Core-shell structure micrometer silicon-carbon composite material, preparation method thereof, electrode and battery

Abstract

The application discloses a core-shell structure microsilicon-carbon composite material, which comprises an inner core formed by microsilicon and a carbon shell layer covering the inner core, wherein the carbon shell layer comprises, in sequence from inside to outside, a dense carbon layer one, a porous carbon layer and a dense carbon layer two. The application further discloses a preparation method of the core-shell structure microsilicon-carbon composite material, an electrode comprising the core-shell structure microsilicon-carbon composite material, a battery comprising the electrode, a circuit comprising the battery and an electric device comprising the circuit.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, specifically to a core-shell structured micron-sized silicon-carbon composite material and its preparation method, as well as electrodes and batteries comprising the core-shell structured micron-sized silicon-carbon composite material. Background Technology

[0002] Currently, silicon materials are considered the most promising next-generation lithium-ion battery anode materials due to their high specific capacity. Nanostructured silicon can alleviate silicon particle breakage to some extent and has become an important research direction. However, the high cost, poor batch stability, high activity leading to easy oxidation, easy agglomeration, and difficulty in dispersion of nano-silicon make its preparation difficult and its consistency poor.

[0003] Micron-sized silicon can solve the above problems, and it is gradually gaining attention due to its low cost, simple preparation process, and high initial efficiency. However, micron-sized silicon has a more severe volume expansion effect and poorer electronic conductivity than nano-sized silicon, which leads to a rapid decline in its cycle performance. Typical core-shell structures are also unable to withstand the volume expansion of silicon.

[0004] Currently, there are very few technologies involving the improvement of micron-sized silicon structures; most are based on the construction of silicon-carbon materials using nano-sized silicon. To alleviate the volume effect of nano-sized silicon materials and maintain particle integrity, constructing porous structures such as core-shell structures to provide space for expansion is the main improvement method. However, the cavities in these structures are directly in contact with the silicon material, preventing electrons and ions from achieving surface diffusion, resulting in only point diffusion. Simultaneously, the stress-free coating layer caused by the reserved space allows primary particles from silicon particle breakage during cycling to scatter within the reserved space, disrupting the diffusion paths of lithium ions and electrons. In summary, this leads to a continuous increase in impedance during electrochemical processes, reduced cycling performance, and an inability to further improve performance. Summary of the Invention

[0005] To overcome the technical difficulties of using micron-sized silicon particles as electrode materials in the prior art, this application aims to provide a core-shell structured micron-sized silicon-carbon composite material and a method for preparing the core-shell structured micron-sized silicon-carbon composite material, which effectively improves the cycle performance and coulombic efficiency of the battery.

[0006] The specific technical solution of this application is as follows:

[0007] 1. A core-shell structured micron-sized silicon-carbon composite material, characterized in that it comprises:

[0008] A core formed from micron-sized silicon; and

[0009] The carbon shell covering the core comprises, from the inside out, a dense carbon layer one, a porous carbon layer and a dense carbon layer two.

[0010] 2. The core-shell structured micron-sized silicon-carbon composite material according to item 1, characterized in that the average particle size D50 of the micron-sized silicon is 1 to 8 μm and the sphericity is 0.3 to 0.95.

[0011] 3. The core-shell structured micron-sized silicon-carbon composite material according to item 1 or 2, characterized in that the thickness of the first dense carbon layer is 0.05% to 1% of the average particle size D50 of the micron-sized silicon, preferably 0.1% to 0.4%;

[0012] Preferably, the porosity of the dense carbon layer is 10% to 50%, more preferably 10% to 30%.

[0013] 4. The core-shell structured micron-sized silicon-carbon composite material according to any one of items 1 to 3, characterized in that the thickness of the porous carbon layer is 5% to 25% of the average particle size D50 of the micron-sized silicon, preferably 10% to 20%;

[0014] Preferably, the pores in the porous carbon layer are formed by a pore-forming agent and an etching agent, wherein the pore-forming agent is selected from one or more of nano zinc oxide, nano magnesium oxide, nano aluminum oxide, nano silicon oxide, nano copper oxide, nano iron oxide and nano manganese oxide;

[0015] Preferably, the average particle size D50 of the pore-forming agent is 50-500 nm, more preferably 50-200 nm;

[0016] Preferably, the average pore size of the porous material is not less than the average particle size D50 of the pore-forming agent;

[0017] Preferably, the etchant is selected from one, two, or three of hydrochloric acid, nitric acid, and hydrofluoric acid.

[0018] 5. The core-shell structured micron-sized silicon-carbon composite material according to any one of items 1 to 4, characterized in that the thickness of the dense carbon layer two is 0.05% to 1% of the average particle size D50 of the micron-sized silicon, preferably 0.1% to 0.2%;

[0019] Preferably, the porosity of the dense carbon layer II is 5% to 30%, more preferably 5% to 25%.

[0020] 6. The core-shell structured micron-sized silicon-carbon composite material according to any one of items 1 to 5, characterized in that the Shore hardness of the carbon shell is 10 to 50 HSD, preferably 25 to 40 HSD.

[0021] 7. The core-shell structured micron-sized silicon-carbon composite material according to any one of items 1 to 6, characterized in that the carbon source of the first dense carbon layer is selected from one or more of pitch, phenolic resin, humic acid, tannic acid, polymeric dopamine, polypyrrole, methane, and ethane; or,

[0022] The carbon source of the porous carbon layer is selected from one or more of the following: asphalt, phenolic resin, humic acid, tannic acid, polydopamine, polypyrrole, methane, and ethane; or...

[0023] The carbon source of the dense carbon layer II is selected from one or more of the following: asphalt, phenolic resin, humic acid, tannic acid, polydopamine, polypyrrole, methane, and ethane.

[0024] 8. The core-shell structured micron-sized silicon-carbon composite material according to any one of items 1 to 7, characterized in that the true density of the core-shell structured micron-sized silicon-carbon composite material is 1.2 to 2.1 g / cc, preferably 1.4 to 1.8 g / cc.

[0025] 9. A method for preparing a core-shell structured micron-sized silicon-carbon composite material, characterized in that it comprises the following steps:

[0026] A carbon source was used to coat micron-sized silicon to obtain composite particles consisting of micron-sized silicon and a dense carbon layer.

[0027] The composite particles were coated with carbon source 2 and a pore-forming agent to obtain composite particles 2.

[0028] The composite particles were sintered in an inert atmosphere and dispersed in an etchant to obtain composite particles three comprising micron-sized silicon, a dense carbon layer one, and a porous carbon layer.

[0029] The composite particles were coated with carbon source three and sintered to obtain a core-shell structured micron silicon-carbon composite material comprising micron silicon, a dense carbon layer one, a porous carbon layer and a dense carbon layer two.

[0030] 10. The method for preparing the core-shell structured micron-sized silicon-carbon composite material according to item 9, characterized in that the composite particles are coated with carbon source two and a pore-forming agent, and then sintered to obtain composite particles two.

[0031] 11. The preparation method according to item 9 or 10, characterized in that the sintering temperature of coating the composite particles with carbon source 3 and then sintering is 600-1100℃, preferably 700-1000℃, and the sintering time of coating the composite particles with carbon source 3 and then sintering is preferably 2-6h.

