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

Abstract

The invention 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. Ethylene tar is adopted as a carbon source, and the carbon-molybdenum disulfide composite negative electrode material has the advantages of being sufficient in yield and low in price; the use of carbon to limit the volume expansion of molybdenum disulfide has great significance. The method is simple in technological process and low in cost, and has industrial production feasibility; the electrochemical performance of the ethylene tar-based composite carbon material in the negative electrode of the sodium-ion battery broadens the selection of production raw materials of the carbon negative electrode of the sodium-ion battery, and lays a foundation for the application of the ethylene tar-based composite carbon material in the field of battery application.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon negative electrode materials for sodium ion batteries, and specifically relates to a carbon-molybdenum disulfide composite negative electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have been widely used in electrochemical energy storage devices, but they can no longer meet the growing energy demand due to the low reserves of lithium. Sodium-ion batteries are considered to be the most promising alternative to lithium-ion batteries because their battery assembly technology is similar to that of lithium-ion batteries and the sodium reserves in the earth's crust are relatively abundant. However, since the atomic radius of metallic sodium is much larger than that of metallic lithium, the graphite anode material of traditional lithium-ion batteries is not suitable for use in sodium-ion batteries. Therefore, there is an urgent need to design new anode materials with larger lattice spacing to achieve higher sodium-ion storage capacity.

[0003] MoS2 is considered a promising negative electrode material for sodium-ion batteries due to its high capacity and graphene-like layered structure. However, the irreversible chemical reaction during the sodiumation / de-sodiumation process is a problem that must be overcome before its practical application; and the MoS2 nanostructure is prone to agglomeration during preparation and use, which will reduce the specific surface area of ​​the material and the exposure of the active sites, thereby affecting the storage and transmission of sodium ions and reducing the reversible specific capacity and cycle performance of the battery. It is urgent to study how to limit the expansion of MoS2 as a negative electrode for sodium-ion batteries. Summary of the invention

[0004] The purpose of the present invention is to provide a carbon-molybdenum disulfide composite negative electrode material and its preparation method and application, so as to overcome the shortcomings of the prior art, use ethylene tar with sufficient output and low price as a carbon source, and prepare an ethylene tar-based composite carbon material, which has great significance for limiting the volume expansion of molybdenum disulfide by using carbon. The method has a simple process and low cost, and is feasible for industrial production.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] In a first aspect, the present invention provides a method for preparing 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 ethylene tar distillation residue with a molybdenum source and a sulfur source and dissolving them in a solvent to obtain a first solid powder;

[0009] (3) carbonizing the first solid powder to obtain a second solid powder;

[0010] (4) The second solid powder is treated with acid and washed with water to obtain a carbon-molybdenum disulfide composite negative electrode material.

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

[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 thiourea, 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 porogen is also added;

[0018] The mass ratio of the porogen to the ethylene tar distillation residue is (1.5-2.5):1;

[0019] The porogen is one of calcium carbonate, silicon dioxide and calcium sulfate;

[0020] The particle size of the porogen is 50-150 nm.

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

[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 0.01-0.03 g / mL, the concentration of the acid is 35-45 wt%, and the treatment time is 1-2 h;

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

[0024] In a second aspect, the present invention provides a carbon-molybdenum disulfide composite negative electrode material prepared by the method for preparing the carbon-molybdenum disulfide composite negative electrode material described in the first aspect.

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

[0026] In a fourth aspect, the present invention 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 described in the second aspect.

[0027] Reaction mechanism: Evenly mixing and distributing carbon materials with molybdenum disulfide is the key to solving the low specific capacity of carbon materials and the poor cycle stability of molybdenum disulfide. The presence of carbon can evenly disperse molybdenum disulfide and avoid the agglomeration of molybdenum disulfide. When the volume of molybdenum disulfide changes, this carbon material can provide certain support and restrictions, making its expansion more uniform and alleviating the structural damage caused by local stress concentration. In addition, the carbon material itself has a certain flexibility, which can provide a buffer space for the volume expansion of molybdenum disulfide during the charging and discharging process, thereby greatly improving its electrochemical performance.

[0028] Beneficial effects of the present invention:

[0029] (1) The present invention uses ethylene tar as raw material, which has the advantage of low price. At the same time, carbon materials have good electrical conductivity. Evenly mixing and compounding with molybdenum disulfide can significantly improve the electron transmission capacity of the composite material, reduce the electron transmission resistance, and make the electrode reaction faster. At the same time, the presence of carbon can change the diffusion path and kinetics of sodium ions in molybdenum disulfide, reducing the diffusion energy barrier of sodium ions.

