CN105977458A - Nano diamond powder and graphene composite electrode material and preparation method thereof - Google Patents

Abstract

The invention discloses a nano-diamond powder/graphene composite electrode material used for a negative electrode of a lithium battery and a preparation method thereof. Specifically, this method uses citric acid, urea, and nano-diamond powder as carbon sources, and undergoes microwave heating treatment to obtain massive solid powder, and then conducts high-temperature carbonization treatment under the protection of inert gas to obtain composite electrode materials; nano-diamond powder can also be It is directly mixed with graphene, treated with high-frequency ultrasonic in absolute ethanol, and then dried to obtain a composite electrode material. The nano-diamond powder/graphene composite electrode material is ground into powder, and fully ground and mixed with other carbon materials under the action of a binder to prepare the negative electrode of the lithium-ion battery. The lithium-ion battery made of the nano-diamond powder/graphene composite electrode material of the method as a cathode has excellent performances such as high specific capacity, good cycle performance, and high charge-discharge coulombic efficiency. Moreover, the preparation method is simple, low in cost, environmentally friendly, and has good application prospects.

Description

Composite electrode material of nano-diamond powder and graphene and preparation method thereof

technical field

The invention belongs to the technical field of negative electrode materials of lithium ion batteries, and relates to a composite electrode material of nano-diamond powder and graphene and a preparation method thereof.

Background technique

Secondary batteries are the core components of modern electronic appliances such as mobile phones, laptop computers, electric tools, electric vehicles, national defense and aviation electronic appliances. Lithium-ion batteries have the advantages of high energy density, long cycle life, no memory effect, and environmental friendliness. , become the first choice in secondary batteries, and the development of high-performance lithium-ion batteries will greatly alleviate energy shortages and improve the environment, which is of great significance to the development of the national economy and the protection of national security. One of the key factors to improve the energy density and cycle performance and life of lithium-ion batteries is the negative electrode material of lithium-ion batteries. At present, the anode materials of commercialized lithium-ion batteries are mainly graphite carbon materials. However, its theoretical lithium intercalation capacity of 372mAhg ^-1 is too low to meet the product demand. People have been developing anode materials with excellent performance to replace graphite carbon materials. Silicon has the highest theoretical specific capacity, which can reach 4200mAhg ^-1 . At room temperature, the actual specific capacity can reach 3579mAhg ^-1 , which has attracted people's attention. However, silicon has poor conductivity, and it is easy to generate a huge volume when deintercalating lithium. Swelling will seriously affect the cycle performance of electrode materials. In recent years, studies have found that tin-based composite oxides such as SnO and SnO ₂ , and transition metal oxides such as FeO, CoO, MoO and Cu ₂ O, have a mass specific capacity greater than 600mAhg ^-1 , but in the process of battery charge and discharge reactions, the volume The change is also very large, causing the failure or even pulverization of the electrode material, resulting in low actual capacity and low cycle stability. As the charge and discharge cycle proceeds, its capacity decays rapidly. Therefore, it is necessary to provide an anode material that is compatible with the mature process, has simple process, low cost, and has excellent electrochemical properties such as high specific capacity, good cycle stability, and good rate performance.

The application number is 201510104614.9, which is a patent application titled "Preparation method of large-scale graphene/graphite composite negative electrode material". Process to prepare graphite oxide, add potassium permanganate and H ₂ O ₂ to further prepare large-scale graphene oxide, and then obtain a mixture solution of large-scale graphene oxide and graphite by ultrasonic treatment, and then anneal to obtain large-scale graphene-graphite composite Negative material. The large-scale graphene/graphite composite anode material prepared by this method has a lithium storage capacity of 372mAhg ^-1 to 401mAhg ^-1 , a coulombic efficiency of 85% to 90%, and a capacity decay of 162mAhg ^-1 at a rate of 5C. Poor, and the preparation process is more complex, and produce greater environmental pollution.

