Silicon-carbon negative electrode material and lithium ion secondary battery

Abstract

The invention relates to the technical field of batteries, in particular to a silicon-carbon negative electrode material and a lithium ion secondary battery. The silicon-carbon negative electrode material comprises silicon-carbon particles, the silicon-carbon particles comprise a matrix, and the matrix comprises a porous carbon matrix and silicon particles located in internal holes of the porous carbon matrix; the porous carbon substrate is provided with open pores and closed pores, the open pores contain silicon particles, the closed pores contain an element K, and based on the total mass of the silicon carbon particles, the mass content of the element K is 50 ppm to 1000 ppm; the silicon-carbon particles comprise halogen, and based on the total mass of the silicon-carbon particles, the mass content of the halogen is 50 ppm to 2000 ppm; the silicon carbon particles and deionized water are mixed according to the mass ratio of 1: 10 to obtain an aqueous solution, the pH value of the aqueous solution at 25 DEG C is pH 1, and the pH 1 is 6-8. Comprising the silicon-carbon negative electrode material disclosed by the invention has the advantages that the expansion rate is improved, and the rate capability and the cycle performance are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a silicon-carbon anode material and a lithium-ion secondary battery including the silicon-carbon anode material. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have become the main power source for portable electronic devices and electric vehicles. However, with industry development, the relatively low theoretical capacity of graphite (372 mAh / g) limits further improvements in the energy density of lithium-ion batteries, making it unable to meet the demands of next-generation lithium-ion batteries. Silicon (Si), with its extremely high theoretical specific capacity (4200 mAh / g), moderate lithium intercalation potential, and abundant natural reserves, is considered the most promising next-generation anode material. However, when lithium ions intercalate / extract from the silicon crystal structure, it causes a huge volume change (approximately 300%) in the silicon material. Repeated expansion and contraction lead to particle pulverization, detachment of the active material from the current collector, and ultimately, rapid capacity decay and deterioration of the battery's cycle performance. Simultaneously, silicon particles have poor conductivity and poor kinetic performance. Related technologies often employ the method of depositing silicon particles within a porous carbon framework with predominantly open pores to limit the expansion of silicon particles during lithium intercalation, but the effect is not ideal. Therefore, it is of great significance to develop a negative electrode active material that can improve kinetic performance and volume expansion while possessing high energy density. Summary of the Invention

[0003] The purpose of this invention is to overcome the aforementioned problems in the prior art and to provide a silicon-carbon anode material and a lithium-ion secondary battery (hereinafter referred to as the battery) including the silicon-carbon anode material. The silicon-carbon anode material comprises silicon-carbon particles composed of a porous carbon matrix and silicon particles, wherein the porous carbon matrix has both closed and open pores. K and halogen elements are also introduced into the silicon-carbon particles. These silicon-carbon particles improve conductivity and alleviate the volume expansion of the material. The battery containing this anode active material exhibits good cycle performance and kinetic performance, with a reduced volume expansion rate.

[0004] The inventors of this invention have discovered that by introducing halogen elements into silicon-carbon particles for use in lithium-ion secondary batteries, the mechanical strength of the SEI film formed on the surface of silicon-carbon particles during battery cycling can be further enhanced, and the chemical composition of the SEI film can be improved. Typically, SEI films are mainly composed of inorganic components such as Li2CO3 and Li2O, and organic components such as alkyl lithium carbonate (ROCO2Li) and ether polymers. They are characterized by being porous, having poor uniformity, and low mechanical strength. In particular, the Young's modulus of the main component, Li2CO3, is only 2GPa-4GPa. However, the SEI film formed with the participation of halogens can have a rigid framework, improve the toughness of the SEI film, and significantly enhance the buffering effect of the SEI film on the volume expansion of silicon particles. It can resist expansion stress, maintain the structural stability and integrity of the SEI film on the surface of silicon-carbon particles, and prevent the SEI film from continuously breaking and reconstructing under stress, which would lead to continuous oxidation of the electrolyte and continuous consumption of active lithium, resulting in a decrease in battery cycle stability and a reduction in the first coulombic efficiency. Furthermore, the closed pores of the silicon-carbon particles also contain element K. When the pH of the aqueous solution of the silicon-carbon particles is limited to the range of 6-8, element K is mainly sealed in the closed pores. On the one hand, it can act as a flexible filler, providing reverse stress support for the amorphous carbon layer when the silicon particles expand in volume, effectively absorbing and dispersing the mechanical stress generated during the expansion of silicon particles, preventing the closed-pore structure from cracking during stress buffering and exposing the fresh surface to the electrolyte, thus improving the cycle stability of the battery. On the other hand, element K can also construct conductive pathways at the interface of silicon-carbon particles and inside the closed-pore structure, improving the overall conductivity of silicon-carbon particles, reducing the internal resistance of the battery, and improving rate performance. When the silicon-carbon material of this invention is applied to lithium-ion secondary batteries, it effectively alleviates the volume expansion of silicon-carbon particles during battery cycling and further improves the conductivity of silicon-carbon particles; thereby improving the overall cycle stability and kinetic performance of the battery.

[0005] Based on this, the present invention proposes the following technical solution:

[0006] The first aspect of this invention provides a silicon-carbon anode material, comprising silicon-carbon particles, the silicon-carbon particles comprising a matrix, the matrix comprising a porous carbon matrix and silicon particles located in the pores within the porous carbon matrix; the porous carbon matrix having open pores and closed pores, the open pores containing silicon particles, the closed pores containing element K, the mass content of element K being 50ppm-1000ppm based on the total mass of the silicon-carbon particles; the silicon-carbon particles comprising halogen, the mass content of halogen being 50ppm-2000ppm based on the total mass of the silicon-carbon particles; the silicon-carbon particles and deionized water are mixed at a mass ratio of 1:10 to obtain an aqueous solution, the pH value of the aqueous solution at 25°C being pH1, and pH1 being 6-8.

[0007] A second aspect of the present invention provides a lithium-ion secondary battery, the lithium-ion secondary battery comprising a negative electrode and an electrolyte, wherein the negative electrode comprises the silicon-carbon negative electrode material provided in the first aspect of the present invention.

[0008] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: (1) The negative electrode active material of the present invention improves structural stability and conductivity, and alleviates volume expansion during charging and discharging.

[0009] (2) The lithium-ion secondary battery of the present invention has good cycle stability and rate performance, and improves the volume expansion rate.

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0011] Figure 1 The image shown is a scanning electron microscope (SEM) image of silicon carbon particles in one embodiment of the present invention.

[0012] Figure 2 The diagram shown is a schematic representation of the structure of silicon-carbon particles in one embodiment of the present invention.

[0013] Figure 3 The image shown is an X-ray diffraction (XRD) pattern of silicon-carbon particles in one embodiment of the present invention.

[0014] Figure reference numerals: 11 is silicon particle, 12 is porous carbon matrix, 21 is closed pore, 22 is open pore, 31 is silicon dioxide phase, and 32 is amorphous carbon layer. Detailed Implementation

[0015] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0016] The first aspect of the present invention provides a silicon-carbon anode material, the silicon-carbon anode material comprising silicon-carbon particles, the silicon-carbon particles comprising a matrix, the matrix comprising a porous carbon matrix and silicon particles located in the pores inside the porous carbon matrix.

[0017] In one embodiment, the silicon particles comprise elemental silicon.

[0018] In this invention, the porous carbon matrix has open pores and closed pores, and the closed pores contain element K. Based on the total mass of the silicon-carbon particles, the mass content of element K is 50ppm-1000ppm, for example, 50ppm, 60ppm, 80ppm, 100ppm, 150ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 800ppm or 1000ppm.

[0019] In one embodiment, the mass content of element K is 100ppm-1000ppm based on the total mass of the silicon-carbon particles.

[0020] In this invention, the element K exists in the form of elemental potassium and potassium-containing compounds.

[0021] In one embodiment, the elemental potassium may be potassium nanoparticles. The potassium-containing compound may also include at least one of potassium-carbon compounds, potassium hydroxide, potassium chloride, and potassium bromide.

[0022] In this invention, the terms "open hole" and "closed hole" have conventional meanings in the art; the "open hole" refers to a pore structure that has good communication with the outer surface of the silicon-carbon particle and is in an open state; the "closed hole" generally refers to a pore structure located inside the silicon-carbon composite particle that is not in communication with its outer surface and is in a closed state.

[0023] In this invention, the silicon carbon particles include halogens, and the mass content of the halogens is 50ppm-2000ppm based on the total mass of the silicon carbon particles, for example, 50ppm, 60ppm, 80ppm, 100ppm, 150ppm, 200ppm, 300ppm, 400ppm, 500ppm, 1000ppm, 1500ppm or 2000ppm.

[0024] In one embodiment, the halogen content is 100ppm-800ppm based on the total mass of the silicon carbon particles.

[0025] In this invention, the halogen includes at least one of the elements Cl, F and Br.

[0026] In this invention, the silicon carbon particles and deionized water are mixed at a mass ratio of 1:10 to obtain an aqueous solution. The pH value of the aqueous solution of the silicon carbon particles at 25°C is pH1, which is 6-8, for example, 6, 6.2, 6.4, 6.8, 7, 7.5 or 8.

[0027] In this invention, pH1 can be determined as follows: the silicon carbon particles are dried in a vacuum oven at 60°C for 2 hours. The dried powder is then mixed with deionized water at a ratio of 1:10 and placed in a sealed container. The mixture is then sonicated at 25°C for 30 minutes. The solution is filtered using a 0.45 μm microporous membrane, and the pH of the collected filtrate is determined at 25°C to be pH1.

[0028] Understandably, pH 1 can reflect the presence of leached soluble alkaline substances in silicon-carbon particles. When pH 1 is within the aforementioned range, it indicates that most of the element K in the silicon-carbon particles is encapsulated within closed pores. When pH 1 is too high (e.g., >8), it indicates that there is too much soluble element K on the surface and in the open pores of the silicon-carbon particles. During battery charging and discharging, element K will dissolve in the electrolyte and migrate to the positive electrode, causing phase transitions or collapse of the positive electrode active material, resulting in battery capacity loss. In addition, element K will preferentially deposit on the material surface before lithium ions to form potassium dendrites, which may puncture the separator, causing an internal short circuit in the battery and triggering thermal runaway.

[0029] By incorporating element K (K) into closed pores and halogens (especially halogens located in open pores) within silicon-carbon particles, effective buffering of silicon material volume expansion and improved conductivity of silicon-carbon particles are achieved. First, the structure of the silicon-carbon particles is controlled so that both closed and open pores coexist within the particles. Unlike conventional silicon-carbon particles with almost no internal pores, the closed-pore structure of the silicon-carbon particles in this invention does not contain silicon particles. When this silicon-carbon anode material is applied to lithium-ion secondary batteries, the pore walls are not subjected to internal expansion stress during battery cycling. Simultaneously, it acts as a buffer against stress generated by volume changes in silicon particles within the open pores, dispersing external compressive stress, preventing the porous carbon matrix from cracking and failing, and improving the structural stability of the silicon-carbon particles. Second, external support is provided for the internal pore structure. Element K, located in the closed pores, can act as a flexible filler within the independent pore structure encased in a carbon layer. When the silicon material undergoes volume expansion, it can provide external support for the carbon particles. The layer provides reverse stress support, enhancing the absorption and dispersion of mechanical stress generated by volume expansion in the closed-cell structure, preventing the rupture of the closed-cell structure from exacerbating electrolyte and active lithium consumption, leading to battery capacity decay and a decrease in initial coulombic efficiency. Simultaneously, potassium has high electronic conductivity, which is beneficial for improving electron transport efficiency within the porous carbon matrix, thus improving the battery's rate performance. Finally, optimizing the mechanical strength and chemical composition of the SEI film by introducing halogens (e.g., elements F, Cl, and Br) into the silicon-carbon particles allows the formation of a LiF / LiCl / LiBr-rich SEI film on the surface of the silicon-carbon particles during battery cycling. LiF possesses a high Young's modulus (6 GPa-10 GPa) and low electronic conductivity (10 GPa-10 GPa). -10LiCl (S / cm) can effectively resist the expansion stress of silicon materials during lithium intercalation, while blocking electron transport and preventing the continuous decomposition of the electrolyte. Although the shear modulus of LiCl (2.5 GPa) is lower than that of LiF, it has higher toughness and can buffer local stress to prevent brittle fracture of the SEI film. At the same time, LiCl and LiF can form a composite SEI film, which promotes the uniform intercalation of lithium ions in silicon-carbon particles by reducing the diffusion barrier of lithium ions and inhibiting the formation of lithium dendrites. LiBr can preferentially react with acidic substances (such as HF) generated by the dissociation of lithium salts, thereby reducing the excessive decomposition of LiPF6 and inhibiting the generation of HF, which is beneficial to improving the stability of the SEI film. In addition, LiBr or its decomposition products (such as Br radicals or HBr) can react with LiPF6 in the electrolyte to promote the formation of a LiF-rich SEI film at the negative electrode.

