Negative electrode material, negative electrode sheet and battery

Abstract

A negative electrode material, a negative electrode sheet and a battery. The negative electrode material comprises a carbon matrix and an active substance, wherein the carbon matrix is provided with pores, and the active substance is at least partially distributed in the pores. The area proportion of the pores having a pore diameter larger than 50 nm in any section of the negative electrode material is α, which satisfies: α≤10%, wherein α is obtained by means of the following test method: in an image as shown by the SEM section treatment of a single negative electrode material particle, any a×b region is selected, where a=1-10 μm and b=1-10 μm, the sum of the sectional areas of pores having a pore diameter larger than 50 nm in the region of the section of the single negative electrode material particle is denoted as S0, the sectional area of the single negative electrode material particle in the region is denoted as S, the area proportion of the pores having a pore diameter larger than 50 nm in the section of the single negative electrode material particle is defined as α', where α'=S0 / S, and α is the arithmetic mean value of α' values of at least 10 negative electrode material particles.

Description

Negative electrode material, negative electrode sheet and battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent applications filed with the National Intellectual Property Administration of China on January 8, 2024, with application number "202410020730.1" and application name "Negative electrode material and preparation method thereof, negative electrode sheet and lithium-ion battery" and the Chinese patent application filed with the National Intellectual Property Administration of China on August 30, 2024, with application number "202411218988.9" and application name "Negative electrode material, negative electrode sheet and battery". The entire contents are incorporated by reference in 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, negative electrode sheets, and 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-based active materials during electrochemical cycling also cause the SEI film formed on their 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. For the carbon coating process, the silicon active material is usually deposited in porous carbon to achieve carbon coating. At present, the preparation of porous carbon by biomass method is an important direction, but the porous carbon prepared by biomass usually has large pores with relatively large diameters. The large number of macropores affects the compaction performance of the porous carbon, making the prepared negative electrode material unable to meet the requirements of high compaction. Moreover, the macropores in the porous carbon are difficult to completely remove because they are generated during the natural growth process, resulting in the deterioration of the initial efficiency, expansion performance and processing performance of the negative electrode material.

[0006] Therefore, developing a negative electrode material with high initial efficiency, high cycle and low expansion performance remains a technical challenge in the field. Summary of the Invention

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

[0008] In a first aspect, an embodiment of the present application provides a negative electrode material, comprising a carbon matrix and an active material, wherein the carbon matrix has pores, the active material is at least partially distributed within the pores, and the area ratio of pores with a pore diameter greater than 50 nm in any cross section of the negative electrode material is α, satisfying: α≤10%;

[0009] Wherein, the α is obtained by the following test method: in the figure shown by the SEM cross-section of a single negative electrode material particle, any a×b area is selected, where a=1μm~10μm, b=1μm~10μm, and the sum of the cross-sectional areas of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle in the region is recorded as S0, and the cross-sectional area of ​​a single negative electrode material particle in the region is recorded as S. The area ratio of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle is defined as α', α'=S0 / S, and α is the arithmetic mean of the α' values ​​of at least 10 negative electrode material particles.

[0010] In a second aspect, an embodiment of the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material distributed on one side of the negative electrode current collector, and the negative electrode active material includes the negative electrode material described in the first aspect.

[0011] In a third aspect, an embodiment of the present application provides a battery, comprising the negative electrode sheet described in the second aspect.

[0012] The technical solution of this application has at least the following beneficial effects:

[0013] The area ratio of pores with a pore diameter greater than 50 nm in any cross section of the negative electrode material of the present application is α, and α≤10%. It can be understood that pores with a pore diameter greater than 50 nm are macropores, that is, α represents the area ratio of macropores in the cross section of the negative electrode material. The area ratio of macropores in the cross section of the negative electrode material of the present application is relatively small. On the one hand, the macropores with a small area ratio can effectively reduce the specific surface area of ​​the negative electrode material. During the first charge and discharge process, it can reduce the occurrence of side reactions between the negative electrode material and the electrolyte, reduce gas production, and improve the first efficiency, expansion performance and cycle performance of the negative electrode material. On the other hand, the macropores with a small area ratio can improve the tap density and compaction density of the negative electrode material, reduce the problems of breakage and cracking of the negative electrode material during the roller pressing process, and improve the processing performance of the negative electrode material. Moreover, the small area ratio of macropores in the cross section of the negative electrode material indicates that the porosity of the negative electrode material is low. The carbon content in the negative electrode material with low porosity is high, which makes the negative electrode material have good electronic conductivity, provides a developed conductive network for the negative electrode material, and improves the conductivity of the negative electrode material. In the cross section of the negative electrode material of the present application, by controlling the area ratio of the macropores in the cross section of the negative electrode material, the conductivity, capacity, initial efficiency, cycle performance and processing performance of the negative electrode material can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present application is further described below with reference to the accompanying drawings and examples.

[0015] FIG1 is a flow chart of the preparation of the negative electrode material of the present application;

[0016] FIG2 is a SEM image of the negative electrode material prepared in Example 1 of the present application at a magnification of 3000;

[0017] FIG3 is a SEM image of a cross section of the negative electrode material prepared in Example 1 of the present application at a magnification of 10,000;

[0018] FIG4 is the first charge and discharge curve of the negative electrode material prepared in Example 1 of the present application;

[0019] FIG5 is a cycle performance curve of the negative electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] The negative electrode material provided in the embodiment of the present application includes a carbon matrix and an active material, the carbon matrix has pores, the active material is at least partially distributed in the pores, the area ratio of pores with a pore diameter greater than 50 nm in any cross section of the negative electrode material is α, and satisfies: α≤10%;

[0025] Wherein, α is obtained by the following test method: in the cross-sectional view shown by SEM section processing of a single negative electrode material particle, any a×b area is selected, where a=1μm~10μm, b=1μm~10μm, the sum of the cross-sectional areas of pores with a pore diameter greater than 50nm in the region of the cross-sectional area of ​​a single negative electrode material particle is recorded as S0, the cross-sectional area of ​​a single negative electrode material particle in the region is recorded as S, and the area ratio of pores with a pore diameter greater than 50nm in the cross-sectional area of ​​a single negative electrode material particle is defined as α', α'=S0 / S, and α is the arithmetic mean of the α' values ​​of at least 10 negative electrode material particles.

[0026] In the above scheme, the area ratio of pores with a pore diameter greater than 50 nm in any cross section of the negative electrode material of the present application is α, and α≤10%. It can be understood that pores with a pore diameter greater than 50 nm are macropores, that is, α represents the area ratio of macropores in the cross section of the negative electrode material. The area ratio of macropores in the cross section of the negative electrode material of the present application is relatively small. On the one hand, the macropores with a relatively small area ratio can effectively reduce the specific surface area of ​​the negative electrode material. During the first charge and discharge process, it can reduce the occurrence of side reactions between the negative electrode material and the electrolyte, reduce gas production, and improve the initial efficiency, expansion performance and cycle performance of the negative electrode material. On the other hand, the macropores with a relatively small area ratio can improve the tap density and compaction density of the negative electrode material, reduce the problems of breakage and cracking of the negative electrode material during the roller pressing process, and improve the processing performance of the negative electrode material. Moreover, the relatively small area ratio of macropores in the cross section of the negative electrode material indicates that the porosity of the negative electrode material is low. The carbon content in the negative electrode material with low porosity is high, which makes the negative electrode material have good electronic conductivity, provides a developed conductive network for the negative electrode material, and improves the conductivity of the negative electrode material. The negative electrode material of the present application can effectively improve the conductivity, capacity, initial efficiency, cycle performance and processing performance of the negative electrode material by controlling the area ratio of the macropores in the cross section of the negative electrode material.

[0027] In the present application, α can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., and of course it can also be other values ​​within the above range, which is not limited in the present application. Within the above-defined range, it indicates that the number of macropores in the cross section of the negative electrode material of the present application is small or the pore size of the macropores is small, which is beneficial to improving the compaction density of the negative electrode material, reducing the specific surface area, and improving the structural stability of the negative electrode material, so that the negative electrode material is not easy to break during processing, thereby improving the processing performance and cycle performance of the negative electrode material. If α is greater than 10%, the pore size of the macropores in the cross section of the negative electrode material is too large or the number of macropores is too large. During the first charge and discharge process, the electrolyte is easy to penetrate into the interior of the negative electrode material particles, resulting in an increase in side reactions between the negative electrode material and the electrolyte. Moreover, the macropores are the location where stress is concentrated inside the negative electrode material. If the pore size of the macropores is too large or the number of macropores is too large, the negative electrode material particles are prone to problems such as rupture and pulverization during the lithium extraction / insertion process, resulting in rapid decay of the cycle performance of the negative electrode material.

[0028] The negative electrode material particles were subjected to SEM section processing, and the area of ​​a single negative electrode material particle and the area of ​​all pores were counted and calculated using the Aztec Feature software of OXFORD Instruments SEM electron microscope. Specifically:

[0029] (1) Electron microscope and energy spectrum conditions

[0030] Electron microscopy: Select a region of target particles that is as monodisperse as possible and adjust appropriate parameters (acceleration voltage 20 kV or 15 kV, electron beam rotation 0 degrees) to obtain a clear backscattered field of view.

[0031] Energy spectrum: During the test, open the AZtec Feature software and execute the probe cooling process. When the blue indicator light on the energy spectrum probe is on, start the test.

[0032] (2) Testing process

[0033] Provide a reference standard sample matrix of the negative electrode material of this application. First, move the field of view to the reference standard matrix, adjust the brightness and contrast, and obtain the grayscale image of the reference standard matrix to ensure that the grayscale of the negative electrode material particles of this application and the reference standard matrix are separated. Note: After the grayscale of the reference image is adjusted, the brightness and contrast of the electron microscope cannot be adjusted.

[0034] Move the field of view to the monodisperse negative electrode material particles, collect the BSE electron image, and adjust and set the appropriate threshold range so that the field of view has typical characteristic particles, moderate size and grayscale, and the particle marking is optimized in this field of view. (Particles can be selected at the time through threshold filtering, magnification-image resolution filtering, pixel filtering, and secondary image filtering)

[0035] Set the negative electrode material particle detection method, filtering conditions and acquisition time, etc. Select pores with a pore size greater than 50nm as the filtering condition. After the settings are completed, click Detect Negative Electrode Material Particles to obtain the list of negative electrode material particles that meet the conditions on the right side of the software (for example: number of pores, element list and content, etc.).

[0036] After the AZtec Feature has finished running, the user can check all detected features in this interface, and can reposition the specified features and re-collect images and spectra. After highlighting the features of interest (i.e., the pores with a pore size greater than 50nm in this application), select any a×b area, where a=1μm~10μm, b=1μm~10μm, and for example, calculate the cross-sectional area of ​​pores with a pore size greater than 50nm in any 10μm×10μm area. During the calculation process, the pores with a pore size greater than 50nm are regarded as the closest regular morphology based on their morphology. For example, the morphology of pores with a pore size greater than 50nm can be regarded as spheres, rectangles, ellipses, etc. that are close to their shapes. The cross-sectional area of ​​pores with a pore size greater than 50nm is calculated according to the area calculation formula of the above regular morphology, and the cross-sectional areas of all pores with a pore size greater than 50nm in the 10μm×10μm area are added to obtain S0, and S is 10×10=100μm 2 , divide S0 and S to obtain the area ratio α' of pores with a pore diameter greater than 50 nm in the cross section of a single negative electrode material particle, and then calculate the arithmetic average of the α' values ​​of at least 10 negative electrode material particles, which is α.

[0037] In some embodiments, the area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material is less than or equal to 5%, and can be specifically 0.1%, 0.5%, 1%, 2%, 3%, 4% or 5%, etc., and of course it can also be other values ​​within the above range, and this application is not limited here. Within the above-mentioned limited range, it shows that the number of macropores with larger pore diameters in the negative electrode material of this application is small, which is beneficial to improving the compaction density of the negative electrode material, improving the structural stability of the negative electrode material, and thus improving the processing performance and cycle performance of the negative electrode material. It can be understood that the area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material is calculated in a similar manner to the area ratio of pores with a pore diameter greater than 50 nm in the negative electrode material.

[0038] In some embodiments, the oil absorption value dbq2 of the carbon matrix satisfies the following: 120 mL / 100 g ≤ dbq2 ≤ 200 mL / 100 g; the oil absorption value dpq1 of the negative electrode material satisfies the following: 30 mL / 100 g ≤ dpq1 ≤ 80 mL / 100 g, and (dbq2 - dbq1) / dbq1 > 0.5. A negative electrode material having the aforementioned specific carbon matrix oil absorption value, negative electrode material oil absorption value, oil absorption difference, and a relatively small macropore area ratio, has its active material primarily incorporated into the carbon matrix and deposited within the pores. This greater influx of active material into the pores of the carbon matrix results in a higher energy density, reduces direct contact between the active material and the electrolyte, reduces the occurrence of adverse side reactions, and improves the cycling performance of the negative electrode material. Furthermore, the deposition of active material within the carbon matrix prevents agglomeration of the active material, thereby reducing the volume expansion of the negative electrode material. Furthermore, the negative electrode material, after depositing the active material, still has a rich pore structure to accommodate oil absorption, further reducing the volume expansion of the negative electrode material.

