A hard carbon composite material for sodium ion batteries and a preparation method thereof

Abstract

The application relates to the field of sodium ion battery electrode material preparation, in particular to a hard carbon composite material for a sodium ion battery and a preparation method thereof, and a preparation method of a hard carbon composite material for a sodium ion battery, which comprises the following steps: adding a thermosetting resin, a metal carbonate compound and an acidic catalyst into a sulfide to perform oxidative crosslinking; etching gas is introduced to perform surface etching, so that a hard carbon precursor material is obtained; and the hard carbon precursor material is used to obtain the hard carbon composite material by using a gas phase deposition method. The technical problem of poor specific capacity and fast charging performance of the prepared hard carbon material in the prior art is solved.

Description

[0001] The present application relates to the field of sodium ion battery electrode material preparation, in particular to a hard carbon composite material for sodium ion batteries and a preparation method thereof.

[0002] Sodium ion batteries have the advantages of low cost, abundant resources and low temperature performance, and are often used as a supplement to lithium ion batteries. The negative electrode material used in sodium ion batteries is mainly hard carbon. Hard carbon material has a large interlayer spacing and a high specific surface area, and is considered to be one of the most promising negative electrode materials for sodium ion batteries.

[0003] In the prior art, resin-based materials have the advantages of high compaction density, high consistency and abundant active points, and are often used as one of the precursors of hard carbon materials. Then, through ball milling, carbonization treatment, etc., hard carbon materials are obtained. However, the current hard carbon materials generally have the technical problems of low specific capacity (300-320 mAh / g), low compaction density (1.0 g / cm3), and poor fast charging ability, etc., which cause the energy density and fast charging performance of the materials to deviate.

[0004] To solve the technical problems of low specific capacity and poor fast charging performance of hard carbon materials in the prior art, the present application provides a hard carbon composite material for sodium ion batteries and a preparation method thereof.

[0005] The technical problem of the present application is solved by providing a preparation method of a hard carbon composite material for sodium ion batteries, comprising the following steps:

[0006] The thermosetting resin, metal carbonate compound and acidic catalyst are added to the sulfide for oxidative crosslinking to obtain a crosslinked material.

[0007] Etching gas is introduced into the crosslinked material for surface etching to obtain a hard carbon precursor material.

[0008] The hard carbon precursor material is obtained by using a gas phase deposition method to obtain a hard carbon composite material.

[0009] Preferably, the thermosetting resin and metal carbonate compound, and acidic catalyst are added to the sulfide for oxidative crosslinking, which specifically comprises the following steps:

[0010] The thermosetting resin, metal carbonate compound and acidic catalyst are added to the sulfide in a predetermined ratio and mixed uniformly to obtain a mixture.

[0011] The mixture is heated to 700-1200℃ under an oxygen atmosphere for oxidative crosslinking for 1-6h to obtain a crosslinked material.

[0012] Preferably, the surface etching by introducing etching gas to obtain a hard carbon precursor material comprises the following steps:​​​

[0013] Cool the crosslinked material to 400-600℃;

[0014] Etching gas is introduced and the surface of the crosslinked material is etched for 0.5-2 hours to obtain hard carbon precursor material.

[0015] Preferably, the process of obtaining hard carbon composite material from hard carbon precursor material using chemical vapor deposition includes the following steps:

[0016] The hard carbon precursor material is transferred into a tubular furnace and natural gas is introduced.

[0017] Heat to 800-1000℃ and hold for 1-6 hours;

[0018] After natural cooling, the hard carbon composite material is obtained by acid washing and drying.

[0019] Preferably, the thermosetting resin includes any one of phenolic resin, epoxy resin, ketol resin, acrylic resin, and polyimide resin.

[0020] Preferably, the metal carbonate compound includes any one of potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate.

[0021] Preferably, the sulfide includes any one of persulfate, sodium or potassium salt of thiosulfate, sodium polysulfide, thiol, thiophenol, and thioether.

[0022] Preferably, the mass ratio of thermosetting resin: metal carbonate: acid catalyst: sulfide is in the range of 100:(5-20).

[0023] (1~5): (1~5).

[0024] Preferably, the acidic catalyst comprises any one of dodecylbenzenesulfonic acid, p-toluenesulfonic acid, dinonylnaphthalenesulfonic acid, and dilauric acid.

