A fast-charging silicon-carbon composite material, a preparation method thereof, a lithium ion battery and an electric device

Abstract

The application provides a fast-charging silicon-carbon composite material and a preparation method thereof, a lithium ion battery and an electric device, and relates to the field of new energy. A first mixture obtained by mixing silicon nanoparticles, a first conductive agent and flake graphite is subjected to spheroidization treatment to obtain a first intermediate product; the first intermediate product is subjected to ultrasonic treatment and airflow classification to obtain a second intermediate product; a second mixture obtained by mixing the second intermediate product and a first binder is subjected to hot isostatic pressing treatment to obtain a third intermediate product; the third intermediate product is subjected to graphitization treatment under a nitrogen atmosphere to obtain a fourth intermediate product; the fourth intermediate product is subjected to surface coating by using a polymer precursor to obtain a fifth intermediate product; and the fifth intermediate product is subjected to carbonization treatment under an inert atmosphere to obtain the fast-charging silicon-carbon composite material; and the polymer precursor comprises a second conductive agent and a second binder. The method is simple to operate and raw materials are easy to obtain.

Description

Technical Field

[0001] This application relates to the field of new energy, and in particular to a fast-charging silicon-carbon composite material and its preparation method, a lithium-ion battery, and electrical equipment. Background Technology

[0002] In recent years, lithium-ion batteries (LIBs) have been widely used in portable devices, electric vehicles, and energy storage grids. Currently, the development of high-specific-capacity, fast-charging active materials and high-load electrodes remains a research hotspot in the field. This is because the specific capacity of commercial graphite electrodes is approaching its theoretical limit (372 mAh g⁻¹). -1 Therefore, anode materials with higher specific capacity are needed to overcome this bottleneck. Silicon (Si) is chosen because of its high specific capacity (3579 mA Hg). -1 Silicon is considered one of the most promising new anode materials. Silicon-based materials exhibit low delithiation potential and relatively low voltage hysteresis during the insertion / extraction process, and their reserves in the Earth's crust (such as silica) are very abundant. However, the huge volume expansion of silicon during charging (ranging from 300% to 400%) leads to the pulverization of silicon particles and the repeated formation of unstable solid-electrolyte interphase (SEI). Furthermore, silicon has low electrical conductivity, and the structure-property relationship between silicon and carbon is very weak, all of which limit its commercial application.

[0003] Graphite anodes possess excellent cycle stability, superior conductivity, and good electrolyte compatibility, making them the mainstream anode material for lithium-ion batteries (LIBs). However, their relatively low theoretical specific capacity limits the improvement of lithium battery energy density. Furthermore, due to the small interlayer spacing and limited internal voids in graphite particles, Li-ion batteries experience performance degradation during high-rate charge and discharge. + The diffusion rate inside the particles is slow, and a large number of lithium ions are deposited on the surface of the negative electrode, which inevitably leads to lithium dendrites and causes a series of safety problems. At the same time, it will also cause internal polarization of the lithium battery, including ohmic polarization, concentration overpotential and charge transfer overpotential. In severe cases, it may even lead to thermal runaway of the lithium battery.

[0004] Therefore, from the perspectives of cost, performance, and safety, constructing a reasonable graphite and nano-silicon composite material is considered the most reasonable direction for exploring new anode materials. Summary of the Invention

[0005] The purpose of this application is to provide a fast-charging silicon-carbon composite material, its preparation method, 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 method for preparing a fast-charging silicon-carbon composite material, comprising:

[0007] A first mixture is obtained by mixing silicon nanoparticles, a first conductive agent, and flake graphite, and the first mixture is then spheroidized to obtain a first intermediate product.

[0008] The first intermediate product was subjected to ultrasonication and airflow fractionation to obtain the second intermediate product.

[0009] The second mixture obtained by mixing the second intermediate product and the first binder is subjected to hot isostatic pressing to obtain the third intermediate product.

[0010] The third intermediate product was graphitized under a nitrogen atmosphere to obtain the fourth intermediate product.

[0011] The fifth intermediate product is obtained by surface coating the fourth intermediate product with a polymer precursor.

[0012] The fifth intermediate product was carbonized under an inert atmosphere to obtain a fast-charging silicon-carbon composite material.

[0013] The polymer precursor includes a second conductive agent and a second binder.

[0014] Optionally, the preparation method of the fast-charging silicon-carbon composite material satisfies at least one of the following conditions:

[0015] A. The D50 of the silicon nanoparticles is 50nm-60nm;

[0016] B. The D50 of the flake graphite is 5μm-12μm;

[0017] C. The D50 of the first adhesive is 0.5μm-5μm;

[0018] D. The first adhesive comprises asphalt;

[0019] E. The first conductive agent and the second conductive agent each independently include one or more of carbon black, conductive carbon fiber, conductive graphite sheet, graphene and carbon nanotubes;

[0020] F. The second adhesive comprises one or more of carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, phenolic resin, and polyacrylic acid.

