Nano silicon carbon composite materials, their preparation methods and uses

Abstract

This application provides a nanosilicon carbon composite material, its preparation method, and uses. The nanosilicon carbon composite material comprises silicon nanoparticles, closed pores, and a turbostratic graphite three-dimensional network structure, where the closed pores are pore volume inaccessible to N2, the closed pores include microporous closed pores, the turbostratic graphite three-dimensional network structure comprises ultralarge interlayer spacing turbostratic graphite, the ultralarge interlayer spacing turbostratic graphite has a layer spacing of 0.40-0.55 nm, and the silicon nanoparticles and closed pores are dispersed in the turbostratic graphite three-dimensional network structure. The nanosilicon carbon composite material effectively mitigates the volume expansion of silicon during charge-discharge cycling, improves electrode cycling stability, and exhibits excellent electrochemical performance when used in lithium-ion secondary batteries.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on and claims priority from a Chinese application having CN application number 202211570400.7 and filing date December 8, 2022, the disclosure of which is hereby incorporated in its entirety into this application. [Technical Field]

[0002] The present invention relates to the field of battery technology, and in particular to nano silicon carbon composite materials, their preparation methods and uses. [Background technology]

[0003] Silicon has an extremely high theoretical capacity and can store Li at room temperature. 15 It is possible to form a Si4 alloy, with a theoretical capacity of 3579 mAh / g, and it is expected to replace conventional graphite anodes and become the anode material for next-generation high-specific-energy lithium-ion batteries.

[0004] Silicon has two problems as an anode material for lithium-ion batteries. Silicon has poor electrical conductivity, which can be solved by using a number of methods, including carbon carriers, carbon compounding, and carbon coating. Second, silicon undergoes large volume expansion and contraction during the lithium absorption and desorption process, which destroys the electrode structure, reduces battery capacity, and reduces cycle efficiency.

[0005] In recent years, the volume expansion of silicon-based anode materials such as silicon oxide anode materials and silicon carbon anode materials has been significantly reduced by optimizing the size and distribution of silicon particles and adjusting and modifying the structure of the anode materials. However, these improvements are still insufficient for practical use. Summary of the Invention [Problem to be solved by the invention]

[0006] The main objective of the present invention is to provide a nano silicon carbon composite material, its preparation method and use, which can effectively alleviate the relatively large volume expansion of silicon in the nano silicon carbon composite material, and solve the problem of poor cycling stability of silicon carbon composite materials in the prior art. [Means for solving the problem]

[0007] To achieve the above object, according to one aspect of the present invention, there is provided a nanosilicon carbon composite material, which comprises silicon nanoparticles, closed pores, and a turbostratic graphite three-dimensional network structure, wherein the closed pores are pore volumes that are inaccessible to N2, and the closed pores include micropores and closed pores, the turbostratic graphite three-dimensional network structure comprises ultra-large interlayer spacing turbostratic graphite, and the layer spacing of the ultra-large interlayer spacing turbostratic graphite is 0.40 to 0.55 nm, and the silicon nanoparticles and closed pores are dispersed in the turbostratic graphite three-dimensional network structure.

[0008] According to another aspect of the present invention, there is provided a method for preparing a nanosilicon carbon composite material, specifically, in step S1, a porous carbon skeleton is provided, the porous carbon skeleton being a three-dimensional network structure formed by turbostratic graphite, and including micropores and closed pores, and the porous carbon skeleton includes ultra-large interlayer spacing turbostratic graphite, and the ultra-large interlayer spacing turbostratic graphite has a layer spacing of 0.40-0.55 nm; in step S2, the porous carbon skeleton of step S1 is contacted with a silicon-containing precursor at 200-1000°C for 0.1-100 hours, and after cooling, the resulting material is crushed and / or classified to obtain a nanosilicon carbon composite material.

[0009] According to another aspect of the present invention, there is provided a negative electrode comprising the nanosilicon carbon composite material described above or the nanosilicon carbon composite material obtained by the above preparation method.

[0010] According to yet another aspect of the present invention, there is provided a battery, comprising a positive electrode and a negative electrode, wherein the negative electrode comprises the nano silicon carbon composite material described above or the nano silicon carbon composite material obtained by the preparation method described above, and preferably the battery is a lithium ion secondary battery. [Effects of the Invention]

[0011] The application of the technical solution of the present invention has the following beneficial effects:

[0012] In response to the problem that lithium absorption in silicon in silicon carbon composites causes volume expansion of the electrode material and further leads to poor cycle stability, the present application provides a nano silicon carbon composite, which comprises silicon nanoparticles, closed pores, and a turbostratic graphite three-dimensional network structure.

[0013] First, the three-dimensional turbostratic graphite network structure in the nano-silicon carbon composite material contains graphite sheet layers with a layer spacing in the range of 0.40 nm to 0.55 nm. The layer spacing of this ultra-large-spacing turbostratic graphite can dynamically store lithium ions, providing a long-term, effective cycling mechanism for dynamic lithium storage and release during the charge-discharge cycle of a lithium-ion battery, and improving the electrode cycling stability.

[0014] The closed pores in the nano silicon carbon composite material include micropores, and the closed pores of this size can dynamically store lithium ions as well during charge-discharge cycles, improving the stability of the electrode cycle.

[0015] Second, the turbostratic graphite structure can absorb the volume expansion of silicon nanoparticles during the charge-discharge cycle, reducing the destruction of the composite structure due to silicon lithiation and improving the electrode cycle stability. The closed pores in the nanosilicon carbon composite can also provide elastic space for the volume expansion of silicon lithiation in the nanosilicon carbon composite, improving the electrode cycle stability.

[0016] In addition, the silicon and carbon elements in the nano-silicon carbon composite are uniformly dispersed at the nanoscale, and the silicon nanoparticles are dispersed in a turbostratic graphite three-dimensional network structure at nano-sized particles, e.g., 2 nm or even smaller. The relatively small size of the silicon particles effectively alleviates the non-uniform deformation caused by the lithium-silicon alloying reaction within the particles, preventing the collapse of the composite structure due to the rupture of silicon particles after multiple charge-discharge cycles, and improving the cycle stability of the composite electrode. [Brief explanation of the drawings]

[0017] The drawings in the specification that form a part of this application are used to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and the description thereof are used to interpret the present invention and are not intended to unduly limit the present invention. [Figure 1] 1 shows an XRD spectrum of the nano silicon carbon composite material obtained in Example 1. [Figure 2] 1 shows N2 adsorption isotherms of the nano silicon carbon composite material obtained in Example 1 and the material after crushing. [Figure 3] 1 shows an HRTEM image of the nano silicon carbon composite material obtained in Example 1. [Figure 4] An example of a method for calculating the volume ratio of ultra-large interlayer spacing turbostratic graphite will be shown below. [Figure 5] 1 shows the Raman spectrum of the nano silicon carbon composite material obtained in Example 1. [Figure 6] 1 shows a cross-sectional SEM photograph of the nanosilicon carbon composite material obtained in Example 1. [Figure 7] 1 shows an SEM-EDS image of the cross section of a particle of the nano silicon carbon composite material obtained in Example 1. [Figure 8] 1 shows the results of a cycle performance test of a whole battery including electrodes made of the nano silicon carbon composite material obtained in Example 1 and a whole battery including electrodes made of the silicon carbon composite material obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] It should be noted that, where no conflict exists, the embodiments and features in the embodiments in the present application can be combined with each other.The present invention will now be described in detail with reference to the drawings and in conjunction with the embodiments.

[0019] 1. Nano silicon carbon composite materials In an exemplary embodiment of the present application, there is provided a nanosilicon carbon composite material, the nanosilicon carbon composite material comprising silicon nanoparticles, closed pores, and a turbostratic graphite three-dimensional network structure, wherein the closed pores are pore volumes inaccessible to N2, the closed pores include micropores and closed pores, the turbostratic graphite three-dimensional network structure comprises ultra-large interlayer spacing turbostratic graphite, and the ultra-large interlayer spacing turbostratic graphite has a layer spacing of 0.40-0.55 nm, and the silicon nanoparticles and closed pores are dispersed in the turbostratic graphite three-dimensional network structure.

[0020] A three-dimensional turbostratic graphite network structure is typically formed during the preparation of carbon materials. The random, disordered stacking of turbostratic graphite leaves open and / or closed micropores (pore diameters less than 2 nm) and mesopores (pore diameters 2-50 nm). The surfaces of the open pores are the surfaces of the in-situ deposition of silicon nanoparticles, and after the deposition is completed, the open pores are filled by the silicon nanoparticles, forming new closed pores within them during the deposition process. Therefore, in this application, the silicon nanoparticles and closed pores are dispersed in the three-dimensional turbostratic graphite network structure. The presence of turbostratic graphite and closed pores can mitigate the volume effect of silicon nanoparticles, reduce the expansion of nanosilicon carbon composites during lithium absorption, prevent the rupture of silicon nanoparticles, and improve the structural stability of the composite. The resulting composite electrodes exhibit relatively good cycling stability. More importantly, the ultra-large interlayer spacing turbostratic graphite and microporous closed pores have certain dynamic lithium storage properties, allowing repeated lithium storage and release during electrochemical cycling, providing a long-term effective lithium storage mechanism, with 1-2 cycles occurring every 5-10 cycles, resulting in a battery cycling efficiency greater than 100%, and thus further improving the battery cycling stability.

[0021] The silicon nanoparticles are silicon nanoparticles formed in situ with a turbostratic graphite three-dimensional network structure. Unlike the submicron-scale (approximately 100 nm) silicon particles obtained by conventional methods such as crushing, grinding, or other grinding processes, the silicon nanoparticles formed in situ are smaller, typically less than 20 nm, preferably less than 5 nm, and more preferably less than 2 nm, and are typically amorphous. XRD analysis of the nano silicon carbon composite material provided herein reveals a single, relatively broad peak packet (Figure 1) without a significant crystalline peak at the Si crystal peak position (2θ = 28.4°). The in situ formed silicon nanoparticles are dispersed in the turbostratic graphite three-dimensional network structure, forming a nanoscale homogeneous mixture with the turbostratic graphite three-dimensional network structure carbon material. Smaller silicon nanoparticles are more advantageous in preventing irreversible destruction of the silicon particle structure due to non-uniform deformation within the particles, and when they are uniformly dispersed in the turbostratic graphite three-dimensional network structure, the ultra-large interlayer spacing turbostratic graphite and closed pores can provide a certain buffer against the volume expansion of silicon during lithium absorption.

