Preparation method for carbon nanotube-sodiophilic metal anode-free sodium metal battery electrode material and use thereof

Abstract

A preparation method for a carbon nanotube-sodiophilic metal anode-free sodium metal battery electrode material. The preparation method comprises the following steps: modifying the carbon nanotubes by using a dielectric barrier plasma device; mixing and stirring the modified carbon nanotubes with a sodiophilic metal salt to obtain a precursor slurry; and drying the precursor slurry, placing the precursor slurry into a tubular furnace after the drying, and heating same for reaction by introducing a reducing gas to obtain a carbon nanotube-sodiophilic metal anode-free sodium metal battery electrode material. The prepared electrode material has a stable structure, excellent conductivity, and excellent sodiophilicity, and can be applied to anode-free sodium metal battery electrode materials. The entire preparation process is controllable, with a short synthesis cycle and simple operation.

Description

A method for preparing carbon nanotube-sodium-philic metal anode-free sodium metal battery electrode material and its application Technical Field

[0001] This invention relates to the field of sodium metal batteries, specifically to a method for preparing a carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material and its application. Background Technology

[0002] In an era of decarbonized energy, electrified transportation, and intelligent equipment, developing renewable energy not only provides a sustainable energy security for humanity but also mitigates problems such as climate change and environmental pollution. Sodium metal, due to its high theoretical capacity, abundant reserves, and low cost, is considered the most likely anode material to replace lithium metal. However, the energy density of sodium-ion batteries is typically less than 150 Wh / kg. -1 It is only half the energy density of similar lithium-ion batteries. Using sodium as the metal anode is the most promising method to improve the energy density of sodium-ion batteries because it has a very high theoretical capacity (1166 mAh g⁻¹). –1 ) and low redox potential (–2.71 V vs standard hydrogen electrode).

[0003] However, sodium metal's high reactivity, soft texture, and viscosity make the processing of ultra-thin sodium metal anodes difficult. Currently, excessively thick sodium metal is often used as the anode, significantly reducing the actual energy density of the battery. "Anode-free" sodium metal batteries (AFSMB) offer advantages such as high energy density, low cost, and high safety, making them one of the most promising next-generation high-energy-density battery systems. However, the sodium source is limited to the cathode material, and irreversible loss of active sodium, unstable solid electrolyte interface phases, and short cycle life severely hinder its development.

[0004] 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 a sodium metal battery electrode material without a negative electrode that has a long cycle life and high energy density.

[0006] On one hand, the present invention provides a method for preparing a carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material, comprising the following steps:

[0007] Step 1: Modify carbon nanotubes using a dielectric barrier plasma device;

[0008] Step 2: The modified carbon nanotubes are mixed and stirred with a sodium-loving metal salt to obtain a precursor slurry.

[0009] Step 3: The precursor slurry is dried. After drying, it is placed in a tube furnace and heated by a reducing gas to obtain carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material.

[0010] Furthermore, the carbon nanotube-sodium-affinic metal anode-free sodium metal battery electrode material has a porous three-dimensional structure, which includes a framework formed by the interwoven carbon nanotubes and a sodium-affinic metal salt uniformly attached to the framework.

[0011] Further, in step one, the modification treatment of the carbon nanotubes includes placing the carbon nanotubes in a dielectric barrier plasma discharge device mold and activating them with an inert gas; the inert gas is one or more combinations of argon, nitrogen, and argon-hydrogen mixture.

[0012] Further, in step two, magnetic stirring is used to obtain the precursor slurry; the magnetic stirring speed is 100 r / min to 300 r / min, and the stirring time is 1 h to 5 h; in step three, the drying treatment is vacuum drying, the vacuum drying time is 10 h to 24 h, and the drying temperature is 40 °C to 80 °C.

[0013] Furthermore, in step three, the heating temperature of the heating reaction is increased to 200℃ to 500℃ at a heating rate of 1℃ / min to 10℃ / min, and then kept at 200℃ to 500℃ for 30min to 5h until the reaction is completed.

[0014] Furthermore, the sodium-loving metal salt is one or more of ferric chloride, tin chloride, silver nitrate, magnesium acetate, etc.; the mass ratio of the sodium-loving metal salt to the carbon nanotube is (0-10):1.

[0015] Secondly, the present invention also provides a carbon nanotube-sodium-affinic metal anode-free sodium metal battery electrode material, wherein the carbon nanotube-sodium-affinic metal anode-free sodium metal battery electrode material is prepared by the carbon nanotube-sodium-affinic metal anode-free sodium metal battery electrode material preparation method described above.

