CN108598450A - A kind of CoP/ nitrogen-doped carbons/graphene nanocomposite material and preparation method thereof - Google Patents

Abstract

The invention discloses a kind of CoP/ nitrogen-doped carbons/graphene nanocomposite materials and preparation method thereof, the composite material is with graphene oxide, cabaltous nitrate hexahydrate, a hydration sodium hypophosphite, 4,4' bipyridyls and 1,3,5 trimesic acids are raw material, are prepared using simple hydro-thermal method and low temperature phosphor method.The method of the present invention is simple, of low cost, and prepared CoP/ nitrogen-doped carbons/graphene composite material is three-dimensional porous structure, can be applied to lithium/anode material of lithium-ion battery and presents good chemical property.

Description

A kind of CoP/nitrogen-doped carbon/graphene nanocomposite material and preparation method thereof

technical field

The invention belongs to the field of electrochemical power sources, and in particular relates to a CoP/nitrogen-doped carbon/graphene nanocomposite material with excellent electrochemical performance and a preparation method thereof.

Background technique

With the development of the new century, industry, agriculture and various economic developments are also very rapid, so human demand for energy is also increasing, and traditional energy such as petroleum, coal and other non-renewable resources have brought huge pollution to the environment , which is not in line with the concept of green, healthy and sustainable development that human beings pursue in the new century. In recent years, human beings have been committed to exploring the development, utilization and energy storage of clean and renewable energy. As an efficient and easy-to-storage electrical energy storage device, lithium-ion battery has received extensive attention and research. Compared with lithium-ion batteries, sodium-ion battery systems are secondary battery systems with the most research value and application prospects since lithium-ion battery systems due to the advantages of rich sodium resources, low price, and high potential.

The anode material of sodium ion battery is one of the important indicators to measure the performance of sodium ion battery. Among them, materials that can undergo conversion reactions with sodium in the negative electrode material include 3d transition metal oxides, sulfides, phosphides, and the like. In fact, most electrode materials have problems such as the actual capacity is far lower than the theoretical capacity, poor rate performance, fast reversible capacity decay, short cycle life, large charge and discharge potential polarization, and large energy loss. These problems are caused by the following reasons: (1) changes in the morphology and microstructure of electrode materials; (2) volume changes of the active materials on the electrodes, which eventually lead to the pulverization of the active materials and the mechanical disintegration of the electrodes; (3) ) Poor electrical conductivity leads to a greatly reduced utilization rate. In addition, compared with 3d transition metal oxides and sulfides, metal phosphides have the smallest polarization effect, high capacity and low voltage plateau. More importantly, transition metal phosphides have less volume expansion, and their metal-like characteristics also mean that transition metal phosphides conduct relatively well. Therefore, finding new negative electrode materials or designing and assembling new negative electrode material structures to achieve high energy and power density, long cycle life, low cost and high safety performance requirements of lithium/sodium ion batteries is the goal that scientists have been pursuing and has become the frontier of research. hotspot.

Contents of the invention

The purpose of the present invention is to address the above problems, to provide a CoP/nitrogen-doped carbon/graphene composite material with high specific capacity, large rate, long life and good stability of lithium/sodium storage performance, and provide the composite material A preparation method is provided.

For the above purpose, the CoP/nitrogen-doped carbon/graphene nanocomposite material of the present invention is prepared by the following method: graphene oxide is ultrasonically dispersed in N,N-dimethylformamide, and then cobalt nitrate hexahydrate is added , 4,4'-bipyridine and 1,3,5-trimellitic acid, stirred at room temperature for 0.5-1 hour, then transferred the resulting suspension into an autoclave, and reacted at 110-130°C for 5-8 hours , naturally cooled to room temperature, centrifuged, washed, and dried; the obtained dry product and sodium hypophosphite monohydrate are placed in an argon atmosphere in a mass ratio of 10 to 20:1, and calcined at 300 to 400 ° C for 1 to 3 hours to obtain CoP/nitrogen-doped carbon/graphene nanocomposites.

In the above preparation method, preferably the mass-volume ratio of graphene oxide to N,N-dimethylformamide is 0.5-0.9mg:1mL, and the mass ratio of graphene oxide to cobalt nitrate hexahydrate is 1:15-30, The molar ratio of cobalt nitrate hexahydrate to 4,4'-bipyridine and 1,3,5-trimesic acid is 1:1:1.

