A cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material and its preparation method and application

Abstract

A cobalt disulfide / boron, nitrogen, and sulfur co-doped porous carbon composite material, its preparation method, and application are described. A colloidal precursor is prepared by mixing the metal-organic framework material ZIF-67, a nitrogen-containing carbon source, a boron source, and a confined solvent. The resulting precursor is subjected to high-temperature confined carbonization and then sulfurization to obtain a composite material composed of fine CoS2 nanoparticles dispersed in a boron, nitrogen, and sulfur co-doped porous carbon matrix. The composite material's large specific surface area enhances electrolyte wetting and penetration; the nanostructured porous carbon and CoS2 effectively shorten charge transfer distances and enhance electrochemical reaction kinetics; and the boron, nitrogen, and sulfur co-doped carbon matrix provides a richer set of electrochemical reaction active sites. Its abundant porous interconnected structure facilitates charge migration, mitigates volume changes in the electrode material during charge and discharge, and improves the electrochemical stability of the electrode material. This composite material can be used as an excellent anode material for sodium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy materials and devices, and in particular relates to a cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material and a preparation method and application thereof. Background Art

[0002] With the goal of coexisting environmental governance and economic development, the development of new clean and environmentally friendly energy sources has become a hotly contested area of ​​research. Electrochemical energy storage technology has become a key enabling technology for optimizing energy transmission, absorbing clean energy, ensuring stable grid operation, and improving power quality. As a new generation of high-performance energy storage devices, lithium-ion batteries (LIBs), with their low self-discharge, high energy density, and long cycle life, have been widely used in smart electric vehicles and various portable electronic products. However, factors such as the scarcity of lithium resources, their uneven geographical distribution, and the escalating cost of energy storage have severely limited the continued development of LIBs in various energy storage applications. Sodium and lithium are elements in the same main group and share similar energy storage mechanisms. Furthermore, sodium's abundance, low solvation effect, and wide temperature adaptability make it a promising candidate to replace LIBs in future large-scale, low-cost energy storage applications.

[0003] As a new type of energy storage battery system, sodium-ion batteries have good application prospects. However, the radius of sodium ions (0.102nm) is larger than that of lithium ions (0.076nm). The larger ion radius makes many electrode materials suitable for lithium storage unsuitable for sodium storage. The lack of high-performance sodium storage electrode materials seriously restricts the development of sodium-ion batteries. As one of the core components of the battery, the negative electrode material of the sodium-ion battery is responsible for providing low redox couples and storing sodium ions, which has a direct impact on the operating voltage and capacity of the battery. Therefore, its electrochemical properties and structural stability are crucial to the energy density, cycle stability and safety performance of the battery. However, the carbon-based materials that are widely used at present have disadvantages such as low sodium storage capacity and poor cycle performance. Therefore, the rational design and construction of high-performance sodium-ion battery negative electrode materials are the key to improving the energy density of sodium-ion batteries and promoting their commercial application process.

[0004] Transition metal sulfides have a high theoretical sodium storage capacity, and their moderate interlayer spacing is conducive to the reversible insertion / extraction of sodium ions. In addition, their metal-sulfur bond binding force is weak, which is beneficial to improving the conversion reaction kinetics between sodium ions and active materials. Therefore, transition metal sulfides have become sodium ion battery negative electrode materials with good development prospects. Among them, compared with other transition metal sulfides, cobalt disulfide (CoS2) has a higher electrical conductivity, which is beneficial to enhancing the electrochemical kinetics in the conversion reaction. However, studies have shown that CoS2 electrode materials will undergo structural collapse due to large volume expansion during the cycle process, causing irreversible electrochemical reactions, resulting in rapid capacity decay in sodium ion batteries and poor cycle performance. Therefore, the rational design of CoS2-based composite materials with stable structure and good electrochemical properties as sodium storage negative electrode materials is of great significance to the development and application of sodium ion batteries. Summary of the Invention

[0005] The purpose of the present invention is to address the shortcomings of existing sodium ion battery negative electrode materials and their preparation technology, and to provide a cobalt disulfide / boron nitrogen and sulfur co-doped porous carbon composite material and its preparation method. The sodium ion battery negative electrode material prepared by the present invention using this composite material exhibits high specific capacity, excellent rate performance and cycle stability.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention proposes a cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material, in which a boron, nitrogen and sulfur co-doped porous carbon matrix is ​​uniformly dispersed with fine CoS2 nanoparticles.

