Prussian blue nanocube@honeycomb carbon composite material and its preparation and application

Abstract

The present invention discloses a Prussian blue nanocube@honeycomb carbon composite material, its preparation method, and its application in preparing lithium-ion battery negative electrodes. The Prussian blue nanocube@honeycomb carbon composite material comprises a three-dimensional honeycomb pore structure in which PBA nanocubes are densely and in-situ grown on the inner surface of the honeycomb pores of the honeycomb carbon. The preparation method involves synthesizing PS spheres, then slowly evaporating the PS spheres and a solution containing dissolved Co(NO3)2 and PVP to dryness, followed by calcination under a protective atmosphere, and finally immersing the spheres in a low-temperature aqueous solution of K3[Fe(CN)6] for a predetermined reaction time to obtain the Prussian blue nanocube@honeycomb carbon composite material. The material synthesis method of the present invention is simple and efficient, significantly improving the specific capacity, cycle performance, and rate capability of PBA.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a Prussian blue (PBA) nanocube@honeycomb carbon composite material and a preparation method and application thereof. Background Art

[0002] The rapid development of smartphones, laptops, hybrid electric vehicles, and all-electric vehicles is placing increasing demands on the performance of their power sources. Anode materials are directly related to the performance of lithium-ion batteries. To improve the energy storage capacity of lithium-ion batteries, developing anode materials with low cost, stable structure, high specific capacity, and long cycle life is a top priority.

[0003] Prussian blue analogue (PBA), the molecular formula can be expressed as A x M[R(CN)6] y □1-y·zH2O, where A represents an alkali metal ion, M and R represent transition metals, and □ represents a vacancy occupied by interstitial water. Its typical structure consists of a perovskite skeleton (CN) - The anion bridges the MN6 and RC6 octahedra, while A + and H2O occupy the interstitial positions. Due to its adjustable and diverse structure, well-developed pores, high surface area, low cost, and easy synthesis, PBA has been widely used in various rechargeable battery systems such as lithium, sodium, and potassium.

[0004] PBA contains a variety of variable-valence metals that provide abundant active sites. Theoretically, it can undergo multi-electron redox reactions at low potentials, achieving high reversible capacity. However, PBA has poor electronic conductivity and prone to structural collapse, resulting in significant capacity loss during cycling, which severely limits its practical application as anode material for lithium-ion batteries.

[0005] To improve the performance of lithium-ion batteries using PBA, researchers have explored various approaches. Patent application publication number CN112694104A reports a manganese-based Prussian blue analogue, patent application publication number CN112142069A reports a Prussian blue analogue, a morphology control method, and its application in lithium-ion battery anodes, patent application publication number CN112110459A reports a Prussian blue single crystal composite material with an internal conductive network, and patent application publication number CN110734077A reports a hierarchically porous Prussian blue nanosphere based on iodine-doped graphene. To improve the conductivity of PBA, compounding PBA with various carbon materials is an effective strategy. However, in most PBA-carbon composites, the PBA is exposed. Once the PBA structure collapses, it will fall off the composite, resulting in rapid capacity decay. Growing PBA inside the composite material can effectively improve the cycling stability of PBA, but relevant reports are still rare. Summary of the Invention

[0006] In response to the deficiencies in the art, the present invention provides a Prussian blue nanocube@honeycomb carbon composite material, which has the characteristics of unique structure, excellent performance and simple synthesis process.

[0007] A Prussian blue nanocube@honeycomb carbon composite material, wherein the carbon material presents a three-dimensional honeycomb pore structure, and PBA nanocubes are in-situ and densely grown on the inner surface of the honeycomb pores of the honeycomb carbon;

[0008] The PBA nanocubes are iron-cobalt PBA with a chemical formula of K2CoFe(CN)6·1.13H2O.

[0009] In a preferred embodiment, in the Prussian blue nanocube@honeycomb carbon composite material, the side length of the PBA nanocube is 2-100 nm.

[0010] In a preferred embodiment, the Prussian blue nanocube@honeycomb carbon composite material, the honeycomb carbon is an amorphous material produced by decomposition of polyvinyl pyrrolidone, and the diameter of the honeycomb pores is 50-1000 nm.

