An intermediate phase carbon microspheres-silicon carbon composite slurry, a preparation method thereof, a negative electrode sheet, a lithium ion battery and an electric device

Abstract

This application provides a mesophase carbon microsphere-silicon-carbon composite slurry and its preparation method, a negative electrode sheet, a lithium-ion battery, and electrical equipment, relating to the field of lithium-ion batteries. The mesophase carbon microsphere-silicon-carbon composite slurry comprises a first component and a second component; the raw materials of the first component, based on 100% by mass, include: 10%-30% silicon-carbon powder, 45%-80% mesophase carbon microspheres, 0.5%-2% conductive powder, 5%-20% conductive slurry, and 0.5%-5% hydrogenated nitrile rubber; the second component includes ethyl acetate and butanone; the mass ratio of the first component to the second component is 1:1-5. This mesophase carbon microsphere-silicon-carbon composite slurry solves the difficulties in preparing mesophase carbon microspheres and silicon-carbon materials using aqueous adhesives, which is beneficial for coating integrity and yield. Simultaneously, the mixing of conductive powder and conductive slurry in the slurry further improves the ionic conductivity of the mesophase carbon microsphere-silicon-carbon composite negative electrode sheet and reduces the polarization of the lithium battery.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and more particularly to a mesophase carbon microsphere-silicon-carbon composite slurry and its preparation method, a negative electrode sheet, a lithium-ion battery, and electrical equipment. Background Technology

[0002] Silicon-carbon materials have advantages such as high capacity and high lithium intercalation potential, but their low compaction density and large lithium intercalation expansion limit their application. Mesophase carbon microspheres have advantages such as high sphericity, high tapping density, and low expansion, and can be used as a matrix for silicon-based materials to buffer the expansion of silicon anodes and improve the compaction density of silicon-carbon materials.

[0003] Currently, most silicon-carbon anode materials are produced using an aqueous homogenization process. Due to the characteristics of silicon-based anode material production processes, nano-silicon particles are inevitably deposited on the surface. These active nano-silicon particles react with water during homogenization to generate hydrogen gas, which easily leads to bubbles in the slurry. Subsequent coating processes may result in defects such as pits and exposed foil. Mesophase carbon microspheres, due to their low surface defects and high sphericity, are difficult to anchor in aqueous slurries by hydrophilic binders. They also have weak interaction with binders such as SBR and CMC, making the slurry prone to sedimentation and causing defects such as exposed foil during coating. Currently, mesophase carbon microsphere anodes on the market must be homogenized using the NMP-PVDF solvent method. However, NMP solvent is corrosive, requires a recycling system, and is not environmentally friendly.

[0004] Therefore, there is an urgent need to provide a negative electrode slurry to solve the above problems. Summary of the Invention

[0005] The purpose of this application is to provide a mesophase carbon microsphere-silicon carbon composite slurry and its preparation method, a negative electrode sheet, a lithium-ion battery, and an electrical device to solve the above-mentioned problems.

[0006] To achieve the above objectives, the first aspect of this application provides a mesophase carbon microsphere-silicon carbon composite slurry, comprising a first component and a second component;

[0007] The raw materials of the first component, based on a total mass of 100%, include:

[0008] Silicon carbide powder 10%-30%, mesophase carbon microspheres 45%-80%, conductive powder 0.5%-2%, conductive slurry 5%-20%, hydrogenated nitrile rubber 0.5%-5%;

[0009] The second component includes ethyl acetate and butanone;

[0010] The mass ratio of the first component to the second component is 1:1-5.

[0011] Optionally, the mesophase carbon microsphere-silicon carbon composite slurry satisfies at least one of the following conditions:

[0012] A. The D50 of the mesophase carbon microspheres is 10μm-15μm;

[0013] B. The dispersion of the mesophase carbon microspheres is 0.9-1.5;

[0014] C. The D50 of the silicon carbide powder is 5μm-8μm;

[0015] D. The dispersion of the silicon carbide powder is 1-1.5;

[0016] E. The silicon-carbon powder is located in the gaps between the mesophase carbon microspheres.

[0017] Optionally, the mesophase carbon microsphere-silicon carbon composite slurry satisfies at least one of the following conditions:

[0018] A. The solid content in the conductive paste is 0.4%-5% by mass;

[0019] B. The conductive agent in the conductive paste includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene;

[0020] C. The solvent in the conductive paste includes ester solvents;

[0021] In some embodiments, ester solvents include methyl acetate and / or propyl acetate;

[0022] D. The conductive powder includes one or more of Super-P, conductive carbon black, and graphene powder.

[0023] Optionally, the mesophase carbon microsphere-silicon carbon composite slurry satisfies at least one of the following conditions:

[0024] A. The second component, based on a total volume of 100%, includes:

[0025] 10%-40% ethyl acetate, 60%-90% butanone;

[0026] B. The viscosity of the mesophase carbon microsphere-silicon carbon composite slurry is 3000 mPa·s-10000 mPa·s.