[0039] For negative electrode materials, pore volume and specific surface area affect their conductivity and the occurrence of side reactions. The larger the pore volume of the negative electrode material and the more pores in the material, the worse the conductivity of the material. The larger the specific surface area, the greater the surface energy of the material, and the more side reactions it will have. In some embodiments, the specific surface area of ​​the carbon matrix is ​​S1 m 2 / g, the pore volume of the carbon matrix is ​​P1cm 3 / g, the specific surface area of ​​the negative electrode material is S2 m 2 / g, the pore volume of the negative electrode material is P2cm 3 / g; S1, P1, S2, and P2 satisfy the following relationship: C1 = S1 / (P1*100); 10≤C1≤25; C2 = S2 / (P2*100); 1≤C2≤50. In order to provide the negative electrode material with sufficient buffer space to alleviate volume expansion during charge and discharge, and to reduce the occurrence of side reactions between the negative electrode material and the electrolyte during charge and discharge, the specific surface area and pore volume of the negative electrode material are limited as described above. At the same time, the specific surface area and pore volume of the carbon matrix are limited to obtain a carbon matrix skeleton with both high pore volume and high structural strength, which facilitates the subsequent deposition of active materials and ensures that the final negative electrode material has sufficient buffer space.

[0040] In some embodiments, the carbon substrate has a specific surface area of ​​500 m 2 / g to 2500m 2 / g, specifically 500m 2 / g、700m 2 / g、900m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g、2200m 2 / g、2500m 2 / g or any value within the range formed by any two of the above values, which is not limited here. The carbon matrix with a specific surface area within the above range has abundant pores, which can accommodate active substances and reserve space for the volume expansion of the active substances.

[0041] In some embodiments, the specific surface area of ​​the negative electrode material is 0.5 m 2 / g to 10m 2 / g. For example, the specific surface area of ​​the negative electrode material can be 0.5m 2 / g、1m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g or any value within the range formed by any two of the above values. When the specific surface area of ​​the negative electrode material is large, the SEI film will consume excessive lithium salt, and the volume effect will easily cause electrical separation between particles, resulting in a decrease in the reversible capacity and coulombic efficiency of the battery. Under the limited specific surface area range of this embodiment, the capacity of the battery's first discharge ratio and the first coulombic efficiency can be more effectively improved.

[0042] In some embodiments, the specific surface area of ​​the negative electrode material is less than or equal to 5 m 2 / g, specifically 0.1m 2 / g, 0.5m 2 / g、1m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g or 5m 2 / g, etc., and of course other values ​​within the above range can also be used, and this application does not limit this. 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 negative electrode material.

[0043] In some embodiments, the pore volume of the negative electrode material is less than or equal to 0.1 cm 3 / g, specifically 0.01cm 3 / g, 0.03cm 3 / g, 0.05cm 3 / g, 0.07cm 3 / g, 0.09cm 3 / g or 0.1cm 3 / g, 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 the number of macropores in the negative electrode material is small or the pore diameter is small, which is beneficial to improving the compaction density of the negative electrode material and thus improving the structural stability of the negative electrode material, making the negative electrode material less likely to break during processing, thereby improving the processing performance and cycle performance of the negative electrode material.

[0044] In some embodiments, the pore volume of the negative electrode material is 0.001 cm 3 / g to 0.1cm 3 / g. For example, the pore volume of the negative electrode material can be 0.001cm 3 / g, 0.003cm 3 / g, 0.005cm 3 / g, 0.008cm 3 / g, 0.01cm 3 / g, 0.03cm 3 / g, 0.05cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g or any value within the range formed by any two of the above values. After the active material is filled in the pores of the carbon matrix, the remaining pores in the carbon matrix can reserve space for the volume expansion of the active material, alleviate the expansion effect of the negative electrode material, and improve the cycle stability of the negative electrode material. The remaining pores in the carbon matrix can also adsorb or accommodate a small amount of gas produced by the reaction of part of the active material with the electrolyte or pulping, thereby improving the gas production phenomenon of the negative electrode material. Under the pore volume defined in this embodiment, the cycle stability of the negative electrode material can be better improved and the gas production phenomenon of the negative electrode material can be improved.

[0045] In some embodiments, the pore volume of the negative electrode material is smaller than that of the carbon matrix. The total pore volume of the negative electrode material is significantly lower than that of the carbon matrix, and the active material can be relatively evenly filled in the pores within the porous framework of the carbon matrix. As a result, the pore volume of most of the pores of the carbon matrix is ​​reduced after being filled with the active material. As a result, the pores of the carbon matrix are effectively and relatively evenly filled with the active material, thereby increasing the specific capacity of the negative electrode material.

[0046] In some embodiments, the ratio of the volume of nitrogen adsorbed by the carbon matrix at 90% partial pressure to the volume of nitrogen adsorbed at 10% partial pressure is A; the ratio of the volume of nitrogen adsorbed by the negative electrode material at 90% partial pressure to the volume of nitrogen adsorbed at 10% partial pressure is B; wherein, 1≤A≤1.9, 1.3≤B≤2.5, and B / A≥1, the carbon matrix with A value within the above range and the negative electrode material with B value within the above range, the carbon matrix has a higher micropore ratio to facilitate the deposition of active substances, and the negative electrode material after the active substance is deposited has a smaller micropore ratio to obtain a negative electrode material with a higher specific capacity.

[0047] In some embodiments, the pores in the carbon matrix include micropores, the volume fraction of the micropores in the total pore volume is greater than or equal to 70%, and the pore diameter of the micropores is less than or equal to 2 nm. For example, the volume fraction of the micropores can be 70%, 75%, 80%, 85%, 90%, 95%, 99%, or any value within a range formed by any two of the foregoing values.

[0048] In some specific embodiments, a carbon matrix obtained after etching the negative electrode material (after etching away the silicon material in the negative electrode material) is tested to obtain the volume ratio of the micropores of the carbon matrix to the total pore volume. Controlling the micropore ratio of the negative electrode material after etching within the above range can reduce the aggregation of the active material on the surface of the carbon matrix during the deposition of the active material, increase the content of the active material in the carbon matrix and the uniformity of the distribution of the active material, thereby improving the specific capacity and mechanical properties of the negative electrode material. The specific method for etching the negative electrode material can be as follows: adding a 1M nitric acid solution to the negative electrode material and soaking it for 4 hours, then dripping a 20% mass fraction HF acid solution into the negative electrode material drop by drop, which will produce yellow smoke, and repeatedly dripping until no yellow smoke is produced in the solution; finally, using a 1M nitric acid solution to digest the residue, and then washing and drying to obtain the negative electrode material after removing the silicon material, i.e., the carbon matrix. The negative electrode material etching method can also be: under stirring, 150mL of 20% mass fraction HF acid solution is added dropwise into 10g of negative electrode material, which will produce SiF4 and H2 gas and release heat. After no gas is generated, the supernatant acid solution is removed by centrifugation, and 150mL of 20% mass fraction 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, and then the negative electrode material is washed with pure water until it is neutral and dried to obtain the negative electrode material after removing the silicon material, that is, the carbon matrix.

[0049] In some specific embodiments, the pore volume of the carbon matrix obtained after etching the negative electrode material (i.e., after etching away the silicon material in the negative electrode material) is 0.3 cm 3 / g to 2cm 3 / g. For example, the pore volume of the carbon matrix obtained after etching the negative electrode material can be 0.3cm 3 / g, 0.5cm3 / g, 0.8cm 3 / g, 1cm 3 / g, 1.5cm 3 / g, 1.8cm 3 / g, 2cm 3 / g or any value within the range formed by any two of the above values. When the negative electrode material is etched (ie, the carbon matrix), it has abundant pores, which can accommodate the active material and reserve space for the volume expansion of the active material.

[0050] In some specific embodiments, the pore volume of the carbon matrix obtained after etching the negative electrode material is 0.5 cm 3 / g to 1.4cm 3 / g. For example, the pore volume can be 0.5cm 3 / g, 0.8cm 3 / g, 1cm 3 / g, 1.2cm 3 / g, 1.4cm 3 / g or any value within the range formed by any two of the above values.

[0051] In some embodiments, the active material includes a simple substance and / or a compound thereof of at least one element selected from Si, Sn, Ge, Pb, Ag, Mg, Zn, Ga, In, Sb, and Bi.

[0052] In some embodiments, the active material includes at least one of a silicon-based material, a tin-based material, a germanium-based material, and a lead-based material. For example, a silicon-based material used as a component of the negative electrode active material can increase the specific capacity of the negative electrode material, thereby increasing the energy density of the secondary battery.

[0053] In some embodiments, the morphology of the active material includes at least one of a dot shape, a sphere shape, an ellipsoid shape, and a flake shape.

[0054] In some embodiments, the purity of the active material is greater than 99%. Taking silicon-based materials as an active material as an example, high-purity silicon-based materials are more conducive to Li-Si alloying with lithium, thereby improving the cycle performance of the battery.

[0055] In some embodiments, the average particle size of the active material (such as silicon material) is 0.1nm to 50nm. For example, the average particle size of the active material can be 0.1nm, 0.5nm, 1nm, 3nm, 5nm, 8nm, 10nm, 20nm, 30nm, 40nm, 50nm or any value within the range consisting of any two of the above values. By setting the average particle size of the active material, the mechanical stress when the active material undergoes volume expansion can be reduced, so that the secondary battery maintains a good battery capacity, and reduces irreversible capacity loss, and can also shorten the electron and ion transmission path. At the same time, the size of the active material is reduced, and the gap between adjacent active materials is increased, which can reserve space for the volume expansion of the active material. Under the average particle size range of the active material defined in this embodiment, a higher battery capacity can be obtained and the volume expansion of the negative electrode material can be alleviated.

[0056] In some embodiments, the average particle size of the active material is further preferably 0.1 nm to 5 nm. For example, the average particle size of the active material can be 0.1 nm, 0.3 nm, 0.5 nm, 0.8 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or any value within the range formed by any two of the above values.

[0057] In some embodiments, the active material includes a silicon-based active material.

[0058] In some embodiments, the silicon-based active material includes at least one of silicon element, silicon oxide, silicon alloy, and silicate.

[0059] In some embodiments, the silicon element comprises at least one of crystalline silicon, amorphous silicon, or a composite of crystalline silicon and amorphous silicon. Preferably, the silicon element is amorphous silicon, which has lower expansion than other types of silicon, thereby improving the problem of large volume expansion of the silicon-carbon anode material during lithium insertion and extraction.

[0060] In some embodiments, silicon oxide comprises silicon oxide SiO x , wherein 0<x≤2, silicon oxide is a silicon-oxygen compound 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. It can be Si, 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.

[0061] In some embodiments, the silicon alloy may be a silicon-lithium alloy, a silicon-magnesium alloy, etc. Of course, it should be noted that, in some cases, the silicon alloy includes elemental silicon particles and alloys.

[0062] In some embodiments, the average particle size of the silicon-based active material is 1 nm to 500 nm, specifically 1 nm, 10 nm, 30 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm or 500 nm, 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-based active 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-based active material is 1 nm to 50 nm, and more preferably, the average particle size of the silicon-based active material is 1 nm to 10 nm. In some embodiments, the test method for the average particle size of the silicon-based active material is to perform mathematical statistics on the diameter of the silicon-based active material in the transmission electron microscope image and calculate the average value.

[0063] In some embodiments, the average pore size of the negative electrode material is 0.45 nm to 50 nm. For example, the average pore size of the negative electrode material can be 0.45 nm, 0.65 nm, 0.85 nm, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or any value within the range formed by any two of the above values. The distribution of the active material in the pores of the carbon matrix will affect the pore volume and average pore size of the negative electrode material. For example, under the same conditions, the more active material adheres to the surface of the carbon matrix, the larger the pore volume of the negative electrode material and the slightly lower average pore size. Under the average pore size range of the negative electrode material defined in this embodiment, the active material can be more distributed in the pores of the carbon matrix to obtain higher negative electrode material cycle performance and capacity retention.

[0064] In some embodiments, the pores of the negative electrode material include micropores, the volume proportion of the micropores in the pores is less than or equal to 10%, and the pore diameter of the micropores is less than or equal to 2 nm. For example, the volume proportion of the micropores of the negative electrode material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value within the range formed by any two of the above values.

[0065] In some embodiments, the pores of the negative electrode material include mesopores, the volume proportion of the mesopores in the pores is greater than or equal to 80%, and the pore diameter of the mesopores is greater than 2 nm and less than or equal to 50 nm. For example, the volume proportion of the mesopores in the negative electrode material can be 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99% or any value within the range formed by any two of the above values.

