Silicon-carbon composite material, negative active material, preparation method of negative active material, negative pole piece, battery and electric device

Abstract

The invention discloses a silicon-carbon composite material, a negative active material, a preparation method of the negative active material, a negative pole piece, a battery and an electric device. The silicon-carbon composite material comprises a porous carbon matrix and silicon particles, at least one part of the silicon particles are distributed in the porous carbon matrix, and in a regional distribution diagram formed by superposing different elements and obtained by characterizing the silicon-carbon composite material by utilizing an X-ray energy spectrum element image analysis technology, the X-ray energy spectrum element image analysis technology is used for representing the silicon-carbon composite material; the ratio Z of the total area of the carbon element in the regional distribution diagram to the total area of the regional distribution diagram is less than or equal to 0.1; a button cell is assembled by a pole piece prepared by using the silicon-carbon composite material as an active material, a lithium piece, a diaphragm and an electrolyte, a charge-discharge cycle test is carried out at 25 DEG C at 0.1 C multiplying power, a first-circle charging dQ / dV curve with dQ / dV as a vertical coordinate and voltage as a horizontal coordinate is obtained, and in the curve, the ratio Y of the peak height of a peak in a 0.4 V-0. 5V region to the peak height of a peak in a 0.25 V-0. 3V region is less than or equal to 0.55. Therefore, high compaction density, high conductivity and good cycle performance can be taken into consideration.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and more particularly, relates to a silicon-carbon composite material, a negative electrode active material, a preparation method thereof, a negative electrode sheet, a battery, and an electrical device. Background Art

[0002] Silicon-carbon composite materials are now regarded as the next-generation lithium-ion battery negative electrode materials most likely to replace traditional graphite. However, due to the huge volume change of silicon particles during the lithium insertion and extraction process, many problems such as the collapse of the electrode structure and the rapid reduction of the cycle life are caused, which limits the wide application of silicon-carbon composite materials. How to better alleviate the volume effect of silicon has become the key direction for the research and improvement of silicon-carbon materials. In recent years, the composite structure design of a new type of silicon-carbon material (porous carbon-deposited nanosilicon) has received extensive attention in the industry. With the help of the rich pore structure inside the porous carbon, gaseous silicon sources are deposited into the pores of the porous carbon at a certain temperature, which not only solves the problem of silicon particle agglomeration and pulverization, but also the carbon matrix increases the electrode structure stability during the lithiation of silicon. However, in the existing preparation process, due to the influence of many factors such as reaction temperature, silane gas concentration, and reaction pressure on the silicon deposition reaction, there is usually a problem of more silicon deposition on the surface of the porous carbon material, that is, there is a problem of surface silicon coating. On the one hand, surface silicon coating will cause premature pore blockage of the porous carbon and reduce the compaction performance of the material; on the other hand, it will lead to an increase in the powder resistivity of the material and a decrease in the cycle performance. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this reason, an object of the present invention is to provide a silicon-carbon composite material, a negative electrode active material, a preparation method thereof, a negative electrode sheet, a battery, and an electrical device to improve the compaction density, conductivity, and cycle performance of the silicon-carbon composite material.

[0004] A first aspect of the present invention provides a silicon-carbon composite material, comprising: a porous carbon matrix and silicon particles, at least a part of the silicon particles being distributed inside the porous carbon matrix, wherein:

[0005] In the area distribution diagram of different element superpositions obtained by characterizing the silicon-carbon composite material using X-ray energy spectrum elemental imaging analysis technology, the ratio of the total area of carbon elements in the area distribution diagram to the total area of the area distribution diagram is Z, and Z≤0.1;

[0006] The pole piece made of the silicon-carbon composite material as the active material is assembled with a lithium piece, a separator, and an electrolyte to form a button cell, and a charge-discharge cycle test is carried out at a rate of 0.1C at 25°C to obtain the first-cycle charge dQ / dV curve with dQ / dV as the ordinate and voltage as the abscissa. In the curve, the ratio of the peak height of the peak in the region of 0.4V - 0.5V to the peak height of the peak in the region of 0.25V - 0.3V is Y, and Y ≤ 0.55.

[0007] The inventors found that the Z value of the silicon-carbon composite material is related to the distribution and deposition saturation rate of silicon particles in the porous carbon matrix. The lower the Z value, the higher the probability of deposition saturation of silicon particles in the porous carbon matrix; the lower the Y value, the lower the probability of the phenomenon of silicon coating on the surface of the silicon-carbon composite material. The silicon-carbon composite material with Z value and Y value meeting the given conditions is beneficial to taking into account higher tap density, higher conductivity, and better cycle performance.

[0008] In addition, the silicon-carbon composite material according to the above embodiments of the present invention may further have the following additional technical features:

[0009] In some embodiments of the present invention, Z ≤ 0.05; and / or, Y ≤ 0.52. Thus, it is beneficial to further take into account higher tap density, higher conductivity, and better cycle performance.

[0010] In some embodiments of the present invention, Z ≤ 0.04; and / or, Y ≤ 0.51. Thus, it is beneficial to further take into account higher tap density, higher conductivity, and better cycle performance.

[0011] In some embodiments of the present invention, in the button cell, the first-cycle charge capacity of the silicon-carbon composite material at 0.8V is 1700 mAh / g - 1900 mAh / g, and the first Coulombic efficiency is 81% - 83%.

[0012] In some embodiments of the present invention, the tap density of the silicon-carbon composite material is 1.3 g / cm 3 ~1.6 g / cm 3 .

[0013] In some embodiments of the present invention, the silicon particles are nano-silicon particles. This is beneficial to further improving the uniformity of the distribution of silicon particles on the surface of the porous carbon matrix in the silicon-carbon composite material.

[0014] In some embodiments of the present invention, the Dv90 particle size of the silicon-carbon composite material is 11 μm - 15 μm, the Dv50 particle size is 6 μm - 8 μm, and the Dv10 particle size is 2 μm - 4 μm.

[0015] The second aspect of the present invention provides a negative electrode active material, which includes the above-mentioned silicon-carbon composite material. The features and effects described for the above-mentioned silicon-carbon composite material also apply to this negative electrode active material, and will not be elaborated here.

[0016] In some embodiments of the present invention, the negative electrode active material further includes: a carbon coating layer, and the carbon coating layer is provided on at least a part of the outer surface of the silicon-carbon composite material. This is beneficial to further improve the conductivity and stability of the negative electrode active material.

[0017] The third aspect of the present invention provides a method for preparing the above-mentioned negative electrode active material, including:

[0018] Feeding a porous carbon matrix and a grinding medium into a reactor, heating under rotational conditions and introducing a gaseous silicon source for a deposition reaction, so that at least a part of silicon particles are deposited inside the porous carbon matrix.

