A silicon-carbon negative electrode sheet, a preparation method thereof, and an application thereof

Abstract

The present invention discloses a silicon-carbon negative electrode sheet and its preparation method and application. The silicon-carbon negative electrode sheet includes a graphene-containing conductive agent, a polymer binder, and a silicon-carbon material; in the Raman spectrum of the graphene, there are D peak and G peak, and I D / I G is below 0.10, and the conductivity of the graphene is 500-5000 S / cm. The lithium-ion battery fabricated by using the silicon-carbon negative electrode sheet of the present invention can construct a developed and effective lamellar structure conductive network with a small amount of addition, effectively inhibit volume expansion, improve the capacity retention rate of the battery, and significantly improve the cycle stability of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and particularly relates to a silicon - carbon negative electrode sheet, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, due to the increasingly serious problems of environmental pollution and resource shortage, clean and efficient new energy technologies have attracted much attention. As an important force in promoting the replacement of traditional fossil energy with clean and efficient energy and a fundamental and key product in promoting the overall development of the clean energy industry, lithium - ion batteries will experience rapid growth in the global energy reform process. Nowadays, lithium - ion batteries are widely used in various fields such as electronic products, electric vehicles, and energy storage power grids because of their high energy density, power density, working voltage, and no memory effect.

[0003] The nano - silicon - carbon composite material is one of the materials with great application potential in the negative electrode materials of lithium - ion batteries, having advantages such as high lithium storage capacity (far higher than that of graphite), good electrical conductivity, small strain, and stable SEI film. However, in the process of preparing the negative electrode sheet, relying solely on the electrical conductivity of the active material itself is far from enough. In order to establish a more efficient conductive network and structure between the positive and negative electrode materials of the battery, it is usually necessary to add a certain amount of carbon - based conductive agent when making the electrode, forming more electron and ion channels between the active materials and between the active materials and the current collector, reducing the contact resistance of the electrode, and accelerating the electron movement rate, thereby improving the charge - discharge efficiency of the electrode. Therefore, as an important component in the negative electrode of lithium - ion batteries, the conductive agent has a great influence on the battery performance.

[0004] Existing conductive agents are mainly carbon materials (such as conductive graphite, conductive carbon black, multi - walled carbon nanotubes, etc.). Although these conductive agents have their own advantages, they still cannot enable the negative electrode material to exhibit its optimal performance in the battery cycle performance. Therefore, it is urgent to develop a new silicon - carbon negative electrode conductive system. Summary of the Invention

[0005] In order to solve the deficiencies of the existing technology, the present invention provides a silicon - carbon negative electrode sheet, a preparation method thereof, and an application thereof. The lithium - ion battery made of the silicon - carbon negative electrode sheet of the present invention can construct a developed and effective sheet - structure conductive network with a small amount of addition, effectively inhibit volume expansion, improve the capacity retention rate of the battery, and significantly improve the cycle stability of the battery.

[0006] In the first aspect of the present invention, a silicon - carbon negative electrode sheet is provided, wherein the silicon - carbon negative electrode sheet includes a conductive agent containing graphene, a polymer binder, and a silicon - carbon material; the Raman spectrum of the graphene has a D peak and a G peak, I D / I GBelow 0.10, the conductivity of the graphene is 500 - 5000 S / cm.

[0007] Further, the mass ratio of the graphene-containing conductive agent, the polymer binder, and the silicon-carbon material is (1 - 10)∶(1 - 10)∶(80 - 95).

[0008] Further, the polymer binder includes one or more of polyacrylic acid (PAA), polymethacrylic acid, sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose, sodium alginate, lithium alginate, styrene-butadiene rubber (SBR). Preferably, the polymer binder includes one or two of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose. More preferably, in the polymer binder, the mass of sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose accounts for 25% - 60%, the mass of polyacrylic acid and / or polymethacrylic acid accounts for 25% - 60%, and the mass of styrene-butadiene rubber accounts for 5% - 50%.

[0009] Further, the graphene-containing conductive agent may further include an auxiliary conductive agent, and the mass ratio of the auxiliary conductive agent to the graphene is (0.1 - 99.5) : (0.5 - 99.9), preferably (50 - 99.5) : (0.5 - 50). The auxiliary conductive agent includes one or a combination of more of graphite, acetylene black, carbon nanotubes, Ketjen black, conductive carbon black, carbon nanotubes. Preferably, conductive carbon black is selected as the auxiliary conductive agent.

[0010] Further, in the graphene-containing conductive agent, based on the mass of the graphene-containing conductive agent, the mass content of the graphene is 0.1% - 100%, preferably 0.5% - 50%.

[0011] Further, the graphene is powder graphene, and the powder graphene has a three-dimensional structure and is a stack of graphene sheets.

[0012] Further, based on the mass of the graphene, the carbon content ≥ 99.50%, preferably 99.80% - 99.95%, and the oxygen content is below 300 ppm.

[0013] Further, the particle size of the graphene is 15 - 35 μm.

[0014] Further, the graphene has a three-dimensional cage-like structure.

[0015] Further, the graphene is a stack of petal-shaped graphene sheets.

[0016] Further, the median particle size of the graphene sheets is 5 - 15 μm, preferably 8 - 15 μm.

[0017] Further, the graphene sheets are 1 - 10 layers thick and have a thickness of 0.5 - 3.0 nm.

[0018] Further, in the Raman spectrum of the graphene, the ratio of I D / I G can be 0.01 - 0.10, further can be 0.03 - 0.10, such as but not limited to 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, etc.

[0019] Further, the electrical conductivity of the graphene is 500 - 5000 S / cm, preferably 1500 - 4000 S / cm, and more preferably 2000 - 3500 S / cm, such as but not limited to 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, etc.

[0020] Further, the specific surface area of the graphene is 50 - 300 m 2 / g, preferably 100 - 250 m 2 / g.

[0021] Further, the tapped density of the graphene is 0.02 - 0.04 g / cm 3 .

[0022] Further, the method for preparing the graphene includes the following steps:

[0023] (1) Graphite is pre - expanded to obtain pre - expanded graphite;

[0024] (2) The pre - expanded graphite obtained in step (1), a wetting agent, and a solvent are mixed, and are sequentially subjected to first high - pressure homogenization treatment and second high - pressure homogenization treatment to obtain a graphene slurry; wherein, the pressure of the second high - pressure homogenization treatment is 10 - 20 MPa higher than that of the first high - pressure homogenization treatment;

[0025] (3) The graphene slurry obtained in step (2) is dried to obtain graphene.

[0026] Further, the pre - expanded graphite obtained in step (1) has an expansion multiple of 200 - 300 times compared with the graphite before pre - expansion.

[0027] Further, the method for pre - expanding the graphite in step (1) is as follows: The graphite powder is heated to 800 - 950 °C and subjected to an expansion treatment for 10 - 60 s to obtain pre - expanded graphite. Among them, the particle size of the graphite powder is 70 - 100 mesh.

[0028] Further, the wetting agent described in step (2) is fatty amine polyoxyethylene ether. The HLB value of the fatty amine polyoxyethylene ether ≥ 12.

[0029] Further, in step (2), the feeding mass ratio of the pre-expanded graphite obtained in step (1) to the wetting agent is 1:0.01 - 0.1. The solid content of the graphene slurry is 0.5wt% - 5.0wt%. The solvent is one or more of water and ethanol.

[0030] Further, in step (2), the pressure of the first high-pressure homogenization treatment is 30 - 40 MPa, and the treatment time is 20 - 60 min. The pressure of the second high-pressure homogenization treatment is 40 - 50 MPa, and the treatment time is 10 - 30 min.

[0031] Further, in the graphene obtained in step (3), the solvent residue content ≤ 0.1wt%.

