Mof / carbon nanotube electrode material and preparation method thereof

Abstract

The application provides a MOF / carbon nanotube electrode material and a preparation method thereof. The preparation method comprises the following steps: modifying and treating carbon nanotubes; mixing the modified carbon nanotubes, a cobalt salt, a nickel salt, terephthalic acid and a solvent to obtain a precursor solution; heating the precursor solution to a reaction end, centrifuging and washing, and then drying to obtain a MOF / carbon nanotube anode-free sodium metal battery electrode material. The electrode material prepared by the method has stable structure and excellent conductivity, can be applied to an anode-free sodium metal battery electrode material, the reaction temperature in the whole preparation process is low, and the method is a preparation method which is controllable in process, short in synthesis period and simple in operation.

Description

Technical Field

[0001] This invention relates to the field of sodium metal batteries, and more specifically, to a MOF / carbon nanotube electrode material and its preparation method, which is particularly suitable for sodium metal batteries without a negative electrode. Background Technology

[0002] The energy crisis is one of the major challenges facing the world today. Traditional energy resources are limited, and the use of fossil fuels and other traditional energy sources produces large amounts of greenhouse gases that impact the environment. While renewable energy has potential, its storage and utilization technologies still face certain limitations. Therefore, the research and development of new, efficient energy storage technologies is particularly important. With the increasing demand for mobile communications, electric vehicles, and renewable energy, energy storage devices such as lithium-ion batteries are gradually becoming mainstream. However, lithium resources are limited and insufficient to meet the rapidly growing demand, while sodium, as one of the most abundant resources on Earth, is considered an ideal alternative to lithium.

[0003] Sodium-ion batteries have attracted widespread attention as a candidate technology to replace lithium-ion batteries. Due to the similarity in electrochemical properties between sodium and lithium ions, sodium-ion batteries are considered promising for playing a significant role in energy storage. However, traditional sodium metal anodes suffer from problems during sodium ion insertion and extraction, such as a tendency to react violently with the electrolyte and the formation of sodium dendrites, leading to issues with the lifespan and safety of liquid batteries. Solid-state sodium metal batteries utilize a solid electrolyte, improving battery safety and cycle life. Simultaneously, the solid electrolyte possesses high ionic conductivity and chemical stability, further enhancing sodium ion transport efficiency and battery performance.

[0004] In the fabrication of solid-state sodium metal batteries, the processing and shaping of ultrathin sodium metal anodes is extremely difficult due to the soft texture and viscosity of sodium. Current research often uses excessively thick sodium metal anodes, significantly reducing the energy density of sodium metal batteries. Furthermore, the poor air stability of sodium makes production, storage, and transportation challenging. The introduction of anode-free sodium metal materials can cleverly solve these problems, maximizing battery energy density, reducing production complexity and cost, and decreasing sodium content, making production, storage, and transportation more convenient and safer. However, due to zero sodium ion excess, the cathode, as the sole sodium ion source, lacks additional sodium to offset irreversible losses, leading to poor reversibility and short lifespan. After the active sodium is consumed, there is also rapid capacity decay and low coulombic efficiency. Summary of the Invention

[0005] In view of the shortcomings of the prior art, one of the objectives of this invention is to solve one or more problems existing in the prior art. For example, one objective of this invention is to provide an electrode material for a negative electrode-free sodium metal battery with good cycle stability and long cycle life.

[0006] One aspect of the present invention provides a method for preparing MOF / carbon nanotube anode-free sodium metal battery electrode material, which may include the following steps: modifying carbon nanotubes; mixing the modified carbon nanotubes, cobalt salt, nickel salt, terephthalic acid and solvent to obtain a precursor solution; heating the precursor solution until the reaction is complete, centrifuging, washing and drying to obtain MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0007] Furthermore, the MOF / carbon nanotube anode-free sodium metal battery electrode material can be a composite material formed by interwoven carbon nanotubes as the framework and MOF dispersed in the framework, wherein the MOF is a spherical porous structure formed by interlaced sheet-like structures.

[0008] Furthermore, the molar ratio of cobalt salt, nickel salt, and terephthalic acid can be (0-1):(0-1):1.

[0009] Furthermore, the mass ratio of the sum of the cobalt salt, nickel salt, and terephthalic acid to the mass of carbon nanotubes can be 100:(1-30).

[0010] Furthermore, heating the precursor solution to the end of the reaction may include placing the precursor solution in a reaction vessel, heating it to 120°C to 200°C at a heating rate of 1°C / min to 10°C / min, and then holding it at 120°C to 200°C for 5h to 8h until the reaction is complete.

[0011] Furthermore, the modification of carbon nanotubes may include heating the carbon nanotubes in a concentrated nitric acid solution, wherein the concentration of the concentrated nitric acid solution can be 4 mol / L to 8 mol / L, and the heating temperature can be 60℃ to 100℃. Preferably, the modification can be carried out under stirring conditions. The stirring can be magnetic stirring, and the magnetic stirring time can be 1 h to 4 h.

[0012] Furthermore, the cobalt salt can be a nitrate or chloride of cobalt; for example, the cobalt salt can be cobalt nitrate hexahydrate or cobalt chloride. The nickel salt can be a nitrate or chloride of nickel; for example, the nickel salt can be nickel nitrate hexahydrate or nickel chloride.