[0019] The method for preparing the negative electrode active material of the present invention has the following beneficial effects: not only is the operation simple and the cost low, but also by mixing the porous carbon matrix and the grinding medium and carrying out the silicon deposition reaction under rotational conditions, on the one hand, it can continuously scour the inner wall of the reactor during the silicon deposition reaction, timely scour down the porous carbon matrix adhering to the inner wall, make the temperature of the porous carbon in the reactor more uniform (optimize heat transfer), and promote the uniform deposition of silicon in the pores of the porous carbon matrix. On the other hand, it is also beneficial to reduce the probability that the open pores on the surface of the porous carbon matrix are covered to form closed pores, thereby further facilitating the deposition of silicon particles inside the porous carbon matrix; further, after the silicon-carbon composite material is prepared, it can be separated from the grinding medium by screening and other methods, and the operation is convenient. Therefore, it is not only beneficial to improve the deposition saturation rate and distribution uniformity of silicon particles in the pores of the porous carbon matrix, but also beneficial to reduce the problem of silicon coating on the surface of the porous carbon matrix, and further beneficial to make the negative electrode active material have both a high tap density, a high conductivity and good cycle performance. In addition, using the above method is also beneficial to fundamentally solve the problem of caking materials on the inner wall of the reactor and further improve the uniformity of the negative electrode active material.

[0020] In some embodiments of the present invention, the grinding medium includes at least one of quartz sand particles, zirconia particles, and stainless steel particles.

[0021] In some embodiments of the present invention, the grinding medium is a spherical medium, and the spherical medium includes at least one of porous balls, solid balls, and hollow balls.

[0022] In some embodiments of the present invention, the particle size of the grinding medium is 0.6 mm to 10 mm. This is beneficial to simultaneously take into account the tap density of the negative electrode active material and the deposition rate of silicon particles inside the porous carbon matrix.

[0023] In some embodiments of the present invention, the mass ratio of the grinding medium to the porous carbon matrix is (0.5 to 2):1. This is beneficial for simultaneously considering the tap density of the anode active material and the deposition rate of silicon particles inside the porous carbon matrix.

[0024] In some embodiments of the present invention, the gaseous silicon source includes elemental silicon gas and / or silane gas.

[0025] In some embodiments of the present invention, the temperature of the deposition reaction is 400°C to 500°C, and the reaction time is 3h to 10h. This is beneficial for reducing the reaction rate of the silicon deposition reaction, promoting the deposition of more silicon particles inside the porous carbon matrix, and at the same time beneficial for considering the reaction efficiency.

[0026] In some embodiments of the present invention, the gaseous silicon source is introduced with the first carrier gas. In the mixture of the gaseous silicon source and the first carrier gas, the volume ratio of the gaseous silicon source is 10v% to 40v%. The first carrier gas includes at least one of nitrogen, argon, hydrogen, ammonia, and phosphine. This is not only beneficial for promoting the slow and uniform deposition of silicon particles inside the porous carbon matrix, but also for reducing the probability that the pores of the porous carbon matrix are blocked by the too-fast deposition rate of silicon particles to form closed pores.

[0027] In some embodiments of the present invention, before introducing the gaseous silicon source, it further includes: replacing the gas in the reactor with a protective gas. This can strictly control the oxygen content in the finally prepared silicon-carbon composite material.

[0028] In some embodiments of the present invention, after the deposition reaction, a carbon source gas is introduced into the reactor for carbon coating reaction.

[0029] In some embodiments of the present invention, the protective gas includes at least one of nitrogen, argon, and hydrogen.

[0030] In some embodiments of the present invention, the carbon source gas includes at least one of methanol, acetone, methane, ethane, propane, and acetylene.

[0031] In some embodiments of the present invention, the temperature of the carbon coating reaction is 500°C to 600°C, and the reaction time is 1h to 2h.

[0032] In some embodiments of the present invention, the carbon source gas is introduced with the second carrier gas. In the mixture of the carbon source gas and the second carrier gas, the volume ratio of the carbon source gas is 10v% to 90v%. The second carrier gas includes at least one of nitrogen, argon, hydrogen, ammonia, and phosphine.

[0033] A fourth aspect of the present invention provides a negative electrode plate, which includes: the above-mentioned silicon-carbon composite material; and / or, the above-mentioned negative electrode active material; and / or, the negative electrode active material prepared by the method for preparing the negative electrode active material described above. During use, this negative electrode plate is beneficial for the battery to have both a relatively high energy density, a relatively low internal resistance, and good cycle performance.

[0034] A fifth aspect of the present invention provides a battery, which includes: the above-mentioned negative electrode plate. This battery can have both a relatively high energy density, a relatively low internal resistance, and good cycle performance.

[0035] A sixth aspect of the present invention provides an electrical device, which includes: the above-mentioned battery. This electrical device has a relatively long battery life and service life of the battery.

[0036] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. Description of the Drawings

[0037] Figure 1 It is a regional distribution diagram of different element superpositions of the silicon-carbon composite material according to an embodiment of the present invention.

[0038] Figure 2 It is a dQ / dV curve of the silicon-carbon composite material used for the first-cycle charging of a button cell according to an embodiment of the present invention.

[0039] Figure 3 It is a process flow diagram of a method for preparing a silicon-carbon composite material according to an embodiment of the present invention.

[0040] Figure 4 It is a process flow diagram of a method for preparing a silicon-carbon composite material according to another embodiment of the present invention. Detailed Embodiments

[0041] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0042] A first aspect of the present invention provides a silicon-carbon composite material. According to an embodiment of the present invention, the silicon-carbon composite material includes: a porous carbon matrix and silicon particles, and at least a part of the silicon particles are distributed inside the porous carbon matrix, where:

[0043] The regional distribution diagram of different element superpositions obtained by characterizing the silicon-carbon composite material using X-ray energy spectrum element imaging analysis technology (EDS-Mapping) (referenceFigure 1 In the understanding, the ratio of the total area of carbon elements in the area distribution map to the total area of the area distribution map is Z, and Z ≤ 0.1;

[0044] A button cell is assembled with a silicon-carbon composite material as the active material, a lithium sheet, a separator, and an electrolyte, and a charge-discharge cycle test is carried out at a rate of 0.1C at 25 °C to obtain the first-cycle charge dQ / dV curve with dQ / dV as the ordinate and voltage as the abscissa (reference Figure 2 In the understanding), in the curve, the ratio of the peak height of the peak in the region of 0.4V - 0.5V to the peak height of the peak in the region of 0.25V - 0.3V is Y. In this dQ / dV curve, the peaks at different positions represent a phase change reaction respectively. For the silicon-carbon composite material, the silicon grains deposited in the pores of the porous carbon are relatively small, and the peak intensity in the region of 0.4V - 0.5V is relatively low; while when there is silicon-rich on the surface, the silicon grain size is larger, and the peak intensity in the region of 0.4 - 0.5V is higher. In the silicon-carbon composite material described in the present invention, Y ≤ 0.55.

[0045] The inventors found that the Z value of the silicon-carbon composite material is related to the distribution and deposition saturation of silicon particles in the porous carbon matrix. The lower the Z value, the higher the probability of deposition saturation of silicon particles in the porous carbon matrix; the lower the Y value, the lower the probability of the existence of silicon-coated surface in the silicon-carbon composite material. The silicon-carbon composite material with Z value and Y value meeting the given conditions is beneficial to taking into account higher tap density, higher conductivity and better cycle performance.

