CN115504461A

CN115504461A - Preparation method of Li ion modified reduced graphene oxide powder

Info

Publication number: CN115504461A
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: 2022-12-23
Anticipated expiration: 2042-09-29
Also published as: CN115504461B

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 a LiOH solution, heating to 40-70 ℃, elutriating in a ceramic rotary instrument for 1.5-3h to carry out Li ion modification treatment on the graphene oxide slurry to obtain GO-Li slurry, homogenizing, carrying out spray granulation on the GO-Li slurry to obtain GO-Li powder, reducing, and drying 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 improve the rate capability of the battery in a targeted manner.

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, the graphene oxidation-reduction preparation process is mature, graphene and derivatives thereof are one of the most large-scale and promising key material resources, and the graphene oxide-reduction preparation process has incomparable research value and application value of other materials. The material is widely concerned by researchers in the field of lithium ion battery research, and compared with the traditional battery material, the unique two-dimensional characteristic of graphene, excellent electric and heat conducting performance and the characteristic of constructing an electric conduction network in point-surface contact with main material particles are considered to be an ideal lithium ion battery material. At present, application research on graphene and derivatives thereof in lithium ion batteries mainly focuses on pole piece 3D conductive network construction and positive and negative electrode material modification.

Compared with the traditional point-line Contact (CNT) and point-point contact (SP) of the conductive material and the anode and cathode materials of the lithium ion battery, the graphene (RGO) which is highly conductive and is in a two-dimensional state like silk has a more ideal point-surface contact mode, and is more ideal in the establishment of a 3D conductive network of a battery pole piece. In addition, the ultra-large specific surface area of the graphene also shows excellent performance in the aspects of modification of the positive and negative main materials, such as loading, surface coating and the like. However, the intrinsic steric hindrance effect of graphene has barrier property for the conduction and transportation of lithium ions in the lithium ion battery, is not beneficial to the improvement of the rate capability of the battery, and mainly represents the ideal long-range ordered arrangement of six-membered ring atoms of graphene, and the gap between six-membered rings formed by six carbon atoms is smaller than the ionic radius of lithium ions. The complete graphene does not allow the positive shuttling of lithium ions, the lithium ion transportation can be only carried out at the edge of the graphene or at the pore defect on the surface of the graphene, and in addition, the free path of the lithium ion transportation is increased to a certain extent due to the agglomeration, folding and stacking of the graphene. After the reduction treatment, although the graphene has high specific surface area and high conductivity, Z-axis electrons of the graphene are in a neutral pi-pi coupling state, and the affinity to ions is reduced.

Aiming at the defects, the invention provides the Li ion modified reduced graphene oxide powder, and the graphene conductive agent prepared from the powder has an auxiliary enhancement effect on lithium ion conduction, and the rate capability of the battery is improved in a targeted manner.

Disclosure of Invention

The first purpose of the invention is to provide a Li ion modified reduced graphene oxide powder, which is prepared by the following specific preparation method:

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

The doping temperature of the Li ions is 40-70 ℃ because if the temperature is lower than 40 ℃, the LiOH solution and the graphene oxide slurry cannot fully react and cannot complete the modification of the graphene oxide slurry, and if the temperature is higher than 70 ℃, the graphene oxide slurry is primarily thermally reduced, and a carboxyl group is arranged on a graphene sheet layer subjected to primary thermal reduction and ionized in water to form electronegativity, so that Li ions are carried out to the graphene sheet layer ⁺ Ions and weakly reduced graphene oxide are mutually adsorbed to form 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 not beneficial to subsequent uniform dispersion, and the agglomerated graphene is thick due to stacking of sheets after reduction, so that the steric hindrance effect of lithium ions is amplified in the de-intercalation process, 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, the LiOH solution has a concentration of 0.2-1M, if the LiOH solution is less than 0.2M, the reaction is slow and insufficient due to too low solution concentration, if the LiOH solution has a concentration higher than 1M, the LiOH solution rapidly reacts with the graphene oxide at the edge due to too high solution concentration, the lithium hydroxide solution is alkaline, when the LiOH solution is added into an acidic graphene oxide aqueous solution, lithium cations in a positive state and carboxylate radicals in a negative state after hydrolysis of the graphene oxide have electrostatic adsorption interaction to make the graphene oxide electrically neutral, the graphene oxide loses a uniform dispersion effect caused by mutual repulsion of the original carboxylate radicals, and agglomeration, precipitation and sedimentation phenomena occur, the agglomerated graphene oxide has a relatively large thickness, is not favorable for subsequent dispersion and has a relatively large steric hindrance effect, is not favorable for large-rate de-intercalation of lithium ions, and influences the process and the rate performance of a battery, typically but not limited, and the LiOH solution has a concentration of 0.2M, 0.4M, 0.5M, 0.6M, 0.8M, and 1.0.0M.

Preferably, the washed graphene oxide slurry has a pH value greater than 3, the washing method can be ceramic rotary washing, and the washing method aims to wash away residual acid in the GO slurry as far as possible and prevent alkaline solution LiOH from preferentially reacting with acid in the slurry to cause waste of raw materials.

Preferably, the homogenization aims at realizing the control of the particle size of GO-Li, and the homogenization method is to homogenize the GO-Li slurry for 3-10 times under the pressure condition of 800-1000mPa s, so that the sheet size of GO-Li is less than 3 μm. The reason is that the GO-Li with large sheet diameter can be agglomerated, folded and stacked, so that the free path of lithium ion transportation is increased to a certain extent, and the rate capability of the battery cannot be greatly improved when the powder is applied to a new energy battery as a conductive material.

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

Preferably, the reduction treatment comprises low reduction treatment and high reduction treatment, the low reduction treatment is that the GO-Li powder is subjected to microwave puffing at a constant temperature of 600-1000 ℃, and the high reduction treatment is that the low-reduced GO-Li powder is carbonized in a nitrogen atmosphere of 1000-1500 ℃. Compared with other reduction modes, the microwave puffing reduction mode can heat the inside and the outside of the material together, avoids the phenomenon of a cold center generated by the traditional high-temperature heating, improves the heat energy utilization rate, and can 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 15h, and in the whole preparation process of the powder, the humidity is controlled to be below 20% rh, so that the phenomenon that the Li ion modified reduced graphene oxide powder absorbs moisture and influences the powder performance is avoided.

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

The third objective of the present invention is to provide a preparation method of a graphene conductive agent, wherein NMP is used as a solvent, PVP is used as a dispersing agent, the Li ion modified reduced graphene oxide powder prepared by any of the above schemes is used as a main material of the conductive agent, and the graphene conductive agent with a solid content of 2.5-4% is prepared according to a dispersion, sand grinding and homogenization preparation process, wherein the mass fraction of PVP in the dispersing agent is 0.6% -1.2%, PVP mainly plays a role in graphene dispersion, when the amount of PVP added is less than 0.6%, the dispersion effect is not good, so that the graphene conductive agent has the defects of sedimentation, large resistance and the like, and when the amount of PVP added is more than 1.2%, the PVP is excessive, so that the conductivity of the conductive agent is reduced.

Drawings

FIG. 1: the results of the rate test of the invention in example 1 and comparative example 1 are shown.

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 the invention may be practiced, and 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 presented for purposes of illustration only and not limitation to describe the features and characteristics of the invention, to set forth the best mode of carrying out the invention, and to sufficiently enable one skilled in the art to practice the invention. It will, however, be understood that various modifications and changes may be made without departing from the scope of the invention as defined in the appended claims. The detailed description and drawings are to be regarded as illustrative rather than restrictive, and any such modifications and variations are intended to be included within the scope of the present invention as described herein. Furthermore, the background is intended to be illustrative of the state of the art as developed and the meaning of the present technology and is not intended to limit the scope of 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; as used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

To make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.

