Silicon-carbon composite material as well as preparation method and application thereof

Abstract

The invention discloses a silicon-carbon composite material as well as a preparation method and application thereof, and relates to the technical field of battery negative electrode materials. The silicon-carbon composite material comprises active substance particles, and the active substance particles comprise a spherical porous carbon skeleton and nanometer silicon particles. The silicon-carbon composite material disclosed by the invention is high in sphericity degree, the poor pressure resistance caused by more edges and corners in the rolling process is avoided, and the problems that a solid electrolyte interface (SEI) film is continuously generated, the capacity is weakened and the circulation becomes poor due to low strength can be improved.

Description

Technical Field

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

[0002] Nowadays, traditional 3C consumer electronics, new energy power batteries, high-power power plants, large energy storage power stations and other fields are inseparable from lithium-ion batteries. As a traditional battery negative electrode material, the actual capacity of graphite has gradually approached its theoretical true capacity with the advancement of technology. In this context, silicon negative electrodes with higher theoretical capacity are considered to be the best candidates for the next generation of large-capacity batteries. In order to inhibit the expansion of silicon during charging and discharging and improve the conductivity of silicon alone, silicon needs to be coated in a porous carbon substrate with a high specific surface area.

[0003] During the battery manufacturing process, there are certain requirements for the strength of silicon-carbon composite materials to prevent roller pressing from causing particle breakage, which in turn causes silicon particles to be exposed, resulting in severe volume expansion during the charge and discharge process, affecting battery performance. The strength of silicon-carbon composite materials is related to many factors, such as material particle size, silicon content, and morphology. Particle breakage caused by roller pressing is closely related to the morphology of silicon-carbon materials. During the battery manufacturing process, irregular silicon-carbon composite materials will be squeezed against each other due to roller pressing, resulting in irregular edges and corners being broken, and internal active substances falling off, which is not conducive to the formation of a stable SEI film.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a silicon-carbon composite material and a preparation method and application thereof, as well as a detection method for the silicon-carbon composite material. The silicon-carbon composite material of the present invention has a high sphericity, which avoids the poor compressive strength caused by more edges and corners during the rolling process, resulting in particle breakage, and can improve the problem of continuous generation of solid electrolyte interface (SEI) film due to low strength, reduced capacity, and poor cycle performance.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a silicon-carbon composite material, the silicon-carbon composite material comprising active material particles, the active material particles comprising a spherical porous carbon skeleton and nano silicon particles;

[0008] The strength of the silicon-carbon composite material is defined by the following formula:

[0009]

[0010] Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of ​​the silicon-carbon composite material after pressing, m2 / g; S1 represents the specific surface area of ​​the silicon-carbon composite material before pressing, m 2 / g.

[0011] Preferably, the specific surface area of ​​the silicon-carbon composite material is 2 to 5 m 2 / g.

[0012] Preferably, the strength of the silicon-carbon composite material when pressed at a pressure of 450 MPa for 30 seconds is above 90%.

[0013] Preferably, the sphericity of the spherical porous carbon is ≥80%.

[0014] Preferably, the interior of the spherical porous carbon contains uniformly distributed micropores and / or mesopores.

[0015] Preferably, the average pore size of the spherical porous carbon is less than 4 nm and the total pore volume is ≥ 0.7 cm 3 / g.

[0016] Preferably, the mesoporosity of the spherical porous carbon is less than 20%, and the microporosity is greater than 80%.

[0017] Preferably, the particle size of the spherical porous carbon is 1 to 60 μm; wherein the D 10 Particle size is 3-7 μm; D 50 Particle size is 8-13 μm; D 90 The particle size is 15~40μm.

[0018] Preferably, the nano-silicon particles are deposited in the pores of the spherical porous carbon.

[0019] Preferably, the silicon content in the silicon-carbon composite material is 40-60%.

[0020] Preferably, the specific capacity of the silicon-carbon composite material is greater than 1500 mAh / g, preferably greater than 1800 mAh / g.

[0021] Preferably, the 200-cycle capacity retention rate of the silicon-carbon composite material is greater than 90%.

[0022] In a second aspect, the present invention provides a method for preparing the silicon-carbon composite material as described in the first aspect, the preparation method comprising the following steps:

[0023] Mixing low-carbon source microspheres, high-carbon source resin and solvent to obtain a mixed solution;

[0024] The mixed solution is spray-dried to obtain spherical particles;

[0025] The small spherical particles are sequentially subjected to carbonization treatment and activation treatment to obtain spherical porous carbon;

[0026] The spherical porous carbon is subjected to vapor deposition to obtain the silicon-carbon composite material.

[0027] Preferably, the residual carbon content of the low-carbon source microspheres is ≤40%.

[0028] Preferably, the residual carbon content of the high carbon source resin is 50-70%.

[0029] Preferably, the low-carbon source microspheres include any one of polystyrene microspheres, polylactic acid microspheres or polyvinylidene fluoride microspheres, or a combination of at least two thereof.

[0030] Preferably, the high carbon source resin is phenolic resin and / or a phenolic resin derivative.

[0031] Preferably, the mass ratio of the low carbon source microspheres to the high carbon source resin is 1:(1-5).

[0032] Preferably, the solvent comprises an alcohol solvent, preferably ethanol.

[0033] Preferably, the solid content of the mixed solution is 30-60 wt %.

[0034] Preferably, the mixed solution further comprises 5-10 wt% of carbon tubes.

[0035] Preferably, the mixed solution further comprises a conductive polymer, and the conductive polymer comprises any one of polyacetylene, polythiophene, polypyrrole or polyaniline, or a combination of at least two thereof.

[0036] Preferably, the spray drying process parameters include: centrifugal disk speed of 24000-30000 rpm; inlet air temperature of 160-230° C.; feed rate of 1.2-4 L / h; induced draft fan frequency of 40-50 Hz.

[0037] Preferably, the temperature of the carbonization treatment is 400-900° C.; and the time of the carbonization treatment is 3-10 hours.

[0038] Preferably, the activation treatment is performed by a physical activation method.

[0039] Preferably, the step of physical activation is: introducing activation gas into the carbon microspheres obtained after carbonization treatment for physical activation.

[0040] Preferably, the activation gas comprises carbon dioxide and / or water vapor.

[0041] Preferably, the temperature of the physical activation is 800-1000° C., and the time of the physical activation is 7-20 h.

[0042] Preferably, the activation treatment further includes a step of removing impurities: the porous carbon microspheres after the activation treatment are acid-washed to remove impurities, and then washed with water and dried.

