CN117438563A - MOF/carbon nano tube electrode material and preparation method thereof - Google Patents

Abstract

The invention provides a MOF/carbon nano tube electrode material and a preparation method thereof. The preparation method comprises the following steps: modifying the carbon nano tube; mixing the modified carbon nano tube, cobalt salt, nickel salt, terephthalic acid and a solvent to obtain a precursor solution; and heating the precursor solution to the end of the reaction, centrifugally washing and drying to obtain the MOF/carbon nano tube negative-electrode-free sodium metal battery electrode material. The electrode material prepared by the method has stable structure and excellent conductivity, can be applied to the electrode material of the non-negative sodium metal battery, has low reaction temperature in the whole preparation process, and is a preparation method with controllable process, short synthesis period and simple operation.

Description

A MOF/carbon nanotube electrode material and its preparation method

Technical field

The present invention relates to the field of sodium metal batteries, and more specifically, to a MOF/carbon nanotube electrode material and a preparation method thereof, which is particularly suitable for sodium metal batteries without negative electrodes.

Background technique

The energy crisis is one of the important challenges facing the world today. Traditional energy resources are limited, and the use of traditional energy sources such as fossil fuels will produce a large amount of greenhouse gases that affect the environment. Although renewable energy has potential, its storage and utilization technology still faces certain limitations. Therefore, the research and development of new high-efficiency energy storage technologies is particularly important. As demand for mobile communications, electric vehicles and renewable energy increases, energy storage devices such as lithium-ion batteries are becoming mainstream. However, lithium resources are limited and insufficient to meet the rapidly growing demand, and sodium, as one of the abundant resources on earth, is considered an ideal substitute after lithium.

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 ions and lithium ions, sodium-ion batteries are expected to play an important role in the field of energy storage. However, traditional sodium metal anodes have problems in the process of sodium ion insertion and extraction. For example, it is easy to react violently with the electrolyte and form sodium dendrites, etc., which leads to problems in the service life and safety of liquid batteries. Solid-state sodium metal batteries use solid-state electrolytes, which improves battery safety and cycle life. At the same time, the solid electrolyte has high ionic conductivity and chemical stability, further improving sodium ion transmission efficiency and battery performance.

In the preparation process of solid-state sodium metal batteries, the processing and shaping of ultra-thin sodium metal negative electrodes is very difficult because metallic sodium is soft and has a certain viscosity. Most of the current research work uses a far excessive amount of ultra-thick sodium metal anode, which greatly reduces the energy density of sodium metal batteries. In addition, due to the poor air stability of metallic sodium, it is difficult to produce, store, and transport. The introduction of negative-electrode sodium metal materials can cleverly solve the above problems. It can maximize battery energy density, reduce production complexity and cost, reduce sodium metal content, and is more convenient and safer in production, storage, transportation operations, etc. However, due to zero excess of sodium ions, the positive electrode, as the only source of sodium ions, has no additional sodium to offset the irreversible loss, and faces the problems of poor reversibility and short life. After the active sodium is consumed, there is also rapid capacity decay and Coulombic efficiency. low question.

Contents of the invention

In view of the deficiencies existing in the prior art, one of the purposes of the present invention is to solve one or more problems existing in the above-mentioned prior art. For example, one of the objects of the present invention is to provide an electrode material for a sodium metal battery without anode that has good cycle stability and long cycle life.

One aspect of the present invention provides a method for preparing MOF/carbon nanotube-free sodium metal battery electrode materials, which may include the following steps: modifying the carbon nanotubes; combining the modified carbon nanotubes, cobalt salt, and nickel Salt, terephthalic acid and solvent are mixed to obtain a precursor solution; the precursor solution is heated to the end of the reaction, centrifuged and washed and dried to obtain MOF/carbon nanotube-free sodium metal battery electrode material.

Furthermore, the MOF/carbon nanotube anode-free sodium metal battery electrode material can be a composite material with intertwined carbon nanotubes as the skeleton and MOF dispersed in the skeleton. The MOF is a spherical-like porous structure formed by interlacing flakes. structure.

Further, the molar ratio of cobalt salt, nickel salt and terephthalic acid may be (0～1):(0～1):1.

Further, the mass ratio of the sum of the masses of cobalt salt, nickel salt and terephthalic acid to the carbon nanotube can be 100: (1-30).

Further, heating the precursor solution to the end of the reaction may include placing the precursor solution in a reaction kettle, raising the temperature to 120°C to 200°C at a heating rate of 1°C/min to 10°C/min, and then heating the precursor solution to 120°C to 200°C. Incubate at 200°C for 5h to 8h until the reaction is completed.

