Silicon-carbon negative electrode material, and preparation method therefor and use thereof

Abstract

A silicon-carbon negative electrode material, and a preparation method therefor and the use thereof. The preparation method comprises the following steps: conveying a silicon powder, a polyoxypropylene-polyoxyethylene copolymer and an organic solvent to a sealing tank having nitrogen protection, and dispersing same to obtain a first slurry; subjecting the first slurry to an aging treatment, a coarse grinding treatment and a fine grinding treatment to obtain a fourth slurry; and mixing the fourth slurry and an organic carbon source, and subjecting the mixture to a dispersion treatment, a spray drying treatment and a sintering treatment to obtain a silicon-carbon negative electrode material. By means of the dispersion treatment, aging treatment, coarse grinding treatment and fine grinding treatment of specific processes, a silicon-carbon negative electrode material having a small particle size and a narrow particle size distribution can be obtained, thereby improving the cycling stability of a battery assembled by means of the silicon-carbon negative electrode material.

Description

A silicon-carbon negative electrode material and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a silicon-carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] Metal alloy materials (such as silicon-carbon materials) are widely used in lithium-ion battery negative electrode materials due to their high specific capacity and high lithium insertion and removal potential. However, the silicon particles in the silicon-carbon material will undergo severe volume expansion during the lithium insertion process, which will cause the active material particles to break and pulverize, and destroy the existing SEI film on the surface of the particles, exacerbating the capacity decay of the battery cell. Currently, the volume expansion of silicon particles is mainly reduced by reducing the particle size, for example, using nano-silicon particles as raw materials. However, due to the high specific surface area of ​​nano-silicon particles, they have poor dispersibility during the preparation process, are easy to agglomerate, and are unevenly distributed. The particle size uniformity of the prepared silicon-carbon negative electrode material is poor, which in turn affects the cycle stability of the silicon-carbon material. Therefore, how to provide a silicon-carbon material with good cycle stability is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0003] The present invention provides a silicon-carbon negative electrode material and its preparation method and application. In the preparation method, by introducing a polyoxypropylene-polyoxyethylene copolymer and coordinating with a specific process, silicon particles with a small particle size, a narrow particle size distribution, and good stability can be obtained. Then, a carbon source with melting properties is combined to achieve uniform coating, thereby avoiding the phenomenon of poor dispersion of silicon particles, easy agglomeration, and uneven carbon layer coating. A silicon-carbon negative electrode material with a small particle size and a narrow particle size distribution can be obtained, thereby improving the cycle stability of a battery assembled with the silicon-carbon negative electrode material. The silicon-carbon negative electrode material provided by the present invention has the advantages of small particle size, narrow particle size distribution, and good uniformity due to the above-mentioned preparation method. The application of the silicon-carbon negative electrode material in a battery is beneficial to improving the cycle stability of the battery. The battery provided by the present invention has excellent cycle stability due to the inclusion of the above-mentioned silicon-carbon negative electrode material.

[0004] A first aspect of the present invention provides a method for preparing a silicon-carbon negative electrode material, comprising the following steps:

[0005] S1: Silicon powder with a Dv50 of 5 μm, polyoxypropylene-polyoxyethylene copolymer, and an organic solvent are transferred to a sealed tank protected by nitrogen and dispersed at a speed of 1000-1500 r / min for 30 minutes to obtain a first slurry; wherein the organic solvent comprises at least one of ethanol, isopropanol, tert-butanol, ethylene glycol, glycerol, and acetone;

[0006] S2: The first slurry is allowed to stand at 30-40° C. for 20-60 minutes for aging to obtain a second slurry;

[0007] S3: conveying the second slurry to a coarse grinder, and coarsely grinding the second slurry using zirconium beads with a particle size of 0.1-0.2 mm for 5-10 hours to obtain a third slurry; wherein the coarse grinding process is performed at a rotation speed of 3000-3400 r / min and a pressure of 1.1-1.2 bar; the Dv50 of the silicon particles in the third slurry is 100-120 nm;

[0008] S4: conveying the third slurry to a fine grinder, and finely grinding the third slurry for 5 to 10 hours using zirconium beads with a particle size of 0.03 to 0.05 mm to obtain a fourth slurry; wherein the fine grinding process is performed at a rotation speed of 2000 to 2500 r / min and a pressure of 1.3 to 1.7 bar;

[0009] The Dv50 of the silicon particles in the fourth slurry is 50-60 nm, and the ratio of the Dv90 of the silicon particles in the fourth slurry to the Dv50 of the silicon particles is (1.35-1.5):1;

[0010] S5: Dispersing the material comprising the fourth slurry and the organic carbon source at a rotation speed of 3500-4000 rpm / min and a pressure of 0.2-0.3 bar for 10 minutes to obtain a fifth slurry having a viscosity of 400-500 cps; the organic carbon source comprises at least one of asphalt, polyacrylonitrile, polyvinyl pyrrolidone, phenolic resin, and epoxy resin;

[0011] S6: conveying the fifth slurry to a spray drying tower with nitrogen protection, and spray drying the slurry at a spray pressure of 0.01-0.1 MPa and an air inlet temperature of 200-300° C., so that the molten organic carbon source is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor; the silicon-carbon precursor has a Dv50 of 6-14.4 μm;

[0012] S7: sintering the silicon-carbon precursor at 800-900° C. for 2.5-3.5 hours to obtain a silicon-carbon negative electrode material, wherein the Dv50 of the silicon-carbon negative electrode material is 5-12 μm; and the ratio of Dv90 to Dv50 of the silicon-carbon negative electrode material is (1.36-1.49):1;

[0013] The particle size corresponding to the cumulative volume fraction of 50% is Dv50, and the particle size corresponding to the cumulative volume fraction of 90% is Dv90.

[0014] In the first slurry, the content of silicon powder is 5.5% by mass to 15% by mass, based on the total mass of the first slurry being 100% by mass;

[0015] In the first slurry, based on the total mass of the first slurry being 100 mass %, the content of the polyoxypropylene-polyoxyethylene copolymer is 0.15 mass % to 1.5 mass %;

[0016] The mass ratio of the silicon powder to the organic carbon source is (3-7): (3-7).

[0017] The preparation method as described above, wherein the outlet temperature of the spray drying is 60-80°C.

[0018] The preparation method as described above, wherein, after the sintering process, further comprises a crushing process and a screening process.

[0019] In the preparation method as described above, in step S5, the material further includes carbon nanotubes.

[0020] In the preparation method as described above, the mass ratio of the carbon nanotubes to the organic carbon source is 1:(1-2).

[0021] The preparation method as described above, wherein the weight average molecular weight of the polyoxypropylene-polyoxyethylene copolymer is 1000-1500.

