CN105576211A - A preparation method of nitrogen-doped carbon-coated graphene material for lithium-ion batteries - Google Patents

Abstract

The invention provides a preparation method of a nitrogen-doped carbon-coated graphene material of a lithium ion battery, which is characterized by comprising the following steps of: a. preparing a graphene oxide suspension: preparing graphite oxide by a hummer method, and ultrasonically stripping the graphite oxide in deionized water to form a graphene oxide suspension; b. preparing a nitrogen-doped carbon-coated graphene material: adding a certain amount of cyanamide aqueous solution into the graphene oxide suspension, uniformly stirring, placing into a closed reaction kettle for hydrothermal reaction, washing a hydrothermal reaction product with deionized water, drying, and performing high-temperature treatment under a protective atmosphere to obtain the nitrogen-doped carbon-coated graphene material of the lithium ion battery. The method is simple, strong in operability and good in repeatability.

Description

A preparation method of nitrogen-doped carbon-coated graphene material for lithium-ion batteries

technical field

The invention belongs to the field of electrochemical materials, and in particular relates to a preparation method of a nitrogen-doped carbon-coated graphene material for a lithium ion battery.

Background technique

Lithium-ion batteries have been widely used in portable devices such as mobile phones, tablets, laptops, cameras, and more. They put forward new requirements for lithium-ion batteries: high rate, high capacity, safety and stability, longer service life, mature technology, cheap price, environmental friendliness and so on. Faced with these new requirements, lithium-ion batteries will face various major challenges in order to be able to quickly adapt to this new generation of the market.

Graphene is a new type of carbon nanomaterial and has become a research hotspot today. Graphene is a new carbonaceous material that is tightly packed into a two-dimensional honeycomb lattice structure by a single layer of sp2 carbon atoms. The basic structural unit is a stable benzene six-membered ring. This special microstructure makes graphene have a larger theoretical specific surface area, resulting in a higher lithium storage capacity. However, a single graphene material is used as an electrode material, which is limited by many factors, such as the graphene specific surface is too large, the sheets are easy to agglomerate, and the irreversible capacity loss is greatly improved (lower first Coulombic efficiency (<73% )) and reduce its conductivity as an electrode material, which has a negative impact on the electrode production process. In particular, when a single graphene electrical material is charged and discharged at a high rate, the capacity decays too quickly.

Carbon-coated core-shell nanostructures have been widely used as electrode materials for LIBs, and these core-shell structures can be obtained by one-step hydrothermal method using carbohydrates as carbon sources. The excellent properties of core/shell materials are related to their unique structures. The performance of core particles is significantly improved with the change of the shell surrounding the core particles. This is due to the synergistic effect of core/shell materials and the interaction between the two will produce The characteristics of multiple functions can overcome most of the defects of each and give full play to the advantages of both. Therefore, the nitrogen-doped carbon-coated graphene material lithium ion battery negative electrode material prepared by the hydrothermal nitrogen doping method used in the present invention has excellent electrochemical performance.

Contents of the invention

The purpose of the present invention is to provide a high-capacity, high-rate nitrogen-doped carbon-coated graphene material preparation method for the poor rate performance of graphene negative electrode materials. The method is simple, operable and repeatable.

In order to realize the above purpose of the present invention, the present invention provides the following technical solutions:

A preparation method of a nitrogen-doped carbon-coated graphene material for a lithium-ion battery, characterized in that it comprises the following steps:

a. Preparation of graphene oxide suspension: graphite oxide was prepared by hummer method, and graphite oxide was ultrasonically peeled off in deionized water to form graphene oxide suspension;

b. Preparation of nitrogen-doped carbon-coated graphene material: add a certain amount of cyanamide aqueous solution to the graphene oxide suspension, stir evenly, put it in a closed reaction kettle for hydrothermal reaction, and deionize the hydrothermal reaction product Washing with water, drying, and high-temperature treatment under a protective atmosphere to obtain a nitrogen-doped carbon-coated graphene material for a lithium-ion battery.

The power of the ultrasonic device described in step a is 200W~500W, and the ultrasonic time is 0.5~2.0h.

The concentration of graphene oxide in the graphene oxide suspension described in step a is 0.1 to 2.0 mg/mL.