The prior art close to the present invention is the patent application No. 201510545536.6, "a graphene-doped porous carbon/ferric oxide nanofiber lithium battery negative electrode material and its preparation method", which utilizes electrospinning Technology prepares polypropylene nitrile/polymethyl methacrylate nanofibers doped with iron salts and graphene, and obtains graphene-doped porous carbon/ferric oxide nanofiber lithium battery anode materials through pre-oxidation and high-temperature carbonization. The graphene-doped porous carbon/ferric oxide nanofiber lithium battery anode material prepared by this method has a lithium storage capacity of 720 mAhg ^-1 ~754 mAhg ^-1 , and a capacity decay of 480 mAhg ^-1 at a rate of 5C. Poor, and Fe ₃ O ₄ will undergo huge volume changes and serious particle agglomeration during the process of intercalation and delithiation, resulting in poor charge, transport and diffusion performance. As a negative electrode material, the cycle stability and rate performance of the battery will be poor. high.

Nano-diamond is an important carbon material. It not only has high hardness, high strength, good chemical stability, and excellent thermal conductivity, but also has a large specific surface area and high surface activity. It is used in composite coatings, precision polishing, mechanical lubrication, drug loading, and magnetic recording , electronic imaging and many other fields have a wide range of applications. Nano-diamonds can be prepared by explosive nano-diamonds, which are usually prepared by detonation of a mixture of graphite powder and explosives under negative oxygen conditions. The use of nano-diamond can increase the adsorption of lithium, improve the reversible capacity and the transmission rate of lithium ions. Diamond nanoparticles have the advantages of stability and small volume change. Introducing nanodiamond and other carbon nanomaterials into a composite structure into a lithium battery cathode will improve the performance of the cathode and the battery.

Contents of the invention

The technical problem to be solved by the present invention is to combine the traditional carbon material graphene and diamond nanomaterials through the selection of functional materials and the design of special structures to obtain a kind of electrochemical performance, low cost, and environmental protection. Electrode materials with new structures.

The present invention adopts a microwave-assisted method to prepare carbon materials, and by adding nano-diamond powders with different mass ratios to carbon reaction precursors, a composite electrode material of nano-diamond powder and graphene nanosheets is obtained, in order to further improve the storage of carbon materials. Lithium properties.

The specific technical scheme of the electrode material of the present invention is as follows.

A kind of nano-diamond powder and graphene composite electrode material, it is characterized in that, be the lamellar structure of multilayer, there is corrugated fold on the surface, nano-diamond particle is adsorbed on the graphene sheet surface; The mass ratio of nano-diamond powder and graphene is 0.066～0.334:1.

The nano-diamond particles have a particle size of 5-10 nm.

There are two methods for the preparation of the above-mentioned nano-diamond powder and graphene composite electrode material - microwave-assisted method and direct mixing method. The specific technical solutions of the preparation method of the electrode material are as follows.

The technical scheme of preparing nano-diamond powder and graphene composite electrode material by microwave-assisted method is: a preparation method of nano-diamond powder and graphene composite electrode material, dissolving citric acid and urea in an appropriate amount of deionized water to form a colorless transparent solution, Then add nano-diamond powder, after high-frequency ultrasonic treatment for 30-60 minutes, place the obtained solution in a microwave oven and heat it for 10-15 minutes at a power of 850W, the solution turns from colorless to yellowish brown, and finally turns into a dark brown solid compound; The obtained solid composite is dried and then carbonized at 900° C. for 2 hours under the protection of an inert gas to obtain the nano-diamond powder and graphene composite electrode material.

Wherein, the mass ratio of citric acid to urea can be 1:3-4; the ratio of the mass of nano-diamond powder to the sum of mass of citric acid and urea is 0.005-0.025:1.

The solid composite is dried at 60-80° C. for 1-2 hours to remove residual moisture.

The technical scheme of preparing nano-diamond powder and graphene composite electrode material by direct mixing method is: a preparation method of nano-diamond powder and graphene composite electrode material, mixing nano-diamond powder and graphene in a mass ratio of 1:3-4 , subjected to high-frequency ultrasonic treatment in absolute ethanol for 6-8h; then the suspension of graphene and nano-diamond powder was dried at 60°C until the absolute ethanol evaporated completely to obtain nano-diamond powder/graphene composite electrode material .

