A nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material, its preparation method and application

Abstract

The present invention provides a nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material, a preparation method thereof and an application thereof, belonging to the technical field of sodium-ion battery electrode materials. The nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material provided by the present invention comprises a heterogeneous structure body and nitrogen-doped porous carbon coated on the surface of the heterogeneous structure body; the heterogeneous structure body comprises nickel disulfide and cobalt disulfide. An internal electric field is formed by nickel disulfide and cobalt disulfide in the heterogeneous structure body of the present invention, which can accelerate the transmission of electrons and ions, improve the adsorption of sodium ions, and further improve the rate performance of the material; the coating of nitrogen-doped porous carbon can significantly improve the conductivity of the composite material and improve the rate performance of the material, and can also effectively avoid volume expansion during the charge and discharge cycle, thereby improving the cycle stability of the composite material.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery electrode materials, and specifically relates to a nickel disulfide / cobalt disulfide / nitrogen-carbon composite material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are considered as a substitute for fossil fuels due to their high energy density and long cycle life. Although lithium-ion batteries have been widely used in daily life and production, they cannot meet the growing demand for energy storage devices due to their low reserves and uneven distribution.

[0003] Sodium is an element in the same main group as lithium but in a different period. It has similar physical and chemical properties, and its abundance in the earth's crust is much higher than that of lithium. This has led people to pay more and more attention to the development of sodium-ion batteries. However, the radius of sodium ions is 1.34 times that of lithium ions, which results in a larger volume expansion and slower kinetics of the negative electrode material during the charge and discharge process.

[0004] According to the sodium storage mechanism, negative electrode materials can be divided into three categories: intercalation type, conversion type and alloy type. Transition metal sulfides belong to the conversion type and have attracted much attention due to their high theoretical specific capacity; cobalt sulfide, in particular, has excellent thermal stability, high theoretical capacity and environmental friendliness; however, its conductivity is poor, and during the sodium insertion / de-sodiumization process, it will have problems such as excessive volume expansion, which will lead to the crushing of electrode materials, and ultimately lead to poor rate performance and cycle performance. Summary of the invention

[0005] The purpose of the present invention is to provide a nickel disulfide / cobalt disulfide / nitrogen-carbon composite material and a preparation method and application thereof. The nickel disulfide / cobalt disulfide / nitrogen-carbon composite material of the present invention has excellent rate performance and cycle performance as a negative electrode material for a sodium ion battery.

[0006] The present invention provides a nickel disulfide / cobalt disulfide / nitrogen-carbon composite material, comprising a heterogeneous structure and nitrogen-doped porous carbon coated on the surface of the heterogeneous structure; the heterogeneous structure comprises nickel disulfide and cobalt disulfide.

[0007] Preferably, the particle size of the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material is 2.5-3.5 μm, and the heterostructure is a flower ball structure formed by assembling nanosheets.

[0008] Preferably, the pore size of the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material is 2 to 5 nm.

[0009] Preferably, the doping amount of nitrogen in the nitrogen-doped porous carbon is 2-6 wt %.

[0010] The present invention also provides a method for preparing the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material described in the above scheme, comprising the following steps:

[0011] A nickel source, a cobalt source and a weakly alkaline compound are dissolved in a polar solvent and then subjected to a solvothermal reaction to obtain nickel-cobalt hydroxide;

[0012] Dispersing the nickel cobalt hydroxide in a Tris-HCl buffer solution, mixing the obtained dispersion with dopamine hydrochloride to carry out a polymerization reaction, and obtaining a nickel cobalt hydroxide coated with polydopamine hydrochloride;

[0013] Carbothermal reduction of the polydopamine hydrochloride coated nickel cobalt hydroxide to obtain nitrogen-doped porous carbon coated nickel cobalt;

[0014] The nitrogen-doped porous carbon-coated nickel-cobalt is mixed with sulfur powder for sulfurization reaction to obtain the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material.

[0015] Preferably, the molar ratio of nickel in the nickel source to cobalt in the cobalt source is 0.8 to 1.2:1;

[0016] The nickel source includes one or more of nickel chloride, nickel nitrate and nickel sulfate; the cobalt source includes one or more of cobalt chloride, cobalt nitrate and cobalt sulfate.