[0025] To solve the above-mentioned technical problems, the present invention also provides a hard carbon composite material for sodium-ion batteries, which is prepared by the above-mentioned method for preparing hard carbon composite material for sodium-ion batteries. The hard carbon composite material has a core-shell structure, with an outer core of amorphous carbon and an inner core of sulfur-doped hard carbon. The proportion of the outer core is 1-5 wt% by weight.

[0026] Compared with the prior art, the present invention provides a hard carbon composite material for sodium-ion batteries and its preparation method, which has the following advantages:

[0027] 1. The preparation method of the hard carbon composite material for sodium ion batteries provided in the embodiment of the present application comprises the following steps: adding a thermosetting resin, a metal carbonate compound and an acidic catalyst into a sulfide for oxidative crosslinking; introducing etching gas for surface etching to obtain a hard carbon precursor material; and obtaining the hard carbon composite material by using a gas phase deposition method. It can be understood that the carbonate compound can generate gas during pyrolysis, thereby leaving nanometer microporous holes to improve the specific capacity of the material; the crosslinking process of the sulfide is beneficial to the formation of a turbostratic structure, thereby improving the storage performance of the material. In addition, the sulfide realizes sulfur doping after carbonization, which can improve the active points of the material and further improve the sodium storage performance of the material; the acidic catalyst mainly plays a role in reducing the decomposition temperature of the carbonate compound and improving the reaction process; the carbon layer of the crosslinked material is etched by etching gas, which is beneficial to the formation of a nano-porous structure on the surface and facilitates the deposition of amorphous carbon, thereby improving the coating integrity of the material; the gas phase deposition method deposits amorphous carbon on the surface to form a shell, which can improve the electronic conductivity of the material, improve the fast charging performance of the sodium ion battery made of the material, and solve the technical problems of poor specific capacity and fast charging performance of the hard carbon material in the prior art.

[0028] 2. In the preparation method of the hard carbon composite material for sodium ion batteries provided in the embodiment of the present application, the metal carbonate compound includes any one of potassium carbonate, potassium bicarbonate, sodium carbonate and sodium bicarbonate. It should be noted that the carbonate compound (sodium carbonate or potassium carbonate, etc.) generates gas during pyrolysis and leaves nanometer microporous holes to improve the specific capacity of the material. In addition, Na+ or K+ generated during the heating process shuttles between the carbon layers, which plays a role in expanding the layers and improving the diffusion coefficient, thereby improving the sodium ion insertion and extraction rate of the hard carbon composite material during the charging and discharging process.

[0029] 3. In the preparation method of the hard carbon composite material for sodium ion batteries provided in the embodiment of the present application, the hard carbon composite material obtained by using the gas phase deposition method on the hard carbon precursor material comprises the following steps: transferring the hard carbon precursor material into a tube furnace and introducing natural gas; heating to 800-1000℃ and maintaining for 1-6h; and obtaining the hard carbon composite material after natural cooling, acid washing and drying in sequence. It should be noted that the gas phase deposition method is used to coat amorphous carbon on the surface to reduce the irreversible capacity, thereby improving the first charge and discharge efficiency and tap density.

[0030] 4. The hard carbon composite material for sodium ion batteries provided in the embodiment of the present application is prepared by using the preparation method of the hard carbon composite material for sodium ion batteries. The hard carbon composite material presents a core-shell structure, the outer core is amorphous carbon, and the inner core is sulfur-doped hard carbon. The proportion of the outer core is 1-5wt%, and the hard carbon composite material has the same beneficial effects as the above-mentioned preparation method of the hard carbon composite material for sodium ion batteries, which will not be described here.

DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0032] Figure 1 is a flowchart of a preparation method of a hard carbon composite material for a sodium ion battery provided by an embodiment of the present application.

[0033] Figure 2 is a flowchart of obtaining a crosslinked material provided by an embodiment of the present application.

[0034] Figure 3 is a flowchart of obtaining a hard carbon precursor provided by an embodiment of the present application.

[0035] Figure 4 is a flowchart of obtaining a hard carbon composite material by a vapor deposition method provided by an embodiment of the present application.

[0036] Figure 5 is an SEM image of a hard carbon composite material prepared by an experimental group 1.