[0027] A second aspect of this application provides a method for preparing the aforementioned mesophase carbon microsphere-silicon carbon composite slurry, comprising:

[0028] The first component and the second component are mixed to prepare the product.

[0029] In some embodiments, mixing is carried out in a mixer, preferably a double planetary mixer. It is understood that other forms of mixers disclosed in the prior art or not disclosed in the new technology, i.e., other types of mixers capable of mixing, can also be used for mixing.

[0030] Optionally, the mixing includes:

[0031] Hydrogenated nitrile rubber and a portion of the second component are first mixed to obtain a first mixture;

[0032] The first mixture and the conductive powder are mixed a second time to obtain a second mixture;

[0033] The second mixture, mesophase carbon microspheres, and silicon carbide powder are mixed in a third mixture to obtain a third mixture.

[0034] The third mixture, the conductive slurry, and the remaining second component are mixed in a fourth mixture to obtain the mesophase carbon microsphere-silicon carbon composite slurry.

[0035] Optionally, the preparation method of the mesophase carbon microsphere-silicon carbon composite slurry satisfies at least one of the following conditions:

[0036] A. The first mixture has a revolution speed of 15 rpm-25 rpm, a dispersion speed of 500 rpm-1500 rpm, a stirring time of 120 min-180 min, and a temperature of 50℃-65℃;

[0037] B. The second mixing includes a first stirring and a second stirring performed sequentially;

[0038] The dispersion speed of the first stirring is 100-500 rpm, and the time is 30-60 min;

[0039] The second stirring motion has a revolution speed of 20-30 rpm, a dispersion speed of 2000-3000 rpm, and a time of 60-180 min;

[0040] The temperatures of the first stirring and the second stirring are each independently 25℃-30℃;

[0041] C. The third mixing includes a third stirring and a fourth stirring performed sequentially;

[0042] The third stirring motion has a revolution speed of 10-15 rpm, a dispersion speed of 500-1000 rpm, and a time of 30-60 min.

[0043] The fourth stirring motion has a revolution speed of 20-30 rpm, a dispersion speed of 2500-3500 rpm, and a time of 120-180 min.

[0044] The temperatures of the third and fourth stirring operations are each independently 25℃-30℃;

[0045] D. The fourth mixture has a revolution speed of 15-25 rpm, a dispersion speed of 1000-2000 rpm, a time of 30-60 min, and a temperature of 25℃-30℃;

[0046] E. Based on the total mass of the second component being 100%, it includes:

[0047] 80%-90% of the second component, and 10%-20% of the remaining second component.

[0048] A third aspect of this application provides a negative electrode sheet comprising the aforementioned mesophase carbon microsphere-silicon carbon composite slurry.

[0049] A fourth aspect of this application provides a lithium-ion battery, including the aforementioned negative electrode sheet.

[0050] The fifth aspect of this application provides an electrical device including the aforementioned lithium-ion battery.

[0051] Compared with the prior art, the beneficial effects of this application include:

[0052] The mesophase carbon microsphere-silicon carbon composite slurry provided in this application uses hydrogenated nitrile butadiene rubber as a binder, which has the advantages of good adhesion and high peel strength. The hydrogenated nitrile butadiene rubber is soluble in the oil-based solvent of the second component. Butanone and ethyl acetate can dissolve the hydrogenated nitrile butadiene rubber. Furthermore, ethyl acetate, as a low-boiling-point solvent and a low-surface-tension solvent, can balance the coating and electrode drying effects, thus preparing an electrode with good surface condition. This mesophase carbon microsphere-silicon carbon composite slurry solves the difficulties in preparing mesophase carbon microspheres and silicon carbon materials using aqueous slurries, which is beneficial to the integrity and yield of coating. At the same time, the slurry contains conductive powder and conductive slurry, which further improves the ionic conductivity of the mesophase carbon microsphere-silicon carbon composite negative electrode and reduces the polarization of lithium batteries.

[0053] The method for preparing mesophase carbon microsphere-silicon carbon composite slurry provided in this application is simple to operate and can uniformly mix the mesophase carbon microsphere-silicon carbon composite slurry, eliminating the disadvantage of gas generation in silicon carbon anode homogenization.

[0054] The negative electrode sheet provided in this application has the characteristics of low expansion and high peel strength.

[0055] The lithium-ion battery provided in this application has the characteristics of long cycle life and high energy density.