[0022] The preparation method as described above, wherein the Dv50 change rate of the fourth slurry after being set aside for 2 days is not higher than 3%;

[0023] The Dv50 change rate of the fourth slurry after being set aside for 6 days is not higher than 5%.

[0024] The second aspect of the present invention provides a silicon-carbon negative electrode material, which is prepared using the preparation method described in the first aspect.

[0025] The third aspect of the present invention provides a battery comprising the silicon-carbon negative electrode material described in the second aspect.

[0026] The implementation of the present invention has at least the following beneficial effects:

[0027] The present invention provides a method for preparing a silicon-carbon negative electrode material. The polyoxypropylene-polyoxyethylene copolymer can form a hydrophobic layer on the surface of silicon powder particles, and can also form micelles to wrap silicon particles through the cross-linked structure of the molecules, effectively isolating the interaction forces between the silicon particles, thereby preventing the formation of agglomerates, helping to improve the dispersibility and stability of the silicon particles, and ensuring the uniformity of the distribution of the silicon particles in the material. At the same time, through dispersion treatment, aging treatment, coarse grinding treatment, and fine grinding treatment in specific processes, it is beneficial to obtain silicon particles with small particle size, narrow particle size distribution, and good stability; and combined with a carbon source with melting properties to achieve uniform coating, a silicon-carbon negative electrode material with small particle size and narrow particle size distribution can be obtained, thereby improving the cycle stability of a battery assembled with the silicon-carbon negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG1 is a flow chart of a method for preparing a silicon-carbon negative electrode material in one embodiment of the present invention;

[0029] FIG2 is a SEM image of the third slurry in Example 1 of the present invention;

[0030] FIG3 is a SEM image of the second slurry in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0032] As shown in FIG1 , the first aspect of the present invention provides a method for preparing a silicon-carbon negative electrode material, comprising the following steps:

[0033] S1: Silicon powder with a Dv50 of 5 μm, polyoxypropylene-polyoxyethylene copolymer, and an organic solvent are transferred to a sealed tank protected by nitrogen and dispersed at a speed of 1000-1500 r / min for 30 minutes to obtain a first slurry; wherein the organic solvent comprises at least one of ethanol, isopropanol, tert-butanol, ethylene glycol, glycerol, and acetone;

[0034] S2: The first slurry is allowed to stand at 30-40° C. for 20-60 minutes for aging to obtain a second slurry;

[0035] S3: The second slurry is conveyed to a coarse grinder and coarsely ground using zirconium beads having a particle size of 0.1-0.2 mm for 5-10 hours to obtain a third slurry; wherein the coarse grinding process is performed at a rotation speed of 3000-3400 rpm and a pressure of 1.1-1.2 bar; the Dv50 of the silicon particles in the third slurry is 100-120 nm;

[0036] S4: conveying the third slurry to a fine grinder, and finely grinding the third slurry for 5-10 hours using zirconium beads having a particle size of 0.03-0.05 mm to obtain a fourth slurry; wherein the fine grinding process is performed at a rotation speed of 2000-2500 r / min and a pressure of 1.3-1.7 bar; the Dv50 of the silicon particles in the fourth slurry is 50-60 nm, and the ratio of the Dv90 of the silicon particles in the fourth slurry to the Dv50 of the silicon particles is (1.35-1.5):1;

[0037] S5: Dispersing the material comprising the fourth slurry and the organic carbon source at a rotation speed of 3500-4000 rpm / min and a pressure of 0.2-0.3 bar for 10 minutes to obtain a fifth slurry having a viscosity of 400-500 cps; the organic carbon source comprises at least one of asphalt, polyacrylonitrile, polyvinyl pyrrolidone, phenolic resin, and epoxy resin;

[0038] S6: conveying the fifth slurry to a spray drying tower with nitrogen protection, and spray drying the slurry at a spray pressure of 0.01-0.1 MPa and an air inlet temperature of 200-300° C., so that the molten organic carbon source is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor; the Dv50 of the silicon-carbon precursor is 6-14.4 μm;

[0039] S7: sintering the silicon-carbon precursor at 800-900° C. for 2.5-3.5 hours to obtain a silicon-carbon negative electrode material; the Dv50 of the silicon-carbon negative electrode material is 5-12 μm; and the ratio of Dv90 to Dv50 of the silicon-carbon negative electrode material is (1.36-1.49):1;

[0040] The particle size corresponding to a cumulative volume fraction of 50% is Dv50, and the particle size corresponding to a cumulative volume fraction of 90% is Dv90. Polyoxypropylene-polyoxyethylene copolymers are soluble in organic solvents. Polyoxypropylene-polyoxyethylene copolymers have polyoxyethylene (PEO) segments and polyoxypropylene (PPO) segments, and their chemical composition is HO(C2H4O)m(C3H6O)nH, where m>0 and n>0. The PEO segments are hydrophilic, and the PPO segments are hydrophobic.

[0041] During the specific preparation process, efficient crushing and uniform dispersion of silicon particles are achieved by precisely controlling equipment parameters, the addition ratio and timing of reaction raw materials, which is conducive to obtaining silicon-carbon negative electrode materials with small particle size, narrow particle size distribution and good uniformity.

[0042] In the present invention, the PEO segments in the first slurry interact with the organic solvent to form a hydrophilic layer, and the PPO segments interact with the surface of the silicon powder particles to form a hydrophobic layer, which effectively isolates the interaction force between the silicon particles, thereby preventing the formation of agglomerates; in addition, the polyoxypropylene polyoxyethylene copolymer molecules, under the action of the organic solvent, form a micellar structure that encapsulates the silicon powder particles. This micellar structure is composed of PEO segments and PPO segments, which can encapsulate the silicon particles, provide a good dispersion environment, enhance the dispersion effect, and ensure the uniformity of the distribution of silicon powder particles in the material, thereby helping to improve the cycle stability of the silicon-carbon negative electrode material. Therefore, the polyoxypropylene polyoxyethylene copolymer introduced in the present invention can effectively inhibit the agglomeration of particles from the dual dispersion mechanism of forming a hydrophobic layer and chemical encapsulation.

[0043] The first slurry is allowed to stand at 30-40° C. for 20-60 minutes to perform an aging treatment on the first slurry, so that the components in the first slurry react more fully, the stability of the first slurry is improved, and a second slurry with excellent stability is obtained.

