Porous graphene slurry as well as preparation method and application thereof

Abstract

The invention provides porous graphene slurry as well as a preparation method and application thereof. The preparation method comprises the following steps: stripping expanded graphite to obtain graphene microchip dispersed slurry; and mixing and dispersing the graphene microchip dispersed slurry and grinding particles to obtain the porous graphene slurry. According to the preparation method provided by the invention, the grinding particles are added into the graphene microchip slurry after primary dispersion, so that the graphene is further stripped and thinned, and meanwhile, the physical collision of the grinding particles and the graphene also generates nanopore channels on the surface of the graphene, and when the graphene is used as the conductive agent of the lithium ion battery, the diffusion of lithium ions is facilitated, and the conductivity of the lithium ion battery is improved. And the high-rate charge-discharge performance of the battery is effectively improved.

Description

Technical Field

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

[0002] Graphene is a new material with a single-layer flake structure composed of carbon atoms. It is a planar film with a honeycomb lattice formed by carbon atoms in sp2 hybrid orbitals, a two-dimensional material with a thickness of only one carbon atom, and has many excellent theoretical properties. It is widely used in energy storage materials, environmental engineering, and sensitive sensing, and is known as "black gold" or "the king of new materials". Moreover, it has broad potential application prospects and has now become the focus of attention and research hotspot worldwide.

[0003] Graphene has excellent electron transport ability and can be used to prepare composite slurries with carbon nanotubes and carbon black as conductive agents for battery materials. By utilizing the synergistic effect of different-dimensional nanocarbon materials, a three-dimensional conductive network is constructed in the electrode to improve the compaction density of the lithium electrode sheet, improve the internal resistance of the battery, and improve the rate performance and cycle life of the battery. However, the two-dimensional structure of graphene leads to poor lithium-ion transport, resulting in a decline in the high-rate charge-discharge performance of the battery. To solve this problem, graphene materials are usually made into small particle sizes and porous channels. Small particle size graphene usually requires a longer stripping and dispersion time, which comes at the cost of sacrificing production capacity; porous graphene provides a fast channel for the insertion and extraction process of lithium ions by creating pores on the surface of graphene in a reasonable way, thus facilitating the diffusion of lithium ions and improving the high-rate charge-discharge performance of the battery. CN106185880A proposes a process of treating with strong acids such as concentrated sulfuric acid and strong oxidants, followed by removing the oxide carrier by pickling after loading the oxide carrier. This process causes relatively large pollution and is not environmentally friendly. CN113942998A proposes a method for preparing porous graphene by a two-step method of carbon dioxide and water vapor. This method has a complex process, high cost, and poor controllability.

[0004] Therefore, how to obtain a porous graphene with simple operation, environmental friendliness, stability, high efficiency, and excellent conductive effect is a technical problem to be solved urgently. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a porous graphene slurry and its preparation method and application. In the preparation method provided by the present invention, grinding particles are added to the graphene microflake slurry after primary dispersion. While further exfoliating and thinning the graphene, the physical collision between the grinding particles and the graphene also generates nanopores on the surface of the graphene. When used as a conductive agent for lithium-ion batteries, it is beneficial to the diffusion of lithium ions and effectively improves the high-rate charge-discharge performance of the battery.

[0006] To achieve the object of this invention, the following technical solutions are adopted in this invention:

[0007] In a first aspect, this invention provides a method for preparing a porous graphene slurry, and the preparation method includes the following steps:

[0008] Exfoliate the expanded graphite to obtain a graphene microflake dispersion slurry;

[0009] Mix and disperse the graphene microflake dispersion slurry with grinding particles to obtain the porous graphene slurry.

[0010] In the preparation method provided by this invention, the grinding particles are added to the graphene microflake slurry after the initial dispersion. While further exfoliating and thinning the graphene, the physical collision between the grinding particles and the graphene also generates nanopores on the surface of the graphene. While preparing the thin-layer graphene, the purpose of creating pores in the graphene is also achieved. At the same time, the presence of the grinding particles does not affect the performance of the porous graphene. When the prepared porous graphene is used as a conductive agent for a lithium-ion battery, it is beneficial to the diffusion of lithium ions and effectively improves the high-rate charge and discharge performance of the battery.

[0011] In this invention, the grinding particles need to be added to the graphene microflake slurry, that is, the graphene sheet layer structure obtained after preliminary exfoliation, to achieve the purpose of creating pores in the graphene. If added in the preliminary exfoliation stage of the expanded graphite (i.e., before the graphene microflake slurry), since the original expanded graphite is relatively thick, pores cannot be effectively opened on its surface, and thus the porous graphene slurry cannot be obtained.

[0012] Preferably, the specific surface area of the expanded graphite is 15 - 100 m 2 / g, such as 15 m 2 / g, 20 m 2 / g, 30 m 2 / g, 40 m 2 / g, 50 m 2 / g, 60 m 2 / g, 70 m 2 / g, 80 m 2 / g, 90 m 2 / g or 100 m 2 / g, etc.

[0013] Preferably, the D50 of the expanded graphite is 2 - 50 μm, such as 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, etc.

