A graphene material for lithium-ion batteries and its preparation method and application

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a graphene material for lithium-ion batteries, a preparation method thereof, and an application thereof. The graphene material for lithium-ion batteries comprises two-dimensional graphene nanosheets having in-plane pores and a wrinkle structure, and the preparation method comprises the following steps: (1) adding carbon and nitrogen organic matter to a heated graphene oxide aqueous solution, mixing them evenly and then heating them again, collecting the mixed material after evaporation of the water, and drying them together; (2) mixing the dried mixed material with a chemical etchant and ball milling the mixed material to obtain a mixed material; (3) using a stepwise heating method to cause the mixed material to undergo a carbonization reaction and an activation reaction in sequence, and washing and drying the mixed material to obtain a graphene material for lithium-ion batteries. When used as a negative electrode active material for lithium-ion batteries, a high initial coulombic efficiency, a high reversible capacity, and good rate performance can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a graphene material for lithium-ion batteries, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries are currently the most representative electrochemical energy storage devices and have been widely used in consumer electronics, electric vehicles, large-scale energy storage, and other fields. To meet the needs of modern human society for a fast-paced lifestyle, the development of lithium-ion battery technology with high energy density, long cycle life, and fast charging capabilities, in order to achieve the goal of charging 90% of the power in 15 minutes, has become an important research and development direction. However, due to the poor reaction kinetics and electrochemical stability of conventional electrode materials, lithium-ion batteries have disadvantages such as low fast-charging capacity, rapid capacity decay during high-current cycling, and poor safety performance, making it difficult to further increase their charging rate.

[0003] Graphite is currently the most commonly used negative electrode material for lithium-ion batteries, providing a reversible capacity of 375 mAh / g and a first coulombic efficiency of over 90%. However, graphite negative electrodes are considered to be the key limiting factor in the fast charging capability of lithium-ion batteries. This is due to the following three reasons: (1) the low interlayer spacing of graphite (0.33 nm) limits the solid-phase diffusion rate of lithium ions; (2) the volume change of graphite during high current charging and discharging is large and solvent co-intercalation occurs easily; (3) the poor reaction kinetics of graphite make it prone to lithium deposition during high current charging, posing a serious safety hazard.

[0004] Graphene, a new type of two-dimensional carbon nanomaterial, offers advantages such as high electrical conductivity and chemical stability, making it an ideal alternative to graphite anode materials for lithium-ion batteries. Graphene also stores lithium ions through adsorption on both sides of its surface, combined with a pseudocapacitive reaction mechanism involving edge defects and surface functional groups. Its theoretical capacity is far greater than that of graphite. However, graphene currently faces numerous challenges as anode materials for lithium-ion batteries, including low initial coulombic efficiency, low electrode packing density, high electrolyte absorption, and the tendency for self-stacking during processing, resulting in poor performance in practical applications. Summary of the Invention

[0005] The purpose of the present invention is to provide a graphene material for lithium-ion batteries in response to the above technical problems, so as to solve the current problems of low first coulombic efficiency of graphene negative electrode, low electrode stacking density, large electrolyte absorption and easy self-stacking during processing. As a negative electrode material for lithium-ion batteries, it can obtain higher first coulombic efficiency, higher reversible capacity and good rate performance.

[0006] The graphene material for lithium-ion batteries in the technical solution of the present invention comprises a two-dimensional graphene nanosheet having in-plane pores and a wrinkle structure, wherein the specific surface area of ​​the two-dimensional graphene nanosheet is 300-800 m 2 / g.

[0007] The abundant in-plane pores in this graphene material help increase the diffusion rate of lithium ions and accelerate the electrochemical reaction rate in the battery, particularly during high-current charge and discharge, resulting in higher battery capacity, coulombic efficiency, and rate performance. Furthermore, the graphene material possesses a corrugated structure, which helps maintain its two-dimensional sheet morphology and forms a close-packed structure during electrode preparation, thereby achieving a high electrode density.

[0008] Furthermore, the two-dimensional graphene nanosheets include the following elements in atomic percentage: carbon content 92-96 at%, nitrogen content 0.5-2 at%, and the remainder oxygen.