[0011] In a preferred embodiment, in the Prussian blue nanocube@honeycomb carbon composite material, the mass percentage of the Prussian blue nanocube is 40%-95%, and the rest is carbon.

[0012] The present invention also provides a method for preparing the Prussian blue nanocube@honeycomb carbon composite material, comprising the steps of:

[0013] (1) Deionized water was heated to 60°C under nitrogen deoxygenation and protection, oleic acid and styrene were added, and then heated to 70°C, K2S2O8 aqueous solution was added to initiate polymerization, and the reaction was stirred for 5-40 hours. The reaction was then heated to 80°C and kept warm for 30 minutes, and cooled to obtain a monodispersed PS sphere emulsion.

[0014] (2) adding polyvinyl pyrrolidone to the PS sphere emulsion obtained in step (1), stirring and heating to 50°C, keeping warm for 30 minutes, then adding Co(NO3)2·6H2O, stirring for 5 hours, and drying the obtained mixed solution at 60°C to obtain the precursor Co(NO3)2@PVP@PS spheres;

[0015] (3) heating the precursor Co(NO3)2@PVP@PS ball obtained in step (2) to 470-490°C under an Ar atmosphere and keeping the temperature for 1-5 hours to obtain a nano-Co3O4@3D honeycomb carbon composite material;

[0016] (4) Adding the nano-Co3O4@3D honeycomb carbon composite material obtained in step (3) to a K3[Fe(CN)6] aqueous solution, reacting at 1-9°C (preferably 1-5°C, further preferably 1-3°C) for 8-24h (preferably 10-24h) to obtain the Prussian blue nano-cube@honeycomb carbon composite material.

[0017] The preparation method of the present invention first synthesizes PS spheres. Then, the PS spheres and a solution containing dissolved Co(NO3)2 and PVP are slowly evaporated to dryness. The mixture is then calcined under a protective atmosphere. Finally, the mixture is immersed in a low-temperature aqueous solution of K3[Fe(CN)6] and reacted for a predetermined period of time to obtain the Prussian blue nanocube-atmospheric carbon honeycomb composite. This method can improve the specific capacity, cycle performance, and rate capability of iron-cobalt PBA.

[0018] In a preferred embodiment, in step (1):

[0019] The usage ratio of deionized water, oleic acid, styrene, and K2S2O8 aqueous solution is 280 mL:200 μL:2-50 mL:10 mL;

[0020] The concentration of the K2S2O8 aqueous solution is 20 mg / mL.

[0021] In a preferred embodiment, in step (2):

[0022] The average molecular weight (MW) of polyvinylpyrrolidone is 58,000;

[0023] The usage ratio of polyvinyl pyrrolidone, PS ball emulsion and Co(NO3)2·6H2O is 0.15g:60mL:0.1-0.6g.

[0024] In a preferred embodiment, in step (4):

[0025] The dosage ratio of nano-Co3O4@3D honeycomb carbon composite material and K3[Fe(CN)6] is 30-50mg:1mmol;

[0026] The concentration of the K3[Fe(CN)6] aqueous solution is 20 mmol / L.

[0027] A preferred preparation method of the Prussian blue nanocube@honeycomb carbon composite material comprises the following steps:

[0028] (1) Add 280 mL of deionized water to a 500 mL three-necked flask, insert a thermometer, a nitrogen inlet tube, and a reflux tube. Heat the solution to 60°C, add 200 μL of oleic acid and 2-50 mL of styrene. Deoxygenate the solution by bubbling nitrogen for 0.5-2 h, then heat the solution to 70°C. Add 10 mL of an aqueous solution containing 200 mg of K₂S₂O₄ to initiate polymerization. Stir the solution continuously for 5-40 h, then heat to 80°C for 30 min, and finally cool to room temperature to obtain a monodisperse polystyrene (PS) sphere emulsion.

[0029] (2) 0.15 g of polyvinylpyrrolidone (PVP, MW58000) was added to 60 mL of the PS sphere emulsion prepared in step (1), stirred and heated to 50 °C, and kept warm for 30 min. Then 0.1-0.6 g of Co(NO3)2·6H2O was added and stirred for 5 h. The resulting mixed solution was dried at 60 °C to form the precursor Co(NO3)2@PVP@PS spheres.

