Negative electrode material and lithium ion battery

Abstract

A negative electrode material and a lithium ion battery. The negative electrode material comprises a porous carbonaceous material, a silicon material is distributed in the porous carbonaceous material, and the negative electrode material has a uniformity of N, wherein N≥80%. In a backscattered electron image obtained by scanning a negative electrode material by using a scanning electron microscope (SEM) under a BSE automatic brightness and contrast mode, in any 100 μm*100 μm area, the number of particles of the negative electrode material which have a first brightness is denoted as C1, wherein the particles of the negative electrode material which have the first brightness represent the negative electrode material having a grayscale value greater than or equal to 5500 in the backscattered electron image; the number of particles of the negative electrode material which have a second brightness is denoted as C2, wherein the particles of the negative electrode material which have the second brightness represent the negative electrode material having a grayscale value less than 5500 in the backscattered electron image; and the uniformity of the negative electrode material in said area is N'=C2 / (C2+C1)*100％, and the uniformity N of the negative electrode material is an arithmetic mean value of at least 10 N'.

Description

Anode materials and lithium-ion batteries

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to a Chinese patent application filed with the Patent Office of China on November 24, 2023, with application number 2023115910846 and application name “Negative electrode material and preparation method thereof, lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application belongs to the technical field of negative electrode materials, and more specifically, relates to negative electrode materials and lithium-ion batteries. Background Art

[0004] Silicon-based anode materials offer advantages such as high specific capacity, low voltage plateau, environmental friendliness, and abundant resources, making them promising alternatives to graphite anodes for next-generation high-energy-density lithium-ion batteries. However, silicon undergoes significant volume changes during the deintercalation / intercalation process, which can easily lead to particle pulverization and subsequent detachment from the current collector. Furthermore, the repeated volume changes of silicon materials during electrochemical cycling also cause the SEI film formed on the silicon surface to be continuously destroyed and regenerated, resulting in continuous consumption of lithium ions and ultimately rapid capacity decay.

[0005] Usually, the silicon negative electrode material is improved by nano-sizing, carbon coating, polymer coating and other processes, which can inhibit the volume expansion of silicon to a certain extent. Usually, silicon is deposited in porous carbon to inhibit the volume expansion of silicon. The biomass method for preparing porous carbonaceous materials is currently the mainstream preparation method. However, the porous carbon prepared by the existing biomass method generally has the phenomenon of uneven activation, and there are more or less particles without pores (and not activated). Such particles have few or no pores due to the lack of activation during the silicon deposition process. Silicon is easily deposited on the surface of the particles, resulting in the deterioration of the expansion performance, cycle performance and rate performance of the negative electrode material.

[0006] Therefore, there is an urgent need to provide a silicon negative electrode material with low expansion, high cycle and high rate performance. Summary of the Invention

[0007] The present application provides a negative electrode material and a lithium-ion battery, which can improve the expansion performance, cycle performance and rate performance of the negative electrode material.

[0008] To achieve the above objectives, the first technical solution of this application is as follows:

[0009] The embodiment of the present application provides a negative electrode material, the negative electrode material comprising a porous carbonaceous material, wherein silicon material is distributed inside the porous carbonaceous material, and the negative electrode material has a uniformity N, N ≥ 80%;

[0010] For the backscattered electron image obtained by scanning the negative electrode material using an SEM scanning electron microscope in the BSE automatic brightness and contrast mode, in any 100μm*100μm area, the number of particles of the negative electrode material with a first brightness is recorded as C1, and the particles of the negative electrode material with the first brightness represent the negative electrode material with a grayscale value greater than or equal to 5500 in the backscattered electron image. The number of particles of the negative electrode material with a second brightness is recorded as C2, and the particles of the negative electrode material with the second brightness represent the negative electrode material with a grayscale value less than 5500 in the backscattered electron image. The uniformity N' of the negative electrode material in the above-mentioned area is equal to C2 / (C2+C1)*100%, and the uniformity N of the negative electrode material is the arithmetic average of the uniformities N' of at least 10 of the above-mentioned areas.

[0011] The technical solution of this application has at least the following beneficial effects:

[0012] The negative electrode material of the present application includes a porous carbon material and a silicon material, and the negative electrode material has a uniformity N, N ≥ 80%, indicating that the negative electrode material of the present application mainly exists in the form of particles with a grayscale value less than 5500 in the backscattered electron image. The particles with a grayscale value less than 5500 in the backscattered electron image indicate that the silicon material in the negative electrode material particles is mainly distributed in the pores of the porous carbon material and is evenly distributed. That is to say, in the present application, taking the total number of negative electrode material particles as 100%, the number of particles in the negative electrode material in which the silicon material is uniformly distributed in the pores of the porous carbon material accounts for greater than or equal to 80%, thereby indicating that the porous carbon material of the present application has uniformly distributed activation pores, and the number of activation pores is appropriate, so that the silicon material can be mainly distributed in the pores of the porous carbon material, with a higher silicon deposition amount. In addition, the uniformity N of the present application is obtained by testing the negative electrode material obtained in any 100μm*100μm area. N≥80% indicates that the number and distribution of activated pores of the porous carbonaceous material of each negative electrode material particle of the present application are highly similar, that is, the negative electrode material of the present application has a porous carbonaceous material with good consistency. The porous carbonaceous material with good consistency can improve the dispersion of the silicon material in the negative electrode material, inhibit the volume effect caused by the agglomeration of the silicon material during the lithium insertion / delithiation process, and reduce the pulverization of the negative electrode material particles. At the same time, during the lithium insertion / delithiation process, the negative electrode material allows the SEI film to be formed in a limited space, which is conducive to the formation of a stable SEI film, improving the structural stability of the negative electrode material, thereby improving the expansion performance, cycle performance and capacity of the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present application is further described below with reference to the accompanying drawings and examples.

[0014] FIG1 is a flow chart of the preparation of the negative electrode material of the present application;

[0015] FIG2 is a SEM image of the negative electrode material prepared in Example 1 of the present application;

[0016] FIG3 is an XRD pattern of the negative electrode material prepared in Example 1 of the present application;

[0017] FIG4 is the first charge and discharge curve of the negative electrode material prepared in Example 1 of the present application;

[0018] FIG5 is a cycle performance curve of the negative electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0019] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0020] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0021] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0022] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0023] The preparation of porous carbon materials by biomass method is the mainstream preparation method at present. However, the porous carbon materials prepared by the existing biomass method generally have the phenomenon of uneven activation, and there are more or less particles without pores (also not activated). Such particles have few or no pores during the silicon deposition process due to lack of activation, resulting in less or almost no silicon deposition, causing the performance of the negative electrode material to deteriorate.

[0024] The embodiment of the present application provides a negative electrode material, including a porous carbonaceous material, wherein silicon material is distributed inside at least a portion of the porous carbonaceous material, and the negative electrode material has a uniformity N, N ≥ 80%;

[0025] For the backscattered electron image obtained by scanning the negative electrode material using a Hitachi S4800 SEM scanning electron microscope in the BSE automatic brightness and contrast mode, in any 100μm*100μm area, the number of particles of the negative electrode material with a first brightness is recorded as C1, and the negative electrode material with the first brightness represents the negative electrode material with a grayscale value greater than or equal to 5500 in the backscattered electron image. The number of particles of the negative electrode material with a second brightness is recorded as C2, and the negative electrode material with the second brightness represents the negative electrode material with a grayscale value less than 5500 in the backscattered electron image. The uniformity N' of the negative electrode material in the above-mentioned area is equal to C2 / (C2+C1)*100%, and the uniformity N of the negative electrode material is the arithmetic average of the uniformities N' of at least 10 of the above-mentioned areas.

[0026] In the above scheme, the negative electrode material of the present application includes a porous carbon material and a silicon material, and the negative electrode material has a uniformity N, N≥80%, indicating that the negative electrode material of the present application mainly exists in the form of particles with a grayscale value less than 5500 in the backscattered electron image. The particles with a grayscale value less than 5500 in the backscattered electron image indicate that the silicon material in the negative electrode material particles is mainly distributed in the pores of the porous carbon material and is evenly distributed. That is to say, in the present application, taking the total number of negative electrode material particles as 100%, the number of particles in the negative electrode material in which the silicon material is uniformly distributed in the pores of the porous carbon material accounts for greater than or equal to 80%, thereby indicating that the porous carbon material of the present application has uniformly distributed activation pores, and the number of activation pores is appropriate, so that the silicon material can be mainly distributed in the pores of the porous carbon material, with a higher silicon material deposition amount. In addition, the present application was obtained by testing the negative electrode material obtained in any 100μm*100μm area, indicating that the number and distribution of activated pores of the porous carbonaceous material of each negative electrode material particle of the present application are highly similar, that is, the negative electrode material of the present application has a porous carbonaceous material with good consistency. The porous carbonaceous material with good consistency can improve the dispersion of the silicon material in the negative electrode material, reduce the volume effect caused by the agglomeration of the silicon material during the lithium insertion / delithiation process, and reduce the pulverization of the negative electrode material particles. At the same time, during the lithium insertion / delithiation process, the negative electrode material allows the SEI film to be formed in a limited space, which is conducive to the formation of a stable SEI film, thereby improving the structural stability of the negative electrode material, thereby improving the expansion performance, cycle performance and capacity of the battery prepared with the negative electrode material.