Use nano-diamond powder and graphene composite electrode materials to make negative electrodes for lithium-ion batteries. The specific process is: crush and grind nano-diamond powder and graphene composite electrode materials until the particle size of the powder reaches nanoscale, and use it with lithium battery cathodes Carbon black (conductive aid) is mixed, ground under the action of polyvinylidene fluoride (PVDF, binder), and a certain amount of 1-methyl-2-pyrrolidone (NMP, solvent) is added so that it is stirred by magnetic force The viscous fluid is stirred into a viscous fluid; the viscous fluid is applied to the current collector and dried at 120°C; finally, it is cut into an electrode shape and compacted to obtain a negative electrode of a lithium-ion battery composed of nano-diamond powder and graphene.

Wherein, nano-diamond powder/graphene composite electrode material by mass ratio: polyvinylidene fluoride: carbon black is 8: 1: 1; Described current collector is copper foil; Drying under described 120 ℃ is at 120 ℃ in a vacuum oven for 12 hours.

The present invention further provides a lithium-ion half-battery: in an anhydrous and oxygen-free environment, the positive electrode uses metal lithium sheet as the counter electrode, and the negative electrode contains the nano-diamond powder/graphene composite material prepared according to the above method. Experimental measurement results show that the obtained carbon composite material is used as the negative electrode material of lithium-ion batteries. After the first charge-discharge cycle, the discharge specific capacity reaches 1085mAhg ^-1 , and the first charge-discharge efficiency is 60%, which is much higher than the theoretical cycle capacity of graphite, which is 372mAhg ^- 1. ¹ . With the increase of the number of cycles, the discharge capacity decreased slightly. After 50 cycles, the charge-discharge capacity reached 650mAhg ^-1 , the capacity retention rate was 59.9%, and the charge-discharge Coulombic efficiency was close to 100%.

The invention utilizes nano-diamond powder/graphene to obtain a novel composite electrode material, and the two form a synergistic effect to prepare a high-performance novel pure carbon lithium-ion battery negative electrode material, which solves the problem of the low specific capacity of commercial graphite negative electrodes and the high capacity of new graphene negative electrodes. Discharge platform, low initial Coulombic efficiency and other issues; nano-diamond powder not only has high hardness and excellent thermal conductivity, but also has large specific surface area and stable structure. The problem of capacity decay, and the large specific surface area of nano-diamond powder is beneficial to the storage of lithium ions, which is very important for improving the specific capacity of negative electrode materials and maintaining good cycle stability. The preparation method of the nano-diamond powder and graphene composite electrode material of the present invention has the advantages of simple process, low cost, easy realization, easy scale-up, etc., and is expected to be mass-produced in the future.

Description of drawings

Figure 1 is a transmission electron microscope image of sample 1#.

Figure 2 is a transmission electron microscope image of sample 4#.

Fig. 3 is a comparison chart of X-ray diffraction (XRD) phase analysis of samples 1# and 4#.

Figure 4 is a comparison of Raman spectra of samples 1# and 4#.

Figure 5 is a comparison chart of the constant rate cycle performance of samples 1# and 4# for the negative electrode charge and discharge capacity of lithium-ion batteries.

Fig. 6 is a comparison chart of sample 1# and 4# used in lithium-ion battery negative electrode charging and discharging capacity variable rate cycle performance.

Fig. 7 is the charge-discharge cyclic voltammetry test chart of sample 1#.

Figure 8 is a test chart of sample 1# constant rate charge and discharge curve.

Fig. 9 is a charge-discharge cyclic voltammetry test chart of sample 4#.

Figure 10 is a test chart of sample 4# constant rate charge and discharge curve.

Figure 11 is the adsorption-desorption curves of samples 1# and 4#.

Figure 12 is a transmission electron microscope image of sample 6#.

detailed description

The present application will be described in further detail below in conjunction with the accompanying drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present application, rather than limiting it in any way.

