Silicon-carbon negative electrode material, preparation method and application thereof

Abstract

The application relates to a silicon-carbon negative electrode material and a preparation method and application thereof. The preparation method comprises the following steps: obtaining soft carbon microspheres by using a first carbon source for thermal polymerization; performing spray coating of the soft carbon microspheres, a second carbon source, graphite carbon nanodots and an activating agent, cooling and solidifying, first heating and activating, then neutralizing with an acid and washing to obtain a porous carbon sphere precursor; under an inert atmosphere, feeding a silicon source into the porous carbon sphere precursor and performing second heating, so that the silicon source is cracked and elemental silicon is deposited and adsorbed inside the porous carbon sphere to obtain a porous silicon-carbon sphere; heating and warming the porous silicon-carbon sphere and feeding an organic gas to form a carbon layer on the surface of the porous silicon-carbon sphere, and finally obtaining the silicon-carbon negative electrode material. The obtained silicon-carbon negative electrode material can avoid separation of the porous carbon sphere and the homogeneous porous carbon layer after external force roller pressing, can prevent particle breakage, can improve the structural strength of the silicon-carbon negative electrode material, and can further improve the capacity of a battery system and the cycle life.

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 3C electronic products, two / four-wheel electric vehicles, and industrial and commercial energy storage due to their long cycle life and high energy density. At the same time, the rapid development of electric vehicles has put forward higher requirements for the energy density of lithium-ion batteries. LIBs are mainly composed of four parts: positive electrode materials, diaphragm materials, negative electrode materials, and copper / aluminum electrode foil materials. Silicon negative electrode materials in negative electrode materials are developing rapidly, with the advantages of low-cost raw materials and high energy density. They are currently a hot area of ​​negative electrode materials. Among them, silicon-carbon negative electrode materials with silane deposited porous carbon can provide a theoretical specific capacity of 1000-1800mAh / g, which is much higher than commercial graphite negative electrodes. It is the preferred negative electrode material for high energy density batteries and one of the candidate materials for the next generation of lithium-ion battery negative electrode materials.

[0003] Compared with graphite negative electrode materials, the tap density of silicon-carbon negative electrode materials is lower, and it is necessary to improve its own strength and density. After rolling, the compaction 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] In order to solve the above technical problems, the present invention provides a silicon-carbon negative electrode material and its preparation method and application. The present invention adjusts the pore distribution of porous carbon balls, forms a heterogeneous porous carbon layer embedded with porous graphite carbon nanodots on the surface of porous carbon balls, and then deposits silicon to obtain a highly tapped silicon-carbon negative electrode material, and the heterogeneous porous carbon layer serves as an internal protective layer of the microspheres; secondly, through the simultaneous activation process of porous carbon balls and heterogeneous porous carbon layers, the silicon-carbon negative electrode material is rolled by external force to avoid the separation of porous carbon balls and heterogeneous porous carbon layers, resulting in particle breakage, thereby improving the structural strength of the silicon-carbon negative electrode material, and thus improving 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 for the first time under an inert atmosphere, and then neutralizing and washing with an acid to obtain a porous carbon sphere precursor;

[0009] S3, under an inert atmosphere, feeding a silicon source into the porous carbon ball precursor, and performing a second heating, so that the silicon source is cracked and silicon element is deposited and adsorbed inside the porous carbon ball precursor, thereby obtaining a porous silicon-carbon ball;

[0010] S4, heating the porous silicon-carbon spheres and introducing organic gas to form a carbon layer on the surface of the porous silicon-carbon spheres, and 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 asphalt, coal-based asphalt, coal-based tar, and petroleum coke;

[0012] The preparation method of the soft carbon microspheres comprises: mixing polyorganosiloxane and a first carbon source, and 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 between these values.

