Bimetal sulfide and biomass carbon composite material for sodium ion battery, negative electrode and negative electrode of sodium ion battery

Abstract

The invention discloses a bimetallic sulfide and biomass carbon composite material for a sodium ion battery, a negative electrode and a negative electrode of the sodium ion battery. In the bimetallic sulfide and biomass carbon composite material for the sodium ion battery provided by the invention, due to the existence of a heterostructure, the transmission rate of sodium ions in the charging and discharging process is accelerated; and due to the existence of a unique porous carbon skeleton derived from diatomite, the structural stability of the Ni3S2atCo9S8-BC anode in the charge-discharge process is ensured. Besides, the metal sulfide particles are limited to the nanometer level, under the synergistic effect of the carbon skeleton, the aggregation phenomenon of the metal sulfide particles in the circulation process can be effectively inhibited, the reversible capacity of 225.36 mAh g <-1 > can still be provided even under the large current density of 10 A g <-1 > after 7000 times of circulation, the capacity retention rate is 65.3%, and the capacity fading rate of each circle is 0.00138%.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly relates to a bimetallic sulfide and biomass carbon composite material for a sodium-ion battery, a negative electrode, and a negative electrode of a sodium-ion battery. Background Art

[0002] Since the metal-sulfur bond in transition metal sulfides (TMs) is relatively weak, it is kinetically favorable for conversion reactions and promotes the enhancement of reaction kinetics. Therefore, it has a high theoretical capacity. In addition, the materials used in the experiment are also metal sulfides with relatively low prices. Therefore, it is considered by many researchers to be a new generation of commercial negative electrode materials for sodium-ion batteries that can replace hard carbon. However, during the redox process of transition metal sulfides, the volume change of bulk materials is severe, resulting in electrode pulverization, thus leading to poor cycle stability; the dissolution of polysulfides in the electrolyte will cause slow Na + diffusion kinetics and poor conductivity, resulting in a series of problems such as a large attenuation of irreversible capacity, limited cycle life, and low rate performance.

[0003] To solve this series of problems, many strategies have been proposed in previous studies. First, reducing TMs particles to the nanoscale significantly reduces the mechanical stress associated with the conversion reaction and simultaneously shortens the diffusion path of Na + , thus alleviating the problems of pulverization and slow ion diffusion kinetics. Second, and the most effective research strategy is to embed TMs nanoparticles in a heteroatom-doped carbon matrix, which improves the conductivity, introduces more active sites for electrochemical energy storage, is conducive to the capture / adsorption of polysulfide intermediates, and avoids the aggregation of TMs nanoparticles, thus alleviating the capacity attenuation problem. Compared with single metal sulfides, bimetallic TMs have higher conductivity and richer active sites. Introducing bimetallic sulfides (or multiphases) with rich phase boundaries avoids deep solid-state diffusion with fast ion diffusion kinetics, and at the same time, the bimetals can form a buffer mechanism with each other to reduce volume changes, thus significantly improving the electrochemical performance.

[0004] More importantly, the introduction of bimetals can form a heterojunction. Generally speaking, the synergistic effect of heterostructure electrodes is significantly better than that of single electrodes. First, heterostructure electrodes can integrate their advantages and offset the disadvantages of each component. Second, heterojunctions usually have a smaller bandgap, so they exhibit superior conductivity and accelerated charge transfer. Third, the strong interaction of heterostructure electrodes can improve the structural stability and lifespan of heterostructure electrodes. Finally, charges are redistributed at the non-uniform boundary, inducing more active sites to adsorb alkali metal ions. Therefore, diverse heterojunction anodes can enhance the storage capacity for sodium ions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a composite material of bimetallic sulfide and biomass carbon for sodium-ion batteries, a negative electrode, and a negative electrode for sodium-ion batteries in view of the deficiencies in the above-mentioned prior art. The present invention prepares a Ni 3 S 2 @Co 9 S 8 -BC composite material of bimetallic sulfide heterostructure and porous carbon. The heterostructure can improve the conductivity and accelerate the charge transfer, and the capacity decay rate is very low even after thousands of cycles at a high current density. The negative electrode sheet prepared from this composite material has good electrochemical performance and cycle life.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: In the first aspect of the present invention, there is provided a composite material of bimetallic sulfide and biomass carbon for sodium-ion batteries, which is prepared by the following steps:

[0007] S1. Prepare a porous carbon skeleton:

[0008] The diatomite is calcined under a protective gas, and then impregnated with an alkali solution, washed, dried, and ball-milled to obtain a porous carbon skeleton, denoted as BC.