[0016] Thirdly, the present invention also provides a method for preparing a composite electrode sheet for a negative electrode-free sodium metal battery, comprising the following steps:

[0017] A slurry is prepared by mixing carbon nanotube-sodium-acid-metal anode-free sodium metal battery electrode material with a binder and a solvent; the slurry is coated onto a negative electrode current collector and dried to obtain a composite electrode sheet; the carbon nanotube-sodium-acid-metal anode-free sodium metal battery electrode material is prepared by the carbon nanotube-sodium-acid-metal anode-free sodium metal battery electrode material preparation method described above, or the carbon nanotube-sodium-acid-metal anode-free sodium metal battery electrode material described above.

[0018] Furthermore, the coating thickness of the slurry on the negative electrode current collector is 0.001 mm to 0.05 mm.

[0019] Fourthly, the present invention also 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 aforementioned method for preparing a composite electrode sheet for a negative electrodeless sodium metal battery.

[0020] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0021] (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 whole preparation process is controllable and the synthesis cycle is short and the operation is simple.

[0022] (2) After the metal salt used in this invention is reduced to metal, the Fe atom metal has an affinity for sodium ions, which induces the deposition and dissolution of sodium during the charging and discharging process of the battery, improves the conductivity of the electrode and the ion transport rate, thereby improving the cycle stability and service life of the battery.

[0023] (3) The electrode material of the present invention has good chemical stability and electrochemical performance, excellent air stability, and high safety.

[0024] (4) The electrode material of the present invention uses MWCNT (multi-walled carbon nanotubes) as a conductive network, which has a high specific surface area, can make the electric field distribution uniform, delay dendrite growth, and is lightweight, which can improve the energy density of sodium metal batteries and extend their cycle life. Attached Figure Description

[0025] 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:

[0026] Figure 1 is a flowchart of the preparation method of carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material of the present invention.

[0027] Figure 2 is the X-ray diffraction (XRD) pattern of the carbon nanotube-iron-anode-free sodium metal battery electrode material obtained in Example 1 of the present invention.

[0028] Figure 3 is a voltage distribution diagram of sodium galvanization at constant current (Na / separator / negative electrode) for a carbon nanotube-iron non-anode sodium metal battery electrode material obtained in Example 1 of the present invention.

[0029] Figure 4 is the first charge-discharge curve of the carbon nanotube-iron non-anode sodium metal battery electrode material (sodium vanadium phosphate / separator / anode) obtained in Example 1 of the present invention.

[0030] Figure 5 is a half-cell (Na / separator / negative electrode) cycling diagram of the carbon nanotube-iron non-anode sodium metal battery electrode material obtained in Example 2 of the present invention.

[0031] Figure 6 is a cycle diagram of the carbon nanotube-iron non-anode sodium metal battery electrode material half-cell (NVP / separator / anode) obtained in Example 3 of the present invention.

[0032] Figure 7 is a rate capability diagram of the half-cell (NVP / separator / negative electrode) of the carbon nanotube-iron non-anode sodium metal battery electrode material obtained in Example 4 of the present invention.

[0033] Figure 8 shows the electrochemical impedance spectroscopy (EIS) of the carbon nanotube-iron-anode-free sodium metal battery electrode material obtained in Example 5 of the present invention.

[0034] Figure 9 is a voltage distribution diagram of sodium galvanization at constant current (Na / separator / negative electrode) obtained by the carbon nanotube anode-free sodium metal battery electrode material of Comparative Example 1 of the present invention.

[0035] Figure 10 is a cycle diagram (NVP / separator / negative electrode) of the carbon nanotube-iron non-anode sodium metal battery electrode material obtained in Comparative Example 2 of the present invention. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. Unless otherwise specified, the experimental methods described in the following embodiments are all routine operations, and the reagents used are commercially available.

[0037] In the following, a carbon nanotube-sodium-loving metal 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.

[0038] One aspect of the present invention provides a method for preparing a carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material, as shown in Figure 1, which specifically includes the following steps:

[0039] S1, carbon nanotubes are modified using a dielectric barrier plasma device;

[0040] S2, the modified carbon nanotubes are mixed and stirred with a sodium-loving metal salt to obtain a precursor slurry; specifically, the modified carbon nanotubes, sodium-loving metal salt and solvent are stirred and mixed to obtain a precursor slurry.

[0041] S3, the precursor slurry is dried, and after drying, it is placed in a tube furnace and heated by a reducing gas to obtain carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material.

[0042] In some embodiments, the modification of carbon nanotubes (CNTs) using a dielectric barrier plasma device is intended to provide nucleation sites for sodium-loving metal salts. After the modified CNTs are mixed with the sodium-loving metal salt, the modification treatment provides active sites for the reduction metal nucleation, allowing the metal to better recombine with the CNTs, enhancing the affinity of the electrode material for sodium ions, and improving the electrochemical performance of the anode-free sodium metal battery. In some embodiments, the modification of carbon nanotubes can be performed using argon dielectric barrier plasma. For example, the plasma device power can be 100W to 400W, and the treatment time can be 1min to 30min; that is, the plasma device power can be 100W, 150W, 200W, 250W, 300W, 350W, or 400W, and the treatment time can be 1min, 2min, 5min, 8min, 10min, 15min, 20min, 25min, or 30min, as long as it is within the aforementioned range. Preferably, the plasma device power can be 300W, and the treatment time can be 5min.