[0066] In some embodiments, the pores of the negative electrode material include macropores, the macropores account for less than or equal to 20% of the pore volume, and the pore diameter of the macropores is greater than 50 nm. For example, the volume percentage of the macropores of the negative electrode material can be 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, or any value within a range between any two of the foregoing values.

[0067] Since the size of the molecules produced by the electrolyte is generally smaller than or equal to the pore size of the micropores, under the action of the strong capillary adsorption capacity of the micropores, the adsorption capacity of the negative electrode material is largely proportional to the pore volume of the micropores. For example, as the volume of the micropores increases, the adsorption capacity of the negative electrode material increases, thereby increasing the side reaction between the negative electrode material and the electrolyte. Therefore, controlling the pore volume ratio of the micropores of the negative electrode material can reduce the reaction sites where the negative electrode material and the electrolyte undergo side reactions, thereby reducing the thickening of the solid electrolyte membrane (SEI membrane) caused by the continuous intrusion of the electrolyte, which is beneficial to improving the cycle performance of the negative electrode material. In addition, the distribution of pores is also closely related to the deposition of active substances. For example, if the active substance is deposited in the pores of the carbon matrix, the proportion of micropores in the material is small. If the active substance is deposited on the surface of the carbon matrix, a good sealing effect (especially micropores) cannot be achieved, which will increase the volume ratio of micropores in the material. The increased volume fraction of mesopores provides ample buffer space for the volume expansion of the active material, effectively mitigating this expansion and reducing the risk of excessive local expansion stress during cycling, which can lead to cracking and pulverization of the negative electrode material due to uneven volume changes in the active material. This helps improve the particle structure stability and cycle stability of the negative electrode material. Controlling the volume fraction of micropores, mesopores, and macropores in the negative electrode material within the aforementioned range further improves the uniformity of the active material distribution within the negative electrode material.

[0068] In some embodiments, the negative electrode material has a median particle size D50 of 5 μm to 20 μm. For example, the negative electrode material may have a median particle size D50 of 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, or any value within a range consisting of any two of the foregoing values. A negative electrode material having a median particle size D50 within the foregoing range is beneficial for improving the cycle performance of the negative electrode material.

[0069] In some embodiments, the median particle size D50 of the negative electrode material is less than or equal to 15 μm, for example, 1 μm, 5 μm, 8 μm, 10 μm, 12 μm, or 15 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 D50 of the negative electrode material within the above range is beneficial to improving the cycle performance of the negative electrode material.

[0070] In some embodiments, the particle size distribution (D90-D10) / D50 of the negative electrode material of the present application is 0.9 to 5. For example, the particle size distribution (D90-D10) / D50 of the negative electrode material can be 0.9, 1, 1.2, 1.5, 2, 2.6, 3, 3.5, 4, 4.3, 4.6, 4.8, 5 or any value within the range formed by any two of the above values. When the particle size distribution of the negative electrode material is within the above range, the large particles with larger particle sizes and the small particles with smaller particle sizes of the negative electrode material can cooperate with each other, and the small particles fill the pores between the large particles, which can increase the tap density of the negative electrode material. Among them, the measured volume-based cumulative particle size distribution D10 represents the particle size corresponding to when the cumulative particle size distribution percentage of the powder reaches 10%, D50 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%, and D90 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 90%.

[0071] In some embodiments, the compaction density of the negative electrode material at a pressure of 1 T is 0.8 g / cm 3 to 1.3g / cm 3 For example, the compaction density of the negative electrode material of the present application at a pressure of 1T can be 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 Or any value within the range formed by any two of the above values. Controlling the compaction density within the above range helps to reduce the diffusion path in the negative electrode material, thereby improving the rate performance of the battery.

[0072] In some embodiments, the tap density of the negative electrode material after 3000 vibrations is 0.5 g / cm 3 Up to 1.5g / cm 3 For example, the tap density can be 0.5 g / cm 3 , 0.7g / cm 3 , 0.9g / cm 3 , 1.1g / cm 3 , 1.3g / cm 3 , 1.5g / cm 3 Or any value within the range formed by any two of the above values. Controlling the tap density within the above range is conducive to forming an appropriate degree of compactness in the internal structure of the negative electrode material, thereby improving the transmission and conduction of electrons, increasing the battery energy density, extending the cycle life, and improving safety performance.

[0073] In some embodiments, the carbon matrix includes at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microbeads, carbon nanotubes, carbon nanofibers, graphene, activated carbon fibers, carbon black, capacitive carbon, mesoporous carbon, and carbon molecular sieves. The carbon matrix selected from the above materials can provide pore distribution sites for the active material and form a conductive network.

[0074] In some embodiments, the median particle size D50 of the carbon matrix is ​​less than or equal to 15 μm, and can specifically be 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, or 15 μm, etc., and can also be other values ​​within the above range, which are not limited by this application. In some embodiments, the method for testing the median particle size of the carbon matrix is ​​to perform mathematical statistics on the carbon matrix diameter in the transmission electron microscope image and calculate the average value.

[0075] In some embodiments, the coating layer accounts for less than or equal to 10% by mass of the negative electrode material. For example, the coating layer accounts for 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or any value within a range formed by any two of the above values. The coating layer can reduce the solubility of the negative electrode material, thereby reducing the amount of gas generated by the reaction of the dissolved active material with the electrolyte. The coating layer accounts for a mass percentage of the negative electrode material within the above range, which can ensure the amount of lithium that can be inserted into the negative electrode material, thereby ensuring the charge and discharge capacity of the battery prepared with the negative electrode material.

[0076] In some embodiments, the powder conductivity of the negative electrode material at a pressure of 20 kN is 0.5 S / cm to 2 S / cm. For example, the powder conductivity of the negative electrode material can be 0.5 S / cm, 0.7 S / cm, 0.9 S / cm, 1.1 S / cm, 1.3 S / cm, 1.5 S / cm, 1.7 S / cm, 1.9 S / cm, 2.0 S / cm, or any value within a range formed by any two of the foregoing values.

[0077] In some embodiments, the average gas production of the negative electrode material at a temperature of 25°C over 7 days is less than or equal to 1 mL / g. For example, the average gas production of the negative electrode material at a temperature of 25°C over 7 days can be 0.1 mL / g, 0.3 mL / g, 0.5 mL / g, 0.7 mL / g, 0.9 mL / g, 1.0 mL / g, or any value within the range formed by any two of the above values. The gas production value of the negative electrode material is controlled within the above range, indicating that most of the active material can be relatively evenly distributed in the pores of the carbon matrix, and the direct contact between the active material and the electrolyte is reduced, thereby reducing the side reactions of the dissolved active material with the electrolyte or slurry (such as the hydrolysis of silicon into silicate and hydrogen), effectively reducing the gas production value of the negative electrode material.

[0078] In some embodiments, the mass proportion of the active substance in the negative electrode material is 40% to 80%, specifically 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%, etc., and of course it can also be other values ​​within the above range, which is not limited in this application.

[0079] In some embodiments, the mass proportion of the carbon matrix in the negative electrode material is 20% to 60%, specifically 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or 60%, etc., and of course it can also be other values ​​within the above range, which is not limited in this application.

[0080] In some embodiments, the mass fraction of carbon in the negative electrode material is 40% to 60%. The carbon comprises both the carbon matrix and the carbon coating. When the mass fraction of carbon is within this range, a sufficient carbon-based matrix can be established, providing ample distribution sites for the active material, facilitating the formation of an effective conductive network and improving electrical conductivity and cycling stability.

[0081] In some embodiments, the mass percentage of silicon in the negative electrode material is 37% to 55%. When the mass percentage of silicon is within this range, the secondary battery can store a higher amount of electricity, that is, has a higher initial discharge specific capacity.

[0082] In some embodiments, the negative electrode material further includes a coating layer distributed over at least a portion of the surface of the carbon matrix. The coating layer can, on the one hand, reduce side reactions caused by the electrolyte entering the negative electrode material, thereby improving the initial efficiency and capacity of the negative electrode material. Furthermore, the coating layer can cooperate with the carbon matrix to mitigate the volume expansion of the active material, thereby reducing the volume expansion of the entire negative electrode material and minimizing swelling of the negative electrode material when it is prepared into a pole piece.

[0083] In some embodiments, the coating layer is at least one of a carbon layer, a metal oxide layer, and a nitride layer.

[0084] 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). The coating layer located on the outer layer of the negative electrode material has good electrical conductivity, which can improve the electrical conductivity of the negative electrode material. On the other hand, it can coat the active material exposed on the surface of the carbon matrix, reducing the continuous oxidation of the exposed active material during storage, reducing the reduction in the specific capacity and first coulombic efficiency (ICE) of the negative electrode material; the coating layer can also reduce direct contact between the active material and the electrolyte, improve the stability of the SEI film, and thus improve the first coulombic efficiency of the negative electrode material.

[0085] In some embodiments, the material of the metal oxide layer includes at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide.

[0086] In some embodiments, the material of the nitride layer includes at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

[0087] In some embodiments, the coating layer may be a single layer formed of a single material, a combination of multiple materials, a multi-layer coating layer formed of a single material, or a multi-layer coating layer formed of multiple materials. The layer structure of the coating layer can be selected based on actual needs. It is understood that a multi-layer coating structure provides a higher density.

[0088] In some embodiments, the thickness of the coating layer is 0.1nm to 3000nm, specifically 0.1nm, 1nm, 50nm, 100nm, 500nm, 1000nm, 2000nm or 3000nm, etc., and of course other values ​​within the above range can also be used, and this application is not limited here. The coating layer can reduce the solubility of the negative electrode material, thereby reducing the amount of gas produced by the reaction of the dissolved active substance with the electrolyte. Controlling the thickness of the coating layer within the above range is beneficial to maintaining the stability of the particle structure of the negative electrode material during the cycle, reducing the exposed active substance on the surface of the negative electrode material, reducing the exposed active substance causing a large amount of SEI to be generated during the charge and discharge process, and improving the specific capacity and electrochemical performance of the negative electrode material. In some embodiments, the thickness of the coating layer is preferably 1nm to 50nm, and more preferably the thickness of the coating layer is 1nm to 30nm. This is conducive to rapid and reversible deintercalation.

[0089] Some embodiments of the present application provide a method for preparing a negative electrode material. FIG1 is a flow chart of the preparation process of the negative electrode material of the present application, including the following steps:

[0090] Step S100: pre-treating the porous carbonaceous raw material to obtain a carbon matrix. The pre-treating of the porous carbonaceous raw material includes the following steps:

[0091] The porous carbonaceous raw material is subjected to a pressure treatment, wherein the pressure of the pressure treatment is greater than or equal to 100 MPa;

[0092] Alternatively, the porous carbonaceous raw material is immersed in a treatment solution under a vacuum pressure of 0.1 Pa to 500 Pa, wherein the treatment solution includes an organic compound with a molecular weight greater than 10,000.

[0093] Step S200 : vapor-phase depositing a carbon matrix using a vapor-phase active material precursor to obtain a negative electrode material.

[0094] In the above scheme, the present application obtains a carbon matrix by pretreating the porous carbon raw material. The pretreatment can be a pressurized treatment or an impregnation treatment of the porous carbon raw material with a treatment solution. The pressurized treatment causes the pores with larger pore sizes in the porous carbon raw material to preferentially crack or be directly crushed, and the micropores and mesopores with smaller pore sizes can be retained during the pressurized treatment, thereby reducing the number of large pores in the carbon matrix. The porous carbon raw material is impregnated with a treatment solution, which includes an organic compound with a molecular weight greater than 10,000. During the impregnation process, due to the effect of capillaries, the molecules of the treatment solution are difficult to enter the micropores, and are mainly filled into the mesopores and macropores of the porous carbon raw material. The organic compound with a molecular weight greater than 10,000 can be preferentially filled into the macropores of the porous carbon raw material, so that the macropores are transformed into macropores, mesopores or micropores with smaller pore sizes, which is beneficial to increase the number of micropores and mesopores in the carbon matrix, while reducing the number and volume proportion of the macropores of the carbon material, reducing the porosity of the carbon matrix, and then using a gas phase active substance precursor to vapor deposit the carbon matrix. On the one hand, the number and volume proportion of the macropores The smaller the size, the better the deposition uniformity of the gas-phase active material precursor in the porous carbon matrix. The active material generated by the gas-phase active material precursor is not easy to agglomerate when deposited in the porous carbon matrix, which can reduce the volume expansion of the negative electrode material. On the other hand, the active material generated by the gas-phase active material precursor is filled in the carbon matrix, which further reduces the number and volume proportion of large pores in the negative electrode material, so that the area proportion of pores with a pore diameter greater than 50nm in the cross section of the negative electrode material is α≤10%, which is beneficial to improve the tap density of the negative electrode material, and then improve the compaction performance of the negative electrode material, reduce the problems of breakage and cracking of the negative electrode material during the roller pressing process, and improve the capacity, first efficiency, cycle performance and processing performance of the negative electrode material.

[0095] The preparation method of the present application is described in detail below in combination with the following examples:

[0096] Step S100: pretreating the porous carbonaceous raw material to obtain a carbon matrix.