[0009] S2. Prepare a precursor:

[0010] The porous carbon skeleton is dispersed in deionized water, Ni 2+ , Co 2+ are added, and then 2-methylimidazole is added, and a hydrothermal reaction is carried out under heating to prepare a precursor.

[0011] S3. Carbonization-sulfurization treatment:

[0012] The precursor is mixed with sublimed sulfur powder, and then calcined under a protective gas to prepare a composite material of a porous carbon skeleton and a bimetallic sulfide heterostructure, that is, the composite material of bimetallic sulfide and biomass carbon for sodium-ion batteries, denoted as Ni 3 S 2 @Co 9 S 8 -BC.

[0013] Preferably, step S1 is specifically as follows:

[0014] The diatomite is sieved through a 50-200 mesh sieve, and then under a protective gas atmosphere, it is heated from room temperature to 600-1000 °C at a rate of 2-10 °C / min, held for 1-4 h, and then naturally cooled to room temperature.

[0015] The obtained powder was dispersed in a KOH solution, stirred at room temperature for 2 - 8 h, then neutralized to pH 7 with an HCl solution, centrifugally washed multiple times with deionized water and alcohol, the solid product was dried at 50 - 70 °C for 6 - 24 h, and finally ball-milled for 6 - 24 h to obtain a porous carbon framework, denoted as BC.

[0016] Preferably, the mass concentration of the KOH solution is 5 - 20%, and the mass concentration of the HCl solution is 2.5 - 10%.

[0017] Preferably, the Ni in step S2 2+ , Co 2+ are introduced by adding water-soluble divalent nickel salts and divalent cobalt salts respectively.

[0018] Preferably, the divalent nickel salt is selected from at least one of NiSO 4 ·6H 2 O, (CH 3 COO) 2 Ni·4H 2 O, and the divalent cobalt salt is selected from at least one of Co(NO 3 ) 2 ·6H 2 O, CoSO 4 ·7H 2 O.

[0019] Preferably, step S2 is specifically as follows:

[0020] Take the porous carbon framework and disperse it in deionized water, add water-soluble divalent nickel salts and divalent cobalt salts, stir to dissolve, then add 2-methylimidazole, stir for 2 - 10 min and then transfer it into a hydrothermal autoclave, carry out hydrothermal reaction at 140 - 160 °C for 3 - 12 hours. After cooling to room temperature, the obtained product is centrifugally washed with deionized water, and the solid product is dried at 50 - 80 °C for 6 - 24 hours to obtain a precursor.

[0021] Preferably, step S3 is specifically as follows:

[0022] Mix the precursor with sublimed sulfur powder, grind for 10 - 40 min, then under the atmosphere of a protective gas, heat from room temperature to 130 - 160 °C at a rate of 2 - 10 °C / min, hold for 0.5 - 2 h and then heat to 400 - 800 °C at a rate of 2 - 10 °C / min, hold for 1.5 - 6 h and then naturally cool to room temperature. The obtained black powder is a composite material of a porous carbon framework and a bimetallic sulfide heterostructure, that is, the bimetallic sulfide and biomass carbon composite material for the sodium-ion battery, denoted as Ni 3 S 2 @Co 9 S 8 -BC.

[0023] Preferably, the protective gas in step S1 is nitrogen with a purity of 99.99%, and the protective gas in step S3 is argon with a purity of 99.99%.

[0024] Preferably, in step S2, the molar ratio of the divalent nickel salt to the divalent cobalt salt is 1:1 to 2.

[0025] Preferably, in step S2, the molar ratio of the divalent nickel salt to 2-methylimidazole is 1:1 to 4.

[0026] Preferably, in step S2, the mass ratio of 2-methylimidazole to the porous carbon framework is 1.5 - 6:0.25 - 1;

[0027] Preferably, in step S2, taking the volume unit as mL and the mass unit as g, the volume of deionized water is 50 - 200 times the mass of the porous carbon framework.

[0028] Preferably, in step S3, the mass ratio of sublimed sulfur powder to the precursor is 1 - 2:1.

[0029] Preferably, the bimetallic sulfide and biomass carbon composite material for sodium-ion batteries is prepared by the following steps:

[0030] S1. Prepare the porous carbon framework:

[0031] Pass diatomite through a 100-mesh sieve, and then, in an atmosphere of protective gas, heat it from room temperature to 800 °C at a rate of 5 °C / min, hold for 2 h, and then naturally cool to room temperature.