[0027] Due to the large difference in electrical conductivity between carbonaceous materials and silicon materials, in the automatic brightness and contrast mode of scanning electron microscope (SEM)-backscattered electron (BSE), the negative electrode material particles with higher conductivity are usually darker in color, that is, the amount of silicon deposited in the porous carbonaceous material in the negative electrode material is less or the color of the porous carbonaceous material particles without silicon deposition is darker. Negative electrode material particles with low electrical conductivity are usually brighter in color, that is, the color of the negative electrode material particles in which silicon material is mainly deposited in the porous carbonaceous material with uniform pore distribution is brighter, usually bright white. This application uses a grayscale value of 5500 as a criterion for determining whether the color of the material particles is dark or bright. Negative electrode materials with a grayscale value greater than or equal to 5500 indicate that the surface of the material is darker, that is, the material particles have a first brightness. Material particles with the first brightness indicate that the silicon material is less deposited inside the negative electrode material particles, that is, the amount of silicon material deposited is less. The negative electrode material with a grayscale value less than 5500 indicates that the material surface is relatively bright, that is, the material particles have a second brightness. The material particles with the second brightness indicate that the silicon material is mainly deposited in the porous carbon material with uniform pore distribution, and the deposition amount of silicon material is large, that is, more silicon material is inside the negative electrode material particles.

[0028] In this application, the uniformity N is tested and calculated by a Hitachi S4800 SEM scanning electron microscope. Specifically, the negative electrode material particles are scanned by adjusting the scanning electron microscope (SEM) in the BSE automatic brightness and contrast mode, and the scanned image is converted into a grayscale image. The grayscale image is calculated using ImageJ image processing software. Specifically, the grayscale image is opened using ImageJ image processing software, and the particle area for which the grayscale value is to be calculated is selected using the "selection box" tool. The selected area is an arbitrary area of ​​100 μm*100 μm. Then, Ctrl+1 and Ctrl+3 are pressed in sequence to obtain the grayscale change curve of all particles. Then, a line tool (rectangular or rounded rectangular selection) is used to draw a perpendicular line to the horizontal axis at each trough point to form multiple different closed figures under the grayscale change curve. Finally, the magic wand (tracing tool) tool is used to click on the closed figures except the head and tail in turn to obtain the total grayscale value of each figure, which is determined to be the grayscale value of multiple particles in the selected area. The above steps are repeated to obtain the uniformity N' of at least 10 selected areas, and then the uniformity N is obtained by calculating the arithmetic average of the uniformity N' of all selected areas.

[0029] In some embodiments, N can be, for example, 80%, 86%, 88%, 90%, 93%, 95%, 97%, 99% and 100%, etc., and of course it can also be other values ​​within the above range, which is not limited in this application. Within the above-defined range, it indicates that the porous carbonaceous material has an appropriate number of uniformly distributed activated pores, so that the silicon material can be mainly distributed in the pores of the porous carbonaceous material, so that the silicon material content in the negative electrode material is high, and the negative electrode material is brighter in the scanning electron microscope (SEM)-backscattered electron (BSE) automatic brightness and contrast mode. If N is less than 80%, it indicates that the uniformity of the distribution of activated pores in the porous carbonaceous material is poor, and there are a certain number of particles with few or no activated pores, resulting in less or almost no deposition of silicon material inside the porous carbonaceous material, thereby resulting in degradation of the performance of the obtained negative electrode material. Preferably, the uniformity of the negative electrode material is 86%≤N≤99%.

[0030] In some embodiments, the silicon material is also distributed on at least a portion of the surface of the porous carbonaceous material.

[0031] In some embodiments, the porous carbonaceous material includes at least one of hard carbon, soft carbon, graphite, mesocarbon microbeads, activated carbon, and carbon gel.

[0032] In some embodiments, the porous carbon material includes micropores, which refer to pores with a pore diameter of less than 2 nm. The micropores are activated pores, which are conducive to the filling of silicon materials. The silicon material filled in the micropores can ensure the structural density of the porous carbon material, so that the negative electrode material will not collapse in structure during the compaction process of preparing the electrode.

[0033] In some embodiments, taking the total number of pores in the porous carbonaceous material as 100%, the number of micropores accounts for greater than or equal to 80%, specifically 80%, 85%, 90%, 92%, 95%, 97% or 99%, etc., and of course other values ​​within the above range can also be used, and this application is not limited thereto. Within the above-defined range, it indicates that there are a large number of activated pores in this application, and the activated pores have an energy storage function, which can reduce the diffusion resistance of the electrolyte and improve the capacity performance and rate performance of the negative electrode material. Preferably, the number of micropores in the porous carbonaceous material accounts for greater than or equal to 90%, and more preferably, the number of micropores in the porous carbonaceous material accounts for greater than or equal to 92%. In this application, the number of micropores is measured by nitrogen desorption. If the number of micropores in the porous carbonaceous material is less than 80%, it indicates that the number of micropores in the porous carbon is small, and the filling amount of the silicon material is small, which is not conducive to improving the capacity performance of the negative electrode material.

[0034] In some embodiments, the pores in the porous carbonaceous material include micropores with a pore size of less than 2 nm, and the volume proportion of the micropores is ≥80% based on the total pore volume. Specifically, the volume proportion of the micropores can be 80%, 82%, 85%, 88%, 90%, 92%, 93%, 95%, 98% or 99%, etc., and of course it can also be other values ​​within the above range, which are not limited here. It can be understood that the size of the silicon material particles deposited in the pores of the porous carbonaceous material is determined by the size of the pores. The higher the volume proportion of the micropores, the smaller the average pore size of the pores of the porous carbonaceous material, and the smaller the particle size of the silicon material particles deposited in the pores of the porous carbonaceous material. The particle size of the silicon material particles deposited in the pores of the porous carbonaceous material is small, and the volume expansion of the negative electrode material during the cycle is small, which is conducive to improving the cycle performance of the negative electrode material.

[0035] In some embodiments, the average pore size of the pores in the porous carbonaceous material is less than or equal to 5 nm, for example, 1 nm, 1.3 nm, 1.8 nm, 2 nm, 3 nm, 4 nm, or 5 nm, and of course other values ​​within the above ranges are also possible, and this application is not limited thereto. Preferably, the average pore size of the pores in the porous carbonaceous material is less than or equal to 2 nm, and preferably, the average pore size of the pores in the porous carbonaceous material is less than or equal to 1.8 nm.

[0036] In some embodiments, the silicon material includes at least one of crystalline silicon, silicon-oxygen material, amorphous silicon, and silicon alloy, and the silicon-oxygen material includes silicon oxide SiO x , wherein 0<x≤2, silicon oxide is a silicon-oxygen composite containing oxygen atoms and silicon atoms, and the molar ratio of oxygen atoms to silicon atoms is 0 to 2 and does not include 0, which can be SiO 0.2 、SiO 0.5 、SiO 0.8 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 Or SiO2, etc., a compound of two or more substances, or a substance with the chemical formula SiO x Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0037] In some embodiments, the silicon material comprises at least one of crystalline silicon, amorphous silicon, or a composite of crystalline silicon and amorphous silicon. Preferably, the silicon material is amorphous silicon, which has lower expansion than other types of silicon, thus helping to alleviate the problem of large volume expansion of silicon-carbon anode materials during lithium insertion and extraction.

[0038] In some embodiments, the silicon material includes silicon particles, and the morphology of the silicon particles includes at least one of a dot-like shape, a sphere, an ellipsoidal shape, and a flake-like shape.

[0039] In some embodiments, the mass content of silicon in the silicon material is ≥99%.

[0040] In some embodiments, the mass proportion of silicon material in the negative electrode material is 30% to 80%, that is, the mass proportion of silicon element in the negative electrode material is 30% to 80%, specifically 30%, 40%, 50%, 60%, 70% and 80%, etc., and of course it can also be other values ​​within the above range. This application is not limited here. Within the above-mentioned limited range, the mass proportion of silicon material in the negative electrode material, that is, the mass proportion of silicon element in the negative electrode material is high, which is beneficial to improving the capacity of the negative electrode material.