[0032] Further, the drying in step (3) is preferably spray drying or freeze drying. Among them, the conditions of spray drying are as follows: the inlet air temperature is 300 - 350 °C, the inlet air temperature is 200 - 250 °C higher than the outlet air temperature, the outlet air temperature is 100 - 130 °C, and the rotational speed of the sprayer centrifugal disk is 20000 - 30000 rpm. The conditions of freeze drying are as follows: the cold trap temperature is not higher than -65 °C, preferably -75 to -70 °C, the temperature of the box partition is not higher than -55 °C, preferably -65 to -60 °C, the heating rate is 0.1 °C / min - 0.5 °C / min, the time for the temperature of the box partition to rise from the initial temperature to 0 °C is not less than 24 h, preferably 26 - 30 h, and the vacuum degree is not higher than 10 Pa, preferably 0.5 - 5 Pa.

[0033] Further, the silicon-carbon material can be a conventional silicon-carbon material used in the negative electrode, and the silicon therein can be one or more of silicon powder, modified silicon powder, and silicon oxide. Preferably, the silicon powder is one or more of single-crystalline silicon, polycrystalline silicon, and amorphous silicon, with a particle size of 30 - 200 nm; the silicon oxide is nano-silicon oxide, with a particle size of 2 nm - 100 nm; the median particle size of the silicon-carbon material is 0.1 - 20 μm, and the designed capacity is 300 - 3000 mAhg -1 . In the silicon-carbon material, the mass content of silicon is 2.5% - 50%.

[0034] The second aspect of the present invention provides a method for preparing the above-mentioned silicon-carbon negative electrode sheet, including the following steps:

[0035] (1) Mix the polymer binder with the solvent to obtain a binder solution;

[0036] (2) Add graphene to the adhesive solution obtained in step (1) for dispersion treatment (preferably, add the auxiliary conductive agent after graphene is uniformly dispersed in the slurry), and obtain the conductive agent slurry after mixing evenly.

[0037] (3) Add silicon-carbon material to the conductive agent slurry obtained in step (2), and after mixing evenly, obtain the negative electrode slurry. Then coat the negative electrode slurry on the negative electrode current collector (such as copper foil) to prepare the silicon-carbon negative electrode sheet.

[0038] Further, the solvent in step (1) is water.

[0039] Further, the solid content of the negative electrode slurry obtained in step (3) is 15% - 40%.

[0040] Further, the time for the dispersion treatment in step (2) is 0.5h - 24h, and the dispersion methods include one or more of stirring, ball milling, ultrasonic dispersion, etc.

[0041] The third aspect of the present invention provides a lithium-ion battery, including the silicon-carbon negative electrode sheet described above as the negative electrode; a positive electrode material containing lithium element, a separator, and an electrolyte.

[0042] Further, the lithium-ion battery includes any one of a liquid lithium-ion battery, a semi-solid lithium-ion battery, or a solid-state lithium-ion battery.

[0043] Further, in the lithium-ion battery, the specific composition of the positive electrode material containing lithium element is not particularly limited, and it can be a positive electrode material containing lithium element commonly used in the art.

[0044] The separator can be selected from various separators used in lithium-ion batteries known to those skilled in the art, such as a polypropylene microporous membrane, a polyethylene felt, a glass fiber felt, or an ultra-fine glass fiber paper.

[0045] The electrolyte can be various conventional electrolytes, such as a non-aqueous electrolyte. The non-aqueous electrolyte is a solution formed by an electrolyte lithium salt in a non-aqueous solvent, and a conventional non-aqueous electrolyte known to those skilled in the art can be used. For example, the electrolyte can be selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), and lithium hexafluorosilicate (LiSiF6). The non-aqueous solvent can be selected from a mixed solution of a chain acid ester and a cyclic acid ester, where the chain acid ester can be at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and dipropyl carbonate (DPC). The cyclic acid ester can be at least one of ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC).

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] (1) The present invention provides a conductive agent for a silicon-carbon negative electrode, which adopts a new graphene with high conductivity and an I D / I G below 0.10, and in combination with an auxiliary conductive agent, can construct a developed and effective sheet structure conductive network with a small amount of addition, effectively inhibit volume expansion, and finally improve the capacity retention rate of the battery, significantly improving the cycle stability of the battery.

[0048] (2) The present invention preferably uses CMC (carboxymethyl cellulose) as the main polymer binder and polyacrylic acid and / or polymethacrylic acid as the auxiliary binder. In this way, through the enhancement of the π-π interaction between the benzene ring in CMC and the new graphene, the adsorption force between graphene and CMC is enhanced, and the viscosity of the CMC aqueous solution is large, and the internal friction can prevent the settlement of graphene, making the conductive paste more stable. PAA (polyacrylic acid) has carboxyl groups, which can not only modify the surface of graphene but also form hydrogen bonds with the hydroxyl groups on the silicon surface, contributing to the dispersion of both in water. At the same time, its high viscosity can act as an adhesive, making the bonding between the negative electrode material and the current collector copper foil firmer, thus contributing to further improving the chemical performance of the battery. Description of the Drawings

[0049] Figure 1 is the SEM photograph of the powdered graphene G-1 obtained in Example 1;

[0050] Figure 2 is the TEM photograph of the powdered graphene G-1 obtained in Example 1;

[0051] Figure 3 is the HR-TEM photograph of the powdered graphene G-1 obtained in Example 1;

[0052] Figure 4 is the Raman spectrogram of the powdered graphene G-1 obtained in Example 1;

[0053] Figure 5 is the XRD pattern of the powdered graphene G-1 obtained in Example 1;

[0054] Figure 6 is the Raman spectrogram of the powdered graphene G-2 obtained in Example 2;

[0055] Figure 7 is the SEM photograph of the powdered graphene DG-1 obtained in Comparative Example 1;

[0056] Figure 8 is the HR-TEM image of the powdered graphene DG-1 obtained in Comparative Example 1;

[0057] Figure 9 is the Raman spectrum of the powdered graphene DG-1 obtained in Comparative Example 1;

[0058] Figure 10 is the cross-sectional SEM image of the negative electrode plate with the addition of the graphene G-1 prepared in Example 1 in Example 3;

[0059] Figure 11 is the battery capacity retention rate after adding the graphene G-1 prepared in Example 1 in Example 3;

[0060] Figure 12 is the cross-sectional SEM image of the negative electrode plate with the addition of the graphene G-2 prepared in Example 2 in Example 4;

[0061] Figure 13 is the battery capacity retention rate of the battery without adding graphene in Comparative Example 4;

[0062] Figure 14 is the cross-sectional SEM image of the negative electrode plate with the addition of the graphene DG-1 prepared in Comparative Example 1 in Comparative Example 5;

[0063] Figure 15 is the battery capacity retention rate after adding the graphene DG-1 prepared in Comparative Example 1 in Comparative Example 5. Detailed Embodiments

[0064] For the convenience of understanding the present invention, the following examples are listed. However, those skilled in the art should understand that the said examples are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0065] All publications, patent applications, patents and other references mentioned in this specification are hereby incorporated by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0066] In the context of this specification, any two or more aspects of the present invention can be combined arbitrarily, and the technical solutions thus formed belong to a part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0067] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless it does not conform to the common understanding of those skilled in the art when based on weight.

[0068] In the present invention, a scanning electron microscope (SEM) is used to characterize the morphology of the electrode material. Specifically, the scanning electron microscope is a TECNAL G2 F20 (200 kv) model from FEI Company in the United States. The test conditions are as follows: the sample is directly pressed on the sample stage containing conductive tape, and then inserted into the electron microscope for observation. The observation uses a magnification of 8000 times.

[0069] In the present invention, a transmission electron microscope (TEM, HR-TEM) with the model JEM-2100 from JEOL Ltd. of Japan is used to characterize the morphology of the electrode material. The test conditions are as follows: the sample is placed on a copper support grid and then inserted into the electron microscope for observation. The observations use magnifications of 17000 times and 380000 times.

[0070] In the present invention, the median particle size of the graphene sheets is obtained by characterization through dynamic light scattering, using a laser particle size analyzer with the model MS-3000 from Malvern Panalytical Company. The test conditions are as follows: the sample is dispersed in deionized water at a concentration of 0.01 mg / ml, ultrasonicated for 10 min and then tested, and the instrument obscuration is set in the range of 5%-20%.