[0032] Disperse the obtained powder in a KOH solution, stir at room temperature for 4 h, then neutralize it with an HCl solution to a pH value of 7, wash it by centrifugation with deionized water and alcohol multiple times, dry the solid product at 60 °C for 12 h, and finally ball-mill it for 12 h to obtain the porous carbon framework, denoted as BC;

[0033] Among them, the mass concentration of the KOH solution is 10%, and the mass concentration of the HCl solution is 50%;

[0034] S2. Prepare the precursor:

[0035] Take the porous carbon framework and disperse it in deionized water, add NiSO 4 ·6H 2 O and Co(NO 3 ) 2 ·6H 2 O, stir to dissolve, then add 2-methylimidazole, stir for 5 min and then transfer it into a hydrothermal autoclave, carry out hydrothermal reaction at 150 °C for 6 hours. After cooling to room temperature, wash the obtained product by centrifugation with deionized water, and dry the solid product at 60 °C for 12 hours to obtain the precursor;

[0036] S3. Carbonization-sulfidation treatment:

[0037] Mix the precursor with sublimed sulfur powder and grind for 20 min. Then, under the atmosphere of protective gas, heat from room temperature to 155 °C at a rate of 5 °C / min, hold for 1 h, then heat to 600 °C at a rate of 5 °C / min, hold for 3 h, and then naturally cool to room temperature. The obtained black powder is a composite material of a porous carbon skeleton and a bimetallic sulfide heterostructure, that is, the bimetallic sulfide and biomass carbon composite material for the sodium-ion battery, denoted as Ni 3 S 2 @Co 9 S 8 -BC.

[0038] In the second aspect of the present invention, a negative electrode for a sodium-ion battery is provided, which is characterized in that it is prepared by the following method:

[0039] Mix the bimetallic sulfide and biomass carbon composite material for the sodium-ion battery, the conductive agent, and the binder as described above in a mass ratio of 8 - 9:0.5 - 1:0.5 - 1, add an appropriate amount of solvent, and ball mill for 4 - 16 h to obtain a slurry; then uniformly coat the prepared slurry on a copper foil and vacuum dry at 80 - 100 °C for 6 - 24 hours to obtain a negative electrode for a sodium-ion battery.

[0040] Preferably, the conductive agent is Super P, the binder is polyvinylidene fluoride (PVDF), and the solvent is N-methylpyrrolidone (NMP).

[0041] In the third aspect of the present invention, a sodium-ion battery is provided, which is characterized in that it includes the negative electrode for a sodium-ion battery as described above.

[0042] The beneficial effects of the present invention are:

[0043] The present invention provides a bimetallic sulfide and biomass carbon composite material for a sodium-ion battery and a negative electrode and a sodium-ion battery for a sodium-ion battery based on the composite material. In the bimetallic sulfide and biomass carbon composite material for a sodium-ion battery provided by the present invention, the presence of the heterostructure accelerates the transmission rate of sodium ions during charge and discharge, and the presence of the unique porous carbon skeleton derived from diatomite ensures the structural stability of the Ni 3 S 2 @Co 9 S 8 -BC anode during charge and discharge. In addition, restricting the metal sulfide particles to the nanoscale and with the synergistic effect of the carbon skeleton can effectively inhibit their aggregation during cycling. Even at a large current density of 10 A g -1 , after 7000 cycles, it can still provide 225.36 mAh g-1 The reversible capacity is [value], the capacity retention rate is 65.3%, and the capacity decay rate per cycle is 0.00138%; the synergistic effect of composite engineering and nanoengineering enables Ni 3 S 2 @Co 9 S 8 -BC composite material to greatly improve its electrochemical performance.

[0044] The bimetallic sulfide and biomass carbon composite material for sodium-ion batteries of the present invention reduces TMs particles to the nanoscale, significantly reducing the mechanical stress associated with the conversion reaction, while shortening the diffusion path of Na + , thus alleviating the problems of pulverization and slow ion diffusion kinetics.

