A multi-walled carbon nanotube composite material embedded with nano bismuth particles, a preparation method thereof, and applications in sodium and potassium ion batteries

Abstract

The present invention discloses a multi-walled carbon nanotube composite material embedded with nano bismuth particles, its preparation method and application in sodium and potassium ion batteries, belonging to the technical field of preparation of negative electrode materials for sodium and potassium ion batteries. First, bismuth metal powder and multi-walled carbon nanotubes are ground according to a mass ratio of 5:3, 2:1 or 7:3, evacuated, sealed and heated to obtain a multi-walled carbon nanotube composite material embedded with nano bismuth particles; then the multi-walled carbon nanotube composite material embedded with nano bismuth particles, a conductive agent and a binder are added to a solvent in a mass ratio of 8:1:1, mixed and stirred evenly at room temperature, coated on a current collector electrode, and dried and left standing to obtain an electrode made of the multi-walled carbon nanotube composite material embedded with nano bismuth particles. The electrode has distinct structural features, the bismuth nanoparticles are 5-10 nm, and it has the characteristics of large specific surface area and excellent electrochemical performance, and has excellent long cycle stability and excellent rate performance when used as a negative electrode material for sodium and potassium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing anode materials for sodium and potassium ion batteries, and particularly relates to a multi-walled carbon nanotube composite material embedded with nano bismuth particles, a preparation method thereof, and an application in sodium and potassium ion batteries. Background Art

[0002] Common lithium ion batteries have low crustal reserves and the problem of safety hazards is becoming increasingly prominent. Compared with lithium ion batteries, sodium and potassium ion batteries have potential advantages of low cost, high safety, and fast charging. In order to improve the performance of sodium and potassium ion batteries, bismuth metal is mostly added to the current anode materials for sodium and potassium ion batteries. Bismuth metal has an ultra-high volume specific capacity (3800 mAh / cm 3 ), about 5 times that of graphite. Bismuth has a layered structure stacked along the Z-axis direction, and the layer spacing is 0.395 nm, which is beneficial to the insertion and extraction of ions. The reaction potential of bismuth is relatively high, about 0.7 V. At this potential, it is difficult for dendrites to grow, which is relatively safe. However, in the commercial process of using bismuth as the anode material for sodium and potassium ion batteries, the liquid phase method is usually used to prepare the electrode, the steps are cumbersome and additional solvents are required. The obtained bismuth particles are generally larger, with an average of more than 50 nm, resulting in a relatively high volume expansion rate during the charge and discharge process of the anode material, which is prone to cause pulverization of the electrode material, thereby leading to a sharp decline in battery performance. Summary of the Invention

[0003] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a multi-walled carbon nanotube composite material embedded with nano bismuth particles, a preparation method thereof, and an application in sodium and potassium ion batteries, so as to solve the problem that when metallic bismuth is used as the anode material for sodium and potassium ion batteries, the volume expansion rate is relatively high during the charge and discharge process, which is prone to cause pulverization of the electrode material, and then lose electrical contact with the current collector, resulting in a decrease in capacity and poor performance.

[0004] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0005] The present invention discloses a multi-walled carbon nanotube composite material embedded with nano bismuth particles, including nano bismuth particles and multi-walled carbon nanotubes. Bismuth particles with a diameter of 5-10 nm are uniformly embedded in the tube walls of the multi-walled carbon nanotubes.

[0006] Preferably, the diameter of the multi-walled carbon nanotubes < 20 nm.

[0007] The present invention also discloses a preparation method of a multi-walled carbon nanotube composite material embedded with nano bismuth particles. Mix and grind bismuth metal powder and multi-walled carbon nanotubes according to a mass ratio of 5:3, 2:1 or 7:3, and evacuate to a pressure value of 1×10 -5 Pa to 1×10 -3Heat Pa and prepare a multi-walled carbon nanotube composite material embedded with nano bismuth particles.

[0008] Preferably, heat for at least 48 hours under the condition of 600 °C to 950 °C.

[0009] Preferably, evacuate to a pressure value of 1×10 -5 Pa to 1×10 -3 Pa in a quartz container and heat.

[0010] Preferably, evacuate with a molecular pump or an ion pump.

