CN104617300A - Method for preparing lithium ion battery anode/cathode material from reduced graphene oxide - Google Patents

Abstract

The invention discloses a method for preparing lithium-ion battery positive and negative electrode materials by using reduced graphene oxide. It is to ultrasonically disperse graphite oxide in an organic solvent to obtain a graphene oxide dispersion; select a suitable reducing agent or directly use a solvent to reduce it, and obtain a graphene oxide with a carrying part through oil bath reflux, hydrothermal method or other reduction methods. Oxygen groups reduce graphene oxide materials. The prepared reduced graphene oxide material is applied to the positive electrode material of the lithium ion battery, which has a high discharge specific capacity of 280mAh/g, and has good cycle stability and excellent rate performance. The prepared reduced graphene oxide material can also be applied to the negative electrode material of lithium-ion batteries. After 100 cycles of charging and discharging, the discharge specific capacity is maintained above 900mAh/g, and the cycle stability is good. It can become the research focus of high-performance and low-cost electrode materials for lithium-ion batteries.

Description

A method for preparing positive and negative electrode materials for lithium-ion batteries by reducing graphene oxide

technical field

The invention belongs to the technical field of energy storage and conversion, and mainly relates to a method for preparing lithium-ion battery positive and negative electrode materials by using reduced graphene oxide.

Background technique

Lithium-ion battery is a new type of chemical power source developed in recent years. It is a hot spot for research and development all over the world. It has the characteristics of small size, light weight, high specific energy, no memory effect, and long cycle life. Widely used in mobile devices, electric vehicle energy and other fields. Among the various components of lithium-ion batteries, electrode materials are the core and key materials of lithium-ion batteries. The quality of electrode materials directly determines the specific energy, cycle life and load resistance of lithium-ion batteries and other key properties. Therefore, the development of high-performance lithium-ion batteries and their electrode materials is of great significance to the improvement of the performance of lithium-ion batteries, especially the development of power-type lithium-ion batteries. In terms of positive electrode materials, the positive electrode materials that are currently studied mainly include Li-Co-O system, Li-Ni-O system, Li-Mn-O system, ternary materials and LiFePO ₄ and other materials, although they have all been obtained to a certain extent. However, there are still disadvantages such as low actual specific capacity (~160 mAh/g), poor cycle stability, limited resources, high price, and poor rate performance. At present, most of the commercialized lithium-ion batteries use lithium cobalt oxide/graphite system. Due to the low theoretical capacity limit of the material itself (graphite: 372 mAh/g), it cannot meet the high energy density and high power requirements of ultra-thin mobile electronic products. Therefore, it is particularly necessary to develop new electrode materials with high specific capacity, high power density, low cost, and environmental friendliness.

Graphene is a carbon single atomic layer nanomaterial composed of two-dimensional honeycomb lattice closely packed. It is considered to be the basic unit of other carbon materials in various dimensions. It has good thermal conductivity, electrical conductivity, high strength and excellent electrochemical stability. sexual performance. Graphene has become an international scientific research hotspot because of its special structure and properties. This two-dimensional carbon material with a single-layer carbon atom thickness has a high theoretical specific surface area (2630m ² /g) and a honeycomb hole structure. In addition, The electron mobility of the material itself reaches 15000cm ² /(v s), the thermal conductivity reaches 5300W/(m K), good chemical stability and other excellent properties make graphene widely used in conductive films, lithium storage devices, nano sensors and Composite materials and other fields have good application value and broad application prospects. Among them, the application of graphene in lithium-ion batteries has also received extensive attention. Due to its high theoretical specific surface area and honeycomb hole structure, it has a high lithium storage capacity. Graphene and graphene-based composites have been extensively studied as anode materials for lithium-ion batteries. However, the agglomeration phenomenon existing in the cycle process of graphene negative electrode materials causes electrode structure damage, making its cycle stability worse; graphene composite negative electrode materials (Sn-based, Si-based, etc.) have a high specific capacity, but the preparation process is complex and costly. high, which limits its practical application.

In 2014, the present invention applied for a patent titled "Preparation Method of Functional Graphene for Lithium-ion Battery Cathode Material". However, with the deepening of research, more extensive and convenient methods have been found to prepare functionalized graphene, and it can be applied to both positive and negative electrode materials. Therefore, the present invention has been further completed on the original basis.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the defects of current lithium-ion battery positive and negative electrode materials and to develop and utilize the excellent properties of graphene. The present invention mainly provides a lithium-ion battery with excellent electrochemical performance and low cost. Graphene electrode material as positive and negative electrodes of lithium-ion batteries.