[0056] The electrical equipment provided in this application features high power, long battery life, and long service life. Attached Figure Description

[0057] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0058] Figure 1 The flowchart shows the preparation method of the mesophase carbon microsphere-silicon carbon composite slurry provided in Example 1. Detailed Implementation

[0059] As used in this article:

[0060] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0061] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0062] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0063] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0064] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0065] The first aspect of this application provides a mesophase carbon microsphere-silicon carbon composite slurry, comprising a first component and a second component;

[0066] The raw materials of the first component, based on a total mass of 100%, include:

[0067] Silicon carbide powder 10%-30%, mesophase carbon microspheres 45%-80%, conductive powder 0.5%-2%, conductive slurry 5%-20%, hydrogenated nitrile rubber 0.5%-5%;

[0068] Optionally, the raw materials of the first component, based on a total mass of 100%, may include silicon carbide powder at any value between 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or 10%-30%; and mesophase carbon microspheres at any value between 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%. The percentages of conductive powder can be any value between 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or 0.5%-2%. The percentages of conductive paste can be any value between 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or 5%-20%. The percentages of hydrogenated nitrile rubber can be any value between 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or 0.5%-5%.

[0069] It is important to note that the macromolecular hydrogenated nitrile butadiene rubber (HNBR) can act as a dispersant and binder for silicon-carbon powder and mesophase carbon microspheres. Through physical interactions such as electrostatic attraction and van der Waals forces, it forms a strong bond with the silicon-carbon anode surface. Simultaneously, it forms chemical bonds on the silicon-carbon powder surface, with the hydrogen atoms (H) of the HNBR forming stable hydrogen bonds with the hydroxyl groups on the silicon surface. This allows the mesophase carbon microspheres and silicon-carbon powder to remain stably suspended in the slurry. After the electrode is formed, the HNBR provides strong adhesion, preventing issues such as powder shedding. Furthermore, the conductive powder and conductive slurry in the slurry can construct a conductive network, giving the electrode optimal conductivity. Additionally, the conductive powder and conductive slurry possess one-dimensional and two-dimensional conductive structures. From a contact structure perspective, the conductive powder (SP) and carbon black form point-contact conductive networks between silicon-carbon and graphite, respectively; the conductive slurry (CNT) and graphene form line- and surface-contact conductive networks between the active materials. The point, line, and surface contact conductive network is more complete, shortens the electron transmission distance, reduces the electron transmission impedance and reduces polarization. In particular, due to the small particle size of the conductive powder, it can be dispersed in the gaps between silicon-carbon and mesophase carbon microspheres, playing a conductive connection role.

[0070] In some embodiments, silicon carbon powder can be prepared by vapor deposition or grinding processes;

[0071] The second component includes ethyl acetate and butanone;

[0072] The mass ratio of the first component to the second component is 1:1-5.

[0073] Optionally, the mass ratio of the first component and the second component can be any value between 1:1, 1:2, 1:3, 1:4, 1:5, or 1:1-5.

[0074] It should be noted that the viscosity of the slurry is optimal and meets the viscosity requirements for coating when the mass ratio of the first component to the second component is 1:1-5.

[0075] In some embodiments, the mesophase carbon microsphere-silicon carbon composite slurry satisfies at least one of the following conditions:

[0076] A. The D50 of the mesophase carbon microspheres is 10μm-15μm;

[0077] Optionally, the D50 of the mesophase carbon microspheres can be any value between 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 10 μm-15 μm;

[0078] B. The dispersion of the mesophase carbon microspheres is 0.9-1.5;

[0079] Optionally, the dispersion of the mesophase carbon microspheres can be any value between 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 or 0.9-1.5;

[0080] C. The D50 of the silicon carbide powder is 5μm-8μm;

[0081] Optionally, the D50 of the silicon carbide powder can be any value between 5μm, 6μm, 7μm, 8μm, or 5μm-8μm;

[0082] D. The dispersion of the silicon carbide powder is 1-1.5;

[0083] Optionally, the dispersion of the silicon carbide powder can be 1, 1.1, 1.2, 1.3, 1.4, 1.5 or any value between 1 and 1.5;

[0084] E. The silicon-carbon powder is located in the gaps between the mesophase carbon microspheres.

[0085] It should be noted that by adjusting the particle size of the mesophase carbon microspheres and silicon carbide powder, the silicon carbide powder can fill the gaps between the mesophase carbon microspheres; at the same time, the mesophase carbon microspheres can act as an expansion buffer matrix for the silicon carbide powder, thus alleviating the expansion of the electrode.

[0086] In some embodiments, the mesophase carbon microsphere-silicon carbon composite slurry satisfies at least one of the following conditions:

[0087] A. The solid content in the conductive paste is 0.4%-5% by mass;

[0088] Optionally, the solid content in the conductive paste can be any value between 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, or 0.4%-5%.

[0089] B. The conductive agent in the conductive paste includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene;

[0090] It is important to note that the conductive agent in the conductive paste can form a conductive network in the paste, further improving the conductivity of the paste. Secondly, the conductive paste can prevent the expansion of silicon carbon particles from causing the failure of the conductive network of the negative electrode. In addition, single-walled carbon nanotubes, multi-walled carbon nanotubes and graphene have high strength and conductivity, and their unique one-dimensional and two-dimensional structures can strongly adhere to the surface of silicon carbon particles.