[0032] 12. The preparation method according to item 10, characterized in that the sintering temperature of coating the composite particles with carbon source two and pore-forming agent and then sintering is 700-1000℃, preferably 800-900℃, and the sintering time of coating the composite particles with carbon source two and pore-forming agent and then sintering is preferably 1-3h.

[0033] 13. The preparation method according to any one of items 9 to 12, characterized in that the coating is a solid phase coating.

[0034] 14. A core-shell structured micron-sized silicon-carbon composite material prepared by any one of items 9 to 13.

[0035] 15. The core-shell structured micron-sized silicon-carbon composite material according to any one of items 1 to 8, or the preparation method according to any one of items 9 to 13, characterized in that the micron-sized silicon is crystalline micron-sized silicon with an average particle size D50 of 1 to 8 μm and a sphericity of 0.3 to 0.8.

[0036] 16. The core-shell structured micron-sized silicon-carbon composite material according to any one of items 1 to 8, or the preparation method according to any one of items 9 to 13, characterized in that the micron-sized silicon is spherical micron-sized silicon, the interior of which is crystalline silicon and the surface of which is amorphous silicon, the average particle size D50 of the spherical micron-sized silicon is 1 to 8 μm, and the sphericity is 0.7 to 0.95;

[0037] Preferably, the average particle size D50 of the spherical micron-sized silicon is 2–5 μm;

[0038] Preferably, the sphericity of the spherical micron-sized silicon is 0.8 to 0.95;

[0039] Preferably, the specific surface area of ​​the spherical micron-sized silicon is 0.5–5 m². 2 / g, preferably 1-4m 2 / g;

[0040] Preferably, the thickness of the amorphous silicon is 1–20 nm, and more preferably 2–10 nm.

[0041] 17. An electrode, characterized in that it comprises an electrode current collector and an electrode active material layer coated on the surface of the electrode current collector, wherein the electrode active material layer comprises a core-shell structured micron-sized silicon-carbon composite material as described in any one of items 1 to 8 and 14, or a core-shell structured micron-sized silicon-carbon composite material prepared by any one of items 9 to 13.

[0042] Preferably, the electrode is a negative electrode.

[0043] 18. A battery, characterized in that it comprises a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the negative electrode described in claim 17.

[0044] The effects of the invention

[0045] (1) The core-shell structured micron-silicon-carbon composite material of this application has the following specific structure: micron-silicon - dense carbon layer one - porous carbon layer - dense carbon layer two. The carbon layers are organically connected and do not exist as separate components. Dense carbon layer one tightly encapsulates the micron-silicon, providing inward pressure during cycling, maintaining physical contact between the small particles generated after the micron-silicon particles break down, and acting as a medium for transmitting expansion force, transferring stress to the porous carbon layer for absorption; and preventing silicon from directly contacting the cavities in the porous carbon layer, preventing the fine particles of silicon after breakage from falling into the cavities and losing electrochemical activity. The porous carbon layer has numerous cavities, which are reversible compression spaces, providing space for the expansion of silicon, and using the reverse effect of stress, compressing dense carbon layer one in the delithiation state, so that dense carbon layer one tightly encapsulates the micron-silicon particles broken down after the electrochemical process, maintaining the ion / electron channel. The dense carbon layer II acts as a robust coating layer, maintaining the structural integrity and mechanical stability of the porous carbon layer under the expansion stress of micron-sized silicon. The combination of the dense carbon layer II and the porous carbon layer effectively absorbs and releases the expansion stress. Simultaneously, the dense carbon layer II isolates the electrolyte from penetration, preventing side reactions between the numerous active sites of the porous carbon layer and the electrolyte, thereby improving cycle performance and coulombic efficiency.

[0046] (2) The porous carbon layer of the core-shell structured micron-sized silicon-carbon composite material of this application has carbon pillars connecting the dense carbon layer one and the dense carbon layer two. During the electrochemical process, the carbon pillars play the role of conducting ions and electrons. This avoids the presence of a cavity layer in the core-shell structure that would hinder the conduction of ions and electrons.

[0047] (3) The core-shell structured micron silicon-carbon composite material of this application can not only alleviate the volume expansion of micron silicon and maintain particle stability, but also provide an inward pressure to the broken particles after the cycle, maintain the physical contact of the particles after the breakage, maintain the electron and ion diffusion path, and improve the cycle performance.

[0048] (4) This application starts with the structural modification of micron-sized silicon, which effectively promotes the practical application of micron-sized silicon. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of a core-shell structured micron-sized silicon-carbon composite material according to a specific embodiment of this application.

[0050] Figure 2 This is a TEM image of a spherical micron-sized silicon according to a specific embodiment of this application.

[0051] Symbol Explanation

[0052] 1 micrometer silicon 2 dense carbon layer 3 porous carbon layer

[0053] 4. Dense carbon layer 2; 5. Crystalline silicon; 6. Amorphous silicon Detailed Implementation

[0054] The present application will now be described in detail. While specific embodiments of the present application are shown below, it should be understood that the present application can be implemented in various forms and should not be limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art.

[0055] It should be noted that the terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to". The subsequent descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0056] 1. Core-shell structured micron-sized silicon-carbon composite material

[0057] On one hand, this application provides a core-shell structured micron-sized silicon-carbon composite material, comprising:

[0058] A core formed from micron-sized silicon; and

[0059] The carbon shell covering the core comprises, from the inside out, a dense carbon layer one, a porous carbon layer and a dense carbon layer two.

[0060] The core-shell structured micron-sized silicon-carbon composite material of this application constructs a cavity within a carbon coating layer, avoiding obstacles to ion and electron conduction caused by direct contact between the cavity and silicon. The inner dense carbon layer encapsulates the micron-sized silicon, and during cycling, the coating layer generates inward pressure, ensuring that even after the micron-sized silicon particles break down, they maintain physical contact and preserve electronic and ion conductivity. The outer dense carbon layer, combined with the inner porous carbon layer, works together to absorb and release expansion stress. Simultaneously, the dense carbon layer isolates the electrolyte from penetration, preventing side reactions between the numerous active sites of the porous carbon layer and the electrolyte, thereby improving cycling performance and coulombic efficiency.

[0061] In this application, "from the inside out" refers to the direction from the core to the carbon shell.

[0062] In one specific implementation, such as Figure 1 As shown, the core-shell structured micron silicon-carbon composite material consists of a core formed of micron silicon 1 and a carbon shell layer covering the core, wherein the carbon shell layer includes, from the inside out, a dense carbon layer 1 2, a porous carbon layer 3 and a dense carbon layer 2 4.

[0063] In one specific embodiment, the average particle size D50 of the micron-sized silicon in this application is 1–8 μm, for example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, etc., and the sphericity is 0.3–0.95, for example, it can be 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.45, 0.46, 0.47, 0.48, 0.4 9, 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, etc.

[0064] In this application, "average particle size D50" refers to the particle size corresponding to 50% of the cumulative particle size distribution of a sample. Physically, it means that particles smaller than D50 account for 50% of the total. Particle size distribution can be detected using conventional instruments known to those skilled in the art, such as a laser particle size analyzer.