[0030] When the content of element K in silicon-carbon particles is within the above range, it can not only improve the overall conductivity of silicon-carbon particles, but also alleviate volume expansion. When the content of element K in silicon-carbon particles is too low (e.g., <100ppm), it cannot form an effective filling in the closed pores to provide stress support for the closed pores, and the effect of alleviating volume expansion is not good. At the same time, it is also insufficient to improve the conductivity of silicon-carbon particles. When the content of element K in silicon-carbon particles is too high (e.g., >1000ppm), element K is easy to dissolve and react with the electrolyte to form KF precipitate, which blocks the ion channels and leads to a decrease in the first coulombic efficiency of silicon-carbon particles.

[0031] like Figure 1 The image shown is a SEM image of silicon-carbon particles according to an embodiment of the present invention. Figure 2 The diagram shows a schematic representation of the structure of silicon-carbon particles according to an embodiment of the present invention, wherein 11 is a silicon particle, 12 is a porous carbon matrix, 21 is a closed pore, 22 is an open pore, 31 is a silicon dioxide phase, 32 is an amorphous carbon layer, element K is distributed inside the closed pore 21, and halogens are distributed inside the open pore 22 and at the junction of silicon particle 11 and porous carbon matrix 12.

[0032] When the halogen content in silicon-carbon particles is within the aforementioned range, it ensures that a LiF / LiCl / LiBr-rich SEI film is formed in situ at the location of maximum stress during the first charge-discharge process of the battery, effectively mitigating the volume expansion of silicon materials. When the halogen content in silicon-carbon particles is too low (e.g., <100ppm), sufficient LiF / LiCl / LiBr cannot be generated in the SEI film formed during battery cycling, resulting in insignificant strengthening effect on the SEI film. The SEI film has low resistance to the expansion stress of silicon materials and is prone to repeated cracking and growth, leading to a decrease in the battery's initial coulombic efficiency and rate performance. When the halogen content in silicon-carbon particles is too high (e.g., >1000ppm), it leads to deterioration of SEI film properties, increased interfacial impedance, and may trigger corrosion side reactions, which is detrimental to the rapid increase in battery capacity and the improvement of internal resistance and cycle performance.

[0033] In this invention, the mass content of element K in the silicon-carbon particles can be obtained by conventional testing methods in the art, such as by inductively coupled plasma mass spectrometry (ICP-MS), specifically as follows: Take about 0.1g of silicon-carbon particles and add 10mL of mixed acid (hydrofluoric acid and nitric acid molar ratio of 1:4) for digestion on a hot plate at 350℃ for 120min. After cooling, make up to 100ml and then dilute 10 times. Take a portion of the solution for analysis by ICP-MS to obtain the mass content of element K in the silicon-carbon particles.

[0034] In this invention, the halogen content in the silicon-carbon particles can be obtained by conventional testing methods in the art, such as ion chromatography (IC), specifically as follows: the material is pretreated using the oxygen bomb combustion method, and tested using an ion chromatograph. The chromatographic column can be a Metrosep A Supp 4 series. The content of a certain halogen in the sample is calculated as [(C-C0)×V] / m, where C is the concentration of a certain halogen ion in the sample solution obtained from the calibration curve, in mg / L; C0 is the concentration of the same halogen ion in the blank solution, in mg / L; V is the final volume of the sample solution, in L; and m is the sample mass, in g.

[0035] In this invention, the silicon-carbon particles further include a carbon layer located on at least a portion of the outer surface of the matrix.

[0036] In one embodiment, the carbon layer includes an amorphous carbon layer with a thickness of 1 nm to 20 nm, such as 1 nm, 2 nm, 4 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm or 20 nm.

[0037] In this invention, "a carbon layer located on at least part of the outer surface of the substrate" means that the coverage of the carbon layer on the outer surface of the substrate can be less than 100% or equal to 100%, that is, the carbon layer can completely cover the substrate or partially cover the substrate.

[0038] In this invention, the projected area of ​​the amorphous carbon layer on the surface of the substrate accounts for 1%-50% of the surface area of ​​the substrate, for example, 1%, 2%, 3%, 5%, 10%, 20%, 30%, 40% or 50%.

[0039] Amorphous carbon layers on the outer surface of the substrate can confine the volume expansion of silicon material in silicon-carbon particles during battery cycling, mitigating side reactions between the electrolyte and silicon-carbon particles to some extent. Compared to silicon, amorphous carbon layers have better conductivity, and their placement on the outer surface of the substrate can improve the overall conductivity of silicon-carbon particles, reducing the transport resistance of lithium ions in the negative electrode active layer. When the thickness of the amorphous carbon layer is too large (e.g., >20nm), the diffusion path of lithium ions in the amorphous carbon becomes longer, which is detrimental to improving the rate performance of the battery. When the thickness of the amorphous carbon layer is too small (e.g., <2nm), it cannot effectively isolate the electrolyte, leading to continuous side reactions, reduced initial coulombic efficiency, and silicon particle breakage, which is also detrimental to improving battery cycle performance.

[0040] Defects exist at the interface between the amorphous carbon layer and the porous carbon matrix and silicon particles, forming a high potential barrier and significantly increasing the interface resistance, hindering electron transport across the interface. However, by introducing element K, K2 can be generated at the interface with silicon particles. x Si y The alloy transition layer forms a conductive path, effectively improving the conductivity of silicon-carbon particles, enhancing their kinetic properties, reducing battery internal resistance, and improving battery rate performance.

[0041] In this invention, the silicon-carbon particles contain a silicon dioxide phase.

[0042] In this invention, the silicon dioxide phase is located on the surface of the substrate and / or within a region formed along the surface of the substrate to a depth d towards the center, where d is 1 nm to 10 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm. In one embodiment, d is 1 nm to 5 nm.

[0043] In this invention, the region formed along the surface of the substrate to a depth of 1 nm-10 nm towards the center contains Si. 4+ .

[0044] In this invention, the orthographic projections of the silica phase and the amorphous carbon layer do not overlap. This is because silica has low surface activity, preventing amorphous carbon from depositing on its surface; instead, it deposits only on the surface of the porous carbon matrix.

[0045] It is understood that "the orthogonal projections of the silica phase and the amorphous carbon layer do not overlap" means that the orthogonal projection of the silica phase on the substrate surface and the orthogonal projection of the amorphous carbon layer on the outer surface of the substrate do not overlap.

[0046] In this invention, the projected area of ​​the silicon dioxide phase on the outer surface of the substrate accounts for 50%-99% of the surface area of ​​the substrate, for example, 50%, 55%, 60%, 65%, 70%, 80%, 90%, 95% or 99%.

[0047] It is understood that the ratio of the projected area of ​​the silica phase on the outer surface of the substrate to the surface area of ​​the substrate represents the coverage of the silica phase on the substrate surface, and the ratio of the projected area of ​​the amorphous carbon layer on the outer surface of the substrate to the surface area of ​​the substrate represents the coverage of the amorphous carbon on the substrate surface.

[0048] By setting a silica phase on the substrate surface, the resulting silicon-carbon anode material can react to generate lithium silicate (Li4SiO4) during lithium intercalation when used in batteries. Lithium silicate has good plasticity, and the silica phase itself is not easily broken. It can effectively buffer the huge volume expansion of silicon material during lithium intercalation, and build a flexible stress buffer layer between silicon-carbon particles and amorphous carbon layer. This enhances the bonding force between the substrate and amorphous carbon layer, prevents the amorphous carbon layer from peeling off due to stress during battery cycling, maintains the integrity of the conductive network, and also prevents fresh silicon particles inside from being exposed and directly contacting the electrolyte, which would cause the SEI film to grow repeatedly and is not conducive to improving the battery cycle stability. If d is too large (e.g., >5nm), the silica phase consumes too much active lithium during battery cycling, leading to a decrease in the initial coulombic efficiency of silicon-carbon particles. Furthermore, the silica phase affects the migration rate of lithium ions, increasing battery impedance and degrading the rate performance of the battery. At the same time, silica has a low lithium storage capacity, and excessive introduction will lead to a decrease in the specific capacity of silicon-carbon particles. If d is too small (e.g., <1nm) and / or the coverage of the silica phase is too small (e.g., <50%), the lithium silicate layer formed by silica has limited binding effect on the lithium intercalation expansion of silicon particles during battery cycling. This leads to the cracking of the silica phase and amorphous carbon layer, increasing the exposure of fresh silicon particles to electrolyte and causing side reactions. This results in increased battery internal resistance, which is not conducive to improving the rate performance and cycle stability of the battery.

[0049] In this invention, d and the thickness of the amorphous carbon layer can be obtained by conventional testing methods in the art, such as using a scanning electron microscope (SEM). The lithium-ion secondary battery is discharged to 0% SOC, the negative electrode is disassembled and removed, and the cross-section of the negative electrode is polished with an argon ion mill. The cross-section is then imaged in the SEM using backscatter imaging mode. After magnification to a certain level, the positions of the amorphous carbon layer (grayish-white) and the silica phase (dark gray) are determined. Ten different points on the amorphous carbon layer are randomly selected to measure the thickness of the amorphous carbon layer, and the average value is taken as the thickness of the amorphous carbon layer. At the location of the silica phase, the shortest distance from the point closest to the inside of the silica phase to the outside of the cross-section is measured from the outer contour of the cross-section to the inside of the cross-section, which is d.

[0050] In this invention, the proportion of the orthographic projection area of ​​the silica phase or the amorphous carbon layer on the outer surface of the substrate to the surface area of ​​the substrate can be obtained by conventional testing methods in the art, such as scanning electron microscopy (SEM). Specifically, after preparing the silicon carbon particles, the images are imaged under a scanning electron microscope. After magnification to a certain magnification, five different silicon carbon particles are selected, and five different regions are selected for each silicon carbon particle. The positions of the amorphous carbon layer (grayish-white) and the silica phase (dark gray) are determined. The area ratio of the amorphous carbon layer and the silica phase in each region is calculated using image analysis software. The average value of each measurement is the proportion of the orthographic projection area of ​​the silica phase or the amorphous carbon layer on the outer surface of the substrate to the surface area of ​​the substrate.

[0051] In this invention, the decrease in the mass content of element K along the direction from the center of the silicon-carbon particle to the surface means that: when several points are randomly selected along the direction from the center of the silicon-carbon particle to the surface to measure the mass content of K, the K content at the points closer to the surface of the silicon-carbon particle is less than the K content at the points away from the surface of the silicon-carbon particle (i.e., closer to the center).

[0052] When element K satisfies the above distribution in silicon-carbon particles, it can be used to improve the conductivity of silicon-carbon particles and enhance their rate performance. Maintaining a high K content in the region near the center ensures that K and its compounds provide external support for expansion stress, thereby alleviating expansion stress and constructing a conductive path. Meanwhile, the low K content in the region near the surface can form a certain transition layer at the interface to improve conductivity and also prevent excessive K from affecting the formation of the SEI film and forming potassium dendrites.

[0053] In this invention, the mass content of element K along the direction from the center of the silicon-carbon particle to the surface can be determined by conventional testing methods in the art, such as scanning electron microscopy-X-ray energy dispersive spectroscopy (SEM-EDS), specifically as follows: The battery is discharged to 0% SOC, the negative electrode is disassembled and removed, and the cross-section of the negative electrode is polished with an argon ion mill. The obtained cross-section is imaged in a scanning electron microscope (SEM) to identify five different silicon-carbon particles. In the SEM-EDS software, an arbitrary straight path passing through the center of the silicon-carbon particle is drawn, and the line scan mode is started. The electron beam moves along the path, and different points are randomly selected from the center to the surface to determine the mass content of element K.