DETAILED DESCRIPTION

[0037] In order to make the objects, technical solutions and advantages of the present application more clear, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0038] Please refer to Figure 1 The first embodiment of the present application provides a preparation method of a hard carbon composite material for a sodium ion battery, comprising the following steps:

[0039] S1: adding a thermosetting resin, a metal carbonate compound and an acidic catalyst into a sulfide to perform oxidative crosslinking, to obtain a crosslinked material;

[0040] S2: introducing an etching gas to perform surface etching on the crosslinked material, to obtain a hard carbon precursor material;

[0041] S3: obtaining a hard carbon composite material by a vapor deposition method using the hard carbon precursor material.

[0042] It should be noted that in step S1, the thermosetting resin includes any one of a phenolic resin, an epoxy resin, a ketone-alcohol resin, an acrylic resin and a polyimide resin. It has a certain chemical composition, can realize qualitative batch production, and the hard carbon produced by different batches has the same performance.

[0043] In some embodiments, a biomass carbon source such as wood can be used as a raw material for processing to obtain a hard carbon precursor material, thereby reducing the cost in mass production process. However, the biomass carbon source has defects such as poor consistency, low specific capacity, and low compaction density. Therefore, the thermosetting resin is used as a high molecular raw material in the present application, which has the characteristics of high consistency, high specific capacity, and high compaction density, thereby improving the energy density of the material, so that the final hard carbon composite material has superior performance.

[0044] The metal carbonate compound includes any one of potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate. It should be noted that the carbonic acid compound can produce gas during pyrolysis, thereby leaving nanometer microporous holes to improve the specific capacity of the material. The sodium ion or potassium ion produced by the chemical reaction and decomposition of the metal carbonate compound such as potassium carbonate and sodium carbonate during heating process shuttles between the carbon layers, plays a role in expanding the layer, and improves the sodium ion insertion and extraction rate in the charge and discharge process of the hard carbon composite material. Specifically, the interlayer spacing of the carbon layer is between 0.37-0.40 nm, which is a layered structure. The diameter of the potassium ion is 0.276 nm, and the diameter of the sodium ion is 0.2 nm. By heating, the potassium ion or sodium ion is volatilized from the carbon layer, thereby expanding the carbon layer and improving the interlayer spacing.

[0045] The acidic catalyst includes any one of dodecyl benzene sulfonic acid, p-toluenesulfonic acid, dinonyl naphthalene sulfonic acid, and dilauryl acid. It should be noted that the acidic catalyst mainly plays a role in reducing the decomposition temperature of the carbonic acid compound and improving the reaction process.

[0046] The sulfide includes any one or several of sodium or potassium peroxymonosulfate, sodium or potassium thiosulfate, sodium polysulfide, mercaptan, thiophenol, and sulfide. It should be noted that the sulfide is beneficial to form a disordered structure during cross-linking, thereby improving the storage performance of the material. In addition, the sulfur doping of the sulfide after carbonization can improve the active sites of the material, and further improve the sodium storage performance of the material.

[0047] Further, please refer to Figure 1 and Figure 2 , step S1 specifically includes:

[0048] S11: The thermosetting resin, the metal carbonate compound, and the acidic catalyst are added to the sulfide in a predetermined ratio and mixed uniformly to obtain a mixture;

[0049] S12: The mixture is heated to 700-1200℃ under an oxygen atmosphere for 1-6h for oxidative cross-linking to obtain a cross-linked material.

[0050] It should be noted that the mass ratio of thermosetting resin: metal carbonate compound: acid catalyst: sulfide is in the range of 100:(5~20):(1~5):(1~5).

[0051] It should be noted that in step S12, the gas flow rate will affect the degree of oxidative crosslinking of the material. In this embodiment, the preferred oxygen gas flow rate is 100-1000 SCCM, specifically 100 SCCM, 500 SCCM, 1000 SCCM, etc. This embodiment does not make any specific limitation.

[0052] It should be noted that in step S12, the heating rate is 1-5℃ / min; it is understandable that by limiting the heating rate, the insufficient oxidative crosslinking caused by heating too fast is avoided, resulting in poor structural stability, while heating too slowly will also affect the efficiency of oxidative crosslinking.

