CN114142002A - Graphene coating modification method - Google Patents
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 189
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 32
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The process flow of the graphene coating modification method based on reasonable selection of the graphene sheet diameter can be briefly described as the following steps: firstly, the primary particles constituting the precoated material (i.e., the secondary particles) are subjected to a laser particle size meter test to obtain the median particle size D of the primary particles1. The particle diameter of the secondary particles required in the scheme is set to be D2Selecting the median diameter D3The graphene pair of (a) is coated, and the sheet diameter dimension D of the graphene pair3Satisfy the mathematical relationship D3=2D2(1 +/-10%) and the sheet diameter is D3The graphene has a sheet diameter of D3＇The graphene oxide is obtained by high-temperature reduction treatment. The invention is instructive to provide a method for selecting stonesThe performance of the pre-coating material can be improved to the maximum extent only by the graphene sheet diameter, modification failure caused by misselecting the graphene sheet diameter is avoided, the graphene can basically and completely coat lithium cobaltate particles, and a plurality of small gaps exist, so that a convenient channel is provided for lithium ion transmission.
Description
Technical Field
The invention relates to the field of carbon coating modification of lithium ion battery materials, in particular to a graphene coating modification method.
Background
Lithium ion batteries are important components in the process of storing and transferring electric energy, and the performance of the lithium ion batteries is particularly critical to the storage and transfer of the electric energy. With the rapid increase of energy demand, new requirements are put forward on the performances of high energy density, high capacity, high rate, high safety and the like of the lithium ion battery. The important performance of the lithium ion battery is mainly determined by the performance of two core parts, namely a positive electrode material and a negative electrode material of the lithium ion battery. In order to improve the performance indexes of the lithium ion battery, researchers strive to develop new positive and negative electrode material systems, such as high-capacity high-nickel ternary positive electrode materials, high-stability lithium iron phosphate positive electrode materials and high-capacity silicon-based negative electrode materials, and modify the traditional electrode materials such as lithium cobalt oxide and the like so as to improve various performance indexes of the lithium ion battery. However, these developed and modified positive and negative electrode materials of the battery have the defects of the same or similar defects while improving certain performances. Although the high-nickel ternary cathode material has higher capacity performance, the stability is poorer; the lithium iron phosphate positive electrode material has excellent performances in stability and safety, but has poor conductivity; although silicon-based negative electrode materials achieve very desirable capacity performance, the problem of huge volume expansion remains to be solved.
In order to improve the comprehensive performance of the developed and modified lithium ion battery anode and cathode materials, research workers perform a plurality of further modification works, such as carbon shell coating modification, doping modification, characteristic structure construction modification and the like. Wherein, the carbon shell coating modification is the simplest and most effective modification means. The carbon material generally has better conductivity and coating property, the carbon shell coating modification can reduce the impedance of the anode and cathode materials of the lithium ion battery and improve the conductivity of the material, for example, the carbon shell coating modification lithium iron phosphate material can improve the conductivity of the lithium iron phosphate material; the carbon shell coating modification can avoid direct contact reaction of the anode and cathode materials and the electrolyte, avoid repeated formation of an SEI film to reduce the first effect, and greatly enhance the stability of the material, for example, the carbon shell coating modification high-nickel ternary anode material can improve the stability and the first effect of the high-nickel ternary material; the carbon material coated on the surface of the material is usually clean carbon or amorphous carbon, which has pores and better mechanical property and is very effective in inhibiting the volume expansion of the material, for example, a silicon-based material modified by coating carbon not only improves the conductivity of the silicon material but also inhibits the volume expansion of the silicon to a certain extent.
Carbon materials are the most abundant, most readily available and inexpensive materials in nature, and although carbon coating modification has a significant effect on improving the overall performance of lithium ion batteries, not all carbon materials have the value of coating modification. Common carbon materials are generally obtained by carbonizing organic carbon sources, which typically have other non-carbon impurity atoms and nuclear functional groups present. In addition, in the carbonization process, the organic carbon source usually undergoes condensation polymerization, hydrolysis, cracking and other reactions to generate gas or small molecules and volatilize, so that the carbon coating layer has a complex three-dimensional pore structure while the carbon residue rate is reduced, and the factors influence the electrical and thermal properties of the carbon material to a certain extent. The method is an important link for promoting the coating modification of the carbon shell to improve the comprehensive performance of the anode and cathode materials of the lithium ion battery.