[0054] It is understood that the aforementioned cross-sectional center is not the geometric center of the silicon-carbon particle in the strict sense. When performing EDS testing, those skilled in the art can reasonably select the scanning area so that the linear scanning area passes near the geometric center of the silicon-carbon particle, and determine the cross-sectional center point by the midpoint of the linear scanning area.

[0055] In this invention, at least a portion of the halogen is located inside the opening, and at least a portion of the halogen is distributed at the interface between the silicon particles and the porous carbon matrix.

[0056] In this invention, based on the pore volume of the silicon-carbon particles, the pore volume ratio of the closed pores is 50%-80%, for example, 50%, 55%, 60%, 65%, 70%, 75% or 80%.

[0057] When the proportion of closed pore volume in the silicon-carbon particles is within the aforementioned range, after chemical vapor deposition, a certain proportion of closed pores still exist inside the resulting silicon-carbon particles. This provides a buffer space for the volume expansion of silicon particles during lithium intercalation, preventing the silicon-carbon particles from breaking and failing. When the proportion of closed pore volume in the silicon-carbon particles is too large (e.g., >80%), the proportion of open pores is too low, resulting in the electrolyte being unable to effectively wet the interior of the silicon-carbon particles, which is detrimental to capacity utilization and battery cycle performance improvement. When the proportion of closed pore volume in the silicon-carbon particles is too small (e.g., <50%), silicon particles are not completely deposited during chemical vapor deposition, resulting in a low silicon content in the silicon-carbon particles, which is detrimental to improving capacity and battery energy density.

[0058] In this invention, the volume ratio of closed pores in the silicon-carbon particles can be obtained by conventional testing methods in the art, such as by gas displacement method, specifically as follows: using helium as the displacement medium, the true volume of the silicon-carbon particles after deducting open pores is calculated using the gas law (PV=nRT), thereby calculating the volume ratio of open pores and closed pores respectively. The formula for calculating the volume ratio of closed pores is as follows: V 闭孔 =(1-V 开孔 / V 总)×100%, where V 总 The total pore volume of silicon-carbon particles, V, can be directly measured by a true density meter. 开孔 The pore volume of the open pores in silicon-carbon particles can be indirectly estimated using the adsorbate filling method.

[0059] In this invention, the median particle size Dv50 of the silicon-carbon particles is Dv 1 50. The silicon-carbon particles are ball-milled at a speed of 200 rpm to 600 rpm (e.g., 200 rpm, 300 rpm, 400 rpm, 500 rpm, or 600 rpm) until the median particle size Dv50 of the silicon-carbon particles is (0.05-0.2) × Dv 1 At 50°C (e.g., 0.05-2 could be 0.05, 0.06, 0.08, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 1.5, or 2), the ball-milled silicon carbide particles are mixed with deionized water at a mass ratio of 1:20 to obtain an aqueous solution. The pH value of the aqueous solution of the ball-milled silicon carbide particles is measured at 25°C to be pH2, which is 7.5-11, for example, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, or 11.

[0060] In this invention, pH1 and pH2 satisfy the condition: pH1 < pH2.

[0061] In this invention, pH2 can be determined as follows: The silicon-carbon granules are milled at 200 rpm-600 rpm until the median particle size Dv50 is (0.05-0.2) × Dv. 1 At 50°C, the ball-milled silicon-carbon particles were dried in a vacuum oven at 60°C for 2 hours. The dried powder was mixed with deionized water at a ratio of 1:10 and placed in a sealed container. The mixture was sonicated at 25°C for 30 minutes and filtered using a 0.45μm microporous membrane. The pH of the collected filtrate was measured at 25°C, which is pH2.

[0062] When pH2 falls within the above range, it indicates that potassium (K) in the closed pores is released due to the disruption of the pores, causing the pH of the resulting clear solution to rise. When pH2 is below the above range (e.g., pH2 < 7.5), it indicates that the content of K in the silicon-carbon particles is less than 100 ppm, which is insufficient to improve the conductivity and expansion rate of the silicon-carbon particles, and is not conducive to further improvement of battery rate performance and cycle stability. When pH2 is above the above range (e.g., pH2 > 11), it indicates that the content of K in the silicon-carbon particles is higher than 1000 ppm, resulting in excessive K in the closed pores. This may embed into the surrounding carbon lattice during battery charging and discharging, causing microcracks to form and rupture in the closed pores of the silicon-carbon particles. The released K will damage the SEI film and form potassium dendrites, which is not conducive to improving the cycle stability of the battery.

[0063] In this invention, the silicon-carbon particles are subjected to X-ray photoelectron spectroscopy analysis. Extending 3 nm from the surface of the silicon-carbon particles inward, the silicon dioxide content is 50%-99%, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 99%.

[0064] In one embodiment, X-ray photoelectron spectroscopy analysis was performed on the silicon-carbon particles, and the silicon dioxide content was 70%-95% extending 3 nm from the surface of the silicon-carbon particles.

[0065] In this invention, the silicon-carbon particles are subjected to X-ray photoelectron spectroscopy analysis. Extending 10 nm from the surface of the silicon-carbon particles inward, the content of silicon dioxide is 0%-10%, for example, 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0066] In one embodiment, X-ray photoelectron spectroscopy analysis was performed on the silicon-carbon particles, and the silicon dioxide content was 6%-9% extending 10 nm from the surface of the silicon-carbon particles.

[0067] Silica can form lithium silicate and lithium oxide components with lithium ions at low potentials, exhibiting high ionic conductivity and good mechanical stability. This allows it to guide the subsequent formation of a denser and more stable SEI film, thereby improving the rate performance of the battery. Along the direction extending from the surface of the silicon-carbon particles towards the center, the silica content gradually decreases, effectively buffering and dissipating the stress generated by the volume expansion of the silicon material. This ensures the integrity of the interface layer and prevents cracks from forming during cycling, which would expose fresh silicon surfaces, accelerate the consumption of electrolyte and active lithium, and lead to a decrease in the battery's initial efficiency.

[0068] In this invention, the silica content on the matrix surface of the silicon-carbon particles can be quantified using X-ray photoelectron spectroscopy (XPS). Specifically, the area A1 of the peak at ~99.3 eV corresponding to elemental silicon in the XPS image is obtained by fitting the peak at ~103.4 eV corresponding to silica, and the area A2 of the peak at ~103.4 eV is obtained by fitting the peak at ~103.4 eV. The silica content on the surface of the silicon-carbon particles is then A2 / (A2+A1)×100%, and the content of low-valent silicon is A1 / (A2+A1)×100%.

[0069] In this invention, the X-ray diffraction pattern of the silicon-carbon particles has diffraction peaks at 2θ = 20°-30°, for example, 20°, 21°, 22°, 23°, 24°, 26°, 28° or 30°.

[0070] When diffraction peaks are present in the XRD pattern of silicon-carbon particles, it indicates the presence of amorphous silicon dioxide within the particles. Amorphous silicon dioxide is chemically stable and can isolate the internal active silicon particles from the electrolyte, preventing excessive side reactions. Furthermore, amorphous silicon dioxide has a random atomic arrangement, resulting in low resistance to lithium-ion transport within it. Figure 3 The image shown is an XRD pattern of silicon-carbon particles in one embodiment of the present invention, where the horizontal axis (2θ) represents the diffraction angle and the vertical axis (Intensity) represents the diffraction intensity.

[0071] In this invention, the X-ray diffraction (XRD) pattern of the silicon-carbon particles can be obtained using conventional testing methods in the art, such as the following method: A Shimadzu XRD-6100 X-ray diffractometer is used for testing. An appropriate amount of silicon-carbon particles is taken as a sample, with a sample volume of 0.5 g / cm². Before testing, the particles are ground into a uniform fine powder and flattened in the sample trough, ensuring a smooth surface. After turning on the equipment, wait 30 minutes for the equipment to stabilize. The Kα line of Cu is used as the incident X-ray, the X-ray source operating voltage is 40 kV, the test power is 2 kW, and the x-axis is 2θ in degrees, the y-axis is signal intensity, the test range is 10–90°, the scanning rate is 5° / min, and the data point interval is 0.02° to acquire the diffraction pattern.

[0072] In this invention, based on the total mass of the silicon-carbon particles, the mass content of silicon is 30%-70%, for example, 30%, 32%, 34%, 36%, 38%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%; the mass content of the porous carbon matrix is ​​30%-70%, for example, 30%, 32%, 34%, 36%, 38%, 40%, 45%, 50%, 55%, 60%, or 70%; and the mass content of the amorphous carbon layer is 2%-5%, for example, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.5%, 4%, 4.5%, or 5%. When the content of each component in the silicon-carbon particles satisfies the above relationships, the silicon-carbon particles have the advantages of high specific capacity, high initial efficiency, and low expansion.

[0073] In this invention, the silicon particles include crystalline silicon and amorphous silicon. Based on the total mass of the silicon particles, the content of the crystalline silicon is 0%-10%, for example, 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%; the content of the amorphous silicon is 90%-100%, for example, 90%, 91%, 92%, 933%, 94%, 95%, 96%, 98% or 100%.

[0074] It is understood that crystalline silicon refers to a crystal structure formed by the periodic and ordered arrangement of atoms in three-dimensional space, forming a long-range ordered crystal structure, while amorphous silicon refers to a crystal structure in which the atomic arrangement lacks long-range periodicity, maintains short-range order only within a few atomic spacings, and has an overall structure of long-range disorder.

[0075] When the content of crystalline silicon and amorphous silicon in silicon-carbon particles is within the above-mentioned range, it can improve the structural stability of silicon-carbon particles, improve the initial coulombic efficiency of the battery, and increase the overall energy density. When the content of crystalline silicon is too high (e.g., >10%), it can lead to the aggravation of silicon-carbon particle pulverization and structural collapse. This is because the anisotropic volume change of crystalline silicon during lithium insertion / extraction generates huge internal shear forces, causing the porous carbon matrix to break. This results in the silicon particle surface being exposed to the electrolyte, continuously forming new and unstable SEI films, continuously consuming active lithium and electrolyte, leading to irreversible capacity decay. In addition, the Li formed during the initial lithiation of crystalline silicon... 15 The Si4 phase exhibits significant irreversibility during delithiation, resulting in a marked decrease in the initial coulombic efficiency of silicon-carbon particles and the overall energy density of the battery.

[0076] In this invention, the content of crystalline silicon and amorphous silicon can be obtained by conventional testing methods in the art, such as Raman spectroscopy. Specifically, a Thermo Fisher Raman spectrometer is used to test the silicon-carbon particles, with a wavenumber range of 400 cm⁻¹. -1 -4000cm -1 Crystalline silicon will be at 520cm -1 A sharp and strong characteristic peak is generated nearby, denoted as characteristic peak 1. For amorphous silicon, this peak occurs at 480 cm⁻¹. -1 A broad and weak characteristic peak, denoted as characteristic peak 2, is generated nearby. After background subtraction and smoothing preprocessing of the obtained spectrum, the peak value at 480 cm⁻¹ is [missing information]. -1 -520cm -1 Peak fitting is performed within the interval to obtain the peak area S1 of characteristic peak 1 and the peak area S2 of characteristic peak 2, respectively. The content of crystalline silicon is S1 / (S1+α×S2)×100%, and the content of amorphous silicon is S2 / (S1+α×S2)×100%, where α is a correction factor obtained by calibration with a standard sample of known proportion, used to correct the difference in Raman scattering cross section between crystalline silicon and amorphous silicon.

[0077] In this invention, the silicon-carbon particles further include heteroatoms, and the mass content of the heteroatoms is 1%-5% based on the total mass of the silicon-carbon particles, for example, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 4.5% or 5%.

[0078] In one embodiment, the heteroatom includes at least one of the elements H, S, P, and N.

[0079] In one embodiment, the heteroatoms are distributed within a porous carbon matrix.

[0080] In yet another embodiment, the heteroatoms are distributed within the amorphous carbon layer.

[0081] Element H comes from porous carbon precursors and the vapor-phase silicon deposition process. It can form Si-H bonds with silicon, thereby improving the electronic conductivity of silicon particles. Element S is doped between the porous carbon matrix framework, which can expand the interlayer spacing and improve the diffusion rate of lithium ions. N atoms can replace C atoms in the porous carbon matrix framework, providing excess electrons, thereby improving the electronic conductivity of the porous carbon matrix and improving the overall conductivity of silicon-carbon particles.