[0053] Understandably, during the heating process, when the temperature reaches 400-600℃, the carbonate will decompose to produce gas, which plays a role in creating pores. This will not be elaborated further in this embodiment.

[0054] For further details, please refer to Figure 1 and Figure 3 Step S2 specifically includes:

[0055] S21: Cool the crosslinked material to 400-600℃;

[0056] S22: Introduce etching gas and etch the surface of the crosslinked material for 0.5-2 hours to obtain hard carbon precursor material.

[0057] It should be noted that steps S21 and S22 are performed sequentially, that is, step S21 is completed first, and then step S22 is performed.

[0058] It should be noted that the etching gas includes one of carbon dioxide and water vapor. Etching the carbon layer of the cross-linked material with the etching gas is beneficial to forming a nanoporous structure on the surface, which facilitates the deposition of amorphous carbon and improves the integrity of the material coating.

[0059] It should be noted that water vapor can react with oxides on the surface of cross-linked materials at high temperatures to form hydroxides, thereby achieving surface corrosion and removing surface impurities; carbon dioxide is an acidic gas that can react with the material surface to achieve surface corrosion and removal. Choosing carbon dioxide or water vapor as etching gases has the advantages of being readily available, easy to operate, and having good safety.

[0060] In this embodiment, a preferred implementation method is to use water vapor to etch at 500°C, so that the final hard carbon precursor material has a good specific surface area and etching depth.

[0061] It should be noted that by limiting the etching time, the etching depth is too deep, thereby causing the hard carbon precursor material to have too many holes and too large specific surface area, further reducing the first charge-discharge efficiency and reducing the tap density; and the etching time is too short, and the surface etching depth is too shallow, which is not conducive to the deposition of amorphous carbon generated by natural gas cracking on the surface.

[0062] It should be noted that the flow rate of the etching gas is 10-100 SCCM, and can be 10 SCCM, 20 SCCM, 50 SCCM, 100 SCCM, which is not limited in the embodiment.

[0063] Further, please refer to Figure 1 and Figure 4 , step S3 specifically comprises:

[0064] S31: transferring the hard carbon precursor material into a tube furnace, and introducing natural gas;

[0065] S32: heating to 800-1000℃, and holding for 1-6h;

[0066] S33: after natural cooling, sequentially passing through acid pickling and drying to obtain a hard carbon composite material.

[0067] It should be noted that in step S31, the gas flow rate of the natural gas is 100-500 SCCM, and can be 100 SCC, 200 SCCM, 500 SCCM, etc., which is not limited in the embodiment.

[0068] It should be noted that the acid pickling can be carried out by immersing in an acid pickling solution such as dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid, etc., such as immersing in dilute hydrochloric acid with a concentration of 2mol / L for 8 hours, which is not limited in the embodiment. After acid pickling, drying is carried out in a vacuum drying box to obtain a hard carbon composite material.

[0069] It should be noted that the deposition of amorphous carbon on the surface by the gas phase deposition method can improve the electronic conductivity of the material, and the fast charging performance of the sodium ion battery made of the material is improved.

[0070] Exemplarily, in order to better reflect that the hard carbon composite material prepared by the embodiment of the present application has better specific capacity and fast charging performance, the present application further sets up an experimental group and a comparison group, as follows:

[0071] Experimental group 1:

[0072] Step S1: 100 g of phenolic resin, 10 g of potassium carbonate, 3 g of dodecyl benzene sulfonic acid and 3 g of potassium persulfate were uniformly mixed, and then oxidatively crosslinked at an oxygen atmosphere, a gas flow rate of 500 SCCM and a temperature rising rate of 3°C / min to 900°C for 3 h.

[0073] Step S2: etching was performed on the surface thereof by passing water vapor gas at a gas flow rate of 50 SCCM at 500°C for 1 h to obtain a hard carbon precursor material.

[0074] Step S3: the hard carbon precursor material was transferred into a tube furnace, natural gas gas was then passed at a flow rate of 500 SCCM, and the temperature was raised to 900°C for deposition for 3 h, and then naturally cooled to room temperature, washed with acid and dried to obtain a hard carbon composite material.

