Negative active material and preparation method thereof, electrode and battery

Abstract

The invention provides a negative electrode active material and a preparation method thereof, an electrode and a battery. The negative electrode active material particles comprise a porous carbon skeleton, nano silicon and an amorphous carbon film; wherein the negative electrode active material particles comprise silicon-deficient particles, the mass content of silicon in the silicon-deficient particles is less than or equal to 15%, the quantity proportion Dlack of the silicon-deficient particles in the negative electrode active material particles is less than or equal to 35%, and the product DS of the mass content Wtotal of silicon in the negative electrode active material and the quantity proportion Dlack of the silicon-deficient particles is less than or equal to 0.15. According to the negative electrode active material provided by the invention, the quantity proportion of the silicon-deficient particles is controlled, the deposition uniformity of the nano silicon in the negative electrode active material is improved, the existence of a large number of invalid porous carbon particles is avoided, and the condition that the nano silicon is seriously enriched in part of particles is also avoided, so that the coulombic efficiency and the cycling stability of the material are improved, and the service life of the material is prolonged. And the circulation expansion is reduced.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular, to a negative electrode active material for a secondary battery and a preparation method thereof, an electrode, and a battery. Background Art

[0002] With the rapid development of electric vehicles, portable electronic devices and other fields, higher requirements are placed on the energy density of batteries. Traditional graphite negative electrode materials can no longer meet the growing demand for energy density. Therefore, the development of new high-capacity negative electrode materials has become a research hotspot. Silicon materials have extremely high theoretical specific capacity, so they are regarded as the ideal choice for the next generation of high-energy density battery negative electrode materials. However, silicon materials have serious volume expansion and contraction problems during battery cycling, leading to the decline of battery performance. Porous silicon-carbon negative electrode materials effectively alleviate the volume expansion problem of silicon materials by introducing porous structures, improve the cycle stability of batteries, and become a strong candidate material for improving battery energy density.

[0003] The preparation of porous silicon-carbon negative electrode materials can be achieved through a variety of methods such as sand milling, template method, chemical vapor deposition, etc. Among them, the core of the chemical vapor deposition method is to introduce silicon source gas (such as silane) into the pores of porous carbon particles, and deposit the gas through high-temperature pyrolysis to form silicon nanoparticles dispersed in the pores of porous carbon. This method can achieve molecular-scale control of the prepared nanomaterials, and the silicon-carbon material components produced by deposition are relatively uniform and the structure is relatively dense. Therefore, this structure effectively alleviates the volume change of silicon materials during the charge and discharge process, and improves the cycle stability and rate performance of the material.

[0004] During the deposition of gas-phase silicon-carbon, the silicon source gas needs to be uniformly deposited inside the porous carbon to form a uniformly distributed silicon-carbon composite material. However, due to the differences in the pore structure and surface properties of the porous carbon, as well as the mass transfer and heat transfer limitations during the deposition process, it is challenging to achieve uniform deposition. In fact, in the existing rotary kiln and fluidized bed processes, it is difficult for porous carbon particles to achieve sufficient fluidization or dispersion, resulting in insufficient contact between some particles and the silicon source gas, making these particles poorly siliconized particles, that is, there is almost no silicon deposition or only a small amount of silicon deposition inside. This part of the poorly siliconized particles still has a large number of pore structures and a large specific surface area. At the same time, their mechanical properties are poor and they are easily broken under extrusion, further exposing a large number of internal pores, resulting in a significant increase in side reactions with the electrolyte, reducing the coulombic efficiency, cycle performance and rate performance of the battery.

[0005] In addition to the presence of silicon-deficient particles, the distribution state of silicon inside and on the surface of porous carbon particles, the uniformity of distribution between different particles, and key parameters such as silicon utilization of the pore volume inside porous carbon particles and residual pore volume all significantly affect the cycle stability and volume expansion rate of the material in the battery. Therefore, strengthening the research on deposition mechanism and optimizing the control of process parameters to achieve uniform deposition, minimize the proportion of silicon-deficient particles, and optimize the distribution of silicon in porous carbon structures have become key issues that need to be urgently addressed in the industry.

[0006] The contents of the background technology section are merely the technologies known to the inventors and do not necessarily represent the prior art in the field. Summary of the invention

[0007] In order to solve at least one of the above technical problems, the present application provides a negative electrode active material for a secondary battery and a preparation method thereof, an electrode, and a battery.

[0008] The negative electrode active material provided in the present application comprises negative electrode active material particles, characterized in that the negative electrode active material particles comprise a porous carbon skeleton, nano-silicon and an amorphous carbon film;

[0009] Wherein, the negative electrode active material particles include silicon-deficient particles, the mass content of silicon in the silicon-deficient particles is ≤15%, and the number of the silicon-deficient particles in the negative electrode active material particles accounts for D lack ≤35%, preferably ≤30%, further preferably ≤25%, more preferably ≤20%;

[0010] The mass content of silicon in the negative electrode active material is W total The number of the silicon-deficient particles accounts for D lack The product DS is ≤0.15, preferably ≤0.125, and more preferably ≤0.1.

[0011] In some embodiments of the present application, the nano-silicon is deposited in the pores of the porous carbon skeleton and / or on the surface of the porous carbon skeleton.

[0012] In some embodiments of the present application, the amorphous carbon film is coated on the surface of the nano-silicon and / or the porous carbon skeleton, and / or the amorphous carbon film is filled in the pores of the porous carbon skeleton.

