Porous matrix, negative electrode material and battery

Abstract

The present invention relates to the technical field of negative electrode materials, and particularly relates to a porous matrix, a negative electrode material and a battery. In the porous matrix, the volume ratio of pores having a pore diameter in the range of 2-3 nm in the total pore volume is greater than or equal to 10%, and the volume ratio of pores having a pore diameter of 2 nm or below in the total pore volume is greater than or equal to 70%. A skeleton structure of the porous matrix can provide dispersion space for silicon particles, such that the silicon particles are compounded in the pores of the porous matrix; and by optimizing the pore size distribution range of the pores of the porous matrix, porous matrix particles can improve the uniformity of the compounded silicon particles during the compounding process of the silicon particles, and the phenomenon of an excessive high local silicon content is reduced. Furthermore, the pores of the porous matrix can reserve space for the volume expansion generated by the silicon particles during an alloying process, thereby mitigating the overlarge local volume change, which is caused by a non-uniform silicon content during a cycling process, of the negative electrode material compounded by the porous matrix and the silicon particles.

Description

Porous matrix, negative electrode material and battery

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on September 28, 2023, with application number 2023112878355 and application name “Negative electrode material and preparation method thereof, lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of negative electrode materials, and in particular to porous substrates, negative electrode materials and batteries. Background Art

[0003] Currently, the anode material for mature commercial lithium-ion batteries is primarily graphite, but its theoretical capacity is only 372 mAh / g, which cannot meet the demand for high-energy-density batteries. Silicon, with its higher theoretical capacity (approximately 3579 mAh / g) and abundant reserves, is widely considered the next-generation anode material for lithium-ion batteries.

[0004] Silicon materials are divided into crystalline silicon and silicon particles. The charge and discharge process of crystalline silicon is slow, and it will pulverize and fall off due to volume expansion during the cycle; while the volume expansion effect of silicon particles is relatively low, and both mechanical stability and electrochemical stability are relatively high. Studies have found that during the lithiation process, the particle size limit of crystalline nano-silicon particles is 150nm, while the particle size limit of amorphous nano-silicon materials is 870nm. Silicon particles undergo smaller physical changes during the first lithiation process than crystalline silicon materials. Existing studies have found through calculations that silicon particle materials have some paths with smaller energy barriers (<0.5eV) than crystalline silicon during the lithiation process. Therefore, silicon particle materials are important next-generation lithium-ion battery negative electrode materials.

[0005] However, silicon particles are typically prepared using vapor deposition, which is costly and energy-intensive, with low raw material utilization and yield, making mass production difficult. Furthermore, silicon particles typically have a nanostructure and a large surface area, making them difficult to disperse. The industry typically uses grinding or the addition of dispersants for dispersion, but these methods are inefficient and prone to environmental pollution, significantly limiting their application as negative electrode materials for lithium batteries. Therefore, dispersing silicon particles for practical application in negative electrode materials remains a challenge.

[0006] Summary of the Invention

[0007] The embodiments of the present application provide a porous matrix, a negative electrode material, and a battery. The porous matrix can solve the technical problem that silicon particles are difficult to be evenly distributed in the negative electrode material.

[0008] In a first aspect, an embodiment of the present application provides a porous matrix, in which the volume proportion of pores with a pore diameter in the range of 2nm to 3nm in the total pore volume is ≥10%, and the volume proportion of pores with a pore diameter below 2nm in the total pore volume is ≥70%.

[0009] In some embodiments, the particle size distribution of the porous matrix satisfies: 0.9≤(D90-D10) / D50≤1.8.

[0010] In some embodiments, the average particle size of the porous matrix satisfies: 2 μm≤D50≤30 μm.

[0011] In some embodiments, the pores of the porous matrix further comprise macropores.

[0012] In some embodiments, the total pore volume in the porous matrix is ​​0.3 cm 3 / g~1.1cm 3 / g.

[0013] In some embodiments, in the porous matrix, the volume proportion of pores with a pore diameter of less than 5 nm in the total pore volume is ≥90%.

[0014] In some embodiments, the specific surface area of ​​the porous matrix is ​​1000 m 2 / g~2200m 2 / g.

[0015] In the second aspect, the present application also proposes a negative electrode material, which includes an active substance, and the active substance includes a porous matrix and silicon particles, at least some of the silicon particles are distributed in the pores of the porous matrix; the negative electrode material forms pores after removing the silicon particles, and in the pores formed by removing the silicon particles from the negative electrode material, the volume proportion of pores with a pore diameter in the range of 2nm to 3nm in the total pore volume is greater than 10%, and the volume proportion of pores with a pore diameter below 2nm in the total pore volume is ≥70%.

[0016] In some embodiments, the negative electrode material contains trace metal elements with a mass percentage of ≤200 ppm.

[0017] In some embodiments, the negative electrode material contains trace metal elements, and the trace metal elements include at least one of Fe, Co, Ni, Cr, Zn, Cu and Al.

[0018] In some embodiments, the negative electrode material contains hydrogen element, and the mass proportion of the hydrogen element is 0.01% to 0.5%.

[0019] In some embodiments, the negative electrode material contains oxygen, and the mass proportion of the oxygen is 0.01% to 2%.

[0020] In some embodiments, the negative electrode material contains nitrogen, and the mass proportion of the nitrogen is 0.01% to 0.5%.

[0021] In some embodiments, the negative electrode material further includes a coating layer, and the coating layer is at least partially located on the surface of the active material.

[0022] In some embodiments, the material of the coating layer includes a carbon material, and the carbon material includes at least one of graphite carbon and amorphous carbon.

[0023] In some embodiments, the material of the coating layer includes a carbon material and a doping element, and the doping element includes at least one of nitrogen, phosphorus, sulfur, and boron.

[0024] In some embodiments, the mass proportion of silicon element in the silicon particles in the negative electrode material is 20% to 55%.

[0025] In some embodiments, the median particle size of the negative electrode material is 5 μm to 20 μm.

[0026] In some embodiments, the specific surface area of ​​the negative electrode material is 5.0 m 2 / g~100m 2 / g.

[0027] In some embodiments, the tap density of the negative electrode material is 0.5 g / cm 3 ~1.5g / cm 3 .

[0028] In some embodiments, the total pore volume of the negative electrode material is 0.001 cm 3 / g~0.1cm 3 / g.

[0029] In some embodiments, the average pore diameter of the pores in the negative electrode material is 5 nm to 50 nm.

[0030] In some embodiments, the 24-hour gas production of the negative electrode material is ≤1 mL / g.

[0031] In some embodiments, the powder conductivity of the negative electrode material under a pressure of 20 kN is 0.5 S / cm to 2 S / cm.

[0032] In some embodiments, the tap density of the negative electrode material is 0.5 g / cm 3 ~1.5g / cm 3 .

[0033] In a third aspect, the present application further proposes a battery comprising the porous matrix described in the first aspect or the negative electrode material described in the second aspect.

[0034] Compared with the prior art, this application has the following beneficial effects:

[0035] The skeleton structure of the porous matrix provided in this application can provide dispersion space for silicon particles, allowing the silicon particles to be composited within the pores of the porous matrix. By optimizing the pore size distribution range of the porous matrix, the porous matrix particles can improve the uniformity of the composite silicon particles during the composite silicon particle process, reducing the phenomenon of excessive local silicon content. Furthermore, the pores of the porous matrix can reserve space for the volume expansion of silicon particles during the alloying process, mitigating the excessive local volume changes caused by uneven silicon content during the cycling of the negative electrode material composited with the porous matrix and silicon particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions of the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0037] FIG1 is an electron microscope schematic diagram of the negative electrode material provided in Example 1 of the present application. DETAILED DESCRIPTION

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] In a first aspect, an embodiment of the present application provides a porous matrix, in which the volume proportion of pores with a pore diameter in the range of 2nm to 3nm in the total pore volume is ≥10%, and the volume proportion of pores with a pore diameter below 2nm in the total pore volume is ≥70%.

