A sodium ion battery negative electrode material and preparation method thereof and a sodium ion battery

Abstract

The present invention provides a sodium-ion battery anode material, a preparation method, and a sodium-ion battery, belonging to the technical field of sodium-ion batteries. The sodium-ion battery anode material comprises a core and a shell coating the core. The core comprises a hard carbon / MOFs composite material, and the shell comprises a graphene layer. The sodium-ion battery anode material achieves high specific capacity, good rate capability, and good cycling performance.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in portable electronics, communications equipment, and electric vehicles due to their high energy density, low self-discharge, long life, environmental friendliness, and reasonable cost. However, limited lithium resources and their uneven distribution worldwide restrict their development. In particular, my country's limited reserves and increasing demand for lithium resources have created an urgent need for alternatives to lithium-ion batteries. Sodium and lithium are members of the same main group, sharing similar physical and chemical properties. Sodium is more than 420 times more abundant in the Earth's crust than lithium, is widely distributed, and is inexpensive. Therefore, sodium-ion batteries, as a complementary alternative to lithium-ion batteries, are becoming a research hotspot within the industry.

[0003] Battery materials directly affect the battery's electrochemical properties, including operating voltage, cycle performance, energy density, and rate capability. The significant difference in ionic radius between sodium and lithium ions prevents the widespread use of graphite anode materials in lithium-ion batteries from being used in sodium-ion batteries. Therefore, the development of sodium-ion battery anode materials with high specific capacity, high rate capability, and long life is essential.

[0004] CN106935856A discloses a method for preparing a carbon-based composite negative electrode material for a sodium ion battery, wherein hard carbon balls are obtained by a hydrothermal method, an iron-containing source and a carbon source are attached or coated on the surface of the hard carbon balls by a liquid phase method to obtain a negative electrode material precursor, and the negative electrode material precursor is subjected to a one-step carbonization to obtain the carbon-based composite negative electrode material. The partially graphitized carbon layer-coated carbon ball composite material prepared by the present invention has the advantages of high conductivity, large interlayer spacing, and moderate specific surface area. The composite material is used in sodium ion batteries and exhibits high cycle performance and excellent rate performance. However, the commonly used coating layer has no reaction activity to sodium ions or the carbon layer spacing is too small to serve as a sodium storage site, which will cause the specific capacity of the carbon-based composite negative electrode material to decrease.

[0005] CN111293301A discloses a soft-hard carbon composite porous anode material for sodium-ion batteries and its preparation method. This composite anode material is prepared from cobalt nitrate, dimethylimidazole, and polyvinyl alcohol. The composite anode material combines the excellent conductivity of soft carbon with the high specific capacity of hard carbon, effectively improving battery stability, cycling performance, and coulombic efficiency of sodium-ion batteries. However, the soft carbon increases the closed porosity of the composite material, reducing the material's rate capability.

[0006] CN115636946A discloses a method for preparing a metal-organic framework material with high exposed active sites and its application. The carbon matrix obtained by in-situ carbonization or graphitization of the organic framework completely encapsulates the electroactive nanoparticles, improves the electronic conductivity of the electrode material, ensures the rapid diffusion of sodium particles / electrons, and protects the electrode material from being destroyed during the charge / discharge process. The metal-organic framework (MOFs) material exhibits excellent rate performance and cycle stability when used as a negative electrode material for SIBs. However, the metal-organic framework (MOFs) material is easy to agglomerate and has poor processing performance compared to hard carbon materials, making it difficult to match the current sodium ion battery manufacturing process.

[0007] In summary, how to design sodium-ion battery anode materials that take into account high specific capacity, good rate performance and cycle performance is the key to the efficient application of sodium-ion batteries in the future. Summary of the Invention

[0008] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present invention provides a sodium ion battery negative electrode material and a preparation method thereof, and a sodium ion battery.

[0009] In a first aspect, the present invention provides a sodium ion battery negative electrode material, which is a core-shell structure consisting of a core and a shell layer coated on the surface of the core, wherein the core includes a hard carbon / MOFs composite material, and the shell layer includes a graphene layer.

[0010] The advantages and technical effects of the sodium ion battery negative electrode material of the present invention are as follows:

[0011] (1) The core includes a hard carbon / MOFs composite material. On the one hand, because MOFs have a larger specific surface area and abundant internal space, MOFs are evenly distributed in the hard carbon structure, which can provide more redox reaction active sites, thereby providing a higher specific capacity. On the other hand, MOFs can promote the Na + and the uniformity of the electric field potential, thereby achieving the Na + Rapid migration and uniform deposition provide better rate performance.

[0012] (2) The core comprises a hard carbon / MOFs composite material. Hard carbon is an extremely excellent anode material for sodium-ion batteries due to its excellent performance and low cost. On the one hand, hard carbon can buffer the expansion of MOFs, improve the stability of the electrode structure, and enhance the cycling performance of the anode material. On the other hand, the unique structure of hard carbon can make MOFs evenly distributed in the hard carbon structure, improving the cycling stability of the anode material.