[0014] Preferably, the thickness of the graphene microflakes in the graphene microflake dispersion slurry is 5-35 nm, such as 5 nm, 10 nm, 15 nm, 25 nm, 30 nm or 35 nm, etc.

[0015] In the present invention, if the thickness of the graphene microflakes is too thin, less than 5 nm, the graphene microflakes are prone to breakage during the process of dispersion exfoliation to form pores; while if the thickness is too thick, exceeding 35 nm, during the dispersion exfoliation process, it is difficult for the grinding particles to create through-holes on its surface.

[0016] Preferably, the exfoliation method includes:

[0017] Perform a first mixing of expanded graphite, a dispersant and a solvent to obtain a premixed solution; perform a first homogeneous dispersion on the premixed solution to obtain a graphene microflake dispersion slurry.

[0018] Preferably, the mass ratio of the expanded graphite to the dispersant is (1-50):1, such as 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1.

[0019] Preferably, the dispersant includes polyvinylpyrrolidone.

[0020] Preferably, the solvent includes N-methylpyrrolidone.

[0021] Preferably, the rotation speed of the first mixing is 1000-3000 rpm, such as 1000 rpm, 1300 rpm, 1500 rpm, 1800 rpm, 2000 rpm, 2300 rpm, 2500 rpm, 2800 rpm or 3000 rpm, etc.

[0022] Preferably, the time of the first mixing is 1-3 h, such as 1 h, 2 h or 3 h, etc.

[0023] Preferably, the pressure of the first homogeneous dispersion is 100-200 MPa, such as 100 MPa, 110 MPa, 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa or 200 MPa, etc.

[0024] In the present invention, if the pressure of the first homogeneous dispersion is too small, less than 100 MPa, the pressure is too small to be conducive to the exfoliation of graphene or the pore diameter of simultaneous pore formation is small, while if the pressure is too large, exceeding 200 MPa, it will cause the graphene microflakes to be too thin, and the pores in the subsequent secondary homogeneous dispersion process are too large, resulting in the breakage of graphene.

[0025] Preferably, the number of times of the first homogeneous dispersion is 1 to 10 times, such as 1 time, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times or 10 times, etc.

[0026] Preferably, the mixing and dispersion include a second homogeneous dispersion.

[0027] Preferably, the pressure of the second homogeneous dispersion is less than the pressure of the first homogeneous dispersion.

[0028] In the present invention, the pressure of the second homogeneous dispersion is less than the pressure of the first homogeneous dispersion, which can better realize the opening of holes on the surface of graphene by abrasive particles while peeling again; if the pressure of the second homogeneous dispersion is greater than or equal to the pressure of the first homogeneous dispersion, it will cause the abrasive particles to violently impact graphene, resulting in too large holes on the surface of graphene and causing fragmentation.

[0029] Preferably, the pressure of the second homogeneous dispersion is 60 to 120 MPa, such as 60 MPa, 70 MPa, 80 MPa, 90 MPa, 100 MPa, 110 MPa or 120 MPa, etc.

[0030] Preferably, the number of times of the second homogeneous dispersion is 1 to 5 times, such as 1 time, 2 times, 3 times, 4 times or 5 times, etc.

[0031] Preferably, the number of graphene layers in the graphene slurry after the mixing and dispersion is < 10 layers.

[0032] Preferably, the surface of the graphene after the mixing and dispersion has a nano-hole structure.

[0033] Preferably, the mass ratio of the graphene microflakes to the abrasive particles is (200 - 20):1, such as 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 110:1, 120:1, 130:1, 140:1, 150:1, 160:1, 170:1, 180:1, 190:1 or 200:1, etc.

[0034] In the present invention, if the mass ratio of the graphene microflakes to the abrasive particles is too small, that is, too many abrasive particles are added, it will instead make the holes on the surface of graphene larger, and its own electronic conductivity becomes worse, resulting in an increase in the AC impedance Rct. If the mass ratio is too large, that is, too few abrasive particles, it is difficult to play a role in pore formation, and the formed holes are too small.

[0035] Preferably, the D50 of the abrasive particles is < 500 nm, such as 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 490 nm, etc.

[0036] Preferably, the abrasive particles include inorganic particles.

[0037] Preferably, the inorganic particles include inorganic ceramic oxide solid electrolyte powders.

[0038] In the present invention, inorganic ceramic oxide solid electrolyte powders are selected as the abrasive particles. On the one hand, their shapes are irregular, the surfaces are sharp, and the hardness is extremely high, which is beneficial to pore formation. On the other hand, the presence of abrasive particles in the obtained porous graphene slurry not only does not affect the electrical properties of the slurry in the lithium battery, but also is beneficial to the diffusion of lithium ions at high rates, improving the rate performance of the battery.

[0039] Preferably, the inorganic ceramic oxide solid electrolyte powder includes any one or a combination of at least two of garnet structure electrolyte powder, sodium superionic conductor structure electrolyte powder, perovskite structure electrolyte powder, or lithium superionic conductor structure electrolyte powder.

[0040] In the present invention, the garnet structure electrolyte powder includes, but is not limited to, LLZO, the perovskite structure electrolyte powder includes, but is not limited to, LLTO, and the lithium superionic conductor structure electrolyte powder is LATP.

