Micron silicon-carbon composite material with core-shell structure and a method for its manufacture, as well as an electrode and a battery

Abstract

The present application discloses a micron silicon-carbon composite material with a core-shell structure, comprising: a core formed from micron silicon and a carbon shell layer applied to the core, the carbon shell layer comprising, from the inside out, successively: a compact carbon layer 1, a porous carbon layer, and a compact carbon layer 2. The present application further discloses a manufacturing process for the micron silicon-carbon composite material with a core-shell structure, an electrode comprising the micron silicon-carbon composite material with a core-shell structure, a battery comprising the electrode, a circuit comprising the battery, and an electrical device comprising the circuit.

Description

Core-shell structure micron silicon-carbon composite material and preparation method, electrode and battery Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a core-shell structured micron silicon-carbon composite material and a preparation method thereof, as well as an electrode and a battery comprising the core-shell structured micron silicon-carbon composite material. Background Art

[0002] Currently, silicon, due to its high specific capacity, is the most promising anode material for next-generation lithium batteries. Nanostructured silicon can mitigate the fragmentation of silicon particles to a certain extent, making it a key research area. However, nanostructured silicon is difficult to prepare and suffers from high cost, poor batch stability, high activity, easy oxidation, agglomeration, and difficulty in dispersion.

[0003] Micronized silicon can solve these problems and is gaining increasing attention due to its low cost, simple preparation process, and high initial efficiency. However, compared to nanosized silicon, micronized silicon suffers from a more dramatic volume expansion effect and poorer electronic conductivity, leading to a rapid decline in its cycling performance. Conventional core-shell structures also struggle to withstand silicon's volume expansion.

[0004] Currently, there are very few technologies involving the improvement of micron silicon structures, and all of them are based on nano-silicon to construct silicon-carbon materials. In order to alleviate the volume effect of nano-silicon materials and maintain the integrity of the particles, the construction of porous structures such as core-shell structures to provide space for expansion is the current main improvement method. However, the cavities in the above structures are directly connected to the silicon material, resulting in the inability of electrons and ions to form surface diffusion, only point diffusion; at the same time, the stress-free coating layer caused by the reserved space will cause the primary particles of the silicon particles to rupture during the cycle to scatter in the reserved space, interrupting the diffusion path of lithium ions and electrons; in summary, the impedance in the electrochemical process continues to increase, the cycle performance decreases, and further performance improvement cannot be achieved.

[0005] Summary of the Invention

[0006] In order to overcome the technical difficulties of using micron silicon particles as electrode materials in the existing technology, the present application aims to provide a core-shell structured micron silicon-carbon composite material and a method for preparing the core-shell structured micron silicon-carbon composite material, which effectively improves the cycle performance and coulombic efficiency of the battery.

[0007] The specific technical solutions of this application are as follows:

[0008] 1. A core-shell structured micron silicon-carbon composite material, characterized in that it comprises:

[0009] a core formed of micrometers of silicon; and

[0010] A carbon shell layer coated on the core, wherein the carbon shell layer comprises a first dense carbon layer, a porous carbon layer and a second dense carbon layer in sequence from the inside to the outside.

[0011] 2. The core-shell structured micron silicon-carbon composite material according to item 1 is characterized in that the average particle size D50 of the micron silicon is 1 to 8 μm and the sphericity is 0.3 to 0.95.

[0012] 3. The core-shell structured micron silicon-carbon composite material according to item 1 or 2, characterized in that the thickness of the dense carbon layer 1 is 0.05% to 1%, preferably 0.1% to 0.4%, of the average particle size D50 of the micron silicon;

[0013] Preferably, the porosity of the dense carbon layer 1 is 10% to 50%, preferably 10% to 30%.

[0014] 4. The core-shell structured micron 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 silicon, preferably 10% to 20%;

[0015] Preferably, the pores of the porous carbon layer are formed by a pore former and an etchant, and the pore former 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;

[0016] Preferably, the average particle size D50 of the pore-forming agent is 50 to 500 nm, preferably 50 to 200 nm;

[0017] Preferably, the average pore size of the porous material is not less than the average particle size D50 of the pore-forming agent;

[0018] Preferably, the etchant is selected from one, two or three of hydrochloric acid, nitric acid and hydrofluoric acid.

[0019] 5. The core-shell structured micron silicon-carbon composite material according to any one of items 1 to 4, characterized in that the thickness of the second dense carbon layer is 0.05% to 1%, preferably 0.1% to 0.2%, of the average particle size D50 of the micron silicon;

[0020] Preferably, the porosity of the second dense carbon layer is 5% to 30%, preferably 5% to 25%.

[0021] 6. The core-shell structured micron silicon-carbon composite material according to any one of items 1 to 5, characterized in that the Shore hardness of the carbon shell layer is 10 to 50 HSD, preferably 25 to 40 HSD.

[0022] 7. The core-shell structured micron silicon-carbon composite material according to any one of items 1 to 6, characterized in that the carbon source of the dense carbon layer is selected from one or more of asphalt, phenolic resin, humic acid, tannic acid, polymerized dopamine, polypyrrole, methane and ethane; or

[0023] The carbon source of the porous carbon layer is selected from one or more of asphalt, phenolic resin, humic acid, tannic acid, polymerized dopamine, polypyrrole, methane and ethane; or,

[0024] The carbon source of the dense carbon layer 2 is selected from one or more of asphalt, phenolic resin, humic acid, tannic acid, polymerized dopamine, polypyrrole, methane and ethane.

[0025] 8. The core-shell structured micron silicon-carbon composite material according to any one of items 1 to 7, characterized in that the core-shell structured micron silicon-carbon composite material has a true density of 1.2 to 2.1 g / cc, preferably 1.4 to 1.8 g / cc.

[0026] 9. A method for preparing a core-shell structured micron silicon-carbon composite material, characterized in that it comprises the following steps:

[0027] Using a carbon source to coat micron silicon, a composite particle comprising micron silicon and a dense carbon layer is obtained;

[0028] Coating the composite particle one with a second carbon source and a pore-forming agent to obtain a second composite particle;

[0029] Sintering the composite particles 2 under an inert atmosphere and dispersing them in an etchant to obtain composite particles 3 comprising micron silicon, a dense carbon layer 1 and a porous carbon layer;

[0030] The composite particles are coated with a third carbon source and sintered to obtain a core-shell structured micron silicon-carbon composite material comprising micron silicon, a first dense carbon layer, a porous carbon layer and a second dense carbon layer.