[0014] In some embodiments of the present invention, the temperature of the first stage is 200-300°C, and the heating time is 1-3 hours; the temperature of the second stage is 350-480°C, and the heating 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°C, 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 performed by spray coating to obtain a coating layer containing an activator. At a high temperature of 500 to 1100° C., the activator generates water at high temperature (water reacts with carbon to generate carbon monoxide and carbon dioxide, consumes carbon, and the carbonaceous surface releases space through each step of consumption reaction to generate gas, and the porous structure carbon layer gradually collapses into pores). The generated water diffuses into the soft carbon microspheres at the same time, and the coating layer and the soft carbon microspheres and graphite carbon nanodots are simultaneously 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 heterogeneous porous carbon layer is formed, and the pores are more continuous and more tightly combined with the carbon layer, thereby avoiding the separation of the porous carbon ball precursor and the heterogeneous 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 form nuclei, promoting the aromatization reaction of asphalt molecules, the discharge of excess hydrogen, and reducing the generation of carbon deposits. After neutralization and washing with hydrochloric acid, the micropore / mesoporous structure in the heterogeneous 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 heterogeneous porous carbon layer). The heterogeneous 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, 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 pore volume of ≤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, dichlorodihydrogensilane, 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 in between these values.

[0030] The temperature of the second heating is 450-750°C;

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

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

[0033] The silicon single substance deposition content accounts for 40% to 80% of the porous silicon carbon sphere, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any value in between.

[0034] In some embodiments of the present invention, in step S4, the heating rate is 1-8°C / min; 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, etc.; the heating temperature is 400-780°C, for example, 400°C, 500°C, 600°C, 700°C, 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, wherein 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 a porous carbon ball, a homogeneous porous carbon layer, and an outer carbon layer 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 to 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 single substance particle size is ≤2nm, and is amorphous single substance silicon;

[0044] The Dv50 of the silicon-carbon negative electrode material is in the range of 0.5 to 35 μm; for example, 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, 33 μm, 34 μm, 35 μm, or any value between these values.

[0045] The actual density of the silicon-carbon negative electrode material is 1.9 to 2.25 m 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 to 1.4 m 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) Premixing the first conductive material, graphite material, and silicon-carbon negative electrode material for 20-60 minutes, adding 50% of the first binder and solvent water, mixing for 30-90 minutes, and kneading, then adding the remaining 50% of the first binder 1, the second conductive material, and water, mixing for 30-120 minutes, and stirring once, controlling the solid content to 35-50%, and then adding the second binder and water for a second stirring, controlling the solid content to 30-55%, and the fineness ≤45 μm, to obtain a negative electrode slurry;

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

[0053] (3) The negative electrode slurry is coated on the copper foil, dried to remove the solvent water, to form a negative electrode slurry layer, and 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, to form a positive electrode slurry layer, and 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 obtained by shaping needle tar, coal tar, asphalt tar, petroleum coke, etc., crushing to particles of 7-9 μm, granulating Dv50 to particles of 11-16 μm, graphitizing at 2900-3250° C., coating, etc.

[0056] The first conductive material and the second conductive material are independently at least one of conductive carbon black, silver powder, nickel powder, graphite whisker, 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 conductive material and the second conductive material may be the same or different.

[0057] The binder (the first binder, the second binder, the third binder) includes one or more of sodium polyacrylate / lithium, polymethyl methacrylate, polyethyl acrylate, sodium polyacrylate / lithium-methyl / ethyl / propyl acrylate, sodium polyacrylate / lithium-acrylonitrile, sodium polyacrylate / lithium-butadiene-acrylonitrile, sodium polyacrylate / lithium-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 binder, the second binder, and the third binder may be the same or different from each other.

[0058] Further, the electrolyte is selected from one or more of lanthanum lithium zirconate (LLZO), lanthanum lithium tantalate (LLTO), lanthanum lithium 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 compared with 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, consumes carbon, and the carbonaceous surface generates gas through each step of consumption reaction to release space, and the carbon layer with a pore structure gradually collapses into pores). The generated water diffuses into the soft carbon microspheres at the same time, 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 heterogeneous porous carbon layer is formed, and the pores are more continuous and more tightly combined with the carbon layer, thereby avoiding the separation of the porous carbon balls and the heterogeneous 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 form nuclei, which promotes the aromatization reaction of asphalt molecules, discharges excess hydrogen, and reduces the formation of carbon deposits. After neutralization and washing with hydrochloric acid, the micropore / mesopore structure in the heterogeneous porous carbon layer becomes more ordered and rich. The heterogeneous 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 according to 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 spectrum of the silicon-carbon negative electrode material obtained in Example 1 of the present invention.