[0097] In some embodiments, step S100 includes: subjecting the porous carbonaceous raw material to a pressure treatment to obtain a carbon matrix, wherein the pressure of the pressure treatment is greater than or equal to 100 MPa.

[0098] In some embodiments, the pressure of the pressure treatment is 100 to 800 MPa, specifically 100 MPa, 150 MPa, 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 500 MPa, 600 MPa, 700 MPa or 800 MPa, etc., and of course it can also be other values ​​within the above range, which is not limited in this application. The pressure of the pressure treatment in this application is relatively large. By pressure-treating the porous carbonaceous raw material, the porous carbonaceous raw material will preferentially produce cracks at the macropores, and then rupture, thereby reducing the number of macropores in the porous carbonaceous raw material. Preferably, the pressure of the pressure treatment is greater than or equal to 150 MPa. If the pressure treatment pressure is less than 100 MPa, it cannot be guaranteed that cracks will be generated at the macropores in the porous carbonaceous raw material, resulting in a large number of macropores in the porous carbonaceous raw material, which is not conducive to improving the compaction density of the negative electrode material.

[0099] In some embodiments, the time of pressurization treatment is 0.5h to 10h, specifically 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0100] In some embodiments, the pressurizing equipment includes at least one of a cold rolling mill and a die press.

[0101] In some embodiments, after the pressure treatment, the step of crushing and screening the pressurized material is further included. During the crushing process, some of the porous carbonaceous raw material is easily broken from the macropores where cracks are generated, further reducing the number of macropores in the carbon matrix.

[0102] In some embodiments, the mesh size of the screening is 10 mesh to 500 mesh, specifically 10 mesh, 50 mesh, 100 mesh, 200 mesh, 300 mesh, 400 mesh or 500 mesh, etc. Of course, it can also be other values ​​within the above range, and this application is not limited here.

[0103] In some embodiments, step S100 includes: immersing the porous carbonaceous raw material in a treatment solution under a vacuum pressure of 0.1 Pa to 500 Pa to obtain a carbon matrix, wherein the treatment solution includes an organic compound with a molecular weight greater than 10,000.

[0104] In some embodiments, the vacuum pressure is 0.1Pa~500Pa, specifically 0.1Pa, 1Pa, 10Pa, 50Pa, 100Pa, 200Pa, 300Pa, 400Pa or 500Pa, etc., and of course other values ​​within the above range can also be used, and this application is not limited thereto. Within the above range, the pressure on the surface of the porous carbonaceous raw material is less than the pressure of the treatment solution, and the treatment solution can be infiltrated into the porous carbonaceous raw material so that the treatment solution enters the interior of the porous carbonaceous raw material through the pores or defects of the porous carbonaceous raw material, thereby serving to fill the macropores in the porous carbonaceous raw material, reduce the number or pore size of the macropores, and enhance the compaction density of the negative electrode material. If the vacuum pressure is greater than 500Pa, it is easy to cause cracks in some mesopores and micropores, making the porosity of the negative electrode material too low, which is not conducive to the deposition of active substances. If the vacuum pressure is less than 0.1Pa, it is not possible to ensure that cracks are generated at the macropores in the porous carbonaceous raw material, resulting in a large number of macropores in the porous carbonaceous raw material, which is not conducive to enhancing the compaction density of the negative electrode material.

[0105] In some embodiments, the treatment solution includes a solute and a solvent, and the solute includes an organic compound with a molecular weight greater than 10,000. Exemplarily, the solute includes at least one of a protein, a nucleic acid, a vinyl polymer, and a monomer cross-linked polymer. The monomer cross-linked polymer can be, for example, polyurethane, polyimide, polyacrylic acid, poly-N-methylpyrrolidone, polyamine, and polyvinyl alcohol. The protein is a macromolecular protein, for example, it can be soy protein and collagen. The main components of soy protein include 11S globulin and 7S globulin, the molecular weight of 11S globulin is 340kDa, and the molecular weight of 7S globulin is 440kDa. Polysaccharides can be, for example, starch and cellulose. The particle size of the solute molecules in the above-mentioned treatment solution is relatively large, which is conducive to preferentially filling the macropores during the impregnation treatment process, so that the pore size of the macropores is reduced, while the pore size of the micropores is too small, making it difficult for the treatment solution to enter the micropores due to capillary action, so that the number of macropores in the porous carbonaceous raw material is greatly reduced, and the number of micropores and mesopores is increased.

[0106] In some embodiments, the solvent includes water and an organic solvent, and the organic solvent includes at least one of an alcohol solvent, an ether solvent, an aliphatic hydrocarbon solvent, a ketone solvent, and dimethyl sulfoxide. Of course, it can also be other types of solvents, which are not limited in this application.

[0107] In some embodiments, the treatment solution includes a vinyl polymer grafted with a polyether polyol. The vinyl polymer may be, for example, polyethylene, polyvinyl chloride, or the like.

[0108] In some embodiments, the particle size of the solute is greater than or equal to 0.5 nm, and can specifically be 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 8 nm, 10 nm, or 15 nm, etc., and can of course also be other values ​​within the above range, which are not limited by the present application. It is understood that the particle size of the solute particles in the treatment solution refers to the equivalent volume diameter, that is, the diameter of a sphere with the same volume as the actual particle of the solute particles in the treatment solution. For example, the particle size of the solute can be measured using the DLS (dynamic light scattering) principle using a BI-90 Plus laser particle size analyzer / zeta potential analyzer.

[0109] In some embodiments, the concentration of the treatment solution is 1 mol / L to 15 mol / L, specifically 1 mol / L, 3 mol / L, 5 mol / L, 7 mol / L, 10 mol / L, 12 mol / L, or 15 mol / L, etc., and of course other values ​​within the above range are also possible, and this application is not limited thereto. Within the above range, it is beneficial for the solute in the treatment solution to enter the pores of the porous carbonaceous raw material, thereby improving the utilization efficiency of the solute.

[0110] In some embodiments, the immersion time is 1 h to 15 h, specifically 1 h, 3 h, 5 h, 7 h, 10 h, 12 h or 15 h, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0111] In some embodiments, the impregnation apparatus comprises a vacuum impregnator.

[0112] In some embodiments, after the porous carbonaceous raw material is immersed in the treatment solution, the method further comprises: drying the immersed material.

[0113] In some embodiments, the drying temperature is -40°C to 600°C, specifically -40°C, -20°C, -10°C, 0°C, 30°C, 50°C, 100°C, 200°C, 300°C, 400°C, 500°C or 600°C, etc. Of course, it can also be other values ​​within the above range, and this application is not limited here.

[0114] In some embodiments, the drying time is 0.5h to 24h, specifically 0.5h, 1h, 3h, 5h, 8h, 12h, 16h, 20h or 24h, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0115] In some embodiments, the porous carbonaceous raw material is prepared by the following method: carbonizing a carbon source, and mixing the carbonized material with an activating agent to perform activation treatment.

[0116] In some embodiments, the carbon source includes at least one of lignin, coconut shells, fruit shells, peanut shells, rice husks, coal-derived biomass, and resin. Coal-derived biomass is biomass briquettes, such as low-pressure compression products of sawdust, agricultural waste, and paper. Resins can include, for example, polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polystyrene (PS).

[0117] In some embodiments, the carbonization temperature is 600°C to 900°C, specifically 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.

[0118] 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.

[0119] 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.

[0120] In some embodiments, after obtaining the carbonized material, the method further includes: pickling the carbonized material, wherein 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.

[0121] In some embodiments, the concentration of the pickling 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 other values ​​within the above range are also possible and are not limited herein. It is understood that the purpose of pickling is to remove impurities from the material. The carbonized material is pickled and then washed with deionized water to a near-neutral state.

[0122] 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.

[0123] In some embodiments, the activator used in the activation treatment can be a gaseous activator or a solid activator. Exemplarily, the gaseous activator includes at least one of water vapor, oxygen and air, and the solid activator includes an alkaline substance, and the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide and rubidium hydroxide.

[0124] In some embodiments, when the activator is a gaseous activator, it reacts with carbon at high temperature through gaseous water vapor, oxygen and air to generate hydrogen and carbon monoxide, which are used to etch the carbonized material to obtain activated pores.

[0125] In some embodiments, the concentration of the gaseous activator is 3% to 20%, specifically 3%, 5%, 7%, 9%, 10%, 12%, 15%, 18%, and 20%, etc., and other values ​​within the above range are also possible, and this application is not limited thereto. Within the above-defined range, the amount of 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 carbonized material, which is conducive to the subsequent filling of the activation pores with the active substance.

[0126] It can be understood that when the activating agent is water vapor, the concentration of the water vapor can be considered as the humidity of the water vapor.

[0127] In some embodiments, when the activator is a solid activator, the mass ratio of the carbonized material to the activator is 1:(0.5-30), specifically 1:0.5, 1:1, 1:5, 1:10, 1:20, and 1:30, etc., and of course other values ​​within the above range are also possible and are not limited here. Within the above-defined range, the amount of 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 carbonized material, which is conducive to the subsequent filling of the activation pores with active substances.

[0128] In some embodiments, the activation treatment time is 1 h to 20 h, for example, it can be 1 h, 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.

[0129] In some embodiments, the temperature of the activation treatment is 500°C to 1200°C, specifically 500°C, 600°C, 700°C, 800°C, 900°C, 950°C, 1000°C, 1100°C and 1200°C, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0130] It is understood that the porous carbon raw material can also be directly purchased through commercial channels to use as a finished porous carbon product.

[0131] Step S200 : vapor-phase depositing a carbon matrix using a vapor-phase active material precursor to obtain a negative electrode material.

[0132] The present application uses a gas-phase active material precursor to perform vapor deposition on a carbon matrix. The gas-phase active material precursor generates an active material that can fill the macropores of the carbon matrix, further reducing the proportion of macropores in the negative electrode material, increasing the compaction density of the negative electrode material, reducing the specific surface area, and reducing problems such as breakage and cracking of the negative electrode material during the rolling process, thereby improving the processing performance and cycle performance of the negative electrode material. Moreover, the active material is not easy to agglomerate when deposited in the carbon matrix, which is beneficial to improving the tap density of the negative electrode material, thereby improving the capacity, initial efficiency and cycle performance of the negative electrode material.

[0133] In some embodiments, the gas-phase reactive species precursor includes a gaseous silicon source.

[0134] In some embodiments, the gaseous silicon source includes at least one of silane, hexasilane, and trisilane.

[0135] In some embodiments, the introduction concentration of the gas-phase active substance precursor is 5% to 30%, specifically 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 26%, 28% or 30%, etc. Of course, it can also be other values ​​within the above range, and this application is not limited here.

[0136] In some embodiments, the temperature of vapor deposition 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.

[0137] In some embodiments, the holding time of vapor deposition 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.

[0138] In some embodiments, after vapor deposition of a carbon matrix using a vapor-phase active material precursor, the method further includes: mixing the vapor-deposited material with a coating material and performing a heat treatment to form a coating layer on the surface of the vapor-deposited material.

[0139] In some embodiments, the coating material includes one of a carbon source, a metal oxide, and a nitride.

[0140] In some embodiments, the nitride includes at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

[0141] In some embodiments, the metal oxide comprises at least one of iron oxide, zinc oxide, tin oxide, copper oxide, and titanium oxide.

[0142] In some embodiments, the carbon source includes at least one of a gaseous carbon source and a solid carbon source.

[0143] In some embodiments, the gaseous carbon source includes at least one of acetylene, methane, propylene, benzene, ethanol, methanol, ethylene, propane, and butane.

[0144] In some embodiments, the flow rate of the gaseous carbon source is 0.1 L / min to 100 L / min, specifically 0.1 L / min, 1 L / min, 10 L / min, 30 L / min, 600 L / min and 100 L / min, etc. Of course, it can also be other values ​​within the above range, and this application is not limited here.

[0145] 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.

[0146] In some embodiments, the mass ratio of the solid carbon source to the material obtained by vapor deposition 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.

[0147] In some embodiments, the heat treatment temperature is 300°C to 1100°C. Specifically, the heat treatment temperature can be, for example, 300°C, 350°C, 400°C, 500°C, 600°C, 650°C, 700°C, 800°C, 900°C, 1000°C, and 1000°C. Of course, it can also be other values ​​within the above range, and this application is not limited thereto. If the heat treatment temperature is lower than 600°C, the coating material will not be completely carbonized, and a dense coating layer cannot be obtained. If the heat treatment temperature is higher than 1100°C, the silicon-based active material will crystallize, resulting in poor cycle performance and expansion performance of the negative electrode material.

[0148] 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.

[0149] In some embodiments, after the vapor deposition material and the coating material are mixed and heated, the method further comprises the steps of screening and grading the obtained material.