Further, modifying the carbon nanotubes may include heating the carbon nanotubes in a concentrated nitric acid solution for modification, wherein the concentration of the concentrated nitric acid solution may be 4 mol/L to 8 mol/L, and the heating temperature may be 60°C. ~100℃. Preferably, the modification can be carried out under stirring conditions. Stirring can be magnetic stirring, and the time of magnetic stirring can be 1h to 4h.

Further, the cobalt salt may be a nitrate or chloride salt of cobalt. For example, the cobalt salt may be cobalt nitrate hexahydrate or cobalt chloride. The nickel salt may be a nitrate or chloride salt of nickel. For example, the nickel salt may be nickel nitrate hexahydrate or nickel chloride.

Further, the solvent may be N,N-dimethylformamide.

Further, the modified carbon nanotubes, cobalt salt, nickel salt, terephthalic acid and solvent can be mixed and magnetically stirred to obtain a precursor solution. The rotation speed of magnetic stirring can be 100r/min ~ 300r/min.

Further, the centrifugal washing liquid can be one or more combinations of deionized water, ethanol, and acetone. The centrifugal speed can be 5000r/min ~ 6500r/min, and the centrifugation time can be 3min ~ 8min.

Further, drying may be air drying. The blast drying time can be 1h~24h, and the drying temperature can be 40℃~80℃.

Further, the carbon nanotubes may be multi-walled carbon nanotubes.

Another aspect of the invention provides a MOF/carbon nanotube-free sodium metal battery electrode material. The MOF/carbon nanotube-free sodium metal battery electrode material is based on interwoven carbon nanotubes as a skeleton, and MOF is dispersed in the skeleton. The composite material formed, in which the MOF is a spherical porous structure formed by interlaced lamellar structures.

Another aspect of the present invention provides a method for preparing composite electrode sheets for sodium metal batteries without negative electrodes, which may include the following steps: mixing MOF/carbon nanotube electrode materials for sodium metal batteries without negative electrodes with adhesives and solvents to obtain a slurry material; apply the slurry on the negative electrode current collector and dry it to obtain a composite electrode sheet.

Further, the thickness of the slurry coated on the negative electrode current collector may be 0.001 mm to 0.02 mm.

Another aspect of the present invention provides a composite sodium metal battery, including a positive electrode, a negative electrode, a separator and an electrolyte. The negative electrode is a composite electrode sheet prepared by the composite electrode sheet preparation method for a negative electrode-free sodium metal battery described above.

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

(1) The electrode material prepared by the method of the present invention has a stable structure and excellent conductive properties, and can be used as an electrode material for sodium metal batteries without negative electrodes. The reaction temperature of the entire preparation process is low, the process is controllable, the synthesis cycle is short, and the operation is simple. Preparation.

(2) In the MOF (Co-Ni metal organic framework) used in the present invention, Ni atom metal has an affinity for sodium ions. It controls the deposition and dissolution of sodium during the battery charging and discharging process and becomes a sodium storage unit. The addition of Co atoms can Improve the conductivity and ion transmission rate of the electrode, thereby improving the cycle stability and service life of the battery.

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

(4) The electrode material of the present invention uses MWCNT (carbon nanotube) as a conductive network and is combined with a high specific surface area MOF material, which can effectively induce the uniform deposition of sodium ions, increase the energy density of sodium metal batteries, and extend its cycle life.

Description of the drawings

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

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

Figure 2 is a scanning electron microscope (SEM) image of the MOF/carbon nanotube negative-electrode-free sodium metal battery electrode material obtained in Example 1 of the present invention.

Figure 3 is another scanning electron microscope (SEM) image of the MOF/carbon nanotube anode-less sodium metal battery electrode material obtained in Example 1 of the present invention.

Figure 4 is a cycle diagram of the MOF/carbon nanotube-free sodium metal battery electrode material half-cell (Na/composite solid electrolyte/negative electrode) obtained in Example 2 of the present invention.

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

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

Figure 7 is an electrochemical impedance spectrum (EIS) of the MOF/carbon nanotube negative-electrode-free sodium metal battery electrode material obtained in Example 5 of the present invention.

Figure 8 is a cycle diagram of the MOF/carbon nanotube-free sodium metal battery electrode material half-cell (Na/composite solid electrolyte/negative electrode) obtained in Comparative Example 1 of the present invention.

Detailed ways

Hereinafter, a MOF/carbon nanotube electrode material and a preparation method thereof according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

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

S01, modification of carbon nanotubes.

S02, mix the modified carbon nanotubes, cobalt salt, nickel salt, terephthalic acid and solvent to obtain a precursor solution.