[0043] The skeleton structure of the porous matrix provided in this application can provide dispersion space for silicon particles, allowing the silicon particles to be composited within the pores of the porous matrix. By optimizing the pore size distribution range of the porous matrix, the porous matrix particles can improve the uniformity of the composite silicon particles during the composite silicon particle process, reducing the phenomenon of excessive local silicon content. Furthermore, the pores of the porous matrix can reserve space for the volume expansion of silicon particles during the alloying process, mitigating the excessive local volume changes caused by uneven silicon content during the cycling of the negative electrode material composited with the porous matrix and silicon particles.

[0044] The porous matrix includes at least one of porous carbon, metal oxides, silicides, silicates, phosphates, titanates and aluminum borates.

[0045] In some embodiments, the particle size distribution of the porous matrix satisfies: 0.9≤(D90-D10) / D50≤1.8; specifically, (D90-D10) / D50 can be 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 or 1.8, and of course it can also be other values ​​within the above range. Among them, (D90-D10) / D50 reflects the particle size distribution span of the porous matrix. When the particle size distribution span is too small, the screening and preparation costs of the porous matrix are high. When the particle size distribution span is too large, it means that the particle size distribution of the porous matrix is ​​wide, and particles of different sizes will lead to uneven deposition of silicon, resulting in excessively high local silicon content, and uneven volume changes of the negative electrode material composited with the porous matrix and silicon particles during the cycle.

[0046] The negative electrode material obtained by compounding the porous matrix with silicon particles can effectively solve the expansion problem of the silicon material during the cycle and can also increase the volume capacity of the negative electrode material.

[0047] In some embodiments, the total pore volume of all pores in the porous matrix is ​​0.3 cm 3 / g~1.1cm 3 / g, specifically 0.3cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g or 1.1cm3 / g, etc., and of course, other values ​​within the above range can also be used, which is not limited here. In this application, the volume distribution of macropores, mesopores and micropores is not limited, and the pore volume of the porous matrix can be controlled to remain within the above range.

[0048] In some embodiments, the average pore size of the porous matrix is ​​1 nm to 20 nm; specifically, it can be 1 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm and 20 nm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0049] In some embodiments, the pores of the porous matrix further comprise macropores.

[0050] It can be understood that macropores are pores with a pore diameter greater than 50 nm, mesopores are pores with a pore diameter between 2 nm and 50 nm, and micropores are pores with a pore diameter less than 2 nm.

[0051] In some embodiments, in the porous matrix, the volume proportion of pores with a pore diameter of less than 5 nm in the total pore volume is ≥90%.

[0052] The porous matrix of the present application includes abundant micropores and mesopores, which allows the porous matrix particles to improve the uniformity of the composite silicon particles during the composite silicon particle process and reduce the phenomenon of excessive silicon content in some areas. In addition, the porous matrix can provide sufficient space to alleviate the volume expansion of silicon particles, reserving space for the volume expansion of silicon during the alloying process, thereby improving the cycle performance of batteries prepared from negative electrode materials composed of porous matrix and silicon particles.

[0053] In some embodiments, the specific surface area of ​​the porous matrix is ​​1000 m 2 / g~2000m 2 / g, specifically 1000m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1800m 2 / g、1900m 2 / g and 2000m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0054] In some embodiments, the average particle size of the porous matrix is: 2μm≤D50≤30μm, specifically 2μm, 5μm, 10μm, 15μm, 20μm, 25μm and 30μm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0055] In a second aspect, an embodiment of the present application provides a negative electrode material, which includes an active substance, the active substance including a porous matrix and silicon particles, at least some of the silicon particles are distributed in the pores of the porous matrix; the negative electrode material forms pores after the silicon particles are removed from the negative electrode material, and in the pores formed by removing the silicon particles from the negative electrode material, the volume proportion of pores with a pore diameter in the range of 2nm to 3nm in the total pore volume is greater than 10%, and the volume proportion of pores with a pore diameter below 2nm in the total pore volume is ≥70%.

[0056] In this application, the negative electrode material is added to concentrated nitric acid with a concentration of 1M and soaked for 4 hours. Then, a 20% mass fraction HF acid solution is dripped into the negative electrode material drop by drop, which will produce yellow smoke. The dripping is repeated many times until no yellow smoke is produced in the solution. Finally, the residue is digested with concentrated nitric acid with a concentration of 1M, and then washed and dried to obtain the negative electrode material after removing the silicon particles.

[0057] The active material of the negative electrode material provided in the present application includes a porous matrix and silicon particles, wherein the skeleton structure of the porous matrix can provide a dispersion space for the silicon particles, so that the silicon particles are compounded in the pores of the porous matrix; by optimizing the pore size distribution range of the pores of the porous matrix, the porous matrix particles can improve the uniformity of the composite silicon particles in the process of composite silicon particles, and reduce the phenomenon of excessive local silicon content. Furthermore, the pores of the porous matrix can reserve space for the volume expansion of the silicon particles during the alloying process, slowing down the local volume change of the negative electrode material due to the uneven silicon content during the cycle; furthermore, the silicon particles are dispersed in the pores of the porous matrix, which can also enhance the structural stability of the negative electrode material and greatly improve the first effect and capacity of the negative electrode material. In the present application, the combination of silicon particles and the porous matrix has a synergistic effect. The porous matrix provides a dispersed space for the silicon particles and can slow down the uneven volume change caused by the alloy reaction between the silicon material and lithium. The presence of silicon particles can further optimize the electrochemical properties of the porous matrix.

[0058] In some embodiments, the average particle size of the silicon particles is ≤5 nm, that is, the nano-scale silicon particles are located in the pores of the porous matrix. The nano-scale silicon particles can achieve relatively uniform volume expansion during the charge and discharge process, which can reduce the breakage and pulverization of the negative electrode material and improve the particle structure stability of the negative electrode material.

[0059] In some embodiments, the negative electrode material includes trace metal elements with a mass ratio of ≤200ppm, which can be 200ppm, 180ppm, 150ppm, 120ppm, 100ppm, 80ppm, 60ppm, 50ppm or 10ppm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0060] In some embodiments, the negative electrode material includes trace metal elements, and the trace metal elements include at least one of Fe, Co, Ni, Cr, Zn, Cu and Al.

[0061] In some embodiments, the mass proportion of hydrogen in the negative electrode material is 0.01% to 0.5%, the mass proportion of oxygen is 0.01% to 1%, and the mass proportion of nitrogen is 0.01% to 0.5%.

[0062] In some embodiments, the active material further comprises silicon particles located on the surface of the porous matrix. Specifically, the silicon particles fill the pores of the porous matrix and are also distributed on the surface of the porous matrix, or located between the porous matrix particles. Some of the silicon particles are located on the surface of the porous matrix, forming a silicon particle layer.

[0063] In some embodiments, the negative electrode material includes a coating layer located on at least a portion of the surface of the active material. The provision of the coating layer can, on the one hand, effectively reduce the direct contact between the more active nano-silicon particles and the water in the slurry, reduce the gas production problem of the negative electrode material during the aqueous slurry process, and reduce the electrolyte entering the negative electrode material to cause side reactions leading to a decrease in the first coulombic efficiency and specific capacity. On the other hand, it can alleviate the volume expansion of the active material, reduce the volume expansion of the entire negative electrode material, reduce the swelling of the electrode sheet prepared from the negative electrode material, and improve the rate performance of the negative electrode material.

[0064] In some embodiments, the coating layer comprises a carbon material. It is understood that when the coating layer comprises a carbon material, side reactions between the electrolyte and the silicon particles can be reduced, further buffering the volume expansion stress of the silicon particles, thereby enabling the negative electrode material to have higher cycle stability and expansion resistance.

[0065] In some embodiments, the carbon material includes at least one of graphene and amorphous carbon. The amorphous carbon can be hard carbon and / or soft carbon.

[0066] In some embodiments, the material of the coating layer includes a carbon material and a doping element, and the doping element includes at least one of nitrogen, phosphorus, sulfur, and boron.

