A kind of negative electrode material of potassium ion battery and preparation method thereof

Abstract

The present invention provides a potassium ion battery negative electrode material and a preparation method thereof, wherein the potassium ion battery negative electrode material is based on exfoliated graphite, and molybdenum disulfide nanosheets with large interlayer spacing are dispersed on the exfoliated graphite substrate to form a molybdenum disulfide / exfoliated graphite composite material with large interlayer spacing, wherein the interlayer spacing of the molybdenum disulfide can reach a large interlayer spacing. Molybdenum disulfide with large interlayer spacing is beneficial to reducing the stress generated by the material during the process of potassium insertion and extraction, thereby improving the cycle stability of the material and the life of the battery. The large interlayer spacing molybdenum disulfide / exfoliated graphite composite material provided by the present invention exhibits good electrochemical performance when applied to potassium ion batteries, and has good application prospects as a negative electrode material for potassium ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrode materials, and in particular to a potassium ion battery negative electrode material and a preparation method thereof. Background Art

[0002] As an emerging electrochemical energy storage system, potassium ion batteries have become one of the research hotspots in recent years. On the one hand, potassium has an abundance of about 2.09% in the earth's crust and its resource reserves are abundant, so the price is relatively low; on the other hand, it has a hydrogen standard electrode potential close to that of lithium (-2.93V vs. SHE), and has the potential to prepare high-energy density full batteries; on the other hand, potassium has the smallest Stokes radius in organic systems, so it has a relatively high ionic conductivity and is expected to prepare batteries with high rate performance. Based on the above analysis, potassium ion batteries have broad development prospects as large-scale energy storage devices in the future.

[0003] Potassium-ion batteries are mainly composed of positive electrodes, negative electrodes, separators and electrolytes. Among them, negative electrode materials are crucial to the practical application of potassium-ion batteries. Graphite is low-priced, highly conductive and easy to industrialize, and is regarded as one of the most promising negative electrode materials for potassium-ion batteries. Potassium ions are similar to lithium ions, but unlike sodium ions, potassium ions can be embedded in the graphite interlayer to form intercalation compounds, and finally form the first-order product KC8, which can release a specific capacity of 279mAh / g. In addition, the graphite negative electrode also has the characteristics of a low voltage platform, which is conducive to improving the energy density of the whole battery. However, graphite as the negative electrode of potassium-ion batteries also faces many challenges. For example, due to the large ionic radius of potassium ions, during the charge and discharge process, the volume of graphite will expand by nearly 60% along the C axis after embedding potassium ions. The destruction of the structure will cause the diffusion kinetics of graphite deintercalation of potassium to be slow, and the rate performance and cycle stability are poor.

[0004] Therefore, it is necessary to develop a better potassium ion battery negative electrode material to improve the electrochemical performance of potassium ion batteries. Summary of the invention

[0005] The object of the present invention is to provide a potassium ion battery negative electrode material and a preparation method thereof, so that the potassium ion battery negative electrode material exhibits better electrochemical performance and improves its application prospect.

[0006] To achieve the above object, the present invention provides a potassium ion battery negative electrode material, which is based on exfoliated graphite, and molybdenum disulfide nanosheets with large interlayer spacing are dispersed on the exfoliated graphite substrate to form a large interlayer spacing molybdenum disulfide / exfoliated graphite composite material, wherein the interlayer spacing of molybdenum disulfide is The molybdenum disulfide / exfoliated graphite composite material with a large interlayer spacing provided by the present invention exhibits good rate performance, high reversible capacitance and excellent cycle stability when used as a negative electrode material for a potassium ion battery.

[0007] Furthermore, in the molybdenum disulfide / exfoliated graphite composite material, the mass ratio of molybdenum disulfide to exfoliated graphite is (0.2-0.4):1.

[0008] Another aspect of the present invention provides a method for preparing the above-mentioned potassium ion battery negative electrode material, which mainly comprises the following steps:

[0009] S1, adding exfoliated graphite to a mixed solution of deionized water and ethanol to obtain an exfoliated graphite dispersion;

[0010] S2, adding polydiallyldimethylammonium chloride and a molybdenum source into deionized water respectively to dissolve them, and then mixing them together to form a mixed solution;

[0011] S3, adding the exfoliated graphite dispersion obtained in S1 to the mixed solution obtained in S2, and then adding a sulfur source, after hydrothermal reaction, vacuum filtering, washing, and drying to obtain a molybdenum disulfide / exfoliated graphite precursor;

[0012] S4, calcining the molybdenum disulfide / exfoliated graphite precursor obtained in S3 under an argon atmosphere to obtain a molybdenum disulfide / exfoliated graphite composite material.