[0022] Closed pores are pores that cannot be accessed by N2, including external open pores that cannot be accessed by N2, and pores that exist inside the nano silicon carbon composite particles and are isolated from the particle surface, the latter of which may also be called internal pores. Closed pores correspond to open pores, and in this application, open pores are pores that can be accessed by N2, and pores that cannot be accessed by N2, are connected to the surface, and are so small in size that only He can access them are treated as closed pores in this application.

[0023] Because nanosilicon carbon composite materials have ultra-large interlayer spacing and closed pores, their skeletal density is necessarily smaller than the theoretical density of non-porous pure silicon and pure carbon materials (e.g., graphite). The volume of closed pores within a material can be calculated from the skeletal density and theoretical density. Generally, the skeletal density of a material is determined by helium pycnometry, and in this specification, the skeletal density of a material determined by helium pycnometry is referred to as the true density of the material.

[0024] The detection of internal pores is estimated by the true density of the composite material obtained by helium pycnometry. If the true density of the material is smaller than the true density of a completely intimately adjoining material with the same elemental composition, it indicates the presence of internal pores. The volume of the internal pores is calculated by subtracting the reciprocal of the true density of the completely intimately adjoining material with the same elemental composition (closed pore volume) from the reciprocal of the true density of the composite material (closed pore volume + intimate volume). The volume of closed pores obtained by testing the true density cannot provide information on their size.

[0025] Analysis of the pore size inside particles can be performed by observing the particle cross-section. By cutting a nanosilicon carbon composite particle to expose the internal cross-section, and observing it under a scanning electron microscope at high magnification, the presence of pores can be observed. These pores are usually not interconnected, and although there may be a small amount of interconnection, they are all covered inside the particle, making them internal pores. Micropores (pore widths less than 2 nm) within the cross-section are difficult to clearly observe due to their small size. Furthermore, quantitative information cannot be obtained from observing the cross-sectional shape, and there is uncertainty due to the influence of the cut surface and cutting effects.

[0026] To obtain detailed information about the closed pore distribution of a composite material, this application proposes that after a certain treatment, the composite material is further subjected to gas adsorption to measure the pore distribution, and the pore distribution results before and after treatment are compared to obtain closed pore distribution information. Conventional gas adsorption methods, such as N2 adsorption / desorption, can measure the volume of open pores accessible to N2 (i.e., the commonly referred to pore volume), but cannot measure the volume that N2 cannot enter or the volume of closed pores inside the material. Nanosilicon carbon composite particles can be crushed, ground, crushed, or otherwise crushed to expose the closed pores inside the particles, creating new open pores that can be measured by N2 adsorption. The newly added pore volume is the closed pore volume, and theoretically, the volume of closed pores detected in this area is less than the actual volume of closed pores. Based on the N2 adsorption test results, the total pore volume of the material can be obtained, and the pore distribution of the material can be analyzed, typically by using the t method to obtain the micropore volume and mesopore volume. Based on the N2 adsorption test results before and after crushing of the nano silicon carbon composite material, the volumes of the micropores and mesopores before and after crushing of the material can be obtained, thereby obtaining information on the closed pores of the micropores and closed pores of the mesopores.

[0027] It should be noted that the pore volume calculated based on the true density measured by helium pycnometry includes / is larger than the closed pore volume obtained by crushing the material mentioned in this application and then performing an N2 adsorption test, because in the pore volume exposed after crushing, some small pores may not be in contact with large N2 molecules.

[0028] In this application, nano silicon carbon composite materials are crushed at 20 MPa, typically held at 20 MPa for 3 minutes, and the resulting powder is subjected to N2 adsorption testing, revealing that the specific surface area and pore volume of the crushed material both increase to a certain extent compared to the uncrushed material. Figure 2 shows the N2 adsorption isotherms of the nano silicon carbon composite material of Example 1 and its post-crushing treatment, showing that the specific surface area and pore volume of the material both increase to a certain extent. The N2 adsorption isotherm of the nano silicon carbon composite material before crushing shows no micropore filling, but after crushing, obvious micropore filling occurs, indicating the presence of closed micropores in the composite. Based on the adsorption isotherms, the open pore volumes of the composite and its post-crushing treatment are calculated to be 0.025 cm3, respectively. 3 / g and 0.046cm 3 / g, and the open pore volumes of the micropores in the composite and crushed materials were calculated based on the adsorption isotherm method: 0 and 0.004 cm3, respectively. 3 / g, so the volume of closed micropores in the composite is 0.004 cm 3 / g.

[0029] The three-dimensional network structure of turbostratic graphite refers to a three-dimensional spatial network structure formed by turbostratic graphite sheet layers. High-resolution transmission electron microscopy (HRTEM) can observe the irregular crystal lattice fringes of turbostratic graphite carbon. Generally, the layer spacing of the turbostratic graphite structure is 0.34-0.40 nm. The nanosilicon carbon composite material provided herein contains ultra-large interlayer spacing turbostratic graphite, which refers to turbostratic graphite with graphite-like sheet layer spacing in the range of 0.40-0.55 nm. Figure 3 shows an HRTEM image of the nanosilicon carbon composite material provided herein. The spacing is 0.40-0.50 nm, and irregular crystal lattice fringes resembling those of worms and earthworms are observed, i.e., the ultra-large interlayer spacing turbostratic graphite sheet layer structure is present. The layer spacing of the turbostratic graphite three-dimensional network structure in the nano silicon carbon composite material can have a wide range, such as 0.34-0.41 nm, 0.34-0.42 nm, 0.34-0.45 nm, 0.34-0.47 nm, 0.34-0.50 nm, 0.34-0.55 nm, 0.35-0.55 nm, 0.37-0.55 nm, 0.38-0.55 nm, 0.35-0.45 nm, 0.35-0.50 nm, 0.36-0.48 nm, 0.36-0.53 nm, 0.37-0.47 nm, 0.37-0.52 nm, 0.38-0.54 nm, etc., and among these, graphite-like sheet layers with a layer spacing of 0.40 nm or more are the ultra-large layer spacing turbostratic graphite of the present invention. In some embodiments, the layer spacing of the ultra-large layer spacing turbostratic graphite in the nano silicon carbon composite material may be, but is not limited to, 0.40-0.42 nm, 0.40-0.43 nm, 0.40-0.45 nm, 0.40-0.46 nm, 0.40-0.49 nm, 0.40-0.51 nm, 0.40-0.53 nm, 0.40-0.54 nm, etc.

[0030] TEM can only observe local information and cannot obtain statistical information about the entire material, which can be reflected by XRD analysis. Turbostratic graphite structure is formed by stacking graphite-like sheet layers, and there is a certain degree of short-range order, but long-range disorder. For the long-range ordered graphite sheet layer structure, a sharp diffraction peak is observed at 2θ=26.4° using X-ray diffraction (XRD), reflecting the ordered structure in the c-axis direction of graphite, and the corresponding carbon hexahedral layer spacing d 002 = 0.337 nm. The turbostratic graphite structure exhibits long-range disorder in the carbon, resulting in a broad peak packet within the 2θ range of 15-38°, with the peak located between 2θ = 23.0-26.6°. Crystalline silicon has a characteristic peak at 2θ = 28.4°. In the nanosilicon carbon composite material of the present application, the silicon exists in the form of nanoparticles, which are small in size and nearly amorphous, forming a broad peak packet at this position. As a result, the diffraction peaks of turbostratic graphite carbon and silicon nanoparticles overlap. As a result, the XRD diffraction curve (Figure 1) exhibits a broad peak packet within the 2θ range of 15-38°, with the peak located between 2θ = 27.0°, making it difficult to analyze silicon and carbon separately.

[0031] By analyzing the XRD results and electrochemical performance of different samples in detail, the inventors found that when nano silicon carbon composites are applied to lithium ion batteries as anode active components, their cycle stability is highly correlated with the relative intensity in the range of 2θ=16.1~22.2° in the XRD results, and the higher the relative intensity in this region, the better the battery cycle stability. For carbon materials, the diffraction in the range of 2θ=16.1~22.2° corresponds to the layer spacing d 002=0.40~0.55nm, which corresponds to the above-mentioned ultra-large interlayer spacing. Therefore, the present application provides a semi-quantitative method based on XRD results to calculate the volume content of ultra-large interlayer spacing turbostratic graphite in nano silicon carbon composites, which is determined by the relative intensity in the range of 2θ=16.1~22.2° in the XRD curve of the composite. Furthermore, it has been found that the cycling stability of batteries using anodes containing the nano silicon carbon composites is positively correlated with the content of ultra-large interlayer spacing turbostratic graphite.

[0032] Taking the nano silicon carbon composite material of Example 1 as an example, as shown in Figure 4, diffraction curve A is the spectral line of the composite material after XRD curve smoothing processing, with its peak point at 2θ = x1° ≥ 27.0°, the peak start point (low-angle peak valley) at 2θ = x0° being located in the range of 2θ = 15 to 22°, and the peak end point (high-angle peak valley) at 2θ = x2° being located in the range of 2θ = 35 to 40°, and if x0° ≤ 16.1°, then x0° = 16.1°. Line B passing through the peak valley position at 2θ = x2° and parallel to the x-axis is used as the background line, and the integral A1 from 2θ = x0 to 22.2° is d 002 ≧0.40nm corresponds to the super-large layer spacing turbostratic graphite, and the integral A2 at 2θ=22.2~x1° is d 002 The curve integral A0 = A1 + A2 from 2θ = x0 to x1° corresponds to normal turbostratic graphite with a spacing of ≦0.40 nm. This is the total amount of carbon in the three-dimensional network structure of turbostratic graphite. A1 / A0 is the ratio of the volume of ultra-large interlayer spacing turbostratic graphite to the volume of the three-dimensional network structure of turbostratic graphite.