[0071] In the present invention, an X-ray diffractometer of the D / max-2200 / PC type from Rigaku Corporation of Japan is used to perform XRD analysis on the prepared ternary cathode material. The analysis test conditions are as follows: the 2θ angle test range is 10°-70°, the scanning speed is 6° / min. The test tube voltage is 40 KV, the current is 40 mA, and the Cu-Kα ray source is used.

[0072] In the present invention, the specific surface area is tested using a specific surface area and pore size distribution analyzer of the ASAP2010 type from Micromeritics Company in the United States. The test conditions are as follows: the temperature is 77 K and the nitrogen environment is used.

[0073] In the present invention, the Raman spectrum uses a laser with a wavelength of 785 nm as the excitation light source and is tested with an Invia / Reflrx Laser Micro-Raman spectrometer. All samples are placed on clean glass slides for testing. Among them, the highest peak height I of the D peak (defect peak) in the wavelength range of 1250-1450 cm -1 , the highest peak height I of the G peak (sp D hybridized carbon atom vibration peak) in the wavelength range of 1500-1700 cm -1 , and the highest peak height I of the 2D peak (D peak second harmonic peak) in the wavelength range of 2600-2800 cm 2 . G -1 2D .

[0074] In the present invention, the method for measuring the expansion ratio is as follows: Take a certain amount of expandable graphite powder, measure the volume of the graphite powder with a graduated cylinder, and then place the above-mentioned graphite powder in a crucible and perform expansion treatment at a specified temperature. After the treated graphite powder returns to room temperature, measure the volume again with a graduated cylinder, and calculate the expansion ratio. The formula is as follows:

[0075] Expansion ratio = (Volume of expanded graphite after treatment - Volume of graphite powder before treatment) / Volume of graphite powder before treatment.

[0076] In the present invention, the method for measuring the solvent residue rate is as follows: Take 1 g of undried graphene powder, place it in a vacuum oven and dry it at 60 °C for 10 h, weigh the graphene powder again, and calculate the solvent residue. The formula is as follows:

[0077] Residue rate % = (1 - Mass of graphene powder after drying in grams) / 1 × 100%.

[0078] In the present invention, the tapped density test is measured using an FT-100E multi-functional tapped density tester produced by Ruike Instrument Co., Ltd., with a test frequency of 200 Hz and 5000 vibration times.

[0079] In the present invention, the conductivity test is carried out using an ST-2258C multi-functional digital four-probe tester produced by Suzhou Jingge Co., Ltd. The sample is prepared by the tablet pressing method. The preparation steps are as follows: Press the prepared graphene powder into a 100-μm sheet at a pressure of 10 MPa, and then test it with a conductivity meter.

[0080] In the present invention, the oxygen content and carbon content tests are carried out using a FlashSmart-1120265 elemental analyzer produced by ThermoFisher Company. Helium gas is used as the carrier gas, and the injection volume is 1 mgx. Based on the mass of the graphene powder.

[0081] The present invention will be described in detail below through examples.

[0082] In the following examples and comparative examples, the room temperature refers to 25 °C.

[0083] In the following examples and comparative examples, the expandable graphite is purchased from Aladdin Reagent Company. The wetting agent is commercially available from Huntsman Chemical Trading Co., Ltd., with the product number Surfonic T-10.

[0084] Example 1

[0085] Graphene preparation:

[0086] (1) Take 100 g (75 mesh) of expandable graphite powder and perform expansion treatment at 900 °C for 20 s to obtain pre-expanded graphite with an expansion ratio of 220 times.

[0087] (2) Take 10 g of pre-expanded graphite, 0.25 g of wetting agent fatty amine polyoxyethylene ether (Surfonic T-10, HLB value is 12.4), and 239.75 g of deionized water from step (1), and add them together into a high-pressure homogenizer. Homogenize at a pressure of 30 MPa for 30 min, then increase the pressure to 45 MPa and homogenize for 30 min to obtain graphene slurry.

[0088] (3) Use a spray drying device to dry the above slurry, control the inlet air temperature at 350 °C, the outlet air temperature at 100 °C, the rotational speed of the sprayer centrifugal disk at 20,000 rpm, and collect the powder at the outlet to obtain the graphene product G-1.

[0089] Figure 1 is the SEM image of the product G-1 obtained in Example 1. From Figure 1 it can be seen that G-1 is a three-dimensional cage-like structure formed by stacking graphene sheets, and the particle size of the powdered graphene is 20 μm - 30 μm. Figure 2 is the TEM image of the product G-1 obtained in Example 1. From Figure 2 it can be seen that the graphene sheets are in a stacked state, which is consistent with the result obtained from the SEM photograph in Figure 1 , indicating that G-1 is a three-dimensional cage-like structure formed by stacking graphene sheets, and the powdered graphene is a stack of petal-shaped graphene sheets. Figure 3 is the HR-TEM image of G-1 in Example 1. From Figure 3 the lattice fringes in it, it can be seen that the graphene sheets in G-1 are few-layer graphene with 4 - 6 layers, and the thickness is about between 1.2 nm and 1.9 nm. The median particle size of the graphene sheets is 8.5 μm.

[0090] Figure 4 is the Raman spectrum of the graphene G-1 obtained in Example 1. From Figure 4 it can be seen that the D band (1354 cm -1 ) of graphene is much smaller than the G band (1574 cm -1 ), and the peak intensity ratio I D / I G is 0.09, indicating that G-1 has fewer defects. In addition, G-1 has an obvious 2D peak at 2709 cm -1 , and combined with Figure 3 further verification shows that G-1 is few-layer graphene. Figure 5XRD pattern of G-1 shows a significant diffraction peak only at 26.63°, without any impurity peaks, indicating that there is no impurity phase formed by oxidation or doping of impurity elements in G-1. It can be known from the test by a sulfur-carbon analyzer that the carbon content of G-1 obtained in Example 1 is 99.95 wt%, and the oxygen content is 140 ppm. The conductivity of G-1 measured by the tablet pressing method is 3200 S / cm, and the tapped density is 0.028 g / cm 3 , with a specific surface area of 180 m 2 / g and a solvent residue rate of 0.1%.

[0091] Example 2

[0092] Preparation of graphene:

[0093] (1) Take 100 g (75 mesh) of expandable graphite powder and perform an expansion treatment at 900 °C for 40 s to obtain pre-expanded graphite with an expansion ratio of 300 times.

[0094] (2) Take 10 g of the above pre-expanded graphite, 0.25 g of fatty amine polyoxyethylene ether (Surfonic T-10, HLB value is 12.4), and 239.75 g of deionized water, and add them together into a high-pressure homogenizer. Homogenize at a pressure of 30 MPa for 60 min, then increase the pressure to 45 MPa and homogenize for 30 min to obtain a graphene slurry.

[0095] (3) Use a spray drying device to dry the above slurry, control the inlet air temperature at 350 °C, the outlet air temperature at 100 °C, the rotational speed of the centrifugal disk of the sprayer at 20000 rpm, and collect the powder at the outlet as the obtained product G-2.

[0096] It can be seen from the SEM image of G-2 that G-2 is a three-dimensional cage-like structure formed by stacking graphene sheets, with a particle size of 18 μm - 22 μm. From the test results of HR-TEM, the graphene sheets in G-2 are few-layer graphene with 4 - 6 layers, and the thickness is about between 1.2 nm and 1.8 nm. From the dynamic light scattering data, the median particle size of the graphene sheets is 10 μm. Figure 6 The Raman spectrum test shows that the peak position of the D band of graphene G-2 is at 1346 cm -1 , and the peak position of the G band is at 1565 cm -1 , and the peak intensity ratio I D / I G is 0.04, indicating that G-2 has fewer defects. In addition, G-2 shows an obvious 2D peak at 2702 cm -1 , further verifying that G-2 is few-layer graphene. In addition, the XRD pattern of G-2 shows a significant diffraction peak only at 26.63°, without any impurity peaks, indicating that there is no impurity phase formed by oxidation or doping of impurity elements in G-2.