[0046] According to the embodiments of the present invention, in the area distribution map of different element superpositions obtained by using X-ray energy spectrum element image analysis technology (EDS-Mapping) to characterize the silicon-carbon composite material, the main elements are silicon and carbon elements, and there may also be a small amount or trace amount of oxygen element. Among them, different elements are presented in different colors on the picture, and the distribution position and distribution state of different elements can be distinguished by colors. The relative uniformity of the distribution of silicon and carbon elements and the area ratio of carbon elements in the area distribution map of different element superpositions reflect to a certain extent the deposition uniformity and deposition saturation rate of silicon on the porous carbon matrix. The lower the Z value, the higher the probability of deposition saturation of silicon particles in the porous carbon matrix. Among them, the total area of carbon elements in the area distribution map can be obtained by statistically analyzing the pixel points of carbon element distribution by conventional methods, and the total area of the area distribution map of different element superpositions can be obtained by statistically analyzing the pixel points of the distribution map of different element superpositions, and then the Z value can be obtained by calculation, where Z ≤ 0.1. For example, the Z value can be 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, etc.

[0047] According to an embodiment of the present invention, when assembling a button cell with a lithium sheet, a separator, and an electrolyte using a silicon-carbon composite material as an active material to prepare an electrode sheet, the silicon-carbon composite material can be used as the active material and mixed with sodium carboxymethyl cellulose (CMC), conductive carbon black (SP), and styrene-butadiene rubber (SBR) in a mass ratio of 94.5:1.5:1.5:2.5 to prepare a slurry, and the slurry is coated on both surfaces of a copper foil current collector with a thickness of 6 μm to 12 μm (the coating thickness on both sides is the same, and the coating areal density is 3 g / cm 2 ~5 g / cm 2 ), vacuum dried, cold pressed, and cut to obtain an electrode sheet; the electrode sheet is regarded as a positive electrode sheet, a lithium sheet is used as a negative electrode sheet, assembled with an electrolyte and a Celgard 2400 separator, and the outer shell is assembled with a button cell using a conventional production process. Among them, the electrolyte is prepared by mixing ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 2:6:2, and then adding the lithium salt LiPF6 to obtain an electrolyte with a lithium salt concentration of 1 mol / L. After the battery assembly is completed, charge and discharge cycle tests are carried out at a rate of 0.1C at 25°C, charge and discharge parameters such as the amount of electricity and the power supply are recorded, and these data are processed to obtain the dQ / dV curve of the value of dQ / dV (ordinate) varying with the voltage (abscissa) during the first charge. In this curve, the peak height of the peak located in the region of 0.4V to 0.5V is the maximum value of dQ / dV corresponding to this peak in the region of 0.4V to 0.5V (denoted as h1), and the peak height of the peak located in the region of 0.25V to 0.3V is the maximum value of dQ / dV corresponding to this peak in the region of 0.25V to 0.3V (denoted as h2). The value of Y reflects the problem of silicon coating on the surface of the porous carbon matrix to a certain extent (that is, more silicon is deposited on the surface of the porous carbon matrix). The lower the value of Y, the lower the probability of the silicon-carbon composite material having a surface silicon coating phenomenon. Based on h2 and h1 (Y = h2 / h1), the value of Y can be calculated. Among them, Y ≤ 0.55. For example, the value of Y can be 0.55, 0.54, 0.53, 0.52, 0.51, 0.5, 0.45, 0.4, 0.35, etc.

[0048] According to an embodiment of the present invention, when the silicon-carbon composite material simultaneously satisfies Z ≤ 0.1 and Y ≤ 0.55, the silicon particles have a high deposition saturation rate on the porous carbon matrix and a relatively high probability of low surface silicon coating. When used in a negative electrode sheet, it is beneficial to simultaneously take into account a relatively high compaction density, a relatively high conductivity, and good cycle performance.

[0049] In some embodiments of the present invention, Z ≤ 0.05; and / or, Y ≤ 0.52. As some examples, Z ≤ 0.05 and Y ≤ 0.52. As described above, when the silicon-carbon composite material further meets the given conditions, the probability of the silicon particles having a high deposition saturation rate and a low silicon surface coverage on the porous carbon matrix is higher, and when it is used in the negative electrode sheet, it is further beneficial to simultaneously take into account a higher compaction density, a higher conductivity, and better cycling performance.

[0050] In some embodiments of the present invention, Z ≤ 0.04; and / or, Y ≤ 0.51. As some examples, Z ≤ 0.04 and Y ≤ 0.51. As described above, when the silicon-carbon composite material further meets the given conditions, the probability of the silicon particles having a high deposition saturation rate and a low silicon surface coverage on the porous carbon matrix is higher, and when it is used in the negative electrode sheet, it is further beneficial to simultaneously take into account a higher compaction density, a higher conductivity, and better cycling performance.

[0051] In some embodiments of the present invention, in a button cell, the initial charge capacity of the silicon-carbon composite material at 0.8V can be 1700 mAh / g to 1900 mAh / g, for example, it can be 1700 mAh / g, 1750 mAh / g, 1800 mAh / g, 1850 mAh / g, 1900 mAh / g, etc., and the first Coulombic efficiency can be 81% to 83%, for example, it can be 81%, 80%, 83%, etc. The silicon-carbon composite material that meets the given conditions is beneficial for the battery to have both a high energy density and a discharge capacity.

[0052] In some embodiments of the present invention, the compaction density of the silicon-carbon composite material can be 1.3 g / cm 3 ~1.6 g / cm 3 , for example, it can be 1.3 g / cm 3 , 1.35 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 , 1.6 g / cm 3 etc. The compaction density of the silicon-carbon composite material can be measured by measuring the thickness and weighing the negative electrode sheet made of the silicon-carbon composite material, washing away the negative electrode material with a mixed solution of acetone and alcohol and drying it, weighing the remaining copper foil thickness and weight, and calculating the compaction density based on the difference between the two weights divided by the area and thickness. This is beneficial for further improving the volumetric energy density of the battery.

[0053] In some embodiments of the present invention, the silicon particles may be nano-silicon particles. In the present invention, the particle size of the silicon particles can be characterized by HRTEM (i.e., high-resolution transmission electron microscopy). Taking a lithium-ion battery as an example, at the microscopic scale, when lithium is inserted into the silicon-based anode active material, lithium ions first accumulate on the particle surface, while the lithium ion concentration at the center of the particle is very low. Therefore, there is a concentration gradient of lithium ions in the radial direction of the particle, and the lithium insertion rate of the silicon near the surface is greater than that of the silicon near the center. Also, because silicon undergoes a huge volume expansion during lithium insertion, the expansion rate of the silicon near the surface does not match that of the silicon near the center, which easily leads to uneven internal and external stresses in the particle, resulting in cracking and pulverization. This not only affects the contact between the silicon-based anode active material and the current collector, making the silicon-based anode active material easily detached from the current collector, causing rapid attenuation of the battery capacity, but also the huge volume change of the silicon-based anode active material during charge and discharge is likely to form an unstable SEI film. During charge and discharge, the volume change of silicon easily causes the rupture and regeneration of the SEI film, resulting in continuous consumption of the electrolyte and the formation of a thick and uneven SEI film, affecting the specific capacity and ion diffusion of the battery. The inventors found that the smaller the size of the silicon particles, the smaller the degree of uneven internal and external stresses in the silicon-carbon composite material during charge and discharge, and the lower the probability of pulverization and cracking. For example, when the particle size of silicon is less than 80 nm, cracking and pulverization basically do not occur. Taking a lithium-ion battery as an example, in the present invention, controlling the silicon particles in the silicon-carbon composite material to be nanoparticles (such as ≤80 nm, or for example, 2 nm to 10 nm, specifically 2 nm, 5 nm, 8 nm, 10 nm, etc.) can significantly improve the problem of the mismatch between the expansion rate of the silicon near the surface and the expansion rate of the silicon near the center of the silicon-carbon composite material particles during charge and discharge, reduce the stress difference inside and outside the particles, and reduce the volume expansion, cracking, and pulverization risks of the silicon-carbon composite material particles during charge and discharge, thereby improving the volume stability and cycling performance of the silicon-carbon composite material. Further, using a porous carbon matrix as the carrier of the nano-silicon particles, on the one hand, the carbon material has a relatively small volume change during charge and discharge, has good cycling stability and conductivity, and on the other hand, can further relieve the volume expansion effect of silicon during charge and discharge by utilizing its porous structure, and thus can further improve the volume stability and cycling performance of the silicon-carbon composite material.

