Negative electrode material and lithium-ion battery

Abstract

The present invention belongs to the technical field of battery negative electrode materials. Disclosed are a negative electrode material and a lithium-ion battery. The negative electrode material comprises a matrix and an active substance, wherein the matrix has pores, and the active substance is at least partially distributed in the pores of the matrix. In addition, the negative electrode material satisfies the following inequation, wherein A is the pore volume of the negative electrode material, with the unit thereof being cm3 / g; and B is the average pore size of the negative electrode material, with the unit thereof being nm. By means of the negative electrode material provided in the embodiments of the present invention, an excellent first-day gas production quantity can be achieved, and the particle strength of the negative electrode material can be improved, thereby reducing the erosion of water molecules on an active substance, such as silicon particles, in the negative electrode material, reducing the first-day gas production quantity of the negative electrode material, and improving the cycling stability of the negative electrode material.

Description

Anode materials and lithium-ion batteries

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411132626.8, filed on August 19, 2024, entitled “Anode Material and Lithium-ion Battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention generally relates to the field of battery anode materials technology. More specifically, this invention relates to an anode material and a lithium-ion battery. Background Technology

[0004] Anode materials are one of the key materials for achieving high capacity and long cycle life in lithium-ion batteries. Traditional graphite anode materials have low capacity, while silicon-based anode materials benefit from silicon's high capacity characteristics. However, silicon anodes experience a volume expansion of over 300% during lithium intercalation, leading to silicon pulverization. Simultaneously, silicon's poor conductivity results in high internal resistance, severely hindering its application.

[0005] To address the aforementioned issues, existing technologies have proposed silicon-carbon anode materials based on porous carbon. Porous carbon materials possess abundant pore structures, providing ample embedding space for nano-silicon materials, suppressing the expansion effect of silicon anode materials, and mitigating their pulverization problem. Simultaneously, the carbon framework of porous carbon exhibits excellent electronic conductivity, providing a well-developed conductive network for silicon anode materials, improving their conductivity, and enhancing their initial efficiency.

[0006] Silicon-carbon anode materials based on porous carbon have large pore volumes and numerous pores, but further coating is still required to reduce the gas generation effect during the silicon-carbon material slurry preparation process. However, current carbon deposition coating processes have low deposition efficiency and incomplete coating, making it difficult to prevent water in the slurry from eroding the silicon in the silicon-carbon product.

[0007] Therefore, there is an urgent need to provide a negative electrode material with extremely high slurry stability and extremely low gas production. Summary of the Invention

[0008] In order to at least solve one or more of the technical problems mentioned above, embodiments of the present invention provide a negative electrode material that can reduce the gas production during the pulping process.

[0009] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising a matrix and an active substance, the matrix having pores, the active substance being at least partially distributed within the pores of the matrix, and the negative electrode material satisfying the following: Where A is the pore volume of the negative electrode material, in cm³. 3 / g, where B is the average pore size of the negative electrode material, in nm.

[0010] In a second aspect, a lithium-ion battery is provided, which includes the negative electrode material of any of the embodiments of the first aspect described above.

[0011] The negative electrode material provided in this embodiment of the invention satisfies the following relationship between its pore volume and average pore size: This indicates that the average pore size and pore volume of the negative electrode material are within a suitable range. During the slurry preparation and battery cycling process, on the one hand, water molecules are bound by their own size effect and hydrogen bonding between water molecules, making it difficult for them to enter the ultra-small pores in the negative electrode material and erode the active material. On the other hand, the negative electrode material has sufficient pore volume to reserve space for the volume expansion of the active material particles, thus alleviating the expansion effect of the negative electrode material and improving the cycle stability of the negative electrode material. It can also adsorb or contain some of the small amount of gas generated by the side reaction between the active material particles and the electrolyte, thus improving the gas generation phenomenon of the negative electrode material.

[0012] If the negative electrode material This indicates that the pore volume or average pore size of the negative electrode material is too small. If the pore volume is too small, there is insufficient pore volume to alleviate the volume expansion of the active material particles, resulting in a poor expansion effect and poor cycle stability of the negative electrode material. If the average pore size is too small, lithium ions cannot enter the pores of the negative electrode material to undergo lithium insertion / extraction reactions with the active material.

[0013] If the negative electrode material This indicates that the pore volume or average pore size of the negative electrode material is too large. If the pore volume is too large, it means the matrix is ​​not well filled with the active material, resulting in lower particle strength. Consequently, the electrode sheets prepared from this material are prone to breakage and cracking during the rolling process, leading to poor processing performance. If the average pore size is too large, water molecules in the electrolyte or slurry can easily enter the negative electrode material through the large pores and react with the active material, causing the active material to be corroded by water molecules. Attached Figure Description

[0014] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding parts, wherein:

[0015] Figure 1 shows a schematic diagram of the preparation method steps of the negative electrode material according to an embodiment of the present invention;

[0016] Figure 2 shows the curve fitting plots of A and B values ​​for Examples 1 to 11. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] It should be understood that the terms "comprising" and "including" as used in the specification and claims of this invention indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0019] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this specification and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0020] As used in this specification and claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if [described condition or event] is detected" may be interpreted, depending on the context, as "once determined," "in response to determination," "once [described condition or event] is detected," or "in response to detection of [described condition or event]."

[0021] One embodiment of this application provides a secondary battery, including a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the casing.

[0022] The outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, a pouch battery for a secondary battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0023] The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The electrode assembly can be a stacked structure, formed by alternating layers of the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding the positive electrode, separator, and negative electrode after they have been stacked sequentially.

[0024] Positive electrode film

[0025] The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive active layer contains a positive active material, which includes compounds that reversibly insert and extract lithium ions (i.e., lithiation intercalation compounds). In some embodiments, the positive active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0026] The positive electrode active layer also includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode active layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0027] The positive electrode active layer may also comprise a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0028] negative electrode sheet

[0029] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material layer includes a negative electrode material.

[0030] The negative electrode material includes a matrix and an active material. The matrix has pores, and the active material is at least partially distributed within the pores of the matrix. A represents the pore volume of the negative electrode material, in cm³. 3 / g, where B is the average pore size of the negative electrode material, in nm.