[0013] (3) The shell layer includes a graphene layer. On the one hand, the hard carbon / MOFs composite material is sealed in the graphene layer, which can prevent the hard carbon / MOFs composite material from dissociating, maintain the electrochemical activity of the negative electrode material, and provide rapid kinetic transfer for sodium ions. On the other hand, the graphene layer can effectively improve the electronic / ionic conductivity of the hard carbon / MOFs composite material, improve the surface defects of the hard carbon material, and improve the first coulombic efficiency of the negative electrode material. On the other hand, the graphene layer can also provide certain active sites to improve the specific capacity of the negative electrode material.

[0014] Optionally, the Dv50 of the hard carbon / MOFs composite material is 3 μm to 6 μm.

[0015] Optionally, the Dv50 of the MOFs is 20 nm to 100 nm.

[0016] Optionally, the mass ratio of the hard carbon to the MOFs is (5-10):1.

[0017] Optionally, the thickness of the graphene layer is 1 nm to 10 nm.

[0018] Optionally, the MOFs are at least one of Sn-MOFs, Se-MOFs, Ni-MOFs, Mn-MOFs, and Co-MOFs.

[0019] In a second aspect, the present invention provides a method for preparing a negative electrode material for a sodium ion battery, which is used to prepare the negative electrode material for a sodium ion battery according to the first aspect, and the preparation method comprises the following steps:

[0020] S1. Preparation of the hard carbon / MOFs composite material

[0021] S1-1, after cleaning the biomass carbon source, pre-oxidize it in a carbonization furnace to obtain a pre-oxidized material;

[0022] S1-2, mixing the pre-oxidized material with pure water, adding hydrochloric acid to soak, washing with pure water until neutral, and filtering to obtain a washed material;

[0023] S1-3, crushing the washed material to obtain a crushed material, adding the crushed material to a sand mill, adding zirconium balls, and sand-milling to obtain a sand-milled material;

[0024] S1-4, dispersing and mixing the sand-milled material with the MOFs at high speed to obtain a mixed material;

[0025] S1-5, spray granulating the mixed material to obtain a spray granulated material;

[0026] S1-6, pyrolyzing the spray-granulated material in a carbonization furnace under an inert atmosphere to obtain the hard carbon / MOFs composite material;

[0027] S2. Preparation of the sodium ion battery negative electrode material

[0028] S2-1, placing the hard carbon / MOFs composite material in a rotary kiln, heating methanol, introducing methanol vapor into the rotary kiln, and carbonizing the hard carbon / MOFs composite material under vacuum conditions, coating the graphene layer on the surface of the hard carbon / MOFs composite material to obtain a carbonized material;

[0029] S2-2, naturally cooling the carbonized material to room temperature under vacuum conditions to obtain the sodium ion battery negative electrode material.

[0030] The advantages and technical effects of the preparation method of the sodium ion battery negative electrode material of the present invention are as follows:

[0031] (1) In step S1, a hard carbon / MOFs composite material is prepared. In the hard carbon / MOFs composite material, MOFs are uniformly dispersed in the hard carbon, which is beneficial to improving the performance of the hard carbon / MOFs composite material.

[0032] (2) In step S2, graphene is directly grown in situ on the hard carbon / MOFs composite material matrix powder particles. The graphene has good in situ bonding with the matrix powder particles, has strong bonding force, and is not easy to fall off, which can ensure that the graphene and the matrix powder particles are evenly dispersed, which is beneficial to improving the performance of the negative electrode material.

[0033] Optionally, the pre-oxidation temperature is 200°C to 300°C, and the pre-oxidation holding time is 15h to 30h; and / or the pyrolysis temperature is 1200°C to 1600°C, and the pyrolysis holding time is 10h to 20h; and / or the carbonization temperature is 1000°C to 1400°C, and the carbonization holding time is 1h to 5h.

[0034] Optionally, the vacuum degree of the vacuum condition is 0.8 Pa to 1.5 Pa, and the pressure of the methanol vapor is maintained at 4 kPa to 8 kPa.

[0035] In a third aspect, the present invention provides a sodium ion battery comprising the sodium ion battery positive electrode material described in the first aspect.

[0036] The advantages and technical effects brought by the sodium ion battery of the present invention are:

[0037] Due to the adoption of the sodium ion battery positive electrode material of the first aspect, the sodium ion battery of the present invention can have high specific capacity, good rate performance and cycle performance, and has good comprehensive performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the structure of the negative electrode material for a sodium ion battery of the present invention;

[0039] Figure 2 This is an SEM image of the sodium ion battery negative electrode material of Example 1;

[0040] Figure 3 This is the rate performance curve of the sodium ion battery negative electrode material of Example 1;

[0041] Description of reference numerals:

[0042] 1-Hard carbon / MOFs composite material; 11-Hard carbon; 12-MOFs; 2-Graphene layer. DETAILED DESCRIPTION

[0043] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0044] In a first aspect, the present invention provides a sodium ion battery negative electrode material, such as Figure 1 As shown, the sodium ion battery negative electrode material is a core-shell structure consisting of a core and a shell layer coated on the surface of the core, the core includes a hard carbon / MOFs composite material 1, the hard carbon / MOFs composite material 1 is composed of hard carbon 11 and MOFs 12 uniformly dispersed in the hard carbon 11, and the shell layer includes a graphene layer 2.