[0013] Furthermore, in step S1, after the exfoliated graphite is added to the mixed solution of deionized water and ethanol, it is necessary to firstly ultrasonically disperse it for 30-120 minutes and then crush the cells for 10-20 minutes, so that the exfoliated graphite is more evenly dispersed in the solution.

[0014] Further, in step S2, the mass ratio of the added polydiallyldimethylammonium chloride and the molybdenum source is 2:1, in step S1 and step S3, the mass ratio of the added exfoliated graphite and the sulfur source is 1:(0.8-2), and in step S2 and step S3, the mass ratio of the added molybdenum source and the sulfur source is 1:2. The present invention obtains molybdenum disulfide with a larger interlayer spacing by controlling the ratio of the added raw materials, and at the same time, the molybdenum disulfide with a larger interlayer spacing is uniformly dispersed on the exfoliated graphite substrate, so that the molybdenum disulfide / exfoliated graphite exhibits better electrochemical performance when used as the negative electrode material of the potassium ion battery.

[0015] Furthermore, in step S2, the molybdenum source is ammonium molybdate, which is more conducive to inserting into the interlayer of molybdenum disulfide, expanding the interlayer spacing, and improving the electrochemical performance of the composite material.

[0016] Furthermore, in step S3, the sulfur source is thiourea or thioacetamide, or a mixture of the two.

[0017] Furthermore, in step S3, the temperature of the hydrothermal reaction is controlled at 180-220°C for 18-22 hours. The present invention can make the MoS2 nanosheets with large interlayer spacing more evenly dispersed on the exfoliated graphite substrate by controlling the temperature and time of the hydrothermal reaction, effectively preventing the agglomeration of MoS2 and deteriorating the electrochemical properties of the material.

[0018] Furthermore, in step S3, the drying condition is freeze-drying at -60°C for 10-12 hours. The freeze-drying method can maintain the original pore structure of the material. When used as an electrode material, it is beneficial to the full contact between the electrode and the electrolyte, reducing the transmission distance of ions in the electrolyte, accelerating the redox reaction, further reducing the accumulation of net charge on the surface of the material, reducing polarization, and thus improving the electrochemical performance of the battery.

[0019] Furthermore, in step S4, the molybdenum disulfide / exfoliated graphite precursor is calcined at a temperature of 700-900°C at a heating rate of 2-8 / min and kept at that temperature for 1-6 hours. The present invention improves the electrochemical performance of the composite material by controlling the calcination temperature and time.

[0020] Beneficial effects of the present invention:

[0021] 1. The molybdenum disulfide / exfoliated graphite composite material provided by the present invention has the following characteristics: 1) Exfoliated graphite can relieve the stress generated by volume expansion and further improve the stability of the electrode; in addition, exfoliated graphite can shorten the ion diffusion distance, which is beneficial to improving the rate performance of the battery. 2) MoS2 with a large interlayer spacing can effectively relieve the mechanical stress during the cycle, which is beneficial to the structural stability of the electrode and improves the specific capacity of the composite material. 3) Molybdenum disulfide with a pseudocapacitive potassium storage mechanism is used to quickly adsorb potassium ions, increase the potassium ion concentration difference between the graphite surface and the bulk phase, and then promote rapid ion diffusion, without losing voltage but accelerating potassium storage kinetics. Therefore, the molybdenum disulfide / exfoliated graphite composite material has a lower discharge voltage platform, better rate performance, higher reversible capacitance and better cycle stability as the negative electrode material of potassium ion batteries, and has good application prospects.

[0022] 2. The preparation method provided by the present invention is simple and feasible, the raw materials are cheap and easily available, the solvent is safe, and it is easy to industrialize production, popularize and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a SEM image of the original exfoliated graphite provided in Example 1 of the present invention.

[0024] Figure 2 This is the XRD diagram of the molybdenum disulfide / exfoliated graphite composite material provided in Example 2 of the present invention.

[0025] Figure 3 This is a TEM image of the molybdenum disulfide / exfoliated graphite composite material provided in Example 2 of the present invention.

[0026] Figure 4 This is a SEM image of the molybdenum disulfide / exfoliated graphite composite material provided in Example 2 of the present invention.