[0043] In some implementations, the sodium affinity of metals, when combined with carbon nanotubes as a conductive network, can effectively induce uniform deposition of sodium ions, thereby increasing the energy density of sodium metal batteries and extending their cycle life.

[0044] In some embodiments, the mass ratio of sodium-loving metal salt to CNTs can be (0–10) g:1 g. The value of the sodium-loving metal salt in the above mass ratio can be 0, or it can be 0.2, 0.5, 0.8, 1, 1.5, 2, 3, 5, 7, 9, or 10, as long as it is within the aforementioned range. For example, the mass ratio of sodium-loving metal salt to CNTs can be (0–9):1, (2–7):1, (4–6):1, or a combination of these ranges. Preferably, the mass ratio of sodium-loving metal salt to CNTs can be 3:1. Under the above preferred ratios, the sodium-loving metal is more uniformly distributed, the porosity is high, the specific surface area is large, dealloying is easier, and it is more conducive to the uniform deposition of sodium metal.

[0045] In some implementations, the sodium-loving metal salt can be one or more combinations of ferric chloride, tin chloride, silver nitrate, magnesium acetate, etc.

[0046] In some implementations, the above adhesive may be polyvinylidene fluoride, polyacrylic acid, or polytetrafluoroethylene.

[0047] In some implementations, a porous three-dimensional structure is formed by interwoven carbon nanotubes as a framework, with a sodium-loving metal uniformly attached to the carbon nanotube walls. The interwoven carbon nanotubes serve as the basic framework of the electrode material, acting as a supporting network. Besides stabilizing the electrode material's structure, this also reduces the local current density. The sodium-loving metal attached to the carbon nanotube walls creates an electrode material where sodium ions can be uniformly deposited, delaying dendrite formation, improving the battery's cycle life, and effectively alleviating the problem of low coulombic efficiency during cycling in anode-less sodium metal batteries. The prepared material exhibits high stability and high electrochemical performance. The uniform current density distribution, temperature field distribution, and stress field distribution of carbon nanotubes further enhance their suitability for anode-less sodium metal battery systems.

[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, which can improve the reaction kinetics of the electrode material during cycling.

[0049] In some embodiments, heating the precursor material with a reducing gas until the reaction is complete may include placing the precursor material in a vacuum tube furnace, heating it to 200°C to 500°C at a heating rate of 1°C / min to 10°C / min, and then holding it at 200°C to 500°C for 30 min to 2 h until the reaction is complete; that is, the heating rate can be 1°C / min, 2°C / min, 4°C / min, 5°C / min, 8°C / min, or 10°C / min; the temperature can be raised to 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, or 500°C; the holding temperature can be 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, or 500°C; and the holding time can be 30 min, 35 min, 40 min, 50 min, 55 min, 1 h, 1.5 h, or 2 h; as long as it is within the aforementioned range. For example, the temperature can be increased to 220℃ to 350℃ in a tube furnace at a heating rate of 3℃ / min to 7℃ / min, and then held at 220℃ to 350℃ for 30min to 60min until the reaction is complete. Alternatively, the temperature can be increased to 280℃ to 440℃ in a tube furnace at a heating rate of 4℃ / min to 6℃ / min, and then held at 280℃ to 440℃ for 1h to 2h until the reaction is complete.

[0050] In some embodiments, the modified carbon nanotubes, sodium-loving metal salt, 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 150 r / min, and the stirring time can be 5 h.

[0051] In some implementations, drying can be vacuum drying. The vacuum drying time can be 8 hours to 24 hours, and the drying temperature can be 40°C to 80°C. For example, the vacuum drying time can be 10 hours to 15 hours, and the drying temperature can be 50°C to 70°C.

[0052] Another aspect of this invention provides a carbon nanotube-sodium-metal-based electrode material for a cathode-free sodium metal battery. This material is a composite material with an interwoven carbon nanotube framework and a sodium-metal-based material uniformly attached to the carbon nanotube walls, forming a porous three-dimensional structure. The carbon nanotubes (CNTs) are modified using a dielectric barrier plasma device. The interwoven carbon nanotubes serve as the basic framework of the electrode material, acting as a supporting network. Besides stabilizing the electrode material's structure, this also reduces the local current density. The carbon nanotubes exhibit uniform current density distribution, temperature field distribution, and stress field distribution, which is beneficial for cathode-free sodium metal battery systems. The sodium-metal-based material, attached to the carbon nanotube walls, creates an electrode material where sodium ions can be uniformly deposited, delaying dendrite formation, improving the battery's cycle life, and effectively alleviating the low coulombic efficiency problem of cathode-free sodium metal batteries during cycling. The prepared material exhibits high stability and high electrochemical performance.