S03, heat the precursor solution to the end of the reaction, centrifuge, wash and dry to obtain MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

In some embodiments, carbon nanotubes (MWCNTs) are modified to increase active sites and oxygen-containing functional groups of the carbon nanotubes. After the modified carbon nanotubes are combined with the MOF, the affinity of the electrode material for sodium ions can be enhanced and the electrochemical performance of the negative electrode-free sodium metal battery can be improved. In certain embodiments, carbon nanotubes can be modified with concentrated nitric acid. For example, the carbon nanotubes can be modified by heating in a concentrated nitric acid solution, where the concentration of the concentrated nitric acid solution can be 4 mol/L to 8 mol/L, and the heating temperature can be 60°C to 100°C. During the modification process, the concentrated nitric acid solution can be stirred, for example, magnetic stirring can be used. The time of magnetic stirring can be 1h~4h. In some embodiments, for example, the carbon nanotubes can be modified under the conditions of a concentrated sulfuric acid concentration of 5 mol/L to 7 mol/L and a heating temperature of 70°C to 90°C.

In some embodiments, cobalt salts, nickel salts, and terephthalic acid are used as raw materials to form MOFs. MOF is Co-Ni metal organic framework. Using terephthalic acid as one of the raw materials to form MOF can make MOF form a lamellar interlaced structure. The lamellar structure can make MOF have a higher specific surface area. When combined with carbon nanotubes as a conductive network, it can effectively induce sodium The uniform deposition of ions improves the energy density of sodium metal batteries and extends the cycle life of sodium metal batteries.

In some embodiments, the molar ratio of cobalt salt, nickel salt and terephthalic acid may be (0～1):(0～1):1. Of course, 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): A combination of 1 or above. Preferably, the molar ratio of cobalt salt, nickel salt and terephthalic acid may be 1:1:1. Under the above preferred ratio, MOF particles grow more uniformly, have higher porosity, and larger specific surface area, which is more conducive to uniform deposition of sodium metal.

In some embodiments, the mass ratio of the sum of the masses of cobalt salt, nickel salt and terephthalic acid to the carbon nanotubes may be 100: (1-30). Regarding the quality of carbon nanotubes used, if the amount of carbon nanotubes used is lower than the lower limit of the above setting range, the conductive properties of the electrode material after MOF and carbon nanotubes are composited will be poor; if the amount of carbon nanotubes used is higher than At the upper limit of the above setting range, the surface of the MOF material will be covered by carbon nanotubes, which will affect the deposition and dissolution of sodium on the MOF material, thereby affecting the electrochemical performance of the electrode material. For example, the mass ratio of the sum of the masses of cobalt salt, nickel salt and terephthalic acid to the carbon nanotube can be 100:(2~28), 100:(15~23), 100:(5~20) or more combination of ranges.

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

In some embodiments, the above solvent may be N,N-dimethylformamide, N-methylpyrrolidone, or acetone.

In some embodiments, the MOF/carbon nanotube anode-free sodium metal battery electrode material is a composite material formed by using interwoven carbon nanotubes as a skeleton and MOF dispersed in the skeleton. As shown in Figure 2, carbon nanotubes are intertwined as the basic skeleton of the electrode material and play the role of a supporting network. In addition to stabilizing the structure of the electrode material, it can also enhance the conductivity of the electrode material. MOF is dispersed in the skeleton formed by carbon nanotubes and grows using carbon nanotubes as the base. Carbon nanotubes are grown with MOF to construct an electrode material that can uniformly deposit sodium ions, which reduces the formation of dead sodium, improves the cycle life of the battery, and effectively alleviates the consumption of active sodium during cycling in sodium metal batteries without negative electrodes. Due to the problem of short lifespan, the prepared materials have high stability and high electrochemical properties. MOF is a porous structure formed by interlaced sheet materials. MOF can be a spherical-like structure. The porous structure formed by the interlacing of sheet materials enables the MOF to have a large specific surface area, which is suitable for the deposition of sodium ions on the surface as sodium metal. The large specific surface area of MOF modifies the current collector, providing a place for the deposition of sodium ions, and can exert the affinity of the central atoms of the MOF for sodium ions to induce uniform deposition of sodium ions.

In some embodiments, the carbon nanotubes can be multi-walled carbon nanotubes. Multi-walled carbon nanotubes can effectively conduct electrons, and the interlayer gaps of multi-walled carbon nanotubes can achieve rapid sodium ion transport and capture charge and discharge products in the electrode during cycling.

