for 6 hours. Then, a tablet was made using a tablet press, and then marked and stored in a sealed bag. Pure sodium was used as the counter electrode, and a glass fiber separator (Whatman GF / D) was sandwiched between the sodium sheet and the electrode. The electrolyte used was 1M NaPF6+EC / DEC+5% FEC.

[0057] Cyclic voltammetry (CV) curves were recorded using an electrochemical workstation (CHI 660E) in a voltage window of 0.01-3.0V, with a scan rate of 0.1mV s -1 .

[0058] The constant current discharge-charge test of the button cell was performed on a CT3002A battery tester (Land, Wuhan), and the test voltage was 0.01-3.0V.

[0059] Example 2

[0060] Different from Example 1, 6g of nano-SiO2 (particle size 100nm) was added as a pore former in step (2). That is, 3g of ethylene tar distillation residue was dissolved in organic reagent CH2Cl2 under normal temperature and pressure and magnetic stirring, then 6g of nano-SiO2, 3g of Na2MoO4 and 6g of CH4N2S were added and mixed thoroughly until CH2Cl2 completely evaporated naturally to obtain a brown-black block solid which was ground to a powder state. The other preparation steps were the same as those of Example 1.

[0061] Comparative Example 1

[0062] Different from Example 1, only 3g of ethylene tar distillation residue was added in step (2). That is, 3g of ethylene tar distillation residue was dissolved in organic reagent CH2Cl2 under normal temperature and pressure and magnetic stirring until CH2Cl2 completely evaporated naturally to obtain a brown-black block solid which was ground to a powder state. The other preparation steps were the same as those of Example 1.

[0063] Comparative Example 2

[0064] Different from Example 1, step (1) was omitted, and only 3g of Na2MoO4 and 6g of CH4N2S were added in step (2). 3g of Na2MoO4 and 6g of CH4N2S were uniformly dispersed in organic reagent CH2Cl2 under normal temperature and pressure and magnetic stirring, and mixed thoroughly until CH2Cl2 completely evaporated naturally to obtain a uniformly dispersed solid powder. The other preparation steps were the same as those of Example 1.

[0065] Comparative Example 3

[0066] Different from Example 1, 3g ethylene tar was directly mixed with 3g Na2MoO4 and 6g CH4N2S, 3g ethylene tar, 3g Na2MoO4 and 6g CH4N2S were uniformly dispersed in organic reagent CH2Cl2 under normal temperature and pressure and magnetic stirring, and fully mixed until CH2Cl2 completely naturally volatilized to obtain a brown-black liquid. Other preparation steps were the same as Example 1.

[0067] Comparative Example 4

[0068] Different from Example 1, starch was used instead of ethylene tar distillation residue, 3g starch was directly mixed with 3g Na2MoO4 and 6g CH4N2S, that is, 3g starch, 3g Na2MoO4 and 6g CH4N2S were uniformly dispersed in organic reagent CH2Cl2 under normal temperature and pressure and magnetic stirring, and fully mixed until CH2Cl2 completely naturally volatilized to obtain a block solid, which was ground to a powder state. Other preparation steps were the same as Example 1.

[0069] Comparative Example 5

[0070] Different from Example 1, a hydrothermal method was used to synthesize molybdenum disulfide-carbon composite material, that is, Na2MoO4, CH4N2S and sucrose with a mass ratio of 1:2:1 were dissolved in 50mL deionized water, stirred uniformly, transferred into a stainless steel reaction kettle, and hydrothermally reacted at 180℃ for 36h. The product was washed by centrifugation with deionized water and dried. It was calcined in a mixed gas of hydrogen and nitrogen (volume ratio 1:9) at 850℃ for 2h.

[0071] Comparative Example 6

[0072] Different from Example 1, step (4) was omitted, that is, the powder prepared in step (3) was not subjected to acid treatment.