[0054] In some embodiments of the present invention, the Dv90 particle size of the silicon-carbon composite material can be 11 μm to 15 μm, the Dv50 particle size can be 6 μm to 8 μm, and the Dv10 particle size can be 2 μm to 4 μm. The volume particle sizes Dv90, Dv50, and Dv10 of the silicon-carbon composite material respectively refer to the particle sizes corresponding to when the cumulative volume distribution percentage reaches 90%, 50%, and 10%, and can be measured by a laser diffraction particle size analyzer with reference to Standard GB / T19077-2016. The volume particle size distribution of the silicon-carbon composite material satisfying the given conditions is beneficial to further obtaining a higher tap density and improving the volume energy density of the battery.

[0055] In some embodiments of the present invention, the type of the porous carbon matrix is not particularly limited, and those skilled in the art can flexibly select according to actual needs. For example, it can include but is not limited to at least one of activated carbon, natural graphite, artificial graphite, and carbon nanotubes. In addition, the mass ratio of the porous carbon matrix to the silicon particles is not particularly limited, and those skilled in the art can flexibly select according to actual needs. For example, it can be 0.90 to 1.25, etc. In the present invention, the content of the porous carbon matrix in the silicon-carbon composite material can be tested by devices such as a sulfur-carbon analyzer, and the composition and content of other elements can be obtained by combining methods such as ICP elemental analysis, and the content of the silicon particles can be obtained by subtraction. Controlling the mass ratio of the porous carbon matrix to the silicon particles within this range in the present invention can not only enable the silicon-carbon composite material to obtain a higher specific capacity, but also take into account the volume expansion of the silicon-carbon composite material, control its volume expansion during charge and discharge within a reasonable range, and further improve the cycle performance of the battery when the silicon-carbon composite material is used in the negative electrode sheet, which is beneficial to obtaining better cycle stability and a longer cycle life.

[0056] The second aspect of the present invention proposes a negative electrode active material. According to the embodiments of the present invention, the negative electrode active material includes the above-mentioned silicon-carbon composite material. The characteristics and effects described for the above-mentioned silicon-carbon composite material also apply to the negative electrode active material, and will not be elaborated here.

[0057] In some embodiments of the present invention, the negative electrode active material further includes: a carbon coating layer, and the carbon coating layer is provided on at least a part of the outer surface of the silicon-carbon composite material. Providing the carbon coating layer can not only prevent the direct contact between the silicon-carbon composite material and the electrolyte, inhibit the excessive growth of the SEI film, but also be beneficial to improving the conductivity of the silicon-carbon composite material, and at the same time be beneficial to further restricting and buffering the volume expansion of the silicon-carbon composite material, and improving the cycle stability of the silicon-carbon composite material during charge and discharge.

[0058] In some embodiments of the present invention, the thickness and / or content of the carbon coating layer are not particularly limited, and those skilled in the art can flexibly select according to actual needs. For example, the thickness of the carbon coating layer can be 1 nm to 100 nm, such as 1 nm, 5 nm, 10 nm, 20 nm, 50 nm, 80 nm, or 100 nm, etc.; and / or, the mass percentage of the carbon coating layer in the silicon-carbon composite material can be 1 wt% to 6 wt%, such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, etc. Meeting the given conditions is beneficial to further taking into account the volume energy density of the negative electrode sheet and the battery.

[0059] Currently, in order to improve the tap density of the silicon-carbon composite material and control the silicon coating problem on the surface of the silicon deposition process, it is mainly controlled by reducing the reaction rate. Common methods include reducing the reaction temperature, regulating the silane flow rate in stages, applying vibration or knocking to the reactor, etc. Among them, the reaction temperature mainly focuses on 450 °C to 520 °C. If the reaction temperature is too high, it is easy to accelerate the reaction rate of silane deposition. When silane encounters the surface of porous carbon, it decomposes, causing premature pore blockage. However, reducing the reaction rate will lead to a significant extension of the reaction time, thereby affecting the production capacity; the silane flow rate is controlled in stages, and the silane flow rate needs to be matched with the acceptance capacity (specific surface area) of the porous carbon. In the later stage of the reaction, the specific surface area of the porous carbon decreases. If the silane flow rate is too high, it will cause premature pore blockage and a decrease in tap density. Therefore, it is necessary to adjust the silane flow rate in real time according to the reaction conditions. By reducing the temperature and flow rate, the surface silicon coating problem can be weakened to a certain extent, but it will increase the operating cost of the device, easily cause safety accidents, and have limited ability to improve the tap density of the material. In addition, applying vibration or knocking to the reactor has limited effect on reducing the degree of surface silicon coating. However, due to the relatively high temperature at the position of the reactor wall during silicon deposition, a lot of agglomerated materials are generated during each reaction (the agglomeration is more obvious in large reactors). The surface of this part of the material has a very high degree of silicon coating and extremely poor electrochemical performance. At present, there is no effective means to completely remove it. The inventor found that for the preparation process of the silicon-carbon composite material, the key to improving the tap density of the material lies in that the silane deposition occurs inside the pores of the porous carbon and there are relatively few closed pores.

[0060] In view of this, the third aspect of the present invention proposes a method for preparing the above-mentioned negative electrode active material. According to the embodiments of the present invention, refer to Figure 3 Understood, this method includes:

[0061] Supply the porous carbon matrix and the grinding medium into the reactor, heat up and introduce the gaseous silicon source for deposition reaction under rotational conditions, so that at least a part of the silicon particles are deposited inside the porous carbon matrix.

