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

Abstract

The present invention relates to a silicon-carbon negative electrode material and its preparation method and application. The preparation method of the present invention comprises the following steps: using a first carbon source to thermally polymerize to obtain soft carbon microspheres; spray coating the soft carbon microspheres, a second carbon source, graphite carbon nanodots, and an activator, cooling and solidifying the same, heating and activating the same for the first time, and then neutralizing and washing the same with an acid to obtain a porous carbon ball precursor; adding a silicon source to the porous carbon ball precursor under an inert atmosphere, and heating the same for the second time, so that the silicon source is cracked and silicon element is deposited and adsorbed inside the porous carbon ball to obtain porous silicon-carbon balls; heating and raising the temperature of the porous silicon-carbon balls, and introducing an organic gas to form a carbon layer on the surface of the porous silicon-carbon balls, and finally obtaining the silicon-carbon negative electrode material. After external force rolling, the silicon-carbon negative electrode material obtained by the present invention can avoid the separation of porous carbon balls and homogeneous porous carbon layers, causing particle breakage, thereby improving the structural strength of the silicon-carbon negative electrode material and thereby improving the capacity and cycle life of the battery system.

Description

Technical Field

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

[0002] Lithium-ion batteries (LIBs) are widely used in consumer electronics, two- and four-wheeled electric vehicles, and industrial and commercial energy storage due to their long cycle life and high energy density. The rapid development of electric vehicles has also placed higher demands on the energy density of LIBs. LIBs primarily consist of four components: cathode material, separator material, anode material, and copper / aluminum electrode foil. Silicon anode materials are rapidly developing within this category, offering advantages such as low-cost raw materials and high energy density. Silicon-carbon anode materials, specifically silane-deposited porous carbon, offer theoretical specific capacities of 1000-1800 mAh / g, significantly exceeding commercial graphite anodes. These materials are the preferred anode materials for high-energy-density batteries and are a candidate for next-generation lithium-ion battery anodes.

[0003] Compared with graphite negative electrode materials, silicon carbon negative electrode materials have lower tap density and need to improve their own strength and density. After roller pressing, the density can reach 1.1-1.4g / cm 3 density, but it is easy to crack after rolling, resulting in the formation of new interfaces, consuming more lithium, and increasing the initial irreversible lithium, which will affect the capacity and cycle life of the battery system, and the impact on the high silicon-based negative electrode battery system is more significant. Summary of the Invention

[0004] To address the above technical issues, the present invention provides a silicon-carbon anode material, its preparation method, and its application. This invention achieves a highly tapped silicon-carbon anode material by regulating the pore distribution of porous carbon spheres, forming a homogeneous porous carbon layer embedded with porous graphite carbon nanodots on the surface of the porous carbon spheres, and then depositing silicon. The homogeneous porous carbon layer serves as an internal protective layer for the microspheres. Furthermore, through a simultaneous activation process of the porous carbon spheres and the homogeneous porous carbon layer, the silicon-carbon anode material is rolled under external force, preventing the separation of the porous carbon spheres and the homogeneous porous carbon layer, which causes particle breakage. This improves the structural strength of the silicon-carbon anode material, thereby increasing the capacity and cycle life of the battery system.

[0005] The present invention achieves the purpose of the present invention through the following scheme:

[0006] The first object of the present invention is to provide a method for preparing a silicon-carbon negative electrode material, comprising the following steps:

[0007] S1, preparing soft carbon microspheres by thermal polymerization using a first carbon source;

[0008] S2, spray coating the soft carbon microspheres, the second carbon source, the graphite carbon nanodots, and the activator, cooling and curing, heating and activating them for the first time under an inert atmosphere, and then neutralizing and washing them with acid to obtain a porous carbon sphere precursor;

[0009] S3. Under an inert atmosphere, a silicon source is introduced into the porous carbon ball precursor and heated for a second time, so that the silicon source is cracked and silicon is deposited and adsorbed inside the porous carbon ball precursor to obtain porous silicon-carbon balls;

[0010] S4, heating the porous silicon-carbon spheres and introducing an organic gas to form a carbon layer on the surface of the porous silicon-carbon spheres, thereby finally obtaining the silicon-carbon negative electrode material.

[0011] In some embodiments of the present invention, in step S1, the first carbon source is selected from one or more of needle coke, pitch coke, petroleum pitch, coal-based pitch, coal-based tar, and petroleum coke;

[0012] The soft carbon microspheres are prepared by mixing polyorganosiloxane and a first carbon source, and then maintaining the mixture at a temperature of 200-300° C. for a certain period of time, and then maintaining the mixture at a temperature of 350-480° C. for a second period of time to obtain the soft carbon microspheres.

[0013] The size of the soft carbon microspheres is between 0.8 and 40 μm, for example, 0.8 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, or any value therebetween.

[0014] In some embodiments of the present invention, the temperature of the first constant temperature stage is 200-300° C., and the heating constant temperature time is 1-3 hours; the temperature of the second constant temperature stage is 350-480° C., and the heating constant temperature time is 5-7 hours;

[0015] The polyorganosiloxane is selected from polydimethylsiloxane, cyclomethicone, aminosiloxane, and polymethylphenylsiloxane;

[0016] The mass ratio of the polyorganosiloxane to the first carbon source is 100:(1-8).

