CN115332518B - Quantum dot tin oxide loaded multiwall carbon nanotube composite material and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of lithium-ion secondary batteries, and discloses a quantum dot tin oxide-loaded multi-wall carbon nanotube composite material, a preparation method and application thereof. Method: 1) Dissolve tin salt in water to obtain tin salt solution; 2) Mix multi-walled carbon nanotubes and tin salt solution to obtain suspension A; 3) Place suspension A in gas-liquid discharge plasma In a bulk reaction device, a discharge reaction is carried out under an argon plasma atmosphere to obtain a suspension B; subsequent processing obtains a multi-walled carbon nanotube composite material loaded with quantum dot tin oxide; the amount of the multi-walled carbon nanotube satisfies: The mass ratio of tin ions to multi-walled carbon nanotubes is (0.04-0.8):1. The method of the invention has the advantages of high efficiency, simple operation and low cost, and can realize the large-scale production of the quantum dot tin oxide carbon composite material. The material of the invention is used in a lithium ion battery, can significantly improve the cycle stability performance of the electrode material and has excellent electrochemical performance.

Description

A kind of quantum dot tin oxide loaded multi-walled carbon nanotube composite material and preparation method thereof and application

technical field

The invention belongs to the technical field of nanometer functional materials and lithium-ion secondary batteries, and specifically relates to a preparation method and application of a quantum dot tin oxide-loaded multi-wall carbon nanotube material using gas-liquid phase plasma discharge reduction technology.

Background technique

Lithium-ion batteries (Lithium-ion Batteries, LIBs) are composed of negative electrode (also known as anode) and positive electrode (cathode) materials, through the reciprocating intercalation and extraction movement of Li ions (Li ⁺ ) between the positive and negative electrodes to achieve electrical energy storage A rechargeable energy storage device. During discharge, Li ions are transported from the anode to the cathode through the nonaqueous electrolyte and separator; during charge, the process is reversed.

LIBs have the advantages of high energy density (high specific capacity), light weight, long life, and no memory effect. The specific capacity of lithium-ion batteries is mainly determined by the positive and negative electrode materials. However, due to the theoretical capacity (~372mAh g ^-1 ) and discharge potential (~0.1V vs. Li ⁺ /Li) of graphite, the anode material currently used in commercial lithium-ion batteries, it is easy to overcharge, especially at low temperatures, resulting in lithium dendrite deposition. Puncture the diaphragm to form a short circuit, and safety accidents) are relatively low, so it cannot meet people's needs for the next generation of lithium-ion batteries (higher capacity, longer life and safety under a wide temperature range). Therefore, there is a need to develop alternative anode materials with high specific capacity, moderate discharge potential, and good cycle performance. Among various anode materials, tin oxide has high theoretical specific capacity (1490mAh g ^-1 , nearly 4 times that of graphite), moderate discharge potential (~0.6V vs. Li ⁺ /Li), easy preparation, and low cost. It has received great attention due to its low cost and environmental friendliness. However, compared with the graphite anode with low capacity but very stable cycle, there are still many challenges that cannot be ignored in the tin oxide anode. First, when the conversion reaction and alloying reaction occur completely, the volume of the anode will expand greatly (~ 300%), the large change in volume during charge and discharge causes the negative electrode material to easily pulverize and fall off; secondly, during the charge/discharge process, the poorly conductive lithium oxide formed on the tin surface will hinder the internal alloy reaction, resulting in The reversibility of the reaction is reduced, and the cycle performance is unstable; in addition, because tin has a low recrystallization temperature (-71 ° C), the tin particles formed by the dealloying reaction are easy to aggregate and grow at room temperature, resulting in a decrease in the kinetics of the electrochemical reaction. Further reduce cyclic reversibility.