[0091] Preferably, the conductive agent includes single-walled carbon nanotubes; since single-walled carbon nanotubes have the highest conductivity and the best strength, they can be used as the preferred conductive agent.

[0092] C. The solvent in the conductive paste includes ester solvents;

[0093] D. The conductive powder includes one or more of Super-P, conductive carbon black, and graphene powder.

[0094] Preferably, the conductive powder includes graphene, which, as a two-dimensional structure, can be dispersed on the surface of silicon carbon to achieve uniform coverage.

[0095] In some embodiments, the mesophase carbon microsphere-silicon carbon composite slurry satisfies at least one of the following conditions:

[0096] A. The second component, based on a total volume of 100%, includes:

[0097] 10%-40% ethyl acetate, 60%-90% butanone;

[0098] Optionally, the second component, based on 100% of the total volume, may include ethyl acetate, which may be any value between 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or between 10% and 40%; and butanone, which may be any value between 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or between 60% and 90%.

[0099] It is important to note that by adjusting the volume ratio of butanone and ethyl acetate, the raw materials in the first component can achieve maximum solubility in the second component.

[0100] B. The viscosity of the mesophase carbon microsphere-silicon carbon composite slurry is 3000 mPa·s-10000 mPa·s.

[0101] Optionally, the viscosity of the mesophase carbon microsphere-silicon carbon composite slurry can be any value between 3000 mPa·s, 4000 mPa·s, 5000 mPa·s, 6000 mPa·s, 7000 mPa·s, 8000 mPa·s, 9000 mPa·s, 10000 mPa·s, or 3000 mPa·s-10000 mPa·s.

[0102] It should be noted that within this viscosity range, the slurry achieves the best leveling effect, has good fluidity, and is easy to obtain a negative electrode sheet with a good surface condition.

[0103] A second aspect of this application provides a method for preparing the aforementioned mesophase carbon microsphere-silicon carbon composite slurry, comprising:

[0104] The first component and the second component are mixed to prepare the product.

[0105] In some embodiments, the mixing includes:

[0106] Hydrogenated nitrile rubber and a portion of the second component are first mixed to obtain a first mixture;

[0107] The first mixture and the conductive powder are mixed a second time to obtain a second mixture;

[0108] The second mixture, mesophase carbon microspheres, and silicon carbide powder are mixed in a third mixture to obtain a third mixture.

[0109] The third mixture, the conductive slurry, and the remaining second component are mixed in a fourth mixture to obtain the mesophase carbon microsphere-silicon carbon composite slurry.

[0110] It should be noted that the second component is added in stages. The second component, which is mixed with the hydrogenated nitrile butadiene rubber, plays a role in dispersing and dissolving the hydrogenated nitrile butadiene rubber. The remaining second component is beneficial for dispersing the conductive slurry and adjusting its viscosity.

[0111] In some embodiments, the method for preparing the mesophase carbon microsphere-silicon carbon composite slurry satisfies at least one of the following conditions:

[0112] A. The first mixture has a revolution speed of 15 rpm-25 rpm, a dispersion speed of 500 rpm-1500 rpm, a stirring time of 120 min-180 min, and a temperature of 50℃-65℃;

[0113] Optionally, the revolution speed of the first mixture can be any value between 15 rpm, 16 rpm, 17 rpm, 18 rpm, 19 rpm, 20 rpm, 21 rpm, 22 rpm, 23 rpm, 24 rpm, 25 rpm, or 15 rpm; the dispersion speed can be 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, or 1500 rpm. The stirring time can be any value between 500 rpm and 1500 rpm, or 120 min, 130 min, 140 min, 150 min, 160 min, 170 min, 180 min, or 120 min - 180 min, or any value between 120 min and 180 min, and the temperature can be any value between 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, or 50℃ - 65℃.

[0114] It should be noted that high-temperature dispersion and mixing can improve the solubility of hydrogenated nitrile rubber, reduce mixing time, and improve mixing efficiency.

[0115] B. The second mixing includes a first stirring and a second stirring performed sequentially;

[0116] The dispersion speed of the first stirring is 100-500 rpm, and the time is 30-60 min;

[0117] Optionally, the dispersion speed of the first stirring can be any value between 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, or 100-500 rpm, and the time can be any value between 30 min, 35 min, 40 min, 45 min, 50 min, or 30-60 min.

[0118] The second stirring motion has a revolution speed of 20-30 rpm, a dispersion speed of 2000-3000 rpm, and a time of 60-180 min;

[0119] Optionally, the revolution speed of the second stirring can be any value between 20 rpm, 21 rpm, 22 rpm, 23 rpm, 24 rpm, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, 30 rpm, or 20-30 rpm; the dispersion speed can be any value between 2000 rpm, 2100 rpm, 2200 rpm, 2300 rpm, 2400 rpm, 2500 rpm, 2600 rpm, 2700 rpm, 2800 rpm, 2900 rpm, 3000 rpm, or 2000-3000 rpm; and the time can be any value between 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 170 min, 180 min, or 60-180 min.