[0041] Preferably, the graphene slurry after mixing and dispersion is mixed and dispersed with a viscosity regulator for a second time to obtain a porous graphene slurry.

[0042] In the present invention, the addition of the viscosity regulator effectively regulates the viscosity of the slurry and increases the storage stability of the slurry, so that the finally obtained porous graphene slurry can be directly used as a conductive agent slurry and can thus be directly used in the preparation process of lithium ion batteries.

[0043] Preferably, the mass ratio of the viscosity regulator to the graphene after mixing and dispersion is 4:6 to 0.5:9.5, such as 0.5:9.5, 1:9, 2:8, 3:7, or 4:6, etc.

[0044] Preferably, the viscosity regulator includes carbon nanotubes.

[0045] Preferably, the specific surface area of the carbon nanotubes is 200 - 1200 m 2 / g, such as 200 m 2 / g, 300 m 2 / g, 400 m 2 / g, 500 m 2 / g, 600 m 2 / g, 700 m 2 / g, 800 m 2 / g, 900 m 2 / g, 1000 m 2 / g, 1100 m 2 / g or 1200 m 2 / g, etc., the diameter of the carbon nanotubes is 1.2 - 50 nm, such as 1.2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, etc.

[0046] Preferably, the particle size of the porous graphene slurry after the secondary mixing and dispersion < 10 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 9.5 μm, etc.

[0047] Preferably, the average pore size of the porous graphene after the secondary mixing and dispersion is 5 - 1500 nm, such as 5 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm or 1500 nm, etc., preferably 10 - 300 nm.

[0048] Preferably, the pore density of the porous graphene after the secondary mixing and dispersion is 1 - 55 pcs / μm, such as 1 pcs / μm, 5 pcs / μm, 10 pcs / μm, 20 pcs / μm, 30 pcs / μm, 40 pcs / μm, 50 pcs / μm or 55 pcs / μm, etc.

[0049] Preferably, the solid content of the porous graphene slurry after the secondary mixing and dispersion is 2 - 20%, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc.

[0050] Preferably, the viscosity of the porous graphene slurry after the secondary mixing and dispersion at a shear rate of 10 s -1 is such that the viscosity at 60 s is 20 - 3000 cps, such as 20 cps, 50 cps, 100 cps, 300 cps, 500 cps, 800 cps, 1000 cps, 1300 cps, 1500 cps, 1800 cps, 2000 cps, 2300 cps, 2500 cps, 2800 cps or 3000 cps, etc.

[0051] As a preferred technical solution, the preparation method includes the following steps:

[0052] Mix expanded graphite, a dispersant, and a solvent at a rotation speed of 1000 - 3000 rpm for the first mixing for 1 - 3 h. The mass ratio of expanded graphite to the dispersant is (1 - 50):1 to obtain a premixed solution; subject the premixed solution to the first homogenizing dispersion at a pressure of 100 - 200 MPa for 1 - 10 times to obtain a graphene microplate dispersion slurry with a graphene microplate thickness of 5 - 35 nm;

[0053] Subject the graphene microplate dispersion slurry and inorganic ceramic oxide solid electrolyte powder to the second homogenizing dispersion at a pressure of 60 - 120 MPa for 1 - 5 times to obtain a dispersion slurry with a nano-porous structure on the graphene surface;

[0054] Perform secondary mixing and dispersion on carbon nanotubes and the dispersion slurry with a nano-porous structure on the graphene surface at a mass ratio of 4:6 - 0.5:9.5 to obtain a porous graphene slurry with an average pore size of 5 - 1500 nm and a pore density of 1 - 55 pcs / μm;

[0055] Among them, the mass ratio of graphene microplates to grinding particles is (200 - 20):1; the pressure of the second homogenizing dispersion is less than that of the first homogenizing dispersion.

[0056] In a second aspect, the present invention provides a porous graphene slurry, which is prepared by the preparation method as described in the first aspect; the porous graphene surface contains nano-pores.

[0057] For the porous graphene slurry provided by the present invention, the surface of the porous graphene contains a nano-porous structure, and the obtained nano-pore size is appropriate, which does not have a great impact on the conductivity of graphene, is more conducive to the transmission of lithium ions under high-rate charge and discharge, and solves the problem of high-rate charge and discharge of conventional graphene.

[0058] In a third aspect, the present invention further provides an application of the porous graphene slurry as described in the second aspect in a lithium-ion battery.

[0059] The porous graphene slurry provided by the present invention can be directly used as a conductive agent slurry for the preparation of a lithium-ion battery, for example, in the preparation process of a positive electrode plate or a negative electrode plate; and for the prepared lithium-ion battery, except for the porous graphene conductive agent provided by the present invention (further including carbon nanotubes), the remaining raw materials, structures, and preparation processes are all conventional technical means, and those skilled in the art can make adaptive selections and adjustments according to actual needs.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] The preparation method provided by the present invention adds grinding particles to the graphene microflake slurry after primary dispersion. While further exfoliating and thinning the graphene, the physical collision between the grinding particles and the graphene also generates nanopores on the surface of the graphene. While preparing the thin-layer graphene, the purpose of creating pores in the graphene is also achieved. At the same time, the presence of the grinding particles does not affect the performance of the porous graphene. When the prepared porous graphene is used as a conductive agent for lithium-ion batteries, it is beneficial to the diffusion of lithium ions and effectively improves the high-rate charge and discharge performance of the battery; moreover, the preparation method is simple to operate, environmentally friendly, stable and efficient. Description of the Drawings

[0062] Figure 1 SEM image of the grinding particles provided for Example 1.