[0044] Grinding the second slurry helps produce silicon particles with a small particle size and narrow particle distribution. The particle size classification of the silicon particles in the slurry can be tested using a laser particle size analyzer. The presence of the polyoxypropylene-polyoxyethylene copolymer prevents agglomeration of silicon particles due to undersized particles in subsequent processing, thereby ensuring uniform distribution. Specifically, in the present invention, coarse grinding is first performed while maintaining a relatively high rotation speed (3000~3400r / min), a relatively low pressure (1.1~1.2bar), and a relatively large zirconium bead particle size (0.1~0.2mm). Then, the rotation speed is reduced (2000~2500r / min), the pressure is increased (1.3~1.7bar), and the zirconium bead particle size is reduced (0.03~0.05mm). Through coarse grinding and fine grinding, the average particle size of the silicon particles can be gradually increased from 3~5μm to 100~120nm, and then from 100~120nm to 50~60nm. Compared with one-step ball milling, this is less likely to cause agglomeration, can improve the stability and dispersibility of the silicon particles in the slurry, and thus improve the uniformity of the silicon-carbon negative electrode material.

[0045] Furthermore, in step S3, the discharge temperature of the third slurry is controlled at 40-45° C., and the cooling water temperature is 8-12° C. In step S4, the discharge temperature of the fourth slurry is controlled at 40-45° C., and the equipment cooling water temperature is 8-12° C.

[0046] In step S5, the material containing the fourth slurry and the organic carbon source can be conveyed to an IMS online dispersion device and dispersed for 10 minutes under nitrogen protection at a speed of 3500-4000 rpm / min and a pressure of 0.2-0.3 bar. The IMS online dispersion device (Intelligence Mixing System) utilizes an online powder and liquid dispersion system. It pumps liquid to generate high-speed flow, creating a strong vacuum in the dispersion zone. This vacuum suction directly draws powder from powder tankers, silos, small bags, and ton bags without loss, and fully disperses and mixes it with the liquid.

[0047] In step S6, since the organic carbon source has the property of melting, the organic carbon source is in a flowing state in the spray dryer, and the molten organic carbon source can be evenly coated on the surface of silicon particles with small particle size and narrow particle size distribution, and a silicon-carbon precursor with a Dv50 of 6~14.4μm can be obtained, which is conducive to the subsequent acquisition of silicon-carbon negative electrode materials with small particle size and narrow particle size distribution, thereby improving uniformity.

[0048] It should be noted that during the spray drying process, the organic solvent evaporates, and the organic carbon source and the polyoxypropylene-polyoxyethylene copolymer are simultaneously coated on the surface of the silicon particles. In other words, the silicon-carbon precursor comprises silicon particles and the polyoxypropylene-polyoxyethylene copolymer and the organic carbon source coated on the surface of the silicon particles. The Dv50 of the silicon-carbon precursor refers to the Dv50 of the silicon particles having the polyoxypropylene-polyoxyethylene copolymer and the organic carbon source coated thereon.

[0049] The organic carbon source includes asphalt and organic polymer; the organic polymer includes at least one of polyacrylonitrile (PAN), polyvinyl pyrrolidone (PVP), phenolic resin and epoxy resin.

[0050] The silicon-carbon precursor is sintered at 800-900°C for 2.5-3.5 hours, and the polyoxypropylene-polyoxyethylene copolymer and the organic carbon source are carbonized to obtain a silicon-carbon negative electrode material with a Dv50 of 5-12 μm. The silicon-carbon negative electrode material has the advantages of small particle size, narrow particle size distribution, and high uniformity. At this time, the silicon-carbon negative electrode material includes silicon particles and a carbon layer coated on the surface of the silicon particles. The carbon layer is obtained by carbonizing the polyoxypropylene-polyoxyethylene copolymer and the organic carbon source. The Dv50 of the silicon-carbon negative electrode material refers to the Dv50 of the silicon particle structure coated with the carbon layer.

[0051] The sintering temperature is 800-900°C, for example, 800°C, 850°C, 900°C or any two thereof, and the sintering time is 2.5-3.5h, for example, 2.5h, 3h, 3.5h or any two thereof.

[0052] According to the research of the present invention, the silicon-carbon negative electrode material prepared by the above-mentioned preparation method, and the battery assembled with the silicon-carbon negative electrode material have excellent cycle stability. This is because, on the one hand, under the action of polyoxypropylene polyoxyethylene copolymer and organic solvent, combined with specific dispersion treatment, aging treatment, coarse grinding treatment, and fine grinding treatment, it helps to improve the dispersibility and stability of silicon particles, ensure the uniformity of distribution of silicon particles in the material, and obtain silicon particles with small particle size, narrow particle size distribution, and good stability, which is conducive to obtaining silicon-carbon negative electrode materials with good uniformity; at the same time, using an organic carbon source as a coating material for silicon particles, the molten organic carbon source is evenly coated on the surface of the silicon particles through spray drying treatment, which is conducive to improving the coating uniformity of the carbon layer, effectively preventing the breakage of silicon particles, and ensuring the cycle stability and structural stability of the silicon-carbon negative electrode material.

[0053] The present invention does not limit the amount of the reaction raw materials and each component. For example, the organic solvent includes at least one of ethanol, isopropanol, tert-butanol, ethylene glycol, glycerol, and acetone; the mass content of silicon powder in the first slurry is 5.5% to 15%, for example, 5.5%, 6%, 7%, 7.5%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range consisting of any two thereof, and the mass concentration of the polyoxypropylene polyoxyethylene copolymer in the first slurry is 0.15% to 1.5%, for example, 0.15%, 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.70%, 0.80%, 0.90%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a range consisting of any two thereof.

[0054] In some embodiments, in step S5, the material further includes carbon nanotubes, that is, the material comprising the fourth slurry, the organic carbon source, and the carbon nanotubes is dispersed at a speed of 3500-4000 rpm / min and a pressure of 0.2-0.3 bar for 10 minutes to obtain a fifth slurry with a viscosity of 400-500 cps, which is then spray-dried to obtain a silicon-carbon precursor comprising silicon particles, an organic carbon source uniformly coated on the surface of the silicon particles, and carbon nanotubes embedded in the organic carbon source. The carbon nanotubes play a complementary role, which is beneficial to improving the conductivity of the silicon-carbon negative electrode material, thereby improving the electrochemical performance of the battery. After sintering, the organic carbon source forms a carbon layer on the surface of the silicon particles, and the carbon nanotubes are embedded in the carbon layer. The carbon layer and carbon nanotubes not only improve the conductivity of the material, but also prevent the silicon particles from breaking and scattering, effectively avoiding the breakage and crushing of the silicon-carbon negative electrode material due to volume changes during the charging and discharging process, and ensuring the cycle stability and structural stability of the silicon-carbon negative electrode material; in addition, it also reduces the direct contact between silicon particles and the electrolyte, improves the electrode / electrolyte interface compatibility, and thus improves the cycle performance.

[0055] The mass ratio of the carbon nanotubes to the organic carbon source is 1:(1-2), such as 1:1, 1:1.5, 1:2 or a range consisting of any two thereof.