[0097] The carbon content of the obtained G-2 is 99.85 wt%, and the oxygen content is 140 ppm; the conductivity of G-2 measured by the tablet pressing method is 2000 S / cm, and the tapped density is 0.029 g / cm 3 , and the specific surface area is 140 m 2 / g, and the solvent residue rate is 0.1%.

[0098] Comparative Example 1

[0099] Preparation of graphene:

[0100] (1) Take 100 g of expandable graphite powder (75 mesh) and perform an expansion treatment at 900 °C for 20 s to obtain pre-expanded graphite with an expansion multiple of 220 times.

[0101] (2) Take 10 g of the above pre-expanded graphite, 0.25 g of alkylphenol polyoxyethylene ether (Teric N6, HLB value is 10.9), and 239.75 g of deionized water, and add them together into a high-pressure homogenizer. Homogenize at a pressure of 30 MPa for 30 min, and increase the pressure to homogenize at a pressure of 45 MPa for 30 min to obtain a graphene slurry.

[0102] (3) Use a spray drying device to dry the above slurry, control the inlet air temperature to be 350 °C, the outlet air temperature to be 100 °C, the rotation speed of the sprayer centrifugal disk to be 20000 rpm, and the powder collected at the outlet is the obtained product DG-1.

[0103] From the SEM image of DG-1 ( Figure 7 ), it can be seen that the graphene in DG-1 is mainly in the form of disordered lamellar aggregates and has no fixed particle size. From Figure 8 the HR-TEM test results, it can be known that the graphene sheets in DG-1 are graphite sheets with 15 - 20 layers, and the thickness is about between 4.5 nm and 6 nm. From Figure 9 the Raman spectrum test shows that the D band peak position of graphene DG-1 is at 1351 cm -1 , and the G band peak position is at 1514 cm -1 , and the peak intensity ratio ID / IG of the two is 0.25, indicating that the defects in DG-1 are significantly more than those in G-1. In addition, the 2D peak of DG-1 at 2702 cm -1 is a wrapped peak and is not obvious, further verifying that DG-1 is graphite sheets with a relatively large number of layers.

[0104] The carbon content of the powdered graphene DG-1 is 99.32 wt%, and the oxygen content is 240 ppm; the conductivity of DG-1 measured by the tablet pressing method is 800 S / cm, and the tapped density is 0.042 g / cm 3 , and the specific surface area is 60 m 2 / g, the solvent residue rate is 0.25%.

[0105] Comparative Example 2

[0106] Graphene preparation:

[0107] (1) Take 100 g (75 mesh) of expandable graphite powder and perform an expansion treatment at 900 °C for 20 s to obtain pre-expanded graphite with an expansion multiple of 220 times.

[0108] (2) Take 10 g of the above pre-expanded graphite, 0.25 g of fatty amine polyoxyethylene ether (Surfonic T-10, HLB value is 12.4), and 239.75 g of deionized water, and add them together into a high-pressure homogenizer. Homogenize at a pressure of 30 MPa for 60 min to obtain an aqueous graphene slurry.

[0109] (3) Use a spray drying device to dry the above slurry, control the inlet air temperature at 350 °C, the outlet air temperature at 100 °C, the rotational speed of the sprayer centrifugal disk at 20000 rpm, and collect the powder at the outlet to obtain the product DG-2.

[0110] From the SEM image of DG-2, it can be seen that graphene in DG-2 is mainly in the form of disordered lamellar aggregates without a fixed particle size. From the HR-TEM test results, it can be known that the graphene sheets in DG-1 are graphite sheets with 10 - 15 layers, and the thickness is about between 3 nm and 4.5 nm. Raman spectroscopy test shows that the peak position of the D band of graphene DG-2 is at 1351 cm -1 , the peak position of the G band is at 1514 cm -1 , and the peak intensity ratio I D / I G is 0.2, indicating that the defects in DG-2 are significantly more than those in G-1. In addition, DG-2 shows a shoulder peak at 2702 cm -1 , which belongs to the 2D peak, only indicating the presence of a small amount of few-layer graphene in DG-2.

[0111] The carbon content of the obtained DG-2 is 99.95 wt%, and the oxygen content is 140 ppm; the conductivity of DG-2 measured by the tablet pressing method is 500 S / cm, the tapped density is 0.08 g / cm 3 , and the specific surface area is 12 m 2 / g, the solvent residue rate is 0.1%.

[0112] Comparative Example 3

[0113] Graphene preparation:

[0114] (1) Take 100 g (75 mesh) of expandable graphite powder and perform an expansion treatment at 900 °C for 20 s to obtain pre-expanded graphite with an expansion multiple of 220 times.

[0115] (2) Take 10 g of the pre-expanded graphite mentioned above, 0.25 g of fatty amine polyoxyethylene ether (Surfonic T-10, HLB value is 12.4), and 239.75 g of deionized water, and add them together into a high-pressure homogenizer. Homogenize at a pressure of 45 MPa for 60 min to obtain an aqueous graphene slurry.

[0116] (3) Use a spray drying device to dry the above slurry. Control the inlet air temperature at 350 °C, the outlet air temperature at 100 °C, the rotational speed of the centrifugal disk of the sprayer at 20000 rpm, and collect the powder at the outlet to obtain the product DG-3.

[0117] It can be seen from the SEM image of DG-3 that DG-3 is composed of disordered graphene sheets and has no fixed particle size. From the HR-TEM test results, it can be known that the graphene sheets in DG-3 are 4-6 layers of graphene, and the thickness is about between 1.2 nm and 1.9 nm. Raman spectroscopy test shows that the peak position of the D band of graphene DG-3 is at 1354 cm -1 , and the peak position of the G band is at 1574 cm -1 , and the peak intensity ratio I D / I G is 0.13, indicating that the defects of DG-3 are similar to those of G-1. In addition, DG-3 shows a sharp peak at 2709 cm -1 , which belongs to the 2D peak, indicating that DG-3 is composed of few-layer graphene. However, due to the relatively dispersed particle size of graphene in DG-3, it is not conducive to industrial applications.

[0118] The carbon content of the obtained DG-3 is 99.95 wt%, and the oxygen content is 140 ppm; the conductivity of DG-3 measured by the tablet pressing method is 1600 S / cm, the tapped density is 0.018 g / cm 3 , the specific surface area is 200 m 2 / g, and the solvent residue rate is 0.1%.

[0119] Example 3

[0120] Uniformly mix 8 g of a 2% sodium carboxymethylcellulose solution and 0.64 g of a 25% polyacrylic acid solution. Add 5 mg of the obtained graphene G-1 and perform dispersion treatment by ball milling for 4 h. After the graphene is uniformly dispersed in the slurry, add 0.495 g of carbon black and mix evenly to obtain a conductive agent slurry. Add 4 g to the obtained conductive agent slurry with a designed capacity of 500 mAhg -1Silicon-carbon material (wherein the silicon is single-crystalline silicon with a particle size of 100 nm, the median particle size of the silicon-carbon material is 16.7 μm, and the mass content of silicon is 5%), ball-milled for 30 minutes to make it evenly mixed. Then add 0.334 g of styrene-butadiene rubber emulsion with a concentration of 50%, and stir for 30 minutes to obtain a negative electrode conductive paste containing graphene. Coat the paste on a copper foil with a coating thickness of 100 μm. After drying at 80 °C to 120 °C under vacuum conditions, a negative electrode sheet is obtained by rolling.

[0121] Figure 10 is the SEM image of the negative electrode sheet obtained in Example 3. As can be seen from Figure 10 it, after adding graphene G-1, there is a sheet-like structure composed of graphene in the electrode sheet, thus forming a planar conductive network in the electrode sheet, effectively reducing the internal resistance of the electrode sheet and playing a role in suppressing the volume expansion of the electrode sheet.