[0045] The sodium ion battery negative electrode material of the present invention is a core-shell structure, and the core comprises a hard carbon / MOFs composite material. Among them, hard carbon has become an extremely excellent negative electrode material for sodium ion batteries due to its excellent performance and low cost, and MOFs can promote the surface Na + and the uniformity of the electric field potential, thereby achieving the Na + The rapid migration and uniform deposition of hard carbon and MOFs provide better rate performance. The core of the sodium-ion battery negative electrode material combines hard carbon and MOFs to give full play to the respective advantages of both. In addition, the hard carbon / MOFs composite material can also suppress the respective shortcomings of hard carbon and MOFs. Specifically, hard carbon can not only buffer the expansion of MOFs, improve the stability of the electrode structure, and enhance the cycle performance of the negative electrode material, but the unique structure of hard carbon can also make MOFs evenly distributed in the hard carbon structure, inhibit the agglomeration of MOFs, and improve the cycle stability of the negative electrode material. MOFs have a larger specific surface area and abundant internal space, so MOFs are evenly distributed in the hard carbon structure, which can provide more active sites for redox reactions, thereby providing a higher specific capacity.

[0046] The sodium ion battery negative electrode material of the present invention has a core-shell structure, and the shell layer includes a graphene layer. On the one hand, the graphene layer can seal the hard carbon / MOFs composite material and prevent the hard carbon / MOFs composite material from dissociating, thereby making the negative electrode material have good electrochemical activity and providing rapid kinetic transfer for sodium ions. On the other hand, the graphene layer can effectively improve the electronic / ionic conductivity of the hard carbon / MOFs composite material, improve the surface defects of the hard carbon material, and improve the first coulombic efficiency of the negative electrode material. On the other hand, the graphene layer can also provide certain active sites to improve the specific capacity of the negative electrode material.

[0047] Based on the above structure, the sodium ion battery negative electrode material of the present invention can have high specific capacity, good rate performance and cycle performance.

[0048] Optionally, the Dv50 of the hard carbon / MOFs composite material is 3μm to 6μm, for example, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, etc. It should be understood that Dv50 is the median particle size of the material, which refers to the particle size value corresponding to when the volume percentage of the particles reaches 50%. The micron-sized hard carbon / MOFs composite material is sealed in the graphene layer, which can prevent the dissociation of the negative electrode material, maintain the electrochemical activity of the negative electrode material, and provide rapid kinetic transfer for sodium ions. When the Dv50 of the hard carbon / MOFs composite material is too small, the number of defects in the negative electrode material increases, which is not conducive to improving the cycle performance of the negative electrode material. When the Dv50 of the hard carbon / MOFs composite material is too large, it is not conducive to improving the rate performance of the negative electrode material.

[0049] Optionally, the MOFs have a Dv50 of 20 nm to 100 nm, such as 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm. When the Dv50 of the MOFs is too small, the negative electrode material tends to agglomerate, which is not conducive to improving the electrical performance of the negative electrode material. When the Dv50 of the MOFs is too large, the negative electrode material tends to expand, which is not conducive to improving the stability of the electrode structure and thus is not conducive to enhancing the cycling performance of the negative electrode material.

[0050] Optionally, the mass ratio of the hard carbon to the MOFs is (5-10):1. When the mass ratio is too small, it is not conducive to buffering the expansion of MOFs, improving the stability of the electrode structure, and thus enhancing the cycle performance of the negative electrode material; it is also not conducive to inhibiting the agglomeration of MOFs, thereby improving the cycle stability of the negative electrode material. When the mass ratio is too large, it is not conducive to promoting the Na + and the uniformity of the electric field potential, which is not conducive to the realization of Na +The rapid migration and uniform deposition of the negative electrode materials are not conducive to improving the rate performance of the negative electrode materials; and the negative electrode materials are not conducive to providing more redox reaction active sites, which is not conducive to improving the specific capacity of the negative electrode materials.

[0051] Optionally, the thickness of the graphene layer is 1 nm to 10 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc. When the thickness of the graphene layer is too thin, it is not conducive to sealing the hard carbon / MOFs composite material. The hard carbon / MOFs composite material is prone to dissociation, which is not conducive to improving the electrochemical activity of the negative electrode material and not easy to provide rapid kinetic transfer for sodium ions. In addition, it is not conducive to improving the electronic / ionic conductivity of the hard carbon / MOFs composite material, and it is not conducive to improving the surface defects of the hard carbon material, which is not conducive to improving the first coulombic efficiency of the negative electrode material. In addition, it is not conducive to providing sufficient active sites, which is not conducive to improving the specific capacity of the negative electrode material. When the thickness of the graphene layer is too thick, it is not conducive to the diffusion of sodium ions during the insertion and extraction process.