[0082] In this invention, the content and distribution of heteroatoms in the silicon-carbon particles can be obtained using conventional testing methods in the art. The content of heteroatoms in the silicon-carbon particles can be determined by elemental analysis. The distribution of heteroatoms can be obtained by SEM-EDS testing. The battery is discharged to 0% SOC, the negative electrode is disassembled and removed, and the cross-section of the negative electrode is polished using an argon ion mill. The obtained cross-section is then imaged using a scanning electron microscope (SEM) to identify five different silicon-carbon particles. The distribution of elements H, S, P, and N is determined by EDS surface scanning.

[0083] In this invention, the specific surface area of ​​the porous carbon matrix is ​​1500 m². 2 / g-2500m 2 / g, for example, 1500m 2 / g, 1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g、2200m 2 / g、2400m 2 / g or 2500m 2 / g.

[0084] In this invention, the pore volume of the porous carbon matrix is ​​1 cm³. 3 / g-1.5cm 3 / g, for example, 1cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g.

[0085] When the specific surface area and pore volume of the porous carbon matrix meet the above-mentioned ranges, it ensures that the silicon-carbon particles maintain high specific capacity after silane deposition, reduces the effective contact area between the resulting silicon-carbon particles and the electrolyte, decreases the formation of the SEI film at the negative electrode and the loss of active lithium, thereby improving the battery's initial coulombic efficiency and cycle stability. However, if the pore volume of the porous carbon matrix is ​​too large (e.g., >1.5 cm), it will negatively impact the battery's performance. 3 / g) and / or excessively large specific surface area (e.g., >2500m²) 2 When the porous carbon matrix has too many pores (e.g., <0.0005 cm³), its overall strength decreases, making it more susceptible to cracking due to expansion stress during cycling, which is detrimental to improving cycling stability. Furthermore, when the pore volume of the porous carbon matrix is ​​too small (e.g., <0.0005 cm³), it also deteriorates. 3 / g) and / or a specific surface area that is too small (e.g., <1500m²). 2 / g), at this time the internal pore structure of the porous carbon matrix is ​​too low, the buffer space reserved inside the porous carbon matrix is ​​insufficient, the ability to withstand expansion stress is poor, and at the same time it cannot provide enough active sites during vapor deposition, which is not conducive to increasing the amount of silicon particles deposited, resulting in a decrease in battery capacity.

[0086] In this invention, based on the pore volume of the porous carbon matrix, the proportion of open pore volume is 95%-99.9%, for example, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, or 99.9%; the proportion of closed pore volume is 0.1%-5%, for example, 0.1%, 0.3%, 0.4%, 0.5%, 1%, 1.5%, 2%, 3%, 4%, or 5%.

[0087] In this invention, the average aperture of the open hole is 2nm-10nm, for example, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm or 10nm; the average aperture of the closed hole is 0.6nm-2nm, for example, 0.6nm, 0.7nm, 0.8nm, 1nm, 1.2nm, 1.4nm, 1.6nm, 1.8nm or 2nm.

[0088] When the ratio of open pores to closed pores in the porous carbon matrix is ​​within the above-mentioned range, the volume expansion of silicon particles during lithium intercalation can be effectively buffered, preventing the porous carbon matrix from cracking and causing silicon-carbon particles to fail. When the proportion of closed pores in the porous carbon matrix is ​​too high (e.g., >5%), the compaction density of the resulting silicon-carbon particles decreases, which is not conducive to improving the overall volumetric energy density of the battery. When the proportion of closed pores in the porous carbon matrix is ​​too low (e.g., <0.1%), there are fewer pre-reserved closed pore structures in the resulting silicon-carbon particles, which is not conducive to further improving the buffering effect against volume expansion stress.

[0089] In this invention, the test method for the pore volume ratio of open and closed pores in the porous carbon matrix can refer to the test method for the pore volume ratio of open and closed pores in the silicon carbon particles. The difference is that the test sample is a porous carbon matrix.

[0090] It is understood that, based on the pore volume of the silicon-carbon material, the proportion of closed pore volume refers to the proportion of closed pore volume in the silicon-carbon material after the silicon particles are deposited on the porous carbon matrix; based on the pore volume of the porous carbon matrix, the proportion of open pore and closed pore volume refers to the proportion of open pore and closed pore volume in the porous carbon matrix before the silicon particles are deposited on the porous carbon matrix.

[0091] In this invention, the median particle size Dv50 of the silicon-carbon particles is Dv 1 50, 1μm≤Dv 1 50≤15μm, for example, 1μm, 2μm, 3μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 15μm.

[0092] In one embodiment, 6μm≤Dv 1 50≤9μm.

[0093] In this invention, the size of the silicon particles is 1nm-100nm, for example, 1nm, 2nm, 3nm, 4nm, 6nm, 10nm, 20nm, 30nm, 40nm, 60nm, 80nm or 100nm.

[0094] It is understood that the size of the silicon particle refers to the shortest distance between any two points on the outer contour of the silicon particle.

[0095] When Dv 1 Smaller particle sizes (e.g., less than 1 μm) result in a larger specific surface area for silicon-carbon particles. During battery charge-discharge cycles, this leads to increased side reactions between the negative electrode active material and the electrolyte, hindering further improvements in the battery's initial coulombic efficiency and volumetric energy density. Furthermore, when Dv... 1 When the silicon particle size is relatively large (e.g., greater than 15 μm), the migration distance of lithium ions in the negative electrode active material increases, affecting the battery's rapid discharge capability and hindering the improvement of battery rate performance. When the silicon particle size is too small (e.g., <1 nm), the specific surface area of ​​the silicon particles is large, and the effective contact area when exposed to the electrolyte is significantly increased, leading to aggravated electrolyte side reactions and hindering the improvement of battery cycle stability. When the silicon particle size is too large (e.g., >100 nm), the diffusion path of lithium ions inside the silicon particles becomes longer, the kinetics deteriorate, and this is also detrimental to the improvement of battery rate performance.

[0096] In this invention, Dv 150 can be obtained by conventional methods in the art, such as using a laser particle size analyzer, as follows: disperse silicon carbon particles in ethanol containing a dispersant (e.g., sodium dodecyl sulfate) (the mass content of the dispersant is 0.02%-0.03%), sonicate for 2 minutes, and then place them in a Malvern particle size analyzer for testing.

[0097] In this invention, the size of the silicon particles can be obtained by conventional methods in the art, such as by using a high-resolution transmission electron microscope (TEM) to prepare silicon carbon particles, image them with TEM, magnify them to a certain magnification, measure the size of 20 different silicon particles, and calculate the average value.

[0098] In this invention, the sphericity of the silicon-carbon particles is 0.7-1, for example, 0.7, 0.75, 0.8, 0.85, 0.9, or 1. In one embodiment, the sphericity of the silicon-carbon particles is 0.8-0.99.

[0099] Controlling the sphericity of silicon-carbon particles can regulate their morphology within a reasonable range, affecting their overall compressive strength and the bond strength between the carbon-based material and the silicon-carbon particles, thus influencing battery performance. When the sphericity of silicon-carbon particles is too small (e.g., <0.7), the particles have many sharp edges, resulting in low compressive strength. Under external pressure, they are prone to breakage, leading to pulverization of the negative electrode sheet. Sharp parts pose a risk of puncturing the separator, causing localized micro-short circuits, resulting in poor K-value and decreased cycle performance.

[0100] In this invention, the sphericity of the silicon-carbon particles can be obtained by conventional testing methods in the art, for example, by the following method: Discharge the battery to 0% SOC, disassemble and remove the negative electrode sheet, or directly remove the negative electrode sheet, polish its cross-section with an argon ion mill, and image the obtained cross-section using a scanning electron microscope (SEM) in backscatter imaging mode; analyze the images of 50 silicon-carbon particles in the SEM image (backscatter mode) of the negative electrode active layer at a certain magnification (e.g., 2500x) using image processing software such as Image Pro Plus, obtain the perimeter and area of ​​each particle, calculate the perimeter equivalent radius r1 and area equivalent radius r2 of each silicon-carbon particle, then the sphericity of each particle S = r2 / r1, and then perform a number-weighted average of the sphericity of each particle to obtain the sphericity of the silicon-carbon particles.

[0101] In this invention, the specific surface area of ​​the silicon-carbon particles is 0.1 m². 2 / g-5m 2 / g, for example, 0.1m 2 / g, 0.2m 2 / g, 0.4m 2 / g, 0.6m2 / g, 0.8m 2 / g, 1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g or 5m 2 / g.

[0102] In this invention, the pore volume of the silicon-carbon particles is 0.0005 cm³. 3 / g-0.002cm 3 / g, for example, 0.0005cm 3 / g, 0.0006cm 3 / g, 0.0008cm 3 / g, 0.001cm 3 / g, 0.0015cm 3 / g or 0.002cm 3 / g.

[0103] When the specific surface area and pore volume of silicon-carbon particles meet the above-mentioned ranges, it ensures that the silicon-carbon particles have a high specific capacity while reducing the effective contact area between the silicon-carbon particles and the electrolyte, thus reducing the formation of the SEI film and the loss of active lithium, thereby improving the initial coulombic efficiency and cycle stability of the battery. However, if the specific surface area of ​​the silicon-carbon particles is too large (e.g., >5 μm²), it indicates a problem. 2 / g) and / or excessively large pore volume (e.g., >0.002cm). 3 When the specific surface area of ​​silicon-carbon particles is too small (e.g., <0.1m²), more SEI film forms on the surface, consuming more lithium ions and resulting in a low initial coulombic efficiency of the battery. 2 / g) and / or pore volume is too small (e.g., <0.0005cm). 3 If the specific surface area is too low ( / g), it will result in insufficient active sites for lithium ions to be inserted into the negative electrode active material. At the same time, the lower specific surface area means that the path for lithium ions to diffuse into the interior of silicon-carbon particles is longer, which leads to a deterioration in the rate performance of the battery.

[0104] In this invention, the weight content of FEC and ethyl fluoroacetate in the electrolyte can be obtained by conventional testing methods in the art, such as gas chromatography or gas chromatography coupled with mass spectrometry.

[0105] In this invention, 200 mg of the silicon carbon particles are taken at 25°C for contact angle testing. The test electrolyte includes ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:7 and 1 mol / L lithium hexafluorophosphate. The contact angle between the silicon carbon particles and the test electrolyte is 20°-40°, for example, 20°, 22°, 24°, 26°, 28°, 30°, 32°, 34°, 36°, 38° or 40°.

[0106] Silicon, as a semiconductor, has an atomic crystal structure on its surface, resulting in a high energy barrier, low surface energy, a large contact angle with the electrolyte, and poor wettability. The surface of silicon dioxide contains numerous silanol groups (Si-OH). These polar hydroxyl groups can form hydrogen bonds with the carbonyl groups (C=O) of carbonate solvents (such as EC and EMC) in the electrolyte, effectively reducing the interfacial energy. This allows the electrolyte to spontaneously spread and wet the silicon dioxide surface, improving ion transport kinetics. Similarly, the amorphous carbon layer on the surface of silicon-carbon particles increases the affinity between the particles and the electrolyte, reduces the contact angle, and improves the wettability between the silicon-carbon particle surface and the electrolyte, thereby enhancing the battery's rate performance.

[0107] In this invention, the contact angle between the silicon carbon particles and the electrolyte can be obtained using conventional testing methods in the art, such as by measuring with a contact angle meter, specifically as follows: Weigh 200 mg of silicon carbon particles, place the particles into a powder tableting mold, press with 10 MPa pressure for 2 minutes, remove the pressed tablet from the mold, transfer the tablet to a glove box and place it in the test chamber of the contact angle meter, use a pipette to draw 3 μL of test electrolyte (solvent is ethylene carbonate and methyl ethyl carbonate in a mass ratio of 3:7, solute is 1 mol / L lithium hexafluorophosphate), slowly squeeze out a drop of electrolyte, and let it fall freely onto the tablet surface. At the instant the droplet contacts the surface (usually within 1-3 seconds), use the high-speed camera of the contact angle meter to take a clear side view of the droplet. Measure at least 3 times at different locations on the same tablet, and measure at least 3 different tablets prepared from the same batch of silicon carbon particles, finally taking the average value and standard deviation.