[0073] II. Performance test

[0074] The ethylene tar used in the application was subjected to vacuum distillation treatment at 350℃ to obtain ethylene tar distillation residue for elemental analysis, and the results are shown in Table 1. The ethylene tar contains a large amount of light components, and if most of the light components are not removed by distillation, it is easy to block the pipeline of the tubular furnace. Similarly, when industrial production is carried out, if the ethylene tar is directly added to the rotary kiln or other horizontal furnace, due to the high viscosity of the ethylene tar, the internal friction between the molecules is large when flowing in the pipeline, and the flow resistance is also large, which is easy to adhere to the inner wall of the pipeline and gradually accumulate to cause pipeline blockage. Therefore, the ethylene tar is first subjected to vacuum distillation to remove most of the light components to obtain a solid residue, and then a step experiment or production is carried out, which can effectively avoid this problem.

[0075] Table 1 Element content in ethylene tar residue

[0076]

[0077] As can be seen from Table 1, the main elements contained in the ethylene tar and the ethylene tar distillation residue prepared after vacuum distillation are C, H and O, and the contents of C and O in the ethylene tar distillation residue after vacuum distillation slightly increase, while the contents of H, N and S decrease, which is because the volatilization of light components during the vacuum distillation process.

[0078] The ethylene tar distillation residue was subjected to infrared spectrum test, and the results are shown in Figure 2 As can be seen from Figure 2 , the main chemical bonds of the ethylene tar distillation residue are C-O, C=C, C=O, C-H and a small part of C-N, among which C=C, C=O and benzene ring etc. can produce conjugation effect. The conjugated structure has higher stability, which is beneficial to retaining more active sites such as C=O in the carbonization process.

[0079] The sample prepared in Example 1 was subjected to SEM and TEM tests, and the results are shown in Figure 3 , wherein (a-c) are SEM pictures, and (d-f) are TEM pictures, wherein the scale in d is 100 nm, the scale in e is 50 nm, and the scale in f is 5 nm. As can be seen from Figure 3 , the carbon and molybdenum disulfide in the prepared carbon-molybdenum disulfide composite negative electrode material are uniformly dispersed together. Figure 5 is the SEM and TEM pictures of the sample in Example 2. Among them, (a-c) are SEM pictures, and (d-f) are TEM pictures, wherein the scale in d is 100 nm, the scale in e is 50 nm, and the scale in f is 5 nm. As can be seen from Figure 5 , the morphology of the prepared carbon-molybdenum disulfide composite negative electrode material is obviously different from that of the sample in Example 1. The sample prepared in Example 2 contains a hollow pore structure, which is caused by the addition of nano-SiO2, which expands the pore number and specific surface area, and the rich pore structure and increased specific surface area provide more active sites for electrochemical reaction, and more ions can react on the electrode surface.

[0080] Figure 4 is the mapping picture of the sample in Example 1, and the scale is 500 nm; Figure 6 is the mapping picture of the sample in Example 2, and the scale is 500 nm. As can be seen from Figure 4 , Figure 6It can be seen from the above table that the main elements C, H, O, N, S, Mo and Na in the samples prepared in Examples 1 and 2 are uniformly distributed, indicating that the carbon and the molybdenum disulfide are uniformly mixed together, which is beneficial to the improvement of the electrochemical performance.

[0081] Figure 7 The XRD patterns of Examples 1 and 2 of the present application are shown in Figure 8. Figure 7 It can be seen from the above table that the main elements C, H, O, N, S, Mo and Na in the samples prepared in Examples 1 and 2 are uniformly distributed, indicating that the carbon and the molybdenum disulfide are uniformly mixed together, which is beneficial to the improvement of the electrochemical performance.

[0082] Figure 8 The Raman spectra of Examples 1 and 2 and Comparative Examples 1 and 2 of the present application are shown in Figure 8. It can be seen from Figure 8 that Examples 1 and 2 have obvious molybdenum disulfide characteristic peaks, which further proves the synthesis of molybdenum disulfide. However, no obvious molybdenum disulfide characteristic peak is observed in Example 2, which may be because most of the molybdenum disulfide is hidden inside the carbon after the pore forming, so that the laser cannot effectively irradiate the molybdenum disulfide, or the Raman scattering signal generated by the molybdenum disulfide is difficult to transmit, so that the characteristic peak cannot be detected. Compared with the XRD of Example 1, the XRD of Example 2 detects significantly reduced molybdenum disulfide crystal faces, which can further support this conclusion.