[0030] (2) During the charge and discharge process of sodium-ion batteries, a single molybdenum disulfide will expand and contract in volume, leading to the destruction and pulverization of the electrode structure, which in turn affects the battery's cycle performance. Carbon materials can serve as a physical support to limit the volume change of molybdenum disulfide, buffer its expansion stress, and reduce structural damage to the electrode material. Carbon materials are evenly dispersed with molybdenum disulfide to prevent them from agglomerating. When molybdenum disulfide changes in volume, carbon materials can provide certain support and restrictions to make its expansion more uniform.

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

[0032] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

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

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

[0035] Figure 3 are SEM and TEM images of the sample in Example 1 of the present invention;

[0036] Figure 4 is the mapping diagram of the sample in Example 1 of the present invention;

[0037] Figure 5 are SEM and TEM images of the sample in Example 2 of the present invention;

[0038] Figure 6 is the mapping diagram of the sample in Example 2 of the present invention;

[0039] Figure 7 is the XRD diagram of Examples 1 and 2 of the present invention;

[0040] Figure 8 are Raman spectra of Examples 1 and 2 of the present invention and Comparative Examples 1 and 2;

[0041] Fig. 9 are the N2 adsorption-desorption curves of Examples 1 and 2 of the present invention;

[0042] Fig.10 is a magnification diagram of Examples 1 and 2 of the present invention and Comparative Examples 1 and 2;

[0043] Fig.11 The results are as follows: Examples 1 and 2 of the present invention and Comparative Examples 1 and 2 at 0.5A g -1 Cyclic performance diagram at current density of ;

[0044] Fig.12 2 is the AC impedance diagram of Examples 1 and 2 of the present invention. DETAILED DESCRIPTION

[0045] In order to make the technical problems and technical solutions to be solved by the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments. Unless otherwise defined, all professional terms used below have the same meaning as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing the specific embodiments in detail and are not intended to limit the scope of protection of the present invention.

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

[0047] 1. Preparation of negative electrode materials

[0048] The present invention aims at solving the existing problems and provides a process flow chart of a method for preparing a carbon-molybdenum disulfide composite negative electrode material. Figure 1 As shown, the following is a detailed description in conjunction with a specific implementation method:

[0049] Example 1

[0050] A method for preparing a carbon-molybdenum disulfide composite negative electrode material for a sodium ion battery comprises the following steps:

[0051] Step (1): Ethylene tar (Sinopec Qingdao Refining and Chemical Co., Ltd.) is subjected to reduced pressure distillation at 350°C, with the distillation pressure close to vacuum, and maintained for 3 hours to obtain ethylene tar distillation residue, which is then ground into ethylene tar distillation residue solid powder of uniform size using a ball mill.

[0052] Step (2): Under normal temperature and pressure and magnetic stirring, 3 g of ethylene tar distillation residue is dissolved in an organic reagent CH2Cl2, followed by adding 3 g of Na2MoO4 and 6 g of CH4N2S. The mixture is mixed thoroughly until CH2Cl2 is completely naturally volatilized to obtain a brown-black block solid, which is then ground into a powder state.

[0053] Step (3): The ground brown-black powder is placed in a porcelain boat, and then placed in a tubular furnace filled with Ar atmosphere for high-temperature carbonization. The carbonization temperature used is 600°C, the carbonization time is 3h, and the carbonization heating rate is 5°C / min. After the carbonization is completed, it is naturally cooled to room temperature and then taken out and ground into a powder.

[0054] Step (4): The powder obtained in step (3) is placed in a 250 ml polytetrafluoroethylene container, 40 wt% HF (solid-liquid ratio 0.02 g / mL) is added, and after being fully washed, the powder is filtered and washed with water to obtain a negative electrode material.

[0055] Step (5): In a glove box filled with argon (H2O<0.01ppm and O2<0.01ppm), the prepared negative electrode material is assembled into a sodium ion battery (CR2032 type button battery). 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, dissolved in N-methylpyrrolidone (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 evenly coated on the surface of the copper foil using a SQZ-type four-sided preparation device, placed in a vacuum drying oven at 120°C for 6 hours, and then made into discs using a tablet press. After marking, they were stored in a sealed bag. Pure sodium was used as the counter electrode, and a glass fiber diaphragm (Whatman GF / D) was sandwiched between the sodium sheet and the electrode. The electrolyte used contained 1M NaPF6+EC / DEC+5%FEC.