Since the discovery of graphene in 2004, graphene was found to be a nearly perfect carbon shell coating material. The graphene has a thickness of 10cm6V. ultra high theoretical mobility of electrons, 5300W/m.k ultra high thermal conductivity, 2630m2The ultra-large theoretical specific surface area of/g, and the graphene two-dimensional nano material has excellent mechanical strength and good flexibility. Therefore, the graphene has great application potential in the field of carbon coating modification of the anode and the cathode of the lithium ion battery. Although graphene has ideal electrical and thermal properties, when graphene is used for coating and modifying a carbon shell of a lithium ion battery, the graphene with the wrong sheet diameter is usually selected for coating and modifying, and the expected modification effect is not achieved, or even is suitable for the contrary. The reason is that lithium ions cannot directly enter positive and negative electrode materials of the lithium ion battery through a six-membered ring of graphene, when the graphene with an excessively large sheet diameter is selected for coating, the graphene is used for closely coating the pre-coating material, and meanwhile, the graphene is used for closely coating the pre-coating materialAnd a large amount of graphene wrinkles exist, so that the free path of lithium ion transmission is greatly increased, and the rapid transmission of lithium ions is hindered. Particularly, during charging and discharging under a high-rate condition, because lithium ions cannot be timely deintercalated, charges in the battery are accumulated, and the polarization in the battery is serious. Meanwhile, the existence of a large number of graphene folds caused by the graphene with an excessively large sheet diameter can reduce the first-effect performance of the battery material to a certain extent. When the small-diameter graphene is selected for coating, because the diameter of the graphene is too small, a large amount of exposed parts exist on the surface of the coating material, so that the electrolyte can directly contact the surface of the coating material and participate in reaction, and the stability of the material is not enhanced to a certain extent, and the capacity, the first effect and other performances of the battery material are improved. Therefore, the reasonable selection of the graphene sheet diameter is particularly important for comprehensively improving the performance of the material for the positive and negative electrode materials of the graphene coated and modified lithium ion battery, otherwise, the performance of the material can be obtained in a negative way.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention mainly aims to provide a graphene coating modification method based on reasonable selection of graphene sheet diameters.
The invention further aims to provide application of the graphene coating modification method based on reasonable selection of the sheet diameter of the graphene.
The purpose of the invention is realized by the following technical scheme:
the invention provides a graphene coating modification method based on reasonable selection of graphene sheet diameter, which mainly comprises the following steps: testing the particle size of the pre-coating material, selecting graphene with a corresponding size, and coating by a certain means. The graphene selected here is preferably Graphene Oxide (GO) or Reduced Graphene Oxide (RGO) obtained by a chemical method, and although graphene can be obtained by a mechanical method, a CVD method and a chemical method, the graphene prepared by the mechanical method has large sheet diameter and weak flexibility and is not beneficial to coating, and the graphene prepared by the traditional CVD method is difficult to strip and has high cost; graphene obtained by the bubble CVD method also has higher cost and the current process is not mature. The graphene prepared by the chemical method can realize the customization and functionalization of the graphene and has mature productThe graphene prepared by the chemical method is usually called graphene oxide, can be reduced and oxidized after reduction treatment, is single-layer graphene, has good mechanical strength and good flexibility, and is an ideal carbon shell coating material. Simultaneously, the raw materials (expanded graphite, natural graphite and vermicular graphite) with different mesh numbers are selected to prepare the graphene with different sheet diameters in a customized manner, and in addition, the small-sheet-diameter graphene can be obtained by carrying out ultrasonic crushing and homogenizing treatment on large sheets of graphene, and the current graphene sheet diameter D can be basically met3Customization at size of 500nm-100 μm. The specific customization process refers to the Chinese invention patent with publication number CN 112374493A.