[0069] Figure 3 It is a 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 rolling.

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

[0072] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but 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 asphalt 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, heat and activate at 850℃ for 4.5h, cool to room temperature, neutralize with 0.43mol / L dilute hydrochloric acid, wash to remove residual activator, wash with water to neutrality, and dry 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 method comprises the following steps: 3 parts by weight of the second carbon source, coal tar, are 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 sent to a spray dryer, and 45 parts by weight of soft carbon microspheres are added, and the mixture is spray-coated with the soft carbon microspheres.

[0078] S2, silicon deposition: the porous carbon ball precursor is sent to a nitrogen inert gas environment, at 550°C, a monosilane silicon source (flow rate 48L / h, deposition time 1.5h) is introduced to crack the silicon source, and silicon is deposited and adsorbed inside the porous carbon ball to obtain a porous silicon-carbon ball, and the silicon deposition content accounts for 48% of the porous silicon-carbon ball;

[0079] S3, outer carbon layer: The 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, until the carbon layer thickness is 14nm (i.e., the carbon layer), and 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 1-2 .

[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 are pre-mixed for 45 minutes, 50 wt% of binder 1 (sodium polyacrylate-methacrylate) and solvent water are 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 are added and mixed for 60 minutes for the first stirring, and the solid content is controlled at 48%. Then, binder 2 ((polystyrene-butadiene-acrylic acid-ethyl acrylate)) and water are added and stirred for the second time, and the solid content is controlled at 39%, and the fineness is ≤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) is pre-mixed, a binder 3 (polyvinylidene fluoride) and NMP are 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) are added and mixed and stirred for the first time, and the solid content is controlled at 76%, and then NMP is added for the second stirring, and the solid content is controlled at 78%, and the fineness is ≤25μm to obtain a positive electrode slurry.

[0083] (3) The negative electrode slurry is coated on the copper foil with a surface density of 0.006 g / 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 structure of the obtained negative electrode sheet is 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 not cracked; 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 graphite negative electrode material + silicon-carbon negative electrode material (mass ratio of 14:86), conductive material (90wt% conductive material 1 + 10wt% conductive material 2), and 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 (98wt% conductive material 1+2wt% 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 difference from Example 1 is only in 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 difference from Example 1 is only the spray coating in "S1, preparation of porous carbon ball precursor": 2.5 parts by mass of the second carbon source coal tar are 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 difference from Example 1 is only in the simultaneous activation in "S1, preparation of porous carbon ball precursor": simultaneous heating activation at 800°C in a nitrogen inert gas environment for 4 h, cooling, neutralization with 0.25 mol / L dilute hydrochloric acid, washing to remove residual activator, washing with water until neutral, and drying to obtain a porous carbon ball precursor with a specific surface area of ​​1710 m 2 / g, pore volume at 0.87cm 3 / g, and the pore volume ≤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, 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 asphalt 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 activators are spray coated and cooled to solidify. In a nitrogen inert gas environment, heat and activate at 880℃ for 4h, cool to room temperature, neutralize with 0.42mol / L dilute hydrochloric acid, wash to remove residual activator, wash with water to neutrality, and dry 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 sent to a nitrogen inert gas environment, at 480°C, a monosilane silicon source (flow rate 48L / h, deposition time 1.5h) is introduced to crack the silicon source, and silicon is deposited and adsorbed inside the porous carbon ball to obtain a porous silicon-carbon ball, and the silicon deposition content accounts for 46% of the porous silicon-carbon ball;

[0099] S3, outer carbon layer: The porous silicon carbon balls are sent to the fluidized bed, and the temperature is raised to 500℃ at 5℃ / min. The organic gas butyne is introduced at a flow rate of 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 asphalt 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 method comprises the following steps: 5 parts by weight of the second carbon source coal tar is softened at 185° C., 0.1 parts by weight of nanographene sheets and 25 parts by weight of potassium hydroxide activator are added and mixed evenly to obtain a mixture, which is sent to a spray dryer, and 60 parts by weight of soft carbon microspheres are added, and the mixture is spray-coated with the soft carbon microspheres.