[0041] In some embodiments, the average particle size of the silicon material is 0.1nm to 500nm, for example, it can be 0.1nm, 1nm, 5nm, 10nm, 30nm, 50nm, 100nm, 200nm, 300nm, 400nm or 500nm, etc., of course, it can also be other values ​​within the above range, and this application is not limited here. Within the above-defined range, it is beneficial to buffer the stress and deformation generated by the silicon material during the process of lithium ion insertion and extraction, and improve the capacity and cycle performance of the negative electrode material. Preferably, the average particle size of the silicon material is 0.1nm to 10nm, and more preferably, the average particle size of the silicon material is 0.1nm to 5nm.

[0042] In some embodiments, the negative electrode material further includes a coating layer distributed over at least a portion of the surface of the porous carbonaceous material. The coating layer can, on the one hand, reduce the amount of electrolyte entering the negative electrode material and causing side reactions that could reduce initial efficiency and capacity. On the other hand, the coating layer can collaborate with the porous carbonaceous material to mitigate the volume expansion of the silicon material, thereby reducing the volume expansion of the entire negative electrode material and minimizing electrode sheet swelling.

[0043] In some embodiments, the coating layer is at least one of a carbon layer, a metal oxide layer, and a nitride layer.

[0044] In some embodiments, the material of the carbon layer includes at least one of graphene, soft carbon, hard carbon and a conductive polymer. Specifically, the conductive polymer includes at least one of polyaniline, polyacetylene, polypyrrole, polythiophene, poly-3-hexylthiophene, poly(p-phenylene vinylene), polypyridine and poly(phenylene vinylene).

[0045] In some embodiments, the metal oxide layer includes at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide.

[0046] In some embodiments, the nitride layer includes at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

[0047] In some embodiments, the coating layer has a thickness of 0.1 nm to 100 nm, specifically 0.1 nm, 1 nm, 10 nm, 30 nm, 50 nm, 70 nm, 90 nm, and 100 nm, and can also have other values ​​within the above range, which are not limited in this application. When the coating layer has a thickness within the above range, it is beneficial to improve the cycle performance of the negative electrode material while taking into account the electrochemical properties such as capacity and rate performance of the negative electrode material.

[0048] In some embodiments, the pore volume of the porous carbonaceous material is greater than or equal to 0.4 cm 3 / g, for example, it can be 0.4cm 3 / g, 0.5cm 3 / g, 0.7cm 3 / g, 1.0cm 3 / g, 1.5cm 3 / g, 2.0cm 3 / g, 2.5cm 3 / g, 3cm 3 / g, 3.5cm 3 / g or 5.0cm 3 / g, etc., of course, it can also be other values ​​within the above range, and this application is not limited here. Within the above-defined range, it shows that the number of activated pores in the porous carbonaceous material of this application is large, which is conducive to the deposition of more silicon material in the porous carbonaceous material and the improvement of the capacity performance of the negative electrode material. Preferably, the pore volume of the porous carbonaceous material is greater than or equal to 0.5cm 3 / g, more preferably, the pore volume of the porous carbonaceous material is greater than or equal to 0.7cm 3 / g.

[0049] In some embodiments, the porous carbonaceous material, that is, the negative electrode material after the silicon material is removed, can also include the following steps: under stirring, 150 mL of 20% by mass HF acid solution is added dropwise into 10 g of the negative electrode material, which will produce SiF4 and H2 gases and release heat. After no gas is generated, the supernatant acid solution is removed by centrifugation, and 150 mL of 20% by mass HF acid solution is added to the negative electrode material again. After stirring for 12 hours, the supernatant acid solution is removed again by centrifugation, and then the negative electrode material is washed with pure water until it is neutral and dried to obtain the negative electrode material after the silicon material is removed.

[0050] In some embodiments, the median particle size of the negative electrode material is less than or equal to 10 μm, for example, 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, or 10 μm, etc., and of course other values ​​within the above range are also possible, and this application is not limited thereto. Controlling the median particle size of the negative electrode material within the above range is beneficial to improving the cycle performance of the battery prepared with the negative electrode material.

[0051] In some embodiments, the specific surface area of ​​the negative electrode material is less than 5 m 2 / g, for example, it can be 1m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g or 4.5m 2 / g, etc., and of course other values ​​within the above range can also be used, and this application does not limit this. It can be understood that controlling the specific surface area of ​​the negative electrode material within the above range can inhibit the volume expansion of the negative electrode material, which is beneficial to improving the cycle performance of the battery prepared with the negative electrode material.

[0052] In some embodiments, the conductivity of the negative electrode material is greater than or equal to 10 -1 S / m, for example, can be 10 -1 S / m, 0.5S / m, 1S / m, 2S / m, 3S / m, 4S / m, 5S / m and 6S / m, etc. Within the above-mentioned limited range, it is beneficial to the transmission of electrons inside the negative electrode material and to the improvement of the rate performance of the battery prepared by the negative electrode material during the charging and discharging process.

[0053] The present application also provides a method for preparing the above-mentioned negative electrode material, as shown in FIG1 , which is a flow chart for preparing the negative electrode material of the present application, including the following steps:

[0054] Step S100, mixing the carbon-based carbonized material with a first activating agent to perform a first activation treatment to obtain an activated material;

[0055] Step S200: Mix the activated material with the second activator for a second activation treatment to obtain a porous carbonaceous material. The amount of the first activator added is 4 to 10 times the amount of the second activator added. The time of the first activation treatment is longer than the time of the second activation treatment.

[0056] Step S300: Mix the porous carbonaceous material and the silicon source and perform heat treatment to obtain a negative electrode material.

[0057] In the above scheme, the present application activates the carbon-based carbonized material twice in sequence. In the first activation treatment, the amount of the first activator added is 4 to 10 times the amount of the second activator added, and the time of the first activation treatment is longer than that of the second activation treatment. This shows that the first activation treatment has a stronger activation ability for the carbon-based carbonized material, which is beneficial for forming more activation pores inside the prepared activation material, and the pore size distribution range of the activation pores is larger. The activation ability of the second activation treatment is weaker, and the second activation treatment can further activate the unactivated areas in the activation material to form activation pores with smaller pore size. At the same time, the pores with too small pore size after the first activation treatment are expanded, so that the prepared porous carbonaceous material contains more and evenly distributed activation pores. The present application can prepare a porous carbon material with good consistency by regulating two activation treatment processes, and then deposit a silicon source in the porous carbon material. The silicon material is mainly distributed in the activated pores of the porous carbon material, thereby improving the dispersion and deposition amount of the silicon material in the negative electrode material, so that the uniformity N of the negative electrode material satisfies N≥80%. In this way, the volume effect caused by the agglomeration of the silicon material during the lithium insertion / delithiation process can be suppressed, and the pulverization of the negative electrode material particles can be reduced. At the same time, during the lithium insertion / delithiation process, the negative electrode material allows the SEI film to be formed in a limited space, which is conducive to the formation of a stable SEI film on the surface of the negative electrode material, improving the structural stability of the negative electrode material, and thus improving the expansion performance, cycle performance and capacity of the negative electrode material. The present application can prepare a porous carbon material with good consistency by regulating the different activation degrees of the two activation treatment processes. The process is simple, can be prepared in large quantities, and can improve the electrochemical performance of the negative electrode material as a battery.

[0058] The preparation method of the present application is described in detail below with reference to the examples:

[0059] Step S100: performing a first mixing of the carbon-based carbonized material and the first activating agent to obtain an activated material.

[0060] In some embodiments, the carbon-based carbonized material is obtained by carbonizing a carbon-based raw material.

[0061] In some embodiments, the carbon-based feedstock includes at least one of lignin, coconut shells, fruit shells, peanut shells, rice husks, coal-based biomass, and resin.

[0062] In some embodiments, the carbonization temperature is 400°C to 900°C, specifically 400°C, 500°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C or 900°C, etc. Of course, it can also be other values ​​within the above range, which is not limited in this application.

[0063] In some embodiments, the carbonization time is 1 h to 20 h, specifically 1 h, 3 h, 5 h, 10 h, 12 h, 15 h, 18 h and 20 h, etc. Of course, it can also be other values ​​within the above range, which is not limited in this application.

[0064] In some embodiments, the carbonization is performed under a protective gas atmosphere, and the protective gas includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0065] In some embodiments, after obtaining the carbon-based carbonized material, the method further includes: pickling the carbon-based carbonized material, where the pickling acid is at least one of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, phosphoric acid, perchloric acid, acetic acid and benzoic acid.