The process flow of the graphene coating modification method based on reasonable selection of the graphene sheet diameter can be briefly described as the following steps: firstly, a laser particle size analyzer test is carried out on primary particles which form a pre-coating material (in the scheme, a lithium ion battery electrode material is adopted as the pre-coating material and is called as secondary particles hereinafter, but the protection scope of the patent is not limited, all materials capable of being coated by oxidized graphene and graphene can be optimally coated by the method), and the median particle size D of the primary particles is obtained1. The particle diameter of the secondary particles required in the scheme is set to be D2Selecting the median diameter D3The graphene pair of (a) is coated, and the sheet diameter dimension D of the graphene pair3Satisfy the mathematical relationship D3=2D2(1 +/-10%) and the median diameter is D3The diameter of the graphene is D from the middle position3＇Obtained by high-temperature reduction of graphene oxide D3＇=D3。
Assuming that the median diameter of the secondary particles is D2=10 μm, the surface area of the precoat particles is then roughly calculated. Here, the precoating material (secondary particles) is simply regarded as D regardless of the appearance of the precoating material (secondary particles)50Spherical body of =10 μm, S =4/3 π R according to surface area of the spherical body2It can be seen that D is selected just to coat the precoating material50Coating graphene with the size of approximately 2R, and preferably, selecting the required graphene sheet diameter D50=2R (1 ± 10%), i.e. graphene sheet diameter D50Is 18-22 μm.
Take graphene negative electrode material as an example. If a small particle size material is used as the pre-coating material, the graphene sheet size can be selected according to the expected coating particle size. For example, to use 100nm silicon particles as the precoating material, the precoating material consisting of several silicon particles is designed to have a particle diameter of 20 μm, and the sheet diameter D is selected50Spraying and granulating the graphene with the particle size of about 40 mu m to obtain the D with uniformly distributed particle size50Graphene-coated silicon particles of =20 μm, and the sheet-diameter-sized graphene-coated silicon secondary particles can obtain the best electrical properties. The pre-coating material can be perfectly coated by reasonably selecting the graphene with the particle size in the coating process, and the graphene has certain folds in the actual coating process, which also indicates that the coating material can be almost completely coated by the graphene and has certain exposed gaps or cracks. The almost completely coated lithium ion anode and cathode material can improve the stability and the conductivity of the material by virtue of the excellent electrical and thermal properties of graphene, and simultaneously enhances the expansion resistance of the material. Meanwhile, although lithium ions cannot directly penetrate through the six-membered ring of the graphene, and the hole defects on the surface of the graphene are relatively limited, a rapid ion transmission channel in the lithium ion deintercalation process is provided due to the existence of individual exposed gaps and cracks in the coating process, so that the free transmission path of the lithium ions is greatly shortened. In addition, although the exposed gaps and seams allow a small part of electrolyte to directly contact with materials to grow SEI films, the damage of irreversible lithium is very small, and the influence on the first effect is limited. The preparation method comprises the steps of mixing the selected graphene with a proper particle size with a pre-coating material, and obtaining the graphene-coated modified material by means of spray drying, ultrasonic, magnetic stirring and the like. When graphene oxide is selected as the coated carbon material, the coated material can be carbonized in an inert atmosphere for reduction.
The graphene coating modification method based on reasonable selection of the sheet diameter of the graphene has great application potential in the aspect of improving the comprehensive performance of the anode and cathode materials of the lithium ion battery. In the aspect of modification of the positive electrode material: the graphene is used for coating and modifying the carbon shell of the lithium iron phosphate positive electrode material, so that the conductivity of the lithium iron phosphate positive electrode material can be improved, and the impedance of the lithium iron phosphate battery can be reduced; the high-nickel ternary cathode material is subjected to carbon coating modification by using graphene, so that the stability of the high-nickel ternary cathode material can be improved. In terms of modification of the anode material: the graphene is used for carrying out carbon coating modification on the silicon-based negative electrode, so that the conductivity of the silicon-based negative electrode material can be improved, and the volume expansion performance of the silicon-based negative electrode material is enhanced. In the aspect of modifying other materials, when the graphene is used for carrying out surface coating modification on other materials, the electric conductivity, the heat conductivity and the mechanical property of the material can be improved.
Compared with the prior art, the invention has the following beneficial effects:
1. the graphene coating modification method based on reasonable graphene sheet diameter selection provided by the invention provides guidance on how to select the graphene sheet diameter to improve the performance of the pre-coating material to the maximum extent, and avoids modification failure caused by wrong graphene sheet diameter selection.
