Multiple granulation silicon-carbon material with self-assembled conductive structure and preparation method and application thereof

Abstract

The application discloses a multi-granulation silicon-carbon material with a self-assembled conductive structure and a preparation method and application thereof, and belongs to the technical field of lithium ion battery materials. In the preparation, carbon sources with a softening point of 150-200 DEG C and nano silicon powder are mixed in a mixer to obtain uniformly mixed materials; a high-temperature coating machine is added for primary sintering, and a mesh sieve is used to obtain sub-micron scale primary granulation silicon-carbon precursor microspheres; the primary granulation silicon-carbon precursor microspheres, carbon additive, graphene oxide, aphanitic graphite and D50=9-12 mu m graphite are uniformly mixed in the mixer, and the materials are added into a high-temperature coating machine for secondary sintering. The application develops a multi-granulation silicon-carbon material with a self-assembled conductive structure, which has high safety in the production process, high initial coulomb efficiency, slow long cycle attenuation and excellent long cycle stability and rate performance, and can relieve the overall expansion rate of the material and improve the electronic / ionic conductivity of the material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode materials, in particular to a multi-granulation silicon-carbon material with self-assembled conductive structure and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries are one of the relatively mature energy storage devices at present, but the theoretical capacity of commercial graphite negative electrode of lithium ion batteries is 372 mAh g -1 , which has failed to meet the needs of the development of the lithium ion battery market. Silicon-based negative electrode materials are considered to be ideal substitutes for graphite negative electrodes because of their ultra-high theoretical capacity (4200 mAh g -1 ). However, silicon-based negative electrode materials will undergo a huge volume expansion / contraction (300 %) during the charging and discharging cycle, which will lead to rapid degradation of electrode performance.

[0003] Silicon-carbon materials are a kind of lithium ion battery negative electrode materials with great potential. The addition of carbon can greatly improve the conductivity of silicon. The tight carbon coating layer can to some extent reduce the adverse effects caused by the material powdering and falling off from the electrode due to the expansion of silicon. The uniform carbon coating layer can also provide a stable structure for the material, which is beneficial to the formation of a stable solid electrolyte interface during the cycle process, reducing the adverse effects of the continuous exposure of new interfaces caused by the expansion of silicon, which consumes lithium and produces new solid electrolyte interfaces, and improving the long cycle stability of the battery.

[0004] There have been extensive and relatively in-depth researches on the application of silicon-carbon negative electrode materials in the industry. For example, Chinese invention patent CN113644252B discloses a preparation process of a nano-sized silicon powder coated with pitch-derived carbon material, which is obtained by adding a surfactant, high-energy ball milling of silicon, and high-temperature carbonization. Although the final product realizes the coating of pitch carbon and improves the conductivity of the silicon-carbon material, it still has a capacity retention rate of 85% after 100 cycles at a current density of 0.5C. However, through the SEM observation of the invention, it is found that only the high-energy ball milling method is not enough to nanoize the micron-sized silicon, and the effect of relieving the expansion of silicon still fails to meet the requirements of industrialization. Moreover, the first coulombic efficiency of this technology is only 78.5%, which limits the application of the material.

[0005] Chinese invention patent application CN116799148A discloses a sheet-shaped three-dimensional silicon-carbon electrode and a preparation method, which is prepared by directly homogenizing sheet-shaped silicon and graphene with a binder and a solvent after pre-mixing, thereby constructing a three-dimensional intercalation structure of sheet-shaped silicon and graphene interlaced in layers in horizontal and vertical directions, which is beneficial to the contact between sheet-shaped silicon and graphene, and the three-dimensional structure is not easily damaged during the rolling process of the electrode, thereby improving the interface contact and structural stability between materials, but the material has the problem of large interface resistance of the contact surface between silicon and graphene due to the low intrinsic conductivity of silicon, and the sheet-shaped silicon cannot be completely covered by the graphene material during the direct homogenization process, part of the exposed silicon will directly contact with the electrolyte, which will expand and crack during the charging and discharging process of the battery, thereby continuously exposing new interfaces to form SEI film and consume lithium, resulting in poor cycle stability of the prepared electrode material.

[0006] Chinese invention patent application CN117038984A discloses a preparation method of a graphene-based silicon-carbon negative electrode material, which comprises the following steps: dispersing nano-silicon powder with a particle size of 100-200 nm in a cationic polyelectrolyte, vacuum drying by suction filtration, and then blending and compounding with graphene dispersed in an anionic polyelectrolyte, then coating the nano-silicon-graphene composite with an organic carbon source, and then molding under a pressure of 10-14 tons and pyrolyzing to obtain a silicon-carbon composite material, and then mixing the silicon-carbon composite material with graphite and coating with an organic carbon source again and pyrolyzing at high temperature to obtain the graphene-based silicon-carbon negative electrode material. The silicon particles can be uniformly embedded in the graphene oxide sheet structure through self-assembly, the mixed material has a rich carbon layer on the surface after carbonization, providing good lithium ion transmission efficiency, and the wrinkles of the graphene provide space for the volume expansion of the nano-silicon, the molding process improves the volume energy density of the material and improves the cycle stability of the material, but the organic carbon source coating method selected in the process is a liquid phase coating process of dissolving asphalt in tetrahydrofuran and then blending and evaporating with the silicon-graphene material, tetrahydrofuran is a 2B carcinogen and is volatile, and the process has certain safety risks in large-scale production and requires high-cost operation equipment; the nano-silicon powder with a particle size of 100-200 nm has a high cost, and the formed silicon oxide layer on the surface is relatively thicker than that of nano-silicon powder with a larger particle size, which finally leads to a first coulomb efficiency of the prepared material far lower than 90%, which is not conducive to the industrial application of the material. SUMMARY

[0007] In order to overcome the performance problems of low first coulomb efficiency, fast long cycle decay and low specific capacity of the existing silicon-carbon material, and solve the production problems of expensive mass production process, existing process, complicated steps, unstable quality and yield of the product, one of the purposes of the present application is to develop a process with high safety in production process, stable production on a large scale, high first coulomb efficiency, good rate performance and slow long cycle decay of the multi-granulation silicon-carbon material with self-assembled conductive structure and a preparation method thereof.

[0008] The second object of the present application is to provide an application of the multi-granulation silicon-carbon material with self-assembled conductive structure in preparing a negative electrode material of a lithium ion battery.

[0009] The object of the present application is achieved by the following technical solutions.

[0010] The preparation method of the multi-granulation silicon-carbon material with self-assembled conductive structure comprises the following steps:

[0011] 1) carbon source with a softening point of 150-200 DEG C and nano silicon powder are mixed in a mixer to obtain a uniformly mixed material; the material is added into a high-temperature coating machine for primary sintering, and then sieved through a 200-500 mesh screen to obtain sub-micron primary granulation silicon-carbon precursor microspheres;

[0012] 2) the primary granulation silicon-carbon precursor microspheres, carbon additive, graphene oxide, aphanitic graphite and D50=9-12 mu m graphite are uniformly mixed in a mixer, and then the material is added into a high-temperature coating machine for secondary sintering to obtain secondary granulation silicon-carbon composite material.

[0013] To further achieve the object of the present application, preferably, the multi-granulation silicon-carbon material further comprises three times granulation of the secondary granulation silicon-carbon composite material or surface modification of the secondary granulation silicon-carbon composite material.