[0120] The temperatures of the first stirring and the second stirring are each independently 25℃-30℃;

[0121] Optionally, the temperatures of the first and second stirring can be independently set to 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, or any value between 25°C and 30°C.

[0122] It should be noted that two stirring processes are used. The first stirring uses low-speed dispersion to initially mix the conductive powder and avoid the conductive powder from escaping under high-speed dispersion. The second stirring uses high-speed dispersion at room temperature, which helps to improve the dispersion effect of the conductive powder in the first mixture.

[0123] C. The third mixing includes a third stirring and a fourth stirring performed sequentially;

[0124] The third stirring motion has a revolution speed of 10-15 rpm, a dispersion speed of 500-1000 rpm, and a time of 30-60 min.

[0125] Optionally, the revolution speed of the third stirring can be any value between 10 rpm, 11 rpm, 12 rpm, 13 rpm, 14 rpm, 15 rpm or 10-15 rpm, the dispersion speed can be any value between 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm or 500-1000 rpm, and the time can be any value between 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min or 30-60 min;

[0126] The fourth stirring motion has a revolution speed of 20-30 rpm, a dispersion speed of 2500-3500 rpm, and a time of 120-180 min.

[0127] Optionally, the revolution speed of the fourth stirring can be any value between 20 rpm, 21 rpm, 22 rpm, 23 rpm, 24 rpm, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, 30 rpm, or 20-30 rpm; the dispersion speed can be any value between 2500 rpm, 2600 rpm, 2700 rpm, 2800 rpm, 2900 rpm, 3000 rpm, 3100 rpm, 3200 rpm, 3300 rpm, 3400 rpm, 3500 rpm, or 2500-3500 rpm; and the time can be any value between 120 min, 130 min, 140 min, 150 min, 160 min, 170 min, 180 min, or 120-180 min.

[0128] The temperatures of the third and fourth stirring operations are each independently 25℃-30℃;

[0129] Optionally, the temperatures of the third and fourth stirring can be independently set to 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, or any value between 25°C and 30°C.

[0130] It is important to note that two stirring processes are employed. The third stirring uses low-speed dispersion to initially mix the mesophase carbon microspheres and silicon carbide powder with the second mixture, thus preventing the mesophase carbon microspheres and silicon carbide powder from escaping under high-speed dispersion. The fourth stirring uses high-speed dispersion at room temperature, which is beneficial for improving the dispersion effect of the mesophase carbon microspheres and silicon carbide powder in the second mixture.

[0131] D. The fourth mixture has a revolution speed of 15-25 rpm, a dispersion speed of 1000-2000 rpm, a time of 30-60 min, and a temperature of 25℃-30℃;

[0132] Optionally, the revolution speed of the fourth mixture can be any value between 15 rpm, 16 rpm, 17 rpm, 18 rpm, 19 rpm, 20 rpm, 21 rpm, 22 rpm, 23 rpm, 24 rpm, 25 rpm, or 15 rpm-25 rpm; the dispersion speed can be any value between 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm, 2000 rpm, or 1000-2000 rpm; the time can be any value between 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, or 30-60 min; and the temperature can be any value between 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, or 25℃-30℃.

[0133] It should be noted that all components in the fourth mixture are liquids, which can be mixed evenly at a moderate stirring speed and time, without the need for high-speed and long-term stirring to achieve a uniform mixing effect.

[0134] E. Based on the total mass of the second component being 100%, it includes:

[0135] 80%-90% of the second component, and 10%-20% of the remaining second component.

[0136] Optionally, the mass of a portion of the second component can be any value between 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or 80%-90% of the total mass of the second component, and the mass of the remaining second component can be any value between 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or 10%-20% of the total mass of the second component.

[0137] A third aspect of this application provides a negative electrode sheet comprising the aforementioned mesophase carbon microsphere-silicon carbon composite slurry.

[0138] A fourth aspect of this application provides a lithium-ion battery, including the aforementioned negative electrode sheet.

[0139] The fifth aspect of this application provides an electrical device including the aforementioned lithium-ion battery.

[0140] Optionally, the electrical equipment may include, but is not limited to, mobile devices, electric vehicles, electric ships, electric aircraft, electric trains and satellites, energy storage systems, etc.; among which, mobile devices may include, but are not limited to, at least one of mobile phones, laptops, etc.; electric vehicles may include, but are not limited to, at least one of pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0141] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0142] Example 1

[0143] The first aspect of this embodiment provides a mesophase carbon microsphere-silicon carbide composite slurry with a viscosity of 6000 mPa·s, comprising a first component and a second component; the raw materials of the first component, based on a total mass of 100%, include:

[0144] 20% silicon carbide powder, 70% mesophase carbon microspheres, 1% conductive powder Super-P powder, 8% conductive slurry, and 1% hydrogenated nitrile rubber.