[0008] The present invention proposes a method for preparing a cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material. First, a mixed colloid is prepared using a metal organic framework (ZIF-67), polyacrylonitrile (PAN) and polyvinyl pyrrolidone (PVP) as a cobalt source, a nitrogen-containing carbon source and a pore-forming agent, respectively, and N,N-dimethylformamide (DMF) as a confined solvent; the mixed colloid is first heated for pre-carbonization, then subjected to high-temperature confined carbonization and boron doped with ammonium borate (NH4HB4O7·3H2O) as a boron source to obtain a metal cobalt nanoparticle / boron nitrogen co-doped carbon composite material (Co / BNC); finally, the mixed colloid is subjected to a sulfurization treatment to obtain a cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material (CoS2 / BNSC).

[0009] As a preferred technical solution of the present invention, the specific steps of the preparation method are as follows:

[0010] (1) ZIF-67 with a dodecahedral shape was prepared by chemical precipitation at room temperature;

[0011] (2) dissolving polyacrylonitrile (PAN) and polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF) at room temperature, then ultrasonically dispersing the ZIF-67 obtained in step (1) in the solution, heating and stirring to evaporate part of the solvent, and obtaining a viscous colloid;

[0012] (3) heating the colloid prepared in step (2) in an inert atmosphere for pre-carbonization, then performing high-temperature confined carbonization and boron doping using ammonium borate (NH4HB4O7·3H2O) as a boron source to obtain a metal cobalt nanoparticle / boron and nitrogen co-doped carbon composite material (Co / BNC);

[0013] (4) The metal cobalt nanoparticles / boron nitrogen co-doped carbon composite material (Co / BNC) obtained in step (3) is mixed with sublimed sulfur powder in a certain proportion, and then subjected to sulfurization treatment under the protection of an inert atmosphere to obtain a cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC).

[0014] As a further preferred technical solution of the present invention, in the method for preparing the cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material:

[0015] Step (1) is specifically as follows: preparing a 2-methylimidazole aqueous solution with a concentration of 1 to 2 mol / L; slowly adding the 2-methylimidazole aqueous solution dropwise to a 0.3 to 0.8 mol / L NaOH aqueous solution to obtain a mixed solution A; preparing a cobalt nitrate (Co(NO3)2·6H2O) aqueous solution with a concentration of 0.3 to 0.8 mol / L, marked as solution B; slowly adding solution B dropwise to solution A, stirring continuously for 6 to 18 hours, centrifuging the precipitate, and vacuum drying at 50 to 80°C for 12 to 24 hours to obtain ZIF-67.

[0016] Step (2) is specifically as follows: 0.2-0.6 g of polyacrylonitrile (PAN) with an average molecular weight of 80,000-150,000 and 0.2-0.5 g of polyvinylpyrrolidone (PVP) with an average molecular weight of 10,000-40,000 are dissolved in 25 mL of N,N-dimethylformamide (DMF), and then 0.1-0.4 g of ZIF-67 is ultrasonically dispersed in the above mixed solution. After continuous stirring for 12-24 hours, the solvent is partially evaporated by heating and stirring at 60-80° C. to obtain a viscous mixed colloid.

[0017] Step (3) is specifically as follows: the colloid prepared in step (2) is heated and pre-carbonized under the protection of an inert atmosphere, wherein the inert atmosphere is a nitrogen / hydrogen mixture with a volume ratio of 5:1, the temperature is 640-680°C, the holding time is 2-4 hours, and the heating rate is 1-2°C / min; then high-temperature confined carbonization is performed and ammonium borate (NH4HB4O7·3H2O) is used as a boron source for boron doping to obtain a metal cobalt nanoparticle / boron-nitrogen co-doped carbon composite material (Co / BNC), wherein the inert atmosphere is nitrogen, the carbonization temperature is 750-850°C, the carbonization time is 2-4 hours, and the heating rate is 2-5°C / min.

[0018] Step (4) is specifically as follows: the metal cobalt nanoparticles / boron nitrogen co-doped carbon composite material (Co / BNC) obtained in step (3) is mixed with sublimed sulfur powder in a mass ratio of 1:10 to 20, and then subjected to sulfurization treatment under argon atmosphere protection to obtain a cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC), wherein the sulfurization temperature is 400 to 450°C, the sulfurization time is 1 to 3 hours, and the heating rate is 1 to 3°C / min.

[0019] In addition, the present invention also proposes the application of the cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material in the negative electrode material of sodium ion battery. The cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material is ground and mixed with a conductive agent and a binder in a certain proportion to obtain a slurry. The obtained slurry is evenly coated on a metal foil, and then vacuum dried. The electrode sheets are cut into electrode sheets with a slicer to obtain the cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon sodium ion battery negative electrode.