[0108] In this invention, the specific surface area and pore volume of the silicon-carbon particles and the porous carbon matrix can be determined by conventional testing methods in the art, such as the Brunauer-Emmett-Teller (BET) test method, measured using a TriStar II specific surface area analyzer, with N2 as the adsorbed gas.

[0109] In this invention, the true density of the silicon-carbon particles is 1.5 g / cm³. 3 -2.3cm 3 / g, for example, 1.5cm 3 / g, 1.6cm 3 / g, 1.8cm 3 / g、2cm 3 / g, 2.2m 3 / g or 2.3cm 3 / g.

[0110] When the true density of the silicon-carbon particles is within the above-mentioned range, it ensures that while the silicon-carbon particles have a high specific capacity, they still contain a certain proportion of closed pores. These closed pores provide a buffer space for the volume expansion during lithium intercalation of the silicon particles, preventing the silicon-carbon particles from breaking. When the true density is relatively low (e.g., less than 1.5 cm³), the true density is lower. 3 When the true density is high (e.g., greater than 2.3 cm³ / g), excessive closed-cell content in silicon-carbon particles can lead to a lower volumetric energy density in the battery; conversely, when the true density is high (e.g., greater than 2.3 cm³ / g), the volumetric energy density is lower. 3 When the content of closed-cell silicon carbon particles is too low ( / g), it is difficult to buffer the volume expansion of silicon, thus affecting the cycle stability of the battery.

[0111] In this invention, the true density of the silicon-carbon particles can be obtained by conventional methods in the art, such as the gas volume displacement method, as follows: the test is performed using a JW-M100A fully automatic true density tester, the test gas is helium, and the test environment temperature is 25℃±2℃.

[0112] In this invention, the surface of the silicon-carbon particles has a plurality of pits. The term "a plurality of" refers to a number of pits ≥ 2.

[0113] The present invention also provides a method for preparing the silicon-carbon particles, comprising at least the following steps: Step 1: Mix the template agent and the K-containing halogen compound with the first solvent to obtain a first mixture. Mix ammonia and tetraethyl orthosilicate (TFOS) with the first mixture to obtain a second mixture and carry out a first reaction to obtain the first product. Step 2: Disperse the first product in anhydrous ethanol, mix it with an ethanol solution of phenolic resin and NaOH to obtain the second product; Step 3: Place the second product in a tube furnace to carry out the second reaction, and after obtaining the third product, mix it with NaOH solution to carry out the third reaction to obtain a porous carbon precursor. Step 4: Mix the porous carbon precursor with a toluene solution of polymethyl methacrylate (PMMA), centrifuge to obtain a precipitate, place the precipitate in a tube furnace, and carry out a fourth reaction to obtain a porous carbon matrix. Step 5: Place the porous carbon matrix in a tube furnace, heat it to the holding temperature under a nitrogen atmosphere, then switch to the first mixed gas for the first deposition. After the first mixed gas is exhausted, switch to the second mixed gas for the oxidation reaction. After the second mixed gas is exhausted, introduce carbon source gas and perform the second deposition to obtain the silicon-carbon particles.

[0114] In this invention, the template agent may include at least one of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (Pluronic F127, hereinafter referred to as F127), poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), and hexadecyltrimethylammonium bromide (CTAB).

[0115] In this invention, the K-containing halogen compound may include potassium chloride, potassium bromide, and potassium fluoride.

[0116] In this invention, the first solvent includes anhydrous ethanol and deionized water, and the volume ratio of the anhydrous ethanol to the deionized water is (1-5):1, for example, it can be 1:1, 2:1, 3:1, 4:1 or 5:1.

[0117] In this invention, the mass ratio of the template agent to the K-containing halogen compound is (1-5):1, for example, it can be 1:1, 2:1, 3:1, 4:1 or 5:1.

[0118] In this invention, the volume ratio of ammonia to tetraethyl orthosilicate in the first solvent is (0.1-1):1, for example, 0.1:1, 0.5:1, 1:1, or 1:1. The concentration of the ammonia can be conventionally selected in the art, for example, 28 wt%.

[0119] In this invention, the first reaction can be a water bath reaction, the temperature of which is 30℃-50℃, for example, 30℃, 35℃, 40℃ or 50℃; the time of which is 4h-10h, for example, 4h, 6h, 8h or 10h.

[0120] In this invention, step 1 further includes: after the first reaction is completed, removing the supernatant by centrifugation, collecting the lower precipitate and washing it with deionized water.

[0121] In this invention, the mass ratio of the ethanol solution of the phenolic resin to NaOH is (30-60):1, for example, 30:1, 40:1, 50:1 or 60:1.

[0122] In this invention, step 2 further includes magnetic stirring at 40℃-80℃ (e.g., 40℃, 50℃, or 80℃) for 8h-15h (e.g., 8h, 10h, or 15h), followed by a second centrifugation and washing with deionized water and / or anhydrous ethanol and drying.

[0123] In this invention, the conditions for the second reaction are as follows: under a N2 atmosphere, the temperature is increased to 700℃-1100℃ (e.g., 700℃, 800℃, 1000℃, or 1100℃) at a heating rate of 1℃ / min-5℃ / min (e.g., 1℃ / min, 3℃ / min, or 5℃ / min), and held at this temperature for 1h-3h (e.g., 1h, 2h, or 3h).

[0124] In this invention, the molar concentration of the NaOH solution is 1 mol / L to 3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0125] In this invention, the conditions for the third reaction are as follows: the reaction temperature is 60℃-100℃, for example, 60℃, 70℃, 80℃, 90℃ or 100℃; the reaction time is 4h-10h, for example, 4h, 5h, 6h, 7h, 8h, 9h or 10h.

[0126] In this invention, step 3 further includes washing with deionized water until the porous carbon precursor is neutral.

[0127] In this invention, the concentration of the toluene solution of PMMA is 0.1 mg / mL to 2 mg / mL, for example, 0.1 mg / mL, 0.5 mg / mL, 1 mg / mL, 1.5 mg / mL or 2 mg / mL.

[0128] In this invention, the ratio of the porous carbon precursor to the toluene solution of PMMA is 0.5 g / 100 mL to 3 g / 100 mL, for example, 0.5 g / 100 mL, 1 g / 100 mL, 2 g / 100 mL, or 3 g / 100 mL. It is understood that the "ratio of the porous carbon precursor to the toluene solution of PMMA" refers to the mass of the porous carbon precursor contained in a certain volume of the toluene solution of PMMA. For example, 0.8 g / 100 mL means that 100 mL of the toluene solution of PMMA contains 0.8 g of the porous carbon precursor.

[0129] In this invention, the first centrifugation time is 1h-10h, for example, 1h, 2h, 5h or 10h.

[0130] In this invention, the conditions for the fourth reaction are as follows: under a N2 atmosphere, the temperature is increased to 300℃-500℃ at a heating rate of 1℃ / min-5℃ / min (e.g., 1℃ / min, 3℃ / min or 5℃ / min), and held at that temperature for 0.1h-2h, e.g., 0.1h, 0.5h, 1h or 2h.

[0131] In this invention, step 4 further includes: vacuum drying the precipitate after the first centrifugation; washing the product with 0.1M HCl after the fourth reaction, performing a third centrifugation and drying.

[0132] In this invention, the first mixed gas comprises an inert gas and a silicon source gas. The inert gas includes at least one of nitrogen (N2), argon, and helium; the silicon source gas includes at least one of silane (SiH4), dichlorosilane, trichlorosilane, and tetrachlorosilane. Based on the total volume of the mixed gas, the proportion of the silicon source gas is 1%-50%, for example, 1%, 10%, 20%, 30%, 40%, or 50%.

[0133] In this invention, nitrogen gas is introduced and the temperature is raised to the holding temperature. The heating rate is 5℃ / min-10℃ / min, for example, 5℃ / min, 6℃ / min, 8℃ / min or 10℃ / min. The holding temperature is 400℃-600℃, for example, 400℃, 500℃ or 600℃.

[0134] In this invention, the conditions for the first deposition are as follows: the flow rate of the first mixed gas is 30 sccm-150 sccm, for example, 30 sccm, 50 sccm, 100 sccm or 150 sccm, and the deposition time is 1h-10h, for example, 1h, 2h, 4h, 6h or 10h.

[0135] In this invention, the second mixed gas comprises nitrogen and oxygen, and the oxygen content is 1%-10% based on the total volume of the second mixed gas, for example, 1%, 2%, 4%, 6%, or 10%. The flow rate of the second mixed gas is 30 sccm-150 sccm, for example, 30 sccm, 50 sccm, 100 sccm, or 150 sccm. The oxidation reaction time is 0.1 h-2 h, for example, 0.1 h, 0.5 h, 1 h, 1.5 h, or 2 h.

[0136] In this invention, the conditions for the second deposition are as follows: the holding temperature is 450℃-550℃ (e.g., 450℃, 500℃ or 550℃), the carbon source flow rate is 50sccm-150sccm (e.g., 50sccm, 100sccm or 150sccm), and the holding time is 1h-3h (e.g., 1h, 2h or 3h).

[0137] In this invention, the carbon source gas includes at least one of methane, ethylene, and acetylene.

[0138] A second aspect of the present invention provides a lithium-ion secondary battery, the lithium-ion secondary battery comprising a negative electrode and an electrolyte, wherein the negative electrode comprises the negative electrode active material provided in the first aspect of the present invention.

[0139] In this invention, the electrolyte comprises fluoroethylene carbonate (FEC) and / or fluoroethyl acetate.

[0140] In this invention, the fluoroethyl acetate includes ethyl difluoroacetate, which includes ethyl 2,2-difluoroacetate and 2,2-difluoroethyl acetate (DFEA).

[0141] In this invention, based on the total mass of the electrolyte, the mass content of the fluoroethylene carbonate is 4%-20%, for example, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18% or 20%.

[0142] In this invention, based on the total mass of the electrolyte, the mass content of the ethyl fluoroacetate is 5%-20%, for example, 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18% or 20%.

[0143] FEC and DFEA are adsorbed onto the Si-O bonds of silica. When the FEC content in the electrolyte is within the aforementioned range, FEC preferentially undergoes reduction and decomposition on the silica surface, making the decomposition of FEC more concentrated and uniform across the entire silica surface, avoiding localized uneven decomposition. The LiF generated from FEC decomposition, together with the lithium silicate and lithium oxide generated from the reduction of the silica surface, forms a composite inorganic SEI film. This structure possesses low impedance, high interfacial stability, and high mechanical strength, effectively suppressing continuous electrolyte decomposition, adapting to the volume expansion of silicon-carbon anode batteries, and synergizing with the highly conductive amorphous carbon layer to optimize interfacial ion / electron transport and improve rate performance. When the FEC content is too low (e.g., below 4%), the insufficient FEC content cannot form an effective protective layer, failing to effectively improve interfacial stability and reduce side reactions. When the content of FEC is too high (e.g., greater than 20%), the excess FEC will decompose incompletely due to the high kinetic energy barrier, producing disordered LiF and organic byproducts. This leads to increased ion transport resistance due to SEI structural inhomogeneity, deteriorating kinetic performance. DFEA has a high reduction potential, providing an additional F source for SEI film formation, further increasing the abundance and density of LiF in the SEI film, forming a more continuous and uniform LiF network, making the SEI film less prone to brittle fracture under mechanical stress. When the content of ethyl fluoroacetate is too high (e.g., >20%), the low dielectric constant of ethyl fluoroacetate leads to a decrease in the overall ionic conductivity of the electrolyte, resulting in deterioration of rate performance. When the content of ethyl fluoroacetate is too low (e.g., <5%), its effect on improving the density and mechanical properties of the SEI film is not significant.

[0144] In this invention, the electrolyte further includes a solvent and a lithium salt additive. Based on the total mass of the electrolyte, the solvent has a mass content of 70%-85%, and the solvent may include at least one of cyclic carbonates (such as ethylene carbonate and propylene carbonate), chain carbonates (such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate), and carboxylic acid esters (such as methyl acetate, ethyl acetate, propyl acetate and ethyl propionate); the lithium salt additive has a mass content of 10%-18%, and the lithium salt additive may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium dioxalateborate, lithium difluorooxalateborate, and lithium perchlorate.