[0014] The three times granulation of the secondary granulation silicon-carbon composite material is obtained by mixing the secondary granulation silicon-carbon composite material, water-soluble phenolic resin, distilled water and anhydrous ethanol, and then stirring and evaporating to dryness; an amorphous carbon layer is added to the secondary granulation silicon-carbon composite material.

[0015] The surface modification of the secondary granulation silicon-carbon composite material is obtained by adding the secondary granulation silicon-carbon composite material, distilled water and high-molecular surfactant into a drying machine, stirring, drying and sieving to obtain a silicon-carbon composite material with a hydrophilic surface.

[0016] Preferably, in the three times granulation, the mass ratio of the secondary granulation silicon-carbon composite material, water-soluble phenolic resin, distilled water and anhydrous ethanol is 5: (1-2): (8-12): (0.5-2).

[0017] In the surface modification, the high-molecular surfactant is one or more of polyethylene glycol, polyvinylpyrrolidone, polyoxyethylene fatty acid ester, sodium carboxymethyl cellulose and polyoxyethylene fatty acid ester; and the mass ratio of the secondary granulation silicon-carbon composite material, distilled water and high-molecular surfactant is (2-3): 10: (0.04-0.06).

[0018] Preferably, in step 1), the carbon source with a softening point of 150-200℃ is one or more of pitch, phenolic resin and glucose; the mass ratio of the carbon source to the nanosilicon sheet is 1:5-2:5;

[0019] In step 2), the carbonizer is one or more of graphite, glucose, needle coke and phenolic resin; the mass ratio of the primary granulated silicon-carbon precursor microspheres, the carbonizer, graphene oxide, aphanitic graphite and D50=9-12μm graphite is 50:(2-4):(2-4):(10-20).

[0020] Preferably, the carbon source needs to be crushed by a crusher before use;

[0021] The aphanitic graphite with Dv50<1μm, also known as earthy graphite, can be used as a carbonizer and a battery material.

[0022] The graphene oxide has a thickness of less than 3nm, a particle size distribution of 20-40μm and a specific surface area of 40-50m 2 / g.

[0023] Preferably, in step 1), the temperature rising procedure of the primary sintering is 0-180℃ for 1-2h, 180℃ for 1-2h, 180-300℃ for 1-2h, 300℃-500℃ for 1-2h and 500℃ for 2-4h.

[0024] In step 2), the temperature rising procedure of the secondary sintering is 0-180℃ for 1-2h, 180℃ for 2-4h, 180-400℃ for 40-60min, 400℃-900℃ for 100-160min and 900℃ for 2-4h.

[0025] The protective atmosphere of argon is added during the primary sintering and the secondary sintering, and the oxygen content is controlled at 1-5ppm.

[0026] Preferably, the silicon powder is prepared by wet sand milling; the rotation speed of the wet sand milling is 1000-1500r / min, the sand milling time is 2-6h, the particle size Dv50 of the silicon powder after grinding is controlled at 400-600nm, the silicon powder is stored and used in vacuum packaging; the solvent for the wet sand milling is one or more of diethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether and oleic acid, and the solid content is controlled at 20-50% during sand milling.

[0027] A multi-granulated silicon-carbon material with a self-assembled conductive structure is prepared by the above preparation method.

[0028] The multi-granulated silicon-carbon material with a self-assembled conductive structure is used for preparing a lithium ion battery negative material.

[0029] Preferably, the preparation of the lithium ion battery negative electrode material is to mix the multiple granulation silicon-carbon material with self-assembled conductive structure, conductive carbon black and / or single-walled carbon nanotubes, CMC and PAA, then to prepare slurry, coat on copper foil, and get lithium ion battery negative electrode sheet; the mass ratio of the multiple granulation silicon-carbon material with self-assembled conductive structure, carbon black and / or single-walled carbon nanotubes, CMC and PAA is (5-16):(3-2):(0.5-2):1.

[0030] Compared with the prior art, the application has the following advantages and beneficial effects:

[0031] 1) The amorphous graphite and graphene oxide are selected as conductive additives to modify the silicon-carbon material, and a self-assembled structure is formed: the carbon source is first melted and discharged, and then cracked into carbon during high-temperature carbonization. The viscosity of the carbon source itself during the melting stage is beneficial to the crosslinking of the sheet-shaped graphene, forming a two-dimensional crosslinked graphene network that can alleviate the expansion of the silicon-carbon monomer. The crosslinked network of sheet-shaped graphene wrapped around the silicon-carbon monomer has good mechanical properties. The amorphous graphite can fill part of the gap between carbon and silicon, which is beneficial to the release of silicon capacity. The large particle size of graphite can be used as the core of the material to realize the assembly of silicon sheets around the graphite particles and the formation of an overall structure with the conductive network, overcoming the capacity decay problem caused by the shedding of small particles during long cycle.

[0032] 2) The crosslinked network can also synergize with the binder, conductive carbon black and single-walled carbon nanotubes to realize the connection between the graphene interconnection networks, and construct a conductive structure with amorphous graphite intercalation and graphene oxide wrapping, which is blended with the carbon coating layer of amorphous graphite, graphite and silicon-carbon material. This structure can bridge between different sub-micron silicon-carbon microspheres, provide more contact sites for the negative electrode material, speed up the electron transfer during the charging and discharging process of the lithium ion battery, and improve the rapid capacity decay of the battery during long cycle due to the loss of contact between the silicon-carbon material and the current collector caused by the pulverization of silicon. This solves the problem of rapid capacity decay of silicon-based materials when activated at a relatively large current, and improves the long cycle stability of the battery prepared from the material.

[0033] 3) Unlike the existing technology that only uses high-energy ball milling method to composite carbon and silicon, which takes a long time and has a large specific surface area after ball milling, leading to low first coulomb efficiency of the material, the present application uses a mixing process followed by carbonization using a coating machine to ensure that the carbon source can form a uniform organic carbon layer on the surface of the nano-silicon powder after reaching the softening point through the stirring process of the coating machine during carbonization. In the subsequent high-temperature carbonization process, it is not easy to agglomerate, and the specific surface area is moderate. At the same time, the organic carbon layer forms a stable physical structure with the silicon core during carbonization.

[0034] 4) The process of high-speed mixing, ball milling, carbonization of coating machine, mixing and drying of drying machine adopted by the present application can realize large-scale production in industry, and the single batch output can reach 70 kg using a 500L high-temperature VC coating machine.

[0035] 5) The metal silicon powder selected by the present application is low in price, and the nano silicon powder prepared through the wet sanding process has obvious high first coulomb efficiency, and the particle size of the silicon powder is stable, the particle size of each batch of nano silicon powder is controllable, and the selection of nano silicon powder can ensure that the asphalt can be more uniform during coating.

[0036] 6) The multiple granulation silicon-carbon material with self-assembled conductive structure has excellent long cycle performance, excellent rate performance, high first efficiency, and can meet the market demand for improving specific energy in the field of lithium ion batteries, and is expected to replace graphite as the next generation of lithium ion battery negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The XRD diagram of the twice granulated silicon-carbon material with self-assembled conductive structure prepared for Example 1 and the once granulated silicon-carbon material prepared for Comparative Example 1.

[0038] Figure 2 The TEM diagram of the twice granulated silicon-carbon material with self-assembled conductive structure prepared for Example 1.