[0063] Figure 2 and Figure 3 SEM image of the porous graphene slurry provided for Example 1.

[0064] Figure 4 and Figure 5 SEM image of the porous graphene slurry provided for Example 2.

[0065] Figure 6 and Figure 7 SEM image of the porous graphene slurry provided for Example 3.

[0066] Figure 8 and Figure 9 SEM image of the porous graphene slurry provided for Comparative Example 1.

[0067] Figure 10 Comparison chart of the EIS curves of the lithium-ion batteries provided for Examples 1-3 and Comparative Example 1.

[0068] Figure 11 Comparison chart of the rate performance of the lithium-ion batteries provided for Examples 1-3 and Comparative Example 1. Detailed Embodiments

[0069] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0070] Example 1

[0071] This example provides a porous graphene slurry. The particle size D50 of the graphene slurry is 4.51 μm, the average pore size is 35 nm, and the rheological viscosity of the slurry is 120 cps.

[0072] The preparation method of the porous graphene slurry is as follows:

[0073] 1 part of polyvinylpyrrolidone and 5 parts of expanded graphite with a particle size D50 of 30 μm were put into 93.71 parts of NMP solvent and pre-dispersed by high-speed dispersion. The rotation speed of the high-speed disperser was 1000 rpm / min and the dispersion time was 1 h;

[0074] The pre-dispersed dispersion slurry was added to a high-pressure homogenizer and homogenized (first homogenization and dispersion) and peeled 3 times at 150 Mpa to obtain a graphene microflake dispersion slurry with a thickness of 20 nm after the first homogenization and peeling;

[0075] 0.025 part of LLZO grinding particles with a particle size of 300 nm (D50) was added to the graphene microflake dispersion slurry after the first homogenization and peeling (the mass ratio of the grinding particles to the graphene microflakes was 1:200), and the second homogenization and peeling (second homogenization and dispersion) was carried out at 80 Mpa in the homogenizer, and the peeling times were 2 times to obtain a graphene dispersion slurry with a number of layers < 10 layers (nano-pores are contained on the graphene surface);

[0076] 0.26 part of nanotubes with a BET of 250 m 2 / g and a tube diameter of 10 - 20 nm was added to the dispersion slurry after the second homogenization and peeling as a viscosity regulator (the mass ratio of graphene to carbon nanotubes was 9.5:0.5), and it was dispersed again by a high-speed disperser. The rotation speed of the equipment was 1000 rpm / min and the dispersion time was 0.5 h, thus obtaining the porous graphene slurry.

[0077] Example 2

[0078] This example provides a porous graphene slurry with a particle size D50 of the graphene slurry of 4.65 μm, an average pore size of 280 nm, and a rheological viscosity of the slurry of 190 cps.

[0079] The preparation method of the porous graphene slurry is as follows:

[0080] 1 part of polyvinylpyrrolidone and 5 parts of expanded graphite with a particle size D50 of 30 μm were put into 93.1 parts of NMP solvent and pre-dispersed by high-speed dispersion. The rotation speed of the high-speed disperser was 1000 rpm / min and the dispersion time was 1 h;

[0081] The pre-dispersed dispersion slurry was added to a high-pressure homogenizer and homogenized (first homogenization and dispersion) and peeled 3 times at 180 Mpa to obtain a graphene microflake dispersion slurry with a thickness of 10 nm after the first homogenization and peeling;

[0082] Add 0.1 part of LATP / LLZ0 / LLTO mixed grinding particles with a particle size of 300 nm to the graphene microflake dispersion slurry obtained by primary homogeneous peeling. The ratio of the three grinding particles is 1:2:1 (the mass ratio of the grinding particles to the graphene microflakes is 1:50). Perform secondary homogeneous peeling at 80 Mpa in a homogenizer for 3 times to obtain a graphene dispersion slurry with a number of layers <10 (the graphene surface contains nano-pores);

[0083] Add BET-300m 2 / g, 0.88 part of nanotubes with a tube diameter of 8 - 15 nm as a viscosity regulator (the mass ratio of graphene to carbon nanotubes is 8.5:1.5), and disperse again through a high-speed disperser. The equipment rotation speed is 1000 rpm / min, and the dispersion time is 0.5 h to obtain the porous graphene slurry.

[0084] Example 3

[0085] This example provides a porous graphene slurry. The particle size D50 of the graphene slurry is 4.58 μm, the average pore size is 85 nm, and the rheological viscosity of the slurry is 280 cps.