[0009] The present invention also aims to provide a method for preparing the above-mentioned graphene material for lithium ion batteries, comprising the following steps:

[0010] (1) Adding carbon and nitrogen organic matter to the heated graphene oxide aqueous solution, mixing them evenly and then heating them again, collecting the mixed materials after the water evaporates and drying them together;

[0011] (2) mixing the dried mixed material 1 with a chemical etchant, and performing ball milling to obtain mixed material 2;

[0012] (3) A step-by-step heating method is used to cause the mixed material 2 to undergo carbonization reaction and activation reaction in sequence, and then the mixed material is washed and dried to obtain graphene material for lithium-ion batteries.

[0013] In the carbonization stage of the present invention, cross-linking and reduction reactions occur between graphene oxide and carbon-nitrogen organic matter, forming a stress-concentrated wrinkle structure on the surface of the graphene nanosheet, thereby obtaining a "chemically hardened" graphene / carbon-nitrogen compound composite material. In the activation stage, a chemical etchant etches the graphene to form a large number of in-plane pores and removes carbon-nitrogen compounds, thereby avoiding the adverse effects of carbon-nitrogen compounds on electrical conductivity. At the same time, under the action of "chemical hardening", the bending deformation of the graphene nanosheet is suppressed, the nanosheet undergoes plastic buckling, and the wrinkle density is further increased, ultimately obtaining a two-dimensional graphene nanosheet with in-plane pores and a wrinkle structure. The graphene material prepared by this method can first avoid the three-dimensional reconstruction effect of graphene by current activation technology, and obtain graphene nanosheets with two-dimensional morphology. The two-dimensional graphene nanosheets can be directionally arranged during the rolling process to form a tightly stacked layered structure to achieve high volume density. Compared with the existing high volume density graphene electrode preparation method such as capillary evaporation-induced densified graphene aerogel, the graphene material prepared by the present invention is a powder material with good processability and is compatible with the current production process of lithium-ion batteries; secondly, the graphene material has in-plane pores, which can provide a transmission channel for lithium ions in a direction perpendicular to the current collector; thirdly, the graphene material can utilize the intrinsic micro-wrinkle structure on its nanosheets to suppress the stacking effect of graphene during the rolling process, thereby maintaining the ion transmission channel in the direction parallel to the current collector while increasing the electrode density. On the one hand, this method effectively avoids the size adaptation and uniform dispersion problems between the two phases of materials currently faced by composite material design processes to suppress graphene stacking; on the other hand, this method avoids the self-stacking problems faced by current porous graphene film preparation technologies during compaction or filtration.

[0014] Furthermore, the solid content of graphene oxide in the graphene oxide aqueous solution in step (1) is 8-12 mg / ml, and the pH value is 4-6.

[0015] Furthermore, the carbon-nitrogen organic matter in step (1) is one or more of thiourea, urea, cyanamide, dicyandiamide, and melamine, preferably melamine.

[0016] Furthermore, in step (1), the mass ratio of graphene oxide to carbon-nitrogen organic matter is 2:8 to 8:2. Preferably, the mass ratio of graphene oxide to carbon-nitrogen organic matter is 3:5 to 5:3. Excessive carbon-nitrogen organic matter will produce excessive wrinkled structures and inhibit the etching effect of the chemical etchant, resulting in a reduction in in-plane pores, thereby leading to a decrease in specific surface area, reversible capacity and rate performance.

[0017] Furthermore, the mixing method in step (1) is to first ultrasonicate for 30 to 40 minutes and then stir for 60 to 80 minutes.

[0018] Furthermore, in step (1), the graphene oxide aqueous solution is heated to 50-80°C, and the secondary heating temperature is 100-120°C.

[0019] Furthermore, in step (2), the chemical etchant is one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, and phosphoric acid, preferably potassium hydroxide.

[0020] Furthermore, in step (2), the mass ratio of the mixed material 1 to the chemical etchant is 1:2 to 1:8. Preferably, the mass ratio of the mixed material 1 to the chemical etchant is 1:2 to 1:5. Increasing the amount of the chemical etchant is beneficial to increasing the specific surface area of ​​the material, obtaining a larger pore structure, and providing more lithium ion diffusion channels. However, excessive use will result in a decrease in electrode density and initial coulombic efficiency.

[0021] Furthermore, in step (2), the ball milling speed is 300-500 rpm, and the ball milling time is 4-6 h.