[0021] Optionally, the preparation method of the fast-charging silicon-carbon composite material satisfies at least one of the following conditions:

[0022] A. The mass of the silicon nanoparticles is 1%-5% of the mass of the first mixture, and the mass of the first conductive agent is 0.1%-1% of the mass of the first mixture;

[0023] B. The mass ratio of the second intermediate product to the first binder is 100:(1-15);

[0024] C. The mass ratio of the polymer precursor to the fourth intermediate is (5-10):100;

[0025] D. The mass ratio of the second conductive agent to the second adhesive is 1:(10-20);

[0026] E. The solid content of the polymer precursor is 10%-15%.

[0027] Optionally, the preparation method of the fast-charging silicon-carbon composite material satisfies at least one of the following conditions:

[0028] A. The spheroidizing treatment time is 0.5h-2h;

[0029] B. The ultrasound duration is 30-120 minutes, and the power is 100kHz-300kHz;

[0030] C. The rotational speed of the airflow stage is 15Hz-30Hz;

[0031] D. The mixing time between the second intermediate product and the first binder is 0.5h-4h.

[0032] Optionally, the temperature of the hot isostatic pressing treatment is 100℃-300℃;

[0033] Preferably, the hot isostatic pressing process includes a first hot isostatic pressing process, a second hot isostatic pressing process, and a third hot isostatic pressing process performed sequentially.

[0034] Preferably, the pressure of the holding platform in the first hot isostatic pressing treatment is 50MPa-90MPa, and the holding time is 60s-480s;

[0035] Preferably, the pressure holding platform pressure of the second hot isostatic pressing treatment is 90MPa-120MPa, and the pressure holding time is 120s-180s;

[0036] Preferably, the pressure of the holding platform in the third hot isostatic pressing treatment is 120MPa-150MPa, and the holding time is 160s-200s.

[0037] Optionally, the preparation method of the fast-charging silicon-carbon composite material satisfies at least one of the following conditions:

[0038] A. The temperature of the graphitization treatment is 2000℃-2400℃, and the time is 8h-10h;

[0039] B. The carbonization process includes a first carbonization process and a second carbonization process performed sequentially;

[0040] Preferably, the temperature of the first carbonization treatment is 150℃-200℃, and the holding time is 1h-2h;

[0041] Preferably, the temperature of the second carbonization treatment is 800℃-1000℃, and the holding time is 3h-4h;

[0042] Preferably, the heating rate of the carbonization process is 5℃ / min-10℃ / min.

[0043] The second aspect of this application provides a fast-charging silicon-carbon composite material, which is prepared by the method for preparing the fast-charging silicon-carbon composite material.

[0044] Optionally, the fast-charging silicon-carbon composite material satisfies at least one of the following conditions:

[0045] A. The silicon content in the fast-charging silicon-carbon composite material is 0.2wt%-20wt%, and the carbon content is 80wt%-99.95wt%.

[0046] B. The D50 of the fast-charging silicon-carbon composite material is 5μm-15μm;

[0047] C. Includes a kernel and a covering layer that sets the surface of the kernel;

[0048] Preferably, the thickness of the coating layer is 0.01nm-100nm.

[0049] A third aspect of this application provides a lithium-ion battery whose raw materials include the aforementioned fast-charging silicon-carbon composite material.

[0050] A fourth 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 method for preparing fast-charging silicon-carbon composite material provided in this application involves mixing silicon nanoparticles, a first conductive agent, and flake graphite and spheroidizing them to obtain multilayered rolled flake graphite coated with silicon nanoparticles and the first conductive agent into near-spherical particles. Ultrasonic and airflow classification are then used to cause collisions between the flake graphite layers and between the near-spherical particles, causing the silicon nanoparticles and the first conductive agent attached to the outer surface of the near-spherical particles to be shaken off and rubbed off, resulting in a more uniform dispersion of the silicon nanoparticles and the first conductive agent deposited between the flake graphite layers. A first binder is then coated onto the surface of the near-spherical particles using a solid-phase coating method. The coated second mixture is then subjected to hot isostatic pressing (densification treatment), and heating is applied during this process to allow the molten first binder to penetrate into the interior of the second mixture under high pressure. Finally, graphitization and liquid-phase coating treatments are performed to obtain the fast-charging silicon-carbon composite material. This method is simple to operate and uses readily available raw materials.

[0053] The fast-charging silicon-carbon composite material provided in this application combines the high capacity of silicon with the excellent conductivity of graphite, possessing advantages such as high energy density, excellent rate performance, and high cycle efficiency, while also being environmentally friendly and sustainable. It uses spherical graphite as a framework, and the layered flake graphite enhances the Li-carbon composite material. + The diffusion rate inside graphite accelerates graphite kinetics. Silicon nanoparticles are located only in the interlayer of flake graphite, not on the surface, which can effectively suppress the volume expansion of silicon and improve the low conductivity of silicon. The surface coating layer can further reduce the volume expansion of silicon, facilitate the rapid transport of ions and electrons, and reduce the contact between the material and the electrolyte, thus significantly improving cycle performance.