In the present invention, the oxygen-containing groups on the surface of graphene oxide are partially reduced to act as active points combined with lithium ions to undergo redox reactions, thereby generating lithium-deintercalation effects, which can be used as positive electrode materials; utilizing the special structural properties of graphene and its surface The defect sites provided by oxygen-containing groups can significantly improve its lithium storage capacity and can be used as negative electrode materials. The reduced graphene oxide prepared by the invention exhibits excellent electrochemical properties as the positive and negative electrode materials of the lithium ion battery. A major innovation of the present invention is that the reduced graphene oxide can be used as both positive and negative electrode materials for lithium-ion batteries, and both exhibit excellent electrochemical properties.

The preparation mechanism of the present invention is:

Reduced graphene oxide is prepared by oxidation-reduction method, and natural graphite is oxidized by strong oxidants such as concentrated sulfuric acid and potassium permanganate to generate a large number of oxygen-containing functional groups on the surface, such as carbonyl, epoxy, hydroxyl and carboxyl, and at the same time make it The spacing between graphite layers expands to obtain graphite oxide products. Due to the presence of a large number of oxygen-containing groups, graphite oxide is poorly conductive, resulting in poor electrochemical performance. The present invention aims to partially reduce the prepared graphite oxide, remove most of the oxygen-containing groups to improve its electrical conductivity, and retain a part of the oxygen-containing groups to undergo redox reactions with lithium ions as active sites for deintercalating lithium ions , and also provide defect sites to improve lithium storage capacity.

The present invention can be realized through the following technical solutions:

A preparation method for partially reduced graphene oxide, comprising the following steps:

(a) Preparation of graphene oxide suspension: Disperse a certain amount of graphite oxide in a certain amount of deionized water/organic solvent, and use an ultrasonic cell pulverizer to sonicate for 10-120 minutes to form a graphene oxide suspension with a concentration of 0.01-100 mg/mL. The graphene suspension is then centrifuged at a rate of 10,000 rpm for 2 to 600 min to remove possible impurities.

(b) Preparation of partially reduced graphene oxide: It can be divided into 2 methods: (1) hydrothermal/solvothermal method; (2) oil bath reflux method.

(1) Evenly mix the graphene oxide suspension prepared in step (a) with a certain amount of reducing agent, place in a polytetrafluoroethylene reactor, and react at 40-400°C for 0.5-500h to obtain part Reduced graphene oxide product.

(2) Evenly mix the graphene oxide suspension prepared in step (a) with a certain amount of reducing agent, place it in a three-necked flask, and reflux in an oil bath at 15~200°C for 0.5~500h under the condition of magnetic stirring, that is A partially reduced graphene oxide product is obtained.

(c) Purification of reduced graphene oxide: the partially reduced graphene oxide product prepared in the two methods of step (b) was filtered and washed with deionized water/absolute ethanol, and the obtained product was frozen for 0.5~200h, Dry in a freeze dryer for 0.5~200h.

Further: the graphite oxide used in step (a) is prepared by the modified Hummers method, and the steps are as follows: (1) Weigh 0.1~5g of graphite powder and 0.05~5g of NaNO ₃ and mix them uniformly; , add 3~100mL concentrated H ₂ SO ₄ and stir evenly, and slowly add 0.5~20g KMnO ₄ and stir for 1~5 hours, after stirring at room temperature for 1~5 days, add 10~500mL H ₂ SO with a concentration of 1%~10% ₄ Stir for 0.5~5 hours; add 0.5~20mL hydrogen peroxide and stir until the solution does not appear bubbles;

(2) Cleaning: wash with 5%~10% HNO ₃ for 2~4 times, then wash with 1%~5% HNO ₃ for 2~3 times; add deionized water and centrifugally wash to pH=7, the obtained solution is in Graphite oxide can be obtained by blast drying at room temperature 25°C.

Further: the organic solvent selected in step (a) includes but not limited to ethanol, ethylene glycol, glycerol, DMF and NMP, among which ethylene glycol is most preferred.

Further: the concentration of the graphene oxide suspension formed in step (a) is 0.01-100 mg/mL, more preferably 0.5-5 mg/mL, and most preferably 1-3 mg/mL.