[0065] In this application, "sphericity" is a parameter characterizing particle morphology. The closer a particle's morphology is to a sphere, the closer its sphericity is to 1. Sphericity is the ratio of the surface area of ​​a sphere of the same volume to the surface area of ​​the object. The sphericity of a sphere is equal to 1, and the sphericity of other objects is less than 1. The formula for the sphericity of any particle is: Where ψ represents particle sphericity, Vp represents particle volume, and Sp represents particle surface area. The sphericity of this application can be detected, for example, by the specific method given in the embodiments, using a dynamic image particle analyzer.

[0066] In one specific embodiment, the thickness of the dense carbon layer is 0.05% to 1% of the average particle size D50 of the micron-sized silicon, for example, it can be 0.05%, 0.07%, 0.09%, 0.1%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, etc., preferably 0.1% to 0.4%. A dense carbon layer encapsulates micron-sized silicon. During cycling, the coating layer exerts inward pressure, ensuring that the broken silicon particles maintain physical contact and preserve electronic and ionic conductivity. If the thickness of the dense carbon layer is too small, it cannot withstand the expansion of the micron-sized silicon and transfer its expansion stress to the porous carbon layer, leading to the failure of the constructed coating layer structure and a decrease in the electrochemical performance of the material. If the thickness of the dense carbon layer is too large, the electronic conductivity channels are affected, which in turn affects the specific capacity and initial efficiency of the material.

[0067] The thickness of the dense carbon layer in this application can be obtained by taking the average value of multiple measurements using a transmission electron microscope. For example, the measurements can be taken at 2 points, 3 points, 4 points, 5 points, 6 points, 7 points, 8 points, 9 points, 10 points, etc.

[0068] In one specific embodiment, the porosity of the first dense carbon layer is 10% to 50%, for example, it can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, etc., preferably 10% to 30%. The first dense carbon layer needs to transfer the force of the expansion of micron-sized silicon to the porous carbon layer, and in this process, it bears a very large force. The relatively small porosity of this application can reduce defects in the carbon layer structure and improve the yield strength of the material. The porosity of the first dense carbon layer of this application can be measured, for example, by a true density meter.

[0069] In one specific embodiment, the thickness of the porous carbon layer is 5% to 25% of the average particle size D50 of the micron-sized silicon, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, etc., preferably 10% to 20%. The thickness of the porous carbon layer in this application can be obtained, for example, by taking the average value of multiple measurements using a transmission electron microscope, for example, 2 points, 3 points, 4 points, 5 points, 6 points, 7 points, 8 points, 9 points, 10 points, etc.

[0070] In one specific embodiment, the pores in the porous carbon layer are formed by a pore-forming agent and an etchant. First, the pore-forming agent is added and mixed with the carbon source, then an etchant capable of reacting with the pore-forming agent is added to form the pores. The reaction products of the pore-forming agent and the etchant, as well as excess etchant, can be removed through cleaning and subsequent sintering steps. The pore-forming agent can be selected from one or more of nano-zinc oxide, nano-magnesium oxide, nano-alumina, nano-silicon oxide, nano-copper oxide, nano-iron oxide, and nano-manganese oxide; the etchant can be selected from one or two or three of hydrochloric acid, nitric acid, and hydrofluoric acid.

[0071] This application achieves a situation where the pore-forming agent particles do not come into close contact with each other by controlling the amount of the pore-forming agent, thus allowing carbon material to remain. When the pore-forming agent is etched with an etchant, the carbon material that previously existed between the particles forms carbon pillars.

[0072] In one specific embodiment, the average particle size D50 of the pore-forming agent is 50–500 nm, for example, it can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc., preferably 50–200 nm. The average pore size of the porous carbon layer is not less than the average particle size D50 of the pore-forming agent. The average pore size of this application can be measured by gas permeation.

[0073] In one specific embodiment, the thickness of the second dense carbon layer is 0.05% to 1% of the average particle size D50 of the micron-sized silicon, for example, it can be 0.05%, 0.07%, 0.09%, 0.1%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, etc., preferably 0.1% to 0.2%. The second dense carbon layer coats the porous carbon layer, serving to seal the porous carbon layer and isolate the electrolyte. If the thickness is too small, the pore structure in the porous carbon layer will be exposed, allowing the electrolyte to penetrate and causing each coating layer to lose its original function; if the thickness is too large, it will reduce the coulombic efficiency of the composite material. The thickness of the dense carbon layer II in this application can be obtained by taking the average value of multiple measurements using a transmission electron microscope, for example, 2 points, 3 points, 4 points, 5 points, 6 points, 7 points, 8 points, 9 points, 10 points, etc.

[0074] In one specific embodiment, the porosity of the dense carbon layer two is 5% to 30%, for example, it can be 5%, 7%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, etc., preferably 5% to 25%. The dense carbon layer two works synergistically with the two internal coating layers to mitigate the expansion of micron-sized silicon. During cycling, it is subjected to the force of micron-sized silicon expansion. If the porosity is too high, there will be more defects in the structure, the yield strength of the structure will decrease, and the structure will be destroyed during cycling. At the same time, the dense carbon layer two also acts as an electrolyte barrier. Excessive porosity will lead to electrolyte penetration, thereby reducing the electrochemical performance of the material. The porosity of the dense carbon layer two in this application can be measured, for example, by a true density meter.

[0075] In one specific embodiment, the Shore hardness of the carbon shell layer is 10–50 HSD, for example, 20 HSD, 25 HSD, 30 HSD, 35 HSD, 40 HSD, 45 HSD, etc., preferably 25–40. The Shore hardness of the carbon shell layer in this application refers to the Shore hardness of the carbon shell layer comprising a dense carbon layer one, a porous carbon layer, and a dense carbon layer two. In this application, "Shore hardness" refers to a method of testing and representing the hardness of a material, measured using a Shore hardness tester. For example, the material can be mixed with a binder and then pressed into a tablet under pressure equal to the maximum pressure that the particles can withstand without breaking (this can be observed and adjusted using SEM), and then the tablet can be used for measurement. A lower Shore hardness indicates better material flexibility and successful construction of the porous structure. However, too low a Shore hardness cannot maintain the structure of the coating layer itself and the stress generated by silicon expansion. An appropriate Shore hardness is necessary to maintain structural stability and absorb volume expansion.

[0076] In one specific embodiment, the true density of the core-shell structured micron-sized silicon-carbon composite material is 1.2–2.1 g / cc, for example, it can be 1.2 g / cc, 1.3 g / cc, 1.4 g / cc, 1.5 g / cc, 1.6 g / cc, 1.7 g / cc, 1.8 g / cc, 1.9 g / cc, 2.0 g / cc, 2.1 g / cc, etc., preferably 1.4–1.8 g / cc. In this application, "true density" refers to the actual mass of a unit volume of solid matter in an absolutely dense state, that is, the density after removing internal pores or voids between particles. The true density of this application is determined using a powder true density tester. For example, the sample can be placed in the true density tester, using helium as a medium, and the pressure in the measuring chamber is gradually increased to a specified value. Then, the helium expands into the expansion chamber. The equilibrium pressure of the two processes is automatically recorded by the instrument. According to the law of conservation of mass, after calibrating the volumes of the measuring chamber and the expansion chamber using a standard sphere, the volume of the sample is determined, and the true density is calculated.