[0039] Figure 3 The SEM diagram of the twice granulated silicon-carbon material with self-assembled conductive structure prepared for Example 1.

[0040] Figure 4 The SEM diagram of the graphene-based once sintered granulated silicon-carbon composite material prepared for Comparative Example 2.

[0041] Figure 5 The long cycle performance curve of the twice granulated silicon-carbon material with self-assembled conductive structure prepared for Example 1 at a current density of 2A g -1

[0042] Figure 6 The infrared spectrum diagram of the twice granulated silicon-carbon material with self-assembled conductive structure prepared for Example 1.

[0043] Figure 7 The XPS high-resolution spectrum diagram of Si 2p of the twice granulated silicon-carbon material with self-assembled conductive structure prepared for Example 1.

[0044] Figure 8 The XPS high-resolution spectrum diagram of C 1s of the twice granulated silicon-carbon material with self-assembled conductive structure prepared for Example 1.

[0045] ​Figure 9 The specific capacity vs. cycle number plot for the first three cycles for the prepared secondary granulated silicon-carbon material with self-assembled conductive structure of Example 1 at 25℃, 0.2 Ag -1 The specific capacity vs. cycle number plot for the first three cycles for the prepared secondary granulated silicon-carbon material with self-assembled conductive structure of Example 1 at 25℃, 0.2 Ag

[0046] Figure 10 The rate performance plot for the prepared secondary granulated silicon-carbon material with self-assembled conductive structure of Example 1 and Example 3 at 0.5-20 A g -1 The rate performance plot for the prepared secondary granulated silicon-carbon material with self-assembled conductive structure of Example 1 and Example 3 at 0.5-20 A g DETAILED DESCRIPTION

[0047] The present application will be further described below in conjunction with examples, comparative examples and the accompanying drawings, but the embodiments of the present application are not limited thereto. It should be noted that if there are processes not specifically described below, they can be implemented or understood by those skilled in the art with reference to the prior art. If the reagents or instruments used are not marked with the manufacturer, they are considered to be conventional products that can be purchased on the market.

[0048] Aphanitic graphite has a crystal size less than 1 μm, a carbon content of 60% to 80%, and high particle mechanical strength, and is one of the conductive agents of the present application, and is distinguished from large-size graphene oxide. The small particles of aphanitic graphite can be used to build a conductive intercalation between sub-micron silicon precursor microspheres, and the high mechanical strength ensures that the conductive structure still exists stably when the silicon expands.

[0049] The present application uses small-size aphanitic graphite, graphene oxide, pitch-derived carbon, and large-particle graphite to assemble specific conductive structures, and realizes different conductive self-assembly structure construction, adjustment of particle size and specific surface area of the material through sintering processes with stirring function, ball milling processes, and water phase mixing processes.

[0050] The present application realizes self-assembly of silicon-carbon and graphene sheets through a simple process flow, enables graphene and conductive carbon black to be compounded with the prepared silicon-carbon material through a pulping and homogenizing process, improves the stability of the negative electrode material and reduces the specific surface area by adding a suitable carbon additive to improve the long cycle stability, and constructs a conductive structure with excellent electron and ion conductivity, which has sub-micron silicon sphere intercalation and outer wrapping of graphene sheets and is rich in pitch-derived carbon, to develop a multiple granulated silicon-carbon material with self-assembled conductive structure, which has moderate specific surface area, high initial coulombic efficiency, good long cycle performance, and good rate performance.

[0051] The present application has a self-assembled conductive structure of multiple granulation silicon carbon material, which is obtained by secondary annealing calcination of loose porous silicon carbon shell layer rich in conductive intercalation coated graphite core in a protective atmosphere; the shell layer is formed by secondary annealing of sub-micron silicon carbon precursor after primary annealing calcination; the outer layer of the material is formed by self-assembly of a graphene cover layer during secondary annealing. The micron porous silicon ball precursor is formed by primary granulation of nano silicon powder, and the precursor particles serve as the silicon skeleton of the porous silicon ball, which is assembled into a multi-scale distributed porous silicon ball aggregate through secondary granulation, and a multi-dimensional conductive network exists in the aggregate. The present application provides a preparation method of multiple granulation silicon carbon material with a self-assembled conductive structure, which comprises the following steps:

[0052] 1) Mix the carbon source with a softening point of 150-200 DEG C and nano silicon powder in a mixer to obtain uniformly mixed material; add a high-temperature coating machine for primary sintering, pass through a 200-500 mesh screen, and obtain sub-micron primary granulation silicon carbon precursor microspheres;

[0053] 2) Mix the primary granulation silicon carbon precursor microspheres, carbon additive, graphene oxide, aphanitic graphite and D50=9-12 mu m graphite in a mixer to obtain uniformly mixed material, and add the material to a high-temperature coating machine for secondary sintering to obtain secondary granulation silicon carbon composite material.

[0054] The multiple granulation silicon carbon material of the present application further comprises three times granulation of the secondary granulation silicon carbon composite material or surface modification of the secondary granulation silicon carbon composite material; the three times granulation of the secondary granulation silicon carbon composite material is mixing the secondary granulation silicon carbon composite material, water-soluble phenolic resin, distilled water and anhydrous ethanol, then stirring and evaporating to obtain; an amorphous carbon layer is added to the secondary granulation silicon carbon composite material; the surface modification of the secondary granulation silicon carbon composite material is adding the secondary granulation silicon carbon composite material, distilled water and a high molecular surfactant to a drying machine, stirring, drying and sieving to obtain a silicon carbon composite material with a hydrophilic surface.

[0055] In the above technical measures, primary granulation forms sub-micron silicon carbon microspheres; secondary granulation forms a wrapping of sub-micron silicon carbon microspheres on the surface of graphite, and at the same time, a conductive structure is constructed through self-assembly of intercalation of small-size aphanitic graphite. Three times granulation uses secondary granulation particles, and a layer of hydrophilic amorphous carbon is wrapped through the way of dissolving water-soluble resin and evaporating; the amorphous carbon layer is different from the carbon layer of good hydrophilicity represented by pitch. Surface modification wraps a hydrophilic layer on the surface of the secondary granulation particles through the way of solvent surfactant and evaporation.

[0056] The reduced graphene oxide, graphene oxide and aphanitic graphite of the present application are all from Guangdong Junchi New Energy Co., Ltd. PAA is from Sichuan Yin Dile Material Science and Technology Group Co., Ltd.; single-walled carbon nanotubes are from Foshan Grefin New Energy Co., Ltd.

[0057] The temperature rising in a certain time range in the present application is controlled to be uniform. Example 1

[0058] A preparation method of a multi-granulation silicon-carbon material with a self-assembled conductive structure, comprising the following steps:

[0059] Take 36 kg of 325 mesh metal silicon powder, disperse it in a stirred tank containing 114 kg of diethylene glycol dimethyl ether solvent, stir and disperse at a speed of 600 r / min for 1 h, pump the suspension into a sand mill through a diaphragm pump, and stir at a speed of 1250 r / min for 4 h. After drying, nano silicon powder is obtained. The Dv50 is controlled to be 550±20 nm according to the sanding time by using a Jinan micro-nano particle size tester Winner2018.