[0145] Among them, the D50 of the mesophase carbon microspheres is 12 μm and the dispersion is 0.9; the D50 of the silicon carbon powder is 6 μm and the dispersion is 1; the solid mass content of the conductive paste is 0.4%, the conductive agent is single-walled carbon nanotubes, and the solvent is ethyl acetate;

[0146] The second component consists of ethyl acetate and butanone, wherein the volume ratio of ethyl acetate to butanone is 10%:90%.

[0147] The mass ratio of the first component to the second component is 1:1.

[0148] The second aspect of this embodiment provides a method for preparing a mesophase carbon microsphere-silicon carbide composite slurry, which involves weighing the materials according to the amounts required in the aforementioned mesophase carbon microsphere-silicon carbide composite slurry, specifically including:

[0149] S1: Preparation of hydrogenated nitrile butadiene rubber solution: Hydrogenated nitrile butadiene rubber powder and part of the second component (accounting for 90% of the total mass of the second component) are mixed in a double planetary mixer and stirred at a linear speed of 15 rpm and 500 rpm for 120 min at a stirring temperature of 55℃.

[0150] S2: Preparation of slurry containing conductive powder: Weigh Super-P powder and add it to the hydrogenated nitrile rubber solution obtained in step S1. Stir for 30 minutes at a revolution speed of 10 rpm and a dispersion speed of 500 rpm. Then stir for 120 minutes at a revolution speed of 25 rpm and a dispersion speed of 3000 rpm. The temperature of the stirring tank is 25℃ for both stirring.

[0151] S3: Preparation of mixed slurry: Mesophase carbon microspheres and silicon carbide powder are respectively added to the slurry of conductive powder prepared in S2 above, and then mixed in a double planetary mixer. The first stirring is carried out for 60 minutes under the conditions of the revolution speed of the mixing tank being 15 rpm and the dispersion speed being 500 rpm. Then, the second stirring is carried out for 180 minutes under the conditions of the revolution speed being 30 rpm and the dispersion speed being 3000 rpm. The temperature of the mixing tank is 25℃ for both stirrings.

[0152] S4: Preparation of mesophase carbon microsphere-silicon carbon composite slurry: The conductive slurry is added to the mixed slurry prepared above. The mixture is stirred for 60 minutes at a revolution speed of 25 rpm and a dispersion speed of 3000 rpm. Then, the remaining second component (accounting for 10% of the total mass of the second component) is added. The mixture is stirred for 30 minutes at a revolution speed of 15 rpm and a dispersion speed of 1500 rpm to obtain the mesophase carbon microsphere-silicon carbon composite negative electrode slurry.

[0153] The preparation process of this mesophase carbon microsphere-silicon carbon composite slurry is as follows: Figure 1 As shown.

[0154] Example 2

[0155] The difference from Example 1 is that the raw materials of the first component in this example, based on a total mass of 100%, include:

[0156] The composition consists of 20% silicon carbide powder, 71% mesophase carbon microspheres, 1% Super-P conductive powder, 5% conductive slurry, and 3% hydrogenated nitrile rubber.

[0157] The preparation method is the same as in Example 1.

[0158] Example 3

[0159] The difference from Example 1 is that the raw materials of the first component in this example, based on a total mass of 100%, include:

[0160] 20% silicon carbide powder, 54% mesophase carbon microspheres, 1% conductive powder Super-P powder, 20% conductive slurry, and 5% hydrogenated nitrile rubber.

[0161] The preparation method is the same as in Example 1.

[0162] Example 4

[0163] The difference from Example 1 is that the volume ratio of ethyl acetate to butanone in the second component of this example is 30%:70%.

[0164] The preparation method is the same as in Example 1.

[0165] Example 5

[0166] The difference from Example 1 is that the raw materials of the first component in this example, based on a total mass of 100%, include:

[0167] The composition consists of 20% silicon carbon powder, 70% mesophase carbon microspheres, 1% conductive graphene powder, 8% conductive slurry, and 1% hydrogenated nitrile rubber.

[0168] The preparation method is the same as in Example 1.

[0169] Example 6

[0170] The difference from Example 1 is: 20% silicon carbon powder, 70% mesophase carbon microspheres, 1% conductive powder Super-P powder, 8% conductive slurry, and 1% hydrogenated nitrile rubber.

[0171] The conductive agent in the conductive paste is graphene.

[0172] The preparation method is the same as in Example 1.

[0173] Example 7

[0174] The difference from Example 1 is that the first and second components provided in Example 1 are directly mixed, with a revolution speed of 15 rpm, a dispersion speed of 1500 rpm, a stirring time of 240 min, and a temperature of 25°C, to obtain an intermediate phase carbon microsphere-silicon carbon composite negative electrode slurry.

[0175] Comparative Example 1

[0176] The difference from Example 1 is that conductive powder is not added and step S2 is omitted, while the rest of the preparation methods and parameters are the same as in Example 1.