[0031] Specifically, the pore volume and average pore size of the negative electrode material satisfy the following relationship: This indicates that the average pore size and pore volume of the negative electrode material are within a suitable range. During the slurry preparation and battery cycling process, on the one hand, water molecules are bound by their own size effect and hydrogen bonding between water molecules, making it difficult for them to enter the ultra-small pores in the negative electrode material and erode the active material. On the other hand, the negative electrode material has sufficient pore volume to reserve space for the volume expansion of the active material particles, thus alleviating the expansion effect of the negative electrode material and improving the cycle stability of the negative electrode material. It can also adsorb or contain some of the small amount of gas generated by the side reaction between the active material particles and the electrolyte, thus improving the gas generation phenomenon of the negative electrode material.

[0032] If the negative electrode material This indicates that the pore volume or average pore size of the negative electrode material is too small. If the pore volume is too small, there is insufficient pore volume to alleviate the volume expansion of the active material particles, resulting in a poor expansion effect and poor cycle stability of the negative electrode material. If the average pore size is too small, lithium ions cannot enter the pores of the negative electrode material to undergo lithium insertion / extraction reactions with the active material.

[0033] If the negative electrode material This indicates that the pore volume or average pore size of the negative electrode material is too large. If the pore volume is too large, it means the matrix is ​​not well filled with the active material, resulting in lower particle strength. Consequently, the electrode sheets prepared from this material are prone to breakage and cracking during the rolling process, leading to poor processing performance. If the average pore size is too large, water molecules in the electrolyte or slurry can easily enter the negative electrode material through the large pores and react with the active material, causing the active material to be corroded by water molecules.

[0034] For example, It can be 0.05, 0.06, 0.116, 0.156, 0.176, 0.177, 0.18, 0.206, 0.221, 0.223, 0.25, 0.281, 0.3, or any value within the range of any two of the above values.

[0035] In some embodiments, the average pore size of the negative electrode material is 0.35 nm to 0.8 nm, and exemplary values ​​can be 0.35 nm, 0.39 nm, 0.4 nm, 0.45 nm, 0.5 nm, 0.6 nm, 0.61 nm, 0.62 nm, 0.63 nm, 0.65 nm, 0.7 nm, 0.71 nm, 0.78 nm, 0.79 nm, 0.8 nm, or any value within any two of the above ranges. It is understood that the average pore size of the negative electrode material being within the above range indicates that the pores in the negative electrode material are primarily ultra-small pores. Water molecules in the electrolyte, bound by their own size effect and hydrogen bonding between water molecules, find it difficult to enter the ultra-small pores to corrode the active material. More specifically, taking silicon-based materials as an example, water molecules find it difficult to enter the pores in the negative electrode material and react with silicon particles. Meanwhile, the average pore size of the anode material is controlled within this range. A smaller pore size in the anode material can improve the particle strength of the anode material and reduce the entry of water molecules into the anode material through the deformation of the flexible pore structure caused by large pore volume, which would lead to the erosion of the active material by water molecules. At the same time, the average pore size of the anode material is not less than 0.35 nm, so as not to affect the entry of lithium ions into the pores of the anode material and the lithium insertion / extraction process of the active material.

[0036] In some embodiments, the pore volume of the negative electrode material is 0.01 cm³. 3 / g~0.1cm 3 / g, for example, can be 0.01cm 3 / g, 0.02cm 3 / g, 0.03cm 3 / g, 0.04cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g, etc., can also be other values ​​within the above range, and are not limited here. After the matrix is ​​filled with active material, the remaining pores in the matrix can reserve space for the volume expansion of active material particles, alleviate the expansion effect of the negative electrode material, improve the cycle stability of the negative electrode material, and can also adsorb or contain some of the small amount of gas generated by the side reaction between the active material particles and the electrolyte, thus improving the gas generation phenomenon of the negative electrode material.

[0037] In some embodiments, the pores in the negative electrode material include mesopores and / or micropores. The smaller pore size in the negative electrode material is beneficial for improving the particle strength of the negative electrode material. Preferably, the pore size range in the negative electrode material is ≤50 nm; more preferably, the pore size range is ≤2 nm. The smaller pore size in the negative electrode material is beneficial for improving the particle strength of the negative electrode material. Specifically, the pore size of the micropores is ≤2 nm, and the pore size of the mesopores is 2-50 nm. The smaller pore size of the negative electrode material helps to alleviate the cycling expansion of the negative electrode material, improving its cycling stability, and also helps to improve the particle strength of the negative electrode material.

[0038] In some embodiments, A and B in the negative electrode material exhibit a positive correlation, with B = kA + z, k = 4.79 ± 0.54, and z = 0.37 ± 0.04. This helps maintain the stability of the negative electrode material structure and obtains a negative electrode material with excellent electrochemical performance. If A is large and B is small, and A and B do not exhibit a positive correlation, it indicates that the negative electrode material has many micropores, which can lead to insufficient silicon filling and low capacity. Furthermore, many micropores can reduce the particle strength of the negative electrode material, making it prone to breakage during rolling and cycling. If A is small and B is large, and A and B do not exhibit a positive correlation, it indicates that the negative electrode material contains many large pores. These pores can decompose the solid conductive interface formed by the electrolyte, leading to a significant decrease in the initial coulombic efficiency.

[0039] In some embodiments, the matrix includes a non-carbon matrix, which comprises at least one of metal oxides, silicides, silicates, phosphates, titanates, and aluminum borates. It is understood that the non-carbon matrix, using the aforementioned materials, can all serve as a supporting framework. Compared to existing conductive carbon matrices, the non-carbon matrix used in this application has better strength and stiffness, thereby enabling the negative electrode material to have a higher compaction density during battery fabrication. This improves the structural stability of the negative electrode material, reduces particle breakage and pulverization, and is beneficial for improving the cycle performance of the negative electrode material. Simultaneously, due to its electronic insulation properties, the non-carbon matrix typically exhibits good ionic conductivity, acting similarly to an artificial SEI film. This slows down the formation of subsequent natural SEI films, reduces direct contact between the negative electrode material and the electrolyte, and minimizes the occurrence of side reactions. In addition, non-carbon matrices have a lower cost advantage compared to carbon matrices. Existing carbon matrices involve high energy consumption and environmental costs due to the complexity of the activation and pore-forming process. However, if porous ceramics or other naturally porous materials are used, the complex pore-forming process is eliminated, thereby reducing the cost to 10% or even less of the cost of porous carbon matrices.

[0040] In some embodiments, the metal oxide includes at least one of aluminum oxide, zirconium oxide, germanium dioxide, and manganese dioxide.

[0041] In some embodiments, the silicide includes at least one of silicon carbide and silicon nitride.