[0013] Furthermore, the solvent can be N,N-dimethylformamide.

[0014] Furthermore, the modified carbon nanotubes, cobalt salt, nickel salt, terephthalic acid, and solvent can be mixed and magnetically stirred to obtain a precursor solution. The magnetic stirring speed can be from 100 r / min to 300 r / min.

[0015] Furthermore, the centrifugal washing solution can be one or a combination of deionized water, ethanol, and acetone. The centrifugation speed can be 5000 r / min to 6500 r / min, and the centrifugation time can be 3 min to 8 min.

[0016] Furthermore, the drying process can be carried out using forced air drying. The drying time can be 1 hour to 24 hours, and the drying temperature can be 40℃ to 80℃.

[0017] Furthermore, carbon nanotubes can be multi-walled carbon nanotubes.

[0018] Another aspect of the present invention provides a MOF / carbon nanotube anode-free sodium metal battery electrode material. The MOF / carbon nanotube anode-free sodium metal battery electrode material is a composite material formed by interwoven carbon nanotubes as a framework and MOF dispersed in the framework, wherein the MOF is a spherical porous structure formed by interlacing sheet-like structures.

[0019] Another aspect of the present invention provides a method for preparing a composite electrode sheet for a non-negative electrode sodium metal battery, which may include the following steps: mixing MOF / carbon nanotube non-negative electrode sodium metal battery material with a binder and a solvent to obtain a slurry; coating the slurry onto a negative electrode current collector and drying it to obtain a composite electrode sheet.

[0020] Furthermore, the thickness of the slurry coating on the negative electrode current collector can be 0.001 mm to 0.02 mm.

[0021] Another aspect of the present invention provides a composite sodium metal battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is a composite electrode sheet prepared by the above-described method for preparing a composite electrode sheet for a negative electrodeless sodium metal battery.

[0022] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0023] (1) The electrode material prepared by the method of the present invention has a stable structure and excellent conductivity. It can be applied to the electrode material of sodium metal battery without negative electrode. The reaction temperature of the whole preparation process is low. It is a preparation method with controllable process, short synthesis cycle and simple operation.

[0024] (2) The MOF (Co-Ni metal-organic framework) used in this invention has Ni atoms that have an affinity for sodium ions. During the charging and discharging process of the battery, it controls the deposition and dissolution of sodium and becomes a sodium storage unit. The addition of Co atoms can improve the conductivity of the electrode and the ion transport rate, thereby improving the cycle stability and service life of the battery.

[0025] (3) The electrode material of the present invention has good chemical stability and electrochemical performance, excellent air stability, and high safety.

[0026] (4) The electrode material of the present invention uses MWCNT (carbon nanotubes) as a conductive network and is combined with MOF material with high specific surface area, which can effectively induce uniform deposition of sodium ions, improve the energy density of sodium metal battery and extend its cycle life. Attached Figure Description

[0027] The above and other objects and features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0028] Figure 1 This is the X-ray diffraction (XRD) pattern of the MOF / carbon nanotube anode-free sodium metal battery electrode material obtained in Example 1 of this invention.

[0029] Figure 2 This is a scanning electron microscope (SEM) image of the MOF / carbon nanotube anode-free sodium metal battery electrode material obtained in Example 1 of this invention.

[0030] Figure 3 This is another scanning electron microscope (SEM) image of the MOF / carbon nanotube anode-free sodium metal battery electrode material obtained in Example 1 of this invention.

[0031] Figure 4 This is a cycling diagram of a half-cell (Na / composite solid electrolyte / negative electrode) of MOF / carbon nanotube sodium metal battery electrode material without negative electrode obtained in Example 2 of the present invention.

[0032] Figure 5 This is a rate capability diagram of the half-cell (Na / composite solid electrolyte / negative electrode) of the MOF / carbon nanotube anode-free sodium metal battery electrode material obtained in Example 3 of the present invention.

[0033] Figure 6 This is a cycle diagram of a full cell (sodium vanadium phosphate / composite polymer solid electrolyte / negative electrode) of the MOF / carbon nanotube anode-free sodium metal battery electrode material obtained in Example 4 of the present invention.

[0034] Figure 7 This is the electrochemical impedance spectroscopy (EIS) of the MOF / carbon nanotube anode-free sodium metal battery electrode material obtained in Example 5 of the present invention.

[0035] Figure 8 This is a cycling diagram of a half-cell (Na / composite solid electrolyte / negative electrode) of MOF / carbon nanotube sodium metal battery electrode material without negative electrode obtained in Comparative Example 1 of this invention. Detailed Implementation

[0036] In the following, a MOF / carbon nanotube electrode material and its preparation method according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0037] One aspect of the present invention provides a method for preparing MOF / carbon nanotube anode-free sodium metal battery electrode material, which may include the following steps:

[0038] S01, modified carbon nanotubes.

[0039] SO2 is used to mix modified carbon nanotubes, cobalt salt, nickel salt, terephthalic acid and solvent to obtain a precursor solution.