[0067] In some embodiments, the thickness of the coating layer is 10 nm to 500 nm; specifically, it can be 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm, etc. Of course, it can also be other values ​​within the above range, which is not limited here. It can be understood that the coating layer can reduce the contact between the active material and the electrolyte, reduce the formation of the passivation film on the surface of the negative electrode material, and improve the reversible capacity of the battery prepared with the negative electrode material. Controlling the thickness of the coating layer within the above range can increase the conductivity of the negative electrode material, reduce the volume expansion of the negative electrode material, and at the same time help to improve the lithium ion transmission efficiency, which is beneficial to improve the high-rate charge and discharge performance and cycle performance of the negative electrode material.

[0068] In some embodiments, the specific surface area of ​​the negative electrode material is 5.0 m 2 / g~100m 2 / g, specifically 5.0m 2 / g, 8.0m 2 / g, 10.5m 2 / g、12m 2 / g、15m 2 / g, 20m 2 / g、30m 2 / g, 50m 2 / g、80m 2 / g or 100m 2 / g, etc., and of course, other values ​​within the above range can also be used, which is not limited here. It can be understood that controlling the specific surface area of ​​the negative electrode material within the above range can slow down the volume expansion of the negative electrode material, which is conducive to improving the cycle performance of the negative electrode material.

[0069] In some embodiments, the median particle size of the negative electrode material is 5 μm to 20 μm, specifically 5 μm, 8 μm, 9 μm, 10 μm, 12 μm, 15 μm, 18 μm, 19 μm, and 20 μm, etc. Of course, it can also be other values ​​within the above range, which is not limited here. Preferably, the median particle size of the negative electrode material is 8 μm to 12 μm. It can be understood that controlling the median particle size 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 tap density of the negative electrode material is 0.5 g / cm 3 ~1.5g / cm 3 , specifically 0.5g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.2g / cm3 and 1.5g / cm 3 Of course, it can also be other values ​​within the above range, which is not limited here. Controlling the tap density of the material within the above range can increase the energy density of the negative electrode material.

[0071] In some embodiments, the total pore volume of the negative electrode material is 0.001 cm 3 / g~0.1cm 3 / g, specifically 0.001cm 3 / g, 0.01cm 3 / g, 0.02cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.08cm 3 / g, 0.09cm 3 / g or 0.1cm 3 / g, etc., and of course other values ​​within the above range are also possible and are not limited here. The total pore volume of the negative electrode material within the above range can not only increase the specific capacity of the negative electrode material, but also ensure that the negative electrode material can retain an appropriate amount of pores to alleviate the volume expansion of silicon particles caused by the lithium insertion and extraction process, which is beneficial to improving the cycle performance of batteries prepared with the negative electrode material.

[0072] In some embodiments, the mass content of silicon in the silicon particles in the negative electrode material is 20% to 55%, specifically 20%, 25%, 28%, 30%, 32%, 34%, 35%, 40%, 45%, 50% or 55%, etc., and of course other values ​​within the above range are also possible, and are not limited here. By controlling the content of silicon particles, the first coulombic efficiency of the negative electrode material can be improved and the volume expansion of the negative electrode material can be alleviated. Preferably, the mass proportion of silicon particles in the negative electrode material is 45% to 55%.

[0073] In some embodiments, the silicon particles include at least one of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and a composite of crystalline silicon and amorphous silicon; specifically, the silicon alloy can 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.

[0074] In some embodiments, the silicon particles include amorphous silicon and / or crystalline silicon; preferably, the silicon particles include amorphous silicon, which expands isotropically during the lithium insertion process, which can reduce the collapse of the pore structure, inhibit the rapid decay of the specific capacity, and improve the lithium insertion cycle performance of the negative electrode material.

[0075] In some embodiments, the negative electrode material has pores, and the average pore diameter of the pores in the negative electrode material is 5 nm to 50 nm, specifically 5 nm, 10 nm, 15 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm and 50 nm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0076] In some embodiments, the 24-hour gas production of the negative electrode material is ≤1 mL / g.

[0077] In some embodiments, the powder conductivity of the negative electrode material under a pressure of 20 kN is 0.5 S / cm to 2 S / cm, specifically 0.5 S / cm, 0.8 S / cm, 1.0 S / cm, 1.2 S / cm, 1.5 S / cm, 1.6 S / cm, 1.8 S / cm, 1.9 S / cm or 2.0 S / cm, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0078] The present application also provides a method for preparing the above-mentioned negative electrode material, comprising the following steps:

[0079] S100, preparing a porous matrix having pores, specifically comprising the following steps:

[0080] (1) Phenolic resin, polyvinyl chloride copolymer, acrylonitrile copolymer, polystyrene copolymer, bio-based resin are selected as precursors

[0081] (2) Regulating the precursor structure through the pre-oxidation process. During the pre-oxidation process, the precursor will undergo a series of reactions such as cyclization, cross-linking, dehydrogenation, and oxidation, and undergo structural evolution, which can provide better strength and thermal stability after the subsequent carbonization process. This process is mainly achieved by adjusting parameters such as oxygen concentration, oxidation temperature, duration, and heating rate.

[0082] (3) Under oxygen-free conditions, a protective gas is introduced and the temperature is adjusted to 600-900 °C without destroying the precursor structure. The sp of the porous carbon is regulated by temperature changes. 2 Hybridize carbon content and remove other impurities besides carbon element.

[0083] (4) The pore size and volume of porous carbon can be controlled by combining the characteristics of different precursor polymers and activators. According to the different performance requirements of porous carbon materials, activators such as alkali, water vapor, CO2, argon, etc. can be selected, and the process parameters such as the amount of activator added, duration, pressure environment, material rotation rate, etc. can be adjusted to prepare porous carbon materials with special pore structure requirements.

[0084] (5) Using an acidic substance such as hydrochloric acid to remove magnetic substances from the porous carbon material to obtain a porous carbon material.

[0085] In the porous matrix, the volume proportion of pores with a pore diameter in the range of 2 nm to 3 nm in the total pore volume is ≥10%, and the volume proportion of pores with a pore diameter below 2 nm in the total pore volume is ≥70%;

[0086] S200 , depositing silicon particles in the pores of the porous matrix to obtain an active material, wherein the negative electrode material includes the active material.

[0087] The present application provides a method for preparing a negative electrode material, which prepares an active substance containing silicon particles and a porous matrix, wherein the silicon particles are filled in the pores of the porous matrix. By optimizing the pore size distribution range of the pores of the porous matrix, the particle size of the deposited silicon particles can be effectively controlled. The pores of the porous matrix can reserve space for the volume expansion of silicon generated during the alloying process, thereby mitigating the adverse effects of the volume expansion of silicon particles during the cycle. Silicon particles with an amorphous structure are filled in the pores of the porous matrix to form a composite structure of a porous matrix-silicon particles, which can also enhance the structural stability of the negative electrode material and significantly improve the initial efficiency and capacity of the negative electrode material.

[0088] The preparation method of the present application is simple. By selecting a porous matrix with specific pores and specific sizes, the silicon particle composite process is precisely controlled so that the silicon particles are evenly dispersed and filled in the pores of the porous matrix, reducing the silicon particles deposited on the surface of the porous matrix. This can effectively reduce the volume expansion of the negative electrode material and further improve the rate performance, capacity and cycle performance of the negative electrode material.

[0089] The preparation method of the present application is described in detail below with reference to the examples:

[0090] Step S100 , preparing an active material containing silicon particles and a porous matrix having pores, wherein the silicon particles are distributed in the pores of the porous matrix.

[0091] In some embodiments, the particle size (D90-D10) / D50 of the porous matrix can specifically be 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 or 1.8, and of course can also be other values ​​within the above range. Among them, (D90-D10) / D50 reflects the particle size distribution span of the porous matrix. When the particle size distribution span is too small, the screening and preparation costs of the porous matrix are high. When the particle size distribution span is too large, it means that the particle size distribution of the porous matrix is ​​wide, and particles of different sizes will cause uneven deposition of silicon particles, thereby resulting in excessively high local silicon particle content, resulting in uneven volume changes of the negative electrode material during cycling.

[0092] In some embodiments, the total pore volume in the porous matrix is ​​0.3 cm 3 / g~1.1cm 3 / g, specifically 0.3cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g or 1.1cm 3 / g, etc., and of course, other values ​​within the above range can also be used, which is not limited here. In this application, the volume distribution of macropores, mesopores and micropores is not limited, and the pore volume of the porous matrix can be controlled to remain within the above range.