[0022] Furthermore, in step (3), the heating rate of the carbonization reaction is 3.0-5.0°C / min, the carbonization temperature is 400-600°C, and the holding time is 4-6 hours; and / or the heating rate of the activation reaction is 10-12°C / min, the activation temperature is 800-1000°C, and the holding time is 1-4 hours.

[0023] Furthermore, in step (1), step (2) and step (3), the drying temperature is 80-100° C., and the drying time is 10-14 h.

[0024] Furthermore, in step (3), deionized water and dilute hydrochloric acid are used for repeated washing 3 to 6 times.

[0025] The technical solution of the present invention also provides a lithium ion battery negative electrode, comprising the above-mentioned graphene material for lithium ion batteries, a conductive agent and a binder.

[0026] Furthermore, the electrode density of the negative electrode of the lithium-ion battery is 1.0~1.5g / cm 3 , with a specific surface area of ​​50~200m 2 / g, thickness is 30~100μm.

[0027] The method for preparing the negative electrode of the lithium-ion battery comprises mixing a graphene material for lithium-ion batteries, a conductive additive and a binder to make an electrode, and then performing a rolling process.

[0028] Furthermore, the mass ratio of the graphene material for lithium-ion batteries, the conductive additive, and the binder is 8.0-9.0:0.5-1.0:0.5-1.0.

[0029] Furthermore, the rolling treatment method is vertical rolling or roller rolling, the rolling pressure is 20~40MPa, and the rolling time is 1.0~3.0min.

[0030] During the rolling process, based on the supporting effect of the wrinkle structure on the surface of graphene nanosheets, the (002) peak position of graphene remains unchanged, and the in-plane pores of 0.7~1nm can be effectively retained, and the electrode specific surface area can be achieved in the range of 50~200m 2 After rolling, the negative electrode of lithium-ion batteries can form a tightly stacked layered structure, and the electrode density can reach 1.0~1.5g / cm 3 The electrode has ion migration channels in two directions, perpendicular and parallel to the current collector, which can realize the rapid transmission of lithium ions in different directions.

[0031] The conductive agent in the negative electrode of the lithium ion battery of the present invention is not limited. Any conductive agent that can be used in lithium ion batteries can be used. The conductive agent can be one or more of conductive carbon black, conductive graphite, and carbon fiber.

[0032] The binder in the negative electrode of the lithium ion battery of the present invention is not limited. Any binder applicable to lithium ion batteries can be used. The binder can be one or more of polyvinylidene fluoride, polyacrylonitrile binders, polyurethane binders, and polyimide binders.

[0033] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0034] (1) The present invention modifies graphene by carbon-nitrogen organic matter, combines carbonization reaction and activation reaction, and obtains two-dimensional graphene nanosheets with in-plane pores and wrinkle structure. As the negative electrode material of lithium-ion batteries, it has high first coulombic efficiency, high reversible capacity and good rate performance.

[0035] (2) The large number of in-plane pore structures in graphene materials can provide lithium ion transmission channels in the direction perpendicular to the current collector, thereby increasing the diffusion rate of lithium ions, accelerating the electrochemical reaction rate in the battery, and improving the electrochemical performance of lithium-ion batteries;

[0036] (3) The wrinkled structure helps graphene maintain its two-dimensional flake morphology during the activation process, thereby enabling the graphene negative electrode to form a good close-packed structure during the rolling process and obtain a higher electrode density;

[0037] (4) The present invention performs conventional rolling treatment on the negative electrode of the lithium-ion battery to form a tightly stacked layered structure. The wrinkled structure can suppress the stacking effect of graphene during the rolling process, so that it has ion migration channels perpendicular and parallel to the direction of the current collector, which can realize the rapid transmission of lithium ions in different directions;

[0038] (5) The graphene material prepared by the present invention is a powder material with good processability and is compatible with the current production process of lithium-ion batteries;

[0039] (6) The preparation method of the graphene material for lithium-ion batteries in the present invention is simple and can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a transmission electron microscope image of the graphene material for lithium-ion batteries obtained in Example 1;

[0041] Figure 2 This is a scanning electron microscope image of the graphene material for lithium-ion batteries obtained in Example 1;