[0040] S03, the precursor solution is heated until the reaction is complete, centrifuged, washed and dried to obtain MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0041] In some embodiments, the modification of carbon nanotubes (MWCNTs) aims to increase the active sites and oxygen-containing functional groups within the carbon nanotubes. The modified carbon nanotubes, when combined with MOFs, enhance the affinity of the electrode material for sodium ions, thereby improving the electrochemical performance of the anode-free sodium metal battery. In some embodiments, the carbon nanotubes can be modified using concentrated nitric acid. For example, the carbon nanotubes can be modified by heating in a concentrated nitric acid solution with a concentration of 4 mol / L to 8 mol / L and a heating temperature of 60°C to 100°C. The concentrated nitric acid solution can be stirred during the modification process, for example, by magnetic stirring. The magnetic stirring time can be 1 h to 4 h. In some embodiments, for example, the carbon nanotubes can be modified under conditions of concentrated sulfuric acid concentration of 5 mol / L to 7 mol / L and a heating temperature of 70°C to 90°C.

[0042] In some implementations, cobalt salts, nickel salts, and terephthalic acid are used as raw materials to form MOFs. MOFs are Co-Ni metal-organic frameworks. Using terephthalic acid as one of the raw materials for MOF formation enables the MOF to form a lamellar interlaced structure. This lamellar structure allows the MOF to have a higher specific surface area. When combined with carbon nanotubes as a conductive network, it can effectively induce uniform deposition of sodium ions, improve the energy density of sodium metal batteries, and extend the cycle life of sodium metal batteries.

[0043] In some embodiments, the molar ratio of cobalt salt, nickel salt, and terephthalic acid can be (0–1):(0–1):1. It should be understood that the values ​​of cobalt salt and nickel salt in the above molar ratio are not 0. For example, the molar ratio of cobalt salt, nickel salt, and terephthalic acid can be (0.1–0.9):(0.1–0.9):1, (0.2–0.7):(0.3–0.8):1, (0.4–0.6):(0.2–0.5):1, or a combination thereof. Preferably, the molar ratio of cobalt salt, nickel salt, and terephthalic acid can be 1:1:1. Under these preferred ratios, MOF particles grow more uniformly, have higher porosity, and a larger specific surface area, which is more conducive to the uniform deposition of sodium metal.

[0044] In some implementations, the mass ratio of the sum of the cobalt salt, nickel salt, and terephthalic acid to the carbon nanotubes can be 100:(1-30). Regarding the mass of carbon nanotubes used, if the amount used is below the lower limit of the above-mentioned range, the conductivity of the electrode material after MOF-carbon nanotube composite will be poor; if the amount used is above the upper limit of the above-mentioned range, the surface of the MOF material will be covered by carbon nanotubes, thereby affecting the deposition and dissolution of sodium on the MOF material, and consequently affecting the electrochemical performance of the electrode material. For example, the mass ratio of the sum of the cobalt salt, nickel salt, and terephthalic acid to the carbon nanotubes can be 100:(2-28), 100:(15-23), 100:(5-20), or a combination thereof.

[0045] In some embodiments, the cobalt salt can be a nitrate or chloride of cobalt, for example, cobalt nitrate hexahydrate or cobalt chloride. The nickel salt can be a nitrate or chloride of nickel, for example, nickel nitrate hexahydrate or nickel chloride.

[0046] In some embodiments, the solvent may be N,N-dimethylformamide, N-methylpyrrolidone, or acetone.

[0047] In some implementations, the MOF / carbon nanotube anode-free sodium metal battery electrode material is a composite material formed by interwoven carbon nanotubes as a framework, with MOF dispersed within the framework. For example... Figure 2As shown, interwoven carbon nanotubes form the basic framework of the electrode material, acting as a supporting network. Besides stabilizing the electrode material's structure, they also enhance its conductivity. MOFs are dispersed within this carbon nanotube framework and grown on a carbon nanotube substrate. The growth of carbon nanotubes with MOFs constructs an electrode material where sodium ions can be uniformly deposited, reducing the formation of dead sodium, improving the battery's cycle life, and effectively alleviating the short lifespan problem of sodium metal batteries without a negative electrode due to the consumption of active sodium during cycling. The prepared material exhibits high stability and high electrochemical performance. MOFs are porous structures formed by interwoven sheet-like materials. MOFs can also have a spherical structure. The porous structure formed by interwoven sheet-like materials allows MOFs to have a large specific surface area, suitable for sodium ions to deposit as sodium metal on the surface. The large specific surface area of ​​MOFs modifies the current collector, providing a site for sodium ion deposition and leveraging the affinity of the MOF central atoms for sodium ions, inducing uniform sodium ion deposition.

[0048] In some implementations, the carbon nanotubes can be multi-walled carbon nanotubes. Multi-walled carbon nanotubes can effectively conduct electrons, and the interlayer spacing of multi-walled carbon nanotubes enables rapid sodium ion transport, allowing charge-discharge products to be captured within the electrode during cycling.