[0060] Primary granulation preparation of the precursor: take the obtained nano silicon powder 1.275 kg, and the asphalt 225 g after being crushed by a crusher, add them into a high-speed stirrer and stir and disperse; after discharging, the powder is added into a coating machine for primary granulation, the stirring speed of the coating machine is controlled to be 20 r / min, argon is introduced through a high-pressure gas cylinder, and the oxygen content is reduced to 1-5 ppm before heating and temperature rising; during the temperature rising process, the temperature is raised from 0-180℃ for 60 min, 180℃ for 2 h, 180-300℃ for 60 min, 300℃-500℃ for 40 min, and 500℃ for 2 h, to obtain primary granulation silicon-carbon precursor microspheres.

[0061] Secondary granulation: take the obtained primary granulation silicon-carbon precursor microspheres 1 kg, asphalt 100 g, graphene oxide 100 g, aphanitic graphite 200 g, and Dv50=10 μm graphite 400 g, mix them uniformly, and add them into a high-temperature coating machine for secondary granulation; the temperature rising program is 0-180℃ for 60 min, 180℃ for 2 h, 180-400℃ for 44 min, 400℃ for 1 h, 400℃-900℃ for 100 min, and 900℃ for 2 h; the protective atmosphere during the high-temperature carbonization process is argon, and the oxygen content is <5 ppm throughout the process; and the secondary granulation silicon-carbon composite material is obtained after discharging.

[0062] Surface modification: take the secondary granulation silicon-carbon composite material 10 kg and polyethylene glycol with a molecular weight of 2000 200 g, add them into a stirred tank, add distilled water and stir for 1 h, add the liquid into a drying machine and evaporate, sieve after discharging, and obtain the secondary granulation silicon-carbon composite material with a self-assembled conductive structure after surface modification.

[0063] Weigh 0.07g of surface-modified secondary granulated silicon-carbon composite material with self-assembled conductive structure, 0.014g of conductive carbon black Super P, 0.25g of single-walled carbon nanotubes, 0.0075g of sodium carboxymethyl cellulose binder, and 0.1875g of PAA binder. Add 2.5ml of deionized water and stir magnetically for 1h. Coat the material onto copper foil (14mm in diameter) with a loading of 0.6mg, dry, and press to form an electrode. Use a lithium metal sheet as the counter electrode and assemble it into a CR 2016 button battery in a glove box.

[0064] Figure 1 The image shows the XRD pattern of the surface-modified secondary granulated silicon-carbon composite material with a self-assembled conductive structure prepared in Example 1. The nano-silicon powder used is consistent with JCPDS No. 27-1402, and no other obvious impurity peaks are present, indicating that the material prepared by this process has high purity.

[0065] Figure 2 The images shown are transmission electron microscope (TEM) images of the self-assembled structure prepared in Example 1. In the images, a) and b) are TEM images of the composite material wrapped with a large sheet of thin-layered graphene oxide with rich folds at different magnifications, respectively. It can be observed that the graphene oxide exists in the outermost layer of the material. In the images, c) and d) show cryptocrystalline graphite conductive intercalations at different magnifications. The layered structure of graphite can be seen. This layered graphite structure is a self-assembled conductive intercalation of the material, which is used to accelerate the electronic / ionic conductivity between silicon-carbon precursor particles.

[0066] Figure 3 This is a SEM image of the secondary granulated silicon-carbon material with a self-assembled conductive structure prepared in Example 1. In the image, e) is the silicon-carbon self-assembled conductive material with a fully encapsulated graphite core, and f) shows small graphite particles in the upper right corner. Figure 3 As shown, large-particle graphite is used as the granulation core, and the primary particles are adhered to the outer layer of graphite through the bonding effect of pitch. (Scanning electron microscopy data are used.) Figure 3 As can be seen in this embodiment, the curled structure around the silicon-carbon monomer is formed by pitch-derived carbon wrapped around the surface of the pulverized graphene sheets. The silicon particles are wrapped by pitch-derived carbon and curled graphene, forming a pitch-coated nano-silicon composite self-assembled structure with graphene conductive framework as the main body.

[0067] Figure 6Infrared spectrum of the secondary granulated silicon-carbon material with self-assembled conductive structure obtained in Example 1. The Si-OC bond is beneficial to the structural stability of the silicon-carbon material. Introducing this covalent bond during the sintering process of oxygen-containing conductive agents such as graphene oxide with the silicon-carbon material can form a more stable chemical structure, which helps improve the overall stability of the negative electrode material. This stability helps reduce material pulverization caused by volume changes during charging and discharging, thereby improving the cycle life of the battery.

[0068] Figure 7 This is an XPS high-resolution spectrum of the Si 2p layer of the secondary granulated silicon-carbon material with a self-assembled conductive structure prepared in Example 1. The spectrum demonstrates the existence of Si-OC bonds, indicating a chemical bond between the surface carbon layer and silicon, rather than a simple physical bond.

[0069] Figure 8 The image shows the XPS high-resolution spectrum of C 1s in the secondary granulated silicon-carbon material with a self-assembled conductive structure prepared in Example 1. Three peaks are observed at 284.19, 284.77, and 285.92 eV, corresponding to the presence of C-Si, CC / C=C, and CO bonds, respectively. (Summary) Figure 8 and Figure 7 It can be determined that there are multiple bonding bridges between the carbon layer and the internal silicon-based material, which is consistent with infrared spectroscopy. Figure 6 They corroborate each other. Example 2

[0070] A method for preparing a multi-granulated silicon-carbon material with a self-assembled conductive structure includes the following steps:

[0071] Take 36 kg of 325 mesh metallic silicon powder and disperse it in a stirred tank containing 114 kg of diethylene glycol dimethyl ether solvent. Stir and disperse at 600 r / min for 1 h. Pump the suspension into a sand mill through a diaphragm pump and mill at 1250 r / min for 4 h. After drying, obtain nano-silicon powder. Test it with a Winner2018 micro-nano particle size analyzer. The Dv50 is controlled to be 550 ± 20 nm according to the milling time.

[0072] Take the obtained nanometer silicon powder 1.275 kg, 125 g of asphalt after crushing by the crusher, 100 g of glucose, add it into the high-speed mixer, stir and disperse; after discharging, add the powder into the coating machine, stir at a speed of 20 r / min, pass argon through the high-pressure cylinder, and wait for the oxygen content to decrease to 1-5 ppm before starting heating; the temperature rising process takes 80 min from 0-300°C, 60 min at 300°C, 60 min from 300-500°C, 80 min from 500-900°C, and 2 h at 900°C. After high-temperature carbonization, discharge and pack to obtain the sintered primary granulated silicon-carbon precursor microspheres.

[0073] Take the obtained graphene-based sub-micron silicon sphere precursor 1 kg, asphalt 100 g, glucose 50 g, aphanitic graphite 200 g, graphene oxide 100 g, and Dv50=10 μm graphite 400 g, mix uniformly, add into the high-temperature coating machine for secondary granulation, the temperature rising program is 60 min from 0-180°C, 2 h at 180°C, 44 min from 180-400°C, 1 h at 400°C, 100 min from 400-900°C, and 2 h at 900°C, the protection atmosphere during high-temperature carbonization is argon, the oxygen content is <5 ppm throughout the process, and the discharge obtains the secondary granulated silicon-carbon composite material.

[0074] Add 1 kg of the secondary granulated silicon-carbon composite material and 20 g of polyethylene glycol into the stirred kettle, add distilled water and stir for 1 h, evaporate the liquid in the drying machine, sieve after discharging, and obtain the surface-modified secondary granulated silicon-carbon composite material with self-assembled conductive structure.