[0150] Some embodiments of the present application also provide another method for preparing a negative electrode material, comprising the following steps:

[0151] Step S1, calcining the metal organic framework at 750° C. to 850° C. under an inert gas atmosphere to obtain a porous carbon material; wherein the metal organic framework is obtained by a coordination reaction between an organic ligand and a zinc ion, and the molar ratio of the organic ligand to the zinc ion is 3 to 5:1;

[0152] Step S2, solid-phase mixing the porous carbon material with an alkali, then heating the mixture to 700° C. to 900° C. at a heating rate of 1° C. / min to 5° C. / min for activation for 1 to 3 hours, washing the mixture to remove residual alkali, and drying the mixture to obtain a carbon matrix;

[0153] Step S3: vapor-depositing the carbon matrix with an active material precursor to obtain a negative electrode material.

[0154] The present invention provides a method for preparing a negative electrode material. First, a metal organic framework containing elements such as C, N, O and Zn is calcined and pyrolyzed to carbonize the carbon element to obtain a carbon skeleton. At the same time, Zn volatilizes in the form of steam at high temperature to form micropores. Gases such as H2, CO, CO2 and NOx generated during the high-temperature pyrolysis process can also play a pore-forming role, and finally a porous carbon material with a microporous structure is formed. The Zn sites retained in the porous carbon material are conducive to the subsequent catalytic growth of Si at the sites, thereby improving the efficiency and uniformity of the deposition of active substances in the pores. The porous carbon material is then mixed with an alkali and activated to obtain a carbon matrix with micropores as the main pore structure, so that it can be used for subsequent vapor deposition. When the active substance is deposited, the active substance enters the pores of the carbon matrix, and the micropores are almost all effectively filled, with mainly unfilled mesopores and a small amount of macroporous structures remaining.

[0155] In some embodiments, in order to obtain a porous carbon material with a more ordered porous structure, the organic ligand is selected from at least one of 2-methylimidazole, benzimidazole, terephthalic acid, and 2,5-dihydroxyterephthalic acid. The organic ligand can form a stable metal-organic framework structure with the zinc ion metal, so that the finally prepared carbon matrix has a special ordered porous structure with a higher specific surface area and mass transfer rate.

[0156] In some embodiments, the zinc ions are provided by a readily soluble salt of zinc, which is selected from at least one of nitrates, chlorides, and acetates; preferably, the steps for preparing the metal organic framework are as follows: dissolving the readily soluble salt of zinc in a first solvent to obtain a metal salt solution, and dissolving the organic ligand in a second solvent to obtain an organic ligand solution; under stirring conditions, the organic ligand solution is added to the metal salt solution, and the organic ligand reacts with the zinc ions to form a metal organic framework; more preferably, after the organic ligand solution is added, it is stirred for 10 to 30 minutes, and then allowed to stand for 12 to 48 hours to precipitate a solid product, and the solid product is washed and vacuum dried to obtain a metal organic framework; more preferably, the first solvent and the second solvent are independently selected from at least one of methanol, ethanol, water, hexanenitrile, acetone, and N,N-dimethylformamide.

[0157] In some embodiments, to obtain a microporous structure with uniform and abundant pores, the heating rate in step S1 is 5°C / min to 15°C / min. For example, the specific heating rate can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, or any value within the range of any two of the above values.

[0158] In some embodiments, the calcination time is 1 h to 3 h, and the specific heating rate can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or any value within the range formed by any two of the above values.

[0159] In some embodiments, in step S1, the inert gas includes at least one of nitrogen or argon.

[0160] In some embodiments, in order to remove impurities in the micropores, step S1 further includes: after the calcination is completed, washing the calcined product with an acid solution; the acid solution is selected from at least one of a hydrofluoric acid aqueous solution, a hydrochloric acid aqueous solution, a sulfuric acid aqueous solution, a nitric acid aqueous solution, and a phosphoric acid aqueous solution; preferably, the concentration of the acidic substance in the acid solution is 0.5 mol / L to 5 mol / L.

[0161] In some embodiments, in order to obtain a richer pore structure, in step S2, the mass ratio of carbon material to alkali is 3 to 5:1, specifically 3:1, 3.2:1, 3.5:1, 3.4:1, 4:1, 4.2:1, 4.5:1, 5:1. Of course, it can also be other values ​​within the above mass ratio range, which is not limited here.

[0162] In some embodiments, in order to remove residual alkaline impurities in the pores, in step S2, washing includes pickling and washing with hot water until neutrality after pickling; preferably, in step S2, the acid solution used in pickling is a hydrochloric acid aqueous solution with a mass fraction of 2% to 8%.

[0163] In some embodiments, the active material precursor includes a silicon source, and a silicon source and a diluent gas are introduced into a carbon matrix to perform a vapor deposition reaction to form silicon particles in the pores of the carbon matrix to obtain a negative electrode material.

[0164] In some embodiments, the silicon source includes at least one of monosilane, disilane, trisilane, and tetrasilane.

[0165] In some embodiments, the temperature of the vapor deposition reaction is 400°C to 600°C. The temperature of the vapor deposition reaction can specifically be 400°C, 420°C, 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C or any value within the range formed by any two of the above values.

[0166] In some embodiments, the time of the vapor deposition reaction is 1h to 20h. The time of the vapor deposition reaction can specifically be 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h or any value within the range formed by any two of the above values; preferably 2h to 10h.

[0167] In some embodiments, the volume of the silicon source introduced is 1% to 80%, based on the sum of the volumes of the silicon source and the dilution gas introduced as 100%; preferably, the silicon source includes at least one of monosilane, disilane, monochlorosilane (monochlorosilane), dichlorosilane (dichlorosilane), trichlorosilane (trichlorosilane), and tetrachlorosilane (tetrachlorosilane); and preferably, the dilution gas is selected from one of an inert gas and hydrogen.

[0168] In some embodiments, after vapor deposition of a carbon matrix using a vapor-phase active material precursor, the method further comprises: mixing the vapor-deposited material with a carbon source and performing a heating treatment to obtain a coating layer.

[0169] An embodiment of the present application further provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material distributed on one side of the negative electrode current collector, wherein the negative electrode active material includes the above-mentioned negative electrode material or the negative electrode material prepared by the above-mentioned preparation method.

[0170] In some embodiments, the critical pressure resistance P of the negative electrode sheet is greater than or equal to 100 MPa, and can specifically be 100 MPa, 120 MPa, 150 MPa, 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 500 MPa, 600 MPa, etc. Of course, it can also be other values ​​within the above range, and this application is not limited here. Within the above range, the critical pressure resistance P of the negative electrode material of the present application is large, indicating that the negative electrode sheet of the present application has excellent pressure resistance, which is beneficial to improving the processing performance of the negative electrode sheet. It can be understood that the critical pressure resistance refers to the pressure when the negative electrode sheet is in a critical state, that is, the maximum pressure at which the negative electrode material particles in the negative electrode sheet do not break. The critical pressure resistance of the negative electrode sheet is obtained by the following test method: the thickness of the negative electrode sheet is 60 μm to 70 μm, and the cross-section of a single negative electrode sheet is observed using an electron scanning microscope SEM. The minimum pressure corresponding to the breakage of the negative electrode material particles is P.

[0171] In some embodiments, the compacted density of the negative electrode sheet is 1.3 g / cm 3 ~1.9g / cm 3 , specifically 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 or 1.9 g / cm 3 Of course, other values ​​within the above range are possible, and this application does not limit this. Within the above-defined range, the compaction density of the negative electrode sheet of this application is relatively high, and the pore size inside the negative electrode sheet is relatively small, which is conducive to improving the capacity, initial efficiency and cycle performance of the negative electrode sheet.

[0172] An embodiment of the present application further provides a secondary battery (such as a lithium-ion battery, a sodium-ion battery, etc.), wherein the secondary battery comprises the above-mentioned negative electrode material or the negative electrode material prepared by the above-mentioned preparation method.

[0173] In some embodiments, the lithium-ion battery of the present application includes any one of a cylindrical battery and a square battery.

[0174] 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.

[0175] 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.

[0176] Example A-1

[0177] (1) The coconut shell was carbonized at a temperature of 850°C, and then pickled with 8 mol / L hydrochloric acid for 5 h. The resulting material was dried and activated by a mixture of water vapor and nitrogen at a water vapor concentration of 12%, an activation time of 7 h, and an activation temperature of 750°C.

[0178] (2) The material obtained in step (1) is placed in a molding machine, the pressure is set to 250 MPa, and the pressing is performed for 50 minutes. Then, the briquette material is crushed, pulverized, and sieved to obtain a carbon matrix.

[0179] (3) The carbon substrate was placed in a CVD device, and then silane was introduced into the CVD device, with the silane concentration controlled at 15%, and the temperature was raised to 490° C. and the reaction was carried out for 7 hours.

[0180] (4) The material obtained in step (3) is placed in a reaction furnace, methane gas is introduced at a concentration of 12%, and heat treated at 720°C for 2 hours. The obtained material is screened and graded to obtain a negative electrode material.

[0181] In this embodiment, the negative electrode material includes a carbon matrix and silicon particles, the carbon matrix has pores, and the silicon particles are filled in the pores of the carbon matrix. The area ratio α of the macropores in the cross section of the negative electrode material is 2.63%. The area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material, the carbon content, the silicon content, the pore volume, the compaction density and the specific surface area test are shown in Table 1.

[0182] As shown in Figure 2, it is an SEM picture of the negative electrode material prepared in Example 1 at a magnification of 3000, and Figure 3 is an SEM picture of the particle cross-section of the negative electrode material prepared in Example 1 at a magnification of 10000. It can be seen from Figures 2 and 3 that a small amount of macropores exist in the negative electrode material prepared in Example 1.

[0183] As shown in FIG4 , it is the first charge and discharge curve of the negative electrode material prepared in Example 1. As can be seen from FIG4 , the first charge and discharge capacity of the negative electrode material is relatively high, with a capacity of 1929 mAh / g and a first efficiency of 92.9%.

[0184] As shown in FIG5 , it is a cycle performance curve of the negative electrode material prepared in Example 1. As can be seen from FIG5 , the negative electrode material has excellent cycle performance, and the capacity retention rate after 50 cycles is 92.5%.

[0185] Example A-2

[0186] (1) The fruit shells were carbonized at a temperature of 850°C, and then pickled with 4 mol / L hydrochloric acid for 5 h. The resulting material was dried and activated by a mixture of water vapor and nitrogen at a water vapor concentration of 12%, an activation time of 8 h, and an activation temperature of 850°C.

[0187] (2) The material obtained in step (1) is placed in a molding machine, the pressure is set to 150 MPa, and the pressing is performed for 50 minutes. Then, the pressed material is crushed, pulverized, and sieved to obtain a carbon matrix.

[0188] (3) The carbon substrate was placed in a CVD device, and then silane was introduced into the CVD device, with the silane concentration controlled at 15%, and the temperature was raised to 490° C. and the reaction was carried out for 7 hours.

[0189] (4) The material obtained in step (3) is placed in a reaction furnace, methane gas is introduced at a concentration of 15%, and heat treated at 720°C for 2 hours. The obtained material is screened and graded to obtain a negative electrode material.

[0190] In this embodiment, the negative electrode material includes a carbon matrix and silicon particles, the carbon matrix has pores, and the silicon particles are filled in the pores of the carbon matrix. The area ratio α of the macropores in the cross section of the negative electrode material is 4.19%. The area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material, the carbon content, the silicon content, the pore volume, the compaction density and the specific surface area test are shown in Table 1.

[0191] Example A-3

[0192] (1) The fruit shells were carbonized at a temperature of 850°C, and then pickled with 4 mol / L hydrochloric acid for 5 h. The resulting material was dried and activated by a mixture of water vapor and nitrogen at a water vapor concentration of 12%, an activation time of 8 h, and an activation temperature of 850°C.

[0193] (2) The material obtained in step (1) is placed in a molding machine, the pressure is set to 100 MPa, and the pressing is performed for 50 minutes. Then, the briquette material is crushed, pulverized, and sieved to obtain a carbon matrix.

[0194] (3) The carbon substrate was placed in a CVD device, and then silane was introduced into the CVD device, with the silane concentration controlled at 15%, and the temperature was raised to 490° C. and the reaction was carried out for 7 hours.

[0195] (4) The material obtained in step (3) is placed in a reaction furnace, methane gas is introduced at a concentration of 15%, and heat treated at 720°C for 2 hours. The obtained material is screened and graded to obtain a negative electrode material.

[0196] In this embodiment, the negative electrode material includes a carbon matrix and silicon particles, the carbon matrix has pores, and the silicon particles are filled in the pores of the carbon matrix. The area ratio α of the macropores in the cross section of the negative electrode material is 9.71%. The area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material, the carbon content, the silicon content, the pore volume, the compaction density and the specific surface area test are shown in Table 1.

[0197] Example A-4

[0198] (1) The fruit shells were carbonized at a temperature of 850°C, and then pickled with 4 mol / L hydrochloric acid for 5 h. The resulting material was dried and activated by a mixture of water vapor and nitrogen at a water vapor concentration of 6%, an activation time of 8 h, and an activation temperature of 550°C.