[0033] In summary, the nanosilicon carbon composite material provided herein comprises silicon nanoparticles, closed pores, and a turbostratic graphite three-dimensional network structure, wherein the closed pores include micropores and closed pores, and the turbostratic graphite three-dimensional network structure comprises ultra-large interlayer spacing turbostratic graphite with a layer spacing of 0.40-0.55 nm. The silicon nanoparticles and closed pores are dispersed within the turbostratic graphite three-dimensional network structure, and the silicon and carbon elements in the nanosilicon carbon composite are uniformly dispersed at the nanoscale. The silicon nanoparticles and closed pores are dispersed within the turbostratic graphite three-dimensional network structure. The presence of turbostratic graphite and closed pores can mitigate the volume effect of the silicon nanoparticles, reduce the expansion of the nanosilicon carbon composite during lithium absorption, prevent the rupture of the silicon nanoparticles, and improve the structural stability of the composite. The resulting composite electrode exhibits relatively good cycle stability. More importantly, the ultra-large interlayer spacing turbostratic graphite and microporous closed pores have certain dynamic lithium storage properties, allowing repeated lithium storage and release during electrochemical cycling, providing a long-term, effective lithium storage mechanism and improving the cycling stability of the battery.

[0034] The theoretical density of pure silicon material is 2.33 g / cm 3 The theoretical density of graphite does not have a specific value depending on the carbon layer spacing, but is 2.09 to 2.33 g / cm 3 The carbon material in the nano silicon carbon composite has a turbostratic graphite three-dimensional network structure, and its theoretical density is 2.09 g / cm 3 Then, the theoretical density of 50%C+50%Si is 2.21g / cm 3 In some embodiments, the nano silicon carbon composite material has a true density of 1.2 to 2.1 g / cm as determined by helium pycnometry. 3 Accordingly, the volume of the inner hole is 0.02 to 0.38 cm 3 / g. Limiting the true density of the nano silicon carbon composite material to this range, compared with other ranges, is advantageous in providing sufficient buffer space for the lithium absorption and expansion of silicon, improving the structural stability of the material and thereby improving the cycle stability of lithium secondary batteries. If the true density is too low (i.e., the pore volume is too large), the nano silicon carbon composite will contain many pores, which can provide buffer space for the lithium absorption and expansion of silicon. However, if the pores are too large during the preparation of the pole pieces, the pole pieces will be easily crushed during the roll pressing process, increasing the specific surface area or causing the silicon to lose electrical contact, reducing the initial coulombic efficiency of the battery or making it difficult to achieve a high green density, reducing the volumetric energy density of the material and limiting its applications.

[0035] In order to further improve the structural stability of the material and the cycle stability of the lithium secondary battery, the true density of the nano silicon carbon composite material is preferably 1.2 to 1.3 g / cm. 3 , 1.3~1.4g / cm 3 , 1.4~1.5g / cm 3 , 1.5~1.6g / cm 3 , 1.6~1.7g / cm 3 , 1.7~1.8g / cm 3 , 1.8~1.9g / cm 3 , 1.9~2.0g / cm 3 , 2.0~2.1g / cm 3 is.

[0036] In some embodiments, the nano silicon carbon composite material contains SiO x where x is 0-2. During the preparation process of nano-silicon carbon composites, oxygen treatment can be introduced at different stages, which can result in the composites containing SiO x Forms SiO xThe introduction of is beneficial to reduce the stress change caused by lithium absorption expansion and lithium release contraction of silicon, and is beneficial to improve the structural strength of the material, and further beneficial to improve its cycle stability in lithium ion batteries.

[0037] In some embodiments, the size of the silicon nanoparticles is 0.5-20 nm, preferably 0.5-2 nm. To better mitigate problems such as stress concentration due to lithium absorption expansion, resulting in silicon particle pulverization, and repeated SEI regeneration, the silicon nanoparticles must have a small size. For example, the size of the silicon nanoparticles may be 0.5-10 nm, 0.5-5 nm, 3-5 nm, 1.5-2.5 nm, or 1-3 nm. In some embodiments, the silicon nanoparticles are amorphous silicon.

[0038] Turbostratic graphite can provide a buffer space for the volume expansion of silicon, which is beneficial for mitigating the volume expansion and contraction during the lithium absorption / desorption process of silicon. Ultra-large interlayer spacing turbostratic graphite also possesses dynamic lithium storage / desorption properties, thereby providing a long-term, effective lithium storage mechanism and further improving the cycle stability of the composite. On the other hand, a high content of ultra-large interlayer spacing turbostratic graphite increases the volume of the composite, reducing its structural stability and its battery performance. Therefore, the content of ultra-large interlayer spacing turbostratic graphite must be controlled within a certain range. In some embodiments, the volume content of ultra-large interlayer spacing turbostratic graphite in the three-dimensional network structure of turbostratic graphite is 10% to 50%, i.e., A1 / A0 is 10% to 50%. For example, A1 / A0 may be, but is not limited to, 13%, 15%, 17%, 20%, 25%, 30%, 35%, 40%, 45%, or 48%. In some embodiments, A1 / A0 may be 11% to 16%, 12% to 22%, 15% to 35%, 24% to 38%, 26% to 42%, 32% to 48%, or 39% to 49%, etc.

[0039] Stacking size L in the c-axis direction of ultra-large layer spacing turbostratic graphite cand size L in the a-axis direction a are important parameters that characterize the turbostratic graphite structure, and the larger both are, the higher the order of the turbostratic graphite, which is unfavorable for the turbostratic graphite's function in buffering the lithium absorption expansion of silicon. In some embodiments, the stacking size L in the c-axis direction of the ultra-large interlayer spacing turbostratic graphite c is 0.4 to 2 nm. That is, the number of stacked layers of the graphite-like sheet layers in the c-axis direction of the ultra-large interlayer spacing turbostratic graphite may be 1, 2, 3, or 4. The selection of the number of stacked layers is related to the layer spacing of the graphite-like sheet layers stacked to form the turbostratic graphite. In some embodiments, the size L of the ultra-large interlayer spacing turbostratic graphite in the a-axis direction a is 2 to 10 nm. For example, L a In some embodiments, L may be, but is not limited to, 2.1 nm, 2.5 nm, 2.7 nm, 3 nm, 3.2 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 8 nm, or 9 nm. a It may be 2 to 4 nm, 3.5 to 5.5 nm, 5 to 8 nm, or 7 to 10 nm, for example.

[0040] Raman Spectroscopic Test (Raman) Results D / I G is commonly used to characterize the degree of disorder in carbon materials. As mentioned above, in nano-Si / C composites, the higher the degree of disorder in the graphite-like sheet layers, the stronger its effect of buffering the lithium absorption expansion of silicon. The Raman spectrum of carbon materials has two characteristic peaks, with peak values ​​between 1310 and 1360 cm. -1 The peak located between 1560 and 1610 cm is the disorder peak (D peak). -1 The peak located between the graphite peak (G peak) is the graphite peak. The integrated area ratio of the D peak to the G peak (I D / I G ) can characterize the degree of disorder or graphitization of a carbon material, and I D / I GThe smaller the value, the lower the degree of disorder and the higher the degree of graphitization. Figure 5 shows the Raman spectrum test results for the nanocomposite material of Example 1. In some examples, the turbostratic graphite three-dimensional network structure in the nanosilicon carbon composite material has a relatively high degree of disorder. The Raman test method was used to determine the I D / I G is 0.5 to 5.0, and preferably, the I D / I G In some other embodiments, the I of the nano silicon carbon composite material is 1.0 to 2.0. D / I G may be 0.5 to 0.95, 0.6 to 1.2, 1.0 to 1.5, 1.8 to 2.5, 2.0 to 2.8, 2.5 to 3.3, 3.3 to 5.0, 3.5 to 5.0, or 4.0 to 5.0, for example.

[0041] In some embodiments, the specific surface area of ​​the nano silicon carbon composite material is between 0.1 and 50 m 2 / g, and the open pore volume is 0.001 to 0.05 cm 3 / g, and the open pore volume is the pore volume accessible to N2. In some other embodiments, the specific surface area of ​​the composite material is 0.2 to 48 m 2 / g, 0.15-19m 2 / g, 1.2-18m 2 / g, 0.15-14m 2 / g, 1.3-13m 2 / g, 0.15~9.8m 2 / g, 1.1-4.9m 2 / g, 5.1-9.9m 2 / g, 16-19m 2 / g, 0.5-30m 2 / g, 7-25m 2 / g, 24-45m 2 / g or 40-50m 2 / g, and the open pore volume of the composite material is 0.002 to 0.048 cm 3 / g, 0.005~0.045cm 3 / g, 0.0015~0.03cm 3 / g, 0.001~0.01cm 3 / g, 0.005~0.02cm 3 / g, 0.015~0.035cm 3 / g, 0.025~0.04cm 3 / g, 0.03~0.045cm 3 / g or 0.04~0.05cm 3 / g, etc.

[0042] In some embodiments, the ratio of the closed pore volume to the open pore volume in the nanosilicon carbon composite is 0.1 to 5. In other embodiments, the ratio of the closed pore volume to the open pore volume in the nanosilicon carbon composite may be 0.1 to 0.9, 0.5 to 1, 1 to 3, 2.5 to 3.5, 3 to 4.5, or 4 to 5, etc. In some embodiments, the closed pore volume of the nanosilicon carbon composite is 0.0001 to 0.25 cm. 3 In some other embodiments, the closed pore volume of the nano silicon carbon composite is 0.0001 to 0.0012 cm. 3 / g, 0.0003~0.0025cm 3 / g, 0.0014~0.0074cm 3 / g, 0.005~0.015cm 3 / g, 0.0001~0.01cm 3 / g, 0.012~0.03cm 3 / g, 0.025~0.04cm 3 / g, 0.03~0.045cm 3 / g, 0.008~0.047cm 3 / g, 0.0005~0.048cm 3 / g, 0.0001~0.0499cm 3 / g, 0.052~0.082cm 3 / g, 0.06~0.1cm 3 / g, 0.075~0.15cm 3 / g, 0.13~0.2cm 3 / g or 0.2 to 0.25 cm 3 / g, etc.