[0086] The preparation method of the porous graphene slurry is as follows:

[0087] Put 1 part of polyvinylpyrrolidone and 5 parts of expanded graphite with a particle size D50 of 30 μm into 92.67 parts of NMP solvent, and perform pre-dispersion through high-speed dispersion. The rotation speed of the high-speed disperser is 1000 rpm / min, and the dispersion time is 1 h;

[0088] Add the pre-dispersed dispersion slurry to a high-pressure homogenizer and perform primary homogeneous (first homogeneous dispersion) peeling at 180 Mpa for 2 times to obtain a graphene microflake dispersion slurry with a thickness of 15 nm after primary homogeneous peeling;

[0089] Add 0.08 part of LATP / LLZ0 / LLTO mixed grinding particles to the graphene microflake dispersion slurry obtained by primary homogeneous peeling. The ratio of the three grinding particles is 1:2:1 (the mass ratio of the grinding particles to the graphene microflakes is 1:62.5). Perform secondary homogeneous peeling at 80 Mpa in a homogenizer for 2 times to obtain a graphene dispersion slurry with a number of layers <10 (the graphene surface contains nano-pores);

[0090] Add BET-350m 23.33 parts of nanotubes with a diameter of 7 - 11 nm are used as a viscosity regulator per gram (the mass ratio of graphene to carbon nanotubes is 8:2), and they are redispersed by a high - speed disperser. The equipment rotation speed is 1000 rpm / min, and the dispersion time is 0.5 h, thus obtaining the porous graphene slurry.

[0091] Example 4

[0092] This example provides a porous graphene slurry. The D50 of the graphene slurry is 4.21 μm, the average pore size is 50 nm, and the rheological viscosity of the slurry is 180 cps.

[0093] The preparation method of the porous graphene slurry is as follows:

[0094] 1 part of polyvinylpyrrolidone and 5 parts of expanded graphite with a D50 of 20 μm are put into 93.39 parts of NMP solvent and pre - dispersed by high - speed dispersion. The rotation speed of the high - speed disperser is 1500 rpm / min, and the dispersion time is 1.5 h;

[0095] The pre - dispersed slurry is added to a high - pressure homogenizer and homogenized (first homogenization and dispersion) at 120 Mpa for 2 times to obtain a graphene micro - sheet dispersion slurry with a thickness of 35 nm after the first homogenization and peeling;

[0096] 0.05 part of LATP grinding particles with a D50 of 200 nm (the mass ratio of grinding particles to graphene micro - sheets is 1:100) is added to the graphene micro - sheet dispersion slurry after the first homogenization and peeling, and secondary homogenization and peeling is carried out at 100 Mpa in the homogenizer for 2 times to obtain a graphene dispersion slurry with less than 10 layers (nano - pores are contained on the graphene surface);

[0097] BET - 250m is added to the dispersion slurry after the secondary homogenization and peeling 2 0.56 part of nanotubes with a diameter of 10 - 20 nm are used as a viscosity regulator per gram (the mass ratio of graphene to carbon nanotubes is 9:1), and they are redispersed by a high - speed disperser. The equipment rotation speed is 1500 rpm / min, and the dispersion time is 1 h, thus obtaining the porous graphene slurry.

[0098] Example 5

[0099] This example provides a porous graphene slurry. The D50 of the graphene slurry is 3.58 μm, the average pore size is 60 nm, and the rheological viscosity of the slurry is 320 cps.

[0100] The preparation method of the porous graphene slurry is as follows:

[0101] Put 1 part of polyvinylpyrrolidone and 5 parts of expanded graphite with a particle size D50 of 20 μm into 92.7 parts of NMP solvent, and perform pre-dispersion by high-speed dispersion. The rotation speed of the high-speed disperser is 1500 rpm / min, and the dispersion time is 1.5 h;

[0102] Add the pre-dispersed dispersion slurry to a high-pressure homogenizer and perform primary homogenization (first homogenization and dispersion) at 180 Mpa for 5 times to obtain a graphene microflake dispersion slurry with a thickness of 5 nm after primary homogenization and peeling;

[0103] Add 0.05 part of LATP grinding particles with a diameter of 200 nm (D50) (the mass ratio of the grinding particles to the graphene microflakes is 1:100) to the graphene microflake dispersion slurry after primary homogenization and peeling, and perform secondary homogenization and peeling at 100 Mpa in the homogenizer for 2 times to obtain a graphene dispersion slurry with less than 10 layers (the graphene surface contains nano-pores);

[0104] Add BET-250m 2 / g, 1.25 parts of nanotubes with a tube diameter of 10 - 20 nm as a viscosity regulator (the mass ratio of graphene to carbon nanotubes is 6:4), and re-disperse with a high-speed disperser. The rotation speed of the equipment is 1500 rpm / min, and the dispersion time is 1 h to obtain the porous graphene slurry.

[0105] Example 6

[0106] The difference between this example and Example 1 is that the pressure for primary homogenization and peeling in this example is 90 MPa.

[0107] The remaining preparation methods and parameters are the same as those in Example 1.

[0108] Example 7

[0109] The difference between this example and Example 1 is that the pressure for primary homogenization and peeling in this example is 250 MPa.

[0110] The remaining preparation methods and parameters are the same as those in Example 1.