[0077] In one specific embodiment, the mass ratio of the carbon shell to the core is 0.16 to 0.5:1, preferably 0.22 to 0.36:1, and for example, it can be 0.16:1, 0.18:1, 0.2:1, 0.22:1, 0.28:1, 0.3:1, 0.32:1, 0.36:1, 0.38:1, 0.4:1, 0.42:1, 0.46:1, 0.48:1, 0.5:1, etc.

[0078] In one specific embodiment, the carbon sources of the dense carbon layer one, the porous carbon layer, and the dense carbon layer two can be completely identical, completely different, or not completely identical. The carbon source in this application is not limited and can be any carbon source. For example, the carbon source of each layer can be selected from one or more of asphalt, phenolic resin, humic acid, tannic acid, polydopamine, polypyrrole, methane, and ethane, preferably one or more of asphalt, phenolic resin, and humic acid.

[0079] In one specific embodiment, the carbon source of the first dense carbon layer is selected from one or more of asphalt, phenolic resin and humic acid; and / or, the carbon source of the porous carbon layer is selected from one or more of asphalt, phenolic resin and humic acid; and / or, the carbon source of the second dense carbon layer is selected from one or more of asphalt, phenolic resin and humic acid.

[0080] 2. Preparation method of core-shell structured micron-sized silicon-carbon composite material

[0081] The inventors of this application have discovered that the core-shell structured micron-sized silicon-carbon composite material of this application can be easily prepared using the following preparation method. Therefore, in another aspect, this application also provides a method for preparing a core-shell structured micron-sized silicon-carbon composite material, which includes the following steps:

[0082] A carbon source was used to coat micron-sized silicon to obtain composite particles consisting of micron-sized silicon and a dense carbon layer.

[0083] The composite particles were coated with carbon source 2 and a pore-forming agent to obtain composite particles 2.

[0084] The composite particles were dispersed in an etchant to obtain composite particles three comprising micron-sized silicon, a dense carbon layer, and a porous carbon layer.

[0085] The composite particles were coated with carbon source three and sintered to obtain a core-shell structured micron silicon-carbon composite material comprising micron silicon, a dense carbon layer one, a porous carbon layer and a dense carbon layer two.

[0086] In one specific embodiment, the preparation method of the core-shell structured micron-sized silicon-carbon composite material of this application includes the following steps:

[0087] A carbon source was used to coat micron-sized silicon to obtain composite particles consisting of micron-sized silicon and a dense carbon layer.

[0088] The composite particles were coated with carbon source 2 and pore-forming agent and sintered to obtain composite particles 2.

[0089] The composite particles were dispersed in an etchant to obtain composite particles three comprising micron-sized silicon, a dense carbon layer, and a porous carbon layer.

[0090] The composite particles were coated with carbon source three and sintered to obtain a core-shell structured micron silicon-carbon composite material comprising micron silicon, a dense carbon layer one, a porous carbon layer and a dense carbon layer two.

[0091] This application does not specify a specific etching time for the etchant; an excess of etchant is acceptable.

[0092] In one specific embodiment, the sintering temperature for coating the micron-sized silicon with the carbon source two and then sintering is 700-1000℃, for example, it can be 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, 920℃, 940℃, 960℃, 980℃, 1000℃, etc., preferably 800-900℃, and the sintering time for coating the micron-sized silicon with the carbon source two and then sintering is preferably 1-3 hours.

[0093] In one specific embodiment, the sintering temperature for coating the composite particles with carbon source three before sintering is 600–1100°C, for example, 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, 920°C, 940°C, 960°C, 980°C, 1000°C, 1020°C, 1040°C, 1060°C, 1080°C, 1100°C, etc., preferably 700–1000°C, and the sintering time for coating the composite particles with carbon source three before sintering is preferably 2–6 hours.

[0094] This application does not limit the sintering apparatus; any apparatus capable of introducing an atmosphere and raising the sintering temperature can be used, such as a dry rotary kiln, electric furnace, tube furnace, box furnace, roller kiln, etc., or oxy-acetylene flame, oxy-hydrogen flame, etc.

[0095] In one specific embodiment, the sintering of this application is carried out under an inert gas atmosphere. The inert atmosphere of this application is not limited and can be any inert atmosphere, such as nitrogen or argon.

[0096] In one specific embodiment, the coating is a solid-phase coating, for example, a mechanical fusion machine can be used for solid-phase coating.

[0097] In one specific embodiment, both the porous carbon layer and the second dense carbon layer are solid-phase coatings, and the first dense carbon layer can be a solid-phase coating, a gas-phase coating, or a liquid-phase coating, preferably the first dense carbon layer is a solid-phase coating.

[0098] In one specific embodiment, the sintering process includes cooling.

[0099] In one specific embodiment, in the preparation method of the core-shell structured micron-sized silicon-carbon composite material, the composite particles are dispersed in an etchant, stirred, filtered, washed, and dried to obtain composite particles comprising micron-sized silicon, a dense carbon layer, and a porous carbon layer.

[0100] In another aspect, this application also provides a core-shell structured micron-sized silicon-carbon composite material prepared by any of the foregoing preparation methods.

[0101] 3. Micron-sized silicon

[0102] In the core-shell structured micron-silicon-carbon composite material of this application, or in the preparation method of the core-shell structured micron-silicon-carbon composite material of this application, the micron-silicon can be crystalline silicon or spherical micron-silicon with amorphous silicon coating crystalline silicon.

[0103] 3.1. Crystalline micron-sized silicon

[0104] The crystalline micron-sized silicon of this application has an average particle size D50 of 1–8 μm, for example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, etc., and a sphericity of 0.3–0.8, for example, it can be 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, etc. 0.44, 0.45, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.8, etc.

[0105] 3.2. Spherical micron-sized silicon

[0106] The spherical micron-sized silicon in this application has a crystalline silicon interior and an amorphous silicon surface. The average particle size D50 of the spherical micron-sized silicon is 1–8 μm, for example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, etc., and the sphericity is 0.7–0. 95, for example, can be 0.7, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, etc.

[0107] Existing micron-sized silicon is irregularly shaped crystalline silicon with many sharp edges on its surface. Crystalline silicon is anisotropic and expands anisotropically. During lithium intercalation, the anisotropic volume expansion can easily lead to failure or damage to particle integrity at the sharp edges. The spherical micron-sized silicon of this application has a certain thickness of amorphous silicon on its surface. Amorphous silicon is isotropic and expands in the same direction, making the anisotropic forces on the outer coating layer of the spherical micron-sized silicon uniform, which is beneficial to maintaining the stability of the particle structure during the electrochemical process.

[0108] In one specific embodiment, the average particle size D50 of the spherical micron silicon of this application is 2 to 5 μm; the sphericity of the spherical micron silicon is 0.8 to 0.95.

[0109] In one specific embodiment, the spherical micron-sized silicon of this application has a specific surface area of ​​0.5–5 m². 2 / g, for example, can be 0.5m 2 / g、1m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g、5m 2 / g, preferably 1-4m 2 / g.

[0110] The specific surface area of ​​the spherical micron-sized silicon in this application can be detected by the specific method given in the examples, and measured using a BET specific surface area tester.