[0045] In the bimetallic sulfide and biomass carbon composite material for sodium-ion batteries of the present invention, charges are redistributed at the non-uniform boundary, inducing more active sites to adsorb alkali metal ions and enhancing the storage capacity for sodium ions; the negative electrode prepared based on this carbon composite material exhibits good energy storage performance and electrochemical reversibility. Description of the Drawings

[0046] Figure 1 SEM image of Ni 3 S 2 @Co 9 S 8 -BC1 prepared in Example 1;

[0047] Figure 2 EDS (energy spectrum analysis) image of Ni 3 S 2 @Co 9 S 8 -BC1 prepared in Example 1;

[0048] Figure 3 TEM image of Ni 3 S 2 @Co 9 S 8 -BC1 prepared in Example 1;

[0049] Figure 4 XRD pattern of Ni 3 S 2 @Co 9 S 8 -BC1 prepared in Example 1;

[0050] Figure 5 Ni 3 S 2 @Co 9 S 8-Cycling performance comparison chart of BC1 to 3;

[0051] Figure 6 Ni prepared in Example 1 3 S 2 @Co 9 S 8 -Cycling performance chart of BC1 at a current density of 10 A / g;

[0052] Figure 7 Ni prepared in Example 1 3 S 2 @Co 9 S 8 -BC1 and Co prepared in Example 4 9 S 8 -Cycling performance comparison chart of sodium-ion batteries assembled with negative electrodes prepared based on BC;

[0053] Figure 8 Ni prepared in Example 1 3 S 2 @Co 9 S 8 -Cycling performance of sodium-ion batteries assembled with negative electrodes prepared based on BC1 at a current density of 10 A / g. Detailed implementation mode

[0054] The following examples are used to further elaborate the present invention in detail, so that those skilled in the art can implement it according to the description in the specification.

[0055] It should be understood that terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0056] Unless otherwise specified, the test methods used in the following examples are all conventional methods. The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified. For those not indicating specific conditions in the following examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For those reagents or instruments not indicating the manufacturer, they are all conventional products that can be purchased through the market.

[0057] Example 1

[0058] A bimetallic sulfide and biomass carbon composite material for sodium-ion batteries is prepared through the following steps:

[0059] S1. Prepare a porous carbon skeleton:

[0060] Sieve diatomite (100 mesh), and then place it in a temperature-controlled tube furnace with nitrogen protection. Heat it from room temperature at a rate of 5 °C·min-1 They were respectively heated to 800 °C, maintained for 2 h, and then naturally cooled to room temperature. The obtained powder was dispersed in a 10% KOH solution, stirred at room temperature for 4 h, and then neutralized to pH 7 with a 5% HCl solution. It was centrifugally washed multiple times with deionized water and alcohol, dried at 60 °C for 12 h, and finally ball-milled in a planetary ball mill for 12 h to obtain a porous carbon framework, denoted as BC;

[0061] S2. Preparation of the precursor:

[0062] 0.5 g of the porous carbon framework was dispersed in 50 ml of deionized water, 2.91 g of NiSO 4 ·6H 2 O and 2.63 g of Co(NO 3 ) 2 ·6H 2 O were added. After stirring and dissolving, 3.28 g of 2-methylimidazole was added. After vigorous stirring for 5 min, it was transferred into a hydrothermal autoclave and subjected to a hydrothermal reaction at 150 °C for 6 h. After cooling to room temperature, the obtained product was centrifugally washed four times with deionized water and placed in a blast drying oven at 60 °C for 12 h to obtain the precursor;

[0063] S3. Carbonization-sulfuration treatment:

[0064] The obtained precursor was mixed with sublimed sulfur powder in a mass ratio of 1:1.5 and ground in a mortar for 20 min. Subsequently, it was placed in a temperature-controlled tubular furnace with argon protection. It was heated from room temperature to 155 °C at 5 °C·min -1 , maintained for 1 h, and then heated to 600 °C at 5 °C·min -1 , maintained for 3 h, and then naturally cooled to room temperature. The obtained black powder was a composite material of a porous carbon framework and a bimetallic sulfide heterostructure, namely the bimetallic sulfide and biomass carbon composite material for the sodium-ion battery, denoted as Ni 3 S 2 @Co 9 S 8 -BC.