[0017] In some embodiments of the present invention, in step S2, the second carbon source is selected from one or more of phenolic resin, asphalt coke, petroleum coke, petroleum asphalt, and coal tar pitch;

[0018] The graphite carbon nanodots are selected from one or more of nanographene sheets, nanographite powders, nanographite sheets, and nanographitized carbon black films;

[0019] The activator is selected from one or more of ammonia, potassium hydroxide, sodium hydroxide, and lithium hydroxide;

[0020] The temperature of the first heating activation is 500~1100℃, and the heating activation time is 3~10h;

[0021] The inert gas in the inert atmosphere is selected from one or more of nitrogen, helium, and argon;

[0022] The acid is selected from hydrochloric acid, and the concentration of the acid is 0.2-2 mol / L;

[0023] The mass ratio of soft carbon microspheres, the second carbon source, graphite carbon nanodots, and the activator is (40-60): (1-8): (0.03-0.2): (12-30);

[0024] In the present invention, the heating activation is carried out by spray coating to obtain a coating layer containing an activator. At a high temperature of 500~1100℃, the activator generates water at high temperature (water reacts with carbon to generate carbon monoxide and carbon dioxide, consuming carbon. The carbonaceous surface generates gas through each consumption reaction, releasing space, and the porous carbon layer gradually collapses into pores). The generated water simultaneously diffuses into the interior of the soft carbon microspheres, and the coating layer, soft carbon microspheres, and graphite carbon nanodots are synchronously activated to form pores. Pores are continuously formed between the coating layer and the soft carbon microspheres, eliminating the interface carbon layer. After neutralization with hydrochloric acid and washing, a homogeneous porous carbon layer is formed, and the pores are more continuous and more tightly combined with the carbon layer, thereby avoiding separation of the porous carbon ball precursor and the homogeneous porous carbon layer.

[0025] It should be noted that: with the addition of graphite carbon nanodots, a large number of aromatic molecules in the reaction system attach to the graphene and nucleate, promoting the aromatization reaction of asphalt molecules, the discharge of excess hydrogen, and the reduction of carbon deposits. After neutralization and washing with hydrochloric acid, the micropore / mesopore structure in the homogeneous porous carbon layer is more ordered and rich (the spray-coated and synchronously activated carbon layer is more ordered, and the carbon layer contains graphite carbon nanodots, so it is called a homogeneous porous carbon layer). The homogeneous porous carbon layer acts as an internal protective layer of the microspheres, enhancing the strength of the silicon-carbon negative electrode material.

[0026] The specific method of the spray coating is as follows: heating the second carbon source to 150-240° C. to soften it, adding graphite carbon nanodots and an activator and mixing them evenly to obtain a mixture, sending it to a spray dryer, then adding soft carbon microspheres, and spraying the mixture to coat the soft carbon microspheres.

[0027] In some embodiments of the present invention, in step S3, the specific surface area of ​​the porous carbon ball precursor is 1200-2600m 2 / g, pore volume is 0.60-1.15cm 3 / g, the volume of pores ≤4nm accounts for more than 60% of the total pore volume;

[0028] The silicon source is selected from one or more of monosilane, disilane, trisilane, dimethylsilane, hexamethyldisilane, dichlorodihydrosilane, trichlorosilane, silicon tetrachloride, and silicon tetrafluoride;

[0029] The flow rate of the silicon source is 30 to 200 L / h; such as 30 L / h, 50 L / h, 80 L / h, 100 L / h, 120 L / h, 150 L / h, 200 L / h, or any value therebetween.

[0030] The temperature of the second heating is 450~750℃;

[0031] The inert gas in the inert atmosphere is selected from one or more of nitrogen, helium, and argon;

[0032] The time for silicon element deposition is 20 minutes to 6 hours; for example, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 1.5 hours, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any value in between these values.

[0033] The silicon element deposition content accounts for 40% to 80% of the porous silicon carbon spheres, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any value therebetween.

[0034] In some embodiments of the present invention, in step S4, the heating rate is 1~8℃ / min; 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, etc.; the heating temperature is 400-780℃, for example, 400℃, 500℃, 600℃, 700℃, etc.

[0035] The organic gas is selected from one or more of butene, ethylene, butyne, acetylene, and propyne;

[0036] The flow rate of the organic gas is 10 to 300 L / h, for example, 10 L / h, 20 L / h, 30 L / h, 50 L / h, 80 L / h, 100 L / h, 120 L / h, 150 L / h, 200 L / h, 300 L / h, or any value therebetween.

[0037] The second object of the present invention is to provide a silicon-carbon negative electrode material prepared by the preparation method. The silicon-carbon negative electrode material is a core-shell structure with a porous carbon ball as the core, and is coated by a homogeneous porous carbon layer on the surface of the porous carbon ball, porous graphite carbon nanodots embedded in the homogeneous porous carbon layer, and an outer carbon layer; silicon element is deposited in the pores of the porous carbon ball and the homogeneous porous carbon layer.

[0038] The silicon-carbon negative electrode material of the present invention comprises porous carbon balls, a homogeneous porous carbon layer combined with the porous carbon balls, porous graphite carbon nanodots embedded in the homogeneous porous carbon layer, and an outer carbon layer of the homogeneous porous carbon layer.

[0039] Furthermore, the silicon-carbon negative electrode material is composed of porous carbon balls, homogeneous porous carbon layers, and outer carbon layers from the inside to the outside.

[0040] In some embodiments of the present invention, the size of the porous carbon balls is between 0.3 and 32 μm; for example, 0.3 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, or any value between these values.

[0041] The thickness of the homogeneous porous carbon layer is 0.02-3 μm, for example, 0.02 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1.0 μm, 2.0 μm, 3.0 μm, or any value therebetween.