[0043] Preferably, the pickling adopts 5-8wt% hydrochloric acid solution.

[0044] Preferably, the pickling temperature is 20 to 100° C., and the pickling time is 1 to 24 hours.

[0045] Preferably, the drying temperature is 70-90°C.

[0046] Preferably, the deposition gas source of the vapor deposition is a mixed gas of a protective gas and a silicon source gas.

[0047] Preferably, the protective gas includes any one of nitrogen, neon, argon, krypton, xenon or radon, or a combination of at least two of them.

[0048] Preferably, the silicon source gas includes any one of monosilane, disilane, dichlorosilane or trichlorosilane, or a combination of at least two thereof.

[0049] Preferably, the silicon source gas further includes a carbon source gas, and the carbon source gas includes any one of methane, ethane, acetylene or ethylene, or a combination of at least two of them.

[0050] Preferably, the volume ratio of the protective gas to the silicon source gas is (10-30):(70-90).

[0051] Preferably, the content of the carbon source gas accounts for 0-30% of the total volume of the silicon source gas.

[0052] Preferably, the ratio of the deposition amount of the vapor deposition to the input material is (0.4-1.5):1.

[0053] Preferably, the temperature of the vapor deposition is 300-800° C., and the time of the vapor deposition is 5-10 hours.

[0054] In a third aspect, the present invention provides a use of the silicon-carbon composite material as described in the first aspect in preparing a negative electrode material for a battery.

[0055] In a fourth aspect, the present invention provides a method for detecting a silicon-carbon composite material. The method comprises the following steps:

[0056] The specific surface area of ​​the silicon-carbon composite material before pressing is obtained and recorded as S1;

[0057] The silicon-carbon composite material is compacted to break the sample, and the specific surface area of ​​the crushed silicon-carbon composite material after pressing is obtained and recorded as S2;

[0058] The specific surface area change rate of the silicon-carbon composite material is calculated by the following formula to characterize the strength of the silicon-carbon composite material;

[0059] The strength of the silicon-carbon composite material is defined by the following formula:

[0060]

[0061] Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of ​​the silicon-carbon composite material before pressing, m 2 / g; S1 represents the specific surface area of ​​the silicon-carbon composite material after pressing, m 2 / g.

[0062] Preferably, the compaction treatment rate is 8-12 mm / min, preferably 10 mm / min.

[0063] Preferably, the holding time of the compaction treatment is 10 to 50 seconds, preferably 30 seconds.

[0064] Preferably, the compaction treatment pressure is 450-500 MPa.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] (1) The present invention utilizes the morphology of carbon microspheres and the high carbon content of phenolic resin to synthesize a carbon substrate with good sphericity. The particle size of the carbon microspheres can be well controlled by spray drying technology, and the particle size uniformity is good.

[0067] (2) Compared with irregular resin-based silicon-carbon composite materials, the silicon-carbon material synthesized by this method has higher strength and does not contain natural biomass-based macropores.

[0068] (3) The silicon-carbon negative electrode material of the present invention has a high degree of sphericity, which avoids the poor compressive resistance caused by having many edges and corners during the rolling process, and can improve the continuous generation of the solid electrolyte interface (SEI) film due to low strength, the weakening of capacity, and the poor cycle performance.

[0069] (4) The present invention quantifies the strength of the silicon-carbon composite material by comparing the rate of change of the specific surface area before and after pressing, and uses a formula to characterize the strength and limit the strength range of the silicon-carbon composite material, thereby avoiding the problems of the traditional use of nanoindenters to detect the strength of silicon-carbon negative electrode materials, such as the sample having no adhesion, being easily pressed away, resulting in a plateau period, erroneous data, and only being able to evaluate a single particle. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0071] Figure 1 This is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Example 1.

[0072] Figure 2 This is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Example 2.

[0073] Figure 3 This is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Example 3.

[0074] Figure 4 This is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Comparative Example 1.

[0075] Figure 5 This is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Comparative Example 2.

[0076] Figure 6 This is a scanning electron microscope image of the carbonized balls prepared in Comparative Example 3.

[0077] Figure 7 This is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Comparative Example 4.

[0078] Figure 8 This is the particle size distribution diagram of the silicon-carbon negative electrode material prepared in Example 1.

[0079] Fig. 9 This is the N2 adsorption-desorption isotherm diagram of the silicon-carbon negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0080] Unless otherwise defined herein, scientific and technical terms used in conjunction with the present invention shall have the meanings commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear, however, in the case of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, unless otherwise stated, the use of "or" means "and / or". In addition, the use of the term "including" and other forms is non-limiting.

[0081] The technical solution of the present invention will be described clearly and completely in conjunction with the embodiments below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0082] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0083] In a first aspect, the present invention provides a silicon-carbon composite material, the silicon-carbon composite material comprising active material particles, the active material particles comprising a spherical porous carbon skeleton and nano silicon particles;

[0084] The strength of the silicon-carbon composite material is defined by the following formula:

[0085]

[0086] Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of ​​the silicon-carbon composite material after pressing, m 2 / g; S1 represents the specific surface area of ​​the silicon-carbon composite material before pressing, m 2 / g.

[0087] In the present invention, nano-silicon particles are deposited into the pores of a spherical porous carbon skeleton by chemical deposition to prepare a silicon-carbon composite material with high sphericity; at the same time, the silicon-carbon composite material is compacted. Since the silicon-carbon composite material is characterized by electron microscopy after compaction, it is found that most particles are broken, and the particles are mainly through-cracked, which increases the specific surface area of ​​the particles. That is, the degree of particle crushing can be quantified by characterizing the specific surface area before and after the particles, and it is found that the compaction density and the applied pressure have a good linear correlation with the specific surface area after compaction. Therefore, the change rate of the specific surface area before and after compaction is used to characterize the strength.

[0088] In an optional embodiment, the specific surface area of ​​the silicon-carbon composite material is 2 to 5 m 2 / g, for example, it can be 2m 2 / g, 2.5m 2 / g, 3m 2 / g, 3.5m 2 / g, 4m 2 / g, 4.5m 2 / g, 5m 2 / g, etc.

[0089] In an optional embodiment, the strength of the silicon-carbon composite material when pressed at a pressure of 450 MPa for 30 seconds is above 90%, for example, it may be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, etc.

[0090] In an optional embodiment, the spherical porous carbon has a sphericity ≥ 80%, for example, it may be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, etc.