[0075] Take 0.07 g of the silicon-carbon composite material, 0.0145 g of conductive carbon black super P, 0.125 g of single-walled carbon nanotubes, 0.0075 g of sodium carboxymethyl cellulose binder, and 0.1875 g of PAA binder, add 2.5 ml of deionized water, magnetically stir for 1 h, coat the material on a copper foil (diameter of 14 mm) with a loading of 0.6 mg, dry, press into a sheet to make an electrode, use a lithium metal sheet as the counter electrode, and assemble into a CR 2016 type button cell in the glove box. Example 3

[0076] A method for preparing a multi-granulated silicon-carbon material with a self-assembled conductive structure, comprising the following steps:

[0077] Take 24 kg of 325 mesh metal silicon powder, disperse it in a stirred tank containing 114 kg of diethylene glycol methyl ether solvent, stir and disperse at a speed of 600 r / min for 1 h, pump the suspension into a sand mill through a diaphragm pump at a speed of 1350 r / min, and sand mill for 3 h. After drying, nano silicon powder is obtained. Test by Jinan micro-nano particle size tester Winner2018. Control Dv50=550±20 nm according to sand milling time.

[0078] Take 1.275 kg of the above nano silicon powder, 225 g of asphalt after crushing by a crusher, and 150 g of needle coke into a high-speed stirrer, stir and disperse; after discharging, add the powder into a ball mill with a ball-to-material ratio of 3:1, ball mill for 8 h, discharge, and add into a coating machine with a stirring speed of 20 r / min. Pass nitrogen or argon through a high-pressure gas cylinder, and wait until the oxygen content is reduced to 1-5 ppm before heating. During the heating process, the temperature is raised from 0-300°C for 80 min, kept at 300°C for 60 min, raised from 300-500°C for 60 min, raised from 500-900°C for 80 min, and kept at 900°C for 2 h. After the first granulation by high-temperature carbonization, discharge and pack to obtain sintered first granulation silicon-carbon precursor microspheres.

[0079] Take 1 kg of the above first granulation silicon-carbon precursor microspheres, 100 g of asphalt, 400 g of graphite with Dv50=10 μm, 100 g of aphanitic graphite, and 100 g of graphene oxide, mix uniformly, and add into a high-temperature coating machine for secondary granulation. The temperature raising program is as follows: 0-180°C for 60 min, kept at 180°C for 2 h, 180-400°C for 44 min, kept at 400°C for 1 h, 400-900°C for 100 min, and kept at 900°C for 2 h. The protective atmosphere during high-temperature carbonization is argon, and the oxygen content is <5 ppm throughout the process. Discharge to obtain secondary granulation silicon-carbon material with self-assembled conductive structure.

[0080] Take 0.07 g of secondary granulation silicon-carbon material with self-assembled conductive structure, 0.0145 g of conductive carbon black super P, 0.125 g of single-walled carbon nanotubes, 0.0075 g of sodium carboxymethyl cellulose binder, and 0.1875 g of PAA binder, add 2.5 ml of deionized water, and magnetically stir for 1 h. Coat the material on a copper foil (diameter 14 mm) with a loading of 0.6 mg, dry, press into a sheet to make an electrode, use a lithium metal sheet as a counter electrode, and assemble into a CR 2016 type button cell in a glove box. Example 4

[0081] A method for preparing a multi-granulation silicon-carbon material with self-assembled conductive structure, comprising the following steps:

[0082] Take 36 kg of 325 mesh metal silicon powder, disperse it in a stirred tank containing 114 kg of diethylene glycol methyl ether solvent, stir and disperse at a speed of 600 r / min for 1 h, pump the suspension into a sand mill through a diaphragm pump, and sand mill at a speed of 1250 r / min for 4 h. After drying, nano-silicon powder is obtained. The Dv50 is controlled to be 550±20 nm according to the sand milling time by using Jinan micro-nano particle size tester Winner2018.

[0083] Preparation of one-time granulated silicon-carbon precursor microspheres: take 1.275 kg of the obtained nano-silicon powder, 225 g of crushed asphalt and 100 g of powdered phenolic resin after crushing by a pulverizer, add them into a high-speed stirrer and stir and disperse; after discharging, add the powder into a coating machine for one-time granulation, control the stirring speed at 20 r / min, pass argon through a high-pressure gas cylinder, and start heating after the oxygen content is reduced to 1-5 ppm; during the heating process, heat at 0-180 ℃ for 60 min, keep at 180 ℃ for 2 h, heat at 180-300 ℃ for 60 min, heat at 300-500 ℃ for 40 min, and keep at 500 ℃ for 2 h to obtain one-time granulated silicon-carbon precursor microspheres.

[0084] Preparation of secondary granulated silicon-carbon composite material: take 1 kg of the obtained one-time granulated silicon-carbon precursor microspheres, 300 g of asphalt, 100 g of graphene oxide, 200 g of aphanitic graphite, and 400 g of Dv50=10 μm graphite, mix uniformly, add them into a high-temperature coating machine for secondary granulation, and heat according to the following procedure: heat at 0-180 ℃ for 60 min, keep at 180 ℃ for 2 h, heat at 180-400 ℃ for 44 min, keep at 400 ℃ for 1 h, heat at 400-900 ℃ for 100 min, and keep at 900 ℃ for 2 h. The protective atmosphere during the high-temperature carbonization process is argon, and the oxygen content is <5 ppm throughout the process. The obtained secondary granulated silicon-carbon composite material has a self-assembled conductive structure.

[0085] Take 0.07 g of the secondary granulated silicon-carbon composite material, 0.0145 g of conductive carbon black super P, 0.125 g of single-walled carbon nanotubes, 0.0075 g of sodium carboxymethyl cellulose binder, and 0.1875 g of PAA binder, add 2.5 ml of deionized water, and magnetically stir for 1 h. Coat the material on a copper foil (diameter of 14 mm) with a loading of 0.6 mg, dry, press into a sheet to make an electrode, use a lithium metal sheet as the counter electrode, and assemble into a CR 2016 type button cell in a glove box. Example 5

[0086] A method for preparing a multi-time granulated silicon-carbon material with a self-assembled conductive structure, comprising the following steps:

[0087] Take 36 kg of 325 mesh metal silicon powder, disperse it in a stirred tank containing 114 kg of diethylene glycol methyl ether solvent, stir and disperse at a speed of 600 r / min for 1 h, pump the suspension into a sand mill through a diaphragm pump, stir at a speed of 1250 r / min for 4 h, dry, and obtain nano silicon powder, test by Jinan micro-nano particle size tester Winner2018, control Dv50=550±20 nm according to the length of sanding.

[0088] Primary granulation of silicon-carbon precursor microspheres: take 1.275 kg of the obtained nano silicon powder, 200 g of crushed asphalt and 100 g of glucose after crushing by a pulverizer, add them into a high-speed stirrer and stir and disperse; after discharging, add the powder into a coating machine for primary granulation, control the stirring speed at 20 r / min, pass argon through a high-pressure cylinder, and start heating after the oxygen content is reduced to 1-5 ppm; during the heating process, heat at 0-180℃ for 60 min, keep at 180℃ for 2 h, heat at 180-300℃ for 60 min, heat at 300℃-500℃ for 40 min, and keep at 500℃ for 2 h, to obtain primary granulated silicon-carbon precursor microspheres.