[0066] In some embodiments, the concentration of the acid washing solution is 1 mol / L to 10 mol / L, for example, 1 mol / L, 3 mol / L, 5 mol / L, 8 mol / L, or 10 mol / L, and of course, other values ​​within the above range are also possible and are not limited herein. It is understood that the purpose of acid washing is to remove impurities from the material. The carbon-based carbonized material is acid washed and then washed with deionized water to neutralize the product.

[0067] In some embodiments, the pickling time is 3 hours to 8 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0068] In some embodiments, the first activating agent includes a basic substance.

[0069] In some embodiments, the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, and rubidium hydroxide.

[0070] In some embodiments, the mass ratio of the carbon-based carbonized material and the first activator is 1:(0.5-30), which can specifically be 1:0.5, 1:1, 1:5, 1:10, 1:20 and 1:30, etc. Of course, it can also be other values ​​within the above range, which is not limited here. Within the above-mentioned limited range, the amount of the first activator added is relatively large, the activation ability is relatively strong, and it can form more and evenly distributed activation pores in the carbon-based carbonized material, which is conducive to the subsequent filling of silicon material in the activation pores. If the amount of the first activator added is too much, the pore size of the pore structure in the activation material will be larger, and the number of pores will be larger, which will easily lead to structural collapse of the negative electrode material during the deintercalation process, resulting in a decrease in the cycle performance of the negative electrode material. If the amount of the first activator added is too little, it will not be possible to form an appropriate number of evenly distributed activation pores inside the carbon-based carbonized material, which is not conducive to the subsequent deposition of the silicon source, and the negative electrode material will have a large volume expansion, resulting in a decrease in the capacity and expansion performance of the negative electrode material.

[0071] In some embodiments, the first activator includes at least one of water vapor, oxygen, and air. The gaseous first activator activates the carbon-based carbonized material by reacting the gaseous water vapor, oxygen, and air with carbon at a high temperature to generate hydrogen and carbon monoxide, which are then used to etch the carbon-based carbonized material to form activated pores.

[0072] In some embodiments, the concentration of the first activator is 3% to 20%, specifically 3%, 5%, 7%, 9%, 10%, 12%, 15%, 18%, and 20%, etc., and of course other values ​​within the above range are also possible, and this application does not impose any limitation thereto. Within the above-defined range, the amount of the first activator added is relatively large, the activation ability is relatively strong, and a large number of evenly distributed activation pores can be formed in the carbon-based carbonized material, which is conducive to the subsequent filling of the silicon material into the activation pores.

[0073] It can be understood that when the first activating agent is water vapor, the concentration of the water vapor can be considered as the humidity of the water vapor.

[0074] In some embodiments, the time of the first activation treatment is 5 h to 20 h, for example, it can be 5 h, 8 h, 10 h, 12 h, 15 h, 18 h or 20 h, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0075] In some embodiments, the temperature of the first activation treatment is 900°C to 1200°C, specifically 900°C, 930°C, 950°C, 1000°C, 1100°C and 1200°C, etc. Of course, it can also be other values ​​within the above range, which is not limited in this application.

[0076] Step S200: Mix the activated material with the second activator for a second activation treatment to obtain a porous carbonaceous material. The amount of the first activator added is 4 to 10 times the amount of the second activator added. The time of the first activation treatment is greater than the time of the second activation treatment.

[0077] In the present application, by limiting the addition amount of the first activator to 4 to 10 times the addition amount of the second activator, the time of the first activation treatment is greater than the time of the second activation treatment, so that the carbon-based carbonized material is activated twice to obtain a porous carbon material with a large number of activated pores and uniform distribution.

[0078] In some embodiments, the amount of the first activator added is 4 to 10 times the amount of the second activator added, specifically 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, and 10 times, etc., and of course it can also be other values ​​within the above range, and this application is not limited thereto. If the amount of the second activator added is too little, the activation ability of the second activation treatment is poor, and it cannot play a role in increasing the activation pores, resulting in a small number of activated pores in the porous carbonaceous material and poor distribution uniformity; if the amount of the second activator added is too much, it is easy to perform secondary pore expansion in the activated pores formed in the first activation treatment to form mesopores or macropores, which is not conducive to the dispersion uniformity of the subsequent silicon source deposition, resulting in poor expansion performance of the prepared negative electrode material.

[0079] It is understood that the first activator and the second activator can be either gaseous or solid. In the case of a gaseous activator, the added amount can be expressed as the concentration of the gaseous activator introduced; in the case of a solid activator, the added amount can be expressed as the mass of the solid activator added. If the first activator is a gaseous activator and the second activator is a solid activator, those skilled in the art can determine the concentration of the gaseous activator and the mass of the solid activator added based on their experience with the activation differences between gaseous and solid activators.

[0080] In some embodiments, the second activating agent comprises a basic substance.

[0081] In some embodiments, the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, and rubidium hydroxide.

[0082] In some embodiments, the mass ratio of the carbon-based carbonized material and the second activator is 1:(0.1-10), which can be specifically 1:0.1, 1:0.5, 1:1.5, 1:3, 1:5 and 1:10, etc. Of course, it can also be other values ​​within the above range, which is not limited here. If the amount of the second activator added is too little, the activated material prepared in step S100 cannot be effectively activated for the second time; if the amount of the second activator added is too large, the pore size after the secondary pore expansion is too large, which affects the subsequent deposition of the silicon material, causing the silicon material to easily agglomerate, resulting in a large volume effect of the negative electrode material, and the negative electrode material is prone to cracking or even pulverization during use, which is not conducive to improving the expansion performance of the material. At the same time, the pore size of the porous carbon is large, causing the material to easily collapse and the structural stability is poor. Preferably, the mass ratio of the carbon-based carbonized material and the second activator is 1:(0.1-3).

[0083] In some embodiments, the second activating agent includes at least one of water vapor, oxygen, and air.

[0084] In some embodiments, the concentration of the second activator is 0.1% to 5%, specifically 0.1%, 0.3%, 0.8%, 1%, 2%, 3%, 4% and 5%, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here. Within the above-mentioned limited range, the amount of the second activator added is small. On the one hand, it can expand the activated pores obtained by the first activation treatment without making the pore diameter after expansion too large, which is conducive to the subsequent filling of silicon material; on the other hand, the second activator can activate the unactivated areas in the activated material to obtain activated pores with smaller pore diameters, so that the prepared porous carbonaceous material has a larger number of activated pores, and the activated pores are more evenly distributed. If the concentration of the second activator is less than 0.1%, the activated material prepared in step S100 cannot be effectively activated for the second time; if the concentration of the second activator is less than 5%, the pore size after the secondary pore expansion is too large, affecting the subsequent deposition of the silicon material, causing the silicon material to easily agglomerate, resulting in a large volume effect of the negative electrode material, and the negative electrode material is prone to cracks or even pulverization during use, which is not conducive to improving the expansion performance of the material. At the same time, the pore size of the porous carbon is large, causing the prepared negative electrode material to easily collapse and have poor structural stability.

[0085] In some embodiments, the time of the second activation treatment is 3h to 10h, for example, it can be 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc., and of course it can also be other values ​​within the above range, which is not limited in this application. Within the above-mentioned limited range, it is beneficial for the prepared porous carbonaceous material to have a large number of evenly distributed activation pores, which is beneficial for the subsequent deposition of silicon material inside the porous carbonaceous material. If the time of the second activation treatment is too short, the activated material prepared in step S100 cannot be effectively activated for a second time, so that the subsequent deposition amount of silicon material inside the porous carbonaceous material is small, resulting in performance degradation; if the time of the second activation treatment is too long, the pore size after the secondary pore expansion is too large, which affects the deposition of subsequent silicon material, resulting in a large volume effect of the negative electrode material. The negative electrode material is prone to cracking or even pulverization during use, which is not conducive to improving the expansion performance of the material. At the same time, the pore size inside the porous carbon is large, which causes the prepared negative electrode material to collapse easily and have poor structural stability.

[0086] In some embodiments, the temperature of the second activation treatment is 800°C to 1000°C, specifically 800°C, 830°C, 85°C, 900°C, 950°C, and 1000°C, etc., and of course other values ​​within the above range can also be used, and this application is not limited thereto. In some embodiments, by limiting the temperature of the first activation treatment to be greater than the temperature of the second activation treatment, the activation degrees of the two activation treatment processes can be different and the difference is large, thereby preparing a porous carbonaceous material with good consistency.

[0087] In summary, the present application prepares a porous carbonaceous material having an adapted number of and uniformly distributed activated pores by regulating the amount of activator added, the activation temperature, and the activation time of the two activation treatments.