Embodiment 1: Microwave-assisted preparation of nano-diamond powder/graphene nanosheet composite electrode material

2g citric acid and 6g urea are dissolved in 30ml deionized water (20～40ml all can be) and form colorless transparent solution, then add 0.16g particle size and be the diamond powder of 5～10nm nanometer (the addition amount of nano diamond powder accounts for citric acid, urea, 1.9% to 2.0% of the mass of the mixture of nano-diamond powder), after high-frequency ultrasonic treatment for 30 to 60 minutes, the resulting solution was placed in a microwave oven and heated at 850W for 10 minutes, and the solution turned from colorless to yellowish brown. The reaction was complete with a dark brown solid. Then the obtained solid composite was moved to a vacuum drying oven and dried at 60° C. for 1 h to remove residual moisture in the molecules. The dried solid composite is crushed and ground into a powder, and the powder particles are less than 10 μm, so as to increase the specific surface area of the material. Put it into a tube furnace, carry out carbonization treatment under the protection of inert gas argon, and calcinate at 900°C for 2 hours. At this time, the obtained carbon composite changed from the original dark brown color to a black blocky solid, and continued to be crushed and ground for 3-4 hours until the particle size of the powder reached the nanometer level. The prepared nano-diamond powder/graphene composite electrode material sample is marked as sample 4#.

In this embodiment, 0.16 g of nano-diamond powder used as a raw material basically remained unchanged or slightly decreased after being prepared into a nano-diamond powder/graphene composite electrode material. The carbon composite finally obtained by carbonization is a mixture of nano-diamond powder and graphene, which is weighed as 0.76g, and the calculated quality of graphene is about 0.6g, that is, the mass ratio of nano-diamond powder and graphene is 0.26:1.

The TEM image of sample 4# is shown in Figure 2, the X-ray diffraction (XRD) spectrum is shown in Figure 3, and the Raman spectrum is shown in Figure 4. The lithium-ion battery negative electrode made of sample 4# is used in lithium-ion batteries, and its performance test is shown in Example 4.

The X-ray diffraction (XRD) phase analysis of sample 4# in this embodiment was carried out on the polycrystalline XRD instrument of XRD-6000, Cu target, Kα radiation source (λ=0.15418nm). In the XRD pattern of Figure 3, two obvious peaks can be seen, which are located near 2θ=26° and 44° respectively, corresponding to the (002) plane and (101) plane of hexagonal graphite. It shows that sample 4# has graphite structure. The diffraction peak shape of sample 4# is sharp and the signal is also good, indicating that sample 4# has good crystallinity. The Raman spectrum (Raman) analysis of sample 4# in this example was carried out on a Renishaw inVia type confocal Raman microscope spectrometer, the light source was Ar ⁺ laser, and the wavelength was 514.5nm. The Raman results are shown in Figure 4. Sample 4# has two distinct characteristic peaks between (800-2000) cm ^-1 , which are the D peak near 1350 cm ^{-1 and the G peak near 1580 cm -1 .} There is a second-order Raman peak (that is, a 2D peak) in the interval of 2650-3000cm ^-1 . For the morphology analysis of sample 4# in this embodiment, a JEM-2200FS field emission transmission electron microscope was used. The TEM picture of sample 4# given in Fig. 2. Figure 2 shows that nano-diamond particles are densely adsorbed on the wrinkled graphene sheet surface, and a large number of nano-diamond particles will increase the specific surface area of the sample (shown by the nitrogen adsorption BET specific surface area test curve in Figure 11), and nano-diamond particles are conducive to improving The storage density and transmission rate of lithium ions can be used as an ideal lithium ion battery material.

The preparation of embodiment 2 pure graphene material (do not add nano-diamond powder) microwave-assisted method

As a comparative example, the raw material ratio (without adding nano-diamond powder) and the process of Example 1 were used to prepare pure graphene materials. Specifically:

Dissolve 2 g of citric acid and 6 g of urea in 30 ml of deionized water to form a colorless transparent solution. After high-frequency ultrasonic treatment for 30 to 60 min, the resulting solution is placed in a microwave oven and heated at 850W for 10 min. The solution turns from colorless to yellowish brown Eventually the reaction ended as a dark brown solid. Then the obtained solid product was moved to a vacuum drying oven and dried at 60° C. for 1 h. The dried solid product is crushed and ground into a powder, and the powder particles are less than 10 μm. Put it into a tube furnace, carry out carbonization treatment under the protection of argon, and calcinate at 900°C for 2 hours. The obtained carbonized solid product is continuously crushed and ground for 3-4 hours until the particle size of the powder reaches nanometer level. The obtained pure graphene material sample is marked as sample 1#.