[0031] 10. The method for preparing a core-shell structured micron silicon-carbon composite material according to item 9 is characterized in that the composite particle 1 is coated with a carbon source 2 and a pore-forming agent, and sintered to obtain a composite particle 2.

[0032] 11. The preparation method according to item 9 or 10 is characterized in that the sintering temperature after coating the composite particle three with carbon source three and then sintering is 600-1100°C, preferably 700-1000°C, and the sintering time after coating the composite particle three with carbon source three and then sintering is preferably 2-6h.

[0033] 12. The preparation method according to item 10 is characterized in that the sintering temperature after sintering the composite particle 1 after coating with carbon source 2 and a pore-forming agent is 700-1000°C, preferably 800-900°C, and the sintering time after sintering the composite particle 1 after coating with carbon source 2 and a pore-forming agent is preferably 1-3h.

[0034] 13. The preparation method according to any one of items 9 to 12, characterized in that the coating is solid phase coating.

[0035] 14. A core-shell structured micron silicon-carbon composite material prepared by the preparation method described in any one of items 9 to 13.

[0036] 15. The core-shell structured micron 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 silicon is crystalline micron silicon, and its average particle size D50 is 1 to 8 μm and its sphericity is 0.3 to 0.8.

[0037] 16. The core-shell structured micron 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 silicon is spherical micron silicon, the interior of which is crystalline silicon and the surface is amorphous silicon, and the average particle size D50 of the spherical micron silicon is 1 to 8 μm and the sphericity is 0.7 to 0.95;

[0038] Preferably, the average particle size D50 of the spherical micron silicon is 2 to 5 μm;

[0039] Preferably, the sphericity of the spherical micron silicon is 0.8 to 0.95;

[0040] Preferably, the specific surface area of ​​the spherical micron silicon is 0.5 to 5 m 2 / g, preferably 1 to 4 m 2 / g;

[0041] Preferably, the thickness of the amorphous silicon is 1 to 20 nm, preferably 2 to 10 nm.

[0042] 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 the core-shell structured micron silicon-carbon composite material according to any one of items 1 to 8 and 14, or the core-shell structured micron silicon-carbon composite material prepared by the preparation method according to any one of items 9 to 13;

[0043] Preferably, the electrode is a negative electrode.

[0044] 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 item 17.

[0045] Effects of the Invention

[0046] (1) The core-shell structure micron silicon-carbon composite material of the present application has a specific structure of micron silicon-dense carbon layer 1-porous carbon layer-dense carbon layer 2. The carbon layers are organically connected and do not exist as separate components. The dense carbon layer 1 tightly wraps the micron silicon, providing inward pressure during the cycle, maintaining physical contact between small particles generated after the micron silicon particles are broken, and at the same time acts as an expansion force transmission medium to transmit stress to the porous carbon layer for absorption; and avoids direct contact between silicon and the cavities in the porous carbon layer, preventing fine particles of silicon after breaking 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 utilizing the reverse effect of stress to compress the dense carbon layer 1 in the delithiation state, so that the dense carbon layer 1 tightly wraps the micron silicon particles broken after the electrochemical process, maintaining the ion / electron channel. The dense carbon layer II acts as a strong coating, maintaining the structural integrity and mechanical stability of the porous carbon layer when subjected to the expansion stress of micron-silicon. Combining with the porous carbon layer, the dense carbon layer II effectively absorbs and releases the expansion stress. Simultaneously, the dense carbon layer II isolates the electrolyte from infiltration, preventing side reactions between the porous carbon layer's numerous active sites and the electrolyte, thereby improving cycling performance and coulombic efficiency.

[0047] (2) The porous carbon layer of the core-shell structured micron silicon-carbon composite material of the present application has a carbon pillar connecting the dense carbon layer 1 and the dense carbon layer 2. The carbon pillar plays a role in conducting ions and electrons during the electrochemical process, thereby avoiding the presence of a cavity layer in the core-shell structure that blocks the conduction of ions and electrons.

[0048] (3) The core-shell structured micron silicon-carbon composite material of the present application can not only alleviate the volume expansion of micron silicon and maintain the stability of the particles, but also provide an inward pressure on the particles that are broken after the cycle, maintain the physical contact of the primary particles after the breakage, maintain the diffusion path of electrons and ions, and improve the cycle performance.

[0049] (4) This application starts with the structural modification of micron silicon and effectively promotes the practical application of micron silicon. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG1 is a schematic structural diagram of a core-shell structured micron silicon-carbon composite material according to a specific embodiment of the present application.

[0051] FIG2 is a TEM image of spherical micron silicon according to a specific embodiment of the present application.

[0052] Explanation of symbols

[0053] 1 micron silicon 2 dense carbon layer 3 porous carbon layer

[0054] 4Dense carbon layer 5Crystalline silicon 6Amorphous silicon DETAILED DESCRIPTION

[0055] The present application is described in detail below. Although 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 by the embodiments described herein. Instead, 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.

[0056] It should be noted that the terms "including" and "comprising" used throughout the specification and claims are open-ended and should be interpreted as "including but not limited to." The specification subsequently describes preferred embodiments of the present application. However, such descriptions are intended to provide a general understanding of the specification and are not intended to limit the scope of the present application. The scope of protection of the present application shall be determined by the appended claims.

[0057] 1. Core-shell structure micron silicon-carbon composite material

[0058] In one aspect, the present application provides a core-shell structured micron silicon-carbon composite material comprising:

[0059] a core formed of micrometers of silicon; and

[0060] A carbon shell layer coated on the core, wherein the carbon shell layer comprises a first dense carbon layer, a porous carbon layer and a second dense carbon layer in sequence from the inside to the outside.

[0061] The core-shell structure micron silicon-carbon composite material of the present application constructs the cavity in the carbon coating layer, avoiding the obstruction of ion and electron conduction caused by direct contact between the cavity and silicon. The internal dense carbon layer 1 wraps the micron silicon, and the coating layer forms an inward pressure during circulation to ensure that the particles of the micron silicon are still in physical contact after being broken, and maintain electronic and ionic conductivity. The dense carbon layer 2 on the surface is combined with the internal porous carbon layer to jointly absorb and release the expansion stress. At the same time, the dense carbon layer 2 isolates the infiltration of the electrolyte, avoiding the numerous active sites of the porous carbon layer from side reactions with the electrolyte, thereby improving the cycle performance and coulombic efficiency.