[0049] In some embodiments, heating the precursor solution to the end of the reaction may include placing the precursor solution in a reaction vessel, heating it to 120°C to 200°C at a heating rate of 1°C / min to 10°C / min, and then holding it at 120°C to 200°C for 5 to 8 hours until the reaction is complete. For example, the temperature may be increased to 150°C to 180°C in the reaction vessel at a heating rate of 3°C / min to 7°C / min, and then held at 150°C to 180°C for 6 to 7 hours until the reaction is complete. As another example, the temperature may be increased to 140°C to 160°C in the reaction vessel at a heating rate of 4°C / min to 6°C / min, and then held at 140°C to 160°C for 5.5 to 7.5 hours until the reaction is complete.

[0050] In some embodiments, the modified carbon nanotubes, cobalt salt, nickel salt, terephthalic acid, and solvent are mixed and magnetically stirred to obtain a precursor solution. The stirring speed can be from 100 r / min to 300 r / min. For example, the stirring speed can be 200 r / min.

[0051] In some embodiments, the centrifugal washing solution can be one or more combinations of deionized water, ethanol, and acetone. The centrifugation speed can be 5000 r / min to 6500 r / min, and the centrifugation time can be 3 min to 8 min. For example, the centrifugation speed can be 5500 r / min, and the centrifugation time can be 5 min.

[0052] In some implementations, drying can be done by forced air drying. The drying time can be 1 hour to 24 hours, and the drying temperature can be 40°C to 80°C. For example, the drying time can be 3 hours to 20 hours, and the drying temperature can be 50°C to 70°C.

[0053] Another aspect of the present invention provides a MOF / carbon nanotube anode-free sodium metal battery electrode material. This MOF / carbon nanotube anode-free sodium metal battery electrode material is a composite material formed by interwoven carbon nanotubes as a framework, with MOF dispersed within the framework. The MOF is a spherical porous structure formed by interlaced sheet-like structures. In the electrode material of the present invention, MWCNTs can effectively conduct electrons, their interlayer gaps enable rapid ion transport, and they can capture charge-discharge products within the electrode during cycling. The sodium-affinity properties of the metal atoms in the MOF can control the uniform deposition of sodium ions, and their good dispersion can serve as sodium ion storage units. The anode-free sodium metal battery electrode material has advantages such as structural stability, excellent electrochemical performance, and uniform nucleation, thereby improving the energy density of sodium metal batteries without sacrificing their cycle performance and extending their service life.

[0054] Another aspect of the present invention provides a method for preparing a composite electrode sheet for a negative electrode-free sodium metal battery, which may include the following steps:

[0055] S01, MOF / carbon nanotube anode-free sodium metal battery electrode material is mixed with binder and solvent to obtain slurry;

[0056] S02, the slurry is coated onto the negative electrode current collector and dried to obtain a composite electrode sheet.

[0057] In some implementations, the binder can be polyvinylidene fluoride, polytetrafluoroethylene emulsion, styrene-butadiene emulsion, or sodium carboxymethyl cellulose, etc. The mass ratio of the MOF / carbon nanotube anode-free sodium metal battery electrode material to the binder can be adjusted according to the actual battery setup requirements. For example, the mass ratio of the MOF / carbon nanotube anode-free sodium metal battery electrode material to the binder can be 9:1, 8:2, or 7:3.

[0058] In some embodiments, the solvent can be 1-methyl-2-pyrrolidone, N-methylpyrrolidone, or dimethyl sulfoxide, etc. After the MOF / carbon nanotube anode-free sodium metal battery electrode material is mixed with the binder and solvent, it can be ground to obtain a slurry. For example, the grinding time can be 20 min to 30 min.

[0059] In some implementations, the negative electrode current collector can be an existing negative electrode current collector such as aluminum foil or copper foil.

[0060] In some embodiments, the thickness of the slurry coating on the negative electrode current collector can be 0.001 mm to 0.02 mm. For example, the coating thickness can be 0.009 mm to 0.015 mm, 0.007 mm to 0.012 mm, 0.01 mm to 0.018 mm, or a combination of the above ranges.

[0061] In some implementations, the slurry coated onto the negative electrode current collector can be dried in a vacuum oven. For example, drying can be performed at a temperature of 50°C to 120°C for 6 to 24 hours.

[0062] Another aspect of the present invention provides a composite sodium metal battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode is a composite electrode sheet prepared by the aforementioned method for preparing a composite electrode sheet for a negative electrodeless sodium metal battery. It should be noted that the "negative electrode" here is a nominal negative electrode, meaning that the composite electrode sheet without active material prepared according to the present invention is used as the negative electrode current collector, and the negative electrode current collector is a nominal "negative electrode." The positive electrode and the negative electrode are located on opposite sides of the separator, and the electrolyte is located between the positive electrode and the negative electrode. The positive electrode can be a sodium metal sheet. The diameter of the sodium metal sheet can be 16 mm, and the thickness can be 0.2 mm to 0.4 mm. Of course, the diameter and thickness of the positive electrode material of the present invention are not limited to these and can be adjusted according to the actual needs of the battery.

[0063] In some embodiments, the electrolyte can be a sodium hexafluorophosphide / sodium tetrafluoroborate / diethylene glycol dimethyl ether solution. The separator can be a polyethylene oxide (PEO) composite solid electrolyte with a thickness of 0.05 mm. Of course, it should be understood that the electrolyte and separator of the composite sodium metal battery of the present invention are not limited thereto.