In the above preparation method, it is preferred to transfer the obtained suspension into an autoclave and react at 120° C. for 6 hours.

In the above preparation method, it is further preferred that the obtained dried product and sodium hypophosphite monohydrate are placed in an argon atmosphere at a mass ratio of 15-18:1, and calcined at 320-350° C. for 2 hours.

For the first time, the present invention combines cobalt-4,4'-bipyridine-1,3,5-trimellitic acid with graphene to obtain cobalt-4,4'-bipyridine-1,3,5-pyridine Benzene tricarboxylic acid/graphene composite material, and then obtained porous CoP/nitrogen-doped carbon/graphene nanocomposite material by low-temperature phosphating. The present invention uniformly disperses nano-CoP particles on the nitrogen-doped carbon/graphene nanocomposite material through a simple and low-cost method, and uses the CoP/nitrogen-doped carbon/graphene nanocomposite material of the present invention as the battery negative electrode material, exhibited superior lithium/sodium storage performance.

Description of drawings

Fig. 1 is the X-ray powder diffraction spectrum of nitrogen-doped graphene, CoP/nitrogen-doped carbon, CoP/nitrogen-doped carbon/graphene nanocomposite prepared in Example 1.

FIG. 2 is an SEM image of the CoP/nitrogen-doped carbon/graphene nanocomposite prepared in Example 1.

3 is a TEM image of the CoP/nitrogen-doped carbon/graphene nanocomposite prepared in Example 1.

Fig. 4 is a lithium storage cycle performance graph of nitrogen-doped graphene, CoP/nitrogen-doped carbon, and the CoP/nitrogen-doped carbon/graphene nanocomposite prepared in Example 1.

Fig. 5 is a lithium storage rate performance diagram of nitrogen-doped graphene, CoP/nitrogen-doped carbon, and the CoP/nitrogen-doped carbon/graphene nanocomposite prepared in Example 1.

6 is a diagram of the sodium storage cycle performance of the CoP/nitrogen-doped carbon/graphene nanocomposite prepared in Example 1.

FIG. 7 is a diagram of the sodium storage rate performance of the CoP/nitrogen-doped carbon/graphene nanocomposite prepared in Example 1.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

Example 1

Add 35 mg of graphene oxide (GO) to 70 mL of N,N-dimethylformamide (DMF) and sonicate for 2 hours to obtain a uniform and dispersed GO/DMF suspension, and then 1.0186 g (3.5 mmol) of hexahydrate Add cobalt nitrate, 0.5466g (3.5mmol) 4,4'-bipyridine and 0.7355g (3.5mmol) 1,3,5-trimellitic acid to the above GO/DMF suspension and stir for 0.5 hours to obtain a purple suspension liquid, and then transferred it into a 100mL autoclave, reacted at 120°C for 6 hours, cooled naturally to room temperature, centrifuged, washed, and dried. The obtained dried product and sodium hypophosphite monohydrate were placed in an argon atmosphere at a mass ratio of 20:1, and calcined at 350° C. for 2 hours to obtain a CoP/nitrogen-doped carbon/graphene nanocomposite material.

Example 2

Add 49mg graphene oxide to 70mL DMF and sonicate for 2 hours to obtain a uniform and dispersed GO/DMF suspension, then add 1.0186g (3.5mmol) cobalt nitrate hexahydrate, 0.5466g (3.5mmol) 4,4' -Bipyridine and 0.7355g (3.5mmol) 1,3,5-trimellitic acid were added to the above GO/DMF suspension and stirred for 0.5 hours to obtain a purple suspension, which was then transferred to a 100mL autoclave, and After reacting at 110°C for 5 hours, cool naturally to room temperature, centrifuge, wash and dry. The obtained dried product and sodium hypophosphite monohydrate were placed in an argon atmosphere at a mass ratio of 15:1, and calcined at 300° C. for 2 hours to obtain a CoP/nitrogen-doped carbon/graphene nanocomposite material.