[0088] Step S300: Mix the porous carbonaceous material and the silicon source and perform heat treatment to obtain the negative electrode material.

[0089] In some embodiments, the silicon source includes at least one of monosilane, hexylsilane, and trisilane.

[0090] In some embodiments, the inlet flow rate of the silicon source is 0.1 L / min to 1000 L / min, specifically 0.1 L / min, 1 L / min, 10 L / min, 100 L / min, 300 L / min, 600 L / min and 1000 L / min, etc. Of course, it can also be other values ​​within the above range, and this application is not limited here.

[0091] In some embodiments, the heat treatment temperature is 300°C to 800°C, specifically 300°C, 400°C, 500°C, 600°C, 700°C and 800°C, etc. Of course, it can also be other values ​​within the above range, which is not limited in this application.

[0092] In some embodiments, the heat treatment time is 2 hours to 25 hours, specifically 2 hours, 5 hours, 10 hours, 15 hours, 20 hours, and 25 hours, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0093] In some embodiments, after the porous carbonaceous material and the silicon source are mixed and subjected to heat treatment, the method further comprises: mixing the heat-treated material and the coating material and subjecting them to heat treatment.

[0094] In some embodiments, the coating material includes one of a carbon source, a metal oxide, and a nitride.

[0095] In some embodiments, the nitride includes at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

[0096] In some embodiments, the metal oxide comprises at least one of iron oxide, zinc oxide, tin oxide, copper oxide, and titanium oxide.

[0097] In some embodiments, the carbon source comprises at least one of a gaseous carbon source and a solid carbon source.

[0098] In some embodiments, the gaseous carbon source includes at least one of acetylene, methane, propylene, benzene, ethanol, methanol, ethylene, propane, and butane.

[0099] In some embodiments, the flow rate of the gaseous carbon source is 0.1 L / min to 1000 L / min, specifically 0.1 L / min, 1 L / min, 10 L / min, 100 L / min, 300 L / min, 600 L / min and 1000 L / min, etc. Of course, it can also be other values ​​within the above range, and this application is not limited here.

[0100] In some embodiments, the solid carbon source includes at least one of sucrose, fructose, glucose, pitch, phenolic resin, polyimide, citric acid, epoxy resin, amino resin, polystyrene, polyacrylic acid, carboxymethyl cellulose, and cellulose acetate butyrate.

[0101] In some embodiments, the mass ratio of the solid carbon source to the material obtained by heat treatment is (1-100):100, specifically 1:100, 10:100, 30:100, 50:100, 80:100 and 100:100, etc. Of course, it can also be other values ​​within the above range, and this application is not limited here.

[0102] In some embodiments, the temperature of the heat treatment is 600°C to 1100°C. Specifically, the temperature of the heat treatment can be, for example, 600°C, 650°C, 700°C, 800°C, 900°C, 1000°C, and 1100°C. Of course, it can also be other values ​​within the above range, and this application is not limited thereto. If the temperature of the heat treatment is lower than 600°C, the carbonization of the coating material is incomplete, and a dense coating layer cannot be obtained. If the temperature of the heat treatment is higher than 1100°C, the silicon material crystallizes, resulting in poor cycle performance and expansion performance of the negative electrode material.

[0103] In some embodiments, the holding time of the heating treatment is 2h to 10h. Specifically, the holding time of the heating treatment can be, for example, 2h, 5h, 7h, 8h and 10h, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0104] In some embodiments, after the heat-treated material and the coating material are mixed and heat-treated, the method further includes the steps of screening and grading the obtained material.

[0105] In a third aspect, the present application provides a lithium-ion battery, which comprises the above-mentioned negative electrode material or the negative electrode material prepared by the above-mentioned preparation method.

[0106] Those skilled in the art will understand that the above-described method for preparing a lithium-ion battery is merely an example, and other methods commonly used in the art may be employed without departing from the disclosure of this application.

[0107] The following further illustrates the embodiments of the present application in multiple embodiments. The embodiments of the present application are not limited to the following specific embodiments. Within the scope of the unchanged main rights, appropriate changes can be made to the implementation.

[0108] Example 1

[0109] (1) 10 g of bamboo charcoal was placed in a carbonization furnace for carbonization treatment at a carbonization temperature of 800 ° C and a carbonization time of 7 h. After carbonization, it was pickled with a hydrochloric acid concentration of 10 mol / L and a pickling time of 5 h to obtain a carbon-based carbonized material.

[0110] (2) The carbon-based carbonized material is dried and then subjected to a steam activation treatment by introducing a mixed gas of water vapor and nitrogen, wherein the water vapor concentration is 9%, the activation time is 18 hours, and the activation temperature is 900° C. to obtain an activated material.

[0111] (3) The activated material was subjected to a secondary water vapor activation treatment by introducing a mixed gas of water vapor and nitrogen with a water vapor concentration of 2%, an activation time of 3 h, and an activation temperature of 900° C. to obtain a porous carbonaceous material.

[0112] (4) The porous carbon material was placed in a CVD device, and then monosilane was introduced into the CVD device, with the concentration of monosilane controlled at 25%, and the temperature was raised to 460° C. and the reaction was carried out for 8 hours.

[0113] (5) The material obtained in step (4) is placed in a reaction furnace, methane gas is introduced, and the concentration of methane is 12%. Heat treatment is performed at 720°C and kept warm for 2 hours. The obtained sample is screened and graded to obtain a negative electrode material.

[0114] The negative electrode material obtained in this embodiment includes a core and a carbon coating layer provided on the surface of the core, the core includes a porous carbonaceous material and silicon particles distributed inside and on the surface of the porous carbonaceous material, the uniformity N of the negative electrode material, the median particle size, specific surface area and conductivity of the negative electrode material prepared in this embodiment, as well as the pore volume of the porous carbonaceous material, the volume proportion of micropores in the porous carbonaceous material, the average pore size and the mass proportion of silicon particles (silicon element) in the negative electrode material are shown in Table 1.

[0115] The scanning electron microscope (SEM) BSE image of the negative electrode material prepared in this embodiment can be seen from Figure 2: typical particles of the first brightness and particles of the second brightness can be distinguished in the negative electrode material prepared in this embodiment, and in the batch of negative electrode materials, the number of negative electrode material particles with the second brightness accounts for a relatively large proportion, indicating that the present application can obtain a negative electrode material in which silicon material is deposited in an appropriate amount and evenly distributed inside a porous carbonaceous material.

[0116] The XRD pattern of the negative electrode material prepared in this embodiment is shown in FIG3 . As can be seen from FIG3 , there is no characteristic peak at the position of 25° to 30° in the negative electrode material, which is a diffraction packet, indicating that amorphous silicon exists in the negative electrode material, that is, the silicon deposited in the porous carbonaceous material is amorphous silicon, which is beneficial to reducing the volume expansion of the negative electrode material.

[0117] The first charge and discharge curve of the negative electrode material prepared in this embodiment is shown in FIG4 . As can be seen from FIG4 , the first charge and discharge capacity of the negative electrode material is relatively high, and the first efficiency is also relatively high.

[0118] The cycle performance curve of the negative electrode material prepared in this embodiment is shown in FIG5 . As can be seen from FIG5 , the negative electrode material has excellent cycle performance, and the capacity retention rate after 50 cycles is 92.2%.

[0119] Example 2

[0120] (1) 10 g of coconut shell was placed in a carbonization furnace for carbonization treatment at a carbonization temperature of 800 ° C and a carbonization time of 10 h. After carbonization, it was pickled with a hydrochloric acid concentration of 10 mol / L and a pickling time of 5 h to obtain a carbon-based carbonized material.

[0121] (2) drying the carbon-based carbonized material and then performing a steam activation treatment, introducing a mixed gas of water vapor and nitrogen, wherein the water vapor concentration is 3.5%, the activation time is 12 hours, and the activation temperature is 950° C. to obtain an activated material;

[0122] (3) The activated material is subjected to a secondary water vapor activation treatment by introducing a mixed gas of water vapor and nitrogen with a water vapor concentration of 0.5%, an activation time of 6 hours, and an activation temperature of 950° C. to obtain a porous carbonaceous material.

[0123] (4) The porous carbon material was placed in a CVD device, and then monosilane was introduced into the CVD device, with the concentration of monosilane controlled at 25%, and the temperature was raised to 460° C. and the reaction was carried out for 8 hours.

[0124] (5) The material obtained in step (4) is placed in a reaction furnace, methane gas is introduced, and the concentration of methane is 12%. Heat treatment is performed at 720°C and kept warm for 2 hours. The obtained sample is screened and graded to obtain a negative electrode material.