[0011] The present invention also discloses the application of the above multi-walled carbon nanotube composite material embedded with nano bismuth particles in the preparation of negative electrode materials for sodium and potassium ion batteries.

[0012] Preferably, a mixture of a multi-walled carbon nanotube composite material embedded with nano bismuth particles, a conductive agent, and a binder is coated on the surface of the current collector electrode of the negative electrode material for sodium and potassium ion batteries.

[0013] Preferably, the conductive agent is conductive carbon black, Super P, or acetylene black, the binder is polyvinylidene fluoride, and the current collector electrode is copper foil.

[0014] The present invention also discloses the application of the above multi-walled carbon nanotube composite material embedded with nano bismuth particles in the preparation of sodium and potassium ion batteries.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] A multi-walled carbon nanotube composite material embedded with nano bismuth particles provided by the present invention has distinct structural characteristics. The diameter of the bismuth nanoparticles is 5 to 10 nm. The structural stress generated by the nano bismuth particles at this size during multiple sodiation / desodiation and potassium insertion / extraction processes is relatively small compared to large-sized bismuth particles, and it is not prone to structural collapse. At the same time, the bismuth particles can have a good synergistic effect with the multi-walled carbon nanotubes. Metallic bismuth provides good electrochemical performance, and the multi-walled carbon nanotubes provide structural support for it. The electrode made of this composite material can be in full contact with the electrolyte, avoiding the problem that the electrode powders into the electrolyte due to volume changes during charge and discharge and detaches from the electrode. The electrode has excellent cycle stability and excellent rate performance and can be used as a negative electrode material for sodium and potassium ion batteries.

[0017] A preparation method of a multi-walled carbon nanotube composite material embedded with nano bismuth particles provided by the present invention. After mixing carbon nanotubes and bismuth powder evenly, using the well-dispersed carbon nanotubes as the support of the three-dimensional network structure, heating under low pressure to reduce the boiling point of bismuth to make it gaseous, and uniformly depositing the vaporized bismuth on the surface of the carbon nanotube network. Through a one-step gas-phase method, a multi-walled carbon nanotube composite material embedded with nano bismuth particles can be obtained. No solvent is required in the whole process, and no impurities will be introduced, which is beneficial to the charge and discharge process of potassium ion / sodium ion batteries with sensitive surface of the negative electrode material, and is conducive to the formation of a stable SEI film during the cycling process, thus being beneficial to the cycling stability of the battery. The preparation process of this method is simple, the cost is low, the energy consumption during the preparation process is low, and it is easy for large-scale commercial and clean production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 XRD pattern of the multi-walled carbon nanotube composite material embedded with nano bismuth prepared in Example 1 of the present invention;

[0019] Figure 2 TEM image of the multi-walled carbon nanotube composite material embedded with nano bismuth particles prepared in Example 1 of the present invention;

[0020] Figure 3 First charge-discharge curve of the negative electrode material used in Example 1 of the present invention in a sodium ion battery at a current density of 1 A / g;

[0021] Figure 4 Cycling performance graph of the negative electrode material used in Example 1 of the present invention in a sodium ion battery at a current density of 1 A / g;

[0022] Figure 5 Cycling performance graph of the negative electrode material used in Example 1 of the present invention in a sodium ion battery at a current density of 10 A / g;

[0023] Figure 6 First charge-discharge curve of the negative electrode material used in Example 1 of the present invention in a potassium ion battery at a current density of 1 A / g;

[0024] Figure 7 Cycling performance graph of the negative electrode material used in Example 1 of the present invention in a potassium ion battery at a current density of 1 A / g;

[0025] Figure 8 Cycling performance graph of the negative electrode material used in Example 1 of the present invention in a potassium ion battery at a current density of 5 A / g;

[0026] Figure 9 Rate performance graph of the negative electrode material of sodium ion battery used in Example 1 of the present invention;

[0027] Figure 10It is the rate performance graph of the negative electrode material potassium ion battery used in Embodiment 1 of the present invention. Detailed implementation manners

[0028] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0029] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0030] The present invention will be further described in detail below with reference to the accompanying drawings:

[0031] A preparation method of a multi-walled carbon nanotube composite material embedded with nano bismuth particles provided by the present invention comprises the following steps:

[0032] Step 1: Using bismuth metal powder and multi-walled carbon nanotubes as raw materials, mixing and grinding them according to a mass ratio of 5:3, 2:1 or 7:3 until the color is uniform within the visible range to the naked eye, obtaining a mixture of bismuth metal powder and multi-walled carbon nanotubes; wherein, the multi-walled carbon nanotubes can be directly purchased or self-made;

[0033] Step 2: Placing the mixture of bismuth metal powder and multi-walled carbon nanotubes obtained in Step 1 in a quartz container, evacuating the quartz container to a pressure value of 1×10 -5 Pa to 1×10 -3 Pa, and sealing the quartz container; wherein, a molecular pump or an ion pump is used to evacuate the quartz container;

[0034] Step 3: Heat the sealed quartz container obtained in Step 2 at 600°C to 950°C for at least 48 hours, cool it to room temperature, and open the sealed quartz container to obtain a multi-walled carbon nanotube composite material embedded with nano bismuth particles; in this composite material, bismuth particles with a diameter of 5 to 10 nm are uniformly embedded in the tube walls of multi-walled carbon nanotubes with a diameter < 20 nm.

[0035] A method for preparing an electrode from a multi-walled carbon nanotube composite material embedded with nano bismuth particles provided by the present invention comprises the following steps:

[0036] Add the multi-walled carbon nanotube composite material embedded with nano bismuth particles obtained in Step 3 above, a conductive agent, and a binder to a solvent in a mass ratio of 8:1:1, mix evenly at room temperature and stir until it becomes a viscous black slurry, coat it on a current collector electrode, dry it at 110°C, and let it stand for more than 12 hours to obtain an electrode made of the multi-walled carbon nanotube composite material embedded with nano bismuth particles;

[0037] Among them, the conductive agent is conductive carbon black, Super P, or acetylene black, the binder is polyvinylidene fluoride (PVDF), the solvent is N-methylpyrrolidone (NMP), and the current collector electrode is copper foil.

[0038] Example 1

[0039] (1) Mix 50 mg of bismuth metal powder (brand: Aladdin, CAS: 7440-69-9, powder size ≥ 200 mesh) and 30 mg of carbon nanotubes evenly, and grind them in a mortar for 30 minutes to obtain a mixture of bismuth metal powder and multi-walled carbon nanotubes;

[0040] (2) Place the mixture of bismuth metal powder and multi-walled carbon nanotubes obtained in Step (1) in a quartz container, evacuate the quartz container with a molecular pump until the air pressure value is 1.0×10 -5 Pa, and then seal the quartz container;

[0041] (3) Heat the sealed quartz container in Step (2) to 650°C at a rate of 2°C / min, keep it at this temperature for 48 hours, then cool it to 500°C and take it out, and let it cool naturally to room temperature to obtain a multi-walled carbon nanotube composite material embedded with nano bismuth particles;

[0042] (4) Dissolve the multi-walled carbon nanotube composite material embedded with nano bismuth particles, conductive carbon black, and PVDF prepared above in NMP in a mass ratio of 8:1:1, adjust it into a uniform slurry, coat it on a copper foil current collector, dry it at 110°C, and let it stand for 14 hours to obtain an electrode made of the multi-walled carbon nanotube composite material embedded with nano bismuth particles. Cut the electrode made of the multi-walled carbon nanotube composite material embedded with nano bismuth particles into electrode sheets with a diameter of 12 mm.

[0043] (5) Use sodium or potassium metal as the counter electrode of the electrode sheet obtained in step (4), and use a glass fiber membrane as the separator between the two; dissolve 1 mol of sodium hexafluorophosphate (NaPF6) in 1 L of diglyme (DIGLYME) as the electrolyte of the sodium-ion battery; dissolve 1 mol of potassium hexafluorophosphate (KPF6) in dimethoxyethane (DME) as the electrolyte of the potassium-ion battery; assemble a CR2025 half-cell in a glove box filled with argon, and perform a constant current charge-discharge test on the sodium battery in the voltage window range of 0.01 - 1.8 V, and perform a constant current charge-discharge test on the potassium battery in the voltage window range of 0.1 - 1.5 V.