Further: the reducing agent in step (b) can be selected from but not limited to hydrazine hydrate, sodium borohydride, potassium borohydride, hydroquinone, hydroiodic acid, ethylenediamine, sodium citrate, vitamin C, the amount of reducing agent The mass ratio of graphite oxide to graphite is 0.1-100:1, preferably 0.5-5:1.

Further: in the method (1) in the step (b), the graphene oxide can be partially reduced by using the reducing property of the water/organic solvent itself without adding a reducing agent.

Further: in the method (2) in the step (b), it is optional not to add a reducing agent, and use organic solvents (alcohols, such as: ethanol, ethylene glycol and glycerol) to partially reduce the graphene oxide itself.

SEM (scanning electron microscope), FTIR (infrared spectrum), XPS (X-ray photoelectron spectroscopy), Raman (Raman spectrum) and other characterization analysis were carried out on the reduced graphene oxide prepared by the present invention, the results are as follows:

SEM characterization description: From SEM, it can be seen that the prepared reduced graphene oxide has a multi-fold sheet-like structure, which is the characteristic structure of composite reduced graphene oxide.

Infrared spectrum FTIR characterization shows that there are more unreduced oxygen-containing functional groups remaining on the surface of the partially reduced reduced graphene oxide.

XPS (X-ray photoelectron spectroscopy) characterization shows that some oxygen-containing functional groups remain on the surface of the prepared reduced graphene oxide material, mainly hydroxyl, carbonyl, epoxy and carboxyl groups.

Raman (Raman spectroscopy) characterization shows that reduced graphene oxide rich in oxygen-containing functional groups has more defect sites, and its order degree is lower than that of graphite.

The present invention focuses on solving:

(1) The modified Hummers method prepares high-quality graphite oxide.

(2) A variety of green and low-cost liquid-phase methods can be used to controlly reduce graphite oxide, retain some oxygen-containing groups, and control the number of oxygen-containing groups on the surface of graphene oxide by controlling the degree of reduction and optimize its electrical conductivity, thereby improving its electrochemical performance.

(3) The controllable partially reduced graphene oxide was applied to the cathode and anode materials of lithium-ion batteries, and the key factors affecting the battery performance were found.

The present invention further discloses the application of the reduced graphene oxide prepared by the above preparation method as positive and negative electrode materials of lithium ion batteries. The results of the test showed:

(1) The partially reduced graphene oxide is applied to the positive electrode material of lithium-ion batteries, and the oxygen-containing groups are used as the active sites for deintercalating lithium, showing excellent electrochemical performance.

(2) Applying partially reduced graphene oxide to the negative electrode material of lithium-ion batteries, taking advantage of the defect sites provided by the oxygen-containing groups and the lithium storage advantages of the reduced graphene oxide structure, exhibits extremely excellent electrochemical performance. The reversible capacity and cycle stability are superior to current commercial graphite and pure graphene anode materials.

(3) When functionalized graphene is used as the positive and negative electrode materials of lithium-ion batteries, the more oxygen-containing groups on the surface, the more defect sites and lithium intercalation active sites are provided, and the greater the lithium storage capacity is, but too much The oxygen content of graphene oxide leads to its poor conductivity and thus reduces its electrochemical performance. The number of oxygen-containing groups and conductivity of graphene oxide can be comprehensively controlled by adjusting the reduction degree of graphene oxide, so as to optimize its electrochemical performance.

In the present invention, the prepared reduced graphene oxide is used as positive and negative active materials, and natural carbon black and binder PVDF (polyvinylidene fluoride) are prepared in a certain ratio (8:1:1) to form a positive electrode for lithium-ion batteries. and negative electrode materials.

The steps of preparation are:

(1) Weigh the electrode active material, natural carbon black, and binder PVDF (polyvinylidene fluoride) according to the ratio of 8:1:1, mix and fully grind (time 3h);

(2) The above-mentioned pasty mixture is evenly coated on aluminum foil and copper foil, wherein the aluminum foil is coated to obtain a positive electrode sheet, and the copper foil is coated to obtain a negative electrode sheet. Vacuum drying at 100°C for 12 hours;

(3) The above-mentioned aluminum foil and copper foil loaded with electrode materials were cut into electrode pieces of required size, and assembled into a button-type electrochemical simulation half-cell in a glove box, in which the reference electrode was a lithium metal sheet.