In order to solve the above problems, some researches have been carried out. For example, the Chinese invention patent application CN201811493527.7 provides a method for preparing quantum dot tin oxide/graphene fluoride composite materials. Thoroughly stir at high temperature for 1 to 5 hours to obtain a tin-containing solution, then mix the solution with the ultrasonically dispersed single-layer graphene fluoride dispersion, undergo solvothermal reaction at 150 to 210°C for 5 to 30 hours, and then centrifuge and dry to obtain Tin oxide quantum dot/fluorinated graphene composite anode material. The quantum dot tin oxide prepared by the method is uniformly dispersed in the interlayer of the fluorinated graphene, and can perform better when applied to a sodium ion battery. However, the experiment of this method takes a long time, consumes a lot of energy, and the preparation process is complicated, which cannot reach the short-flow process required for large-scale production. Chinese invention patent CN201610048028.1 utilizes the hydrolysis characteristics of SnCl ₂ 2H ₂ O, introduces thiourea as a catalyst and stabilizer, stirs at room temperature for 12-24 hours, and obtains a yellow, clear and transparent SnO ₂ quantum dot solution, and combines with carbon nano After mixing and stirring for a period of time, the tubes were filtered and dried to obtain the quantum dot tin oxide/carbon nanotube composite material. The preparation process of the method does not require high-temperature reaction, the energy consumption is low, and the experimental operation is relatively simple, and it can show better electrochemical performance when applied to the negative electrode of lithium-ion batteries. However, the proportion of tin oxide quantum dots prepared by this method is too high, and the particle distribution is very dense, which makes the quantum dot particles easy to aggregate and become larger, which is not conducive to cycle stability. Looking at most of the current methods for preparing quantum dot tin oxide composite materials, none of them can achieve the controllable preparation of uniform nanometer small-sized tin oxide under the premise of simple, efficient and clean production, which greatly limits the quantum dot tin oxide composite materials. Scale production and application promotion of material negative electrodes in practice.

Contents of the invention

In order to overcome the above-mentioned shortcomings of the existing quantum dot tin oxide carbon composite material, the present invention aims to provide a quantum dot tin oxide loaded multi-wall carbon nanotube composite material and an efficient preparation method thereof. The invention utilizes solvated electrons with strong reducibility in gas-liquid plasma to induce quantum dot tin oxide particles (~5nm) with uniform size to be loaded on multi-walled carbon nanotubes (MWCNTs) in a short period of time (5-30 minutes). ), it has the characteristics of simple operation, low preparation cost, high efficiency and reliability, and is easy to realize large-scale production. In lithium-ion batteries, the extremely small size of tin oxide (about 5nm) can significantly increase the reaction area and effectively shorten the diffusion distance of Li ⁺ . The volume change brought about by the charging and discharging process can improve the electrode kinetics and cycle performance.

Another object of the present invention is to provide the application of the above-mentioned quantum dot tin oxide-loaded multi-walled carbon nanotube composite material in the negative electrode of lithium-ion batteries. The quantum dot tin oxide-loaded multi-wall carbon nanotube composite material has higher cycle stability than ordinary tin oxide negative electrodes, and can achieve higher specific capacity and coulombic efficiency than multi-wall carbon nanotubes, and is more It satisfies its requirements as a lithium-ion battery anode material well.

The object of the invention is achieved through the following technical solutions:

A preparation method of quantum dot tin oxide loaded multi-wall carbon nanotube composite material, comprising the following steps:

(1) tin salt is dissolved in water to obtain tin salt solution;

(2) Mixing the multi-walled carbon nanotubes and the tin salt solution to obtain a suspension A;

(3) The suspension A obtained in step (2) is placed in a gas-liquid discharge plasma reaction device, and the discharge reaction is carried out under an argon plasma atmosphere to obtain a suspension B; subsequent processing to obtain a quantum dot oxidation Tin-supported multi-walled carbon nanotube composites.

The tin salt described in the step (1) comprises tin chloride (analytical pure AR, ≥98%), stannous chloride (AR, ≥98%), tin sulfate (AR, ≥98%) containing crystal water or not containing crystal water 98%), stannous sulfate (AR, ≥98%) or more.

The mass ratio of the tin salt to water is (10-200mg): 30ml.

The amount of multi-walled carbon nanotubes added in step (2) satisfies that the mass ratio of tin ions in the tin salt to multi-walled carbon nanotubes is (0.04-0.8):1.