[0017] Preferably, the molar ratio of the nickel source to the weakly alkaline compound is 1:1.5 to 3.5;

[0018] The weakly alkaline compound includes one or more of urea, ammonia water, ammonium fluoride and hexamethylenetetramine.

[0019] Preferably, the temperature of the solvent thermal reaction is 120-180° C. and the time is 6-18 hours.

[0020] Preferably, the temperature of the vulcanization reaction is 320-380° C., and the time is 3-15 hours.

[0021] The present invention also provides the use of the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material described in the above scheme or the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material prepared by the preparation method described in the above scheme as a negative electrode material in a sodium ion battery.

[0022] The present invention provides a nickel disulfide / cobalt disulfide / nitrogen-carbon composite material, including a heterostructure and nitrogen-doped porous carbon coated on the surface of the heterostructure; the heterostructure includes nickel disulfide and cobalt disulfide. The nickel disulfide and cobalt disulfide in the heterostructure of the present invention form a built-in electric field, which can accelerate the transmission of electrons and ions, improve the adsorption of sodium ions, and thus improve the rate performance of the material; the coating of nitrogen-doped porous carbon can significantly improve the conductivity of the composite material to improve the rate performance of the material, and can also effectively avoid volume expansion during the charge and discharge cycle, thereby improving the cycle stability of the composite material. The results of the embodiment show that the sodium ion battery prepared by the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material of the present invention has a specific capacity of 371.4mAh / g at a current density of 40A / g, and maintains a specific capacity of up to 581.8mAh / g after 300 cycles at a current density of 2A / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XRD pattern of the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material of Example 1;

[0024] Figure 2 This is a SEM image of the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material of Example 1;

[0025] Figure 3 TEM image of the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material of Example 1;

[0026] Figure 4 HRTEM image of the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material of Example 1;

[0027] Figure 5 The nitrogen adsorption-desorption isotherms and pore size distribution of the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material of Example 1;

[0028] Figure 6 The cycle performance test results of sodium ion batteries of application example 1 and comparative application examples 1 to 2 are shown;

[0029] Figure 7 The rate performance test results of sodium ion batteries of application example 1 and comparative application examples 1 to 2 are shown;

[0030] Figure 8 The following are the test results of the cycle performance of the sodium ion batteries of Application Examples 1 to 3. DETAILED DESCRIPTION

[0031] The present invention provides a nickel disulfide / cobalt disulfide / nitrogen-carbon composite material, comprising a heterogeneous structure and nitrogen-doped porous carbon coated on the surface of the heterogeneous structure; the heterogeneous structure comprises nickel disulfide and cobalt disulfide.

[0032] In the present invention, the particle size of the nickel disulfide / cobalt disulfide / nitrogen carbon composite material is preferably 2.5-3.5 μm, more preferably 2.8-3.2 μm. In the present invention, the doping amount of nitrogen in the nitrogen-doped porous carbon is 2-6 wt%. The pore size of the nickel disulfide / cobalt disulfide / nitrogen carbon composite material is 2-5 nm, more preferably 3-4 nm. Nitrogen-doped porous carbon can improve electrical conductivity, thereby improving sodium storage performance.

[0033] The nickel disulfide and cobalt disulfide in the heterogeneous structure of the present invention form a built-in electric field, which can accelerate the transmission of electrons and ions, improve the adsorption of sodium ions, and thus improve the rate performance of the material; the coating of nitrogen-doped porous carbon can effectively avoid volume expansion during the charge and discharge cycle, thereby improving the cycle stability of the composite material.

[0034] The present invention also provides a method for preparing the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material described in the above scheme, comprising the following steps:

[0035] A nickel source, a cobalt source and a weakly alkaline compound are dissolved in a polar solvent and then subjected to a solvothermal reaction to obtain nickel-cobalt hydroxide;

[0036] Dispersing the nickel cobalt hydroxide in a Tris-HCl buffer solution, mixing the obtained dispersion with dopamine hydrochloride to carry out a polymerization reaction, and obtaining a nickel cobalt hydroxide coated with polydopamine hydrochloride;

[0037] Carbothermal reduction of the polydopamine hydrochloride coated nickel cobalt hydroxide to obtain nitrogen-doped porous carbon coated nickel cobalt;

[0038] The nitrogen-doped porous carbon-coated nickel-cobalt is mixed with sulfur powder for sulfurization reaction to obtain the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material.

[0039] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known in the art.