In some embodiments, heating the precursor solution to the end of the reaction may include placing the precursor solution in a reaction kettle, raising the temperature to 120°C to 200°C at a heating rate of 1°C/min to 10°C/min, and then Incubate at 120°C to 200°C for 5h to 8h until the reaction is completed. For example, the reaction kettle can be heated to 150°C to 180°C at a heating rate of 3°C/min to 7°C/min, and then kept at 150°C to 180°C for 6h to 7h until the reaction is completed. For another example, the reaction kettle can be heated to 140°C to 160°C at a heating rate of 4°C/min to 6°C/min, and then kept at 140°C to 160°C for 5.5h to 7.5h until the reaction is completed.

In some embodiments, the modified carbon nanotubes, cobalt salt, nickel salt, terephthalic acid and solvent may be mixed and magnetically stirred to obtain a precursor solution. The rotation speed of magnetic stirring can be 100r/min ~ 300r/min. For example, the rotation speed of magnetic stirring can be 200 r/min.

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

In some embodiments, drying may be air drying. The blast drying time can be 1h~24h, and the drying temperature can be 40℃~80℃. For example, the blast drying time can be 3h to 20h, and the drying temperature can be 50°C to 70°C.

Another aspect of the present invention provides a 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 intertwined carbon nanotubes as a skeleton and MOF dispersed in the skeleton. Among them, MOF is a spherical-like porous structure formed by interlaced sheet structures. The MWCNT in the electrode material of the present invention can effectively conduct electrons, and its layer gap can realize rapid ion transmission, and can capture charge and discharge products in the electrode during circulation; the sodium-philic property of the metal atoms in the MOF can control the uniform deposition of sodium ions. Good dispersion can become a sodium ion storage unit. Negative-free sodium metal battery electrode materials have the advantages of stable structure, excellent electrochemical performance, and uniform nucleation, which can increase the energy density of sodium metal batteries without sacrificing their cycle performance and extending their service life.

Another aspect of the present invention provides a method for preparing composite electrode sheets for sodium metal batteries without negative electrodes, which may include the following steps:

S01, mix the MOF/carbon nanotube-free sodium metal battery electrode material with a binder and solvent to obtain a slurry;

S02, apply the slurry on the negative electrode current collector and dry it to obtain a composite electrode sheet.

In some embodiments, the adhesive may be polyvinylidene fluoride, polytetrafluoroethylene emulsion, styrene-butadiene emulsion, sodium carboxymethylcellulose, or the like. The mass ratio of MOF/carbon nanotube anode-free sodium metal battery electrode material and binder can be adjusted according to the actual battery setting requirements. For example, the mass ratio of MOF/carbon nanotube-free sodium metal battery electrode material to binder can be 9:1, 8:2 or 7:3.

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

In some embodiments, the negative electrode current collector may be an existing negative electrode current collector such as aluminum foil or copper foil.

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

In some embodiments, the slurry coated on the negative electrode current collector can be dried in a vacuum oven. For example, drying can be done at a temperature of 50°C to 120°C for 6 to 24 hours.

Another aspect of the present invention provides a composite sodium metal battery, including a positive electrode, a negative electrode, a separator and an electrolyte. The negative electrode is a composite electrode sheet prepared by the composite electrode sheet preparation method for a negative electrode-free sodium metal battery described above. Here, it is required It should be noted that the "negative electrode" here is the nominal negative electrode, that is, the composite electrode sheet without active materials prepared in the present invention is used as the negative electrode current collector, and the negative electrode current collector is the nominal "negative electrode". The positive electrode and the negative electrode are located on both sides of the separator, and the electrolyte is located between the positive electrode and the negative electrode. The positive electrode may be a sodium metal sheet. The diameter of the sodium metal sheet can be 16mm, and the thickness can be 0.2mm~0.4mm. Of course, the diameter and thickness of the cathode material of the present invention are not limited to this and can be adjusted according to the actual needs of the battery.

In some embodiments, the electrolyte may be a sodium hexafluorophosphide/sodium tetrafluoroboride/diglyme solution. The separator can be a polyethylene oxide (PEO) composite solid electrolyte with a thickness of 0.05mm. 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.

In order to better understand the present invention, the content of the present invention is further clarified below with reference to specific examples, but the content of the present invention is not limited only to the following examples.

Example 1

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

Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid with a molar ratio of 1:1:1 into the beaker, add 1wt% modified MWCNT and 120ml of N,N-dimethylmethane. Amide solvent, stir magnetically for 3 hours at a stirring rate of 300 r/min, and uniformly mix to obtain a precursor solution.