[0122] The resistivity of the electrode sheet is measured to be 0.343 Ω / cm using a four-probe tester.

[0123] Test experiment: Take the negative electrode sheet obtained in Example 3, use a lithium metal sheet as the positive electrode, use a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then use a Blue Power LAND battery test system to conduct electrochemical performance tests. The test temperature is 25 °C, the charge-discharge rate of the first cycle is 0.05C, the voltage range is 0.005V - 1.5V, the cycle charge-discharge rate is 0.2C, and the voltage range is 0.005V - 1.5V. The test results are as Figure 11 shown: The initial Coulomb efficiency is 86.6%; at 0.2C, the capacity retention rate after 100 cycles is 94.3%, and the capacity retention rate is still above 72% after 400 cycles.

[0124] Example 4

[0125] Mix 8 g of sodium carboxymethyl cellulose solution with a concentration of 2% and 0.64 g of polyacrylic acid solution with a concentration of 25% evenly. Add 5 mg of the obtained graphene G-2, and perform dispersion treatment by ball-milling for 4 h. After the graphene is evenly dispersed in the paste, add 0.495 g of carbon black and mix evenly to obtain a conductive agent paste. Add 4 g of silicon-carbon material with a designed capacity of 500 mAhg -1 (the same as in Example 3) to the obtained conductive agent paste, ball-mill for 30 minutes to make it evenly mixed. Then add 0.334 g of styrene-butadiene rubber emulsion with a concentration of 50%, and stir for 30 minutes to obtain a negative electrode conductive paste containing graphene. Coat the paste on a copper foil with a coating thickness of 100 μm. After drying at 80 °C to 120 °C under vacuum conditions, a negative electrode sheet is obtained by rolling.

[0126] Figure 12It is the SEM image of the negative electrode sheet obtained in Example 4. After adding graphene G-2, there is a sheet structure composed of graphene in the electrode sheet, thus forming a planar conductive network in the electrode sheet, effectively reducing the internal resistance of the electrode sheet and playing a role in suppressing the volume expansion of the electrode sheet.

[0127] The resistivity of the electrode sheet was measured to be 0.435 Ω / cm using a four-probe tester.

[0128] Test experiment: Take the negative electrode sheet obtained in Example 4, use a lithium metal sheet as the positive electrode, use a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then, use a BlueTEC LAND battery test system to conduct electrochemical performance tests. The test temperature is 25 °C, the charge-discharge rate of the first cycle is 0.05C, the voltage range is 0.005V - 1.5V, the cyclic charge-discharge rate is 0.2C, and the voltage range is 0.005V - 1.5V. The test results are as follows: The initial Coulomb efficiency is 86.5%; at 0.2C, the capacity retention rate after 100 cycles is 92.7%, and the capacity retention rate after 400 cycles is about 65%.

[0129] Example 5

[0130] Uniformly mix 12.5 g of a 1% sodium carboxymethylcellulose solution and 1.2 g of a 25% polyacrylic acid solution. Add 5 mg of the obtained graphene G-1 and perform dispersion treatment by ball milling for 4 h. After the graphene is uniformly dispersed in the slurry, add 0.495 g of carbon black and mix evenly to obtain a conductive agent slurry. Add 4 g of silicon-carbon material (the same as in Example 3) with a designed capacity of 500 mAh / g -1 to the obtained conductive agent slurry, and ball mill for 30 minutes to make it evenly mixed. Then add 0.15 g of a 50% styrene-butadiene rubber emulsion and stir for 30 minutes to obtain a graphene-containing negative electrode conductive slurry. Coat the slurry on a copper foil with a coating thickness of 100 μm. After drying at 80 °C - 120 °C under vacuum conditions, roll press to obtain a negative electrode sheet.

[0131] After adding graphene G-1, there is a sheet structure composed of graphene in the electrode sheet, thus forming a planar conductive network in the electrode sheet, effectively reducing the internal resistance of the electrode sheet and playing a role in suppressing the volume expansion of the electrode sheet.

[0132] The resistivity of the electrode sheet was measured to be 0.475 Ω / cm using a four-probe tester.

[0133] Test experiment: Take the negative electrode sheet obtained in Example 5, use a lithium metal sheet as the positive electrode, use a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then, use a Blue Power LAND battery test system to conduct electrochemical performance tests. The test temperature is 25 °C, the charge-discharge rate of the first cycle is 0.05C, the voltage range is 0.005V - 1.5V, the cyclic charge-discharge rate is 0.2C, and the voltage range is 0.005V - 1.5V. The test results are as follows: The initial Coulomb efficiency is 86.0%; at 0.2C, the capacity retention rate after 100 cycles is 90.1%, and the capacity retention rate after 400 cycles is about 55%.

[0134] Example 6

[0135] Mix 10 g of a 3% sodium carboxymethyl cellulose solution and 0.5 g of a 25% polyacrylic acid solution evenly. Add 5 mg of the obtained graphene G-1 and perform dispersion treatment by ball milling for 4 h. After the graphene is evenly dispersed in the slurry, add 0.495 g of carbon black and mix evenly to obtain a conductive agent slurry. Add 4 g of a silicon-carbon material (the same as in Example 3) with a designed capacity of 500 mAh / g -1 to the obtained conductive agent slurry, and ball mill for 30 minutes to make it evenly mixed. Then add 0.15 g of a 50% styrene-butadiene rubber emulsion and stir for 30 minutes to obtain a graphene-containing negative electrode conductive slurry. Coat the slurry on a copper foil with a coating thickness of 100 μm. After drying at 80 °C - 120 °C under vacuum conditions, roll press to obtain a negative electrode sheet.

[0136] After adding graphene G-1, there is a lamellar structure composed of graphene in the electrode sheet, thus forming a planar conductive network in the electrode sheet, effectively reducing the internal resistance of the electrode sheet and playing a role in suppressing the volume expansion of the electrode sheet.

[0137] The resistivity of the electrode sheet measured by a four-probe tester is 0.497 Ω / cm.

[0138] Test experiment: Take the negative electrode sheet obtained in Example 6, use a lithium metal sheet as the positive electrode, use a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then, use a Blue Power LAND battery test system to conduct electrochemical performance tests. The test temperature is 25 °C, the charge-discharge rate of the first cycle is 0.05C, the voltage range is 0.005V - 1.5V, the cyclic charge-discharge rate is 0.2C, and the voltage range is 0.005V - 1.5V. The test results are as follows: The initial Coulomb efficiency is 86.4%; at 0.2C, the capacity retention rate after 100 cycles is 89.8%, and the capacity retention rate after 400 cycles is about 55%.

[0139] Example 7

[0140] Add 5 mg of the obtained graphene G-1 to 12.5 g of a sodium alginate solution with a concentration of 4%, and perform dispersion treatment by ball milling for 4 h. After the graphene is uniformly dispersed in the slurry, add 0.495 g of carbon black and mix evenly to obtain a conductive agent slurry. Add 4 g of silicon-carbon material with a designed capacity of 500 mAh / g -1 (same as Example 3), and ball mill for 2 h to make it evenly mixed, obtaining a graphene-containing negative electrode conductive slurry. Coating the slurry on a copper foil with a coating thickness of 100 μm. After drying at 80 °C to 120 °C for 12 h under vacuum conditions, a negative electrode plate is obtained through roll pressing.

[0141] After adding graphene G-1, there is a lamellar structure composed of graphene in the electrode plate, thus forming a planar conductive network in the electrode plate, effectively reducing the internal resistance of the electrode plate and playing a role in inhibiting the volume expansion of the electrode plate.

[0142] The resistivity of the electrode plate is measured to be 0.408 Ω / cm using a four-probe tester.