[0042] In some embodiments, the silicate includes at least one selected from cordierite, mullite, and zeolite. It is understood that the silicate in this application is primarily a natural silicate mineral, wherein cordierite (magnesium aluminum silicate) has the chemical formula Mg₂Al₄Si₅O. 18 It may contain elements such as Na, K, Ca, Fe, Mn, and H2O; mullite, with the chemical formula 3Al2O3-2SiO2; zeolite (aluminosilicate), with the chemical formula A m B p O 2p ·nH2O, where A represents cations, usually including monovalent or divalent metal ions such as Ca, Na, K, Ba, and Sr; B represents the basic units that make up the zeolite framework, namely Si and Al atoms; p is the valence of the cation; m is the number of cations A; and n is the number of water molecules.

[0043] In some embodiments, the phosphate includes at least one of aluminum phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate, and lanthanum phosphate.

[0044] In some embodiments, the titanate includes at least one of calcium titanate, iron titanate, lithium titanate, and barium titanate. In some embodiments, the carbon matrix has pores, which facilitates the provision of more deposition sites for active materials, allowing active materials to be deposited at least within the pores of the carbon matrix. Simultaneously, the porous framework of the carbon matrix can form a conductive network, facilitating electron transport during charge and discharge, thereby reducing polarization of the battery material and improving conductivity and cycle stability.

[0045] In some embodiments, the matrix includes a carbon matrix, which comprises one or more of the following: artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene. The selection of any of these materials as the carbon matrix can provide pore distribution sites for the active material and form a conductive network.

[0046] In some embodiments, the active material includes one or more of silicon-based materials, tin-based materials, germanium-based materials, and lead-based materials. For example, using silicon-based materials as a component of the negative electrode active material can improve the specific capacity of the negative electrode material, thereby increasing the energy density of the secondary battery.

[0047] In some embodiments, the active material includes a silicon-based material, which includes one or more of amorphous silicon, crystalline silicon, a composite of crystalline and amorphous silicon, silicon oxide, and silicon alloy. For example, amorphous silicon expands isotropically during lithium intercalation, which can reduce pore collapse, suppress the rapid decay of the specific capacity of the anode material, and is more conducive to improving the lithium intercalation cycle performance of the anode material.

[0048] In some embodiments, the morphology of the active substance includes one or more of the following: dot-like, spherical, ellipsoidal, and sheet-like.

[0049] In some embodiments, the purity of the active material is greater than 99%. Taking silicon-based materials as an example, high-purity silicon-based materials are more conducive to Li-Si alloying with lithium, thereby improving the cycle performance of lithium-ion batteries.

[0050] In some embodiments, the pore volume of the negative electrode material is 0.01 cm³. 3 / g to 0.1cm 3 / g. For example, the pore volume of the negative electrode material can be 0.01cm³. 3 / g, 0.02cm 3 / g, 0.03cm 3 / g, 0.04cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g or any value within the range of any two of the above values. After the active material is filled into 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 contain some of the small amount of gas generated by the reaction of the active material with the electrolyte or pulping side reaction, and improve the gas generation phenomenon of the negative electrode material.

[0051] In some embodiments, the powder conductivity of the negative electrode material at a pressure of 20 kN is between 10 S / cm and 25 S / cm. For example, the powder conductivity of the negative electrode material can be 10 S / cm, 11 S / cm, 13 S / cm, 15 S / cm, 18 S / cm, 20 S / cm, 22 S / cm, 25 S / cm, or any value within the range of any two of the above values.

[0052] In some embodiments, the first-day gas production of the negative electrode material at 25°C is 5–150 cc / Kg. For example, the first-day gas production of the negative electrode material at 25°C can be 5 cc / Kg, 10 cc / Kg, 30 cc / Kg, 50 cc / Kg, 100 cc / Kg, 150 cc / Kg, or any value within the range of any two of the above values. Controlling the first-day gas production of the negative electrode material within the above range indicates that most of the active material can be relatively uniformly distributed within the pores of the carbon matrix. This reduces the direct contact between the active material and the electrolyte, thereby reducing side reactions (such as silicon hydrolysis into silicates and hydrogen) between the dissolved active material and the electrolyte or during slurry preparation, effectively lowering the gas production value of the negative electrode material.

[0053] In some embodiments, the particle strength of the negative electrode material is 100–500 MPa. For example, the particle strength of the negative electrode material can be 100 MPa, 150 MPa, 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, or any value within the range of any two of the above values. This can further improve the stability of the negative electrode material particles, reduce particle breakage, and thus further improve the volumetric energy density of the battery.

[0054] In some embodiments, the particle strength of the negative electrode material is 105–165 MPa. For example, the particle strength of the negative electrode material can be 105 MPa, 110 MPa, 113 MPa, 115 MPa, 125 MPa, 135 MPa, 145 MPa, 155 MPa, 165 MPa, or any value within the range of any two of the above values.

[0055] In some embodiments, the particle strength of the negative electrode material is 205–465 MPa. For example, the particle strength of the negative electrode material can be 205 MPa, 220 MPa, 243 MPa, 285 MPa, 325 MPa, 375 MPa, 395 MPa, 415 MPa, 465 MPa, or any value within the range of any two of the above values.

[0056] In some embodiments, the median particle size D50 of the negative electrode material is 1 μm to 20 μm, and can be exemplarily 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 18 μm, 20 μm, etc., and of course, other values ​​within the above range are also possible, without limitation. For example, in some embodiments, the median particle size D50 of the negative electrode material is 5 μm to 15 μm. The median particle size D50 of the negative electrode material directly affects the specific surface area and electron transport path of the negative electrode material. Smaller particle size usually means a larger specific surface area, which is beneficial to the electrochemical reaction and the rapid charge transport, thereby improving the power density and energy density of the battery; smaller particle size can reduce the volume change of the material during lithium-ion insertion / extraction cycles, which helps to reduce the stress and deformation of the structure, thereby extending the cycle life of the battery; the range of median particle size D50 can also further affect the pore structure and pore volume of the negative electrode material, affecting the particle space collapse ratio of the negative electrode material. Preferably, the median particle size D50 of the negative electrode material is 2 μm to 10 μm.

[0057] In some embodiments, the carbon content of the negative electrode material is between 40% and 65% by mass, based on the mass of the negative electrode material. The carbon content includes a carbon matrix and a carbon coating layer. When the carbon content is within this range, a sufficient carbon-based substrate can be established, providing ample distribution sites for the active material, which is beneficial for forming an effective conductive network and improving conductivity and cycle stability.