[0030] (3) 200 mg of the precursor prepared in step (2) was heated to 470-490° C. under an Ar atmosphere and kept warm for 1-5 h to obtain a nano-Co 3 O 4 @ honeycomb carbon composite material.

[0031] (4) 1 mmol of K3[Fe(CN)6] was dissolved in 50 mL of deionized water, and then 30-50 mg of the nano-Co3O4@honeycomb carbon composite material prepared in step (3) was added. The mixed solution was immersed in a water bath at 1-9°C (preferably 1-5°C, more preferably 1-3°C) for 8-24 h (preferably 10-24 h). The product was centrifuged, washed with ethanol several times, and dried at 60°C to obtain a Prussian blue nanocube@honeycomb carbon composite material.

[0032] The present invention also provides the use of the Prussian blue nanocube@honeycomb carbon composite material in preparing a negative electrode of a lithium ion battery.

[0033] In one preferred embodiment, the Prussian blue nanocube@honeycomb carbon composite material of the present invention is used to prepare a lithium-ion battery negative electrode: the Prussian blue nanocube@honeycomb carbon composite material, acetylene black conductive agent, and PVDF binder are weighed at a mass ratio of 8:1:1. The PVDF is dissolved in an appropriate amount of N-methylpyrrolidone and stirred until completely dissolved. The ground active material and acetylene black are then added to the solution, and stirring is continued to ensure a uniform slurry. The slurry is then evenly coated onto a 12 mm diameter copper foil disc, dried in a vacuum oven at 100°C, and finally flattened on a tablet press at a pressure of 10 MPa to produce an electrode sheet.

[0034] In a glove box filled with high-purity argon, the prepared electrode sheet, lithium sheet, and separator were assembled into a CR2025 button-type lithium-ion battery. The electrolyte was an EC / DMC solution containing 1 mol / L LiPF6. The charge-discharge and cycling performance of the lithium-ion battery was tested using a Xinwei battery testing system.

[0035] The present invention can obtain a Prussian blue nanocube@honeycomb carbon composite material with high specific capacity, excellent cycle performance and rate performance.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1) Precursor synthesis is very simple, requiring only mixing and drying a PS sphere emulsion with Co(NO3)2 and PVP. Solution drying achieves three objectives: After drying, the PS spheres form a dense, three-dimensional stack, preparing the structure for the construction of three-dimensional honeycomb pores. Simultaneously, PVP precipitates from the solution, filling the gaps between the PS spheres and tightly adhering to the surface of the PS spheres, solidifying the dense, three-dimensional stacking structure of the PS spheres and providing material for the construction of three-dimensional honeycomb pores. Simultaneously, Co(NO3)2 precipitates from the solution and settles at the interface between PVP and the PS spheres, providing a critical growth foundation for the in-situ growth of nano-Co3O4 on the inner surface of the three-dimensional honeycomb carbon pores, ultimately encapsulating Prussian blue nanocubes within the three-dimensional honeycomb carbon pores. If nano-Co3O4 is added directly to the solution, or if Co(NO3)2 is added but first precipitated with an alkali to form a cobalt oxide precursor, the nano-Co3O4 or cobalt oxide precursor will not be able to enter the interface between PVP and the PS spheres after the solution dries, nor will it be able to enter the pores of the honeycomb carbon, thus failing to form the composite material structure of the present invention.

[0038] 2) The intermediate product, nano-Co3O4@honeycomb carbon composite material, is obtained through a simple calcination. This single calcination achieves three goals: the PS spheres decompose and vaporize, generating pores and forming a three-dimensional honeycomb pore structure; the PVP decomposes into an amorphous carbon framework, preserving the honeycomb pores created by the PS spheres; and the Co(NO3)2 decomposes into nano-Co3O4, which adheres to the inner surface of the honeycomb carbon pores. The calcination temperature is critical: too low a temperature prevents the complete decomposition of the Co(NO3)2; too high a temperature causes the carbon to reduce the Co3O4 to metallic cobalt.

