Negative electrode material and secondary battery

Abstract

A negative electrode material and a secondary battery. The negative electrode material comprises a silicon-carbon material, the silicon-carbon material comprises a silicon-based material and a carbon-based material, and at least part of the carbon-based material is distributed in the silicon-based material. The negative electrode material is tested by means of a Raman spectrum, and the negative electrode material has a first characteristic peak at 515±10 cm-1, a second characteristic peak at 305±10 cm-1, and a third characteristic peak at 925±10 cm-1. The peak intensity of the first, second and third characteristic peaks is respectively M1, M2 and M3. Q is defined as the oxygen protection degree of the silicon-based material, and Q=M1 / M2+M1 / M3, where 1.5≤Q≤4.5, and M2>M3. The Q value of the silicon-based material of the negative electrode material is controlled to be between 1.5-4.5, such that side reactions between the negative electrode material and an electrolyte can be reduced, and an appropriate amount of oxides can also be formed on the surface of the silicon-based material, thereby relieving the volume expansion of the silicon-based material.

Description

Anode materials and secondary batteries

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411377512.X, filed on September 27, 2024, entitled “Anode Material and Secondary Battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of negative electrode materials. Specifically, it relates to a negative electrode material and a secondary battery. Background Technology

[0004] In recent years, lithium-ion batteries have been widely used in electric vehicles and consumer electronics due to their high energy density, excellent output power, long cycle life, and low environmental pollution. To further improve the energy density of lithium-ion batteries, the research and development of anode materials, especially silicon anode materials, has become particularly important. However, silicon anode materials undergo significant volume expansion (over 300%) during lithium insertion / extraction, which can lead to pulverization and detachment from the current collector during charge / discharge. This disrupts the electrical contact between the active material and the current collector, resulting in decreased electrochemical performance, capacity decay, and reduced cycle stability, hindering commercial application. To address the aforementioned poor conductivity and cycle stability issues of silicon anode materials, researchers have attempted to coat silicon-based materials with carbon-based materials. However, existing carbon coating processes are quite complex, and simple carbon coating alone cannot effectively improve the electrochemical performance of silicon-carbon anode materials.

[0005] Therefore, in order to overcome the problems of large volume expansion, poor cycle performance and poor conductivity of silicon in the existing technology, it is urgent to develop a silicon-carbon anode material with good conductivity and long cycle life to meet the needs of practical applications. Summary of the Invention

[0006] In order to at least solve one or more of the technical problems mentioned above, this application proposes solutions to improve the prior art in several aspects.

[0007] In a first aspect, this application relates to a negative electrode material, said negative electrode material comprising a silicon-carbon material, the silicon-carbon material comprising a silicon-based material and a carbon-based material, wherein at least a portion of said carbon-based material is distributed within said silicon-based material;

[0008] The negative electrode material was tested using Raman spectroscopy, and the negative electrode material was measured at 515±10 cm⁻¹. -1The anode material exhibits a first characteristic peak at a depth of 305±10 cm⁻¹, with a peak intensity of M1. -1 The anode material exhibits a second characteristic peak at a depth of 925±10 cm⁻¹, with a peak intensity of M². -1 The third characteristic peak is defined as M3. Q is defined as the oxygen protection degree of the silicon-based material. The following relationship exists between Q and M1, M2, and M3 of the negative electrode material: Q = M1 / M2 + M1 / M3, 1.5 ≤ Q ≤ 4.5 and M2 > M3.

[0009] In a second aspect, this application provides a secondary battery comprising the negative electrode material described in the first aspect.

[0010] The secondary battery provided by the second aspect of this application has advantages such as high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion.

[0011] The advantages of this application will be partially explained in the following description. Attached Figure Description

[0012] The above and other objects, features, and advantages of exemplary embodiments of this disclosure will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this disclosure are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding parts, wherein:

[0013] Figure 1 shows the Raman spectrum of the negative electrode material in Example 1;

[0014] Figure 2 shows a scanning electron microscope image of the negative electrode material in Example 1;

[0015] Figure 3 shows the XRD pattern of the negative electrode material in Example 1;

[0016] Figure 4 shows the cycle performance curves of the negative electrode material in Example 1, where the charge / discharge current is 1000 mA / g. Detailed Implementation

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

[0018] It should be understood that the terms "comprising" and "including" used in the specification and claims of this application 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 application. 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] The specific embodiments of this application are described in detail below with reference to the accompanying drawings. Unless otherwise specified, the materials, reagents and equipment used in the embodiments of this application are obtained through conventional commercial channels.

[0022] One embodiment of this application provides a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, an electrode assembly, and an electrolyte / electrolyte. Both the electrode assembly and the electrolyte / electrolyte are located within the casing.

[0023] 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.

[0024] The secondary battery 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.

[0025] Positive electrode film

[0026] The positive electrode 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 capable of reversibly intercalating and deintercalating metal ions. In some embodiments, the positive active material may include lithium transition metal composite oxides, sodium transition metal composite oxides, etc. The 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).

[0027] negative electrode sheet

[0028] 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.

[0029] During battery operation, that is, when the battery is in a discharge state, metal ions (such as lithium ions) in the negative electrode are released from the lattice of the negative electrode material, pass through the electrolyte / electrolyte through the separator, and are embedded in the lattice of the positive electrode material.

[0030] Conversely, when the battery is charged by applying an external circuit, the oxidation of the positive electrode material causes metal ions (such as lithium ions) in the positive electrode to be released from the lattice of the positive electrode material, pass through the electrolyte / electrolyte through the separator, and move to the negative electrode; at the same time, the negative electrode material undergoes a reduction reaction, causing metal ions to be embedded in the lattice of the negative electrode material.

[0031] As metal ions move back and forth between the positive and negative electrodes, the battery can achieve the discharge and charge process in thousands of cycles.

[0032] The performance of anode materials incorporating silicon-based and carbon-based materials is primarily influenced by the properties of the respective materials. These materials exhibit both interference and synergistic effects. Only by maximizing the positive synergistic effect between silicon-based and carbon-based materials while suppressing their negative interference can anode materials incorporating both materials achieve optimal electrochemical performance.