[0044] The test results are as follows. From Figure 1 the X-ray diffraction phase analysis results, it can be seen that the diffraction peaks of the prepared material are consistent with the standard card peaks, indicating that the composite contains metallic bismuth and carbon materials. From Figure 2 the microscopic morphology diagram, it can be seen that the diameter of the nano-bismuth is 5 - 10 nm, and it is evenly embedded on the wall of multi-walled carbon nanotubes with a diameter of less than 20 nm. From Figure 3 it can be seen that in the sodium-ion battery, under the condition of a current density of 1 A / g, the first charge specific capacity of the electrode made of the composite material with nano-bismuth embedded on the wall of the multi-walled carbon nanotubes reaches 319.6 mAh / g, and the charge-discharge efficiency is as high as 64.96%. From Figure 4 it can be seen that in the sodium-ion battery, under the condition of a current density of 1 A / g, the first charge specific capacity of the electrode made of the composite material with nano-bismuth embedded on the wall of the multi-walled carbon nanotubes reaches 319.6 mAh / g, and the charge specific capacity after 1000 cycles of charging is 236.7 mAh / g. From Figure 5 it can be seen that in the sodium-ion battery, under the condition of a current density of 10 A / g, the first charge specific capacity of the electrode made of the composite material with nano-bismuth embedded on the wall of the multi-walled carbon nanotubes reaches 376.3 mAh / g, and the charge specific capacity after 8000 cycles of charging is 212.8 mAh / g. From Figure 6 it can be seen that in the potassium-ion battery, under the condition of a current density of 1 A / g, the first charge specific capacity of the electrode made of the composite material with nano-bismuth embedded on the wall of the multi-walled carbon nanotubes reaches 336.7 mAh / g, and the charge-discharge efficiency is as high as 71.7%. From Figure 7 it can be seen that in the potassium-ion battery, under the condition of a current density of 1 A / g, the first charge specific capacity of the electrode made of the composite material with nano-bismuth embedded on the wall of the multi-walled carbon nanotubes reaches 336.7 mAh / g, and the charge specific capacity after 600 cycles of charging is 257.4 mAh / g. From Figure 8It can be seen that in the potassium ion battery, under the condition of a current density of 5 A / g, the initial charge specific capacity of the electrode made of the composite material with multi-walled carbon nanotubes embedded with nano-bismuth reaches 334.9 mAh / g, and the charge specific capacity after 100 cycles is 298.5 mAh / g. From Figure 9 It can be known that the reversible specific capacities of the sodium ion secondary battery with the battery negative electrode material prepared in Example 1 are 304.4, 294.3, 286.4, 274.1, and 248 mAh / g at current densities of 1, 2, 5, 10, and 20 A / g respectively, indicating stable cycling. From Figure 10 It can be known that the reversible specific capacities of the potassium ion secondary battery with the battery negative electrode material prepared in Example 1 are 317, 308.4, 298.8, 285.6, and 251.2 mAh / g at current densities of 1, 2, 5, 10, and 20 A / g respectively, indicating stable cycling.

[0045] Example 2

[0046] (1) Mix 80 mg of bismuth metal powder (brand: Aladdin, CAS: 7440-69-9, powder size ≥ 200 mesh) and 40 mg of carbon nanotubes evenly, and grind them in a mortar for 40 minutes to obtain a mixture of bismuth metal powder and multi-walled carbon nanotubes;

[0047] (2) Place the mixture of bismuth metal powder and multi-walled carbon nanotubes obtained in step (1) in a quartz container, and use a molecular pump to evacuate the quartz container to a pressure value of 3.0×10 -4 Pa, and then seal the quartz container;

[0048] (3) Heat the sealed quartz container in step (2) to 950 °C at a rate of 2 °C / min, keep it at this temperature for 48 h, then cool it to 500 °C and take it out, and naturally cool it to room temperature to obtain a multi-walled carbon nanotube composite material embedded with nano-bismuth particles; Observed by TEM images, in this composite material, bismuth particles with a diameter of 5 - 10 nm are evenly embedded in the tube walls of multi-walled carbon nanotubes with a diameter < 20 nm;

[0049] (4) Dissolve 80 mg of the above-prepared multi-walled carbon nanotube composite material embedded with nano-bismuth particles, 10 mg of Super P, and 10 mg of PVDF in NMP, adjust them into a uniform slurry and coat it on a copper foil current collector, and after drying at 110 °C and standing for 12 h, an electrode made of the multi-walled carbon nanotube composite material embedded with nano-bismuth particles is obtained.