Example 3

Add 63mg graphene oxide to 70mL DMF and sonicate for 2 hours to obtain a uniform and dispersed GO/DMF suspension, then add 1.0186g (3.5mmol) cobalt nitrate hexahydrate, 0.5466g (3.5mmol) 4,4' -Bipyridine and 0.7355g (3.5mmol) 1,3,5-trimellitic acid were added to the above GO/DMF suspension and stirred for 0.5 hours to obtain a purple suspension, which was then transferred to a 100mL autoclave, and After reacting at 130°C for 8 hours, it was naturally cooled to room temperature, centrifuged, washed, and dried. The obtained dry product and sodium hypophosphite monohydrate were placed in an argon atmosphere at a mass ratio of 18:1, and calcined at 320° C. for 2 hours to obtain a CoP/nitrogen-doped carbon/graphene nanocomposite material.

The inventors used X-ray diffractometer, scanning electron microscope and transmission electron microscope to characterize the structure and morphology of the sample obtained in Example 1, and the results are shown in Figures 1-3. It can be seen from Figure 1 that the XRD pattern of the sample contains the diffraction peaks of CoP and graphene. It can be seen from the SEM image of Figure 2 that there are a large number of CoP particles in the sample and the CoP nanoparticles are uniformly dispersed in the nitrogen-doped carbon/graphene The composite material with a three-dimensional structure can also be proved from Figure 3 that the ultra-small CoP nanoparticles are uniformly dispersed on the nitrogen-doped carbon/graphene sheet structure, and the diameter of the CoP particles is about 5nm. In addition, the X-ray powder diffraction spectrum of the product obtained in Example 2 and Example 3 is the same as in Example 1, and the SEM and TEM figures show that the samples obtained in Example 2 and Example 3 are similar to the morphology of the sample in Example 1, both Composite materials for porous materials.

In order to prove the beneficial effects of the present invention, the inventor sampled the composite materials of the above-mentioned Examples 1 to 3, prepared them into working electrodes respectively, and then assembled them into lithium-ion batteries and sodium-ion batteries respectively, and tested the electrochemical performance of the batteries. The specific test conditions as follows:

(1) Preparation of working electrode

Mix the powdery composite material prepared in the above examples with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1; then drop in excess N-methylpyrrolidone to stir the mixture; mix the mixture The uniform slurry is evenly coated on the nickel foam disc, and placed in a vacuum drying oven at 80°C to dry; finally, it is placed under a tablet machine to be flattened and weighed. According to the feeding ratio, the mass of the active material in the electrode is 1.8±0.1 mg/cm ² .

(2) Li-ion battery assembly

The pole piece prepared by the above step (1) is used as the working electrode, pure metal Li is used as the counter electrode and the reference electrode, the separator is a commercial polypropylene porous membrane, and the electrolyte used is a concentration of 1mol/L LiPF ₆ / Ethylene carbonate-dimethyl carbonate-ethyl methyl carbonate (volume ratio 1:1:1).

(3) Sodium ion battery assembly

With the pole piece prepared by the above step (1) as the working electrode, pure metal Na as the counter electrode and reference electrode, the diaphragm is a commercial polypropylene porous membrane, and the electrolyte is 1mol/L NaClO ₄ /propylene carbonate-carbonic acid Vinyl ester (volume ratio 1:1, and containing 5vol% fluoroethylene carbonate).

The above assembly process is completed in a glove box filled with Ar atmosphere, and finally sealed with a sealing machine.

(4) Electrochemical performance test

The electrochemical performance test of lithium/sodium ion battery is through the assembled CR2025 button battery as the test device. The specific capacity, cycle stability and rate performance are tested by Wuhan Landian CT2001A battery tester, and the test results are shown in Figures 4-7.