[0064] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0065] Example 1

[0066] Step 1: Mix MWCNT powder with 8mol / L concentrated nitric acid at a mass-volume ratio of 1mg:1ml, stir magnetically at 80℃ for 1h, centrifuge and dry to obtain modified MWCNT.

[0067] Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid in a molar ratio of 1:1:1 to a beaker, add 1 wt% modified MWCNT and 120 ml of N,N-dimethylformamide solvent, and stir magnetically for 3 h at a stirring speed of 300 r / min. After uniform mixing, a precursor solution is obtained.

[0068] Step 3: Add the precursor solution to a solvothermal reactor and heat it to 180°C at a rate of 3°C / min. Then keep it at this temperature for 8 hours and cool it to room temperature in a muffle furnace. Then use ethanol as a washing agent and centrifuge at 5000 r / min for 3 minutes. Take it out and put it into a forced-air drying oven and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0069] MOF / carbon nanotube anode-free sodium metal battery electrode material was mixed with polyvinylidene fluoride at a mass ratio of 9:1, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto aluminum foil, vacuum dried at 120℃, and then cut into sheets to prepare the anode sheet. A sodium metal sheet was used as the positive electrode, 0.1M NaBF4 and 0.9M NaPF6 were dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte was used as the separator to assemble a composite coin cell.

[0070] The X-ray diffraction (XRD) pattern of the composite electrode material obtained in this embodiment is shown below. Figure 1 As shown, the XRD diffraction peaks correspond to the characteristic peaks, and after combining MWCNT, only the diffraction peaks are superimposed without any impurity peaks appearing. Figure 2 and Figure 3 The image shows a scanning electron microscope (SEM) image of the composite electrode material obtained in this embodiment. It can be seen from the image that the MOF and MWCNTs are well integrated. The MWCNTs are cross-linked to form storage cells, providing skeletal support. The MOF is well dispersed in the material, inducing uniform sodium ion deposition and improving battery lifespan. Furthermore, from... Figure 2 and Figure 3 As can be seen, the metal-organic framework is a spherical structure with a diameter of a few micrometers composed of sheet structures. This structure has a large specific surface area, which is suitable for sodium ions to be deposited on the surface as sodium metal.

[0071] Example 2

[0072] Step 1: Mix MWCNT powder with 8mol / L concentrated nitric acid at a mass-volume ratio of 1mg:1ml, stir magnetically at 80℃ for 1h, centrifuge and dry to obtain modified MWCNT.

[0073] Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid in a molar ratio of 1:1:1 to a beaker, add 30wt% modified MWCNT and 120ml of N,N-dimethylformamide solvent, and stir magnetically for 3h at a stirring speed of 300r / min. After uniform mixing, a precursor solution is obtained.

[0074] Step 3: Add the precursor solution to a solvothermal reactor and heat it to 180°C at a rate of 3°C / min. Then keep it at this temperature for 8 hours and cool it to room temperature in a muffle furnace. Then use ethanol as a washing agent and centrifuge at 5000 r / min for 3 minutes. Take it out and put it into a forced-air drying oven and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0075] MOF / carbon nanotube anode-free sodium metal battery electrode material was mixed with polyvinylidene fluoride at a mass ratio of 9:1, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto aluminum foil, vacuum dried at 120℃, and then cut into sheets to prepare the anode sheet. A sodium metal sheet was used as the positive electrode, 0.1M NaBF4 and 0.9M NaPF6 were dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte was used as the separator to assemble a composite coin cell.

[0076] The battery assembled with the composite electrode material obtained in this embodiment exhibits the following cycle performance at 110 mA / g within a voltage range of 0V to 2.5V: Figure 4 As shown, the initial discharge specific capacity is 95 mAh / g, and the coulombic efficiency is close to 100% after 500 cycles.

[0077] Example 3

[0078] Step 1: Mix MWCNT powder with 8mol / L concentrated nitric acid at a mass-volume ratio of 1mg:1ml, stir magnetically at 80℃ for 1h, centrifuge and dry to obtain modified MWCNT.

[0079] Step 2: Cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid in a molar ratio of 1:1:1 are added to a beaker, along with 10 wt% modified MWCNT and 120 ml of N,N-dimethylformamide solvent. The mixture is magnetically stirred for 3 h at a stirring rate of 300 r / min until homogeneous, thus obtaining the precursor solution.

[0080] Step 3: Add the precursor solution to a solvothermal reactor and heat it to 180°C at a rate of 3°C / min. Then keep it at this temperature for 8 hours and cool it to room temperature in a muffle furnace. Then use ethanol as a washing agent and centrifuge at 5000 r / min for 3 minutes. Take it out and put it into a forced-air drying oven and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0081] MOF / carbon nanotube anode-free sodium metal battery electrode material was mixed with polyvinylidene fluoride at a mass ratio of 9:1, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto aluminum foil, vacuum dried at 120℃, and then cut into sheets to prepare the anode sheet. A sodium metal sheet was used as the positive electrode, 0.1M NaBF4 and 0.9M NaPF6 were dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte was used as the separator to assemble a composite coin cell.