Step 3: Add the precursor solution into the solvothermal reaction kettle, raise the temperature to 180°C at a heating rate of 3°C/min, then keep it warm for 8 hours, cool it to room temperature with the muffle furnace, and then use ethanol as a detergent at a rotation speed of 5000r /min for 3 minutes, take it out and put it into a blast drying oven, and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

Mix the MOF/carbon nanotube-free sodium metal battery electrode material and polyvinylidene fluoride at a mass ratio of 9:1, add 1-methyl-2-pyrrolidone solvent and grind for 20 minutes, then apply it on aluminum foil and vacuum at 120°C. After drying, cut into pieces to prepare negative electrode sheets. A composite button battery is assembled using a metal sodium sheet as the positive electrode, 0.1M NaBF4 and 0.9M NaPF ₆ dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte as the separator.

The X-ray diffraction (XRD) pattern of the composite electrode material obtained in this example is shown in Figure 1. The XRD diffraction peaks correspond to the characteristic peaks, and after compounding the MWCNT, only the diffraction peaks are superimposed and no impurity peaks appear. Figures 2 and 3 are scanning electron microscope (SEM) images of the composite electrode material obtained in this embodiment. It can be seen from the figures that the MOF and MWCNT are well combined, and the MWCNT are connected in a cross-linked manner to form a memory unit. With the support function of the skeleton, the MOF is well dispersed in the material, which can induce the uniform deposition of sodium ions and extend the service life of the battery. Moreover, it can be seen from Figures 2 and 3 that the metal organic framework is composed of a spherical structure with a diameter of several microns, which is composed of a lamellar structure. This structure has a large specific surface area and is suitable for the deposition of sodium ions on the surface as sodium metal.

Example 2

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

Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid with a molar ratio of 1:1:1 into the beaker, add 30wt% modified MWCNT and 120ml of N,N-dimethylmethane. Amide solvent, stir magnetically for 3 hours at a stirring rate of 300 r/min, and uniformly mix to obtain a precursor solution.

Step 3: Add the precursor solution into the solvothermal reaction kettle, raise the temperature to 180°C at a heating rate of 3°C/min, then keep it warm for 8 hours, cool it to room temperature with the muffle furnace, and then use ethanol as a detergent at a rotation speed of 5000r /min for 3 minutes, take it out and put it into a blast drying oven, and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

Mix the MOF/carbon nanotube-free sodium metal battery electrode material and polyvinylidene fluoride at a mass ratio of 9:1, add 1-methyl-2-pyrrolidone solvent and grind for 20 minutes, then apply it on aluminum foil and vacuum at 120°C. After drying, cut into pieces to prepare negative electrode sheets. A composite button battery is assembled using a metal sodium sheet as the positive electrode, 0.1M NaBF ₄ and 0.9M NaPF ₆ dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte as the separator.

The cycle performance of the battery assembled from the composite electrode material obtained in this example at 110mA/g in the voltage range of 0V to 2.5V is shown in Figure 4. The first discharge specific capacity is 95mAh/g, and the Coulombic efficiency after 500 cycles is close to 100%.

Example 3

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

Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid with a molar ratio of 1:1:1 into the beaker, add 10wt% modified MWCNT and 120ml of N,N-dimethylmethane. Amide solvent, stir magnetically for 3 hours at a stirring rate of 300 r/min, and uniformly mix to obtain a precursor solution.

Step 3: Add the precursor solution into the solvothermal reaction kettle, raise the temperature to 180°C at a heating rate of 3°C/min, then keep it warm for 8 hours, cool it to room temperature with the muffle furnace, and then use ethanol as a detergent at a rotation speed of 5000r /min for 3 minutes, take it out and put it into a blast drying oven, and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

Mix the MOF/carbon nanotube-free sodium metal battery electrode material and polyvinylidene fluoride at a mass ratio of 9:1, add 1-methyl-2-pyrrolidone solvent and grind for 20 minutes, then apply it on aluminum foil and vacuum at 120°C. After drying, cut into pieces to prepare negative electrode sheets. A composite button battery is assembled using a metal sodium sheet as the positive electrode, 0.1M NaBF ₄ and 0.9M NaPF ₆ dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte as the separator.

The battery assembled with the composite electrode material obtained in this embodiment has a current density of 500mA/g, 1000mA/g, 1500mA/g, 2000mA/g, 2500mA/g, 3000mA/g, 3500mA/g in the voltage range of 0V to 2.5V. The cycle performance at g and 4000mA/g current density is shown in Figure 5. The capacity retention rate is still very good when the current density reaches 4000mA/g.

Example 4

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

Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid with a molar ratio of 1:1:1 into the beaker, add 15wt% modified MWCNT and 120ml of N,N-dimethylmethane. Amide solvent, stir magnetically for 3 hours at a stirring rate of 300 r/min, and uniformly mix to obtain a precursor solution.