[0020] Further preferably, the preparation method is to grind and mix the cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material with a conductive agent and a binder in a mass ratio of 8:1:1 to obtain a slurry, and then evenly coat the obtained slurry on aluminum foil or copper foil, and then vacuum dry it at 70°C for 24 hours, and then cut it into electrode sheets with a slicer to obtain the cobalt disulfide / boron nitrogen sulfur co-doped porous carbon sodium ion battery negative electrode material.

[0021] The area mass of the active material in the cobalt disulfide / boron nitrogen sulfur co-doped porous carbon sodium ion battery negative electrode material prepared by the above method is 1.0-2.0 mg / cm 2 , where the mass ratio of CoS2 is 15-30%.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The cobalt disulfide / boron, nitrogen, and sulfur co-doped porous carbon composite material prepared by the present invention can make CoS2 nanoparticles uniformly dispersed in the porous carbon matrix, effectively avoiding the problem of nanoparticle agglomeration and shortening the charge migration path within the composite material; due to the thermal decomposition and volatilization of polyvinyl pyrrolidone (PVP), it can give the composite material a larger specific surface area, enhancing the infiltration and penetration of the electrolyte; in this composite material, the boron, nitrogen, and sulfur co-doped carbon matrix can provide more abundant electrochemical reaction active sites, and its abundant porous interconnected structure is conducive to enhancing charge migration, while alleviating the volume change of the electrode material during the charge and discharge process, thereby improving the electrochemical stability of the electrode material. Thanks to this unique structural design, when the prepared cobalt disulfide / boron, nitrogen, and sulfur co-doped porous carbon composite material is used as the negative electrode material of sodium ion batteries, the electrode material has the advantages of high specific capacity, excellent rate performance and cycle stability.

[0024] In addition, the preparation method of this composite material is simple and easy to control, has good repeatability and high yield, which is conducive to industrial promotion and provides a new way to prepare sodium ion battery negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the SEM morphology of the metal cobalt nanoparticles / boron and nitrogen co-doped porous carbon composite material (Co / BNC) in Example 1.

[0026] Figure 2 This is the SEM morphology of the cobalt disulfide / boron nitrogen and sulfur co-doped porous carbon composite material (CoS2 / BNSC) in Example 1.

[0027] Figure 3 1 is the XRD curve of the metal cobalt nanoparticles / boron and nitrogen co-doped porous carbon composite material (Co / BNC) in Example 1.

[0028] Figure 4 2 is the XRD curve of the cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC) in Example 1.

[0029] Figure 5 This is the XPS full spectrum (a) of the cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC) in Example 1 and the XPS high-resolution spectra of C1s (b), N 1s (c), B 1s (d), S 2p (e), and Co 2p (f) elements.

[0030] Figure 6 The sodium ion half-cell assembled based on CoS2 / BNSC electrode material in Example 1 was tested at 100 mA·g -1 Cycling performance test results under different current densities.

[0031] Figure 7These are the rate performance test results of the sodium ion half-cell assembled based on the CoS2 / BNSC electrode material in Example 1.

[0032] Figure 8 These are the cycling performance test results of the sodium ion full battery assembled based on the CoS2 / BNSC negative electrode material in Example 1 at a current density of 0.5C.

[0033] Figure 9 These are the rate performance test results of the sodium ion full battery assembled based on the CoS2 / BNSC negative electrode material in Example 1.

[0034] Figure 10 The sodium ion half-cell assembled based on Co / BNC electrode material in Comparative Example 1 was tested at 100 mA·g -1 Cycling performance test results under different current densities.

[0035] Figure 11 These are the rate performance test results of the sodium ion half-cell assembled based on Co / BNC electrode materials in Comparative Example 1. DETAILED DESCRIPTION

[0036] The cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material provided by the present invention and its preparation method and application are further described in detail below with reference to the examples and drawings.

[0037] Example 1

[0038] This embodiment provides a cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material. First, a mixed colloid is prepared using a metal organic framework (ZIF-67), polyacrylonitrile (PAN) and polyvinyl pyrrolidone (PVP) as a cobalt source, a nitrogen-containing carbon source and a pore-forming agent, respectively, and N,N-dimethylformamide (DMF) as a confined solvent; the mixed colloid is first heated for pre-carbonization, then subjected to high-temperature confined carbonization and boron doped with ammonium borate (NH4HB4O7·3H2O) as a boron source to obtain a metal cobalt nanoparticle / boron nitrogen co-doped carbon composite material (Co / BNC); finally, the mixed colloid is subjected to a sulfurization treatment to obtain a cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material (CoS2 / BNSC), which is used as a negative electrode material for sodium ion batteries.