2. The invention provides a graphene coating modification method based on reasonable graphene sheet diameter selection, innovatively provides a relation between graphene sheet diameter selection and particle diameter of pre-coating material particles, and the mathematical relation is DGraphene=2DMaterial。
3. The graphene coating modification method based on reasonable selection of the graphene sheet diameter is suitable for modification of any lithium ion battery anode and cathode material, and can comprehensively improve the stability, the electrical conductivity, the thermal conductivity and the volume expansion performance of the material.
4. The graphene coating modification method based on reasonable selection of the graphene sheet diameter also provides important reference for the research of coating modification of the graphene on the carbon shells of other materials.
Drawings
FIG. 1 shows that in example 1 of the present invention, under the condition of selecting 80nm silicon particles as the coating material, the target median diameter D is obtained3Graphene coating modification of =15 μmSEM images of sexual silicon secondary particles;
fig. 2 is a particle size distribution diagram of graphene coated modified silicon secondary particles obtained in example 1 of the present invention;
fig. 3 (a) is an SEM image of lithium cobaltate before being coated and modified with graphene in example 2 of the present invention, and (b) is an SEM image of lithium cobaltate after being coated and modified with graphene.
Detailed Description
The following examples are presented to further illustrate the present invention and should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.
The following are specific examples:
example 1
The invention utilizes a graphene coating modification method based on reasonable graphene sheet diameter selection to obtain graphene coating modified silicon secondary particles with target particle diameter D50=15 μm under the condition of selecting 80nm silicon particles as coating materials, and the method comprises the following specific steps:
(1) the purchased silicon powder is subjected to particle size test by using a laser particle sizer, and the test result shows that D1=80nm, the present embodiment expects to obtain D2Graphene coated modified silicon secondary particles of =15 μm.
(2) According to the mathematical relationship between the graphene sheet diameter and the pre-coating material particles: d3=2D2(1. + -. 10%) and the diameter D of the plate is selected3＇Graphene oxide of =20 μm as a coating material.
(3) Taking 40g of median particle diameter D1Putting the =80nm silicon powder into 8L of deionized water, and stirring for 5 hours by using an electric stirrer at the rotating speed of 400r/min to fully disperse the silicon powder in the deionized water.
(4) Adding 5ml of graphene oxide (D) with the mass fraction of 2%50=1 μm) was added to the precursor solution of step (3), and the mixture was sufficiently stirred for 1 hour at a rotation speed of 400r/min using an electric stirrer, so that the graphene oxide was sufficiently dispersed. Eyes of whichThe method is characterized in that hydroxyl functional groups on the surface of small-diameter graphene oxide and hydroxyl functional groups on the surface of silicon particles are utilized to react so as to realize the electrical bridging effect between the silicon particles.
(5) Taking 50ml of graphene oxide (D) with the mass fraction of 2%3＇=30 μm) was added to the precursor solution of step (3), and the mixture was sufficiently stirred for 4 hours at a rotation speed of 400r/min using an electric stirrer, so that the graphene oxide was sufficiently dispersed. The method mainly aims to use graphene to carry out carbon shell coating modification to obtain the silicon secondary particle anode material with the target particle size.
(6) And (3) using a spray granulation instrument, setting the air inlet temperature of the spray granulation instrument to be 220, setting the peristaltic speed to be 15% and the spraying efficiency to be 100%, and after the air inlet temperature is stable, carrying out spray granulation on the prepared slurry.
(7) And (3) carbonizing the spray-granulated silicon secondary particles obtained in the step (6) for 3h at 900 ℃ in an inert atmosphere, wherein the temperature rise rate of the carbonization temperature is 5 ℃/min, simultaneously performing heat preservation treatment at 200 ℃ and 600 ℃ for 2h, and finally heating to 900 ℃ for carbonization treatment to obtain the graphene-coated silicon secondary particles.
(8) Testing the material obtained in the step (7) by using a laser particle sizer, wherein the test result shows that the median particle size D of the graphene-coated silicon secondary particles50=11 μm, in accordance with the calculation results.