[0039] 3) The reaction temperature of nano-Co3O4@honeycomb carbon and K3[Fe(CN)6] must be strictly controlled. Above 10°C, due to the rapid reaction between Co3O4 and K3[Fe(CN)6], most of the PBA grows outside the honeycomb carbon, with only a very small amount growing inside the pores. Within the 1-9°C temperature range, and particularly within the 1-5°C range, PBA essentially grows within the honeycomb carbon pores, with PBA growing in every pore. The reaction time also needs to be controlled at low temperatures. If the reaction time is too short, PBA growth is insufficient, and a large amount of Co3O4 remains.

[0040] 4) Due to the closed nature of the carbon pores, even if PBA undergoes structural collapse and pulverization during the charge-discharge cycle, it remains confined within the carbon pores and can still participate in the charge-discharge reaction, which ensures PBA's high cycle stability. PBA is separated by honeycomb pores, effectively solving the problem of PBA reaggregation during the charge-discharge process, ensuring the material's high electrochemical activity and high lithium battery performance.

[0041] 5) The PBA is in close contact with the honeycomb carbon, which effectively improves the electrical conductivity of the PBA, significantly enhancing its rate performance. The liquid electrolyte can penetrate and be stored inside the honeycomb pores, which not only meets the electrochemical reaction requirements of the PBA inside the pores but also produces an unexpected effect: a polymer gel film forms inside the honeycomb pores. This polymer gel film wraps around the PBA on the inner surface of the honeycomb pores, thereby improving the cycling performance and reversible capacity of the PBA.

[0042] 6) Compared with the traditional independent carbon hollow spheres that encapsulate electrode materials, the three-dimensional honeycomb carbon with PBA encapsulated in each honeycomb hole realizes a highly integrated and ordered structure. It is the most efficient form of utilization of the hollow structure, can significantly improve the loose and tight density of the electrode material, and plays an important role in improving the volume energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a scanning electron microscope (SEM) photograph of the PS sphere prepared in Example 1;

[0044] Figure 2This is the SEM image of the precursor Co(NO3)2@PVP@PS sphere prepared in Example 1;

[0045] Figure 3 This is the SEM photo of the nano-Co3O4@honeycomb carbon prepared in Example 1;

[0046] Figure 4 This is the SEM image of the PBA nanocube@honeycomb carbon prepared in Example 1;

[0047] Figure 5 This is a transmission electron microscope (TEM) image of the PBA nanocube@honeycomb carbon prepared in Example 1;

[0048] Figure 6 This is the XRD pattern of the PBA nanocube@honeycomb carbon prepared in Example 1;

[0049] Figure 7 The PBA nanocube@honeycomb carbon prepared in Example 1 was heated to a current density of 0.5 A g -1 cycle performance.

[0050] Figure 8 This is the rate performance of the PBA nanocube@honeycomb carbon prepared in Example 1. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are intended to illustrate the present invention and are not intended to limit the scope of the invention. The operating methods in the following examples where no specific conditions are specified are generally performed under conventional conditions or as recommended by the manufacturer.

[0052] Example 1

[0053] (1) Add 280 mL of deionized water to a 500 mL three-necked flask, insert a thermometer, a nitrogen inlet tube, and a reflux tube. Heat the solution to 60°C, add 200 μL of oleic acid and 7 mL of styrene. Deoxygenate the solution by bubbling nitrogen for 1 hour, then heat the solution to 70°C. Add 10 mL of an aqueous solution containing 200 mg of K₂S₂O₄ to initiate polymerization. Stir the solution continuously for 10 hours, then heat to 80°C and maintain for 30 minutes. Finally, cool to room temperature to obtain a monodisperse polystyrene (PS) sphere emulsion.

[0054] (2) 0.15 g of polyvinylpyrrolidone (PVP, MW58000) was added to 60 mL of the PS sphere emulsion prepared in step (1), stirred and heated to 50 °C, and kept warm for 30 min. Then 0.29 g of Co(NO3)2·6H2O was added and stirred for 5 h. The resulting mixed solution was dried at 60 °C to form the precursor Co(NO3)2@PVP@PS spheres.