[0039] This embodiment provides a method for preparing a cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon electrode material for a sodium ion battery negative electrode, comprising the following steps:

[0040] Step (1): Weigh 6.8 g of 2-methylimidazole (C4H6N2) and dissolve it in 50 mL of deionized water to prepare a 1.6 mol / L 2-methylimidazole aqueous solution. Slowly add the 2-methylimidazole aqueous solution dropwise to 50 mL of a 0.5 mol / L NaOH aqueous solution to obtain a mixed solution A. Weigh 2.9 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and dissolve it in 50 mL of deionized water to prepare a 0.4 mol / L cobalt nitrate aqueous solution, labeled as solution B. Slowly add solution B dropwise to solution A, continue stirring for 12 h, centrifuge the precipitate, and vacuum dry at 60°C for 24 h to obtain ZIF-67.

[0041] Step (2): 0.4 g of polyacrylonitrile (PAN) (average molecular weight 80,000) and 0.3 g of polyvinylpyrrolidone (PVP) (average molecular weight 40,000) were dissolved in 25 mL of N,N-dimethylformamide (DMF). Then, 0.2 g of ZIF-67 was ultrasonically dispersed in the above mixed solution. After continuous stirring for 24 h, the solvent was partially evaporated by heating and stirring at 80°C to obtain a viscous mixed colloid.

[0042] Step (3): The colloid prepared in step (2) is heated and pre-carbonized under the protection of an inert atmosphere, wherein the inert atmosphere is a nitrogen / hydrogen mixture with a volume ratio of 5:1, the temperature is 650°C, the holding time is 4 hours, and the heating rate is 1°C / min; then, high-temperature confined carbonization is performed and boron doping is performed using ammonium borate (NH4HB4O7·3H2O) as a boron source to obtain a metal cobalt nanoparticle / boron and nitrogen co-doped carbon composite material (Co / BNC), wherein the inert atmosphere is nitrogen, the carbonization temperature is 800°C, the carbonization time is 3 hours, and the heating rate is 3°C / min.

[0043] Step (4): The metal cobalt nanoparticles / boron nitrogen co-doped carbon composite material (Co / BNC) obtained in step (3) is mixed with sublimed sulfur powder in a mass ratio of 1:15, and then subjected to sulfurization treatment under argon atmosphere protection to obtain a cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC), wherein the sulfurization temperature is 420°C, the sulfurization time is 2h, and the heating rate is 2°C / min.

[0044] Step (5): Grind and mix the cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material prepared in step (4) with a conductive agent and a binder in a mass ratio of 8:1:1 to obtain a slurry, evenly coat the obtained slurry on aluminum foil, and then vacuum dry it at 70°C for 24 hours, and then cut it into electrode sheets with a slicer to obtain a cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon sodium ion battery negative electrode material. The area mass of the active material in the negative electrode material is 1.2 mg / cm 2 , of which CoS2 accounts for 24% by mass.

[0045] See also Figure 1 , This figure is a SEM morphology of the metal cobalt nanoparticles / boron and nitrogen co-doped porous carbon composite material (Co / BNC) prepared in this embodiment. As can be seen from the figure, the carbon matrix has a porous interconnected structure, which provides a convenient channel for charge migration; in addition, the porous structure can greatly increase the specific surface area of ​​the composite material, which is conducive to enhancing the infiltration and penetration of the electrolyte. Figure 3 It can be seen that metal cobalt nanoparticles with an average diameter of about 50 nm are dispersed in the porous carbon matrix, providing a basis for subsequent sulfurization treatment.

[0046] See also Figure 2 , This figure is a SEM morphology of cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC) obtained by sulfurization treatment of metal cobalt nanoparticles / boron nitrogen co-doped porous carbon composite material (Co / BNC). Figure 4 It can be seen that CoS2 (average diameter is about 40nm) nanoparticles are uniformly dispersed in the boron, nitrogen and sulfur co-doped porous carbon matrix. The micro-nano structure of CoS2 particles can effectively shorten the charge transfer path and enhance the electrochemical reaction kinetics; in addition, the porous carbon matrix can effectively alleviate the volume change of the electrode material during charging and discharging, thereby improving the cycle stability of the electrode material.