[0111] The spherical micron-sized silicon particles of this application have a moderate particle size distribution and high sphericity. This structural advantage gives them a lower specific surface area, higher particle flowability, and higher tap density, which reduces the difficulty of subsequent processes and helps maintain the stability of the particle structure during the electrochemical process.

[0112] In one specific embodiment, the thickness of the amorphous silicon in the spherical micron-sized silicon of this application is 1 to 20 nm, for example, it can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, etc., preferably 2 to 10 nm. The thickness of the amorphous silicon can be obtained, for example, by taking the average value of multiple measurements using a transmission electron microscope, for example, it can be 2 points, 3 points, 4 points, 5 points, 6 points, 7 points, 8 points, 9 points, 10 points, etc.

[0113] The structure of the spherical micron-sized silicon in this application is as follows: Figure 2 As shown in the TEM image, the portion with visible lattice fringes on the left is crystalline silicon 5 inside the spherical micron-sized silicon; the portion without lattice fringes on the right is amorphous silicon 6 on the outer layer of the spherical micron-sized silicon. In one specific embodiment, as... Figure 2 As shown, the outer layer of amorphous silicon has a thickness of 10 nm.

[0114] 3.3. Preparation method of spherical micron-sized silicon

[0115] The spherical micron-sized silicon of this application can be easily prepared by the following method, which includes the following steps:

[0116] Spherical micron-sized silicon is obtained by sintering, holding, cooling and crushing crystalline micron-sized silicon under an inert atmosphere.

[0117] Here, the crystalline micron-sized silicon refers to the crystalline micron-sized silicon of the prior art. In one specific embodiment, the average particle size D50 of the crystalline micron-sized silicon is 1–8 μm, for example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, etc., and the sphericity of the crystalline micron-sized silicon is 0.3–0.7, for example, it can be 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, etc. The average particle size D50 of the spherical micron-sized silicon in this application is less than or equal to the average particle size D50 of the crystalline micron-sized silicon, and the sphericity of the spherical micron-sized silicon in this application is greater than the sphericity of the crystalline micron-sized silicon.

[0118] Here, the inert atmosphere is not limited and can be any inert atmosphere, such as nitrogen or argon.

[0119] In one specific embodiment, the sintering temperature is 1300–1600℃, for example, it can be 1300℃, 1310℃, 1320℃, 1330℃, 1340℃, 1350℃, 1360℃, 1370℃, 1380℃, 1390℃, 1400℃, 1410℃, 1420℃, 1430℃, 144℃, 1450℃, 1460℃, 1470℃, 1480℃, 1490℃, 1500℃, 1510℃, 1520℃, 1530℃, 1540℃, 1550℃, 1560℃, 1570℃, 1580℃, 1590℃, 1600℃, etc., preferably 1400–1500℃. When the temperature is raised to near the melting point of crystalline silicon, the reactivity at the edges is higher than that at the bulk, so the edges melt first. As a result, the silicon material at the edges undergoes reorganization or transfer due to surface tension, transforming the edges into a smooth structure and increasing sphericity. This application does not limit the sintering apparatus; any device capable of raising the sintering temperature can be used, such as a dry rotary kiln, electric furnace, tube furnace, box furnace, roller kiln, etc. For example, oxy-acetylene flame or oxy-hydrogen flame sintering can also be used.

[0120] In one specific embodiment, the temperature is increased to the sintering temperature at a heating rate of 1 to 10 °C / min, preferably 3 to 6 °C / min. The heating rate can be, for example, 1 °C / min, 1.5 °C / min, 2 °C / min, 2.5 °C / min, 3 °C / min, 3.5 °C / min, 4 °C / min, 4.5 °C / min, 5 °C / min, 5.5 °C / min, 6 °C / min, 6.5 °C / min, 7 °C / min, 7.5 °C / min, 8 °C / min, 8.5 °C / min, 9 °C / min, 9.5 °C / min, 10 °C / min, etc.

[0121] In one specific embodiment, the sintering temperature is higher than 1300°C. When the temperature reaches 1300°C, the temperature is increased at a rate of 3–6°C / min to the sintering temperature. When the temperature reaches 1300°C, the heating rate needs to be adjusted to prevent it from being too fast, so as to avoid the rapid melting of silicon edges causing particles to stick together. Although adhesion can be broken up, the breaking process may create new edges.

[0122] In one specific embodiment, the heat preservation time is 0.5 to 10 hours, for example, it can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, etc., preferably 0.5 to 4 hours. If the heat preservation time is too short, the edges and corners will not melt sufficiently, resulting in poor sphericity; if the heat preservation time is too long, the edges and corners will melt sufficiently and may cause contact transfer between particles, leading to adhesion.

[0123] In one specific embodiment, the cooling rate is 10–100 °C / min, for example, it can be 10 °C / min, 15 °C / min, 20 °C / min, 25 °C / min, 30 °C / min, 35 °C / min, 40 °C / min, 45 °C / min, 50 °C / min, 55 °C / min, 60 °C / min, 65 °C / min, 70 °C / min, 75 °C / min, 80 °C / min, 85 °C / min, 90 °C / min, 95 °C / min, 100 °C / min, etc., preferably 50–80 °C / min. By controlling the cooling rate, crystal dislocations are formed, resulting in a layer of amorphous silicon. Controlling the cooling rate at 10–100 °C / min allows the thickness of the amorphous silicon to reach 1–20 nm. This application does not limit the cooling device; any device capable of cooling can be used, such as purging a low-temperature inert atmosphere.

[0124] When the core-shell structure composite material comprising spherical micron-sized silicon is applied in lithium-ion batteries, the spherical micron-sized silicon expands isotropically. Its spherical structure improves the continuity of the surface coating, and the coating layer experiences uniform stress during expansion. The composite material overcomes the large expansion effect of micron-sized silicon, thereby reducing battery deformation during cycling and improving battery safety. Simultaneously, the composite material maintains structural stability during cycling, preventing the growth of irreversible SEI films and electrolyte penetration, thus improving battery cycle performance.

[0125] 4. Electrodes

[0126] On the other hand, this application also provides an electrode, which includes an electrode current collector and an electrode active material layer coated on the electrode current collector. The electrode active material layer contains at least spherical micron-sized silicon as the electrode active material, wherein the spherical micron-sized silicon is any of the aforementioned spherical micron-sized silicon or spherical micron-sized silicon prepared using any of the aforementioned preparation methods of this application. The electrode active material layer may also contain any of the aforementioned core-shell structure composite materials of this application. The electrode of this application is preferably a negative electrode.

[0127] 4.1. Electrode active materials

[0128] The electrode active material of the present application may be a negative electrode active material, which is not particularly limited, and those negative electrode active materials commonly used in the art can be used.

[0129] Preferably, the electrode active material takes the spherical micron silicon of the present application as a main component.

[0130] In addition to the spherical micron silicon of the present application, the electrode active material layer may further contain other electrode active materials. Hereinafter, other electrode active materials will be described.