[0042] Figure 3 Scanning electron microscope images of the lithium-ion battery negative electrode obtained in Example 1 before and after compaction: a) before compaction; b) after compaction;

[0043] Figure 4 The X-ray diffraction curves of the negative electrode of the lithium-ion battery obtained in Example 1 before and after compaction;

[0044] Figure 5 This is a scanning electron microscope image of the graphene material for lithium-ion batteries obtained in Comparative Example 1;

[0045] Figure 6 This is a scanning electron microscope image of the graphene material for lithium-ion batteries obtained in Comparative Example 2. DETAILED DESCRIPTION

[0046] The technical solution of the present invention will be further described below by means of specific examples and accompanying drawings. It should be understood that the specific embodiments described herein are only used to help understand the present invention and are not intended to be limiting of the present invention. The accompanying drawings used herein are only for the purpose of better illustrating the present invention and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0047] Example 1

[0048] The method for preparing the negative electrode of the lithium ion battery of this embodiment comprises the following steps:

[0049] (1) Weigh 300 mg of melamine and add it to 50 ml of graphene oxide aqueous solution (solid content 10 mg / ml, pH 7, mass ratio of graphene oxide to melamine 5:3). Stir at 60 °C for 1 h and ultrasonicate for 30 min to obtain a uniform solution. Heat the uniform solution to a "boiling state" of 105 °C and continue stirring until the water evaporates completely. Dry the product at 80 °C for 12 h to obtain a mixed material 1.

[0050] (2) 500 mg of mixed material 1 was mixed with 1.5 g of potassium hydroxide and ball milled at 300 rpm for 5 h to obtain mixed material 2;

[0051] (3) The mixed material 2 was placed in a corundum crucible and heat-treated in a tube furnace with argon as the protective atmosphere and a gas flow rate of 20 cc / min. The temperature was raised to 550 °C at a rate of 3.3 °C / min and kept at that temperature for 4 h to carbonize the mixed material. The temperature was then raised to 1000 °C at a rate of 10 °C / min and kept at that temperature for 1 h to activate the mixed material. After cooling, the product was filtered and washed with 1 mol / L dilute hydrochloric acid and deionized water, and dried at 80 °C for 12 h to obtain a graphene material for lithium-ion batteries (with a specific surface area of ​​575 m 2 / g, carbon content is 96at%, nitrogen content is 0.7at%);

[0052] (4) Using ethanol as solvent, graphene material for lithium-ion batteries, conductive carbon black and polytetrafluoroethylene were mixed evenly in a mass ratio of 9.0:0.5:0.5 to make a film with a thickness of 380 μm and a surface loading of 5 mg / cm 2 The thin film electrode was vertically rolled at a pressure of 20 MPa and a holding time of 1.0 min to obtain a lithium-ion battery negative electrode with a thickness of 44 μm.

[0053] Example 2

[0054] The method for preparing the negative electrode of the lithium ion battery of this embodiment comprises the following steps:

[0055] (1) Weigh 300 mg of urea and add it to 50 ml of graphene oxide aqueous solution (solid content 10 mg / ml, pH 7). Stir at 60 °C for 1 h and ultrasonicate for 30 min to obtain a uniform solution. Heat the uniform solution to a "boiling state" of 105 °C and continue stirring until the water evaporates completely. Dry the product at 80 °C for 12 h to obtain a mixed material 1.

[0056] (2) 500 mg of mixed material 1 was mixed with 2.0 g of potassium hydroxide and ball milled at 300 rpm for 5 h to obtain mixed material 2;

[0057] (3) The mixed material 2 was placed in a corundum crucible and heat-treated in a tube furnace with argon as the protective atmosphere and a gas flow rate of 20 cc / min. The temperature was raised to 600 °C at 3.3 °C / min and kept at this temperature for 4 h to carbonize the mixed material. The temperature was then raised to 1000 °C at 10 °C / min and kept at this temperature for 1 h to activate the mixed material. After cooling, the product was filtered and washed with 1 mol / L dilute hydrochloric acid and deionized water, and dried at 80 °C for 12 h to obtain a graphene material for lithium-ion batteries (with a specific surface area of ​​602 m 2 / g, carbon content is 94.3at%, nitrogen content is 0.5at%);

[0058] (4) Using ethanol as solvent, graphene material for lithium-ion batteries, conductive carbon black and polytetrafluoroethylene were mixed evenly in a mass ratio of 9.0:0.5:0.5 to make a film with a thickness of 380 μm and a surface loading of 5 mg / cm 2 The thin film electrode was vertically rolled at a pressure of 30 MPa and a holding time of 1.5 min to obtain a lithium-ion battery negative electrode with a thickness of 41 μm.