[0047] See also Figure 5 , This figure shows the full XPS spectrum (a) and the XPS high-resolution spectra of C1s (b), N 1s (c), B 1s (d), S 2p (e), and Co 2p (f) elements of cobalt disulfide / boron nitrogen and sulfur co-doped porous carbon composite material (CoS2 / BNSC). Figure 5 (a) It can be seen that the CoS2 / BNSC composite material contains six elements: C, B, N, O, S, and Co. Among them, the O element mainly comes from the adsorption of moisture in the air and surface oxidation. In the high-resolution spectrum of C1s ( Figure 5 (b)) There are five characteristic peaks: CB bond (284.0eV), C=C bond (284.7eV), CO / C=N bond (285.4eV), CNB bond (286.5eV) and O=CO bond (288.9eV); in the high-resolution spectrum of N1s ( Figure 5 (c)) There are four characteristic peaks: pyridine-N bond (397.9eV), CNB bond (398.9eV), pyrrole-N bond (400.1eV) and graphite-N bond (401.4eV); in the high-resolution spectrum of B1s ( Figure 5(d)) There are three characteristic peaks: NBC bond (191.8eV), B-CO2 bond (192.3eV) and BO bond (192.8eV); in the high-resolution spectrum of S2p ( Figure 5 (e)), the peaks at binding energies of 163.2 eV and 164.6 eV correspond to S 2p in CoS2, respectively. 3 / 2 and S 2p 1 / 2 , the peak with a binding energy of 168.1 eV corresponds to C-SO x -C(x=2,3,4) bonds; in the high-resolution spectrum of Co 2p ( Figure 5 (f)), the peaks at binding energies of 778.8 eV and 793.9 eV correspond to Co 2p in CoS2, respectively. 3 / 2 and Co 2p 1 / 2 , the peaks at binding energies of 783.4 eV and 802.6 eV correspond to Co 2p 3 / 2 and Co 2p 1 / 2 XPS results indicate that boron, nitrogen, and carbon form bonds within the cobalt disulfide / boron, nitrogen, and sulfur co-doped porous carbon composite (CoS2 / BNSC). Furthermore, excessive addition of sublimated sulfur powder during the sulfurization process causes sulfur to form bonds with carbon, forming a boron, nitrogen, and sulfur co-doped carbon material. The boron, nitrogen, and sulfur co-doped carbon matrix provides more active sites for electrochemical reactions, thereby enhancing the electrochemical reaction kinetics.

[0048] The CoS2 / BNSC electrode material prepared in this example was used as the working electrode, the sodium sheet was used as the counter electrode, the GF / D glass microfiber membrane was used as the separator, sodium perchlorate NaClO4 was used as the solute, and ethylene carbonate EC and dimethyl carbonate DMC with a volume ratio of 1:1 were used as the solvent. The concentration of the prepared solution was 1 mol·L -1 The solution was prepared and 5 wt% of fluoroethylene carbonate (FEC) was added as the electrolyte; finally, a 2032 button-type sodium ion half-cell was assembled and charge and discharge tests were performed, with the test voltage window being 0.01-3 V.

[0049] See also Figure 6 The figure shows the sodium ion half-cell assembled based on CoS2 / BNSC electrode material in this embodiment at 100mA·g -1 Cyclic performance test results under current density. As shown in the figure, the current density is 100mA·g -1 When the first charge and discharge specific capacities of the electrode are 828 and 1317 mAh·g -1 The initial coulombic efficiency is 62.9%. The main reasons for the low initial coulombic efficiency are: 1) side reactions between inactive components in the electrolyte and sodium metal; 2) formation of solid electrolyte interface film (SEI film) on the electrode surface; 3) partial Na+ Ions are irreversibly embedded in the host material. After 100 cycles, the capacity remains at 787 mAh g -1 , the Coulomb efficiency is 99.9%, and the decay rate per cycle is about 0.05%, showing excellent cycle stability.

[0050] See also Figure 7 The figure shows the rate performance test results of the sodium ion half-cell assembled based on the CoS2 / BNSC electrode material in Example 1. As shown in the figure, the current density is 0.1~2.0A·g -1 The range of the step increases, the electrode is 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0A·g -1 The average capacities were 814, 777, 675, 593, 450, 361, and 186 mAh·g, respectively. -1 When the current density returns to 0.1 A g -1 When the capacity is still up to 793mAh g -1 , showing good rate performance.

[0051] The CoS2 / BNSC electrode material prepared in this example was used as the negative electrode, sodium vanadium phosphate (Na3V2(PO4)3) was used as the positive electrode, GF / D glass microfiber membrane was used as the separator, sodium perchlorate NaClO4 was used as the solute, and ethylene carbonate EC and dimethyl carbonate DMC with a volume ratio of 1:1 were used as the solvent. The concentration of the prepared solution was 1 mol·L -1 The solution was prepared by adding 5 wt% of fluoroethylene carbonate (FEC) as the electrolyte, and a 2032 button-type sodium ion full battery was assembled and subjected to charge and discharge tests. The test voltage window was 2.2-3.7 V.