[0043] In some embodiments, the composite material further contains closed mesopores. In this application, a cross-section of a nanosilicon carbon composite material was obtained by Ar ion polishing, and field emission scanning electron microscopy (FEM) observation (Figure 6) revealed the presence of pores of 10-50 nm in the cross-section of the material, indicating the presence of closed mesopores in the material. The ratio of the volume of closed micropores to the volume of closed mesopores in the closed pores is 0.05-5. As can be seen from the N2 adsorption isotherms (Figure 2) of the nanosilicon carbon composite material of Example 1 and its crushed counterpart, not only is there a newly added micropore filling phenomenon after crushing, but the mesopore adsorption volume also increases significantly, meaning that both closed micropores and closed mesopores are present in the composite material. Based on the results of the adsorption isotherms and the t method, the open pore volumes of the mesopores in the composite material and its crushed counterpart were 0.025 cm3, respectively. 3 / g and 0.042cm 3 / g, and therefore the volumes of the micropores and mesopores in the composite material are 0.004 cm 3 / g and 0.017cm 3 / g, and the volume ratio of closed micropores to closed mesopores is 0.24. In some other embodiments, the ratio of the volume of closed micropores to the volume of closed mesopores in the closed pores may be 0.05 to 0.1, 0.1 to 0.3, 0.25 to 0.5, 0.3 to 0.8, 0.5 to 0.9, 0.8 to 1, 1 to 3, 2.5 to 3.5, 3 to 4.5, or 4 to 5, etc.

[0044] As mentioned above, nanosilicon carbon composites contain closed pores, which can buffer the volume expansion caused by lithium absorption in silicon. Closed pores include micropores and mesopores. Micropores with sizes between 0.4 and 0.8 nm can dynamically store lithium ions during charge-discharge cycles, improving the electrode's cycling stability. In this study, N2 adsorption / desorption tests were performed on the composite material and samples crushed at 20 MPa. The results of the N2 adsorption / desorption tests were analyzed in combination with other methods to calculate the content of open and closed pores in the material, as well as the content of micropores and mesopores within the open and closed pores. In some embodiments, the volume of micropores in the nanosilicon carbon composite is between 0.00005 and 0.21 cm3. 3 / g, and the closed mesopore volume of the nanosilicon carbon composite is 0.00017~0.24cm 3 In some other embodiments, the micropore closed pore volume of the nano silicon carbon composite is 0.00005 to 0.00015 cm 3 / g, 0.00012~0.00035cm 3 / g, 0.0003~0.0007cm 3 / g, 0.0005~0.001cm 3 / g, 0.001~0.003cm 3 / g, 0.0025~0.0065cm 3 / g, 0.006~0.009cm 3 / g, 0.008~0.02cm 3 / g, 0.015~0.035cm 3 / g, 0.03~0.07cm 3 / g, 0.06~0.1cm 3 / g, 0.09~0.14cm 3 / g, 0.13~0.18cm 3 / g or 0.15 to 0.21 cm 3 / g, and the mesopore closed pore volume of the nano silicon carbon composite material may be 0.00017 to 0.00035 cm 3 / g, 0.00019~0.0004cm 3 / g, 0.00034~0.00068cm 3 / g, 0.00065~0.001cm3 / g, 0.0009~0.002cm 3 / g, 0.0018~0.005cm 3 / g, 0.0045~0.009cm 3 / g, 0.008~0.024cm 3 / g, 0.01~0.035cm 3 / g, 0.02~0.048cm 3 / g, 0.047~0.075cm 3 / g, 0.07~0.1cm 3 / g, 0.09~0.15cm 3 / g, 0.12~0.18cm 3 / g, 0.15~0.23cm 3 / g or 0.20~0.24cm 3 / g, etc.

[0045] In some embodiments, the silicon content of the nanosilicon carbon composite material is 5-95 wt%. For example, the silicon content of the nanosilicon carbon composite material may be, but is not limited to, 35 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, or 70 wt%. In other embodiments, the silicon content of the nanosilicon carbon composite material may be 10-80 wt%, 5-20 wt%, 15-45 wt%, 30-75 wt%, 60-80 wt%, or 75-90 wt%.

[0046] In some embodiments, the silicon and carbon elements in the nano silicon carbon composite are uniformly dispersed at the nanoscale. Figure 7 shows an SEM-EDS image of the cross section of the nano silicon carbon composite of Example 1 after being polished with Ar ions, which shows that the carbon and silicon elements within the particles are uniformly dispersed at the nanoscale.

[0047] In some embodiments, silicon nanoparticles are obtained by chemical vapor deposition of silicon-containing precursors in turbostratic graphitic three-dimensional network structures at temperatures between 150 and 1000° C. Preferably, the silicon-containing precursors include, but are not limited to, one or more of monosilane, disilane, trisilane, halogenated silanes, polysilanes, siloles and their derivatives, and silafluorenes and their derivatives.

[0048] The turbostratic graphite three-dimensional network structure originates from the carbon material, and the type of carbon material or carbon precursor and its processing method have a significant impact on the turbostratic graphite three-dimensional network structure, the open pore volume and closed pore volume of the carbon material, and the distribution of open and closed pores. The open pores of carbon materials mainly consisting of a turbostratic graphite three-dimensional network structure are the sites for chemical vapor deposition of silicon-containing precursors, and at the same time, their pore structure and size restrict silicon nanoparticles to a relatively small size range, and the deposition of silicon-containing precursors also forms new closed pores. The turbostratic graphite three-dimensional network structure, silicon nanoparticles, and closed pores are the three basic components of the nanocomposite material of this application, all of which are closely related directly or indirectly to the carbon material. In some embodiments, the turbostratic graphitic three-dimensional network structure is derived from a carbon material, including, but not limited to, hard carbon, graphite, amorphous carbon, graphene, carbon materials prepared by pyrolysis and / or activation from polymer precursors, carbon materials prepared by pyrolysis and / or activation from biomass precursors, and carbon materials prepared by pyrolysis and / or activation from fossil carbon sources.

[0049] Doping the carbon precursor followed by carbonization and activation of the carbon material, or doping the carbon precursor followed by further carbonization and activation, can further increase the interlayer spacing of the hard carbon turbostratic graphite sheet layers and increase the pore volume of the carbon material, including the open pore volume and closed pore volume. In some embodiments, the carbon material for preparing the turbostratic graphite three-dimensional network structure contains one or more elements such as N, P, S, and B. Typical examples include N-doped porous carbon skeletons, P-doped porous carbon skeletons, and N / P co-doped porous carbon skeletons. In other embodiments, the carbon material for preparing the turbostratic graphite three-dimensional network structure contains one or more metal elements such as Na, K, Mg, Ca, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge. In yet other embodiments, the carbon material from which the turbostratic graphite three-dimensional network structure is prepared contains one or more elements, such as N, P, S, B, Na, K, Mg, Ca, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, etc. In some embodiments, the turbostratic graphite three-dimensional network structure is obtained after the carbon material is activated, including, but not limited to, contacting the carbon material with one or more of HO, CO, O, O, etc. at high temperature, and / or mixing the carbon material with one or more of NaOH, KOH, NaCO, KCO, potassium acetate, NaO, KO, NaO, KO, HPO, ZnCl, etc., followed by high temperature in an inert gas.

[0050] In some embodiments, the nanosilicon carbon composite material includes a surface coating layer, which can further improve the electrochemical performance of the nanosilicon carbon composite material. The thickness of the surface coating layer may be 0.2-500 nm, for example, but not limited to, 0.5 nm, 5 nm, 10 nm, 20 nm, 30 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, or 400 nm. In some embodiments, the thickness of the surface coating layer may be 0.2-20 nm, 10-100 nm, 100-300 nm, or 200-500 nm. The material for the surface coating layer may include, but is not limited to, one or more of a solid electrolyte, a conductive polymer, a carbonaceous material, a metal, an alloy, and a metal oxide. In some embodiments, the surface coating layer includes, but is not limited to, one or more of lithium hydroxide, lithium carbonate, lithium fluoride, lithium phosphate, lithium metaphosphate, aluminum dihydrogen phosphate, lithium metaaluminate, lithium aluminum phosphate, aluminum phosphate, aluminum metaphosphate, aluminum oxide, aluminum oxide monohydrate, aluminum oxide trihydrate, aluminum hydroxide, alumina sol, aluminum isopropoxide, magnesium oxide, magnesium hydroxide, zinc oxide, zinc hydroxide, titanium oxide, zirconium oxide, LiPON (lithium nitrophosphoric oxide), LLZO (lithium lanthanum zirconium oxygen), LATP (lithium titanium aluminum phosphate), LLTO (lithium lanthanum titanium oxygen), lithium germanium phosphorus sulfide, and the like; one or more of polymers and lithium complexes thereof, such as polyethylene oxide, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, and the like; LISICON-type solid electrolyte, NASICION-type solid electrolyte, perovskite-type solid electrolyte, garnet-type solid electrolyte, and sulfide solid electrolyte.

[0051] In some embodiments, the median diameter d of the nano silicon carbon composite 50 is 2 to 20 μm, and preferably, the median diameter d 50is 4 to 12 μm, and more preferably, the median diameter d 50 For example, the median diameter d of the nano silicon carbon composite material is 8 to 12 μm. 50 In some embodiments, the minimum particle size d of the nano silicon carbon composite material may be, but is not limited to, 3-5 μm, 6-7 μm, 8-10 μm, 10-12 μm, 9.5-10.5 μm, or 10-11 μm. min is 0.1 to 5 μm, and preferably, the minimum particle size d of the nano silicon carbon composite material min For example, the minimum particle size d of the nano silicon carbon composite material is 0.4 to 4 μm. min In some embodiments, the maximum particle size d of the nano silicon carbon composite material may be, but is not limited to, 0.3 to 0.5 μm, 0.5 to 1.5 μm, 1 to 3 μm, 2.5 to 3.5 μm, or 3.5 to 4.5 μm. max is 15 to 50 μm, and preferably, the maximum particle size d of the nano silicon carbon composite material max For example, the maximum particle size d of the nano silicon carbon composite material is 20 to 40 μm. max The thickness may be, but is not limited to, 18 to 22 μm, 20 to 30 μm, 25 to 35 μm, 30 to 40 μm, or 40 to 45 μm.

[0052] II. Preparation method of nano silicon carbon composite material In another exemplary embodiment of the present application, a method for preparing a nanosilicon carbon composite material is provided. The method specifically includes, in step S1, providing a porous carbon skeleton, the porous carbon skeleton having a three-dimensional network structure formed by turbostratic graphite and including micropores and closed pores, and the porous carbon skeleton including ultra-large interlayer spacing turbostratic graphite, the ultra-large interlayer spacing turbostratic graphite having a layer spacing of 0.40-0.55 nm; and in step S2, contacting the porous carbon skeleton of step S1 with a silicon-containing precursor at 200-1000°C for 0.1-100 hours, and then cooling the resulting material, followed by crushing and / or classifying to obtain a nanosilicon carbon composite material.