[0054] The lithium-ion battery and electrical equipment provided in this application have high energy density, excellent rate performance, high cycle efficiency, good cycle performance, and long service life. Attached Figure Description

[0055] 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.

[0056] Figure 1 This is a schematic diagram of the structure of a fast-charging silicon-carbon composite material;

[0057] Figure 2 SEM image of the mixture obtained by mixing the spherical particles and the binder provided in Example 1;

[0058] Figure 3 The image shows a SEM image of the mixture after hot isostatic pressing as 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] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0062] 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.

[0063] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0064] "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 (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0065] "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).

[0066] The first aspect of this application provides a method for preparing a fast-charging silicon-carbon composite material, comprising:

[0067] A first mixture is obtained by mixing silicon nanoparticles, a first conductive agent, and flake graphite, and the first mixture is then spheroidized to obtain a first intermediate product.

[0068] It should be noted that flake graphite has a certain degree of elasticity to support the volume expansion of silicon during charging and discharging, which greatly improves the cycle performance of the material. The curling of flake graphite coats the silicon powder, which improves the volume expansion of silicon powder during charging and discharging. Moreover, by utilizing the adhesiveness of the first conductive agent, a composite material with better coating effect is obtained, thereby greatly improving the cycle performance and rate performance of the material.

[0069] In some embodiments, a high-speed fusion machine is used to mix silicon nanoparticles, a first conductive agent, and flake graphite by high-speed fusion, extrusion, and stirring; a honeycomb mill is used for spheroidization treatment, which successfully embeds silicon nanoparticles and the first conductive agent into the interlayer of expanded graphite while ensuring the spheroidization of flake graphite.

[0070] The first intermediate product was subjected to ultrasonication and airflow fractionation to obtain the second intermediate product.

[0071] It should be noted that ultrasound and airflow classification can shake and rub off the silicon nanoparticles and the first conductive agent deposited on the outer surface of flake graphite, and the silicon nanoparticles and the first conductive agent deposited between the flake graphite layers are more evenly dispersed.

[0072] The second mixture obtained by mixing the second intermediate product and the first binder is subjected to hot isostatic pressing to obtain the third intermediate product.

[0073] It should be noted that the hot isostatic pressing (HIP) process can reduce the porosity inside the flake graphite layers, while allowing the silicon nanoparticles to be in closer contact with the flake graphite layers. Furthermore, the first binder melts during the heating process and penetrates into the particles under external high pressure to achieve better bonding and coating effects.

[0074] The third intermediate product was graphitized under a nitrogen atmosphere to obtain the fourth intermediate product.

[0075] It should be noted that graphitization is used to convert the first binder into graphitized carbon. During the graphitization process, the carbon atoms rearrange themselves, making the bonding force between the sheets tighter. This is beneficial to the expansion and pulverization of nano-silicon inside the sheets. Furthermore, graphitization will further increase the isotropy of the flake graphite particles.

[0076] The fifth intermediate product is obtained by surface coating the fourth intermediate product with a polymer precursor.

[0077] The fifth intermediate product was carbonized under an inert atmosphere to obtain a fast-charging silicon-carbon composite material.

[0078] The polymer precursor includes a second conductive agent and a second binder.

[0079] It is important to note that polymer precursors can not only isolate silicon from the electrolyte, but also effectively improve the migration rate of lithium ions, thereby improving charge-discharge efficiency and cycle performance.

[0080] In some embodiments, the method for preparing the fast-charging silicon-carbon composite material satisfies at least one of the following conditions:

[0081] A. The D50 of the silicon nanoparticles is 50nm-60nm;

[0082] Optionally, the D50 of the silicon nanoparticles can be any value between 50nm, 55nm, 60nm, or 50nm-60nm.

[0083] It should be noted that when the D50 of silicon nanoparticles is 50nm-60nm, the volume expansion of silicon-carbon anodes during charging and discharging can be effectively reduced. At the same time, the particle size has good dispersibility. When the particle size is less than 50nm, it is easy to agglomerate during the mixing process.

[0084] In some embodiments, silicon nanoparticles include sheet-like or granular forms;

[0085] B. The D50 of the flake graphite is 5μm-12μm;

[0086] Optionally, the D50 of flake graphite can be any value between 5μm, 7μm, 9μm, 10μm, 12μm or 5μm-12μm;

[0087] C. The D50 of the first adhesive is 0.5μm-5μm;

[0088] Optionally, the D50 of the first adhesive can be any value between 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, or 0.5μm-5μm;

[0089] D. The first adhesive comprises asphalt;

[0090] It should be noted that asphalt has certain adhesion and fluidity at its softening point and has a higher carbon residue than other coating materials. At the same time, the soft carbon coating layer formed after asphalt carbonization has better compatibility with the electrolyte and can significantly reduce the specific surface area of ​​the sample.