[0199] (2) The material obtained in step (1) is placed in a molding machine, the pressure is set to 300 MPa, and the pressing is performed for 30 minutes. Then, the briquette material is crushed, pulverized, and sieved to obtain a carbon matrix.

[0200] (3) placing the carbon substrate in a CVD device, then introducing silane into the CVD device with a silane concentration controlled at 22%, raising the temperature to 490°C, and reacting for 7 hours;

[0201] (4) The material obtained in step (3) is placed in a reaction furnace, methane gas is introduced at a concentration of 15%, and heat treated at 720°C for 2 hours. The obtained material is screened and graded to obtain a negative electrode material.

[0202] In this embodiment, the negative electrode material includes a carbon matrix and silicon particles. The area ratio α of the macropores in the cross section of the negative electrode material is 1.98%. The area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material, the carbon content, the silicon content, the pore volume, the compacted density and the specific surface area test are shown in Table 1.

[0203] Example A-5

[0204] (1) The fruit shells were carbonized at a temperature of 850°C, and then pickled with 4 mol / L hydrochloric acid for 5 h. The resulting material was dried and activated by a mixture of water vapor and nitrogen at a water vapor concentration of 12%, an activation time of 8 h, and an activation temperature of 850°C.

[0205] (2) Dissolve 10 g of soy protein in 90 mL of water to obtain a treatment solution with a concentration of 10 mol / L. Place the material obtained in step (1) in a vacuum impregnation machine, add the treatment solution, set the vacuum pressure to 500 Pa, press for 50 minutes, and then heat treat at 500°C for 4 hours to obtain a carbon matrix.

[0206] (3) The carbon substrate was placed in a CVD device, and then silane was introduced into the CVD device, with the silane concentration controlled at 15%, and the temperature was raised to 540° C. and the reaction was carried out for 5 hours.

[0207] (4) The material obtained in step (3) is placed in a reaction furnace, methane gas is introduced at a concentration of 15%, and heat treated at 720°C for 2 hours. The obtained material is screened and graded to obtain a negative electrode material.

[0208] In this embodiment, the negative electrode material includes a carbon matrix and silicon particles, the carbon matrix has pores, and the silicon particles are filled in the pores of the carbon matrix. The area ratio α of the macropores in the cross section of the negative electrode material is 9.81%. The area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material, the carbon content, the silicon content, the pore volume, the compaction density and the specific surface area test are shown in Table 1.

[0209] Example A-6

[0210] (1) The fruit shells were carbonized at a temperature of 850°C, and then pickled with 4 mol / L hydrochloric acid for 5 h. The resulting material was dried and activated by a mixture of water vapor and nitrogen at a water vapor concentration of 12%, an activation time of 8 h, and an activation temperature of 850°C.

[0211] (2) Dissolve 10 g of soy protein in 90 mL of water to obtain a treatment solution with a concentration of 10 mol / L. Place the material obtained in step (1) in a vacuum impregnation machine, add the treatment solution, set the vacuum pressure to 201 Pa, press for 50 minutes, and then heat treat at 500°C for 4 hours to obtain a carbon matrix.

[0212] (3) The carbon substrate was placed in a CVD device, and then silane was introduced into the CVD device, with the silane concentration controlled at 15%, and the temperature was raised to 540° C. and the reaction was carried out for 5 hours.

[0213] (4) The material obtained in step (3) is placed in a reaction furnace, methane gas is introduced at a concentration of 15%, and heat treated at 720°C for 2 hours. The obtained material is screened and graded to obtain a negative electrode material.

[0214] In this embodiment, the negative electrode material includes a carbon matrix and silicon particles, the carbon matrix has pores, and the silicon particles are filled in the pores of the carbon matrix. The area ratio α of the macropores in the cross section of the negative electrode material is 7.64%. The area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material, the carbon content, the silicon content, the pore volume, the compaction density and the specific surface area test are shown in Table 1.

[0215] Example A-7

[0216] (1) The fruit shells were carbonized at a temperature of 850°C, and then pickled with 4 mol / L hydrochloric acid for 5 h. The resulting material was dried and activated by a mixture of water vapor and nitrogen at a water vapor concentration of 12%, an activation time of 8 h, and an activation temperature of 850°C.

[0217] (2) 10 g of soy protein was dissolved in 90 mL of water to obtain a treatment solution having a concentration of 10 mol / L. The material obtained in step (1) was placed in a vacuum impregnation machine, the treatment solution was added, the vacuum pressure was set to 47 Pa, and the mixture was pressed for 50 min. The mixture was then heat treated at 500 ° C for 4 h to obtain a carbon matrix.

[0218] (3) The carbon substrate was placed in a CVD device, and then silane was introduced into the CVD device, with the silane concentration controlled at 15%, and the temperature was raised to 540° C. and the reaction was carried out for 5 hours.

[0219] (4) The material obtained in step (3) is placed in a reaction furnace, methane gas is introduced at a concentration of 15%, and heat treated at 720°C for 2 hours. The obtained material is screened and graded to obtain a negative electrode material.

[0220] In this embodiment, the negative electrode material includes a carbon matrix and silicon particles, the carbon matrix has pores, and the silicon particles are filled in the pores of the carbon matrix. The area ratio α of the macropores in the cross section of the negative electrode material is 4.11%. The area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material, the carbon content, the silicon content, the pore volume, the compaction density and the specific surface area test are shown in Table 1.

[0221] Example A-8

[0222] (1) The fruit shells were carbonized at a temperature of 850°C, and then pickled with 4 mol / L hydrochloric acid for 5 h. The resulting material was dried and activated by a mixture of water vapor and nitrogen at a water vapor concentration of 12%, an activation time of 8 h, and an activation temperature of 850°C.

[0223] (2) Dissolve 10 g of soy protein in 90 mL of water to obtain a treatment solution with a concentration of 10 mol / L. Place the material obtained in step (1) in a vacuum impregnation machine, add the treatment solution, set the vacuum pressure to 0.1 Pa, press for 50 minutes, and then heat treat at 500°C for 4 hours to obtain a carbon matrix.

[0224] (3) The carbon substrate was placed in a CVD device, and then silane was introduced into the CVD device, with the silane concentration controlled at 15%, and the temperature was raised to 540° C. and the reaction was carried out for 5 hours.

[0225] (4) The material obtained in step (3) is placed in a reaction furnace, methane gas is introduced at a concentration of 15%, and heat treated at 720°C for 2 hours. The obtained material is screened and graded to obtain a negative electrode material.

[0226] In this embodiment, the negative electrode material includes a carbon matrix and silicon particles, the carbon matrix has pores, and the silicon particles are filled in the pores of the carbon matrix. The area ratio α of the macropores in the cross section of the negative electrode material is 2.47%. The area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material, the carbon content, the silicon content, the pore volume, the compacted density and the specific surface area test are shown in Table 1.

[0227] Example A-9

[0228] The difference from Example A-1 is that in step (2): 10 g starch (C6H 10 O5) 74 The treated solution was dissolved in 82 mL of DMSO, and the concentration of the treated solution was 10 mol / L. The material obtained in step (1) was placed in a vacuum impregnation machine, and the treated solution was added. The vacuum pressure was set to 500 Pa, and the mixture was pressed for 50 minutes. The mixture was then heat treated at 500°C for 4 hours to obtain a carbon matrix.

[0229] In this embodiment, the negative electrode material includes a carbon matrix and silicon particles, the carbon matrix has pores, and the silicon particles are filled in the pores of the carbon matrix. The area ratio α of the macropores in the cross section of the negative electrode material is 8.41%. The area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material, the carbon content, the silicon content, the pore volume, the compaction density and the specific surface area test are shown in Table 1.

[0230] Example A-10

[0231] The difference from Example A-1 is that in step (2): 10 g of polyvinyl chloride (C2H3Cl) 160 The treated solution was dissolved in 68 mL of dichloroethane, and the concentration of the treated solution was 10 mol / L. The material obtained in step (1) was placed in a vacuum impregnation machine, and the treated solution was added. The vacuum pressure was set to 500 Pa, and the mixture was pressed for 50 minutes. The mixture was then heat treated at 500°C for 4 hours to obtain a carbon matrix.

[0232] In this embodiment, the negative electrode material includes a carbon matrix and silicon particles, the carbon matrix has pores, and the silicon particles are filled in the pores of the carbon matrix. The area ratio α of the macropores in the cross section of the negative electrode material is 7.81%. The area ratio of pores with a pore diameter greater than or equal to 500 nm in the cross section of the negative electrode material, the carbon content, the silicon content, the pore area, the compaction density and the specific surface area test are shown in Table 1.

[0233] Example A-11

[0234] Different from Example A-1, the pressure in step (2) is 800 MPa.

[0235] Example A-12

[0236] Different from Example A-1, step (4) was not performed.

[0237] Example A-13

[0238] Different from Example A-5, step (4) was not performed.

[0239] Comparative Example A-1

[0240] The difference from Example A-1 is that step (2) is not performed.

[0241] Comparative Example A-2

[0242] The difference from Example A-1 is that the pressure in step (2) is 90 MPa.

[0243] Comparative Example A-3

[0244] The difference from Example A-5 is that step (2) is not performed.

[0245] Comparative Example A-4

[0246] The difference from Example A-5 is that the pressure in step (2) is normal pressure, specifically 101 kPa.

[0247] Comparative Example A-5

[0248] The difference from Example A-5 is that in step (2), 10 g of starch (C6H 10 O5) 40 Dissolve in 82 mL of DMSO to obtain a treatment solution.

[0249] Performance Test (I)

[0250] 1. Use BET pore distribution to test the pore volume size of the negative electrode material.

[0251] 2. Before etching the silicon-based active material in the negative electrode material, the mass M1 of the negative electrode material is tested. After etching the silicon-based active material with HF, the mass of the negative electrode material is tested again as M2. M2 / M1 is the mass ratio of the carbon matrix in the negative electrode material, and (M1-M2) / M1 is the mass ratio of the silicon-based active material in the negative electrode material.

[0252] 3. Use a laser particle size analyzer to test the median particle size of the negative electrode material.

[0253] 4. After using HF to etch the silicon-based active material in the negative electrode material, the average pore size of the pores was tested using a US Micromeritics ASAP 2460 fully automatic specific surface area and porosity analyzer. The gas used during the test was CO2 or N2.

[0254] 5. Testing method for the median particle size of silicon-based active materials: Perform mathematical statistics on the diameters of silicon-based active materials in transmission electron microscope images and calculate the average value.

[0255] 6. The electrochemical performance of the negative electrode material was tested using the following method:

[0256] A negative electrode material, conductive agent, and binder were dissolved in a solvent at a mass ratio of 94:1:5, controlling the solid content to 50%. The mixture was then coated onto a copper foil current collector and vacuum-dried to produce a negative electrode sheet. 18650 cylindrical cells were then assembled using conventional production processes using a ternary positive electrode sheet prepared using a 1 mol / L LiPF6 / EC+DMC+EMC (v / v / v = 1:1:1) electrolyte, a Celgard 2400 separator, and a casing. Cylindrical cells were tested for charge and discharge at room temperature using a LAND battery test system from Wuhan Jinnuo Electronics Co., Ltd., with a constant current of 0.2C and a charge and discharge voltage limit of 2.75 to 4.2V. The test results are shown in Tables 1 and 2, where Examples A-1 to A-10 are designated S1 to S10, and Comparative Examples A-1 to A-4 are designated D1 to D4.

[0257] 7. Use the following method to perform a withstand voltage test on the negative electrode:

[0258] The negative electrode material, conductive agent and binder with a mass ratio of 94:2:4 are dissolved in a solvent, and the solid content is controlled at 30%. The above mixture is coated on a copper foil current collector and vacuum dried to obtain a negative electrode sheet. Then, a roller machine is used to roll the negative electrode sheet according to the set pressure. The thickness of the negative electrode sheet is controlled at 60μm~70μm. Then, the negative electrode sheet is cross-sectionally tested to observe whether there is any particle breakage in the negative electrode sheet. The minimum pressure value corresponding to particle breakage is the critical withstand pressure P of the negative electrode sheet.

[0259] 8. Test the compaction density of the negative electrode according to Appendix L of GBT 24533-2019.

[0260] Table 1. Alpha test of negative electrode materials of various embodiments and comparative examples

[0261] Table 2. Performance test of negative electrode materials and negative electrode sheets prepared in various embodiments and comparative examples

[0262] As shown in Tables 1 and 2, the number and volume of macropores in the negative electrode material prepared in this application are relatively small, satisfying α ≤ 10%. This can effectively reduce the specific surface area of ​​the negative electrode material. During the initial charge and discharge process, it can reduce the occurrence of side reactions between the negative electrode material and the electrolyte, reduce gas production, and improve the initial efficiency, expansion performance, and cycle performance of the negative electrode material. Moreover, the relatively small number and volume proportion of macropores can increase the tap density and compacted density of the negative electrode material, reduce the occurrence of breakage and cracking of the negative electrode material during the roller pressing process, and improve the processing performance of the negative electrode material.