[0062] The method for preparing the negative electrode active material of the present invention has the following beneficial effects: It is not only simple to operate and low in cost, but also by mixing the porous carbon matrix with the grinding medium and carrying out the silicon deposition reaction under rotational conditions, on the one hand, it can continuously scour the reactor wall during the silicon deposition reaction, timely scour down the porous carbon matrix adhering to the wall, make the temperature of the porous carbon in the reactor more uniform (optimize heat transfer), and promote the uniform deposition of silicon in the pores of the porous carbon matrix. On the other hand, it is also beneficial to reduce the probability that the open pores on the surface of the porous carbon matrix are covered to form closed pores, which further facilitates the deposition of silicon particles inside the porous carbon matrix; further, after the silicon-carbon composite material is prepared, it can be separated from the grinding medium by screening and other methods, which is convenient to operate. Thus, it is not only beneficial to improve the deposition saturation rate and distribution uniformity of silicon particles in the pores of the porous carbon matrix, but also beneficial to reduce the problem of silicon coating on the surface of the porous carbon matrix, and further beneficial to make the negative electrode active material have both a high tap density, a high conductivity and good cycle performance. In addition, adopting the above method is also beneficial to fundamentally solve the problem of caking material on the reactor wall, further improve the uniformity of the negative electrode active material, and obtain a negative electrode active material that meets the characteristics of the above silicon-carbon composite material. In summary, the negative electrode active material prepared by this method has the characteristics of less caking, good uniformity, low degree of silicon coating on the surface, and high tap density, and has a high energy density and good cycle performance in terms of electrochemical performance.

[0063] In some embodiments of the present invention, the material and specific type of the grinding medium are not particularly limited, and those skilled in the art can flexibly select according to actual needs. For example, the material of the grinding medium may include but is not limited to at least one of quartz sand particles, zirconia particles, and stainless steel particles; and / or, the material of the grinding medium may include but is not limited to spherical media, and the spherical media may include but is not limited to at least one of porous balls, solid balls, and hollow balls. In addition, the reactor may include but is not limited to a rotary kiln reactor, and the rotary kiln reactor and zirconium beads can play a synergistic role in continuously extruding the porous carbon particles to achieve uniform deposition of silane and improve the tap density of the negative electrode active material.

[0064] In some embodiments of the present invention, the particle size of the grinding medium can be 0.6 mm to 10 mm, for example, it can be 0.6 mm, 1 mm, 2 mm, 5 mm, 8 mm, 10 mm, etc. The increase in the particle size of the grinding medium is beneficial to improving the grinding intensity and effect, reducing the particle size of the negative electrode active material. By controlling the particle size of the grinding medium within the given range, the uniformity and particle size of the overall particle size distribution of the negative electrode active material can be taken into account, the tap density of the negative electrode active material can be improved, and at the same time, sufficient grinding intensity can be provided, so that when the grinding medium flushes the reactor wall, the porous carbon adhered to the wall can be flushed off in time, making the temperature of the porous carbon in the reactor more uniform (optimizing heat transfer), promoting the uniform and slow decomposition and deposition of silane in the pores of the porous carbon, reducing the probability of closed pores in the silicon-carbon composite material, and further improving the tap density of the negative electrode active material. Thus, it is beneficial to take into account both the tap density of the negative electrode active material and the deposition rate of silicon particles inside the porous carbon matrix.

[0065] In some embodiments of the present invention, the mass ratio of the grinding medium to the porous carbon matrix can be (0.5 to 2):1, for example, it can be 0.5 / 1, 0.8 / 1, 1 / 1, 1.2 / 1, 1.5 / 1, 1.8 / 1, 2 / 1, etc. The increase in the relative amount of the grinding medium is also beneficial to improving the grinding intensity and effect, reducing the particle size of the negative electrode active material. By controlling the particle size of the grinding medium within the given range, the uniformity and particle size of the overall particle size distribution of the negative electrode active material can be taken into account, the tap density of the negative electrode active material can be improved, and at the same time, sufficient grinding intensity can be provided, so that when the grinding medium flushes the reactor wall, the porous carbon adhered to the wall can be flushed off in time, making the temperature of the porous carbon in the reactor more uniform (optimizing heat transfer), promoting the uniform and slow decomposition and deposition of silane in the pores of the porous carbon, reducing the probability of closed pores in the silicon-carbon composite material, and further improving the tap density of the negative electrode active material. Thus, it is beneficial to take into account both the tap density of the negative electrode active material and the deposition rate of silicon particles inside the porous carbon matrix.

[0066] In some embodiments of the present invention, the gaseous silicon source can include elemental silicon gas and / or silane gas. As some specific examples, the elemental silicon gas can be obtained by gasifying elemental silicon powder, and the elemental silicon powder can be single-crystalline silicon and / or polycrystalline silicon with a silicon content preferably not less than 99%; as other specific examples, the silane gas can include, but is not limited to, compounds containing silicon and hydrogen such as SiH4, Si2H6, etc.

[0067] In some embodiments of the present invention, the temperature of the deposition reaction can be 400°C to 500°C, and the reaction time can be 3 h to 10 h. For example, the temperature of the deposition reaction can be 400°C, 420°C, 450°C, 480°C, 500°C, etc., and the reaction time can be 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h, etc. Meeting the given conditions is beneficial to reducing the reaction rate of the silicon deposition reaction, solving the problem that silicon deposits when it encounters the surface of porous carbon or silane decomposes when it encounters the surface of porous carbon, which causes premature pore blockage of the porous carbon matrix, promoting more silicon particles to deposit inside the porous carbon matrix, reducing the probability that the open pores of the porous carbon matrix are blocked and closed due to the too-fast deposition rate of silicon particles, improving the tap density of the negative electrode active material, and at the same time being beneficial to taking into account the reaction efficiency.

[0068] In some embodiments of the present invention, the gaseous silicon source can be introduced with the first carrier gas. In the mixture of the gaseous silicon source and the first carrier gas, the volume percentage of the gaseous silicon source can be 10 v% to 40 v%, such as 10 v%, 15 v%, 20 v%, 25 v%, 30 v%, 35 v%, or 40 v%, etc. The first carrier gas can include but is not limited to at least one of nitrogen, argon, hydrogen, ammonia, and phosphine. Controlling the volume percentage of the gaseous silicon source to meet the given conditions is beneficial to further reducing the reaction rate of the silicon deposition reaction. Thus, it is not only beneficial to promoting the slow and uniform deposition of more silicon particles inside the porous carbon matrix, reducing the probability that the open pores of the porous carbon matrix are blocked and closed due to the too-fast deposition rate of silicon particles, but also beneficial to taking into account the reaction efficiency. In addition, introducing ammonia and / or phosphine is beneficial to introducing a small amount or trace amount of nitrogen doping and / or phosphorus doping, thereby further improving the conductivity of the silicon-carbon composite material.

[0069] In some embodiments of the present invention, it is understood that Figure 4 before introducing the gaseous silicon source, it can also include: replacing the gas in the reactor with a protective gas. This can strictly control the oxygen content in the finally prepared silicon-carbon composite material. Thus, it can not only improve the volume stability and capacity retention rate of the silicon-carbon composite material during charge and discharge, but also take into account a relatively high initial efficiency, which is beneficial to obtaining good cycle performance, high specific capacity, and first Coulomb efficiency. As some specific examples, the protective gas can include but is not limited to at least one of nitrogen, argon, and hydrogen.