The mixing refers to stirring evenly; the stirring speed is 100-400 rpm, and the stirring time is 1-6 hours.

The conditions of the discharge reaction in step (3): the control input voltage is 20-80 volts, the output high voltage is 1-10 kV, the discharge frequency is 10-100 kHz, and the discharge treatment time is 5-30 minutes.

The gas-liquid discharge plasma reaction device includes a needle-shaped hollow electrode, a reactor body and a disk electrode. The reactor body is a cavity with openings at both ends, the bottom of the reactor body is closed by a disc electrode, and the needle-shaped hollow electrode is placed in the cavity of the reactor body through the opening at the upper end of the reactor body. The needle-shaped hollow electrode is provided with an air inlet. One end of the needle-shaped hollow electrode provided with an air inlet is connected to the negative output end of the rectifier, and one end of the gas outlet is placed in the reactor main body; the disc electrode is connected to the positive output end of the rectifier; the gas outlet of the needle-shaped hollow electrode It is connected with the gas storage device; the rectifier is connected with the power supply.

The main body of the reactor is a cylindrical reactor made of polytetrafluoroethylene; the needle-shaped hollow electrode is made of stainless steel, and the disc electrode is a graphite electrode; the depth of the main body of the reactor is 50 mm, and the diameter of the inner wall is 60 mm. mm. After adding the suspension A, the depth of the suspension A is 25-35 mm, and the distance between the liquid level of the suspension A and the lower end of the needle-shaped hollow electrode is 2-5 mm.

In step (3), the flow rate of argon in the needle-shaped hollow electrode is 5-20 mL/min, and the purity is 99.999%.

The plasma discharge in the present invention is a pulsed DC discharge.

The subsequent treatment refers to filtration and drying. The drying is vacuum drying, the degree of vacuum is 5000-10000Pa, the drying temperature is 60-80°C, and the drying time is 8-12 hours.

The quantum dot tin oxide-loaded multi-walled carbon nanotube composite material of the present invention realizes that nano-sized tin oxide particles are evenly loaded on the multi-walled carbon nanotubes, wherein the loading capacity is 15% to 30%, and the size of the loaded particles is about 5nm , and there is no agglomeration of metal particles due to excessive reduction.

The quantum dot tin oxide loaded multi-wall carbon nanotube composite material prepared by plasma reduction is applied in lithium ion batteries.

The principle of the invention is: first dissolving tin salt in water to obtain a tin ion solution, adding multi-wall carbon nanotubes and continuously stirring so that tin ions are uniformly dispersed around the multi-wall carbon nanotubes. The strong reducing solvated electrons generated by the plasma discharge will reduce the tin ions adsorbed on the multi-walled carbon nanotubes into tin metal particles, which are easily oxidized into tin oxide particles by oxygen in water due to their extremely small particle size. and adsorbed on multi-walled carbon nanotubes.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) The present invention adopts a liquid-phase discharge plasma system, and under the action of the plasma and the liquid phase, a large number of strongly reducing solvated electrons are generated, which can quickly and efficiently reduce and adsorb most of the tin ions in the solution to the multi-walled carbon Nanotube material surface.

(2) The present invention can reduce metallic tin through a simple one-step liquid-phase discharge plasma treatment method and be quickly oxidized to tin oxide loaded on the surface of multi-walled carbon nanotube material, the discharge reaction time can be controlled within 30 minutes, and the operation is simple , the process flow is short, the efficiency and reliability are high, the preparation cost is low, and large-scale production can be easily realized.

(3) The quantum dot tin oxide-loaded multi-walled carbon nanotube composite material prepared by the present invention has excellent electrochemical performance when applied to the negative electrode of lithium-ion batteries, and can have higher cycle stability than commercial tin oxide material negative electrodes Compared with multi-walled carbon nanotubes, it can achieve higher specific capacity and Coulombic efficiency.