Step 3: Add the precursor solution into the solvothermal reaction kettle, raise the temperature to 180°C at a heating rate of 3°C/min, then keep it warm for 8 hours, cool it to room temperature with the muffle furnace, and then use ethanol as a detergent at a rotation speed of 5000r /min for 3 minutes, take it out and put it into a blast drying oven, and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

Mix the MOF/carbon nanotube-free sodium metal battery electrode material and polyvinylidene fluoride at a mass ratio of 9:1, add 1-methyl-2-pyrrolidone solvent and grind for 20 minutes, then apply it on aluminum foil and vacuum at 120°C. After drying, cut into pieces to prepare negative electrode sheets. A composite button battery is assembled using a metal sodium sheet as the positive electrode, 0.1M NaBF ₄ and 0.9M NaPF ₆ dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte as the separator.

The battery assembled with the composite electrode material obtained in this example is cycled 5 times at a current density of 4000mA/g in the voltage range of 0V to 2.5V, and then changed to a small current density of 500mA/g, as shown in Figure 6. Cycling the negative electrode side with high current density first can nucleate sodium ions uniformly and generate a thin SEI to ensure the cycle stability of sodium-ion batteries. Figure 6 shows that the discharge specific capacity of the battery assembled from the composite electrode material obtained in this example decreases slowly, the capacity retention rate is high, and the battery has good electrochemical performance.

Example 5

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

Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid with a molar ratio of 1:1:1 into the beaker, add 20wt% modified MWCNT and 120ml of N,N-dimethylmethane. Amide solvent, stir magnetically for 3 hours at a stirring rate of 300 r/min, and uniformly mix to obtain a precursor solution.

Step 3: Add the precursor solution into the solvothermal reaction kettle, raise the temperature to 180°C at a heating rate of 3°C/min, then keep it warm for 8 hours, cool it to room temperature with the muffle furnace, and then use ethanol as a detergent at a rotation speed of 5000r /min for 3 minutes, take it out and put it into a blast drying oven, and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

Mix the MOF/carbon nanotube-free sodium metal battery electrode material and polyvinylidene fluoride at a mass ratio of 9:1, add 1-methyl-2-pyrrolidone solvent and grind for 20 minutes, then apply it on aluminum foil and vacuum at 120°C. After drying, cut into pieces to prepare negative electrode sheets. A composite button battery is assembled using a metal sodium sheet as the positive electrode, 0.1M NaBF ₄ and 0.9M NaPF ₆ dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte as the separator.

The AC impedance test of the battery assembled from the composite electrode material obtained in this example is shown in Figure 7. It can be seen that there is a low impedance between the electrolyte material and the electrode material, indicating that the composite electrode material has excellent interfacial dynamics.

Example 6

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

Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid with a molar ratio of 0.5:0.5:1 into the beaker, add 25wt% modified MWCNT and 120ml of N,N-dimethylmethane. Amide solvent, stir magnetically for 3 hours at a stirring rate of 300 r/min, and uniformly mix to obtain a precursor solution.

Step 3: Add the precursor solution to the solvothermal reaction kettle, raise the temperature to 185°C at a heating rate of 3°C/min, then keep it warm for 8 hours, cool it to room temperature with the muffle furnace, and then use ethanol as a detergent at a rotation speed of 5000r /min for 4 minutes, take it out and put it into a blast drying oven, and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

Mix the MOF/carbon nanotube-free sodium metal battery electrode material and polyvinylidene fluoride at a mass ratio of 9:1, add 1-methyl-2-pyrrolidone solvent and grind for 20 minutes, then apply it on aluminum foil and vacuum at 120°C. After drying, cut into pieces to prepare negative electrode sheets. A composite button battery is assembled using a metal sodium sheet as the positive electrode, 0.1M NaBF ₄ and 0.9M NaPF ₆ dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte as the separator.

The battery assembled with the composite electrode material obtained in this embodiment has stable electrochemical performance and long cycle life in the voltage range of 0V to 2.5V.

Example 7

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

Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid with a molar ratio of 0.2:0.6:1 into the beaker, add 5wt% modified MWCNT and 120ml of N,N-dimethylmethane. Amide solvent, stir magnetically for 3 hours at a stirring rate of 300 r/min, and uniformly mix to obtain a precursor solution.