[0052] See also Figure 8 The figure shows the cycling performance test results of the full battery assembled based on the CoS2 / BNSC sodium ion battery negative electrode material in Example 1 at a current density of 0.5C. As shown in the figure, at a current density of 0.5C, the initial capacity of the full battery in this example is 103mAh·g -1 After 55 cycles, the battery capacity is 98 mAh g -1 , showing good cycling stability.

[0053] See also Figure 9The figure shows the rate performance test results of the full battery assembled based on the CoS2 / BNSC sodium ion battery negative electrode material in Example 1. As shown in the figure, the current density increases in a step-by-step manner in the range of 0.2-3.0C. The average capacity of the battery in this example at 0.5, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 6.0, and 8.0C is 101, 99, 98, 97, 95, 94, 92, 91, 89, 84, and 80 mAh·g, respectively. -1 When the current density returns to 0.5C, the capacity reaches 98mAh·g -1 , showing good rate performance.

[0054] The above battery performance test results show that the cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC) provided by the present invention has excellent electrochemical performance when used as a negative electrode material for sodium ion batteries. This is mainly attributed to the fact that the larger specific surface area of ​​this composite material enhances the penetration and infiltration of the electrolyte; the CoS2 nanoparticles with micro-nano structure and dispersed distribution shorten the charge transfer path; the boron nitrogen sulfur co-doped carbon matrix can provide more abundant electrochemical reaction active sites, and its abundant porous interconnected structure is conducive to enhancing charge migration, while alleviating the volume change of the electrode material during charging and discharging, and improving the electrochemical stability of the electrode material. The sodium storage mechanism of the active substance is: Na + ions undergo reversible insertion / extraction reactions with porous carbon, and Na + Ions undergo reversible intercalation-conversion reaction with CoS2 nanoparticles Thanks to the good synergistic effect of the two, the sodium ion battery negative electrode material has the advantages of high specific capacity, long cycle life and good rate performance.

[0055] Comparative Example 1

[0056] In order to compare and illustrate the effect of the active material CoS2 nanoparticles in the cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material provided by the present invention on the electrochemical properties of the electrode material, the method for preparing the sodium ion battery negative electrode material in this comparative example is basically the same as that in Example 1, with the only difference being that the sulfurization process in step (4) is removed to prepare the boron and nitrogen co-doped porous carbon sodium ion battery negative electrode material containing cobalt metal nanoparticles.

[0057] The Co / BNC electrode material prepared in this comparative example was used as the working electrode, the sodium sheet was used as the counter electrode, the GF / D glass microfiber membrane was used as the separator, sodium perchlorate NaClO4 was used as the solute, and ethylene carbonate EC and dimethyl carbonate DMC with a volume ratio of 1:1 were used as the solvent. The concentration of the prepared solution was 1 mol·L -1The solution was prepared and 5 wt% of fluoroethylene carbonate (FEC) was added as the electrolyte; a 2032 button-type sodium ion half-cell was assembled and charge and discharge tests were performed, with the test voltage window being 0.01-3 V.

[0058] See also Figure 10 The figure shows the sodium ion half-cell assembled based on Co / BNC electrode material in Comparative Example 1 at 100 mA·g -1 Cycling performance under current density. The initial charge and discharge specific capacities are 328.5 and 648.4 mAh g -1 The initial coulombic efficiency is 50.6%; after 100 cycles, the capacity remains at 247 mAh g -1 The decay rate per cycle is about 0.25%, indicating that the capacity and cycle stability of the Co / BNC negative electrode material in Comparative Example 1 are significantly lower than those of the CoS2 / BNC negative electrode material in Example 1. The main reason is that Na + The ions only undergo intercalation reactions in the Co / BNC composite material, and the low initial Coulombic efficiency also reduces the capacity output during subsequent cycles.

[0059] See also Figure 11 , which is the rate performance test result of the sodium ion half-cell assembled based on Co / BNC electrode material in Comparative Example 1. As shown in the figure, the current density is 0.1~2.0A·g -1 The range of the step increases, the electrode is 0.1, 0.2, 0.4, 0.6, 1.0, 2.0A·g -1 The average capacities were 280, 249, 223, 205, 161, 147, and 109 mAh·g, respectively. -1 When the current density returns to 0.1 A g -1 The average capacity is 268 mAh g -1 , the rate performance is significantly lower than that of the negative electrode material in Example 1.