Example 1

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

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

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

4) Carrying out spray granulation on the homogenized GO-Li slurry at 180 ℃ to obtain GO-Li powder;

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

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

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

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

The 3D conductive network of the electrode was built up with LCO as the positive electrode base material, 1% RGO-Li conductive agent added, 1.5% pvdf as a binder added, homogenized, coated, and assembled into a battery. The magnification test was performed under the conditions of 0.1C, 0.2C, 0.5C, 1C, 3C, 5C, 7C, and the cycle test was performed under the condition of 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 rate at 157 weeks of 3C cycle was 88.79%.

Examples 2 to 4

The set of examples were conducted to investigate the effect of doping temperature of LiOH solution and graphene oxide slurry on the electrical conductivity of RGO-Li (i.e., li ion modified reduced graphene oxide powder). Different from example 1, the reaction temperatures in step 2) of examples 2-4 are 10 ℃, 80 ℃ and 100 ℃, respectively, which are the same as example 1 and are not described herein again. At a reaction temperature of 80 ℃ and 100 ℃, the GO slurry has a jelly-like phenomenon, which may be a hydrogel state formed by Li + and-COO-under GO hydrolysis conditions.

Similarly, LCO was used as the positive electrode main material, 1% RGO-Li conductive agent was added to build up a 3D conductive network of the electrode, 1.5% pvdf was added as a binder, and homogenization, coating, and battery assembly were performed. The rate test was performed under 0.1C, 0.2C, 0.5C, 1C, 3C, 5C, 7C conditions, and the cycle test was performed under 3C conditions.

From the above experimental results, both too low temperature and too high temperature are not favorable for reaction, the reaction is slow when the temperature is too low, the reduction of graphene oxide can be accelerated when the temperature is too high, the reduction is often accompanied with the occurrence of agglomeration, stacking, sedimentation and other phenomena, and the steric hindrance effect of lithium ions is not caused under the conditions of subsequent dispersion and high-rate charge and discharge of the conductive agent.

Examples 5 to 8

This group of examples was conducted to investigate the effect of the LiOH solution concentration on the performance of RGO-Li conductive agents, and unlike example 1, examples 5-8 were conducted in step 2) with LiOH solutions at concentrations of 0.1M, 0.4M, 1.2M, and 2M, respectively, which were the same as example 1 and are not repeated herein. When the concentration of the LiOH solution was 0.1M, the reaction rate was significantly reduced, and more time was required than in example 1 to complete the reaction. When the concentration of the LiOH solution is 1.2M, the GO is agglomerated and separated out to a certain extent, and when the concentration of the LiOH solution is 2M, a large amount of the GO is agglomerated and separated out.

The data result shows that the LiOH concentration is an important factor influencing the quality of the RGO-Li conductive agent, when the LiOH concentration is too low, the reaction rate is obviously slowed down, and when the LiOH concentration is too high, the LiOH solution rapidly reacts with the graphene oxide at the edge to generate the phenomena of aggregation, precipitation and sedimentation of the graphene oxide, so that the performance of the conductive agent is reduced.

Examples 9 to 11

This set of examples was conducted to investigate the effect of GO-Li particle size on RGO-Li conductive agent performance, and unlike example 1, in step 3), examples 9-11 were conducted to homogenize the obtained GO-Li slurry under pressure conditions of 1000bar, 900bar, 600bar for 5 times, respectively, and to perform particle size control treatment to obtain GO-Li slurry with particle size of 2.0 μm, 3.6 μm, 4.5 μm, and to build up 3D conductive network of electrode by adding 1% of RGO-Li conductive agent, and to add 1.5% pvdf as binder, to homogenize, coat, and assemble battery, using LCO as positive electrode main material, as well. The rate test was performed under 0.1C, 0.2C, 0.5C, 1C, 3C, 5C, 7C conditions, and the cycle test was performed under 3C conditions.