[0093] In some embodiments, the average pore size of the porous matrix is ​​1 nm to 20 nm; specifically, it can be 1 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm and 20 nm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0094] In some embodiments, the pores of the porous matrix further comprise macropores.

[0095] It can be understood that macropores are pores with a pore diameter greater than 50 nm, mesopores are pores with a pore diameter between 2 nm and 50 nm, and micropores are pores with a pore diameter less than 2 nm.

[0096] In some embodiments, in the porous matrix, the volume proportion of pores with a pore diameter of less than 5 nm in the total pore volume is ≥90%.

[0097] The pores of the porous matrix of the present application include abundant micropores and mesopores, which can effectively control the particle size of the silicon particles formed by deposition, so that the porous matrix can have enough space to alleviate the volume expansion of the silicon particles, and the silicon particles are filled in the pores, optimizing the pore distribution of the porous matrix. It can also reserve space for the volume expansion of silicon generated during the alloying process, and slow down the adverse effects of the volume expansion of silicon particles during the cycle process; the silicon particles are dispersed in the pores of the porous matrix, and can also effectively improve the first efficiency and capacity of the negative electrode material, stabilize the electrolyte interface, and make the negative electrode material have high first efficiency, high reversible capacity and expansion resistance.

[0098] In some embodiments, the specific surface area of ​​the porous matrix is ​​1000 m 2 / g~2000m 2 / g, specifically 1000m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1800m 2 / g、1900m 2 / g and 2000m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0099] In some embodiments, the negative electrode material includes trace metal elements with a mass ratio of ≤200ppm, which can be 200ppm, 180ppm, 150ppm, 120ppm, 100ppm, 80ppm, 60ppm, 50ppm or 10ppm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0100] In some embodiments, the negative electrode material includes trace metal elements, and the trace metal elements include at least one of Fe, Co, Ni, Cr, Zn, Cu and Al.

[0101] In some embodiments, the mass proportion of hydrogen in the negative electrode material is 0.01% to 0.5%, the mass proportion of oxygen is 0.01% to 1%, and the mass proportion of nitrogen is 0.01% to 0.5%.

[0102] In some embodiments, the mass percentage of silicon particles in the negative electrode material is 20% to 55%, and specifically can be 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 45%, 50%, 53%, or 55%, etc., and of course other values ​​within the above range are also possible and are not limited here. Preferably, the mass percentage of silicon particles in the negative electrode material is 45% to 55%.

[0103] The negative electrode material obtained by compounding the porous matrix with silicon particles can effectively solve the expansion problem of the silicon material during the cycle, maintain the stability of the battery material, and also increase the volume capacity of the negative electrode material.

[0104] In some embodiments, the average particle size of the silicon particles is ≤5 nm, that is, the nano-scale silicon particles are located in the pores of the porous matrix. The nano-scale silicon particles can achieve relatively uniform volume expansion during the charge and discharge process, which can reduce the breakage and pulverization of the negative electrode material and improve the particle structure stability of the negative electrode material.

[0105] In some embodiments, the average particle size of the active substance is 5 μm to 20 μm, specifically 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm and 20 μm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0106] In some embodiments, the step of preparing the active material containing silicon particles includes: introducing a silicon-containing gas source into the porous matrix under a protective gas to perform a vapor phase chemical deposition reaction.

[0107] Specifically, the porous substrate can be placed in the reaction chamber of a vapor phase chemical deposition reactor, the reaction chamber is purged with nitrogen several times to remove impurities, a protective gas is introduced, and then the temperature is increased at a heating rate of 10°C / min to 15°C / min until it reaches 400°C to 500°C and is kept warm for 2h to 6h, a silicon-containing gas source is introduced into the reaction chamber, the silicon-containing gas source decomposes in the pores of the porous substrate to form silicon particles, and the silicon particles are deposited in the pores and on the surface of the porous substrate.

[0108] In some embodiments, the silicon-containing source gas includes at least one of silane, disilane, trisilane, and tetrasilane.

[0109] In some embodiments, the volume ratio of the silicon-containing gas source to the protective gas is 1:(1-10), specifically 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0110] In some embodiments, the protective gas includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0111] In some embodiments, the flow rates of the silicon-containing source gas and the protective gas are between 100 sccm and 500 sccm, and may specifically be 100 sccm, 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm, or 500 sccm, etc., and other values ​​within the aforementioned ranges are also possible and are not limited herein. Preferably, the flow rates of the silicon-containing source gas and the protective gas are between 200 sccm and 300 sccm.

[0112] In some embodiments, a doping gas is introduced during the vapor phase chemical deposition reaction, and the doping gas includes at least one of ammonia and phosphine.

[0113] In some embodiments, the vapor chemical deposition reaction is carried out in a vapor deposition reactor, and the rotation speed of the vapor deposition reactor is 3r / min to 10r / min, specifically 3r / min, 5r / min, 6r / min, 7r / min, 8r / min or 10r / min, etc., which is not limited here.

[0114] In some embodiments, the temperature of the vapor phase chemical deposition reaction is 400°C to 500°C, and the holding time is 2h to 6h; the reaction temperature can be specifically 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 470°C, 480°C or 500°C, etc., and the holding time can be specifically 2h, 3h, 4h, 5h or 6h, etc., of course, it can also be other values ​​within the above range, which is not limited here.

[0115] In some embodiments, the gas pressure of the vapor phase chemical deposition reaction is 100 Torr to 760 Torr, specifically 100 Torr, 200 Torr, 300 Torr, 400 Torr, 450 Torr, 500 Torr, 600 Torr, 700 Torr or 760 Torr, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0116] In some embodiments, the step of preparing an active material containing silicon particles and a porous matrix includes: introducing a silicon-containing gas source into the porous matrix under a protective gas to carry out a vapor phase chemical deposition reaction, wherein at least part of the silicon particles formed by decomposition of the silicon-containing gas source are filled in the pores of the porous matrix.

[0117] In some embodiments, the step of preparing an active material containing silicon particles and a porous matrix includes: dispersing the porous matrix, silicon particles or a silicon particle precursor in a solvent, mixing and then removing the solvent to obtain the active material.

[0118] It is understood that the porous matrix can be infiltrated with silicon particles or silicon particle precursors into the pores of the porous matrix using a suspension infiltration method to improve the composite efficiency and uniformity of the two. Specifically, the solution can be infiltrated into the pores of the porous matrix under normal pressure, pressure, or vacuum, and then the solvent can be evaporated to convert the precursor into silicon particle particles. The above steps can be repeated to increase the content of the introduced silicon particle material.

[0119] In some embodiments, the silicon particles can be prepared by vapor deposition, chemical reduction, or grinding.

[0120] In some embodiments, the silicon particle precursor includes at least one of monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0121] In some embodiments, the solvent includes an organic solvent and / or an inorganic solvent.

[0122] In some embodiments, the solvent comprises water.

[0123] In some embodiments, the solvent includes at least one of a hydrocarbon organic solvent, an ether organic solvent, an alcohol organic solvent, an ester organic solvent, an organic solvent containing a nitrogen functional group, and an organic solvent containing a sulfur functional group.

[0124] In some embodiments, the hydrocarbon organic solvent can be a substituted or unsubstituted aliphatic hydrocarbon or aromatic hydrocarbon. For example, the substituted aliphatic hydrocarbon can be a chlorinated hydrocarbon, such as dichloromethane, chloroform, tetrachloromethane, 1,2-dichloroethane, and trichloroethylene; unsubstituted hydrocarbons, such as pentane, n-hexane, a mixture of hexane isomers, heptane, octane, washing gasoline, petroleum ether, benzene, toluene, and xylene.

[0125] In some embodiments, the ether organic solvent includes at least one of dioxane, pyrofuran, diethyl ether, diisopropyl ether, and diglyme.

[0126] In some embodiments, the alcohol organic solvent includes at least one of methanol, ethanol, propanol, butanol, and benzyl alcohol.