[0013] In some embodiments of the present application, the powder resistivity of the negative electrode active material particles is ≤60Ω·cm, preferably ≤40Ω·cm, further preferably ≤20Ω·cm, and more preferably ≤10Ω·cm.

[0014] In some embodiments of the present application, the specific surface area of ​​the negative electrode active material particles is ≤60m 2 / g, preferably ≤35m2 / g, more preferably ≤20m 2 / g, more preferably ≤10m 2 / g.

[0015] In some embodiments of the present application, the median particle size of the negative electrode active material particles is 1 to 15 μm, preferably 2 to 12 μm.

[0016] In some embodiments of the present application, the mass content of silicon in the negative electrode active material is W total It is 30-80%, preferably 35-65%.

[0017] In some embodiments of the present application, the median particle size of the nano-silicon is ≤10 nm, preferably ≤5 nm, and more preferably ≤3 nm.

[0018] The electrode provided in the present application includes any of the negative electrode active materials described above.

[0019] The battery provided in the present application includes the electrode described above.

[0020] The present application provides a method for preparing a negative electrode active material, wherein the negative electrode active material comprises negative electrode active material particles, and the preparation method comprises:

[0021] The preparation of the negative electrode active material particles comprises:

[0022] preparing a porous carbon framework;

[0023] Depositing nano-silicon on the porous carbon skeleton; and

[0024] Coating an amorphous carbon film on the porous carbon skeleton on which the nano-silicon is deposited;

[0025] The negative electrode active material particles contain silicon-deficient particles, the mass content of silicon in the silicon-deficient particles is ≤15%, and the number of the silicon-deficient particles in the negative electrode active material particles accounts for D lack ≤35%, preferably ≤30%, further preferably ≤25%, more preferably ≤20%;

[0026] The mass content of silicon in the negative electrode active material is W total The number of the silicon-deficient particles accounts for D lack The product DS is ≤0.15, preferably ≤0.125, and more preferably ≤0.1.

[0027] The negative electrode active material provided by the present application controls the proportion of the number of silicon-deficient particles therein, improves the deposition uniformity of nano-silicon in the negative electrode active material, avoids the presence of a large number of invalid porous carbon particles, and also avoids the situation where nano-silicon is severely enriched in some particles. Therefore, the material has a denser and more evenly distributed structure, reduces the specific surface area of ​​the material, improves the mechanical strength and compressive resistance, effectively alleviates the volume change of the silicon material during the charging and discharging process, improves the coulombic efficiency and cycle stability of the material, and reduces the cycle expansion.

[0028] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The following is a detailed description of the implementation methods of the present application in conjunction with the accompanying drawings. Here, the accompanying drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application.

[0030] Figure 1 The present invention is a flowchart of a process for preparing negative electrode active material particles of a negative electrode active material according to an exemplary embodiment of the present application.

[0031] Figure 2 This is the X-ray diffraction pattern of the negative electrode active material prepared in Example 1 of the present application.

[0032] Figure 3 Part of the results of the scanning electron microscope image and energy spectrum point scanning at 20 kV of the negative electrode active material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0033] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present application. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0034] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the various specific processes and material examples provided by the present application, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.

[0035] The following is a more detailed description of the specific implementation of the present application in conjunction with the accompanying drawings and examples, so that the scheme of the present application and its advantages in various aspects can be better understood. However, the specific implementation and examples described below are only for the purpose of illustration, and are not intended to limit the present application.

[0036] [Negative electrode active material]

[0037] The negative electrode active material provided by the present application comprises negative electrode active material particles, wherein the negative electrode active material particles comprise a porous carbon skeleton, nano-silicon and an amorphous carbon film.

[0038] The porous carbon skeleton has a large number of pores. Optionally, nano-silicon is deposited in the pores of the porous carbon skeleton and / or on the surface of the porous carbon skeleton. For example, nano-silicon is deposited on the bottom surface of the pores of the porous carbon skeleton, or nano-silicon is deposited on the pore walls of the pores of the porous carbon skeleton, or nano-silicon is deposited on the surface of the porous carbon skeleton.

[0039] Optionally, the amorphous carbon film is coated on the surface of the nano-silicon and / or the porous carbon skeleton, and / or the amorphous carbon film is filled in the pores of the porous carbon skeleton. For example, the amorphous carbon film is coated on the surface of the nano-silicon, or the amorphous carbon film is coated on the surface of the porous carbon skeleton, or the amorphous carbon film is coated on the bottom surface of the pores of the porous carbon skeleton, or the amorphous carbon film is coated on the sidewalls of the pores of the porous carbon skeleton.

[0040] Among them, the negative electrode active material particles contain silicon-deficient particles. In this application, negative electrode active material particles with a silicon mass content of ≤15% are referred to as silicon-deficient particles. Optionally, the mass content of silicon in the negative electrode active material particles (also referred to as porous carbon particles in this application) is measured using a scanning electron microscope at 20kV.

[0041] For example, using the energy spectrum analysis (EDS) function of the Hitachi SU8010 scanning electron microscope (SEM), the particles are scanned at 20 kV to obtain information on the types and contents of elements in the particles. In order to statistically analyze the uniformity of the silicon-carbon negative electrode active material, when preparing the EDS energy spectrum sample, the sample particles are laid flat on the conductive carbon glue to ensure that there is only one layer of particles on the carbon glue to avoid stacking of multiple layers of particles. When collecting the EDS signal of the particles, all particles with a diameter ≥ 2 μm appearing in the image are scanned at 1000 times, and the energy spectrum signals of all particles are collected to ensure that the number of collected particles is ≥ 500 (if there are less than 500 particles in one image, the particle energy spectrum signals of multiple areas are collected). The energy spectrum signals of the collected particles are statistically analyzed, and particles with a silicon mass content of ≤ 15% are defined as silicon-deficient particles. The number of silicon-deficient particles is calculated as a percentage D. lack .