According to the data result, the steric hindrance effect of the graphene to the lithium ions can be reduced through particle size control, after the particle size of the graphene is reduced, a large number of gaps can be created when a conductive network is built, the gaps can be used as fast channels for lithium ion transportation, the lithium ions can enter active material particles through the edges and the gaps of the graphene when the lithium ions are de-embedded, and therefore the particle size control is beneficial to reducing the steric hindrance effect of the graphene to the lithium ions.

Examples 12 to 13

This group of examples was conducted to investigate the effect of ambient humidity on the performance of the RGO-Li conductive agent, and unlike example 1, examples 12-13 were conducted to rate test and cycle test the prepared batteries by the same method and conditions, respectively, by controlling ambient humidity at 60%rh, 80%.

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

Comparative example 1

The difference between the comparative example and the example 1 is that no LiOH aqueous solution is used in the step 2) to participate in the reaction, that is, the comparative example does not perform Li ion doping modification treatment on graphene oxide, and other steps are the same as those in the example 1 and are not described again. The prepared battery is subjected to rate test and cycle test by the same method and conditions.

From the above results, the performance of the graphene conductive agent prepared by taking the Li ion modified reduced graphene oxide as a raw material is greatly improved compared with that of a common graphene conductive agent, which can be attributed to that the lithium ion modified graphene enhances the affinity of the graphene for lithium ions to a certain extent, and the lithium ions are continued at the edge of the graphene and the surface cavity defect, so that the lithium ion can be guided to pass through a fast channel of a lithium-philic site, and the rate capability can be improved.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of Li ion modified reduced graphene oxide powder is characterized by comprising the following steps: slowly adding the washed graphene oxide slurry into a LiOH solution, heating to 40-70 ℃, elutriating in a ceramic rotary instrument for 1.5-3h to perform Li ion modification treatment on the graphene oxide slurry to obtain GO-Li slurry, homogenizing and spray granulating the GO-Li slurry to obtain GO-Li powder, and performing reduction and drying treatment to obtain Li ion modified reduced graphene oxide powder.

2. The method for preparing the Li ion-modified reduced graphene oxide powder according to claim 1, wherein the concentration of the LiOH solution is 0.2 to 1M.

3. The method for preparing the Li ion-modified reduced graphene oxide powder according to claim 1, wherein the PH of the washed graphene oxide slurry is greater than 3.

4. The preparation method of the Li ion modified reduced graphene oxide powder as claimed in claim 1, wherein the homogenization treatment is to homogenize the GO-Li slurry under the pressure condition of 800-1000 mPa-s for 3-10 times so that the diameter of GO-Li sheets is less than 3 μm.

5. 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 and a high reduction treatment, the low reduction treatment is to perform microwave puffing on the GO-Li powder at a constant temperature of 600-1000 ℃, and the high reduction treatment is to perform carbonization on the low-reduced GO-Li powder at a nitrogen atmosphere of 1000-1500 ℃.

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

7. The method for producing a Li ion-modified reduced graphene oxide powder according to claim 1, wherein the ambient humidity is controlled to < 20%.

8. A graphene conductive agent, which is characterized by comprising the Li ion-modified reduced graphene oxide powder according to any one of claims 1 to 7, wherein the solid content of the Li ion-modified reduced graphene oxide powder is 2.5 to 4%.

9. A preparation method of a graphene conductive agent is characterized in that NMP is used as a solvent, PVP is used as a dispersing agent, li ion modified reduced graphene oxide powder according to any one of claims 1 to 7 is used as a main material of the conductive agent, and the graphene conductive agent with the solid content of 2.5-4% is prepared by a preparation process of dispersing, sand grinding and homogenizing.

10. The method for preparing the graphene conductive agent according to claim 9, wherein the mass fraction of the dispersant PVP is 0.2 to 0.8.