[0058] In some embodiments, the mass percentage of silicon in the negative electrode material is between 35% and 60%, depending on the mass percentage of the negative electrode material. When the mass percentage of silicon is within this range, the lithium battery can store a higher amount of electricity, i.e., a higher initial discharge specific capacity.

[0059] In some embodiments, the negative electrode material further includes a coating layer disposed on at least a portion of the surface of the substrate or the active material. The coating layer comprises a carbon material, including one or more of graphene, soft carbon, and hard carbon. The coating layer on the outer layer of the negative electrode material has good electrical conductivity, which can improve the conductivity of the negative electrode material. Furthermore, it can coat the active material exposed on the surface of the substrate, reducing the continuous oxidation of the exposed active material during storage and minimizing the decrease in specific capacity and initial coulombic efficiency (ICE) of the negative electrode material. The coating layer can also reduce the direct contact between the active material and the electrolyte, improving the stability of the SEI film, thereby improving the initial coulombic efficiency of the negative electrode material.

[0060] In some embodiments, the coating layer can be a single-layer coating layer formed from a single material, a coating layer formed from a combination of multiple materials, a multi-layer coating layer formed from a single material, or a multi-layer coating layer formed from multiple materials, etc., and the layer structure of the coating layer can be selected according to actual needs. It is understood that when the coating layer has a multi-layer coating structure, the density is higher.

[0061] In some embodiments, the thickness of the coating layer is from 1 nm to 300 nm. For example, the thickness of the coating layer can be 1 nm, 30 nm, 50 nm, 150 nm, 200 nm, 250 nm, 300 nm, or any value within the range of 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. Controlling the thickness of the coating layer within the above range is beneficial for maintaining the stability of the particle structure of the negative electrode material during cycling, reducing the amount of exposed active material on the surface of the negative electrode material, reducing the amount of SEI generated during charge and discharge due to exposed active material, and improving the specific capacity and electrochemical performance of the negative electrode material.

[0062] In some embodiments, the thickness of the coating layer is preferably 1 nm to 50 nm, and more preferably, the thickness of the coating layer is 1 nm to 30 nm, which is beneficial to the rapid and reversible insertion and extraction of lithium ions.

[0063] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0064] Figure 1 shows a schematic diagram of the preparation method steps of the negative electrode material according to an embodiment of the present invention.

[0065] As shown in Figure 1, the preparation method of the negative electrode material includes:

[0066] The first step, S1, involves crushing the biomass raw material, followed by acid washing, water washing, and drying to obtain a D50 of 0.3–3 mm, an iron and potassium content of less than 1000 ppm, and a pore volume of 0.2–0.5 cm. 3 / g of carbon precursor.

[0067] D50 represents the median particle size. The particle size of the above materials can be tested using a Malvern laser particle size analyzer (Mastersizer 3000). The particle size distribution is determined by laser diffraction, and the cumulative particle size distribution is based on a volume reference. D10 represents the particle size corresponding to a cumulative particle size distribution percentage of 10%, D50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%, and D90 represents the particle size corresponding to a cumulative particle size distribution percentage of 90%.

[0068] Specifically, biomass raw materials such as olive shells, walnut shells, or apricot shells are crushed into particles with a D50 of 0.3–3 mm. These particles are then sequentially subjected to hydrochloric acid washing, hydrofluoric acid washing, and water washing to remove inorganic impurities. Finally, they are dried to obtain a carbon precursor. The parameters for crushing and washing the biomass raw materials can be adjusted according to existing technology. In this embodiment of the invention, the preferred parameters are: hydrochloric acid concentration of 0.5–2 M and washing time of 6–12 h; hydrofluoric acid concentration of 0.5–2 M and washing time of 6–12 h; water washing time of 6–12 h; and drying temperature of 80–100 °C for 6–12 h. More preferably, the olive shells are mechanically crushed to obtain coarse material with D50 = 2.0 mm. The coarse material is then acid-washed with 2M hydrochloric acid for 6 hours, followed by acid-washing with 0.5M hydrofluoric acid for 6 hours, then washed with water for 6 hours, and finally dried at 100°C for 12 hours to obtain the carbon precursor.

[0069] In the second step S2, the carbon precursor is carbonized at high temperature, activated, and then crushed and classified to obtain porous carbon materials.

[0070] Specifically, the carbon precursor is carbonized in a controlled environment with temperature and atmosphere to ensure the production of high-quality activated carbon. The carbonized material then undergoes activation treatment to increase its pore structure and surface area, thereby improving its adsorption capacity. Finally, it is pulverized and classified to obtain particles with a D50 of 5μm–15μm and a D00 > 2μm, which are used as porous carbon materials; or particles with a D50 of 2–10μm are also used as porous carbon materials.

[0071] The methods for carbonization, activation, and pulverization / gradation can be any scheme described in the prior art or any scheme invented in the future, as long as the obtained porous carbon material meets the following requirements: oxygen content < 4% and pore volume 0.6–0.9 cm³. 3 / g, D50 of 5-15μm or D50 of 2-10μm is acceptable.

[0072] In a preferred embodiment of the present invention, during the carbonization process, the high-temperature carbonization equipment can be a box furnace, kiln, or rotary kiln, the high-temperature carbonization temperature is 600–700°C, and the carbonization time is 1–6 hours. The inert gas can be nitrogen, helium, or argon, and the gas flow rate is 2 L / h–100 L / h. During the activation process, the activation equipment can be a box furnace, kiln, rotary kiln, activation furnace, etc., the activation temperature is 700–900°C, and the activation method can be physical activation or chemical activation. Physical activation can be CO2 activation or steam activation, and chemical activation can be alkali activation or zinc salt activation. The alkali activator can be sodium hydroxide, potassium hydroxide, sodium salt, potassium salt, etc., and the zinc salt activator can be zinc acetate, zinc chloride, zinc nitrate, zinc oxide, etc. The activation gas flow rate for physical activation is 1–15 L / min, the mass ratio of activator to carbon precursor for chemical activation is 0.2–5, and the activation time is 1–24 hours. The feeding frequency for crushing and classifying is 5–50 Hz, the classification frequency is 5–50 Hz, and the oxygen content of the porous carbon material after crushing and classification is <4%, with a pore volume of 0.6–0.9 cm³. 3 / g, the D50 of the particles is 5~15μm or 2~10μm.