[0033] This application provides an anode material comprising a silicon-carbon material, which includes silicon-based and carbon-based materials, with at least a portion of the carbon-based material distributed within the silicon-based material. Raman spectroscopy was used to test the anode material, and the anode material was found to be within a range of 515±10 cm⁻¹. -1 The first characteristic peak is located at 305±10 cm⁻¹, and the peak intensity of the first characteristic peak is M1; the negative electrode material has a peak intensity of M1 at 305±10 cm⁻¹. -1 The anode material exhibits a second characteristic peak at 925±10 cm⁻¹, with a peak intensity of M². -1 The third characteristic peak is defined as M3. Q is defined as the oxygen protection degree of the silicon-based material. The following relationship exists between Q and M1, M2, and M3 of the negative electrode material: Q = M1 / M2 + M1 / M3, 1.5 ≤ Q ≤ 4.5 and M2 > M3.

[0034] In the above scheme, the first characteristic peak (515±10cm) -1 The first characteristic peak can be used to characterize the resonant vibration peaks between Si-Si atoms in crystalline silicon. Its peak intensity and shape can reflect the crystal structure and impurity content of silicon. When the first characteristic peak deviates, it can reflect the stress distribution on the surface of the Si single crystal. Specifically, if stress exists in an object, certain stress-sensitive spectral bands will shift and deform. Within the elastic range, the change in Raman peak frequency shift is proportional to the applied stress. When subjected to compressive stress, the spectral band shifts towards higher frequencies; conversely, when subjected to tensile stress, the spectral band shifts towards lower frequencies. The second characteristic peak (305±10cm) -1 The Si-O-Si vibrational peaks used to characterize stable silicon oxide represent the structure and quality of crystalline silicon oxide in the anode material. The third characteristic peak (925±10 cm⁻¹) -1The Si-O vibrational peaks, used to characterize amorphous silicon oxide, represent the thickness and content of the unstable silicon oxide layer on the surface of silicon particles in the anode material. Controlling the intensity of the second characteristic peak (M2) to be higher than that of the third characteristic peak (M3) can reduce the activity of oxygen in the silicon-based material, decrease side reactions between silicon oxide and the electrolyte in the anode material, reduce the formation of irreversible lithium silicate, and improve the initial coulombic efficiency of the anode material. Simultaneously, controlling the oxygen protection degree (Q) of the silicon-based material between 1.5 and 4.5, i.e., adjusting the oxidation degree on the surface of the silicon particles and keeping it within a reasonable range, can reduce the occurrence of side reactions between the anode material and the electrolyte, and allow an appropriate amount of oxide to form on the surface of the silicon-based material as a rigid protective layer, mitigating the volume expansion of the silicon-based material, thereby improving the specific capacity and cycle performance of the battery prepared from the anode material. When the Q value is <1.5, the content of the oxide layer on the surface of the silicon-based material is relatively high, leading to a decrease in the specific capacity and initial efficiency of the battery prepared from the anode material, failing to meet application requirements. When the Q value is greater than 4.5, the oxide layer on the surface of the silicon-based material is thin, which cannot effectively reduce the side reactions caused by the contact between the silicon-based material and the electrolyte, and reduces the ability of the silicon-based material to alleviate the volume expansion, resulting in poor cycle life of the battery made of the negative electrode material.

[0035] In some embodiments, the Q value can be 1.5, 2.0, 2.5, 3.0, 3.35, 3.5, 4.0, 4.5 or any value within the range of any two of the above values. For example, the value of Q can be 1.5≤Q≤3.5 or 3.5≤Q≤4.5.

[0036] In some embodiments, the value of Q can be: 1.5≤Q≤3.35.

[0037] In some embodiments, in the negative electrode material, at least a portion of the carbon-based material is distributed within the silicon-based material, and multiple silicon-based material particles constitute the matrix of the negative electrode material. The silicon-based material has pores, and at least a portion of the carbon-based material can be located within the pores of the silicon-based material, forming the pores of the negative electrode material together with the silicon-based material. Filling the pores of the silicon-based material with carbon-based material in this way can improve the rigidity and strength of the negative electrode material.

[0038] In other embodiments, at least a portion of the silicon-based material is distributed within the carbon-based material in the negative electrode material. Multiple carbon-based material particles constitute the matrix of the negative electrode material. The carbon-based material has pores, and at least a portion of the silicon-based material can be located within these pores, forming the pores of the negative electrode material together with the carbon-based material. Filling the pores of the carbon-based material with silicon-based material in this way can, on the one hand, buffer the expansion of the silicon-based material, and on the other hand, improve the rigidity and strength of the negative electrode material.

[0039] In some embodiments, the carbon-based material may include at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene. The selection of any of these materials allows the carbon-based material to form a conductive network with the silicon-based material.

[0040] By rationally designing the carbon-based raw materials for anode materials, the volume expansion of anode materials can be effectively suppressed, and the structural damage of anode materials during cycling can be reduced; it can also enhance the mechanical strength and compressive strength of anode materials.

[0041] In some embodiments, the negative electrode material further includes a coating layer disposed on at least a portion of the surface of the silicon-carbon material, wherein the protective strength H of the coating layer is ≥85%.

[0042] The test method for the protective strength H includes: immersing m1 g of negative electrode material in m1*10 g of hydrofluoric acid solution, where the mass concentration of hydrofluoric acid in the solution is 20%, mechanically stirring for 2 hours, separating the solid and liquid, washing the solid material for residual hydrofluoric acid with deionized water and anhydrous ethanol sequentially, and then vacuum drying at 60℃ to obtain m2 g of material. H = m2 / m1×100%, and H is defined as the protective strength of the coating layer.

[0043] In some embodiments, the protective strength H of the coating layer of the negative electrode material is ≥90%.

[0044] In some embodiments, the H value can be 85%, 86%, 87%, 88%, 90%, 95%, 99%, 100%, or any value within the range of any two of the above values.