[0143] Testing experiment: Take the negative electrode plate obtained in Example 7, use a lithium metal sheet as the positive electrode, use a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then, use a BlueTEC LAND battery test system to conduct electrochemical performance tests. The test temperature is 25 °C, the charge-discharge rate of the first cycle is 0.05 C, the voltage range is 0.005 V - 1.5 V, the cycle charge-discharge rate is 0.2 C, and the voltage range is 0.005 V - 1.5 V. Test results: The initial Coulomb efficiency is 84.5%; at 0.2 C, the capacity retention rate after 100 cycles is 88%. After 200 cycles, material shedding occurs on the electrode plate.

[0144] Example 8

[0145] Uniformly mix 8 g of a sodium carboxymethyl cellulose solution with a concentration of 5% and 0.2 g of a polyacrylic acid solution with a concentration of 25%. Add 5 mg of the obtained graphene G-1, and perform dispersion treatment by ball milling for 4 h. After the graphene is uniformly dispersed in the slurry, add 0.495 g of carbon black and mix evenly to obtain a conductive agent slurry. Add 4 g of silicon-carbon material with a designed capacity of 500 mAh / g -1 (same as Example 3), and ball mill for 30 minutes to make it evenly mixed. Then add 0.1 g of a styrene-butadiene rubber latex with a concentration of 50%, and stir for 30 minutes to obtain a graphene-containing negative electrode conductive slurry. Coating the slurry on a copper foil with a coating thickness of 100 μm. After drying at 80 °C to 120 °C under vacuum conditions, a negative electrode plate is obtained through roll pressing.

[0146] After adding graphene G-1, there is a lamellar structure composed of graphene in the electrode plate, forming a conductive lamella while playing a role in inhibiting the volume expansion of the electrode plate.

[0147] The resistivity of the electrode sheet was measured to be 0.628 Ω / cm using a four-probe tester.

[0148] Test experiment: Take the negative electrode sheet obtained in Example 8, use a lithium metal sheet as the positive electrode, use a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then, use a BlueTEC LAND battery test system to conduct electrochemical performance tests. The test temperature is 25 °C, the charge-discharge rate of the first cycle is 0.05C, the voltage range is 0.005V - 1.5V, the cycle charge-discharge rate is 0.2C, and the voltage range is 0.005V - 1.5V. Test results: The initial Coulomb efficiency is 84.4%; at 0.2C, after 100 cycles, the capacity retention rate is 88.6%. After 200 cycles, material shedding occurred on the electrode sheet, and the adhesiveness was slightly poor.

[0149] Example 9

[0150] 10 g of a 0.5% sodium carboxymethylcellulose solution was uniformly mixed with 1.6 g of a 25% polyacrylic acid solution. 5 mg of the obtained graphene G-1 was added, and ball milling was performed for 4 h for dispersion treatment. After the graphene was uniformly dispersed in the slurry, 0.495 g of carbon black was added and mixed evenly to obtain a conductive agent slurry. -1 To the obtained conductive agent slurry, 4 g of a silicon-carbon material with a designed capacity of 500 mAh / g (the same as in Example 3) was added, and ball milling was performed for 30 minutes to make it uniformly mixed. Then, 0.1 g of a 50% styrene-butadiene rubber emulsion was added, and after stirring for 30 minutes, a negative electrode conductive slurry containing graphene was obtained. The slurry was coated on a copper foil with a coating thickness of 100 μm. After drying at 80 °C - 120 °C under vacuum conditions, a negative electrode sheet was obtained by rolling.

[0151] After adding graphene G-1, there is a lamellar structure composed of graphene in the electrode sheet, which forms a conductive sheet layer and at the same time plays a role in inhibiting the volume expansion of the electrode sheet. A small part of the graphene aggregates together in a cage-like structure and is not better dispersed.

[0152] The resistivity of the electrode sheet was measured to be 0.628 Ω / cm using a four-probe tester.

[0153] Test experiment: Take the negative electrode sheet obtained in Example 9, use a lithium metal sheet as the positive electrode, use a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then, use the Blue Power LAND battery test system to conduct electrochemical performance tests. The test temperature is 25°C, the charge-discharge rate of the first cycle is 0.05C, the voltage range is 0.005V - 1.5V, the cyclic charge-discharge rate is 0.2C, and the voltage range is 0.005V - 1.5V. Test results: The initial Coulomb efficiency is 83.5%; at 0.2C, the capacity retention rate after 100 cycles is 88.1%, and the capacity retention rate after 400 cycles is about 45%.

[0154] Example 10

[0155] Mix 8 g of a 2% sodium carboxymethylcellulose solution and 0.64 g of a 25% polyacrylic acid solution evenly. Add 2.5 mg of the obtained graphene G-1 and perform dispersion treatment by ball milling for 4 h. After the graphene is evenly dispersed in the slurry, add 0.4975 g of carbon black and mix evenly to obtain a conductive agent slurry. Add 4 g of silicon-carbon material (the same as in Example 3) with a designed capacity of 500 mAh / g -1 to the obtained conductive agent slurry, and ball mill for 30 minutes to make it evenly mixed. Then add 0.334 g of a 50% styrene-butadiene rubber emulsion, stir for 30 minutes, and obtain a negative electrode conductive slurry containing graphene. Coat the slurry on a copper foil with a coating thickness of 100 μm. After drying at 80°C - 120°C under vacuum conditions, roll press to obtain a negative electrode sheet.

[0156] It can be seen from the SEM results that after adding graphene G-1, there is a lamellar structure composed of graphene in the electrode sheet, thus forming a planar conductive network in the electrode sheet, effectively reducing the internal resistance of the electrode sheet and playing a role in suppressing the volume expansion of the electrode sheet.

[0157] The resistivity of the electrode sheet measured by a four-probe tester is 0.392 Ω / cm.

[0158] Test experiment: Take the negative electrode sheet obtained in Example 10, use a lithium metal sheet as the positive electrode, use a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then, use the Blue Power LAND battery test system to conduct electrochemical performance tests. The test temperature is 25°C, the charge-discharge rate of the first cycle is 0.05C, the voltage range is 0.005V - 1.5V, the cyclic charge-discharge rate is 0.2C, and the voltage range is 0.005V - 1.5V. Test results: The initial Coulomb efficiency is 87.5%; at 0.2C, the capacity retention rate after 100 cycles is 92.3%, and the capacity retention rate after 400 cycles is about 50%.

[0159] Example 11

[0160] Mix 8 g of a 2% sodium carboxymethylcellulose solution with 0.64 g of a 25% polyacrylic acid solution evenly. Add 0.25 g of the obtained graphene G-1 and perform dispersion treatment by ball milling for 4 h. After the graphene is evenly dispersed in the slurry, add 0.25 g of carbon black and mix evenly to obtain a conductive agent slurry. Add 4 g of silicon-carbon material (the same as in Example 3) with a designed capacity of 500 mAhg -1 and ball mill for 30 minutes to make it mix evenly. Then add 0.334 g of a 50% styrene-butadiene rubber emulsion and stir for 30 minutes to obtain a graphene-containing negative electrode conductive slurry. Coat the slurry on a copper foil with a coating thickness of 100 μm. After drying at 80 °C to 120 °C under vacuum conditions, roll press to obtain a negative electrode sheet.

[0161] After adding graphene G-1, there is a sheet structure composed of graphene in the electrode sheet, thus forming a planar conductive network in the electrode sheet, effectively reducing the internal resistance of the electrode sheet and playing a role in suppressing the volume expansion of the electrode sheet.

[0162] The resistivity of the electrode sheet is measured to be 0.294 Ω / cm using a four-probe tester.

[0163] Test experiment: Take the negative electrode sheet obtained in Example 11, use a lithium metal sheet as the positive electrode, use a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then use a BlueTEC LAND battery test system to conduct electrochemical performance tests. The test temperature is 25 °C, the first charge-discharge rate is 0.05C, the voltage range is 0.005V - 1.5V, the cycle charge-discharge rate is 0.2C, and the voltage range is 0.005V - 1.5V. Test results: The first Coulomb efficiency is 85.3%; at 0.2C, the capacity retention rate after 100 cycles is 91.5%, and the capacity retention rate after 400 cycles is about 66%.