[0073] More preferably, the carbon precursor is placed in a rotary kiln, argon gas with a flow rate of 10 L / h is introduced, and carbonization is carried out at 700°C for 4 h. Then, the temperature is maintained at 700°C for 12 h, and steam is introduced at a flow rate of 15 L / min for 12 h for steam activation. After the activated material cools down, the activated material is taken out and subjected to air jet milling and classification to obtain a porous carbon material with D50 = 8.3 μm.

[0074] In the third step S3, silicon is deposited on the porous carbon material to obtain a silicon-carbon material with a silicon content of 35% to 60%.

[0075] Specifically, porous carbon material is placed in a vapor deposition furnace or horizontal reactor, and an inert gas with a carrier gas flow rate of 50–1000 sccm and a gaseous silicon source with a flow rate of 10–500 sccm are introduced. The deposition temperature is controlled at 400–800°C, and the deposition time is 1–10 hours until a silicon-carbon material with a silicon content (mass percentage) of 35%–60% is obtained. The gaseous silicon source can be silane or disilane, and the inert gas can be nitrogen, helium, or argon. Preferably, the porous carbon material is placed in a vapor deposition furnace, and 500 sccm of nitrogen and 200 sccm of silicon source are introduced, and deposition is carried out at 600°C for 5 hours to obtain a silicon-carbon material with a silicon content of 45%. The silicon-carbon material meets the following parameters: pore volume < 0.1 cm³. 3 / g, specific surface area <200m² 2 / g.

[0076] In the fourth step S4, the porosity of the silicon-carbon material is adjusted to obtain the negative electrode material.

[0077] Specifically, the reactor after silicon deposition is cooled to a low temperature (below 120°C) in a nitrogen or inert gas atmosphere. A surface pore conditioner is added to the reactor and the temperature is raised to the melting temperature, causing the surface pore conditioner to melt, adhere to the surface of the silicon-carbon material, and encapsulate the silicon-carbon material. Then, the temperature is raised further until the encapsulation layer is carbonized to obtain the negative electrode material.

[0078] The inert gas can be helium or argon, and the flow rate of the carrier gas is 50 to 1000 sccm.

[0079] The surface pore regulator can be at least one of glucose, sucrose, asphalt, or resin.

[0080] The surface pore size regulator has a D50 of <50 μm.

[0081] The mass ratio of surface pore modifier to silicon carbide material is 0.05 to 1.

[0082] The melting temperature of the surface porosity regulator is 140–450℃, and the melting temperature is maintained for 2–6 hours.

[0083] The heating rate for carbonizing the encapsulation layer is 100–1000℃ / h, the carbonization temperature of the encapsulation layer is 600–750℃, and the carbonization time of the encapsulation layer is 2–6h.

[0084] Preferably, the vapor deposition furnace after silicon deposition is cooled to 110°C in argon gas. Sucrose powder with D50 = 40μm is added to the vapor deposition furnace, and the mass ratio of sucrose to silicon-carbon material is 0.5. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates the silicon-carbon material. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 2 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0085] In the negative electrode material, the silicon content ranges from 35% to 60%, the D50 is 5 to 15 μm, and the pore volume is 0.01 to 0.1 cm³. 3 / g, with an average pore size of 0.35–0.8 nm, and A represents the pore volume, and B represents the average pore diameter.

[0086] Tests revealed that the anode material also possesses the following characteristics: the first-day gas production of the anode material at 25°C is 5–150 cc / kg; the particle strength of the anode material is 105–165 MPa or 205–465 MPa; the conductivity of the anode material is 10–25 S / cm; the capacity of the battery prepared from the anode material is 1800–2300 mAh / g; and the initial efficiency of the battery prepared from the anode material is 90–94%.

[0087] Example 1

[0088] Step 1: Mechanically crush the olive shells to obtain coarse material with D50 = 2.0 mm. Then, the coarse material is acid-washed with 2M hydrochloric acid for 6 hours, then acid-washed with 0.5M hydrofluoric acid for 6 hours, then washed with water for 6 hours, and finally dried at 100℃ for 12 hours to obtain carbon precursor.

[0089] Step 2: Place the carbon precursor in a rotary kiln, introduce argon gas at a flow rate of 10 L / h, and carbonize at 650℃ for 4 hours. Then, heat the carbonized material to 900℃ and simultaneously introduce water steam at a flow rate of 15 L / min for 12 hours for steam activation, until the pore volume of the activated material reaches 0.9 cm³. 3 / g, with an average pore size of 2.0nm; after the activated material cools, it is taken out and subjected to air jet milling and classification to obtain porous carbon material with D50 = 7.3μm and D00 = 2.5μm.

[0090] Step 3: Place the porous carbon material in a vapor deposition furnace, introduce 500 sccm of argon gas and 200 sccm of silicon source, and deposit at 600℃ for 5 hours to obtain a silicon-carbon material with a silicon content of 50%.

[0091] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0092] Example 2

[0093] Steps 1 to 3 are the same as in Example 1.

[0094] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 24.2 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose powder, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0095] Example 3

[0096] Steps 1 to 3 are the same as in Example 1.

[0097] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 48.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose powder, which adheres to the surface of the silicon-carbon material and encapsulates the silicon-carbon material. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0098] Example 4

[0099] Steps 1 to 3 are the same as in Example 1.

[0100] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.08. Then, the temperature is raised to 170°C to melt the sucrose powder, which adheres to the surface of the silicon-carbon material and encapsulates the silicon-carbon material. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0101] Example 5

[0102] Steps 1 to 3 are the same as in Example 1.

[0103] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.24. Then, the temperature is raised to 170°C to melt the sucrose powder, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0104] Example 6

[0105] Steps 1 to 3 are the same as in Example 1.

[0106] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.74. Then, the temperature is raised to 170°C to melt the sucrose powder, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0107] Example 7

[0108] Steps 1 to 3 are the same as in Example 1.

[0109] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.98. Then, the temperature is raised to 170°C to melt the sucrose powder, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0110] Example 8

[0111] Steps 1 to 3 are the same as in Example 1.

[0112] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose powder, which adheres to the surface of the silicon-carbon material and encapsulates the silicon-carbon material. After holding the temperature for 2 hours, the temperature is raised to 600°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0113] Example 9

[0114] Steps 1 to 3 are the same as in Example 1.

[0115] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 750°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0116] Example 10

[0117] Steps 1 to 3 are the same as in Example 1.