[0070] In some embodiments of the present invention, it is understood that Figure 4 after the deposition reaction, a carbon source gas can be introduced into the reactor for carbon coating reaction. This is further beneficial to forming a carbon coating layer. Among them, the carbon source gas can include but is not limited to at least one of methanol, acetone, methane, ethane, propane, and acetylene.

[0071] In some embodiments of the present invention, the temperature of the carbon coating reaction can be 500°C to 600°C, such as 500°C, 550°C or 600°C, etc., and the reaction time can be 1 h to 2 h. Controlling the above reaction conditions is beneficial to avoid carbon crystallization or too large grain size due to too high temperature, and at the same time is also beneficial to avoid the problem of low carbon source cracking efficiency due to too low temperature. Controlling the above deposition time is beneficial to control the thickness of the carbon coating layer and obtain a carbon coating layer with an appropriate thickness.

[0072] In some embodiments of the present invention, the carbon source gas can be introduced with the second carrier gas. In the mixed gas composed of the carbon source gas and the second carrier gas, the volume ratio of the carbon source gas can be 10 v% to 90 v%, such as 10 v%, 20 v%, 30 v%, 40 v%, 50 v%, 60%, 70%, 80%, 90%, etc. Meeting the given conditions is beneficial to further control the carbon deposition rate and obtain a carbon coating layer with uniform thickness. As some specific examples, the second carrier gas can include at least one of nitrogen, argon, hydrogen, ammonia, and phosphine.

[0073] The fourth aspect of the present invention provides a negative electrode sheet. According to the embodiments of the present invention, the negative electrode sheet may include: the above-mentioned silicon-carbon composite material; and / or, the above-mentioned negative electrode active material; and / or, the negative electrode active material prepared by the method for preparing the negative electrode active material described above. Among them, the characteristics and effects described for the above-mentioned silicon-carbon composite material, negative electrode active material, and the method for preparing the negative electrode active material also apply to the negative electrode sheet, and will not be elaborated here. Generally speaking, the negative electrode sheet is beneficial to endow the battery with a relatively high energy density, a relatively low internal resistance, and good cycle performance during use.

[0074] The fifth aspect of the present invention provides a battery. According to the embodiments of the present invention, the battery includes: the above-mentioned negative electrode sheet. The battery can have a relatively high energy density, a relatively low internal resistance, and good cycle performance. Exemplarily, the battery can be a lithium-ion battery.

[0075] The sixth aspect of the present invention provides an electrical device, which includes: the above-mentioned battery. The electrical device has a long battery life and a long service life of the battery. It should be noted that the specific type of the electrical device is not particularly limited, and those skilled in the art can flexibly select according to actual needs. For example, the electrical device can include, but is not limited to, electronic products, vehicles, household appliances, etc. Among them, electronic products include, but are not limited to, mobile phones, computers, game consoles, etc., and vehicles include, but are not limited to, pure electric vehicles, hybrid electric vehicles, etc.

[0076] The solution of the present application will be described below through specific embodiments. It should be noted that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specifying specific technologies or conditions in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0077] Example 1

[0078] Put 500 g of porous carbon matrix and 500 g of zirconium beads with a particle size of 5 mm into a rotary kiln reactor, and then introduce nitrogen at a flow rate of 2 L / min for replacement. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min, and set the kiln rotation speed at 25 Hz. After the reactor temperature rises to 450 °C, introduce silane gas at a flow rate of 1 L / min, hydrogen at a flow rate of 2 L / min, and phosphine gas at a flow rate of 0.5 L / min, and continue the deposition reaction for 6.7 h, during which the furnace tube of the equipment is continuously knocked. After the silicon deposition is completed, raise the temperature of the reactor to 550 °C, introduce acetylene at a flow rate of 1 L / min, nitrogen at a flow rate of 2 L / min, and ammonia at a flow rate of 0.5 L / min, and continue the deposition reaction for 2 h. After the reaction is completed, cool down in a nitrogen atmosphere at a flow rate of 2 L / min. After cooling to room temperature, discharge the material, and use a 200-mesh sieve to filter and collect the material under the sieve as the finished silicon-carbon composite material.

[0079] Example 2

[0080] Put 500 g of porous carbon matrix and 1000 g of zirconium beads with a particle size of 2 mm into a rotary kiln reactor, and then introduce nitrogen at a flow rate of 2 L / min for replacement. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min, and set the kiln rotation speed at 25 Hz. After the reactor temperature rises to 480 °C, introduce silane gas at a flow rate of 1 L / min, hydrogen at a flow rate of 2 L / min, and phosphine gas at a flow rate of 0.5 L / min, and continue the deposition reaction for 6.7 h, during which the furnace tube of the equipment is continuously knocked. After the silicon deposition is completed, raise the temperature of the reactor to 550 °C, introduce acetylene at a flow rate of 1 L / min, nitrogen at a flow rate of 2 L / min, and ammonia at a flow rate of 0.5 L / min, and continue the deposition reaction for 2 h. After the reaction is completed, cool down in a nitrogen atmosphere at a flow rate of 2 L / min. After cooling to room temperature, discharge the material, and use a 200-mesh sieve to filter and collect the material under the sieve as the finished silicon-carbon composite material.

[0081] The prepared silicon-carbon composite material was tested in a coin-type half-cell in the same manner as in Example 1.

[0082] Example 3

[0083] Add 500 g of porous carbon matrix and 250 g of zirconium beads with a particle size of 10 mm into a rotary kiln reactor, and then introduce nitrogen at a flow rate of 2 L / min for replacement. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min, and set the rotary kiln speed at 25 Hz. After the reactor temperature rises to 450 °C, introduce silane gas at a flow rate of 1 L / min and hydrogen at a flow rate of 2 L / min, and continue the deposition reaction for 6.7 h, during which the furnace tube of the equipment is continuously tapped. After the silicon deposition is completed, raise the reactor temperature to 550 °C, introduce acetylene at a flow rate of 1 L / min and nitrogen at a flow rate of 2 L / min, and continue the deposition reaction for 2 h. After the reaction is completed, cool down under a nitrogen atmosphere at a flow rate of 2 L / min. After cooling to room temperature, discharge the material, and use a 200-mesh sieve to filter and collect the undersize as the finished silicon-carbon composite material.

[0084] Perform coin-type half-cell tests on the prepared silicon-carbon composite material in the same manner as in Example 1.

[0085] Example 4

[0086] Add 500 g of porous carbon matrix and 500 g of zirconium beads with a particle size of 0.6 mm into a rotary kiln reactor, and then introduce nitrogen at a flow rate of 2 L / min for replacement. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min, and set the rotary kiln speed at 25 Hz. After the reactor temperature rises to 500 °C, introduce silane gas at a flow rate of 1 L / min and hydrogen at a flow rate of 2 L / min, and continue the deposition reaction for 6.7 h, during which the furnace tube of the equipment is continuously tapped. After the silicon deposition is completed, raise the reactor temperature to 600 °C, introduce acetylene at a flow rate of 1 L / min and nitrogen at a flow rate of 2 L / min, and continue the deposition reaction for 2 h. After the reaction is completed, cool down under a nitrogen atmosphere at a flow rate of 2 L / min. After cooling to room temperature, discharge the material, and use a 200-mesh sieve to filter and collect the undersize as the finished silicon-carbon composite material.