Step 3: Add the precursor solution to the solvothermal reaction kettle, raise the temperature to 190°C at a heating rate of 3°C/min, then keep it warm for 8 hours, cool it to room temperature with the muffle furnace, and then use ethanol as a detergent at a rotation speed of 5000r /min for 5 minutes, take it out and put it into a blast drying oven, and dry it at 80°C for 5 hours to obtain a powder, which is the target product MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

Mix the MOF/carbon nanotube-free sodium metal battery electrode material and polyvinylidene fluoride at a mass ratio of 9:1, add 1-methyl-2-pyrrolidone solvent and grind for 20 minutes, then apply it on aluminum foil and vacuum at 120°C. After drying, cut into pieces to prepare negative electrode sheets. A composite button battery is assembled using a metal sodium sheet as the positive electrode, 0.1M NaBF ₄ and 0.9M NaPF ₆ dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte as the separator.

The battery assembled with the composite electrode material obtained in this embodiment has stable electrochemical performance and long cycle life in the voltage range of 0V to 2.5V.

Example 8

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

Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid with a molar ratio of 0.8:0.3:1 into the beaker, add 10wt% modified MWCNT and 120ml of N,N-dimethylmethane. Amide solvent, stir magnetically for 3 hours at a stirring rate of 300 r/min, and uniformly mix to obtain a precursor solution.

Step 3: Add the precursor solution to the solvothermal reaction kettle, raise the temperature to 195°C at a heating rate of 3°C/min, then keep it warm for 8 hours, cool it to room temperature with the muffle furnace, and then use ethanol as a detergent at a rotation speed of 5000r /min for 6 minutes, take it out and put it into a blast drying oven, and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

Mix the MOF/carbon nanotube-free sodium metal battery electrode material and polyvinylidene fluoride at a mass ratio of 9:1, add 1-methyl-2-pyrrolidone solvent and grind for 20 minutes, then apply it on aluminum foil and vacuum at 120°C. After drying, cut into pieces to prepare negative electrode sheets. A composite button battery is assembled using a metal sodium sheet as the positive electrode, 0.1M NaBF ₄ and 0.9M NaPF ₆ dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte as the separator.

The battery assembled with the composite electrode material obtained in this embodiment has stable electrochemical performance and long cycle life in the voltage range of 0V to 2.5V.

Example 9

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

Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid with a molar ratio of 0.7:0.6:1 into the beaker, add 20wt% modified MWCNT and 120ml of N,N-dimethylmethane. Amide solvent, stir magnetically for 3 hours at a stirring rate of 300 r/min, and uniformly mix to obtain a precursor solution.

Step 3: Add the precursor solution to the solvothermal reaction kettle, raise the temperature to 200°C at a heating rate of 5°C/min, then keep it warm for 8 hours, cool it to room temperature with the muffle furnace, and then use ethanol as a detergent at a rotation speed of 5000r /min for 7 minutes, take it out and put it into a blast drying oven, and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

Mix the MOF/carbon nanotube-free sodium metal battery electrode material and polyvinylidene fluoride at a mass ratio of 9:1, add 1-methyl-2-pyrrolidone solvent and grind for 20 minutes, then apply it on aluminum foil and vacuum at 120°C. After drying, cut into pieces to prepare negative electrode sheets. A composite button battery is assembled using a metal sodium sheet as the positive electrode, 0.1M NaBF ₄ and 0.9M NaPF ₆ dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte as the separator.

The battery assembled with the composite electrode material obtained in this embodiment has stable electrochemical performance and long cycle life in the voltage range of 0V to 2.5V.

Example 10

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

Step 2: Add cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid with a molar ratio of 1:1:1 into the beaker, add 30wt% modified MWCNT and 120ml of N,N-dimethylmethane. Amide solvent, stir magnetically for 3 hours at a stirring rate of 300 r/min, and uniformly mix to obtain a precursor solution.

Step 3: Add the precursor solution to the solvothermal reaction kettle, raise the temperature to 180°C at a heating rate of 10°C/min, then keep it warm for 8 hours, cool it to room temperature with the muffle furnace, and then use ethanol as a detergent at a rotation speed of 5000r /min for 8 minutes, take it out and put it into a blast drying oven, and dry it at 80°C for 5 hours to obtain the powder, which is the target product MOF/carbon nanotube-free negative electrode sodium metal battery electrode material.

Mix the MOF/carbon nanotube-free sodium metal battery electrode material and polyvinylidene fluoride at a mass ratio of 9:1, add 1-methyl-2-pyrrolidone solvent and grind for 20 minutes, then apply it on aluminum foil and vacuum at 120°C. After drying, cut into pieces to prepare negative electrode sheets. A composite button battery is assembled using a metal sodium sheet as the positive electrode, 0.1M NaBF ₄ and 0.9M NaPF ₆ dissolved in ethylene glycol dimethyl ether as the electrolyte, and a polyethylene oxide (PEO) composite solid electrolyte as the separator.