[0056] In some embodiments, the outlet temperature of the spray drying process is 60-80°C. In some embodiments, the sintering process further includes crushing and screening. In some embodiments, the weight-average molecular weight of the polyoxypropylene-polyoxyethylene copolymer is 1000-1500. In some embodiments, the Dv50 change rate of the fourth slurry after 2 days of storage is no more than 3%; and the Dv50 change rate of the fourth slurry after 6 days of storage is no more than 5%.

[0057] A second aspect of the present invention provides a silicon-carbon anode material, produced using the preparation method of the first aspect. This silicon-carbon anode material has a core-shell structure consisting of silicon particles coated with a carbon layer. Because it is produced using the preparation method of the first aspect, this silicon-carbon anode material has a small particle size, a narrow particle size distribution, and good uniformity, resulting in excellent electrical conductivity and cycling stability.

[0058] A third aspect of the present invention provides a battery comprising the silicon-carbon negative electrode material of the second aspect. Specifically, the silicon-carbon negative electrode material is coated on a current collector, dried, and cut to obtain a negative electrode sheet, wherein the current collector may be copper foil.

[0059] The above-mentioned battery also includes a positive electrode sheet and a separator. The preparation method of the battery includes the following steps: the negative electrode sheet, the separator and the positive electrode are made into a button battery or a soft-pack battery, thereby producing a battery.

[0060] The present invention will be further described below by way of specific examples and comparative examples. Unless otherwise specified, the reagents, materials, and instruments used below are all conventional reagents, conventional materials, and conventional instruments, all of which are commercially available. The reagents and materials involved can also be synthesized by conventional synthesis methods. The raw materials selected are shown in Table 1 and are as follows:

[0061] Table 1

[0062]

[0063] The CAS number of the graphite flakes is 7782-42-5, the molecular weight is 12, and it was purchased from Shanghai Shanshan Technology Co., Ltd.; the CAS number of the carbon nanotubes is 308068-56-6, the molecular weight is 12, and it was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0064] Example 1

[0065] The method for preparing the silicon-carbon negative electrode material of this embodiment includes the following steps:

[0066] (1) 130 g of silicon powder (Dv50: 5 μm) was mixed with 1603 g of ethanol, and then polyoxypropylene-polyoxyethylene copolymer was added and transported to a sealed tank under nitrogen protection. The mixture was dispersed at a speed of 1000 r / min for 30 min to obtain a first slurry. At this time, the mass content of silicon powder in the first slurry was 7.5%, and the mass concentration of polyoxyethylene-polyoxypropylene copolymer was 0.15%;

[0067] (2) The first slurry was allowed to stand at 30°C for 60 minutes for aging to obtain a second slurry;

[0068] (3) The second slurry was transported to a coarse grinder and coarsely ground for 8 h using zirconium beads with a particle size of 0.1 mm to obtain a third slurry with silicon particles having a Dv50 of 100 nm; wherein the coarse grinding process was performed at a rotation speed of 3400 r / min and a pressure of 1.2 bar;

[0069] (4) The third slurry was transported to a fine grinder and finely ground for 8 h using zirconium beads with a particle size of 0.03 mm to obtain a fourth slurry with a Dv50 of 51 nm. The fine grinding speed was 2500 r / min and the pressure was 1.7 bar. The ratio of Dv90 of the silicon particles to Dv50 of the silicon particles in the fourth slurry was 1.4:1.

[0070] (5) The fourth slurry and 55.7 g of asphalt were dispersed at a rotation speed of 4000 rpm / min and a pressure of 0.2 bar for 10 minutes to obtain a fifth slurry with a viscosity of 410 cps;

[0071] (6) The fifth slurry is transported to a spray drying tower with nitrogen protection, and spray-dried under the conditions of a spray pressure of 0.1 MPa and an inlet air temperature of 250°C, so that the molten asphalt is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor;

[0072] (7) The silicon-carbon precursor was calcined at 850 °C and kept warm for 3 h under nitrogen protection throughout the process to obtain a silicon-carbon negative electrode material.

[0073] Example 2

[0074] The method for preparing the silicon-carbon negative electrode material of this embodiment includes the following steps:

[0075] (1) 130 g of silicon powder (Dv50: 5 μm) was mixed with 1170 g of isopropyl alcohol, and then polyoxypropylene-polyoxyethylene copolymer was added and transported to a sealed tank under nitrogen protection. The mixture was dispersed at a speed of 1500 r / min for 30 min to obtain a first slurry. At this time, the mass content of silicon powder in the first slurry was 10%, and the mass concentration of polyoxyethylene-polyoxypropylene copolymer was 0.6%;

[0076] (2) The first slurry was allowed to stand at 40°C for 20 minutes for aging treatment to obtain a second slurry;

[0077] (3) The second slurry was transported to a coarse grinder and coarsely ground for 10 h using zirconium beads with a particle size of 0.2 mm to obtain a third slurry with silicon particles having a Dv50 of 110 nm; wherein the coarse grinding process was performed at a rotation speed of 3000 r / min and a pressure of 1.1 bar;

[0078] (4) The third slurry was conveyed to a fine grinder and finely ground for 8 h using zirconium beads with a particle size of 0.05 mm to obtain a fourth slurry with a Dv50 of 58 nm. The fine grinding speed was 2000 r / min and the pressure was 1.3 bar. The ratio of Dv90 of the silicon particles to Dv50 of the silicon particles in the fourth slurry was 1.35:1.

[0079] (5) The fourth slurry and 303 g of asphalt were dispersed at a rotation speed of 3500 rpm / min and a pressure of 0.3 bar for 10 minutes to obtain a fifth slurry with a viscosity of 482 cps;

[0080] (6) The fifth slurry is transported to a spray drying tower with nitrogen protection, and spray-dried under the conditions of a spray pressure of 0.05 MPa and an inlet air temperature of 300°C, so that the molten asphalt is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor;

[0081] (7) The silicon-carbon precursor was calcined at 850 °C and kept warm for 3 h under nitrogen protection throughout the process to obtain a silicon-carbon negative electrode material.