[0075] Experiment group 2:

[0076] Step S1: 100 g of epoxy resin, 5 g of potassium bicarbonate, 1 g of p-toluenesulfonic acid and 1 g of potassium thiosulfate were uniformly mixed, and then oxidatively crosslinked at an oxygen atmosphere, a gas flow rate of 100 SCCM and a temperature rising rate of 1°C / min to 700°C for 6 h.

[0077] Step S2: etching was performed on the surface thereof by passing carbon dioxide gas at a gas flow rate of 10 SCCM at 400°C for 2 h to obtain a hard carbon precursor material.

[0078] Step S3: the hard carbon precursor material was transferred into a tube furnace, natural gas gas was then passed at a flow rate of 100 SCCM, and the temperature was raised to 800°C for deposition for 6 h, and then naturally cooled to room temperature, washed with acid and dried to obtain a hard carbon composite material.

[0079] Experiment group 3:

[0080] Step S1: 100 g of ketone-alcohol resin, 20 g of sodium polysulfide, 5 g of dinonyl naphthalene sulfonic acid and 5 g of mercaptan were uniformly mixed, and then oxidatively crosslinked at an oxygen atmosphere, a gas flow rate of 1000 SCCM and a temperature rising rate of 5°C / min to 1200°C for 1 h.

[0081] Step S2: etching was then performed on the surface thereof by passing water vapor gas at a gas flow rate of 100 SCCM at 700°C for 0.5 h to obtain a hard carbon precursor material.

[0082] Step S3: the hard carbon precursor material was transferred into a tube furnace, natural gas gas was then passed at a flow rate of 500 SCCM, and the temperature was raised to 1000°C for deposition for 1 h, and then naturally cooled to room temperature, washed with acid and dried to obtain a hard carbon composite material.

[0083] Comparative Group 1: Different from Experimental Group 1, no potassium carbonate and potassium persulfate are added, and the others are the same as Experimental Group 1.

[0084] Comparative Group 2: Different from Experimental Group 1, no carbon dioxide etching gas is passed, and the others are the same as Experimental Group 1.

[0085] Comparative Group 3: Different from Experimental Group 1, step S3 is not used, and steps S1 and S2 are the same, and the hard carbon precursor material is directly used as the negative electrode material in step S2.

[0086] (1) SEM test

[0087] Please refer to Figure 5 , Figure 5 The SEM test results of the hard carbon composite material prepared for Experimental Group 1 are shown in the figure, wherein the dotted line represents the scale of the figure, and the length of the dotted rectangle represents 10 um. It can be seen that the size distribution of the composite material is uniform, and there is slight connection, and the particle size is between 5-10 um.

[0088] (2) Physicochemical property test

[0089] The specific surface area, tap density, and powder conductivity of the hard carbon composite material of the test examples and comparative examples are tested according to the national standard GB / T-24533-2019 "Lithium Ion Battery Graphite Negative Electrode Material"; and the diffusion coefficient of the material is tested by GITT, and the particle size La is tested by XRD. The test results are shown in Table 1.

[0090] (3) Button cell test

[0091] The hard carbon composite materials in Experimental Groups 1-3 and Comparative Groups 1-3 are used as lithium ion battery negative electrode materials to assemble button cells. The specific preparation method of the negative electrode material is as follows: the negative electrode sheet is prepared by mixing the hard carbon composite material, CMC, SBR, SP, and H2O in a mass ratio of 95:2.5:1.5:1:150; sodium sheet is used as the counter electrode; NaPF6(solvent EC:DEC:PC:propylene glycol polyoxypropylene ether = 1:2:1:0.05, concentration 1.3 mol / L) is used as the electrolyte; and the composite film of polyethylene PE, polypropylene PP, and polyethylene propylene PEP is used as the separator. The button cell is assembled in an argon-filled glove box. The electrochemical performance is tested on a Wuhan Lan Dian CT2001A battery tester, the charge and discharge voltage range is 0.00V to 2.0V, the charge and discharge rate is 0.1C, and the first discharge capacity and first efficiency, DCR, cycle performance (0.5C / 0.5C, 100 weeks), and rate performance (2C / 0.1C) of the button cell are tested. The test results are shown in Table 1.