[0065] Example 2

[0066] A bimetallic sulfide and biomass carbon composite material for a sodium-ion battery is prepared by the following steps:

[0067] S1. Preparation of the porous carbon framework:

[0068] The diatomite was sieved (100 mesh), and then placed in a temperature-controlled tubular furnace with nitrogen protection. It was heated from room temperature to 5 °C·min -1They were respectively heated to 800 °C, kept for 2 h and then naturally cooled to room temperature. The obtained powder was dispersed in a 10% KOH solution and stirred at room temperature for 4 h. Then it was neutralized to pH 7 with a 5% HCl solution, centrifugally washed multiple times with deionized water and alcohol, dried at 60 °C for 12 h, and finally ball-milled in a planetary ball mill for 12 h to obtain a porous carbon framework, denoted as BC;

[0069] S2. Preparation of the precursor:

[0070] 0.5 g of the porous carbon framework was dispersed in 50 ml of deionized water, 3.49 g of NiSO 4 ·6H 2 O and 3.16 g of Co(NO 3 ) 2 ·6H 2 O were added. After stirring and dissolving, 3.94 g of 2-methylimidazole was added. After vigorous stirring for 5 min, it was transferred into a hydrothermal autoclave and subjected to a hydrothermal reaction at 150 °C for 6 h. After cooling to room temperature, the obtained product was centrifugally washed four times with deionized water and dried in a forced-air drying oven at 60 °C for 12 h to obtain the precursor;

[0071] S3. Carbonization-sulfuration treatment:

[0072] The obtained precursor was mixed with sublimed sulfur powder at a mass ratio of 1:1.5 and ground in a mortar for 20 min. Subsequently, it was placed in a temperature-controlled tubular furnace with argon protection and heated from room temperature to 155 °C at a rate of 5 °C·min -1 and kept for 1 h, then heated to 600 °C at a rate of 5 °C·min -1 and kept for 3 h, and then naturally cooled to room temperature. The obtained black powder was a composite material of a porous carbon framework and a bimetallic sulfide heterostructure, namely the bimetallic sulfide and biomass carbon composite material for sodium-ion batteries, denoted as Ni 3 S 2 @Co 9 S 8 -BC2.

[0073] Example 3

[0074] A bimetallic sulfide and biomass carbon composite material for sodium-ion batteries is prepared by the following steps:

[0075] S1. Preparation of the porous carbon framework:

[0076] The diatomite was sieved (100 mesh) and then placed in a temperature-controlled tubular furnace with nitrogen protection. It was heated from room temperature to 5 °C·min -1They were respectively heated to 800 °C, maintained for 2 h and then naturally cooled to room temperature. The obtained powder was dispersed in a 10% KOH solution, stirred at room temperature for 4 h, and then neutralized to pH 7 with a 5% HCl solution. It was centrifugally washed multiple times with deionized water and alcohol, dried at 60 °C for 12 h, and finally ball-milled in a planetary ball mill for 12 h to obtain a porous carbon skeleton, denoted as BC;

[0077] S2. Preparation of the precursor:

[0078] 0.5 g of the porous carbon skeleton was dispersed in 50 ml of deionized water, 2.33 g of NiSO 4 ·6H 2 O and 2.10 g of Co(NO 3 ) 2 ·6H 2 O were added. After stirring and dissolving, 2.62 g of 2-methylimidazole was added. After vigorous stirring for 5 min, it was transferred into a hydrothermal autoclave and subjected to a hydrothermal reaction at 150 °C for 6 h. After cooling to room temperature, the obtained product was centrifugally washed four times with deionized water and placed in a forced-air drying oven at 60 °C for 12 h to obtain the precursor;

[0079] S3. Carbonization-sulfurization treatment:

[0080] The obtained precursor was mixed with sublimed sulfur powder at a mass ratio of 1:1.5 and ground in a mortar for 20 min. Subsequently, it was placed in a temperature-controlled tubular furnace with argon protection. It was heated from room temperature to 155 °C at 5 °C·min -1 and maintained for 1 h, then heated to 600 °C at 5 °C·min -1 and maintained for 3 h, and then naturally cooled to room temperature. The obtained black powder was a composite material of a porous carbon skeleton and a bimetallic sulfide heterostructure, namely the bimetallic sulfide and biomass carbon composite material for the sodium-ion battery, denoted as Ni 3 S 2 @Co 9 S 8 -BC3.