[0060] The half-cell performance test results in Comparative Example 1 show that when cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC) is used as the negative electrode material of sodium ion battery, the active material CoS2 based on the reversible embedding-conversion reaction provides a higher specific capacity for the electrode material, while the capacity provided by the porous carbon based on the embedding reaction is limited.

[0061] Since the performance test results of the sodium ion half-cell assembled based on Co / BNC electrode material are worse than those of CoS2 / BNSC electrode material, the performance of the full battery assembled based on Co / BNC negative electrode material was not tested.

[0062] Example 2

[0063] The preparation method of this embodiment is the same as that of Example 1, except that the mass of the pore-forming agent polyvinyl pyrrolidone (PVP) in step (2) is adjusted to 0.2g, and other conditions remain unchanged. Compared with the CoS2 / BNSC composite material prepared in Example 1, the content of the pore-forming agent is reduced in this embodiment, resulting in a higher density of the prepared CoS2 / BNSC composite material, which is not conducive to the construction of a stable porous interconnected structure, reduces the infiltration and penetration of the electrolyte into the active material, and also hinders the migration and diffusion rate of the charge on the surface of the active material, reduces the electrochemical reaction kinetics, and causes the electrochemical performance of the electrode material to decline. In the half-cell test, the current density is 100mA·g -1 When the initial charge and discharge specific capacities of the electrode materials are 621 and 1171 mAh·g -1 The initial coulombic efficiency is about 53%; after 100 cycles, the capacity remains at 513 mAh g -1 The decay rate per cycle is about 0.17%. In addition, the capacity, cycle stability and rate performance of the full battery are also reduced.

[0064] Example 3

[0065] The preparation method of this embodiment is the same as that of Example 1, except that the heating rate during colloid pre-carbonization is increased to 2°C / min in step (3), and other conditions remain unchanged. Compared with Example 1, the heating rate during colloid pre-carbonization is increased in this embodiment, resulting in a too fast thermal decomposition rate of polyvinyl pyrrolidone (PVP) during the pre-carbonization process, which has an adverse effect on the formation of a cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC) with a stable structure, and reduces the electrochemical performance of the CoS2 / BNSC electrode material. In the half-cell test, the current density is 100mA·g -1 When the initial charge and discharge specific capacities of the electrodes are 398 and 972 mAh g -1 The initial coulombic efficiency is about 40.9%; after 100 cycles, the capacity remains at 303 mAh g -1 The decay rate per cycle is about 0.24%. In addition, the capacity, cycle stability and rate performance of the full battery are also reduced.

[0066] Example 4

[0067] The preparation method of this embodiment is the same as that of Example 1, except that the high temperature confined carbonization temperature in step (3) is reduced to 750°C, and other conditions remain unchanged. Compared with Example 1, the high temperature carbonization temperature of the mixed colloid is reduced in this embodiment, resulting in a decrease in the degree of graphitization of the porous carbon in the CoS2 / BNSC composite material, thereby slowing down the electrochemical kinetics of the CoS2 / BNSC electrode material. In the half-cell test, the current density is 100mA·g -1When the first charge and discharge specific capacities of the electrode are 673 and 1204 mAh·g -1 The initial coulombic efficiency is about 55.9%, and after 100 cycles, the capacity remains at 572 mAh g -1 The decay rate per cycle is about 0.15%. In addition, the capacity, cycle stability and rate performance of the full battery are also reduced.

[0068] Example 5

[0069] The preparation method of this embodiment is the same as that of Example 1, except that the sulfurization time in step (4) is reduced to 1 h, and other conditions remain unchanged. Compared with Example 1, the sulfurization time of the Co / BNC composite material in this embodiment is reduced, resulting in insufficient sulfurization treatment of the Co / BNC composite material, resulting in a low content of active substance CoS2 in the CoS2 / BNSC electrode material and a significant decrease in electrochemical performance. In the half-cell test, the current density is 100 mA g -1 When the initial charge and discharge specific capacities of the electrode materials are 421 and 820 mAh g -1 The initial coulombic efficiency is about 51.3%, and after 100 cycles, the capacity remains at 332 mAh g -1 The decay rate per cycle is about 0.21%. In addition, the capacity, cycle stability and rate performance of the full battery are also reduced.

[0070] The above content is merely an example and explanation of the concept of the present invention. Various modifications or additions to the described specific embodiments or replacements made by technicians in this technical field in a similar manner shall fall within the scope of protection of the present invention as long as they do not deviate from the concept of the invention or exceed the scope defined by the claims.