[0082] The battery assembled with the composite electrode material obtained in this embodiment exhibits the following cycling performance within a voltage range of 0V to 2.5V at current densities of 500mA / g, 1000mA / g, 1500mA / g, 2000mA / g, 2500mA / g, 3000mA / g, 3500mA / g, and 4000mA / g: Figure 5 As shown, the capacity retention remains excellent even at a current density of 4000 mA / g.

[0083] Example 4

[0084] Step 1: Mix MWCNT powder with 8mol / L concentrated nitric acid at a mass-volume ratio of 1mg:1ml, stir magnetically at 80℃ for 1h, centrifuge and dry to obtain modified MWCNT.

[0085] Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid in a molar ratio of 1:1:1 to a beaker, add 15wt% modified MWCNT and 120ml of N,N-dimethylformamide solvent, and stir magnetically for 3h at a stirring speed of 300r / min. After uniform mixing, a precursor solution is obtained.

[0086] Step 3: Add the precursor solution to a solvothermal reactor and heat it to 180°C at a rate of 3°C / min. Then keep it at this temperature for 8 hours and cool it to room temperature in a muffle furnace. Then use ethanol as a washing agent and centrifuge at 5000 r / min for 3 minutes. Take it out and put it into a forced-air drying oven and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0087] MOF / carbon nanotube anode-free sodium metal battery electrode material was mixed with polyvinylidene fluoride at a mass ratio of 9:1, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto aluminum foil, vacuum dried at 120℃, and then cut into sheets to prepare the anode sheet. A sodium metal sheet was used as the positive electrode, 0.1M NaBF4 and 0.9M NaPF6 were dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte was used as the separator to assemble a composite coin cell.

[0088] The battery assembled with the composite electrode material obtained in this embodiment, after cycling 5 times at a current density of 4000 mA / g within a voltage range of 0V to 2.5V, and then cycling at a lower current density of 500 mA / g, exhibits the following performance: Figure 6 As shown, cycling the negative electrode side with a high current density first allows sodium ions to nucleate uniformly and generates a thin SEI to ensure the cycle stability of the sodium-ion battery. Figure 6 This indicates that the battery assembled with the composite electrode material obtained in this embodiment exhibits a slow decrease in discharge specific capacity, a high capacity retention rate, and good electrochemical performance.

[0089] Example 5

[0090] Step 1: Mix MWCNT powder with 8mol / L concentrated nitric acid at a mass-volume ratio of 1mg:1ml, stir magnetically at 80℃ for 1h, centrifuge and dry to obtain modified MWCNT.

[0091] Step 2: Cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid in a molar ratio of 1:1:1 are added to a beaker, along with 20wt% modified MWCNT and 120ml of N,N-dimethylformamide solvent. The mixture is magnetically stirred for 3h at a stirring rate of 300r / min until homogeneous, thus obtaining the precursor solution.

[0092] Step 3: Add the precursor solution to a solvothermal reactor and heat it to 180°C at a rate of 3°C / min. Then keep it at this temperature for 8 hours and cool it to room temperature in a muffle furnace. Then use ethanol as a washing agent and centrifuge at 5000 r / min for 3 minutes. Take it out and put it into a forced-air drying oven and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0093] MOF / carbon nanotube anode-free sodium metal battery electrode material was mixed with polyvinylidene fluoride at a mass ratio of 9:1, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto aluminum foil, vacuum dried at 120℃, and then cut into sheets to prepare the anode sheet. A sodium metal sheet was used as the positive electrode, 0.1M NaBF4 and 0.9M NaPF6 were dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte was used as the separator to assemble a composite coin cell.

[0094] The battery assembled with the composite electrode material obtained in this embodiment underwent AC impedance testing as follows: Figure 7 As shown, the low impedance between the electrolyte material and the electrode material indicates that the composite electrode material has excellent interfacial dynamics.

[0095] Example 6

[0096] Step 1: Mix MWCNT powder with 8mol / L concentrated nitric acid at a mass-volume ratio of 1mg:1.5ml, stir magnetically at 80℃ for 1h, centrifuge and dry to obtain modified MWCNT.

[0097] Step 2: Cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid in a molar ratio of 0.5:0.5:1 are added to a beaker, along with 25wt% modified MWCNT and 120ml of N,N-dimethylformamide solvent. The mixture is magnetically stirred for 3 hours at a stirring rate of 300r / min until homogeneous, thus obtaining the precursor solution.

[0098] Step 3: Add the precursor solution to a solvothermal reactor and heat it to 185°C at a rate of 3°C / min. Then keep it at this temperature for 8 hours and cool it to room temperature in a muffle furnace. Then use ethanol as a washing agent and centrifuge at 5000 r / min for 4 minutes. Take it out and put it into a forced-air drying oven and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0099] MOF / carbon nanotube anode-free sodium metal battery electrode material was mixed with polyvinylidene fluoride at a mass ratio of 9:1, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto aluminum foil, vacuum dried at 120℃, and then cut into sheets to prepare the anode sheet. A sodium metal sheet was used as the positive electrode, 0.1M NaBF4 and 0.9M NaPF6 were dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte was used as the separator to assemble a composite coin cell.

[0100] The battery assembled with the composite electrode material obtained in this embodiment exhibits stable electrochemical performance and long cycle life within a voltage range of 0V to 2.5V.

