CN115504461B

CN115504461B - Preparation method of Li-ion modified reduced graphene oxide powder

Info

Publication number: CN115504461B
Application number: CN202211199576.6A
Authority: CN
Inventors: 蔡金明; 陈其赞; 汤小辉
Original assignee: Guangdong Morion Nanotech Co Ltd
Current assignee: Guangdong Morion Nanotech Co Ltd
Priority date: 2022-09-29
Filing date: 2022-09-29
Publication date: 2023-07-21
Anticipated expiration: 2042-09-29
Also published as: CN115504461A

Abstract

The invention provides a preparation method of Li ion modified reduced graphene oxide powder and a conductive agent prepared by taking the powder as a raw material, wherein the preparation method of the powder comprises the following steps: slowly adding the washed graphene oxide slurry into LiOH solution, heating to 40-70 ℃, then panning the graphene oxide slurry in a ceramic rotary instrument for 1.5-3h, carrying out Li ion modification treatment on the graphene oxide slurry to obtain GO-Li slurry, homogenizing the GO-Li slurry, carrying out spray granulation on the GO-Li slurry to obtain GO-Li powder, reducing and drying the GO-Li powder to obtain Li ion modified reduced graphene oxide powder, wherein the graphene conductive agent prepared from the powder has an auxiliary enhancement effect on lithium ion conduction, and can pertinently improve the rate performance of a battery.

Description

Preparation method of Li-ion modified reduced graphene oxide powder

Technical Field

The invention belongs to the field of graphene, and particularly relates to a preparation method of Li-ion modified reduced graphene oxide powder and application of the modified reduced graphene oxide powder in new energy.

Background

Graphene has ultrahigh heat conduction coefficient and electronic conduction performance, at present, graphene oxidation-reduction preparation technology is mature, graphene and derivatives thereof are one of key material resources with the largest scale and prospect, and have research value and application value incomparable with other materials. The material is widely focused by scientific researchers in the field of lithium ion battery research, and is considered to be an ideal lithium ion battery material compared with the traditional battery material, and the graphene has unique two-dimensional characteristics, excellent electric and heat conductivity and the characteristic of building a conductive network in point-to-surface contact with main material particles. At present, application research of graphene and derivatives thereof in lithium ion batteries is mainly focused on pole piece 3D conductive network construction and anode and cathode material modification.

Compared with the traditional point-line Contact (CNT) and point-point contact (SP) of the conductive material and the anode material of the lithium ion battery, the graphene (RGO) which is highly conductive and in a two-dimensional state like silk has a more ideal point-surface contact mode, and is more ideal in the construction of a 3D conductive network of a battery pole piece. In addition, the ultra-large specific surface area of graphene also shows excellent performance in terms of anode and cathode main material modification, such as loading, surface coating and the like. However, the intrinsic steric hindrance effect of graphene has a barrier effect on the conduction and transportation of lithium ions in a lithium ion battery, is unfavorable for the improvement of the rate performance of the battery, and mainly represents an ideal graphene long-range ordered six-membered ring atomic arrangement, and a six-membered ring intermediate space formed by six carbon atoms is smaller than the ionic radius of the lithium ions. The complete graphene does not allow the lithium ions to shuttle from front to back, and lithium ion transport can only be performed at the edges of the graphene or at the defects of pores on the surface of the graphene, and in addition, the free path of lithium ion transport is increased to a certain extent due to aggregation, wrinkling and stacking of the graphene. After the reduction treatment, the graphene has high specific surface area and high conductivity, but the Z-axis electron of the graphene is in a neutral pi-pi coupling state, so that the affinity to ions is reduced.

In order to overcome the defects, the invention provides the Li-ion modified reduced graphene oxide powder, and the graphene conductive agent prepared by using the powder has an auxiliary enhancement effect on lithium ion conduction and can pertinently improve the rate capability of a battery.

Disclosure of Invention

The first object of the present invention is to provide a Li ion modified reduced graphene oxide powder, which is specifically prepared as follows:

slowly adding the washed graphene oxide slurry into LiOH solution, heating to 40-70 ℃, then panning in a ceramic rotary instrument for 1.5-3h, carrying out Li ion modification treatment on the graphene oxide slurry to obtain GO-Li slurry, homogenizing, spraying and granulating the GO-Li slurry to obtain GO-Li powder, and carrying out reduction and drying treatment to obtain the Li ion modified reduced graphene oxide powder.