Claims

1. A method for preparing a cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material, characterized in that: The specific steps are as follows: (1) ZIF-67 with a dodecahedral shape was prepared by chemical precipitation at room temperature; A 1-2 mol / L aqueous solution of 2-methylimidazole was prepared; this 2-methylimidazole aqueous solution was slowly added dropwise to a 0.3-0.8 mol / L aqueous solution of NaOH to obtain a mixed solution A; a 0.3-0.8 mol / L aqueous solution of cobalt nitrate (Co(NO3)2·6H2O) was prepared, labeled as solution B; solution B was slowly added dropwise to solution A, and the mixture was stirred for 6-18 hours. The precipitate was then centrifuged and vacuum dried at 50-80°C for 12-24 hours to obtain ZIF-67. (2) Dissolving polyacrylonitrile (PAN) and polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF) at room temperature, then ultrasonically dispersing the ZIF-67 obtained in step (1) in the solution, heating and stirring to evaporate part of the solvent, and obtaining a viscous colloid; Dissolve 0.2-0.6 g of polyacrylonitrile (PAN) with an average molecular weight of 80,000-150,000 and 0.2-0.5 g of polyvinylpyrrolidone (PVP) with an average molecular weight of 10,000-40,000 in 25 mL of N,N-dimethylformamide (DMF). Then, weigh 0.1-0.4 g of ZIF-67 and ultrasonically disperse it in the mixed solution. Stir continuously for 12-24 h, then heat at 60-80°C with stirring to evaporate part of the solvent to obtain a viscous mixed colloid. (3) heating the colloid prepared in step (2) in an inert atmosphere for pre-carbonization, then performing high-temperature confined carbonization and boron doping using ammonium borate (NH4HB4O7·3H2O) as a boron source to obtain a metal cobalt nanoparticle / boron and nitrogen co-doped carbon composite material (Co / BNC); The colloid prepared in step (2) is heated and pre-carbonized under the protection of an inert atmosphere, wherein the inert atmosphere is a nitrogen / hydrogen mixture with a volume ratio of 5:1, the temperature is 640~680℃, the holding time is 2~4 h, and the heating rate is 1~2℃ / min; then high-temperature confined carbonization is performed and boron doping is performed using ammonium borate (NH4HB4O7·3H2O) as a boron source to obtain a metal cobalt nanoparticle / boron and nitrogen co-doped carbon composite material (Co / BNC), wherein the inert atmosphere is nitrogen, the carbonization temperature is 750~850℃, the carbonization time is 2~4 h, and the heating rate is 2~5℃ / min; (4) mixing the metal cobalt nanoparticles / boron nitrogen co-doped carbon composite material (Co / BNC) obtained in step (3) with sublimed sulfur powder in a certain proportion, and performing a sulfurization treatment under the protection of an inert atmosphere to obtain a cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC), wherein fine CoS2 nanoparticles are uniformly dispersed in the boron nitrogen sulfur co-doped porous carbon matrix; The metal cobalt nanoparticles / boron nitrogen co-doped carbon composite material (Co / BNC) obtained in step (3) is mixed with sublimed sulfur powder in a mass ratio of 1:10~20, and then subjected to sulfurization treatment under argon atmosphere protection to obtain cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC), wherein the sulfurization temperature is 400~450℃, the sulfurization time is 1~3 h, and the heating rate is 1~3℃ / min.

2. Application of the cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material prepared by the method according to claim 1 in a negative electrode material for a sodium ion battery, characterized in that: The cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon composite material is ground and mixed with a conductive agent and a binder in a certain proportion to obtain a slurry, which is then evenly coated on a metal foil, vacuum-dried, and then cut into electrode sheets using a slicer to obtain a cobalt disulfide / boron, nitrogen and sulfur co-doped porous carbon sodium ion battery negative electrode.

3. The use according to claim 2, characterized in that Cobalt disulfide / boron nitrogen sulfur co-doped porous carbon composite material (CoS2 / BNSC) was ground and mixed with a conductive agent and a binder in a mass ratio of 8:1:1 to obtain a slurry. The obtained slurry was evenly coated on aluminum foil or copper foil, and then vacuum dried at 70°C for 24 hours. The electrode sheets were then cut into electrode sheets using a slicer to obtain cobalt disulfide / boron nitrogen sulfur co-doped porous carbon sodium ion battery negative electrode material.

4. The use according to claim 3, characterized in that The area mass of the active material in the prepared cobalt disulfide / boron nitrogen and sulfur co-doped porous carbon sodium ion battery anode material is 1.0~2.0 mg / cm 2 , of which CoS2 accounts for 15~30% by mass.

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