[0055] (3) 200 mg of the precursor prepared in step (2) was heated to 480° C. under an Ar atmosphere and kept warm for 3 h to obtain a nano-Co 3 O 4 @ honeycomb carbon composite material.

[0056] (4) 1 mmol of K3[Fe(CN)6] was dissolved in 50 mL of deionized water, and then 40 mg of the nano-Co3O4@honeycomb carbon composite material prepared in step (3) was added. The mixed solution was immersed in a water bath at 3°C for 10 h, and the product was centrifuged, washed with ethanol several times, and dried at 60°C to obtain the Prussian blue nanocube@honeycomb carbon composite material.

[0057] Figure 1 These are synthetic PS spheres with uniform particle size of approximately 200-220nm. The PS spheres have distinct outlines, smooth surfaces, and good dispersion. Figure 1 This is the morphology of the PS ball emulsion after slow evaporation. It can be found that the PS balls are densely packed, which provides a structural basis for building honeycomb pores. Figure 2 This is an SEM image of the Co(NO3)2@PVP@PS sphere precursor. It can be seen that the precursor is a dense three-dimensional deposit with no separate PS spheres or Co(NO3)2 present, indicating that the three have been successfully mixed together. Figure 3 This is an SEM image of nano-Co3O4@honeycomb carbon. The decomposition of the PS spheres produces numerous macropores, distributed throughout the surface and interior of the product, creating a typical honeycomb pattern. Numerous Co3O4 nanoparticles grow on the surface of the honeycomb pores. These particles are uniformly small and free of aggregation. The macropore diameter is approximately 200 nm. Figure 4 This is an SEM photo of PBA nanocubes@honeycomb carbon. It can be seen that the honeycomb pores of the honeycomb carbon remain intact and the structure has not changed. The nanoparticles grown on the inner surface of the honeycomb pores have not changed much either, but some particles show a fuzzy cubic shape. Figure 5 This TEM image of PBA nanocubes in honeycomb carbon shows uniform growth of nanoparticles on the inner surface of the carbon honeycomb pores. Some particles exhibit a distinct cubic shape, with side lengths of 10-20 nm. Thermogravimetric analysis reveals a dehydrated PBA content of 74.98% and a crystalline water content of 4.35%, resulting in a total of 79.33% PBA, with the remainder being carbon.

[0058] Figure 6The XRD pattern of PBA nanocubes@honeycomb carbon shows that the product's diffraction peaks can all be assigned to K2CoFe(CN)6, indicating iron-cobalt PBA. The absence of diffraction peaks for Co(NO3)2 and Co3O4 indicates complete decomposition of Co(NO3)2 and complete conversion of Co3O4 to PBA. Therefore, combined with the thermogravimetric analysis results, the chemical formula of Prussian blue can be determined to be K2CoFe(CN)6·1.13H2O.

[0059] The PBA nanocube@honeycomb carbon composite material of the present invention was used to make a lithium-ion battery negative electrode: the PBA nanocube@honeycomb carbon composite material, acetylene black conductive agent, and PVDF binder were weighed at a mass ratio of 8:1:1. The PVDF was dissolved in an appropriate amount of N-methylpyrrolidone and stirred until completely dissolved. The ground active material and acetylene black were then added to the solution, and stirring was continued to ensure a uniform slurry. The slurry was then evenly coated onto a 12mm diameter copper foil disc, dried in a vacuum oven at 100°C, and finally flattened on a tablet press at a pressure of 10 MPa to produce the electrode sheet.

[0060] In a glove box filled with high-purity argon, the prepared electrode sheet, lithium sheet, and separator were assembled into a CR2025 button-type lithium-ion battery. The electrolyte was an EC / DMC solution containing 1 mol / L LiPF6. The charge-discharge and cycling performance of the lithium-ion battery was tested using a Xinwei battery testing system.