The reason why the doping temperature of the Li ions is 40-70 ℃ is that if the temperature is lower than 40 ℃, the LiOH solution and the graphene oxide slurry cannot sufficiently react, the modification of the graphene oxide slurry cannot be completed, if the temperature is higher than 70 ℃, the graphene oxide slurry is primarily thermally reduced, and the primarily thermally reduced graphene sheet layer has carboxyl groups which ionize in water to be electronegative, so that Li is ⁺ Ionic and weakly reduced graphene oxide phasesThe mutual adsorption forms a hydrogel state, meanwhile, partial oxidation of graphene oxide leads to local agglomeration and stacking when the temperature is too high, the agglomerated graphene oxide is unfavorable for subsequent uniform dispersion, and graphene of the agglomerated part after reduction is thicker due to stacking of sheets, so that the steric hindrance effect of lithium ions in the deintercalation process is amplified, and the rate performance of the battery is reduced. Typically, but not by way of limitation, the doping temperature of the Li ions is 40 ℃, 50 ℃, 60 ℃, 70 ℃.

Preferably, if the concentration of the LiOH solution is 0.2-1M, if the concentration of the LiOH solution is lower than 0.2M, the reaction is slow and insufficient, if the concentration of the LiOH solution is higher than 1M, the LiOH solution rapidly reacts with the marginal graphene oxide, and when the lithium hydroxide solution is alkaline and is added into an acidic graphene oxide aqueous solution, electrostatic adsorption interaction exists between positive lithium cations and carboxylate radicals in negative states of graphene oxide, so that the graphene oxide is electrically neutral, the uniform dispersion effect caused by mutual repulsion of carboxylate ions is lost, agglomeration, precipitation and sedimentation phenomena occur, the thickness of the agglomerated graphene oxide is larger, the subsequent dispersion is unfavorable, the large steric hindrance effect exists, the large-scale deintercalation of lithium ions is unfavorable, the technological process and the battery rate performance are affected, and the concentration of the LiOH solution is typically but not limited, namely 0.2M, 0.4M, 0.5M, 0.6M, 0.8M and 1.0M.

Preferably, the PH of the washed graphene oxide slurry is greater than 3, and the washing method may be ceramic spin washing, so as to wash out residual acid in the GO slurry as much as possible, and prevent the alkaline solution LiOH from preferentially reacting with the acid in the slurry, thereby wasting raw materials.

Preferably, the homogenization aims at realizing the particle size control of the GO-Li, and the homogenization method is to perform homogenization treatment on the GO-Li slurry for 3-10 times under the pressure condition of 800-1000 mPas, so that the GO-Li sheet diameter is less than 3 mu m. The large-sheet-diameter GO-Li can be agglomerated, wrinkled and stacked, so that the free range of lithium ion transportation is increased to a certain extent, and the powder can not greatly improve the rate performance of the battery when being used as a conductive material on a new energy battery.

Preferably, the spray granulation is to spray the homogenized GO-Li slurry at 100-200 ℃ to obtain GO-Li powder.

Preferably, the reduction treatment comprises a low reduction treatment and a high reduction treatment, wherein the low reduction treatment is to carry out microwave puffing on the GO-Li powder at the constant temperature of 600-1000 ℃, and the high reduction treatment is to carbonize the low reduction GO-Li powder in the nitrogen atmosphere of 1000-1500 ℃. Compared with other reduction modes, the microwave puffing reduction can heat the materials inside and outside together, avoid the phenomenon of a cold center generated by traditional high-temperature heating, improve the heat energy utilization rate and achieve the same or better reduction effect at lower reaction temperature.

Preferably, the drying treatment is carried out in a vacuum drying oven, the drying temperature is 120-180 ℃, the drying time is more than 15 hours, and in the whole preparation process of the powder, the humidity is controlled below 20%rh, so that the reduced graphene oxide powder modified by Li ions is prevented from absorbing moisture, and the performance of the powder is prevented from being influenced.