The electrochemical performance test of the electrode material is as follows:

The positive pole piece was assembled into a CR2032 button-type simulated half-battery in a glove box, and a constant current charge-discharge test was performed to test its reversible specific capacity and cycle performance. The test conditions are: voltage range: 1.5~4.5V; current density: 50 mA/g; number of cycles: 100.

The negative pole piece was assembled into a CR2032 button-type simulated half battery in a glove box, and a constant current charge and discharge test was performed to test its reversible specific capacity and cycle performance. The test conditions are: voltage range: 0.01~3V; current density: 100 mA/g; number of cycles: 100.

Due to the implementation of the above technical solutions, the present invention has the following advantages and innovations compared with the prior art:

(1) Using natural graphite as raw material, the cost is low, and the partially reduced reduced graphene oxide (RGO) is prepared by the improved Hummers method combined with simple hydrothermal method and solvothermal method. The structure is stable and the quality is high.

(2) Water, ethylene glycol, sodium citrate and other green reducing agents can be selected, which are environmentally friendly and economical. The reduction degree of the prepared reduced graphene oxide (RGO) and the number of oxygen-containing groups on the surface can be adjusted and controlled.

(3) The prepared RGO is rich in oxygen-containing functional groups (carbonyl, hydroxyl, carboxyl, etc.), and when applied to lithium-ion battery cathode materials, it has high discharge specific capacity, excellent rate performance and good cycle stability ( After 100 cycles at a current density of 50mA/g, the reversible specific capacity remains above 250 mAh/g), which is better than the current commercial lithium cobalt oxide material (actual capacity 140 mAh/g); (4) The prepared RGO is used in lithium ion As a battery negative electrode material, due to the large number of defect sites and its three-dimensional structural characteristics, it shows a reversible specific capacity superior to commercial graphite materials and graphene negative electrodes, and its cycle stability is greatly improved (100mA/g current density After 100 cycles, the reversible specific capacity reaches 900 mAh/g.

Description of drawings:

Figure 1 a, b, and c are the SEM (scanning electron microscope) images of graphene oxide, ethylene glycol-reduced graphene oxide, and reduced graphene oxide reduced by water-solvent hydrothermal reduction, respectively, and Figure 1d is the reduction-oxidation of water-solvent hydrothermal reduction TEM (Transmission Electron Microscope) image of graphene; it can be observed that graphene oxide has a multi-folded sheet-like structure, and the reduced graphene oxide sheet becomes thinner and smaller after partial reduction, and presents many nanometer to micrometer-scale pores Structure, TEM image shows a transparent tulle-like structure, with typical morphology of graphene.

Figure 2 is the infrared spectrum (FTIR) diagram of reduced graphene oxide and graphene oxide, both of which are the test results of graphite oxide (GO) used in Example 1 and the prepared reduced graphene oxide sample. It can be seen that the reduction and oxidation Compared with graphene oxide, the oxygen-containing functional groups on the surface of graphene are greatly reduced, but they are partially retained. At the same time, it can be seen that the degree of reduction will be higher and the residual oxygen-containing groups will be less when the hydrothermal reaction time is prolonged.

Figure 3 is the XPS full spectrum of the three samples prepared in Example 1. It can be seen that with the prolongation of the hydrothermal reaction time, the oxygen content decreases, which is the same as the result of the FTIR test.

Fig. 4a is a graph showing the cycle performance curves of the graphene oxide (GO) used in Example 4 and three reduced graphene oxide (RGO) samples as cathode materials for lithium-ion batteries. Among them, RGO-I is the sample of hydrothermal reduction for 1h, RGO-II is the sample of hydrothermal reduction for 6h, and RGO-III is the sample of hydrothermal reduction for 12h. It can be seen that the discharge specific capacity of graphene oxide as the positive electrode material is low. The cycle performance is poorer than that of partially reduced graphene oxide; the reduced graphene oxide after hydrosolvothermal reduction exhibits extremely high specific capacity and excellent cycle stability; and the oxygen-containing oxygen contained on the surface of the reduced graphene oxide The more functional groups, the greater the specific capacity, and the specific capacity of the sample RGO-I reduced for 1h reached 280mAh/g, and the cycle stability was very good.

Fig. 4 b is the charge-discharge curve diagram when the sample RGO-I tests the rate performance in embodiment 4, and the charge-discharge current density is respectively 50mA/g, 100mA/g, 200mA/g, 400mA/g, and the current density is 400 mA/g , its reversible discharge specific capacity still reaches 175 mAh/g, showing extremely excellent rate performance, and can realize high-current charge and discharge.