[0263] In Comparative Examples A-1 and A-2, the porous carbonaceous raw material was not pressurized in Comparative Example A-1, and the pressure at which the porous carbonaceous raw material was pressurized in Comparative Example A-2 was too small, resulting in a large number of macropores in the negative electrode material and a large pore diameter, causing the negative electrode material to have low capacity, low initial efficiency, and poor cycle performance. Moreover, when the negative electrode material is prepared into a negative electrode sheet, the critical withstand pressure P and compaction density of the negative electrode sheet are small, resulting in deterioration in the processing performance of the negative electrode sheet.

[0264] In comparative example A-3, the porous carbonaceous raw material was not treated with a treatment solution impregnation treatment, resulting in a large number of macropores in the negative electrode material, causing the negative electrode material to have low capacity, low initial efficiency and poor cycle performance. Moreover, the negative electrode material was prepared into a negative electrode plate, and the critical pressure P and compaction density of the negative electrode plate were relatively low, resulting in deterioration in the processing performance of the negative electrode plate.

[0265] The pressure of the immersion treatment in Comparative Example A-4 is normal pressure, which makes it difficult for the treatment solution to enter the macropores of the carbon matrix, resulting in a large number of macropores in the negative electrode material, causing the negative electrode material to have low capacity, low initial efficiency and poor cycle performance. Moreover, the negative electrode material is prepared into a negative electrode sheet, and the critical pressure P and compaction density of the negative electrode sheet are relatively small, resulting in deterioration of the processing performance of the negative electrode sheet.

[0266] Example B-1

[0267] Step 1. Preparation of a metal-organic framework: 3 mol of Zn(NO3)2·6H2O is dissolved in 3 L of methanol to obtain a metal salt solution, 12 mol of 2-methylimidazole is dissolved in 3 L of methanol to obtain an organic ligand solution, the organic ligand solution is quickly added to the metal salt solution while stirring, and after stirring for 15 minutes after the addition is completed, the resulting solution is allowed to stand for 24 hours to precipitate a solid product. Finally, the resulting solid product is washed with methanol several times and vacuum dried at 80°C for 12 hours to obtain a metal-organic framework.

[0268] Step 2: Place the metal organic framework in a tubular furnace, heat it to 800°C at a heating rate of 10°C / min in an argon environment and keep it at a constant temperature for 2 hours for calcination. After the calcination is completed, cool it naturally to room temperature, and then wash the calcined product with 2 mol / L HF aqueous solution and distilled water multiple times to remove residual metal impurities. Finally, vacuum dry it at 80°C for 12 hours to obtain a porous carbon material.

[0269] Step 3. The mass ratio of the porous carbon material to KOH is 4:1, and the activation is carried out at 800°C, the heating rate is 2°C / min, and the activation time is 2h. The activated product is washed with a 5% hydrochloric acid aqueous solution and hot water to neutrality, and then dried to obtain a carbon matrix.

[0270] Step 4: Place the carbon substrate in a CVD device, then introduce monosilane and N2 into the CVD device at a volume ratio of 1:3, raise the temperature to 500°C for vapor deposition reaction, the reaction time is 5 hours, and the deposition pressure is set to 10 kPa to obtain the negative electrode material.

[0271] Example B-2

[0272] Step 1. Preparation of a metal-organic framework: 4 mol of ZnCl2·4H2O is dissolved in 4 L of methanol to obtain a metal salt solution, 12 mol of benzimidazole is dissolved in 4 L of methanol to obtain an organic ligand solution, the organic ligand solution is rapidly added to the metal solution while stirring, and after stirring for 15 minutes after the addition is complete, the resulting solution is allowed to stand for 24 hours to precipitate a solid product. Finally, the resulting solid product is washed with methanol multiple times and vacuum dried at 80°C for 12 hours to obtain a metal-organic framework.

[0273] Step 2: Place the precursor in a tubular furnace, heat it to 850°C at a heating rate of 5°C / min in an argon environment and keep it at a constant temperature for 1 hour for calcination. After the calcination is completed, cool it naturally to room temperature, and then wash the calcined product with 2mol / LHF aqueous solution and distilled water multiple times to remove residual metal impurities. Finally, vacuum dry it at 80°C for 12 hours to obtain a porous carbon material.

[0274] Step 3. The mass ratio of the porous carbon material to KOH is 4:1, and the activation is carried out at 700°C, the heating rate is 5°C / min, and the activation time is 2h. The activated product is washed with a 5% hydrochloric acid aqueous solution and hot water to neutrality, and then dried to obtain a carbon matrix.

[0275] Step 4: Place the carbon substrate in a CVD device, then introduce disilane and H2 into the CVD device at a volume ratio of 1:6, raise the temperature to 580°C for vapor deposition reaction, the reaction time is 10 hours, and the deposition pressure is set to 5kPa to obtain the negative electrode material.

[0276] Example B-3

[0277] Step 1. Preparation of a metal-organic framework: 2 mol of Zn(CH3COOH)2·2H2O is dissolved in 2 L of methanol to obtain a metal salt solution, 10 mol of terephthalic acid is dissolved in 2 L of methanol to obtain an organic ligand solution, the organic ligand solution is quickly added to the metal solution while stirring, and after stirring for 15 minutes after the addition is completed, the resulting solution is allowed to stand for 24 hours to precipitate a solid product. Finally, the resulting solid product is washed with methanol several times and vacuum dried at 80°C for 12 hours to obtain a metal-organic framework.

[0278] Step 2: Place the precursor in a tubular furnace, heat it to 750°C at a heating rate of 15°C / min in an argon environment and keep it at a constant temperature for 3 hours for calcination. After the calcination is completed, cool it naturally to room temperature, and then wash the calcined product with 2mol / LHF aqueous solution and distilled water multiple times to remove residual metal impurities. Finally, vacuum dry it at 80°C for 12 hours to obtain a porous carbon material.

[0279] Step 3. The mass ratio of the porous carbon material to KOH is 4:1, and the activation is carried out at 900°C, the heating rate is 1°C / min, and the activation time is 2h. The activated product is washed with a 5% hydrochloric acid aqueous solution and hot water to neutrality, and then dried to obtain a carbon matrix.

[0280] Step 4: Place the carbon substrate in a CVD device, then introduce trichlorosilane and H2 into the CVD device at a volume ratio of 3:2. Raise the temperature to 600°C for vapor deposition reaction. The reaction time is 2 hours and the deposition pressure is set to 1 kPa to obtain the negative electrode material.

[0281] Example B-4

[0282] The only difference from Example B-1 is that step 4 further includes preparing a coating layer on the product obtained after the vapor deposition reaction is completed. The specific steps are as follows:

[0283] The product obtained after the vapor deposition reaction is placed in a reactor, and methane gas is introduced at a methane flow rate of 10 L / min. It is heat treated at 750°C and kept warm for 4 hours. The obtained material is screened and graded to obtain the negative electrode material.

[0284] Wherein, the thickness of the coating layer in the negative electrode material is 200nm.

[0285] Example B-5

[0286] The same as Example B-1, except that 2-methylimidazole is replaced by terephthalic acid.

[0287] Example B-6

[0288] The same as Example B-1, except that 2-methylimidazole is replaced by 2,5-dihydroxyterephthalic acid.

[0289] Example B-7

[0290] The same as Example B-1, except that the amount of 2-methylimidazole used in step 1 is 15 mol.

[0291] Example B-8

[0292] The same as Example B-1, except that the activation temperature in step 3 is 900°C.

[0293] Example B-9

[0294] The only difference from Example B-1 is that the heating rate in step 3 is 4°C / min.

[0295] Comparative Example B-1

[0296] The only difference between this method and Example B-1 is that the amount of 2-methylimidazole used in step 1 is 18 mol.

[0297] Comparative Example B-2

[0298] The only difference between this embodiment and Example B-1 is that the activation temperature in step 3 is 1000°C.

[0299] Comparative Example B-3

[0300] The only difference from Example B-1 is that the heating rate in step 3 is 8° C. / min.

[0301] Performance testing:

[0302] (1) Material α test:

[0303] α is obtained by the following test method: in the figure shown by SEM cross-section processing of a single negative electrode material particle, any a×b area is selected, where a=1μm~10μm, b=1μm~10μm, the sum of the cross-sectional areas of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle in the region is recorded as S0, the cross-sectional area of ​​a single negative electrode material particle in the region is recorded as S, and the area ratio of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle is defined as α', α'=S0 / S, 10 negative electrode material particles are tested, α is the arithmetic mean of the α' values ​​of the 10 negative electrode material particles, and the test results of α' and α of the negative electrode material are shown in Table 3.

[0304] (2) Pore size, pore size distribution (volume ratio of micropores, mesopores and macropores), pore volume and specific surface area test: The test was performed using a specific surface area and pore size analyzer (TriStar 3000, Micromeritics, USA).

[0305] Among them, HF was used to etch the silicon-based active material in the negative electrode material to obtain a carbon matrix, which was used as the object for testing to obtain the micropore ratio, specific surface area and pore volume of the carbon matrix. The micropore ratio test results are shown in Table 4, and the specific surface area S2 and pore volume P2 of the carbon matrix are shown in Table 5;

[0306] The pore size distribution and average pore size test results of the negative electrode material are shown in Table 4, and the specific surface area S1 and pore volume P1 of the negative electrode material are shown in Table 3.

[0307] (3) Particle size and particle size distribution test: The D10, D50, and D90 of the material were measured using a laser particle size analyzer. The particle size D50 and particle size distribution (D90-D10) / D50 of the negative electrode material are shown in Table 4.

[0308] (4) Test method for average particle size of silicon-based active material: The diameter of silicon-based active material in the transmission electron microscope image is mathematically counted and the average value is calculated to obtain the average particle size of the active material. The result is shown in 4.

[0309] (5) Carbon content test: The carbon content (mass percentage) of the material was tested using an infrared carbon-sulfur analyzer (CSI, Elt, Germany). The results are shown in Table 5.

[0310] (6) Silicon content test: The silicon content of the material was tested in accordance with GBT / 38823-2020. The test equipment was an atmosphere furnace (Sigma SGM.VB11 / 17DF). The test parameters were a burning temperature of 1300°C. The results are shown in Table 5.

[0311] (7) Tap density test: The tap density of the material was tested using a tap density meter (DAT-6-220, Quantachrome, USA). The specific steps are as follows: the sample was placed in a measuring cylinder and vibrated 3000 times. The volume of the measuring cylinder after tapping was read and the tap density was calculated. The tap density test results of the negative electrode material are shown in Table 6.

[0312] (8) Compaction density test: The compaction density of the material was tested using a compaction density meter (McNor, CARVER 4350) in accordance with GB / T 24533-2019. The compaction density test results of the negative electrode material are shown in Table 6.

[0313] (9) Powder conductivity test: The conductivity of the material under a pressure of 20 kN was tested using a powder resistance test system (Mitsubishi Chemical, Japan, MCP-PD51). The powder conductivity of the negative electrode material under 20 kN is shown in Table 6.

[0314] (10) Oil absorption test: Using an oil absorption tester (ASAHI SOUKEN, S-500, Japan), a powder sample was placed in a mixing chamber. Oil (DBP) was then dripped into the sample at a constant rate while stirring with a rotor at 630 r / min. The oil absorption (mL / 100 g) of the sample was calculated by measuring the viscosity change with torque. The oil absorption data are shown in Table 6.

[0315] (11) Gas production test:

[0316] 1.1. Prepare various slurries in a certain proportion (add water to CMC to form glue after uniform dispersion. The mass percentage of CMC in the glue is 1.4%. Take 10g of glue and mix it with 10g of sample to make slurry).

[0317] 1.2. At room temperature (25°C), put the slurry into an aluminum-plastic film bag, record the slurry mass, and then seal it to form a sealed aluminum-plastic film bag.

[0318] 1.3. Measure the volume of gas generated: Fix the sealed aluminum-plastic film bag at the bottom of the container and completely immerse it in water. Record the initial volume of the aluminum-plastic film bag, and then record the volume of the aluminum-plastic film bag every 24 hours for 7 consecutive days.

[0319] 1.4. The 7-day average gas production of the negative electrode material was calculated based on the volume change of the aluminum-plastic film. The results are shown in Table 6.

[0320] (12) Battery performance test:

[0321] 1.1. First charge and discharge specific capacity and first coulombic efficiency test: A negative electrode slurry was prepared according to the mass ratio of negative electrode material, conductive carbon black, and PPA at 70:15:15. The slurry was coated on copper foil and dried to form a negative electrode sheet. A metal lithium sheet was used as the counter electrode. The coin cell was assembled into a button cell in an Ar gas-filled glove box. The coin cell was then charged and discharged at a current density of 0.1C in the charge and discharge range of 0.01V to 1.5V. The first discharge specific capacity and first coulombic efficiency (ICE) of the coin cell are shown in Table 7.