The second object of the invention is to provide a graphene conductive agent, which comprises the Li-ion modified reduced graphene oxide powder prepared by any scheme, wherein the solid content of the Li-ion modified reduced graphene oxide powder is 2.5-4%.

According to the preparation method of the graphene conductive agent, NMP is used as a solvent, PVP is used as a dispersing agent, li ion modified reduced graphene oxide powder prepared by any scheme is used as a conductive agent main material, the graphene conductive agent with solid content of 2.5-4% is prepared by a dispersing, sand grinding and homogenizing preparation process, the mass fraction of PVP of the dispersing agent is 0.6% -1.2%, PVP mainly plays a role in dispersing graphene, the dispersing effect is poor when PVP is added by less than 0.6%, the defects of sedimentation, large resistance and the like of the graphene conductive agent are caused, and when the PVP addition amount is more than 1.2%, PVP is excessive, the conductivity of the conductive agent is reduced.

Drawings

Fig. 1: inventive example 1 and comparative example 1 are graphs of the results of the rate tests.

Detailed Description

The following detailed description of exemplary embodiments of the invention refers to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration exemplary embodiments in which features of the invention are identified by reference numerals. The following more detailed description of the embodiments of the invention is not intended to limit the scope of the invention, as claimed, but is merely illustrative and not limiting of the invention's features and characteristics in order to set forth the best mode of carrying out the invention and to sufficiently enable those skilled in the art to practice the invention. It will be understood that various modifications and changes may be made without departing from the scope of the invention as defined by the appended claims. The detailed description and drawings are to be regarded in an illustrative rather than a restrictive sense, and if any such modifications and variations are desired to be included within the scope of the invention described herein. Furthermore, the background art is intended to illustrate the status and meaning of the development of the technology and is not intended to limit the invention or the application and field of application of the invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention; the term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

In order to make the technical problems, technical solutions and advantages to be solved more apparent, the following detailed description will be given with reference to the accompanying drawings and specific embodiments.

Example 1

The embodiment provides a preparation method of Li-ion modified reduced graphene oxide powder and a preparation method of a graphene conductive agent using the Li-ion modified reduced graphene oxide powder as a raw material, which comprises the following specific steps:

1) Taking GO slurry with the solid content of 2% as a raw material, and cleaning the pH value of the GO slurry to 3.2 through ceramic rotary cleaning for 10 hours, wherein the step aims to clean residual sulfuric acid and hydrochloric acid in the GO slurry as much as possible;

2) The GO slurry is prepared by the following volume ratio: liOH solution = 10:1, slowly adding a LiOH aqueous solution with the concentration of 0.5M into the GO slurry with the pH value of 3.2 obtained in the step 1) under the stirring condition, heating the mixed solution to 50 ℃, and loading the mixed solution into a ceramic rotary instrument through a disc pump for continuous elutriation for 2 hours to obtain GO-Li slurry;

3) Homogenizing the GO-Li slurry obtained in the step under the pressure condition of 800 mPa.s for 5 times, and performing particle size control treatment to obtain GO-Li slurry with the particle size of 2.8 mu m;

4) Spraying and granulating the homogenized GO-Li slurry in an atmosphere of 180 ℃ to obtain GO-Li powder;

5) Carrying out microwave puffing treatment on the GO-Li powder at a constant temperature of 800 ℃ for 40s to obtain low-reduction rGO-Li powder;

6) Carbonizing the low-reduction rGO-Li powder in a nitrogen atmosphere at 1350 ℃ for 10 hours to obtain high-reduction RGO-Li powder;

7) Baking the RGO-Li powder obtained for 20 hours in a vacuum drying oven at 150 ℃, wherein the step aims to avoid the RGO-Li powder with high specific surface area from absorbing moisture, and the preparation environment humidity is controlled to be less than 20%;

8) The preparation method comprises the steps of taking NMP as a solvent, PVP as a dispersing agent, RGO-Li as a main material of the conductive agent, and preparing the graphene conductive agent according to a dispersing, sand grinding and homogenizing preparation process, wherein the sand grinding design rotating speed is 2000r/min, the sand grinding is circulated for 10 times, the homogenizing pressure is 800 mPa.S, the homogenizing is circulated for 5 times, the design mass fraction of the dispersing agent PVP is 0.6%, and the RGO-Li conductive agent with 3.6% of solid content and 3.0% of carbon content is obtained.