[0082] Example 3

[0083] The method for preparing the silicon-carbon negative electrode material of this embodiment includes the following steps:

[0084] (1) 130 g of silicon powder (Dv50: 5 μm) was mixed with 910 g of tert-butanol, and then polyoxypropylene-polyoxyethylene copolymer was added and transported to a sealed tank under nitrogen protection. The mixture was dispersed at a speed of 1200 r / min for 30 min to obtain a first slurry. At this time, the mass content of silicon powder in the first slurry was 12.5%, and the mass concentration of polyoxyethylene-polyoxypropylene copolymer was 1.25%;

[0085] (2) The first slurry was allowed to stand at 35°C for 40 minutes for aging to obtain a second slurry;

[0086] (3) The second slurry was transported to a coarse grinder and coarsely ground for 6 h using zirconium beads with a particle size of 0.2 mm to obtain a third slurry with silicon particles having a Dv50 of 112 nm; wherein the coarse grinding process was performed at a rotation speed of 3200 r / min and a pressure of 1.1 bar;

[0087] (4) The third slurry was conveyed to a fine grinder and finely ground using zirconium beads with a particle size of 0.04 mm for 7 h to obtain a fourth slurry with a Dv50 of 56 nm. The fine grinding speed was 2400 r / min and the pressure was 1.5 bar. The ratio of Dv90 of the silicon particles to Dv50 of the silicon particles in the fourth slurry was 1.45:1.

[0088] (5) The fourth slurry and 87 g of epoxy resin were dispersed at a speed of 3800 rpm / min and a pressure of 0.3 bar for 10 minutes to obtain a fifth slurry with a viscosity of 462 cps;

[0089] (6) The fifth slurry is transported to a spray drying tower with nitrogen protection, and spray-dried under the conditions of a spray pressure of 0.1 MPa and an inlet air temperature of 300°C, so that the molten epoxy resin is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor;

[0090] (7) The silicon-carbon precursor was calcined at 850 °C and kept warm for 3 h under nitrogen protection throughout the process to obtain a silicon-carbon negative electrode material.

[0091] Example 4

[0092] The method for preparing the silicon-carbon negative electrode material of this embodiment includes the following steps:

[0093] (1) 130 g of silicon powder (Dv50: 5 μm) was mixed with 736 g of tert-butanol, and then polyoxypropylene-polyoxyethylene copolymer was added and transported to a sealed tank under nitrogen protection. The mixture was dispersed at a speed of 1300 r / min for 30 min to obtain a first slurry. At this time, the mass content of silicon powder in the first slurry was 15%, and the mass concentration of polyoxyethylene-polyoxypropylene copolymer was 0.30%;

[0094] (2) The first slurry was allowed to stand at 40°C for 20 minutes for aging treatment to obtain a second slurry;

[0095] (3) The second slurry was transported to a coarse grinder and coarsely ground for 5 h using zirconium beads with a particle size of 0.1 mm to obtain a third slurry with silicon particles having a Dv50 of 105 nm; wherein the coarse grinding process was performed at a rotation speed of 3200 r / min and a pressure of 1.1 bar;

[0096] (4) The third slurry was transferred to a fine grinder and finely ground using zirconium beads with a particle size of 0.03 mm for 9 h to obtain a fourth slurry with a Dv50 of 52 nm. The fine grinding speed was 2000 r / min and the pressure was 1.3 bar. The ratio of Dv90 of the silicon particles to Dv50 of the silicon particles in the fourth slurry was 1.5:1.

[0097] (5) The fourth slurry and 87 g of phenolic resin were dispersed at a speed of 3500 rpm / min and a pressure of 0.3 bar for 10 minutes to obtain a fifth slurry with a viscosity of 414 cps;

[0098] (6) The fifth slurry is transported to a spray drying tower with nitrogen protection, and spray-dried under the conditions of a spray pressure of 0.1 MPa and an inlet air temperature of 300°C, so that the molten phenolic resin is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor;

[0099] (7) The silicon-carbon precursor was calcined at 850 °C and kept warm for 3 h under nitrogen protection throughout the process to obtain a silicon-carbon negative electrode material.

[0100] Example 5

[0101] The method for preparing the silicon-carbon negative electrode material of this embodiment includes the following steps:

[0102] (1) 20 g of silicon powder (Dv50: 5 μm) was mixed with 350 mL of glycerol, and then polyoxypropylene-polyoxyethylene copolymer was added and transported to a sealed tank under nitrogen protection. The mixture was dispersed at a speed of 1500 r / min for 30 min to obtain a first slurry. At this time, the mass content of silicon powder in the first slurry was 5.5%, and the mass concentration of polyoxyethylene-polyoxypropylene copolymer was 0.33%;

[0103] (2) The first slurry was allowed to stand at 40°C for 20 minutes for aging treatment to obtain a second slurry;

[0104] (3) The second slurry was transported to a coarse grinder and coarsely ground for 9 hours using zirconium beads with a particle size of 0.2 mm to obtain a third slurry with silicon particles having a Dv50 of 109 nm; wherein the coarse grinding process was performed at a rotation speed of 3000 r / min and a pressure of 1.1 bar;

[0105] (4) The third slurry was transferred to a fine grinder and finely ground using zirconium beads with a particle size of 0.05 mm for 5 h to obtain a fourth slurry with a Dv50 of 58 nm. The fine grinding speed was 2000 r / min and the pressure was 1.3 bar. The ratio of Dv90 of the silicon particles to Dv50 of the silicon particles in the fourth slurry was 1.37:1.

[0106] (5) The fourth slurry and 20 g of polyvinyl pyrrolidone were dispersed at a speed of 3500 rpm / min and a pressure of 0.3 bar for 10 minutes to obtain a fifth slurry with a viscosity of 485 cps;

[0107] (6) The fifth slurry is transported to a spray drying tower with nitrogen protection, and spray-dried under the conditions of a spray pressure of 0.1 MPa and an inlet air temperature of 300°C, so that the molten polyvinyl pyrrolidone is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor;

[0108] (7) The silicon-carbon precursor was calcined at 850 °C and kept warm for 3 h under nitrogen protection throughout the process to obtain a silicon-carbon negative electrode material.

[0109] Example 6

[0110] The method for preparing the silicon-carbon negative electrode material of this embodiment includes the following steps:

[0111] (1) 20 g of silicon powder (Dv50: 5 μm) was mixed with 350 mL of acetone, and then polyoxypropylene-polyoxyethylene copolymer was added and transported to a sealed tank under nitrogen protection. The mixture was dispersed at a speed of 1500 r / min for 30 min to obtain a first slurry. At this time, the mass content of silicon powder in the first slurry was 5.5%, and the mass concentration of polyoxyethylene-polyoxypropylene copolymer was 0.25%.

[0112] (2) The first slurry was allowed to stand at 40°C for 20 minutes for aging treatment to obtain a second slurry;

[0113] (3) The second slurry was transported to a coarse grinder and coarsely ground for 10 h using zirconium beads with a particle size of 0.2 mm to obtain a third slurry with silicon particles having a Dv50 of 110 nm; wherein the coarse grinding process was performed at a rotation speed of 3000 r / min and a pressure of 1.1 bar;

[0114] (4) The third slurry was conveyed to a fine grinder and finely ground using zirconium beads with a particle size of 0.05 mm for 4 h to obtain a fourth slurry with a Dv50 of 55 nm. The fine grinding speed was 2000 r / min and the pressure was 1.3 bar. The ratio of Dv90 of the silicon particles to Dv50 of the silicon particles in the fourth slurry was 1.36:1.