[0089] Secondary granulation of silicon-carbon composite material: take 1 kg of the obtained primary granulated silicon-carbon precursor microspheres, 300 g of asphalt, 100 g of graphene oxide, 200 g of aphanitic graphite, and 400 g of Dv50=10 μm graphite, mix uniformly, add them into a high-temperature coating machine for secondary granulation, and the heating program is as follows: heat at 0-180℃ for 60 min, keep at 180℃ for 2 h, heat at 180-400℃ for 44 min, keep at 400℃ for 1 h, heat at 400℃-900℃ for 100 min, and keep at 900℃ for 2 h; the protective atmosphere during high-temperature carbonization is argon, and the oxygen content is <5 ppm throughout the process; discharge to obtain secondary granulated silicon-carbon composite material with self-assembled conductive structure.

[0090] Third coating of phenolic resin: take 50 g of secondary granulated silicon-carbon composite material, add 10 g of water-soluble phenolic resin, add 500 ml of distilled water and 50 g of anhydrous ethanol, stir for 1 h, evaporate the distilled water and anhydrous ethanol mixed solvent, obtain a mixture of water-soluble resin wrapped silicon-carbon composite material, pour into a porcelain boat, and carbonize at 900℃ to obtain a third coated silicon-carbon composite material, and the water-soluble phenolic resin is from Shanghai Yiluofe Company.

[0091] Take 0.07 g of three times coated silicon-carbon composite material, 0.0145 g of conductive carbon black super P, 0.125 g of single-walled carbon nanotubes, 0.0075 g of sodium carboxymethyl cellulose binder, 0.1875 g of PAA binder, add 2.5 ml of deionized water, magnetically stir for 1 h, coat the material on a copper foil (diameter 14 mm), the loading is 0.6 mg, dry, press into an electrode, use a metal lithium sheet as the counter electrode, assemble into a CR 2016 type button cell in the glove box. The CR2016 type button cell process is the same as example 1.

[0092] Comparative example 1

[0093] A method for preparing a one-time granulated silicon-carbon material, comprising the following steps:

[0094] Take 1.275 kg of nanosilicon powder prepared under the same conditions as example 1, 225 g of asphalt after being crushed by a crusher, and 150 g of graphene oxide, add them to a high-speed stirrer, stir and disperse at a frequency of 20 Hz for 1 h.

[0095] After discharging, add the above material to a high-temperature coating machine, stir at a speed of 20 r / min, pass nitrogen or argon through a high-pressure gas cylinder, and wait for the oxygen content to drop to 1-5 ppm before starting heating; during the heating process, 0-180℃ for 60 min, 180℃ for 2 h, 180-300℃ for 60 min, 300℃-900℃ for 100 min, 900℃ for 2 h, to obtain a one-time granulated silicon-carbon material.

[0096] The CR2016 type button cell process and test conditions are the same as example 1.

[0097] Comparative example 2

[0098] A method for preparing a high-performance silicon-carbon composite material on a large scale and designing a composite self-assembly structure, comprising the following steps:

[0099] (1) Take 1.275 kg of nanosilicon powder in example 1, 225 g of asphalt after being crushed by a crusher, take 100 g of asphalt, 100 g of graphene oxide, and 400 g of graphite, add them to a high-speed stirrer, stir and disperse; after discharging, add the powder to a ball mill, the ball-to-material ratio is 6:1, and ball mill for 8 h.

[0100] (2) The above-mentioned nano-silicon powder and asphalt mixed material after ball milling is added to a coating machine, the stirring speed is 20 r / min, nitrogen or argon is introduced through a high-pressure gas cylinder, and heating is started after the oxygen content is reduced to 1-5 ppm; the temperature is raised from 0-300°C for 80 min, kept at 300°C for 60 min, raised from 300-500°C for 60 min, raised from 500-900°C for 80 min, and kept at 900°C for 2 h. After high-temperature carbonization, the material is discharged and packaged to obtain the sintered.

[0101] 0.07 g of unmodified silicon-carbon composite material, 0.0145 g of conductive carbon black super P, 0.125 g of single-walled carbon nanotubes, 0.0075 g of sodium carboxymethyl cellulose binder, and 0.1875 g of PAA binder are weighed, 2.5 ml of deionized water is added, and magnetic stirring is performed for 1 h. The material is coated on a copper foil (diameter of 14 mm) with a loading of 0.6 mg, dried, and pressed into an electrode. A metal lithium sheet is used as the counter electrode, and a CR 2016 type button cell is assembled in a glove box.

[0102] Figure 4 The scanning electron microscope image of the graphene-based particles prepared by only one granulation for Comparative Example 2 shows that the graphene wrinkle structure and large sheet structure can be observed, and the silicon-carbon material is attached in the graphene wrinkle structure. The mechanical properties of graphene itself can help the silicon-carbon material to maintain contact points with the material during the volume expansion and contraction during charging and discharging. This structure design is beneficial to improving the long cycle stability of the material. However, this structure only uses one coating, and the material structure has the problem of not being tightly wrapped enough, and the capacity retention rate is lower than that of the embodiment.

[0103] Comparative Example 3

[0104] A large-scale preparation of a high-performance silicon-carbon composite material and a composite self-assembly structure design thereof, comprising the following steps:

[0105] 1 kg of silicon-carbon precursor material of Example 1 is used for carbon coating on the material surface by gas phase deposition method to form a uniform carbon layer wrapped by small molecule gas carbon source. The experimental temperature is 760°C, and the carbon content of gas phase deposition coating accounts for 10% of the total weight of the sample.

[0106] 1 kg of CVD silicon-carbon composite material and 20 g of polyethylene glycol are added to a stirred tank, distilled water is added and stirred for 1 h, the liquid is added to a drying machine and evaporated, and the material is sieved after discharge to obtain the CVD silicon-carbon composite material of Comparative Example 3.

[0107] 0.07 g of the silicon-carbon composite material prepared by the CVD method, 0.0145 g of conductive carbon black super P, 0.125 g of single-walled carbon nanotubes, 0.0075 g of sodium carboxymethyl cellulose binder, 0.1875 g of PAA binder, and 2.5 ml of deionized water were weighed, magnetically stirred for 1 h, and coated on a copper foil (14 mm in diameter) to obtain a loading of 0.6 mg. The material was dried and pressed into an electrode. A lithium metal sheet was used as the counter electrode to assemble a CR 2016 type coin cell battery in a glove box.

[0108] Performance test

[0109] The materials prepared in the above examples and comparative examples were characterized by thermogravimetric analysis (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Fourier infrared spectroscopy (FTIR) to analyze the morphology, component content, and chemical bond type of the materials.

[0110] X-ray diffraction was performed on the materials using a German D8 Advance X-ray diffractometer, with a Cu target as the radiation source, a ray wavelength λ CuKα = 0.15406 nm, an angle of 5°≤2θ≤90°, a test voltage of 40 kV, and a current of 40 mA. Fourier transform infrared spectroscopy was performed using a German Bruker Tensor, with a collection range of 0~3000 cm -1 . Specific surface area analysis was performed using a Beijing Belsize 3H-200PSI, with N2 as the adsorption gas. X-ray photoelectron spectroscopy was performed using a Kratos Axis UltraDLD. Scanning electron microscopy was performed using a German LEO 1530VP cold field SEM to analyze the microstructure of the material. Transmission electron microscopy was performed using a Japanese JEM-2100HR TEM to observe the internal structure of the material.