[0027] Figure 5 This is a SEM image of the molybdenum disulfide / exfoliated graphite composite material provided in Example 3 of the present invention.

[0028] Figure 6 This is a SEM image of the molybdenum disulfide / exfoliated graphite composite material provided in Example 4 of the present invention.

[0029] Figure 7 This is a graph showing the cycling performance of the molybdenum disulfide / exfoliated graphite composite material provided in Example 2 of the present invention as a negative electrode for a potassium ion battery at a current density of 100 mA / g.

[0030] Figure 8 This is a charge and discharge curve diagram of the molybdenum disulfide / exfoliated graphite composite material provided in Example 2 of the present invention as the negative electrode of a potassium ion battery at a current density of 100 mA / g.

[0031] Fig. 9 This is a rate performance diagram of the molybdenum disulfide / exfoliated graphite composite material provided in Example 2 of the present invention as a potassium ion negative electrode at different current densities.

[0032] Fig.10 This is a graph showing the cycling performance of the molybdenum disulfide / exfoliated graphite composite material provided in Example 2 of the present invention as a negative electrode for a lithium-ion battery at a current density of 1000 mA / g.

[0033] Fig.11 This is a graph showing the cycling performance of the molybdenum disulfide / exfoliated graphite composite material provided in Example 3 of the present invention as a negative electrode for a potassium ion battery at a current density of 100 mA / g.

[0034] Fig.12 This is a graph showing the cycling performance of the molybdenum disulfide / exfoliated graphite composite material provided in Example 4 of the present invention as a negative electrode for a potassium ion battery at a current density of 100 mA / g.

[0035] Fig.13 This is a rate performance diagram of the exfoliated graphite provided in Example 1 of the present invention as the negative electrode of a potassium ion battery at different current densities. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that the exfoliated graphite is obtained by a known and publicly available preparation method, and the remaining raw materials are purchased through commercial channels.

[0038] Example 1. Preparation of original exfoliated graphite

[0039] Weigh 180 mg of exfoliated graphite, add 25 ml of deionized water and 5 ml of ethanol, ultrasonically disperse for 120 minutes, and crush the cells for 20 minutes to obtain an exfoliated graphite dispersion. The exfoliated graphite dispersion was transferred to a 100 ml reactor for hydrothermal reaction at 200 ° C for 20 hours. After the system was cooled to room temperature, vacuum filtered, washed alternately with water and ethanol 3 times each, and the obtained product was freeze-dried at -60 ° C for 12 hours to obtain the original exfoliated graphite precursor. The precursor product was transferred to a porcelain ark, then placed in a tubular furnace, and heated to 800 ° C at a heating rate of 3 ° C / min under the protection of an argon atmosphere, and kept warm for 2 hours to obtain the original exfoliated graphite, referred to as EG.

[0040] Example 2: Preparation of MoS2 / Exfoliated Graphite Composite Material

[0041] S1. Add 180 mg of exfoliated graphite to 25 ml of deionized water and 5 ml of ethanol, perform ultrasonic dispersion for 120 minutes, and crush the cells for 20 minutes to obtain an exfoliated graphite dispersion;

[0042] S2, add 225 mg of polydiallyldimethylammonium chloride into 20 ml of deionized water to dissolve, add 112.5 mg of ammonium molybdate tetrahydrate into 10 ml of deionized water to dissolve, and then mix the two solutions together and stir for 30 minutes;

[0043] S3, adding the exfoliated graphite dispersion of S1 to the mixed solution of S2, and then adding 225 mg of thiourea, stirring for 30 minutes, and then transferring to a 100 ml reactor, and hydrothermally reacting at 200° C. for 20 hours, cooling to room temperature, and vacuum filtering, the product was washed alternately with water and ethanol for 3 times, and the product was freeze-dried at -60° C. for 12 hours to obtain a molybdenum disulfide / exfoliated graphite precursor;

[0044] S4. The molybdenum disulfide / exfoliated graphite precursor prepared in S3 was transferred into a porcelain ark, placed in a test tube furnace, heated to 800° C. at a heating rate of 3° C. / min under an argon atmosphere, and kept at this temperature for 2 hours to obtain molybdenum disulfide / exfoliated graphite with a large interlayer spacing.