[0062] In this application, "from inside to outside" refers to the direction from the inner core to the carbon shell.

[0063] In a specific embodiment, as shown in Figure 1, the core-shell structured micron silicon-carbon composite material consists of: a core formed of micron silicon 1 and a carbon shell layer coated on the core, wherein the carbon shell layer includes a dense carbon layer 2, a porous carbon layer 3 and a dense carbon layer 4 from the inside to the outside.

[0064] In a specific embodiment, the average particle size D50 of the micron silicon of the present application is 1 to 8 μm, for example, 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 to 0.95, for example, 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, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75 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.

[0065] The "average particle size D50" used herein refers to the particle size at which the cumulative particle size distribution of a sample reaches 50%. Its physical meaning is that particles smaller than this diameter account for 50% of the total particle size. Particle size distribution can be measured using conventional instruments used by those skilled in the art, such as a laser particle size analyzer.

[0066] The term "sphericity" used in this application is a parameter that characterizes particle morphology. The closer a particle's morphology is to a sphere, the closer its sphericity is to 1. The 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 1, while the sphericity of other objects is less than 1. The formula for the sphericity of any particle is: Wherein, ψ is the particle sphericity, Vp is the particle volume, and Sp is the particle surface area. The sphericity of the present application can be detected, for example, by the specific method given in the examples, using a dynamic image particle analyzer.

[0067] In a specific embodiment, the thickness of the dense carbon layer 1 is 0.05% to 1% of the average particle size D50 of the micron 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%. The dense carbon layer 1 wraps the micron silicon, and the coating layer forms inward pressure during circulation to ensure that the micron silicon particles maintain physical contact after being broken, maintaining electronic and ionic conductivity; if the thickness of the dense carbon layer 1 is too small, it cannot withstand the expansion of the micron silicon and transfers its expansion stress to the porous carbon layer, resulting in 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 1 is too large, the electronic conduction channel is affected, while also affecting the specific capacity and initial efficiency of the material.

[0068] The thickness of the dense carbon layer 1 of the present application can be obtained by taking the average value of multiple point 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.

[0069] In a specific embodiment, the porosity of the dense carbon layer 1 is 10% to 50%, for example, 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 dense carbon layer 1 needs to transfer the force of the expansion of the micron silicon to the porous carbon layer, and it is subjected to a very large force in this process. The smaller porosity of the present application can reduce defects in the carbon layer structure and increase the yield strength of the material. The porosity of the dense carbon layer 1 of the present application can be measured, for example, by a true density tester.

[0070] In a specific embodiment, the thickness of the porous carbon layer is 5% to 25% of the average particle size D50 of the micron silicon, for example, 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 of the present application can be obtained by taking the average value of multiple points measured by transmission electron microscopy, for example, 2 points, 3 points, 4 points, 5 points, 6 points, 7 points, 8 points, 9 points, 10 points, etc.

[0071] In one embodiment, the pores of the porous carbon layer are formed by a pore former and an etchant. The pore former is first added and mixed with a carbon source, and then an etchant capable of reacting with the pore former is added to form the pores. The reaction products of the pore former and the etchant, as well as excess etchant, can be removed by washing and subsequent sintering steps. The pore former can be 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; and the etchant can be selected from one, two, or three of hydrochloric acid, nitric acid, and hydrofluoric acid.

[0072] By controlling the amount of the pore-forming agent, the present invention can prevent the pore-forming agent particles from being in close contact with each other, thereby allowing the presence of carbon material. When the pore-forming agent is etched by the etchant, the carbon material previously present between the particles forms carbon pillars.

[0073] In one embodiment, the average particle size D50 of the pore-forming agent is 50 to 500 nm, for example, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc., preferably 50 to 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 the present application can be measured by gas permeation.

[0074] In one embodiment, the thickness of the second dense carbon layer is 0.05% to 1% of the average particle size D50 of the micron silicon, for example, 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 is coated on the porous carbon layer, sealing the porous carbon layer and isolating the electrolyte. If the thickness is too small, the pore structure of the porous carbon layer will be exposed, allowing the electrolyte to penetrate, causing the coating layer structure to lose its original function; if the thickness is too large, the coulombic efficiency of the composite material will be reduced. The thickness of the dense carbon layer 2 of the present application can be obtained by taking the average value of multiple point 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.

[0075] In a specific embodiment, the porosity of the dense carbon layer 2 is 5% to 30%, for example, 5%, 7%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, etc., preferably 5% to 25%. The dense carbon layer 2 works synergistically with the two internal coating layers to alleviate the expansion of micron silicon. During the cycle, it will be affected by the force of the expansion of micron silicon. If the porosity is too high, there will be many defects in the structure, the yield strength of the structure will decrease, and the structure will be destroyed during the cycle. At the same time, the dense carbon layer 2 also plays a role in isolating the electrolyte. Excessive porosity will lead to the infiltration of the electrolyte, thereby reducing the electrochemical performance of the material. The porosity of the dense carbon layer 2 of the present application can be measured, for example, by a true density tester.

[0076] In a specific embodiment, the Shore hardness of the carbon shell layer is 10 to 50HSD, for example, 20HSD, 25HSD, 30HSD, 35HSD, 40HSD, 45HSD, etc., preferably 25 to 40. The Shore hardness of the carbon shell layer in the present application refers to the Shore hardness of the carbon shell layer including the dense carbon layer 1, the porous carbon layer and the dense carbon layer 2. The "Shore hardness" in the present application refers to a test and expression method for the hardness of a material, which is measured using a Shore hardness tester. For example, the material can be mixed with a binder and then pressed into a tablet. The pressure is the maximum pressure that the particles can withstand without breaking (which can be observed and adjusted using a SEM), and then the tablet is used for measurement. The smaller the Shore hardness, the better the softness of the material, indicating the successful construction of the pore structure. However, a Shore hardness that is too small cannot maintain the structure of the coating layer itself and the stress generated by silicon expansion. Only an appropriate Shore hardness can maintain its own structural stability and absorb volume expansion.

[0077] In a specific embodiment, the true density of the core-shell structured micron silicon-carbon composite material is 1.2 to 2.1 g / cc, for example, 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 to 1.8 g / cc. "True density" in this application refers to the actual mass of a solid substance per unit volume in an absolutely dense state, that is, the density after removing internal pores or gaps between particles. The true density of this application is measured using a powder true density tester. For example, the sample can be placed in a true density tester, helium is used as the medium, the measuring chamber is gradually pressurized to a specified value, and 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, the volume of the measuring chamber and the expansion chamber is calibrated by a standard ball, and then the volume of the sample is determined to calculate the true density.