[0040] The invention dissolves a nickel source, a cobalt source and a weakly alkaline compound in a polar solvent and then performs a solvent thermal reaction to obtain nickel-cobalt hydroxide.

[0041] In the present invention, the molar ratio of nickel in the nickel source to cobalt in the cobalt source is preferably 0.8-1.2:1, more preferably 1.9-1:1; the nickel source preferably includes one or more of nickel chloride, nickel nitrate and nickel sulfate; the cobalt source preferably includes one or more of cobalt chloride, cobalt nitrate and cobalt sulfate. In the present invention, the molar ratio of the nickel source to the weak alkaline compound is preferably 1:1.5-5, more preferably 1:2-4, and further preferably 1:2.5-3.5; the weak alkaline compound preferably includes one or more of urea, ammonia water, ammonium fluoride and hexamethylenetetramine. In the present invention, the volume ratio of the total amount of the nickel salt and the cobalt salt to the polar solvent is preferably 2mmol:20-60mL, more preferably 2mmol:30-50mL, and further preferably 2mmol:40-45mL. In the present invention, the polar solvent preferably includes N,N-dimethylformamide and monohydric alcohol; the volume ratio of N,N-dimethylformamide to monohydric alcohol is preferably 1:2 to 4, more preferably 1:2.5 to 3. In the present invention, the monohydric alcohol preferably includes methanol and / or ethanol.

[0042] In the present invention, the dissolution is preferably carried out under the condition of magnetic stirring. In the present invention, the temperature of the solvothermal reaction is preferably 120-180°C, more preferably 150-160°C; the time is preferably 6-18h, more preferably 10-16h, and further preferably 12-14h. During the solvothermal reaction, cobalt ions and nickel ions coprecipitate to form flower-shaped nickel-cobalt hydroxide. In the present invention, nickel-cobalt hydroxide includes nickel hydroxide and cobalt hydroxide.

[0043] After the solvent thermal reaction, the present invention preferably washes and dries the solvent thermal reaction product to obtain the nickel cobalt hydroxide. The present invention has no special limitation on the washing, and the solvent and unreacted raw materials can be fully removed. Specifically, in the embodiment of the present invention, the washing is to wash alternately with deionized water and alcohol three times. The present invention has no special limitation on the drying, and it can be dried to constant weight using a scheme familiar to those skilled in the art. Specifically, in the embodiment of the present invention, the drying is drying at 60°C in a vacuum drying oven for 12 hours.

[0044] After obtaining nickel cobalt hydroxide, the present invention disperses the nickel cobalt hydroxide in a Tris-HCl buffer solution, mixes the obtained dispersion with dopamine hydrochloride for polymerization reaction, and obtains nickel cobalt hydroxide coated with poly dopamine hydrochloride. In the present invention, the mass ratio of the nickel cobalt hydroxide to dopamine hydrochloride is preferably 1 to 3:1, more preferably 1.5 to 2.5:1, and further preferably 1.8 to 2:1. In the present invention, the mass ratio of the nickel cobalt hydroxide to the volume ratio of the Tris-HCl buffer solution is preferably 1.2 mg:1 mL, and the pH value of the Tris-HCl buffer solution is preferably 8 to 9, and further preferably 8.6. In the present invention, the temperature of the polymerization reaction is preferably 25 to 40°C, more preferably 30 to 35°C, and the time is preferably 3 to 12h, more preferably 5 to 10h, and further preferably 6 to 8h. During the polymerization reaction, dopamine hydrochloride generates poly dopamine hydrochloride coated on the surface of the nickel cobalt hydroxide.

[0045] After the polymerization reaction is completed, the present invention preferably washes, separates and dries the polymerization reaction product to obtain nickel cobalt hydroxide coated with poly dopamine hydrochloride (referred to as nickel cobalt hydroxide @ PDA). The present invention has no particular limitation on the washing, separation and drying, and a pure, constant-weight nickel cobalt hydroxide coated with poly dopamine hydrochloride can be obtained by using a scheme well known to those skilled in the art.