Description of drawings

Fig. 1 is the schematic diagram of gas-liquid discharge plasma reaction device;

Fig. 2 is the XRD diffractogram of quantum dot tin oxide loaded multi-walled carbon nanotubes in embodiment 1, the standard PDF card that comprises multi-walled carbon nanotubes and tin oxide among the figure;

Fig. 3 is the TEM picture of quantum dot tin oxide loaded multi-walled carbon nanotubes in embodiment 1;

Fig. 4 is the thermogravimetric graph of quantum dot tin oxide loaded multi-walled carbon nanotubes in embodiment 1;

Figure 5 shows the cycle performance of quantum dot tin oxide-loaded multi-walled carbon nanotubes used as electrodes in lithium-ion battery half-cells at low current densities (0.1A g ^-1 ) in Example 1, compared to that of multi-walled carbon nanotubes cycle performance;

Fig. 6 is the coulombic efficiency diagram of quantum dot tin oxide-loaded multi-walled carbon nanotubes used as electrodes in Li-ion battery half-cells cycled at a low current density (0.1A g ^-1 ) in Example 1, compared to multi-walled carbon nanotubes Coulombic efficiency of the tube;

Fig. 7 is the TEM figure of embodiment 2 quantum dot tin oxide loaded multi-walled carbon nanotubes;

FIG. 8 is a TEM image of multi-walled carbon nanotubes supported by quantum dot tin oxide in Example 3. FIG.

Detailed ways

In order to better understand the present invention, the present invention will be further described below in conjunction with the examples and accompanying drawings, but the embodiments of the present invention are not limited thereto.

As shown in Figure 1, the gas-liquid discharge plasma reaction device used in the present invention includes a voltage device, a reaction device, and a gas delivery device. The voltage device includes a common power supply 1 and a rectifier 2, and the reaction device includes a needle-shaped hollow electrode 3, a reaction device The device body 4 and the disk electrode 5. The reactor body is a cavity with openings at both ends, the bottom of the reactor body is closed by a disc electrode, and the needle-shaped hollow electrode is placed in the cavity of the reactor body through the opening at the upper end of the reactor body. The needle-shaped hollow electrode is provided with an air inlet. One end of the needle-shaped hollow electrode provided with an air inlet is connected to the negative output end of the rectifier, and one end of the gas outlet is placed in the reactor main body; the disc electrode is connected to the positive output end of the rectifier; the gas outlet of the needle-shaped hollow electrode Connect with the gas transmission device; connect the rectifier with the power supply. The needle-shaped hollow electrode 3 and the disc electrode 5 are made of stainless steel and graphite respectively; the main body of the reactor is made of polytetrafluoroethylene, the depth of the main body is 50 mm, and the inner wall diameter is 60 mm; the gas delivery device includes an argon gas cylinder 6 and The air tube 7 connecting the argon cylinder and the needle-shaped hollow electrode.

When the reaction occurs, the depth of the suspension A added to the main body of the reactor for reaction is 5-30 mm, and the distance between the liquid level of the suspension and the lower end of the needle-shaped hollow electrode is 2-5 mm, which is the discharge distance or discharge gap . The argon flow rate in the needle-shaped hollow electrode is 5-20 ml/min, and the purity is above 99.999%.

The plasma power supply used in the present invention is manufactured by Nanjing Suman Plasma Technology Co., Ltd., model CTP-2000K; meanwhile, in order to utilize the characteristics of DC discharge as much as possible, a rectifier is used to change the output signal of the plasma power supply into a pulsed DC signal.

Example 1

(1) 98% analytically pure SnCl ₂ ·2H ₂ O (48 mg) was dissolved in deionized water (30 mL), and stirred for 10 minutes under a magnetic stirring condition of 300 rpm to obtain solution A;

(2) Add 150 mg of high-purity multi-walled carbon nanotubes (purchased from Kena Carbon New Material Co., Ltd., purity > 97%, tube diameter 3-15 μm, tube length 15-30 μm) to solution A obtained in step (1) , continue stirring for 1h to obtain a black suspension B;

(3) The black suspension B obtained in step (2) is transferred to the main body of the gas-liquid discharge plasma cylinder reactor. Gas (10 ml/min, purity 99.999%) blows the liquid surface directly through the needle-shaped hollow electrode, connects the plasma power supply, and continuously and stably reacts under the conditions of an input voltage of 40 volts, an output high voltage of 5 kV, and a discharge frequency of 34.5 kHz for 10 minutes, a black suspension C was obtained;

(4) The black suspension C in step (3) is filtered by suction to wash impurities and solid-liquid separation, and then the solid black product washed and separated is vacuum-dried at 70°C for 12h under a vacuum of 10000Pa to obtain a product with a size of The quantum dot tin oxide metal-loaded multi-walled carbon nanotube composite material with about 5nm is denoted as 1-QDSnO ₂ /MWCNTs.