[0078] In a 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, for example, 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.

[0079] In one embodiment, the carbon sources of the first dense carbon layer, the porous carbon layer, and the second dense carbon layer can be completely identical, completely different, or not completely identical. The carbon source of the present application is not limited and can be any carbon source. The carbon source of each layer can be, for example, selected from one or more of asphalt, phenolic resin, humic acid, tannic acid, polymerized dopamine, polypyrrole, methane, and ethane, preferably selected from one or more of asphalt, phenolic resin, and humic acid.

[0080] In a specific embodiment, the carbon source of the dense carbon layer one 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 dense carbon layer two is selected from one or more of asphalt, phenolic resin and humic acid.

[0081] 2. Preparation method of core-shell structured micron silicon-carbon composite material

[0082] The inventors of the present application have discovered that the core-shell structured micron silicon-carbon composite material of the present application can be easily prepared using the following preparation method. Therefore, on the other hand, the present application also provides a method for preparing the core-shell structured micron silicon-carbon composite material, which comprises the following steps:

[0083] Using a carbon source to coat micron silicon, a composite particle comprising micron silicon and a dense carbon layer is obtained;

[0084] Coating the composite particle one with a second carbon source and a pore-forming agent to obtain a second composite particle;

[0085] Dispersing the composite particles 2 in an etchant to obtain composite particles 3 including micron silicon, a dense carbon layer 1 and a porous carbon layer;

[0086] The composite particles are coated with a third carbon source and sintered to obtain a core-shell structured micron silicon-carbon composite material comprising micron silicon, a first dense carbon layer, a porous carbon layer and a second dense carbon layer.

[0087] In a specific embodiment, the preparation method of the core-shell structured micron silicon-carbon composite material of the present application comprises the following steps:

[0088] Using a carbon source to coat micron silicon, a composite particle comprising micron silicon and a dense carbon layer is obtained;

[0089] Coating the composite particle one with a second carbon source and a pore-forming agent, and sintering to obtain a second composite particle;

[0090] Dispersing the composite particles 2 in an etchant to obtain composite particles 3 including micron silicon, a dense carbon layer 1 and a porous carbon layer;

[0091] The composite particles are coated with a third carbon source and sintered to obtain a core-shell structured micron silicon-carbon composite material comprising micron silicon, a first dense carbon layer, a porous carbon layer and a second dense carbon layer.

[0092] The present application does not impose any specific limitation on the etching time of the etchant, and an excess of etchant is sufficient.

[0093] In a specific embodiment, in a specific embodiment, the sintering temperature of the micron silicon coated with the carbon source two and then sintered is 700-1000°C, for example, it can be 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, etc., preferably 800-900°C, and the sintering time of the micron silicon coated with the carbon source two and then sintered is preferably 1-3h.

[0094] In a specific embodiment, the sintering temperature of the composite particles three after being coated with carbon source three and then sintered is 600-1100°C, for example, it can be 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 of the composite particles three after being coated with carbon source three and then sintered is preferably 2-6h.

[0095] There is no limitation on the sintering device in this application. Any device that can introduce atmosphere and increase sintering temperature can be used, such as a dry rotary kiln, an electric furnace, a tubular furnace, a box furnace, a roller kiln, etc. For example, sintering can be performed using an oxygen-acetylene flame, an oxygen-hydrogen flame, etc.

[0096] In a specific embodiment, the sintering of the present application is performed under an inert gas. The inert atmosphere of the present application is not limited and can be any inert atmosphere, such as nitrogen or argon.

[0097] In a specific embodiment, the coating is solid phase coating, for example, solid phase coating can be performed using a mechanical fusion machine.

[0098] In a specific embodiment, the porous carbon layer and the second dense carbon layer are both solid-phase coated, and the first dense carbon layer can be solid-phase coated, gas-phase coated or liquid-phase coated. Preferably, the first dense carbon layer is solid-phase coated.

[0099] In a specific embodiment, the sintering includes cooling.

[0100] In a specific embodiment, in the preparation method of the core-shell structured micron silicon-carbon composite material, the composite particles are dispersed in an etchant, stirred, filtered, washed, and dried to obtain composite particles three including micron silicon, a dense carbon layer, and a porous carbon layer.

[0101] On the other hand, the present application also provides a core-shell structured micron silicon-carbon composite material prepared by any of the aforementioned preparation methods.

[0102] 3. Micron silicon

[0103] In the core-shell structured micron silicon-carbon composite material of the present application, or in the preparation method of the core-shell structured micron silicon-carbon composite material of the present application, the micron silicon may be crystalline silicon, or spherical micron silicon in which amorphous silicon covers crystalline silicon.

[0104] 3.1. Crystalline Micron Silicon

[0105] The average particle size D50 of the crystalline micron silicon of the present application is 1 to 8 μm, for example, 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 to 0.8, for example, 0.3, 0.31, 0.32, 0.33, 034, 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, 0.49, 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.

[0106] 3.2. Spherical Microsilicon

[0107] The interior of the spherical micron silicon of the present application is crystalline silicon and the surface is amorphous silicon. The average particle size D50 of the spherical micron silicon is 1 to 8 μm, for example, 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 to 0. 95, for example, it 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.

[0108] Existing micronized silicon is an irregular crystalline silicon with numerous sharp corners on its surface. Crystalline silicon is anisotropic and expands in different directions. During lithium insertion into silicon, this anisotropic volume expansion can easily cause failure at these corners or damage particle integrity. The spherical micronized silicon in this application has a certain thickness of amorphous silicon on its surface. This is isotropic and expands in the same direction in all directions, resulting in uniform forces acting on its outer coating in all directions, which helps maintain the stability of the particle structure during electrochemical processes.

[0109] In a specific embodiment, the average particle size D50 of the spherical micron silicon of the present application is 2 to 5 μm; and the sphericity of the spherical micron silicon is 0.8 to 0.95.

[0110] In a specific embodiment, the specific surface area of ​​the spherical micron silicon of the present application is 0.5 to 5 m 2 / g, for example, 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, etc., preferably 1 to 4 m 2 / g.

[0111] The specific surface area of ​​the spherical micron silicon of the present application can be measured by the specific method given in the examples, using a BET specific surface tester.