[0059] Example 3

[0060] The only difference between this embodiment and embodiment 1 is that in step (1), 500 mg of melamine is weighed and added to 30 ml of graphene oxide aqueous solution (the mass ratio of graphene oxide to melamine is 3:5).

[0061] Example 4

[0062] The only difference between this embodiment and embodiment 1 is that in step (1), 600 mg of melamine is weighed and added to 30 ml of graphene oxide aqueous solution (the mass ratio of graphene oxide to melamine is 6:3).

[0063] Example 5

[0064] The only difference between this embodiment and embodiment 1 is that in step (2), 500 mg of mixed material 1 is mixed with 4.0 g of potassium hydroxide.

[0065] Example 6

[0066] The only difference between this embodiment and embodiment 1 is that the pressure for vertically rolling the electrode in step (4) is 40 MPa.

[0067] Comparative Example 1

[0068] The method for preparing the negative electrode of the lithium ion battery of this comparative example comprises the following steps:

[0069] (1) Weigh 300 mg of melamine and add it to 50 ml of graphene oxide aqueous solution (solid content 10 mg / ml, pH 7, mass ratio of graphene oxide to melamine 5:3). Stir at 60 °C for 1 h and ultrasonicate for 30 min to obtain a homogeneous solution. Heat the homogeneous solution to a "boiling state" at 105 °C and continue stirring until the water evaporates completely. Dry the product at 80 °C for 12 h and ball mill at 300 rpm for 5 h to obtain a mixed material.

[0070] (2) The mixed material was placed in a corundum crucible and heat-treated in a tube furnace with argon as the protective atmosphere and a gas flow rate of 20 cc / min. The temperature was raised to 550 °C at a rate of 3.3 °C / min and kept at that temperature for 4 h to carbonize the mixed material. After cooling, the product was filtered and washed with 1 mol / L dilute hydrochloric acid and deionized water, and dried at 80 °C for 12 h to obtain graphene material for lithium-ion batteries.

[0071] (3) Using ethanol as solvent, graphene material for lithium-ion batteries, conductive carbon black and polytetrafluoroethylene were mixed evenly in a mass ratio of 9.0:0.5:0.5 to make a film with a thickness of 380 μm and a surface loading of 5 mg / cm 2 The thin film electrode was vertically rolled at a pressure of 20 MPa and a holding time of 1.0 min to obtain a lithium-ion battery negative electrode with a thickness of 31 μm.

[0072] Comparative Example 2

[0073] The method for preparing the negative electrode of the lithium ion battery of this comparative example comprises the following steps:

[0074] (1) Weigh 300 mg of melamine and add it to 50 ml of graphene oxide aqueous solution (solid content 10 mg / ml, pH 7, mass ratio of graphene oxide to melamine 5:3). Stir at 60 °C for 1 h and ultrasonicate for 30 min to obtain a uniform solution. Heat the uniform solution to a "boiling state" of 105 °C and continue stirring until the water evaporates completely. Dry the product at 80 °C for 12 h to obtain a mixed material 1.

[0075] (2) 500 mg of mixed material 1 was mixed with 1.5 g of potassium hydroxide and ball milled at 300 rpm for 5 h to obtain mixed material 2;

[0076] (3) The mixed material 2 was placed in a corundum crucible and heat-treated in a tube furnace with argon as the protective atmosphere. The temperature was raised to 1000°C at a rate of 10°C / min and kept at that temperature for 1 hour to activate the mixed material. After cooling, the product was filtered and washed with 1 mol / L dilute hydrochloric acid and deionized water, and dried at 80°C for 12 hours to obtain a graphene material for lithium-ion batteries.