[0045] Example 3: Preparation of MoS2 / Exfoliated Graphite Composite Material

[0046] S1. Add 180 mg of exfoliated graphite to 25 ml of deionized water and 5 ml of ethanol, perform ultrasonic dispersion for 120 minutes, and crush the cells for 20 minutes to obtain an exfoliated graphite dispersion;

[0047] S2, add 150 mg of polydiallyldimethylammonium chloride into 20 ml of deionized water to dissolve, add 75 mg of ammonium molybdate tetrahydrate into 10 ml of deionized water to dissolve, and then mix the two solutions together and stir for 30 minutes;

[0048] S3, adding the exfoliated graphite dispersion of S1 to the mixed solution of S2, and then adding 150 mg of thiourea, stirring for 30 minutes, and then transferring to a 100 ml reactor, and keeping the hydrothermal reaction at 180° C. for 22 hours, cooling to room temperature, vacuum filtering, and washing the product with water and ethanol alternately for 3 times, and freeze-drying the product at -60° C. for 12 hours to obtain a molybdenum disulfide / exfoliated graphite precursor;

[0049] S4. The molybdenum disulfide / exfoliated graphite precursor prepared in S3 was transferred into a porcelain ark, placed in a test tube furnace, heated to 700° C. at a heating rate of 2° C. / min under an argon atmosphere, and kept at this temperature for 2 hours to obtain molybdenum disulfide / exfoliated graphite with a large interlayer spacing.

[0050] Example 4. Preparation of MoS2 / Exfoliated Graphite Composite Material

[0051] S1. Add 180 mg of exfoliated graphite to 25 ml of deionized water and 5 ml of ethanol, perform ultrasonic dispersion for 120 minutes, and crush the cells for 20 minutes to obtain an exfoliated graphite dispersion;

[0052] S2, add 300 mg of polydiallyldimethylammonium chloride into 20 ml of deionized water to dissolve, add 150 mg of ammonium molybdate tetrahydrate into 10 ml of deionized water to dissolve, and then mix the two solutions together and stir for 30 minutes;

[0053] S3, adding the exfoliated graphite dispersion of S1 to the mixed solution of S2, and then adding 300 mg of thiourea, stirring for 30 minutes, transferring to a 100 ml reactor, keeping it in 220 ° C hydrothermal for 18 hours, cooling to room temperature, vacuum filtering, washing the product with water and ethanol alternately for 3 times, and freeze-drying the product at -60 ° C for 12 hours to obtain a molybdenum disulfide / exfoliated graphite precursor;

[0054] S4. The molybdenum disulfide / exfoliated graphite precursor prepared in S3 was transferred into a porcelain ark, placed in a test tube furnace, heated to 800° C. at a heating rate of 9° C. / min under an argon atmosphere, and kept at this temperature for 2 hours to obtain molybdenum disulfide / exfoliated graphite with a large interlayer spacing.

[0055] Example 5. Preparation of MoS2 / Exfoliated Graphite Composite Material

[0056] In this embodiment, the experimental steps and experimental conditions are the same as those in the second embodiment, except that in this embodiment, in step S3, the temperature of the hydrothermal reaction is 150° C. and the reaction time is 30 hours.

[0057] Example 6. Preparation of MoS2 / Exfoliated Graphite Composite Material

[0058] In this embodiment, the experimental steps and experimental conditions are the same as those in the second embodiment, except that in this embodiment, in step S3, the temperature of the hydrothermal reaction is 250° C. and the reaction time is 15 hours.

[0059] Example 7. Preparation of MoS2 / Exfoliated Graphite Composite Material

[0060] In this embodiment, the experimental steps and experimental conditions are the same as those in the second embodiment, except that in this embodiment, the molybdenum source is sodium molybdate and the sulfur source is thioacetamide.

[0061] Example 8. Preparation of MoS2 / Exfoliated Graphite Composite Material

[0062] In this embodiment, the experimental steps and experimental conditions are the same as those in the second embodiment, except that in this embodiment, in step S4, the calcination temperature is controlled at 400° C. and kept at this temperature for 6 hours.

[0063] Example 9. Preparation of MoS2 / Exfoliated Graphite Composite Material

[0064] In this embodiment, the experimental steps and experimental conditions are the same as those in the second embodiment, except that in this embodiment, in step S4, the calcination temperature is controlled at 1000° C. and kept at this temperature for 1 hour.