[0042] Optionally, in the present application, the amount of silicon-deficient particles in the negative electrode active material particles is D lack ≤35%, preferably ≤30%, further preferably ≤25%, more preferably ≤20%.

[0043] In the deposition process of gas-phase silicon carbon, the silicon source gas is first adsorbed by the porous carbon skeleton, then decomposed at high temperature to form nano-silicon, and then deposited. Due to the differences in the pore structure and surface properties of the porous carbon skeleton, as well as the mass transfer and heat transfer limitations during the deposition process, it is challenging to achieve uniform deposition. In fact, in the existing rotary kiln and fluidized bed processes, it is difficult for the porous carbon skeleton to achieve sufficient fluidization or dispersion, resulting in insufficient contact between some particles and the silicon source gas, which becomes a "dead corner" area for fluidization or dispersion, making these particles under-siliconized particles, that is, there is almost no silicon deposition or only a small amount of silicon deposition inside. Some porous carbon skeletons are also limited by the differences in their pore structure and surface properties. The kinetics during the silicon deposition reaction is poor, and the adsorption and decomposition reactions are significantly slower than other particles, which also causes them to become under-siliconized particles. These under-siliconized particles still have a large number of pore structures and a large specific surface area. At the same time, their mechanical properties are poor, and they are easy to break under extrusion, further exposing a large number of pores inside, resulting in a significant increase in side reactions with the electrolyte, reducing the coulombic efficiency, cycle performance and rate performance of the battery. In this application, the ratio of silicon-deficient particles to the number of negative electrode active material particles is D lack Controlling it at ≤35%, preferably ≤30%, further preferably ≤25%, and more preferably ≤20%, can effectively improve the distribution uniformity of nano-silicon in the negative electrode active material, reduce the specific surface area of ​​the material, improve the mechanical strength and compressive resistance, and can effectively reduce the volume change of the silicon material during the charge and discharge process, and improve the coulombic efficiency and cycle stability of the material.

[0044] Further, in the present application, the mass content of silicon in the negative electrode active material is W total The proportion of silicon-deficient particles D lack The product DS is ≤0.15, preferably ≤0.125, and more preferably ≤0.1.

[0045] Due to the structural limitations of the pore volume and pore size distribution inside the porous carbon skeleton, there is an upper limit to the mass content of silicon that can be accommodated inside each porous carbon skeleton. When the mass content of silicon in the actual deposition is lower than the upper limit it can accommodate, the porous carbon skeleton still has a residual pore structure, which may be partially filled in the subsequent amorphous carbon coating process, or it may remain in the final product. The residual pore structure is conducive to improving the ability of the silicon-carbon material to accommodate and buffer the expansion and contraction of silicon nanoparticles in the battery, effectively reducing its volume change during the charge and discharge process, improving cycle stability and reducing expansion. On the contrary, when the mass content of silicon in the actual deposition is higher than the upper limit that the porous carbon particles can accommodate, the excess silicon will form a single silicon layer with a certain thickness on the surface of the particles, or form single silicon particles, resulting in serious aggravation of the side reaction with the electrolyte, a significant deterioration of the cycle, and a significant increase in expansion.

[0046] When DS≤0.15 (preferably ≤0.125, more preferably)≤0.1, the presence of a large number of invalid porous carbon particles can be effectively avoided, and the situation where nano-silicon is severely enriched in some particles can also be avoided.

[0047] Optionally, the powder resistivity of the negative electrode active material particles is ≤60Ω·cm, preferably ≤40Ω·cm, further preferably ≤20Ω·cm, and more preferably ≤10Ω·cm.

[0048] As mentioned above, when the mass content of silicon in the actual deposition on the porous carbon particles is higher than the upper limit that it can accommodate, the excess silicon will form a single silicon layer with a certain thickness on the surface of the particles, which will cause the powder resistance of the material to increase significantly. When the powder resistance of the negative electrode active material particles is controlled at ≤60Ω·cm, preferably ≤40Ω·cm, further preferably ≤20Ω·cm, and more preferably ≤10Ω·cm, it means that the single silicon layer on the surface of the particles is thin, or there is no single silicon layer on the surface of the particles, so the improvement effect on the cycle is significant.

[0049] Optionally, the specific surface area of ​​the negative electrode active material particles is BET ≤ 60 m 2 / g, preferably ≤35m 2 / g, more preferably ≤20m 2 / g, more preferably ≤10m 2 / g.

[0050] Optionally, the median particle size D of the negative electrode active material particles v 50 is 1 to 15 μm, preferably 2 to 12 μm.

[0051] Optionally, the mass content of silicon in the negative electrode active material is W total The content of the carbonyl group is 30-80%, preferably 35-65%. At this time, the material has a very high reversible capacity, and also has excellent cycle performance and low expansion rate.