[0053] 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:

[0054] Carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material is mixed with binder and solvent to obtain a slurry; the slurry is coated on the anode current collector and dried to obtain a composite electrode sheet.

[0055] In some implementations, the binder can be polyvinylidene fluoride, polyacrylic acid, or polytetrafluoroethylene, etc. The mass ratio of the carbon nanotube-sodium-metal-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 carbon nanotube-sodium-metal-anode-free sodium metal battery electrode material to the conductive agent can be 9:1, 7:3, or 9.5:0.5. After mixing the carbon nanotube-sodium-metal-anode-free sodium metal battery electrode material and the binder, they can be ground to obtain a mixture. For example, the grinding time can be 20 min to 30 min.

[0056] In some implementations, the negative electrode current collector can be an existing negative electrode current collector such as aluminum foil, copper foil, zinc foil, or iron foil.

[0057] In some embodiments, the thickness of the slurry coating on the negative electrode current collector can be 0.001 mm to 0.05 mm; specifically, the slurry coating thickness can be 0.001 mm, 0.002 mm, 0.005 mm, 0.008 mm, 0.01 mm, 0.015 mm, 0.02 mm, 0.025 mm, 0.03 mm, 0.035 mm, 0.04 mm, 0.045 mm, or 0.05 mm, as long as it is within the aforementioned range. For example, the coating thickness can be 0.009 mm to 0.045 mm, 0.007 mm to 0.012 mm, 0.01 mm to 0.018 mm, or a combination of the above ranges.

[0058] Another aspect of the present invention provides a composite negative electrode-free 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 electrode-free sodium metal battery. The positive electrode and the negative electrode are located on opposite sides of the separator. 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 0.1 mm to 0.5 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.

[0059] In some embodiments, the electrolyte can be a sodium hexafluorophosphide / sodium tetrafluoroborate / diethylene glycol dimethyl ether solution. The separator can be a polypropylene membrane. It should be understood, however, that the electrolyte and separator of the composite sodium metal battery of the present invention are not limited thereto.

[0060] 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.

[0061] Example 1

[0062] Step 1: Place MWCNT (multi-walled carbon nanotube) powder in a dielectric barrier plasma mold, introduce nitrogen gas, adjust the voltage to 150V / 200V and the current to 2A / 1.5A, and ensure that the process is carried out for 5 minutes at a power of 300W to obtain the processed MWCNT.

[0063] Step 2: Add the sodium-loving metal salts FeCl3 and MWCNT in a mass ratio of 3:1 to a beaker, add 10 ml of N-methylpyrrolidone, and stir on a magnetic stirrer for 5 hours to ensure that FeCl3 and MWCNT are fully mixed.

[0064] Step 3: Place the precursor slurry in an 80℃ vacuum drying oven and dry for 8 hours. After drying, place it in a tube furnace and heat it to 350℃ at a heating rate of 5℃ / min. Then keep it at that temperature for 3 hours and introduce reducing gas to heat until the reaction is complete. Cool it to room temperature with the tube furnace and then take it out to obtain the powder, which is the target product MWCNT-Fe anode-free sodium metal battery electrode material.

[0065] MWCNT-Fe sodium metal battery electrode material without a negative electrode was mixed with polyvinylidene fluoride at a mass ratio of 8:2, and after grinding for 20 min with 1-methyl-2-pyrrolidone solvent, it was coated onto copper foil, vacuum dried at 120℃, and then cut into sheets to prepare the negative electrode sheet. A sodium metal sheet was used as the positive electrode, 1M NaPF6 dissolved in ethylene glycol dimethyl ether was used as the electrolyte, and a polypropylene membrane (PP membrane) was used as the separator to assemble a composite coin cell.

[0066] Figure 2 shows the X-ray diffraction (XRD) pattern of the composite electrode material obtained in this embodiment. The XRD diffraction peaks correspond to the characteristic peaks, and after the composite with the sodium-loving metal Fe, only the diffraction peaks are superimposed without any impurity peaks. Figure 3 is a voltage distribution diagram of sodium plating at constant current on the carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material obtained in Example 1 of this invention (Na / separator / anode). It can be seen from the figure that the electrode material has a low nucleation overpotential, and sodium is easily deposited on the electrode surface after being composited with the sodium-loving metal. Figure 4 shows the first charge-discharge curve of the battery (NVP / separator / anode) of the composite electrode material obtained in this embodiment. It can be seen from the figure that the first discharge capacity is as high as 87.9 mAh g. -1 .