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

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

[0059] Example 2

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

[0061] Comparative Example 1

[0062] The difference from Example 1 is that only 3 g of ethylene tar distillation residue is added in step (2), that is, 3 g of ethylene tar distillation residue is dissolved in an organic reagent CH2Cl2 at room temperature and pressure under magnetic stirring until CH2Cl2 is completely naturally volatilized to obtain a brown-black block solid, which is then ground into a powder state. The other preparation steps are the same as those in Example 1.

[0063] Comparative Example 2

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

[0065] Comparative Example 3

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

[0067] Comparative Example 4

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

[0069] Comparative Example 5

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

[0071] Comparative Example 6

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

[0073] 2. Performance Test

[0074] The ethylene tar used in the present invention was subjected to vacuum distillation at 350°C to obtain an ethylene tar distillation residue for elemental analysis, and the results are shown in Table 1. Ethylene tar contains a large amount of light components. If most of the light components are not removed by distillation, it is easy to block the pipeline of the tubular furnace. Similarly, in industrial production, if ethylene tar is directly added to a horizontal furnace such as a rotary kiln, due to the high viscosity of ethylene tar, when it flows in the pipeline, the internal friction between its molecules is large, and the flow resistance is also large, and it is easy to adhere to the inner wall of the pipeline, gradually accumulate and cause pipeline blockage. This problem can be effectively avoided by first subjecting ethylene tar to vacuum distillation to remove most of the light components to obtain a solid residue before conducting a further experiment or production.

[0075] Table 1 Element contents in ethylene tar residue

[0076]

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

[0078] The infrared spectrum of ethylene tar distillation residue was tested, and the results were as follows: Figure 2 As shown. Figure 2 It can be seen that the main chemical bonds of ethylene tar distillation residue are CO, C=C, C=O, CH and a small amount of CN, among which C=C, C=O and benzene ring will produce conjugation effect. The conjugated structure has higher stability and is conducive to retaining more active sites, such as C=O, during the carbonization process.

[0079] The samples prepared in Example 1 were subjected to SEM and TEM tests, and the results were as follows: Figure 3 As shown, (ac) are SEM images, (df) are TEM images, where the scale bar in d is 100nm, the scale bar in e is 50nm, and the scale bar in f is 5nm. Figure 3 It can be seen that carbon and molybdenum disulfide are uniformly dispersed in the prepared carbon-molybdenum disulfide composite negative electrode material. Figure 5 These are the SEM and TEM images of the sample in Example 2 of the present invention. (ac) are SEM images, (df) are TEM images, and the scale bar in d is 100nm, the scale bar in e is 50nm, and the scale bar in f is 5nm. Figure 5 In (ac), it can be clearly observed that the morphology of the prepared carbon-molybdenum disulfide composite negative electrode material is significantly 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, thereby expanding the number of pores and specific surface area. The rich pore structure and increased specific surface area provide more active sites for electrochemical reactions, and more ions can react on the electrode surface.

[0080] Figure 4 is the mapping diagram of the sample in Example 1 of the present invention, with a scale of 500 nm; Figure 6 This is the mapping diagram of the sample in Example 2 of the present invention, with a scale of 500 nm. Figure 4 , Figure 6It can be seen that the main elements C, H, O, N, S, Mo, and Na in the samples prepared in Example 1 and Example 2 are evenly distributed, indicating that the carbon and molybdenum disulfide are mixed more evenly, which is beneficial to the improvement of the electrochemical performance.

[0081] Figure 7 It is the XRD diagram of Examples 1 and 2 of the present invention. Figure 7 It can be seen that Examples 1 and 2 have obvious characteristic peaks of molybdenum disulfide, indicating that molybdenum disulfide has been successfully synthesized.

[0082] Figure 8 It is the Raman spectra of Examples 1 and 2 of the present invention and Comparative Examples 1 and 2. As can be seen from Figure 8, Example 1 and Comparative Example 2 have obvious characteristic peaks of molybdenum disulfide, which further proves the synthesis of molybdenum disulfide. However, the characteristic peak of molybdenum disulfide was not clearly observed in Example 2. This may be because most of the molybdenum disulfide was hidden inside the carbon after pore formation, so that the laser could not effectively irradiate the molybdenum disulfide, or the Raman scattering signal generated by molybdenum disulfide was difficult to transmit, so that its characteristic peak could not be detected. Compared with the XRD of Example 1, the molybdenum disulfide crystal planes detected by the XRD of Example 2 are significantly reduced, which can further support this conclusion.