[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), and silicon-carbon negative electrode material are pre-mixed for 60 minutes, 50 wt% of binder 1 (sodium polyacrylate-methacrylate) and solvent water are added and mixed for 60 minutes for kneading, and then the remaining 50 wt% of binder 1, conductive material 2 (single-walled carbon nanotubes), and water are added and mixed for 60 minutes for the first stirring, and the solid content is controlled at 48%. Then, binder 2 ((polystyrene-butadiene-acrylic acid-ethyl acrylate)) and water are added and stirred for the second time, and the solid content is controlled at 39%, and the fineness is ≤30 μm to obtain a 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) is pre-mixed, a binder 3 (polyvinylidene fluoride) and NMP are 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) are added, mixed and stirred once, and the solid content is controlled at 75%, and then NMP is added for a second stirring, and the solid content is controlled at 71%, and the fineness is ≤25μm to obtain a positive electrode slurry.

[0105] (3) The negative electrode slurry is coated on the copper foil with a surface density of 0.06 g / cm 2 , drying to remove solvent water, forming a negative electrode slurry layer, rolling, drying, and die-cutting to obtain a negative electrode sheet; the positive electrode slurry is coated on an aluminum foil with a surface density of 0.023g / 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 graphite negative electrode material + silicon-carbon negative electrode material (mass ratio of 14:86), conductive material (90wt% conductive material 1 + 10wt% conductive material 2), and 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 (98wt% conductive material 1+2wt% 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 difference from Example 6 is only in 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 with 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 until neutral, and drying to obtain a porous carbon ball precursor. The specific surface area of ​​the porous carbon ball precursor is 2040m 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 is introduced (flow rate 45L / h, deposition time 2.2h) 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, and the characterization of the obtained negative electrode sheet is shown in Figure 5 ,It can be seen from the picture that 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 in 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] Under an environment of 25°C, the coulombic efficiency test of the silicon-carbon negative electrode materials obtained in the embodiment and the comparative example is as follows:

[0126] 1) The negative electrode material, SP conductive agent, and binder (5 parts of polyacrylic acid-acrylate, 5 parts of styrene-butadiene-acrylate copolymer) obtained in the examples and comparative examples 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℃, and dry under pressure for 12 hours.

[0127] 2) The electrode is punched into a disc, the metal lithium sheet is used as the counter electrode, the electrolyte is added, the half-cell is assembled, and it is left to stand for 6 hours.

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

[0129] 4) 1.5 V coulombic efficiency = first charge (lithium removal) specific capacity in the range of 0.005-1.5 V / first discharge (lithium insertion) specific capacity in the range of 0.005-1.5 V. The experimental results are shown in Table 1.

[0130] 2. Negative electrode resistance test:

[0131] In an environment of 25°C, use the positive and negative connectors of a diaphragm resistor to test the blank value, and then use the positive and negative connectors of a diaphragm resistor 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. Ratio test:

[0133] The lithium-ion secondary batteries obtained in the examples and comparative examples were flammed at 45°C / 25°C, left to stand at 40°C for 48 hours and at 25°C for 24 hours, and then discharged at 0.5C to 2.8V. Then, at 25°C, the battery was clamped with a U-shaped clamp with a clamp force of 325kg, and charged at a constant current of 0.5C to 4.25V, and charged at a constant voltage of 4.25V to a current of <0.05C, with the charging capacity recorded as C0.5; discharged at a constant current of 0.5C to 2.8V, with the discharge capacity recorded as Capacity 0.5C. Then, the battery was discharged at a constant current of 2C, 3C, and 4C to 2.8V, with the discharge capacity 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] After the lithium-ion secondary batteries obtained in the examples and comparative examples were left to stand for 2 days at 25°C, they were first discharged at 0.5C to 2.8V. At 25°C, the battery was clamped with a U-shaped clamp with a clamp force of 325kg. The charging process is: 2C constant current charging to 4.0V, constant voltage 4.0V charging to current <0.5C, resting for 5 minutes, then 1C constant current charging to 4.2V, constant voltage 4.2V charging to current <0.1C, resting for 5 minutes, then 0.5C constant current charging to 4.25V, constant voltage 4.25V charging to current <0.05C; the discharge process is: resting for 5 minutes, 0.5C constant current discharge to 2.8V, and so on until the discharge capacity is 80% of the initial 0.5C constant current discharge to 2.8V capacity, and then stop the test. The experimental results are shown in Table 4.