[0131] As the negative electrode active material, for example, carbon materials such as graphite (natural graphite, artificial graphite, etc.) which is highly crystalline carbon, low crystalline carbon (soft carbon), hard carbon, carbon black (Ketjen Black (registered trademark), acetylene black, channel black, lamp black, oil-furnace carbon black, thermal cracking carbon black, etc.), fullerenes, carbon nanotubes, carbon nanofibers, carbon nanobulbs, carbon filaments can be enumerated. In addition, as the negative electrode active material, elementary substances of elements that can be alloyed with lithium such as Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, and oxides and carbides containing these elements can also be enumerated. As such oxides, silicon monoxide (SiO), SiO x (0<x<2), stannic dioxide (SnO2), SnO x (0<x<2), SnSiO3, etc. can be enumerated, and as carbides, silicon carbide (SiC), etc. can be enumerated. In addition, as the negative electrode active material, metal materials such as lithium metal, lithium-titanium composite oxides (such as lithium titanate Li4Ti5O 12 ) and other lithium-transition metal composite oxides can also be enumerated. However, it is not limited to these materials, and conventionally known materials that can be used as negative electrode active materials for lithium-ion batteries can be used. One of these negative electrode active materials may be used alone, or two or more of them may be used in combination.

[0132] 4.2. Electrode Current Collector

[0133] The electrode current collector of the present application may be a negative electrode current collector, which is composed of a conductive material. There is no particular limitation on the thickness of the electrode current collector. The thickness of the electrode current collector is usually about 0.1 to 1000 μm, preferably about 1 to 100 μm. There is no particular limitation on the shape of the electrode current collector. There is no particular limitation on the material constituting the electrode current collector. For example, it may be copper.

[0134] 4.3. Electrodes

[0135] The electrode can be prepared by forming the active material layer on the electrode current collector using conventional and well-known methods, but is not limited to this. Those skilled in the art can select an appropriate method to manufacture the electrode based on the type of battery to be manufactured.

[0136] Electrodes using electrode active materials can be manufactured using conventional methods. That is, the electrode active material, conductive agent, and binder and thickener used as needed can be dry-mixed and formed into a sheet, and then the sheet material can be pressed onto the electrode current collector. Alternatively, these materials can be dissolved or dispersed in a liquid medium to form a slurry, which can be coated onto the electrode current collector and dried, thereby forming an electrode active material layer on the electrode current collector, thus obtaining the electrode.

[0137] As a conductive agent, it can contain any other components that can be used as a conductive agent. For example, it can also contain: metallic materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke, etc. These conductive agents can be used alone, or two or more can be combined in any combination and proportion.

[0138] Furthermore, the electrode active material layer may also include a binder. There are no particular limitations on the binder used to manufacture the electrode active material layer; in the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used in manufacturing the electrode is acceptable.

[0139] As a solvent used to form the slurry, any solvent that can dissolve or disperse the electrode active material, conductive agent, binder, and thickener as needed is acceptable. There are no special restrictions on its type; any solvent among aqueous solvents and organic solvents can be used.

[0140] Thickeners are commonly used to adjust the viscosity of slurries. The electrode active material layer may also contain a thickener. There are no particular limitations on the type of thickener used.

[0141] 5. Battery

[0142] The electrodes of this application can be used in batteries. Therefore, on the other hand, this application also provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the aforementioned negative electrode of this application.

[0143] In this application, a battery refers to a single physical module comprising one or more individual battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application may include a battery module or a battery pack, etc.

[0144] The battery cell of this application may include one or more of the following: lithium-ion secondary battery, lithium-ion primary battery, lithium-sulfur battery, sodium-lithium-ion battery, sodium-ion battery, and magnesium-ion battery; this application is not limited to these categories. The battery cell of this application may be cylindrical, flat, cuboid, or other shapes, and the embodiments of this application are not limited to these shapes. Battery cells are generally classified into three types according to their packaging method: cylindrical battery cells, prismatic battery cells, and pouch battery cells; this application is not limited to these types.

[0145] The separator is typically disposed between the positive and negative electrodes. There are no special restrictions on the material and shape of the separator, and any known separator can be used. For example, materials such as resin, glass fiber, and inorganic materials can be used, preferably porous sheets or non-woven fabric-like materials with excellent liquid retention properties.

[0146] An electrolyte is filled between the positive and negative electrodes. The electrolyte can be an aqueous electrolyte or a non-aqueous electrolyte. Furthermore, the electrolyte can be an electrolyte solution, a polymeric gel electrolyte, or a solid polymeric electrolyte.

[0147] Example

[0148] This application provides a general and / or specific description of the materials and methods used in the experiments. In the following examples, reagents or instruments whose manufacturers are not specified are all commercially available reagents or instruments.

[0149] Example 1-1

[0150] The spherical micron-sized silicon of this embodiment is prepared according to the following steps:

[0151] 1 kg of crystalline micron-sized silicon with a D50 of 5 μm and a sphericity of 0.3 was heated to 1400 °C at a rate of 5 °C / min under a nitrogen atmosphere, held at that temperature for 5 h, and then cooled to room temperature at a rate of 50 °C / min. The silicon was then removed and crushed to obtain spherical micron-sized silicon with a D50 of 4 μm and a sphericity of 0.8.

[0152] Examples 1-2

[0153] The spherical micron-sized silicon in this embodiment is prepared according to the following steps:

[0154] 1 kg of crystalline micron-sized silicon with a D50 of 6 μm and a sphericity of 0.5 was heated to 1500 °C at a rate of 10 °C / min under a nitrogen atmosphere, held at that temperature for 2 h, and then cooled to room temperature at a rate of 100 °C / min. The silicon was then removed and crushed to obtain spherical micron-sized silicon with a D50 of 6 μm and a sphericity of 0.9.

[0155] Examples 1-3

[0156] The spherical micron-sized silicon in this embodiment is prepared according to the following steps:

[0157] 1 kg of crystalline micron-sized silicon with a D50 of 2 μm and a sphericity of 0.6 was heated to 1400 °C at 3 °C / min under a nitrogen atmosphere, held at that temperature for 4 h, and then cooled to room temperature at a rate of 60 °C / min. The silicon was then removed and crushed to obtain spherical micron-sized silicon with a D50 of 2 μm and a sphericity of 0.95.

[0158] Examples 1-4

[0159] The spherical micron-sized silicon in this embodiment is prepared according to the following steps:

[0160] 1 kg of crystalline micron-sized silicon with a D50 of 4 μm and a sphericity of 0.3 was heated to 1450 °C at a rate of 5 °C / min under a nitrogen atmosphere, held at that temperature for 5 h, and then cooled to room temperature at a rate of 80 °C / min. The silicon was then removed and crushed to obtain spherical micron-sized silicon with a D50 of 3 μm and a sphericity of 0.8.

[0161] Examples 1-5

[0162] The difference between this embodiment and embodiments 1-3 is that the sintering temperature is 1600℃.

[0163] Examples 1-6

[0164] The difference between this embodiment and embodiments 1-3 is that the sintering temperature is 1300℃.

[0165] Examples 1-7

[0166] The difference between this embodiment and embodiments 1-3 is that the sintering temperature is 1500℃.

[0167] Examples 1-8

[0168] The difference between this embodiment and embodiments 1-3 is that the heating rate is 1℃ / min.

[0169] Examples 1-9

[0170] The difference between this embodiment and embodiments 1-3 is that the heating rate is 10℃ / min.