FIG. 5 is a graph showing cycle performance curves of three samples tested in Example 5 as negative electrode materials for lithium-ion batteries. It can be seen that the 6h hydrothermal reduction sample RGO-II exhibited the most excellent performance, and its first-cycle discharge specific capacity reached 2560 mAh/g. Although the irreversible capacity appeared in the first few cycles, after 100 cycles of charge-discharge cycles, its The discharge specific capacity is still stable above 900 mAh/g, and it has excellent lithium storage performance and cycle stability.

Detailed ways

The following examples facilitate a better understanding of the present invention, but do not limit the present invention. The experimental methods in the following examples are conventional methods unless otherwise specified. The test materials used in the following examples, natural carbon black and binder PVDF, are commercially available, and others are purchased from reagent stores unless otherwise specified.

The preferred embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Example 1

The first example: (1) The first step is to improve the Hummers method to prepare graphite oxide: 1. Weigh 1g graphite powder and 0.5g NaNO ₃ and mix evenly; 2. Add 5mL concentrated H ₂ SO ₄ and stir evenly under the condition of ice-water bath , and slowly add 1.5g KMnO ₄ and stir for 1 hour; 3. After stirring at room temperature for 5 days, add 50 mL of 5% H ₂ SO ₄ and stir for 1 hour; 4. Add an appropriate amount (about 3 mL) of hydrogen peroxide (H ₂ O ₂ ) Stir until there are no bubbles in the solution; 5. Clean, wash twice with 10% _HNO3 in a 4000mL beaker, and then wash twice with 5% _HNO3 ; 6. Add deionized water and centrifugally wash until pH = 7. The resulting solution was air-dried at room temperature of 25°C to obtain graphite oxide.

The second example: (2) The first step is to improve the Hummers method to prepare graphite oxide: 1. Weigh 5g of graphite powder and 5g of NaNO ₃ and mix evenly; 2. Under the condition of ice-water bath, add 100mL of concentrated H ₂ SO ₄ and stir evenly. And slowly add 20g KMnO ₄ and stir for 5 hours; 3. After stirring at room temperature for 2 days, add 500mL of 2% H ₂ SO ₄ and stir for 5 hours; 4. Add an appropriate amount (about 20mL) of hydrogen peroxide (H ₂ O ₂ ) and stir until Until the solution does not appear bubbles; 5. Cleaning, in a 4000mL large beaker, wash with 5% HNO ₃ for 4 times, and then wash with 3% HNO ₃ for 3 times; 6. Add deionized water and centrifugally wash until pH=7, The resulting solution was air-dried at a normal temperature of 25°C to obtain graphite oxide.

The second step, water solvent hydrothermal reduction of graphene oxide: 1. The prepared graphite oxide is fully ground to obtain a brownish-yellow powder (graphite oxide); 2. Weigh a certain amount of graphite oxide powder and disperse it in a certain amount of deionized water, After ultrasonic peeling by ultrasonic cell pulverizer for 30 minutes, a graphene oxide dispersion with a concentration of 3 mg/mL was obtained; 3. Centrifuge the above dispersion in a centrifuge at a speed of 10,000 rpm for 30 minutes to remove the centrifuged impurities; 4. Measure 40mL of the graphene oxide dispersion and place it in three 50mL polytetrafluoroethylene reactors, and react the three reactors at 180°C for 1h, 6h and 12h respectively; 5. After freezing the obtained product for 12h Dry in a vacuum freeze dryer for 24 hours to obtain reduced graphene oxide (RGO) products, named RGO-I, RGO-II and RGO-III, respectively.

Example 2

The first step is the same as the first example of embodiment 1: (1)

The second step, sodium citrate oil bath reflux method to reduce graphene oxide: 1. The prepared graphite oxide is fully ground to obtain a brownish-yellow powder (graphite oxide); 2. Weigh 200mg of graphite oxide powder and disperse it in 100mL of deionized water , after 30 minutes of ultrasonic peeling by an ultrasonic cell pulverizer to obtain a graphene oxide dispersion with a concentration of 2 mg/mL; 3. Centrifuge the above dispersion in a centrifuge at a speed of 10,000 rpm for 40 minutes to remove the centrifuged impurities; 4. Weigh 2g of sodium citrate and add it to the above-mentioned graphene oxide dispersion, and reflux the reaction in an oil bath at 80°C for 12 hours under vigorous stirring; 5. Extract and wash the above-mentioned reaction product with deionized water, and freeze the product After 12 hours, dry in a vacuum freeze dryer for 24 hours to obtain the reduced graphene oxide (RGO) product.