[0050] Example 3

[0051] (1) Mix 70 mg of bismuth metal powder (brand: Aladdin, CAS: 7440-69-9, powder size ≥ 200 mesh) and 30 mg of carbon nanotubes evenly, and grind them in a mortar for 32 minutes to obtain a mixture of bismuth metal powder and multi-walled carbon nanotubes;

[0052] (2) Place the mixture of bismuth metal powder and multi-walled carbon nanotubes obtained in step (1) in a quartz container, and use an ion pump to evacuate the quartz container until the air pressure value reaches 1×10 -3 Pa, then seal the quartz container;

[0053] (3) Heat the sealed quartz container in step (2) to 800 °C at a rate of 2 °C / min, hold for 48 h, then cool to 500 °C and take it out, and naturally cool to room temperature to obtain a multi-walled carbon nanotube composite material embedded with nano-bismuth particles; Observed by TEM image, in this composite material, bismuth particles with a diameter of 5 - 10 nm are evenly embedded in the tube wall of multi-walled carbon nanotubes with a diameter < 20 nm;

[0054] (4) Dissolve 80 mg of the above-prepared multi-walled carbon nanotube composite material embedded with nano-bismuth particles, 10 mg of acetylene black, and 10 mg of PVDF in NMP, adjust it into a uniform slurry and coat it on a copper foil current collector, and after drying at 110 °C and standing for 15 h, an electrode made of the multi-walled carbon nanotube composite material embedded with nano-bismuth particles is obtained.

[0055] The above content is only to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A multi-walled carbon nanotube composite material embedded with nano bismuth particles, characterized in that, It includes nano bismuth particles and multi-walled carbon nanotubes. Bismuth particles with a diameter of 5-10 nm are evenly embedded in the tube walls of the multi-walled carbon nanotubes; The multi-walled carbon nanotube composite material embedded with nano bismuth particles is obtained by mixing bismuth metal powder and multi-walled carbon nanotubes in a mass ratio of 5:3, 2:1 or 7:3, grinding them, evacuating to an air pressure value of 1×10 -5 Pa to 1×10 -3 Pa and then heating.

2. The multi-walled carbon nanotube composite material embedded with nano bismuth particles according to claim 1, wherein The diameter of the multi-walled carbon nanotubes < 20 nm.

3. The preparation method of a multi-walled carbon nanotube composite material embedded with nano bismuth particles as claimed in claim 1 or 2, characterized in that, Mix bismuth metal powder and multi-walled carbon nanotubes in a mass ratio of 5:3, 2:1 or 7:3, grind them, evacuate to a pressure value of 1×10 -5 Pa to 1×10 -3 Pa and heat to obtain a multi-walled carbon nanotube composite material embedded with nano-bismuth particles.

4. The preparation method of a multi-walled carbon nanotube composite material embedded with nano bismuth particles according to claim 3, characterized in that, Heat for at least 48 hours under the condition of 600 °C - 950 °C.

5. The preparation method of a multi-walled carbon nanotube composite material embedded with nano bismuth particles according to claim 3, characterized in that, Vacuum the quartz container to a pressure value of 1×10 -5 Pa~1×10 -3 Pa and heat it.

6. The preparation method of a multi-walled carbon nanotube composite material embedded with nano bismuth particles according to claim 3, characterized in that, Use a molecular pump or an ion pump to evacuate the air.

7. Application of a multi-walled carbon nanotube composite material embedded with nano bismuth particles as described in claim 1 or 2 in the preparation of the negative electrode material for sodium and potassium ion batteries.

8. The application according to claim 7, characterized in that A mixture of a multi-walled carbon nanotube composite material embedded with nano bismuth particles, a conductive agent, and a binder is coated on the surface of the current collector electrode of the negative electrode material for sodium and potassium ion batteries.

9. The application according to claim 8, characterized in that, The conductive agent is conductive carbon black, Super P, or acetylene black, the binder is polyvinylidene fluoride, and the current collector electrode is copper foil.

10. Application of a multi-walled carbon nanotube composite material embedded with nano bismuth particles as described in claim 1 or 2 in the preparation of sodium and potassium ion batteries.

Images