[0046] After obtaining the nickel cobalt hydroxide coated with poly hydrochloride dopamine, the present invention performs a carbon thermal reduction reaction on the nickel cobalt hydroxide coated with poly hydrochloride dopamine to obtain nitrogen-doped porous carbon-coated nickel cobalt (denoted as NiCo@NC). In the present invention, the temperature of the carbon thermal reduction reaction is preferably 600-900°C, more preferably 700-800°C, and the insulation time is preferably 2-6h, more preferably 3-5h, and further preferably 4-4.5h. In the present invention, the carbon thermal reduction reaction is preferably carried out in an inert gas. In the present invention, the inert gas preferably includes argon. In the carbon thermal reduction, nickel cobalt hydroxide generates nickel cobalt elemental and nitrogen-doped porous carbon.

[0047] After obtaining the nitrogen-doped porous carbon-coated nickel-cobalt, the present invention mixes the nitrogen-doped porous carbon-coated nickel-cobalt with sulfur powder for sulfurization reaction to obtain the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material (denoted as NiS 2 / CoS 2@NC). In the present invention, the mass ratio of the nitrogen-doped porous carbon-coated nickel-cobalt to the sulfur powder is preferably 1:1.7-2.3, more preferably 1:1.8-2. In the present invention, the temperature of the sulfurization reaction is preferably 320-380°C, more preferably 350-360°C, and the time is preferably 3-15h, more preferably 6-12h, more preferably 8-10h. In the present invention, the sulfurization reaction is preferably carried out in an inert gas, and the inert gas is preferably argon. In the sulfurization reaction, the sulfur powder reacts with nickel / cobalt to generate nickel disulfide / cobalt disulfide.

[0048] The present invention uses solvent thermal reaction, polymerization reaction, carbonization reduction and sulfurization reaction to obtain NiS 2 / CoS 2 The surface is coated with a layer of nitrogen-doped porous carbon and applied to the negative electrode material of sodium ion battery; the conductivity of the composite material can be significantly improved by coating with nitrogen-doped porous carbon shell, while further improving the structural stability of the composite material.

[0049] The preparation method of the invention is simple and easy to control, has a wide source of raw materials and is highly industrially applicable.

[0050] The present invention also provides the use of the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material described in the above scheme or the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material prepared by the preparation method described in the above scheme as a negative electrode material in a sodium ion battery.

[0051] The application preferably comprises the following steps:

[0052] The nickel disulfide / cobalt disulfide / nitrogen-carbon composite material, conductive carbon black, polyvinylidene fluoride and N-methylpyrrolidone are mixed to obtain a slurry;

[0053] The slurry is coated on a copper foil and then dried to obtain a working electrode;

[0054] The working electrode, sodium block, separator and electrolyte are assembled into a sodium ion battery in a glove box.

[0055] In the present invention, the NiS 2 / CoS 2 The mass ratio of @NC, conductive carbon black and polyvinylidene fluoride is preferably 8:1:1. 2 / CoS 2 The mass ratio of @NC to the volume ratio of N-methylpyrrolidone is preferably 8 mg:60 μL. The drying is preferably carried out under vacuum conditions, the drying temperature is preferably 80°C, and the drying time is preferably 12 hours. In the present invention, the separator is preferably Whatman GF / A. In the present invention, the electrolyte system is 1M NaCF 3 SO 3In the present invention, the sodium ion battery preferably comprises a button battery.

[0056] In order to further illustrate the present invention, the nickel disulfide / cobalt disulfide / nitrogen-carbon composite material provided by the present invention and its preparation method and application are described in detail below in combination with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] 2mmol of nickel chloride, 2mmol of cobalt chloride and 10mmol of urea were added to a mixed solution of 20mL of N,N-dimethylformamide and 60mL of methanol, and magnetic stirring was performed to form a uniform solution. The above solution was placed in a high-pressure hydrothermal autoclave and heated at 150°C for 12h. The solution was washed alternately with deionized water and alcohol three times, and dried in a vacuum drying oven at 60°C for 12h to obtain nickel cobalt hydroxide.

[0059] 120 mg of nickel cobalt hydroxide was uniformly dispersed in 100 mL of Tris-HCl buffer solution with a pH of 8.6, and 60 mg of dopamine hydrochloride was added. The mixture was stirred at 25°C for 6 h, and then washed and dried to obtain nickel cobalt hydroxide@PDA.

[0060] The obtained nickel cobalt hydroxide@PDA was subjected to carbothermal reduction reaction in argon at 800°C for 2 h to obtain NiCo@NC.

[0061] The obtained NiCo@NC was fully mixed with sulfur powder in a mass ratio of 1:2 and sulfurized for 9 h at 350 °C in an argon atmosphere to obtain NiS 2 / CoS 2 @NC.