[0042] The thickness of the outer carbon layer is between 0.8 and 55 nm, for example, 0.8 nm, 1 nm, 1.5 nm, 2 nm, 3 nm, 5 nm, 7 nm, 10 nm, 12 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 55 nm, or any value therebetween.

[0043] The silicon element has a particle size of ≤2nm and is amorphous silicon element;

[0044] The Dv50 of the silicon-carbon negative electrode material is 0.5~35μm; for example, 0.5μm, 1.0μm, 1.5μm, 2.0μm, 2.5μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, or any value between these values.

[0045] The actual density of the silicon-carbon negative electrode material is 1.9~2.25m 3 / g; for example, 1.9cm 3 / g, 1.95m 3 / g, 2.0m 3 / g, 2.05m 3 / g, 2.1m 3 / g, 2.15m 3 / g, 2.20m 3 / g, 2.25m 3 / g, or any value in between these values.

[0046] The tap density of the silicon-carbon negative electrode material is 0.9~1.4m 3 / g; for example, 1.0m 3 / g, 1.1m 3 / g, 1.2m 3 / g, 1.3m 3 / g, 1.4m 3 / g, 1.5m 3 / g, or any value in between these values.

[0047] Furthermore, the XRD diffraction pattern test conditions are Cu target, scanning angular velocity of 0.2-8 degrees / min, and test angle range of 10-80 degrees.

[0048] The third object of the present invention is to provide a negative electrode sheet comprising the silicon-carbon negative electrode material.

[0049] A fourth object of the present invention is to provide a secondary battery comprising the negative electrode sheet.

[0050] The secondary battery is prepared by the following method:

[0051] (1) Premix the first conductive material, graphite material, and silicon-carbon negative electrode material for 20-60 minutes, add 50% of the first binder and solvent water and mix for 30-90 minutes for kneading, then add the remaining 50% of the first binder 1, the second conductive material, and water and mix for 30-120 minutes for a first stirring, controlling the solid content to 35-50%, then add the second binder and water and stir for a second time, controlling the solid content to 30-55%, and the fineness ≤45μm to obtain the negative electrode slurry;

[0052] (2) Pre-mixing the first conductive material and the positive electrode material, adding the third binder and NMP and kneading them, then adding the remaining third binder, the second conductive material, the solvent NMP, and the electrolyte, mixing them once, controlling the solid content to 75-85%, then adding NMP and stirring them again, controlling the solid content to 60-80%, and the fineness ≤25μm, to obtain the positive electrode slurry;

[0053] (3) The negative electrode slurry is coated on the copper foil, dried to remove the solvent water, forming a negative electrode slurry layer, which is then rolled, dried, and die-cut to obtain a negative electrode sheet; the positive electrode slurry is coated on the aluminum foil, dried to remove NMP, forming a positive electrode slurry layer, which is then rolled, dried, and die-cut to obtain a positive electrode sheet;

[0054] (4) The positive electrode sheet, separator, and negative electrode sheet are stacked / wound into a bare battery cell, and the tabs are welded, glued, shelled, liquid-filled, formed, and capacity-divided to form a secondary battery.

[0055] Furthermore, the graphite material is at least one graphite negative electrode material selected from needle tar, coal tar, asphalt tar, petroleum coke, etc., which is shaped, crushed to 7-9 μm particles, granulated to 11-16 μm particles with Dv50, graphitized at 2900-3250° C., and coated.

[0056] The first and second conductive materials are independently at least one of conductive carbon black, silver powder, nickel powder, graphite whiskers, conductive Ketjen black, conductive acetylene black, conductive graphite, conductive graphene, single-walled carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes. The first and second conductive materials may be the same or different.

[0057] The binders (first binder, second binder, and third binder) include one or more of sodium / lithium polyacrylate, polymethyl methacrylate, polyethyl acrylate, sodium / lithium polyacrylate-methyl / ethyl / propyl acrylate, sodium / lithium polyacrylate-acrylonitrile, sodium / lithium polyacrylate-butadiene-acrylonitrile, sodium / lithium polyacrylate-methyl / ethyl / propyl acrylate-acrylonitrile-styrene, polystyrene-butadiene, polystyrene-butadiene-methyl / ethyl / propyl acrylate, polystyrene-butadiene-acrylic acid-methyl / ethyl / propyl acrylate, polystyrene-butadiene-acrylic acid-methyl / ethyl / propyl acrylate-acrylonitrile, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, and polyvinylidene fluoride. The first, second, and third binders may be the same as or different from each other.

[0058] Furthermore, the electrolyte is selected from one or more of lithium lanthanum zirconate (LLZO), lithium lanthanum tantalate (LLTO), lithium lanthanum zirconate tantalate (LLZTO), lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF–HFP), polymethyl methacrylate (PMMA), lithium indium chloride (Li3InCl6), lithium indium bromide (Li3InBr6), lithium yttrium chloride (LiYCl), lithium yttrium bromide (LiYBr), lithium chlorophosphosulfate (LiPSCl), and lithium germanium phosphosulfate (LiGePS).

[0059] Furthermore, the positive electrode material is selected from any one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium-rich manganese base, lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium manganese oxide, lithium nickel manganese oxide, and sulfur positive electrode.

[0060] Furthermore, the surface density of the negative electrode slurry coated on the foil is 0.003-0.024 g / cm 2 , or any value between these values, the surface density of the positive electrode slurry coated on the foil is 0.010-0.065g / cm 2 , or any value in between these values.

[0061] Furthermore, the mass ratios of graphite material + silicon-carbon negative electrode material, conductive material (first conductive material, second conductive material), and binder (first binder, second binder) in the negative electrode slurry are 86-99, 0.2-6, and 0.8-8.