[0091] E. The first conductive agent and the second conductive agent each independently include one or more of carbon black, conductive carbon fiber, conductive graphite sheet, graphene and carbon nanotubes;

[0092] Preferably, the first conductive agent includes carbon nanotubes. Since silicon nanoparticles are semiconductor materials with low conductivity and undergo volume expansion exceeding 300% during electrochemical charging and discharging, when the first conductive agent includes carbon nanotubes, its one-dimensional structure more easily forms an effective conductive network, compensating for the poor conductivity of silicon-based anodes. Furthermore, carbon nanotubes possess high elasticity and strength, effectively connecting material particles during silicon-based material expansion, reducing the shedding of active material, and improving the structural stability of the anode material. A schematic diagram of the structure of the fast-charging silicon-carbon composite material prepared when the first conductive agent includes carbon nanotubes is shown below. Figure 1 As shown;

[0093] F. The second adhesive comprises one or more of carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, phenolic resin, and polyacrylic acid.

[0094] It is important to note that the addition of a second binder can bind multiple small particles together into a larger particle, increasing the tap density of the sample, reducing the anisotropy of the sample, and allowing lithium ions to insert between graphite layers from all directions, thus achieving high-rate fast charging performance.

[0095] In some embodiments, the method for preparing the fast-charging silicon-carbon composite material satisfies at least one of the following conditions:

[0096] A. The mass of the silicon nanoparticles is 1%-5% of the mass of the first mixture, and the mass of the first conductive agent is 0.1%-1% of the mass of the first mixture;

[0097] Optionally, the mass of the silicon nanoparticles can be any value between 1%, 2%, 3%, 4%, 5% or 1%-5% of the mass of the first mixture, and the mass of the first conductive agent can be any value between 0.1%, 0.5%, 1% or 0.1%-1% of the mass of the first mixture.

[0098] B. The mass ratio of the second intermediate product to the first binder is 100:(1-15);

[0099] Optionally, the mass ratio of the second intermediate product to the first binder can be any value between 100:1, 100:2, 100:4, 100:6, 100:8, 100:10, 100:12, 100:13, 100:14, 100:15 or 100:(1-15);

[0100] C. The mass ratio of the polymer precursor to the fourth intermediate is (5-10):100;

[0101] Optionally, the mass ratio of the polymer precursor to the fourth intermediate can be any value between 5:100, 6:100, 7:100, 8:100, 9:100, 10:100 or (5-10):100;

[0102] D. The mass ratio of the second conductive agent to the second adhesive is 1:(10-20);

[0103] Optionally, the mass ratio of the second conductive agent to the second adhesive can be any value between 1:10, 1:15, 1:20 or 1:(10-20);

[0104] E. The solid content of the polymer precursor is 10%-15%.

[0105] Optionally, the solid content of the polymer precursor can be any value between 10%, 11%, 12%, 13%, 14%, 15%, or 10%-15%.

[0106] In some embodiments, the method for preparing the fast-charging silicon-carbon composite material satisfies at least one of the following conditions:

[0107] A. The spheroidizing treatment time is 0.5h-2h;

[0108] Optionally, the spheroidizing treatment time can be any value between 0.5h, 1h, 1.5h, 2h, or 0.5h-2h;

[0109] B. The ultrasound duration is 30-120 minutes, and the power is 100kHz-300kHz;

[0110] Optionally, the ultrasound time can be any value between 30 min, 60 min, 90 min, 120 min or 30 min-120 min, and the power can be any value between 100 kHz, 200 kHz, 300 kHz or 100 kHz-300 kHz.

[0111] C. The rotational speed of the airflow stage is 15Hz-30Hz;

[0112] Optionally, the rotational speed for airflow gradation can be any value between 15Hz, 20Hz, 25Hz, 30Hz, or 15Hz-30Hz.

[0113] D. The mixing time between the second intermediate product and the first binder is 0.5h-4h.

[0114] Optionally, the mixing time between the second intermediate product and the first binder can be any value between 0.5h, 1h, 2h, 3h, 4h, or 0.5h-4h.

[0115] In some embodiments, the temperature of the hot isostatic pressing treatment is 100°C-300°C;

[0116] Optionally, the temperature for hot isostatic pressing can be 100℃, 200℃, 300℃ or any value between 100℃ and 300℃;

[0117] Preferably, the hot isostatic pressing process includes a first hot isostatic pressing process, a second hot isostatic pressing process, and a third hot isostatic pressing process performed sequentially.

[0118] Preferably, the pressure of the holding platform in the first hot isostatic pressing treatment is 50MPa-90MPa, and the holding time is 60s-480s;

[0119] Optionally, the pressure holding platform pressure of the first hot isostatic pressing treatment can be any value between 50MPa, 60MPa, 70MPa, 80MPa, 90MPa or 50MPa-90MPa, and the pressure holding time can be any value between 60s, 120s, 180s, 240s, 300s, 360s, 420s, 480s or 60s-480s;

[0120] Preferably, the pressure holding platform pressure of the second hot isostatic pressing treatment is 90MPa-120MPa, and the pressure holding time is 120s-180s;

[0121] Optionally, the pressure holding platform pressure of the second hot isostatic pressing treatment can be any value between 90MPa, 100MPa, 110MPa, 120MPa or 90MPa-120MPa, and the pressure holding time can be any value between 120s, 140s, 160s, 180s or 120s-180s.