[0083] Fig. 9 2 are the N2 adsorption-desorption curves of Examples 1 and 2 of the present invention. It can be seen that the pores of the negative electrode material prepared in Example 1 are relatively sparse and the specific surface area is small. The specific surface area and pores of Example 2 are significantly improved compared with those of Example 1. This is because the addition of nano-SiO2 increases its specific surface area, and a large number of pore structures are formed inside the material. The rich pore structure provides more active sites for electrochemical reactions, and more ions can react on the electrode surface.

[0084] Fig.10 It is a ratio diagram of Examples 1 and 2 of the present invention and Comparative Examples 1 and 2. Fig.10 It can be seen that Example 1 has good -1 The discharge specific capacities at current densities of 820.39, 328.65, 292.81, 256.56, 226.57, and 193.96 mAh g -1 Example 2 at 0.05, 0.1, 0.2, 0.5, 1 and 2A g -1 The discharge specific capacities at current densities of 1558.64, 388.00, 355.44, 285.88, 249.38, and 216.89 mAh g -1 Comparative Example 1 at 0.05, 0.1, 0.2, 0.5, 1 and 2A g -1The discharge specific capacities at current densities of 722.48, 244.04, 220.58, 192.34, 164.60, and 127.40 mAh g -1 Comparative Example 2 at 0.05, 0.1, 0.2, 0.5, 1 and 2A g -1 The discharge specific capacities at current densities of 900.54, 406.98, 389.59, 358.71, 330.06, and 306.94 mAh g -1 .

[0085] From the above results, it can be seen that the addition of nano-SiO2 in Example 2 will lead to improved charge and discharge performance, because the addition of nano-SiO2 will increase its specific surface area, and a large number of pore structures will be formed inside the material. The rich pore structure provides more active sites for electrochemical reactions, and more ions can react on the electrode surface, thereby improving the specific capacity. The addition of only ethylene tar distillation residue in Comparative Example 1 will lead to reduced charge and discharge performance, because there is only carbon in it and no in-situ synthesized molybdenum disulfide that can provide a high specific capacity is added. The omission of the addition of ethylene tar distillation residue in Comparative Example 2 will lead to improved charge and discharge performance, because it is mainly in-situ synthesized molybdenum disulfide that can provide a high specific capacity and only a small amount of carbon.

[0086] Fig.11 The results are as follows: Examples 1 and 2 of the present invention and Comparative Examples 1 and 2 at 0.5A g -1 Table 2 shows the electrochemical performance of the embodiments and comparative examples.

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

[0088]

[0089]

[0090] From Table 2 and Fig.11It 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%). This is because the addition of nano-SiO2 will affect the interfacial bonding force between the carbon layer and molybdenum disulfide, destroying the originally good interfacial contact, making it difficult for the carbon layer to effectively play a buffering and protective role. Molybdenum disulfide is easily separated from the carbon layer when the volume changes, which leads to structural instability and a decrease in cycle performance. Compared with Example 1, Comparative Example 1 has good cycle stability, and the capacity retention rate after 300 cycles is 89.2%. Adding only ethylene tar distillation residue will lead to better cycle performance. This is because Comparative Example 1 contains only carbon but not in-situ synthesized molybdenum disulfide that 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%. Omitting the addition of ethylene tar distillation residue will lead to a significant decrease in cycle electrical performance. This is because there is no carbon to limit the volume expansion of molybdenum disulfide, and the capacity attenuation caused by its volume expansion is too serious.

[0091] Comparative Example 3 3g of ethylene tar was directly mixed with 3g of Na2MoO4 and 6g of CH4N2S. Under normal temperature and pressure and magnetic stirring, 3g of ethylene tar, 3g of Na2MoO4, and 6g of CH4N2S were uniformly dispersed in an organic reagent CH2Cl2, and fully mixed until CH2Cl2 was completely naturally volatilized to obtain a brown-black liquid. The material obtained after carbonization was used as a negative electrode material for a sodium ion battery. Compared with Example 1, its specific capacity and cycle performance were not much different, but it was easy to block the pipeline of a tubular furnace because it was a liquid feed. Similarly, if ethylene tar is directly added to a horizontal furnace such as a rotary kiln during industrial production, due to the high viscosity of ethylene tar, when it flows in a pipeline, its intermolecular internal friction is large, and its flow resistance is also large, and it is easy to adhere to the inner wall of the pipeline, gradually accumulating and causing pipeline blockage, which is not conducive to industrial production.