[0067] Example 2

[0068] Step 1: Place MWCNT powder in a dielectric barrier plasma mold, introduce nitrogen gas, adjust the voltage to 150V / 200V and the current to 2A / 1.5A, and ensure that the process is carried out for 5 minutes at a power of 300W to obtain the processed MWCNT.

[0069] Step 2: Add the sodium-loving metal salts FeCl3 and MWCNT in a mass ratio of 4:1 to a beaker, add 10 ml of N-methylpyrrolidone, and stir on a magnetic stirrer for 5 hours to ensure that FeCl3 and MWCNT are fully mixed.

[0070] Step 3: Place the precursor slurry in an 80℃ vacuum drying oven and dry for 8 hours. After drying, place it in a tube furnace and heat it to 350℃ at a heating rate of 5℃ / min. Then keep it at that temperature for 3 hours and introduce reducing gas to heat until the reaction is complete. Cool it to room temperature with the tube furnace and then take it out to obtain the powder, which is the target product MWCNT-Fe anode-free sodium metal battery electrode material.

[0071] MWCNT-Fe sodium metal battery electrode material without a negative electrode 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 copper foil, vacuum dried at 120℃, and then cut into sheets to prepare the negative electrode sheet. A sodium metal sheet was used as the positive electrode, 1M NaPF6 dissolved in ethylene glycol dimethyl ether was used as the electrolyte, and a polypropylene membrane (PP membrane) was used as the separator to assemble a composite coin cell.

[0072] The battery assembled with the composite electrode material obtained in this embodiment has a voltage range of 0V to 3V and a current of 3mA / cm. -2 The cycling performance at current density is shown in Figure 5, pre-tested at 0.1 mA cm⁻¹. -2 SEI is generated after 5 cycles at low current density, and the coulombic efficiency is close to 100% after 250 hours of cycling.

[0073] Example 3

[0074] Step 1: Place MWCNT powder in a dielectric barrier plasma mold, introduce nitrogen gas, adjust the voltage to 150V / 200V and the current to 2A / 1.5A, and ensure that the process is carried out for 5 minutes at a power of 300W to obtain the processed MWCNT.

[0075] Step 2: Add the sodium-loving metal salts FeCl3 and MWCNT in a mass ratio of 5:1 to a beaker, add 10 ml of N-methylpyrrolidone, and stir on a magnetic stirrer for 5 hours to ensure that FeCl3 and MWCNT are fully mixed.

[0076] Step 3: Place the precursor slurry in an 80℃ vacuum drying oven and dry for 8 hours. After drying, place it in a tube furnace and heat it to 350℃ at a heating rate of 5℃ / min. Then keep it at that temperature for 3 hours and introduce reducing gas to heat until the reaction is complete. Cool it to room temperature with the tube furnace and then take it out to obtain the powder, which is the target product MWCNT-Fe anode-free sodium metal battery electrode material.

[0077] MWCNT-Fe sodium metal battery electrode material without a negative electrode 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 copper foil, vacuum dried at 120℃, and then cut into sheets to prepare the negative electrode sheet. A sodium metal sheet was used as the positive electrode, 1M NaPF6 dissolved in ethylene glycol dimethyl ether was used as the electrolyte, and a polypropylene membrane (PP membrane) was used as the separator to assemble a composite coin cell.

[0078] The battery assembled from the composite electrode material obtained in this embodiment operates at a current density of 117.6 mAh g⁻¹ within a voltage range of 2.5V to 3.8V. -1 The cycling performance at current density is shown in Figure 6, with an initial discharge specific capacity of 85.4 mAh g⁻¹.-1 After 120 cycles, the Coulomb efficiency reached 95.4%.

[0079] Example 4

[0080] Step 1: Place MWCNT powder in a dielectric barrier plasma mold, introduce nitrogen gas, adjust the voltage to 150V / 200V and the current to 2A / 1.5A, and ensure that the process is carried out for 5 minutes at a power of 300W to obtain the processed MWCNT.

[0081] Step 2: Add the sodium-loving metal salts FeCl3 and MWCNT in a mass ratio of 6:1 to a beaker, add 10 ml of N-methylpyrrolidone, and stir on a magnetic stirrer for 5 hours to ensure that FeCl3 and MWCNT are fully mixed.

[0082] Step 3: Place the precursor slurry in an 80℃ vacuum drying oven and dry for 8 hours. After drying, place it in a tube furnace and heat it to 350℃ at a heating rate of 5℃ / min. Then keep it at that temperature for 3 hours and introduce reducing gas to heat until the reaction is complete. Cool it to room temperature with the tube furnace and then take it out to obtain the powder, which is the target product MWCNT-Fe anode-free sodium metal battery electrode material.