[0111] The materials prepared in the above examples and comparative examples were tested by constant current charge and discharge, rate performance, impedance, and long cycle tests to study the resistance of the material surface, long cycle stability, large current interference resistance, and lithium storage mechanism.

[0112] This invention primarily improves upon the traditional sand-milling silicon-coated carbon process to prepare silicon-carbon composite materials with uniform carbon layer coating, moderate specific surface area, high specific capacity, environmental friendliness, and low cost. A simple process was used to achieve the self-assembly of silicon-carbon and graphene, exploring a process route for the mass production of graphene-coated silicon-carbon materials. Furthermore, the impact of increased carbon content on the rate performance of the material was investigated through subsequent secondary coating. After the batteries prepared in the above examples were placed for 24 hours, they were all tested using a battery tester (Shenzhen Xinwei) and BTS8.0.0 software. The test temperature was 25℃, and the current density was 0.2-20 A·g⁻¹. Constant current charge-discharge (discharge cutoff voltage 0.01 V, charging cutoff voltage 2 V) was applied to various types of batteries to test their long-cycle performance. The electrochemical performance of the examples and comparative samples is detailed in Table 1. Table 1 includes five examples and three comparative examples related to the preparation of multi-granulated silicon-carbon materials with self-assembled conductive structures. Examples 1 and 2 used a secondary coating process to construct self-assembled conductive structures and then performed surface modification to obtain surface-modified secondary granulated silicon-carbon composite materials with self-assembled conductive structures. Examples 3 and 4 both used a secondary coating process to construct self-assembled conductive structures. Example 5, based on Example 1, added a water-soluble resin re-coating, achieving a layer of hard carbon on the surface of the secondary granulated particles to further enhance the material's resistance to silicon expansion stress, resulting in a tertiary coated silicon-carbon composite material. Comparative Example 1 is a material prepared by primary granulation without the addition of multi-scale conductive agents. Comparative Example 2 is a material prepared by primary granulation using only a single coating process, combining multiple conductive agents with silicon nanoparticles. Comparative Example 3 is a sample with secondary carbon coating using the CVD method.

[0113] Table 1

[0114]

[0115] As shown in Table 1, Examples 1-5 differ from existing materials in that they possess a multi-layered self-assembled conductive structure with graphite as the core, achieving an initial coulombic efficiency of over 85.63% at 2A g. -1 After 600 cycles at a current density, it still has 785.78 mAh g. -1 The above-mentioned charging specific capacity and capacity retention rate of 58.09%-75.36% are achieved through multiple granulation processes and adjustment of the Dv50 to 5-10μm. The specific surface area of ​​the embodiment can be controlled between 5.9121-17.82m². 2 g -1 All meet the requirements of the national standard GB / T 38823-2020. All are 2A g. -1The capacity retention rate of the composite material examples 1-5 using the multiple granulation process is 58.09%-75.36%, which is significantly higher than the 34.39%-40.32% of the comparative examples 1 and 2 using only one granulation process.

[0116] The process used in comparative example 3 is a common CVD carbon coating method. The material prepared by this method has a capacity retention rate of 54.85% after 600 cycles, which seems to be similar to the retention rate of 58.09% of technical example 2 used in the present application. However, the comprehensive performance of the product obtained by comparative example 3 is definitely inferior to the worst case of the present application. More importantly, the coating process used in the secondary granulation of the present application is simpler, safer and lower in cost compared to the CVD process, and has a significant advantage in large-scale production.

[0117] Comparative example 2 only uses one granulation high-temperature sintering process. The conductive agent and silicon nanoparticles are mixed using a simple mixing process. The specific surface area of the material is 29.4520m 2 g -1 and the particle size Dv50=1.456μm, which is smaller than the index of commercial silicon carbon (Dv50 of commercial silicon carbon is generally between 5-10μm, 1.456μm is too small and will agglomerate when using a pulper to make pulp). Comparative example 2 has a charge specific capacity of only 529.34mAh g -1 mAh g -1 at a current density of 2A g -1 , and a capacity retention rate of 34.39%; while the worst case of the present application, example 2, has a charge specific capacity of only 874.62mAh g -1 mAh g -1 at a current density of 2A g -1 , and a capacity retention rate of 58.09%; the preparation method of the multiple granulation silicon-carbon material with self-assembled conductive structure of the present application significantly improves the rate performance and material cycle retention rate.

[0118] Figure 5 Figure 1 is a long cycle performance graph of the surface-modified secondary granulation silicon-carbon composite material with self-assembled conductive structure of the present example 1. The material still has a charge specific capacity of 1047.08mAh g -1 mAh g -1 at a current density of 2A g -1 , and a charge specific capacity of 861.94mAh g -1 at a current density of 2A g -1At current densities of 4A g, the capacity retention rate after 600 cycles is higher than 60%, which is 20% higher than that of Comparative Example 1, demonstrating high stability. The example also exhibits good rate performance: at higher current densities such as 4A g... -1 8A g -1 Below, the capacity remains at 750mAh g -1 Above, the capacity retention rate after 300 laps is 70%, significantly higher than the capacity and retention rate of Comparative Example 1. Figure 10 Rate performance test, 20A g -1 At current densities above 500 mAh g, the material in Example 1 still exhibits a current density higher than 500 mAh g. -1 The capacity retention rate, through the above comparison, proves that the material with secondary granulation to achieve self-assembled conductive structure has superior performance in resisting high current impact compared with the material without secondary granulation. By adding conductive agents of different sizes, the self-assembled conductive structure has more electron / ion channels and conductive sites, which improves the rate performance and solves the capacity decay problem caused by loss of contact due to pulverization during long cycling of silicon-based materials.

[0119] Data from Example 1 and Comparative Example 1 show that the multi-self-assembled structure constructed based on secondary granulation exhibits significant advantages in the cyclic stability of the material, even at the same 2A g. -1 After 600 cycles at a current density of [insert current density here], the first-stage granules exhibited only 40.32% capacity retention, lower than the 73.50% retention of the sample after secondary granulation. Regarding rate performance, Example 1 at 4 A g [insert current density here]... -1 With 8A g -1 The remaining charge capacity showed no significant difference after 300 cycles at high current density, demonstrating the structural advantage of this design in resisting the impact of high current density. Due to the use of a secondary coating process and a multi-scale conductive structure, when electrons / ions migrate at high rates, the self-assembled conductive structure facilitates conduction. For example, the cryptocrystalline graphite intercalation ensures rapid electron / ion conduction between silicon precursors, and the large-sheet graphene ensures a rapidly conductive layered structure between the large particles of the secondary coating. The active material silicon can combine with lithium ions in a shorter time, releasing capacity. The effective secondary coating can alleviate the expansion of silicon materials. The graphite particle core acts as an internal support, improving the pulverization problem of isolated silicon-based materials. The external carbon layer and the self-assembled conductive structure alleviate the expansion stress of silicon materials. In practical applications, this design can reduce the expansion rate of the battery cell. In consumer battery applications such as e-cigarettes and emergency power supplies that require high-rate instantaneous discharge, this structural design can protect the negative electrode of the material.