[0053] In some embodiments, the porous carbon skeleton of step S1 can be prepared from a carbon precursor via pyrolysis and / or activation. The carbon precursor can include one or more of a polymer precursor, a biomass precursor, and a fossil carbon source. For example, the carbon precursor can be, but is not limited to, one or more of glucose, sucrose, maltose, lactose, cyclodextrin, starch, glycogen, cellulose, hemicellulose, lignin, epoxy resin, thermoplastic phenolic resin, thermosetting phenolic resin, polyoxymethylene resin, urea resin, furaldehyde resin, furfural acetone resin, acrylic resin, coconut shell, rice husk, and wood. In some embodiments, the pyrolysis temperature is 600-1800°C, and the pyrolysis time is 0.5-10 hours. The pyrolysis temperature and pyrolysis time may vary, and for example, the pyrolysis temperature may be 650 to 950°C, 900 to 1100°C, 1050 to 1250°C, 1200 to 1400°C, 1350 to 1550°C, or 1500 to 1750°C, and the pyrolysis time may be 1 to 2 hours, 1.5 to 3 hours, 2 to 5 hours, 4 to 8 hours, 5 to 10 hours, or the like.

[0054] Doping modification of carbon materials can alter the internal and surface structure of the carbon material, and proper control can improve the layer spacing and degree of disorder of the turbostratic graphite three-dimensional network structure in the porous carbon. In some embodiments, one or more hetero elements can be introduced into the porous carbon skeleton in step S1, and the hetero elements can be one or more of elements such as N, P, S, and B. In other embodiments, the hetero elements can include one or more metal elements such as Na, K, Mg, Ca, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge. In still other embodiments, the hetero elements can include one or more of elements such as N, P, S, B, Na, K, Mg, Ca, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge. The doping method can be any technical method commonly used in the art, and a detailed description thereof will be omitted here.

[0055] Activation can further improve the turbostratic graphite layer spacing and the degree of disorder, and more importantly, can increase the pore volume and specific surface area of ​​the carbon material, which is beneficial for the subsequent deposition of silicon-containing precursors to form silicon nanoparticles and achieve an appropriate silicon deposition amount. Activation methods include, but are not limited to, contacting the carbon material with one or more of H2O, CO2, O2, O3, etc. at high temperature, and / or mixing the carbon material with one or more of NaOH, KOH, Na2CO3, K2CO3, potassium acetate, Na2O, K2O, Na2O2, K2O2, Na2O, K2O, H3PO4, ZnCl2, etc., followed by high temperature treatment in an inert gas atmosphere, where the high temperature treatment is at 600-1500°C for 0.5-30 hours. The temperature and time of the high-temperature treatment process may vary, and for example, the temperature of the high-temperature treatment may be 650 to 750°C, 700 to 800°C, 750 to 950°C, 900 to 1000°C, 950 to 1200°C, 1150 to 1350°C, or 1300 to 1450°C, and the time of the high-temperature treatment may be 1 to 3 hours, 2 to 5 hours, 5 to 10 hours, 8 to 20 hours, or 15 to 25 hours.

[0056] The porous carbon skeleton should have an appropriate particle size. If the particle size is too small, it will be easily blown away by the airflow during the chemical vapor deposition process in step S2, resulting in a decrease in the utilization rate of the porous carbon skeleton. If the particle size is too large, the contact efficiency between the porous carbon skeleton and the silicon-containing precursor during the chemical vapor deposition process will be reduced, affecting the effective deposition of silicon particles. In some embodiments, the median diameter d of the porous carbon skeleton is 50 is 2 to 100 μm, and the maximum particle diameter d max Preferably, the median diameter d of the porous carbon skeleton is less than 200 μm. 50 is 5 to 30 μm, and the maximum particle size d max The median diameter of the porous carbon skeleton, d, is less than 200 μm. 50 may be, for example, 5 to 10 μm, 7 to 15 μm, 10 to 20 μm, 15 to 25 μm, or 20 to 30 μm, and the maximum particle size d of the porous carbon skeleton maxmay be, for example, less than 190 μm, less than 180 μm, less than 150 μm, less than 100 μm, less than 70 μm, or less than 50 μm, etc. In the present application, the shape of the porous carbon skeleton is not limited, and may be, for example, a spherical shape, an oval spherical shape, etc., but is not limited to these.

[0057] The porous carbon skeleton should have a relatively large specific surface area and abundant pore structure, thereby providing sites and spaces for silicon nanoparticle deposition. The specific surface area and pore distribution of the porous carbon skeleton directly affect the silicon deposition effect, which in turn affects the specific surface area of ​​the composite and the size of the silicon nanoparticles in the composite. In some embodiments, the specific surface area of ​​the porous carbon skeleton is 100-3500 m 2 / g, and the pore volume is 0.1 to 3.0 cm 3 / g. Preferably, the specific surface area of ​​the porous carbon skeleton is 400 to 2500 m 2 / g. The pore volume is 0.3 to 1.5 cm 3 For example, the specific surface area of ​​a porous carbon skeleton is 420 m 2 / g, 450m 2 / g, 500m 2 / g, 600m 2 / g, 800m 2 / g, 1000m 2 / g, 1300m 2 / g, 1500m 2 / g, 1800m 2 / g, 2000m 2 / g, 2200m 2 / g, 2400m 2 / g, 2450m 2 / g, or a range consisting of any two thereof. The pore volume of the porous carbon skeleton is 0.35 cm 3 / g, 0.4cm 3 / g, 0.6cm 3 / g, 0.8cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.4cm 3 / g, 1.45cm 3 / g, or a range consisting of any two of these. In some embodiments, the porous carbon skeleton comprises micropores, mesopores, and macropores, the pore volumes of which are 30% to 98%, 1% to 50%, and 1% to 20%, respectively, of the total pore volume.

[0058] In step S2, a silicon-containing precursor is contacted with the porous carbon skeleton obtained in step S1 at a constant temperature to allow chemical vapor deposition of the silicon-containing precursor onto the porous carbon skeleton. As is well known to those skilled in the art, the gas containing the silicon-containing precursor in step S2 further comprises an inert gas. In some embodiments, the silicon-containing precursor in step S2 includes, but is not limited to, one or more of monosilane, disilane, trisilane, halogenated silane, polysilane, silole and its derivatives, and silafluorene and its derivatives. The inert gas includes, but is not limited to, one or more of N2, Ar, and He. In some embodiments, the volume content of the silicon-containing precursor in the gas mixture containing the silicon-containing precursor and the inert gas is 1% to 50%. For example, the volume content of the silicon-containing precursor in the gas mixture containing the silicon-containing precursor and the inert gas may be, but is not limited to, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, or a range consisting of any two of these.

[0059] In some embodiments, the reactor for carrying out the chemical vapor deposition reaction is any one or a combination of a rotary kiln, a ladle furnace, an inner kettle furnace, a roller hearth kiln, a push plate kiln, an atmospheric box furnace, and a tube furnace, and the solid-gas two-phase contacting manner in the chemical vapor deposition process is any one or a combination of a fixed bed, a moving bed, a fluidized bed, and an ebullated bed.

[0060] In some embodiments, the silicon-containing precursor and the porous carbon skeleton obtained in step S2 are contacted at 200-1000° C. for 0.1-100 hours. The deposition temperature can be, but is not limited to, 250° C., 300° C., 400° C., 500° C., 600° C., 700° C., 800° C., or 900° C., and the deposition time can be, but is not limited to, 0.5 hours, 1 hour, 2 hours, 5 hours, 8 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 40 hours, 50 hours, 60 hours, 80 hours, or 100 hours. The appropriate deposition time is related to the deposition temperature; the higher the temperature, the faster the silicon chemical vapor deposition rate. If the deposition time is too long, silicon particles tend to aggregate and grow on the outer surface of the porous carbon skeleton. Large silicon particles tend to cause a relatively large volume effect in the composite electrode during charging and discharging, resulting in poor battery cycling performance. Silicon deposition at low temperatures can result in slow deposition rates and low utilization of the silicon-containing precursor. Short deposition times can result in low silicon loading, making it difficult to achieve a high composite gram capacity. Therefore, it is important to select an appropriate deposition time based on the chemical vapor deposition temperature in step S2.

[0061] The method of crushing the material obtained in step S2 includes, but is not limited to, one or a combination of the following: artificial grinding, mechanical grinding, ball milling, and jet milling. In some embodiments, the median diameter d of the nano silicon carbon composite material obtained after the crushing and / or classification process is 50 is 2 to 20 μm. Preferably, the minimum particle size d of the obtained nano silicon carbon composite material min is 0.1 to 5 μm, and the maximum particle size d max is 15 to 50 μm.

[0062] In some embodiments, step S2 further includes contacting the porous carbon skeleton with the mixture of silicon-containing precursor and oxygen-containing precursor at 200-1000°C for 0.1-100 hours, and then crushing and / or classifying the resulting material after cooling to obtain a nanosilicon carbon composite. The oxygen-containing precursor may be introduced simultaneously with the silicon-containing precursor or may be introduced intermittently and alternately with the silicon-containing precursor. The introduction of the oxygen-containing precursor may result in the formation of SiO in silicon nanoparticles. x The latter effectively binds the silicon nanoparticles, further reducing the lithium absorption expansion of silicon and improving the cycle stability of the composite electrode. x The presence of can also improve the structural strength of the composite material, thereby further improving its cycling stability.

[0063] In order to further buffer the volume effect of silicon nanoparticles and improve the cycling stability of the composite electrode, the oxygen-containing precursor preferably includes, but is not limited to, one or more of the group consisting of O2, O3, HO, CO2, methanol, ethanol, isopropyl alcohol, and acetone.

[0064] In some embodiments, step S2 further includes contacting the porous carbon skeleton with a mixture of a silicon-containing precursor and a carbon-containing precursor at 200-1000°C for 0.1-100 hours, and then crushing and / or classifying the resulting material after cooling to obtain a nanosilicon-carbon composite. The introduction of the carbon-containing precursor can form Si-C-Si bonding regions within the silicon nanoparticles, which effectively bind the silicon nanoparticles. The carbon layer structure can further buffer the lithium absorption expansion of the silicon, thereby reducing the lithium absorption expansion of the silicon and improving the cycling stability of the composite electrode. The presence of Si-C-Si can also improve the structural strength of the composite, thereby further improving its cycling stability.