[0087] Perform coin-type half-cell tests on the prepared silicon-carbon composite material in the same manner as in Example 1.

[0088] Example 5

[0089] Add 500 g of porous carbon matrix and 500 g of stainless steel balls with a particle size of 5 mm into a rotary kiln reactor, and then introduce nitrogen at a flow rate of 2 L / min for replacement. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min, and set the rotary kiln speed at 25 Hz. After the reactor temperature rises to 470 °C, introduce silane gas at a flow rate of 1 L / min and nitrogen at a flow rate of 2 L / min, and continue the deposition reaction for 6.7 h, during which the furnace tube of the equipment is continuously tapped. After the silicon deposition is completed, raise the reactor temperature to 550 °C, introduce acetylene at a flow rate of 1 L / min and ammonia at a flow rate of 2 L / min, and continue the deposition reaction for 2 h. After the reaction is completed, cool down in a nitrogen atmosphere at a flow rate of 2 L / min. After cooling to room temperature, discharge the material, and use a 200-mesh sieve to filter and collect the undersize as the finished silicon-carbon composite material.

[0090] Perform coin-type half-cell tests on the prepared silicon-carbon composite material in the same manner as in Example 1.

[0091] Example 6

[0092] Add 500 g of porous carbon matrix and 1000 g of zirconium balls with a particle size of 5 mm into a rotary kiln reactor, and then introduce nitrogen at a flow rate of 2 L / min for replacement. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min, and set the rotary kiln speed at 25 Hz. After the reactor temperature rises to 450 °C, introduce silane gas at a flow rate of 1 L / min, nitrogen at a flow rate of 2 L / min, and ammonia at a flow rate of 0.5 L / min, and continue the deposition reaction for 6.7 h, during which the furnace tube of the equipment is continuously tapped. After the silicon deposition is completed, raise the reactor temperature to 520 °C, introduce acetylene at a flow rate of 1 L / min and ammonia at a flow rate of 2 L / min, and continue the deposition reaction for 2 h. After the reaction is completed, cool down in a nitrogen atmosphere at a flow rate of 2 L / min. After cooling to room temperature, discharge the material, and use a 200-mesh sieve to filter and collect the undersize as the finished silicon-carbon composite material.

[0093] Perform coin-type half-cell tests on the prepared silicon-carbon composite material in the same manner as in Example 1.

[0094] Comparative Example 1

[0095] Add 500 g of porous carbon matrix into a rotary kiln reactor, and then introduce nitrogen at a flow rate of 2 L / min for replacement. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min, and set the rotary kiln speed at 25 Hz. After the reactor temperature rises to 450 °C, introduce silane gas at a flow rate of 1 L / min and nitrogen at a flow rate of 2 L / min, and continue the deposition reaction for 6.5 h, during which the furnace tube of the equipment is continuously knocked. After the silicon deposition is completed, raise the reactor temperature to 550 °C, introduce acetylene at a flow rate of 1 L / min and nitrogen at a flow rate of 2 L / min, and continue the deposition reaction for 2 h. After the reaction is completed, cool down under a nitrogen atmosphere of 2 L / min. After cooling to room temperature, discharge the material, and use a 200-mesh sieve to filter and collect the undersize as the finished silicon-carbon composite material.

[0096] Comparative Example 2

[0097] Add 500 g of porous carbon raw material and 500 g of zirconium balls with a particle size of 0.1 mm into a rotary kiln reactor, and then introduce nitrogen at a flow rate of 2 L / min for replacement. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min, and set the rotary kiln speed at 25 Hz. After the reactor temperature rises to 450 °C, introduce silane gas at a flow rate of 1 L / min and nitrogen at a flow rate of 2 L / min, and continue the deposition reaction for 6.5 h, during which the furnace tube of the equipment is continuously knocked. After the silicon deposition is completed, raise the reactor temperature to 550 °C, introduce acetylene at a flow rate of 1 L / min and nitrogen at a flow rate of 2 L / min, and continue the deposition reaction for 2 h. After the reaction is completed, cool down under a nitrogen atmosphere of 2 L / min. After cooling to room temperature, discharge the material, and use a 200-mesh sieve to filter and collect the undersize as the finished silicon-carbon composite material.

[0098] Comparative Example 3

[0099] Add 500 g of porous carbon raw material and 100 g of zirconium balls with a particle size of 5 mm into a rotary kiln reactor, and then introduce nitrogen at a flow rate of 2 L / min for replacement. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min, and set the rotary kiln speed at 25 Hz. After the reactor temperature rises to 450 °C, introduce silane gas at a flow rate of 1 L / min and nitrogen at a flow rate of 2 L / min, and continue the deposition reaction for 6.5 h, during which the furnace tube of the equipment is continuously knocked. After the silicon deposition is completed, raise the reactor temperature to 550 °C, introduce acetylene at a flow rate of 1 L / min and nitrogen at a flow rate of 2 L / min, and continue the deposition reaction for 2 h. After the reaction is completed, cool down under a nitrogen atmosphere of 2 L / min. After cooling to room temperature, discharge the material, and use a 200-mesh sieve to filter and collect the undersize as the finished silicon-carbon composite material.

[0100] (1) Test the silicon-carbon composite materials prepared in each example and comparative example:

[0101] (1-1) Measure the thickness and weight of the negative electrode sheet made of the silicon-carbon composite material. Wash the negative electrode material with a mixed solution of acetone and alcohol and dry it. Weigh the remaining copper foil thickness and weight. Divide the difference in weight before and after by the area and thickness to calculate the compaction density;

[0102] (1-2) Perform elemental surface scanning (X-ray energy spectrum elemental image analysis) on the above silicon-carbon composite material using a scanning electron microscope, and draw a regional distribution map of the superposition of different elements, including elements such as carbon, silicon, and oxygen. Calculate the Z value based on the area occupied by carbon element / the area of the regional distribution map image;

[0103] (1-3) Charge and discharge the silicon-carbon composite material using a coin cell, draw a dQ / dV curve, record the peak height at 0.25V - 0.3V in the curve as h1, and record the peak height in the region of 0.4V - 0.5V in the curve as h2. Calculate the Y value (Y = h2 / h1).

[0104] (2) Test the electrochemical performance of the silicon-carbon composite materials prepared in each example and comparative example:

[0105] Preparation of the electrode sheet: Use the silicon-carbon composite material as the active material, mix the active material, sodium carboxymethyl cellulose (CMC), conductive carbon black (SP), and styrene-butadiene rubber (SBR) in a mass ratio of 94.5:1.5:1.5:2.5 to prepare a slurry, and coat the slurry on both sides of the copper foil current collector. The areal density of the double-sided coating is 4g / cm 2 , vacuum dry, cold press, and cut to obtain the electrode sheet;

[0106] Preparation of the electrolyte: Mix ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 2:6:2, and then add the lithium salt LiPF6 to obtain an electrolyte with a lithium salt concentration of 1mol / L;

[0107] Assemble the negative electrode sheet with a lithium sheet, electrolyte, and Celgard 2400 separator, and assemble a button battery using a conventional production process for the outer shell.