(9) And (3) taking 0.9g of the silicon-carbon negative electrode material obtained in the step (7), 2g of CNT conductive agent with the mass fraction of 4.6%, 1.4g of PVDF binder with the mass fraction of 8%, and adding a proper amount of NMP for battery batching. And coating, drying and slicing to obtain the silicon-carbon negative electrode.
(10) And assembling the button cell according to a conventional method, and performing an on-machine test, wherein the test result shows that the first effect is 91.5%, the cell is cycled for 20 weeks and 40 weeks under the condition of 0.1 ℃, two cells are respectively taken out for disassembly, the thickness of a pole piece of the tester is changed, the result shows that the cycle is 20 weeks, the thickness of the pole piece is not obviously changed, the cycle is 40 weeks, and the thickness of the pole piece is increased by 8.7%.
From example 1, it can be found that graphene oxide having a median sheet diameter of 20 μm is used for the median particlesSilicon powder with the diameter of 80nm is coated, and graphene-coated silicon secondary particles are obtained after high-temperature carbonization treatment, and the structure is shown in figure 1. The particle size distribution is shown in fig. 2, that is, the mathematical relationship between the graphene sheet diameter and the pre-coating material particles satisfies: d3=2D2（1±10%）。
Example 2
To verify the mathematical relationship of the graphene platelet size of example 1 to the pre-coated material particles: d3=2D2(1. + -. 10%), in this example the median particle diameter D is selected by sieving and testing1Lithium cobaltate with the particle size of 15 mu m is used as a base material (namely primary particles) for graphene coating modification, and D is selected3＇And (3) coating and modifying graphene oxide with the particle size of 30 μm. The experiment aims to improve the stability and the gram volume of the lithium cobaltate through simple graphene-coated surface modification. The graphene coating modification process is simple, and comprises the following specific steps:
(1) adding 50ml of graphene oxide (with the median particle diameter D) with the mass fraction of 2% into 8L of deionized water3＇=30 μm), and fully stirring for 1 hour at a rotation speed of 400r/min by using an electric stirrer to obtain a uniformly dispersed graphene oxide solution.
(2) 40g of a medium particle size D obtained by sieving1Putting lithium cobaltate of =15 μm into the graphene oxide solution obtained in the step (1) of example 2, and stirring the solution for 5 hours at a rotation speed of 400r/min by using an electric stirrer to sufficiently disperse lithium cobaltate powder particles in the graphene oxide solution; because lithium cobaltate powder serving as the positive electrode is different from silicon powder, the phenomenon of aggregation of a plurality of particles cannot occur in the coating process, and therefore, the pre-coating material (i.e. secondary particles) in the embodiment consists of single primary particles and meets the requirement D2=D1。
(3) And (3) using a spray granulation instrument, setting the air inlet temperature of the spray granulation instrument to be 220, setting the peristaltic speed to be 15% and the spraying efficiency to be 100%, and after the air inlet temperature is stable, carrying out spray granulation on the prepared slurry.
(4) Carbonizing the spray-granulated graphene-coated lithium cobaltate obtained in the step (2) for 3h at 900 ℃ in an inert atmosphere, wherein the temperature rise rate of the carbonization temperature is 5 ℃/min, meanwhile, carrying out heat preservation treatment at 200 ℃ and 600 ℃ for 2h, and finally heating to 900 ℃ for carbonization treatment to obtain graphene-coated lithium cobaltate secondary particles.
(5) And (4) characterizing by using an electron microscope, and observing whether the graphene is moderate in the conductive coating state of lithium cobaltate.
SEM test results show that the graphene has an ideal coating effect on lithium cobaltate, the graphene can completely coat lithium cobaltate particles, and small gaps exist, so that a convenient channel is provided for lithium ion transmission. In accordance with the expected results.
The electrical property test result shows that the capacity of the graphene-coated and modified lithium cobaltate under the test condition of 0.1C is improved by 5 percent compared with the capacity of the lithium cobaltate cathode material without the graphene-coated and modified lithium cobaltate.