The XRD diffraction pattern of the multi-walled carbon nanotube composite material supported by quantum dot tin oxide metal in this embodiment is shown in FIG. 2 . Compared with the XRD of the original multi-walled carbon nanotubes, the XRD of the quantum dot tin oxide metal-supported multi-walled carbon nanotubes composite material has a carbon peak, and a tin oxide peak with higher intensity appears at 26.5°, resulting in the original 26.2° In addition, the amorphous peak at 33.5° and the obvious peak at 52° correspond to the peak of tin oxide, which indicates that the composite of tin oxide-loaded multi-walled carbon nanotubes was successfully prepared by plasma discharge Material.

The TEM image of the quantum dot tin oxide metal-loaded multi-walled carbon nanotube composite material of this embodiment is shown in Figure 3. It can be clearly seen that particles with a size of about 5 nm are loaded on a single multi-walled carbon nanotube, wherein the nanometer size The apparent lattice fringes of the particles measured at 0.34 nm correspond to the (1 1 0) plane of tin oxide, proving that they are tin oxide quantum dots. In addition, the clear lattice fringes at the edges of the multi-walled carbon nanotubes correspond to the multi-walled carbon nanotubes The (0 0 2) surface. This result further illustrates the successful synthesis of quantum dot tin oxide metal-supported multi-walled carbon nanotubes. In addition, the thermogravimetric curve of 1-QDSnO ₂ /MWCNTs is shown in Figure 4 under the air atmosphere test condition of 25°C-650°C, and the calculated tin oxide loading is 22%.

In a glove box (H ₂ O<0.1%, O ₂ <0.1%), the prepared quantum dot tin oxide-loaded multi-walled carbon nanotube composite material was used as the positive electrode, Calgard 2025 was used as the diaphragm, the metal lithium sheet was used as the negative electrode, and lithium hexafluorophosphate was used as the negative electrode. Electrolyte salt (solvent: EC:DEC=2:1), pressed into a pole piece with a diameter of 12mm, and assembled with a CR2016 button battery case to form a half-cell. The prepared half-battery was tested for charge and discharge performance in the LAND battery test system. The specific parameters are as follows: As shown in Figure 5, when the current density is 0.1A g ^-1 The thermally synthesized micron-scale tin oxide and commercial tin oxide have a rapid capacity decay. In contrast, 1-QDSnO ₂ /MWCNTs exhibits the same excellent capacity as MWCNTs although the capacity is not as high as the former two in the early cycle. Excellent cycle stability, and the capacity is higher than that of hydrothermally synthesized micron-sized tin oxide and commercial tin oxide after about 30 cycles. After 50 cycles, the specific capacities of 1-QDSnO ₂ /MWCNTs and MWCNTs are 525mA hg ^-1 and 365mA g ^-1 , the hydrothermally synthesized micron tin oxide and commercial SnO ₂ decay to 403mAh g ^-1 and 411mA hg ^-1 , respectively. In addition, it is worth noting that in the comparison of Coulombic efficiency at low current density in Figure 6, the Coulombic efficiency of multi-walled carbon nanotubes loaded with quantum dots tin oxide has been greatly improved, which shows that compared with the original multi-walled carbon Due to the large specific surface area of nanotubes, an unstable SEI film is formed, and the SEI film of quantum dots loaded with tin oxide is more stable.