Sample 1# is compared with sample 4# as a comparative sample, and the results are as follows.

The XRD result of sample 1# is shown in Figure 3. Two obvious peaks can also be seen in the XRD pattern, which are located near 2θ=26° and 44° respectively, corresponding to the (002) plane and (101) plane of hexagonal graphite. . It shows that both samples 1# and 4# have graphite structure. In the spectrum, the diffraction peak shape of sample 4# is sharper than that of sample 1#, and the signal is slightly better, indicating that the crystallinity of sample 4# is higher than that of sample 1#, and the material of sample 4# has a good layered structure , which is more suitable for intercalation and extraction of lithium ions. The Raman spectrum (Raman) analysis results of sample 1# are shown in Figure 4. Sample 1# also has two obvious characteristic peaks between (800-2000) cm ^-1 , which are D near 1350 cm ^-1 peak and the G peak around 1580 cm ^-1 . There is a second-order Raman peak (that is, a 2D peak) in the interval of 2650-3000cm ^-1 . The morphology of sample 1# is shown in the transmission electron microscope picture in Figure 1. It can be seen from Figure 1 that the sample is a multi-layer sheet structure with a certain degree of wrinkles on the surface, such as corrugation. The lithium-ion battery negative electrode made of sample 1# is used in lithium-ion batteries, and its performance test is shown in Example 5. It can be seen from Example 5 that the performance of the lithium-ion battery negative electrode made by sample 4# for lithium-ion batteries is much better than that of sample 1#.

Embodiment 3 Microwave-assisted preparation of nano-diamond powder/graphene nanosheet composite electrode material

Dissolve 2g citric acid and 6g urea in 30ml deionized water and add 0.04g, 0.08g, 0.20g of diamond powder with a particle size of 5-10nm nanometers respectively, 0.5%, 1.0%, 2.5% of the powder mixture quality), through the same high-frequency ultrasonic treatment as in Example 1, microwave oven heating, drying in a vacuum oven, crushing and grinding, carbonization treatment under the protection of inert gas argon, continue Crushing and grinding, the prepared nano-diamond powder/graphene composite electrode material samples are marked as sample 2#, sample 3#, and sample 5#.

To sample 2#, sample 3#, sample 5#, the quality of graphene calculated by weighing is about 0.6g. The mass ratios of nano-diamond powder and graphene are 0.066:1, 0.13:1, and 0.33:1, respectively.

Sample 2#, sample 3#, and sample 5# can all be used as negative electrode materials for lithium-ion batteries.

The electrode material preparation of embodiment 4 nano-diamond powder and graphene direct mixing

This embodiment provides another method for preparing a nano-diamond/graphene electrode according to the present invention. Directly mix the nano-diamond powder and the graphene at a mass ratio of 1:3-4, and conduct high-frequency ultrasonic treatment in absolute ethanol for 6-8 hours to make the two mix more fully. Then the suspension of graphene and nano-diamond powder was moved to a vacuum drying oven, and dried at 60°C until the complete evaporation of absolute ethanol. Finally, the dried solid mixture is crushed and thoroughly ground to a powder. The obtained nano-diamond powder/graphene composite electrode material is designated as sample 6#.

Fig. 12 is the sample 6# TEM picture that the mixture of commercial graphene and nano-diamond powder makes, can find out from the picture that nano-diamond crystal grain is dispersed on the surface of graphene sheet, forms nano-diamond powder/graphene composite Electrode material, obtains the result close to embodiment 1 and 2.