[0112] The spherical micron silicon particles of the present application have a moderate size distribution and high sphericity. Such structural advantages give them a lower specific surface area, higher particle fluidity and higher tap density, thereby reducing the difficulty of subsequent processes and facilitating the maintenance of particle structure stability during the electrochemical process.

[0113] In a specific embodiment, the thickness of the amorphous silicon in the spherical micron silicon of the present 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 by, for example, performing multi-point measurement and taking the average value through 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.

[0114] The structure of the spherical micron-silicon of the present application is shown in the TEM image of Figure 2. The portion on the left side of the image with visible lattice fringes represents the crystalline silicon 5 within the spherical micron-silicon; the portion on the right side without lattice fringes represents the amorphous silicon 6 in the outer layer of the spherical micron-silicon. In one specific embodiment, as shown in Figure 2, the thickness of the outer amorphous silicon layer is 10 nm.

[0115] 3.3. Preparation of spherical micronized silicon

[0116] The spherical micron silicon of the present application can be simply prepared by the following method, which includes the following steps:

[0117] The crystalline micron silicon is sintered, kept warm, cooled and crushed in an inert atmosphere to obtain spherical micron silicon.

[0118] Here, the crystalline micron silicon is crystalline micron silicon of the prior art. In one specific embodiment, the average particle size D50 of the crystalline micron silicon is 1 to 8 μm, for example, 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. The sphericity of the crystalline micron silicon is 0.3 to 0.7, for example, 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 silicon of the present application is less than or equal to the average particle size D50 of the crystalline micron silicon, and the sphericity of the spherical micron silicon of the present application is greater than the sphericity of the crystalline micron silicon.

[0119] Here, the inert atmosphere is not limited and can be any inert atmosphere, such as nitrogen or argon.

[0120] In a specific embodiment, the sintering temperature is 1300-1600°C, for example, it can be 1300°C, 1310°C, 1320°C, 1330°C, 1340°C, 1350°C, 1360°C, 1370°C, 1380°C, 1390°C, 1400°C, 1410°C, 1420°C, 1430°C, 144°C, 1450°C, 1460°C, 1470°C, 1480°C, 1490°C, 1500°C, 1510°C, 1520°C, 1530°C, 1540°C, 1550°C, 1560°C, 1570°C, 1580°C, 1590°C, 1600°C, etc., preferably 1400-1500°C. The temperature is raised to near the melting point of crystalline silicon. Since the reaction activity at the corners is higher than that of the bulk, the corners melt first. As a result, the silicon material at the corners reorganizes or shifts due to surface tension, transforming the corners into a smooth structure and increasing the sphericity. The present application does not limit the sintering apparatus. Any apparatus capable of sintering and heating can be used, such as a dry rotary kiln, an electric furnace, a tubular furnace, a box furnace, a roller kiln, etc. For example, sintering can be performed using an oxygen-acetylene flame, an oxygen-hydrogen flame, etc.

[0121] In a 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.

[0122] In one embodiment, the sintering temperature is greater than 1300°C. When the temperature reaches 1300°C, the temperature is increased to the sintering temperature at a rate of 3-6°C / min. When the temperature reaches 1300°C, the rate of increase should be adjusted to avoid excessive melting of silicon corners, which may cause particle adhesion. Although adhesion can be broken, the crushing process may also create corners.

[0123] In one embodiment, the holding time is 0.5 to 10 hours, for example, 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 holding time is too short, the edges and corners are not fully melted, and the sphericity is not high. If the holding time is too long, the edges and corners are fully melted and may cause contact transfer between the particles, resulting in adhesion.

[0124] In a specific embodiment, the cooling rate is 10 to 100°C / min, for example, 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 to 80°C / min. The cooling rate is controlled to dislocate the crystal form and form a layer of amorphous silicon. The cooling rate is controlled at 10 to 100°C / min, and the thickness of the amorphous silicon can reach 1 to 20 nm. There is no limitation on the cooling device in this application, and any device that can cool the temperature can be used, for example, it can be a method of purging a low-temperature inert atmosphere.

[0125] When the core-shell composite material comprising spherical micron-silicon described herein is used in a lithium-ion battery, the spherical micron-silicon expands isotropically. Its spherical structure improves the continuity of the surface coating, ensuring uniform stress on the coating during expansion. This composite material overcomes the significant expansion effect of the micron-silicon, thereby reducing battery deformation during cycling and improving battery safety. Furthermore, the composite material maintains structural stability during cycling, preventing the growth of irreversible SEI films on the interface and electrolyte infiltration, thereby improving the battery's cycling performance.

[0126] 4. Electrodes

[0127] In another aspect, the present application further provides an electrode, comprising an electrode current collector and an electrode active material layer coated on the electrode current collector, wherein the electrode active material layer comprises at least spherical micron silicon as the electrode active material, wherein the spherical micron silicon is any of the aforementioned spherical micron silicon or spherical micron silicon prepared using any of the aforementioned preparation methods of the present application. The electrode active material layer may further comprise any of the aforementioned core-shell structure composite materials of the present application. The electrode of the present application is preferably a negative electrode.

[0128] 4.1. Electrode active materials

[0129] The electrode active material of the present application may be a negative electrode active material, and there is no particular limitation thereto. Negative electrode active materials commonly used in the art may be used.

[0130] Preferably, the electrode active material uses the spherical micron silicon of the present application as a main component.

[0131] In addition to the spherical micron silicon of the present application, the electrode active material layer may further include other electrode active materials. Other electrode active materials are described below.

[0132] As the negative electrode active material, for example, the following can be cited: graphite as highly crystalline carbon (natural graphite, artificial graphite, etc.), low crystalline carbon (soft carbon), hard carbon, carbon black (Ketjen Black (registered trademark), acetylene black, channel black, lamp black, oil furnace black, thermal black, etc.), fullerene, carbon nanotube, carbon nanofiber, carbon nanonub, carbon fiber filament, etc. carbon materials. In addition, as the negative electrode active material, the following can also be cited: elemental substances of elements 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, etc., oxides and carbides containing these elements. As such oxides, silicon monoxide (SiO), SiO x (0 < x < 2), tin dioxide (SnO2), SnO x (0 < x < 2), SnSiO3, etc. As carbides, silicon carbide (SiC), etc. can be cited. In addition, as the negative electrode active material, the following can also be cited: metal materials such as lithium metal, lithium-titanium composite oxides (for example, lithium titanate Li4Ti5O 12 ).) and other lithium-transition metal composite oxides. However, it is not limited to these materials, and conventionally well-known materials that can be used as the negative electrode active material for a lithium ion battery can be used. These negative electrode active materials can be used alone or in combination of two or more.

