Graphene for improving electrode compaction density, method for preparing the same, and application thereof, and electrode sheet and method for manufacturing the same

Abstract

The application discloses a preparation method of graphene for improving electrode compaction density, and is characterized in that the method comprises the following steps: (1) granulating graphene oxide to obtain graphene oxide particles, and drying the graphene oxide particles; (2) performing puffing treatment on the dried graphene oxide particles in an inert gas condition, wherein the highest puffing temperature is 235-385 DEG C, the temperature is kept in the range for 5-40 min, and the temperature rising rate is 2-8 DEG C / min; (3) heating the puffing product to 1000-1500 DEG C in an inert atmosphere, and keeping the temperature for 2-4 h to obtain graphene powder. The application further discloses corresponding graphene, application of the graphene in electrode sheets and a manufacturing method of the corresponding electrode sheets. The graphene disclosed by the application can improve electrode compaction density.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and more specifically, to a method for preparing graphene. Background Technology

[0002] Graphene is a novel material with a single-layer sheet-like structure composed of carbon atoms. 2 Hybridized orbitals form a hexagonal honeycomb lattice in a planar thin film, which is a two-dimensional material only one atom thick. Its unique structural characteristics endow it with excellent electrical, mechanical, thermal, and optical properties.

[0003] In existing technologies, dry electrode fabrication typically employs powder coating or binder fibrillation techniques. However, both of these techniques require the conductive agent powder to be uniformly mixed with the main material in a completely solvent-free state before use. This necessitates that the conductive agent be easily and uniformly dispersed between the main materials during the physical mixing process. Because stress cannot be transferred and released during the rolling process, this results in a hard surface and significant thickness on the positive electrode sheet.

[0004] The content of the background section is merely the technology known to the inventor and does not necessarily represent the prior art in this field. Summary of the Invention

[0005] In view of the above problems, the present invention designs and prepares a graphene conductive agent for improving the compaction density of the electrode, thereby improving the compaction density of the electrode and reducing the thickness of the electrode sheet;

[0006] This invention discloses a method for preparing graphene for improving electrode compaction density, comprising the following steps:

[0007] (1) Granulate graphene oxide to obtain graphene oxide particles, and dry the graphene oxide particles.

[0008] Before drying GO, it is granulated. The main purposes of this step are twofold: first, to ensure the uniformity of the dried particles; and second, because the aspect ratio of GO is greater than that of liquid crystal materials, it can be regarded as a liquid crystal polymer material. Under the action of a forced-air drying oven, the layered arrangement of GO will become more orderly. Reducing the more orderly arranged GO material will yield a denser graphene powder material.

[0009] (2) The dried graphene oxide particles are expanded under inert gas conditions. The maximum expansion temperature is 235-385℃, and the temperature is maintained for 5-40 minutes within this temperature range. The heating rate is 2-8℃ / min.

[0010] By utilizing a slow heating method with a heating rate of 2-8℃ / min, not only can the heating of GO blocks be more uniform, but the expansion rate can also be controlled, resulting in a more uniform number of layers in the expanded product. During the expansion process, when the maximum temperature inside the furnace is below 235℃, a large portion of the oxygen-containing groups cannot be detached; when the maximum temperature inside the furnace is above 385℃, the H2O molecules generated by thermal reduction are prone to react with the C on the graphene in a water-gas reaction, causing more defects in the graphene surface. Furthermore, the higher the heating temperature, the faster the functional groups of graphene oxide are eliminated, but when the temperature exceeds 385℃, the number of layers in the expanded product will be smaller. When the number of layers in the expanded product is smaller, more wrinkles will be generated on the surface, and its lubrication effect will be reduced.

[0011] (3) The expanded product in step (2) is heated to 1000-1500℃ under inert gas conditions and kept at that temperature for 2-4 hours to obtain graphene powder.

[0012] Furthermore, in step (1), the O content of graphene oxide accounts for ≥45% of the weight of graphene oxide, and the C content accounts for <55% of the weight of graphene oxide.

[0013] Preferably, the O content accounts for 45% to 60% of the weight of graphene oxide, and the carbon content accounts for 41% to 55% of the weight of graphene oxide.