[0322] 1.2. Capacity retention rate and electrode thickness expansion rate test: A negative electrode slurry was prepared by mixing a mixture of negative electrode material and graphite, Super-P, KS-6, CMC, and SBR in a mass ratio of 92:2:2:2:2, coated on copper foil, and dried to form a negative electrode sheet. The proportion of negative electrode material and graphite in the mixture of negative electrode material and graphite was determined by the initial lithium removal capacity of the manufactured lithium battery (in this test, the initial lithium removal capacity of the lithium battery was uniformly 480 mAh / g). A button cell was assembled in a glove box filled with Ar gas using a metal lithium sheet as the counter electrode. The button cell was then subjected to 50 repeated charge and discharge tests in the charge and discharge range of 0.01 V to 1.5 V at a current density of 1 C to obtain the capacity retention rate and the electrode thickness expansion rate after 50 cycles of the battery. See Table 7 for details.

[0323] Table 3

[0324] Table 4

[0325] Table 5

[0326] Table 6

[0327] Note: The volume ratio of nitrogen adsorbed by the carbon matrix at 90% partial pressure to the volume ratio of nitrogen adsorbed at 10% partial pressure is A; the volume ratio of nitrogen adsorbed by the negative electrode material at 90% partial pressure to the volume ratio of nitrogen adsorbed at 10% partial pressure is B.

[0328] Table 7

[0329] As shown in Tables 3 to 7, the number and volume of macropores in the negative electrode materials prepared in Examples B-1 to B-9 of the present application are relatively small. The area ratio of pores with a pore diameter greater than 50 nm in any cross-section of the negative electrode material satisfies α≤10%, which can effectively reduce the specific surface area of ​​the negative electrode material. During the initial charge and discharge process, it can reduce the occurrence of side reactions between the negative electrode material and the electrolyte, reduce gas production, and improve the initial efficiency, expansion performance, and cycle performance of the negative electrode material. Moreover, the relatively small number and volume ratio of macropores can increase the tap density and compacted density of the negative electrode material, reduce problems such as breakage and cracking of the negative electrode material during the roller pressing process, and improve the processing performance of the negative electrode material.

[0330] The negative electrode materials prepared in Examples B-1 to B-9 of the present invention have a smaller oil absorption value of the negative electrode material (dpq1 is 43ml / 100g to 68ml / 100g), a larger difference in oil absorption value before and after silicon deposition ((dpq2-dpq1) / dpq1 is 1.33 to 3.19), and a smaller macropore area ratio (the area ratio of pores with a pore diameter greater than 50nm is α≤10%). The above data show that more silicon material in the negative electrode material enters the carbon matrix and is mainly deposited in the pores of the carbon matrix, and the negative electrode material after the silicon material is deposited is mainly mesopores that are not completely filled with micropores. When the above material is used as a negative electrode material, it can reduce the direct contact between silicon particles and the electrolyte, reduce the occurrence of adverse side reactions between the negative electrode material and the electrolyte, improve the cycle performance of the material, and make the negative electrode material have a higher capacity retention rate. As shown in Table 7, the battery capacity retention rate of the negative electrode materials prepared in Examples B-1 to B-9 after 50 cycles is above 90%; in addition, the pores after silicon deposition still have a rich mesoporous structure, which can reduce the volume expansion of the negative electrode material. As shown in Table 7, the electrode thickness expansion rate of the negative electrode materials prepared in Examples B-1 to B-9 after 50 cycles is less than 40%, and the macropore volume and area of ​​the negative electrode materials after silicon deposition account for a small proportion, which can improve the tap density of the negative electrode material (as shown in Table 6, the tap density of the negative electrode materials prepared in Examples is 0.7 g / cm 3 and above), and effectively reduce the specific surface area of ​​the composite material (as shown in Table 5, compared with the carbon matrix, the specific surface area and pore volume of the negative electrode material obtained after silicon deposition on the carbon matrix in the embodiment are significantly reduced), thereby reducing the occurrence of side reactions between the material and the electrolyte during the first charge and discharge process, and improving the first efficiency, expansion performance and cycle performance of the negative electrode material.

[0331] A higher amount of organic ligand was added to Comparative Example B-1 to obtain a negative electrode material with a higher proportion of macropore area (19.9%). Compared with Example B-1, the pore volume of the carbon matrix increased slightly and the pore volume of the negative electrode material remained basically unchanged. The specific surface areas of the carbon matrix and the negative electrode material were greatly improved, and the proportion of macropores (23%) increased significantly, resulting in the deterioration of the first efficiency and expansion performance of the negative electrode material, especially the significant decrease in the first coulomb.

[0332] In comparative example B-2, a higher activation temperature was used to obtain a negative electrode material with a higher proportion of macropore area and volume. Compared with example B-1, the specific surface area of ​​the carbon matrix increased significantly while the pore volume of the carbon matrix remained unchanged, indicating that at a lower activation temperature, as the activation temperature increases, the specific surface area and pore volume of the porous carbon material increase, which is conducive to the formation of mesopores. If the temperature is too high, excessive vaporization may cause the collapse of the pores to form macropores that are interconnected, resulting in a significant increase in the specific surface area of ​​the carbon matrix. Under the same silicon deposition process as example B-1, the proportion of macropore area and volume of the obtained negative electrode material increases, resulting in the deterioration of the initial efficiency and expansion performance of the negative electrode material, especially a significant decrease in the cycle performance.

[0333] In comparative example B-3, a higher heating rate was used to obtain a negative electrode material with a higher macropore area and volume ratio. When the heating rate was low, the reaction between the activator KOH and the carbon material was relatively mild, and a large number of microporous structures were formed during the reaction. As the heating rate increased, the high-temperature activation process became more and more intense, and the erosion of KOH became stronger, causing the pore walls of the carbon material to become thinner and thinner, causing the previously formed micropores to continue to expand and transform into mesopores and macropores. In comparative example B-3, at a higher heating rate (8°C / min), a negative electrode material with a higher macropore area and volume ratio was prepared, which reduced the initial efficiency, expansion performance and cycle performance of the negative electrode material.

[0334] 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 carbon matrix and an active material, wherein the carbon matrix has pores, the active material is at least partially distributed in the pores, and the area ratio of pores with a pore diameter greater than 50 nm in any cross section of the negative electrode material is α, satisfying: α≤10%; Wherein, the α is obtained by the following test method: in the figure shown by SEM section processing of a single negative electrode material particle, select any a×b area, wherein a=1μm~10μm, b=1μm~10μm, the sum of the cross-sectional areas of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle in the region is recorded as S0, the cross-sectional area of ​​a single negative electrode material particle in the region is recorded as S, and the area ratio of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle is defined as α', α'=S0 / S, and α is the arithmetic mean of the α' values ​​of at least 10 negative electrode material particles.

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 (8): (1) The pore volume of the negative electrode material is less than or equal to 0.1 cm 3 / g; (2) The pore volume of the negative electrode material is 0.001 cm 3 / g to 0.1cm 3 / g; (3) The area of ​​pores with a pore diameter of 500 nm or more in the cross section of the negative electrode material accounts for less than or equal to 5%; (4) The pores of the negative electrode material include micropores, the volume proportion of the micropores in the pores is less than or equal to 10%, and the pore diameter of the micropores is less than or equal to 2 nm; (5) The pores of the negative electrode material include mesopores, the volume proportion of the mesopores in the pores is greater than or equal to 80%, and the pore diameter of the mesopores is greater than 2 nm and less than or equal to 50 nm; (6) The pores of the negative electrode material include macropores, the volume proportion of the macropores in the pores is less than or equal to 20%, and the pore diameter of the macropores is greater than 50 nm; (7) The average pore size of the negative electrode material is 0.45 nm to 50 nm; (8) The pore volume of the negative electrode material is smaller than the pore volume of the carbon matrix.

3. The negative electrode material according to claim 1, characterized in that The active substance includes at least one of the following characteristics (1) to (5): (1) The active material comprises a single substance and / or a compound of at least one element selected from Si, Sn, Ge, Pb, Ag, Mg, Zn, Ga, In, Sb, and Bi; (2) The active material includes a silicon-based active material; (3) The active material includes a silicon-based active material, and the silicon-based active material includes at least one of crystalline silicon, amorphous silicon, a composite of crystalline silicon and amorphous silicon, silicon oxide, silicon alloy, and silicate; (4) The active material includes a silicon-based active material, and the median particle size of the silicon-based active material is 1 nm to 500 nm; (5) The average particle size of the active material is 0.1 nm to 50 nm.

4. 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 (3): (1) The oil absorption value dbq2 of the carbon matrix satisfies: 120 ml / 100 g ≤ dbq2 ≤ 200 ml / 100 g, the oil absorption value dpq1 of the negative electrode material satisfies: 30 ml / 100 g ≤ dpq1 ≤ 80 ml / 100 g, and (dbq2-dbq1) / dbq1>0.5; (2) The specific surface area of ​​the carbon matrix is ​​S1m 2 / g, the pore volume of the carbon matrix is ​​P1cm 3 / g, the specific surface area of ​​the negative electrode material is S2m 2 / g, the pore volume of the negative electrode material is P2cm 3 / g; S1, P1cm 3 / g, S2m 2 / g, P2cm 3 / g satisfies the following relationship: C1=S1 / (P1*100), 10≤C1≤25， C2=S2 / (P2*100), 1≤C2≤50； (3) the ratio of the volume of nitrogen adsorbed by the carbon matrix at 90% partial pressure to the volume of nitrogen adsorbed at 10% partial pressure is A, and the ratio of the volume of nitrogen adsorbed by the negative electrode material at 90% partial pressure to the volume of nitrogen adsorbed at 10% partial pressure is B, Among them, 1≤A≤1.9, 1.3≤B≤2.5, and B / A≥1.

5. The negative electrode material according to claim 1, characterized in that The carbon matrix includes at least one of the following features (1) to (3): (1) The carbon matrix includes at least one of activated carbon, activated carbon fiber, carbon black, capacitor carbon, mesoporous carbon, carbon nanotubes and carbon molecular sieves, artificial graphite, natural graphite, amorphous carbon, mesophase carbon microbeads, carbon nanofibers and graphene; (2) The median particle size of the carbon matrix is ​​less than or equal to 15 μm; (3) The specific surface area of ​​the carbon matrix is ​​500 m 2 / g to 2500m 2 / g.

6. The negative electrode material according to claim 1, characterized in that The carbon matrix includes at least one of the following features (1) to (2): (1) The pore volume of the carbon matrix is ​​0.3 cm 3 / g to 2cm 3 / g; (2) The pores in the carbon matrix include micropores, the volume proportion of the micropores in the total pore volume is greater than or equal to 70%, and the pore diameter of the micropores is less than or equal to 2 nm.

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 (2): (1) The specific surface area of ​​the negative electrode material is 0.5 m 2 / g to 10m 2 / g; (2) The specific surface area of ​​the negative electrode material is less than or equal to 5 m 2 / g.

8. 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 (3): (1) The median particle size D50 of the negative electrode material is less than or equal to 15 μm; (2) The median particle size D50 of the negative electrode material is 5 μm to 20 μm; (3) The particle size distribution (D90-D10) / D50 of the negative electrode material is 0.9 to 5.

9. 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 compaction density of the negative electrode material under a pressure of 1T is 0.8 g / cm 3 Up to 1.3g / cm 3 ; (2) The tap density of the negative electrode material after 3000 vibrations is 0.5 g / cm 3 Up to 1.5g / cm 3 .

10. 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 powder conductivity of the negative electrode material under a pressure of 20 kN is 0.5 S / cm to 2 S / cm; (2) The average gas production of the negative electrode material at 25° C. over 7 days is less than or equal to 1 mL / g.

11. 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 mass proportion of the carbon matrix in the negative electrode material is 20% to 60%; (2) The mass proportion of carbon element in the negative electrode material is 40% to 60%; (3) The mass proportion of the active material in the negative electrode material is 40% to 80%; (4) The mass percentage of silicon in the negative electrode material is 37% to 55%.

12. 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 carbon matrix, and 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; preferably, the conductive polymer includes at least one of polyaniline, polyacetylene, polypyrrole, polythiophene, poly-3-hexylthiophene, poly(p-phenylene vinylene), polypyridine and poly(phenylene vinylene); (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 3000 nm.

13. A negative electrode plate, characterized in that: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material distributed on one side of the negative electrode current collector, and the negative electrode active material comprises the negative electrode material according to any one of claims 1 to 12.

14. The negative electrode sheet according to claim 13, characterized in that: The negative electrode plate includes at least one of the following features (1) to (2): (1) The critical withstand pressure P of the negative electrode plate is greater than or equal to 100 MPa; (2) The compaction density of the negative electrode sheet is 1.3 g / cm 3 ~1.9g / cm 3 ; The critical withstand pressure P of the negative electrode plate is obtained by the following test method: the thickness of the negative electrode plate is 60 μm to 70 μm, and a cross section of a single negative electrode plate is observed using an electron scanning microscope SEM. The minimum pressure corresponding to the crushing of the negative electrode material particles is P.

15. A battery, characterized in that: The battery comprises the negative electrode sheet according to claim 13 or 14.

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