[0083] MWCNT-Fe sodium metal battery electrode material without a negative electrode 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 copper foil, vacuum dried at 120℃, and then cut into sheets to prepare the negative electrode sheet. A sodium metal sheet was used as the positive electrode, 1M NaPF6 dissolved in ethylene glycol dimethyl ether was used as the electrolyte, and a polypropylene membrane (PP membrane) was used as the separator to assemble a composite coin cell.

[0084] The battery assembled with the composite electrode material obtained in this embodiment exhibits cycling performance at different current densities within a voltage range of 0V to 2.5V, as shown in Figure 7. The current density reaches 352.8 mAh g. -1 At that time, the Coulomb efficiency was still above 90%.

[0085] Example 5

[0086] Step 1: Place MWCNT powder in a dielectric barrier plasma mold, introduce nitrogen gas, adjust the voltage to 150V / 200V and the current to 2A / 1.5A, and ensure that the process is carried out for 5 minutes at a power of 300W to obtain the processed MWCNT.

[0087] Step 2: Add the sodium-loving metal salts FeCl3 and MWCNT in a mass ratio of 7:1 to a beaker, add 10 ml of N-methylpyrrolidone, and stir on a magnetic stirrer for 5 hours to ensure that FeCl3 and MWCNT are fully mixed.

[0088] Step 3: Place the precursor slurry in an 80℃ vacuum drying oven and dry for 8 hours. After drying, place it in a tube furnace and heat it to 350℃ at a heating rate of 5℃ / min. Then keep it at that temperature for 3 hours and introduce reducing gas to heat until the reaction is complete. Cool it to room temperature with the tube furnace and then take it out to obtain the powder, which is the target product MWCNT-Fe anode-free sodium metal battery electrode material.

[0089] MWCNT-Fe sodium metal battery electrode material without a negative electrode 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 copper foil, vacuum dried at 120℃, and then cut into sheets to prepare the negative electrode sheet. A sodium metal sheet was used as the positive electrode, 1M NaPF6 dissolved in ethylene glycol dimethyl ether was used as the electrolyte, and a polypropylene membrane (PP membrane) was used as the separator to assemble a composite coin cell.

[0090] Figure 8 shows the AC impedance test of the battery assembled with the composite electrode material obtained in this embodiment. 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.

[0091] Example 6

[0092] Step 1: Place MWCNT powder in a dielectric barrier plasma mold, introduce nitrogen gas, adjust the voltage to 150V / 200V and the current to 2A / 1.5A, and ensure that the process is carried out for 5 minutes at a power of 300W to obtain the processed MWCNT.

[0093] Step 2: Add the sodium-loving metal salts FeCl3 and MWCNT in a mass ratio of 8:1 to a beaker, add 10 ml of N-methylpyrrolidone, and stir on a magnetic stirrer for 5 hours to ensure that FeCl3 and MWCNT are fully mixed.

[0094] Step 3: Place the precursor slurry in an 80℃ vacuum drying oven and dry for 8 hours. After drying, place it in a tube furnace and heat it to 350℃ at a heating rate of 5℃ / min. Then keep it at that temperature for 3 hours and introduce reducing gas to heat until the reaction is complete. Cool it to room temperature with the tube furnace and then take it out to obtain the powder, which is the target product MWCNT-Fe anode-free sodium metal battery electrode material.

[0095] MWCNT-Fe sodium metal battery electrode material without a negative electrode 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 copper foil, vacuum dried at 120℃, and then cut into sheets to prepare the negative electrode sheet. A sodium metal sheet was used as the positive electrode, 1M NaPF6 dissolved in ethylene glycol dimethyl ether was used as the electrolyte, and a polypropylene membrane (PP membrane) was used as the separator to assemble a composite coin cell.

[0096] 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 2.5V to 3.8V.

[0097] Example 7

[0098] Step 1: Place MWCNT powder in a dielectric barrier plasma mold, introduce nitrogen gas, adjust the voltage to 150V / 200V and the current to 2A / 1.5A, and ensure that the process is carried out for 5 minutes at a power of 300W to obtain the processed MWCNT.

[0099] Step 2: Add the sodium-loving metal salts FeCl3 and MWCNT in a mass ratio of 9:1 to a beaker, add 10 ml of N-methylpyrrolidone, and stir on a magnetic stirrer for 5 hours to ensure that FeCl3 and MWCNT are fully mixed.

[0100] Step 3: Place the precursor slurry in an 80℃ vacuum drying oven and dry for 8 hours. After drying, place it in a tube furnace and heat it to 350℃ at a heating rate of 5℃ / min. Then keep it at that temperature for 3 hours and introduce reducing gas to heat until the reaction is complete. Cool it to room temperature with the tube furnace and then take it out to obtain the powder, which is the target product MWCNT-Fe anode-free sodium metal battery electrode material.