[0118] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose powder, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 2 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0119] Example 11

[0120] Steps 1 to 3 are the same as in Example 1.

[0121] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 6 hours to carbonize the encapsulation layer, thus obtaining the anode material.

[0122] Example 12

[0123] In step 2, after the activated material cools down, it is taken out and subjected to air jet milling and classification to obtain porous carbon material with D50 = 2.1 μm and D00 = 1.5 μm.

[0124] The other steps are the same as in Example 1.

[0125] Example 13

[0126] In step 2, after the activated material cools down, it is taken out and subjected to air jet milling and classification to obtain porous carbon material with D50 = 4.1 μm and D00 = 1.9 μm.

[0127] The other steps are the same as in Example 1.

[0128] Example 14

[0129] In step 2, after the activated material cools down, it is taken out and subjected to air jet milling and classification to obtain porous carbon material with D50 = 6.2 μm and D00 = 2.5 μm.

[0130] The other steps are the same as in Example 1.

[0131] Example 15

[0132] In step 4, the surface porosity regulator was replaced with vapor-phase carbon deposition coating. Ethylene was introduced at a rate of 20 L / min, and carbon deposition coating was carried out at a constant temperature of 650 °C for 2 h to obtain the anode material.

[0133] The other steps are the same as in Example 1.

[0134] Example 16

[0135] In step 4, the surface porosity modifier was replaced with vapor-phase carbon deposition coating. Ethylene was introduced at a rate of 20 L / min, and carbon deposition coating was carried out at a constant temperature of 650 °C for 4 h to obtain the anode material.

[0136] The other steps are the same as in Example 1.

[0137] Example 17

[0138] In step 4, the surface porosity modifier was replaced with vapor-phase carbon deposition coating. Ethylene was introduced at a rate of 20 L / min, and carbon deposition coating was carried out at a constant temperature of 650 °C for 6 h to obtain the anode material.

[0139] The other steps are the same as in Example 1.

[0140] Comparative Example 1

[0141] Steps 1 to 3 are the same as in Example 1.

[0142] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 53 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0143] Comparative Example 2

[0144] Steps 1 to 3 are the same as in Example 1.

[0145] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm, then heated to 170°C and held at that temperature for 2 hours. After that, the temperature is increased to 650°C at a rate of 500°C / h and held at that temperature for 4 hours to obtain the anode material.

[0146] Comparative Example 3

[0147] Steps 1 to 3 are the same as in Example 1.

[0148] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.02. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates the silicon-carbon material. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0149] Comparative Example 4

[0150] Steps 1 to 3 are the same as in Example 1.

[0151] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 1.2. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0152] Comparative Example 5

[0153] Steps 1 to 3 are the same as in Example 1.

[0154] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 550°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0155] Comparative Example 6

[0156] Steps 1 to 3 are the same as in Example 1.

[0157] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 800°C at a rate of 500°C / h and held for 4 hours to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0158] Comparative Example 7

[0159] Steps 1 to 3 are the same as in Example 1.

[0160] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates it. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 1 hour to carbonize the encapsulation layer, thus obtaining the negative electrode material.

[0161] Comparative Example 8

[0162] Steps 1 to 3 are the same as in Example 1.

[0163] Step 4: After silicon deposition, the vapor deposition furnace is cooled to 110°C in argon gas at a flow rate of 500 sccm. Sucrose powder with a D50 of 9.3 μm is added to the vapor deposition furnace. The mass ratio of sucrose powder to silicon-carbon anode material is 0.50. Then, the temperature is raised to 170°C to melt the sucrose, which adheres to the surface of the silicon-carbon material and encapsulates the silicon-carbon material. After holding the temperature for 2 hours, the temperature is raised to 650°C at a rate of 500°C / h and held for 7 hours to carbonize the encapsulation layer, thus obtaining the anode material.

[0164] Comparative Example 9

[0165] In step 2, the carbonized material is heated to 900℃ and simultaneously purged with 30L / min of steam for 8 hours for steam activation, until the pore volume of the activated material reaches 0.9cm³. 3 / g, with an average pore size of 3.0nm;

[0166] The other steps are the same as in Example 1.

[0167] Comparative Example 10

[0168] In step 3, 500 sccm of argon gas and 600 sccm of silicon source are introduced, and silicon-carbon material with a silicon content of 40% is obtained by deposition at 600℃ for 0.5 h.

[0169] The other steps are the same as in Example 1.

[0170] In this invention, performance tests were conducted on Examples 1 to 17, and Comparative Examples 1 to 10. The test results are shown in Tables 1 and 2. The performance testing method is as follows:

[0171] (1) Pore volume and average pore size test: Using the iPore620 pore size tester and BET pore size distribution test method, the total pore volume, pore size distribution range of all pores and average pore size of the material were obtained by DFT simulation analysis using the isothermal adsorption characteristic curve of nitrogen.

[0172] (2) First day gas production test: (1) At room temperature of 25℃, CMC was glued at a ratio of 1.4%. After being dispersed evenly, 20g of glue solution and 20g of sample were mixed to obtain a slurry. The components of the slurry were mixed to form a slurry. (2) The slurry was put into an aluminum-plastic film bag and the mass of the slurry was recorded. (3) Then it was sealed to form a sealed aluminum-plastic film bag. (4) The volume of gas produced was measured: The sealed aluminum-plastic film bag was fixed at the bottom of the container and completely submerged in water. The volume of the aluminum-plastic film bag was recorded. (5) After a fixed time (24h), the volume of the aluminum-plastic film bag was recorded again. (6) The gas production of the negative electrode material was calculated based on the change in the volume of the aluminum-plastic film. The unit is cc / Kg.

[0173] (3) Conductivity test: The resistance of the powder under 20KN pressure was measured by using the MCP-PD51 powder conductivity tester from Mitsubishi Chemical, Japan, and the four-probe method was used to determine the volume resistivity of the sample. The conductivity of the powder was calculated by the instrument program.

[0174] (4) Particle strength test: Using a Shimadzu DUH-211S dynamic microhardness tester, under the action of electromagnetic force, the force corresponding to the indenter of the instrument gradually increases at a certain speed. When the particle reaches its fracture point, it fractures. At this time, due to the disappearance of the resistance on the indenter, its displacement drops rapidly. The instrument determines the fracture point (rapid increase in displacement) by recording the displacement of the indenter in real time, and records the pressure on the particle at this time. The particle strength of the material is obtained based on the relationship between pressure, particle size, and particle strength (Cx=2480×Force / (πD^2)). 100 single particles are randomly tested to obtain 100 particle strength values, and the average value is taken as the average particle strength of the sample.