[0164] Example 12

[0165] Mix 8 g of a 2% sodium carboxymethylcellulose solution with 0.64 g of a 25% polyacrylic acid solution evenly. Add 0.4 g of the obtained graphene G-1 and perform dispersion treatment by ball milling for 4 h. After the graphene is evenly dispersed in the slurry, add 0.1 g of carbon black and mix evenly to obtain a conductive agent slurry. Add 4 g of silicon-carbon material (the same as in Example 3) with a designed capacity of 500 mAhg -1 and ball mill for 30 minutes to make it mix evenly. Then add 0.334 g of a 50% styrene-butadiene rubber emulsion and stir for 30 minutes to obtain a graphene-containing negative electrode conductive slurry. Coat the slurry on a copper foil with a coating thickness of 100 μm. After drying at 80 °C to 120 °C under vacuum conditions, roll press to obtain a negative electrode sheet.

[0166] After adding graphene G-1, there is a lamellar structure composed of graphene in the electrode sheet, thus forming a planar conductive network in the electrode sheet, effectively reducing the internal resistance of the electrode sheet and playing a role in suppressing the volume expansion of the electrode sheet.

[0167] The resistivity of the electrode sheet was measured to be 0.255 Ω / cm using a four-probe tester.

[0168] Test experiment: Take the negative electrode sheet obtained in Example 12, use a lithium metal sheet as the positive electrode, use a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then, use a Blue Power LAND battery test system to conduct electrochemical performance tests. The test temperature is 25 °C, the charge-discharge rate of the first cycle is 0.05C, the voltage range is 0.005V - 1.5V, the cycle charge-discharge rate is 0.2C, and the voltage range is 0.005V - 1.5V. Test results: The initial Coulomb efficiency is 82.9%; at 0.2C, the capacity retention rate after 100 cycles is 93.9%, and the capacity retention rate after 400 cycles is about 60%.

[0169] Example 13

[0170] 8 g of a 2% sodium carboxymethylcellulose solution and 0.64 g of a 25% polyacrylic acid solution were uniformly mixed. 0.5 mg of the obtained graphene G-1 was added, and ball milling was performed for 4 h for dispersion treatment. After the graphene was uniformly dispersed in the slurry, 0.495 g of carbon black was added and mixed evenly to obtain a conductive agent slurry. -1 To the obtained conductive agent slurry, 4 g of silicon-carbon material (the same as in Example 3) with a designed capacity of 500 mAh / g was added, and ball milling was performed for 30 minutes to make it uniformly mixed. Then, 0.334 g of a 50% styrene-butadiene rubber emulsion was added, and after stirring for 30 minutes, a negative electrode conductive slurry containing graphene was obtained. The slurry was coated on a copper foil with a coating thickness of 100 μm. After drying at 80 °C - 120 °C under vacuum conditions, a negative electrode sheet was obtained by rolling.

[0171] After adding graphene G-1, there is a lamellar structure composed of graphene in the electrode sheet, thus forming a planar conductive network in the electrode sheet, effectively reducing the internal resistance of the electrode sheet and playing a role in suppressing the volume expansion of the electrode sheet.

[0172] The resistivity of the electrode sheet was measured to be 0.343 Ω / cm using a four-probe tester.

[0173] Test experiment: Take the negative electrode sheet obtained in Example 13, use a lithium metal sheet as the positive electrode, a 1 mol / L LiPF6 solution as the electrolyte, and a polypropylene microporous membrane as the separator to assemble a CR2016 button battery. Then, use a Blue Energy LAND battery test system to conduct electrochemical performance tests. The test temperature is 25 °C, the charge-discharge rate of the first cycle is 0.05C, the voltage range is 0.005V - 1.5V, the cycle charge-discharge rate is 0.2C, and the voltage range is 0.005V - 1.5V. Test results: The first Coulomb efficiency is 88.9%; at 0.2C, the capacity retention rate after 100 cycles is 81.2%, and the capacity decays to 0 after 250 cycles.

[0174] Comparative Example 4

[0175] Mix 8 g of a 2% sodium carboxymethyl cellulose solution and 0.42 g of a 5% polyacrylic acid solution evenly. Add 0.5 g of carbon black and mix evenly by ball milling to obtain a conductive agent slurry. Add 4 g of silicon-carbon material (the same as in Example 3) to the obtained conductive agent slurry, and ball mill for 30 minutes to make it mix evenly. Then add 0.334 g of a 50% styrene-butadiene rubber emulsion and stir for 30 minutes to obtain a negative electrode conductive slurry. Coat the slurry on a copper foil with a coating thickness of 100 μm. After drying at 80 °C - 120 °C under vacuum conditions, roll press to obtain a negative electrode sheet. The resistivity of the sheet measured by a four-probe tester is 5.08 Ω / cm.

[0176] Test experiment: Take the negative electrode sheet obtained in Comparative Example 4 as the negative electrode, and the rest is the same as in Example 3. The test results are as Figure 13 shown: The first Coulomb efficiency is 89%, at 0.2C, the capacity retention rate after 100 cycles is 80.9%, and the capacity retention rate decays to 0 after 180 cycles.

[0177] Comparative Example 5

[0178] Mix 8 g of a 2% sodium carboxymethyl cellulose solution and 0.42 g of a 5% polyacrylic acid solution evenly. Add 5 mg of DG-1 graphene prepared in Comparative Example 1, and conduct dispersion treatment by ball milling for 4 h. After the graphene is evenly dispersed in the slurry, add 0.495 g of carbon black and mix evenly to obtain a conductive agent slurry. Add 4 g of silicon-carbon material (the same as in Example 3) to the obtained conductive agent slurry, and ball mill for 30 minutes to make it mix evenly. Then add 0.334 g of a 50% styrene-butadiene rubber emulsion and stir for 30 minutes to obtain a graphene-containing negative electrode conductive slurry. Coat the slurry on a copper foil with a coating thickness of 100 μm. After drying at 80 °C - 120 °C under vacuum conditions, roll press to obtain a negative electrode sheet.

[0179] Figure 14 is the SEM image of the negative electrode sheet obtained in Comparative Example 5. From Figure 14It can be seen that there is some graphene with a planar structure in the electrode sheet after adding graphene DG-1, but no large graphene sheet structure is formed.

[0180] The resistivity of the electrode sheet was measured to be 0.970 Ω / cm using a four-probe tester.

[0181] Test experiment: The negative electrode sheet obtained in Comparative Example 5 was used as the negative electrode, and the rest was the same as in Example 3. The test results are as Figure 15 shown: The initial Coulomb efficiency was 85.5%. At 0.2C, the capacity retention rate after 100 cycles was 87.9%. After 200 cycles, the capacity retention rate decayed to 21%.

[0182] Comparative Example 6

[0183] 8 g of a 2% sodium carboxymethyl cellulose solution was uniformly mixed with 0.42 g of a 5% polyacrylic acid solution. 5 mg of DG-2 graphene prepared in Comparative Example 2 was added, and ball milling was carried out for 4 h for dispersion treatment. After the graphene was uniformly dispersed in the slurry, 0.495 g of carbon black was added and mixed evenly to obtain a conductive agent slurry. 4 g of silicon-carbon material (the same as in Example 3) was added to the obtained conductive agent slurry, and ball milling was carried out for 30 minutes to make it evenly mixed. Then 0.334 g of a 50% styrene-butadiene rubber emulsion was added, and after stirring for 30 minutes, a negative electrode conductive slurry containing graphene was obtained. The slurry was coated on a copper foil with a coating thickness of 100 μm. After drying at 80 °C to 120 °C under vacuum conditions, a negative electrode sheet was obtained by rolling.

[0184] It can be seen from the SEM characterization that there is some graphene with a planar structure in the electrode sheet after adding graphene DG-2, but no large graphene sheet structure is formed.

[0185] The resistivity of the electrode sheet was measured to be 2.082 Ω / cm using a four-probe tester.