[0062] Furthermore, the mass ratio of the positive electrode material, the conductive material (the first conductive material, the second conductive material), the binder (the third binder), and the electrolyte in the positive electrode slurry is (84-99): (0.2-6): (0.6-8): (0.2-2).

[0063] The above technical solution of the present invention has the following advantages over the prior art:

[0064] The present invention obtains a coating layer containing an activator by spray coating. At a high temperature of 500-1100°C, the activator generates water at high temperature (water reacts with carbon to generate carbon monoxide and carbon dioxide, consuming carbon. Gas is generated on the carbonaceous surface through each consumption reaction, releasing space, and a porous carbon layer is generated, which gradually collapses into pores). The generated water simultaneously diffuses into the interior of the soft carbon microspheres, and the coating layer and the soft carbon microspheres are synchronously activated to form pores. Pores are continuously formed between the coating layer and the soft carbon microspheres, and the interface carbon layer is eliminated. After neutralization with hydrochloric acid and washing, a homogeneous porous carbon layer is formed, and the pores are more continuous and more tightly combined with the carbon layer, thereby avoiding separation of the porous carbon balls and the homogeneous porous carbon layer in the silicon-carbon negative electrode material.

[0065] With the addition of graphite carbon nanodots, a large number of aromatic molecules in the reaction system attach to the graphene and nucleate near it, promoting the aromatization reaction of asphalt molecules, discharging excess hydrogen, and reducing the formation of carbon deposits. After neutralization and washing with hydrochloric acid, the micropore / mesopore structure in the homogeneous porous carbon layer becomes more ordered and rich. The homogeneous porous carbon layer acts as an internal protective layer of the microspheres, enhancing the strength of the silicon-carbon negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0067] Figure 1 The porous carbon ball precursor of Example 1 of the present invention has a pore volume of 0.82 cm 3 / g, and the volume of pores ≤4nm accounts for 76% of the total pore volume.

[0068] Figure 2 This is the XRD pattern of the silicon-carbon negative electrode material obtained in Example 1 of the present invention.

[0069] Figure 3 Schematic diagram of the silicon-carbon negative electrode material according to an embodiment of the present invention.

[0070] Figure 4 This is the SEM of the negative electrode sheet obtained in Example 1 of the present invention after roller pressing.

[0071] Figure 5 This is the SEM of the negative electrode sheet obtained in Comparative Example 1 of the present invention after roller pressing. DETAILED DESCRIPTION

[0072] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0073] Example 1

[0074] This embodiment provides a preparation method and application of a porous carbon ball precursor and a silicon-carbon negative electrode material, as shown below:

[0075] S1. Preparation of porous carbon ball precursor: The first carbon source pitch coke is thermally polymerized to obtain 0.8~40μm soft carbon microspheres, and the soft carbon microspheres, the second carbon source coal tar, nanographite sheets, and activator are spray coated and cooled to solidify. In a nitrogen inert gas environment, the mixture is heated and activated at 850℃ for 4.5h, cooled to room temperature, neutralized and washed with 0.43mol / L dilute hydrochloric acid to remove the residual activator, washed with water until neutral, and dried to obtain a porous carbon ball precursor. The specific surface area of ​​the porous carbon ball precursor is 1670m 2 / g, pore volume at 0.82cm 3 / g, of which the pore volume with pore size ≤4nm accounts for 76% of the total pore volume.

[0076] The specific preparation steps of the soft carbon microspheres are as follows: 100 parts by weight of polydimethylsiloxane and 4 parts by weight of needle coke are mixed in a stirred reactor, first heated at 280°C and stabilized for 2 hours, then heated at 450°C and stabilized for 6 hours, cooled, centrifuged, and washed to obtain the soft carbon microspheres.

[0077] The spray coating comprises the following steps: 3 parts by weight of coal tar, a second carbon source, is softened at 220° C., 0.05 parts by weight of nanographite sheets and 12 parts by weight of a sodium hydroxide activator are added and mixed evenly to obtain a mixture, which is then fed to a spray dryer, and 45 parts by weight of soft carbon microspheres are added, and the mixture is spray-coated on the soft carbon microspheres.

[0078] S2. Silicon deposition: The porous carbon ball precursor is placed in a nitrogen inert gas environment at 550°C, and a monosilane silicon source (flow rate 48 L / h, deposition time 1.5 h) is introduced to crack the silicon source and deposit silicon element inside the porous carbon ball to obtain porous silicon-carbon balls. The silicon deposition content accounts for 48% of the porous silicon-carbon balls.

[0079] S3, outer carbon layer: porous silicon carbon balls are sent to the fluidized bed, and the temperature is raised to 500℃ at 5℃ / min. The flow rate of organic gas acetylene is 75L / h, and the carbon layer thickness is 14nm (i.e., the carbon layer). The particle size of 2.3-29μm and the true density of 2.08m 3 / g, tap density is 1.06m 3 / g of silicon-carbon negative electrode material, the structural characterization diagram of the obtained silicon-carbon negative electrode material is shown in Figures 1 and 2 .

[0080] Application in secondary batteries:

[0081] (1) Conductive material 1 (conductive carbon black), graphite negative electrode material (obtained by shaping and crushing petroleum coke into particles of 7-9 μm, granulating Dv50 to 12.3 μm particles, graphitizing at 3160°C, and coating), and silicon-carbon negative electrode material were pre-mixed for 45 minutes, 50 wt% of binder 1 (sodium polyacrylate-methyl acrylate) and solvent water were added and mixed for 60 minutes for kneading, and then the remaining 50% of binder 1, conductive material 2 (single-walled carbon nanotubes), and water were added and mixed for 60 minutes for the first stirring, and the solid content was controlled at 48%. Then, binder 2 ((polystyrene-butadiene-acrylic acid-ethyl acrylate)) and water were added and stirred for the second time, and the solid content was controlled at 39%. The fineness was ≤45 μm to obtain a negative electrode slurry.