[0133] 4.2. Electrode current collector <0OO0290>The electrode current collector of the present application can be a negative electrode current collector, which is composed of a conductive material. There is no special 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 special limitation on the material constituting the electrode current collector. For example, it can be copper.

[0135] 4.3. Electrode

[0136] The electrode can be prepared by forming the active material layer on the electrode current collector by a conventionally well-known method, but it is not limited thereto. Those skilled in the art can select a suitable method to manufacture the electrode according to the type of battery to be manufactured.

[0137] The manufacture of electrodes using electrode active materials can be carried out using conventional methods. That is, the electrode active material and the conductive agent, as well as the binder and thickener used as needed, can be dry-mixed and formed into a sheet, and then the sheet material is pressed onto the electrode collector, or the materials are dissolved or dispersed in a liquid medium to form a slurry, and the slurry is applied to the electrode collector and dried to form an electrode active material layer on the electrode collector, thereby obtaining an electrode.

[0138] The conductive agent may include any other component that can function as a conductive agent. For example, it may include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbon materials such as amorphous carbon such as needle coke. These conductive agents may be used alone or in combination of two or more in any combination and ratio.

[0139] In addition, the electrode active material layer may further include a binder. There is no particular limitation on the binder used to produce the electrode active material layer. When a coating method is used, any binder can be used as long as it is soluble or dispersible in the liquid medium used to produce the electrode.

[0140] The solvent used to form the slurry is not particularly limited as long as it can dissolve or disperse the electrode active material, the conductive agent, the binder, and, if necessary, the thickener. Both aqueous solvents and organic solvents can be used.

[0141] Thickeners are generally used to adjust the viscosity of the slurry. The electrode active material layer may further include a thickener. There are no particular limitations on the thickener.

[0142] 5.Battery

[0143] The electrode of the present application can be used in a battery. Therefore, on the other hand, the present application also provides a battery, which includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the negative electrode is the negative electrode described above in the present application.

[0144] In this application, a battery refers to a single physical module that includes one or more 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.

[0145] The battery cells of the present application may include one or more of lithium-ion secondary batteries, lithium-ion primary batteries, lithium-sulfur batteries, sodium-lithium-ion batteries, sodium-ion batteries, and magnesium-ion batteries, and the present application is not limited to this. The battery cells of the present application may be cylindrical, flat, rectangular, or other shapes, and the embodiments of the present application are not limited to this. Battery cells are generally divided into three types according to the packaging method: cylindrical battery cells, square battery cells, and soft-pack battery cells, and the present application is not limited to this.

[0146] The separator is typically positioned between the positive electrode and the negative electrode. The separator's material and shape are not particularly limited, and any known separator can be used. For example, a separator made of resin, glass fiber, or an inorganic material can be used, preferably a porous sheet or non-woven fabric with excellent liquid retention.

[0147] An electrolyte is filled between the positive electrode and the negative electrode. The electrolyte can be an aqueous electrolyte or a non-aqueous electrolyte. In addition, the electrolyte can be an electrolyte solution, a polymer gel electrolyte, or a solid polymer electrolyte.

[0148] Example

[0149] This application provides a general and / or specific description of the materials and experimental methods used in the experiments. In the following examples, the reagents or instruments used without indicating the manufacturer are all conventional reagents or instruments that can be purchased commercially.

[0150] Example 1-1

[0151] The spherical micron silicon of this embodiment is prepared by the following steps:

[0152] 1 kg of crystalline micron 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, kept at that temperature for 5 hours, and then cooled to room temperature at a rate of 50°C / min. The silicon was taken out and crushed to obtain spherical micron silicon with a D50 of 4 μm and a sphericity of 0.8.

[0153] Example 1-2

[0154] The spherical micron silicon of this embodiment is prepared by the following steps:

[0155] 1 kg of crystalline micron 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, kept warm for 2 hours, and then cooled to room temperature at a rate of 100°C / min. The silicon was taken out and crushed to obtain spherical micron silicon with a D50 of 6 μm and a sphericity of 0.9.

[0156] Examples 1-3

[0157] The spherical micron silicon of this embodiment is prepared by the following steps:

[0158] 1 kg of crystalline micron silicon with a D50 of 2 μm and a sphericity of 0.6 was heated to 1400°C at a rate of 3°C / min under a nitrogen atmosphere, kept at that temperature for 4 hours, and then cooled to room temperature at a rate of 60°C / min. The silicon was taken out and crushed to obtain spherical micron silicon with a D50 of 2 μm and a sphericity of 0.95.

[0159] Examples 1-4

[0160] The spherical micron silicon of this embodiment is prepared by the following steps:

[0161] 1 kg of crystalline micron 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, kept at that temperature for 5 hours, and then cooled to room temperature at a rate of 80°C / min. The product was taken out and crushed to obtain spherical micron silicon with a D50 of 3 μm and a sphericity of 0.8.

[0162] Examples 1-5

[0163] The difference between this embodiment and embodiments 1-3 is that the sintering temperature is 1600°C.

[0164] Examples 1-6

[0165] The difference between this embodiment and embodiments 1-3 is that the sintering temperature is 1300°C.

[0166] Examples 1-7

[0167] The difference between this embodiment and embodiments 1-3 is that the sintering temperature is 1500°C.

[0168] Examples 1-8

[0169] The difference between this embodiment and embodiments 1-3 is that the heating rate is 1° C. / min.

[0170] Examples 1-9

[0171] The difference between this embodiment and embodiments 1-3 is that the heating rate is 10° C. / min.

[0172] Examples 1-10

[0173] The difference between this embodiment and embodiments 1-3 is that the holding time is 0.5 h.

[0174] Examples 1-11

[0175] The difference between this embodiment and embodiments 1-3 is that the holding time is 10 hours.

[0176] Examples 1-12

[0177] The difference between this embodiment and embodiments 1-3 is that the cooling rate is 10° C. / min.

[0178] Examples 1-13

[0179] The difference between this embodiment and embodiments 1-3 is that the cooling rate is 100° C. / min.

[0180] Examples 1-14

[0181] The difference between this embodiment and embodiment 3 is that the cooling rate is 50° C. / min.

[0182] Examples 1-15

[0183] The difference between this embodiment and embodiments 1-3 is that the cooling rate is 80° C. / min.