[0092] Table 1 is a comparison table of the physicochemical property test and the performance test of the button cell of experimental groups 1-3 and comparative groups 1-3

[0093]

[0094] As can be seen from Table 1, the diffusion coefficient, tap density and specific capacity of the hard carbon negative electrode composite material obtained from experimental groups 1-3 are superior to those of comparative groups 1-2, because the addition of metal carbonate compound in the thermosetting resin material generates gas by pyrolysis of the carbonic compound (sodium carbonate or potassium carbonate, etc.) and leaves nanometer micropores, thereby improving the specific capacity of the material, and Na+ or K+ generated in the heating process shuttles between the carbon layers, thereby expanding the layer and improving the diffusion coefficient, and the surface of the material is coated with amorphous carbon by using the gas phase deposition method, thereby reducing the irreversible capacity, improving the initial efficiency and tap density.

[0095] (4) Liquid absorption capacity and liquid retention rate test

[0096] The hard carbon composite material in experimental groups 1-3 and comparative groups 1-2 is mixed and coated to prepare a negative electrode sheet, layered oxides (NaFe1 / 3Mn1 / 3Ni1 / 3O2) are used as the positive electrode, and NaPF6 (solvent: EC: DEC: PC: propylene glycol polyoxypropylene ether = 1:2:1:0.05, concentration 1.3 mol / L) is used as the electrolyte to prepare a 5 Ah soft package battery for testing the liquid absorption capacity and the liquid retention rate, respectively.

[0097] Liquid absorption capacity: 1 mL of a burette is used to absorb electrolyte V = 1 mL, one drop is added on the surface of the electrode sheet, and timing is performed until the electrolyte is completely absorbed, and the time t is recorded. The test results are shown in Table 2.

[0098] Liquid retention rate test: the theoretical liquid absorption amount m1 of the electrode sheet is calculated according to the electrode sheet parameters, and the weight m2 of the electrode sheet is weighed, then the electrode sheet is soaked in the electrolyte for 24 h, the weight of the electrode sheet is weighed as m3, the liquid absorption amount m3-m2 of the electrode sheet is calculated, and the liquid retention rate is calculated according to the following formula: liquid retention rate = (m3-m2)*100% / m1, and the test results are shown in Table 2.

[0099] Table 2 is a comparison table of the liquid absorption speed and the liquid retention rate test of the battery prepared from experimental groups 1-3 and comparative groups 1-2

[0100] Serial number Suction speed (S) Liquid retention rate Experimental group 1 54 90.1％ Experimental group 2 61 88.7％ Experimental group 3 48 92.1％ Comparative group 1 88 84.9％ Comparative group 2 96 82.1％

[0101] As can be seen from Table 2, the liquid absorption and retention capacity of the negative electrode prepared from the composite material obtained from experimental groups 1-3 is significantly superior to that of the comparative groups, because the hard carbon material in the experimental groups has a high specific surface area, thereby improving the liquid absorption and retention performance of the electrode sheet.

[0102] (5) Rate performance test

[0103] The hard carbon composite materials in the experimental groups 1-3 and the comparative group 1-2 were prepared into negative electrode sheets by slurry mixing and coating, and 5 Ah soft package batteries were prepared by using layered oxides (NaFe1 / 3Mn1 / 3Ni1 / 3O2) as positive electrodes and NaPF6 (solvent: EC: DEC: PC: propylene glycol polyoxypropylene ether = 1:2:1:0.05, concentration 1.3 mol / L) as electrolyte, to test the rate performance.

[0104] The rate performance of the soft package batteries was tested, the charge and discharge voltage range was 1-4.0 V, the temperature was 25±3.0℃, the charging was performed at 1.0 C and 3.0 C, and the discharging was performed at 1.0 C, and the test results are shown in Table 3.

[0105] Table 3 is a rate performance test comparison table of the experimental groups 1-3 and the comparative group 1-2.

[0106]

[0107] As shown in Table 3, the rate charging performance of the soft package batteries in Examples 1-3 is obviously better than that of the comparative example, that is, the charging time is shorter, and the main reason is that the sulfur doping in the sulfide carbonization process improves the electronic conductivity of the material and the electronic conductivity of the material coated with amorphous carbon on the surface by the gas phase deposition method, and the power performance of the material is improved.