[0082] (2) Conductive material 1 (conductive carbon black), positive electrode material (lithium nickel cobalt manganese oxide (LiNi 0.92 Co 0.04 Mn 0.4 O2) pre-mixed, binder 3 (polyvinylidene fluoride) and NMP were added for kneading, and then the remaining binder 3 (polyvinylidene fluoride), conductive material 2 (single-walled carbon nanotubes), solvent NMP, electrolyte lithium aluminum germanium phosphate (LAGP) / lithium aluminum titanium phosphate (LATP) were added and mixed and stirred for the first time, and the solid content was controlled at 76%. NMP was added for the second stirring, and the solid content was controlled at 78%. The fineness was ≤25μm to obtain the positive electrode slurry.

[0083] (3) The negative electrode slurry is coated on the copper foil with a surface density of 0.006g / cm 2 , drying to remove the solvent water, forming a negative electrode slurry layer, rolling, drying, and die-cutting to obtain a negative electrode sheet, and the obtained negative electrode sheet was structurally characterized. The results are shown in Figure 4 As can be seen from the figure, the white part is the silicon-carbon negative electrode material, which is basically crack-free; the positive electrode slurry is coated on the aluminum foil with a surface density of 0.025g / cm 2 , drying to remove NMP, forming a positive electrode slurry layer, rolling, drying, and die-cutting to obtain a positive electrode sheet.

[0084] (4) The positive electrode sheet, separator, and negative electrode sheet are stacked / wound into a bare battery cell, and the tabs are welded, glued, shelled, liquid-filled, formed, and capacity-divided to form a secondary battery.

[0085] The mass ratio of the graphite negative electrode material + silicon-carbon negative electrode material (mass ratio of 14:86), the conductive material (90wt% conductive material 1 + 10wt% conductive material 2), and the binder (75wt% binder 1 + 25wt% binder 2) in the negative electrode slurry is 95:0.5:5.

[0086] The mass ratio of the positive electrode material, the conductive material (98 wt% conductive material 1+2 wt% conductive material 2), the binder (binder 3) and the electrolyte in the positive electrode slurry is 97.8:0.4:1.5:0.3.

[0087] Example 2

[0088] The only difference from Example 1 is the soft carbon microspheres in "S1, preparation of porous carbon ball precursor": 100 parts by mass of polysiloxane and 5 parts by mass of needle coke are mixed in a stirred reactor, first heated at 240°C and stabilized for 2 hours, then heated at 480°C and stabilized for 5 hours, cooled, centrifuged, and washed to obtain soft carbon microspheres.

[0089] Example 3

[0090] The only difference from Example 1 is the spray coating in "S1, preparation of porous carbon ball precursor": 2.5 parts by mass of coal tar, the second carbon source, is softened at 220°C, 0.08 parts by mass of nanographite flakes and 15 parts by mass of sodium hydroxide activator are added and mixed evenly to obtain a mixture, which is sent to a spray dryer, and 50 parts by mass of soft carbon microspheres are added, and the mixture is spray-coated on the soft carbon microspheres.

[0091] Example 4

[0092] The only difference from Example 1 is the simultaneous activation in "S1, preparation of porous carbon ball precursor": simultaneous heating activation at 800 ° C for 4 h under a nitrogen inert gas environment, cooling, neutralization with 0.25 mol / L dilute hydrochloric acid, washing to remove residual activator, washing with water to neutrality, and drying to obtain a porous carbon ball precursor. The specific surface area of ​​the porous carbon ball precursor is 1710 m 2 / g, pore volume at 0.87cm 3 / g, and the volume of pores ≤4nm accounts for 81% of the total pore volume.

[0093] Example 5

[0094] The only difference from Example 1 is "S3, silicon deposition": the porous carbon ball precursor is sent to an inert gas environment, and at 550°C, a silane silicon source (flow rate 40L / h, deposition time 2h) is introduced to crack the silicon source, and silicon element is deposited and adsorbed inside the porous carbon balls to obtain porous silicon-carbon balls. The silicon deposition content accounts for 47% of the porous silicon-carbon balls.

[0095] Example 6

[0096] This embodiment provides a preparation method and application of a porous carbon ball precursor and a silicon-carbon negative electrode material, as shown below:

[0097] S1. Preparation of porous carbon ball precursor: The first carbon source pitch coke is thermally polymerized to obtain 0.8~40μm soft carbon microspheres, and the soft carbon microspheres, the second carbon source coal tar, nanographene sheets, and activator are spray coated and cooled to solidify. In a nitrogen inert gas environment, the mixture is heated and activated at 880℃ for 4h, cooled to room temperature, neutralized and washed with 0.42mol / L dilute hydrochloric acid to remove the residual activator, washed with water until neutral, and dried to obtain a porous carbon ball precursor. The specific surface area of ​​the porous carbon ball precursor is 1890m 2 / g, pore volume at 0.86cm 3 / g, of which the pore volume with a pore size of ≤4nm accounts for 78% of the total pore volume.