[0081] Example 4

[0082] A bimetallic sulfide and biomass carbon composite material for a sodium-ion battery is prepared by the following steps:

[0083] S1. Preparation of the porous carbon skeleton:

[0084] The diatomite was sieved (100 mesh) and then placed in a temperature-controlled tubular furnace with nitrogen protection. It was heated from room temperature to 5 °C·min -1They were separately heated to 800 °C, maintained for 2 h and then naturally cooled to room temperature. The obtained powder was dispersed in a 10% KOH solution, stirred at room temperature for 4 h, and then neutralized to pH 7 with a 5% HCl solution. It was centrifugally washed multiple times with deionized water and alcohol, dried at 60 °C for 12 h, and finally ball-milled in a planetary ball mill for 12 h to obtain a porous carbon skeleton, denoted as BC;

[0085] S2. Preparation of the precursor:

[0086] 0.5 g of the porous carbon skeleton was dispersed in 50 ml of deionized water, 2.63 g of Co(NO 3 ) 2 ·6H 2 O was added. After stirring and dissolving, 3.28 g of 2-methylimidazole was added. After vigorous stirring for 5 min, it was transferred into a hydrothermal autoclave and subjected to a hydrothermal reaction at 150 °C for 6 h. After cooling to room temperature, the obtained product was centrifugally washed four times with deionized water and placed in a blast drying oven at 60 °C for 12 h to obtain the precursor;

[0087] S3. Carbonization-sulfidation treatment:

[0088] The obtained precursor was mixed with sublimed sulfur powder at a mass ratio of 1:1.5 and ground in a mortar for 20 min. Subsequently, it was placed in a temperature-controlled tube furnace protected by argon. It was heated from room temperature to 155 °C at a rate of 5 °C·min -1 and maintained for 1 h, then heated to 600 °C at a rate of 5 °C·min -1 and maintained for 3 h, and then naturally cooled to room temperature. The obtained black powder was a composite material of a porous carbon skeleton and a bimetallic sulfide heterostructure, namely the bimetallic sulfide and biomass carbon composite material for sodium ion batteries, denoted as Co 9 S 8 -BC.

[0089] Example 5

[0090] A negative electrode for a sodium ion battery, using the bimetallic sulfide and biomass carbon composite material for sodium ion batteries prepared in Examples 1-4 respectively, and the following method was used to prepare the negative electrode for a sodium ion battery:

[0091] The bimetallic sulfide and biomass carbon composite material for sodium ion batteries (all the carbon composite products prepared in Examples 1-4), a conductive agent (Super P), and a binder (polyvinylidene fluoride, PVDF) were mixed evenly at a mass ratio of 8:1:1, 800 μL of NMP was added to prepare a slurry, and it was ball-milled in a planetary ball mill for 8 h. Then the prepared slurry was evenly coated on a copper foil and vacuum-dried at 80 °C for 12 h to obtain the negative electrode for a sodium ion battery using the bimetallic sulfide and biomass carbon composite material.

[0092] Characterization of Materials

[0093] (1) Electron Microscopy Characterization

[0094] Reference Figure 1 is Ni 3 S 2 @Co 9 S 8 SEM image of NiS@CoS-BC1, clearly showing metal sulfide particles embedded in the porous carbon framework in the picture;

[0095] Reference Figure 2 is Ni 3 S 2 @Co 9 S 8 EDS image of NiS@CoS-BC1, showing the uniform distribution of four elements Ni, Co, S, and C in the picture;

[0096] Reference Figure 3 is Ni 3 S 2 @Co 9 S 8 TEM image of NiS@CoS-BC1, it can be seen that there are also nano metal sulfide particles embedded inside the porous carbon framework, the particle size range is 50 - 200 nm, and it also shows the 311 and 420 crystal planes of CoS and the lattice spacings of the -111 and 111 crystal planes of NiS. 9 S 8 and the 311 and 420 crystal planes of CoS as well as the lattice spacings of the -111 and 111 crystal planes of NiS. 3 S 2 of NiS.

[0097] Reference Figure 4 is Ni 3 S 2 @Co 9 S 8 XRD image of NiS@CoS-BC1, all characteristic peaks correspond to the standard PDF cards of CoS (73 - 1442) and NiS (76 - 1870). 9 S 8 (73 - 1442) and NiS 3 S 2 (76 - 1870).

[0098] Reference Figure 5 is Co 9 S 8 XRD images of CoS-BC and BC, all characteristic peaks correspond to the standard PDF card of CoS (86 - 2273). 9 S 8 (86 - 2273).

[0099] Performance Testing

[0100] Button cell assembly method: Assemble button half-cells in a glove box filled with argon gas. Use sodium flakes as the counter electrode, a CR2025 battery case, a Whatman glass fiber separator, and 1.0M NaPF 6 in DME electrolyte. The sealing pressure of the button cell is 50 Mpa.