[0061] Figure 7 The PBA nanocube@honeycomb carbon composite material prepared in Example 1 was heated to a current density of 0.5 A g -1 In the first 134 cycles, the discharge capacity is stable at 1006 mAh g -1 After that, the discharge capacity dropped slightly and stabilized at 890mAhg -1 The cycling performance of PBA nanocube@honeycomb carbon composite material is better than that of an iron-manganese PBA reported in the invention patent application with publication number CN112694104A at a current density of 0.5A g -1 The discharge capacity after 200 cycles is about 300 mAh g -1 , which is superior to the iron-nickel-manganese PBA reported in the invention patent application with publication number CN112142069A at a current density of 0.5A g -1 The discharge capacity after 200 cycles is about 500 mAh g -1 , which is superior to the iron-manganese PBA reported in the invention patent application with publication number CN109742398A at a current density of 0.1A g -1 The discharge capacity after 30 cycles is about 650 mAh g -1 .

[0062] Figure 8 The rate performance of the PBA nanocube@honeycomb carbon prepared in Example 1 is shown in Figure 1. The current density is 0.1, 0.2, 0.5, 1, 2, 5A g -1 , the average discharge capacity is 1265, 1105, 972, 794, 645, 374 mAh g -1 The rate performance of PBA nanocubes@honeycomb carbon is superior to that of an iron-manganese PBA reported in the invention patent application with publication number CN109742398A, and also superior to that of a hierarchical porous Prussian blue nanosphere based on iodine-doped graphene wrapped in the invention patent application with publication number CN110734077A.

[0063] Example 2

[0064] (1) Add 280 mL of deionized water to a 500 mL three-necked flask, insert a thermometer, a nitrogen inlet tube, and a reflux tube. Heat the solution to 60°C, add 200 μL of oleic acid and 20 mL of styrene. Deoxygenate the solution by bubbling nitrogen for 1 hour, then heat the solution to 70°C. Add 10 mL of an aqueous solution containing 200 mg of K₂S₂O₄ to initiate polymerization. Stir the solution continuously for 18 hours, then heat to 80°C for 30 minutes, and finally cool to room temperature to obtain a monodisperse polystyrene (PS) sphere emulsion.

[0065] The subsequent process is the same as that in Example 1.

[0066] The structure of the product PBA nanocube@honeycomb carbon is similar to that of Example 1, with the main difference being that the diameter of the PS sphere is increased to 250-270 nm, and the diameter of the honeycomb pores of the synthesized honeycomb carbon is changed to 250 nm.

[0067] Example 3

[0068] (1) Add 280 ml of deionized water to a 500 ml three-necked flask, insert a thermometer, a nitrogen inlet tube, and a reflux tube. Heat the solution to 60°C, add 200 μL of oleic acid and 7 mL of styrene. Deoxygenate the solution with nitrogen bubbling for 1 hour, then heat the solution to 70°C. Add 10 mL of an aqueous solution containing 200 mg of K₂S₂O₄ to initiate polymerization. Stir the solution continuously for 10 hours, then heat to 80°C for 30 minutes, and finally cool to room temperature to obtain a monodisperse polystyrene (PS) sphere emulsion.

[0069] (2) 0.15 g of polyvinylpyrrolidone (PVP, MW58000) was added to 60 mL of the PS sphere emulsion prepared in step (1), stirred and heated to 50 °C, and kept warm for 30 min. Then 0.20 g of Co(NO3)2·6H2O was added and stirred for 5 h. The resulting mixed solution was dried at 60 °C to form the precursor Co(NO3)2@PVP@PS spheres.

[0070] The subsequent process is the same as that in Example 1.

[0071] The structure of the product PBA nanocube@honeycomb carbon is similar to that of Example 1, with the main differences being that the mass percentage of PBA is changed to 72.1%, with the remainder being carbon; and the side length of the PBA nanocube is changed to 5-15 nm.