[0127] In some embodiments, the ester organic solvent includes at least one of ethyl acetate, butyl acetate, propyl propionate, ethyl butyrate, and ethyl isobutyrate.

[0128] In some embodiments, the organic solvent containing nitrogen functional groups includes at least one of nitrobenzene, dimethylformamide, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone.

[0129] In some embodiments, the organic solvent containing sulfur functional groups may be dimethyl sulfoxide.

[0130] In some embodiments, the solvent includes at least one of ethanol and 2-propanol, dimethylformamide, N-methyl-2-pyrrolidone, N-methyl-2-pyrrolidone, and monomethyl sulfoxide.

[0131] In some embodiments, mixing is performed at 760 Torr, negative pressure, or vacuum.

[0132] In some embodiments, the mixing pressure is 1 Torr to 760 Torr, and the mixing temperature is 300°C to 450°C; the mixing pressure can specifically be 100 Torr, 200 Torr, 300 Torr, 400 Torr, 450 Torr, 500 Torr, 600 Torr, 700 Torr or 760 Torr, etc., and the mixing temperature can specifically be 300°C, 320°C, 350°C, 360°C, 380°C, 400°C or 450°C, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0133] In some embodiments, the step of preparing the active material containing silicon particles and a porous matrix includes: dispersing the porous matrix, silicon particles or a silicon particle precursor in a solvent, and adding an oxygen-free polymer.

[0134] In some embodiments, the oxygen-free polymer includes at least one of polyacrylonitrile, polyolefin, polyethylene halide, polyvinyl aromatic compound or polyaromatic compound, asphalt, and tar. The addition of the oxygen-free polymer enables the porous matrix to be composited with the silicon particles while also achieving coating, requiring only subsequent carbonization.

[0135] The polyolefin may specifically be polyethylene or ethylene-propylene-diene terpolymer; the polyethylene halide may specifically be polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride or polytetrafluoroethylene.

[0136] The polyvinyl aromatic compound or polyaromatic compound may specifically be polyaniline, polystyrene, polybenzimidazole, or polypyrrole.

[0137] The asphalt or tar may specifically be petroleum asphalt or hard coal tar pitch.

[0138] In some embodiments, the oxygen-free polymer includes at least one of polyacrylonitrile, polyaniline, and polystyrene. In particular, the oxygen-free polymer is preferably polyacrylonitrile.

[0139] In some embodiments, the solvent removal method comprises at least one of spray drying, filtration, rotary evaporation and freeze drying.

[0140] In some embodiments, the temperature for removing the solvent is controlled to be 300°C to 1100°C, specifically 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C or 1100°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0141] In some embodiments, the method for removing the solvent includes spray drying, and the inlet temperature of the spray drying is controlled to be 100℃~400℃, the outlet temperature is 20℃~250℃, the pressure is 5Mpa~150Mpa, and the feed rate is 2m3 / h~200m3 / h.

[0142] The inlet temperature can be specifically 100℃, 150℃, 200℃, 250℃, 300℃, 350℃ or 400℃, etc., the outlet temperature can be specifically 20℃, 50℃, 80℃, 100℃, 150℃, 200℃ or 250℃, etc., and the pressure can be specifically 5Mpa, 10Mpa, 30Mpa, 50Mpa, 80Mpa, 100Mpa, 120Mpa or 150Mpa, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0143] Step S300 , coating the active material to obtain a negative electrode material.

[0144] In the above technical solution, the surface of the active material is coated to form a coating layer on the surface of the active material, which can further reduce the volume expansion of the negative electrode material, improve the conductivity of the negative electrode material, and reduce the side reactions caused by the electrolyte entering the interior of the negative electrode material, resulting in a decrease in the initial coulombic efficiency and specific capacity. While improving the conductivity of the material, it effectively reduces the occurrence of gas production of the negative electrode material during the large-scale water system slurry process, and reduces the swelling of the electrode sheet prepared from the negative electrode material.

[0145] In some embodiments, the active material is subjected to a carbon coating treatment, and the carbon coating treatment includes at least one of solid-phase carbon coating, liquid-phase carbon coating, and gas-phase carbon coating.

[0146] In some embodiments, the step of carbon-coating the active material includes: heating the active material, introducing a protective gas and a carbon source gas, and thermally cracking the carbon source gas to obtain a negative electrode material.

[0147] In some embodiments, the carbon source gas is a hydrocarbon.

[0148] In some embodiments, the carbon source gas includes at least one of methane, ethane, propane, ethylene, acetylene, gaseous benzene, gaseous toluene, gaseous xylene, gaseous ethanol, and gaseous acetone;

[0149] In some embodiments, the thermal cracking temperature is 500° C. to 700° C., and the holding time is 1 hour to 6 hours. The thermal cracking temperature can be 500° C., 510° C., 530° C., 550° C., 580° C., 600° C., 650° C., 680° C., or 700° C., and the holding time can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours, and other values ​​within the above range are also possible, and are not limited here.

[0150] In some embodiments, the reaction gas pressure of thermal cracking is 10 Torr to 760 Torr; specifically, it can be 100 Torr, 200 Torr, 300 Torr, 400 Torr, 450 Torr, 500 Torr, 600 Torr, 700 Torr or 760 Torr, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0151] In some embodiments, the volume ratio of the carbon source gas to the protective gas is 1:(1-10), specifically 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0152] In some embodiments, the flow rate of the carbon source gas is 100 sccm to 500 sccm; specifically, it can be 100 sccm, 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm or 500 sccm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0153] By controlling the volume ratio of the carbon source gas to the protective gas, the gas flow rate, the reaction pressure and other parameters, the porous matrix obtained by the cracking of the carbon source gas can be deposited on the surface of the active material to form a coating layer of appropriate thickness.

[0154] In some embodiments, the step of coating the active material includes: carbonizing the mixture obtained by mixing the active material with a solid carbon source to obtain the negative electrode material.

[0155] In some embodiments, the temperature of the carbonization treatment is 600°C to 1200°C, and the time of the carbonization treatment is 2h-20h; the temperature of the carbonization treatment can specifically be 600°C, 650°C, 700°C, 750°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C, etc., and the time of the carbonization treatment can specifically be 2h, 4h, 6h, 8h or 20h, etc., of course, it can also be other values ​​within the above range, which is not limited here.

[0156] In some embodiments, the solid carbon source includes at least one of sugars, esters, hydrocarbons, organic acids, and high molecular weight polymers;

[0157] In some embodiments, the solid carbon source includes at least one of polyvinyl chloride, polyvinyl butyral, polyacrylonitrile, polyacrylic acid, polyethylene glycol, polypyrrole, polyaniline, sucrose, glucose, maltose, citric acid, asphalt, furfural resin, epoxy resin and phenolic resin.

[0158] In some embodiments, the solid carbon source and the active material can be mixed by VC mixing, fusion, ball milling, three-dimensional mixing, fluidized bed mixing, etc.

[0159] In some embodiments, the equipment used for solid-phase carbon coating is at least one of a rotary kiln, a box furnace, a roller kiln, a tunnel kiln, and a push plate kiln.

[0160] In some embodiments, the mass ratio of the solid carbon source to the active substance is 5:(5-95), specifically 5:5, 5:10, 5:20, 5:30, 5:40, 5:50, 5:60, 5:70, 5:80 or 5:95, etc.

[0161] By controlling the mass ratio of the solid carbon source to the active material, the solid carbon source and the active material are fully mixed, which is conducive to the solid carbon source being evenly attached to the surface of the active material to form a coating layer of appropriate thickness.

[0162] In some embodiments, the step of coating the active material includes: carbonizing the mixture obtained by mixing the active material with a liquid carbon source to obtain the negative electrode material.

[0163] In some embodiments, the mass ratio of the liquid carbon source to the active substance is 5:(5-95), specifically 5:5, 5:10, 5:20, 5:30, 5:40, 5:50, 5:60, 5:70, 5:80 or 5:95, etc.