[0077] (4) Using ethanol as solvent, graphene material for lithium-ion batteries, conductive carbon black and polytetrafluoroethylene were mixed evenly in a mass ratio of 9.0:0.5:0.5 to make a film with a thickness of 380 μm and a surface loading of 5 mg / cm 2 The thin film electrode was vertically rolled at a pressure of 20 MPa and a holding time of 1.0 min to obtain a lithium-ion battery negative electrode with a thickness of 78 μm.

[0078] Comparative Example 3

[0079] The method for preparing the negative electrode of the lithium ion battery of this comparative example comprises the following steps:

[0080] (1) Weigh 300 mg of melamine and add it to 50 ml of graphene oxide aqueous solution (solid content 10 mg / ml, pH 7, mass ratio of graphene oxide to melamine 5:3). Stir at 60 °C for 1 h and ultrasonicate for 30 min to obtain a uniform solution. Heat the uniform solution to a "boiling state" of 105 °C and continue stirring until the water evaporates completely. Dry the product at 80 °C for 12 h to obtain a mixed material 1.

[0081] (2) 500 mg of mixed material 1 was mixed with 1.5 g of potassium hydroxide and ball milled at 300 rpm for 5 h to obtain mixed material 2;

[0082] (3) The mixed material 2 was placed in a corundum crucible and heat-treated in a tube furnace with argon as the protective atmosphere and a gas flow rate of 20 cc / min. The temperature was raised to 550 °C at a rate of 3.3 °C / min and kept at that temperature for 4 h to carbonize the mixed material. The temperature was then raised to 1000 °C at a rate of 10 °C / min and kept at that temperature for 1 h to activate the mixed material. After cooling, the product was filtered and washed with 1 mol / L dilute hydrochloric acid and deionized water, and dried at 80 °C for 12 h to obtain graphene material for lithium-ion batteries.

[0083] (4) Using ethanol as solvent, graphene material for lithium-ion batteries, conductive carbon black and polytetrafluoroethylene were mixed evenly in a mass ratio of 9.0:0.5:0.5 to make a film with a thickness of 380 μm and a surface loading of 5 mg / cm 2 electrodes.

[0084] Comparative Example 4

[0085] The only difference between this comparative example and Example 1 is that in step (1), 900 mg of melamine was weighed and added to 10 ml of graphene oxide aqueous solution (the mass ratio of graphene oxide to melamine was 9:1).

[0086] Comparative Example 5

[0087] The only difference between this comparative example and Example 1 is that in step (1), 100 mg of melamine was weighed and added to 90 ml of graphene oxide aqueous solution (the mass ratio of graphene oxide to melamine was 1:9).

[0088] Comparative Example 6

[0089] The only difference between this comparative example and Example 1 is that in step (2), 500 mg of mixed material 1 is mixed with 0.5 g of potassium hydroxide.

[0090] Comparative Example 7

[0091] The only difference between this comparative example and Example 1 is that in step (2), 500 mg of mixed material 1 is mixed with 4.5 g of potassium hydroxide.

[0092] Comparative Example 8

[0093] The method for preparing the negative electrode of the lithium ion battery of this comparative example comprises the following steps:

[0094] (1) 500 mg of graphene oxide was mixed with 1.5 g of potassium hydroxide and ball milled at 300 rpm for 5 h to obtain a mixed material;

[0095] (2) The mixed material was placed in a corundum crucible and heat treated in a tube furnace with argon as the protective atmosphere and a gas flow rate of 20 cc / min. The temperature was raised to 550 °C at a rate of 3.3 °C / min and kept at that temperature for 4 h to carbonize the mixed material. The temperature was then raised to 1000 °C at a rate of 10 °C / min and kept at that temperature for 1 h to activate the mixed material. After cooling, the product was filtered and washed with 1 mol / L dilute hydrochloric acid and deionized water, and dried at 80 °C for 12 h to obtain graphene material for lithium-ion batteries.

[0096] (3) Using ethanol as solvent, graphene material for lithium-ion batteries, conductive carbon black and polytetrafluoroethylene were mixed evenly in a mass ratio of 9.0:0.5:0.5 to make a film with a thickness of 380 μm and a surface loading of 5 mg / cm 2 The thin film electrode was vertically rolled at a pressure of 20 MPa and a holding time of 1.0 min to obtain a lithium-ion battery negative electrode with a thickness of 73 μm.