[0186] Test experiment: The negative electrode sheet obtained in Comparative Example 6 was used as the negative electrode, and the rest was the same as in Example 3. The test results are as follows: The initial Coulomb efficiency was 85.5%. At 0.2C, the capacity retention rate after 100 cycles was 86.4%. After 300 cycles, the capacity retention rate decayed to 20%.

[0187] Comparative Example 7

[0188] 8 g of a sodium carboxymethyl cellulose solution with a concentration of 2% was uniformly mixed with 0.42 g of a polyacrylic acid solution with a concentration of 5%. 5 mg of DG-3 graphene prepared in Comparative Example 2 was added, and ball milling was carried out for 4 h for dispersion treatment. After the graphene was uniformly dispersed in the slurry, 0.495 g of carbon black was added and mixed evenly to obtain a conductive agent slurry. 4 g of silicon-carbon material (the same as in Example 3) was added to the obtained conductive agent slurry, and ball milling was carried out for 30 minutes to make it uniformly mixed. Then 0.334 g of a styrene-butadiene rubber emulsion with a concentration of 50% was added, and after stirring for 30 minutes, a negative electrode conductive slurry containing graphene was obtained. The slurry was coated on a copper foil with a coating thickness of 100 μm. After drying at 80 °C to 120 °C under vacuum conditions, a negative electrode sheet was obtained by rolling.

[0189] It can be seen from the SEM characterization that there are some graphene with planar structures in the electrode sheet after adding graphene DG-3, but no large graphene sheet structures are formed.

[0190] The resistivity of the electrode sheet was measured to be 1.334 Ω / cm using a four-probe tester.

[0191] Test experiment: The negative electrode sheet obtained in Comparative Example 7 was used as the negative electrode, and the rest was the same as in Example 3. The test results are as follows: The initial Coulomb efficiency was 85.8%. At 0.2 C, the capacity retention rate after 100 cycles was 85.0%. After 250 cycles, the capacity retention rate decreased to 20%.

[0192] The embodiments described in the present invention are only used to illustrate the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, that is, the present invention does not depend on the steps described in the above embodiments to be implemented. In summary, any improvements made by those skilled in the art to the present invention, including the replacement of the raw materials and additives described in the present invention, the selection of specific implementation manners, etc., all belong to the protection scope and disclosure scope of the present invention.

Claims

1. A silicon-carbon negative electrode sheet, characterized in that, The silicon-carbon negative electrode sheet includes a graphene-containing conductive agent, a polymer binder, and a silicon-carbon material; in the Raman spectrum of the graphene, there are D peak and G peak, and I D / I G is below 0.10, the conductivity of the graphene is 2000-3500 S / cm; the graphene is powder graphene, which is a stack of petal-shaped graphene sheets and has a three-dimensional cage structure; the particle size of the graphene is 15-35 μm; the median particle size of the graphene sheets is 5-15 μm; the graphene sheets are 1-10 layers and the thickness is 0.5-3.0 nm; the tapped density of the graphene is 0.02-0.04 g / cm 3 ; in the graphene described above, based on the mass of the graphene, the carbon content is ≥99.50% and the oxygen content is below 300 ppm.

2. The silicon-carbon negative electrode sheet according to claim 1, characterized in that, The mass ratio of the graphene-containing conductive agent, polymer binder, and silicon-carbon material is (1-10):(1-10):(80-95).

3. The silicon-carbon negative electrode sheet according to claim 1 or 2, characterized in that, The polymer binder includes one or more of polyacrylic acid, polymethacrylic acid, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, lithium alginate, and styrene-butadiene rubber.

4. The silicon-carbon negative electrode sheet according to claim 3, wherein The polymer binder includes one or two of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

5. The silicon-carbon negative electrode sheet according to claim 3, characterized in that, In the polymer binder, the mass of sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose accounts for 25%-60%, the mass of polyacrylic acid and / or polymethacrylic acid accounts for 25%-60%, and the mass of styrene-butadiene rubber accounts for 5%-50%.

6. The silicon-carbon negative electrode sheet according to claim 1, wherein, The graphene-containing conductive agent further includes an auxiliary conductive agent; the mass ratio of the auxiliary conductive agent to graphene is (0.1-99.5):(0.5-99.9).

7. The silicon-carbon negative electrode sheet according to claim 6, characterized in that, The mass ratio of the auxiliary conductive agent to graphene is (50-99.5):(0.5-50).

8. The silicon-carbon negative electrode sheet according to claim 6, wherein The auxiliary conductive agent is selected from one or more of graphite, acetylene black, carbon nanotubes, Ketjen black, and conductive carbon black.

9. The silicon-carbon negative electrode sheet according to claim 6, wherein, The auxiliary conductive agent is conductive carbon black.

10. The silicon-carbon negative electrode sheet according to claim 1, characterized in that, In the graphene, based on the mass of graphene, the carbon content is 99.80%-99.95%.

11. The silicon-carbon negative electrode sheet according to claim 1, characterized in that, The median particle size of the graphene sheets is 8-15 μm.

12. The silicon-carbon negative electrode sheet according to claim 1, characterized in that, In the Raman spectrum of the graphene, I D / I G is 0.01 - 0.

10.

13. The silicon-carbon negative electrode sheet according to claim 1, characterized in that, In the Raman spectrum of the graphene, I D / I G is 0.03 - 0.

10.

14. The silicon-carbon negative electrode sheet according to claim 1, wherein, The specific surface area of the graphene is 50 - 300 m 2 / g.

15. The silicon-carbon negative electrode sheet according to claim 1, characterized in that, The specific surface area of the graphene is 100 - 250 m 2 / g.

16. The method for preparing the silicon-carbon negative electrode sheet according to any one of claims 1-5, 10-15, includes the following steps: (1) Mix the polymer binder with a solvent to obtain a binder solution; (2) Add graphene to the binder solution obtained in step (1) for dispersion treatment, and after mixing evenly, obtain a conductive agent slurry; (3) Add the silicon-carbon material to the conductive agent slurry obtained in step (2), and after mixing evenly, obtain a negative electrode slurry, and then coat the negative electrode slurry on a negative electrode current collector to prepare a silicon-carbon negative electrode sheet.

17. The preparation method according to claim 16, characterized in that, In step (1), the solvent is water.

18. The preparation method according to claim 16, characterized in that, In step (2), add the auxiliary conductive agent after the graphene is evenly dispersed in the slurry.

19. The preparation method according to claim 16, characterized in that, In step (3), the solid content of the negative electrode slurry is 15%-40% by mass.

20. The preparation method according to claim 16, characterized in that, The method for preparing the graphene includes the following steps: (1) Graphite is pre-expanded to obtain pre-expanded graphite; (2) Mix the pre-expanded graphite obtained in step (1), a wetting agent, and a solvent, and sequentially perform a first high-pressure homogenization treatment and a second high-pressure homogenization treatment to obtain a graphene slurry; wherein, the pressure of the second high-pressure homogenization treatment is 10-20 MPa higher than that of the first high-pressure homogenization treatment; the wetting agent is fatty amine polyoxyethylene ether; (3) Dry the graphene slurry obtained in step (2) to obtain graphene.

21. The preparation method according to claim 20, wherein, In the method for preparing the graphene, in step (2), the pressure of the first high-pressure homogenization treatment is 30-40 MPa, and the treatment time is 20-60 min; the pressure of the second high-pressure homogenization treatment is 40-50 MPa, and the treatment time is 10-30 min.

22. The preparation method according to claim 20, wherein, In the method for preparing the graphene, the HLB value of the fatty amine polyoxyethylene ether is ≥12.

23. A lithium-ion battery, characterized in that, Use the silicon-carbon negative electrode sheet according to any one of claims 1-15 as the negative electrode.

24. The lithium ion battery according to claim 23, characterized in that, The lithium-ion battery includes a liquid lithium-ion battery, a semi-solid lithium-ion battery or a solid-state lithium-ion battery.

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