[0120] Figure 9 The surface-modified secondary granulated silicon-carbon material with a self-assembled conductive structure prepared in Example 1 was subjected to oxidation at 25°C and 0.2 A g.-1 The first three circle charge-discharge specific capacity curves at a current density of 0.5-20 A g-1. The figure shows that the voltage window is 0.01-2 V, the first coulombic efficiency of the material is greater than 88%, the charge specific capacity is 2062.90 mAh g-1 -1 .

[0121] Figure 10 The rate performance graph of the prepared secondary granulated silicon-carbon material with self-assembled conductive structure of Example 1 and Example 3 is 0.5-20 A g-1 -1 The figure shows that the reversible capacity size of the material in response to different current shocks is tested by the test process from small current to large current, compared with 20 A g-1 -1 The reversible specific capacity after the current density shock of 0.5-20 A g-1 -1 The reversible specific capacity after the current density shock of 0.5-20 A g-1 -1 The reversible specific capacity of the material after the current density shock of 0.5-20 A g-1 -1 The reversible specific capacity of the material after the current density shock of 0.5-20 A g-1 -1 The reversible specific capacity of the material after the current density shock of 0.5-20 A g-1

[0122] From the above examples, the present application has the following characteristics:

[0123] The graphite used in the present application is the material core, and the outer layer is wrapped with silicon-carbon. The composite material prepared by using graphene oxide as a conductive network and cryptocrystalline graphite as a conductive intercalation structure shows excellent cycle stability at 4 A g-1 -1 And 8 A g-1 -1 The large current density, which shows that the adhesion of pitch-derived carbon on graphene is beneficial to the formation of a more tightly wrapped conductive carbon layer of the silicon-carbon composite graphene material, and reflects the role of the structure in relieving the expansion stress of silicon. According to the transmission electron microscope and scanning electron microscope results, the successful preparation of the self-assembled structure can be observed.

[0124] The silicon-carbon composite graphene material of the present application as a high-performance lithium ion battery negative material has excellent lithium ion transmission rate, long cycle stability, rate performance and higher specific capacity, and is suitable for new energy automobile power battery field and has significant advantages in consumer battery field, and is especially suitable for emergency power supply requiring instantaneous high-rate discharge.

[0125] The above examples are only used to explain the present application, but not to limit the present application. Changes, replacements, modifications, etc. made by those skilled in the art without departing from the spirit and essence of the present application shall belong to the protection scope of the present application.

Claims

1. A method for producing a multi-granulated silicon-carbon material with self-assembled conductive structures, characterized in that It comprises the following steps: 1) carbon source with softening point of 150-200 DEG C and nano silicon powder are put into a mixer to mix, to obtain a mixture; add a high temperature coating machine once sintering, over 200-500 mesh sieve, to obtain a sub-micron size once granulation silicon carbon precursor microspheres; the carbon source with softening point of 150-200 DEG C is one of the following three cases: (1) pitch; (2) pitch and phenolic resin combination; (3) pitch and glucose combination; the temperature rising procedure of the once sintering is 0-180 DEG C uniform speed heating 1-2h, 180 DEG C heat preservation 1-2h, 180-300 DEG C uniform speed heating 1-2h, 300 DEG C-500 DEG C uniform speed heating 1-2h, 500 DEG C heat preservation 2-4h; 2) the once granulation silicon carbon precursor microspheres, carbon additive, graphene oxide, aphanitic graphite, D50=9-12 μm graphite are put into a mixer to mix uniformly, the material is added to a high temperature coating machine to sinter twice, to obtain secondary granulation silicon carbon composite material; the carbon additive is pitch, or is a combination of pitch and glucose; the temperature rising procedure of the twice sintering is 0-180 DEG C uniform speed heating 1-2h, 180 DEG C heat preservation 2-4h, 180-400 DEG C uniform speed heating 40-60min, heat preservation 1-2h, 400 DEG C-900 DEG C uniform speed heating 100-160min, 900 DEG C heat preservation 2-4h.

2. The method of claim 1, wherein the method further comprises: The multiple granulation silicon carbon material further comprises that the secondary granulation silicon carbon composite material is subjected to thrice granulation or the secondary granulation silicon carbon composite material is subjected to surface modification; The thrice granulation of the secondary granulation silicon carbon composite material is obtained by mixing the secondary granulation silicon carbon composite material, water-soluble phenolic resin, distilled water and anhydrous ethanol, stirring and evaporating; an amorphous carbon layer is added to the secondary granulation silicon carbon composite material; The surface modification of the secondary granulation silicon carbon composite material is obtained by mixing the secondary granulation silicon carbon composite material, distilled water and high molecular surfactant, stirring, drying and sieving, to obtain a silicon carbon composite material with hydrophilic surface.

3. The method of claim 2, wherein the method further comprises: In the thrice granulation, the mass ratio of the secondary granulation silicon carbon composite material, water-soluble phenolic resin, distilled water and anhydrous ethanol is 5:(1-2):(8-12):(0.5-2); In the surface modification, the high molecular surfactant is one or more of polyethylene glycol, polyvinylpyrrolidone, polyoxyethylene fatty acid ester and sodium carboxymethyl cellulose; the mass ratio of the secondary granulation silicon carbon composite material, distilled water and high molecular surfactant is (2-3):10:(0.04-0.06).

4. The method of claim 1, wherein the method further comprises: In step 1), the mass ratio of the carbon source and nano silicon powder is 1:5-2:

5.

5. The method of claim 4, wherein the method further comprises: The carbon source is first crushed by a crusher before use; The Dv50 of the aphanitic graphite is less than 1 μm; The thickness of the graphene oxide is less than 3nm, the particle size is distributed between 20-40μm, and the specific surface area is 40-50m 2 / g.

6. The method of claim 1, wherein the method further comprises: Argon gas is added in the process of the once sintering and the twice sintering to form a protective atmosphere, and the oxygen content is controlled at 1-5 ppm.

7. The method of claim 1, wherein the method further comprises: The nano-silicon powder is prepared by wet sanding; the rotation speed of the wet sanding is 1000-1500 r / min, the sanding duration is 2-6 h, the particle size Dv50 of the silicon powder after grinding is controlled to be 400-600 nm, and the silicon powder is stored and used by vacuum packaging; the solvent for the wet sanding is selected from one or more of diethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether and oleic acid, and the solid content is controlled to be 20-50% during sanding.

8. A multi-granulated silicon-carbon material with self-assembled conductive structures, characterized in that, It is prepared by the preparation method of any one of claims 1-7.

9. Use of the multi-granulated silicon-carbon material with self-assembled conductive structure of claim 8 in the preparation of a lithium ion battery negative electrode material.

10. Use of the multi-granulated silicon-carbon material with self-assembled conductive structure according to claim 9 for the preparation of a negative electrode material for lithium-ion batteries, characterized in that, The lithium ion battery negative electrode material is prepared by mixing the multi-granulated silicon-carbon material with self-assembled conductive structure, a conductive agent, CMC and PAA to make a slurry, and coating the slurry on a copper foil to obtain a lithium ion battery negative electrode sheet; the mass ratio of the multi-granulated silicon-carbon material with self-assembled conductive structure, the conductive agent, CMC and PAA is (5-16):(3-2):(0.5-2):1; and the conductive agent is carbon black and / or single-walled carbon nanotubes.

Images