[0097] Comparative Example 9

[0098] The method for preparing the negative electrode of the lithium ion battery of this comparative example comprises the following steps:

[0099] (1) Graphene oxide was placed in a corundum crucible and heat treated in a tube furnace with argon as the protective atmosphere and a gas flow rate of 20 cc / min. The temperature was raised to 550 °C at a rate of 3.3 °C / min and kept at that temperature for 4 h to carbonize the mixture. The temperature was then raised to 1000 °C at a rate of 10 °C / min and kept at that temperature for 1 h to activate the mixture. After cooling, the product was filtered and washed with 1 mol / L dilute hydrochloric acid and deionized water, and dried at 80 °C for 12 h to obtain graphene material for lithium-ion batteries.

[0100] (2) Using ethanol as solvent, graphene material for lithium-ion batteries, conductive carbon black and polytetrafluoroethylene were mixed in a mass ratio of 9.0:0.5:0.5 to make a film with a thickness of 380 μm and a surface loading of 5 mg / cm 2 The thin film electrode was vertically rolled at a pressure of 20 MPa and a holding time of 1.0 min to obtain a lithium-ion battery negative electrode with a thickness of 33 μm.

[0101] The lithium-ion battery negative electrode obtained in the above examples and comparative examples was assembled into a button cell using metallic lithium as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 in EC / DMC (vol. 1:1) as the lithium-ion battery electrolyte. Constant current charge and discharge tests were performed. The current density of constant current charge and discharge was 1C = 375mA / g, and the voltage range during the test was set to 0.01~3V vs. Li / Li. + , the experimental data are shown in Table 1.

[0102] Table 1 Button battery performance data

[0103]

[0104] According to the data in Table 1, Comparative Example 1 is not activated, and the surface of the graphene material obtained has a large number of wrinkled structures and almost no pores. The compaction density of the negative electrode of the lithium ion battery is high, the lithium ion transmission channel inside the negative electrode of the lithium ion battery is small, the battery capacity is low, and the rate performance is poor. Comparative Example 2 is directly activated at high temperature without carbonization, and the graphene material obtained has a large number of pores and no wrinkled structure, and the compaction density of the negative electrode of the lithium ion battery is low. Comparative Example 3 is not rolled, and the compaction density of the negative electrode of the lithium ion battery is low and the first coulomb efficiency is low. Comparative Example 4 uses a large amount of graphene oxide and a small amount of melamine, and has a small surface wrinkle structure, and the compaction density of the negative electrode of the lithium ion battery is low. Comparative Example 5 uses a small amount of graphene oxide and a large amount of melamine, and has a large surface wrinkle structure. The graphene activation effect is poor, the lithium ion transmission channel inside the negative electrode of the lithium ion battery is small, and the battery rate performance is poor. In comparative example 6, the amount of potassium hydroxide etchant used is small, the resulting graphene material has fewer pores, the compaction density of the lithium ion battery negative electrode is high, the lithium ion transmission channel inside the negative electrode of the lithium ion battery is small, and the battery rate performance is poor. In comparative example 7, the amount of potassium hydroxide etchant used is large, the resulting graphene material has more pores, the compaction density of the lithium ion battery negative electrode is low, and the battery's first coulombic efficiency and capacity are both low. In comparative example 8, graphene oxide is etched to form pores to obtain a large number of pore structures, and the battery's first coulombic efficiency is low. In comparative example 9, conventional graphene oxide is used to prepare the lithium ion battery negative electrode, the lithium ion transmission channel is limited, and the battery capacity and rate performance are poor.

[0105] Figure 1 It can be seen that the graphene material for lithium ion batteries obtained in Example 1 contains a pore structure with a diameter of 0.9 to 2.2 nm. Figure 2 It can be seen that the graphene material for lithium-ion batteries obtained in Example 1 is a two-dimensional nanosheet with a large number of wrinkled structures on the surface. Figure 3 It can be seen that after rolling, the thickness of the lithium-ion battery negative electrode obtained in Example 1 is reduced to about 44 μm, forming a tightly packed layered electrode structure. Figure 4 It can be seen that the peak position of (002) of the lithium ion battery negative electrode obtained in Example 1 remains unchanged after rolling, and the self-stacking of graphene is effectively suppressed. Figure 5 It can be seen that in Comparative Example 1, only carbonization was performed without activation, and the surface wrinkle structure density was low. Figure 6 It can be seen that in Comparative Example 2, high-temperature activation was performed directly without carbonization, and the obtained graphene material formed a three-dimensional cross-linked structure with a large number of pores and no wrinkle structure on the surface.