[0108] Charge and discharge the prepared coin cell at a rate of 0.1C at 25°C, record the initial charge specific capacity and discharge specific capacity, and calculate the initial Coulomb efficiency. Use the initial discharge specific capacity as the initial capacity, repeat the above cyclic operation, record the discharge specific capacity after 50 cycles, and calculate the discharge capacity retention rate.

[0109] Table 1 Partial differences and test results of Examples 1 - 6 and Comparative Examples 1 - 3

[0110]

[0111] Results and conclusions:

[0112] It can be seen from the above examples and comparative examples that the silicon-carbon composite materials with lower Z values and Y values have higher tap density, reversible capacity, initial efficiency, and cycling performance. In addition, adding grinding media during the reaction process for preparing the silicon-carbon composite material is beneficial to reducing the Z value and Y value of the product. The lower the Z value, the smaller the proportion of carbon not saturated and deposited by silicon particles, and the higher the capacity and tap density of the electrode of the product; moreover, the lower the Y value, the lower the probability of silicon-rich on the surface of the porous carbon matrix, and the higher the initial efficiency and cycling retention rate of the product. Combining Example 1 and Comparative Example 1, it can be known that no grinding balls were added during the preparation of the silicon-carbon composite material in Comparative Example 1, and the Z value and Y value of the product are higher. The main reason for the analysis is that there are many porous carbon particles with undeposited silicon in the product, and the surface of other porous carbon with deposited silicon is severely silicon-rich, corresponding to the performance that the reversible capacity, initial efficiency, and cycling capacity retention rate of the product are all lower. In addition, increasing the particle size of the grinding media and / or the mass ratio of the grinding media to the porous carbon matrix is beneficial to further reducing the Z value and Y value of the product. Combining Example 1 and Comparative Examples 1-2, it can be known that the reduction amplitude of the Z value and Y value of the product prepared in Comparative Example 2 is small. The possible reason for the analysis is that the particle size of the grinding media used is small, the impact force generated is relatively weak, and the grinding effect on the material is limited, resulting in an insignificant reduction in the Z value of the product, and there are still many carbons not saturated and deposited by silicon particles, and the improvement of the reversible capacity, initial efficiency, and cycling capacity retention rate of the material is not obvious; in addition, in Comparative Example 3, the reversible capacity, initial efficiency, and cycling capacity retention rate of the prepared silicon-carbon composite material are slightly worse than those in Comparative Example 1. The main reason for the analysis is that the addition amount of the grinding media is small, the function of dispersing and breaking up the particle aggregates is reduced, and caking is formed between some particles during the preparation process and finally evolves into large particles with severely silicon-rich surfaces.

[0113] In the description of this specification, the descriptions with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0114] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, Comprising: A porous carbon matrix and silicon particles, at least a part of the silicon particles being distributed inside the porous carbon matrix, wherein: In the area distribution map of the superposition of different elements obtained by characterizing the silicon-carbon composite material using X-ray energy spectrum elemental imaging analysis technology, the ratio of the total area of carbon elements in the area distribution map to the total area of the area distribution map is Z, and Z ≤ 0.1; Using the silicon-carbon composite material as the active material to prepare a pole piece, which is assembled with a lithium piece, a separator, and an electrolyte to form a button battery, and performing charge and discharge cycle tests at a rate of 0.1C at 25°C, obtaining the first-cycle charge dQ / dV curve with dQ / dV as the ordinate and voltage as the abscissa. In this curve, the ratio of the peak height of the peak in the 0.4V - 0.5V region to the peak height of the peak in the 0.25V - 0.3V region is Y, and Y ≤ 0.

55.

2. The silicon-carbon composite material according to claim 1, wherein Z ≤ 0.05; and / or, Y ≤ 0.

52.

3. The silicon-carbon composite material according to claim 1, wherein Z ≤ 0.04; and / or, Y ≤ 0.

51.

4. The silicon-carbon composite material according to any one of claims 1 to 3, characterized in that Satisfying at least one of the following conditions: In the button battery, the first-cycle charge capacity of the silicon-carbon composite material at 0.8V is 1700 mAh / g - 1900 mAh / g, and the first Coulombic efficiency is 81% - 83%; The tap density of the silicon-carbon composite material is 1.3 g / cm 3 ~1.6 g / cm 3 ; The silicon particles are nano-silicon particles; The Dv90 particle size of the silicon-carbon composite material is 11μm - 15μm, the Dv50 particle size is 6μm - 8μm, and the Dv10 particle size is 2μm - 4μm.

5. A negative electrode active material, characterized in that, Comprising the silicon-carbon composite material according to any one of claims 1 - 4.

6. The negative electrode active material according to claim 5, characterized in that, Further comprising: A carbon coating layer provided on at least a part of the outer surface of the silicon-carbon composite material.

7. A method for preparing the negative electrode active material according to claim 5 or 6, characterized in that, Comprising: Feeding the porous carbon matrix and the grinding medium into a reactor, heating under rotational conditions and introducing a gaseous silicon source for a deposition reaction, so that at least a part of the silicon particles are deposited inside the porous carbon matrix.

8. The method according to claim 7, wherein Satisfying at least one of the following conditions: The grinding medium includes at least one of quartz sand particles, zirconia particles, and stainless steel particles; The grinding medium is a spherical medium, and the spherical medium includes at least one of porous spheres, solid spheres, and hollow spheres; The particle size of the grinding medium is 0.6mm - 10mm; The mass ratio of the grinding medium to the porous carbon matrix is (0.5 - 2):1; The gaseous silicon source includes elemental silicon gas and / or silane gas; The temperature of the deposition reaction is 400°C - 500°C, and the reaction time is 3h - 10h; The gaseous silicon source is introduced with a first carrier gas. In the mixture of the gaseous silicon source and the first carrier gas, the volume percentage of the gaseous silicon source is 10v% - 40v%, and the first carrier gas includes at least one of nitrogen, argon, hydrogen, ammonia, and phosphine.

9. The method according to claim 7 or 8, characterized in that, Before introducing the gaseous silicon source, it further includes: replacing the gas in the reactor with a protective gas; and / or, After the deposition reaction, introducing a carbon source gas into the reactor for a carbon coating reaction.

10. The method according to claim 9, wherein Satisfying at least one of the following conditions: The protective gas includes at least one of nitrogen, argon, and hydrogen; The carbon source gas includes at least one of methanol, acetone, methane, ethane, propane, and acetylene; The temperature of the carbon coating reaction is 500°C to 600°C, and the reaction time is 1 h to 2 h; The carbon source gas is introduced with the second carrier gas. In the mixed gas composed of the carbon source gas and the second carrier gas, the volume percentage of the carbon source gas is 10 v% to 90 v%. The second carrier gas includes at least one of nitrogen, argon, hydrogen, ammonia, and phosphine.

11. A negative electrode plate, characterized in that, It includes the silicon-carbon composite material according to any one of claims 1 to 4; and / or, the negative electrode active material according to claim 5 or 6; and / or, the negative electrode active material prepared by the method according to any one of claims 7 to 10.

12. A battery, characterized in that, It includes the negative electrode plate according to claim 11.

13. An electrical device, characterized in that, It includes the battery according to claim 12.

Images