[0014] In the preparation method of graphene, GO raw materials with an O content ≥ 45% are preferred. GO in this range has a higher content of oxygen-containing functional groups, which provides sufficient motive force in the thermal reduction process. Under the same processing conditions, the number of graphene layers prepared is smaller, thereby achieving a higher conductivity of graphene.

[0015] Furthermore, the volume of the granules obtained in step (1) is ≤8cm³. 3 and ≥125μm 3 ; and / or,

[0016] In step (1), the drying temperature is 30℃-65℃, and the drying time is 10h-24h; and / or,

[0017] The inert gas in step (2) is nitrogen.

[0018] Furthermore, in step (1), the drying temperature is 45℃-60℃, and the drying time is 12-16 hours; and / or,

[0019] In step (1), the drying process is preferably carried out in a forced-air drying oven; and / or,

[0020] In step (2), the preferred puffing temperature is 285–300°C, and the time is 10–30 min; and / or,

[0021] In step (2), the heating rate is preferably 4-6 °C / min; and / or,

[0022] In step (3), the preferred heating temperature is 1100–1300℃, and the preferred calcination time is 2.5–3.5 h; and / or,

[0023] The inert gas in step (3) is nitrogen.

[0024] Furthermore, the particle size of the graphene powder in step (3) is reduced to ≤10μm; the method for reducing the particle size is preferably accomplished by air jet milling.

[0025] The present invention also discloses a graphene for improving the compaction density of an electrode, characterized in that it is prepared by the method for preparing the graphene for improving the compaction density of an electrode.

[0026] The present invention also discloses the application of the graphene in electrode sheets.

[0027] This invention also discloses a method for preparing an electrode sheet, comprising the following steps:

[0028] The active material, the graphene and PTFE are mixed to obtain a uniform powder, which is then continuously rolled into an electrode sheet.

[0029] The active material is preferably ternary polycrystalline high-nickel NCM811; and / or,

[0030] The thickness of the electrode sheet is no higher than 68±5μm.

[0031] Furthermore, the mass ratio of the graphene, ternary polycrystalline high-nickel NCM811, and PTFE is 97:2.5:0.5; and / or,

[0032] The preferred mixing method is to use a high-speed airflow shearing machine for mixing.

[0033] The present invention also discloses an electrode sheet composed of an active material, the graphene and PTFE, wherein the thickness of the electrode sheet is not higher than 68±5μm;

[0034] The active material is preferably ternary polycrystalline high-nickel NCM811; and / or,

[0035] The active material, graphene, and PTFE are present in a mass ratio of 97:2.5:0.5.

[0036] In this patent, the graphene material is finally reduced to ≤10μm using an air jet mill. Since the particle size of the current positive electrode active material is basically ≤10μm, the graphene material, as a dry electrode conductive agent, needs to be matched with the corresponding active material. Therefore, this step is necessary. However, this step is not mandatory. For example, when the corresponding active material and its particle size change, the graphene of this invention can also be changed accordingly to match the active material. It can even have a different particle size from the active material, as long as it can achieve its function as a dry electrode conductive agent.

[0037] Compared to other conductive agents, at the same addition amount of 0.5%, using an active material (NCM811): conductive agent: PTFE (DuPont X601, 99% purity) ratio of 97:2.5:0.5, and following a mixing-rolling process to fabricate electrode sheets, the electrode sheet thickness using graphene prepared by this method can be rolled to 68±5 μm. In comparison, adding our SE1233 graphene results in an electrode sheet thickness of 112±10 μm, while adding sp (Cabot) results in a thickness of 171±5 μm, and adding oligowalled carbon nanotubes (LG) results in a thickness of 168±5 μm. Therefore, in terms of electrode thinning, the graphene material in this patent exhibits the best performance among currently known conductive agents.

[0038] This invention discloses a method for preparing graphene, which has electrical conductivity and high self-lubricating properties. It is suitable as a conductive agent in the dry electrode fabrication process of positive electrode and can improve the electrode compaction density.

[0039] Introducing super-lubricating two-dimensional graphene material into the electrode sheet reduces surface stress during the rolling process through interlayer sliding and low shear force. Compared with traditional conductive additives, graphene achieves high conductivity while enhancing the compaction density of the electrode sheet, which will greatly promote the realization of dry cathode manufacturing process.