[0091] In an optional embodiment, the interior of the spherical porous carbon contains uniformly distributed micropores and / or mesopores.

[0092] In an optional embodiment, the spherical porous carbon has an average pore size of less than 4 nm and a total pore volume of ≥0.7 cm 3 / g, for example, 0.7 cm 3 / g, 0.75cm 3 / g, 0.8cm 3 / g, 0.85cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, etc.

[0093] In an optional embodiment, the mesoporosity of the spherical porous carbon is <20%, for example, it may be 19%, 18%, 17%, 16%, 15%, 14%, 12%, 10%, 8%, 6%, 4%, 2%, 1%, etc.

[0094] In an optional embodiment, the microporosity of the spherical porous carbon is >80%, for example, it may be 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, etc.

[0095] In an optional embodiment, the particle size of the spherical porous carbon is 1 to 60 μm, for example, it can be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc.

[0096] In an optional embodiment, the D of the spherical porous carbon 10 The particle size is 3 to 7 μm, for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, etc.

[0097] In an optional embodiment, the D of the spherical porous carbon 50 The particle size is 8 to 13 μm, for example, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, etc.

[0098] In an alternative embodiment, D 90 The particle size is 15 to 40 μm, for example, it can be 15 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm, etc.

[0099] In an optional embodiment, the nano-silicon particles are deposited in the pores of the spherical porous carbon.

[0100] In an optional embodiment, the silicon content in the silicon-carbon composite material is 40-60%, for example, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, etc.

[0101] In an optional embodiment, the specific capacity of the silicon-carbon composite material is greater than 1500mAh / g, for example, it can be 1501mAh / g, 1505mAh / g, 1510mAh / g, 1550mAh / g, 1600mAh / g, 1650mAh / g, 1700mAh / g, 1750mAh / g, 1780mAh / g, 1790mAh / g, 1800mAh / g, 1820mAh / g, 1830mAh / g, 1840mAh / g, 1850mAh / g, 1860mAh / g, 1870mAh / g, 1880mAh / g, 1890mAh / g, 1900mAh / g, etc., and the preferred specific capacity is greater than 1800mAh / g.

[0102] In an optional embodiment, the 200-cycle capacity retention rate of the silicon-carbon composite material is greater than 90%, for example, it may be 90%, 92%, 94%, 95%, 96%, 98%, 99%, etc.

[0103] In a second aspect, the present invention provides a method for preparing the silicon-carbon composite material as described in the first aspect, the preparation method comprising the following steps:

[0104] Mixing low-carbon source microspheres, high-carbon source resin and solvent to obtain a mixed solution;

[0105] The mixed solution is spray-dried to obtain spherical particles;

[0106] The small spherical particles are sequentially subjected to carbonization treatment and activation treatment to obtain spherical porous carbon;

[0107] The spherical porous carbon is subjected to vapor deposition to obtain the silicon-carbon composite material.

[0108] The present invention utilizes the mixture of microspheres with low synthetic carbon content and resin liquid with high carbon source, and then forms small balls through spray drying treatment, and adjusts the particle size of spherical carbon by adjusting the curing conditions of spray drying to prepare spherical carbon with high carbon content and good sphericity. Further, chemical and physical methods are used to form pores, and in the process of carbonization and activation pore formation, there is no hollow phenomenon, and there are no large pores inside, which causes the weakening of strength, thereby preparing spherical porous carbon with high sphericity and high strength. Finally, nano silicon particles are deposited in the pores of the spherical porous carbon skeleton through vapor deposition to prepare a silicon-carbon composite material with high sphericity. At the same time, the higher the sphericity, the poor compressive strength caused by more edges and corners can be avoided during the rolling process, and the solid electrolyte interface (SEI) film is continuously generated due to low strength, the capacity is weakened, and the cycle is poor. In particular, the strength of the spherical silicon-carbon composite material under a pressure of 450MPa for 30s is above 90%, but the strength of the irregular silicon-carbon composite material is less than 90%.

[0109] In an optional embodiment, the residual carbon content of the low-carbon source microspheres is ≤40%, for example, it can be 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc.

[0110] In an optional embodiment, the residual carbon content of the high carbon source resin is 50-70%, for example, it can be 50%, 55%, 60%, 65%, 70%, etc.

[0111] In an optional embodiment, the low carbon source microspheres include any one of polystyrene microspheres, polylactic acid microspheres or polyvinylidene fluoride microspheres, or a combination of at least two thereof. The high carbon source resin is phenolic resin and / or a phenolic resin derivative.

[0112] In an optional embodiment, the mass ratio of the low carbon source microspheres to the high carbon source resin is 1:(1-5), for example, it can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, etc.

[0113] In an optional embodiment, the solvent comprises an alcohol solvent, preferably ethanol;

[0114] In an optional embodiment, the solid content of the mixed liquid is 30-60wt%, for example, it may be 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt% and the like.

[0115] In an optional embodiment, the mixed solution further comprises 5-10 wt% of carbon tubes, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt% and the like.

[0116] It should be noted that, in the present invention, in addition to the fusion of microspheres and the resin with a high carbon source, a certain amount of carbon tubes may also be added to further increase the conductivity of the silicon-carbon composite material.

[0117] In an optional embodiment, the mixed solution further includes a conductive polymer, and the conductive polymer includes any one of polyacetylene, polythiophene, polypyrrole or polyaniline, or a combination of at least two thereof.

[0118] It should be noted that, in the present invention, in addition to fusing the microspheres with the resin having a high carbon source, a certain amount of conductive polymer may also be added to increase active defects, thereby further increasing the conductivity of the silicon-carbon composite material.

[0119] In an optional embodiment, the spray drying process parameters include: a centrifugal disk speed of 24,000 to 30,000 rpm; an inlet air temperature of 160 to 230° C.; a feed rate of 1.2 to 4 L / h; and an induced draft fan frequency of 40 to 50 Hz.

[0120] In an optional embodiment, the centrifugal disk rotates at a speed of 24,000 to 30,000 rpm, for example, 24,000 rpm, 25,000 rpm, 26,000 rpm, 27,000 rpm, 28,000 rpm, 29,000 rpm, 30,000 rpm, etc.

[0121] In an optional embodiment, the inlet air temperature is 160-230°C, for example, it can be 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, etc.