[0171] Examples 1-10

[0172] The difference between this embodiment and embodiments 1-3 is that the heat preservation time is 0.5h.

[0173] Examples 1-11

[0174] The difference between this embodiment and embodiments 1-3 is that the heat preservation time is 10 hours.

[0175] Examples 1-12

[0176] The difference between this embodiment and embodiments 1-3 is that the cooling rate is 10℃ / min.

[0177] Examples 1-13

[0178] The difference between this embodiment and embodiments 1-3 is that the cooling rate is 100℃ / min.

[0179] Examples 1-14

[0180] The difference between this embodiment and Embodiment 3 is that the cooling rate is 50℃ / min.

[0181] Examples 1-15

[0182] The difference between this embodiment and embodiments 1-3 is that the cooling rate is 80℃ / min. The parameters, reagents, and product parameters for each embodiment are listed in Tables 1 and 2 below:

[0183] Table 1

[0184]

[0185] Table 2

[0186]

[0187] Example 2-1

[0188] (1) Take 1 kg of crystalline micron-sized silicon with a D50 of 4 μm and a sphericity of 0.8 and mix it evenly with 100 g of asphalt. Place it in a mechanical fusion machine for coating to obtain composite particles.

[0189] (2) Take 100g asphalt, 300g of nano magnesium oxide with D50 of 200nm and 1kg of composite particles one, mix them evenly, place them in a mechanical fusion machine for coating, sinter at 800℃ for 4h under nitrogen atmosphere, cool down, and obtain composite particles two.

[0190] (3) The composite particles were dispersed in hydrochloric acid, stirred for 4 hours, filtered, washed and dried to obtain composite particles.

[0191] (4) Mix 1 kg of composite particles with 50 g of asphalt evenly, mechanically fuse them, and then sinter them at 800 °C for 4 h under a nitrogen atmosphere to obtain a core-shell structured micron silicon-carbon composite material.

[0192] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 20 nm, the thickness of the porous carbon layer is 1 μm, and the thickness of the second dense carbon layer is 5 nm.

[0193] Example 2-2

[0194] The difference between this embodiment and Embodiment 2-1 is that the sphericity of the crystalline micron-sized silicon is 0.3.

[0195] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 14 nm, the thickness of the porous carbon layer is 0.8 μm, and the thickness of the second dense carbon layer is 4 nm.

[0196] Example 2-3

[0197] The difference between this embodiment and Embodiment 2-1 is that the D50 of the crystalline micron-sized silicon is 8 μm.

[0198] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 12 nm, the thickness of the porous carbon layer is 0.64 μm, and the thickness of the second dense carbon layer is 3.2 nm.

[0199] Examples 2-4

[0200] The difference between this embodiment and Embodiment 2-1 is that the pore-forming agent is nano-alumina.

[0201] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 20 nm, the thickness of the porous carbon layer is 0.92 μm, and the thickness of the second dense carbon layer is 5 nm.

[0202] Examples 2-5

[0203] The difference between this embodiment and Embodiment 2-1 is that the average particle size D50 of the pore-forming agent is 50 nm.

[0204] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 20 nm, the thickness of the porous carbon layer is 1.24 μm, and the thickness of the second dense carbon layer is 3.6 nm.

[0205] Examples 2-6

[0206] The difference between this embodiment and Embodiment 2-1 is that the average particle size D50 of the pore-forming agent is 500 nm.

[0207] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 20 nm, the thickness of the porous carbon layer is 0.76 μm, and the thickness of the second dense carbon layer is 6 nm.

[0208] Examples 2-7

[0209] The difference between this embodiment and embodiment 2-1 is that the carbon source in steps (1), (2) and (4) is phenolic resin.

[0210] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 16 nm, the thickness of the porous carbon layer is 0.68 μm, and the thickness of the second dense carbon layer is 4 nm.

[0211] Examples 2-8

[0212] The difference between this embodiment and embodiment 2-1 is that the carbon source in steps (1), (2) and (4) is humic acid.

[0213] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 16 nm, the thickness of the porous carbon layer is 1.12 μm, and the thickness of the second dense carbon layer is 6 nm.

[0214] Examples 2-9

[0215] The difference between this embodiment and Embodiment 2-1 is that the amount of nano-magnesium oxide is 100g.

[0216] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 20 nm, the thickness of the porous carbon layer is 0.2 μm, and the thickness of the second dense carbon layer is 5 nm.

[0217] Example 2-10

[0218] The difference between this embodiment and Embodiment 2-1 is that the amount of nano-magnesium oxide is 250g.

[0219] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 20 nm, the thickness of the porous carbon layer is 0.6 μm, and the thickness of the second dense carbon layer is 5 nm.

[0220] Example 2-11

[0221] The difference between this embodiment and embodiment 2-1 is that the sintering temperature in steps (2) and (4) is 1000℃.

[0222] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 18 nm, the thickness of the porous carbon layer is 0.88 μm, and the thickness of the second dense carbon layer is 4 nm.

[0223] Example 2-12

[0224] The difference between this embodiment and embodiment 2-1 is that the sintering temperature in steps (2) and (4) is 700℃.

[0225] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the first dense carbon layer is 24 nm, the thickness of the porous carbon layer is 1.24 μm, and the thickness of the second dense carbon layer is 7.2 nm.

[0226] Example 2-13

[0227] The difference between this embodiment and embodiment 2-1 is that carbon source one is 200g and carbon source three is 400g.

[0228] Example 2-14

[0229] The difference between this embodiment and Embodiments 2-11 is that the crystalline micron-sized silicon with a D50 of 4 μm and a sphericity of 0.8 is replaced with the spherical micron-sized silicon with a D50 of 4 μm, a sphericity of 0.8, an interior of crystalline silicon, and a surface of amorphous silicon prepared in Embodiments 1-1.

[0230] Comparative Example 1

[0231] (1) Take 1 kg of crystalline micron silicon with a D50 of 4 μm and a sphericity of 0.8 and mix it evenly with 250 g of asphalt. Place it in a mechanical fusion machine for coating and sinter at 800 °C for 4 h under a nitrogen atmosphere to obtain the core-shell structured micron silicon-carbon composite material of this comparative example.

[0232] In the obtained core-shell structured micron-sized silicon-carbon composite material, the thickness of the carbon layer is 55 nm.

[0233] Table 3

[0234]

[0235] Table 4

[0236]

[0237]

[0238] Experimental Example 1: Lithium-ion Battery Preparation and Performance Testing

[0239] The core-shell composite material (90 wt%) obtained in Examples 2-1 to 2-13 was mixed with conductive agent (1 wt% CNT and 3 wt% SP), binder (4 wt% CMC and 2 wt% SBR), and deionized water to form a slurry. This slurry was then coated, dried, and cut to obtain lithium electrode sheets. Here, "wt%" represents the percentage of each component by weight of the core-shell composite material, conductive agent, and binder. The lithium electrode sheets and conventional electrolyte were assembled into coin cells and subjected to charge-discharge tests. The test conditions were: activation at 0.1C / 0.1C for 2 cycles and cycling at 0.3C / 0.3C within a voltage range of 5 mV–0.8V. The electrochemical performance parameters of the batteries made from the materials of Examples 2-1 to 2-13 are shown in Table 5 below.