[0175] (5) Particle size testing method: The particle size testing method refers to GB / T 19077-2016. The cumulative particle size distribution of the negative electrode material was measured by the Malvern laser particle size analyzer (Mastersizer 3000) and laser diffraction method. The median particle size D50 represents the particle size corresponding to 50% of the cumulative particle size distribution.

[0176] (6) Test method for the mass content of silicon in anode materials:

[0177] Using the Nanyang Xinyu SA2-9-17TP box-type atmosphere furnace: the negative electrode material is burned in an oxygen atmosphere, causing silicon and silicon suboxide in the negative electrode material to react to form silicon dioxide, and carbon is burned into carbon dioxide and discharged. The silicon content in the negative electrode material is then calculated by weighing.

[0178] (7) Test method for carbon content in negative electrode material: Refer to Appendix A of GB / T 38823-2020, "Test method for carbon content". Use a Bruker G4 ICARUS HF infrared carbon-sulfur analyzer. The negative electrode material sample is burned in a high-temperature, oxygen-rich environment. The carbon contained in the sample is oxidized into carbon dioxide. The generated gas enters the infrared detector with the carrier gas. The carbon content in the negative electrode material can be calculated by quantitatively analyzing the changes in the carbon dioxide signal.

[0179] (8) Test method for coating thickness: The negative electrode material is cut by an ion mill and the average thickness of the coating on the material surface is measured in SEM.

[0180] (9) Electrochemical performance test: The negative electrode material, conductive agent (Super P) and polyacrylic latex (LA133) are mixed into a slurry in a mass ratio of 70:15:15 and uniformly coated onto copper foil. After drying, the electrode sheet is prepared, assembled into a button cell, and its capacity and first efficiency are tested on the Blue Battery Test Cabinet M340A.

[0181] Table 1

[0182] Note: For the specific process parameters in Examples 15 to 17 above, please refer to the specific examples.

[0183] Table 2

[0184] As shown in Tables 1 and 2, by controlling the particle size of the added pore regulator, the feed ratio of the pore regulator to the silicon-carbon material, and the carbonization temperature and duration during the carbonization process, the pore volume and average pore size of the anode material can be effectively adjusted, and the average pore size and pore volume of the anode material can be controlled within a certain range. Within a certain range, the negative electrode material can utilize the steric hindrance of water molecules and the hydrogen bonding between water molecules to prevent water molecules in the slurry from entering the pores of the negative electrode material and reacting with active materials such as silicon particles to generate gas. This reduces the gas generation effect of the negative electrode material during the slurry and electrode sheet preparation process, and reduces the capacity decay and expansion of the negative electrode material. Compared with Example 1, Comparative Example 9 does not satisfy the proportional relationship between A and B of this product. Its pore volume is smaller, while its average pore size is larger. These large pores can be invaded by electrolyte, causing the electrolyte to decompose in these pores to form a solid conductive interface, consuming the electrolyte and causing a significant decrease in the initial coulombic efficiency. Comparative Example 10 also does not satisfy the proportional relationship between A and B of this product. Its pore volume is larger, while its average pore size is smaller. This is because the small pores are not effectively filled by silicon, resulting in insufficient silicon filling and insufficient product capacity. At the same time, the larger pore volume also leads to a decrease in particle strength.

[0185] As can be seen from Examples 1 to 3 and Comparative Example 1, when the particle size of the surface pore regulator is too large, the number of surface pore regulator particles of the same mass decreases, resulting in fewer but larger droplets generated during melting. When these large droplets collide and adhere to the silicon-carbon material in the vapor deposition furnace, they cause uneven encapsulation of the silicon-carbon material, leading to a larger pore volume and average pore size in the prepared anode material, thus compromising the anode material's performance. If the pore size is large, water molecules in the electrolyte or slurry can easily enter the negative electrode material through the large pores and react with the active material, causing the active material to be eroded by water molecules. This reduces the negative electrode material's ability to prevent water molecule erosion of the active material. Conversely, numerous small droplets allow for more uniform and effective coating of the silicon-carbon material, significantly reducing the pore volume and average pore size of the prepared negative electrode material. As the value decreases, water molecules are bound by their own size effect and hydrogen bonding between water molecules during the slurry preparation and battery cycling process, making it difficult for them to enter the ultra-small pores in the negative electrode material to erode the active material. This allows the prepared negative electrode material to effectively prevent water molecules from eroding the active material.

[0186] As can be seen from Examples 1, 4 to 7 and Comparative Examples 2 to 4, when the mass ratio of surface pore modifier to silicon-carbon material is too large, the encapsulation is tight, and the pore volume and average pore size of the prepared negative electrode material are small, resulting in a smaller negative electrode material. A low surface pore size ratio results in excessively thick encapsulation of silicon-carbon material due to a large number of surface pore conditioner droplets, potentially leading to particle agglomeration and excessively large particle size in the final anode material, making slurry preparation difficult. Simultaneously, the increased percentage of carbon content in the anode material reduces the percentage of silicon content, resulting in a decrease in capacity. When the mass ratio of surface pore conditioner to silicon-carbon material is too small, the number of droplets generated by the melting of surface pore conditioner particles is insufficient to completely encapsulate the silicon-carbon material, leading to excessively large pore volume and average pore size in the prepared anode material. If the value is too high, the negative electrode material has a lower ability to prevent water molecules from eroding the active material.

[0187] As can be seen from Examples 1, 8, and 9 and Comparative Examples 5 and 6, when the carbonization temperature of the surface pore conditioner is insufficient, the graphitization degree of the encapsulation layer is low, unstable, and easily worn. The prepared anode material has high pore volume and large average pore size. Excessive carbonization temperature of the surface pore modifier leads to low conductivity and low initial efficiency in the anode material. When the carbonization temperature is too high, the graphitization degree of the encapsulation layer is high, resulting in low pore volume and small pore size, which negatively impacts the prepared anode material. The value decreases, the conductivity of the negative electrode material is high, and the initial efficiency is high, but it will cause the crystallinity of the deposited active material such as silicon particles to be high and silicon carbide to be produced. Although the particle strength of the prepared negative electrode material increases, the capacity of the negative electrode material is severely degraded.