[0052] Optionally, the median particle size of nano silicon is ≤10nm, preferably ≤5nm, and further preferably ≤3nm. When silicon nanoparticles within this range undergo a cycle of lithium ion insertion and extraction, the particles expand little and are not easy to break, so that the cycle expansion of the lithium ion secondary battery using the material is small and the cycle is stable. Since nano silicon is mainly deposited in the pores of the porous carbon skeleton or coated on the pore surface of the porous carbon skeleton, the pore size and distribution structure of the porous carbon skeleton determine the size of the nano silicon particles.

[0053] The negative electrode active material provided by the present application controls the proportion of the number of silicon-deficient particles therein, improves the deposition uniformity of nano-silicon in the negative electrode active material, avoids the presence of a large number of invalid porous carbon particles, and also avoids the situation where nano-silicon is severely enriched in some particles. Therefore, the material has a denser and evenly distributed structure, reduces the specific surface area of ​​the material, improves the mechanical strength and compressive resistance, effectively alleviates the volume change of the silicon material during the charging and discharging process, improves the coulombic efficiency and cycle stability of the material, and also makes the battery using the negative electrode active material have a higher energy density, a better cycle life and a lower expansion rate.

[0054]

Method for preparing negative electrode active material

[0055] Figure 1 A method for preparing negative electrode active material particles of a negative electrode active material provided in an embodiment of the present application is shown, comprising the following steps S1 to S3.

[0056] S1: Preparation of porous carbon framework.

[0057] Porous carbon skeletons refer to carbon materials with pore structures of different sizes. According to the pore size, porous carbon skeletons can be divided into three types: microporous carbon skeletons (pore size less than 2 nanometers), mesoporous carbon skeletons (pore size between 2 and 50 nanometers) and macroporous carbon skeletons (pore size greater than 50 nanometers). Porous carbon skeletons have the characteristics of adjustable pore structure, large specific surface area, good conductivity and good stability. Among them, porous carbon materials with different pore sizes, pore volumes and porosities can be obtained by adjusting the preparation method and process parameters.

[0058] At present, commonly used porous carbon skeletons include biomass porous carbon, resin-based porous carbon, graphite-based porous carbon, coal-based porous carbon, etc. There are many methods for preparing porous carbon skeletons, including template method, laser ablation method, activation method, gel crystallization method, salting-out method, co-precipitation method, emulsion liquid film method, etc. Among them, the activation method includes physical activation method and chemical activation method. The physical activation method is to carbonize the carbon precursor at high temperature (usually above 800°C), and then use water vapor or carbon dioxide as an activator to react with the carbon precursor to achieve the purpose of pore formation. The chemical activation method is to use chemical reagents (such as KOH, KHCO3, NaHCO3, H3PO4 or ZnCl2, etc.) to react with the carbon precursor under high temperature conditions to achieve the purpose of pore formation.

[0059] In the present application, the specific surface area of ​​the porous carbon skeleton selected can be 1000 to 3000 m 2 / g, preferably 1400 to 3000 m 2 / g. The pore volume of the selected porous carbon skeleton can be 0.5 to 1.5 cm 3 / g, preferably 0.55 to 1.4 cm 3 / g. The average adsorption pore size of the selected porous carbon skeleton may be ≤10nm, more preferably ≤5nm, and more preferably ≤3nm. The average adsorption pore size mentioned here refers specifically to the average adsorption pore size calculated by the specific surface area analyzer test (BET model). The porous carbon skeleton may contain micropores, mesopores and macropores at the same time, and may also contain closed pores and through pores at the same time.

[0060] In this application, the median particle size D of the porous carbon skeleton selected is v 50 may be 1-15 μm, preferably 2-12 μm. The particle size distribution Span of the selected porous carbon skeleton may be ≤2, preferably ≤1.6, and more preferably ≤1.4.

[0061] S2: Deposition of nano-silicon on the porous carbon skeleton.

[0062] The porous carbon skeleton is placed in a reaction furnace, and then a silicon source gas is introduced into the reaction furnace. The silicon source gas is adsorbed into the porous carbon skeleton, and then a pyrolysis reaction occurs at a high temperature to generate nano-silicon. The reaction furnace may include a vertical fluidized bed, a horizontal fluidized bed, a stirred fluidized bed, a vibrating fluidized bed, a rotary kiln, a tubular furnace or a vapor deposition furnace, etc. The silicon source gas may include silane (SiH4), dichlorosilane (SiH2Cl2), trichlorosilane (SiHCl3), silicon tetrachloride (SiCl4), etc. In the reaction process, by controlling the reaction temperature, gas flow rate, concentration of silicon source gas (ratio of silicon source gas to protective gas), stirring intensity, rotation speed, fluidization intensity, reaction time and equipment structure design, a silicon-carbon negative electrode active material with different uniformities of nano-silicon distribution can be obtained. The reaction temperature may be 460 to 580°C. The protective gas may include nitrogen, argon, etc.

[0063] In order to further optimize the structure and uniformity of the negative electrode active material, a multi-step siliconization method can also be used to achieve the deposition of nano-silicon.

[0064] S3: An amorphous carbon film is coated on a porous carbon skeleton deposited with nano-silicon.

[0065] After the deposition of nano-silicon is completed, the porous carbon skeleton and nano-silicon can be coated with an amorphous carbon layer in the original reactor, or the porous carbon material deposited with nano-silicon can be transferred to another carbon coating reactor through a transfer device protected by an inert gas for coating with an amorphous carbon layer. The carbon coating reactor may include a fluidized bed, a rotary kiln, a tubular furnace or a vapor deposition furnace. The carbon source used in this step may be a hydrocarbon gas, and the decomposition temperature of the hydrocarbon gas may be 480 to 750°C. At the same time, a multi-step carbon coating method can also be used to achieve effective coating of an amorphous carbon film layer.