The concentration of the cyanamide aqueous solution described in step b is 20wt% ~ 50wt%.

The mass ratio of cyanamide described in step b and graphene oxide is 1～5:80.

The temperature of the solvent heat treatment in step b is 160-200° C., and the time is 4-10 hours.

The temperature of the high temperature treatment in step b is 600-100° C., and the time is 1-6 hours.

The protective atmosphere described in step b is any one of nitrogen, argon, helium, neon, krypton and xenon.

A lithium battery, characterized in that: the lithium-ion battery nitrogen-doped carbon-coated graphene material prepared by any one of claims 1-8 is used.

The present invention has following advantage and beneficial effect:

(1) The nitrogen-doped carbon-coated graphene material with high specific capacity and good rate prepared by the present invention has not been reported in the literature for lithium-ion battery anode materials, and has a good application and development prospect.

(2) The present invention realizes the nitrogen-doped carbon-coated graphene material of the negative electrode material of the lithium ion battery prepared by nitrogen-doped carbon in one step of hydrothermal treatment. This kind of structural material can increase the specific surface area of nitrogen-doped carbon-coated graphene materials, which is conducive to improving the lithium storage specific capacity of nitrogen-doped carbon-coated graphene materials, and is conducive to the penetration of electrolytes, preventing the reduction of graphene. The agglomeration and overlap in the process can improve the electronic conductivity of nitrogen-doped carbon-coated graphene material anode materials, and provide research ideas for seeking new lithium-ion battery anode materials.

(3) In the preparation process of lithium ion nitrogen-doped carbon-coated graphene material negative electrode material: graphite oxide was prepared by hummer method, and then graphite oxide was ultrasonically dispersed in deionized water to form a hydrophilic graphene oxide suspension, oxidized The surface of graphene contains a large number of carboxyl, hydroxyl, carbonyl and other oxygen-containing groups. Then add cyanamide, stir evenly, and put it into a closed reactor for hydrothermal reaction. Under the high temperature and high pressure environment of the reactor, cyanamide will polymerize and coat the surface of graphene oxide. At the same time, cyanamide will also combine with graphite Groups on the surface of the alkene react to polymerize. In particular, during the entire hydrothermal reaction process, graphene oxide curls, folds, and forms a three-dimensional three-dimensional structure. Then, the precursor obtained by hydrothermal treatment is carbonized at a high temperature under a protective atmosphere to obtain a nitrogen-doped carbon-coated graphene material.

Description of drawings

Figure 1 is a transmission electron microscope image (TEM) of graphene oxide.

Fig. 2 is a transmission electron microscope image (TEM) and element mapping of the nitrogen-doped carbon-coated graphene material in Example 1.

Fig. 3 is the charge-discharge curve of the nitrogen-doped carbon-coated graphene material in Example 1 at a current density of 0.01-3.0V and 200mA/g.

Fig. 4 is the cycle curve of the nitrogen-doped carbon-coated graphene material in Example 1 at 0.01-3.0V and 200mA/g current density.

Fig. 5 is the rate cycle curve of the nitrogen-doped carbon-coated graphene material in Example 1 at a voltage of 0.01-3.0V.

Fig. 6 is the XRD spectrum of the nitrogen-doped carbon-coated graphene material in Example 2.

Fig. 7 is the cycle curve of the nitrogen-doped carbon-coated graphene material in Example 2 at 0.01-3.0V and 200mA/g current density.

Fig. 8 is the rate cycle curve of the nitrogen-doped carbon-coated graphene material in Example 3 at a voltage of 0.01-3.0V.

detailed description

In order to illustrate the present invention in more detail, the following preparation examples are given. However, the scope of the present invention is not limited thereto.

Embodiment 1, the preparation method of nitrogen-doped carbon-coated graphene material, comprises the following steps:

Graphite oxide was prepared by the hummer method, 80 mg of graphite oxide was sonicated in 70 mL of deionized water with a 250W ultrasonic instrument for 1 hour to form a graphene oxide suspension, then 10 mL of cyanamide aqueous solution (50wt%) was added, stirred evenly, and put into 100 mL for reaction In the kettle, hydrothermal reaction was carried out at 180°C for 6 hours, the hydrothermal reaction product was washed with deionized water, dried, and treated at a high temperature of 700°C for 2 hours under a nitrogen atmosphere to obtain a nitrogen-doped carbon-coated graphene material.