[0122] In an optional embodiment, the feed rate is 1.2 to 4 L / h, for example, it may be 1.2 L / h, 1.4 L / h, 1.6 L / h, 1.8 L / h, 2 L / h, 2.2 L / h, 2.4 L / h, 2.6 L / h, 2.8 L / h, 3 L / h, 3.2 L / h, 3.4 L / h, 3.6 L / h, 3.8 L / h, 4 L / h, etc.

[0123] In an optional embodiment, the frequency of the induced draft fan is 40-50 Hz, for example, it can be 40 Hz, 42 Hz, 44 Hz, 46 Hz, 48 Hz, 50 Hz, etc.

[0124] In an optional embodiment, the temperature of the carbonization treatment is 400-900°C, for example, it can be 400°C, 450°C, 500°C, 550°C, 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, etc.

[0125] In an optional embodiment, the carbonization treatment time is 3 to 10 hours, for example, it can be 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0126] In an optional embodiment, the activation treatment includes physical activation and / or chemical activation.

[0127] In an optional embodiment, the activation treatment is performed by a physical activation method.

[0128] In an optional embodiment, the physical activation step is: introducing activation gas into the carbon microspheres obtained after the carbonization treatment to perform physical activation.

[0129] In an optional embodiment, the activation gas includes carbon dioxide and / or water vapor.

[0130] In an optional embodiment, the temperature of the physical activation is 800-1000°C, for example, it can be 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, 940°C, 960°C, 980°C, 1000°C, etc.

[0131] In an optional embodiment, the physical activation time is 7 to 20 hours, for example, it can be 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, etc.

[0132] In an optional embodiment, the activation treatment further includes a step of removing impurities: the porous carbon microspheres after the activation treatment are acid-washed to remove impurities, and then washed with water and dried.

[0133] In an optional embodiment, the pickling uses a 5-8wt% hydrochloric acid solution, for example, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, etc.

[0134] In an optional embodiment, the pickling temperature is 20-100°C, for example, it can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, etc.

[0135] In an optional embodiment, the pickling time is 1 to 24 hours, for example, it can be 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, etc.

[0136] In an optional embodiment, the drying temperature is 70-90°C, for example, 70°C, 75°C, 80°C, 85°C, 90°C, etc.

[0137] In an optional embodiment, the deposition gas source of the vapor deposition is a mixed gas of a protective gas and a silicon source gas.

[0138] In an optional embodiment, the protective gas includes any one of nitrogen, neon, argon, krypton, xenon or radon, or a combination of at least two of them.

[0139] In an optional embodiment, the silicon source gas includes any one of monosilane, disilane, dichlorosilane or trichlorosilane, or a combination of at least two thereof.

[0140] In an optional embodiment, the volume ratio of the protective gas to the silicon source gas is (10-30):(70-90);

[0141] Here, “10-30” may be, for example, 10, 12, 15, 18, 20, 22, 25, 28, 30, etc.;

[0142] Among them, “70-90” can be, for example, 70, 72, 75, 78, 80, 82, 85, 88, 90, etc.

[0143] In an optional embodiment, the ratio of the deposition amount of the vapor deposition to the input material is (0.4-1.5):1, for example, it can be 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, etc.

[0144] In an optional embodiment, the temperature of the vapor deposition is 300-800°C, for example, it can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, etc.

[0145] In an optional embodiment, the vapor deposition time is 5 to 10 hours, for example, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0146] In an optional embodiment, the method for preparing the silicon-carbon composite material comprises the following steps:

[0147] S1. Preparation of low carbon source microspheres / high carbon source resin mixed solution:

[0148] The low-carbon source microspheres and the high-carbon source resin are mixed and dispersed in a solvent to obtain a mixed solution;

[0149] S2. Spray drying:

[0150] The mixed solution obtained in S1 is spray-dried to obtain spherical particles with a sphericity greater than 80%;

[0151] S3, Carbonization treatment:

[0152] The small spherical particles obtained in S2 are carbonized under an inert atmosphere to obtain carbonized carbon microspheres;

[0153] S4, activation treatment:

[0154] The carbonized carbon microspheres obtained in S3 are activated to obtain porous carbon microspheres;

[0155] S5. Impurity Removal:

[0156] The porous carbon microspheres obtained in S4 are acid-washed to remove impurities, then washed with water and dried;

[0157] S6. Chemical Vapor Deposition:

[0158] The impurity-free porous carbon microspheres obtained in S5 are subjected to chemical vapor deposition to obtain the silicon-carbon composite material.

[0159] In a third aspect, the present invention provides an application of the silicon-carbon composite material in preparing a negative electrode material for a battery.

[0160] In a fourth aspect, the present invention provides a method for detecting a silicon-carbon composite material, the method comprising the following steps:

[0161] The specific surface area of ​​the silicon-carbon composite material before pressing is obtained and recorded as S1;

[0162] The silicon-carbon composite material is compacted to break the sample, and the specific surface area of ​​the broken silicon-carbon composite material after the test is obtained and recorded as S2;

[0163] The specific surface area change rate of the silicon-carbon composite material is calculated by the following formula to characterize the strength of the silicon-carbon composite material;

[0164] The strength of the silicon-carbon composite material is defined by the following formula:

[0165]

[0166] Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of ​​the silicon-carbon composite material after pressing, m2 / g; S1 represents the specific surface area of ​​the silicon-carbon composite material before pressing, m 2 / g.

[0167] The present invention does not limit the test method for the specific surface area of ​​the silicon-carbon composite material. For example, the BET method can be used for testing.

[0168] The present invention does not limit the instrument used for compaction of the silicon-carbon composite material. Preferably, a compaction density meter is used for compaction.

[0169] In the present invention, the compaction density meter is combined with the specific surface area meter to quantify the strength of the silicon-carbon composite negative electrode material by comparing the change rate of the specific surface area before and after pressing. After pressing, the silicon-carbon material was characterized by electron microscopy and found that most particles were broken, mainly through cracks, and the specific surface area of ​​the particles was increased. The degree of particle breakage was quantified by characterizing the specific surface area before and after the particles.

[0170] In an optional embodiment, a laser particle size analyzer may be used to test the particle size distribution of silicon-carbon powder in accordance with GB / T 19077. During the process of testing the particle size of the silicon-carbon composite material, if two identical samples are compared, D(50) may be controlled to be the same.

[0171] In an optional embodiment, the conditions for crushing the sample by compaction treatment must meet the following requirements: setting appropriate pressurization and decompression displacements, holding pressure and holding time, so that the particles of the sample are crushed under the same pressure (i.e. ensuring that the pressurization time and holding time are capable of crushing the sample).