[0062] The NiS obtained in Example 1 2 / CoS 2 @NC was subjected to XRD analysis, and the results were as follows Figure 1 As shown. Figure 1 It can be seen that Figure 1 There is no characteristic peak of impurities in the NiS 2 / CoS 2 @NC has high purity.

[0063] The NiS obtained in Example 1 2 / CoS 2 @NC conducted SEM analysis, the results are as follows Figure 2 As shown. Figure 2 It can be seen that the prepared NiS 2 / CoS 2 @NC is in the shape of a flower ball, with a particle size of 3 microns.

[0064] The NiS obtained in Example 1 2 / CoS 2 @NC conducted TEM analysis, and the results were as follows Figure 3 As shown. Figure 3 It can be seen that NiS 2 / CoS 2 @NC is wrapped in a layer of nitrogen and carbon.

[0065] The NiS obtained in Example 1 2 / CoS 2 @NC conducted HRTEM analysis, the results are as follows Figure 4 As shown. Figure 4 It can be seen that NiS 2 / CoS 2 @NC has a clear phase interface, and the lattice spacing corresponds to NiS 2 and CoS 2 The existence of heterostructure is confirmed.

[0066] The NiS obtained in Example 1 2 / CoS 2 @NC conducted nitrogen adsorption and desorption experiments and pore size distribution measurements. The results are as follows Figure 5 As shown. Figure 5 It can be seen that the isotherm curve of the sample shows a typical type IV isotherm curve with an obvious hysteresis loop, which represents the mesoporous characteristics. 2 / CoS 2 The specific surface area of ​​@NC is 17.56m 2 g -1 , the pore size is mainly 3.8nm.

[0067] Example 2

[0068] 120 mg of the nickel cobalt hydroxide of Example 1 was uniformly dispersed in 100 mL of Tris-HCl buffer solution with a pH of 8.6, and 40 mg of dopamine hydrochloride was added. The mixture was stirred for 6 h, washed, and dried to obtain nickel cobalt hydroxide@PDA;

[0069] The obtained nickel cobalt hydroxide@PDA was subjected to carbothermal reduction reaction in argon at 800°C for 2 h to obtain NiCo@NC.

[0070] The obtained NiCo@NC was fully mixed with sulfur powder in a mass ratio of 1:2 and sulfurized for 9 h at 350 °C in an argon atmosphere to obtain NiS 2 / CoS 2 @NC-2.

[0071] Example 3

[0072] 120 mg of the nickel cobalt hydroxide of Example 1 was uniformly dispersed in 100 mL of Tris-HCl buffer solution with a pH of 8.6, and 120 mg of dopamine hydrochloride was added. The mixture was stirred for 6 h, washed, and dried to obtain nickel cobalt hydroxide@PDA;

[0073] The obtained nickel cobalt hydroxide@PDA was subjected to carbothermal reduction reaction in argon at 800°C for 2 h to obtain NiCo@NC.

[0074] The obtained NiCo@NC was fully mixed with sulfur powder in a mass ratio of 1:2 and sulfurized for 9 h at 350 °C in an argon atmosphere to obtain NiS 2 / CoS 2 @NC-3.

[0075] Comparative Example 1

[0076] 4 mmol of nickel chloride and 10 mmol of urea were added to a mixed solution of 20 mL of N,N-dimethylformamide and 60 mL of methanol, and magnetic stirring was performed to form a uniform solution. The solution was placed in a high-pressure hydrothermal autoclave and heated at 150°C for 12 hours. The solution was washed alternately with deionized water and alcohol three times, and dried in a vacuum drying oven at 60°C for 12 hours to obtain nickel hydroxide.

[0077] 120 mg of nickel hydroxide was uniformly dispersed in 100 mL of Tris-HCl buffer solution with a pH of 8.6, and 60 mg of dopamine hydrochloride was added. After stirring for 6 h, the mixture was washed and dried to obtain nickel hydroxide@PDA.

[0078] The obtained nickel cobalt hydroxide@PDA was subjected to carbothermal reduction reaction in argon at 800°C for 2 h to obtain Ni@NC.

[0079] The obtained Ni@NC was fully mixed with sulfur powder in a mass ratio of 1:2 and sulfurized for 9 h at 350 °C in an argon atmosphere to obtain NiS 2 @NC.