[0083] Figure 9 The N2 adsorption-desorption curves of Examples 1 and 2 of the present application are shown in Figure 8. It can be seen that the pore of the negative electrode material prepared in Example 1 is relatively rare and the specific surface area is small. The specific surface area and the pore of Example 2 are obviously improved compared with Example 1, because the addition of nano-SiO2 will increase the specific surface area, and a large number of pore structures are formed inside the material, which provides more active sites for electrochemical reaction, and more ions can react on the electrode surface.

[0084] Figure 10 The rate graph of Examples 1 and 2 and Comparative Examples 1 and 2 of the present application is shown in Figure 8. It can be seen from Figure 8 that the discharge specific capacity of Example 1 at a current density of 0.05, 0.1, 0.2, 0.5, 1 and 2 A g Figure 10 is 820.39, 328.65, 292.81, 256.56, 226.57 and 193.96 mAh g -1 , respectively. The discharge specific capacity of Example 2 at a current density of 0.05, 0.1, 0.2, 0.5, 1 and 2 A g -1 is 1558.64, 388.00, 355.44, 285.88, 249.38 and 216.89 mAh g -1 , respectively. The discharge specific capacity of Comparative Example 1 at a current density of 0.05, 0.1, 0.2, 0.5, 1 and 2 A g -1 is 820.39, 328.65, 292.81, 256.56, 226.57 and 193.96 mAh g -1mAh g-1, 244.04, 220.58, 192.34, 164.60, 127.40 mAh g-1 -1 mAh g-1, 406.98, 389.59, 358.71, 330.06, 306.94 mAh g-1 -1 mAh g-1, 406.98, 389.59, 358.71, 330.06, 306.94 mAh g-1 -1 .

[0085] From the above results, it can be seen that the addition of nano-SiO2 in Example 2 will cause the charge and discharge performance to improve, because the addition of nano-SiO2 will increase its specific surface area, a large number of pore structures are formed inside the material, the rich pore structure provides more active sites for electrochemical reaction, more ions can react on the electrode surface, thereby improving the specific capacity. The addition of ethylene tar distillation residue in Comparative Example 1 will cause the charge and discharge performance to decrease, because only carbon is present without the doping of in-situ synthesized molybdenum disulfide which can provide high specific capacity. The omission of the addition of ethylene tar distillation residue in Comparative Example 2 will cause the charge and discharge performance to improve, because the in-situ synthesized molybdenum disulfide which can provide high specific capacity is mainly present and only a small amount of carbon is present.

[0086] Figure 11 is the cycle performance chart of Example 1, 2 and Comparative Example 1, 2 at a current density of 0.5 A g-1. Table 2 is the electrochemical performance of the examples and comparative examples. -1

[0087] Table 2 is the electrochemical performance of the examples and comparative examples

[0088]

[0089]

[0090] From Table 2 and Figure 11 ​It can be seen that the capacity retention rate of Example 2 after 300 cycles is 60.6%, which is significantly lower than that of Example 1 (80%), because the addition of nano-SiO2 affects the interfacial bonding force between the carbon layer and the molybdenum disulfide, which destroys the original good interface contact, and the carbon layer is difficult to effectively play a buffering and protection role, and the molybdenum disulfide is easy to separate from the carbon layer when the volume changes, thereby causing the structure to be unstable and the cycle performance to decrease. Compared with Example 1, Comparative Example 1 has good cycle stability, and the capacity retention rate after 300 cycles is 89.2%, and the addition of ethylene tar distillation residue only leads to better cycle performance, because Comparative Example 1 only contains carbon and does not contain in-situ synthesized molybdenum disulfide which is easy to cause volume expansion. Compared with Example 1, Comparative Example 2 has poor cycle stability, and the capacity retention rate after 300 cycles is 11.6%, and the omission of ethylene tar distillation residue leads to a significant decrease in cycle performance, because there is no carbon to limit the volume expansion of molybdenum disulfide, and the volume expansion brings too serious capacity attenuation.