[0040] High compaction density significantly improves the uniformity of electrode pore size and void distribution, reducing contact resistance and charge transfer impedance. One advantage of dry electrode fabrication compared to wet methods is the ease with which high compaction density can be achieved. This process primarily involves pressing more active electrode material onto the substrate under high pressure, increasing areal density to enhance compaction density. Generally, higher compaction density results in higher battery capacity; compaction density = areal density / electrode thickness. Reducing electrode thickness can improve compaction density. However, higher areal density lengthens the lithium-ion migration path, increasing internal resistance and causing congestion. This prevents complete lithium-ion insertion / extraction within a short time, leading to capacity loss and a gradual decrease in capacity retention. Conversely, reducing electrode thickness shortens the lithium-ion transport distance, thus improving capacity retention and cycle stability.

[0041] Graphene's extremely high modulus, toughness, and self-lubricating properties make it suitable as a conductive agent when added to positive electrode active materials. In dry electrode fabrication, it provides excellent friction buffering during the mixing and rolling processes, protecting the active material from damage. Furthermore, due to its self-lubricating properties, graphene enhances the ductility of the film during rolling, thereby increasing the compaction density and reducing the thickness of the electrode sheet.

[0042] There are many ways to prepare graphene, but conventional methods such as mechanical exfoliation, CVD, and epitaxial growth are difficult to achieve in order to meet the requirements of being used as a conductive agent and lubricant in battery systems and to produce it in large quantities.

[0043] The graphene powder material prepared by this invention meets the requirements of dry electrode fabrication from both economic and performance perspectives. The graphene powder material prepared by this invention possesses both thinness and flexibility, as well as a smooth surface, enabling the graphene to encapsulate the positive electrode active material while providing lubrication points for the stretching and thinning of the electrode sheet during rolling. Detailed Implementation

[0044] In the following description, only certain exemplary embodiments are depicted simply. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the description is to be considered exemplary in nature and not restrictive.

[0045] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0046] 1. Synthesis of raw material GO (graphene oxide):

[0047] 1. Selection of raw material GO:

[0048] GO filter cake synthesized by the Hummers method was selected as the raw material, wherein the O content of graphene oxide accounted for ≥45% of the weight of graphene oxide, and the C content accounted for <55% of the weight of graphene oxide; preferably, the O content was 45%–60%, and the carbon content was 41%–55%. When the O content was <45%, GO had fewer oxygen-containing functional groups, and the prepared graphene layers were thicker.

[0049] 2. Raw material GO drying treatment

[0050] The GO filter cake obtained above is granulated, and the volume of the granulated particles is ≤8cm³. 3 The blocky material is subjected to low-temperature drying in a forced-air drying oven at a temperature of 30℃-65℃, such as 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, and 65℃, with 45℃-60℃ being preferred; the drying time is 10h-24h, such as 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, and 24h, with 12h-16h being preferred. When the volume of the blocky material is >8cm³... 3 When the GO blocks are too large, uneven temperatures may occur inside and outside the blocks, resulting in cracks on the surface of the GO while the inside remains undried. When the drying temperature is below 30°C, it is difficult to dry the GO blocks. When the drying temperature is above 65°C, the surface of the GO blocks is easily reduced, affecting the subsequent thermal reduction of GO.

[0051] 3. Thermal reduction and densification treatment of GO

[0052] Dry GO blocks are placed in a nitrogen-filled furnace at room temperature and then slowly expanded. The furnace temperature is raised to a maximum of 235–385°C, for example, 235°C, 240°C, 245°C, 250°C, 255°C, 260°C, 265°C, 270°C, 275°C, 280°C, 285°C, 290°C, 295°C, 300°C, 305°C, 310°C, 315°C, 320°C, 325°C, 330°C, 335°C, 340°C, 345°C, 350°C, 355°C, 360°C, 365°C. The furnace temperature is set at 5℃, 370℃, 375℃, 380℃, or 385℃, with a preferred temperature range of 285-300℃. The temperature is maintained within this range for 5-40 minutes, for example, 10-30 minutes, 10-15 minutes, 20-25 minutes, 30-35 minutes, or 40 minutes. The heating rate is 2-8℃ / min, for example, 2-6℃ / min, 3-4℃ / min, 5-6℃ / min, or 7-6℃ / min. This yields expanded reduced graphene oxide (rGO) powder material. When the highest furnace temperature is below 235℃, a large portion of the oxygen-containing groups cannot detach. When the highest furnace temperature is above 385℃, the H2O molecules generated by thermal reduction readily react with the carbon atoms on the graphene in a water-gas reaction, resulting in more defects within the graphene surface. When the heating rate is below 2℃ / min, the oxygen-containing functional groups in GO detach too slowly, resulting in insufficient puffing power and a thicker number of rGO layers. When the heating rate is above 8℃ / min, the oxygen-containing functional groups in GO will detach rapidly and explode instantaneously, resulting in a smaller number of rGO layers.