The battery assembled with the composite electrode material obtained in this embodiment has stable electrochemical performance and long cycle life in the voltage range of 0V to 2.5V.

Comparative example 1

Compared with Example 2, the difference between this Comparative Example 1 and Example 2 is that the mass proportion of the modified MWCNT is 35% of the sum of the mass of cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid. The other preparation methods are the same. The cycle performance of the battery assembled from the composite electrode material obtained in Comparative Example 1 is in the voltage range of 0V to 2.5V and the current density is 110mA/g, as shown in Figure 8. The first cycle discharge specific capacity is 102mAh/g, and then The capacity begins to decrease and stabilizes after 50 cycles. After 500 cycles, the capacity is close to 70mAh/g. The discharge of the surface battery decreases faster than the capacity, and the capacity retention rate is low. The reason is that if too much carbon nanotubes are added, part of the surface of the MOF material will be covered by carbon nanotubes, thereby reducing the deposition of sodium ions on the MOF material and causing greater side reactions. Therefore, the mass proportion of MWCNT is set to less than 30% of the sum of the mass of cobalt nitrate hexahydrate, nickel nitrate hexahydrate and terephthalic acid.

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

Claims (10)

1. A method for preparing MOF/carbon nanotube anode-free sodium metal battery electrode material, which is characterized by comprising the following steps: Modification of carbon nanotubes; Mix the modified carbon nanotubes, cobalt salt, nickel salt, terephthalic acid and solvent to obtain a precursor solution; The precursor solution is heated to the end of the reaction, centrifuged, washed and dried to obtain a MOF/carbon nanotube-free negative electrode sodium metal battery electrode material. 2. The preparation method of MOF/carbon nanotube-free sodium metal battery electrode material according to claim 1, characterized in that the MOF/carbon nanotube-free sodium metal battery electrode material is based on interwoven carbon nanotubes as a skeleton, A composite material formed by MOF dispersed in the skeleton. The MOF is a spherical-like porous structure formed by interlaced lamellar structures. 3. The MOF/carbon nanotube-free sodium metal battery electrode material preparation method according to claim 1 or 2, characterized in that the molar ratio of cobalt salt, nickel salt and terephthalic acid is (0~1): (0～1):1. 4. The MOF/carbon nanotube-free sodium metal battery electrode material preparation method according to claim 3, characterized in that the mass ratio of the sum of the masses of cobalt salt, nickel salt and terephthalic acid to the carbon nanotube is 100:(1～30). 5. The MOF/carbon nanotube-free sodium metal battery electrode material preparation method according to claim 1, 2 or 4, characterized in that heating the precursor solution to the end of the reaction includes placing the precursor solution in a reaction kettle , after heating to 120°C to 200°C at a heating rate of 1°C/min to 10°C/min, then keep it at 120°C to 200°C for 5h to 8h until the reaction is completed. 6. The preparation method of MOF/carbon nanotube-free sodium metal battery electrode material according to claim 1, 2 or 4, characterized in that modifying the carbon nanotubes includes placing the carbon nanotubes in a concentrated nitric acid solution. Modification is carried out by heating, wherein the concentration of the concentrated nitric acid solution is 4 mol/L to 8 mol/L, and the heating temperature is 60°C to 100°C. 7. A MOF/carbon nanotube-free sodium metal battery electrode material prepared by the MOF/carbon nanotube-free sodium metal battery electrode material preparation method according to any one of claims 1 to 6, characterized in that , MOF/carbon nanotube anode-free sodium metal battery electrode material is a composite material formed by intertwined carbon nanotubes as a skeleton and MOF dispersed in the skeleton. Among them, MOF is a spherical-like porous structure formed by interlaced sheet structures. 8. A method for preparing composite electrode sheets for sodium metal batteries without negative electrodes, which is characterized by comprising the following steps: The MOF/carbon nanotube anode-free sodium metal battery electrode material prepared by the preparation method of any one of claims 1 to 6 or the MOF of claim 7 /Carbon nanotube-free sodium metal battery electrode material is mixed with a binder and solvent to obtain a slurry; The slurry is coated on the negative electrode current collector and dried to obtain a composite electrode sheet. 9. The method for preparing composite electrode sheets for negative electrode-free sodium metal batteries according to claim 8, characterized in that the thickness of the slurry coated on the negative electrode current collector is 0.001 mm to 0.02 mm. 10. A composite sodium metal battery, including a positive electrode, a negative electrode, a separator and an electrolyte, characterized in that the negative electrode is a composite electrode sheet prepared by the composite electrode sheet preparation method for a negative electrode-free sodium metal battery according to claim 8 or 9.