[0125] The negative electrode material obtained in this embodiment includes a core and a carbon coating layer provided on the surface of the core, the core includes a porous carbonaceous material and silicon particles distributed inside and on the surface of the porous carbonaceous material, the uniformity N of the negative electrode material, the median particle size, specific surface area and conductivity of the negative electrode material prepared in this embodiment, as well as the pore volume of the porous carbonaceous material, the volume proportion of micropores in the porous carbonaceous material, the average pore size and the mass proportion of silicon particles (silicon element) in the negative electrode material are shown in Table 1.

[0126] Example 3

[0127] (1) 10 g of fruit shell was placed in a carbonization furnace for carbonization treatment at a carbonization temperature of 950 ° C and a carbonization time of 5 h. After carbonization, it was pickled with a hydrochloric acid concentration of 10 mol / L and a pickling time of 5 h to obtain a carbon-based carbonized material.

[0128] (2) drying the carbon-based carbonized material and then performing a steam activation treatment, introducing a mixed gas of water vapor and nitrogen, wherein the water vapor concentration is 5.7%, the activation time is 14 hours, and the activation temperature is 950° C., to obtain an activated material;

[0129] (3) The activated material is subjected to alkali activation treatment, the alkali is sodium hydroxide, the addition amount of sodium hydroxide is 3% of the weight of the shell, the activation time is 9 hours, the activation temperature is 950°C, and a porous carbonaceous material is obtained.

[0130] (4) The porous carbon material was placed in a CVD device, and then monosilane was introduced into the CVD device, with the concentration of monosilane controlled at 25%, and the temperature was raised to 460° C. and the reaction was carried out for 8 hours.

[0131] (5) The material obtained in step (4) is placed in a reaction furnace, methane gas is introduced, and the concentration of methane is 12%. Heat treatment is performed at 720°C and kept warm for 2 hours. The obtained sample is screened and graded to obtain a negative electrode material.

[0132] The negative electrode material obtained in this embodiment includes a core and a carbon coating layer provided on the surface of the core, the core includes a porous carbonaceous material and silicon particles distributed inside and on the surface of the porous carbonaceous material, the uniformity N of the negative electrode material, the median particle size, specific surface area and conductivity of the negative electrode material prepared in this embodiment, as well as the pore volume of the porous carbonaceous material, the volume proportion of micropores in the porous carbonaceous material, the average pore size and the mass proportion of silicon particles (silicon element) in the negative electrode material are shown in Table 1.

[0133] Example 4

[0134] (1) 10 g of fruit shell was placed in a carbonization furnace for carbonization treatment at a carbonization temperature of 950 ° C and a carbonization time of 5 h. After carbonization, it was pickled with a hydrochloric acid concentration of 10 mol / L and a pickling time of 5 h to obtain a carbon-based carbonized material.

[0135] (2) drying the carbon-based carbonized material and performing a steam activation treatment, introducing a mixed gas of water vapor and nitrogen, wherein the water vapor concentration is 14.5%, the activation time is 8 hours, and the activation temperature is 990° C. to obtain an activated material;

[0136] (3) The activated material is subjected to a secondary water vapor activation treatment by introducing a mixed gas of water vapor and nitrogen with a water vapor concentration of 1.5%, an activation time of 5 h, and an activation temperature of 850° C. to obtain a porous carbonaceous material.

[0137] (4) The porous carbon material was placed in a CVD device, and then monosilane was introduced into the CVD device, with the concentration of monosilane controlled at 25%, and the temperature was raised to 460° C. and the reaction was carried out for 8 hours.

[0138] (5) The material obtained in step (4) is placed in a reaction furnace, methane gas is introduced, and the concentration of methane is 12%. Heat treatment is performed at 720°C and kept warm for 2 hours. The obtained sample is screened and graded to obtain a negative electrode material.

[0139] The negative electrode material obtained in this embodiment includes a core and a carbon coating layer provided on the surface of the core, the core includes a porous carbonaceous material and silicon particles distributed inside and on the surface of the porous carbonaceous material, the uniformity N of the negative electrode material, the median particle size, specific surface area and conductivity of the negative electrode material prepared in this embodiment, as well as the pore volume of the porous carbonaceous material, the volume proportion of micropores in the porous carbonaceous material, the average pore size and the mass proportion of silicon particles (silicon element) in the negative electrode material are shown in Table 1.

[0140] Example 5

[0141] (1) 10 g of fruit shell was placed in a carbonization furnace for carbonization treatment at a carbonization temperature of 950 ° C and a carbonization time of 5 h. After carbonization, it was pickled with a hydrochloric acid concentration of 10 mol / L and a pickling time of 5 h to obtain a carbon-based carbonized material.

[0142] (2) drying the carbon-based carbonized material and then performing a steam activation treatment, introducing a mixed gas of water vapor and nitrogen, wherein the water vapor concentration is 20%, the activation time is 5 hours, and the activation temperature is 1050° C., to obtain an activated material;

[0143] (3) The activated material is subjected to a secondary water vapor activation treatment by introducing a mixed gas of water vapor and nitrogen with a water vapor concentration of 5%, an activation time of 3 hours, and an activation temperature of 900° C. to obtain a porous carbonaceous material.

[0144] (4) The porous carbon material was placed in a CVD device, and then monosilane was introduced into the CVD device, with the concentration of monosilane controlled at 25%, and the temperature was raised to 460° C. and the reaction was carried out for 8 hours.

[0145] (5) The material obtained in step (4) is placed in a reaction furnace, methane gas is introduced, and the concentration of methane is 12%. Heat treatment is performed at 720°C and kept warm for 2 hours. The obtained sample is screened and graded to obtain a negative electrode material.

[0146] The negative electrode material obtained in this embodiment includes a core and a carbon coating layer provided on the surface of the core, the core includes a porous carbonaceous material and silicon particles distributed inside and on the surface of the porous carbonaceous material, the uniformity N of the negative electrode material, the median particle size, specific surface area and conductivity of the negative electrode material prepared in this embodiment, as well as the pore volume of the porous carbonaceous material, the volume proportion of micropores in the porous carbonaceous material, the average pore size and the mass proportion of silicon particles (silicon element) in the negative electrode material are shown in Table 1.

[0147] Example 6

[0148] (1) 10 g of fruit shell was placed in a carbonization furnace for carbonization treatment at a carbonization temperature of 950 ° C and a carbonization time of 5 h. After carbonization, it was pickled with a hydrochloric acid concentration of 10 mol / L and a pickling time of 5 h to obtain a carbon-based carbonized material.

[0149] (2) subjecting the carbon-based carbonized material to alkali activation treatment, wherein the alkali is sodium hydroxide, the amount of sodium hydroxide added is 15% of the weight of the shell, the activation time is 10 hours, and the activation temperature is 950° C., to obtain an activated material;

[0150] (3) The activated material is subjected to a secondary alkali activation treatment, wherein the alkali is sodium hydroxide, the amount of sodium hydroxide added is 3% of the weight of the shell, the activation time is 5 hours, and the activation temperature is 850° C. to obtain a porous carbonaceous material.

[0151] (4) The porous carbon material was placed in a CVD device, and then monosilane was introduced into the CVD device, with the concentration of monosilane controlled at 25%, and the temperature was raised to 460° C. and the reaction was carried out for 8 hours.

[0152] (5) The material obtained in step (4) is placed in a reaction furnace, methane gas is introduced, and the concentration of methane is 12%. Heat treatment is performed at 720°C and kept warm for 2 hours. The obtained sample is screened and graded to obtain a negative electrode material.

[0153] The negative electrode material obtained in this embodiment includes a core and a carbon coating layer provided on the surface of the core, the core includes a porous carbonaceous material and silicon particles distributed inside and on the surface of the porous carbonaceous material, the uniformity N of the negative electrode material, the median particle size, specific surface area and conductivity of the negative electrode material prepared in this embodiment, as well as the pore volume of the porous carbonaceous material, the volume proportion of micropores in the porous carbonaceous material, the average pore size and the mass proportion of silicon particles (silicon element) in the negative electrode material are shown in Table 1.

[0154] Example 7

[0155] (1) 10 g of fruit shell was placed in a carbonization furnace for carbonization treatment at a carbonization temperature of 950 ° C and a carbonization time of 5 h. After carbonization, it was pickled with a hydrochloric acid concentration of 10 mol / L and a pickling time of 5 h to obtain a carbon-based carbonized material.