[0101] Figure 6 For the Ni prepared in Examples 1 to 3 3 S 2 @Co 9 S 8 -BC1 to 3, it is a comparative chart of the cycling performance of the sodium-ion batteries assembled with the anodes prepared based on them. It can be seen from the figure that the reversible capacity of the Ni 3 S 2 @Co 9 S 8 -BC1 material corresponding to Example 1 is the highest.

[0102] Figure 7 For the Ni prepared in Example 1 and Example 4 3 S 2 @Co 9 S 8 -BC1 and Co 9 S 8 -BC, it is a comparative chart of the cycling performance of the sodium-ion batteries assembled with the anodes prepared based on them. It can be seen from the figure that the reversible capacity of the material Co 9 S 8 -BC corresponding to Example 4 lacking the bimetallic heterojunction is significantly lower than that of the Ni 3 S 2 @Co 9 S 8 -BC1 material corresponding to Example 1, proving that the bimetallic heterojunction can improve the reversible capacity of the material.

[0103] Figure 8 For the Ni prepared in Example 1 3 S 2 @Co 9 S 8 -BC1, it is the cycling performance of the sodium-ion battery assembled with the anode prepared based on it at a current density of 10 A / g. It can be seen from the figure that after 10,000 cycles, the material can still provide a reversible capacity of 181.32 mAh / g, and the capacity decay rate per cycle is 0.004%, indicating that the anode material has good long-cycle performance.

[0104] From the above test results, it can be seen that the bimetallic sulfide and biomass carbon composite electrode material prepared by the present invention improves the long-cycle stability of the battery.

[0105] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details.

Claims

1. A bimetallic sulfide and biomass carbon composite material for sodium ion batteries, characterized in that: It is prepared by the following steps: S1. Preparation of porous carbon skeleton: The diatomite was calcined under protective gas, then impregnated with alkali solution, washed, dried, and ball-milled to obtain a porous carbon skeleton, which was denoted as BC. S2. Preparation of precursor: The porous carbon skeleton was dispersed in deionized water and Ni 2+ 、Co 2+ , then add 2-methylimidazole, and perform hydrothermal reaction under heating to prepare a precursor; S3, Carbonization-sulfurization treatment: The precursor is mixed with sublimated sulfur powder and then calcined under protective gas to prepare a composite material of porous carbon skeleton and bimetallic sulfide heterostructure, that is, the bimetallic sulfide and biomass carbon composite material for sodium ion battery, recorded as Ni3S2@Co9S8-BC.

2. The bimetallic sulfide and biomass carbon composite material for sodium ion battery according to claim 1, characterized in that: Step S1 is specifically as follows: The diatomaceous earth is passed through a 50-200 mesh sieve, and then heated from room temperature to 600-1000°C at a rate of 2-10°C / min in a protective gas atmosphere, maintained for 1-4 hours, and then naturally cooled to room temperature. The obtained powder was dispersed in KOH solution, stirred at room temperature for 2-8 h, then neutralized with HCl solution to pH 7, washed by centrifugation with deionized water and alcohol for multiple times, and the solid product was dried at 50-70 °C for 6-24 h, and finally ball-milled for 6-24 h to obtain a porous carbon skeleton, denoted as BC; The mass concentration of the KOH solution is 5-20%, and the mass concentration of the HCl solution is 2.5-10%.

3. The bimetallic sulfide and biomass carbon composite material for sodium ion battery according to claim 1, characterized in that: Ni in step S2 2+ 、Co 2+ They are introduced by adding water-soluble divalent nickel salt and divalent cobalt salt respectively; The divalent nickel salt is selected from at least one of NiSO4·6H2O and (CH3COO)2Ni·4H2O, and the divalent cobalt salt is selected from at least one of Co(NO3)2·6H2O and CoSO4·7H2O.

4. The bimetallic sulfide and biomass carbon composite material for sodium ion battery according to claim 2, characterized in that: Step S2 is specifically as follows: The porous carbon skeleton is dispersed in deionized water, and water-soluble divalent nickel salt and divalent cobalt salt are added. After stirring and dissolving, 2-methylimidazole is added. After stirring for 2 to 10 minutes, the mixture is transferred into a hydrothermal kettle and subjected to hydrothermal reaction at 140 to 160° C. for 3 to 12 hours. After cooling to room temperature, the obtained product is washed by centrifugation with deionized water, and the solid product is dried at 50 to 80° C. for 6 to 24 hours to obtain a precursor.