[0164] In some embodiments, the liquid carbon source comprises at least one of n-hexane, toluene, benzene, xylene, methanol, ethanol, propanol, butanol, pentanol, acetone, butanone, 2-pentanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and amyl acetate;

[0165] In some embodiments, the flow rate of the liquid carbon source is 1 mL / min to 200 mL / min; specifically, it can be 1 mL / min, 1 mL / min, 1 mL / min, 1 mL / min, 1 mL / min, 1 mL / min, 1 mL / min, or 1 mL / min.

[0166] In some embodiments, the temperature of the carbonization treatment is 600° C. to 1200° C., and the time of the carbonization treatment is 2 h to 20 h.

[0167] By controlling parameters such as the mass ratio of the liquid carbon source to the active material and the flow rate of the liquid carbon source, it is beneficial to fully mix the liquid carbon source and the active material, and to coat the surface of the active material with the liquid carbon source. In addition, part of the liquid carbon source penetrates into the active material to form a coating layer of appropriate thickness, which is beneficial to improving the rate performance of the negative electrode material and reducing the volume expansion of the negative electrode material.

[0168] In a third aspect, the present application provides a lithium-ion battery, which comprises the above-mentioned negative electrode material or the negative electrode material prepared by the above-mentioned preparation method.

[0169] 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.

[0170] 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.

[0171] Test method:

[0172] 1. Particle Size: Particle size is measured using Mastersizer 3000 laser diffraction technology. When a laser beam passes through a dispersed particle sample, the particle size measurement is completed by measuring the intensity of the scattered light. The data is then used to analyze and calculate the particle size distribution that forms the scattering spectrum. D50: The particle size corresponding to the cumulative particle size distribution percentage of a sample reaches 50%. Its physical meaning is that 50% of the particles have a particle size larger than this, and 50% of the particles have a particle size smaller than this. D50 is also called the median particle size. The D90 particle size, D50 particle size, and D10 particle size are the equivalent diameters of the largest particles in the distribution curve when the cumulative distribution reaches 90%, 50%, and 10%, respectively.

[0173] Observe the particles of the material through a field emission scanning electron microscope or a transmission electron microscope, randomly measure the particle size of 100 particles of the material using a scale, and take the average value of the particle size as the average particle size of the material. If this method is used for testing, the D90 particle size, D50 particle size, and D10 particle size are the equivalent diameters of the largest particles when the cumulative distribution in the distribution curve is 90%, 50%, and 10%, respectively.

[0174] 2. Specific surface area: The specific surface area was measured using a Micromeritics TriStar 3000 specific surface area and pore size analyzer (USA).

[0175] 3. Tap density: Use a vibrator to weigh a certain amount of sample and vibrate 3000 times at 300 times / min to test the tap density.

[0176] 4. SEM test: Scanning electron microscopy characterization was performed on a transmission electron microscope with an operating voltage of 200 kV to observe the structure of the negative electrode material.

[0177] 5. Coating thickness: The material is sectioned using a FIB-SEM device, and the average coating thickness is measured in the SEM.

[0178] 6. Powder Conductivity: The volume resistivity of the negative electrode material powder is measured using the four-probe method. The instrument measures the resistance of the powder under five pressure points: 4, 8, 12, 16, and 20 kN. The computer then automatically calculates the conductivity and resistivity of the negative electrode material powder.

[0179] 7. Characterization of silicon particles in the negative electrode material: The diffraction peaks were measured using an X-ray diffractometer (XRD) to confirm the type of silicon. The characteristic peak at 2θ = 28.4° was the characteristic peak of silicon particles.

[0180] 8. Test of silicon content in negative electrode material:

[0181] Use a box-type atmosphere furnace (brand: Nanyang Xinyu, model: SA2-9-17TP) to burn in an oxygen atmosphere, so that the silicon and silicon oxide in the sample react to form silicon dioxide. After the carbon is burned, it is converted into carbon dioxide and discharged. The silicon content is calculated by weighing.

[0182] 9. Average pore size of porous matrix and negative electrode material: the average pore size calculated from the total pore volume of the material and the cumulative total pore surface area by BJH (Barrett-Joyner-Halenda) adsorption.

[0183] 10. The pore volume of a porous matrix or anode material refers to the total volume of pores per unit mass of the porous matrix or anode material. The pore volume of a porous matrix can be measured by gas adsorption measurements. Nitrogen adsorption is a technique for characterizing the porosity and pore size distribution of a material by condensing a gas in the pores of a solid. As the pressure increases, the gas first condenses in the pores with the smallest diameter, and the pressure increases until a saturation point is reached, at which all pores are filled with liquid. The nitrogen pressure is then gradually reduced to evaporate the liquid from the system. Analysis of the adsorption and desorption isotherms makes it possible to determine the pore volume and pore size distribution, as well as the contribution of the respective pore volumes of micropores, mesopores and macropores to the total pore volume.

[0184] 11. Gas production test method:

[0185] The anode material was slurried with sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive graphite (KS-6), and carbon black (SP) in a ratio of 92:2:2:2:2. The slurry was then placed into an aluminum-plastic film bag, and the slurry mass was recorded. The bag was then sealed to form a sealed aluminum-plastic film bag. The volume of gas generated was measured by fixing the sealed aluminum-plastic film bag to the bottom of a container and completely immersing it in water. The volume of the aluminum-plastic film bag was recorded. After 24 hours, the volume of water discharged from the aluminum-plastic film bag was again recorded. The gas generation of the silicon anode material was calculated based on the volume change of the aluminum-plastic film bag (unit: ml / g).

[0186] 12. Electrical performance test:

[0187] The negative electrode material was mixed with sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive graphite (KS-6) and carbon black (SP) in a ratio of 92:2:2:2:2 to prepare a slurry, uniformly coated on copper foil and dried to form a negative electrode sheet, which was assembled into a button battery in an argon atmosphere glove box. The separator used was a polypropylene microporous membrane, the electrolyte used was 1 mol / L lithium hexafluorophosphate (the solvent was a mixed slurry of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate), and the counter electrode used was a metal lithium sheet.

[0188] The negative electrode materials prepared in the examples and comparative examples were prepared into batteries, and a discharge specific capacity test was performed on a Blue Power CT2001A battery testing system. The ratio of the amount of electricity discharged in one hour to the battery capacity was the discharge specific capacity.

[0189] Batteries made from the silicon-carbon composite materials prepared in the Examples and Comparative Examples were tested for initial coulombic efficiency using a Blue Power CT2001A battery testing system at a charge and discharge current of 0.05C. The measured initial coulombic efficiency is the average of 3-5 button cells for each material.

[0190] Example 1

[0191] A method for preparing a negative electrode material comprises the following steps:

[0192] (1) A porous substrate (No. 1, see Table 1 for specific parameters) was selected and placed in a chemical vapor deposition reaction chamber. The reaction chamber was repeatedly purged with nitrogen for 3-5 times, and then the nitrogen was turned off and argon gas was introduced at a flow rate of 400 sccm. The temperature was then raised to 450°C at a heating rate of 10°C / min. After being kept at this temperature for 1 hour, the argon gas was turned off and high-purity silane gas (99.9999%) was introduced at a flow rate of 100 sccm. The speed was controlled at 10 r / min and kept at this temperature for 6 hours. The silane gas was then turned off, argon gas was introduced, and the temperature was cooled to room temperature to obtain an active material.

[0193] (2) After the active material is cooled to room temperature, argon gas is continued to be introduced at a flow rate of 400 sccm, and then the temperature is raised to 600°C at a heating rate of 10°C / min. After being kept at this temperature for 1 hour, the argon gas is turned off and ethylene gas is introduced at a flow rate of 100 sccm. The speed is controlled at 10 r / min and the pressure is 10 Torr. The temperature is kept for 0.5 hour. Subsequently, the ethylene gas is turned off, argon gas is introduced, and the temperature is lowered to room temperature to obtain the negative electrode material.

[0194] The negative electrode material prepared in this embodiment includes an active material and a coating layer located on at least a portion of the surface of the active material, wherein the active material includes a porous matrix and silicon particles filling the pores of the porous matrix, wherein the coating layer is a carbon layer.