Example 3

The first step is the same as the first example of embodiment 1: (2)

The second step is sodium borohydride reduction of graphene oxide: 1. The prepared graphite oxide is fully ground to obtain a brownish-yellow powder (graphite oxide); 2. Weigh 50 mg of graphite oxide powder and disperse it in 100 mL of deionized water. Ultrasonic peeling with a pulverizer for 15 minutes to obtain a graphene oxide dispersion with a concentration of 0.5 mg/mL; 3. Centrifuge the above dispersion in a centrifuge at a speed of 10,000 rpm for 20 minutes to remove the centrifuged impurities; 4. Weigh 0.1 Add 1 g of sodium borohydride to the above graphene oxide dispersion, and react at room temperature for 6 hours under vigorous stirring; 5. Extract and wash the above reaction product with deionized water, freeze the product for 12 hours and dry it in a vacuum freeze dryer for 24 hours The reduced graphene oxide (RGO) product is obtained.

Example 4

Electrode preparation and electrochemical performance test

The first step, using the graphene oxide prepared in Example 1 and different reduced graphene oxide samples to prepare the lithium ion battery positive electrode material method:

The graphene oxide prepared in Example 1, reduced graphene oxide RGO-I, RGO-II, RGO-III, natural carbon black, and binder PVDF (polyvinylidene fluoride) were prepared in a certain ratio (mass ratio 8 :1:1) to prepare lithium-ion battery cathode materials, the detailed method is:

(1) Weigh 0.032g of graphene oxide GO, 0.004g of natural carbon black, and 0.004g of binder PVDF according to the ratio of 8:1:1, add a small amount of solvent NMP (1-methyl-2-pyrrolidone) and mix them. Fully grind (time 2h) to obtain paste A; according to the steps of preparing paste A, respectively use reduced graphene oxide RGO-I, RGO-II and RGO-III to prepare pastes I, II and III;

(2) Coat the above-mentioned pasty mixture on aluminum foil respectively, and dry it under vacuum at 100°C for 12 hours;

(3) Cut the above-mentioned aluminum foil loaded with electrode materials into electrode sheets of the required size to obtain 4 kinds of positive electrode sheets, dry them in vacuum at 80°C for 12 hours, and assemble them into CR2025 button cells in a glove box respectively. for lithium flakes.

The constant current charge-discharge cycle performance test was carried out on the above-mentioned button battery. The specific charge-discharge voltage range was 1.5-4.5V, and the charge-discharge current was 50mA/g. The results are shown in Figure 4a.

The rate performance test was carried out on the button battery composed of reduced graphene oxide RGO-I. The specific charge and discharge voltage range was 1.5~4.5V, and the charge and discharge current were 50mA/g, 100mA/g, 200mA/g, 400mA/g, The charge and discharge curves at different current densities are shown in Figure 4b.

Example 5

Electrode preparation and electrochemical performance test

The first step, adopt the different reduced graphene oxide samples prepared in embodiment 1 to prepare the method for lithium-ion battery negative electrode material:

Respectively the reduced graphene oxide RGO-I, RGO-II, RGO-III prepared in Example 1 and natural carbon black, binder PVDF (polyvinylidene fluoride) in a certain ratio (mass ratio 8:1:1 ) to be prepared as lithium-ion battery negative electrode material, the detailed method is:

(1) Weigh 0.04g of reduced graphene oxide RGO-I, 0.005g of natural carbon black, 0.005g of binder PVDF and add a small amount of solvent NMP (1-methyl-2-pyrrolidone) according to the ratio of 8:1:1 Mix and fully grind (time 2h) to obtain paste I; according to the steps of preparing paste I, use reduced graphene oxide RGO-II and RGO-III to prepare paste II and III respectively.

(2) Coat the above paste mixture on the copper foil respectively, and dry it in vacuum at 100℃ for 12h;

(3) The above-mentioned copper foil loaded with electrode materials was cut into electrode sheets of the required size to obtain three kinds of negative electrode sheets, dried in vacuum at 80°C for 12 hours, and assembled into CR2025 button cells in a glove box respectively. The electrodes are lithium sheets.