[0053] 4. Heat repair and size control of rGO

[0054] The above-mentioned expanded product rGO was calcined under nitrogen atmosphere at a furnace temperature of 1000–1500℃, for example 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, or 1500℃, preferably 1100–1300℃; calcined for 2–4 hours, for example 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours, preferably 2.5–3.5 hours, to obtain conductive graphene powder material. The high-temperature repaired graphene powder material was then used to reduce the particle size to ≤10μm using methods such as air jet milling.

[0055] This patent utilizes an air jet mill to reduce graphene material to ≤10μm. The size of the graphene can be adjusted according to the particle size of the active material, allowing graphene to be prepared in sizes such as 2μm, 5μm, 8μm, and 10μm to suit the corresponding main material. This patent primarily uses NCM with a particle size of approximately 10μm as the active material for research. However, reducing the graphene particle size to ≤10μm is not mandatory. When the corresponding active material and its particle size change (e.g., greater than 10μm), the graphene of this invention can also be modified accordingly (with a particle size also greater than 10μm) to match the active material, or even have a different particle size, as long as it fulfills its function as a conductive agent in dry electrodes.

[0056] 5. Characterization and testing of graphene materials

[0057] The test method for the mass fraction of C and O elements is: DB32 / T 3595-2019 (Jiangsu Provincial Local Standard) Determination of Carbon, Hydrogen, Nitrogen, Sulfur and Oxygen Content in Graphene Materials - Elemental Analyzer Method

[0058] The test method for specific surface area (BET) is as follows: Refer to GB / T 7702.20-1997 (National Standard of the People's Republic of China) Test Methods for Pore Volume Determination of Coal-based Granular Activated Carbon.

[0059] For details on the conductivity testing method, please refer to the literature: “Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide”, Carbon, Sasha Stankovich, Dmitriy A. Dikin, et al., (2007), Vol. 45, pp. 1558-1565.

[0060] C content (%) O content (%) <![CDATA[BET(m 2 / g)]]> Electrical conductivity (S / m) ≥98 ≤0.1 260-350 <![CDATA[10 4 -10 6 ]]>

[0061] As shown in Table 1, C (wt%) ≥ 98% and O (wt%) ≤ 0.1%, indicating that the GO raw material was almost completely reduced to form graphene; BET was within the range of 260-350m. 2 / g, calculated according to the theoretical specific surface area of ​​graphene, when the specific surface area of ​​graphene is between 260-350m² 2 At a density of / g, this graphene falls within the 7-10 layer thickness range, with an electrical conductivity ranging from 10. 4 ~10 6 The S / m ratio indicates that oligolayer graphene has good electrical conductivity.

[0062] 6. Graphene powder material is used as a conductive agent in the dry fabrication of electrode sheets.

[0063] Conductive agent (graphene powder), ternary polycrystalline high-nickel NCM811 (Rongbai), and polytetrafluoroethylene (PTFE) (refrigerated storage) are mixed in a certain proportion. A high-speed airflow shearing machine can be used for mixing to obtain a uniform powder. The powder is then continuously rolled into electrode sheets, and the thickness of the electrode sheets is tested.

[0064] The present invention will be further illustrated by the following embodiments.

[0065] Example 1

[0066] This embodiment illustrates a method for preparing graphene, the preparation process of which includes the following steps:

[0067] GO filter cake synthesized by the Hummers method was selected as raw material, wherein the O content of GO was 45% and the C content of GO was 54.2%.

[0068] The GO filter cake obtained above was granulated to a volume of 8 cm³. 3 The blocky material was dried at a low temperature of 65℃ in a forced-air drying oven for 10 hours.