[0122] Preferably, the pressure of the holding platform in the third hot isostatic pressing treatment is 120MPa-150MPa, and the holding time is 160s-200s.

[0123] Optionally, the pressure holding platform pressure of the third hot isostatic pressing treatment can be any value between 120MPa, 130MPa, 140MPa, 150MPa or 120MPa-150MPa, and the pressure holding time can be any value between 160s, 170s, 180s, 190s, 200s or 160s-200s.

[0124] It should be noted that the first, second and third hot isostatic pressing treatments are performed in sequence. The purpose of setting up three levels of hot isostatic pressing is to prevent the sample from breaking due to excessive pressure. Providing three levels of pressure can better play a buffering role, and the molten asphalt can better penetrate into the particle under the three levels of pressure.

[0125] In some embodiments, the method for preparing the fast-charging silicon-carbon composite material satisfies at least one of the following conditions:

[0126] A. The temperature of the graphitization treatment is 2000℃-2400℃, and the time is 8h-10h;

[0127] Optionally, the graphitization temperature can be any value between 2000℃, 2100℃, 2200℃, 2300℃, 2400℃ or 2000℃-2400℃, and the time can be any value between 8h, 9h, 10h or 8h-10h.

[0128] It is important to note that, due to the porosity between the graphite flakes after spheroidizing, and the poor contact between the dispersed silicon nanosheets and the graphite flakes, hot isostatic pressing (HIP) densification is performed. Under high temperature and pressure, molten, fluid, low-temperature asphalt is impregnated between the graphite flakes to fill the pores and achieve adhesion. At the same time, it better adheres the silicon nanosheets to the graphite flakes. The flexibility between the flakes can better buffer the volume expansion of the silicon nanosheets, and the strong adhesion of the asphalt better inhibits the slippage between the graphite flakes under external pressure, which can better improve the hardness and strength of the graphite material.

[0129] Because the volume expansion of silicon during electrochemical charging and discharging can break graphite sheets and the bonding force between silicon and carbon is generally weak, this can easily lead to poor contact between silicon and graphite. Through graphitization, the pitch impregnated between graphite sheets is transformed into artificial graphite. During graphitization, carbon atoms rearrange under high temperature, causing the pitch carbon and graphite carbon between the sheets to combine, further strengthening the bonding force between the sheets and better coping with the volume expansion of silicon. In addition, the external pitch coating can also reduce the specific surface area and orientation degree of spherical graphite.

[0130] B. The carbonization process includes a first carbonization process and a second carbonization process performed sequentially;

[0131] Preferably, the temperature of the first carbonization treatment is 150℃-200℃, and the holding time is 1h-2h;

[0132] Optionally, the temperature of the first carbonization treatment can be any value between 150℃, 160℃, 170℃, 180℃, 190℃, 200℃ or 150℃-200℃, and the isothermal time can be any value between 1h, 1.5h, 2h or 1h-2h.

[0133] Preferably, the temperature of the second carbonization treatment is 800℃-1000℃, and the holding time is 3h-4h; optionally, the temperature of the second carbonization treatment can be any value between 800℃, 900℃, 1000℃ or 800℃-1000℃, and the holding time can be any value between 3h, 3.5h, 4h or 3h-4h.

[0134] Preferably, the heating rate of the carbonization process is 5℃ / min-10℃ / min.

[0135] Optionally, the heating rate for carbonization can be any value between 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or 5℃ / min-10℃ / min. It is important to note that two-stage carbonization ensures complete carbonization of the coating agent, allowing it to uniformly coat the particle surface and thus reducing the particle specific surface area.

[0136] The second aspect of this application provides a fast-charging silicon-carbon composite material, which is prepared by the method for preparing the fast-charging silicon-carbon composite material.

[0137] In some embodiments, the fast-charging silicon-carbon composite material satisfies at least one of the following conditions:

[0138] A. The silicon content in the fast-charging silicon-carbon composite material is 0.2wt%-20wt%, and the carbon content is 80wt%-99.95wt%.

[0139] Optionally, the silicon content in the fast-charging silicon-carbon composite material can be any value between 0.2wt%, 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, or 0.2wt%-20wt%, and the carbon content can be any value between 80wt%, 85wt%, 90wt%, 95wt%, 99wt%, 99.95wt%, or 80wt%-99.95wt%.