[0177] Comparative Example 2

[0178] The difference from Example 1 is that no conductive paste is added and step S4 is omitted, while the rest of the preparation methods and parameters are the same as in Example 1.

[0179] Comparative Example 3

[0180] The difference from Example 1 is that the D50 of the mesophase carbon microspheres is 5 μm, and the D50 of the silicon carbide powder is 10 μm.

[0181] Comparative Example 4

[0182] The difference from Example 1 is that no mesophase carbon microspheres are added.

[0183] Comparative Example 5

[0184] The difference from Example 1 is that no silicon carbide powder is added.

[0185] Comparative Example 6

[0186] The difference from Example 1 is that hydrogenated nitrile rubber is replaced with an equal mass of polyvinylidene fluoride.

[0187] Comparative Example 7

[0188] The difference from Example 1 is that ethyl acetate is not added to the second component.

[0189] Comparative Example 8

[0190] The difference from Example 1 is that no butanone is added to the second component.

[0191] Comparative Example 9

[0192] The difference from Example 1 is that the volume ratio of ethyl acetate to butanone in the second component is 5%:95%.

[0193] Comparative Example 10

[0194] The difference from Example 1 is that the mass ratio of the first component to the second component is 1:6.

[0195] The mesophase carbon microsphere-silicon-carbon composite slurry prepared in the examples and comparative examples was coated on the surface of copper foil to obtain mesophase carbon microsphere-silicon-carbon composite negative electrode sheets. After being rolled to a certain thickness, the 24H electrode sheet roll rebound and peel force were tested. The above silicon-carbon negative electrode sheet and positive electrode sheet were stacked, packaged, injected with liquid, formed, capacity tested, aged, and sorted to prepare lithium batteries with mesophase carbon microsphere-silicon-carbon negative electrodes. Then, the prepared lithium batteries were tested for initial discharge specific capacity, first-cycle coulombic efficiency, and 1000-cycle capacity retention rate at 25°C using a blue electric test cabinet. The test results are shown in Table 1.

[0196] Table 1 Performance Tests

[0197]

[0198] analyze:

[0199] As can be seen from the above tests, compared with Example 1, as the mass ratio of hydrogenated nitrile rubber in Example 2 increases, the rebound expansion of the electrode decreases. The addition of higher hydrogenated nitrile rubber enhances the adhesion of the electrode, which is beneficial to the cycle performance.

[0200] As can be seen from Examples 1 and 3, as the mass ratio of conductive paste and hydrogenated nitrile rubber increases, the electrode rebound and full-charge expansion decrease. This is because the high adhesion of hydrogenated nitrile rubber and the strength of conductive paste powder constrain the expansion of silicon-carbon material. Due to the increase in the proportion of conductive paste, its film resistivity also decreases significantly.

[0201] As can be seen from Examples 1 and 4, the optimal ratio of ethyl acetate to methyl ethyl ketone is 30%:70%. At this ratio, methyl ethyl ketone has strong solubility and can fully dissolve hydrogenated nitrile rubber. Ethyl acetate has the lowest boiling point and lowest surface tension, which balances the coating and drying effect, keeping the electrode in a good coating state, thereby improving battery performance.

[0202] Comparing Examples 1 and 5, it can be seen that the performance of conductive graphene powder is greater than that of SuperP, and the conductivity and strength of two-dimensional sheet graphene are higher than those of SuperP, resulting in lower film resistance and better cycle performance of the electrode.

[0203] Comparing Examples 1 and 6, it can be seen that graphene outperforms single-walled carbon nanotubes in conductive pastes. Graphene, being a two-dimensional layered distribution, has a closer contact with the surface of the active material. The conductive paste with added graphene can also significantly reduce impedance and improve conductivity.

[0204] Comparing Examples 1 and 7, it can be seen that the electrode prepared by directly mixing the first and second components has poor performance. This may be due to the uneven dispersion of silicon carbon and graphite active materials with conductive powder, resulting in poor electrode performance.

[0205] Comparing Example 1 with Comparative Examples 1 and 2, it can be seen that conductive paste and conductive powder affect the electrode film resistance. Comparative Examples 1 and 2, without the addition of conductive powder and conductive paste, will result in higher battery impedance and poorer cycle performance.

[0206] Comparing Example 1 and Comparative Example 3, it can be seen that when the particle size of the mesophase carbon microspheres is smaller than that of the silicon-carbon powder, the mesophase carbon microspheres cannot provide an expansion gap for the silicon-carbon anode, resulting in poor cycle performance and large expansion.

[0207] Comparing Example 1 with Comparative Examples 4 and 5, it can be seen that the silicon-carbon anode is the essential factor affecting electrode expansion and performance degradation. A single silicon-carbon anode expands significantly, and without intermediate phase carbon microspheres as a buffer matrix, the battery cycle performance degrades rapidly.