[0172] In an optional embodiment, the specific process of the compaction treatment is: weigh an appropriate amount of silicon-carbon powder sample into a sample bin of a compaction density meter; set compaction test conditions: set appropriate pressurization and decompression displacements, holding pressure and holding time, so that the sample particles are broken under the same pressure (ensure that the pressurization time and holding time can crush the sample); after the test, use a withdrawing rod to withdraw the sample and collect the sample after compression; mix the collected sample for testing.

[0173] In an optional embodiment, the compaction treatment rate is 8-12 mm / min, for example, 8 mm / min, 9 mm / min, 10 mm / min, 11 mm / min, 12 mm / min, etc., preferably 10 mm / min.

[0174] In an optional embodiment, the holding time of the compaction treatment is 10 to 50 s, for example, 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s, etc., preferably 30 s.

[0175] In an optional embodiment, the pressure of the compaction treatment is 450-500 MPa, for example, it can be 450 MPa, 460 MPa, 470 MPa, 480 MPa, 490 MPa, 500 MPa, etc.

[0176] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0177] Some raw material parameters in the following examples are as follows:

[0178] Carbon microspheres with low carbon source: Beijing Dekedaojin Technology Co., Ltd.; model: PSC002000, residual carbon content is 15-20%, and particle size is 2um.

[0179] Solid resin with high carbon source: Guangzhou Shuangli Rubber Raw Materials Trading Co., Ltd.; model: 9003-35-4, residual carbon content is 50-70%.

[0180] Example 1

[0181] This embodiment provides a silicon-carbon composite material, which is prepared by the following steps:

[0182] S1. Carbon microspheres with a residual carbon content of 15% and resin with a residual carbon content of 55% are mixed and dispersed in anhydrous ethanol in a mass ratio of 1:1 to form a spray liquid with a solid content of 30%.

[0183] S2. The above spray liquid is subjected to a spraying experiment: spray curing conditions: atomizing disk speed: 28000 rpm, air inlet temperature: 175°C, feed rate: 1.8 L / h, induced draft fan frequency: 50 Hz, and the sprayed particle size is 5-20 μm carbon microsphere particles.

[0184] S3. The solidified carbon microsphere particles are heat treated in a nitrogen atmosphere at a heating rate of 10 / min and a heat treatment temperature of 400°C for 5 hours to obtain carbonized carbon microspheres.

[0185] S4. Put the carbonized carbon microspheres into a rotary kiln with good sealing performance, rotate the kiln at a frequency of 30 Hz, introduce water vapor, and the gas flow rate is 12 L / min. The heating rate of the rotary kiln is 10°C / min, and the temperature is raised to 900°C, kept warm for 8 hours, and then cooled to room temperature to obtain the material.

[0186] S5. Soak the material obtained in S4 with 6.5% HCl and heat to 60° C. and stir for 1 hour. Then wash with pure water until neutral and dry at 80° C. to obtain spherical porous carbon.

[0187] The sphericity of the spherical porous carbon is 92.5%; the interior of the spherical porous carbon contains uniformly distributed micropores and mesopores, and the average pore size of the spherical porous carbon is 1.89 nm; the total pore volume of the spherical porous carbon with an average pore size less than 4 nm is 0.84 cm 3 / g; the mesoporosity of the spherical porous carbon is 19%, and the microporosity is 81%; the particle size of the spherical porous carbon is 8.3 μm; wherein the D 10 Particle size: 3.5 μm; D 50 Particle size: 8.3 μm; D 90 The particle size is 19.8μm.

[0188] S6. Place the spherical porous carbon material obtained in S5 into a rotary kiln with good sealing performance, rotate the kiln at a frequency of 40 Hz, and introduce a deposition gas source that is a mixture of protective gas and silicon source: a mixture of nitrogen and monosilane (the volume ratio of nitrogen to monosilane is 20:80), the ratio of deposition amount to input material is 0.6, the deposition temperature is 500°C, and the deposition time is 6 hours to obtain the silicon-carbon composite material.

[0189] Figure 1 This is a scanning electron microscope image of the silicon-carbon composite material prepared in Example 1. Figure 1 As shown, low-carbon source microspheres are combined with high-carbon source resin bases, and the particle size of spherical carbon is controlled by spray drying to prepare a high-carbon carbon substrate with good sphericity; and when this method is used to prepare carbon-based microspheres, there is no hollow phenomenon during the carbonization and alkali activation pore-forming process, and there are no large pores inside to cause a decrease in strength.

[0190] Example 2

[0191] This embodiment provides a silicon-carbon composite material, which is different from the embodiment 1 only in that the spray curing conditions of S2 are different, as shown below:

[0192] S2. The above spray liquid was subjected to a spraying experiment: spray curing conditions: atomizing disk speed: 28000 rpm, air inlet temperature: 190, feed rate: 2.3 L / h, induced draft fan frequency: 50 Hz, and the sprayed particle size was 6-40 μm carbon microsphere particles.

[0193] Figure 2 This is a scanning electron microscope image of the silicon-carbon composite material prepared in Example 2. Figure 1 As shown, low-carbon source microspheres are combined with high-carbon source resin bases, and the particle size of spherical carbon is controlled by spray drying to prepare a high-carbon carbon substrate with good sphericity; and when this method is used to prepare carbon-based microspheres, there is no hollow phenomenon during the carbonization and alkali activation pore-forming process, and there are no large pores inside to cause a decrease in strength.

[0194] Example 3

[0195] This embodiment provides a silicon-carbon composite material, which is different from the embodiment 1 only in that the spray curing conditions of S2 are different, as shown below:

[0196] S2. The above spray liquid is subjected to a spraying experiment: spray curing conditions: atomizing disk speed: 28000 rpm, air inlet temperature: 200, feed rate: 3.2 L / h, induced draft fan frequency: 50 Hz, and the sprayed particle size is 5-20 μm carbon microsphere particles.

[0197] Figure 3 This is a scanning electron microscope image of the silicon-carbon composite material prepared in Example 3. Figure 1 As shown, low-carbon source microspheres are combined with high-carbon source resin bases, and the particle size of spherical carbon is controlled by spray drying to prepare a high-carbon carbon substrate with good sphericity; and when this method is used to prepare carbon-based microspheres, there is no hollow phenomenon during the carbonization and alkali activation pore-forming process, and there are no large pores inside to cause a decrease in strength.