[0066] In the present application, the content of silicon-deficient particles in the negative electrode active material particles can be controlled by adjusting the specific process parameters of steps S1 to S3, so that the number of silicon-deficient particles in the negative electrode active material particles accounts for D lack ≤35%, and the mass content of silicon in the negative electrode active material is W total The proportion of silicon-deficient particles D lack The product DS is ≤0.15. Specifically, by controlling the appropriate stirring frequency and gas flow rate, the material can be fully fluidized, the agglomeration can be opened, the reaction gas and the material particles can be fully contacted, and uniform and efficient adsorption and reaction can be achieved, while avoiding the state of channel flow and excessive bubbling fluidization. In addition, by designing the reaction temperature zone, the material can achieve the reaction of adsorption of silicon-containing reaction gas (such as silane) and deposition of silicon nanoparticles at different temperatures in the reactor, which is conducive to improving the uniformity of the reaction.

[0067]

Characterization method of negative electrode active materials

[0068] 1. Material testing: The following equipment was used to characterize the negative electrode active materials prepared in each embodiment and comparative example: Dandong BetterSize 2600 laser particle size analyzer was used to test the particle size distribution of the negative electrode active materials. Rigaku miniFlex600 powder X-ray diffractometer (XRD) was used to test the components and crystal structure of the obtained negative electrode materials. Quantachrome Instruments' NOVA 4200e specific surface area tester was used to test the specific surface area of ​​the negative electrode active materials. The specific surface area test requirements are as follows: Weigh the sample with a sample tube, use nitrogen, and use a multi-point method to test the specific surface area of ​​the sample in the relative pressure range of p / p0=0.05~0.3. The ELEMENTRAC CS-i Elt carbon-sulfur analyzer was used to test the carbon mass content W of the sample. c The standard sample is 41% carbon by mass. The equipment is calibrated with the standard sample before testing the carbon mass content. The mass content of silicon in the negative electrode active material W total The following formula is used for calculation: The mass content of silicon W total =1-W c The ST2722-SD powder low resistance tester produced by Suzhou Jingge was used to measure the resistivity of the negative electrode active material at different pressures, and the resistivity at 20 MPa was taken as the powder resistivity of the material.

[0069] The surface morphology of the negative electrode active material was observed using a Hitachi SU8010 scanning electron microscope (SEM). At the same time, the energy spectrum analysis (EDS) function of the scanning electron microscope was used to scan the particles at 20 kV to obtain information on the element types and element contents in the particles. In order to statistically analyze the uniformity of the silicon-carbon negative electrode active material, when preparing the EDS energy spectrum sample, the sample particles were laid flat on the conductive carbon glue to ensure that there was only one layer of particles on the carbon glue to avoid multi-layer particle stacking. When collecting the EDS signal of the particles, all particles with a diameter ≥2 μm appearing in the image were scanned at 1000 times, and the energy spectrum signals of all particles were collected to ensure that the number of collected particles was ≥500 (if there were less than 500 particles in one image, the particle energy spectrum signals of multiple regions were collected). The energy spectrum signals of the collected particles were statistically analyzed, and particles with a silicon mass content of ≤15% were defined as silicon-deficient particles. The number of silicon-deficient particles was counted as a percentage D. lack .

[0070] 2. Preparation and testing of half-cell pole pieces: Take 80 parts of the above-mentioned negative electrode active material, 9.7 parts of conductive carbon black, 0.3 parts of single-walled carbon nanotubes, and 10 parts of a binder, apply a slurry in an aqueous system, and then dry and roll to obtain a negative electrode pole piece containing the negative electrode active material of the present application.

[0071] The negative electrode sheet containing the negative electrode active material of the present application was stacked with the separator, lithium sheet, and stainless steel gasket in sequence, and 200 μL of electrolyte was dripped and sealed to form a 2016-type lithium-ion half-cell. The capacity and discharge efficiency were tested using a small (micro) current range device of Wuhan Blue Electric Electronics Co., Ltd. The capacity and first cycle efficiency of the pure material half-cell containing the negative electrode active material of the present application were measured.

[0072] 3. Preparation and testing of full battery pole pieces: Take 20 parts of the above-mentioned negative electrode active material, 74 parts of artificial graphite, 2.5 parts of conductive additives, and 3.5 parts of binder, apply a slurry in an aqueous system, and then dry and roll to obtain a negative electrode pole piece containing the negative electrode active material of the present application.

[0073] The negative electrode sheets of the negative electrode active materials prepared in the examples and comparative examples were cut, vacuum baked, wound together with the paired ternary positive electrode sheets and separators, and placed in aluminum plastic shells of corresponding sizes, injected with a certain amount of electrolyte, degassed and sealed, and a lithium-ion full battery of about 3.2Ah was obtained after formation. The battery was then cycled 1C / 1C at 45°C to obtain the capacity retention rate after 1000 cycles, and the battery expansion rate after 1000 cycles was tested.

[0074] The present invention will be described below with reference to specific embodiments. The process condition values ​​taken in the following embodiments and comparative examples are exemplary, and their possible numerical ranges are as shown in the aforementioned summary of the invention. For process parameters not particularly noted, conventional techniques can be used. Unless otherwise specified, reagents and instruments used in the technical scheme provided by the present invention can be purchased from conventional channels or the market. It should be noted that, in the absence of conflict, the features in the embodiments in this application and the embodiments can be combined with each other.