[0136] Table 1 Coulombic efficiency of the batteries obtained in the examples and comparative examples

[0137]

[0138]

[0139] Table 2 Negative electrode resistance obtained in Examples and Comparative Examples

[0140] Resistance / mΩ Example 1 1.7 Example 2 1.4 Example 3 1.8 Example 4 1.1 Example 5 1.8 Example 6 1.6 Example 7 1.4 Example 8 1.9 Example 9 1.8 Example 10 1.6 Comparative Example 1 5.7 Comparative Example 2 2.4 Comparative Example 3 4.1

[0141] Table 3 Rate of the batteries obtained in the examples and comparative examples

[0142]

[0143]

[0144] Table 4 Cycling conditions of the batteries obtained in the examples and comparative examples

[0145] Cycle Test Example 1 1257 Example 2 1244 Example 3 1270 Example 4 1231 Example 5 1231 Example 6 1206 Example 7 1264 Example 8 1259 Example 9 1366 Example 10 1448 Comparative Example 1 1157 Comparative Example 2 1044 Comparative Example 3 870

[0146] According to Tables 1, 2, 3, and 4, compared with Comparative Examples 1, 2, and 3, each embodiment adds nanographite sheets and activators through 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 heterogeneous porous carbon layers in the silicon-carbon negative electrode material, resulting in particle breakage, reduced resistivity of the negative electrode material, resulting in the formation of new interfaces, and consuming more lithium; in addition, the structural strength of the silicon-carbon negative electrode material is improved, thereby improving the coulomb efficiency, electrode electronic conductivity, battery rate, and cycle life.

[0147] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the 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 for the first time under an inert atmosphere, and then neutralizing and washing with an acid to obtain a porous carbon sphere precursor; S3, under an inert atmosphere, feeding a silicon source into the porous carbon ball precursor, and performing a second heating, so that the silicon source is cracked and silicon element is deposited and adsorbed inside the porous carbon ball precursor, thereby obtaining a porous silicon-carbon ball; S4, heating the porous silicon-carbon spheres and introducing organic gas to form a carbon layer on the surface of the porous silicon-carbon spheres, and finally obtaining the silicon-carbon negative electrode material.

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 asphalt, coal-based asphalt, coal-based tar, and petroleum coke; The preparation method of the soft carbon microspheres comprises: mixing polyorganosiloxane and a first carbon source, and performing a first stage of heating at a temperature of 200-300° C. for a certain time, and then performing a second stage of heating at a constant 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 1-3h; the temperature of the second stage heating is 350-480℃, and the heating constant temperature time is 5-7h; 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 graphite carbon nanodots are selected from one or more of nanographene sheets, nanographite powders, nanographite sheets, and nanographitized carbon black films; The activator is selected from one or more of ammonia, potassium hydroxide, sodium hydroxide and lithium hydroxide; The temperature of the first heating activation is 500-1100°C, and the heating activation time is 3-10h; 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 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, adding soft carbon microspheres, and spraying the mixture to coat the soft carbon microspheres.

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 pore volume of ≤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, dichlorodihydrogensilane, trichlorosilane, silicon tetrachloride, and silicon tetrafluoride; The flow rate of the silicon source is 30 to 200 L / h; The temperature of the second heating is 450-750°C; The time for silicon element deposition is 20min to 6h; The silicon single substance deposition content accounts for 40% to 80% of the porous silicon carbon sphere.

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 to 300 L / h.

7. A silicon-carbon negative electrode material, characterized in that: The silicon-carbon negative electrode material is prepared by the preparation method described in any one of claims 1 to 6, wherein 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.

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

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

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

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