[0065] To further buffer the volume effect of silicon nanoparticles and improve the cycling stability of the composite electrode, the carbon-containing precursor preferably includes, but is not limited to, one or more of the group consisting of methane, ethane, ethylene, acetylene, propane, propylene, and propyne.

[0066] In some embodiments, the preparation of the nano-silicon carbon composite material further comprises step S3, in which the nano-silicon carbon composite material obtained in step S2 is subjected to a surface coating treatment. The surface coating can further improve the electrochemical performance of the nano-silicon carbon composite material. The material of the surface coating layer can include, but is not limited to, one or more of a solid electrolyte, a conductive polymer, a carbonaceous material, a metal, an alloy, and a metal oxide. In some embodiments, the surface coating layer includes, but is not limited to, one or more of lithium hydroxide, lithium carbonate, lithium fluoride, lithium phosphate, lithium metaphosphate, aluminum dihydrogen phosphate, lithium metaaluminate, lithium aluminum phosphate, aluminum phosphate, aluminum metaphosphate, aluminum oxide, aluminum oxide monohydrate, aluminum oxide trihydrate, aluminum hydroxide, alumina sol, aluminum isopropoxide, magnesium oxide, magnesium hydroxide, zinc oxide, zinc hydroxide, titanium oxide, zirconium oxide, LiPON (lithium nitrophosphoric oxide), LLZO (lithium lanthanum zirconium oxygen), LATP (lithium titanium aluminum phosphate), LLTO (lithium lanthanum titanium oxygen), lithium germanium phosphorus sulfide, and the like; one or more of polymers and lithium complexes thereof, such as polyethylene oxide, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, and the like; LISICON-type solid electrolyte, NASICION-type solid electrolyte, perovskite-type solid electrolyte, garnet-type solid electrolyte, and sulfide solid electrolyte. The surface coating process employs coating methods commonly used in the art, such as chemical vapor deposition (CVD) coating, atomic layer deposition (ALD) coating, sol-gel coating, or hydrothermal / solvent thermal coating, and the specific steps are not described herein. The thickness of the surface coating layer is 0.2 to 500 nm. For example, the thickness of the surface coating layer may be, but is not limited to, 0.5 nm, 5 nm, 10 nm, 20 nm, 30 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, or 400 nm. In some embodiments, the thickness of the surface coating layer may be, but is not limited to, 0.2 to 20 nm, 10 to 100 nm, 100 to 300 nm, or 200 to 500 nm.

[0067] 3. Negative electrode In another exemplary embodiment of the present application, there is provided a negative electrode comprising any of the nanosilicon carbon composite materials described above or obtained by any of the preparation methods described above.

[0068] 4.Battery In yet another exemplary embodiment of the present application, a battery is provided, the battery including a positive electrode and a negative electrode, wherein the negative electrode comprises any of the nanosilicon carbon composite materials described above or a nanosilicon carbon composite material obtained by any of the preparation methods described above. In some embodiments of the present application, the battery is a lithium ion secondary battery. It should be understood that the nanosilicon carbon composite materials provided herein can also be applied to other types of batteries, which are not limited thereto and are also within the scope of protection of the present application.

[0069] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the drawings and specific embodiments in the specification.

[0070] Example 1 Step S1: Coal asphalt was heated to 800°C at 2°C / min in a N2 atmosphere and held at that temperature for 2 hours. The resulting material was crushed and classified, then mixed with KOH in a ratio of m(KOH):m(C) = 1:2, and activated at 800°C for 2 hours to obtain a porous carbon skeleton.

[0071] Step S2: The porous carbon skeleton obtained in step S1 is placed in an atmosphere furnace, heated from room temperature to 600°C at 2°C / min in an N2 atmosphere, held at 600°C for 30 hours in a 20% SiH4-N2 mixed atmosphere, and then cooled naturally under N2 protection. The skeleton is then crushed and classified, and the median diameter d 50 Nano silicon carbon composites with a particle size of 8.5 μm were obtained.

[0072] Example 2 Step S1: Sucrose was heated to 800°C at 2°C / min in a N2 atmosphere and held for 2 hours, then heated to 900°C in a 20% CO2-N2 mixed gas and held for 2 hours. The resulting material was crushed and classified to obtain a porous carbon skeleton.

[0073] Step S2: Compared with Step S2 in Example 1, the median diameter d of the nano silicon carbon composite material obtained after crushing and classification is 50 The difference is that the thickness is 7.9 μm.

[0074] Example 3 Step S1: Petroleum coke was heated to 800°C at 2°C / min in a N2 atmosphere and held at that temperature for 2 hours. The resulting material was crushed and classified, then mixed with K2CO3 in a ratio of m(K2CO3):m(C) = 1:4, and activated at 900°C for 2 hours to obtain a porous carbon skeleton.

[0075] Step S2: Compared with Step S2 in Example 1, the median diameter d of the nano silicon carbon composite material obtained after crushing and classification is 50 The difference is that the thickness is 9.2 μm.

[0076] Example 4 Step S1: Sucrose and melamine were mixed in a mass ratio of 10:1 and polished, then heated to 800°C at 2°C / min in a N2 atmosphere and held for 5 hours, then heated to 900°C in water vapor and held for 2 hours, and the resulting material was crushed and classified to obtain a porous carbon skeleton.

[0077] Step S2: The porous carbon skeleton particles obtained in step S1 are placed in an atmospheric furnace, heated from room temperature to 300°C at a rate of 2°C / min in an N2 atmosphere, and then held at 300°C for 20 hours in a 20% Si2H6-N2 mixed atmosphere. The temperature is then naturally lowered under N2 protection. The resulting material is crushed and classified to determine the median diameter d 50 Nano silicon carbon composites with a particle size of 8.8 μm were obtained.

[0078] Example 5 Step S1: Cellulose and phytic acid were mixed in a mass ratio of 10:1, and then heated to 800°C at a rate of 2°C / min in a N2 atmosphere and held there for 2 hours. The resulting material was crushed and classified, then mixed with KOH in a ratio of m(KOH):m(C) = 1:5, and activated at 800°C for 2 hours to obtain a porous carbon skeleton.

[0079] Step S2: Compared with Step S2 in Example 4, the deposition temperature was changed to 500°C, the time was 15 hours, and the median diameter d 50 The difference is that the thickness is 6.8 μm.

[0080] Example 6 Step S1: Cellulose was heated to 800°C at a rate of 2°C / min in a N2 atmosphere and held at that temperature for 2 hours. The resulting material was crushed and classified, then mixed with KOH in a ratio of m(KOH):m(C) = 1:3, and activated at 800°C for 2 hours to obtain a porous carbon skeleton.

[0081] Step S2: Compared with Step S2 in Example 1, the volume concentration of SiH in the SiH-N mixed gas was changed to 30%, the deposition temperature was 700°C, and the time was 18 hours. The median diameter d of the nano silicon carbon composite material obtained after crushing and classification was 50 The difference is that the thickness is 6.7 μm.

[0082] Example 7 Step S1: Cellulose was heated to 900°C at 2°C / min in a N2 atmosphere and held at that temperature for 2 hours. The resulting material was crushed and classified, then uniformly mixed with KOH solution in a ratio of m(KOH):m(C) = 1:2, stirred at 90°C until the solvent completely evaporated, dried, placed in an atmospheric furnace, and activated at 800°C for 2 hours to obtain a porous carbon skeleton.

[0083] Step S2: Compared with Step S2 in Example 1, the median diameter d of the nano silicon carbon composite material obtained after crushing and classification is 50 The difference is that the diameter is 7.1 μm.

[0084] Example 8 Step S1: Coal asphalt was heated to 800°C at 2°C / min in a N2 atmosphere and held at that temperature for 2 hours, then held at 1000°C in water vapor for 2 hours. The resulting material was crushed and classified, then dispersed in a 0.1M Al(NO3)3 aqueous solution, ultrasonically treated, stirred, and the excess liquid was filtered off. The mixture was then dried in an oven at 80°C and sintered at 400°C for 2 hours in a N2 atmosphere to obtain a porous carbon skeleton.

[0085] Step S2: Compared with Step S2 in Example 1, the median diameter d of the nano silicon carbon composite material obtained after crushing and classification is 50 The difference is that the thickness is 6.9 μm.

[0086] Example 9 This embodiment differs from the first embodiment in that it further includes step S3.

[0087] Step S3: The nanosilicon carbon composite material obtained in step S2 was placed in a high-temperature furnace, heated to 800°C at 2°C / min in a N2 atmosphere, and held in a 50% C2H2-N2 mixed gas atmosphere for 0.5 hours to obtain a carbon-coated nanosilicon carbon composite material. The carbon coating layer had a thickness of 10 nm.

[0088] Example 10 This embodiment differs from the first embodiment in that it further includes step S3.

[0089] Step S3: The obtained nano silicon carbon composite particles were dispersed in a 5% Al(NO3)3 aqueous solution, subjected to ultrasonic treatment, stirred, and the excess liquid was filtered off. After drying in an oven at 80°C, the mixture was sintered at 400°C for 2 hours in a N2 atmosphere to obtain an Al2O3-coated nano silicon carbon composite. The thickness of the Al2O3 coating layer was 5 nm.

[0090] Example 11 This embodiment differs from the first embodiment in that it further includes step S3.

[0091] Step S3: The nanosilicon carbon composite material obtained in step S2 was added to a 1.5 wt% LiPO3 aqueous solution, mixed uniformly, and then spray-dried to obtain a nanosilicon carbon composite material with a LiPO3 coating layer on the surface. The LiPO3 coating layer had a thickness of 5 nm.

[0092] Example 12 This embodiment differs from the first embodiment in that oxygen gas is further introduced in step S2.

[0093] Step S2: The porous carbon skeleton obtained in step S1 is placed in an atmospheric furnace, heated from room temperature to 600°C at 2°C / min in a N2 atmosphere, held at 600°C for 30 hours in a 20% SiH4-0.01% O2-N2 mixed atmosphere, and then cooled naturally under N2 protection. The skeleton is then crushed and classified, and the median diameter d 50 Nano silicon carbon composites with a particle size of 8 μm were obtained.

[0094] Example 13 This embodiment differs from the first embodiment in that carbon dioxide is further introduced in step S2.