[0195] [Corrected 03.07.2024 in accordance with Rule 91] Figure 1 is a TEM image of a cross-section of the negative electrode material prepared in Example 1. As shown in Figure 1, some 5-50 nm pores remain within the negative electrode material. These pores provide space for silicon expansion, further reducing the expansion effect. Other parameters are detailed in Table 1.

[0196] Example 2

[0197] A method for preparing a negative electrode material comprises the following steps:

[0198] (1) An appropriate amount of magnesium powder was placed in a quartz boat in a quartz tube, 20 g of a porous matrix (No. 2, see Table 1 for specific parameters) was added to a round-bottom flask, and liquid SiCl4 was placed in the round-bottom flask. Argon was introduced to remove oxygen from the device. (3) The round-bottom flask was connected to the quartz tube with a glass tube. The quartz tube was heated to 380°C under inert gas protection and kept warm for 4 to 8 hours for reduction. After the reduction reaction product was cooled, it was washed with dilute hydrochloric acid and ethanol, and the washed product was dried to obtain the active substance.

[0199] (2) After the active material is placed in the chemical vapor deposition reaction chamber, argon gas is introduced at a flow rate of 400 sccm, and then the temperature is raised to 600°C at a heating rate of 10°C / min. After being kept at this temperature for 1 hour, the argon gas is turned off and ethylene gas is introduced at a flow rate of 100 sccm. The speed is controlled at 10 r / min and kept at this temperature for 1 hour. Subsequently, the ethylene gas is turned off, argon gas is introduced, and the temperature is lowered to room temperature to obtain the negative electrode material.

[0200] The negative electrode material prepared in this embodiment includes an active material and a coating layer located on at least a portion of the surface of the active material. The active material includes a porous matrix and silicon particles filling the pores of the porous matrix. The coating layer is a carbon layer. Other parameters are detailed in Table 1.

[0201] Example 3

[0202] The difference from Example 1 is that a porous matrix (No. 3, specific parameters are shown in Table 1) is used;

[0203] (2) The active material and 3 μm pitch powder were mixed at a mass ratio of 1.3:1. After mechanical mixing for 10 minutes using a VC mixer, the temperature was raised to 300°C under a nitrogen atmosphere while stirring, and then maintained for 30 minutes. The mixture was then slowly cooled to room temperature. The pitch-coated material was kept at 400°C for 2 hours in an argon inert atmosphere, then heated to 700°C for carbonization for 2 hours. The negative electrode material was then naturally cooled to obtain.

[0204] The negative electrode material prepared in this embodiment includes an active material and a coating layer located on at least a portion of the surface of the active material. The active material includes a porous matrix and silicon particles filling the pores of the porous matrix. The coating layer is a carbon layer. Other parameters are detailed in Table 1.

[0205] Example 4

[0206] The difference from Example 1 is that a porous matrix (No. 4, see Table 1 for specific parameters) is used;

[0207] (1) A porous substrate (specific parameters are shown in Table 1) was selected and placed in a chemical vapor deposition reaction chamber. The reaction chamber was repeatedly purged with nitrogen for 3-5 times, and then the nitrogen was turned off and argon gas was introduced at a flow rate of 400 sccm. The temperature was then raised to 450°C at a heating rate of 10°C / min. After being kept at this temperature for 1 hour, the argon gas was turned off and high-purity silane gas (99.9999%) was introduced at a flow rate of 100 sccm. The speed was controlled at 10 r / min and kept at this temperature for 7 hours. The silane gas was then turned off, argon gas was introduced, and the temperature was cooled to room temperature to obtain an active material.

[0208] The negative electrode material prepared in this embodiment includes an active material and a coating layer located on at least a portion of the surface of the active material. The active material includes a porous matrix and silicon particles filling the pores of the porous matrix. The coating layer is a carbon layer. Other parameters are detailed in Table 1.

[0209] Example 5

[0210] The difference from Example 1 is that: the porous matrix (No. 5, see Table 1 for specific parameters) is different;

[0211] (2) After the active material is cooled to room temperature, argon gas is continued to be introduced at a flow rate of 400 sccm, and then the temperature is raised to 600°C at a heating rate of 10°C / min. After being kept at this temperature for 1 hour, the argon gas is turned off and acetylene gas is introduced at a flow rate of 100 sccm. The speed is controlled at 10 r / min and the pressure is 10 Torr. The temperature is kept for 0.5 hour. Subsequently, the ethylene gas is turned off, argon gas is introduced, and the temperature is lowered to room temperature to obtain the negative electrode material.

[0212] The negative electrode material prepared in this embodiment includes an active material and a coating layer located on at least a portion of the surface of the active material. The active material includes a porous matrix and silicon particles filling the pores of the porous matrix. The coating layer is a carbon layer. Other parameters are detailed in Table 1.

[0213] Example 6

[0214] (1) A porous substrate (No. 4, specific parameters are shown in Table 1) was selected and placed in a chemical vapor deposition reaction chamber. The reaction chamber was repeatedly purged with nitrogen for 3-5 times, and then the nitrogen was turned off and argon gas was introduced at a flow rate of 400 sccm. The temperature was then raised to 450°C at a heating rate of 10°C / min. After being kept at this temperature for 1 hour, the argon gas was turned off and high-purity silane gas (99.9999%) was introduced at a flow rate of 100 sccm. The speed was controlled at 10 r / min and kept at this temperature for 8 hours. The silane gas was then turned off, argon gas was introduced, and the temperature was cooled to room temperature to obtain an active material.

[0215] (2) After the active material is cooled to room temperature, argon gas is continued to be introduced at a flow rate of 400 sccm, and then the temperature is raised to 650°C at a heating rate of 10°C / min. After being kept at this temperature for 1 hour, the argon gas is turned off and ethylene gas is introduced at a flow rate of 100 sccm. The speed is controlled at 10 r / min and the pressure is 10 Torr. The temperature is kept for 2 hours. Subsequently, the ethylene gas is turned off, argon gas is introduced, and the temperature is lowered to room temperature to obtain the negative electrode material.

[0216] The negative electrode material prepared in this embodiment includes an active material and a coating layer located on at least a portion of the surface of the active material. The active material includes a porous matrix and silicon particles filling the pores of the porous matrix. The coating layer is a carbon layer. Other parameters are detailed in Table 1.

[0217] Example 7

[0218] The difference from Example 1 is that:

[0219] (1) A porous substrate (No. 1, specific parameters are shown in Table 1) was selected and placed in a chemical vapor deposition reaction chamber. The reaction chamber was repeatedly purged with nitrogen for 3-5 times, and then the nitrogen was turned off and argon gas was introduced at a flow rate of 400 sccm. The temperature was then raised to 450°C at a heating rate of 10°C / min. After being kept at this temperature for 1 hour, the argon gas was turned off and high-purity silane gas (99.9999%) was introduced at a flow rate of 100 sccm. The speed was controlled at 10 r / min and kept warm for 3 hours. The silane gas was then turned off, argon gas was introduced, and the temperature was cooled to room temperature to obtain a composite.

[0220] Example 8

[0221] The difference from Example 1 is that:

[0222] (1) A porous substrate (No. 5, specific parameters are shown in Table 1) was selected and placed in a chemical vapor deposition reaction chamber. The reaction chamber was repeatedly purged with nitrogen for 3-5 times, and then the nitrogen was turned off and argon gas was introduced at a flow rate of 400 sccm. The temperature was then raised to 450°C at a heating rate of 10°C / min. After being kept at this temperature for 1 hour, the argon gas was turned off and high-purity silane gas (99.9999%) was introduced at a flow rate of 100 sccm. The speed was controlled at 5 r / min and kept at this temperature for 8 hours. The silane gas was then turned off, argon gas was introduced, and the temperature was cooled to room temperature to obtain an active material.

[0223] (2) The active material and 3 μm pitch powder were mixed at a mass ratio of 1.3:1. After mechanical mixing for 10 minutes using a VC mixer, the temperature was raised to 300°C under a nitrogen atmosphere while stirring, and then maintained for 30 minutes. The mixture was then slowly cooled to room temperature. The pitch-coated material was kept at 400°C for 2 hours in an argon inert atmosphere, then heated to 700°C for carbonization for 2 hours. The negative electrode material was then naturally cooled to obtain.