Embodiment 5 makes the negative electrode of lithium-ion battery with nano-diamond powder/graphene nanosheet composite material

The lithium-ion battery negative electrode is composed of 80wt% nano-diamond/graphene composite material (active material), 10wt% binder (polyvinylidene fluoride, PVDF) and 10wt% conductive agent carbon black. The three were mixed and ground for 0.5h, then put into a container, and a certain amount of 1-methyl-2-pyrrolidone (NMP, solvent) was added into the container, and then placed on a magnetic stirrer and stirred at a constant speed for 6h, so that the mixture became a viscous fluid. Copper foil is used as a current collector, and the above-mentioned mixed viscous material is coated on the copper foil, and the coating density must be uniform. The temperature of the vacuum drying oven was set at 120° C., and the above-mentioned copper foil smear was taken and placed in the drying oven. After timing for 12 hours, it was taken out for use. The prepared copper foil smear is cut into several electrode discs with a special cutter mold, and then the active material on the pole piece is compacted with a tablet press to make it fully contact with the current collector to prevent material stripping.

Embodiment 6: the making and performance test of lithium-ion battery

Taking samples 1# and 4# as typical representatives, test their performance for lithium-ion batteries. Sample 1# of pure graphene nanosheets was used as a comparative sample. The lithium-ion battery prepared for this test is a CR-2025 button battery. The negative electrode material is composed of 80wt% active material, 10wt% binder (polyvinylidene fluoride, PVDF) and 10wt% conductive agent carbon black, and copper foil is used as a current collector. The prepared copper foil smear is cut into several electrode discs with a special cutter mold, and then the active material on the electrode sheet is compacted with a tablet press to make it fully contact with the current collector. Then weigh the mass of the electrode sheet for the calculation of subsequent specific capacity parameters, etc. Take the matching battery positive and negative shells, gaskets, shrapnel, polypropylene diaphragm, electrolyte, electrode sheets, etc., and operate in accordance with the production regulations of lithium batteries, operate safely and orderly in the glove box, and package the battery. The batteries prepared by using samples 1# and 4# as negative electrode active materials of lithium batteries are marked as S1 and S2, respectively.

1) Charge and discharge rate test

The batteries S1 and S2 prepared in Example 3 were tested in the blue electric test system. At 25°C, discharge to 0.02V according to a certain discharge current; after the discharge, the battery stands still for 3 minutes; The current density is constant current discharge to 0.02V; after the battery is fully charged, let it stand for 3 minutes, and then charge it under the same conditions. The electrochemical performance test results are shown in Figure 5. It can be seen from the figure that the first discharge and charge specific capacities of sample 4# reached 1085mAhg ^-1 and 749mAhg ^-1 respectively, and the first discharge efficiency was 61%. increases, the discharge capacity decreases slightly, the charge and discharge capacity of the 50th cycle is 646mAhg ^-1 , which is close to twice the theoretical capacity of graphite, and the charge and discharge Coulombic efficiency is close to 100%. The first cycle capacities of sample 1# are 874.7mAhg ^-1 and 444.2mAhg ^-1 respectively, the first discharge efficiency is 51%, the capacity remains around 300mAhg ^-1 after stable cycles, and the coulombic efficiency is close to 100%. This capacity is lower than that of sample 4#.

Variable magnification discharge, set to 0.2C, 0.5C, 1C, 5C, 10C in turn, to test the reversible specific capacity of batteries S1 and S2. The electrochemical performance test results are shown in Figure 6. It can be seen from the figure that the battery S2 made of nano-diamond powder/graphene nanosheet composite material (sample 4#) has good specific capacity and retention rate under the condition of variable rate charge and discharge, showing excellent electrochemical performance. performance.

2) Charge and discharge cyclic voltammetry test

The cyclic voltammetry test conditions are that the test temperature is controlled at 25°C, the electrochemical workstation is used, the scanning speed is set to 0.1mV/s, and samples 1# and 4# are selected as electrode active materials. The cyclic voltammetry curves of the first 5 cycles are shown in Figures 7 and 8 respectively. It can be seen that except for the special peak in the first cycle, the CV curve tends to be stable after the second cycle. It can be seen from the figure that the stability of sample 4# is better than that of sample 1#. In the first cycle curve, the broad characteristic peak at 0.3V to 1.0V corresponds to the generation of solid electrolyte interfacial film (SEI). The SEI film is a passivation layer covering the surface of the electrode material when the electrode material and the electrolyte react at the solid-liquid phase interface during the first charge and discharge process of the lithium-ion battery. This passivation layer can prevent the electrolyte from further reaction, thereby improving the stability of the battery. A more stable SEI film formed by electrodes with nanodiamonds is conducive to obtaining batteries with excellent characteristics