[0045] The uniformity and density of the coating layer play a crucial role in the performance of silicon-based materials. Poor integrity and density of the coating layer not only lead to direct contact between the silicon-based material and the electrolyte, causing severe side reactions and resulting in a decrease in the specific capacity and initial efficiency of the entire anode material, rendering it unusable, but also, due to the reduced mechanical strength of the coating layer, it fails to effectively mitigate the volume expansion of the silicon-based material, thus deteriorating the cycle performance of the battery fabricated from the anode material. The anode material provided in this application reduces side reactions between the anode material and the electrolyte and improves the electrochemical performance of the anode material by controlling the ratio range of the Raman characteristic peaks of the anode material and simultaneously improving the protective strength of the coating layer.

[0046] In some embodiments, the coating layer includes at least one of carbon materials, metal oxides, and nitrides.

[0047] In some embodiments, the coating layer may include a carbon material, which may be selected from at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, graphene, soft carbon, and hard carbon.

[0048] In some embodiments, at least a portion of the carbon-based material is distributed on the surface of the silicon-based material and forms the coating layer. The carbon-based material and the coating layer are the same material, which simplifies the preparation process of the anode material.

[0049] In some embodiments, the coating layer may include a metal oxide, which may include at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide.

[0050] In some embodiments, the coating layer may include a nitride, which includes at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

[0051] In some embodiments, the thickness of the coating layer can be from 0.1 nm to 100 nm. For example, the thickness of the coating layer can be 0.1 nm, 5 nm, 10 nm, 30 nm, 50 nm, 80 nm, 100 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 silicon-based 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 and can reduce the exposed active material on the surface of the negative electrode material. Furthermore, the thickness of the coating layer can be from 1 nm to 50 nm, and even further, the thickness of the coating layer can be from 1 nm to 20 nm, thereby facilitating the rapid and reversible insertion and extraction of lithium ions.

[0052] 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.

[0053] In some embodiments, the silicon-based material includes primary particles with an average particle size of 1 nm to 20 nm. The average particle size of the primary particles in the silicon-based material can be 1 nm, 2 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, or any value within the range of any two of the above values, and is not limited herein. Controlling the average particle size of the primary particles in the silicon-based material to between 1 nm and 20 nm can adjust the specific surface area and electron transport path of the anode material, which is beneficial for improving the electrochemical performance of the anode material.

[0054] In some embodiments, the silicon-based material comprises primary particles, which include silicon grains with an average size of 0.5 nm to 10 nm. The average size of the silicon grains can be 0.5 nm, 0.8 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 8 nm, 10 nm, or any value within the range of any two of the above values, and is not limited herein. Smaller nanoscale silicon grain sizes typically have higher specific surface areas, which is beneficial for charge transport and ion diffusion in the anode material, suppresses volume expansion, and thus improves the electrochemical performance, stability, and cycle life of the anode material. Further, the average grain size of the silicon-based material can be 2 nm to 10 nm.

[0055] In the application, "primary particle" refers to the first-order structure of a single particle, while "secondary particle" refers to an aggregate of primary particles formed by physical or chemical bonding between them, i.e., a second-order structure. The application does not specifically describe the aggregation or combination process of the primary particles that constitute the secondary particle. Primary particles generally include single crystals and polycrystalline materials. A single grain generally refers specifically to a single crystal.

[0056] In some embodiments, the median particle size of the negative electrode material is 0.2 μm-18 μm. The median particle size of the negative electrode material can be 0.2 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, or any value within the range of any two of the above values, and is not limited herein. The median particle size of the negative electrode material directly affects its specific surface area and electron transport path. Smaller particle size generally means a larger specific surface area, which is beneficial for electrochemical reactions and 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, helping to reduce structural stress and deformation, thereby extending the cycle life of the battery. Further, the median particle size of the negative electrode material can be 1 μm to 10 μm.

[0057] In some embodiments, the specific surface area of ​​the negative electrode material is 0.8 m². 2 / g-25m 2 / g. The specific surface area of ​​the negative electrode material can be 0.8m². 2 / g, 1m 2 / g、2m 2 / g、3m 2 / g、5m 2 / g、8m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g or any value within the range of any two of the above values, without limitation. Within the above range, it is beneficial to the electrochemical reaction and rapid charge transport of the battery prepared with the negative electrode material, thereby improving the electrochemical performance of the negative electrode material. Furthermore, the specific surface area of ​​the negative electrode material can be 2m². 2 / g~10m 2 / g.

[0058] In some embodiments, the powder compaction density of the negative electrode material is 0.8 g / cm³. 3 -1.5g / cm 3 The compacted density of the negative electrode material powder can be 0.8 g / cm³. 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 Or any value within the range of any two of the above values, without limitation. Within the above compaction density range, the negative electrode material possesses suitable charge transport rate and electrolyte contact area, as well as suitable structural stability. Furthermore, the powder compaction density of the negative electrode material can be 1 g / cm³. 3 ~1.2g / cm 3 ...

[0059] In some embodiments, the carbon content in the negative electrode material is 15%-65% by mass percentage, based on the mass of the negative electrode material. The carbon content in the negative electrode material can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or any value within the range of any two of the above values, and is not limited herein. Within the above range, by adjusting the carbon content, the electrochemical performance and structural stability of the negative electrode material can be optimized. Further, the carbon content of the negative electrode material can be 20% to 60%.

[0060] In some embodiments, the oxygen content in the negative electrode material is ≤10% by mass percentage, based on the mass of the negative electrode material. The oxygen content in the negative electrode material can be 1%, 2%, 3%, 4%, 5%, 6%, 8%, or any value within the range of any two of the above values.

[0061] In some embodiments, the negative electrode material has pores, and the average pore diameter of the negative electrode material is 0.5 nm-50 nm. The average pore diameter can be 0.5 nm, 1 nm, 2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, or any value within the range of any two of the above values. If the average pore diameter of the negative electrode material is too large, the electrolyte can easily penetrate into the particles of the negative electrode material during the charging and discharging process, leading to an increase in side reactions between the negative electrode material and the electrolyte. Moreover, as large pores are locations of stress concentration within the negative electrode material, an excessively large average pore diameter makes the negative electrode material particles prone to cracking and pulverization during lithium insertion / extraction processes, resulting in a rapid decline in the cycle performance of the battery made from the negative electrode material.