[0156] (2) subjecting the carbon-based carbonized material to alkali activation treatment, wherein the alkali is sodium hydroxide, the amount of sodium hydroxide added is 10% of the weight of the fruit shell, the activation time is 12 hours, and the activation temperature is 1000° C. to obtain an activated material;

[0157] (3) The activated material is subjected to a secondary alkali activation treatment, wherein the alkali is sodium hydroxide, the amount of sodium hydroxide added is 1% of the mass of the shell, the activation time is 3 hours, and the activation temperature is 850° C. to obtain a porous carbonaceous material.

[0158] (4) The porous carbon material was placed in a CVD device, and then monosilane was introduced into the CVD device, with the concentration of monosilane controlled at 25%, and the temperature was raised to 460° C. and the reaction was carried out for 8 hours.

[0159] (5) The material obtained in step (4) is placed in a reaction furnace, methane gas is introduced, and the concentration of methane is 12%. Heat treatment is performed at 720°C and kept warm for 2 hours. The obtained sample is screened and graded to obtain a negative electrode material.

[0160] The negative electrode material obtained in this embodiment includes a core and a carbon coating layer provided on the surface of the core, the core includes a porous carbonaceous material and silicon particles distributed inside and on the surface of the porous carbonaceous material, the uniformity N of the negative electrode material, the median particle size, specific surface area and conductivity of the negative electrode material prepared in this embodiment, as well as the pore volume of the porous carbonaceous material, the volume proportion of micropores in the porous carbonaceous material, the average pore size and the mass proportion of silicon particles (silicon element) in the negative electrode material are shown in Table 1.

[0161] Comparative Example 1

[0162] (1) The bamboo charcoal is placed in a carbonization furnace for carbonization treatment at a carbonization temperature of 800°C for 7 hours. After carbonization, it is pickled at a hydrochloric acid concentration of 10 mol / L for 5 hours to obtain a carbon-based carbonized material.

[0163] (2) The carbon-based carbonized material is placed in a CVD device, and then monosilane is introduced into the CVD device, the concentration of monosilane is controlled to be 25%, the temperature is raised to 460° C., and the reaction is carried out for 8 hours.

[0164] (3) The material obtained in step (2) is placed in a reaction furnace, methane gas is introduced, and the methane concentration is 12%. Heat treatment is performed at 720°C and kept warm for 2 hours. The obtained sample is screened and graded to obtain a negative electrode material.

[0165] Comparative Example 2

[0166] The difference from Example 1 is that step (3) is not performed, and the activated material obtained in step (2) is directly subjected to step (4).

[0167] Comparative Example 3

[0168] Different from Example 1, step (2) is not performed, and the carbon-based carbonized material obtained in step (1) is directly subjected to step (3).

[0169] Comparative Example 4

[0170] (1) 10 g of fruit shell was placed in a carbonization furnace for carbonization treatment at a carbonization temperature of 950 ° C and a carbonization time of 5 h. After carbonization, it was pickled with a hydrochloric acid concentration of 10 mol / L and a pickling time of 5 h to obtain a carbon-based carbonized material.

[0171] (2) drying the carbon-based carbonized material and then performing a steam activation treatment, introducing a mixed gas of water vapor and nitrogen, wherein the water vapor concentration is 9%, the activation time is 18 hours, and the activation temperature is 900° C., to obtain an activated material;

[0172] (3) The activated material was subjected to a secondary water vapor activation treatment by introducing a mixed gas of water vapor and nitrogen with a water vapor concentration of 9%, an activation time of 16 h, and an activation temperature of 900° C. to obtain a porous carbonaceous material.

[0173] (4) The porous carbon material was placed in a CVD device, and then monosilane was introduced into the CVD device, with the concentration of monosilane controlled at 25%, and the temperature was raised to 460° C. and the reaction was carried out for 8 hours.

[0174] (5) The material obtained in step (4) is placed in a reaction furnace, methane gas is introduced, and the concentration of methane is 12%. Heat treatment is performed at 720°C and kept warm for 2 hours. The obtained sample is screened and graded to obtain a negative electrode material.

[0175] Comparative Example 5

[0176] (1) 10 g of fruit shell was placed in a carbonization furnace for carbonization treatment at a carbonization temperature of 950 ° C and a carbonization time of 5 h. After carbonization, it was pickled with a hydrochloric acid concentration of 10 mol / L and a pickling time of 5 h to obtain a carbon-based carbonized material.

[0177] (2) drying the carbon-based carbonized material and performing a steam activation treatment, introducing a mixed gas of water vapor and nitrogen, wherein the water vapor concentration is 9%, the activation time is 2 hours, and the activation temperature is 900° C., to obtain an activated material;

[0178] (3) The activated material is subjected to a secondary water vapor activation treatment by introducing a mixed gas of water vapor and nitrogen with a water vapor concentration of 2%, an activation time of 12 h, and an activation temperature of 900° C. to obtain a porous carbonaceous material.

[0179] (4) The porous carbon material was placed in a CVD device, and then monosilane was introduced into the CVD device, with the concentration of monosilane controlled at 25%, and the temperature was raised to 460° C. and the reaction was carried out for 8 hours.

[0180] (5) The material obtained in step (4) is placed in a reaction furnace, methane gas is introduced, and the concentration of methane is 12%. Heat treatment is performed at 720°C and kept warm for 2 hours. The obtained sample is screened and graded to obtain a negative electrode material.

[0181] Performance Testing

[0182] 1. Use BET pore distribution to test the pore volume of porous carbon materials. Before testing the porosity, the silicon material in the negative electrode material needs to be etched away using HF.

[0183] 2. The number or volume of micropores in porous carbonaceous materials is determined by nitrogen desorption.

[0184] The pore size distribution data of the material was obtained by using the Lihua Lianke iPore620 pore size tester and the BET pore size distribution test method, utilizing the isothermal adsorption characteristic curve of nitrogen and DFT simulation analysis, thereby obtaining the number of micropores, average pore size, pore volume, and BET specific surface area of ​​the material.

[0185] 3. Measure the mass of the negative electrode material before etching the silicon material, M1. Measure the mass of the negative electrode material after etching the silicon material with HF, M2. (M2 - M1) / M2 is the mass percentage of the silicon material in the negative electrode material. Alternatively, use a box-type atmosphere furnace (model: SA2-9-17TP) to burn the sample in an oxygen atmosphere, causing the silicon and silicon oxide in the sample to react to form silicon dioxide. The carbon is then burned and released as carbon dioxide. Calculate the mass of the silicon in the negative electrode material by weighing.

[0186] 4. Use a laser particle size analyzer to test the median particle size of the negative electrode material.

[0187] Particle size is measured using a Mastersizer 3000 laser diffraction technique. When a laser beam passes through a dispersed particle sample, the particle size measurement is accomplished by measuring the intensity of the scattered light. This data is then used to analyze and calculate the particle size distribution that forms the scattering spectrum. D50: The particle size corresponding to the 50% cumulative particle size distribution percentage of a sample's volume distribution. Its physical meaning is that 50% of the particles have a larger diameter than this, and 50% of the particles have a smaller diameter than this. D50 is also called the median particle size. The D90, D50, and D10 particle sizes are the equivalent diameters of the largest particles in the volume distribution curve at 90%, 50%, and 10% cumulative distributions, respectively.

[0188] 5. After etching the silicon material in the porous carbon material with HF, the average pore size of the pores was measured using a Micromeritics ASAP 2460 fully automatic surface area and porosity analyzer from the United States. The gas used in the test was CO2 or N2.

[0189] Etching method: Add a 1M nitric acid solution to the negative electrode material and soak it for 4 hours. Then, add a 20% by mass HF acid solution dropwise to the negative electrode material, which will produce yellow smoke. Repeat the addition until no yellow smoke is produced in the solution. Finally, use a 1M nitric acid solution to digest the residue, then wash and dry it to obtain the negative electrode material after the silicon material has been removed. The etching method can also be the following steps: While stirring, add 150mL of a 20% by mass HF acid solution dropwise to 10g of the negative electrode material. This will produce SiF4 and H2 gases and release heat. After no gas is generated, the supernatant acid solution is removed by centrifugation. Then, 150mL of a 20% by mass HF acid solution is added to the negative electrode material again. After stirring for 12 hours, the supernatant acid solution is removed by centrifugation again. Then, the negative electrode material is washed with pure water until neutral and dried to obtain the negative electrode material after the silicon material has been removed.

[0190] 6. Testing method for average particle size of silicon material: Perform mathematical statistics on the diameter of silicon material in transmission electron microscope images.

[0191] 7. The model of the scanning electron microscope is Hitachi S4800. The test conditions are: voltage 3 kV, current size 10 μA.

[0192] 8. Coating thickness: The material is sectioned using a FIB-SEM device, and the average coating thickness is measured in the SEM.