[0069] Dry GO blocks were placed in a nitrogen-filled furnace at room temperature and then slowly expanded. The furnace temperature was raised to 385°C and held for 5 minutes. The heating rate was 2°C / min, and the expanded product, reduced graphene oxide (rGO) powder material, was obtained.

[0070] The conductive graphene powder material was obtained by calcining rGO at 1000℃ for 4 hours under nitrogen atmosphere. The particle size of the high-temperature repaired graphene powder material was reduced to ≤10μm by means of air jet milling and other methods.

[0071] The test results are shown in the table below:

[0072] C content (%) O content (%) <![CDATA[BET(m 2 / g)]]> Electrical conductivity (S / m) 98.6 0.05 293 <![CDATA[10 5 ]]>

[0073] Ternary polycrystalline high-nickel NCM811 (Rongbai), conductive agent (graphene powder), and PTFE (refrigerated storage) were mixed in a mass ratio of 97:2.5:0.5 and then mixed using a high-speed airflow shearing machine to obtain a uniform powder. The powder was then continuously rolled into electrode sheets. The average thickness of the electrode sheets was measured to be 67.5 μm.

[0074] Example 2

[0075] This embodiment illustrates a method for preparing graphene, the preparation process of which includes the following steps:

[0076] GO filter cake synthesized by the Hummers method was selected as raw material, with an O content of 47.1% and a C content of 50.3%.

[0077] The GO filter cake obtained above was granulated to a volume of 6 cm³. 3 The blocky material was dried at a low temperature of 45°C in a forced-air drying oven for 18 hours.

[0078] Dry GO blocks were placed in a nitrogen-filled furnace at room temperature and then slowly expanded. The furnace temperature was raised to 350°C and held for 20 minutes at a rate of 5°C / min to obtain the expanded product, reduced graphene oxide (rGO) powder material.

[0079] The conductive graphene powder material was obtained by calcining rGO at 1300℃ for 3 hours under nitrogen atmosphere. The particle size of the high-temperature repaired graphene powder material was reduced to ≤10μm by means of air jet milling and other methods.

[0080] The test results are shown in the table below:

[0081] C content (%) O content (%) <![CDATA[BET(m 2 / g)]]> Electrical conductivity (S / m) 99.1 0.01 335 <![CDATA[10 5 ]]>

[0082] Ternary polycrystalline high-nickel NCM811 (Chengbai), conductive agent (graphene powder), and PTFE (refrigerated storage) were mixed in a mass ratio of 97:2.5:0.5 and then mixed using a high-speed airflow shearing machine to obtain a uniform powder. The powder was then continuously rolled into electrode sheets. The average thickness of the electrode sheets was measured to be 65.3 μm.

[0083] Example 3

[0084] This embodiment illustrates a method for preparing graphene, the preparation process of which includes the following steps:

[0085] GO filter cake synthesized by the Hummers method was selected as raw material, wherein the O content of GO was 50.3% and the C content of GO was 47.5%.

[0086] The GO filter cake obtained above was granulated to a volume of 6 cm³. 3 The blocky material was dried at a low temperature of 30°C in a forced-air drying oven for 24 hours.

[0087] Dry GO blocks were placed in a nitrogen-filled furnace at room temperature and then slowly expanded. The furnace temperature was raised to 235°C and held for 40 minutes at a rate of 8°C / min to obtain the expanded product, reduced graphene oxide (rGO) powder material.

[0088] The conductive graphene powder material was obtained by calcining rGO at 1500℃ for 2 hours under nitrogen atmosphere. The particle size of the high-temperature repaired graphene powder material was reduced to ≤10μm using methods such as air jet milling.

[0089] The test results are shown in the table below:

[0090] C content (%) O content (%) <![CDATA[BET(m 2 / g)]]> Electrical conductivity (S / m) 98.7 0.03 328 <![CDATA[10 5 ]]>

[0091] Ternary polycrystalline high-nickel NCM811 (Chengbai), conductive agent (graphene powder), and PTFE (refrigerated storage) were mixed in a mass ratio of 97:2.5:0.5 and then mixed using a high-speed airflow shearing machine to obtain a uniform powder. The powder was then continuously rolled into electrode sheets. The average thickness of the electrode sheets was measured to be 66.8 μm.