[0052] Optionally, the MOFs are at least one of Sn-MOFs, Se-MOFs, Ni-MOFs, Mn-MOFs, and Co-MOFs. When the MOFs are the above materials, it is beneficial to improve the specific capacity and rate performance of the negative electrode material.

[0053] In a second aspect, the present invention provides a method for preparing a negative electrode material for a sodium ion battery, which is used to prepare the negative electrode material for a sodium ion battery according to the first aspect, and the preparation method comprises the following steps:

[0054] S1. Preparation of the hard carbon / MOFs composite material

[0055] S1-1, after cleaning the biomass carbon source, pre-oxidize it in a carbonization furnace to obtain a pre-oxidized material;

[0056] S1-2, mixing the pre-oxidized material with pure water, adding hydrochloric acid to soak, washing with pure water until neutral, and filtering to obtain a washed material;

[0057] S1-3, crushing the washed material to obtain a crushed material, adding the crushed material to a sand mill, adding zirconium balls, and sand-milling to obtain a sand-milled material;

[0058] S1-4, dispersing and mixing the sand-milled material with the MOFs at high speed to obtain a mixed material;

[0059] S1-5, spray granulating the mixed material to obtain a spray granulated material;

[0060] S1-6, pyrolyzing the spray-granulated material in a carbonization furnace under an inert atmosphere to obtain the hard carbon / MOFs composite material;

[0061] S2. Preparation of the sodium ion battery negative electrode material

[0062] S2-1, placing the hard carbon / MOFs composite material in a rotary kiln, heating methanol, introducing methanol vapor into the rotary kiln, and carbonizing the hard carbon / MOFs composite material under vacuum conditions, coating the graphene layer on the surface of the hard carbon / MOFs composite material to obtain a carbonized material;

[0063] S2-2, naturally cooling the carbonized material to room temperature under vacuum conditions to obtain the sodium ion battery negative electrode material.

[0064] Pre-oxidation can convert unstable functional groups in the biomass carbon source into stable carbonyl groups, and the biomass molecules initiate cross-linking to form an amorphous carbon structure. After the pre-oxidized material is soaked in hydrochloric acid, the ash remaining inside the material (such as inorganic salts such as metal compounds) can be removed. The washed material can be sand-milled to control the particle size of the sand-milled material, which is beneficial for the subsequent pyrolysis process to fully contact the sand-milled material with MOFs, so that MOFs are evenly dispersed in the hard carbon. The mixed material is spray-granulated on the one hand to remove moisture therein to avoid negative effects on the battery, and on the other hand for granulation. The spray-granulated material is pyrolyzed under an inert atmosphere to convert the amorphous carbon structure into hard carbon, thereby obtaining a hard carbon / MOFs composite material. Methanol vapor is carbonized under vacuum conditions to coat a layer of graphene on the surface of the hard carbon / MOFs composite material to obtain a carbonized material. The carbonized material is cooled under vacuum conditions to obtain the target product of the present invention, the sodium ion battery negative electrode material.

[0065] Optionally, in step S1-1, the biomass carbon source is at least one of glucose, sucrose, starch, cellulose, lignin, sawdust, bamboo chips, coconut shells and nut shells.

[0066] Optionally, in step S1-1, the pre-oxidation temperature is 200°C to 300°C, for example, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, etc., and the pre-oxidation holding time is 15h to 30h, for example, 15h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, etc. When the pre-oxidation temperature is too low or the pre-oxidation holding time is too short, it is not conducive to the conversion of the biomass carbon source into an amorphous carbon structure. When the pre-oxidation temperature is too high or the pre-oxidation holding time is too long, it is not conducive to cost reduction and efficiency improvement.

[0067] Optionally, in step S1-2, the pre-oxidized material is mixed with the pure water in a mass ratio of 1:(1~2), for example, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, etc.; the molar concentration of hydrochloric acid is 1mol / L~2mol / L, for example, 1mol / L, 1.2mol / L, 1.4mol / L, 1.6mol / L, 1.8mol / L, 2mol / L, etc.; the pre-oxidized material is mixed with pure water and hydrochloric acid, and the pH of the solution after stabilization is 3~4.

[0068] Optionally, in step S1-2, the soaking time is 8 hours to 14 hours, for example, 8 hours, 10 hours, 12 hours, 14 hours, etc.

[0069] Optionally, in step S1-3, the volume ratio of the crushed material to the zirconium balls is (30-40): (60-70), for example, 30:70, 30:65, 30:60, 40:70, 40:65, 40:60, etc.; the sand milling time is 12h-24h, for example, 12h, 15h, 20h, 24h, etc.; the particle size of the zirconium balls is 0.01-0.1mm, for example, 0.01mm, 0.02mm, 0.04mm, 0.06mm, 0.08mm, 0.1mm, etc.; the linear speed of the sand mill is 9m / s-12m / s, for example, 9m / s, 10m / s, 11m / s, 12m / s, etc.