[0111] Example 8

[0112] The difference between this example and Example 1 is that the thickness of the graphene microflake dispersion slurry in this example is 45 nm, and in the preparation parameters, the pre-dispersed dispersion slurry is added to a high-pressure homogenizer and primary homogenization (first homogenization and dispersion) is performed at 100 Mpa for 2 times.

[0113] The remaining preparation methods and parameters are the same as those in Example 1.

[0114] Example 9

[0115] The difference between this example and Example 1 is that in this example, the thickness of the graphene nanoplatelet dispersion slurry is 3 nm. In the preparation parameters, the pre-dispersed dispersion slurry is added to a high-pressure homogenizer and homogenized (first homogenization and dispersion) 10 times at 200 Mpa.

[0116] The remaining preparation methods and parameters are the same as those in Example 1.

[0117] Example 10

[0118] The difference between this example and Example 1 is that in this example, the mass ratio of graphene nanoplatelets to grinding particles is 10:1.

[0119] The remaining preparation methods and parameters are the same as those in Example 1.

[0120] Example 11

[0121] The difference between this example and Example 1 is that in this example, the mass ratio of graphene nanoplatelets to grinding particles is 250:1.

[0122] The remaining preparation methods and parameters are the same as those in Example 1.

[0123] Example 12

[0124] The difference between this example and Example 1 is that in this example, the pressure of the secondary homogenization is 150 MPa.

[0125] The remaining preparation methods and parameters are the same as those in Example 1.

[0126] Example 13

[0127] The difference between this example and Example 1 is that in this example, the pressure of the secondary homogenization is 50 MPa.

[0128] The remaining preparation methods and parameters are the same as those in Example 1.

[0129] Example 14

[0130] The difference between this example and Example 1 is that the mixing process of the viscosity regulator is not carried out, that is, the porous graphene slurry after secondary homogenization and dispersion is the final graphene slurry.

[0131] The remaining preparation methods and parameters are the same as those in Example 1.

[0132] Comparative Example 1

[0133] The difference between this comparative example and Example 1 is that in the preparation process of this comparative example, grinding particles are not added.

[0134] The remaining preparation methods and parameters are the same as those in Example 1.

[0135] Comparative Example 2

[0136] The difference between this comparative example and Example 1 is that in this comparative example, the abrasive particles are added during the primary homogenization and peeling process, rather than during the secondary homogenization process.

[0137] The remaining preparation methods and parameters are the same as those in Example 1.

[0138] Figure 1 The SEM image of the abrasive particles provided in Example 1 is shown. From Figure 1 it can be seen that the abrasive particles are irregular in shape, with sharp surfaces, and the particle size is less than 500 nm.

[0139] Figure 2 and Figure 3 The SEM image of the porous graphene slurry provided in Example 1 is shown.

[0140] Figure 4 and Figure 5 The SEM image of the porous graphene slurry provided in Example 2 is shown.

[0141] Figure 6 and Figure 7 The SEM image of the porous graphene slurry provided in Example 3 is shown.

[0142] Figure 8 and Figure 9 The SEM image of the porous graphene slurry provided in Comparative Example 1 is shown.

[0143] From Figures 2 - 9 it can be seen that in Comparative Example 1, no abrasive particles are added, and there are no pores on the surface of the graphene in the prepared graphene slurry; while in the graphene slurries prepared in Examples 1 - 3, there are through - holes of different sizes on the surface of the graphene, indicating that the preparation method provided by the present invention not only obtains graphene but also realizes the purpose of creating pores in graphene.

[0144] Table 1 shows the average values of the particle size D50, pore size, and the rheological viscosity of the porous graphene slurries provided in Examples 1 - 14 and Comparative Examples 1 - 2.

[0145] Table 1

[0146]

[0147] The porous graphene slurry provided in Example 1-14 and Comparative Example 1-2 is used for the preparation of lithium ion batteries. The specific preparation process is as follows: the positive electrode lithium iron phosphate: conductive slurry (graphene slurry provided in Example 1-14 and Comparative Example 1-2): binder PVDF: NMP are fully mixed in a mass ratio of 100:10:3:75, and then coated on aluminum foil. The wet material thickness is 200μm, and after drying at 120℃+1h, a circular electrode sheet with a diameter of 1.2cm is obtained after rolling and punching at 15Mpa. In a glove box filled with argon, a lithium sheet is used as the counter electrode, and then in order, a negative electrode shell, a lithium sheet, a diaphragm, an electrolyte, an electrode sheet, a gasket and a reed sheet are added. Finally, the positive electrode shell is covered and the battery is clamped with plastic tweezers to a sheet press and pressed at 900N to obtain a complete CR2032 button battery.