[0095] Step S2: The porous carbon skeleton obtained in step S1 is placed in an atmosphere furnace, heated from room temperature to 600°C at 2°C / min in an N2 atmosphere, then changed to a 20% SiH4-N2 mixed gas atmosphere, and maintained at 600°C for 2 hours in a 20% SiH4-N2 mixed gas atmosphere to deposit silicon. Then, the atmosphere is changed to N2, the temperature is lowered to 200°C, and then changed to a 1% CO2-N2 mixed gas atmosphere, and maintained at 200°C for 12 minutes in a 1% CO2-N2 mixed gas atmosphere to perform oxygen-containing treatment. Then, the atmosphere is changed to N2 and the temperature is raised to 600°C. In this way, the porous carbon skeleton is subjected to 15 cycles of silicon deposition and oxygen-containing treatment, and then cooled naturally under the protection of N2. The porous carbon skeleton is then crushed and classified to obtain a median diameter d 50 Nano silicon carbon composites with a particle size of 8 μm were obtained.

[0096] Example 14 This example differs from Example 1 in that acetylene is further introduced in step S2.

[0097] Step S2: The porous carbon skeleton obtained in step S1 is placed in an atmosphere furnace, heated from room temperature to 600°C at 2°C / min in an N2 atmosphere, held at 600°C for 30 hours in a 20% SiH4-0.1% C2H2-N2 mixed atmosphere, and then cooled naturally under N2 protection. The skeleton is then crushed and classified, and the median diameter d 50 Nano silicon carbon composites with a particle size of 10 μm were obtained.

[0098] Example 15 This example differs from Example 1 in that ethylene is further introduced in step S2.

[0099] Step S2: The porous carbon skeleton obtained in step S1 is placed in an atmosphere furnace, heated from room temperature to 600°C at 2°C / min in a N2 atmosphere, held at 600°C for 30 hours in a 20% SiH4-0.1% C2H4-N2 mixed atmosphere, and then cooled naturally under N2 protection. The skeleton is then crushed and classified, and the median diameter d 50 Nano silicon carbon composites with a particle size of 10 μm were obtained.

[0100] (Comparative Example 1) Step S1: Cellulose was heated to 800°C at a rate of 2°C / min in an N2 atmosphere and held at that temperature for 2 hours. The resulting material was crushed and classified to obtain a porous carbon skeleton.

[0101] Step S2: Compared with Step S2 in Example 1, the median diameter d of the nano silicon carbon composite material obtained after crushing and classification is 50 The difference is that the thickness is 8.9 μm.

[0102] (Comparative Example 2) Step S1: Carbon black was heated to 1000°C at 2°C / min in a N2 atmosphere and held for 2 hours, then held at 800°C in water vapor for 10 hours, and the resulting material was crushed and classified to obtain a porous carbon skeleton.

[0103] Step S2: Compared with Step S2 in Example 1, the median diameter d of the nano silicon carbon composite material obtained after crushing and classification is 50The difference is that the thickness is 4.8 μm.

[0104] Electrode, half-cell preparation and electrochemical performance testing: The nano silicon carbon composites prepared in Examples 1 to 11 and the silicon carbon composites prepared in Comparative Examples 1 and 2 were used as negative electrode active materials to prepare negative electrode sheets, which were then used to prepare CR2032 button batteries using conventional methods, and the batteries were subjected to electrochemical performance tests. The specific test methods are as follows:

[0105] (1) Assembly of half-cell: A CR2032 button cell was assembled in a glove box. A metallic lithium sheet was used as the counter electrode, a polypropylene microporous membrane was used as the separator, and the electrolyte was LiPF6 dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC = 1:1), where the LiPF6 concentration was 1 mol / L.

[0106] Charge and discharge tests are performed on the batteries using the LAND battery test system.

[0107] (2) Cycle gram capacity and initial efficiency test: After leaving a CR2032 button battery for 6 hours, it was discharged at 0.05C to 0.005V, and then further discharged at 0.01C to 0.005V. After leaving it for 5 minutes, it was charged at a constant current of 0.05C to 1.5V. The initial lithium release gram capacity is the gram capacity (or mass specific capacity) of the electrode material, and the ratio of the initial lithium release capacity to the initial lithium absorption capacity is the initial coulombic efficiency of the battery.

[0108] Preparation of whole cells and testing of electrochemical performance: The nanosilicon carbon composites prepared in Examples 1 to 11 and the silicon carbon composites prepared in Comparative Examples 1 and 2 were used as negative electrode active materials. Electrode sheets containing the negative electrode active materials were used to prepare soft-pack batteries in a conventional manner, and electrochemical performance tests were performed. The soft-pack batteries were prepared in a dehumidified chamber with a dew point of -45°C. A charge-discharge cycle test was performed on the batteries using the LANBTS battery testing system. The specific test method is as follows:

[0109] (1) Preparation of positive electrode sheet: The positive electrode active material LiCoO2, the conductive agent SuperP, the binder PVDF, and the solvent NMP were mixed uniformly in a mass ratio of 92:3:5:150 by stirring, and then the mixture was uniformly applied to the positive electrode current collector and dried at 80°C to obtain a positive electrode sheet.

[0110] (2) Preparation of negative electrode sheet: The negative electrode active material, the conductive agent SuperP, the binder polyacrylic acid, and the solvent deionized water were mixed uniformly in a mass ratio of 95:1:4:120, and then uniformly applied to the negative electrode current collector. The mixture was then dried at 100°C to obtain a negative electrode sheet.

[0111] (3) The positive and negative electrode sheets were stacked in a rectangular shape and separated by a polypropylene separator to form a battery cell, which was then sealed in an aluminum-plastic bag. The corresponding volume of electrolyte was then poured into the bag and vacuum-sealed to obtain a soft-pack battery. The electrolyte was a mixture of LiPF6, EC, and DEC, with a LiPF6 concentration of 1 mol / L and an EC / DEC volume ratio of 1:1.

[0112] (4) Formation and capacity screening: After electrolyte injection and sealing, the batteries were subjected to formation, then left to stand for 12 hours in a thermostatic chamber at 25°C. They were then charged to 3.3 V at a constant current of 0.02 C, left for 30 minutes, charged to 3.8 V at a constant current of 0.025 C, left for 10 minutes, and charged to 4.2 V at a constant current of 0.33 C. After formation, the batteries were evacuated and the gas bag was removed. Capacity screening was then performed. The batteries were then charged to 4.45 V at a constant current of 0.33 C, left for 10 minutes, discharged to 3 V at a constant current of 1 C, left for 10 minutes, and discharged to 3 V at a constant current of 0.33 C. This completed the capacity screening. The ratio of the discharge capacity divided by the charge capacity in the formation and capacity screening of soft-pack batteries was the initial efficiency of the battery.

[0113] (5) 25°C cycle test: The battery was placed in a thermostatic box at 25°C, charged at a constant current of 1 C to 4.45 V, and then further charged at a constant voltage of 4.45 V until the current reached 0.1 C. After allowing to stand for 10 minutes, the battery was discharged at a constant current of 1 C to 3.0 V and allowed to stand for 10 minutes. The above charge and discharge steps were repeated until the discharge capacity fell below 80% of the initial discharge capacity. The number of cycles obtained at this time was the cycle life of the soft-pack battery, and the cycle capacity retention rate at the 100th cycle was recorded.

[0114] (6) 45℃ cycle test: The battery is placed in a thermostatic box at 45℃, and the other steps are the same as those in the 25℃ cycle test.

[0115] The basic physical properties and electrochemical performance test results of the nano silicon carbon composite materials prepared in Examples 1 to 11 and the silicon carbon composite materials prepared in Comparative Examples 1 and 2 are shown in Tables 1 and 2.

[0116] [Table 1]

[0117] [Table 2]

[0118] As can be seen from Tables 1 and 2, compared to the silicon carbon composite materials prepared in the comparative examples, the nano silicon carbon composite materials prepared in the examples of the present application all contain silicon nanoparticles, ultra-large interlamellar spacing turbostratic graphite, and micro-closed pores. When applied to lithium ion secondary batteries, the nano silicon carbon composite materials prepared in the examples of the present application have higher gram capacity and higher initial coulombic efficiency, significantly improved capacity retention, and excellent electrochemical performance.

[0119] The gram capacity of Example 1 reached 1982 mAh / g, the initial coulombic efficiency was 93.2%, and the whole battery achieved a capacity retention rate of 96.7% at 1C / 1C at 25°C. Examples 2 and 3 used different carbon precursor materials and activation methods. Due to the nature of the resulting porous carbon skeleton, the proportion of ultra-large interlayer spacing in the resulting nano-silicon carbon composite was low, resulting in slightly reduced cycle stability. The capacity retention rates at 100 cycles were 94.5% and 95.9%, respectively. Due to the nature of the pore structure of the porous carbon skeleton used, the gram capacity also decreased somewhat in Examples 2 and 3. Example 8 involved the loading of thin-layered Al2O3 on the carbon particles, which reduced the silicon content of the composite and the ultra-large interlayer spacing turbostratic graphite content, resulting in a somewhat reduced gram capacity and capacity retention rate at 100 cycles.

[0120] In Examples 4-6, nano-silicon carbon composites were prepared by doping and / or activating the carbon material with elements, resulting in nano-silicon carbon composites with a relatively high ultra-large interlayer spacing turbostratic graphite content (A1 / A0). By adjusting the type, concentration, and deposition temperature of the silicon-containing precursor, the resulting composites possessed abundant microporous closed pores. The entire battery containing the composite electrode exhibited a capacity retention rate of over 97.8% after 100 charge-discharge cycles. The ultra-large interlayer spacing turbostratic graphite and microporous closed pores possessed dynamic lithium storage properties, allowing repeated lithium storage and release during electrochemical cycling, providing a long-term, effective lithium storage mechanism and improving the battery's cycling stability. During the cycling process, one or two cycles occurred every 5-10 cycles, resulting in a battery cycling efficiency greater than 100%. This significantly improved battery cycling stability compared to conventional cycling processes, where the cycle efficiency was always less than 100%. In addition, as in Examples 4 and 5, by introducing a doping element at a certain ratio, the silicon content was reduced compared to Example 1, and therefore the gram capacity was reduced to some extent. In Example 7, the A1 / A0 was reduced to some extent compared to Example 6, and at the same time, the same silicon-containing precursor deposition conditions as in Example 1 were employed, so the micropore closed pore volume was closer to Example 1. Therefore, the gram capacity retention rate at the 100th cycle was lower than in Example 6 to some extent, and was close to Example 1, at 96.8%.