[0070] Optionally, in step S1-3, the Dv50 of the sand-polished material is 0.01 μm to 0.1 μm.

[0071] Optionally, in step S1-4, the mass ratio of the sand-milled material to the MOFs is (10-20):1, for example, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, etc. If this mass ratio is too small, the proportion of hard carbon in the hard carbon / MOFs composite is too small, which is not conducive to enhancing the cycle performance and cycle stability of the negative electrode material. If this mass ratio is too large, the proportion of MOFs in the hard carbon / MOFs composite is too small, which is not conducive to improving the rate performance and specific capacity of the negative electrode material.

[0072] Optionally, in step S1-5, the temperature of the spray granulation is 150° C. to 200° C., and the feed flow rate of the spray granulation is 100 mL / min to 300 mL / min, for example, 100 mL / min, 150 mL / min, 200 mL / min, 250 mL / min, 300 mL / min, etc. When the temperature of the spray granulation is too low or the feed flow rate is too high, it is not conducive to sufficient drying. When the temperature of the spray granulation is too high or the feed flow rate is too low, it is not conducive to cost reduction and efficiency improvement.

[0073] Optionally, in step S1-5, the Dv50 of the spray-granulated material is 3 μm to 6 μm. Since the thickness of the carbon coating layer in the last step is nanometer-scale, the Dv50 of the spray-granulated material is close to the particle size of the final negative electrode material.

[0074] Optionally, in step S1-6, the pyrolysis temperature is 1200° C. to 1600° C., for example, 1200° C., 1300° C., 1400° C., 1500° C., 1600° C., etc., and the pyrolysis holding time is 10 hours to 20 hours, for example, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, etc. When the pyrolysis temperature is too low or the pyrolysis holding time is too short, it is not conducive to the full conversion of the amorphous carbon structure into hard carbon. When the pyrolysis temperature is too high or the pyrolysis holding time is too long, it is not conducive to cost reduction and efficiency improvement.

[0075] Optionally, in step S1-6, the inert atmosphere is nitrogen and / or argon.

[0076] Optionally, in step S2-1, the vacuum condition has a vacuum degree of 0.8 Pa to 1.5 Pa, such as 0.8 Pa, 0.9 Pa, 1 Pa, 1.1 Pa, 1.2 Pa, 1.3 Pa, 1.4 Pa, 1.5 Pa, etc.; the flow rate of the methanol vapor is controlled by the vacuum degree, and the pressure of the methanol vapor is maintained at 4 kPa to 8 kPa, such as 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, etc. When the vacuum degree is too low, impurities are easily introduced. When the vacuum degree is too high, the equipment requirements are too high. When the pressure of the methanol vapor is too low, it is not conducive to forming a graphene layer of sufficient thickness. When the pressure of the methanol vapor is too high, the formed graphene layer is too thick.

[0077] Optionally, in step S2-1, the carbonization temperature is 1000°C to 1400°C, for example, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, etc.; and the carbonization holding time is 1 hour to 5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours. When the carbonization temperature is too low or the carbonization holding time is too short, it is not conducive to the formation of the graphene layer. When the carbonization temperature is too high or the carbonization holding time is too long, it is not conducive to cost reduction and efficiency improvement.

[0078] Optionally, in step S2-1, the rotation speed of the rotary kiln is 18r / min to 22r / min, for example, 18r / min, 19r / min, 20r / min, 21r / min, 22r / min, etc.; the heating rate of the rotary kiln is 10℃ / min to 14℃ / min, for example, 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, etc.

[0079] In a third aspect, the present invention provides a sodium ion battery comprising the sodium ion battery positive electrode material described in the first aspect.

[0080] Due to the adoption of the sodium ion battery positive electrode material of the first aspect, the sodium ion battery of the present invention can have high specific capacity, good rate performance and cycle performance, and has good comprehensive performance.

[0081] Optionally, the positive electrode material of the sodium ion battery includes at least one of sodium iron phosphate, sodium vanadium phosphate, sodium iron pyrophosphate, sodium nickel iron manganate, sodium copper iron manganate, etc.

[0082] The present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0083] Example 1

[0084] This embodiment provides a sodium ion battery negative electrode material with high specific capacity, good rate performance and cycle performance. The sodium ion battery negative electrode material is composed of a hard carbon / Se-MOFs composite material coated with a graphene layer. The Dv50 of the hard carbon / Se-MOFs composite material is 4 μm, the Dv50 of Se-MOFs is 20 nm, the mass ratio of hard carbon to Se-MOFs is 8:1, and the thickness of the graphene layer is 2 nm.