[0101] Example 7

[0102] Step 1: Mix MWCNT powder with 8mol / L concentrated nitric acid at a mass-volume ratio of 1mg:2ml, stir magnetically at 80℃ for 1h, centrifuge and dry to obtain modified MWCNT.

[0103] Step 2: Cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid in a molar ratio of 0.2:0.6:1 are added to a beaker, along with 5 wt% modified MWCNT and 120 ml of N,N-dimethylformamide solvent. The mixture is magnetically stirred for 3 h at a stirring rate of 300 r / min until homogeneous, thus obtaining the precursor solution.

[0104] Step 3: Add the precursor solution to a solvothermal reactor and heat it to 190°C at a rate of 3°C / min. Then keep it at this temperature for 8 hours and cool it to room temperature in a muffle furnace. Then use ethanol as a washing agent and centrifuge at 5000 r / min for 5 minutes. Take it out and put it into a forced-air drying oven and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0105] MOF / carbon nanotube anode-free sodium metal battery electrode material was mixed with polyvinylidene fluoride at a mass ratio of 9:1, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto aluminum foil, vacuum dried at 120℃, and then cut into sheets to prepare the anode sheet. A sodium metal sheet was used as the positive electrode, 0.1M NaBF4 and 0.9M NaPF6 were dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte was used as the separator to assemble a composite coin cell.

[0106] The battery assembled with the composite electrode material obtained in this embodiment exhibits stable electrochemical performance and long cycle life within a voltage range of 0V to 2.5V.

[0107] Example 8

[0108] Step 1: Mix MWCNT powder with 8mol / L concentrated nitric acid at a mass-volume ratio of 1mg:2.5ml, stir magnetically at 80℃ for 1h, centrifuge and dry to obtain modified MWCNT.

[0109] Step 2: Cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid in a molar ratio of 0.8:0.3:1 are added to a beaker, along with 10 wt% modified MWCNT and 120 ml of N,N-dimethylformamide solvent. The mixture is magnetically stirred for 3 h at a stirring rate of 300 r / min until homogeneous, thus obtaining the precursor solution.

[0110] Step 3: Add the precursor solution to a solvothermal reactor and heat it to 195°C at a rate of 3°C / min. Then keep it at this temperature for 8 hours and cool it to room temperature in a muffle furnace. Then use ethanol as a washing agent and centrifuge at 5000 r / min for 6 minutes. Take it out and put it into a forced-air drying oven and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0111] MOF / carbon nanotube anode-free sodium metal battery electrode material was mixed with polyvinylidene fluoride at a mass ratio of 9:1, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto aluminum foil, vacuum dried at 120℃, and then cut into sheets to prepare the anode sheet. A sodium metal sheet was used as the positive electrode, 0.1M NaBF4 and 0.9M NaPF6 were dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte was used as the separator to assemble a composite coin cell.

[0112] The battery assembled with the composite electrode material obtained in this embodiment exhibits stable electrochemical performance and long cycle life within a voltage range of 0V to 2.5V.

[0113] Example 9

[0114] Step 1: Mix MWCNT powder with 7mol / L concentrated nitric acid at a mass-volume ratio of 1mg:3ml, stir magnetically at 80℃ for 1h, centrifuge and dry to obtain modified MWCNT.

[0115] Step 2: Cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid in a molar ratio of 0.7:0.6:1 are added to a beaker, along with 20wt% modified MWCNT and 120ml of N,N-dimethylformamide solvent. The mixture is magnetically stirred for 3 hours at a stirring rate of 300r / min until homogeneous, thus obtaining the precursor solution.

[0116] Step 3: Add the precursor solution to a solvothermal reactor and heat it to 200°C at a rate of 5°C / min. Then keep it at this temperature for 8 hours and cool it to room temperature in a muffle furnace. Then use ethanol as a washing agent and centrifuge at 5000 r / min for 7 minutes. Take it out and put it into a forced-air drying oven and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0117] MOF / carbon nanotube anode-free sodium metal battery electrode material was mixed with polyvinylidene fluoride at a mass ratio of 9:1, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto aluminum foil, vacuum dried at 120℃, and then cut into sheets to prepare the anode sheet. A sodium metal sheet was used as the positive electrode, 0.1M NaBF4 and 0.9M NaPF6 were dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte was used as the separator to assemble a composite coin cell.

[0118] The battery assembled with the composite electrode material obtained in this embodiment exhibits stable electrochemical performance and long cycle life within a voltage range of 0V to 2.5V.

[0119] Example 10

[0120] Step 1: Mix MWCNT powder with 8mol / L concentrated nitric acid at a mass-volume ratio of 1mg:1ml, stir magnetically at 80℃ for 1h, centrifuge and dry to obtain modified MWCNT.

[0121] Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid in a molar ratio of 1:1:1 to a beaker, add 30wt% modified MWCNT and 120ml of N,N-dimethylformamide solvent, and stir magnetically for 3h at a stirring speed of 300r / min. After uniform mixing, a precursor solution is obtained.

[0122] Step 3: Add the precursor solution to a solvothermal reactor and heat it to 180°C at a rate of 10°C / min. Then keep it at this temperature for 8 hours and cool it to room temperature in a muffle furnace. Then use ethanol as a washing agent and centrifuge at 5000 r / min for 8 minutes. Take it out and put it into a forced-air drying oven and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF / carbon nanotube anode-free sodium metal battery electrode material.