5. The bimetallic sulfide and biomass carbon composite material for sodium ion battery according to claim 1, characterized in that: Step S3 is specifically as follows: The precursor is mixed with sublimated sulfur powder and ground for 10 to 40 minutes. Then, under a protective gas atmosphere, the temperature is raised from room temperature to 130 to 160°C at a rate of 2 to 10°C / min, maintained for 0.5 to 2 hours, and then raised to 400 to 800°C at a rate of 2 to 10°C / min. After being maintained for 1.5 to 6 hours, the temperature is naturally lowered to room temperature. The obtained black powder is a composite material of a porous carbon skeleton and a bimetallic sulfide heterostructure, that is, the bimetallic sulfide and biomass carbon composite material for sodium ion batteries, recorded as Ni3S2@Co9S8-BC.

6. The bimetallic sulfide and biomass carbon composite material for sodium ion battery according to claim 1, characterized in that: The protective gas in step S1 is nitrogen with a purity of 99.99%, and the protective gas in step S3 is argon with a purity of 99.99%.

7. The bimetallic sulfide and biomass carbon composite material for sodium ion battery according to claim 1, characterized in that: In step S2, the molar ratio of the divalent nickel salt to the divalent cobalt salt is 1:1-2, the molar ratio of the divalent nickel salt to 2-methylimidazole is 1:1-4, and the mass ratio of 2-methylimidazole to the porous carbon skeleton is 1.5-6:0.25-1; In step S2, the volume of deionized water is 50 to 200 times the mass of the porous carbon skeleton, measured in units of volume (mL) and mass (g); In step S3, the mass ratio of sublimated sulfur powder to precursor is 1-2:

1.

8. The bimetallic sulfide and biomass carbon composite material for sodium ion battery according to any one of claims 1 to 7, characterized in that: It is prepared by the following steps: S1. Preparation of porous carbon skeleton: The diatomaceous earth was passed through a 100-mesh sieve, and then heated from room temperature to 800°C at a rate of 5°C / min in a protective gas atmosphere, maintained for 2 hours, and then naturally cooled to room temperature. The obtained powder was dispersed in KOH solution, stirred at room temperature for 4 h, then neutralized with HCl solution to pH 7, washed by centrifugation with deionized water and alcohol several times, and the solid product was dried at 60 °C for 12 h, and finally ball-milled for 12 h to obtain a porous carbon skeleton, denoted as BC; Wherein, the mass concentration of KOH solution is 10%, and the mass concentration of HCl solution is 50%; S2. Preparation of precursor: The porous carbon skeleton was dispersed in deionized water, NiSO4·6H2O and Co(NO3)2·6H2O were added, and 2-methylimidazole was added after stirring to dissolve. After stirring for 5 minutes, the mixture was transferred into a hydrothermal reactor and subjected to hydrothermal reaction at 150°C for 6 hours. After cooling to room temperature, the obtained product was washed by centrifugation with deionized water, and the solid product was dried at 60°C for 12 hours to obtain a precursor. S3, Carbonization-sulfurization treatment: The precursor was mixed with sublimated sulfur powder and ground for 20 minutes. Then, under a protective gas atmosphere, the temperature was raised from room temperature to 155°C at a rate of 5°C / min, maintained for 1 hour, and then raised to 600°C at a rate of 5°C / min. After maintaining for 3 hours, the temperature naturally dropped to room temperature. The obtained black powder was a composite material of a porous carbon skeleton and a bimetallic sulfide heterostructure, that is, the bimetallic sulfide and biomass carbon composite material for sodium ion batteries, recorded as Ni3S2@Co9S8-BC.

9. A sodium ion battery negative electrode, characterized in that: It is prepared by the following method: The bimetallic sulfide for sodium ion battery according to any one of claims 1 to 8 is mixed evenly with a biomass carbon composite material, a conductive agent and a binder in a mass ratio of 8 to 9: 0.5 to 1: 0.5 to 1, a solvent is added, and ball milling is performed for 4 to 16 hours to obtain a slurry; then the prepared slurry is evenly coated on a copper foil, and vacuum dried at 80 to 100° C. for 6 to 24 hours to obtain a sodium ion battery negative electrode.

10. A sodium ion battery, characterized in that: It includes the sodium ion battery negative electrode as claimed in claim 9.

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