[0092] Comparative Example 1 (with a faster heating rate during puffing treatment)

[0093] This embodiment illustrates a method for preparing graphene, the preparation process of which includes the following steps:

[0094] GO filter cake synthesized by the Hummers method was selected as raw material, with an O content of 47.1% and a C content of 50.3%.

[0095] The GO filter cake obtained above was granulated to a volume of 6 cm³. 3 The blocky material was dried at a low temperature of 45°C in a forced-air drying oven for 18 hours.

[0096] Dry GO blocks were placed in a nitrogen-filled furnace at room temperature and then expanded. The furnace temperature was raised to 400°C at a rate of 15°C / min to obtain the expanded product, reduced graphene oxide (rGO) powder material.

[0097] The conductive graphene powder material was obtained by calcining rGO at 1300℃ for 3 hours under nitrogen atmosphere. The particle size of the high-temperature repaired graphene powder material was reduced to ≤10μm by means of air jet milling and other methods.

[0098] The test results are shown in the table below:

[0099] C content (%) O content (%) <![CDATA[BET(m 2 / g)]]> Electrical conductivity (S / m) 99.1 0.01 495 <![CDATA[10 4 ]]>

[0100] Ternary polycrystalline high-nickel NCM811 (Chengbai), conductive agent (graphene powder), and PTFE (refrigerated storage) were mixed in a mass ratio of 97:2.5:0.5 and then mixed using a high-speed airflow shearing machine to obtain a uniform powder. The powder was then continuously rolled into electrode sheets. The average thickness of the electrode sheets was measured to be 130.1 μm.

[0101] Comparative Example 2 (without granulation)

[0102] This embodiment illustrates a method for preparing graphene, the preparation process of which includes the following steps:

[0103] GO filter cake synthesized by the Hummers method was selected as raw material, with an O content of 47.1% and a C content of 50.3%.

[0104] The GO filter cake obtained above was subjected to low-temperature drying in a blower oven at 45°C for 18 hours.

[0105] Dry GO blocks were placed in a nitrogen-filled furnace at room temperature and then slowly expanded. The maximum temperature inside the furnace was raised to 350°C at a rate of 5°C / min, resulting in expanded product reduced graphene oxide (rGO) powder material.

[0106] The conductive graphene powder material was obtained by calcining rGO at 1300℃ for 3 hours under nitrogen atmosphere. The particle size of the high-temperature repaired graphene powder material was reduced to ≤10μm by means of air jet milling and other methods.

[0107] The test results are shown in the table below:

[0108] C content (%) O content (%) <![CDATA[BET(m 2 / g)]]> Electrical conductivity (S / m) 97.8 0.08 204 <![CDATA[10 3 ]]>

[0109] Ternary polycrystalline high-nickel NCM811 (Chengbai), conductive agent (graphene powder), and PTFE (refrigerated storage) were mixed in a mass ratio of 97:2.5:0.5 and then mixed using a high-speed airflow shearing machine to obtain a uniform powder. The powder was then continuously rolled into electrode sheets. The average thickness of the electrode sheets was measured to be 93.2 μm.

[0110] Comparative Example 3 (O content < 45%)

[0111] This embodiment illustrates a method for preparing graphene, the preparation process of which includes the following steps:

[0112] GO filter cake synthesized by the Hummers method was selected as raw material, with an O content of 42.7% and a C content of 55.1%.

[0113] The GO filter cake obtained above was granulated to a volume of 6 cm³. 3 The blocky material was dried at a low temperature of 45°C in a forced-air drying oven for 18 hours.

[0114] Dry GO blocks were placed in a nitrogen-filled furnace at room temperature and then slowly expanded. The maximum temperature inside the furnace was raised to 350°C at a rate of 5°C / min, resulting in expanded product reduced graphene oxide (rGO) powder material.

[0115] The conductive graphene powder material was obtained by calcining rGO at 1300℃ for 3 hours under nitrogen atmosphere. The particle size of the high-temperature repaired graphene powder material was reduced to ≤10μm by means of air jet milling and other methods.