[0091] Comparative Example 3 directly mixes 3g of ethylene tar with 3g of Na2MoO4 and 6g of CH4N2S, and under normal temperature and pressure and magnetic stirring, 3g of ethylene tar, 3g of Na2MoO4 and 6g of CH4N2S are uniformly dispersed in the organic reagent CH2Cl2, and are fully mixed until the CH2Cl2 completely evaporates to obtain a brown-black liquid. After carbonization, the material obtained is used as a negative electrode material for sodium ion batteries. Compared with Example 1, its specific capacity and cycle performance are not much different, but because it is a liquid feed, it is easy to block the pipeline of the tubular furnace. Similarly, if ethylene tar is directly added to a rotary kiln or other horizontal furnace during industrial production, due to the high viscosity of ethylene tar, the intermolecular friction between the molecules is large when flowing in the pipeline, and the flow resistance is also large, which is easy to adhere to the inner wall of the pipeline and gradually accumulate to cause pipeline blockage, which is not conducive to industrial production.

[0092] Comparative Example 4 uses starch instead of ethylene tar distillation residue, and directly mixes 3g of starch with 3g of Na2MoO4 and 6g of CH4N2S, and under normal temperature and pressure and magnetic stirring, 3g of starch, 3g of Na2MoO4 and 6g of CH4N2S are uniformly dispersed in the organic reagent CH2Cl2, and are fully mixed until the CH2Cl2 completely evaporates to obtain a white solid powder. After carbonization, it is used as a negative electrode material for sodium ion batteries. Its discharge specific capacity is 204.46mAh g -1 at a current density of 0.5A g -1 , and the cycle capacity retention rate after 300 cycles is 76.7%, which is lower than the negative electrode material provided in Example 1.

[0093] Comparative Example 5 synthesized a molybdenum disulfide-carbon composite material using a hydrothermal method. Na₂MoO₄, CH₄N₂S, and sucrose (mass ratio 1:2:1) were dissolved in 50 mL of deionized water, stirred thoroughly, and transferred to a stainless steel reactor. The mixture was then hydrothermally reacted at 180 °C for 36 h. The product was washed by centrifugation with deionized water and dried. The resulting material was calcined at 850 °C for 2 h in a mixture of hydrogen and nitrogen (volume ratio 1:9) to obtain the anode material for sodium-ion batteries. Its 0.5 A g... -1 The discharge specific capacity at the specified current density is 210.46 mAh g. -1 The cycle capacity retention rate after 300 cycles was 75.4%, which is lower than that of the negative electrode material provided in Example 1.

[0094] Comparative Example 6 differs from Example 1 in that the acid treatment step was omitted. Its 0.5Ag -1 The discharge specific capacity at the specified current density is 245.80 mAh g. -1 The cycle capacity retention rate after 300 cycles was 78.6%, which was slightly lower than that of Example 1. This is because the material may contain some impurities that affect its electrochemical performance if it is not acid-washed, and the lack of fully open pores is also not conducive to the material storing sodium ions.