[0184] The parameter conditions, reagents, product parameters, etc. of each embodiment are listed in the following Tables 1 and 2:

[0185] Table 1

[0186]

[0187] Table 2

[0188]

[0189] Example 2-1

[0190] (1) 1 kg of crystalline micron silicon with a D50 of 4 μm and a sphericity of 0.8 was mixed evenly with 100 g of asphalt and placed in a mechanical fusion machine for coating to obtain composite particles 1;

[0191] (2) 100 g of asphalt, 300 g of nano-magnesium oxide with a D50 of 200 nm, and 1 kg of composite particle 1 were mixed uniformly, placed in a mechanical fusion machine for coating, and sintered at 800 ° C for 4 h under a nitrogen atmosphere, and then cooled to obtain composite particle 2;

[0192] (3) dispersing the composite particles 2 in hydrochloric acid, stirring for 4 hours, filtering, washing, and drying to obtain composite particles 3;

[0193] (4) 1 kg of composite particles 3 was mixed evenly with 50 g of asphalt, mechanically fused, and sintered at 800 °C for 4 h in a nitrogen atmosphere to obtain a core-shell structured micron silicon-carbon composite material.

[0194] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 20 nm, the thickness of the porous carbon layer is 1 μm, and the thickness of the dense carbon layer 2 is 5 nm.

[0195] Example 2-2

[0196] The difference between this embodiment and embodiment 2-1 is that the sphericity of the crystalline micron silicon is 0.3.

[0197] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 14 nm, the thickness of the porous carbon layer is 0.8 μm, and the thickness of the dense carbon layer 2 is 4 nm.

[0198] Example 2-3

[0199] The difference between this embodiment and embodiment 2-1 is that the D50 of the crystalline micron silicon is 8 μm.

[0200] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 12 nm, the thickness of the porous carbon layer is 0.64 μm, and the thickness of the dense carbon layer 2 is 3.2 nm.

[0201] Examples 2-4

[0202] The difference between this embodiment and embodiment 2-1 is that the pore-forming agent is nano-alumina.

[0203] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 20 nm, the thickness of the porous carbon layer is 0.92 μm, and the thickness of the dense carbon layer 2 is 5 nm.

[0204] Examples 2-5

[0205] The difference between this embodiment and embodiment 2-1 is that the average particle size D50 of the pore-forming agent is 50 nm.

[0206] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 20 nm, the thickness of the porous carbon layer is 1.24 μm, and the thickness of the dense carbon layer 2 is 3.6 nm.

[0207] Examples 2-6

[0208] The difference between this embodiment and embodiment 2-1 is that the average particle size D50 of the pore-forming agent is 500 nm.

[0209] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 20 nm, the thickness of the porous carbon layer is 0.76 μm, and the thickness of the dense carbon layer 2 is 6 nm.

[0210] Examples 2-7

[0211] The difference between this embodiment and embodiment 2-1 is that the carbon source in steps (1), (2) and (4) is phenolic resin.

[0212] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 16 nm, the thickness of the porous carbon layer is 0.68 μm, and the thickness of the dense carbon layer 2 is 4 nm.

[0213] Examples 2-8

[0214] The difference between this embodiment and embodiment 2-1 is that the carbon source in steps (1), (2) and (4) is humic acid.

[0215] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 16 nm, the thickness of the porous carbon layer is 1.12 μm, and the thickness of the dense carbon layer 2 is 6 nm.

[0216] Examples 2-9

[0217] The difference between this embodiment and embodiment 2-1 is that the amount of nano magnesium oxide is 100 g.

[0218] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 20 nm, the thickness of the porous carbon layer is 0.2 μm, and the thickness of the dense carbon layer 2 is 5 nm.

[0219] Example 2-10

[0220] The difference between this embodiment and embodiment 2-1 is that the amount of nano magnesium oxide is 250 g.

[0221] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 20 nm, the thickness of the porous carbon layer is 0.6 μm, and the thickness of the dense carbon layer 2 is 5 nm.

[0222] Example 2-11

[0223] The difference between this embodiment and embodiment 2-1 is that the sintering temperature in steps (2) and (4) is both 1000°C.

[0224] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 18 nm, the thickness of the porous carbon layer is 0.88 μm, and the thickness of the dense carbon layer 2 is 4 nm.

[0225] Example 2-12

[0226] The difference between this embodiment and embodiment 2-1 is that the sintering temperature in steps (2) and (4) is both 700°C.

[0227] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the dense carbon layer 1 is 24 nm, the thickness of the porous carbon layer is 1.24 μm, and the thickness of the dense carbon layer 2 is 7.2 nm.

[0228] Example 2-13

[0229] The difference between this embodiment and embodiment 2-1 is that the amount of carbon source 1 is 200 g and the amount of carbon source 3 is 400 g.

[0230] Examples 2-14

[0231] The difference between this embodiment and embodiment 2-11 is that the crystalline micron silicon with D50 of 4 μm and sphericity of 0.8 is replaced by the spherical micron silicon with D50 of 4 μm, sphericity of 0.8, crystalline silicon inside and amorphous silicon on the surface prepared in embodiment 1-1.

[0232] Comparative Example 1

[0233] (1) 1 kg of crystalline micron silicon with a D50 of 4 μm and a sphericity of 0.8 was mixed evenly with 250 g of asphalt, placed in a mechanical fusion machine for coating, and sintered at 800°C for 4 h in a nitrogen atmosphere to obtain a core-shell structured micron silicon-carbon composite material of this comparative example.

[0234] In the obtained core-shell structured micron silicon-carbon composite material, the thickness of the carbon layer is 55 nm.

[0235] Table 3

[0236]

[0237] Table 4

[0238]

[0239]

[0240] Test Example 1 Lithium Battery Preparation and Performance Testing

[0241] The core-shell structure composite material (90 wt%) obtained in Examples 2-1 to 2-13 was mixed with a conductive agent (1 wt% CNT and 3 wt% SP), a binder (4 wt% CMC and 2 wt% SBR) and deionized water to form a slurry, which was then coated, dried and cut to obtain lithium electrode sheets, where "wt%" represents the percentage of each component in the total weight of the core-shell structure composite material, the conductive agent and the binder. The lithium electrode sheets and conventional electrolyte were assembled into button-type half-cells for charge and discharge tests. The test conditions were: in the voltage range of 5mV-0.8V, activated at 0.1C / 0.1C for 2 cycles and cycled at 0.3C / 0.3C. After testing, the electrochemical performance parameters of the batteries made with the materials of Examples 2-1 to 2-13 are shown in Table 5 below.