[0098] S2. Silicon deposition: The porous carbon ball precursor is placed in a nitrogen inert gas environment at 480°C, and a monosilane silicon source (flow rate 48 L / h, deposition time 1.5 h) is introduced to crack the silicon source and deposit silicon element inside the porous carbon ball to obtain porous silicon-carbon balls. The silicon deposition content accounts for 46% of the porous silicon-carbon balls.

[0099] S3, outer carbon layer: porous silicon carbon balls are sent to the fluidized bed, and the temperature is raised to 500℃ at 5℃ / min, and the flow rate of organic gas butyne is introduced at 70L / h until the carbon layer thickness is 12nm (i.e., the carbon layer), and the particle size of 2.3-24μm and the true density of 2.12m 3 / g, tap density is 1.08m3 / g of silicon-carbon negative electrode material.

[0100] The specific preparation steps of the soft carbon microspheres are as follows: 100 parts by weight of polydimethylsiloxane and 8 parts by weight of coal-based pitch are mixed in a stirred reactor, first heated at 240°C and stabilized for 2 hours, then heated at 450°C and stabilized for 6 hours, cooled, centrifuged, and washed to obtain the soft carbon microspheres.

[0101] The spray coating comprises the following steps: softening 5 parts by weight of the second carbon source, coal tar, at 185° C., adding 0.1 parts by weight of nanographene sheets and 25 parts by weight of a potassium hydroxide activator, and mixing them uniformly to obtain a mixture, which is then fed to a spray dryer, and then adding 60 parts by weight of soft carbon microspheres, and spray-coating the soft carbon microspheres with the mixture.

[0102] Application in secondary batteries:

[0103] (1) Conductive material 1 (conductive carbon black), graphite negative electrode material (needle coke shaping, crushing to 6-8 μm particles, granulation Dv50 to 11.5 μm particles, 3120 ° C graphitization, coating), silicon carbon negative electrode material were pre-mixed for 60 minutes, 50 wt% binder 1 (sodium polyacrylate-methyl acrylate) and solvent water were added and mixed for 60 minutes for kneading, and then the remaining 50 wt% binder 1, conductive material 2 (single-walled carbon nanotubes) and water were added and mixed for 60 minutes for the first stirring, and the solid content was controlled at 48%. Then, binder 2 ((polystyrene-butadiene-acrylic acid-ethyl acrylate)) and water were added and stirred for the second time, and the solid content was controlled at 39%. The fineness was ≤30 μm to obtain negative electrode slurry.

[0104] (2) Conductive material 1 (conductive carbon black), positive electrode material (lithium nickel cobalt manganese oxide (LiNi 0.92 Co 0.04 Mn 0.4 O2) pre-mixed, binder 3 (polyvinylidene fluoride) and NMP were added for kneading, and then the remaining binder 3 (polyvinylidene fluoride), conductive material 2 (single-walled carbon nanotubes), solvent NMP, electrolyte lithium aluminum germanium phosphate (LAGP) / lithium aluminum titanium phosphate (LATP) were added and mixed and stirred once, and the solid content was controlled at 75%. NMP was added for a second stirring, and the solid content was controlled at 71%. The fineness was ≤25μm to obtain the positive electrode slurry.

[0105] (3) The negative electrode slurry is coated on the copper foil with a surface density of 0.06g / cm 2 The solvent water is dried to form a negative electrode slurry layer, which is then rolled, dried, and die-cut to obtain a negative electrode sheet; the positive electrode slurry is coated on an aluminum foil with a surface density of 0.023 g / cm 2 , drying to remove NMP, forming a positive electrode slurry layer, rolling, drying, and die-cutting to obtain a positive electrode sheet.

[0106] (4) The positive electrode sheet, separator, and negative electrode sheet are stacked / wound into a bare battery cell, and the tabs are welded, glued, shelled, liquid-filled, formed, and capacity-divided to form a secondary battery.

[0107] The mass ratio of the graphite negative electrode material + silicon-carbon negative electrode material (mass ratio of 14:86), the conductive material (90wt% conductive material 1 + 10wt% conductive material 2), and the binder (75wt% binder 1 + 25wt% binder 2) in the negative electrode slurry is 95:0.5:5.

[0108] The mass ratio of the positive electrode material, the conductive material (98 wt% conductive material 1+2 wt% conductive material 2), the binder (binder 3) and the electrolyte in the positive electrode slurry is 97.8:0.4:1.5:0.3.

[0109] Example 7

[0110] The only difference from Example 6 is the soft carbon microspheres in "S1 porous carbon ball precursor preparation": 100 parts by mass of polysiloxane and 8 parts by mass of coal-based asphalt are mixed in a stirred reactor, first heated at 240°C and stabilized for 2 hours, then heated at 480°C and stabilized for 5 hours, cooled, centrifuged, and washed to obtain soft carbon microspheres.

[0111] Example 8

[0112] The difference from Example 6 is only the spray coating in "Preparation of S1 porous carbon ball precursor": 2.5 parts by mass of the second carbon source coal tar are softened at 220°C, 0.06 parts by mass of nanographene sheets and 12 parts by mass of potassium hydroxide activator are added and mixed evenly to obtain a mixture, which is sent to a spray dryer, and 50 parts by mass of soft carbon microspheres are added, and the mixture is spray-coated on the soft carbon microspheres.

[0113] Example 9

[0114] The only difference from Example 6 is the simultaneous heating activation in "S1 porous carbon ball precursor preparation": simultaneous activation at 850 ° C for 6 h in a nitrogen inert gas environment, cooling, neutralization with 0.5 mol / L dilute hydrochloric acid, washing to remove residual activator, washing with water to neutrality, and drying to obtain a porous carbon ball precursor. The specific surface area of ​​the porous carbon ball precursor is 2040 m 2 / g, pore volume at 91cm 3 / g, of which the pore volume with a pore size of ≤4nm accounts for 83% of the total pore volume.