[0085] The preparation method of the sodium ion battery negative electrode material comprises the following steps:

[0086] S1. Preparation of hard carbon / MOFs composite material: Coconut shells were cleaned and pre-oxidized in a carbonization furnace at 250°C for 20 hours to obtain a pre-oxidized material. The pre-oxidized material was mixed with pure water at a mass ratio of 1:2, soaked in 1 mol / L hydrochloric acid for 12 hours, washed with pure water until the pH was neutral, and filtered to obtain a washed material. The washed material was pulverized to obtain a crushed material. The crushed material was added to a sand mill and added with zirconium balls with a particle size of 0.01 mm at a volume ratio of 40:70. The material was then sand-milled at a linear speed of 8 m / s for 18 hours to obtain a milled material with a Dv50 of 0.05 μm. The milled material was then dispersed and mixed with Se-MOFs with a Dv50 of 20 nm at a mass ratio of 16:1 to obtain a mixed material. The mixed material was spray granulated at a temperature of 160°C and a feed rate of 160 mL / min, resulting in a spray-granulated material with a Dv50 of 4 μm. The spray-granulated material was pyrolyzed in a carbonization furnace at 1400°C for 15 hours under nitrogen to produce a hard carbon / MOFs composite material.

[0087] S2. Preparation of negative electrode materials for sodium ion batteries: Place the hard carbon / MOFs composite material in a vacuum rotary kiln and evacuate it to a vacuum degree of 1.2 KPa. Heat the methanol liquid and introduce 6 KPa methanol vapor into the rotary kiln. The rotation speed of the rotary kiln is 20 r / min. Heat the rotary kiln to 1400°C at a heating rate of 10°C / min and maintain it at this temperature for 15 hours. Cool the sample naturally to room temperature under vacuum to obtain the negative electrode material for sodium ion batteries.

[0088] Example 2

[0089] This embodiment provides a sodium ion battery negative electrode material with high specific capacity, good rate performance and cycle performance. The sodium ion battery negative electrode material is composed of a hard carbon / Se-MOFs composite material coated with a graphene layer. The Dv50 of the hard carbon / Se-MOFs composite material is 4 μm, the Dv50 of Se-MOFs is 20 nm, the mass ratio of hard carbon and Se-MOFs is 5:1, and the thickness of the graphene layer is 2 nm.

[0090] The preparation method of the sodium ion battery negative electrode material is the same as that of Example 1, except that the mass ratio of the sand-milled material to Se-MOFs is 10:1.

[0091] Example 3

[0092] This embodiment provides a sodium ion battery negative electrode material with high specific capacity, good rate performance and cycle performance. The sodium ion battery negative electrode material is composed of a hard carbon / Se-MOFs composite material coated with a graphene layer. The Dv50 of the hard carbon / Se-MOFs composite material is 4 μm, the Dv50 of Se-MOFs is 20 nm, the mass ratio of hard carbon to Se-MOFs is 10:1, and the thickness of the graphene layer is 2 nm.

[0093] The preparation method of the sodium ion battery negative electrode material is the same as that of Example 1, except that the mass ratio of the sand-milled material to Se-MOFs is 20:1.

[0094] Example 4

[0095] This embodiment provides a sodium ion battery negative electrode material and a preparation method thereof with high specific capacity, good rate performance and cycle performance, which are the same as the sodium ion battery negative electrode material and the preparation method thereof in Example 1, except that Se-MOFs are replaced by Sn-MOFs.

[0096] Example 5

[0097] This embodiment provides a sodium ion battery negative electrode material and a preparation method thereof with high specific capacity, good rate performance and cycle performance, which are the same as the sodium ion battery negative electrode material and the preparation method thereof in Example 1, except that Se-MOFs are replaced by Ni-MOFs.

[0098] Comparative Example 1

[0099] This comparative example provides a sodium ion battery negative electrode material, which is composed of a hard carbon / Se-MOFs composite material. The Dv50 of the hard carbon / Se-MOFs composite material is 4μm, the Dv50 of Se-MOFs is 20nm, and the mass ratio of hard carbon to Se-MOFs is 8:1.

[0100] The method for preparing the negative electrode material for a sodium ion battery is the same as step S1 of the preparation method of Example 1, and step S2 of the preparation method of Example 1 is omitted.

[0101] Comparative Example 2

[0102] This comparative example provides a sodium ion battery negative electrode material with high specific capacity, good rate performance and cycle performance. The sodium ion battery negative electrode material is composed of hard carbon coated with a graphene layer, the Dv50 of the hard carbon is 4μm, and the thickness of the graphene layer is 2nm.

[0103] The preparation method of the sodium ion battery negative electrode material comprises the following steps:

[0104] S1. Preparation of hard carbon material: Coconut shells were cleaned and pre-oxidized in a carbonization furnace at 250°C for 20 hours to obtain a pre-oxidized material. The pre-oxidized material was mixed with pure water in a mass ratio of 1:2, soaked in 1 mol / L hydrochloric acid for 12 hours, washed with pure water until the pH was neutral, and filtered to obtain a washed material. The washed material was pulverized to obtain a pulverized material. The pulverized material was added to a sand mill and 0.01 mm zirconium balls were added at a volume ratio of 40:70. The material was then sand-milled at a linear speed of 8 m / s for 18 hours to obtain a Dv50 of 0.05 μm. The sand-milled material was spray-granulated at a temperature of 160°C and a feed rate of 160 mL / min to obtain a spray-granulated material with a Dv50 of 4 μm. The spray granulated material was pyrolyzed at 1400°C for 15 h in a carbonization furnace under nitrogen to obtain a hard carbon material.