[0065] Example 10. Preparation of MoS2 / Exfoliated Graphite Composite Material

[0066] In this embodiment, the experimental steps and experimental conditions are the same as those in Example 2, except that in this embodiment, in step S4, the heating rate is 9°C / min, the calcination temperature is controlled at 900°C, and the temperature is kept at 900°C for 1 hour.

[0067] Figure 1 , Figure 4 , Figure 5 and Figure 6 SEM images of the original exfoliated graphite prepared in Example 1 and the molybdenum disulfide / exfoliated graphite composite materials prepared in Example 2, Example 3 and Example 4 are provided. Figure 1 It can be seen that the original exfoliated graphite obtained in Example 1 is a flake structure with a relatively smooth surface. Figure 4 , Figure 5 It can be seen that in the molybdenum disulfide / exfoliated graphite composite materials prepared in Example 2 and Example 3, many MoS2 nanosheets are evenly distributed on the exfoliated graphite substrate; Figure 6 It can be seen that in the molybdenum disulfide / exfoliated graphite composite material prepared in Example 4, part of the MoS2 itself agglomerated and was not completely coated on the exfoliated graphite. Therefore, by controlling the ratio of the raw materials, it is possible to prevent the MoS2 from agglomerating itself and make the MoS2 evenly distributed on the exfoliated graphite substrate.

[0068] In the molybdenum disulfide / exfoliated graphite composite materials prepared in Examples 2 to 10, the interlayer spacing of MoS2 has expanded to varying degrees. between. Figure 2 The XRD diagram of the molybdenum disulfide / exfoliated graphite composite material prepared in Example 2 shows that the sharp diffraction peak at 2θ=26.5° corresponds to graphite, and its peak shape is sharp, indicating high crystallinity. The diffraction peak at 2θ=8.1° corresponds to molybdenum disulfide. From this, it can be inferred that the interlayer spacing of MoS2 in the molybdenum disulfide / exfoliated graphite composite material prepared in Example 2 is Interlayer spacing compared to ordinary MoS2 Compared with the figure, it has expanded by about 50%, indicating that the insertion of residual carbon after carbonization of polydiallyldimethylammonium chloride has expanded its interlayer spacing.

[0069] Figure 3 This is a TEM image of the molybdenum disulfide / exfoliated graphite composite material prepared in Example 2. The lattice fringes of graphite and expanded MoS2 can be clearly observed in the image, indicating that MoS2 with a large interlayer spacing is uniformly distributed on the surface of the exfoliated graphite substrate.

[0070] The electrochemical performance of the original exfoliated graphite prepared in Example 1 and the molybdenum disulfide / exfoliated graphite composite material prepared in Example 2 was tested. The test method was to mix the active material: conductive agent SuperP: polyvinylidene fluoride PVDF in a mass ratio of 8:1:1, add N-methylpyrrolidone NMP as a dispersant to make a slurry, evenly coat it on a copper foil, vacuum dry it at 120°C for 12h, cut it into pole pieces with a diameter of 12mm, and assemble a potassium ion half-cell in an argon-protected glove box. The assembled half-cell battery shell model is CR 2016, with metallic potassium as the counter electrode, glass fiber as the diaphragm, and the electrolyte is 0.8mol / L KPF6 dissolved in EC (ethylene carbonate): DEC (diethyl carbonate) = 1: 1 (v / v).

[0071] After the assembled potassium ion battery was left to stand for 12 h, the charge and discharge test was performed at a current density of 100 mA / g, and the voltage window was set at 0.01-3.0 V. Figure 7 It can be seen that the molybdenum disulfide / exfoliated graphite composite material prepared in Example 2 as a negative electrode still has a specific capacity of 292 mAh / g after 250 discharge cycles. Fig.10 It can be seen that the charge and discharge test was carried out at a current density of 1000 mA / g, and the specific capacity of 295 mAh / g can still be maintained after 200 cycles. The molybdenum disulfide / exfoliated graphite composite material prepared in Example 2 as the negative electrode of the potassium ion battery exhibits a high specific capacity and excellent cycle stability. Figure 8 From the charge and discharge curves provided, it can be seen that after the second cycle, the specific capacity provided below 0.36V voltage is about 277mAh / g. This stage is mainly provided by graphite intercalation compounds formed by potassium intercalation in graphite, which is conducive to improving the energy density of potassium ion full batteries. Fig. 9 It can be seen that the discharge specific capacity is still as high as 126 mAh / g and 61 mAh / g at current densities of 3.2 A / g and 6.4 A / g. The molybdenum disulfide / exfoliated graphite composite material prepared in Example 2 exhibits excellent rate performance as the negative electrode of the potassium ion battery.