[0075] Example 1-1

[0076] Take 1000g of biomass activated carbon, its D v 50 is 7μm, Span is 1.3, and the specific surface area of ​​the raw material is 2000m 2 / g, the average adsorption pore diameter is 2nm, and the pore volume is 0.72cm 3 / g. The porous carbon raw material was put into a vertical fluidized bed with a stirring frequency of 30Hz and a nitrogen flow rate of 10L / min. After the temperature was raised to 540℃ at a rate of 5℃ / min, silane was introduced with a silane flow rate of 5L / min and kept at 540℃ for 150min. After the insulation was completed, the silane was turned off, and the temperature was continued to rise to 640℃. Then, acetylene was introduced at 5L / min, and the acetylene was turned off after 150min of insulation, and the furnace was cooled naturally.

[0077] The negative electrode active material obtained by the above steps was tested by a carbon-sulfur analyzer and the carbon content was 57.33%. Since the material contains almost only carbon and silicon elements, the silicon content is W total The specific surface area of ​​the material is 60m 2 / g, the powder resistance is 51.97Ω·cm, and its XRD spectrum is as follows Figure 2 shown.

[0078] The morphology and elements of the material were analyzed using a scanning electron microscope. The SEM photos and energy spectrum results are shown in Figure 3 shown. Figure 3 Only the energy spectrum results of 18 particles in this area are shown. It can be seen that the mass content of silicon in 6 of them is less than 15%, which are poorly siliconized particles. Using the statistical method mentioned above, the energy spectrum of more than 500 particles with a diameter of ≥ 2μm is taken, and the proportion of poorly siliconized particles is calculated to obtain D lack is 34.8%. Therefore, the mass content of silicon W total and the proportion of silicon-deficient particles D lack The product DS is 0.148.

[0079] The pure first efficiency (pure FCE) of the negative electrode active material was 88.4% through half-cell testing. Then the silicon-carbon negative electrode and graphite were mixed (20% silicon-carbon negative electrode was added) and assembled into a 3.2Ah soft-pack full battery for a 45°C cycle test. After 1000 cycles of 1C / 1C long cycles, the cycle retention rate was 80.5% and the battery cell expansion rate was 25.4%.

[0080] The results are shown in Table 1.

[0081] Example 1-2

[0082] Using raw materials and processes similar to those of Example 1-1, only the stirring frequency was adjusted to 35 Hz, the silane flow rate was adjusted to 4 L / min, and the insulation time of silicon deposition was adjusted to 188 min.

[0083] The negative electrode active material obtained by the above steps is tested by a carbon-sulfur analyzer and the carbon content is 57.17%, so the silicon content is 42.83%. The specific surface area of ​​the material is 53.8m 2 / g, and the powder resistance is 34.48Ω·cm. Using the above characterization method and statistical method, D lack is 32.2%. Therefore, the mass content of silicon W total and the proportion of silicon-deficient particles D lack The product DS is 0.138.

[0084] The first efficiency of the pure negative electrode active material was 89.1% through a half-cell test. The full battery containing the negative electrode active material was subjected to a cycle test at 45°C. The cycle retention rate after 1000 cycles was 81.2%, and the battery cell expansion rate was 23.5%.

[0085] The results are shown in Table 1.

[0086] Examples 1-3

[0087] A process similar to that of Example 1-1 was used, except that the raw material was replaced with D v 50 is 8.5 μm, and Span is 1.3. The results are shown in Table 1.

[0088] Examples 1-4

[0089] The raw materials and process were similar to those in Example 1-1, except that the flow rate of silane was adjusted to 3 L / min and the holding time of silicon deposition was adjusted to 260 min. The results are shown in Table 1.

[0090] Examples 1-5

[0091] The raw materials and processes similar to those of Examples 1-4 were used, except that the holding time of silicon deposition was adjusted to 280 min. The results are shown in Table 1.

[0092] Examples 1-6

[0093] The raw materials and process were similar to those in Example 1-2, except that the flow rate of silane was adjusted to 3.5 L / min and the holding time of silicon deposition was adjusted to 240 min. The results are shown in Table 1.

[0094] Examples 1-7

[0095] Using raw materials and processes similar to those of Examples 1-6, the stirring frequency was adjusted to 45 Hz. The results are shown in Table 1.

[0096] Examples 1-8

[0097] Using raw materials and processes similar to those of Example 1-7, the temperature of silicon deposition was adjusted to 510° C. and the stirring frequency was adjusted to 50 Hz. The results are shown in Table 1.

[0098] Examples 1-9

[0099] Using raw materials and processes similar to those of Example 1-8, the holding time of silicon deposition was adjusted to 265 minutes. The results are shown in Table 1.

[0100] Examples 1-10

[0101] Using a raw material process similar to 1-6, the temperature of silicon deposition was adjusted to 520°C, the nitrogen flow rate was adjusted to 15 L / min, and the stirring frequency was adjusted to 55 Hz. The results are shown in Table 1.

[0102] Examples 1-11

[0103] Take 1000g of resin activated carbon, D v 50 is 6.5μm, Span is 1.2, and the specific surface area of ​​the raw material is 2050m 2 / g, the average adsorption pore diameter is 2nm, and the pore volume is 0.95cm 3 / g. The porous carbon raw material was put into a rotary kiln with a stirring frequency of 15Hz and a nitrogen flow rate of 7L / min. After heating to 550°C at a rate of 5°C / min, silane was introduced with a silane flow rate of 3L / min and kept at 550°C for 290min. After the insulation was completed, the silane was turned off, and then the temperature was continued to rise to 640°C, and then 3L / min of acetylene was introduced. After keeping the temperature for 250min, the acetylene was turned off and the furnace was cooled naturally. The results of the obtained materials are shown in Table 1.