[0072] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A Prussian blue nanocube@honeycomb carbon composite material, characterized in that: In the Prussian blue nanocube@honeycomb carbon composite material, the carbon material presents a three-dimensional honeycomb pore structure, and PBA nanocubes are in-situ and densely grown on the inner surface of the honeycomb pores of the honeycomb carbon; The PBA nanocubes are iron-cobalt PBA with the chemical formula K2CoFe(CN)6·1.13H2O; The preparation method of the Prussian blue nanocube@honeycomb carbon composite material comprises the following steps: (1) Deionized water was heated to 60°C under nitrogen deoxygenation and protection, oleic acid and styrene were added, and then heated to 70°C, K2S2O8 aqueous solution was added to initiate polymerization, and the reaction was stirred for 5-40 hours. The reaction was then heated to 80°C and kept warm for 30 minutes, and cooled to obtain a monodispersed PS sphere emulsion. (2) adding polyvinyl pyrrolidone to the PS sphere emulsion obtained in step (1), stirring and heating to 50°C, keeping warm for 30 minutes, then adding Co(NO3)2·6H2O, stirring for 5 hours, and drying the obtained mixed solution at 60°C to obtain the precursor Co(NO3)2@PVP@PS spheres; (3) heating the precursor Co(NO3)2@PVP@PS ball obtained in step (2) to 470-490°C under an Ar atmosphere and keeping the temperature for 1-5 hours to obtain a nano-Co3O4@3D honeycomb carbon composite material; (4) Adding the nano-Co3O4@3D honeycomb carbon composite material obtained in step (3) to a K3[Fe(CN)6] aqueous solution, reacting at 1-9°C for 8-24h to obtain the Prussian blue nano-cube@honeycomb carbon composite material.

2. The Prussian blue nanocube@honeycomb carbon composite material according to claim 1, characterized in that: The side length of the PBA nanocube is 2-100 nm.

3. The Prussian blue nanocube@honeycomb carbon composite material according to claim 1, characterized in that: The honeycomb carbon is an amorphous material produced by decomposing polyvinyl pyrrolidone, and the diameter of the honeycomb pores is 50-1000 nm.

4. The Prussian blue nanocube@honeycomb carbon composite material according to claim 1, characterized in that: In the Prussian blue nanocube@honeycomb carbon composite material, the mass percentage of the Prussian blue nanocube is 40-95%, and the rest is carbon.

5. The method for preparing the Prussian blue nanocube@honeycomb carbon composite material according to any one of claims 1 to 4, characterized in that: Including steps: (1) Deionized water was heated to 60°C under nitrogen deoxygenation and protection, oleic acid and styrene were added, and then heated to 70°C, K2S2O8 aqueous solution was added to initiate polymerization, and the reaction was stirred for 5-40 hours. The reaction was then heated to 80°C and kept warm for 30 minutes, and cooled to obtain a monodispersed PS sphere emulsion. (2) adding polyvinyl pyrrolidone to the PS sphere emulsion obtained in step (1), stirring and heating to 50°C, keeping warm for 30 minutes, then adding Co(NO3)2·6H2O, stirring for 5 hours, and drying the obtained mixed solution at 60°C to obtain the precursor Co(NO3)2@PVP@PS spheres; (3) heating the precursor Co(NO3)2@PVP@PS ball obtained in step (2) to 470-490°C under an Ar atmosphere and keeping the temperature for 1-5 hours to obtain a nano-Co3O4@3D honeycomb carbon composite material; (4) Adding the nano-Co3O4@3D honeycomb carbon composite material obtained in step (3) to a K3[Fe(CN)6] aqueous solution, reacting at 1-9°C for 8-24h to obtain the Prussian blue nano-cube@honeycomb carbon composite material.

6. The preparation method according to claim 5, characterized in that In step (1): The usage ratio of deionized water, oleic acid, styrene, and K2S2O8 aqueous solution is 280 mL:200 μL:2-50 mL:10 mL; The concentration of the K2S2O8 aqueous solution is 20 mg / mL.

7. The preparation method according to claim 5, characterized in that In step (2): The average molecular weight of polyvinylpyrrolidone is 58,000; The usage ratio of polyvinyl pyrrolidone, PS ball emulsion and Co(NO3)2·6H2O is 0.15g:60mL:0.1-0.6g.

8. The preparation method according to claim 5, characterized in that In step (4): The dosage ratio of nano-Co3O4@3D honeycomb carbon composite material and K3[Fe(CN)6] is 30-50mg:1mmol; The concentration of the K3[Fe(CN)6] aqueous solution is 20 mmol / L.

9. Use of the Prussian blue nanocube@honeycomb carbon composite material according to any one of claims 1 to 4 in preparing a negative electrode for a lithium-ion battery.

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