[0080] Comparative Example 2

[0081] 4 mmol of cobalt chloride and 10 mmol of urea were added to a mixed solution of 20 mL of N, N-dimethylformamide and 60 mL of methanol, and magnetic stirring was performed to form a uniform solution. The solution was placed in a high-pressure hydrothermal autoclave and heated at 150°C for 12 hours. The solution was washed alternately with deionized water and alcohol three times, and dried in a vacuum drying oven at 60°C for 12 hours to obtain cobalt hydroxide.

[0082] 120 mg of cobalt hydroxide was uniformly dispersed in 100 mL of Tris-HCl buffer solution with a pH of 8.6, and 60 mg of dopamine hydrochloride was added. After stirring for 6 h, the mixture was washed and dried to obtain nickel cobalt hydroxide @PDA;

[0083] The obtained cobalt hydroxide@PDA was subjected to carbothermal reduction reaction under argon to obtain Co@NC.

[0084] The obtained Co@NC was fully mixed with sulfur powder in a mass ratio of 1:2 and sulfurized for 9 h at 350 °C in an argon atmosphere to obtain CoS 2 @NC.

[0085] Application Example 1

[0086] The NiS prepared in Example 1 2 / CoS 2 @NC material is used as active material and assembled into sodium ion battery for electrochemical performance testing. The process is as follows:

[0087] The NiS of Example 1 2 / CoS 2 @NC, conductive carbon black and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, and the NiS 2 / CoS 2 The mass ratio of @NC to volume of N-methylpyrrolidone was 8 mg: 60 μL. N-methylpyrrolidone was added and mixed evenly to form a slurry. 100 g of the slurry was applied to an area of ​​120 cm with a four-sided coater. 2 The prepared composite material was used as the working electrode and the sodium block was used as the counter electrode to test its electrochemical performance. The diaphragm was Whatman GF / A and the electrolyte system was 1M NaCF 3 SO 3 The solute is diethylene glycol dimethyl ether and the solvent is diethylene glycol dimethyl ether.

[0088] Comparative application example 1

[0089] The only difference from Application Example 1 is that the NiS prepared in Comparative Example 1 2 @NC materials as active materials.

[0090] Comparative Application Example 2

[0091] The only difference from Application Example 1 is that the CoS prepared in Comparative Example 2 2 @NC materials as active materials.

[0092] The sodium ion batteries assembled in Example 1 and Comparative Example 1-2 were tested for cycle performance. The results are as follows: Figure 6 As shown. Figure 6 It can be seen that when the current density is 2A / g for 300 cycles, the NiS prepared in Example 1 2 / CoS 2 The reversible specific capacity of the @NC heterostructure composite material can reach 581.8 mAh / g. 2 The reversible specific capacity of @NC can reach 27.1 mAh / g. 2 The reversible specific capacity of @NC can reach 437.0mAh / g.

[0093] The sodium ion battery rate performance of Application Example 1 and Comparative Application Examples 1 to 2 was measured under different current density conditions. The results are as follows Figure 7 As shown. Figure 7 It can be seen that when the current density is 2, 5, 10, 20 and 40 A / g, the NiS prepared in Example 1 2 / CoS 2 The reversible specific capacities of the @NC heterostructure composite materials were 832.2, 741.1, 649.2, 544.8, and 371.4 mAh / g, respectively. When the current density returned to 2 A / g, the reversible specific capacity remained at 722.3 mAh / g. 2 The reversible specific capacities of @NC were 428.6, 211.8, 100.7, 44.8, and 17.6 mAh / g, respectively. When the current density returned to 2 A / g, the reversible specific capacity remained at 249.8 mAh / g. 2 The reversible specific capacities of @NC are 653.1, 485.6, 346.8, 167.5, and 73.1 mAh / g, respectively. When the current density returns to 2 A / g, the reversible specific capacity remains at 538.4 mAh / g. By comparing Application Example 1 and Comparative Application Examples 1 to 2, it can be seen that NiS 2 / CoS 2 @NC's rate performance and cycle performance are significantly higher than those of single-component materials.

[0094] Application Example 2

[0095] The only difference from Application Example 1 is that the NiS prepared in Example 2 is used. 2 / CoS 2 @NC materials as active materials.