[0208] Comparing Example 1 and Comparative Example 6, it can be seen that hydrogenated nitrile rubber has higher bonding strength than polyvinylidene fluoride. Due to its higher bonding strength, it can maintain the integrity of the negative electrode structure and contribute to the improvement of cycle performance.

[0209] Comparing Example 1 with Comparative Examples 7-9, it can be seen that the slurry has better performance when both ethyl acetate and methyl ethyl ketone are present as dispersion solvents. The optimal ratio is 10% to 90% by volume of ethyl acetate and methyl ethyl ketone. Methyl ethyl ketone can fully dissolve and disperse hydrogenated nitrile rubber, while ethyl acetate can balance the coating effect, prevent electrode cracking, and give the electrode the best performance.

[0210] Compared to Example 1, Comparative Example 10 has an increased proportion of the second component, more solvent components in the slurry, lower system viscosity, and unstable slurry, which leads to poor coating effect and weaker overall battery performance.

[0211] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0212] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A mesophase carbon microsphere-silicon carbon composite slurry, characterized in that, Includes the first component and the second component; The raw materials of the first component, based on a total mass of 100%, have the following composition: Silicon carbide powder 10%-30%, mesophase carbon microspheres 45%-80%, conductive powder 0.5%-2%, conductive slurry 5%-20%, hydrogenated nitrile rubber 0.5%-5%; The second component consists of ethyl acetate and butanone; The mass ratio of the first component to the second component is 1:1-5; The D50 of the mesophase carbon microspheres is 10μm-15μm; The D50 of the silicon carbide powder is 5μm-8μm; The conductive agent in the conductive slurry includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene. The conductive powder includes one or more of conductive carbon black and graphene powder. The second component, based on a total volume of 100%, has the following composition: 10%-40% ethyl acetate, 60%-90% butanone.

2. The mesophase carbon microsphere-silicon carbon composite slurry according to claim 1, characterized in that, At least one of the following conditions must be met: B. The dispersion of the mesophase carbon microspheres is 0.9-1.5; D. The dispersion of the silicon carbide powder is 1-1.5; E. The silicon-carbon powder is located in the gaps between the mesophase carbon microspheres.

3. The mesophase carbon microsphere-silicon carbon composite slurry according to claim 1, characterized in that, At least one of the following conditions must be met: A. The solid content in the conductive paste is 0.4%-5% by mass; C. The solvent in the conductive paste includes ester solvents.

4. The mesophase carbon microsphere-silicon carbon composite slurry according to any one of claims 1-3, characterized in that, The viscosity of the mesophase carbon microsphere-silicon carbon composite slurry is 3000 mPa·s-10000 mPa·s.

5. A method for preparing the mesophase carbon microsphere-silicon carbon composite slurry according to any one of claims 1-4, characterized in that, include: The first component and the second component are mixed to prepare the product.

6. The method for preparing the mesophase carbon microsphere-silicon carbon composite slurry according to claim 5, characterized in that, The mixture includes: Hydrogenated nitrile rubber and a portion of the second component are first mixed to obtain a first mixture; The first mixture and the conductive powder are mixed a second time to obtain a second mixture; The second mixture, mesophase carbon microspheres, and silicon carbide powder are mixed in a third mixture to obtain a third mixture. The third mixture, the conductive slurry, and the remaining second component are mixed in a fourth mixture to obtain the mesophase carbon microsphere-silicon carbon composite slurry.

7. The method for preparing the mesophase carbon microsphere-silicon carbon composite slurry according to claim 6, characterized in that, At least one of the following conditions must be met: A. The first mixture has a revolution speed of 15 rpm-25 rpm, a dispersion speed of 500 rpm-1500 rpm, a stirring time of 120 min-180 min, and a temperature of 50℃-65℃; B. The second mixing includes a first stirring and a second stirring performed sequentially; The dispersion speed of the first stirring is 100-500 rpm, and the time is 30-60 min; The second stirring motion has a revolution speed of 20-30 rpm, a dispersion speed of 2000-3000 rpm, and a time of 60-180 min; The temperatures of the first stirring and the second stirring are each independently 25℃-30℃; C. The third mixing includes a third stirring and a fourth stirring performed sequentially; The third stirring motion has a revolution speed of 10-15 rpm, a dispersion speed of 500-1000 rpm, and a time of 30-60 min. The fourth stirring motion has a revolution speed of 20-30 rpm, a dispersion speed of 2500-3500 rpm, and a time of 120-180 min. The temperatures of the third and fourth stirring operations are each independently 25℃-30℃; D. The fourth mixture has a revolution speed of 15-25 rpm, a dispersion speed of 1000-2000 rpm, a time of 30-60 min, and a temperature of 25℃-30℃; E. Based on the total mass of the second component being 100%, it includes: 80%-90% of the second component, and 10%-20% of the remaining second component.

8. A negative electrode sheet, characterized in that, Includes the mesophase carbon microsphere-silicon carbon composite slurry according to any one of claims 1-4.

9. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 8.

10. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 9.

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