[0062] In some embodiments, the negative electrode material has pores, and the porosity of the negative electrode material is 0.5%-15%. The porosity of the negative electrode material can be 0.5%, 1%, 2%, 3%, 5%, 8%, 10%, 15%, or any value within the range of any two of the above values. Excessive porosity (greater than 15%) leads to an overly loose structure of the negative electrode material, while insufficient porosity (less than 0.5%) results in the negative electrode material failing to effectively mitigate the volume expansion of the silicon material, causing it to break and pulverize. During cycling, batteries made from negative electrode materials experience significant volume changes due to the loose structure or pulverization of the negative electrode material, leading to capacity decay. Controlling the porosity within the range of 0.5%-15% can effectively extend the lifespan and cycle stability of batteries made from negative electrode materials. Limiting the porosity range can also adjust the specific surface area and ion diffusion path of the negative electrode material, which is beneficial for improving the electron transport rate and ion diffusion rate of the negative electrode material, thereby improving the charge and discharge efficiency of batteries made from negative electrode materials.

[0063] Secondly, embodiments of this application provide a method for preparing a negative electrode material, the method comprising the following steps:

[0064] Step S1: The silicon monoxide raw material is subjected to a high-temperature heat treatment to obtain the first product.

[0065] Specifically, silicon monoxide raw material is placed in a reaction apparatus (e.g., an atmosphere furnace) and subjected to a high-temperature heat treatment under a protective atmosphere to obtain the first product. The main purpose of subjecting the first material to a high-temperature heat treatment is to pretreat the silicon monoxide raw material, promote the pyrolysis and crystallization process of silicon monoxide, stabilize the structure of the first product, prepare it for subsequent chemical reactions and composite steps, and ensure that the first product has a certain crystal structure and chemical activity.

[0066] In some embodiments, the median particle size D50 of the silicon monoxide raw material is 0.1 μm to 18 μm. Exemplarily, it can be 0.1 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, or 18 μm, etc. Within the above-mentioned range, it helps to ensure the uniformity and consistency of the silicon monoxide raw material during heat treatment and chemical reaction processes. At the same time, a smaller particle size helps to improve the specific capacity of the battery and reduce the volume expansion of the negative electrode material. Further, the median particle size D50 of the silicon monoxide raw material can be 2 μm to 15 μm. The particle size testing method for the above-mentioned silicon monoxide raw material can be tested using a Malvern laser particle size analyzer (Mastersizer 3000), using laser diffraction to measure the volumetric cumulative particle size distribution. D50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%.

[0067] In some embodiments, the first sintering involves heating to 550°C–1250°C at a rate of 1°C / min–20°C / min and holding at that temperature for 3–12 hours. Exemplary values ​​include 550°C, 600°C, 700°C, 800°C, 850°C, 900°C, 950°C, 1000°C, and 1250°C, and other values ​​within the aforementioned range are also possible; this application does not impose any limitations on these values. Appropriate heating rates, sintering temperatures, and holding times help the pretreated silicon monoxide raw material form a specific crystal structure, providing a foundation for subsequent reactions with metal reducing agents.

[0068] In some embodiments, the protective atmosphere for the primary high-temperature heat treatment is at least one of argon, nitrogen, and helium.

[0069] Step S2: The first product is mixed with a metal reducing agent in a certain proportion and then subjected to a second sintering treatment to obtain the second product.

[0070] Specifically, the first product and a metal reducing agent are mixed evenly in a certain proportion and then placed in a reaction apparatus (e.g., a reactor). A protective gas is introduced to replace the air, and a second sintering process is performed. After cooling, the second product is obtained. The addition of the metal reducing agent is intended to induce a chemical reaction with the first product. For example, using silicon monoxide as the first material, the reaction of the first product with the metal reducing agent can form a silicon metal compound or a silicon metal alloy. The second sintering process also helps to ensure the uniformity and stability of the negative electrode material.

[0071] In some embodiments, the metal reducing agent may include at least one of magnesium powder, aluminum powder, and lithium powder. All of the above-mentioned metal reducing agents have good reducing properties, which is beneficial for the reduction and alloying of the first product; at the same time, the introduction of the metal reducing agent also helps to improve the conductivity, ion diffusion performance, and cycle stability of the negative electrode material.

[0072] In some embodiments, the mass ratio of the first product to the metal reducing agent is 1:(0.2 to 1.2), and exemplary ratios can be 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, or 1:1.2, etc., and more commonly, 1:(0.2 to 0.8). A suitable ratio can achieve a better reaction between the first product and the metal reducing agent.

[0073] In some embodiments, the secondary sintering involves raising the temperature at a rate of 1°C / min to 20°C / min to a secondary sintering temperature of 250°C to 850°C and holding it at that temperature for 1 hour to 24 hours. Exemplary values ​​include 250°C, 350°C, 400°C, 500°C, 600°C, 700°C, 800°C, or 850°C. The secondary sintering temperature can further be 300°C to 600°C, but other values ​​within the aforementioned range are also possible and are not limited herein. By using appropriate heating rates, sintering temperatures, and holding times, sufficient temperature and time can be ensured to promote the reaction between the first product and the metal reducing agent, and to improve the crystallinity and crystal structure stability of the second product.

[0074] Step S3: The second product is purified by etching with an etching solution to remove byproducts and obtain a silicon-based material precursor.

[0075] It is understood that by etching, a primary particle with pores is obtained, which is a silicon-based material precursor. This facilitates the subsequent entry of carbon matrix material into the pores of the primary particle. Compared with a primary particle without pores, the primary particle in this embodiment can alleviate the volume expansion of the silicon-based material itself. The anode material prepared by the preparation method of this application embodiment has better expansion performance.

[0076] In some embodiments, the mass ratio of the second product to the etching solution is 1:(5-20), specifically, it can be, for example, 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20 or any combination of these values, or other values ​​within the above range, which are not limited here.

[0077] In some embodiments, the etching solution includes at least one of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and ammonium bifluoride.