[0116] The test results are shown in the table below:

[0117] C content (%) O content (%) <![CDATA[BET(m 2 / g)]]> Electrical conductivity (S / m) 98.3 0.13 240 <![CDATA[10 3 ]]>

[0118] Ternary polycrystalline high-nickel NCM811 (Chengbai), conductive agent (graphene powder), and PTFE (refrigerated storage) were mixed in a mass ratio of 97:2.5:0.5 and then mixed using a high-speed airflow shearing machine to obtain a uniform powder. The powder was then continuously rolled into electrode sheets. The average thickness of the electrode sheets was measured to be 88.6 μm.

[0119] As can be seen from the examples and comparative examples, the graphene material prepared by the present invention has higher BET and conductivity than the comparative example, and the electrode sheet prepared by the invention has lower thickness and higher conductivity.

[0120] Although exemplary embodiments of the invention have been shown in the foregoing disclosure, it should be noted that various changes and modifications can be made without departing from the scope defined by the claims. Furthermore, while elements of the invention may be described or claimed individually, it is also contemplated that multiple elements may be included, unless explicitly limited to a single element.

[0121] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing graphene for improving electrode compaction density, characterized in that, Includes the following steps: (1) Granulate graphene oxide to obtain graphene oxide particles, and dry the graphene oxide particles. (2) The dried graphene oxide particles are expanded under inert gas conditions. The maximum expansion temperature is 235-385℃, and the temperature is maintained for 5-40 minutes within this temperature range. The heating rate is 2-8℃ / min. (3) The expanded product in step (2) is heated to 1000-1500℃ under inert gas conditions and kept at that temperature for 2-4 hours to obtain graphene powder.

2. The method for preparing graphene for improving electrode compaction density according to claim 1, characterized in that, In step (1), the O content of graphene oxide accounts for ≥45% of the weight of graphene oxide, and the C content accounts for <55% of the weight of graphene oxide. Preferably, the O content accounts for 45% to 60% of the weight of graphene oxide, and the carbon content accounts for 41% to 55% of the weight of graphene oxide.

3. The method for preparing graphene for improving electrode compaction density according to claim 2, characterized in that, The volume of the granules obtained in step (1) is ≤8cm. 3 and ≥125μm 3 ; and / or, In step (1), the drying temperature is 30℃-65℃, and the drying time is 10h-24h; and / or, The inert gas in step (2) is nitrogen.

4. The method for preparing graphene for improving electrode compaction density according to claim 3, characterized in that, In step (1), the drying temperature is 45℃-60℃, and the drying time is 12-16 hours; and / or, In step (1), the drying process is preferably carried out in a forced-air drying oven; and / or, In step (2), the preferred puffing temperature is 285–300°C, and the time is 10–30 min; and / or, In step (2), the heating rate is preferably 4-6 °C / min; and / or, In step (3), the preferred heating temperature is 1100–1300℃, and the preferred calcination time is 2.5–3.5 h; and / or, The inert gas in step (3) is nitrogen.

5. The method for preparing graphene for improving electrode compaction density according to any one of claims 1-4, characterized in that, The particle size of the graphene powder in step (3) is reduced to ≤10μm; the particle size reduction method is preferably carried out by air jet milling.

6. A type of graphene for improving electrode compaction density, characterized in that, The graphene is prepared by the method for improving the compaction density of the electrode as described in any one of claims 1-5.

7. The application of graphene as described in claim 6 in an electrode sheet.

8. A method for preparing an electrode sheet, characterized in that, Includes the following steps: The active material, the graphene described in claim 6, and PTFE are mixed to obtain a uniform powder, which is then continuously rolled into an electrode sheet. The active material is preferably ternary polycrystalline high-nickel NCM811; and / or, The thickness of the electrode sheet is no higher than 68±5μm.

9. The method for preparing the electrode sheet according to claim 8, characterized in that, The graphene, ternary polycrystalline high-nickel NCM811, and PTFE have a mass ratio of 97:2.5:0.5; and / or, The mixing method involves using a high-speed airflow shearing machine for mixing.

10. An electrode sheet, characterized in that, Composed of active materials, graphene as described in claim 6, and PTFE, the electrode sheet thickness is not higher than 68±5μm; The active material is preferably ternary polycrystalline high-nickel NCM811; and / or, The active material, graphene as described in claim 6, and PTFE are present in a mass ratio of 97:2.5:0.5.