[0115] (5) The fourth slurry and 20 g of polyacrylonitrile were dispersed at a speed of 3500 rpm / min and a pressure of 0.3 bar for 10 minutes to obtain a fifth slurry with a viscosity of 443 cps;

[0116] (6) The fifth slurry is transported to a spray drying tower with nitrogen protection, and spray-dried under the conditions of a spray pressure of 0.01 MPa and an inlet air temperature of 300°C, so that the molten polyacrylonitrile is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor;

[0117] (7) The silicon-carbon precursor was calcined at 850 °C and kept warm for 3 h under nitrogen protection throughout the process to obtain a silicon-carbon negative electrode material.

[0118] Example 7

[0119] The preparation method is basically the same as that of Example 1, except that in step (5), "55.7 g asphalt" is replaced by "55.7 g asphalt and 28 g carbon nanotubes", and other conditions remain unchanged.

[0120] Comparative Example 1

[0121] (1) 130 g of silicon powder (average particle size of 5 μm) was mixed with 1603 g of ethanol to obtain a first slurry. At this time, the mass content of silicon powder in the first slurry was 7.5%;

[0122] (2) The first slurry was sand-milled in a 0.5 L sand-milling jar at a speed of 3200 r / min and a grinding ball diameter of 0.1 mm for 12 h to obtain a second slurry; the Dv50 of the silicon particles in the second slurry was 70 nm, and the Dv90 of the silicon particles in the second slurry was 112 nm;

[0123] (3) mixing the second slurry and the polyoxyethylene-polyoxypropylene copolymer to obtain a mixed slurry, wherein the mass concentration of the polyoxyethylene-polyoxypropylene copolymer in the mixed slurry is 6%;

[0124] (4) The mixed slurry was mixed with 55.7 g of asphalt and then spray-dried at a temperature of 240 °C and an outlet temperature of 60 °C, with nitrogen protection throughout the process, to obtain a silicon / carbon source composite material; the obtained silicon / carbon source composite material was calcined at 850 °C and kept warm for 3 h, with nitrogen protection throughout the process, to obtain a silicon-carbon negative electrode material.

[0125] Comparative Example 2

[0126] (1) 130 g of silicon powder (average particle size of 5 μm) was mixed with 1170 g of ethanol to obtain a first slurry, wherein the mass content of silicon powder in the first slurry was 10%;

[0127] (2) The first slurry was sand-milled in a 0.5 L sand-milling jar at a speed of 3200 r / min and a grinding ball diameter of 0.1 mm for 17 h to obtain a second slurry; the Dv50 of the silicon particles in the second slurry was 75 nm, and the Dv90 of the silicon particles in the second slurry was 118 nm;

[0128] (3) The second slurry was mixed with 55 g of asphalt and spray-dried at 240 °C, with an outlet temperature of 60 °C and nitrogen protection throughout the process to obtain a silicon / carbon source composite material; the obtained silicon / carbon source composite material was calcined at 850 °C and kept warm for 3 h, with nitrogen protection throughout the process to obtain a silicon-carbon composite material.

[0129] Comparative Example 3

[0130] The preparation method is basically the same as that of Example 1, except that step (2) is not included, and the first slurry is directly subjected to step (3). Other conditions remain unchanged, specifically:

[0131] (1) 130 g of silicon powder (Dv50: 5 μm) was mixed with 1603 g of ethanol, and then polyoxypropylene-polyoxyethylene copolymer was added and transported to a sealed tank under nitrogen protection. The mixture was dispersed at a speed of 1000 r / min for 30 min to obtain a first slurry. At this time, the mass content of silicon powder in the first slurry was 7.5%, and the mass concentration of polyoxyethylene-polyoxypropylene copolymer was 0.15%;

[0132] (2) The first slurry was transferred to a coarse grinder and coarsely ground for 8 h using zirconium beads with a particle size of 0.1 mm to obtain a second slurry with silicon particles having a Dv50 of 140 nm; wherein the coarse grinding process was performed at a rotation speed of 3400 r / min and a pressure of 1.2 bar;

[0133] (3) The second slurry was transported to a fine grinder and finely ground for 8 h using zirconium beads with a particle size of 0.03 mm to obtain a third slurry with silicon particles having a Dv50 of 65 nm and a Dv90 of 104 nm; wherein the fine grinding speed was 2500 r / min and the pressure was 1.7 bar;

[0134] (4) The third slurry and 55.7 g of asphalt were dispersed at a speed of 4000 rpm / min and a pressure of 0.2 bar for 10 minutes to obtain a fourth slurry with a viscosity of 532 cps;

[0135] (5) The fourth slurry is transported to a spray drying tower with nitrogen protection, and spray-dried under the conditions of a spray pressure of 0.1 MPa and an inlet air temperature of 250°C, so that the molten asphalt is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor;

[0136] (6) The silicon-carbon precursor was calcined at 850°C for 3 hours under nitrogen protection to obtain a silicon-carbon negative electrode material.

[0137] Comparative Example 4

[0138] The preparation method is basically the same as that of Example 1, except that in step (3), the coarse grinding process uses zirconium beads with a particle size of 0.5 mm and a rotation speed of 2000 r / min. Other conditions remain unchanged, specifically:

[0139] (1) 130 g of silicon powder (Dv50: 5 μm) was mixed with 1603 g of ethanol, and then polyoxypropylene-polyoxyethylene copolymer was added and transported to a sealed tank under nitrogen protection. The mixture was dispersed at a speed of 1000 r / min for 30 min to obtain a first slurry. At this time, the mass content of silicon powder in the first slurry was 7.5%, and the mass concentration of polyoxyethylene-polyoxypropylene copolymer was 0.15%;

[0140] (2) The first slurry was allowed to stand at 30°C for 60 minutes for aging to obtain a second slurry;

[0141] (3) The second slurry was transported to a coarse grinder and coarsely ground for 8 h using zirconium beads with a particle size of 0.5 mm to obtain a third slurry with silicon particles having a Dv50 of 155 nm; wherein the coarse grinding speed was 2000 r / min and the pressure was 1.2 bar;

[0142] (4) The third slurry was transported to a fine grinder and finely ground for 8 h using zirconium beads with a particle size of 0.03 mm to obtain a fourth slurry with silicon particles having a Dv50 of 80 nm and a Dv90 of 122 nm; wherein the fine grinding speed was 2500 r / min and the pressure was 1.7 bar;

[0143] (5) The fourth slurry and 55.7 g of asphalt were dispersed at a speed of 4000 rpm / min and a pressure of 0.2 bar for 10 minutes to obtain a fifth slurry with a viscosity of 570 cps;

[0144] (6) The fifth slurry is transported to a spray drying tower with nitrogen protection, and spray-dried under the conditions of a spray pressure of 0.1 MPa and an inlet air temperature of 250°C, so that the molten asphalt is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor;

[0145] (7) The silicon-carbon precursor was calcined at 850 °C and kept warm for 3 h under nitrogen protection throughout the process to obtain a silicon-carbon negative electrode material.