Figure 5 shows the cycle performance of quantum dot tin oxide-loaded multi-walled carbon nanotubes used as electrodes in lithium-ion battery half-cells at low current densities (0.1A g ^-1 ) in Example 1, compared to that of multi-walled carbon nanotubes cycle performance;

Fig. 6 is the coulombic efficiency diagram of quantum dot tin oxide-loaded multi-walled carbon nanotubes used as electrodes in Li-ion battery half-cells cycled at a low current density (0.1A g ^-1 ) in Example 1, compared to multi-walled carbon nanotubes Coulombic efficiency of the tube.

Example 2

(1) 98% analytically pure SnCl ₄ ·5H ₂ O (75 mg) was dissolved in deionized water (30 mL), and stirred for 8 minutes under a magnetic stirring condition of 100 rpm to obtain solution A;

(2) Add 150 mg of high-purity multi-walled carbon nanotubes (purchased from Kena Carbon New Material Co., Ltd., purity > 97%, tube diameter 3-15 μm, tube length 15-30 μm) to solution A obtained in step (1) , continue stirring for 3h to obtain a black suspension B;

(3) The black suspension B obtained in step (2) is transferred to the main body of the gas-liquid discharge plasma cylinder reactor. Gas (20 ml/min, purity 99.999%) blows directly to the liquid surface through the needle-shaped hollow electrode, connects the plasma power supply, and continuously and stably reacts for 30 hours under the conditions of input voltage 80 volts, output high voltage 10 kV, and discharge frequency 65 kHz. minutes, a black suspension C was obtained;

(4) The black suspension C in step (3) is filtered by suction to wash impurities and solid-liquid separation, and then the solid black product that is washed and separated is vacuum-dried at 80°C for 8h under a vacuum of 5000Pa to obtain a product with a size of The quantum dot tin oxide metal-supported multi-walled carbon nanotube composite material with a size of about 5nm is denoted as 2-QDSnO ₂ /MWCNTs.

The reaction product is also quantum dot tin oxide particles with a size of about 5 nanometers supported on multi-walled carbon nanotubes (as shown in FIG. 7 ). 7 is a TEM image of multi-walled carbon nanotubes supported by quantum dot tin oxide in Example 2.

The 2-QDSnO ₂ /MWCNTs material prepared in this example can be used as the negative electrode of lithium-ion batteries, which can effectively improve the cycle stability of the tin oxide composite negative electrode. The presence of tin oxide can greatly improve the capacity and formation of original multi-walled carbon nanotubes A more stable SEI film, the test result is similar to Example 1.

Example 3

(1) 98% analytically pure SnSO ₄ (48 mg) was dissolved in deionized water (30 mL), and stirred for 5 minutes under a magnetic stirring condition of 400 rpm to obtain solution A;

(2) Add 150 mg of high-purity multi-walled carbon nanotubes (purchased from Kena Carbon New Material Co., Ltd., purity > 97%, tube diameter 3-15 μm, tube length 15-30 μm) to solution A obtained in step (1) , continue to stir for 2h to obtain suspension B;

(3) The black suspension B obtained in step (2) is transferred to the gas-liquid discharge plasma cylinder reactor, the distance between the liquid level of the suspension and the lower end of the needle-shaped hollow electrode is 3 millimeters, and the high-purity argon gas is controlled. (15 ml/min, purity 99.999%) directly blow the liquid surface through the needle-shaped hollow electrode, turn on the plasma power supply, and continue to react stably for 20 minutes under the conditions of an input voltage of 20 volts, an output high voltage of 1 kV, and a discharge frequency of 30 kHz , to obtain a black suspension C;

(4) Suction filter the black suspension C in step (3) to wash impurities and separate solid and liquid, and then dry the solid black product D washed and separated at 60°C for 12 hours under a vacuum of 8000 Pa to obtain a size The quantum dot tin oxide metal-loaded multi-walled carbon nanotube composite material with a size of about 5nm is recorded as 3-QDSnO ₂ /MWCNTs.

The reaction product is also quantum dot tin oxide particles with a size of about 5 nanometers supported on multi-walled carbon nanotubes (as shown in FIG. 8 ).

FIG. 8 is a TEM image of multi-walled carbon nanotubes supported by quantum dot tin oxide in Example 3. FIG.