[0072] Depend on Figure 11-13 It can be seen that the molybdenum disulfide / exfoliated graphite composite material prepared in Example 2 has better electrochemical performance as the negative electrode of the potassium ion battery than that prepared in Example 1, Example 3 and Example 4.

[0073] Table 1 shows the battery performance data of the molybdenum disulfide / exfoliated graphite composite material provided in Example 2 and Examples 5 to 10 of the present invention as the negative electrode of the potassium ion battery under different conditions.

[0074]

[0075] As can be seen from the above table, from the data of Example 2, Example 5 and Example 6, as the hydrothermal reaction temperature increases and the time is extended, molybdenum disulfide may agglomerate, deteriorating the material performance. From the data of Example 2 and Example 7, it can be seen that compared with sodium molybdate, ammonium molybdate is more conducive to improving battery performance. From the data of Example 2, Example 8 and Example 9, it can be seen that too low annealing temperature will destroy the chain structure of PDDA itself and reduce the conductivity of the polymer itself, while high temperature carbonization of PDDA is conducive to improving the crystallinity of residual carbon and increasing conductivity, while too high annealing temperature will cause molybdenum disulfide to agglomerate, so a suitable annealing temperature is beneficial to improving battery performance. From the data of Example 2 and Example 10, it can be seen that a suitable heating rate is beneficial to the electrochemical properties of the material.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode material for a potassium ion battery, characterized in that: The negative electrode material of the potassium ion battery is a molybdenum disulfide / exfoliated graphite composite material formed by dispersing molybdenum disulfide nanosheets with large interlayer spacing on the exfoliated graphite substrate with exfoliated graphite as the substrate, and the interlayer spacing of molybdenum disulfide in the molybdenum disulfide / exfoliated graphite composite material is 8.84-10.36Å; the preparation method of the negative electrode material of the potassium ion battery comprises the following steps: S1, adding exfoliated graphite to a mixed solution of deionized water and ethanol to obtain an exfoliated graphite dispersion; S2, adding polydiallyldimethylammonium chloride and a molybdenum source into deionized water respectively to dissolve, and then mixing them together to form a mixed solution; S3, adding the exfoliated graphite dispersion obtained in S1 to the mixed solution obtained in S2, and then adding a sulfur source, after hydrothermal reaction, vacuum filtering, washing, and drying to obtain a molybdenum disulfide / exfoliated graphite precursor; S4, calcining the molybdenum disulfide / exfoliated graphite precursor obtained in S3 under an argon atmosphere to obtain a molybdenum disulfide / exfoliated graphite composite material; Wherein, in the step S4, the calcination conditions of the molybdenum disulfide / exfoliated graphite precursor are to increase the temperature to 700-900° C. at a heating rate of 2-8° C. / min and keep the temperature for 1-6 hours.

2. The potassium ion battery negative electrode material according to claim 1, characterized in that In the molybdenum disulfide / exfoliated graphite composite material, the mass ratio of molybdenum disulfide to exfoliated graphite is (0.2-0.4):

1.

3. The potassium ion battery negative electrode material according to claim 1, characterized in that In the step S1, the exfoliated graphite is added to deionized water and ethanol and then ultrasonically dispersed for 30-120 minutes, and then the cells are crushed for 10-20 minutes.

4. The potassium ion battery negative electrode material according to claim 1, characterized in that In the step S2, the mass ratio of the added polydiallyldimethylammonium chloride and the molybdenum source is 2:1; in the step S1 and the step S3, the mass ratio of the added exfoliated graphite and the sulfur source is 1:(0.8-2); in the step S2 and the step S3, the mass ratio of the added molybdenum source and the sulfur source is 1:

2.

5. The potassium ion battery negative electrode material according to claim 1, characterized in that In the step S2, the molybdenum source is ammonium molybdate.

6. The potassium ion battery negative electrode material according to claim 1, characterized in that In step S3, the sulfur source is thiourea and / or thioacetamide.

7. The potassium ion battery negative electrode material according to claim 1, characterized in that In step S3, the temperature of the hydrothermal reaction is controlled at 180-220° C. and maintained for 18-22 hours.

8. The potassium ion battery negative electrode material according to claim 1, characterized in that In step S3, the drying condition is freeze drying at -60°C for 10-12 hours.

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