LCO is used as a positive electrode main material, 1% of RGO-Li conductive agent is added for 3D conductive network construction of an electrode, 1.5% of PVDF is added as a binder for homogenization, coating and battery assembly. Multiplying power tests were performed at 0.1C, 0.2C, 0.5C, 1C, 3C, 5C, 7C, and cycling tests were performed at 3C, and the results showed that: the specific capacities of the batteries under the conditions of 0.1C, 0.2C, 0.5C, 1C, 3C, 5C and 7C are 162.91mAh/g, 160.35mAh/g, 158.39mAh/g, 157.70mAh/g, 150.95mAh/g, 132.60mAh/g and 112.04mAh/g respectively; the capacity retention at 157 weeks of 3C cycle was 88.79%.

Examples 2 to 4

The group of examples is to explore the influence of the doping temperature of LiOH solution and graphene oxide slurry on the conductive performance of RGO-Li (i.e. Li ion modified reduced graphene oxide powder). Unlike example 1, examples 2 to 4 were each at a reaction temperature of 10℃and 80℃and 100℃in step 2), which is the same as example 1, and a detailed description thereof is omitted. At a reaction temperature of 80℃and 100℃the GO slurry appears jelly-like, which may be the state of-COO-forming hydrogels under the conditions of hydrolysis of Li+ and GO.

LCO is also taken as a positive electrode main material, 1% of RGO-Li conductive agent is added for 3D conductive network construction of the electrode, 1.5% of PVDF is added as a binder, and homogenization, coating and battery assembly are carried out. The rate tests were performed at 0.1C, 0.2C, 0.5C, 1C, 3C, 5C, 7C, and the cycle test was performed at 3C.

According to the experimental results, the reaction is not facilitated due to the fact that the temperature is too low and the temperature is too high, the reaction is slow when the temperature is too low, reduction of graphene oxide is accelerated when the temperature is too high, the reduction is often accompanied by agglomeration, stacking, sedimentation and other phenomena, and the subsequent dispersion of the conductive agent and the steric hindrance effect of lithium ions caused under the condition of high-rate charge and discharge are not facilitated.

Examples 5 to 8

The set of examples is to explore the effect of the concentration of the LiOH solution on the performance of the RGO-Li conductive agent, unlike example 1, examples 5-8 in step 2) had the concentration of the LiOH solution of 0.1M, 0.4M, 1.2M, 2M, respectively, and the other examples are the same as example 1, and are not repeated here. When the concentration of LiOH solution was 0.1M, the reaction rate was significantly reduced, and more time than in example 1 was required for the reaction to be complete. When the concentration of the LiOH solution is 1.2M, the phenomenon of aggregation and precipitation of GO occurs to a certain extent, and when the concentration of the LiOH solution is 2M, the phenomenon of aggregation and precipitation of GO occurs in a large amount.

From the data, the concentration of LiOH is an important factor affecting the quality of the RGO-Li conductive agent, when the concentration of LiOH is too low, the reaction rate is obviously slowed down, and when the concentration of LiOH is too high, the LiOH solution reacts with the graphene oxide at the edge rapidly to cause aggregation, precipitation and sedimentation of the graphene oxide, thereby reducing the performance of the conductive agent.

Examples 9 to 11

This group of examples was designed to investigate the effect of the size of the GO-Li particle on the performance of RGO-Li conductive agent, unlike example 1, examples 9-11 homogenized the resulting GO-Li slurry 5 times under 1000bar, 900bar, 600bar pressure, respectively, and particle size control treatment to obtain GO-Li slurries with particle sizes of 2.0 μm, 3.6 μm, and 4.5 μm, and likewise with LCO as the positive electrode host material, 1% of RGO-Li conductive agent was added for electrode 3D conductive network construction, 1.5% pvdf was added as the binder, and homogenization, coating, and battery assembly were performed. The rate tests were performed at 0.1C, 0.2C, 0.5C, 1C, 3C, 5C, 7C, and the cycle test was performed at 3C.