[0105] S2. Preparation of negative electrode materials for sodium ion batteries: Place the hard carbon material in a vacuum rotary kiln and evacuate it to a vacuum degree of 1.2 KPa. Heat the methanol liquid and introduce 6 KPa methanol vapor into the rotary kiln. The rotation speed of the rotary kiln is 20 r / min. Heat the rotary kiln to 1400°C at a heating rate of 10°C / min and maintain it at this temperature for 15 hours. Cool the sample naturally to room temperature under vacuum to obtain the negative electrode material for sodium ion batteries.

[0106] Comparative Example 3

[0107] This comparative example provides a sodium ion battery negative electrode material, which is composed of Se-MOFs coated with a graphene layer, the Dv50 of Se-MOFs is 20 nm, and the thickness of the graphene layer is 2 nm.

[0108] The preparation method of the sodium ion battery negative electrode material comprises the following steps:

[0109] Se-MOFs with a Dv50 of 20 nm were placed in a vacuum rotary kiln and evacuated to a vacuum degree of 1.2 KPa. The methanol solution was heated and 6 KPa methanol vapor was introduced into the rotary kiln. The rotation speed of the rotary kiln was 20 r / min, and the temperature of the rotary kiln was increased to 1400°C at a heating rate of 10°C / min and maintained at this temperature for 15 hours. The sample was naturally cooled to room temperature under vacuum to obtain a sodium ion battery negative electrode material.

[0110] Preparation of button battery: The negative electrode materials of each embodiment and comparative example were prepared into a negative electrode sheet in a glove box, and the negative electrode sheet, separator, electrolyte and counter electrode (sodium sheet) were assembled in sequence to obtain a CR2032 button battery.

[0111] Preparation of soft-pack batteries: In a glove box, the negative electrode materials of each embodiment and comparative example are prepared into negative electrode sheets, and the sodium nickel iron manganese oxide positive electrode sheet, negative electrode sheet and polyethylene diaphragm (for example, PE+OBS diaphragm) are stacked and assembled and baked until the moisture content is qualified, and the electrolyte is injected. After hot pressing and high-temperature standing, the battery is packaged, and after volume separation, the battery is allowed to stand at room temperature to obtain a soft-pack 505060 finished battery.

[0112] Performance testing:

[0113] (1) Morphology: The SEM image of the sodium ion negative electrode material of Example 1 was tested using a scanning electron microscope. Figure 2 .

[0114] (2) Specific capacity and rate performance: The specific capacity and rate performance of the negative electrode materials of each embodiment and comparative example were tested at 25°C on an electrochemical workstation battery test system. The tested current densities were 0.1A / g, 0.2A / g, 0.5A / g, 1A / g, 2A / g, and 5A / g. The charge and discharge voltage window was 0.05V to 1.5V. The specific capacity of the negative electrode materials of each embodiment and comparative example is shown in Table 1. The rate performance of the negative electrode materials of Example 1 is shown in Table 2. Figure 3 .

[0115] (3) Cycling performance: The cycling performance of the soft-pack batteries assembled with the negative electrode materials of the various embodiments and comparative examples was tested at 25°C on an electrochemical workstation battery testing system. The tested charge and discharge current density was 0.5C / 1C, and the charge and discharge voltage window was 2.0V to 4.0V, as shown in Table 1. It should be noted that the SOH (state of health) in Table 1 represents the life or health of the battery. 80% SOH means that after a certain number of cycles, the life or health of the battery reaches 80% of the life or health of the battery before cycling.

[0116] Table 1. Specific capacity and cycle performance of sodium ion battery negative electrode materials of Examples 1 to 5 and Comparative Examples 1 to 3

[0117]

[0118] Figure 2 The figure shows an SEM image of the sodium ion negative electrode material of Example 1. It can be seen that the morphology of the sodium ion negative electrode material of Example 1 is spherical, and the MOFs are uniformly dispersed in the hard carbon.

[0119] Figure 3 This is the rate performance curve of the sodium ion battery negative electrode material of Example 1. Figure 3 It can be seen that the negative electrode material for sodium ion batteries of Example 1 has good rate performance. It can be seen from Examples 1 to 5 in Table 1 that the negative electrode materials for sodium ion batteries of Examples 1 to 5 all have high specific capacity and good cycle performance.

[0120] From the comparison of the charge-withdrawal specific capacity data at different rates between Example 1 and Comparative Example 1 in Table 1, it can be seen that the in situ grown graphene layer can effectively improve the rate performance of the hard carbon / MOFs composite material, improve the surface defects of the hard carbon material, and provide certain active sites, thereby increasing the specific capacity of the material and optimizing the cycle performance.