[0148] The prepared lithium-ion batteries provided in Examples 1-14 and Comparative Examples 1-2 were subjected to performance tests. After the assembled batteries were left for 12 hours, electrochemical tests were performed on a Xinwei charge and discharge test cabinet. Among them, the charge and discharge voltage was set to 2.75-4.3V, and the battery was activated (formed) for the first charge and discharge at a rate of 0.2C, and the charge and discharge gap was left for 5 minutes; the formed battery was charged and discharged at different charge and discharge rates of 0.1C, 0.2C, 0.3C, 0.5C, 1C, 2C, 3C, 4C to 5C in turn, and the ratio of the capacity value at the 5C rate to the capacity value at the initial 0.1C rate was finally obtained, which is the rate performance (i.e., the 5C capacity retention rate). The electrochemical impedance spectroscopy (EIS) test used a Swiss Metrohm electrochemical workstation, the instrument model was PGSTAT204, and the test frequency was 0.1-105Hz. The test results are shown in Table 2.

[0149] Figure 10 The EIS curve comparison diagram of the lithium ion battery provided by Examples 1-3 and Comparative Example 1 is shown. Figure 10 It can be seen that in Examples 1-3, since the graphene surface has holes of suitable sizes, the reaction impedance of the lithium ion extraction and insertion reaction during the charge and discharge process is smaller, and its AC impedance Rct is also smaller.

[0150] Figure 11 A comparison of the rate performance of the lithium ion batteries provided in Examples 1-3 and Comparative Example 1 is shown. Figure 11 It can be seen that in Comparative Example 1, since there are no holes on the graphene surface, when discharging at a high rate of 5C, ion transmission needs to "bypass" the two-dimensional sheet of graphene, and the resistance to its escape and embedding is greater, and the discharge capacity retention rate at 5C is only 60.3%; in Examples 1-3, since the graphene surface has holes, lithium ions can pass through quickly at a high rate, so that the 5C capacity retention rate can reach 70%.

[0151] Table 2

[0152] AC impedance Rct (Ω) Retention rate of 5C capacity (%) Example 1 25.41 71.90 Example 2 38.59 68.97 Example 3 27.09 71.37 Example 4 26.42 70.08 Example 5 28.68 71.05 Example 6 41.16 60.25 Example 7 68.73 59.72 Example 8 44.62 57.72 Example 9 88.56 65.62 Example 10 57.62 64.53 Example 11 36.15 60.10 Example 12 52.73 59.72 Example 13 40.36 60.82 Example 14 29.81 70.23 Comparative Example 1 42.22 60.30 Comparative Example 2 41.15 59.98

[0153] Combined with Figures 1 - 11 and Table 1 - Table 2, it can be seen that:

[0154] From the data results of Example 1, Example 6 and Example 7, it can be seen that during the first homogeneous dispersion process, if the pressure is too small, the pores of the obtained porous graphene will be smaller, and if the pressure is too large, the graphene microflakes will be thinner, and the graphene will be broken during the subsequent pore - forming process of the secondary homogeneous dispersion.

[0155] From the data results of Example 1, Example 8 and Example 9, it can be seen that if the thickness of the graphene microflakes is too thick, it will be difficult to form pores, and it is very difficult to generate nano - pores on the surface of the graphene. If the thickness is too thin, it will be easily broken.

[0156] From the data results of Example 1, Example 10 and Example 11, it can be seen that if the mass ratio of the graphene microflakes to the grinding particles is too small, that is, too many grinding particles are added, it will instead make the pores on the surface of the graphene larger, the electronic conductivity of itself becomes worse, and the AC impedance Rct becomes larger. If the mass ratio is too large, that is, too few grinding particles are added, it is very difficult to play a role in pore - forming, and the formed pores are too small.

[0157] From the data results of Example 1, Example 12 and Example 13, it can be seen that if the pressure of the second homogeneous dispersion is too large, equal to or greater than the pressure of the first homogeneous dispersion, it will make the pores on the surface of the graphene larger, and the electronic conductivity of itself becomes worse. If the pressure is too small, it is very difficult to form pores on the surface of the graphene.

[0158] From the data results of Example 1 and Example 14, it can be seen that after the second homogeneous dispersion, the addition of the viscosity regulator further increases the viscosity of the slurry, thereby improving the storage stability of the slurry.

[0159] From the data results of Example 1 and Comparative Examples 1 - 2, it can be seen that in the present invention, the addition and addition sequence of the grinding particles are crucial. Without adding the grinding particles, graphene with pores cannot be obtained; and by adjusting the addition sequence of the grinding particles and adding them during the first homogeneous dispersion process, due to the relatively thick thickness of the original expanded graphite, it is also impossible to effectively open pores on its surface.

[0160] In summary, in the preparation method provided by the present invention, grinding particles are added to the graphene microflake slurry after primary dispersion. While further exfoliating and thinning the graphene, the physical collision between the grinding particles and the graphene also generates nanopores on the surface of the graphene. While preparing the thin-layer graphene, the purpose of creating pores in the graphene is also achieved. At the same time, the presence of the grinding particles does not affect the performance of the porous graphene. When the prepared porous graphene is used as a conductive agent for lithium-ion batteries, it is beneficial to the diffusion of lithium ions and effectively improves the high-rate charge and discharge performance of the battery; and the preparation method is simple to operate, environmentally friendly, stable and efficient.

[0161] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a porous graphene slurry, characterized in that, The preparation method includes the following steps: Exfoliate the expanded graphite to obtain a graphene microplate dispersion slurry; Mix and disperse the graphene microplate dispersion slurry with grinding particles to obtain the porous graphene slurry.