[0145] In this invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side of the surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, which includes the silicon-carbon particles and / or carbon-based materials. The carbon-based materials include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, and hard carbon.

[0146] In this invention, the lithium-ion secondary battery further includes a positive electrode sheet, which comprises a positive current collector and a positive active layer located on at least one side of the surface of the positive current collector. The positive active layer comprises a positive active material, which can be a positive active material known in the art for lithium-ion secondary batteries. The positive active material can be selected from lithium cobalt oxide (LiCoO2), lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium nickel oxide, lithium nickel manganese oxide, lithium manganese iron phosphate, and lithium-rich manganese-based materials.

[0147] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0148] In this invention, the term "0% SOC" refers to the battery being discharged to 2.5V at 0.02C.

[0149] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0150] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0151] The following preparation examples illustrate the silicon-carbon particles of the present invention: Preparation Example 1: Step 1: Mix F127 and KCl at a mass ratio of 2:1 with the first solvent (anhydrous ethanol and deionized water at a volume ratio of 2:1) to obtain the first mixture. Add ammonia water and stir magnetically for 10 min. Then slowly add TFOS to obtain the second mixture at a volume ratio of 1:2. The second mixture is then subjected to a water bath reaction at 40°C for 6 h. Centrifuge to collect the precipitate and wash with ethanol and deionized water to obtain the first product. Step 2: Disperse the first product in anhydrous ethanol, and mix it with 20 wt% ethanol solution of phenolic resin and NaOH at a mass ratio of 50:1. Stir magnetically at 60°C for 12 h, collect the precipitate by centrifugation and wash it with ethanol and deionized water to obtain the second product. Step 3: Place the second product in a tube furnace and heat it to 900℃ for 2 hours under N2 atmosphere at a rate of 1℃ / min. After obtaining the third product, mix the second product with 2 mol / L NaOH solution and react at 90℃ for 6 hours. After centrifugation, wash with deionized water until neutral to obtain a porous carbon precursor. Step 4: Mix the porous carbon precursor and a toluene solution of 1 mg / mL PMMA at a ratio of 1 g / 100 mL, sonicate for 10 min, shake at low speed for 6 h, remove the supernatant by centrifugation, and vacuum dry at 60 °C for 1 h to obtain a precipitate. Place the precipitate in a tube furnace and heat it to 350 °C at 2 °C / min under N2 atmosphere and hold for 30 min. Wash it with 0.1 mol / L HCl at 60 °C to obtain a porous carbon matrix. Step 5: Place the porous carbon matrix in a tube furnace and heat it to 500°C at a rate of 10°C / min under a nitrogen atmosphere. Then switch to a first mixed gas (silane:nitrogen volume ratio of 2:8) with a flow rate of 60 sccm for the first deposition at 500°C for 3 hours. After the first mixed gas is exhausted, switch to a second mixed gas (oxygen:nitrogen volume ratio of 0.05:0.95) with a flow rate of 60 sccm for oxidation reaction and hold at that temperature for 15 minutes. After the second mixed gas is exhausted, introduce acetylene gas with a flow rate of 10 sccm and heat to 550°C for the second deposition for 2 hours to obtain the silicon-carbon particles, denoted as SC-1.

[0152] At this point, the mass content of K in the silicon-carbon particles is 637 ppm, the content of Cl is 685 ppm, pH1 is 7.41, pH2 is 8.12, and pH1 < pH2; the projected area of ​​the silica phase and the amorphous carbon layer on the surface of the matrix accounts for 62.3% and 37.7% of the matrix surface area, respectively, with d = 3 nm and the thickness of the amorphous carbon layer being 10 nm; the mass content of K decreases along the direction from the center of the silicon-carbon particles to the surface, at least some Cl is distributed inside the open pores, and at least some halogens are distributed at the interface between the silicon particles and the porous carbon matrix; based on the pore volume of the silicon-carbon particles, the closed... The pore volume ratio is 65.2%; the average pore diameter of open pores is 6.7 nm, and the average pore diameter of closed pores is 1.4 nm; X-ray photoelectron spectroscopy (XPS) analysis of silicon-carbon particles shows that the silicon dioxide content is 82.72% extending 3 nm inward from the surface of the silicon-carbon particles; XPS analysis of silicon-carbon particles shows that the silicon dioxide content is 7.15% extending 10 nm inward from the surface of the silicon-carbon particles; diffraction peaks exist in the X-ray diffraction pattern of silicon-carbon particles at 2θ = 20°-30°; the content of crystalline silicon in the silicon particles is 5.4%, and the content of amorphous silicon is 94.6%; the median particle size Dv of silicon-carbon particles is... 1 The particle size of silicon carbide particles is 8.72 μm, the average particle size is 6.5 nm, the sphericity is 0.935, and the specific surface area is 0.424 m². 2 / g, pore volume is 0.0013cm³ 3 / g, true density is 2.04g / cm³ 3The silicon-carbon particles contain 51.25% silicon by mass, the porous carbon matrix contains 44.62% porous carbon by mass, and amorphous carbon by mass. Based on the pore volume of the porous carbon matrix, open pores account for 98.5% of the volume, closed pores account for 1.5%, and the specific surface area of ​​the porous carbon matrix is ​​2086 m². 2 / g, pore volume is 1.316cm³ 3 / g.

[0153] Preparation Example 2: Step 1: F127 and KCl are mixed with the first solvent (anhydrous ethanol and deionized water in a volume ratio of 2:1) at a mass ratio of 5:1 to obtain the first mixture. Ammonia water is added and the mixture is magnetically stirred for 10 min. Then TFOS is slowly added to obtain the second mixture, with a volume ratio of ammonia water to TFOS of 0.67:1. The second mixture is then subjected to a water bath reaction at 40°C for 6 h. The precipitate is collected by centrifugation and washed with ethanol and deionized water to obtain the first product. Step 2: Disperse the first product in anhydrous ethanol, and mix it with 20 wt% ethanol solution of phenolic resin and NaOH at a mass ratio of 50:1. Stir magnetically at 60°C for 12 h, collect the precipitate by centrifugation and wash it with ethanol and deionized water to obtain the second product. Step 3: Place the second product in a tube furnace and heat it to 800℃ at 1℃ / min under N2 atmosphere and hold for 1h to obtain the third product. Then mix the second product with 2mol / L NaOH solution and react at 90℃ for 6h. After centrifugation, wash with deionized water until neutral to obtain porous carbon precursor. Step 4: Mix the porous carbon precursor and a toluene solution of 1 mg / mL PMMA at a ratio of 1 g / 100 mL, sonicate for 10 min, shake at low speed for 6 h, centrifuge to remove the supernatant, and vacuum dry at 60 °C for 1 h to obtain a precipitate. Place the precipitate in a tube furnace and heat it to 300 °C at 2 °C / min under N2 atmosphere and hold for 1.5 h. Wash it with 0.1 mol / L HCl at 60 °C to obtain a porous carbon matrix. Step 5: Place the porous carbon matrix in a tube furnace and heat it to 400°C at a rate of 10°C / min under a nitrogen atmosphere. Then switch to a first mixed gas (silane:nitrogen volume ratio of 2:8) with a flow rate of 60 sccm for the first deposition at 400°C for 3 hours. After the first mixed gas is exhausted, switch to a second mixed gas (oxygen:nitrogen volume ratio of 0.05:0.95) with a flow rate of 60 sccm for oxidation reaction and hold at that temperature for 15 minutes. After the second mixed gas is exhausted, introduce acetylene gas with a flow rate of 10 sccm and heat to 550°C for the second deposition for 2 hours to obtain the silicon-carbon particles, denoted as SC-2.

[0154] At this point, the mass content of K in the silicon-carbon particles is 102 ppm, the content of Cl is 100 ppm, pH1 is 6.12, pH2 is 7.52, and pH1 < pH2; the projected area of ​​the silica phase and the amorphous carbon layer on the surface of the matrix accounts for 61.8% and 38.2% of the matrix surface area, respectively, with d = 3 nm and the thickness of the amorphous carbon layer being 10 nm; the mass content of K decreases along the direction from the center of the silicon-carbon particles to the surface, at least some Cl is distributed inside the open pores, and at least some halogens are distributed at the interface between the silicon particles and the porous carbon matrix; based on the pore volume of the silicon-carbon particles, the closed... The pore volume accounts for 50.4% of the total volume; closed pores account for 0.5%, and the average pore diameter of open pores is 2.1 nm. X-ray photoelectron spectroscopy (XPS) analysis of the silicon-carbon particles shows that the silicon dioxide content is 71.65% extending 3 nm inward from the surface; XPS analysis of the silicon-carbon particles shows that the silicon dioxide content is 6.33% extending 10 nm inward from the surface; diffraction peaks are present in the X-ray diffraction pattern of the silicon-carbon particles at 2θ = 20°-30°; the content of crystalline silicon in the silicon particles is 1.3%, and the content of amorphous silicon is 98.7%; the median particle size Dv of the silicon-carbon particles is... 1 The particle size of silicon carbide particles is 6.2 μm, the average particle size is 2 nm, the sphericity is 0.814, and the specific surface area is 0.385 m². 2 / g, pore volume is 0.0012cm³ 3 / g, true density is 1.93g / cm³ 3 The silicon-carbon particles contain 52.19% silicon by mass, the porous carbon matrix contains 43.57% porous carbon by mass, and amorphous carbon by mass. Based on the pore volume of the porous carbon matrix, the open pore volume accounts for 99.5%, the average pore diameter of the closed pores is 0.8 nm, and the specific surface area of ​​the porous carbon matrix is ​​2495 m². 2 / g, pore volume is 1.034cm³ 3 / g.

[0155] Preparation Example 3: Step 1: F127 and KCl are mixed with the first solvent (anhydrous ethanol and deionized water in a volume ratio of 2:1) at a mass ratio of 1.67:1 to obtain the first mixture. Ammonia water is added and the mixture is magnetically stirred for 10 min. Then TFOS is slowly added to obtain the second mixture, with a volume ratio of ammonia water to TFOS of 0.45:1. The second mixture is then subjected to a water bath reaction at 40°C for 6 h. The precipitate is collected by centrifugation and washed with ethanol and deionized water to obtain the first product. Step 2: Disperse the first product in anhydrous ethanol, and mix it with 20 wt% ethanol solution of phenolic resin and NaOH at a mass ratio of 50:1. Stir magnetically at 60°C for 12 h, collect the precipitate by centrifugation and wash it with ethanol and deionized water to obtain the second product. Step 3: Place the second product in a tube furnace and heat it to 1000℃ at 1℃ / min under N2 atmosphere for 3 hours to obtain the third product. Then mix the second product with 2 mol / L NaOH solution and react at 90℃ for 6 hours. After centrifugation, wash with deionized water until neutral to obtain the porous carbon precursor. Step 4: Mix the porous carbon precursor and a toluene solution of 1 mg / mL PMMA at a ratio of 1 g / 100 mL, sonicate for 10 min, shake at low speed for 6 h, centrifuge to remove the supernatant, and vacuum dry at 60 °C for 1 h to obtain a precipitate. Place the precipitate in a tube furnace and heat it to 400 °C at 2 °C / min under N2 atmosphere and hold for 30 min. Wash it with 0.1 mol / L HCl at 60 °C to obtain a porous carbon matrix. Step 5: Place the porous carbon matrix in a tube furnace and heat it to 600°C at a rate of 10°C / min under a nitrogen atmosphere. Then switch to a first mixed gas (silane:nitrogen volume ratio of 2:8) with a flow rate of 60 sccm for the first deposition at 600°C for 3 hours. After the first mixed gas is exhausted, switch to a second mixed gas (oxygen:nitrogen volume ratio of 0.05:0.95) with a flow rate of 60 sccm for oxidation reaction and hold at that temperature for 15 minutes. After the second mixed gas is exhausted, introduce acetylene gas with a flow rate of 10 sccm and heat to 550°C for the second deposition for 2 hours to obtain the silicon-carbon particles, denoted as SC-3.