[0198] Example 4

[0199] This embodiment provides a silicon-carbon composite material, which is different from Embodiment 1 in that, in S1, the mass ratio of the low-carbon source microspheres to the high-carbon source resin is 1:5, and the other steps are completely consistent with Embodiment 1.

[0200] Example 5

[0201] This embodiment provides a silicon-carbon composite material, which is different from Embodiment 1 in that the temperature of S3 carbonization treatment is 600° C.; the time of the carbonization treatment is 10 h, and the other steps are completely consistent with Embodiment 1.

[0202] Example 6

[0203] This embodiment provides a silicon-carbon composite material, which is different from Embodiment 1 in that the temperature of S3 carbonization treatment is 900°C; the time of the carbonization treatment is 3 hours, and the other steps are completely consistent with Embodiment 1.

[0204] Example 7

[0205] This embodiment provides a silicon-carbon composite material, which is different from Embodiment 1 in that the activation temperature in S4 is 800° C., the activation time is 20 h, and the other steps are completely consistent with Embodiment 1.

[0206] Example 8

[0207] This embodiment provides a silicon-carbon composite material, which is different from Embodiment 1 in that the activation temperature in S4 is 1000° C., the activation time is 7 h, and the other steps are completely consistent with Embodiment 1.

[0208] Example 9

[0209] This embodiment provides a silicon-carbon composite material, which is different from Embodiment 1 in that the ratio of deposition amount to input material is 0.4, the deposition temperature is 300° C., the deposition time is 10 h, and the other steps are completely consistent with Embodiment 1.

[0210] Example 10

[0211] This embodiment provides a silicon-carbon composite material, which is different from Embodiment 1 in that the ratio of deposition amount to input material is 1.5, the deposition temperature is 800° C., the deposition time is 5 h, and the other steps are completely consistent with Embodiment 1.

[0212] Comparative Example 1

[0213] This comparative example provides a silicon-carbon composite material, which is prepared by the following steps:

[0214] S1. Disperse a resin with a carbon residue of 55% in anhydrous ethanol to form a spray liquid with a solid content of 30%.

[0215] S2. The above spray liquid is subjected to a spraying experiment: spray curing conditions: atomizing disk speed: 28000 rpm, air inlet temperature: 175°C, feed rate: 1.8 L / h, induced draft fan frequency: 50 Hz, sprayed particle size is 5-20 μm carbon microsphere particles, sphericity is 70-80%.

[0216] S3. The solidified carbon microsphere particles are heat treated in a nitrogen atmosphere at a heating rate of 10 / min and a heat treatment temperature of 400°C for 5 hours to obtain carbonized carbon microspheres.

[0217] S4. Put the carbonized carbon microspheres into a rotary kiln with good sealing performance, rotate the kiln at a frequency of 30 Hz, introduce water vapor, and the gas flow rate is 12 L / min. The heating rate of the rotary kiln is 10°C / min, and the temperature is raised to 900°C, kept warm for 8 hours, and then cooled to room temperature to obtain the material.

[0218] S5. Soak the material obtained in S4 with 6.5% HCl and heat to 60° C. and stir for 1 hour. Then wash with pure water until neutral and dry at 80° C. to obtain spherical porous carbon.

[0219] S6. Place the spherical porous carbon material obtained in S5 into a rotary kiln with good sealing performance, rotate the kiln at a frequency of 40 Hz, and introduce a deposition gas source that is a mixture of protective gas and silicon source: a mixture of nitrogen and monosilane (the volume ratio of nitrogen to monosilane is 20:80), the ratio of deposition amount to input material is 0.6, the deposition temperature is 500°C, and the deposition time is 6 hours to obtain the silicon-carbon composite material.

[0220] Figure 4 This is an electron microscope image of the silicon-carbon composite material prepared in Comparative Example 1. Figure 4 As shown, without adding low-carbon source microspheres, only high-carbon source resin liquid is spray-dried and granulated, and the sphericity of the silicon-carbon composite material prepared by this method is poor.

[0221] Comparative Example 2

[0222] This comparative example provides a silicon-carbon composite material, which is prepared by the following steps:

[0223] S1. Dissolve a resin with a residual carbon content of 55% in anhydrous ethanol to form a resin liquid with a solid content of 30%, and then cure the resin liquid in a vacuum oven at 120° C. for 4 hours.

[0224] S2. The solidified carbon particles are heat treated in a nitrogen atmosphere at a heating rate of 10 / min and a heat treatment temperature of 400°C for 5 hours to obtain a pre-carbonized material.

[0225] S3. Use a crusher to crush the pre-carbonized material into millimeter-level uniform particles for later use.

[0226] S4. Put the carbonized carbon microspheres into a rotary kiln with good sealing performance, rotate the kiln at a frequency of 30 Hz, introduce water vapor, and the gas flow rate is 12 L / min. The heating rate of the rotary kiln is 10°C / min, and the temperature is raised to 900°C, kept warm for 8 hours, and then cooled to room temperature to obtain the material.

[0227] S5. Soak the material obtained in S4 with 6.5% HCl and heat to 60°C and stir for 1 hour. Then wash with pure water until neutral and dry at 80°C.

[0228] S6. Use air flow pulverizing equipment to pulverize the material in S5 to D50 = 5-12 μm.

[0229] S7. Put the material obtained in S6 into a rotary kiln with good sealing performance, rotate the kiln at a frequency of 40 Hz, and introduce a deposition gas source that is a mixture of protective gas and silicon source: a mixture of nitrogen and monosilane (the volume ratio of nitrogen to monosilane is 20:80), the ratio of deposition amount to input material is 0.6, the deposition temperature is 500°C, and the deposition time is 6 hours to obtain the silicon-carbon composite material.

[0230] Figure 5 This is an electron microscope image of the silicon-carbon composite material prepared in Comparative Example 2. Figure 5 As shown, without adding low-carbon source microspheres and without using the spray drying method, the obtained silicon-carbon composite material is in an irregular state.

[0231] Comparative Example 3

[0232] This comparative example provides a carbon microsphere particle, which is prepared by the following steps:

[0233] S1. The carbon microspheres with a residual carbon content of 15% are directly cured in a vacuum oven at 120° C. for 4 hours.

[0234] S2. The solidified carbon microsphere particles are heat treated in a nitrogen atmosphere at a heating rate of 10°C / min and a heat treatment temperature of 400°C for 5 hours for carbonization.

[0235] Figure 6 This is an electron microscope image of the silicon material prepared in Comparative Example 3. Figure 6 As shown in the figure, the small balls collapsed and became hollow after carbonization.