[0101] MWCNT-Fe sodium metal battery electrode material without a negative electrode 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 copper foil, vacuum dried at 120℃, and then cut into sheets to prepare the negative electrode sheet. A sodium metal sheet was used as the positive electrode, 1M NaPF6 dissolved in ethylene glycol dimethyl ether was used as the electrolyte, and a polypropylene membrane (PP membrane) was used as the separator to assemble a composite coin cell.

[0102] 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 2.5V to 3.8V.

[0103] Example 8

[0104] Step 1: Place MWCNT powder in a dielectric barrier plasma mold, introduce nitrogen gas, adjust the voltage to 150V / 200V and the current to 2A / 1.5A, and ensure that the process is carried out for 5 minutes at a power of 300W to obtain the processed MWCNT.

[0105] Step 2: Add the sodium-loving metal salts FeCl3 and MWCNT in a mass ratio of 10:1 to a beaker, add 10 ml of N-methylpyrrolidone, and stir on a magnetic stirrer for 5 hours to ensure that FeCl3 and MWCNT are fully mixed.

[0106] Step 3: Place the precursor slurry in an 80℃ vacuum drying oven and dry for 8 hours. After drying, place it in a tube furnace and heat it to 350℃ at a heating rate of 5℃ / min. Then keep it at that temperature for 3 hours and introduce reducing gas to heat until the reaction is complete. Cool it to room temperature with the tube furnace and then take it out to obtain the powder, which is the target product MWCNT-Fe anode-free sodium metal battery electrode material.

[0107] MWCNT-Fe sodium metal battery electrode material without a negative electrode 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 copper foil, vacuum dried at 120℃, and then cut into sheets to prepare the negative electrode sheet. A sodium metal sheet was used as the positive electrode, 1M NaPF6 dissolved in ethylene glycol dimethyl ether was used as the electrolyte, and a polypropylene membrane (PP membrane) was used as the separator to assemble a composite coin cell.

[0108] 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 2.5V to 3.8V.

[0109] Example 9

[0110] Step 1: Place MWCNT powder in a dielectric barrier plasma mold, introduce nitrogen gas, adjust the voltage to 100V and the current to 2A, and ensure that the process is carried out for 5 minutes at a power of 200W to obtain the processed MWCNT.

[0111] Step 2: Add the sodium-loving metal salts FeCl3 and MWCNT in a mass ratio of 3:1 to a beaker, add 10 ml of N-methylpyrrolidone, and stir on a magnetic stirrer for 5 hours to ensure that FeCl3 and MWCNT are fully mixed.

[0112] Step 3: Place the precursor slurry in an 80℃ vacuum drying oven and dry for 8 hours. After drying, place it in a tube furnace and heat it to 350℃ at a heating rate of 5℃ / min. Then keep it at that temperature for 3 hours and introduce reducing gas to heat until the reaction is complete. Cool it to room temperature with the tube furnace and then take it out to obtain the powder, which is the target product MWCNT-Fe anode-free sodium metal battery electrode material.

[0113] MWCNT-Fe sodium metal battery electrode material without a negative electrode 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 copper foil, vacuum dried at 120℃, and then cut into sheets to prepare the negative electrode sheet. A sodium metal sheet was used as the positive electrode, 1M NaPF6 dissolved in ethylene glycol dimethyl ether was used as the electrolyte, and a polypropylene membrane (PP membrane) was used as the separator to assemble a composite coin cell.

[0114] 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 2.5V to 3.8V.

[0115] Example 10

[0116] Step 1: Place MWCNT powder in a dielectric barrier plasma mold, introduce nitrogen gas, adjust the voltage to 70V and the current to 4A, and ensure that the process is carried out for 5 minutes at a power of 280W to obtain the processed MWCNT.

[0117] Step 2: Add the sodium-loving metal salts FeCl3 and MWCNT in a mass ratio of 3:1 to a beaker, add 10 ml of N-methylpyrrolidone, and stir on a magnetic stirrer for 5 hours to ensure that FeCl3 and MWCNT are fully mixed.

[0118] Step 3: Place the precursor slurry in an 80℃ vacuum drying oven and dry for 8 hours. After drying, place it in a tube furnace and heat it to 350℃ at a heating rate of 5℃ / min. Then hold it at that temperature for 30 minutes and introduce reducing gas to heat until the reaction is complete. Cool it to room temperature with the tube furnace and then take it out to obtain the powder, which is the target product MWCNT-Fe anode-free sodium metal battery electrode material.

[0119] MWCNT-Fe sodium metal battery electrode material without a negative electrode 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 copper foil, vacuum dried at 120℃, and then cut into sheets to prepare the negative electrode sheet. A sodium metal sheet was used as the positive electrode, 1M NaPF6 dissolved in ethylene glycol dimethyl ether was used as the electrolyte, and a polypropylene membrane (PP membrane) was used as the separator to assemble a composite coin cell.