From the data result, the steric effect of graphene on lithium ions can be reduced through particle size control, a large number of gaps can be formed when a conductive network is built after the particle size of the graphene is reduced, the conductive network can be used as a rapid channel for transporting lithium ions, and lithium ions can enter active material particles through edges and gaps of the graphene during deintercalation, so that the steric effect of the graphene on the lithium ions can be reduced through particle size control.

Examples 12 to 13

This group of examples was conducted to investigate the effect of ambient humidity on the performance of RGO-Li conductive agents, and examples 12 to 13 were conducted to measure the rate and cycle of the battery prepared by the same method and conditions, except that the ambient humidity was controlled to 60% rh and 80% rh, respectively, as in example 1.

From the above results, it is known that the humidity has a large influence on the performance of the conductive agent, because graphene has a large specific surface area and is easy to absorb moisture, and even layering phenomenon occurs in the conductive agent slurry when the environmental humidity is too high, resulting in slurry failure.

Comparative example 1

The difference between this comparative example and example 1 is that no LiOH aqueous solution is used to participate in the reaction in step 2), i.e., the graphene oxide is not subjected to Li ion doping modification treatment in this comparative example, and other steps are the same as those in example 1, and will not be described again. And performing multiplying power test and cycle test on the prepared battery by using the same method and conditions.

From the above results, it can be seen that, compared with the common graphene conductive agent, the graphene conductive agent prepared by using the reduced graphene oxide modified by Li ions as the raw material has greatly improved performance, which is attributable to that the graphene modified by Li ions enhances the affinity of graphene to lithium ions to a certain extent, and the lithium ions continue at the edge and surface hole defect of the graphene, thereby being beneficial to guiding the rapid passage of lithium ions from the lithium-philic site and improving the rate capability.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims

1. The preparation method of the Li-ion modified reduced graphene oxide powder is characterized by comprising the following steps of: slowly adding the washed graphene oxide slurry into LiOH solution, heating to 40-70 ℃, then panning the graphene oxide slurry in a ceramic rotary instrument for 1.5-3h, carrying out Li ion modification treatment on the graphene oxide slurry to obtain GO-Li slurry, then homogenizing and spray granulating the GO-Li slurry to obtain GO-Li powder, reducing and drying the GO-Li powder to obtain Li ion modified reduced graphene oxide powder, wherein the concentration of the LiOH solution is 0.2-1M, homogenizing the GO-Li slurry for 3-10 times under the pressure condition of 800-1000 mPa.s, so that the particle diameter of the GO-Li sheet is less than 3 mu M, and controlling the environmental humidity to be less than 20%rh in the preparation process of the Li ion modified reduced graphene oxide powder.

2. A method of preparing the Li-ion modified reduced graphene oxide powder of claim 1, wherein the pH of the washed graphene oxide slurry is > 3.

3. The method for preparing the Li-ion modified reduced graphene oxide powder according to claim 1, wherein the reduction treatment comprises a low reduction treatment of microwave puffing the GO-Li powder at a constant temperature of 600 to 1000 ℃ and a high reduction treatment of carbonizing the low-reduced GO-Li powder in a nitrogen atmosphere of 1000 to 1500 ℃.

4. The method for preparing Li-ion modified reduced graphene oxide powder according to claim 1, wherein the drying treatment is performed in a vacuum drying oven at a drying temperature of 120-180 ℃ for a drying time of > 15h.

5. A graphene conductive agent, characterized in that the graphene conductive agent comprises the Li-ion modified reduced graphene oxide powder prepared by the method of any one of claims 1 to 4, and the solid content of the Li-ion modified reduced graphene oxide powder is 2.5 to 4%.

6. The preparation method of the graphene conductive agent is characterized in that NMP is used as a solvent, PVP is used as a dispersing agent, the Li ion modified reduced graphene oxide powder prepared by the method of any one of claims 1-4 is used as a conductive agent main material, and the graphene conductive agent with the solid content of 2.5-4% is prepared by a preparation process of dispersion, sand grinding and homogenization.

7. The method for preparing the graphene conductive agent according to claim 6, wherein the mass fraction of the dispersant PVP is 0.6% -1.2%.