[0140] B. The D50 of the fast-charging silicon-carbon composite material is 5μm-15μm;

[0141] Optionally, the D50 of the fast-charging silicon-carbon composite material can be any value between 5μm, 10μm, 15μm, or 5μm-15μm;

[0142] C. Includes a kernel and a covering layer that sets the surface of the kernel;

[0143] In some embodiments, the core comprises stacked spheroidized flake graphite and silicon nanoparticles, a first conductive agent, and graphite disposed between the flake graphite. The graphite is obtained by impregnating asphalt into the gaps between the flake graphite, silicon nanoparticles, and the first conductive agent through hot isostatic pressing and then graphitizing it. The coating layer comprises a first coating layer and a second coating layer disposed sequentially, with the first coating layer disposed between the core and the second coating layer. The first coating layer comprises an asphalt coating layer, and the second coating layer comprises a polymer coating. For example, when the first conductive agent comprises carbon nanotubes, the structure of the fast-charging silicon-carbon composite material is shown below. Figure 1 As shown.

[0144] Preferably, the thickness of the coating layer is 0.01nm-100nm.

[0145] Optionally, the thickness of the coating layer can be 0.01nm, 0.1nm, 1nm, 10nm, 100nm, or any value between 0.01nm and 100nm.

[0146] A third aspect of this application provides a lithium-ion battery whose raw materials include the aforementioned fast-charging silicon-carbon composite material.

[0147] A fourth aspect of this application provides an electrical device including the aforementioned lithium-ion battery.

[0148] It should be noted that electrical equipment may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc.; among them, 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.

[0149] 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.

[0150] Example 1

[0151] The first aspect of this embodiment provides a method for preparing fast-charging silicon-carbon composite materials, the specific steps of which are as follows:

[0152] S1: Mix flake graphite, silicon nanoparticles and conductive carbon black at a mass ratio of 94:5:1 and stir for 1 hour;

[0153] S2: The material mixed in step S1 is spheroidized using a honeycomb mill for 0.5 hours;

[0154] S3: The spherical particles prepared in step S2 are subjected to ultrasonic vibration and airflow classification. The ultrasonic time is 30 min and the power is 100 kHz; the rotation speed of airflow classification is 30 Hz.

[0155] S4: Mix the spherical particles prepared in step S3 with the binder asphalt at a mass ratio of 100:8, and stir for 1 hour. The SEM image of the resulting mixture is shown below. Figure 2 As shown;

[0156] S5: The mixture from step S4 is subjected to hot isostatic pressing (HIP). The first stage holding pressure is 90 MPa for 480 s, the second stage holding pressure is 120 MPa for 180 s, and the third stage holding pressure is 150 MPa for 200 s. The SEM image of the mixture after HIP is as follows: Figure 3 As shown;

[0157] S6: The product from step S5 is graphitized in a graphitization furnace under a N2 atmosphere, wherein the graphitization temperature is 2400℃ and the graphitization time is 4h.

[0158] S7: Depolymerize and disperse the product from step S6 to obtain spherical graphite particles with a median particle size D50 between 8 and 15 μm.

[0159] S8: The product from step S7 is liquid-phase coated with a polymer precursor to obtain spherical graphite particles with a median particle size D50 between 10-20 μm. The polymer precursor consists of carbon nanotubes and phenolic resin in a mass ratio of 1:15 and has a solid content of 15%.

[0160] S9: The product from step S8 is subjected to high-temperature carbonization. In an Ar atmosphere, a gradient heating method is used for high-temperature shaping. The first stage temperature is 150℃ and the holding time is 2h; the second stage temperature is 1000℃ and the holding time is 3h; the heating rate is 5℃ / min, and finally fast-charging silicon-carbon composite material is obtained.

[0161] Example 2

[0162] The difference from Example 1 is that in step S4, the spherical particles and the binder asphalt are in a mass ratio of 100:12.

[0163] Example 3

[0164] The difference from Example 1 is that in step S4, binder bitumen 280 is used.

[0165] Example 4

[0166] The difference from Example 1 is that in step S5, the first-stage pressure holding pressure is 50 MPa and the holding time is 480 s, the second-stage pressure holding pressure is 90 MPa and the holding time is 180 s, and the third-stage pressure holding pressure is 120 MPa and the holding time is 200 s.

[0167] Example 5

[0168] The difference from Example 1 is that in step S1, the flake graphite, silicon nanoparticles and conductive carbon black are in a mass ratio of 94.5:5:0.5.

[0169] Example 6

[0170] The difference from Example 1 is that in step S1, conductive carbon black is replaced with carbon nanotubes.

[0171] Comparative Example 1

[0172] The difference from Example 1 is that the polymer precursor in step S8 is replaced with liquid asphalt.

[0173] Comparative Example 2

[0174] The difference from Example 1 is that the polymer precursor in step S8 is replaced with phenolic resin.

[0175] Comparative Example 3

[0176] The difference from Example 1 is that in step S6, the graphitization temperature is 1800°C.

[0177] Comparative Example 4

[0178] The difference from Example 1 is that in step S9, the temperature of the second stage is 800°C.

[0179] Comparative Example 5

[0180] The difference from Example 1 is that no conductive agent is added in step S1.

[0181] Comparative Example 6

[0182] The difference from Example 1 is that silicon nanoparticles are not added in step S1.