[0095] Figure 12 These are the AC impedance diagrams from embodiments 1 and 2 of the present invention, with a test frequency range from 0.01 Hz to 100 kHz. From... Figure 12 It can be seen that the resistance of Example 2 is higher than that of Example 1. This may be because the hole-forming process destroys the structural integrity of carbon and molybdenum disulfide itself. The original continuous carbon layer and molybdenum disulfide crystal structure are good channels for electron conduction. After hole-forming, these channels are broken or twisted, and electrons will encounter more scattering and obstruction during conduction, thus increasing the resistance.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon-molybdenum disulfide composite negative electrode material, characterized by, The method comprises the following steps: (1) preparing ethylene tar distillation residue by vacuum distillation of ethylene tar; (2) mixing the ethylene tar distillation residue, a molybdenum source and a sulfur source in a solvent to prepare a first solid powder; (3) carbonizing the first solid powder to prepare a second solid powder; (4) acid treating the second solid powder, and then washing with water to obtain a carbon-molybdenum disulfide composite negative electrode material. In step (1), the temperature of the vacuum distillation treatment is 300-400°C. In step (4), the acid treatment is as follows: the solid-liquid ratio of the second solid powder to the acid is 0.01-0.03 g / mL, the concentration of the acid is 35-45wt%, and the treatment time is 1-2h.

2. The method of claim 1, wherein the carbon-molybdenum disulfide composite negative electrode material is prepared by the steps of: mixing a carbon material and a molybdenum source to form a mixture; and heating the mixture to form the carbon-molybdenum disulfide composite negative electrode material. In step (1), the pressure of the vacuum distillation is 0-100 pa, and the time is 2-3h.

3. The method of claim 1, wherein the carbon-molybdenum disulfide composite negative electrode material is prepared by the steps of: mixing a carbon material and a molybdenum source to form a mixture; and heating the mixture at a temperature of 300-800°C in a sulfur atmosphere. In step (2), the mass ratio of the molybdenum source to the sulfur source is 1:(1.5-2.5); The mass ratio of the ethylene tar distillation residue to the molybdenum source is (1-3):

1.

4. The method of claim 3, wherein the carbon-molybdenum disulfide composite negative electrode material is prepared by the steps of: mixing a carbon material and a molybdenum source to form a mixture; and heating the mixture to form the carbon-molybdenum disulfide composite negative electrode material. In step (2), the molybdenum source is one of sodium molybdate, ammonium molybdate, magnesium molybdate and potassium molybdate; The sulfur source is one of thiourea, ammonium thiocyanate, CH4N2S, ammonium sulfide, sodium sulfide, potassium sulfide and sodium thiosulfate; The solvent is one of dichloromethane, ethanol, cyclohexane and acetone. 5.The method of claim 1, wherein the carbon-molybdenum disulfide composite negative electrode material is prepared by the steps of: mixing a carbon material, a molybdenum source, and a sulfur source to form a mixture; and heating the mixture to obtain the carbon-molybdenum disulfide composite negative electrode material. In step (2), a pore former is also added; The mass ratio of the pore former to the ethylene tar distillation residue is (1.5-2.5):1; The pore former is one of calcium carbonate, silicon dioxide and calcium sulfate; The particle size of the pore former is 50-150 nm. 6.The method of claim 1, wherein the carbon-molybdenum disulfide composite negative electrode material is prepared by the steps of: mixing a carbon material, a molybdenum source, and a sulfur source to form a mixture; and heating the mixture to obtain the carbon-molybdenum disulfide composite negative electrode material. In step (3), the carbonization treatment is as follows: under an inert atmosphere, the temperature is 550-650°C, the heating rate is 1-5 ℃ / min, and the time is 2-5h. 7.The method of claim 1, wherein the carbon-molybdenum disulfide composite negative electrode material is prepared by the steps of: mixing a carbon material, a molybdenum source, and a sulfur source to form a mixture; and heating the mixture at a temperature of 300-600 ℃ in a vacuum or an inert gas atmosphere. In step (4), the acid is one of HF, HCl and HNO3.

8. A carbon-molybdenum disulfide composite negative electrode material prepared by the method of any one of claims 1-7.

9. Use of the carbon-molybdenum disulfide composite negative electrode material of claim 8 in the preparation of a sodium ion battery negative electrode material.

10. A sodium-ion battery, characterized in that, A sodium ion battery comprises a positive electrode, a negative electrode, an electrolyte, a separator and a current collector, wherein the negative electrode is the carbon-molybdenum disulfide composite negative electrode material of claim 8.

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