[0188] As can be seen from Examples 1, 10, and 11 and Comparative Examples 7 and 8, when the carbonization time of the surface pore conditioner is insufficient, the graphitization degree of the encapsulation layer will be lower, unstable, and prone to wear. The resulting negative electrode material will have high pore volume and large pore size. An excessively high value results in low conductivity and low initial efficiency for the negative electrode material. When the carbonization time of the surface pore conditioner is too long, the graphitization degree of the encapsulation layer is high, resulting in low pore volume and small pore size. The value decreases, the conductivity of the negative electrode material is high, and the initial efficiency is high, but it will also cause the crystallinity of the deposited active material, such as silicon particles, to be high and produce silicon carbide, which leads to increased particle strength, but severe capacity decay.

[0189] As can be seen from Examples 1 and 12-14, the smaller the porous carbon particles produced by crushing and grading, the smaller the silicon-carbon particles obtained. Smaller silicon-carbon particles mix more evenly with the surface pore regulator, resulting in a more uniform and dense encapsulation layer. The pore volume A and average pore diameter B are smaller, the gas production is lower, the particle strength is higher, and the expansion rate is lower. However, the compaction of small particles is slightly lower, the particle contact is poor, which leads to a decrease in powder conductivity and a decrease in the initial coulombic efficiency.

[0190] Without using a pore conditioner, a vapor-phase carbon deposition coating process was used. As can be seen from Examples 15-17 and Examples 1, 3, and 4, although Examples 15-17 met the requirements... and The values ​​are similar to those of Examples 2 and 3, but the average pore size of Examples 15-17 exceeds the range of 0.35 nm to 0.8 nm (the average pore size is relatively large; the carbon interlayer spacing is the smallest, ~0.34 nm). This results in a decreased ability to isolate the slurry electrolyte, a dramatic increase in gas production, and limited improvements in initial coulombic efficiency and expansion rate compared to Comparative Example 2 (without surface porosity treatment). Although its capacity, particle strength, and conductivity are relatively excellent, its overall performance is inferior to the product using a pore-conditioning agent process.

[0191] Furthermore, curve fitting was performed on the A and B values ​​of Examples 1 to 11, as shown in Figure 2. It can be seen from Figure 2 that the A and B values ​​are positively correlated, A = kB + z, where k is the positive correlation coefficient k = 4.79 ± 0.54 and z = 0.37 ± 0.04.

[0192] The negative electrode material provided in this embodiment of the invention can achieve excellent first-day gas production, improve the particle strength of the material, reduce the erosion of active materials such as silicon particles by water molecules, reduce the first-day gas production of the negative electrode material, and improve the cycle stability of the negative electrode material.

[0193] While numerous embodiments of the invention have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will occur to those skilled in the art without departing from the spirit and essence of the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in the practice of the invention. The appended claims are intended to define the scope of protection of the invention and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes a matrix and an active material. The matrix has pores, and the active material is at least partially distributed within the pores of the matrix. Furthermore, the negative electrode material satisfies the following conditions: Where A is the pore volume of the negative electrode material, in cm. 3 / g, where B is the average pore size of the negative electrode material, in nm.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The pores include mesopores and / or micropores; (2) B=kA+z, k=4.79±0.54, z=0.37±0.

04.

3. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) It can be any value within the range of 0.05, 0.06, 0.116, 0.156, 0.176, 0.177, 0.18, 0.206, 0.221, 0.223, 0.25, 0.281, 0.3, or any two of the above values. (2) The pore volume of the negative electrode material is 0.01 cm³. 3 / g to 0.1cm 3 / g; (3) The pore volume of the negative electrode material is 0.01 cm³. 3 / g, 0.02cm 3 / g, 0.03cm 3 / g, 0.04cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g can be any value within the range of any two of the above values; (4) The average pore size of the negative electrode material is 0.35 nm to 0.8 nm; (5) The average pore size of the negative electrode material is 0.35nm, 0.39nm, 0.4nm, 0.45nm, 0.5nm, 0.6nm, 0.61nm, 0.62nm, 0.63nm, 0.65nm, 0.7nm, 0.71nm, 0.78nm, 0.79nm, 0.8nm or any value within the range of any two of the above values.

4. The negative electrode material as described in claim 1, characterized in that, The matrix includes a carbon matrix, which includes one or more of the following: artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene.

5. The negative electrode material as described in claim 1, characterized in that, The matrix includes a non-carbon matrix, which includes at least one of metal oxides, silicides, silicates, phosphates, titanates, and aluminum borates.

6. The negative electrode material as described in claim 1, characterized in that, The active material includes one or more of silicon-based materials, tin-based materials, germanium-based materials, and lead-based materials.

7. The negative electrode material as described in claim 4, characterized in that, The active material includes silicon-based materials, which include one or more of amorphous silicon, crystalline silicon, a composite of crystalline and amorphous silicon, silicon oxide, and silicon alloy.

8. The negative electrode material according to claim 7, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) Based on the mass of the negative electrode material, the mass percentage of silicon in the negative electrode material is 35% to 60%; (2) Based on the mass of the negative electrode material, the mass percentage of carbon in the negative electrode material is 40% to 65%.

9. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The median particle size D50 of the negative electrode material is 5 μm to 15 μm; (2) The median particle size D50 of the negative electrode material is 2 μm to 10 μm; (3) The median particle size D50 of the negative electrode material is 1μm to 20μm.

10. The negative electrode material according to claim 1, characterized in that, The negative electrode material also possesses at least one of the following characteristics: (1) The first-day gas production of the negative electrode material at 25°C is 5-150cc / kg; (2) The powder conductivity of the negative electrode material under 20kN pressure is 10-25S / cm.

11. The negative electrode material according to claim 1, characterized in that, The negative electrode material also possesses at least one of the following characteristics: (1) The particle strength of the negative electrode material is 105-165 MPa; (2) The particle strength of the negative electrode material is 205-465 MPa; (3) The particle strength of the negative electrode material is 100-500 MPa.

12. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The morphology of the active substance includes at least one of the following: dot-shaped, spherical, ellipsoidal and sheet-like; (2) The purity of the active substance is greater than 99%.

13. The negative electrode material according to claim 1, characterized in that, The negative electrode material further includes a coating layer, which is disposed on at least a portion of the surface of the substrate and / or the active material.

14. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The coating layer comprises a carbon material, wherein the carbon material comprises at least one of graphene, soft carbon and hard carbon; (2) The thickness of the coating layer is 1 to 300 nm.

15. A lithium-ion battery, characterized in that, The lithium-ion battery contains the negative electrode material according to any one of claims 1 to 14.

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