Electrochemical performance test of the lithium ion nitrogen-doped carbon-coated graphene material prepared in Example 1:

Mix the lithium-ion nitrogen-doped carbon-coated graphene material prepared in Example 1 with conductive carbon black and binder polyvinylidene chloride (PVDF) at a mass ratio of 8:1:1, and then add an appropriate amount of N-methylpyrrolidone (NMP) was stirred evenly, coated on copper foil, dried in a vacuum oven at 90°C, and cut into pieces on a punching machine to obtain nitrogen-doped carbon-coated graphene material electrode sheets. The obtained electrode was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the electrolyte was a mixed system containing 1MLiPF6/(EC+DMC) (volume ratio: 1:1), and the separator was a microporous polypropylene membrane (Celgard2400). Ar) assembled into a 2025-type button cell in the glove box.

The testing equipment and methods are as follows:

The instrument used for TEM analysis is the JSM-2010 projection electron microscope (TEM) of Nippon Electronics Co., Ltd. to observe the microscopic morphology of the sample surface. The acceleration voltage is 200KV. .

The instrument used for XRD analysis is the XD-2 X-ray diffractometer (XRD) of Beijing Puxi General Instrument Co., Ltd. to characterize the crystal phase structure material of the final product prepared. The test conditions are Cu target, Kα radiation, 36kV, 30mA, step width ^0.02o , scan range 10～ ^80o . The sample is powder placed in the groove of the sample table and flattened for direct detection.

The instrument used for the charge and discharge test is the BTS51800 battery test system of Shenzhen Newwell Electronics Co., Ltd., the model is CT-3008W, and the electrochemical test is performed within the voltage range of 0.01-3.0V.

It can be seen from Figure 1 that the prepared graphene oxide has a two-dimensional sheet structure. It can be seen from Figure 2 that after the hydrothermal reaction, the graphene oxide is curled and folded to form a three-dimensional structure, and the surface of the graphene is coated with nitrogen-doped carbon formed by hydrothermal glucose and cyanamide. The element mapping shows that the nitrogen-doped Evenly mixed.

From Figures 3 and 4, it can be seen that the specific capacity of the material reaches 575mAh/g for the first time at 0.01-3.0V, 200mA/g current density, and the specific capacity remains at 380mAh/g after 100 cycles of discharge. It can be seen from Figure 5 that the material has good rate cycle performance at different current densities of 0.01-3.0V, and the discharge specific capacity reaches 248mAh/g at a current density of 1680mA/g.

Embodiment 2, the preparation method of lithium ion nitrogen-doped carbon-coated graphene material, comprises the following steps:

Graphite oxide was prepared by the hummer method, 80 mg of graphite oxide was sonicated in 60 mL of deionized water with a 250 W ultrasonic instrument for 1 hour to form a graphene oxide suspension, then 20 mL of cyanamide aqueous solution (50wt%) was added, stirred evenly, and put into 100 mL for reaction In the still, 160°C hydrothermal reaction for 10 hours, the hydrothermal reaction product was washed with deionized water, dried, and treated at 600°C under nitrogen atmosphere for 2 hours to obtain a nitrogen-doped carbon-coated graphene material.

The electrochemical performance test method of the lithium ion nitrogen-doped carbon-coated graphene material prepared in embodiment 2 is the same as embodiment 1:

It can be seen from Figure 6 that the XRD pattern of the material has a steamed bun peak at about 23°, which is a typical characteristic peak of glucose hydrothermal carbon, and the characteristic peak of graphene does not appear because the content of graphene in the composite material is small , and graphene is well dispersed. It can be seen from Figure 7 that the specific capacity of the material reaches 475mAh/g for the first time at 0.01-3.0V, 200mA/g current density, and the specific capacity remains at 362.5mAh/g after 100 cycles.