The 3-QDSnO ₂ /MWCNTs material prepared in this example can be used as the negative electrode of lithium-ion batteries, which can effectively improve the cycle stability of the tin oxide composite negative electrode. The presence of tin oxide can greatly increase the capacity of the original multi-walled carbon nanotubes and form more It is a stable SEI film, and the test result is similar to Example 1.

Example 4

(1) Dissolve 98% analytically pure Sn(SO ₄ ) ₂ ·2H ₂ O (100 mg) in deionized water (30 mL), and stir for 5 minutes under a magnetic stirring condition of 300 rpm to obtain solution A;

(2) Add 150 mg of high-purity multi-walled carbon nanotubes (purchased from Kena Carbon New Material Co., Ltd., purity > 97%, tube diameter 3-15 μm, tube length 15-30 μm) to solution A obtained in step (1) , continue to stir for 2h to obtain suspension B;

(3) The black suspension B obtained in step (2) is transferred to the main body of the gas-liquid discharge plasma cylinder reactor. Gas (15 ml/min, purity 99.999%) blows directly to the liquid surface through the needle-shaped hollow electrode, connects the plasma power supply, and continuously and stably reacts under the conditions of an input voltage of 30 volts, an output high voltage of 4 kV, and a discharge frequency of 34.5 kHz for 25 minutes, a black suspension C was obtained;

(4) Suction filter the black suspension C in step (3) to wash the impurities and separate the solid and liquid, then dry the washed and separated solid black product D at 60°C for 12h under a vacuum of 6000Pa to obtain Quantum Dot tin oxide metal-supported multi-walled carbon nanotube composite material, denoted as 4-QDSnO ₂ /MWCNTs.

The 4-QDSnO ₂ /MWCNTs material prepared in this example can be used as the negative electrode of lithium-ion batteries, which can effectively improve the cycle stability of the tin oxide composite negative electrode. The presence of tin oxide can greatly improve the capacity of the original multi-walled carbon nanotubes and form more It is a stable SEI film, and the test result is similar to Example 1.

Example 5

(1) Dissolve 98% analytically pure Sn(SO ₄ )·2H ₂ O (200 mg) in deionized water (30 mL), and stir for 5 minutes under a magnetic stirring condition of 400 rpm to obtain solution A;

(2) Add 150 mg of high-purity multi-walled carbon nanotubes (purchased from Kena Carbon New Material Co., Ltd., purity > 97%, tube diameter 3-15 μm, tube length 15-30 μm) to solution A obtained in step (1) , continue to stir for 2h to obtain suspension B;

(3) Transfer the black suspension B obtained in step (2) to the main body of the gas-liquid discharge plasma cylinder reactor, the distance between the liquid level of the suspension and the lower end of the needle-shaped hollow electrode is 5 millimeters, and the high-purity argon gas is controlled (15 ml/min, purity 99.999%) directly blow the liquid surface through the needle-shaped hollow electrode, turn on the plasma power supply, and continue to react stably for 30 minutes under the conditions of input voltage 60 volts, output high voltage 8 kV, and discharge frequency 60 kHz , to obtain a black suspension C;

(4) Pass the black suspension C in step (3) through suction filtration to wash impurities and solid-liquid separation, and then wash and separate the solid black product D under a vacuum of 8000Pa at 60°C for 12h to obtain Quantum Dot tin oxide metal-supported multi-walled carbon nanotube composite material, denoted as 5-QDSnO ₂ /MWCNTs.

The 5-QDSnO ₂ /MWCNTs material prepared in this example can be used as the negative electrode of lithium-ion batteries, which can effectively improve the cycle stability of the tin oxide composite negative electrode. The presence of tin oxide can greatly improve the capacity of the original multi-walled carbon nanotubes and form more It is a stable SEI film, and the test result is similar to Example 1.