Figure 4 shows in a comparative manner the nitrogen-doped graphene, CoP/nitrogen-doped carbon composite material and the CoP/nitrogen-doped carbon/graphene nanocomposite prepared in Example 1 at a current density of 0.2A g ^- Lithium storage cycle performance under ¹ . It can be seen from the figure that the reversible specific capacity of the CoP/nitrogen-doped carbon/graphene nanocomposite material is as high as 634mAh/g after being charged and discharged 100 times, and the Coulombic efficiency is about 99%. However, the nitrogen-doped graphene and CoP/nitrogen-doped carbon composites show continuous and large attenuation phenomenon, and the reversible specific capacities are only 287 and 129mAh/g after charging and discharging for 100 times. Figure 5 is a graph of the rate performance of the above materials with a current density from 0.25 to 4A/g and back to 0.25A/g. Obviously, the average reversible specific capacities of the CoP/nitrogen-doped carbon/graphene nanocomposites prepared in Example 1 are 755, 639, 576, 541 and 507mAh/g, respectively. When the circulating current is reduced to 0.25A/g, the average discharge specific capacitance of the composite can still recover to 647mAh/g. At the same current density, nitrogen-doped graphene and CoP/nitrogen-doped carbon composites show poor rate performance. It can be seen from both Figures 4 and 5 that the CoP/nitrogen-doped carbon/graphene nanocomposite material prepared in Example 1 of the present invention shows excellent lithium storage performance. After testing, compared with the lithium storage performance of the CoP/nitrogen-doped carbon/graphene nanocomposite obtained in Example 2 and Example 3, the difference in specific capacity is only ±3%.

Figure 6 shows the sodium storage cycle performance of the CoP/nitrogen-doped carbon/graphene nanocomposite prepared in Example 1 at a current density of 0.1A g ^-1 . It can be seen from the figure that the reversible specific capacity of the CoP/nitrogen-doped carbon/graphene nanocomposite material can reach 555mAh/g after charging and discharging 100 times, and the Coulombic efficiency is about 99%. Fig. 7 is a graph of the rate performance of the CoP/nitrogen-doped carbon/graphene nanocomposite prepared in Example 1 at a current density from 0.1 to 3.2 A/g and back to 0.1 A/g. It is obvious that the average reversible specific capacities of CoP/nitrogen-doped carbon/graphene nanocomposites are 680, 588, 497, 434, 380, and 337 mAh/g, respectively. When the circulating current is reduced to 0.1A/g, the average discharge specific capacitance of the composite can still recover to 563mAh/g. It can be seen from Figures 6 and 7 that the CoP/nitrogen-doped carbon/graphene composite material prepared in Example 1 of the present invention shows excellent sodium storage performance. After testing, compared with the lithium storage performance of the CoP/nitrogen-doped carbon/graphene nanocomposite obtained in Example 2 and Example 3, the difference in specific capacity is only ±4%.

Claims (6)

1. a kind of preparation method of CoP/ nitrogen-doped carbons/graphene composite material, it is characterised in that：By graphene oxide ultrasound point It dissipates in n,N-Dimethylformamide, adds cabaltous nitrate hexahydrate, 4,4'- bipyridyls and 1,3,5- trimesic acids, room temperature Gained suspension, is then transferred in autoclave, is reacted 5~8 hours at 110~130 DEG C by stirring 0.5~1 hour, naturally cold But room temperature, centrifugation, washing, drying are arrived；Gained desciccate and a waterside sodium phosphate are 10~20 in mass ratio:1 is placed in argon gas In atmosphere, is calcined 1~3 hour at 300~400 DEG C, obtain CoP/ nitrogen-doped carbons/graphene nanocomposite material.

2. the preparation method of CoP/ nitrogen-doped carbons/graphene nanocomposite material according to claim 1, feature exist In：Quality-volume ratio of the graphene oxide and N,N-dimethylformamide is 0.5~0.9mg:1mL.

3. the preparation method of CoP/ nitrogen-doped carbons/graphene nanocomposite material according to claim 2, feature exist In：The mass ratio of the graphene oxide and cabaltous nitrate hexahydrate is 1:15~30, cabaltous nitrate hexahydrate and 4,4'- bipyridyls, The molar ratio of 1,3,5- trimesic acids is 1:1:1.

4. the preparation method of CoP/ nitrogen-doped carbons/graphene nanocomposite material according to claim 1, feature exist In：Gained suspension is transferred in autoclave, is reacted 6 hours at 120 DEG C.

5. the preparation method of CoP/ nitrogen-doped carbons/graphene nanocomposite material according to claim 1, feature exist In：Gained desciccate and a waterside sodium phosphate are 15~18 in mass ratio:1 is placed in argon gas atmosphere, at 320~350 DEG C Calcining 2 hours.

6. CoP/ nitrogen-doped carbons/graphene nanocomposite material that Claims 1 to 5 any one method is prepared.