[0096] Application Example 3

[0097] The only difference from Application Example 1 is that the NiS prepared in Example 3 is used. 2 / CoS2 @NC materials as active materials.

[0098] The sodium ion batteries assembled in Example 2 and 3 were tested for cycle performance. The results are as follows: Figure 8 As shown. Figure 8 It is known that, under the condition of current density of 2A / g, 300 cycles are carried out, and the NiS prepared in Example 2 2 / CoS 2 The reversible specific capacity of the @NC-2 heterostructure composite material can reach 163.8 mAh / g. The reversible specific capacity of the NiS2 / CoS2@NC-3 prepared in Example 3 can reach 300.9 mAh / g.

[0099] By comparing Application Example 1 and Application Examples 2 to 3, it can be seen that the NiS in Application Example 1 2 / CoS 2 @NC cycle performance is significantly higher than that of application examples 2 to 3.

[0100] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material, characterized in that, it comprises a heterostructure and nitrogen-doped porous carbon coated on the surface of the heterostructure; the heterostructure comprises nickel disulfide and cobalt disulfide; the heterostructure is a flower ball structure formed by assembling nanosheets; The preparation method of the nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material comprises the following steps: Dissolve a nickel source, a cobalt source, and a weak basic compound in a polar solvent and then carry out a solvothermal reaction to obtain flower-like nickel cobalt hydroxide; the molar ratio of nickel in the nickel source to cobalt in the cobalt source is 0.8~1.2:1; Disperse the nickel cobalt hydroxide in a Tris-HCl buffer solution, mix the obtained dispersion with dopamine hydrochloride and carry out a polymerization reaction to obtain nickel cobalt hydroxide coated with poly-dopamine hydrochloride; Carry out a carbothermal reduction reaction on the nickel cobalt hydroxide coated with poly-dopamine hydrochloride to obtain nickel cobalt coated with nitrogen-doped porous carbon; Mix the nickel cobalt coated with nitrogen-doped porous carbon with sulfur powder and carry out a sulfidation reaction to obtain the nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material.

2. The nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material according to claim 1, characterized in that, the particle size of the nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material is 2.5~3.5 μm.

3. The nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material according to claim 1, characterized in that, the pore size of the nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material is 2~5 nm.

4. The nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material according to claim 1 or 3, characterized in that, the nitrogen doping amount in the nitrogen-doped porous carbon is 2~6 wt%.

5. The preparation method of the nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material according to any one of claims 1 to 4, characterized in that, it comprises the following steps: Dissolve a nickel source, a cobalt source, and a weak basic compound in a polar solvent and then carry out a solvothermal reaction to obtain flower-like nickel cobalt hydroxide; the molar ratio of nickel in the nickel source to cobalt in the cobalt source is 0.8~1.2:1; Disperse the nickel cobalt hydroxide in a Tris-HCl buffer solution, mix the obtained dispersion with dopamine hydrochloride and carry out a polymerization reaction to obtain nickel cobalt hydroxide coated with poly-dopamine hydrochloride; Carry out a carbothermal reduction reaction on the nickel cobalt hydroxide coated with poly-dopamine hydrochloride to obtain nickel cobalt coated with nitrogen-doped porous carbon; Mix the nickel cobalt coated with nitrogen-doped porous carbon with sulfur powder and carry out a sulfidation reaction to obtain the nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material.

6. The preparation method according to claim 5, characterized in that, the nickel source includes one or more of nickel chloride, nickel nitrate, and nickel sulfate; the cobalt source includes one or more of cobalt chloride, cobalt nitrate, and cobalt sulfate.

7. The preparation method according to claim 5, characterized in that, the molar ratio of the nickel source to the weak basic compound is 1:1.5~3.5; the weak basic compound includes one or more of urea, ammonia water, ammonium fluoride, and hexamethylenetetramine.

8. The preparation method according to claim 5 or 6 or 7, characterized in that, The temperature of the solvothermal reaction is 120~180 °C, and the time is 6~18 h.

9. According to the preparation method described in claim 5, characterized in that the temperature of the sulfidation reaction is 320~380 °C, and the time is 3~15 h.

10. Application of the nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material according to any one of claims 1 to 4 or the nickel disulfide / cobalt disulfide / nitrogen-doped carbon composite material prepared by the preparation method according to any one of claims 5 to 9 as a negative electrode material in a sodium-ion battery.

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