[0092] Comparative Example 4: Starch was used instead of ethylene tar distillation residue. 3g starch was directly mixed with 3g Na2MoO4 and 6g CH4N2S. 3g starch, 3g Na2MoO4 and 6g CH4N2S were uniformly dispersed in an organic reagent CH2Cl2 under normal temperature and pressure and magnetic stirring. The mixture was fully mixed until CH2Cl2 was completely volatilized naturally to obtain a white solid powder, which was then carbonized and used as a negative electrode material for sodium ion batteries. -1 The discharge capacity at the current density is 204.46 mAh g -1 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 used a hydrothermal method to synthesize a molybdenum disulfide-carbon composite material, that is, Na2MoO4, CH4N2S and sucrose in a mass ratio of 1:2:1 were dissolved in 50mL of deionized water, stirred evenly, transferred to a stainless steel reactor, and hydrothermally reacted at 180℃ for 36h. The product was washed with deionized water by centrifugation and dried. The material obtained by calcining at 850℃ for 2h in a mixture of hydrogen and nitrogen (volume ratio 1:9) was used as a negative electrode material for sodium ion batteries. Its 0.5A g -1 The discharge capacity at the current density is 210.46 mAh g -1 The cycle capacity retention rate after 300 cycles is 75.4%, which is lower than the negative electrode material provided in Example 1.

[0094] Comparative Example 6 is different from Example 1 in that the acid treatment step is omitted. -1 The discharge capacity at the current density is 245.80 mAh g -1 The cycle capacity retention rate after 300 cycles is 78.6%, which is slightly lower than that of Example 1. This is because the material may contain some impurities that affect its electrochemical properties without acid washing, and the pores that are not fully opened are not conducive to the material storing sodium ions.

[0095] Fig.12 1 and 2 are AC impedance diagrams of embodiments 1 and 2 of the present invention, and the test frequency range is 0.01 Hz to 100 kHz. Fig.12 It can be seen that Example 2 has a higher resistance than Example 1. This may be because the pore-forming process destroys the structural integrity of carbon and molybdenum disulfide itself. The originally continuous carbon layer and molybdenum disulfide crystal structure are good channels for electron conduction. After pore formation, these channels are interrupted or distorted. Electrons will encounter more scattering and obstacles during the conduction process, thereby increasing the resistance.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a carbon-molybdenum disulfide composite negative electrode material, characterized in that: The following steps are involved: (1) subjecting ethylene tar to vacuum distillation to obtain ethylene tar distillation residue; (2) mixing ethylene tar distillation residue with a molybdenum source and a sulfur source and dissolving them in a solvent to obtain a first solid powder; (3) carbonizing the first solid powder to obtain a second solid powder; (4) The second solid powder is treated with acid and washed with water to obtain a carbon-molybdenum disulfide composite negative electrode material.

2. The method for preparing a carbon-molybdenum disulfide composite negative electrode material according to claim 1, characterized in that: In step (1), the temperature of the reduced pressure distillation treatment is 300-400°C, the pressure is 0-100 Pa, and the time is 2-3 hours.

3. The method for preparing the carbon-molybdenum disulfide composite negative electrode material according to claim 1, characterized in that: 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 for preparing the carbon-molybdenum disulfide composite negative electrode material according to claim 3, characterized in that: 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 for preparing the carbon-molybdenum disulfide composite negative electrode material according to claim 1, characterized in that: In step (2), a porogen is also added; The mass ratio of the porogen to the ethylene tar distillation residue is (1.5-2.5):1; The porogen is one of calcium carbonate, silicon dioxide and calcium sulfate; The particle size of the porogen is 50-150 nm.

6. The method for preparing the carbon-molybdenum disulfide composite negative electrode material according to claim 1, characterized in that: In step (3), the carbonization treatment is carried out under an inert atmosphere at a temperature of 550-650°C, a heating rate of 1-5°C / min, and a time of 2-5h.

7. The method for preparing a carbon-molybdenum disulfide composite negative electrode material according to claim 1, characterized in that: 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 35-45 wt%, and the treatment time is 1-2 h; The acid is one of HF, HCl and HNO3.

8. A carbon-molybdenum disulfide composite negative electrode material obtained by the method for preparing a carbon-molybdenum disulfide composite negative electrode material according to any one of claims 1 to 7.

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

10. A sodium ion battery, characterized in that: The invention 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 as claimed in claim 8.

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