Claims (7)

1. A preparation method of a quantum dot tin oxide loaded multi-wall carbon nano tube composite material is characterized by comprising the following steps: the method comprises the following steps:

(1) Dissolving tin salt in water to obtain a tin salt solution;

(2) Uniformly mixing the multiwall carbon nanotube with a tin salt solution to obtain a suspension A;

(3) Placing the suspension A obtained in the step (2) into a gas-liquid discharge plasma reaction device, wherein the distance between the liquid surface of the suspension A and the lower end of a needle-shaped hollow electrode in the gas-liquid discharge plasma reaction device is 2-5 mm, and performing discharge reaction in an argon plasma atmosphere to obtain a suspension B; carrying out subsequent treatment to obtain a quantum dot tin oxide loaded multi-wall carbon nano tube composite material;

the dosage of the multi-wall carbon nano tube is as follows: the mass ratio of the tin ions to the multiwall carbon nanotubes is (0.04-0.8): 1;

conditions of the discharge reaction: controlling the input voltage to be 20-80V, the output high voltage to be 1-10 kilovolts, the discharge frequency to be 10-100 kilohertz, and the treatment duration to be 5-30 minutes;

the subsequent treatment refers to filtration and drying; the drying is vacuum drying, the vacuum degree is 5000-10000 Pa, the drying temperature is 60-80 ℃, and the time is 8-12 hours.

2. The method for preparing the quantum dot tin oxide supported multi-wall carbon nanotube composite material according to claim 1, which is characterized in that: the tin salt in the step (1) comprises more than one of tin chloride, stannous chloride, tin sulfate and stannous sulfate containing or not containing crystal water;

argon enters a discharge plasma reaction device through the needle-shaped hollow electrode in the step (3);

the flow rate of argon in the needle-shaped hollow electrode is 5-20 mL/min, and the purity is 99.999%;

the plasma discharge is a pulsed dc discharge.

3. The method for preparing the quantum dot tin oxide supported multi-wall carbon nanotube composite material according to claim 1, which is characterized in that: the mass volume ratio of the tin salt to the water is (10-200 mg) 30ml;

the step (2) of evenly mixing is evenly stirring; the stirring speed is 100-400 rpm, and the stirring time is 1-6 h.

4. The method for preparing the quantum dot tin oxide supported multi-wall carbon nanotube composite material according to claim 1, which is characterized in that: the gas-liquid discharge plasma reaction device comprises a needle-shaped hollow electrode, a reactor main body and a disc electrode; the reactor main body is a cavity with two open ends, the bottom of the reactor main body is closed by a disc electrode, and the needle-shaped hollow electrode is arranged in the cavity of the reactor main body through an opening at the upper end of the reactor main body; the needle-shaped hollow electrode is provided with an air inlet, one end of the needle-shaped hollow electrode, which is provided with the air inlet, is connected with the negative electrode output end of the rectifier, and one end of the air outlet is arranged in the reactor main body; the disc electrode is connected with the positive electrode output end of the rectifier; the air outlet of the needle-shaped hollow electrode is connected with the air storage device; the rectifier is connected with a power supply.

5. The method for preparing the quantum dot tin oxide supported multi-wall carbon nano tube composite material, which is characterized in that: the reactor main body is a cylindrical reactor, and is made of polytetrafluoroethylene; the needle-shaped hollow electrode is made of stainless steel, and the disc electrode is a graphite electrode; the depth of the reactor main body is 50 mm, and the diameter of the inner wall is 60 mm; and after the suspension A is added, the depth of the suspension A is 25-35 mm.

6. A quantum dot tin oxide supported multiwall carbon nanotube composite obtained by the method of any one of claims 1 to 5, characterized in that: the quantum dot tin oxide is loaded on the multiwall carbon nanotube composite material, nano-sized tin oxide particles are uniformly loaded on the multiwall carbon nanotube, the tin oxide loading is 15% -30% of the total mass of the quantum dot tin oxide loaded on the multiwall carbon nanotube composite material, and the size of the tin oxide particles is 4-6 nm.

7. The application of the quantum dot tin oxide loaded on the multi-wall carbon nano tube composite material according to claim 6, which is characterized in that: the quantum dot tin oxide is loaded on the multiwall carbon nanotube composite material and is used for a lithium ion battery as a negative electrode.

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