2. The preparation method of the porous graphene slurry according to claim 1, wherein, The specific surface area of the expanded graphite is 15 to 100 m 2 / g; Preferably, the D50 of the expanded graphite is 2 - 50 μm; Preferably, the thickness of the graphene microplates in the graphene microplate dispersion slurry is 5 - 35 nm.

3. The preparation method of the porous graphene slurry according to claim 1 or 2, characterized in that, The exfoliation method includes: Perform a first mixing of the expanded graphite, dispersant, and solvent to obtain a premixed solution; perform a first homogeneous dispersion on the premixed solution to obtain a graphene microplate dispersion slurry; Preferably, the mass ratio of the expanded graphite to the dispersant is (1 - 50):1; Preferably, the dispersant includes polyvinylpyrrolidone; Preferably, the solvent includes N-methylpyrrolidone; Preferably, the rotation speed of the first mixing is 1000 - 3000 rpm; Preferably, the time of the first mixing is 1 - 3 h; Preferably, the pressure of the first homogeneous dispersion is 100 - 200 MPa; Preferably, the number of times of the first homogeneous dispersion is 1 - 10 times.

4. The preparation method of the porous graphene slurry according to claim 3, characterized in that, The mixing and dispersion includes a second homogeneous dispersion; Preferably, the pressure of the second homogeneous dispersion is less than the pressure of the first homogeneous dispersion; Preferably, the pressure of the second homogeneous dispersion is 60 - 120 MPa; Preferably, the number of times of the second homogeneous dispersion is 1 - 5 times; Preferably, the number of graphene layers in the graphene slurry after mixing and dispersion < 10 layers; Preferably, the surface of the graphene after mixing and dispersion has a nano-porous structure.

5. The preparation method of the porous graphene slurry according to any one of claims 1-4, characterized in that, The mass ratio of the graphene microplates to the grinding particles is (200 - 20):1; Preferably, the D50 of the grinding particles < 500 nm; Preferably, the grinding particles include inorganic particles; Preferably, the inorganic particles include inorganic ceramic oxide solid electrolyte powders; Preferably, the inorganic ceramic oxide solid electrolyte powders include any one or at least two combinations of garnet structure electrolyte powders, sodium superionic conductor structure electrolyte powders, perovskite structure electrolyte powders, or lithium superionic conductor structure electrolyte powders.

6. The preparation method of the porous graphene slurry according to any one of claims 1-5, characterized in that, Perform a secondary mixing and dispersion of the graphene slurry after mixing and dispersion with a viscosity regulator to obtain a porous graphene slurry; Preferably, the mass ratio of the viscosity regulator to the graphene after mixing and dispersion is 4:6 - 0.5:9.5; Preferably, the viscosity regulator includes carbon nanotubes; Preferably, the specific surface area of the carbon nanotubes is 200 to 1200 m 2 / g, and the tube diameter of the carbon nanotubes is 1.2 to 50 nm.

7. The preparation method of the porous graphene slurry according to claim 6, characterized in that, The particle size of the porous graphene slurry after the secondary mixing and dispersion < 10 μm; Preferably, the average pore size in the porous graphene after the secondary mixing and dispersion is 5 - 1500 nm, preferably 10 - 300 nm; Preferably, the pore density in the porous graphene after the secondary mixing and dispersion is 1 - 55 pcs / μm; Preferably, the solid content of the porous graphene slurry after the secondary mixing and dispersion is 2 - 20%; Preferably, the viscosity of the porous graphene slurry after secondary mixing and dispersion is 20 to 3000 cps at a shear rate of 10 s -1 and 60 s 8. The preparation method of the porous graphene slurry according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: The expanded graphite, dispersant and solvent are subjected to first mixing at a rotation speed of 1000 - 3000 rpm for 1 - 3 h, and the mass ratio of the expanded graphite to the dispersant is (1 - 50):1 to obtain a premixed solution; the premixed solution is subjected to first homogeneous dispersion at a pressure of 100 - 200 MPa for 1 - 10 times to obtain a graphene microplate dispersion slurry with the thickness of the graphene microplates being 5 - 35 nm; The graphene microplate dispersion slurry and the inorganic ceramic oxide solid electrolyte powder are subjected to second homogeneous dispersion at a pressure of 60 - 120 MPa for 1 - 5 times to obtain a dispersion slurry with a nano - pore structure on the surface of the graphene; The carbon nanotubes and the dispersion slurry with a nano - pore structure on the surface of the graphene are subjected to secondary mixing and dispersion at a mass ratio of 4:6 - 0.5:9.5 to obtain a porous graphene slurry with the average pore size being 5 - 1500 nm and the pore density being 1 - 55 pcs / μm; Among them, the mass ratio of the graphene microplates to the grinding particles is (200 - 20):1; the pressure of the second homogeneous dispersion is less than the pressure of the first homogeneous dispersion.

9. A porous graphene slurry, characterized in that, The porous graphene slurry is prepared by the preparation method according to any one of claims 1 - 8; the surface of the porous graphene contains nano - pores.

10. An application of the porous graphene slurry according to claim 9 in a lithium - ion battery.

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