[0120] 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 2.5V to 3.8V.

[0121] Comparative Example 1

[0122] The difference between Comparative Example 1 and Example 1 is that the mass ratio of MWCNTs to sodium-loving metal salt FeCl3 is 1:0, while the other preparation methods are the same. Figure 9 shows the voltage distribution of the battery assembled with the composite electrode material obtained in Comparative Example 1 after galvanic electroplating with sodium. The nucleation overpotential is as high as 22 mV, indicating a large nucleation barrier for sodium ions deposited on the electrode sheet. The reason for this is that the carbon nanotubes without the addition of a sodium-loving metal have a large specific surface area and low ionic conductivity, making it easy for active sodium ions to undergo side reactions with the electrolyte. Therefore, it is necessary to add a sodium-loving metal to improve the electrochemical performance of the battery.

[0123] Comparative Example 2

[0124] The difference between Comparative Example 2 and Example 1 is that the MWCNT was not treated with a dielectric barrier plasma device; the other preparation methods are the same. The battery assembled from the composite electrode material obtained in Comparative Example 1 was cycled at 2.5V–3.8V, as shown in Figure 10. After 200 cycles, the capacity decreased to 17.3 mAh g. -1 The reason for this is that the carbon nanotubes (CNTs) were not treated with dielectric barrier plasma, resulting in uneven metal nucleation distribution, easy aggregation, and a greater reaction with active sodium ions. This led to uneven deposition and high aggregation stress, making them prone to cracking. Therefore, CNTs need to be treated with dielectric barrier plasma to improve the electrochemical performance of the battery.

[0125] 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.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material, characterized in that, Includes the following steps: Step 1: Modify carbon nanotubes using a dielectric barrier plasma device; Step 2: The modified carbon nanotubes are mixed and stirred with a sodium-loving metal salt to obtain a precursor slurry. Step 3: The precursor slurry is dried. After drying, it is placed in a tube furnace and heated by a reducing gas to obtain carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material.

2. The method for preparing carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material according to claim 1, characterized in that, The carbon nanotube-sodium-affinic metal anode-free sodium metal battery electrode material has a porous three-dimensional structure, which includes a framework formed by the interwoven carbon nanotubes and a sodium-affinic metal salt uniformly attached to the framework.

3. The method for preparing the carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material according to claim 1 or 2, characterized in that, In step one, the modification treatment of the carbon nanotubes includes placing the carbon nanotubes in a dielectric barrier plasma discharge device mold and activating them by introducing an inert gas; the inert gas is one or more combinations of argon, nitrogen, and argon-hydrogen mixture.

4. The method for preparing carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material according to claim 1, 2 or 3, characterized in that, In step two, the precursor slurry is obtained by magnetic stirring; the stirring speed is 100 r / min to 300 r / min, and the stirring time is 1 h to 5 h; in step three, the drying treatment is vacuum drying, the vacuum drying time is 10 h to 24 h, and the drying temperature is 40 ℃ to 80 ℃.

5. The method for preparing carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material according to claim 1, 2 or 3, characterized in that, In step three, the heating temperature of the heating reaction is increased to 200℃ to 500℃ at a heating rate of 1℃ / min to 10℃ / min, and then kept at 200℃ to 500℃ for 30min to 5h until the reaction is completed.

6. The method for preparing carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material according to claim 1, 2 or 3, characterized in that, The sodium-loving metal salt is one or more of ferric chloride, tin chloride, silver nitrate, magnesium acetate, etc.; the mass ratio of the sodium-loving metal salt to the carbon nanotube is (0-10):

1.

7. A carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material, characterized in that... The carbon nanotube-sodium-acid-metal anode-free sodium metal battery electrode material is prepared using the method described in any one of claims 1 to 6.

8. A method for preparing a composite electrode sheet for a sodium metal battery without a negative electrode, characterized in that, Includes the following steps: A slurry is prepared by mixing a carbon nanotube-sodium-acid-philic metal anode-free sodium metal battery electrode material with an adhesive and a solvent; the slurry is coated onto a negative electrode current collector and dried to obtain a composite electrode sheet; the carbon nanotube-sodium-acid-philic metal anode-free sodium metal battery electrode material is the carbon nanotube-sodium-acid-philic metal anode-free sodium metal battery electrode material as described in any one of claims 1 to 6. It is prepared by the method of preparing battery electrode materials, or it is the carbon nanotube-sodium-loving metal anode-free sodium metal battery electrode material as described in claim 7.

9. The method for preparing a composite electrode sheet for a negative electrode-free sodium metal battery according to claim 8, characterized in that, The coating thickness of the slurry on the negative electrode current collector is 0.001 mm to 0.05 mm.

10. A composite sodium metal battery, comprising 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 method for preparing a negative electrode-free sodium metal battery as described in claim 8 or 9.

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