[0242] Table 5

[0243] No. First reversible capacity First coulombic efficiency 50 cycles retention rate Example 2-1 281689.284 Example 2-2 282489.162 Example 2-3 286989.856 Example 2-4 282189.283

[0244] Example 2-5 278588.988 Example 2-6 280288.578 Example 2-7 267887.269 Example 2-8 284389.679 Example 2-9 282189.456 Example 2-10 284289.876 Example 2-11 286390.188 Example 2-12 276388.672 Example 2-13 195783.690 Example 2-14 285190.392 Comparative Example 1 276290.828

[0245] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application in any other manner. Any person skilled in the art may utilize the above disclosed technical content to modify or modify the present application into equivalent embodiments with equivalent variations. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present application and are based on the technical essence of the present application shall still fall within the scope of protection of the present application.

Claims

1. A core-shell structured micron silicon-carbon composite material, characterized in that: It includes: A core formed of micrometers of silicon; and A carbon shell layer coated on the core, wherein the carbon shell layer comprises a first dense carbon layer, a porous carbon layer and a second dense carbon layer in sequence from the inside to the outside.

2. The core-shell structured micron silicon-carbon composite material according to claim 1, characterized in that: The average particle size D50 of the micron silicon is 1 to 8 μm, and the sphericity is 0.3 to 0.

95.

3. The core-shell structured micron silicon-carbon composite material according to claim 1 or 2, characterized in that: The thickness of the dense carbon layer 1 is 0.05% to 1% of the average particle size D50 of the micron silicon, preferably 0.1% to 0.4%; Preferably, the porosity of the dense carbon layer 1 is 10% to 50%, preferably 10% to 30%.

4. The core-shell structured micron silicon-carbon composite material according to any one of claims 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 silicon, preferably 10% to 20%; Preferably, the pores of the porous carbon layer are formed by a pore former and an etchant, and the pore former 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; Preferably, the average particle size D50 of the pore-forming agent is 50 to 500 nm, preferably 50 to 200 nm; Preferably, the average pore size of the porous material is not less than the average particle size D50 of the pore-forming agent; Preferably, the etchant is selected from one, two or three of hydrochloric acid, nitric acid and hydrofluoric acid.

5. The core-shell structured micron silicon-carbon composite material according to any one of claims 1 to 4, characterized in that: The thickness of the second dense carbon layer is 0.05% to 1% of the average particle size D50 of the micron silicon, preferably 0.1% to 0.2%; Preferably, the porosity of the second dense carbon layer is 5% to 30%, preferably 5% to 25%.

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

7. The core-shell structured micron silicon-carbon composite material according to any one of claims 1 to 6, characterized in that: The carbon source of the dense carbon layer 1 is selected from one or more of asphalt, phenolic resin, humic acid, tannic acid, polymerized dopamine, polypyrrole, methane and ethane; or, The carbon source of the porous carbon layer is selected from one or more of asphalt, phenolic resin, humic acid, tannic acid, polymerized dopamine, polypyrrole, methane and ethane; or, The carbon source of the dense carbon layer 2 is selected from one or more of asphalt, phenolic resin, humic acid, tannic acid, polymerized dopamine, polypyrrole, methane and ethane.

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

9. A method for preparing a core-shell structured micron silicon-carbon composite material, characterized in that: It includes the following steps: Using a carbon source to coat micron silicon, a composite particle comprising micron silicon and a dense carbon layer is obtained; Coating the composite particle one with a second carbon source and a pore-forming agent to obtain a second composite particle; Sintering the composite particles (2) under an inert atmosphere and dispersing them in an etchant to obtain composite particles (3) comprising micron silicon, a dense carbon layer (1) and a porous carbon layer; The composite particles are coated with a third carbon source and sintered to obtain a core-shell structured micron silicon-carbon composite material comprising micron silicon, a first dense carbon layer, a porous carbon layer and a second dense carbon layer.

10. The method for preparing the core-shell structured micron silicon-carbon composite material according to claim 9, characterized in that: The composite particle one is coated with a second carbon source and a pore-forming agent, and sintered to obtain a second composite particle.

11. The preparation method according to claim 9 or 10, characterized in that: The sintering temperature of the composite particles three coated with carbon source three and then sintered is 600-1100° C., preferably 700-1000° C., and the sintering time of the composite particles three coated with carbon source three and then sintered is preferably 2-6 hours.

12. The preparation method according to claim 10, characterized in that The sintering temperature of the composite particle 1 coated with the carbon source 2 and the pore-forming agent and then sintered is 700-1000°C, preferably 800-900°C, and the sintering time of the composite particle 1 coated with the carbon source 2 and the pore-forming agent and then sintered is preferably 1-3h.

13. The preparation method according to any one of claims 9 to 12, characterized in that The coating is solid phase coating.

14. A core-shell structured micron silicon-carbon composite material prepared by the preparation method according to any one of claims 9 to 13.

15. The core-shell structured micron silicon-carbon composite material according to any one of claims 1 to 8, or the preparation method according to any one of claims 9 to 13, characterized in that: The micron silicon is crystalline micron silicon, with an average particle size D50 of 1 to 8 μm and a sphericity of 0.3 to 0.

8.

16. The core-shell structured micron silicon-carbon composite material according to any one of claims 1 to 8, or the preparation method according to any one of claims 9 to 13, characterized in that: The micron silicon is spherical micron silicon, the interior of which is crystalline silicon and the surface is amorphous silicon, the average particle size D50 of the spherical micron silicon is 1 to 8 μm, and the sphericity is 0.7 to 0.95; Preferably, the average particle size D50 of the spherical micron silicon is 2 to 5 μm; Preferably, the sphericity of the spherical micron silicon is 0.8 to 0.95; Preferably, the specific surface area of ​​the spherical micron silicon is 0.5 to 5 m 2 / g, preferably 1 to 4 m 2 / g; Preferably, the thickness of the amorphous silicon is 1 to 20 nm, preferably 2 to 10 nm.

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 the core-shell structure micron silicon-carbon composite material according to any one of claims 1 to 8 and 14, or the core-shell structure micron silicon-carbon composite material prepared by the preparation method according to any one of claims 9 to 13; Preferably, the electrode is a negative electrode.

18. A battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the negative electrode is the negative electrode according to claim 17.

Images