[0121] Compared with Examples 4 to 6, Examples 9 to 11 have a nano silicon carbon composite material with a surface coating layer, which has a small specific surface area and open pore volume. This significantly improves the initial coulomb efficiency of the electrode, reaching 93% or more. Meanwhile, although the composite material also has a relatively high closed pore ratio, the content of micropores in the closed pores is somewhat lower. As a result, the cycle stability of the composite electrode is somewhat reduced compared to Examples 4 to 6, but still remains above 97%.

[0122] In the composite materials obtained in Examples 12 and 13, the introduction of a very small amount of oxygen-containing precursor resulted in the formation of SiO on the silicon nanoparticles. xThe formation of Si-C-Si domains effectively mitigates the lithium absorption expansion of silicon and improves the structural stability of the material, thereby improving the cycle stability of the composite material in lithium-ion batteries. However, the presence of oxygen atoms reduces the gram capacity and initial coulombic efficiency of the composite material to some extent. In the composite materials of Examples 14 and 15, the introduction of a hydrocarbon-based substance forms Si-C-Si domains in the silicon nanoparticles, effectively mitigating the lithium absorption expansion of silicon and improving the cycle stability of the composite material in lithium-ion batteries. Therefore, all of the composite materials obtained in Examples 12 to 15 have high capacity retention rates at the 100th cycle.

[0123] The silicon content of the composite materials obtained in Comparative Examples 1 and 2 was relatively low, resulting in a gram capacity of less than 1450 mAh / g. More importantly, neither of them contained ultra-large interlamellar spacing turbostratic graphite or microporous closed pores. As a result, the cycling stability of the electrodes containing the composite materials was poor, even after 100 charge / discharge cycles. The capacity retention rate of the composite obtained in Comparative Example 1 was only 88.6%, while the capacity retention rate of the composite obtained in Comparative Example 2 was less than 80%, resulting in the battery failing.

[0124] FIG. 8 shows the results of a cycle performance test of a whole battery including electrodes made of the nanosilicon carbon composite material obtained in Example 1 and a whole battery including electrodes made of the silicon carbon composite material obtained in Comparative Example 1. The whole battery including electrodes made of the nanosilicon carbon composite material prepared in Example 1 had a capacity retention rate of 96.7% after 100 charge / discharge cycles, while the whole battery including electrodes made of the silicon carbon composite material prepared in Comparative Example 1 had a capacity retention rate of only 88.6% after 100 charge / discharge cycles.

[0125] The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Those skilled in the art can make various modifications and changes to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A nanosilicon carbon composite material, comprising silicon nanoparticles, closed pores, and a turbostratic graphite three-dimensional network structure; The closed pores are N ２ is the inaccessible pore volume, and the closed pores include micropores, The three-dimensional network structure of turbostratic graphite includes ultra-large interlayer spacing turbostratic graphite, and the interlayer spacing of the ultra-large interlayer spacing turbostratic graphite is 0.40 nm to 0.55 nm; The nanosilicon carbon composite material is characterized in that the silicon nanoparticles and the closed pores are dispersed in the turbostratic graphite three-dimensional network structure.

2. The nano silicon carbon composite material of claim 1, wherein the silicon nanoparticles have a size of 0.5 nm to 20 nm, preferably 0.5 nm to 2 nm, and more preferably, the silicon nanoparticles are amorphous silicon.

3. 3. The nanosilicon carbon composite material according to claim 1, wherein the volume content of the ultra-large interlayer spacing turbostratic graphite in the turbostratic graphite three-dimensional network structure is 10% to 50%.

4. The stacking size L of the ultra-large interlayer spacing turbostratic graphite in the c-axis direction ｃ is between 0.4 nm and 2 nm, and / or The size L of the ultra-large interlayer spacing turbostratic graphite in the a-axis direction ａ The nanosilicon carbon composite material according to any one of claims 1 to 3, characterized in that the average particle size is 2 nm to 10 nm.

5. The nano silicon carbon composite has a turbostratic graphite three-dimensional network structure with a high degree of disorder. Ｄ / I Ｇ The nanosilicon carbon composite material according to any one of claims 1 to 4, wherein is 0.5 to 5.

0.

6. The specific surface area of ​​the nano silicon carbon composite material is 0.1 m ２ / g to 50m ２ / g, and the open pore volume is 0.001 cm ３ / g to 0.05 cm ３ / g, and the open pore volume is N ２ 6. The nanosilicon carbon composite material of claim 1, wherein the accessible pore volume is

7. 7. The nanosilicon carbon composite material according to claim 1, wherein the ratio of the volume of the closed pores to the volume of the open pores in the nanosilicon carbon composite material is 0.1 to 5.

8. 8. The nanosilicon carbon composite material according to claim 1, wherein the closed pores further comprise closed mesopores, and the ratio of the volume of the closed micropores to the volume of the closed mesopores is 0.05 to 5.

9. The nano silicon carbon composite material is ｘ 2. The nano silicon carbon composite material of claim 1, comprising:

10. 2. The nano silicon carbon composite material according to claim 1, wherein the content of silicon element in the nano silicon carbon composite material is 5 wt% to 95 wt%.

11. 3. The nano silicon carbon composite material according to claim 1, wherein the silicon and carbon elements in the nano silicon carbon composite material are dispersed at a nanoscale.

12. The nanosilicon carbon composite material according to any one of claims 1, 2 and 10, characterized in that the silicon nanoparticles are obtained by chemical vapor deposition of a silicon-containing precursor in a turbostratic graphite three-dimensional network structure at 150°C to 1000°C, and preferably the silicon-containing precursor is one or more selected from the group consisting of monosilane, disilane, trisilane, halogenated silane, polysilane, silole and its derivatives, and silafluorene and its derivatives.

13. The turbostratic graphite three-dimensional network structure is derived from a carbon material, and the carbon material includes, but is not limited to, hard carbon, graphite, amorphous carbon, graphene, a carbon material prepared by pyrolysis and / or activation from a polymer precursor, a carbon material prepared by pyrolysis and / or activation from a biomass precursor, and a carbon material prepared by pyrolysis and / or activation from a fossil carbon source; The nano silicon carbon composite material of claim 1, characterized in that the carbon material used to prepare the turbostratic graphite three-dimensional network structure preferably contains one or more of N, P, S, and B elements.

14. The turbostratic graphite three-dimensional network structure is obtained after the carbon material is activated, and the activation method is to activate the carbon material by ２ O, CO ２ , O ２ , O ３ and / or contacting the carbon material with one or more of NaOH, KOH, Na ２ CO ３ , K. ２ CO ３ , potassium acetate, Na ２ O.K. ２ O, Na ２ O ２ , K. ２ O ２ , Na ２ O.K. ２ O, H ３ P.O. ４ , ZnCl ２ 14. The nano silicon carbon composite material of claim 13, wherein the method further comprises subjecting the nano silicon carbon composite to high temperatures in an inert gas after mixing with one or more of:

15. The nano silicon carbon composite material includes a surface coating layer, and the thickness of the surface coating layer is 0.2 nm to 500 nm; Preferably, the material of the surface coating layer is one or more selected from the group consisting of a solid electrolyte, a conductive polymer, a carbonaceous material, a metal, an alloy, and a metal oxide; The nanosilicon carbon composite material according to claim 1, wherein the surface coating layer is preferably one or more selected from the group consisting of lithium hydroxide, lithium carbonate, lithium fluoride, lithium phosphate, lithium metaphosphate, aluminum dihydrogen phosphate, lithium metaaluminate, lithium aluminum phosphate, aluminum phosphate, aluminum metaphosphate, aluminum oxide, aluminum oxide monohydrate, aluminum oxide trihydrate, aluminum hydroxide, alumina sol, aluminum isopropoxide, magnesium oxide, magnesium hydroxide, zinc oxide, zinc hydroxide, titanium oxide, zirconium oxide, LiPON, LLZO, LATP, LLTO, and lithium germanium phosphosulfide; and / or one or more selected from the group consisting of polyethylene oxide, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, and lithium complexes thereof; and / or one or more selected from the group consisting of lisicon-type solid electrolytes, nasicion-type solid electrolytes, perovskite-type solid electrolytes, garnet-type solid electrolytes, and sulfide solid electrolytes.

16. The nano silicon carbon composite material has a true density of 1.2 g / cm3 as determined by helium pycnometry. ３ ~2.1 g / cm ３ 2. The nanosilicon carbon composite material of claim 1, wherein:

17. A method for preparing a nano silicon carbon composite material, the method specifically comprising: In step S1, a porous carbon skeleton is provided, the porous carbon skeleton having a three-dimensional network structure formed by turbostratic graphite and including micropores and closed pores, the porous carbon skeleton including ultra-large interlayer spacing turbostratic graphite, the interlayer spacing of the ultra-large interlayer spacing turbostratic graphite being 0.40 nm to 0.55 nm; In step S2, the porous carbon skeleton and the silicon-containing precursor in step S1 are contacted at 200°C to 1000°C for 0.1 hours to 100 hours, and the resulting material is cooled and then crushed and / or classified to obtain a nanosilicon carbon composite material; Preferably, in step S3, the nanosilicon carbon composite material obtained in step S2 is subjected to a surface coating.

18. Step S2 further comprises contacting the porous carbon skeleton with the mixture of the silicon-containing precursor and the oxygen-containing precursor at 200°C to 1000°C for 0.1 hours to 100 hours, and then cooling the resulting material, followed by crushing and / or classifying the resulting material to obtain the nano silicon carbon composite material; or 18. The method for preparing a nano silicon carbon composite material according to claim 17, further comprising the steps of contacting the porous carbon skeleton with the mixture of the silicon-containing precursor and the carbon-containing precursor at 200°C to 1000°C for 0.1 hours to 100 hours, and then cooling the resulting material, followed by crushing and / or classifying the resulting material to obtain the nano silicon carbon composite material.

19. A negative electrode comprising the nanosilicon carbon composite material according to any one of claims 1 to 16 or the nanosilicon carbon composite material obtained by the preparation method according to claim 17.

20. A battery comprising a positive electrode and a negative electrode, wherein the negative electrode comprises the nano silicon carbon composite material according to any one of claims 1 to 16 or the nano silicon carbon composite material obtained by the preparation method according to claim 17, and preferably the battery is a lithium ion secondary battery.

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