[0078] In some embodiments, the molar concentration of the etching solution is 1-10 mol / L.

[0079] In some embodiments, the etching reaction time is 0.5h to 10h, specifically, it can be 0.5h, 1h, 2h, 4h, 6h, 8h, 9h, 10h or any combination of these values, without limitation.

[0080] In some embodiments, the etching reaction temperature is ≤30°C, specifically, it can be, for example, 30°C, 28°C, 25°C, 20°C, 15°C, or any combination of these values, or other values ​​within the above range, which are not limited here.

[0081] In some embodiments, the method further includes washing and drying the etching reaction product at a drying temperature ≤85°C.

[0082] In some embodiments, the oxygen content in the silicon-based precursor is <6% by mass. Specifically, it can be, for example, 5.9%, 4.9%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, or any combination of these values. Of course, it can also be other values ​​within the above range, which are not limited here.

[0083] In some embodiments, the water content in the silicon-based material precursor is <1.5% by mass, specifically it can be, for example, 1.49%, 0.99%, 0.9%, 0.8%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, or any combination of these values, or other values ​​within the above range, which are not limited here.

[0084] In some embodiments, the median particle size of the silicon-based material precursor is 0.1 μm-15 μm.

[0085] In some embodiments, the silicon grain size of the silicon-based material precursor is 0.2 nm to 16 nm.

[0086] In some embodiments, the porosity of the silicon-based material precursor is 25%-65%.

[0087] In some embodiments, the specific surface area of ​​the silicon-based material precursor is 250 m². 2 / g-650m 2 / g.

[0088] In some embodiments, the average pore volume of the silicon-based material precursor is 0.24 cm³. 3 / g-0.66cm 3 / g.

[0089] Step S4: Carbon-based material is deposited inside the silicon-based material precursor by pulsed chemical vapor deposition and pores are reserved to obtain silicon-carbon composite material.

[0090] In some embodiments, the pulsed chemical vapor deposition method deposits carbon-based materials inside a silicon-based material precursor and leaves pores. The specific steps include: placing the silicon-based material precursor in a reactor, replacing the air therein with an inert gas, heating it to a certain temperature, and then introducing a gaseous carbon source using a pulsed gas injection method. By controlling the amount of gas entering for a short time, the deposition rate and efficiency of the internal carbon-based material are changed. Then, carbon is continuously deposited inside by continuously introducing the carbon source. After holding at the temperature for a certain time, the carbon source undergoes a thermal decomposition reaction, resulting in the deposition of carbon-based materials inside the silicon-based material precursor and the leaving of pores inside, thus obtaining a silicon-carbon composite material.

[0091] The heating rate of the gaseous carbon deposition in the pulsed chemical vapor deposition is 1℃ / min-30℃ / min. The reaction temperature of the gaseous carbon deposition in the pulsed chemical vapor deposition is 200℃-1050℃. The holding time of the gaseous carbon deposition in the pulsed chemical vapor deposition is 1h-24h. The gaseous carbon source in the pulsed chemical vapor deposition includes at least one selected from acetylene, methane, ethylene, propane, toluene, cyclohexane, ethanol, ethylene, propylene, pyrrole, and acetonitrile. The flow rate of the gaseous carbon source in the pulsed chemical vapor deposition is 0.1L / min-10L / min. The pulse frequency is 10Hz-500Hz. The pulse duration is 10ms-800ms. The pulse duration is 1h-8h.

[0092] Step S5: The silicon-carbon composite material is surface coated with a coating material, which includes at least one of carbon material, metal oxide layer, and nitride.

[0093] In some embodiments, a dense coating layer is deposited on the surface of a silicon-carbon composite material using fluidized bed chemical vapor deposition. Taking a carbon coating layer as an example, the specific steps include: placing the silicon-carbon composite material in a vertical fluidized bed apparatus, replacing the air with an inert gas or nitrogen, heating to a certain temperature, and then introducing an inert gas or nitrogen as the driving gas for the material, thus placing the material in a fluidized state. A certain flow rate of gaseous carbon source is then introduced, and after holding at the temperature for a certain time, the carbon source undergoes a thermal decomposition reaction, resulting in the deposition of a dense carbon layer on the surface of the silicon-carbon composite material, thus obtaining the negative electrode material.

[0094] In some embodiments, the inert gas includes one or more of helium, neon, argon, and krypton.

[0095] The heating rate of the gaseous carbon deposition in the fluidized bed chemical vapor deposition is 1℃ / min-20℃ / min. The flow rate of the motive gas used for the gaseous carbon deposition in the fluidized bed chemical vapor deposition is 1.5L / min-25L / min. The reaction temperature of the gaseous carbon deposition in the fluidized bed chemical vapor deposition is 600℃-1150℃. The holding time of the gaseous carbon deposition in the fluidized bed chemical vapor deposition is 0.5h-24h. The gaseous carbon source in the fluidized bed chemical vapor deposition includes at least one selected from acetylene, methane, ethylene, propane, toluene, cyclohexane, ethanol, ethylene, propylene, and liquefied petroleum gas. The flow rate of the gaseous carbon source in the fluidized bed chemical vapor deposition is 0.5L / min-15L / min.

[0096] The reaction of a metal reducing agent with the first product reduces silicon oxide in the first product to elemental silicon, thereby controlling the intensity of the first characteristic peak. Etching with an etching solution removes oxygen from the surface of the silicon-based material, controlling the intensity of the second and third characteristic peaks, thus modulating the oxygen protection level of the silicon-based material. Furthermore, carbon-based materials are deposited inside the silicon-based precursor using pulsed chemical vapor deposition (PVD) with pre-reserved pores, while a dense carbon layer is also deposited on its surface using fluidized bed PVD, ultimately forming the anode material.