[0156] At this point, the mass content of K in the silicon-carbon particles is 759 ppm, the content of Cl is 772 ppm, pH1 is 7.63, pH2 is 8.29, and pH1 < pH2; the projected area of ​​the silica phase and the amorphous carbon layer on the surface of the matrix accounts for 62.5% and 37.5% of the matrix surface area, respectively, with d = 3 nm and the thickness of the amorphous carbon layer being 10 nm; the mass content of K decreases along the direction from the center of the silicon-carbon particles to the surface, at least some Cl is distributed inside the open pores, and at least some halogens are distributed at the interface between the silicon particles and the porous carbon matrix; based on the pore volume of the silicon-carbon particles, closed pores... The pore volume ratio was 79.6%; the average pore diameter of open pores was 9.8 nm, and the average pore diameter of closed pores was 1.9 nm; X-ray photoelectron spectroscopy analysis of the silicon-carbon particles showed that the silicon dioxide content was 94.43% extending 3 nm inward from the surface of the silicon-carbon particles; X-ray photoelectron spectroscopy analysis of the silicon-carbon particles showed that the silicon dioxide content was 8.86% extending 10 nm inward from the surface of the silicon-carbon particles; diffraction peaks were observed in the X-ray diffraction pattern of the silicon-carbon particles at 2θ = 20°-30°; the content of crystalline silicon in the silicon particles was 9.8%, and the content of amorphous silicon was 90.2%; the median particle size Dv of the silicon-carbon particles was... 1 The particle size of silicon carbide particles is 7.78 μm, the average particle size is 9.5 nm, the sphericity is 0.992, and the specific surface area is 0.447 m². 2 / g, pore volume is 0.001cm³ 3 / g, true density is 1.98g / cm³ 3 The silicon-carbon particles contain 51.77% silicon by mass, 44.15% porous carbon matrix by mass, and 4.08% amorphous carbon by mass. Based on the pore volume of the porous carbon matrix, open pores account for 95.2% of the volume, closed pores account for 4.8%, and the specific surface area of ​​the porous carbon matrix is ​​1523 m². 2 / g, pore volume is 1.497cm³ 3 / g.

[0157] Preparation Example 4: The preparation examples in this group were used to verify the "content of element K and halogens in silicon-carbon particles". This was achieved by changing the mass ratio of the template agent and KCl and / or the types of halogen compounds containing K, as detailed below: Preparation Example 4a was carried out in accordance with Preparation Example 1, except that the mass ratio of F127 to KCl was 10:1. The resulting silicon-carbon particles were designated as SC-4a. In this case, the mass content of K in the silicon-carbon particles was 54 ppm, the content of Cl was 51 ppm, pH1 was 6.1, pH2 was 7.49, and pH1 < pH2. Preparation Example 4b was carried out in accordance with Preparation Example 1, except that the mass ratio of F127 to KCl was 1.25:1. The resulting silicon-carbon particles were designated as SC-4b. In this case, the mass content of K in the silicon-carbon particles was 997 ppm, the content of Cl was 1995 ppm, pH1 was 7.96, pH2 was 9.01, and pH1 < pH2. Preparation Example 4c was carried out in accordance with Preparation Example 1, except that KCl was replaced with KF of the same mass fraction. The resulting silicon-carbon particles were denoted as SC-4c. In this case, the mass content of K in the silicon-carbon particles was 642 ppm, the content of F was 681 ppm, and pH1 < pH2. Preparation Example 4d was carried out in accordance with Preparation Example 1, except that KCl was replaced with KBr of the same mass fraction. The resulting silicon-carbon particles were denoted as SC-4d. At this time, the mass content of K in the silicon-carbon particles was 639 ppm, the content of F was 682 ppm, and pH1 < pH2.

[0158] Preparation Example 5: The preparation examples in this group are used to verify the "ratio of the projected area of ​​the silica phase and the amorphous carbon layer on the substrate surface to the substrate surface area" and / or the "thickness of the amorphous carbon layer and the depth (d) of the region where the silica phase is located". This is achieved by changing the "flow rate of the second mixed gas and / or the deposition time of the second deposition", as follows: Preparation Example 5a was performed in accordance with Preparation Example 1, except that the flow rate of the second mixed gas was 30 sccm and the deposition time of the second deposition was 1 h. The resulting silicon-carbon particles were designated SC-5a. In this case, the projected area of ​​the silica phase and the amorphous carbon layer on the substrate surface accounted for 50.8% and 49.2% of the substrate surface area, respectively, with a diameter (d) of 1 nm and a thickness of 2 nm for the amorphous carbon layer. X-ray photoelectron spectroscopy analysis of the silicon-carbon particles showed that the silica content was 12.24% extending 3 nm inward from the surface of the silicon-carbon particles. X-ray photoelectron spectroscopy analysis of the silicon-carbon particles showed that the silica content was 0% extending 10 nm inward from the surface of the silicon-carbon particles. Preparation Example 5b was performed in accordance with Preparation Example 1, except that the flow rate of the second mixed gas was 100 sccm and the deposition time of the second deposition was 3 h. The resulting silicon-carbon particles were designated SC-5b. In this case, the projected area of ​​the silica phase and the amorphous carbon layer on the substrate surface accounted for 98.5% and 1.5% of the substrate surface area, respectively, with d being 10 nm and the thickness of the amorphous carbon layer being 18 nm. X-ray photoelectron spectroscopy analysis of the silicon-carbon particles showed that the silica content was 98.6% extending 3 nm inward from the surface of the silicon-carbon particles. X-ray photoelectron spectroscopy analysis of the silicon-carbon particles showed that the silica content was 9.7% extending 10 nm inward from the surface of the silicon-carbon particles.

[0159] Preparation Example 6: This preparation example was used to verify the "volume percentage of closed pores in silicon-carbon particles" by changing the holding temperature and holding time of the second reaction, as follows: Preparation Example 6a was carried out in accordance with Preparation Example 1, except that the holding temperature of the second reaction was 700°C and the holding time was 1 h. The resulting silicon-carbon particles were designated as SC-6a. In this case, based on the pore volume of the silicon-carbon particles, the proportion of closed pores was 45.7%. Preparation Example 6b was carried out in accordance with Preparation Example 1, except that the holding temperature of the second reaction was 1100°C and the holding time was 4h. The resulting silicon-carbon particles were denoted as SC-6b. At this time, based on the pore volume of the silicon-carbon particles, the proportion of closed pore volume was 82.9%.

[0160] Preparation Example 7: The preparation was carried out in accordance with Example 1, except that the content of crystalline silicon in the silicon particles was changed by first heating to 800°C in step 5. The resulting silicon-carbon particles were designated as SC-7. At this time, the content of crystalline silicon in the silicon particles was 15.81%, and the content of amorphous silicon was 84.19%. In the X-ray diffraction pattern of the silicon-carbon particles, there were diffraction peaks at 2θ=20°-30°, and the diffraction peaks were sharper.

[0161] Preparation Example 8: The preparation examples in this group are used to verify the "change of heteroatoms," which is achieved by replacing the phenolic resin with other carbon sources, as detailed below: Preparation Example 8a was carried out in accordance with Preparation Example 1, and the resulting silicon-carbon particles were designated as SC-8a. The difference was that the silicon-carbon particles contained the elements H, S, and N, and the mass content of heteroatoms in the silicon-carbon particles was 1.22%. Preparation Example 8b was carried out with reference to Preparation Example 1, and the resulting silicon-carbon particles were designated as SC-8b. The difference was that the silicon-carbon particles contained elements H, S and N, and the mass content of heteroatoms in the silicon-carbon particles was 4.97%.

[0162] Preparation Example 9: The preparation examples in this group are used to verify the "median particle size Dv of silicon-carbon particles". 1 "50" is achieved through sieving using a porous carbon matrix, as detailed below: Preparation Example 9a was performed in accordance with Preparation Example 1, and the resulting silicon-carbon particles were designated SC-9a. The difference was that the median particle size Dv of the silicon-carbon particles was... 1 50 is 14.7 μm; Preparation Example 9b was performed in accordance with Preparation Example 1, and the resulting silicon-carbon particles were designated SC-9a. The difference was that the median particle size Dv of the silicon-carbon particles was... 1 50 is 4.3μm.

[0163] Preparation Example 10: The preparation was carried out in accordance with Preparation Example 1, except that the volume ratio of ammonia to TFOS was 0.2:1. The resulting silicon carbide particles were designated as SC-10, and the sphericity of the silicon carbide particles was 0.675.

[0164] Preparation Example 11: This group of preparation examples is used to verify the "mass content of silicon in silicon-carbon particles," which is achieved by changing the deposition time of the first deposition, as follows: Preparation Example 11a was performed in accordance with Preparation Example 1, except that the deposition time for the first deposition was 1 hour. The resulting silicon-carbon particles were designated as SC-11a. In this case, the mass content of silicon in the silicon-carbon particles was 30.53%, the mass content of the porous carbon matrix was 65.35%, and the mass content of amorphous carbon was 4.12%. Preparation Example 11b was carried out with reference to Preparation Example 1. The deposition time for the first deposition was 5 hours. The resulting silicon-carbon particles were designated as SC-11b. At this time, the mass content of silicon in the silicon-carbon particles was 69.94%, the mass content of the porous carbon matrix was 25.93%, and the mass content of amorphous carbon was 4.13%.

[0165] In Preparation Examples 1-11, unless otherwise stated, the following conditions are met: The specific surface area of ​​the silicon-carbon particles is all within 0.1 m². 2 / g-5m 2 Within the range of / g, the pore volume is consistently within 0.0005 cm³. 3 / g-0.002cm 3 Within the range of / g, the true density is consistently around 1.5cm³. 3 / g-2.3cm 3 Within the range of / g; the specific surface area of ​​the porous carbon matrix is ​​all within 1500m². 2 / g-2500m 2 Within the range of / g, the pore volume is consistently within 1cm³. 3 / g-1.5cm 3 Within the range of / g; the contact angle between silicon carbon particles and the test electrolyte is within the range of 20°-40°.

[0166] Comparative preparation group 1: The preparation examples in this group were used to verify the "content of element K and halogens in silicon-carbon particles". This was achieved by changing the mass ratio of the template agent and KCl and / or the types of halogen compounds containing K, as detailed below: Comparative preparation example 1a was carried out with reference to preparation example 1, except that the mass ratio of F127 to KCl was 5:6. The resulting silicon-carbon particles were denoted as SC-D1a. At this time, the mass content of K element in the silicon-carbon particles was 1557 ppm, the content of Cl element was 2213 ppm, pH1 was 8.35, pH2 was 9.52, and pH1 < pH2. Comparative preparation example 1b was performed with reference to preparation example 1, except that KCl was replaced with NaCl of the same mass fraction. The resulting silicon-carbon particles were denoted as SC-D1b. In this case, the mass content of K element in the silicon-carbon particles was 0 ppm, the content of Cl element was 0 ppm, pH1 was 6.72, pH2 was 6.72, and pH1=pH2.

[0167] Comparative preparation example 2: The preparation was carried out in accordance with Preparation Example 1, except that KCl was not added in step 1, and KCl was added after the formation of phenolic resin in step 2. The resulting silicon carbon particles were denoted as SC-D2. At this time, the K element was not encapsulated in closed pores, pH1 was 9.15, pH2 was 9.33, and pH1 < pH2.

[0168] Comparative preparation example 3: The preparation was carried out in accordance with Preparation Example 1, except that the holding temperature of the second reaction was 600°C, and the resulting silicon-carbon particles were designated as SC-D3. At this time, the mass content of K in the silicon-carbon particles was 645 ppm, the content of Cl was 712 ppm, the pore volume ratio of the closed pores in the silicon-carbon particles was 5.6%, the volume ratio of the open pores in the porous carbon matrix was 99.98%, the volume ratio of the closed pores was 0.02%, the pH was 8.5, the pH was 8.6, and pH1 < pH2.

[0169] Comparative preparation example 4: The preparation was carried out in accordance with Example 1, except that PMMA encapsulation was not used on the porous carbon precursor in step 4. The resulting silicon-carbon particles were designated as SC-D4. At this time, the mass content of K in the silicon-carbon particles was 558 ppm, the content of Cl was 712 ppm, the pore volume ratio of the closed pores in the silicon-carbon particles was 15.2%, the volume ratio of the open pores in the porous carbon matrix was 99.7%, the volume ratio of the closed pores was 0.3%, the pH was 7.82, the pH was 7.95, pH1 < pH2, and the mass content of K in the silicon-carbon particles increased from the center to the surface.

[0170] The following examples illustrate the lithium-ion secondary battery of the present invention.