[0146] Comparative Example 5

[0147] The preparation method is basically the same as that of Example 1, except that in step (4), the fine grinding process uses zirconium beads with a particle size of 0.07 mm and a rotation speed of 3000 r / min, specifically:

[0148] (1) 130 g of silicon powder (Dv50: 5 μm) was mixed with 1603 g of ethanol, and then polyoxypropylene-polyoxyethylene copolymer was added and transported to a sealed tank under nitrogen protection. The mixture was dispersed at a speed of 1000 r / min for 30 min to obtain a first slurry. At this time, the mass content of silicon powder in the first slurry was 7.5%, and the mass concentration of polyoxyethylene-polyoxypropylene copolymer was 0.15%;

[0149] (2) The first slurry was allowed to stand at 30°C for 60 minutes for aging to obtain a second slurry;

[0150] (3) The second slurry was transported to a coarse grinder and coarsely ground for 8 h using zirconium beads with a particle size of 0.1 mm to obtain a third slurry with silicon particles having a Dv50 of 100 nm; wherein the coarse grinding process was performed at a rotation speed of 3400 r / min and a pressure of 1.2 bar;

[0151] (4) The third slurry was transported to a fine grinder and finely ground for 8 h using zirconium beads with a particle size of 0.07 mm to obtain a fourth slurry with silicon particles having a Dv50 of 65 nm and a Dv90 of 99 nm; wherein the fine grinding speed was 3000 r / min and the pressure was 1.7 bar;

[0152] (5) The fourth slurry and 55.7 g of asphalt were dispersed at a speed of 4000 rpm / min and a pressure of 0.2 bar for 10 minutes to obtain a fifth slurry with a viscosity of 530 cps;

[0153] (6) The fifth slurry is transported to a spray drying tower with nitrogen protection, and spray-dried under the conditions of a spray pressure of 0.1 MPa and an inlet air temperature of 250°C, so that the molten asphalt is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor;

[0154] (7) The silicon-carbon precursor was calcined at 850 °C and kept warm for 3 h under nitrogen protection throughout the process to obtain a silicon-carbon negative electrode material.

[0155] Comparative Example 6

[0156] The preparation method is basically the same as that of Example 1, except that in step (5), asphalt is replaced by graphite sheets, and other conditions remain unchanged.

[0157] Test example

[0158] 1. Use Malvern 3000 laser particle size analyzer to measure Dv50 and Dv90 of silicon-carbon precursor and silicon-carbon anode material;

[0159] The particle size of the silicon particles in the slurry was measured using a Malvern 3000 laser particle size analyzer. The specific measurement method is as follows: 4 mL of the slurry was taken out and diluted 10 times, and then the particle size was measured to obtain the particle size classification results of the silicon particles in the slurry, namely the Dv50 and Dv90 values;

[0160] The slurry was potentiometrically analyzed using a BeNano 90 Zeta potentiometric analyzer. The polished slurry was then subjected to storage stability testing. Specifically, the particle size was measured after 2 and 6 days of storage. The D50 change rate was calculated as: Dv50 change rate = (Dv50 of silicon particles in the slurry after storage - Dv50 of silicon particles in the slurry before storage) / Dv50 of silicon particles in the slurry before storage. The test results are shown in Table 2.

[0161] 2. Cycle performance and cycle stability test

[0162] The silicon-carbon composite material of the embodiment and comparative example, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC-Na) and N-methyl pyrrolidone (NMP) were mixed in a mass ratio of 80:10:10 and stirred evenly to prepare a negative electrode slurry. The slurry was coated on a copper foil (9 μm thick) with a coating density of 1.6 mg / cm². After drying and roller pressing, a negative electrode sheet (24 μm thick and 16 mm in diameter) was obtained. The conductive carbon black was purchased from SP Conductive Agent, Tianjin Yiborui Chemical Co., Ltd.; the CAS number of sodium carboxymethyl cellulose is 9004-32-4.

[0163] Battery assembly: In an argon-filled glove box, a CR2032 button-type half-cell is installed. The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence to form a battery cell. A punching die is used to punch out an aluminum-plastic film, and then the battery cell is encapsulated with the punched aluminum-plastic film. The film is baked until the moisture content is acceptable, and the electrolyte is injected. After formation and secondary sealing, the button-type battery is obtained.

[0164] Among them, the metal lithium sheet is the positive electrode sheet (thickness 1mm, diameter 16mm), the separator is Celgard 2500 from Cluder (diameter 18mm, thickness 25μm), the electrolyte includes 1mol / L lithium hexafluorophosphate (LiPF6) electrolyte, and the electrolyte solvent is ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) with a volume ratio of 1:1:1.

[0165] Cycling performance test: using a new well test cabinet, with a voltage range of 0.1~2V, and testing the initial discharge capacity and first cycle coulombic efficiency at 0.1C;

[0166] Cycling stability test: Cycling was performed at 0.1C. The number of cycles was recorded when the capacity retention rate reached 80%. The test results are shown in Table 3.

[0167] Table 2

[0168]

[0169] It should be noted that in Table 2, the Dv50 change rate after 2 days of shelving and the Dv50 change rate after 6 days of shelving in Examples 1-7 refer to the Dv50 change rate of the fourth slurry in step (4) after 2 days of shelving and 6 days of shelving, respectively; the Dv50 change rate after 2 days of shelving and the Dv50 change rate after 6 days of shelving in Comparative Examples 1-2 refer to the Dv50 change rate of the second slurry in step (2) after 2 days of shelving and 6 days of shelving; in Comparative Example 3, the Dv50 change rate after 2 days of shelving and the Dv50 change rate after 6 days of shelving refer to the Dv50 change rate of the third slurry in step (3) after 2 days of shelving and 6 days of shelving; the Dv50 change rate after 2 days of shelving and the Dv50 change rate after 6 days of shelving in Comparative Examples 4-6 refer to the Dv50 change rate of the fourth slurry in step (4) after 2 days of shelving and 6 days of shelving.

[0170] Table 3

[0171]

[0172] According to Figures 2 and 3, the particle size of the silicon particles in the slurry of Example 1 is smaller and the distance between the particles is larger, indicating that it is not easy to agglomerate; while in the slurry of Comparative Example 1, although the grinding time is longer, the particle size of the silicon particles is larger and the distance between the particles is smaller, indicating that there is more agglomeration.