Comparative example 1
The comparative example differs from example 1 in that the example selects the sheet diameter D3＇Graphene oxide of =40 μm instead of D in example 13＇The operation of the other steps was the same as in example 1 except for graphene oxide of =30 μm. The purpose of this is to verify whether the expected 0.5D can be obtainedGrapheneThe modified secondary particles are coated with graphene of a particle size. The obtained sample is subjected to laser granularity characterization test, and the result shows that D is obtained50Graphene coated modified secondary particles of =20 μm, validating the conclusion of example 1.
Comparative example 2
This example differs from comparative example 2 in that D is selected3＇80 μm graphene oxide substituted for D3＇The coating modification experiment was performed on graphene oxide of =30 μm, and the other steps were performed in the same manner as in example 2. The method aims to explore the influence on the material performance when graphene with a larger sheet diameter is selected for image coating modification.
The SEM results showed that the lithium cobaltate particles were completely coated and a large number of wrinkles were present on the surface. The electrical test results show that the capacity of the lithium cobaltate material coated in the embodiment is 2% lower than that of the material without the coating modification treatment.
The reason is that the lithium cobaltate particles are closely coated by the graphene with the excessively large sheet diameter, the free path of lithium ion transmission is increased by a large number of folds, meanwhile, because the lithium ions cannot penetrate through the six-membered ring of the graphene film, the individually 'perfectly coated' particles become 'dead lithium sources' because the lithium ions cannot realize the insertion and removal activities, and the particles are reversely modified under the influence of various factors.
Comparative example 3
This comparative example differs from example 2 in that D is selected3＇Small-diameter graphene oxide substitute D of =2 μm3＇The coating modification experiment was performed on graphene oxide of =30 μm, and the other steps were performed in the same manner as in example 2. The method aims to explore the influence of small-particle-size graphene coating modification on the electrical properties of lithium cobaltate.
The embodiments of the present invention are not limited to the above-described embodiments, and any other changes, modifications, substitutions, combinations and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention.
Claims (10)
1. A graphene coating modification method is characterized by comprising the following steps:
1) setting the median particle diameter of the secondary particles for coating modification by graphene to D2The secondary particles comprise one or more median particle diameters D1Primary particles of (a);
2) selecting the sheet diameter D of the graphene of the coating material3The sheet diameter of the graphene satisfies the mathematical relation D3=2D2(1 +/-10%); the graphene oxide sheet diameter for preparing the graphene satisfies the mathematical relationship D3＇=D3；
3) The median particle diameter is D1The primary particles are put into a solvent to be uniformly dispersed;
4) taking enough tablets with the diameter D3＇The graphene oxide is put into the dispersion liquid of the primary particles and fully stirred to obtain slurry;
5) and (3) performing spray granulation on the slurry prepared in the step (3) by using a spray granulation instrument to obtain the secondary particles coated with the graphene oxide on the outer layer.
2. The graphene coating modification method according to claim 1, wherein: the primary particles are silicon powder, and the median particle diameter D1Less than 1 μm.
3. The graphene coating modification method according to claim 2, wherein: in the step 3, the solvent of the primary particles is deionized water, and the primary particles are fully dispersed in the deionized water by adopting an electronic stirrer.
4. The graphene coating modification method according to claim 3, wherein: in the step 5, the air inlet temperature of the spray granulation instrument is set to be 220, the peristaltic speed is 15%, the spraying efficiency is 100%, and after the air inlet temperature is stable, the prepared slurry is subjected to spray granulation.
5. The graphene coating modification method according to any one of claims 2 to 4, wherein: in the step 3, graphene oxide with the mass fraction of 2% and the median particle size of 1 μm is added into the system.
6. The graphene coating modification method according to claim 5, wherein: the carbonization treatment temperature in the step 6 is 600-.
7. The graphene coating modification method according to claim 1, wherein: the primary particles are lithium cobaltate with the median particle size of 15 mu m; graphene oxide meso-platelet diameter D for coating the secondary particles3＇And 30 μm.
8. The graphene coating modification method according to claim 7, wherein: the secondary particle is composed of one of the primary particles.
9. The graphene coating modification method according to claim 1, wherein: after the step 5, carbonizing the secondary particles obtained by spray granulation to obtain the secondary particles coated with the graphene on the outer layer.
10. The graphene coating modification method according to claim 1, wherein: before the step 1, the particle size of the primary particles is measured by a laser particle sizer to obtain the median particle size D of the primary particles1。
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