[0183] Comparative Example 7

[0184] The difference from Example 1 is that step S5 is not performed, that is, hot isostatic pressing is not performed.

[0185] Comparative Example 8

[0186] The difference from Example 1 is that no asphalt is added, that is, step S4 is not performed.

[0187] The relevant product parameters of the composite materials prepared in the above embodiments and comparative examples are shown in Table 1.

[0188] Table 1 Product Parameters

[0189] Test components D10(μm) D50(μm) D90(μm) Coating thickness (nm) Example 1 8.4 14.5 30.2 30 Example 2 9.6 15.2 31.6 50 Example 3 9.5 14.8 31.4 55 Example 4 10.4 14.9 30.5 36 Example 5 9.8 15.5 31.8 29 Example 6 8.4 14.5 30.4 33 Comparative Example 1 8.6 14.7 31.4 37 Comparative Example 2 9.4 15.8 29.6 35 Comparative Example 3 9.8 15.1 32.4 39 Comparative Example 4 10.2 14.5 29.8 36 Comparative Example 5 10.4 14.6 30.1 40 Comparative Example 6 10.3 14.3 31.8 31 Comparative Example 7 8.4 14.1 31.4 38 Comparative Example 8 8.4 14.6 30.2 10

[0190] The composite materials prepared in the above embodiments and comparative examples were used to prepare lithium-ion batteries. The specific steps are as follows:

[0191] Specific capacity testing method: In coin cells, the capacity of the battery material is calculated by constant current charge and discharge test method based on the mass of silicon-based anode material. Specific capacity = material capacity / mass of active material.

[0192] First-cycle efficiency test method: First-cycle efficiency mainly refers to the efficiency of the battery during the first discharge process, that is, the ratio of discharge capacity to charging capacity.

[0193] Cycle count test method: The battery cycle count test method involves subjecting the battery to multiple charge-discharge cycles to evaluate its performance and lifespan. One cycle is defined as the period from the start of the charging program to the complete termination of the next discharge program. The prepared batteries are then subjected to performance tests, including specific capacity, capacity retention rate after 500 cycles at 0.5C / 1C, and capacity retention rate at 3C discharge. Specific data are shown in Table 2.

[0194] Table 2 Performance Tests

[0195]

[0196] analyze:

[0197] As demonstrated by the above experiments, the lithium-ion battery prepared from the fast-charging silicon-carbon composite material provided in this application exhibits excellent performance, including high energy density, superior rate capability, and high cycle efficiency. In particular, Example 6 demonstrates higher specific capacity, higher capacity retention, and lower electrode expansion rate. This is primarily because the nano-silicon particles are uniformly coated within the flake graphite, and the volume expansion of silicon is effectively suppressed by the strong adhesion of the asphalt. The use of the second coating agent further enhances the uniform coating effect. After hot isostatic pressing and graphitization, the layers become more firmly bonded through carbon atom rearrangement. The interlayer carbon nanotubes maintain the conductive pathway while simultaneously separating the Si particles, providing them with expansion space and buffering the severe volume effect of Si. This effectively restrains the graphite sheet detachment caused by the compression of the graphite sheets due to the volume expansion of silicon, preventing electrode pulverization during cycling. By combining an inner closed but adaptable overlapping graphite sheet layer with an outer open soft carbon porous structure, the inner closed shell can simultaneously stabilize the interface between silicon, carbon, and the electrolyte. Meanwhile, the inner carbon nanotubes significantly promote the efficient and rapid transport of electrons and lithium ions, while the outer open soft carbon porous structure creates a stable and powerful electron and lithium ion transport pathway throughout the electrode. The carbon nanotubes between the layers extend to the outside and cross-link with the conductive agent in the outer layer, constructing a rapid lithium ion and electron conduction network, promoting interfacial electron transfer and improving the diffusion coefficient of lithium ions in the electrode. This achieves the synergistic construction of electron and lithium ion transport pathways from the material scale to the electrode scale, thereby improving the material's cycle life, coulombic efficiency, and superior rate performance. Furthermore, the flexibility of the graphite sheet layer can effectively suppress the expansion effect of silicon.

[0198] In Comparative Example 1, when asphalt was used for liquid phase coating treatment, uneven dispersion led to particle agglomeration, resulting in poor performance of the material.

[0199] In Comparative Example 2, when using resin for liquid phase coating treatment, the high viscosity of the resin caused severe particle adhesion, resulting in a large particle size in the finished product.

[0200] In Comparative Example 3, the graphitization temperature was too low to fully graphitize the coated soft carbon, resulting in poor particle uniformity after graphitization.

[0201] In Comparative Example 4, the coating layer could not be completely carbonized due to the lower carbonization temperature, resulting in poor cycle stability.

[0202] In Comparative Example 5, the absence of a conductive agent led to lithium death during cycling, resulting in low sample capacity and poor cycling performance.

[0203] In Comparative Example 6, the absence of nano-silicon resulted in a lower capacity of the sample, failing to meet the standards for silicon-carbon anode materials.