[0193] 9. Powder Conductivity: The volume resistivity of the negative electrode material powder was measured using the four-probe method using Mitsubishi Chemical's MCP-PD51 powder resistance test system. The instrument tested the resistance of the powder at five pressure points: 4, 8, 12, 16, and 20 kN. The computer then automatically calculated the conductivity and resistivity of the negative electrode material powder.

[0194] 10. Specific surface area: The specific surface area was measured using a Micromeritics TriStar 3000 specific surface area and pore size analyzer (USA).

[0195] 11. The electrochemical performance of the negative electrode material was tested using the following method:

[0196] The negative electrode material, conductive agent, and binder were dissolved in a solvent at a ratio of 94:1:5 by mass, with a solids content controlled at 50%. The mixture was then coated onto a copper foil current collector and vacuum-dried to produce the negative electrode. 18650 cylindrical cells were then assembled using conventional production processes using a ternary positive electrode prepared using a 1 mol / L LiPF6 / EC+DMC+EMC (v / v = 1:1:1) electrolyte, a Celgard 2400 separator, and a casing. Cylindrical cells were tested on a LAND battery test system from Wuhan Jinnuo Electronics Co., Ltd. at room temperature using a 0.2C constant current and a voltage limit of 2.75 to 4.2 V. The test results are shown in Tables 1 and 2.

[0197] Table 1. Test results of uniformity of negative electrode materials of various embodiments and comparative examples

[0198] Table 2. Performance test results of negative electrode materials of various embodiments and comparative examples

[0199] As shown in Tables 1 and 2, the negative electrode materials prepared in Examples 1 to 7 of the present application include a porous carbonaceous material and a silicon material, and the negative electrode materials have a uniformity N, N ≥ 80%, indicating that the porous carbonaceous material of the present application has uniformly distributed activated pores, and the number of activated pores is appropriate, so that the silicon material can be mainly distributed in the pores of the porous carbonaceous material. In addition, the present application is tested on the negative electrode material obtained in any 100 μm * 100 μm area, indicating that the number and distribution of activated pores of the porous carbonaceous material of each negative electrode material particle of the present application are highly similar, that is, the negative electrode material of the present application has a porous carbonaceous material with good consistency. The porous carbonaceous material with good consistency can improve the dispersibility of the silicon material in the negative electrode material, inhibit the volume effect caused by the agglomeration of the silicon material during the lithium insertion / delithiation process, and reduce the pulverization of the negative electrode material particles. At the same time, during the lithium insertion / delithiation process, the negative electrode material allows the SEI film to be formed in a limited space, which is conducive to the formation of a stable SEI film on the surface of the negative electrode material, improving the structural stability of the negative electrode material, thereby improving the expansion performance, cycle performance and capacity of the negative electrode material.

[0200] The carbon-based carbonized material in Comparative Example 1 was not activated and the silicon source was directly deposited, resulting in very little deposition of silicon material in the negative electrode material and too small a uniformity N of the negative electrode material. As a result, the battery prepared with the negative electrode material had problems such as low capacity, large expansion and poor cycle performance.

[0201] In Comparative Example 2, only the activation treatment of step (2) is performed on the carbon-based carbonized material, and the activation treatment of step (3) is not performed, so that the distribution uniformity of the activated pores in the porous carbonaceous material is not as good as that in Example 1. The silicon source is deposited on the porous carbonaceous material, so that the distribution uniformity of the silicon material in the porous carbonaceous material is poor, and the uniformity N of the negative electrode material is less than 80%, which does not meet the range specified in this application, resulting in poor expansion and cycle performance of the negative electrode material.

[0202] In Comparative Example 3, only the activation treatment of step (3) is performed on the carbon-based carbonized material, resulting in a smaller number of activated pores in the porous carbonaceous material, and the distribution uniformity is not as good as in Example 1 and Comparative Example 2. The silicon source is deposited on the porous carbonaceous material, resulting in poor distribution uniformity of the silicon material in the porous carbonaceous material, and a small amount of silicon material deposited in the porous carbonaceous material. The uniformity N of the negative electrode material is less than 80%, which does not meet the range specified in this application, resulting in poor expansion performance and cycle performance of the negative electrode material.

[0203] In Comparative Example 4, two activation treatments were performed, and the degree of the two activation treatments was not much different, resulting in the prepared porous carbon material having a larger number of pores and a larger pore diameter, which easily caused the silicon material to agglomerate inside the porous carbon material. The uniformity N of the negative electrode material was less than 80%, which did not meet the specified range of this application, resulting in poor expansion performance of the negative electrode material.

[0204] In Comparative Example 5, two activation treatments were performed, and the time for the first activation treatment was much shorter than that for the second activation treatment. The pore volume of the prepared porous carbonaceous material was small, resulting in less deposition of the silicon source inside the negative electrode material. The uniformity N of the negative electrode material was less than 80%, which did not meet the specified range of this application, resulting in poor capacity performance and cycle performance of the negative electrode material.

[0205] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material comprises a porous carbonaceous material, silicon material is distributed inside the porous carbonaceous material, and the negative electrode material has a uniformity N, N≥80%; In the backscattered electron image obtained by scanning the negative electrode material in the BSE automatic brightness and contrast mode using a SEM scanning electron microscope, in any 100μm*100μm area, the number of particles of the negative electrode material with a first brightness is recorded as C1, and the particles of the negative electrode material with the first brightness represent the negative electrode material with a grayscale value greater than or equal to 5500 in the backscattered electron image. The number of particles of the negative electrode material with a second brightness is recorded as C2, and the particles of the negative electrode material with the second brightness represent the negative electrode material with a grayscale value less than 5500 in the backscattered electron image. The negative electrode material has a uniformity N'=C2 / (C2+C1)*100% in the above-mentioned area, and the uniformity N of the negative electrode material is the arithmetic mean of the uniformities N' of at least 10 of the above-mentioned areas.

2. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following features (1) to (2): (1) The porous carbonaceous material includes micropores, and the number of the micropores accounts for greater than or equal to 80% based on the total number of pores in the porous carbonaceous material being 100%; (2) The porous carbonaceous material includes micropores, and the volume proportion of the micropores is greater than or equal to 80% based on the total pore volume in the porous carbonaceous material.

3. The negative electrode material according to claim 1, characterized in that The average pore size of the pores in the porous carbonaceous material is less than or equal to 5 nm.

4. The negative electrode material according to claim 1, characterized in that The silicon material accounts for 30% to 80% by mass of the negative electrode material.

5. The negative electrode material according to claim 1, characterized in that The silicon material is also distributed on at least a portion of the surface of the porous carbonaceous material.

6. The negative electrode material according to claim 1, characterized in that The porous carbonaceous material includes at least one of hard carbon, soft carbon, graphite, mesophase carbon microbeads, activated carbon and carbon gel.

7. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following features (1) to (4): (1) The silicon material includes silicon particles, and the morphology of the silicon particles includes at least one of a dot shape, a sphere, an ellipsoid shape, and a flake shape; (2) The silicon material includes at least one of crystalline silicon, silicon-oxygen material, amorphous silicon and silicon alloy; (3) The average particle size of the silicon material is 0.1 nm to 500 nm; (4) The mass content of silicon element in the silicon material is ≥99%.

8. The negative electrode material according to claim 1, characterized in that The negative electrode material further includes a coating layer distributed on at least a portion of the surface of the porous carbonaceous material.

9. The negative electrode material according to claim 8, characterized in that The negative electrode material includes at least one of the following features (1) to (4): (1) The coating layer includes a carbon layer, and the material of the carbon layer includes at least one of graphene, soft carbon, hard carbon and a conductive polymer; (2) The coating layer includes a metal oxide layer, and the material of the metal oxide layer includes at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide and vanadium oxide; (3) The coating layer includes a nitride layer, and the material of the nitride layer includes at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride and carbon nitride; (4) The thickness of the coating layer is 0.1 nm to 100 nm.

10. The negative electrode material according to claim 1, characterized in that The median particle size of the negative electrode material is less than or equal to 10 μm.

11. The negative electrode material according to claim 1, characterized in that The specific surface area of ​​the negative electrode material is less than 5m 2 / g.

12. The negative electrode material according to claim 1, characterized in that The conductivity of the negative electrode material is greater than or equal to 10 -1 S / m.

13. The negative electrode material according to claim 1, characterized in that The pore volume of the porous carbonaceous material is greater than or equal to 0.4 cm 3 / g.

14. A lithium ion battery, characterized in that: The lithium ion battery comprises the negative electrode material according to any one of claims 1 to 13.

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