[0236] Comparative Example 4

[0237] This comparative example provides a silicon-carbon composite material, which is different from Example 1 in that, in S1, the mass ratio of the carbon microspheres with a residual carbon content of 15% to the resin with a residual carbon content of 55% is 2:1, and the other steps are completely consistent with Example 1.

[0238] Comparative Example 5

[0239] This comparative example provides a silicon-carbon composite material, which is different from Example 1 in that, in S1, the mass ratio of the carbon microspheres with a residual carbon content of 15% to the resin with a residual carbon content of 55% is 1:6, and the other steps are completely consistent with Example 1.

[0240] Comparative Example 6

[0241] This comparative example provides a silicon-carbon composite material, which is prepared by the following steps:

[0242] S1. Carbon microspheres with a residual carbon content of 15% and resin with a residual carbon content of 55% are mixed and dispersed in anhydrous ethanol in a mass ratio of 1:1 to form a spray liquid with a solid content of 30%.

[0243] S2. Stir the mixed solution and heat and cure it for 8 hours to form carbon microspheres with a sphericity of 60-70%.

[0244] S3. The solidified carbon microsphere particles are heat treated in a nitrogen atmosphere at a heating rate of 10 / min and a heat treatment temperature of 400°C for 5 hours to obtain carbonized carbon microspheres.

[0245] S4. Put the carbonized carbon microspheres into a rotary kiln with good sealing performance, rotate the kiln at a frequency of 30 Hz, introduce water vapor, and the gas flow rate is 12 L / min. The heating rate of the rotary kiln is 10°C / min, and the temperature is raised to 900°C, kept warm for 8 hours, and then cooled to room temperature to obtain the material.

[0246] S5. Soak the material obtained in S4 with 6.5% HCl and heat to 60° C. and stir for 1 hour. Then wash with pure water until neutral and dry at 80° C. to obtain spherical porous carbon.

[0247] S6. Place the spherical porous carbon material obtained in S5 into a rotary kiln with good sealing performance, rotate the kiln at a frequency of 40 Hz, and introduce a deposition gas source that is a mixture of protective gas and silicon source: a mixture of nitrogen and monosilane (the volume ratio of nitrogen to monosilane is 20:80), the ratio of deposition amount to input material is 0.6, the deposition temperature is 500°C, and the deposition time is 6 hours to obtain the silicon-carbon composite material.

[0248] Figure 7 This is an electron microscope image of the carbon silicon material prepared in Comparative Example 4. Figure 7 As shown, without spray drying, the sphericity of the silicon-carbon composite material obtained is low.

[0249] Comparative Example 7

[0250] This comparative example provides a silicon-carbon composite material, which differs from Example 1 in that, in S2, the spray drying process parameters include: the centrifugal disk speed is 20000 rpm; the inlet air temperature is 250°C; the feed rate is 4.5 L / h; the induced draft fan frequency is 35 Hz, and the other steps are exactly the same as in Example 1.

[0251] Comparative Example 8

[0252] This comparative example provides a silicon-carbon composite material, which is different from Example 1 in that, in S2, the spray drying process parameters include: the centrifugal disk speed is 32000 rpm; the inlet air temperature is 150°C; the feed rate is 1.0 L / h; the induced draft fan frequency is 55 Hz, and the other steps are exactly the same as Example 1.

[0253] Test Example 1

[0254] Test samples: the silicon-carbon composite materials provided in Examples 1 to 10 and the composite materials provided in Comparative Examples 1 to 8;

[0255] Test method:

[0256] (1) Particle size test:

[0257] Use a laser particle size analyzer to test the particle size distribution of the powder in accordance with the provisions of GB / T 19077, and test the particle size of the silicon-carbon composite material;

[0258] (2) Strength test:

[0259] Use a specific surface area tester to test the specific surface area of ​​the silicon-carbon composite material before pressing, and record it as S1; place the silicon-carbon composite material in a sample bin of a compaction density meter, and perform compaction treatment (compacting conditions are 10 mm / min, holding time is 60 s, and pressure is 450 MPa) to break the sample, and then use a specific surface area tester to test the specific surface area of ​​the broken silicon-carbon composite material after pressing, and record it as S2; calculate the specific surface area change rate of the silicon-carbon composite material by the following formula to characterize the strength of the silicon-carbon composite material;

[0260] The strength of the silicon-carbon composite material is defined by the following formula:

[0261]

[0262] Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of ​​the silicon-carbon composite material after pressing, m 2 / g; S1 represents the specific surface area of ​​the silicon-carbon composite material before pressing, m 2 / g.

[0263] (3) Capacity: At 25°C, first discharge at 0.1C to 0.005V, then discharge at 0.08C to 0.001V, discharge at 0.05C to 0.001V, discharge at 0.02C to 0.001V, and let stand for 10 min; then charge at 0.1C to 1.5V, let stand for 10 min, and record the charge and discharge capacity after the first cycle.

[0264] (4) 200-cycle capacity retention rate: Cycle 200 times in the above manner, record the charge and discharge capacity after 200 cycles, and calculate the capacity retention rate after 200 cycles: 200-cycle capacity retention rate = 200th cycle discharge capacity / first cycle discharge capacity × 100%.

[0265] The specific test results are shown in Table 1:

[0266] Table 1

[0267]

[0268]

[0269] As shown in Table 1, the specific surface area of ​​the silicon-carbon composite material of the present invention is 2 to 5 m 2 / g; the strength of the silicon-carbon composite material when pressed for 30s at a pressure of 450MPa is above 90%; the specific capacity of the silicon-carbon composite material is greater than 1500mAh / g, and the 200-cycle capacity retention rate of the silicon-carbon composite material is greater than 90%. This shows that the silicon-carbon composite material of the present invention has a high sphericity, which avoids the poor compressive resistance caused by more edges and corners during the rolling process, and can improve the problems of continuous generation of solid electrolyte interface (SEI) film, weakened capacity, and poor cycle performance due to low strength.

[0270] in, Figure 8 This is a particle size distribution diagram of the silicon-carbon composite material prepared in Example 1. Fig. 9 This is the N2 adsorption-desorption isotherm diagram of the silicon-carbon composite material prepared in Example 1. Figure 8 and Fig. 9 As shown, the single-point BET specific surface area of ​​the silicon-carbon composite material is 0.20000:1014.12875 (m 2 / g); total pore volume: 0.84cm 3 / g; Micropore volume: 0.68cm 3 / g; average pore size: 1.89nm; mesoporosity: 19%; microporosity: 81%.