[0104] Examples 1-12

[0105] The raw materials and processes similar to those of Example 1-11 were used, except that the holding time of silicon deposition was adjusted to 250 min. The results are shown in Table 1.

[0106] Examples 1-13

[0107] Using raw materials and processes similar to those of Example 1-11, only the stirring frequency was adjusted to 20 Hz and the holding time of silicon deposition was extended to 301 min. The results are shown in Table 1.

[0108] Examples 1-14

[0109] Using raw materials and processes similar to those of Example 1-13, only the stirring frequency was adjusted to 17 Hz, the silane flow rate was adjusted to 1.5 L / min, and the holding time of silicon deposition was adjusted to 602 min. The results are shown in Table 1.

[0110] Examples 1-15

[0111] The raw materials and process parameters similar to those of Example 1-11 were adopted, but the equipment was changed to a horizontal fluidized bed, which has both the function of rotating the rotary kiln and the function of fluidizing the powder by the fluidized bed. The other process parameters were similar to those of Example 1-11. The results are shown in Table 1.

[0112] Examples 1-16

[0113] The raw materials and process parameters were similar to those of Example 1-15, but the holding time of silicon deposition was adjusted to 235 min. At the same time, the material obtained after discharging from the horizontal fluidized bed was put into the rotary kiln again, the stirring frequency was 15 Hz, the nitrogen flow rate was 7 L / min, and the temperature was raised to 600 ° C at a rate of 5 ° C / min. Then, 3 L / min of acetylene was introduced, and the acetylene was turned off after holding for 100 min, and the furnace was cooled naturally. The results of the obtained materials are shown in Table 1.

[0114] Examples 1-17

[0115] The raw materials and process parameters similar to those of Example 1-15 were used, but the holding time of silicon deposition was adjusted to 326 min. The results of the obtained materials are shown in Table 1.

[0116] Examples 1-18

[0117] Using raw materials and processes similar to those of Example 1-15, only the silane flow rate was adjusted to 1.5 L / min, the silicon deposition temperature was adjusted to 530° C., and the silicon deposition time was adjusted to 580 min. The results are shown in Table 1.

[0118] Examples 1-19

[0119] Using raw materials and processes similar to those of Example 1-18, only the stirring frequency was adjusted to 20 Hz and the nitrogen flow rate was adjusted to 11 L / min. The results are shown in Table 1.

[0120] Examples 1-20

[0121] A process similar to that of Example 1-19 was adopted, except that the raw material was replaced with spherical resin carbon. v 50 is 6.2μm, Span is 1.4, and the specific surface area of ​​the raw material is 1950m 2 / g, the average adsorption pore diameter is 2nm, and the pore volume is 0.80cm 3 / g. The results are shown in Table 1.

[0122] Embodiment 1-21

[0123] Using the process and raw materials similar to those of Example 1-20, only D v 50 is adjusted to 8μm, Span is adjusted to 1.2, and the results are shown in Table 1.

[0124] Examples 1-22

[0125] Take 1000g of resin activated carbon, D v 50 is 9μm, Span is 1.1, and the specific surface area of ​​the raw material is 2150m 2 / g, the average adsorption pore diameter is 2nm, and the pore volume is 0.90cm3 / g. The porous carbon raw material is put into a vertical fluidized bed with a stirring speed of 50Hz and a nitrogen flow rate of 15L / min. After heating to 540℃ at a rate of 5℃ / min, it enters the insulation stage, and silane is introduced with a silane flow rate of 5L / min. After insulation for 100min, the silane is turned off, and then the nitrogen flow rate is adjusted to 30L / min, the stirring speed is 75Hz, and insulation is performed for 15min. Then the nitrogen flow rate is adjusted back to 15L / min, the stirring speed is returned to 50Hz, and silane is continued to be introduced with a flow rate of 2L / min, and insulation is performed for 185min. Subsequently, insulation is completed, silane is turned off, and then the temperature is continued to rise to 640℃, followed by the introduction of 3L / min of acetylene, and the acetylene is turned off after insulation for 250min, and the furnace is cooled naturally. The results of the obtained materials are shown in Table 1.

[0126] Examples 1-23

[0127] Using a process similar to that of Example 1-22 and the raw materials of Example 1-21, the results of the obtained materials are shown in Table 1.

[0128] Comparative Example 1-1

[0129] Using a process and raw materials similar to those of Example 1-1, only the stirring frequency was adjusted to 20 Hz and the nitrogen flow rate was adjusted to 5 L / min. The results of the obtained materials are shown in Table 1.

[0130] Comparative Example 1-2

[0131] Using a process and raw materials similar to those of Example 1-2, only the holding time of silicon deposition was extended to 210 min. The obtained material results are shown in Table 1.

[0132] Comparative Example 1-

[0133] Using a process and raw materials similar to those of Example 1-5, only the holding time of silicon deposition was extended to 336 min. The obtained material results are shown in Table 1.