[0097] Employing a pulsed air intake method allows for precise control of the carbon deposition rate within the material. This enables the deposition of carbon-based materials while simultaneously reserving pores, thereby modulating the porosity of the anode material and mitigating the volume expansion of silicon-based materials. Furthermore, fluidized bed chemical vapor deposition (FCVD) further uniformly coats the material surface, forming a dense coating layer. This effectively reduces the direct penetration of electrolyte into the anode material particles through the pore structure, minimizing side reactions between the electrolyte and silicon-based materials and improving the cycle performance of the battery fabricated from the anode material. Through the synergistic effect of pulsed carbon deposition and coating processes, both internal pore reservation and dense surface coating are achieved in the anode material. Controlling the protective strength H of the coating layer to ≥85% reduces the expansion rate of the anode material, facilitating the formation of a stable solid electrolyte film on its surface and improving material stability, ultimately enhancing the electrochemical performance of the anode material.

[0098] Thirdly, the present invention provides a secondary battery, the secondary battery comprising the negative electrode material described in the first aspect or the negative electrode material prepared by the preparation method described in the second aspect.

[0099] The secondary battery provided in the third aspect of the present invention has advantages such as high capacity, high initial efficiency, long cycle life, excellent rate performance and low expansion.

[0100] Specific embodiments and comparative examples

[0101] Example 1

[0102] (1) Place the silicon monoxide raw material in an atmosphere furnace, and heat it to 950°C at a heating rate of 3°C / min under the protection of argon atmosphere. After holding at the temperature for 5 hours, cool it to obtain the first product.

[0103] (2) After the first product and the aluminum powder are mixed evenly at a molar ratio of 1:0.5, the mixture is placed in a reactor, a protective gas is introduced to replace the air, and the mixture is heated to 650°C at a heating rate of 3°C / min. After holding at the temperature for 4 hours, the mixture is cooled to obtain the second product.

[0104] (3) The second product is put into the etching solution for purification treatment. The mass ratio of the second product to the etching solution is 1:5. The concentration of the etching solution is 6 mol / L. The etching solution includes hydrochloric acid and hydrofluoric acid. The etching reaction time is 1.5 h. The etching reaction temperature is controlled at 25 °C. After washing and drying, the silicon-based material precursor is obtained.

[0105] (4) Place 500g of silicon-based material precursor into a rotary atmosphere furnace, replace the air in it with an inert gas, and heat it to 750℃ at a heating rate of 3℃ / min under the protection of argon atmosphere. Then set the acetylene gas flow rate to 2.5L / min, introduce the carbon source into the pulse generator, set the pulse frequency to 50Hz, the pulse duration to 200ms, and the pulse duration to 3h. After turning off the pulse generator, continue to introduce acetylene gas at a flow rate of 2.5L / min for 2h, and then cool to obtain silicon-carbon composite material.

[0106] (5) Place 1 kg of silicon-carbon composite material in a vertical fluidized bed device, replace the air in it with an inert gas, introduce 3 L / min of argon as the power gas, heat it to 750°C at a heating rate of 3°C / min, then introduce 2 L / min of propane as the carbon source gas, keep it at the temperature for 3 h, and then cool it to obtain the negative electrode material.

[0107] Detailed physicochemical parameters of the negative electrode material in this embodiment are shown in Table 1.

[0108] Figure 1 is the Raman spectrum of the negative electrode material in this embodiment; Figure 2 is the scanning electron microscope image of the negative electrode material in this embodiment; Figure 3 is the XRD pattern of the negative electrode material in this embodiment; Figure 4 is the cycle performance curve of the battery prepared by the negative electrode material in this embodiment, with a charge / discharge current of 1000 mA / g.

[0109] As can be seen from the Raman spectrum in Figure 1, the negative electrode material exhibits high performance at 516 cm⁻¹. -1 The peak intensity of the first characteristic peak at 3716 cm⁻¹ is 3716; at 308 cm⁻¹... -1 The peak intensity of the second characteristic peak at 925 cm⁻¹ is 2315; at 925 cm⁻¹...-1 The peak intensity of the first characteristic peak at the location is 2124, and the calculated Q value is 3.35.

[0110] As can be seen from the scanning electron microscope image in Figure 2, the surface of the prepared silicon-carbon anode material is relatively smooth and there are no cracks.

[0111] As can be seen from the XRD pattern in Figure 3, the three strong peaks at 28.4°, 47.3° and 56.1° correspond to the three strong peaks of silicon (JCPDS No. 27-1402), and there are basically no impurity phases. According to the Scherrer formula, the silicon grain size is calculated to be 3.5 nm.

[0112] As shown in Figure 4, the material exhibits excellent cycling performance, maintaining 83.4% capacity retention after 50 cycles at a current of 0.25C.

[0113] Example 2

[0114] (1) Place the silicon monoxide raw material in an atmosphere furnace, and heat it to 970°C at a heating rate of 3°C / min under the protection of argon atmosphere. After holding at the temperature for 6 hours, cool it to obtain the first product.

[0115] (2) After the first product and the aluminum powder are mixed evenly in a molar ratio of 1:0.3, the mixture is placed in a reactor, a protective gas is introduced to replace the air, and the mixture is heated to 650°C at a heating rate of 3°C / min. After holding at the temperature for 4 hours, the mixture is cooled to obtain the second product.

[0116] (3) The second product is put into the etching solution for purification treatment. The mass ratio of the second product to the etching solution is 1:10, the concentration of the etching solution is 3 mol / L, the etching reaction time is 2.5 h, and the etching reaction temperature is controlled at 25 °C. After washing and drying, the silicon-based material precursor is obtained.

[0117] (4) Place 500g of silicon-based material precursor into a rotary atmosphere furnace, replace the air in it with an inert gas, and heat it to 700℃ at a heating rate of 3℃ / min under the protection of argon atmosphere. Then set the acetylene gas flow rate to 0.5L / min, introduce the carbon source into the pulse generator, set the pulse frequency to 500Hz, the pulse duration to 10ms, and the pulse duration to 8h. After turning off the pulse generator, continuously introduce acetylene gas at a flow rate of 2.5L / min for 1h, and cool to obtain silicon-carbon composite material.

[0118] (5) Place 1 kg of silicon-carbon composite material in a vertical fluidized bed device, replace the air in it with an inert gas, introduce 4 L / min of argon as the power gas, heat it to 650°C at a heating rate of 5°C / min, then introduce 3 L / min of propane as the carbon source gas, keep it at the temperature for 4 h, and then cool it to obtain the negative electrode material.