[0240] Table 5

[0241]

[0242]

[0243] The above description is merely a preferred embodiment of this application and is not intended to limit the application in any other way. Any person skilled in the art may make changes or modifications to the disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the protection scope of this application.

Claims

1. A core-shell structured micron-sized silicon-carbon composite material, characterized in that, It includes: A core formed from micron-sized silicon; and A carbon shell covering the core, wherein the carbon shell comprises, from the inside out, a dense carbon layer one, a porous carbon layer and a dense carbon layer two; The average particle size D50 of the micron-sized silicon is 1~8μm, and the sphericity is 0.3~0.95; The thickness of the porous carbon layer is 5% to 25% of the average particle size D50 of the micron-sized silicon. The pores in the porous carbon layer are formed by a pore-forming agent and an etching agent; The average particle size D50 of the pore-forming agent is 50~500nm; The average pore size of the porous structure is not less than the average particle size D50 of the pore-forming agent; The porosity of the first dense carbon layer is 10%~50%; The porosity of the dense carbon layer 2 is 5%~30%.

2. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The thickness of the first dense carbon layer is 0.05% to 1% of the average particle size D50 of the micron-sized silicon.

3. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The thickness of the first dense carbon layer is 0.1% to 0.4% of the average particle size D50 of the micron-sized silicon.

4. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The porosity of the first dense carbon layer is 10% to 30%.

5. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The thickness of the porous carbon layer is 10% to 20% of the average particle size D50 of the micron-sized silicon.

6. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The pore-forming agent is selected from one or more of nano zinc oxide, nano magnesium oxide, nano aluminum oxide, nano silicon oxide, nano copper oxide, nano iron oxide, and nano manganese oxide.

7. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The average particle size D50 of the pore-forming agent is 50~200nm.

8. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The etching agent is selected from one, two, or three of hydrochloric acid, nitric acid, and hydrofluoric acid.

9. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The thickness of the dense carbon layer II is 0.05% to 1% of the average particle size D50 of the micron-sized silicon.

10. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The thickness of the dense carbon layer II is 0.1% to 0.2% of the average particle size D50 of the micron-sized silicon.

11. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The porosity of the dense carbon layer 2 is 5%~25%.

12. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The Shore hardness of the carbon shell is 10~50 HSD.

13. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The Shore hardness of the carbon shell is 25~40 HSD.

14. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The carbon source of the first dense carbon layer is selected from one or more of the following: asphalt, phenolic resin, humic acid, tannic acid, polydopamine, polypyrrole, methane, and ethane; or, The carbon source of the porous carbon layer is selected from one or more of the following: asphalt, phenolic resin, humic acid, tannic acid, polydopamine, polypyrrole, methane, and ethane; or... The carbon source of the dense carbon layer II is selected from one or more of the following: asphalt, phenolic resin, humic acid, tannic acid, polydopamine, polypyrrole, methane, and ethane.

15. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The true density of the core-shell structured micron-sized silicon-carbon composite material is 1.2~2.1 g / cc.

16. The core-shell structured micron-sized silicon-carbon composite material according to claim 1, characterized in that, The true density of the core-shell structured micron-sized silicon-carbon composite material is 1.4~1.8 g / cc.

17. The core-shell structured micron-sized silicon-carbon composite material according to any one of claims 1 to 16, characterized in that, The micron-sized silicon is crystalline micron-sized silicon with an average particle size D50 of 1~8μm and a sphericity of 0.3~0.

8.

18. The core-shell structured micron-sized silicon-carbon composite material according to any one of claims 1 to 16, characterized in that, The micron-sized silicon is spherical, with crystalline silicon inside and amorphous silicon on the surface. The average particle size D50 of the spherical micron-sized silicon is 1~8μm, and the sphericity is 0.7~0.

95.

19. The core-shell structured micron-sized silicon-carbon composite material according to claim 18, characterized in that, The average particle size D50 of the spherical micron-sized silicon is 2~5μm.

20. The core-shell structured micron-sized silicon-carbon composite material according to claim 18, characterized in that, The sphericity of the spherical micron-sized silicon is 0.8 to 0.

95.

21. The core-shell structured micron-sized silicon-carbon composite material according to claim 18, characterized in that, The specific surface area of ​​the spherical micron-sized silicon is 0.5~5m². 2 / g.

22. The core-shell structured micron-sized silicon-carbon composite material according to claim 18, characterized in that, The specific surface area of ​​the spherical micron-sized silicon is 1~4m². 2 / g.

23. The core-shell structured micron-sized silicon-carbon composite material according to claim 18, characterized in that, The thickness of the amorphous silicon is 1~20nm.

24. The core-shell structured micron-sized silicon-carbon composite material according to claim 18, characterized in that, The thickness of the amorphous silicon is 2~10nm.

25. A method for preparing a core-shell structured micron-sized silicon-carbon composite material according to any one of claims 1 to 24, characterized in that, It includes the following steps: A carbon source was used to coat micron-sized silicon to obtain composite particles consisting of micron-sized silicon and a dense carbon layer. The composite particles were coated with carbon source 2 and a pore-forming agent to obtain composite particles 2. The composite particles were sintered in an inert atmosphere and dispersed in an etchant to obtain composite particles three comprising micron-sized silicon, a dense carbon layer one, and a porous carbon layer. The composite particles were coated with carbon source three and sintered to obtain a core-shell structured micron silicon-carbon composite material comprising micron silicon, a dense carbon layer one, a porous carbon layer and a dense carbon layer two.

26. The method for preparing the core-shell structured micron-sized silicon-carbon composite material according to claim 25, characterized in that, The composite particles were coated with carbon source 2 and a pore-forming agent and then sintered to obtain composite particles 2.

27. The preparation method according to claim 25, characterized in that, The sintering temperature for coating the composite particles with carbon source 3 and then sintering is 600~1100℃.

28. The preparation method according to claim 25, characterized in that, The sintering temperature for coating the composite particles with carbon source 3 and then sintering is 700~1000℃.

29. The preparation method according to claim 25, characterized in that, The sintering time for coating the composite particles with carbon source 3 and then sintering is 2-6 hours.

30. The preparation method according to claim 26, characterized in that, The composite particles were coated with carbon source 2 and pore-forming agent and then sintered at a temperature of 700~1000℃.

31. The preparation method according to claim 26, characterized in that, The composite particles were coated with carbon source 2 and pore-forming agent and then sintered at a temperature of 800~900℃.

32. The preparation method according to claim 26, characterized in that, The sintering time for coating the composite particles with carbon source 2 and pore-forming agent and then sintering is 1~3h.

33. The preparation method according to claim 25, characterized in that, The coating is a solid phase coating.

34. An electrode, characterized in that, It includes an electrode current collector and an electrode active material layer coated on the surface of the electrode current collector, wherein the electrode active material layer comprises a core-shell structured micron-sized silicon-carbon composite material as described in any one of claims 1 to 24.

35. The electrode according to claim 34, characterized in that, The electrode is the negative electrode.

36. A battery, characterized in that, It includes a positive electrode, a negative electrode, a membrane, and an electrolyte, wherein the negative electrode is the electrode described in claim 34 or 35.

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