[0224] The negative electrode material prepared in this embodiment includes an active material and a coating layer located on at least a portion of the surface of the active material. The active material includes a porous matrix and silicon particles filling the pores of the porous matrix. The coating layer is a carbon layer. Other parameters are detailed in Table 1.

[0225] Comparative Example 1:

[0226] The difference from Example 1 is that a different porous matrix (No. 6, specific parameters are shown in Table 1) is used.

[0227] The negative electrode material prepared in this embodiment includes an active material and a coating layer located on at least a portion of the surface of the active material. The active material includes a porous matrix and silicon particles filling the pores of the porous matrix. The coating layer is a carbon layer. Other parameters are detailed in Table 1.

[0228] Comparative Example 2:

[0229] The difference from Example 3 is that a different porous matrix (No. 7, specific parameters are shown in Table 1) is used.

[0230] The negative electrode material prepared in this embodiment includes an active material and a coating layer located on at least a portion of the surface of the active material. The active material includes a porous matrix and silicon particles filling the pores of the porous matrix. The coating layer is a carbon layer. Other parameters are detailed in Table 1.

[0231] Table 1. Performance parameter results of porous matrix

[0232] Table 2 Comparison of electrochemical performance data of examples and comparative examples

[0233] As shown in Tables 1 and 2, in the negative electrode materials prepared in Examples 1 to 8, the particle size of the silicon particles formed by deposition can be effectively controlled by optimizing the pore size distribution of the pores of the porous matrix. The pores of the porous matrix can reserve space for the volume expansion of silicon generated during the alloying process, thereby slowing down the adverse effects of the volume expansion during the cycle. The amorphous silicon particles are filled in the pores of the porous matrix to form a composite structure of a porous matrix-silicon particles, which can also enhance the structural stability of the negative electrode material and greatly improve the first efficiency and capacity of the negative electrode material. The active material is then coated, which can, on the one hand, reduce the side reactions caused by the electrolyte entering the negative electrode material, resulting in a decrease in the first coulomb efficiency and specific capacity. On the other hand, it can improve the conductivity of the material while effectively reducing the occurrence of gas production during the large-scale water system homogenization process, thereby reducing the swelling of the electrode sheet prepared from the negative electrode material.

[0234] In the preparation process of Example 7, since the deposition time of silane was only 3 hours, the silicon content in the negative electrode material was relatively low, only 17.9%. Therefore, the first coulombic efficiency of the negative electrode material dropped significantly.

[0235] During the preparation process of Example 8, the deposition time of silane was increased to 8 hours, resulting in a higher silicon content in the negative electrode material of 58.2%. Therefore, the first coulombic efficiency and reversible capacity of the negative electrode material prepared in Example 8 were improved compared with those in Example 1. However, the battery cycle expansion rate of the prepared negative electrode material increased, and the cycle performance of the material decreased. In addition, the electrical conductivity of the negative electrode material decreased slightly, and the gas production value increased compared with that in Example 1.

[0236] The negative electrode material prepared in Comparative Example 1 adopts the porous matrix No. 6. The volume of pores in the porous matrix with a pore diameter in the range of 2nm to 3nm accounts for only 3% of the total pore volume, and the particle size distribution of the porous matrix is ​​relatively wide. Particles of different sizes will cause the deposited silicon particles to be uneven in size, resulting in excessively high local silicon content, resulting in uneven volume changes of the material during the cycle, and a significant increase in gas production.

[0237] In the negative electrode material prepared in Comparative Example 2, the volume of pores below 2 nm in the porous matrix accounts for only 30% of the total pore volume, indicating that the number of micropores in the porous matrix is ​​too small and the total pore volume is also low, that is, there is not enough space inside the porous carbon for silicon particles to deposit, resulting in low capacity and initial efficiency of the negative electrode material.

[0238] 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, improvements, etc. made within the scope of protection of the present application shall be included within the scope of protection of the present application.

Claims

1. A porous matrix, characterized in that: In the porous matrix, the volume proportion of pores with a pore diameter in the range of 2nm to 3nm in the total pore volume is ≥10%, and the volume proportion of pores with a pore diameter below 2nm in the total pore volume is ≥70%.

2. The porous matrix according to claim 1, characterized in that The porous matrix includes at least one of the following features (1)-(2): (1) The particle size distribution of the porous matrix satisfies: 0.9≤(D 90 -D 10 ) / D 50 ≤1.8; (2) The average particle size of the porous matrix satisfies: 2 μm ≤ D 50 ≤30μm.

3. The porous matrix according to claim 1, characterized in that The porous matrix includes at least one of the following features (1)-(3): (1) The pores of the porous matrix also include macropores; (2) The total pore volume in the porous matrix is ​​0.3 cm 3 / g~1.1cm 3 / g; (3) In the porous matrix, the volume proportion of pores with a pore diameter of less than 5 nm in the total pore volume is ≥ 90%.

4. The porous matrix according to claim 1, characterized in that The specific surface area of ​​the porous matrix is ​​1000 m 2 / g~2200m 2 / g.

5. A negative electrode material, characterized in that: The negative electrode material includes an active substance, and the active substance includes a porous matrix and silicon particles, at least part of the silicon particles are distributed in the pores of the porous matrix; the negative electrode material forms pores after removing the silicon particles, and in the pores formed by removing the silicon particles from the negative electrode material, the volume proportion of pores with a pore diameter in the range of 2nm to 3nm in the total pore volume is greater than 10%, and the volume proportion of pores with a pore diameter below 2nm in the total pore volume is ≥70%.

6. The negative electrode material according to claim 5, characterized in that The negative electrode material includes at least one of the following features (1) to (2): (1) The negative electrode material contains trace metal elements with a mass percentage of ≤200 ppm; (2) The negative electrode material contains trace metal elements, and the trace metal elements include at least one of Fe, Co, Ni, Cr, Zn, Cu and Al.

7. The negative electrode material according to claim 5, characterized in that The negative electrode material includes at least one of the following features (1) to (3): (1) The negative electrode material contains hydrogen, and the mass percentage of the hydrogen is 0.01% to 0.5%; (2) The negative electrode material contains oxygen, and the mass percentage of the oxygen is 0.01% to 2%; (3) The negative electrode material contains nitrogen, and the mass percentage of the nitrogen is 0.01% to 0.5%.

8. The negative electrode material according to claim 5, characterized in that The negative electrode material further includes a coating layer, and the coating layer is at least partially located on the surface of the active material.

9. The negative electrode material according to claim 8, characterized in that The coating layer includes at least one of the following features (1) to (2): (1) The material of the coating layer includes a carbon material, and the carbon material includes at least one of graphite carbon and amorphous carbon; (2) The material of the coating layer includes a carbon material and a doping element, and the doping element includes at least one of nitrogen, phosphorus, sulfur and boron.

10. The negative electrode material according to claim 5, characterized in that The mass proportion of silicon element in the silicon particles in the negative electrode material is 20% to 55%.

11. The negative electrode material according to claim 5, characterized in that The negative electrode material includes at least one of the following features (1) to (3): (1) The median particle size of the negative electrode material is 5 μm to 20 μm; (2) The specific surface area of ​​the negative electrode material is 5.0 m 2 / g~100m 2 / g; (3) The tap density of the negative electrode material is 0.5 g / cm 3 ~1.5g / cm 3 .

12. The negative electrode material according to claim 5, characterized in that The negative electrode material includes at least one of the following features: (1) The total pore volume of the negative electrode material is 0.001 cm 3 / g~0.1cm 3 / g; (2) The average pore diameter of the pores in the negative electrode material is 5 nm to 50 nm.

13. The negative electrode material according to claim 5, characterized in that The 24-hour gas production of the negative electrode material is ≤1 mL / g.

14. The negative electrode material according to claim 5, characterized in that The powder conductivity of the negative electrode material under a pressure of 20 kN is 0.5 S / cm to 2 S / cm.

15. A battery, characterized in that: It comprises the porous matrix according to any one of claims 1 to 4 or the negative electrode material according to any one of claims 5 to 14.

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