[0134] Table 1

[0135]

[0136]

[0137] As shown in Table 1, when D lack The larger it is, the more silicon-deficient particles there are. These silicon-deficient particles still have a large number of pore structures, so their specific surface area is large. At the same time, their mechanical properties are poor, and they are easily broken under extrusion, further exposing a large number of pores inside, resulting in a significant increase in side reactions with the electrolyte. Therefore, the first efficiency of the half-cell of pure material is often low, and the high-temperature cycle performance of the full battery using this negative electrode material is poor, and the cycle expansion is large.

[0138] On the other hand, in addition to the proportion of silicon-deficient particles, the distribution of silicon inside and on the surface of porous carbon particles and the uniformity of distribution among different particles also have a significant impact on performance. lack ≤35%, preferably ≤30%, more preferably ≤25%, more preferably ≤20%, and DS is controlled at ≤0.15, preferably ≤0.125, more preferably ≤0.1, which can effectively avoid the presence of a large number of invalid porous carbon particles, and also avoid the situation where nano-silicon is seriously enriched in some particles, and avoid the situation where a certain thickness of single silicon layer appears on the surface of some particles. Therefore, it can effectively improve the distribution uniformity of nano-silicon in the negative electrode active material, reduce the specific surface area and powder resistance of the material, improve the mechanical strength and compressive performance, can effectively reduce the volume change of silicon material during charging and discharging, and improve the coulombic efficiency and cycle stability of the material.

[0139] Example 2-1

[0140] Using a process and raw materials similar to those of Example 1-10, only the nitrogen flow rate was adjusted to 14 L / min and the silicon deposition time was delayed by 10 min. The results are shown in Table 2.

[0141] Example 2-2

[0142] The process of Example 2-1 was adopted, and only the raw material was replaced with D v 50 is 7μm, Span is 1.3, and the specific surface area of ​​the raw material is 2500m 2 / g, the average adsorption pore diameter is 1.2nm, and the pore volume is 0.68cm 3 / g. The results are shown in Table 2.

[0143] Example 2-3

[0144] The process of Example 2-1 was adopted, and only the raw material was replaced with D v 50 is 7μm, Span is 1.3, and the specific surface area of ​​the raw material is 1580m 2 / g, the average adsorption pore diameter is 3.6nm, and the pore volume is 0.92cm 3 / g. The results are shown in Table 2.

[0145] Table 2

[0146]

[0147] As shown in Table 2, the average adsorption pore size of the porous carbon skeleton determines the average particle size of nano-silicon. The average particle size of nano-silicon is preferably ≤5 nm, and more preferably ≤3 nm, so as to obtain better battery performance.

[0148] The above description is only an example embodiment of the present application and is not intended to limit the present application. Although the present application is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A negative electrode active material, comprising negative electrode active material particles, characterized in that: The negative electrode active material particles include porous carbon skeleton, nano silicon and amorphous carbon film; The negative electrode active material particles contain silicon-deficient particles, the mass content of silicon in the silicon-deficient particles is ≤15%, and the number of the silicon-deficient particles in the negative electrode active material particles accounts for D lack ≤35%, preferably ≤30%, further preferably ≤25%, more preferably ≤20%; The mass content of silicon in the negative electrode active material is W total The number of the silicon-deficient particles accounts for D lack The product DS is ≤0.15, preferably ≤0.125, and more preferably ≤0.

1.

2. The negative electrode active material according to claim 1, characterized in that The nano-silicon is deposited in the pores of the porous carbon skeleton and / or on the surface of the porous carbon skeleton.

3. The negative electrode active material according to claim 1, characterized in that The amorphous carbon film is coated on the surface of the nano-silicon and / or the porous carbon skeleton, and / or the amorphous carbon film is filled in the pores of the porous carbon skeleton.

4. The negative electrode active material according to claim 1, characterized in that The powder resistivity of the negative electrode active material particles is ≤60Ω·cm, preferably ≤40Ω·cm, more preferably ≤20Ω·cm, and more preferably ≤10Ω·cm; and / or The specific surface area of ​​the negative electrode active material particles is ≤60m 2 / g, preferably ≤35m 2 / g, more preferably ≤20m 2 / g, more preferably ≤10m 2 / g.

5. The negative electrode active material according to claim 1, characterized in that The median particle size of the negative electrode active material particles is 1 to 15 μm, preferably 2 to 12 μm.

6. The negative electrode active material according to claim 1, characterized in that The mass content of silicon in the negative electrode active material is W total It is 30-80%, preferably 35-65%.

7. The negative electrode active material according to claim 1, characterized in that The median particle size of the nano-silicon is ≤10 nm, preferably ≤5 nm, and more preferably ≤3 nm.

8. An electrode, characterized in that: The negative electrode active material comprises any one of claims 1 to 7.

9. A battery, characterized in that: Comprising the electrode according to claim 8.

10. A method for preparing a negative electrode active material, wherein the negative electrode active material comprises negative electrode active material particles, characterized in that: The preparation method comprises: The preparation of the negative electrode active material particles comprises: preparing a porous carbon framework; Depositing nano-silicon on the porous carbon skeleton; and Coating an amorphous carbon film on the porous carbon skeleton on which the nano-silicon is deposited; The negative electrode active material particles contain silicon-deficient particles, the mass content of silicon in the silicon-deficient particles is ≤15%, and the number of the silicon-deficient particles in the negative electrode active material particles accounts for D lack ≤35%, preferably ≤30%, further preferably ≤25%, more preferably ≤20%; The mass content of silicon in the negative electrode active material is W total The number of the silicon-deficient particles accounts for D lack The product DS is ≤0.15, preferably ≤0.125, and more preferably ≤0.1.

Images