[0106] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the spirit of the present invention and are not intended to limit the manner in which the present invention is intended to be implemented. Persons skilled in the art may make various modifications, additions, or substitutions to the described embodiments, and it is not necessary or possible to provide a comprehensive list of all possible embodiments. However, any obvious changes or modifications arising from the essential spirit of the present invention remain within the scope of protection of the present invention, and interpreting them as any additional limitations would be contrary to the spirit of the present invention.

Claims

1. A graphene material for lithium-ion batteries, characterized in that: The invention comprises a two-dimensional graphene nanosheet having in-plane pores and a wrinkle structure, wherein the specific surface area of ​​the two-dimensional graphene nanosheet is 300 to 800 m 2 / g; The preparation method of graphene material for lithium-ion battery comprises the following steps: (1) Adding carbon and nitrogen organic matter to the heated graphene oxide aqueous solution, mixing them evenly and then heating them again, collecting the mixed materials after the water evaporates and drying them together; (2) mixing the dried mixed material 1 with a chemical etchant, and performing ball milling to obtain mixed material 2; (3) Using a step-by-step heating method to make the mixed material 2 undergo carbonization reaction and activation reaction successively, and then washing and drying to obtain graphene material for lithium-ion batteries; In step (2), the chemical etchant is one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, and phosphoric acid; In step (3), the heating rate of the carbonization reaction is 3.0~5.0℃ / min, the carbonization temperature is 400~600℃, and the holding time is 4~6h; the heating rate of the activation reaction is 10~12℃ / min, the activation temperature is 800~1000℃, and the holding time is 1~4h.

2. The graphene material for lithium-ion batteries according to claim 1, wherein The two-dimensional graphene nanosheets include the following elements in atomic percentage: carbon content 92-96 at%, nitrogen content 0.5-2 at%, and the remainder oxygen.

3. A method for preparing a graphene material for lithium-ion batteries according to claim 1, characterized in that: The following steps are involved: (1) Adding carbon and nitrogen organic matter to the heated graphene oxide aqueous solution, mixing them evenly and then heating them again, collecting the mixed materials after the water evaporates and drying them together; (2) mixing the dried mixed material 1 with a chemical etchant, and performing ball milling to obtain mixed material 2; (3) Using a step-by-step heating method to make the mixed material 2 undergo carbonization reaction and activation reaction successively, and then washing and drying to obtain graphene material for lithium-ion batteries; In step (2), the chemical etchant is one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, and phosphoric acid; In step (3), the heating rate of the carbonization reaction is 3.0~5.0℃ / min, the carbonization temperature is 400~600℃, and the holding time is 4~6h; the heating rate of the activation reaction is 10~12℃ / min, the activation temperature is 800~1000℃, and the holding time is 1~4h.

4. The method for preparing a graphene material for lithium ion batteries according to claim 3, wherein: The solid content of graphene oxide in the graphene oxide aqueous solution in step (1) is 8-12 mg / ml, and the pH value is 7.

5. The method for preparing a graphene material for lithium ion batteries according to claim 3, wherein: In step (1), the mass ratio of graphene oxide to carbon-nitrogen organic matter is 2:8 to 8:

2.

6. The method for preparing a graphene material for lithium ion batteries according to claim 3, wherein: In step (1), the graphene oxide aqueous solution is heated to 50-80°C, and the secondary heating temperature is 100-120°C.

7. The method for preparing a graphene material for lithium ion batteries according to claim 3, wherein: The mass ratio of the mixed material 1 to the chemical etchant is 1:2~1:

8.

8. A lithium ion battery negative electrode, characterized in that The invention comprises the graphene material for lithium-ion batteries according to claim 1, a conductive agent and a binder.

9. The lithium-ion battery negative electrode according to claim 8, characterized in that: The electrode density of the lithium ion battery negative electrode is 1.0-1.5 g / cm 3 , with a specific surface area of ​​50~200m 2 / g, thickness is 30~100μm.

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