[0119] Detailed physicochemical parameters of the negative electrode material in this embodiment are shown in Table 1.

[0120] Example 3

[0121] (1) Place the silicon monoxide raw material in an atmosphere furnace, and heat it to 970°C at a heating rate of 3°C / min under the protection of argon atmosphere. After holding at the temperature for 6 hours, cool it to obtain the first product.

[0122] (2) After the first product and the aluminum powder are mixed evenly in a molar ratio of 1:0.3, the mixture is placed in a reactor, a protective gas is introduced to replace the air, and the mixture is heated to 650°C at a heating rate of 3°C / min. After holding at the temperature for 4 hours, the mixture is cooled to obtain the second product.

[0123] (3) The second product is put into the etching solution for purification treatment. The mass ratio of the second product to the etching solution is 1:10, the concentration of the etching solution is 8 mol / L, the etching reaction time is 2.5 h, and the etching reaction temperature is controlled at 25 °C. After washing and drying, the silicon-based material precursor is obtained.

[0124] (4) Place 500g of silicon-based material precursor into a rotary atmosphere furnace, replace the air in it with an inert gas, and heat it to 900℃ at a heating rate of 3℃ / min under the protection of argon atmosphere. Then set the acetylene gas flow rate to 9.5L / min, introduce the carbon source into the pulse generator, set the pulse frequency to 10Hz, the pulse duration to 800ms, and the pulse duration to 4h. After the pulse is turned off, continue to introduce acetylene gas at a flow rate of 1.5L / min for 2h, and cool to obtain silicon-carbon composite material.

[0125] (5) Place 1 kg of silicon-carbon composite material in a vertical fluidized bed device, replace the air in it with an inert gas, introduce 4 L / min of argon as the power gas, heat it to 650°C at a heating rate of 5°C / min, then introduce 3 L / min of propane as the carbon source gas, keep it at the temperature for 4 h, and then cool it to obtain the negative electrode material.

[0126] Detailed physicochemical parameters of the silicon-carbon anode material in this embodiment are shown in Table 1.

[0127] Example 4

[0128] (1) Place the silicon monoxide raw material in an atmosphere furnace, and heat it to 750°C at a heating rate of 3°C / min under the protection of argon atmosphere. After holding at the temperature for 5 hours, cool it to obtain the first product.

[0129] (2) After the first product and magnesium powder are mixed evenly in a molar ratio of 1:0.2, the mixture is placed in a reactor, a protective gas is introduced to replace the air, and the mixture is heated to 620°C at a heating rate of 3°C / min. After holding at the temperature for 5 hours, the mixture is cooled to obtain the second product.

[0130] (3) The second product is put into the etching solution for purification treatment. The mass ratio of the second product to the etching solution is 1:10, the concentration of the etching solution is 10 mol / L, the etching reaction time is 1.5 h, and the etching reaction temperature is controlled at 25 °C. After washing and drying, the silicon-based material precursor is obtained.

[0131] (4) Place 500g of silicon-based material precursor into a rotary atmosphere furnace, replace the air in it with an inert gas, and heat it to 950℃ at a heating rate of 3℃ / min under the protection of argon atmosphere. Then set the acetylene gas flow rate to 10L / min, introduce the carbon source into the pulse generator, set the pulse frequency to 10Hz, the pulse duration to 800ms, and the pulse duration to 8h. After turning off the pulse generator, continue to introduce acetylene gas at a flow rate of 0.1L / min for 3h, and cool to obtain silicon-carbon composite material.

[0132] (5) Place 1 kg of silicon-carbon composite material in a vertical fluidized bed device, replace the air in it with an inert gas, introduce 4 L / min of argon as the power gas, heat it to 600℃ at a heating rate of 5℃ / min, then introduce 1 L / min of propane as the carbon source gas, keep it at the temperature for 2 h, and then cool it to obtain the negative electrode material.

[0133] The remaining parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0134] Example 5

[0135] The negative electrode material was prepared in basically the same way as in Example 1, except that the heating temperature in step (1) was 780°C and the concentration of the etching solution in step (3) was 1 mol / L.

[0136] Example 6

[0137] The negative electrode material was prepared in basically the same way as in Example 1, except that the etching time in step (3) was 3 hours.

[0138] Example 7

[0139] The negative electrode material was prepared in basically the same way as in Example 1, except that the reaction temperature in step (5) was 850°C.

[0140] Example 8

[0141] The negative electrode material was prepared in basically the same way as in Example 1, except that the carbon source concentration in step (5) was 8 L / min.

[0142] Comparative Example 1

[0143] Steps (1), (2), (3), and (5) are basically the same as in Example 1, while step (4) is conventional CVD.

[0144] (4) Place 500g of silicon-based material precursor into a rotary atmosphere furnace, replace the air in it with an inert gas, heat it to 750℃ at a heating rate of 3℃ / min under the protection of argon atmosphere, set the acetylene gas flow rate to 2.5L / min, and continuously introduce acetylene gas for 5h, and then cool to obtain silicon-carbon composite material.

[0145] Detailed physicochemical parameters of the negative electrode material in this embodiment are shown in Table 1.

[0146] Comparative Example 2

[0147] Steps (1), (3), (4), and (5) are basically the same as in Example 1, except that aluminum powder is not added in step (2).

[0148] (2) The first product is placed in a reactor, and a protective gas is introduced to replace the air. The product is heated to 650°C at a heating rate of 3°C / min, held for 4 hours, and then cooled to obtain the second product.

[0149] Detailed physicochemical parameters of the negative electrode material in this embodiment are shown in Table 1.

[0150] Comparative Example 3

[0151] Steps (1), (4), and (5) are basically the same as in Example 1. In step (2), excess magnesium powder is added. In step (3), the mass ratio of the second product to the etching solution is 1:25, the concentration of the etching solution is 11 mol / L, and the etching reaction time is 4.5 h.

[0152] (2) The first product and magnesium powder are mixed evenly at a molar mass ratio of 1:3, placed in a reactor, and a protective gas is introduced to replace the air. The mixture is heated to 650°C at a heating rate of 3°C / min, held for 4 hours, and then cooled to obtain the second product.