[0108] The second embodiment of the present application provides a hard carbon composite material for sodium ion batteries, which is prepared by using the preparation method of the hard carbon composite material for sodium ion batteries in the first embodiment, and the hard carbon composite material has a core-shell structure, the outer core is amorphous carbon, and the inner core is sulfur-doped hard carbon, the proportion of the outer core is 1-5 wt%, and the hard carbon composite material has the same beneficial effects as the method of the hard carbon composite material for sodium ion batteries, which will not be repeated here.

[0109] The third embodiment of the present application further provides a sodium ion battery, which uses the hard carbon composite material for sodium ion batteries provided in the second embodiment as a negative electrode material, and has the same beneficial effects as the method of the hard carbon composite material for sodium ion batteries, which will not be repeated here.

[0110] Compared with the prior art, the hard carbon composite material for sodium ion batteries and the preparation method thereof provided by the present application have the following advantages:

[0111] 1. The preparation method of the hard carbon composite material for sodium ion batteries provided in the embodiment of the present application comprises the following steps: adding a thermosetting resin, a metal carbonate compound and an acidic catalyst into a sulfide for oxidative crosslinking; introducing etching gas for surface etching to obtain a hard carbon precursor material; and obtaining the hard carbon composite material by using a gas phase deposition method. It can be understood that the carbonate compound can generate gas during pyrolysis, thereby leaving nanometer microporous holes to improve the specific capacity of the material; the crosslinking process of the sulfide is beneficial to the formation of a turbostratic structure, thereby improving the storage performance of the material. In addition, the sulfide realizes sulfur doping after carbonization, which can improve the active points of the material and further improve the sodium storage performance of the material; the acidic catalyst mainly plays a role in reducing the decomposition temperature of the carbonate compound and improving the reaction process; the carbon layer of the crosslinked material is etched by the etching gas, which is beneficial to the formation of a nano-porous structure on the surface and facilitates the deposition of amorphous carbon, thereby improving the coating integrity of the material; the gas phase deposition method deposits amorphous carbon on the surface to form a shell, which can improve the electronic conductivity of the material, improve the fast charging performance of the sodium ion battery made of the material, and solve the technical problems of poor specific capacity and fast charging performance of the hard carbon material in the prior art.

[0112] 2. In the preparation method of the hard carbon composite material for sodium ion batteries provided in the embodiment of the present application, the metal carbonate compound includes any one of potassium carbonate, potassium bicarbonate, sodium carbonate and sodium bicarbonate. It should be noted that the carbonate compound (sodium carbonate or potassium carbonate, etc.) generates gas during pyrolysis and leaves nanometer microporous holes to improve the specific capacity of the material. In addition, Na+ or K+ generated during the heating process shuttles between the carbon layers, which plays a role in expanding the layers and improving the diffusion coefficient, thereby improving the sodium ion insertion and extraction rate of the hard carbon composite material in the charging and discharging process.

[0113] 3. In the preparation method of the hard carbon composite material for sodium ion batteries provided in the embodiment of the present application, the hard carbon composite material obtained by using the gas phase deposition method on the hard carbon precursor material comprises the following steps: transferring the hard carbon precursor material into a tube furnace and introducing natural gas; heating to 800-1000℃ and maintaining for 1-6h; and obtaining the hard carbon composite material after natural cooling, acid washing and drying in sequence. It should be noted that the amorphous carbon is coated on the surface by using the gas phase deposition method, which reduces the irreversible capacity and improves the first charge and discharge efficiency and tap density.

[0114] 4. The hard carbon composite material for sodium ion batteries provided in the embodiment of the present application is prepared by using the preparation method of the hard carbon composite material for sodium ion batteries. The hard carbon composite material presents a core-shell structure, the outer core is amorphous carbon, and the inner core is sulfur-doped hard carbon. The proportion of the outer core is 1-5wt% according to the weight percentage. The hard carbon composite material has the same beneficial effects as the above-mentioned preparation method of the hard carbon composite material for sodium ion batteries, and will not be described here.

[0115] In the embodiments provided in the present application, it should be understood that "B corresponding to A" means that B is associated with A, and B can be determined according to A. However, it should also be understood that the determination of B according to A does not mean that B is determined only according to A, but B can also be determined according to A and / or other information.

[0116] It should be understood that "one embodiment" or "an embodiment" mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. Those skilled in the art should also know that the embodiments described in the specification are optional embodiments, and the actions and modules involved are not necessarily required by the present application.