[0123] MOF / carbon nanotube anode-free sodium metal battery electrode material was mixed with polyvinylidene fluoride at a mass ratio of 9:1, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto aluminum foil, vacuum dried at 120℃, and then cut into sheets to prepare the anode sheet. A sodium metal sheet was used as the positive electrode, 0.1M NaBF4 and 0.9M NaPF6 were dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte was used as the separator to assemble a composite coin cell.

[0124] The battery assembled with the composite electrode material obtained in this embodiment exhibits stable electrochemical performance and long cycle life within a voltage range of 0V to 2.5V.

[0125] Comparative Example 1

[0126] The difference between Comparative Example 1 and Example 2 is that the mass percentage of modified MWCNT is 35% of the sum of the masses of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and terephthalic acid; the other preparation methods are the same. The battery assembled with the composite electrode material obtained in Comparative Example 1 exhibits the following cycling performance within a voltage range of 0V to 2.5V and a current density of 110mA / g: Figure 8As shown, the initial discharge specific capacity was 102 mAh / g, followed by a decrease in capacity. It stabilized after 50 cycles, and after 500 cycles, the capacity approached 70 mAh / g. The surface cell exhibited a rapid decrease in discharge specific capacity and low capacity retention. The reason for this is that excessive carbon nanotubes (MWCNTs) would partially cover the surface of the MOF material, reducing sodium ion deposition and leading to significant side reactions. Therefore, the mass percentage of MWCNTs was set to less than 30% of the sum of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and terephthalic acid.

[0127] Although the invention has been described above in conjunction with exemplary embodiments, those skilled in the art will understand that various modifications and changes can be made to the exemplary embodiments of the invention without departing from the spirit and scope defined by the claims.

Claims

1. A method for preparing MOF / carbon nanotube-based sodium metal battery electrode material without a negative electrode, characterized in that, Includes the following steps: Modification treatment of carbon nanotubes; The modified carbon nanotubes, cobalt salt, nickel salt, terephthalic acid and solvent were mixed to obtain a precursor solution. The precursor solution was heated until the reaction was complete, centrifuged, washed, and dried to obtain the MOF / carbon nanotube anode-free sodium metal battery electrode material. MOF / carbon nanotube anode-free sodium metal battery electrode material is a composite material formed by interwoven carbon nanotubes as the framework and MOF dispersed in the framework. Among them, MOF is a spherical porous structure formed by interlaced sheet-like structures. The mass ratio of the sum of the cobalt salt, nickel salt, and terephthalic acid to the mass of carbon nanotubes is 100:(1~30); The carbon nanotubes are multi-walled carbon nanotubes.

2. The method for preparing MOF / carbon nanotube anode-free sodium metal battery electrode material according to claim 1, characterized in that, The molar ratio of cobalt salt, nickel salt and terephthalic acid is (0~1):(0~1):1, and the values ​​of cobalt salt and nickel salt are not 0.

3. The method for preparing MOF / carbon nanotube anode-free sodium metal battery electrode material according to claim 1, characterized in that, Heating the precursor solution to the end of the reaction involves placing the precursor solution in a reaction vessel, heating it to 120℃~200℃ at a heating rate of 1℃ / min~10℃ / min, and then holding it at 120℃~200℃ for 5h~8h until the reaction is complete.

4. The method for preparing MOF / carbon nanotube anode-free sodium metal battery electrode material according to claim 1, characterized in that, The modification treatment of carbon nanotubes includes heating the carbon nanotubes in a concentrated nitric acid solution, wherein the concentration of the concentrated nitric acid solution is 4 mol / L to 8 mol / L, and the heating temperature is 60℃ to 100℃.

5. A MOF / carbon nanotube anode-free sodium metal battery electrode material prepared by the method for preparing MOF / carbon nanotube anode-free sodium metal battery electrode material according to any one of claims 1 to 4, characterized in that, MOF / carbon nanotube anode-free sodium metal battery electrode material is a composite material formed by interwoven carbon nanotubes as the framework and MOF dispersed in the framework. Among them, MOF is a spherical porous structure formed by interlaced sheet-like structures.

6. A method for preparing a composite electrode sheet for a sodium metal battery without a negative electrode, characterized in that, Includes the following steps: The MOF / carbon nanotube non-anode sodium metal battery electrode material prepared by the method of preparing MOF / carbon nanotube non-anode sodium metal battery electrode material according to any one of claims 1 to 4, or the MOF / carbon nanotube non-anode sodium metal battery electrode material according to claim 5, is mixed with a binder and a solvent to obtain a slurry. The slurry is coated onto the negative electrode current collector and dried to obtain a composite electrode sheet.

7. The method for preparing a composite electrode sheet for a negative electrode-free sodium metal battery according to claim 6, characterized in that, The slurry is coated on the negative electrode current collector with a thickness of 0.001mm~0.02mm.

8. A composite sodium metal battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode is the composite electrode sheet prepared by the method for preparing a negative electrode-free sodium metal battery according to claim 6 or 7.

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