[0204] In Comparative Example 7, without hot isostatic pressing, the volume expansion of nano-silicon during cycling can cause the sheets to detach, resulting in electrode powder shedding and affecting cycling performance.

[0205] In Comparative Example 8, the absence of asphalt coating resulted in a larger specific surface area, lower initial efficiency, poor high and low temperature cycling performance, and weaker van der Waals forces between graphite sheets, leading to sheet detachment due to the volume expansion of nano-silicon.

[0206] 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.

[0207] 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 method for preparing a fast-charging silicon-carbon composite material, characterized in that, The application relates to a fast-charging silicon-carbon composite material and a preparation method thereof. A first mixture is prepared by mixing silicon nanoparticles, a first conductive agent and flake graphite, and the first mixture is subjected to spheroidization treatment to obtain a first intermediate product; The first intermediate product is a kind of spherical particles coated with multi-layer curled flake graphite, silicon nanoparticles and the first conductive agent; The first intermediate product is subjected to ultrasonic treatment and airflow classification to obtain a second intermediate product; A second mixture is prepared by mixing the second intermediate product and a first binder, and the second mixture is subjected to hot isostatic pressing treatment to obtain a third intermediate product; The third intermediate product is subjected to graphitization treatment in a nitrogen atmosphere to obtain a fourth intermediate product; The fourth intermediate product is coated with a polymer precursor to obtain a fifth intermediate product; The fifth intermediate product is subjected to carbonization treatment in an inert atmosphere to obtain the fast-charging silicon-carbon composite material; The polymer precursor comprises a second conductive agent and a second binder; The D50 of the flake graphite is 5-12 mu m; The D50 of the silicon nanoparticles is 50-60 nm; The first binder comprises asphalt; The temperature of the hot isostatic pressing treatment is 100-300 DEG C; the hot isostatic pressing treatment comprises first, second and third hot isostatic pressing treatments which are sequentially performed; The pressure holding platform pressure of the first hot isostatic pressing treatment is 50-90 MPa, and the pressure holding time is 60-480 s; The pressure holding platform pressure of the second hot isostatic pressing treatment is 90-120 MPa, and the pressure holding time is 120-180 s; The pressure holding platform pressure of the third hot isostatic pressing treatment is 120-150 MPa, and the pressure holding time is 160-200 s; The temperature of the graphitization treatment is 2000-2400 DEG C, and the time is 8-10 h; The mass of the silicon nanoparticles is 1-5% of the mass of the first mixture, and the mass of the first conductive agent is 0.1-1% of the mass of the first mixture; The mass ratio of the second conductive agent to the second binder is 1:(10-20); The carbonization treatment comprises first and second carbonization treatments which are sequentially performed; The temperature of the first carbonization treatment is 150-200 DEG C, and the constant temperature time is 1-2 h; The temperature of the second carbonization treatment is 900-1000 DEG C, and the constant temperature time is 3-4 h; The temperature rising rate of the carbonization treatment is 5-10 DEG C / min.

2. The method of claim 1, wherein the fast-charging silicon-carbon composite is prepared by the steps of: At least one of the following conditions is met: A. The D50 of the first binder is 0.5-5 mu m; B. The first conductive agent and the second conductive agent each independently comprise one or more of carbon black, conductive carbon fiber, conductive graphite sheet, graphene and carbon nanotube; C. The second binder comprises one or more of carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, phenolic resin and polyacrylic acid.

3. The method of claim 1, wherein the fast-charging silicon-carbon composite is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the fast-charging silicon-carbon composite. At least one of the following conditions is met: A. The mass ratio of the second intermediate product to the first binder is 100:(1-15). B. the mass ratio of the polymer precursor to the fourth intermediate product is (5-10): 100; C. the solid content of the polymer precursor is 10%-15%.

4. The method of claim 1, wherein the fast-charging silicon-carbon composite is prepared by the steps of: At least one of the following conditions is met: A. the spheroidization time is 0.5h-2h; B. the ultrasonic time is 30min-120min, and the power is 100kHz-300kHz; C. the rotation speed of the airflow classification is 15Hz-30Hz; D. the mixing time of the second intermediate product and the first binder is 0.5h-4h.

5. A fast-charging silicon-carbon composite material, characterized by, Prepared by the preparation method of the fast-charging silicon-carbon composite material according to any one of claims 1-4.

6. The fast-charging silicon-carbon composite material of claim 5, wherein, At least one of the following conditions is met: A. the silicon content in the fast-charging silicon-carbon composite material is 0.2wt%-20wt%, and the carbon content is 80wt%-99wt%; B. the D50 of the fast-charging silicon-carbon composite material is 5μm-15μm; C. the fast-charging silicon-carbon composite material comprises a core and a coating layer arranged on the surface of the core; The thickness of the coating layer is 0.01nm-100nm.

7. A lithium-ion battery, characterized by The raw material comprises the fast-charging silicon-carbon composite material according to claim 5 or 6.

8. An electric device, characterized by The lithium ion battery comprises the lithium ion battery according to claim 7.

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