[0115] Example 10

[0116] The only difference from Example 5 is "S3 silicon deposition": the porous carbon ball precursor is sent to an inert gas environment, at 560°C, a silane silicon source (flow rate 45L / h, deposition time 2.2h) is introduced to crack the silicon source, and silicon element is deposited and adsorbed inside the porous carbon balls to obtain porous silicon-carbon balls. The silicon deposition content accounts for 49% of the porous silicon-carbon balls.

[0117] Comparative Example 1

[0118] The difference from Example 1 is that: No activator was added during the spray coating. The characterization of the obtained negative electrode sheet is shown in Figure 5 As can be seen from the figure, the white part is the silicon-carbon negative electrode material, and some cracks have appeared.

[0119] Comparative Example 2

[0120] The difference from Example 1 is that no nano-graphite sheets are added during the spray coating.

[0121] Comparative Example 3

[0122] The difference from Example 1 is that no spray coating treatment is performed.

[0123] Performance Testing

[0124] 1.1.5V Coulomb efficiency test:

[0125] At 25°C, the coulombic efficiency of the silicon-carbon negative electrode materials obtained in the examples and comparative examples was tested:

[0126] 1) The negative electrode material obtained in the examples and comparative examples, the SP conductive agent, and the binder (5 parts of polyacrylic acid-acrylate and 5 parts of styrene-butadiene-acrylate copolymer) were mixed and stirred for 360 minutes and coated on copper foil. The coating surface density was 3 mg / cm 2 , rolled to 0.93g / cm 3 , vacuum oven at 80℃, maintain pressure and dry for 12h.

[0127] 2) Punch the electrode into a disc, use the metal lithium sheet as the counter electrode, add electrolyte, assemble the half-cell, and let it stand for 6 hours.

[0128] 3) Discharge: 0.1C discharge to 0.005V, let it stand for 5 minutes, 0.02C discharge to 0.005V, let it stand for 5 minutes, 0.01C discharge to 0.005V, let it stand for 5 minutes, 0.1C charge to 1.5V.

[0129] 4) 1.5V Coulombic efficiency = initial charge (lithiation removal) specific capacity in the 0.005-1.5V range / initial discharge (lithiation insertion) specific capacity in the 0.005-1.5V range. Experimental results are shown in Table 1.

[0130] 2. Negative electrode resistance test:

[0131] In an environment of 25°C, use the upper and lower positive and negative connectors of the film resistance meter to test the blank value, and then use the upper and lower positive and negative connectors of the film resistance meter to measure the negative electrode resistance. The actual negative electrode resistance = the test resistance value minus the blank value. The experimental results are shown in Table 2.

[0132] 3. Rate test:

[0133] The lithium-ion secondary batteries obtained in the examples and comparative examples were flammed and diluted to capacity at 45°C / 25°C, then allowed to stand at 40°C for 48 hours and at 25°C for 24 hours. The batteries were then discharged at 0.5C to 2.8V. Again, at 25°C, using a U-shaped clamp with a 325kg clamping force, the batteries were charged at a constant current of 0.5C to 4.25V, and then charged at a constant voltage of 4.25V until the current was less than 0.05C. The charge capacity was recorded as C0.5. The batteries were then discharged at a constant current of 0.5C to 2.8V, and the discharge capacity was recorded as Capacity 0.5C. The batteries were then discharged at constant currents of 2C, 3C, and 4C to 2.8V. The discharge capacities were recorded as Capacity 2.0C, Capacity 3.0C, and Capacity 4.0C. The 2C, 3C, and 4C rate discharge characteristics are as follows: capacity 2.0C / capacity 0.5C, capacity 3.0C / capacity 0.5C, and capacity 4.0C / capacity 0.5C. The larger the value, the better the charge and discharge and rate performance. The experimental results are shown in Table 3.

[0134] 4. Cycle test:

[0135] The lithium-ion secondary batteries obtained in the examples and comparative examples were left to stand for 2 days at 25°C, and then discharged at 0.5C to 2.8V. At 25°C, a U-shaped clamp with a clamping force of 325kg was used to clamp the battery. The charging process was as follows: 2C constant current charging to 4.0V, constant voltage charging at 4.0V to a current of less than 0.5C, resting for 5 minutes, then 1C constant current charging to 4.2V, constant voltage charging at 4.2V to a current of less than 0.1C, resting for 5 minutes, then 0.5C constant current charging to 4.25V, constant voltage charging at 4.25V to a current of less than 0.05C; the discharging process was as follows: resting for 5 minutes, then 0.5C constant current discharging to 2.8V, and so on until the discharge capacity reached 80% of the initial capacity at 0.5C constant current discharging to 2.8V, and then the test was stopped. The experimental results are shown in Table 4.

[0136] Table 1 Coulombic efficiency of batteries obtained in Examples and Comparative Examples

[0137]

[0138] Table 2 Negative electrode resistance obtained in Examples and Comparative Examples

[0139]

[0140] Table 3 Rate of batteries obtained in Examples and Comparative Examples

[0141]

[0142] Table 4 Cycling conditions of the batteries obtained in the examples and comparative examples

[0143]

[0144] According to Tables 1, 2, 3, and 4, compared with Comparative Examples 1, 2, and 3, each embodiment adds nanographite sheets and activators by spray coating, and the pores are more continuous and the carbon layer is more tightly combined, and the electronic conductivity is more continuous, thereby avoiding the separation of porous carbon balls and homogeneous porous carbon layers in the silicon-carbon negative electrode material, which causes particle breakage and reduces the resistivity of the negative electrode material, resulting in the formation of a new interface and the consumption of more lithium; in addition, the structural strength of the silicon-carbon negative electrode material is improved, thereby improving the coulombic efficiency, electrode electronic conductivity, battery rate, and cycle life.