[0173] According to Tables 2 and 3, the present invention introduces a polyoxypropylene polyoxyethylene copolymer and adjusts the dispersion treatment, aging treatment, coarse grinding treatment, and fine grinding treatment of a specific process to obtain a slurry with a smaller particle size (small Dv50), a narrower particle size distribution (small Dv90:Dv50 ratio), and good stability (small Dv50 change rate), and further improves the uniformity and electrochemical performance of the silicon-carbon negative electrode material. This is because the present invention specifically matches the specific parameters of each process in the preparation method, so that each process works synergistically to improve the comprehensive performance of the silicon-carbon negative electrode material. Even if the comparative example is ground for a longer time than the example, it cannot achieve a small particle size and a narrow particle size distribution. The inventor believes that although the grinding time is long and small-sized silicon particles can be obtained, the small-sized silicon particles are easy to agglomerate together in a short time, and the silicon particles with larger particle size are still in the slurry (as shown in Figure 3).

[0174] By comparing Example 1 with Comparative Examples 3-6, it can be seen that the introduction of polyoxypropylene polyoxyethylene copolymer, dispersion treatment, aging treatment, coarse grinding treatment, fine grinding treatment and introduction of organic carbon source in the present invention are synergistic, and only by cooperating with each other can the uniformity and electrochemical performance of the silicon-carbon negative electrode material be improved.

[0175] As can be seen from Table 2, the D50 change rate of the silicon particles in the slurry of the embodiment after being set aside for 2 days and 6 days is much lower than that of the comparative example, and the absolute value of the potential is also higher than that of the comparative example. The higher the absolute value of the potential, the more stable the dispersion system of the particles. This shows that the present invention can improve the dispersibility of silicon particles, improve production efficiency, and maintain stable dispersion of silicon particles.

[0176] According to Table 3, the silicon-carbon negative electrode material provided by the present invention has excellent cycle stability and coulombic efficiency. The initial discharge capacity of the battery assembled with the negative electrode material is ≥1879 mAh / g, the first-cycle coulombic efficiency is ≥82.5%, and when the cycle retention rate is 80%, it can be cycled for at least 362 cycles.

[0177] The above describes in detail the preferred embodiments of the present invention and their experimental verification. It should be understood that a person skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solution that can be derived by a person skilled in the art through logical analysis, deduction, or limited experimentation based on the concepts of the present invention and the prior art shall be within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized in that: The following steps are involved: S1: Silicon powder with a Dv50 of 5 μm, polyoxypropylene-polyoxyethylene copolymer, and an organic solvent are transported to a sealed tank with nitrogen protection, and dispersed for 30 minutes at a rotation speed of 1000-1500 r / min to obtain a first slurry; wherein the organic solvent includes at least one of ethanol, isopropanol, tert-butanol, ethylene glycol, glycerol, and acetone; S2: allowing the first slurry to stand at 30-40° C. for 20-60 min for aging to obtain a second slurry; S3: conveying the second slurry to a coarse grinder, and coarsely grinding the second slurry for 5-10 hours using zirconium beads with a particle size of 0.1-0.2 mm to obtain a third slurry; wherein the rotation speed of the coarse grinding is 3000-3400 r / min and the pressure is 1.1-1.2 bar; the Dv50 of the silicon particles in the third slurry is 100-120 nm; S4: conveying the third slurry to a fine grinder, and fine grinding the third slurry for 5 to 10 hours using zirconium beads with a particle size of 0.03 to 0.05 mm to obtain a fourth slurry; wherein the rotation speed of the fine grinding process is 2000 to 2500 r / min and the pressure is 1.3 to 1.7 bar; The Dv50 of the silicon particles in the fourth slurry is 50-60 nm, and the ratio of the Dv90 of the silicon particles in the fourth slurry to the Dv50 of the silicon particles is (1.35-1.5): 1; S5: dispersing the material including the fourth slurry and the organic carbon source at a rotation speed of 3500-4000 rpm / min and a pressure of 0.2-0.3 bar for 10 minutes to obtain a fifth slurry with a viscosity of 400-500 cps; the organic carbon source includes at least one of asphalt, polyacrylonitrile, polyvinyl pyrrolidone, phenolic resin, and epoxy resin; S6: conveying the fifth slurry to a spray drying tower with nitrogen protection, spray drying is performed under the conditions of a spray pressure of 0.01-0.1 MPa and an air inlet temperature of 200-300° C., so that the molten organic carbon source is evenly coated on the surface of the silicon particles to obtain a silicon-carbon precursor; the Dv50 of the silicon-carbon precursor is 6-14.4 μm; S7: sintering the silicon-carbon precursor at 800-900° C. for 2.5-3.5 h to obtain a silicon-carbon negative electrode material, wherein the Dv50 of the silicon-carbon negative electrode material is 5-12 μm; and the ratio of Dv90 to Dv50 of the silicon-carbon negative electrode material is (1.36-1.49):1; Among them, the particle size corresponding to the cumulative volume fraction of 50% is Dv50, and the particle size corresponding to the cumulative volume fraction of 90% is Dv90.

2. The preparation method according to claim 1, characterized in that: In the first slurry, based on the total mass of the first slurry being 100 mass %, the content of silicon powder is 5.5 mass % to 15 mass %; In the first slurry, based on the total mass of the first slurry being 100 mass %, the content of the polyoxypropylene-polyoxyethylene copolymer is 0.15 mass % to 1.5 mass %; The mass ratio of the silicon powder to the organic carbon source is (3-7): (3-7).

3. The preparation method according to claim 1 or 2, characterized in that: The outlet temperature of the spray drying is 60-80°C.

4. The preparation method according to claim 1, characterized in that: After the sintering process, it also includes crushing and screening processes.

5. The preparation method according to claim 1, characterized in that: In step S5, the material further includes carbon nanotubes.

6. The preparation method according to claim 5, characterized in that: The mass ratio of the carbon nanotubes to the organic carbon source is 1:(1-2).

7. The preparation method according to claim 1, characterized in that: The weight average molecular weight of the polyoxypropylene-polyoxyethylene copolymer is 1000-1500.

8. The preparation method according to claim 1, characterized in that: The Dv50 change rate of the fourth slurry after being set aside for 2 days is not higher than 3%; the Dv50 change rate of the fourth slurry after being set aside for 6 days is not higher than 5%.

9. A silicon-carbon negative electrode material, characterized in that: The method is prepared by the method according to any one of claims 1 to 8.

10. A battery, characterized in that: Including the silicon-carbon negative electrode material as described in claim 9.

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