[0171] Example 1: (1) Preparation of positive electrode: Lithium cobalt oxide, polyvinylidene fluoride (PVDF 500), positive electrode conductive agent Super P, and N-methylpyrrolidone (NMP) were mixed in a weight ratio of 97:2:3 and continuously stirred in a mixer to form a homogeneous, flowing positive electrode slurry. The positive electrode slurry was then coated onto an 8 μm thick aluminum foil and dried in a 120°C vacuum oven for 6 hours. After rolling and slitting, the positive electrode sheet was obtained.

[0172] (2) Preparation of negative electrode sheet: Artificial graphite, silicon carbide particles SC-1, negative electrode conductive agent Super P, carbon nanotubes, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed with water in a weight ratio of 93:5:0.5:0.5:0.5 and continuously stirred under the action of a mixer to form a homogeneous and fluid negative electrode slurry. Subsequently, the negative electrode slurry was coated onto the surface of a 10 μm thick copper foil and dried in a vacuum oven at 120°C for 6 hours. Then, it was rolled and slit to obtain the desired negative electrode sheet.

[0173] (3) Electrolyte preparation: In an argon-filled glove box (moisture content <1 ppm, oxygen content <1 ppm), ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate solvents are mixed in a mass ratio of 15:15:50:20 to form a homogeneous solvent. 15% LiPF6, 15% FEC, and 13% DFEA based on the total mass of the electrolyte are slowly added and stirred until homogeneous to obtain the electrolyte.

[0174] (4) Preparation of the diaphragm: A 2μm polyvinylidene fluoride and burlite mixed layer is coated on both sides of an 8μm polyethylene substrate.

[0175] (5) Preparation of lithium-ion secondary batteries: The positive electrode, separator, and negative electrode are stacked and wound to obtain a core; then the core is placed in an aluminum-plastic film, and electrolyte is injected into the dried core. After vacuum sealing, room temperature aging, and high temperature formation, the desired lithium-ion secondary battery is obtained.

[0176] Examples 2 through 11 were all carried out in accordance with Example 1, except that in the preparation of the negative electrode, silicon-carbon particles SC-1 were replaced with other silicon-carbon particles of equal mass, as shown in Table 1.

[0177] Example 12 group: This set of examples is used to verify the impact of changes in "FEC content", as detailed below: Example 12a is based on Example 1, except that the FEC content in the electrolyte is 4%; Example 12b is based on Example 1, except that the FEC content in the electrolyte is 20%.

[0178] Example 13 group: This set of examples is used to verify the impact of changes in "ethyl fluoroacetate", as detailed below: Example 13a is based on Example 1, except that the DFEA content in the electrolyte is 5%; Example 13b is based on Example 1, except that the DFEA content in the electrolyte is 50%. Example 13c is based on Example 1, except that DFEA in the electrolyte is replaced with an equal mass fraction of ethyl 2,2-difluoroacetate.

[0179] Comparative Examples 1-4 were all carried out in accordance with Example 1, except that in the preparation of the negative electrode, the silicon-carbon particles SC-1 were replaced with other silicon-carbon particles of equal mass, as shown in Table 1.

[0180] Test example: (1) Initial Coulomb efficiency: The batteries prepared in the embodiments of the present invention and the batteries prepared in the comparative examples were placed at 25℃±5℃ for 10 min; then charged at 3mA for 10 min, and placed at 10 min; then charged at a constant current of 0.1C to the upper limit cutoff voltage of 4.5V (cutoff current 0.02C), and the battery charging capacity was recorded; after placing at 10 min, the batteries were discharged at a constant current of 0.1C to the lower limit voltage of 3.0V, and the battery discharge capacity was recorded. The initial coulombic efficiency = (discharge capacity / charge capacity) × 100%. The test results are recorded in Table 1.

[0181] (2) Cyclic capacity retention: The batteries prepared in the embodiments of the present invention and the batteries prepared in the comparative examples were charged at a constant current of 0.5C to 4.53V, charged at a constant voltage of 0.1C, and allowed to stand for 10 minutes; then discharged at 0.2C to 3.0V and allowed to stand for 10 minutes. The initial discharge capacity of the battery at this time was measured and recorded as T0. After 500T cycles, the discharge capacity on the 500th cycle was measured and recorded as Tx. The capacity retention rate after 500T cycles is calculated as Tx / T0 × 100%. The test results are recorded in Table 1.

[0182] (3) Thickness expansion rate test: Before cycling, the initial thickness of the batteries prepared in the embodiments of the present invention and the batteries prepared in the comparative examples was measured and recorded using a PPG thickness gauge, denoted as H1. The batteries were charged at a constant current of 0.5C to 4.53V, then charged at a constant voltage of 0.1C. After standing for 10 minutes, they were discharged at 0.2C to 3V, and stood for 10 minutes. After cycling 500T, the batteries were fully charged, and the current thickness of the batteries was measured using a PPG thickness gauge, denoted as H2. The thickness change rate of the batteries was calculated using the following formula: (H2-H1) / H1×100%. The test results are recorded in Table 1.

[0183] (4) Ratio performance test: The batteries prepared in the embodiments of the present invention and the batteries prepared in the comparative examples were charged to 4.53V at a constant current of 0.2C, and then charged at a constant voltage of 4.53V with a cutoff current of 0.02C. After standing for 10 minutes, they were discharged to 3.0V at current densities of 0.2C and 1C, respectively. The ratio of the 1C discharge capacity to the 0.2C discharge capacity is the rate discharge capability of the battery. The test results are recorded in Table 1. Table 1 is as follows: In Example 5a, the depth (d) of the region where the silica phase is distributed along the direction from the substrate surface towards the center decreases, and the thickness of the amorphous carbon layer decreases. At this time, the stress buffering effect formed by the silica phase between the amorphous carbon layer and the substrate is weakened, and the amorphous carbon layer has a poor binding effect on the volume expansion of silicon particles, resulting in an increase in the battery expansion rate. At the same time, the side reactions between silicon carbon particles and electrolyte increase, leading to a decrease in battery cycle performance. In Example 5a, the thickness and d of the amorphous carbon layer are both at a higher level, and the projected area of ​​the silica phase is larger, which helps to alleviate volume expansion and reduce the side reactions caused by the exposure of fresh silicon particles, thereby improving the battery cycle performance. However, since the silica phase has poor ionic conductivity, it is not conducive to lithium ion transport. An excessively thick amorphous carbon layer will also increase the ion transport path, which will lead to a decrease in the rate performance of the battery.

[0184] As can be seen from Table 1, the lithium-ion secondary battery prepared in this invention has better cycle performance and kinetic performance than the comparative example, and the volume expansion rate is reduced.

[0185] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material includes silicon-carbon particles, the silicon-carbon particles include a matrix, and the matrix includes a porous carbon matrix and silicon particles located in the pores inside the porous carbon matrix. The porous carbon matrix includes open pores and closed pores. The open pores contain silicon particles, and the closed pores contain element K. Based on the total mass of the silicon-carbon particles, the mass content of element K is 50ppm-1000ppm. The silicon-carbon particles include halogens, and the mass content of the halogens is 50ppm-2000ppm based on the total mass of the silicon-carbon particles. The silicon carbon particles and deionized water are mixed at a mass ratio of 1:10 to obtain an aqueous solution, and the pH value of the aqueous solution at 25°C is pH1, which is 6-8.

2. The silicon-carbon anode material according to claim 1, wherein, The silicon-carbon particles also include a carbon layer located on at least a portion of the outer surface of the matrix; Preferably, the carbon layer comprises an amorphous carbon layer, the thickness of which is 1 nm-20 nm.

3. The silicon-carbon anode material according to claim 1, wherein the silicon-carbon particles contain a silicon dioxide phase; And / or, the silica phase is located on the surface of the substrate and / or in a region formed along the surface of the substrate to a depth d toward the center, where d is 1 nm-10 nm; Preferably, d is 1nm-5nm; More preferably, the region formed along the surface of the substrate to a depth of 1 nm-10 nm towards the center contains Si. 4+ .

4. The silicon-carbon anode material according to claim 1, wherein, Based on the total mass of the silicon-carbon particles, the mass content of element K is 100ppm-1000ppm; And / or, based on the total mass of the silicon carbide particles, the mass content of the halogen is 100ppm-800ppm; And / or, the halogen includes at least one of the elements Cl, F and Br; Preferably, the mass content of element K decreases along the direction from the center of the silicon-carbon particle towards the surface; Preferably, at least a portion of the halogen is distributed inside the opening, and at least a portion of the halogen is distributed at the interface between the silicon particles and the porous carbon matrix.

5. The silicon-carbon anode material according to claim 1, wherein, The median particle size Dv50 of the silicon-carbon particles is Dv 1 50. The silicon-carbon particles are ball-milled at a speed of 200 rpm-600 rpm until the median particle size Dv50 is (0.05-0.2) × Dv. 1 At 50°C, the ball-milled silicon carbon particles were mixed with deionized water at a mass ratio of 1:20 to obtain an aqueous solution. The pH value of the aqueous solution of the ball-milled silicon carbon particles was measured at 25°C to be pH2, which was 7.5-11. Preferably, pH1 and pH2 satisfy the condition: pH1 < pH2.

6. The silicon-carbon anode material according to claim 1, wherein, X-ray photoelectron spectroscopy analysis of the silicon-carbon particles showed that the silicon dioxide content was 50%-99% extending 3 nm inward from the surface of the silicon-carbon particles. And / or, X-ray photoelectron spectroscopy analysis is performed on the silicon-carbon particles, extending 10 nm inward from the surface of the silicon-carbon particles, and the silicon dioxide content is 0%-10%; And / or, in the X-ray diffraction pattern of the silicon-carbon particles, there are diffraction peaks at 2θ = 20°-30°.

7. The silicon-carbon anode material according to claim 1, wherein, Based on the total mass of the silicon-carbon particles, the mass content of silicon element is 30%-70%; And / or, the silicon particles comprise crystalline silicon and amorphous silicon, wherein, based on the total mass of the silicon particles, the content of crystalline silicon is 0%-10% and the content of amorphous silicon is 90%-100%; Preferably, the silicon-carbon particles further include heteroatoms, and the mass content of the heteroatoms is 1%-5% based on the total mass of the silicon-carbon particles; More preferably, the heteroatom includes at least one of the elements H, S, P and N.

8. The silicon-carbon anode material according to claim 1, wherein, Based on the pore volume of the silicon-carbon particles, the closed-pore volume accounts for 20%-80% of the total pore volume. And / or, the average pore size of the open pore is 2nm-10nm, and the average pore size of the closed pore is 0.6nm-2nm; And / or, the median particle size Dv50 of the silicon-carbon particles is Dv 1 50, 1μm≤Dv 1 50≤15μm; And / or, the size of the silicon particles is 1nm-100nm; And / or, the sphericity of the silicon-carbon particles is 0.7-1; And / or, the specific surface area of ​​the silicon-carbon particles is 0.1 m². 2 / g-5m 2 / g; And / or, the pore volume of the silicon carbide particles is 0.0005 cm³. 3 / g-0.002cm 3 / g; And / or, the true density of the silicon-carbon particles is 1.5 cm³. 3 / g-2.3cm 3 / g; And / or, at 25°C, 200 mg of the silicon carbon particles are taken for contact angle testing, wherein the test electrolyte includes ethylene carbonate and methyl ethyl carbonate in a mass ratio of 3:7 and 1 mol / L lithium hexafluorophosphate, and the contact angle between the silicon carbon particles and the test electrolyte is 20°-40°.

9. A lithium-ion secondary battery, characterized in that, The lithium-ion secondary battery includes a negative electrode and an electrolyte, wherein the negative electrode comprises the silicon-carbon negative electrode material as described in any one of claims 1-8.

10. The lithium-ion secondary battery according to claim 9, wherein, The electrolyte comprises fluoroethylene carbonate and / or fluoroethyl acetate; And / or, the fluoroethyl acetate includes ethyl difluoroacetate, which includes at least one of ethyl 2,2-difluoroacetate and ethyl 2,2-difluoroacetate; And / or, based on the total mass of the electrolyte, the mass content of the fluoroethylene carbonate is 4%-20%; And / or, based on the total mass of the electrolyte, the mass content of the ethyl fluoroacetate is 5%-50%.

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