[0145] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain 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, preparing soft carbon microspheres by thermal polymerization using a first carbon source; S2, spray coating the soft carbon microspheres, the second carbon source, the graphite carbon nanodots, and the activator, cooling and curing, heating and activating them for the first time under an inert atmosphere, and then neutralizing and washing them with acid to obtain a porous carbon sphere precursor; S3. Under an inert atmosphere, a silicon source is introduced into the porous carbon ball precursor and heated for a second time, so that the silicon source is cracked and silicon is deposited and adsorbed inside the porous carbon ball precursor to obtain porous silicon-carbon balls; S4, heating the porous silicon-carbon spheres to a high temperature and introducing an organic gas to form a carbon layer on the surface of the porous silicon-carbon spheres, thereby finally obtaining the silicon-carbon negative electrode material; The graphite carbon nanodots are selected from one or more of nanographene sheets, nanographite powders, nanographite sheets, and nanographitized carbon black films; The specific method of the spray coating is as follows: heating the second carbon source to 150-240° C. to soften it, adding graphite carbon nanodots and an activator and mixing them evenly to obtain a mixture, sending it to a spray dryer, then adding soft carbon microspheres, and spraying the mixture to coat the soft carbon microspheres; The activator is selected from one or more of ammonia, potassium hydroxide, sodium hydroxide, and lithium hydroxide; The mass ratio of the soft carbon microspheres, the second carbon source, the graphite carbon nanodots, and the activator is (40-60): (1-8): (0.03-0.2): (12-30); The silicon-carbon negative electrode material is a core-shell structure, with a porous carbon ball as the core, and is coated by a homogeneous porous carbon layer on the surface of the porous carbon ball, porous graphite carbon nanodots embedded in the homogeneous porous carbon layer, and an outer carbon layer; silicon is deposited in the pores of the porous carbon ball and the homogeneous porous carbon layer.

2. The preparation method according to claim 1, characterized in that In step S1, the first carbon source is selected from one or more of needle coke, pitch coke, petroleum pitch, coal-based pitch, coal-based tar, and petroleum coke; The preparation method of the soft carbon microspheres comprises: mixing polyorganosiloxane and a first carbon source, heating at a temperature of 200-300° C. for a certain time, and then heating at a second temperature for a certain time to obtain the soft carbon microspheres; The size of the soft carbon microspheres is between 0.8 and 40 μm.

3. The preparation method according to claim 2, characterized in that The temperature of the first stage heating is 200-300℃, and the heating constant temperature time is 1-3 hours; the temperature of the second stage heating is 350-480℃, and the heating constant temperature time is 5-7 hours; The polyorganosiloxane is selected from polydimethylsiloxane, cyclomethicone, aminosiloxane, and polymethylphenylsiloxane; The mass ratio of the polyorganosiloxane to the first carbon source is 100:(1-8).

4. The preparation method according to claim 1, characterized in that In step S2, the second carbon source is selected from one or more of phenolic resin, asphalt coke, petroleum coke, petroleum asphalt, and coal tar pitch; The temperature of the first heating activation is 500~1100℃, and the heating activation time is 3~10h.

5. The preparation method according to claim 1, characterized in that In step S3, the specific surface area of ​​the porous carbon ball precursor is 1200-2600m 2 / g, pore volume is 0.60-1.15cm 3 / g, the volume of pores ≤4nm accounts for more than 60% of the total pore volume; The silicon source is selected from one or more of monosilane, disilane, trisilane, dimethylsilane, hexamethyldisilane, dichlorodihydrosilane, trichlorosilane, silicon tetrachloride, and silicon tetrafluoride; The flow rate of the silicon source is 30~200L / h; The temperature of the second heating is 450~750℃; The time for silicon element deposition is 20min~6h; The silicon element deposition content accounts for 40% to 80% of the porous silicon carbon spheres.

6. The preparation method according to claim 1, characterized in that In step S4, the heating rate is 1-6°C / min; the heating temperature is 400-780°C; The organic gas is selected from one or more of butene, ethylene, butyne, acetylene, and propyne; The flow rate of the organic gas is 10~300L / h.

7. A silicon-carbon negative electrode material, characterized in that: The silicon-carbon negative electrode material is prepared by the preparation method according to any one of claims 1 to 6, wherein the silicon-carbon negative electrode material has a core-shell structure, with a porous carbon ball as the core, and is coated by a homogeneous porous carbon layer on the surface of the porous carbon ball, porous graphite carbon nanodots embedded in the homogeneous porous carbon layer, and an outer carbon layer; silicon element is deposited in the pores of the porous carbon ball and the homogeneous porous carbon layer.

8. The silicon-carbon negative electrode material according to claim 7, characterized in that: The size of the porous carbon balls is 0.3-32 μm; The thickness of the homogeneous porous carbon layer is 0.02~3μm; The thickness of the outer carbon layer is 0.8~55nm; The Dv50 of the silicon-carbon negative electrode material is 0.5-35 μm.

9. A negative electrode sheet, characterized in that: Including the silicon-carbon negative electrode material according to claim 8.

10. A secondary battery, characterized in that: The invention comprises the negative electrode sheet as claimed in claim 9.

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