Embodiment 3, the preparation method of lithium ion nitrogen-doped carbon-coated graphene material, comprises the following steps:

Graphite oxide was prepared by the hummer method, 80 mg of graphite oxide was sonicated in 65 mL of deionized water for 1.5 hours with a 250W ultrasonic instrument to form a graphene oxide suspension, then 15 mL of cyanamide aqueous solution (50wt%) was added, stirred evenly, and put into 100 mL for reaction In the still, 170°C hydrothermal reaction for 8 hours, the hydrothermal reaction product was washed with deionized water, dried, and treated at 800°C for 2 hours under a nitrogen atmosphere to obtain a nitrogen-doped carbon-coated graphene material.

The electrochemical performance testing method of the lithium ion nitrogen-doped carbon-coated graphene material prepared in embodiment 3 is the same as in embodiment 1:

It can be seen from Figure 8 that the material has good rate cycle performance at 0.01-3.0V and different current densities, and the discharge specific capacity reaches 180mAh/g at a current density of 1680mA/g.

Comparative example 1, the preparation method of lithium ion nitrogen-doped carbon-coated graphene material, comprises the following steps:

Graphite oxide was prepared by the hummer method. 80 mg of graphite oxide was sonicated in 65 mL of deionized water with a 250 W ultrasonic instrument for 1.5 hours to form a graphene oxide suspension, which was placed in a 100 mL reactor and subjected to hydrothermal reaction at 170 °C for 8 hours. The reaction product was washed with deionized water, dried, and treated at 800° C. for 2 hours under a nitrogen atmosphere to obtain a graphene material.

The electrochemical performance test method of the graphene material prepared by comparative example 1 is identical with embodiment 1:

The rate cycle performance at different current densities is poor, and the specific discharge capacity is less than 130mAh/g.

It can be concluded from the data that the lithium ion battery prepared by the lithium ion nitrogen-doped carbon-coated graphene material prepared by the preparation method of the present invention has excellent rate cycle performance at different electric densities, and has a significant difference compared with the comparative example. Advantage.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention , should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (9)

1. a preparation method for lithium ion battery nitrogen-doped carbon coated graphite alkene material, is characterized in that comprising the following steps:

A, preparation graphene oxide suspension: adopt hummer legal system for graphite oxide, by graphite oxide ultrasonic strip off formation graphene oxide suspension in deionized water;

B, prepare nitrogen-doped carbon coated graphite alkene material: in graphene oxide suspension, add a certain amount of cyanamide aqueous solution; stir; put into closed reactor and carry out hydro-thermal reaction; hydro-thermal reaction product is spent deionized water; dry; high-temperature process under protective atmosphere, obtains lithium ion battery nitrogen-doped carbon coated graphite alkene material.

2. the preparation method of lithium ion battery nitrogen-doped carbon coated graphite alkene material according to claim 1, is characterized in that: the power of the Vltrasonic device described in step a is 200W ~ 500W, and ultrasonic time is 0.5 ~ 2.0h.

3. the preparation method of lithium ion battery nitrogen-doped carbon coated graphite alkene material according to claim 1, is characterized in that: the concentration 0.1 ~ 2.0mg/mL of graphene oxide in the graphene oxide suspension described in step a.

4. the preparation method of lithium ion battery nitrogen-doped carbon coated graphite alkene material according to claim 1, is characterized in that: the cyanamide concentration of aqueous solution described in step b is 20wt% ~ 50wt%.

5. the preparation method of lithium ion battery nitrogen-doped carbon coated graphite alkene material according to claim 1, is characterized in that: the cyanamide described in step b and the mass ratio of graphene oxide are 1 ~ 5:80.

6. the preparation method of lithium ion battery nitrogen-doped carbon coated graphite alkene material according to claim 1, it is characterized in that: the solvent heat treatment temperature described in step b is 160 ~ 200 DEG C, the time is 4 ~ 10 hours.

7. the preparation method of lithium ion battery nitrogen-doped carbon coated graphite alkene material according to claim 1, it is characterized in that: the high-temperature process temperature described in step b is 600 ~ 100 DEG C, the time is 1 ~ 6 hour.

8. the preparation method of lithium ion battery nitrogen-doped carbon coated graphite alkene material according to claim 1, is characterized in that: the protective atmosphere described in step b is any one of nitrogen, argon gas, helium, neon, Krypton and xenon.

9. a lithium battery, is characterized in that: have employed lithium ion battery nitrogen-doped carbon coated graphite alkene material prepared by any one of claim 1-8.