[0117] In various embodiments of the present application, it should be understood that the size of the sequence number of each process described above does not mean the inevitable sequence of execution, and the execution sequence of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0118] In the flowcharts and block diagrams in the drawings of the present application, the possible implementation architecture, function and operation of the system, method and computer program product according to various embodiments of the present application are illustrated. In this regard, each block in the flowchart or block diagram can represent a module, a program segment or a part of code containing one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks can also occur in different order from that marked in the drawings. For example, two blocks represented in succession can actually be executed substantially in parallel, and sometimes they can be executed in reverse order, which is determined based on the functions involved. It should be particularly noted that each block in the block diagram and / or flowchart, and the combination of blocks in the block diagram and / or flowchart, can be implemented by a dedicated hardware-based system performing the specified functions or operations, or can be implemented by a combination of special-purpose hardware and computer instructions.

[0119] The above has carried out the detailed introduction to the hard carbon composite material for the sodium ion battery and the preparation method thereof disclosed in the embodiment of the application, the principle and the implementation mode of the application are described in this paper by applying specific examples, the above embodiment is only used for helping understanding the method of the application and its core idea; at the same time, for the general technical personnel in the art, according to the idea of the application, the specific implementation mode and the application range will have changes, and the above is not understood as the limitation of the application, any modification, equivalent replacement and improvement within the principle of the application should be included in the protection scope of the application.

Claims

1. A method for preparing a hard carbon composite material for a sodium-ion battery, characterized by, The method comprises the following steps: adding a thermosetting resin, a metal carbonate compound and an acidic catalyst into a sulfide to mix uniformly to obtain a mixture, the mass ratio of the thermosetting resin, the metal carbonate compound, the acidic catalyst and the sulfide being in the range of 100: (5-20): (1-5): (1-5); the metal carbonate compound comprising any one of potassium carbonate, potassium bicarbonate, sodium carbonate and sodium bicarbonate; oxidizing and cross-linking the mixture in an oxygen atmosphere with a flow rate of 100-1000 SCCM at a rate of 1-5℃ / min to 700-1200℃ for 1-6h to obtain a cross-linked product; cooling the cross-linked product to 400-600℃, and etching the surface of the cross-linked product by introducing carbon dioxide as an etching gas for 0.5-2h to obtain a hard carbon precursor material; transferring the hard carbon precursor material into a tube furnace, introducing natural gas, heating to 800-1000℃, and holding for 1-6h, and then sequentially performing acid washing and drying to obtain a hard carbon composite material.

2. The method for preparing a hard carbon composite material for a sodium ion battery according to claim 1, characterized in that: during the process of oxidizing and cross-linking, sodium ions or potassium ions produced by the decomposition of the metal carbonate compound during heating shuttle between carbon layers, and the interlayer spacing of the carbon layers is expanded to 0.37-0.40nm.

3. The method for preparing a hard carbon composite material for sodium-ion batteries as described in claim 2, characterized in that, The flow rate of the etching gas is 10-100 SCCM.

4. The method for preparing a hard carbon composite material for a sodium-ion battery according to claim 1, characterized in that, The flow rate of the natural gas is 100-500 SCCM.

5. The method for preparing a hard carbon composite material for sodium-ion batteries as described in claim 1, characterized in that, The thermosetting resin comprises any one of phenolic resin, epoxy resin, ketone-alcohol resin, acrylic resin and polyimide resin.

6. The method for preparing a hard carbon composite material for sodium-ion batteries as described in claim 1, characterized in that, The sulfide comprises any one of sodium or potassium peroxysulfate, sodium or potassium thiosulfate, sodium polysulfide, mercaptan, sulfenol and sulfide.

7. The method for preparing a hard carbon composite material for sodium-ion batteries as described in claim 1, characterized in that, The acidic catalyst comprises any one of dodecyl benzene sulfonic acid, p-toluenesulfonic acid, dinonyl naphthalene sulfonic acid and dilauryl acid.

8. A hard carbon composite material for sodium ion batteries, prepared by the method according to any one of claims 1 to 7, characterized in that, The hard carbon composite material presents a core-shell structure, the outer core being amorphous carbon and the inner core being sulfur-doped hard carbon, the proportion of the outer core being 1-5wt% by weight.

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