The constant current charge and discharge cycle performance test was carried out on the above-mentioned button batteries respectively. The specific charge and discharge voltage range was 0.01~3V, and the charge and discharge current was 100mA/g. The cycle performance and discharge specific capacity are shown in Figure 5.

Example 6

Electrode preparation and electrochemical performance test

The first step, using the reduced graphene oxide (RGO) sample prepared in Example 2 to prepare the cathode material for lithium-ion batteries: the method for preparing the cathode material in Example 4 is the same.

The second step, battery assembly and electrochemical performance testing, is the same as in Example 4. Its cycle performance and rate performance are excellent.

Through the implementation of the above examples, it can be concluded that:

(1) The reduced graphene oxide prepared in the present invention can be used as anode and cathode materials for lithium-ion batteries.

(2) When reduced graphene oxide is used as a cathode material for lithium-ion batteries, as the oxygen-containing functional groups on its surface increase, its specific capacity increases and its cycle stability is better. It can be seen that the key factor affecting the increase in its specific capacity is the surface Oxygen-containing functional groups increased.

(3) When reduced graphene oxide is used as the anode material of lithium-ion batteries, the oxygen-containing functional groups and defect sites on its surface can improve the lithium storage capacity, and the conductivity of the material is also a key influencing factor.

(4) The present invention has prepared lithium-ion positive and negative electrode graphene materials with high specific capacity, excellent cycle performance and rate performance, which is of great significance for promoting the development of high-performance lithium-ion batteries and solving energy shortages. .

The above-described embodiments only express several preferred implementations of the present invention, and its description is relatively specific and detailed, but it cannot be interpreted as a limitation to the protection scope of the patent of the present invention, and the protection scope of the patent of the present invention is therefore dependent claims shall prevail.

Claims (8)

1. a kind of method adopting reduction graphene oxide to prepare positive and negative electrode material of lithium ion battery is characterized in that carrying out by following steps: (1) Modified Hummers method to prepare graphite oxide: 1) Weigh 0.1~5g of graphite powder and 0.05~5g of NaNO ₃ and mix evenly; 2) Under the condition of ice-water bath, add 3~100mL concentrated H ₂ SO ₄ and stir evenly, and slowly add 0.5~20g KMnO ₄ and stir for 0.5~5 hours; 3) After stirring at room temperature for 1 to 5 days, add 10 to 500 mL of H ₂ SO ₄ with a concentration of 1% to 10% (w/w) and stir for 0.5 to 5 hours; 4) Add 0.5~20mL hydrogen peroxide and stir until the solution has no bubbles; 5) Cleaning, wash in a beaker with 5%~10% (w/w) HNO ₃ for 2~4 times, then wash with 1%~5% (w/w) HNO ₃ for 2~3 times; 6) Centrifuge and wash with deionized water until pH = 7, and air-dry the resulting solution at room temperature 25°C to obtain graphite oxide; (2) Ultrasonic disperse graphite oxide in water/organic solvent to obtain a graphene oxide dispersion; select a suitable reducing agent for reduction, and reduce graphene oxide by oil bath reflux, hydrothermal method or other reduction methods to obtain the carrying part containing Oxygen group reduced graphene oxide material; (3) Freeze-drying the aforementioned product to obtain a solid reduced graphene oxide product. 2. The preparation method according to claim 1, characterized in that: in step (2), the organic solvent is ethanol, ethylene glycol, glycerol, DMF (dimethylformamide), NMP (N- methylpyrrolidone), acetic acid or n-butanol. 3. The preparation method according to claim 1, characterized in that: in step (2), the reducing agent is hydrazine hydrate, sodium borohydride, potassium borohydride, hydroquinone, hydroiodic acid, ethylenediamine , sodium citrate, vitamin C, glucose, ammonia or urea. 4. The preparation method according to claim 1, characterized in that: in step (2), the concentration of the graphene oxide suspension formed in is 0.01-100 mg/mL. 5. The preparation method according to claim 1, characterized in that: in step (2), the mass ratio of the amount of reducing agent to the amount of graphite oxide is 0.1-1000:1. 6. The preparation method as claimed in claim 1, characterized in that: if the oil bath method is used in step (2), the reaction temperature is 15-200°C. 7. The preparation method according to claim 1, characterized in that: if the hydrothermal method is used in step (2), the reaction temperature is 40-400°C. 8. The reduced graphene oxide prepared by the method of claim 1 is used to prepare the application of lithium-ion battery positive electrode material and negative electrode material.