3) Constant rate charge and discharge curve test

The constant rate charge and discharge curves of batteries S1 and S2 prepared with samples 1# and 4# as electrode active materials are shown in Figures 9 and 10, respectively. The rate is 0.2C and the voltage range is 0.02-3V. A representative 5th degree curve. In the first charge and discharge curve, it can be seen that there is a relatively obvious discharge platform near 0.6V, corresponding to the SEI peak of the CV curve. The charge-discharge capacity tends to be stable in subsequent cycles. This indicates that the irreversible loss of capacity mainly occurs during the first charging and discharging process. As shown in Figure 9, the initial cycle capacities of sample 1# are 874.7 and 444.2mAhg ^-1 respectively, and the initial discharge efficiency is 51%. From Figure 10, it can be seen that the initial discharge and charge specific capacities of sample 4# have reached 1085 and 1085 respectively. 749mAhg ^-1 , much higher than graphite's theoretical capacity of 372mAhg ^-1 , irreversible capacity of 336mAhg ^-1 , first discharge efficiency of 61%, higher than sample 1#. There is almost no change in the charge-discharge curve, indicating good cycle stability. In summary, the battery S2 made of nano-diamond powder/graphene nanosheet composite (sample 4#) has better specific capacity and retention rate than the battery S1 made of (sample 1#), showing excellent performance. electrochemical performance.

Claims (7)

1. A kind of nano-diamond powder and graphene composite electrode material, it is characterized in that, be the sheet structure of multilayer, there is corrugated fold on the surface, nano-diamond particle is adsorbed on the graphene sheet surface; The quality of nano-diamond powder and graphene The ratio is 0.066～0.334:1. 2. The nano-diamond powder and graphene composite electrode material according to claim 1, characterized in that, the nano-diamond particles have a particle size of 5-10 nm. 3. a preparation method of nano-diamond powder and graphene composite electrode material according to claim 1, citric acid and urea are dissolved in an appropriate amount of deionized water to form a colorless transparent solution, then add nano-diamond powder, through high-frequency ultrasonic treatment 30 ~60min, put the obtained solution in a microwave oven and heat it under 850W power for 10~15min, the solution turns from colorless to yellowish-brown and finally into a dark brown solid compound; dry the obtained solid compound under the protection of an inert gas Carbonization treatment at 900°C for 2 hours to obtain nano-diamond powder and graphene composite electrode material. 4. the preparation method of nano-diamond powder and graphene composite electrode material according to claim 3 is characterized in that, the mass ratio of citric acid and urea is 1: 3～4; The quality of nano-diamond powder and citric acid and urea The ratio of the sum of the masses is 0.005-0.025:1. 5. a preparation method of nano-diamond powder and graphene composite electrode material according to claim 1, nano-diamond powder and graphene are mixed by mass ratio 1: 3～4, in dehydrated alcohol through high-frequency ultrasonic treatment 6 ~8h; then dry the suspension of graphene and nano-diamond powder at 60°C until absolute ethanol is completely evaporated to obtain a nano-diamond powder/graphene composite electrode material. 6. the purposes of a kind of nano-diamond powder and graphene composite electrode material of claim 1, for making the negative electrode of lithium-ion battery; Concrete process is: nano-diamond powder and graphene composite electrode material are crushed and ground until powder The body particle size reaches nanoscale, mixed with carbon black, ground under the action of polyvinylidene fluoride, and added 1-methyl-2-pyrrolidone to stir it into a viscous fluid with a magnetic stirrer; apply the viscous fluid to The current collector is dried at 120°C; finally, it is cut into an electrode shape and compacted to obtain a negative electrode of a lithium-ion battery composed of nano-diamond powder and graphene. 7. the purposes of nano-diamond powder and graphene composite electrode material according to claim 6 is characterized in that, by mass ratio nano-diamond powder/graphene composite electrode material: polyvinylidene fluoride: carbon black is 8: 1: 1. The current collector is copper foil; the drying at 120°C is drying in a vacuum oven at 120°C for 12 hours.