[0121] From the comparison of the specific capacity data of Example 1 and Comparative Example 2 at different rates in Table 1, it can be seen that MOFs can provide more redox reaction active sites, thereby providing a higher specific capacity, and it can promote the Na +and the uniformity of the electric field potential, thereby achieving the Na + Rapid migration and uniform deposition provide better rate performance.

[0122] From the comparison of the charge-withdrawal specific capacity data of Example 1 and Comparative Example 3 at different rates in Table 1, it can be seen that the unique structure of the hard carbon / MOFs composite material can make MOFs evenly distributed in the hard carbon structure, avoid MOFs material agglomeration, and effectively improve the material's cycle stability and rate performance.

[0123] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0124] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A sodium ion battery negative electrode material, characterized in that The sodium ion battery negative electrode material is a core-shell structure consisting of a core and a shell layer coated on the surface of the core, the core comprises a hard carbon / MOFs composite material, the MOFs are Se-MOFs, and the shell layer comprises a graphene layer; the preparation method of the sodium ion battery negative electrode material comprises the following steps: S1. Preparation of the hard carbon / MOFs composite material S1-1, after cleaning the biomass carbon source, pre-oxidize it in a carbonization furnace to obtain a pre-oxidized material; S1-2, mixing the pre-oxidized material with pure water, adding hydrochloric acid to soak, washing with pure water until neutral, and filtering to obtain a washed material; S1-3, crushing the washed material to obtain a crushed material, adding the crushed material to a sand mill, adding zirconium balls, and sand-milling to obtain a sand-milled material; S1-4, dispersing and mixing the sand-milled material with the MOFs at high speed to obtain a mixed material; S1-5, spray granulating the mixed material to obtain a spray granulated material; S1-6, pyrolyzing the spray-granulated material in a carbonization furnace under an inert atmosphere at a temperature of 1200° C. to 1600° C. to obtain the hard carbon / MOFs composite material; S2. Preparation of the sodium ion battery negative electrode material S2-1, placing the hard carbon / MOFs composite material in a rotary kiln, heating methanol, introducing methanol vapor into the rotary kiln, and carbonizing the hard carbon / MOFs composite material under vacuum conditions, coating the graphene layer on the surface of the hard carbon / MOFs composite material to obtain a carbonized material; S2-2, naturally cooling the carbonized material to room temperature under vacuum conditions to obtain the sodium ion battery negative electrode material.

2. The sodium ion battery negative electrode material according to claim 1, characterized in that The Dv50 of the hard carbon / MOFs composite material is 3 μm to 6 μm.

3. The sodium ion battery negative electrode material according to claim 1, characterized in that The Dv50 of the MOFs is 20 nm to 100 nm.

4. The sodium ion battery negative electrode material according to claim 1, characterized in that The mass ratio of the hard carbon to the MOFs is (5-10):

1.

5. The sodium ion battery negative electrode material according to claim 1, characterized in that The thickness of the graphene layer is 1 nm to 10 nm.

6. The method for preparing a negative electrode material for a sodium ion battery according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Preparation of the hard carbon / MOFs composite material S1-1, after cleaning the biomass carbon source, pre-oxidize it in a carbonization furnace to obtain a pre-oxidized material; S1-2, mixing the pre-oxidized material with pure water, adding hydrochloric acid to soak, washing with pure water until neutral, and filtering to obtain a washed material; S1-3, crushing the washed material to obtain a crushed material, adding the crushed material to a sand mill, adding zirconium balls, and sand-milling to obtain a sand-milled material; S1-4, dispersing and mixing the sand-milled material with the MOFs at high speed to obtain a mixed material; S1-5, spray granulating the mixed material to obtain a spray granulated material; S1-6, pyrolyzing the spray-granulated material in a carbonization furnace under an inert atmosphere at a temperature of 1200° C. to 1600° C. to obtain the hard carbon / MOFs composite material; S2. Preparation of the sodium ion battery negative electrode material S2-1, placing the hard carbon / MOFs composite material in a rotary kiln, heating methanol, introducing methanol vapor into the rotary kiln, and carbonizing the hard carbon / MOFs composite material under vacuum conditions, coating the graphene layer on the surface of the hard carbon / MOFs composite material to obtain a carbonized material; S2-2, naturally cooling the carbonized material to room temperature under vacuum conditions to obtain the sodium ion battery negative electrode material.

7. The method for preparing a negative electrode material for a sodium ion battery according to claim 6, wherein: The pre-oxidation temperature is 200°C to 300°C, and the pre-oxidation holding time is 15h to 30h; the pyrolysis holding time is 10h to 20h; and / or the carbonization temperature is 1000°C to 1400°C, and the carbonization holding time is 1h to 5h.

8. The method for preparing a negative electrode material for a sodium ion battery according to claim 6, wherein: The vacuum degree of the vacuum condition is 0.8 Pa to 1.5 Pa, and the pressure of the methanol vapor is maintained at 4 kPa to 8 kPa.

9. A sodium ion battery, characterized in that: The negative electrode material for a sodium ion battery comprises the negative electrode material according to any one of claims 1 to 5.

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