[0271] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that: The silicon-carbon composite material comprises active material particles, wherein the active material particles comprise a spherical porous carbon skeleton and nano-silicon particles; The strength of the silicon-carbon composite material is defined by the following formula: Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of ​​the silicon-carbon composite material after pressing, m 2 / g; S1 represents the specific surface area of ​​the silicon-carbon composite material before pressing, m 2 / g.

2. The silicon-carbon composite material according to claim 1, characterized in that: The specific surface area of ​​the silicon-carbon composite material is 2 to 5 m 2 / g; Preferably, the strength of the silicon-carbon composite material when pressed at a pressure of 450 MPa for 30 seconds is above 90%.

3. The silicon-carbon composite material according to claim 1 or 2, characterized in that: The sphericity of the spherical porous carbon is ≥80%; Preferably, the interior of the spherical porous carbon contains uniformly distributed micropores and / or mesopores; Preferably, the average pore size of the spherical porous carbon is less than 4 nm and the total pore volume is ≥ 0.7 cm 3 / g; Preferably, the mesoporosity of the spherical porous carbon is less than 20%, and the microporosity is greater than 80%; Preferably, the particle size of the spherical porous carbon is 1 to 60 μm; wherein the D 10 Particle size is 3-7 μm; D 50 Particle size is 8-13 μm; D 90 The particle size is 15~40μm.

4. The silicon-carbon composite material according to claim 1 or 2, characterized in that: The nano silicon particles are deposited in the pores of the spherical porous carbon; Preferably, the silicon content in the silicon-carbon composite material is 40-60%; Preferably, the specific capacity of the silicon-carbon composite material is greater than 1500 mAh / g, preferably greater than 1800 mAh / g; Preferably, the 200-cycle capacity retention rate of the silicon-carbon composite material is greater than 90%.

5. A method for preparing the silicon-carbon composite material according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: The low carbon source microspheres, the high carbon source resin and the solvent are mixed to obtain a mixed solution; The mixed solution is spray-dried to obtain spherical particles; The small spherical particles are sequentially subjected to carbonization treatment and activation treatment to obtain spherical porous carbon; The spherical porous carbon is subjected to vapor deposition to obtain the silicon-carbon composite material.

6. The method for preparing the silicon-carbon composite material according to claim 5, characterized in that: The residual carbon content of the low carbon source microspheres is ≤40%; the residual carbon content of the high carbon source resin is 50-70%; Preferably, the low-carbon source microspheres include any one of polystyrene microspheres, polylactic acid microspheres or polyvinylidene fluoride microspheres, or a combination of at least two thereof; Preferably, the high carbon source resin is a phenolic resin and / or a phenolic resin derivative; Preferably, the mass ratio of the low carbon source microspheres to the high carbon source resin is 1:(1-5); Preferably, the solvent comprises an alcohol solvent, preferably ethanol; Preferably, the solid content of the mixed solution is 30-60wt%; Preferably, the mixed solution further comprises 5-10wt% of carbon tubes; Preferably, the mixed solution further comprises a conductive polymer, and the conductive polymer comprises any one of polyacetylene, polythiophene, polypyrrole or polyaniline, or a combination of at least two thereof.

7. The method for preparing the silicon-carbon composite material according to claim 5, characterized in that: The spray drying process parameters include: centrifugal disc speed of 24000-30000rpm; air inlet temperature of 160-230°C; feed rate of 1.2-4L / h; induced draft fan frequency of 40-50Hz; Preferably, the temperature of the carbonization treatment is 400-900°C; the time of the carbonization treatment is 3-10 hours; Preferably, the activation treatment is carried out by a physical activation method; Preferably, the physical activation step comprises: introducing activation gas into the carbon microspheres obtained after carbonization treatment for physical activation; Preferably, the activation gas comprises carbon dioxide and / or water vapor; Preferably, the temperature of the physical activation is 800-1000°C, and the time of the physical activation is 7-20h; Preferably, the activation treatment further includes a step of removing impurities: acid washing the activated porous carbon microspheres to remove impurities, then washing with water and drying; Preferably, the pickling adopts 5-8wt% hydrochloric acid solution; Preferably, the pickling temperature is 20 to 100° C., and the pickling time is 1 to 24 hours; Preferably, the drying temperature is 70-90°C; Preferably, the deposition gas source of the vapor deposition is a mixed gas of a protective gas and a silicon source gas; Preferably, the protective gas includes any one of nitrogen, neon, argon, krypton, xenon or radon, or a combination of at least two thereof; Preferably, the silicon source gas includes any one of monosilane, disilane, dichlorosilane or trichlorosilane, or a combination of at least two thereof; Preferably, the silicon source gas further includes a carbon source gas, and the carbon source gas includes any one of methane, ethane, acetylene or ethylene, or a combination of at least two thereof; Preferably, the volume ratio of the protective gas to the silicon source gas is (10-30):(70-90); Preferably, the content of the carbon source gas accounts for 0 to 30% of the total volume of the silicon source gas; Preferably, the ratio of the deposition amount of the vapor deposition to the input material is (0.4-1.5):1; Preferably, the temperature of the vapor deposition is 300-800° C., and the time of the vapor deposition is 5-10 hours.

8. Use of the silicon-carbon composite material according to any one of claims 1 to 4 in preparing a negative electrode material for a battery.

9. A method for testing the strength of a silicon-carbon composite material, characterized in that: The detection method comprises the following steps: The specific surface area of ​​the silicon-carbon composite material before pressing is obtained and recorded as S1; The silicon-carbon composite material is subjected to a compaction treatment to break the sample, and the specific surface area of ​​the crushed silicon-carbon composite material after the pressing is obtained and recorded as S2; The specific surface area change rate of the silicon-carbon composite material is calculated by the following formula to characterize the strength of the silicon-carbon composite material; The strength of the silicon-carbon composite material is defined by the following formula: Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of ​​the silicon-carbon composite material after pressing, m 2 / g; S1 represents the specific surface area of ​​the silicon-carbon composite material before pressing, m 2 / g.

10. The method for detecting the silicon-carbon composite material according to claim 9, characterized in that: The compaction rate is 8-12 mm / min, preferably 10 mm / min; Preferably, the holding time of the compaction treatment is 10 to 50 seconds, preferably 30 seconds; Preferably, the compaction treatment pressure is 450-500 MPa.

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