[0153] (3) The second product is put into the etching solution for purification treatment. The mass ratio of the second product to the etching solution is 1:25, the concentration of the etching solution is 11 mol / L, the etching reaction time is 4.5 h, and the etching reaction temperature is controlled at 25 °C. After washing and drying, the silicon-based material precursor is obtained.

[0154] Detailed physicochemical parameters of the negative electrode material in this embodiment are shown in Table 1.

[0155] Test method:

[0156] 1) Raman testing of negative electrode materials:

[0157] Raman spectra were measured using a HORIBA XPLORA laser confocal Raman spectrometer (Japan), including Raman peak positions, peak intensities, and full width at half maximum (FWHM). Specifically, the sample was placed on the sample stage of the Raman spectrometer, ensuring alignment with the laser beam. Testing conditions included a 532 nm laser and a testing range of 100 cm⁻¹. -1 -3000cm -1 Zero-point calibration is performed using standard materials to ensure the precision and accuracy of the spectrum. The sample is excited using a laser, and the frequency and intensity of the scattered light are measured.

[0158] 2) Test method for specific surface area of ​​negative electrode material:

[0159] Specific surface area and specific pore volume testing methods: Using the ASAP2406 surface area and pore size analyzer from Micco (USA), at liquid nitrogen temperature, the equilibrium adsorption amount of nitrogen on the surface of an object is related to its specific surface area and other characteristics. Combining the law of the change of adsorption amount with relative pressure during the adsorption process, various models can be fitted to calculate the specific surface area.

[0160] 3) Test of protective strength H of the coating layer:

[0161] A negative electrode material with a mass of m1 g was immersed in a hydrofluoric acid solution with a mass concentration of 10*m1 g and a hydrofluoric acid concentration of 20%. After mechanical stirring for 2 hours, the solid and liquid were separated. The residual hydrofluoric acid in the solid material was washed sequentially with deionized water and anhydrous ethanol. Then, the material was vacuum dried at 60℃ for 12 hours to obtain m2 g of material. The protective strength of the coating layer was calculated as H = m2 / m1 × 100%.

[0162] 4) Particle size of the negative electrode material:

[0163] The particle size distribution method is in accordance with GB / T 19077-2016. The D50 value was measured using a Malvern laser particle size analyzer (Mastersizer 3000), exhibiting a symmetrical distribution resembling a normal distribution. In its volumetric baseline distribution, the cumulative 50% diameter is D50, and so on, with the cumulative 90% diameter being D90 and the cumulative 10% diameter being D10. An exemplary laser particle size analyzer used is the Mastersizer 3000 from Malvern Instruments Ltd., UK.

[0164] 5) Test method for compacted density:

[0165] Using a CARVER 4350.22 powder compaction density tester from the USA, a sample of a specified mass m was placed in a mold and a pressure of 1.0T was applied. After holding the pressure for 30 seconds, the pressure was released and the thickness was measured. The compaction density was then calculated.

[0166] 6) Test methods for oxygen and carbon content in negative electrode materials:

[0167] The oxygen content was measured using Fourier transform infrared spectroscopy, and the carbon content was tested using thermogravimetric analysis.

[0168] 7) SEM testing:

[0169] Scanning electron microscopy (SEM) characterization was performed using a transmission electron microscope at an operating voltage of 200 kV. The structure of the negative electrode material was observed, and the thickness of the coating layer was measured. For example, the coating layer thickness was determined by cross-sectioning the material using a FIB-SEM device. Ten particles were randomly selected from the SEM, and the coating layer thickness was measured three times for each particle. The average coating layer thickness was then obtained.

[0170] 8) Test method for average particle size in one test:

[0171] The material was sectioned using a FIB-SEM device. The size of 20 primary particles was measured in the SEM, and the average value was calculated as the average size of the primary particles.

[0172] 9) Test method for average silicon grain size:

[0173] The XRD pattern of the sample was measured using an X-ray diffractometer. The half-peak height and width of the diffraction peaks and the corresponding Bragg angles were obtained using Jade software. The average grain size of the nano-silicon was calculated using the Scherrer formula D = Kγ / B cosθ.

[0174] 10) Porosity testing methods:

[0175] Mercury intrusion porosimetry (MIP) is a method for calculating porosity by measuring the pressure change of mercury within the pores of a material. This method uses a high-performance, fully automated mercury intrusion porosimetry instrument, such as the AutoPore IV 9500 from Micron Instruments, to inject mercury into the pores of the material. Based on the changes in mercury volume and pressure, the porosity and pore distribution can be calculated.

[0176] 11) Test method for the average pore size of negative electrode materials:

[0177] The tests were conducted using an ASAP2460 instrument from Micron Technology, USA. The pore volume V was determined using the BJH Desorption Cumulative Volume of Pores model. Calculated within the aperture range.

[0178] Micropore and mesopore analyses were performed using Micromeretics ASAP 2460. At liquid nitrogen temperature, the equilibrium adsorption amount of nitrogen on an object's surface is related to its pore size and other properties. By combining the relationship between adsorption amount and relative pressure during the adsorption process, various models can be fitted to calculate the pore size. The software report uses density functional theory (DFT) to calculate the pore size distribution.

[0179] After the above tests, the negative electrode materials prepared in Examples 1-8 and Comparative Examples 1-3 are sample numbers S1-S8 and R1-R3, respectively; the performance parameters of the negative electrode materials are shown in Table 1:

[0180] Table 1

[0181] 8) Electrochemical testing:

[0182] 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 form a slurry. The slurry was then uniformly coated onto copper foil and dried to form a negative electrode sheet. The negative electrode sheet was then assembled into a coin cell in an argon atmosphere glove box. The separator used was a polypropylene microporous membrane, and the electrolyte used was 1 mol / L lithium hexafluorophosphate (the solvent was a mixture of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate). The counter electrode used was a lithium metal sheet.

[0183] The discharge specific capacity of the above 12 groups of batteries was tested on the Landian CT2001A battery testing system. The ratio of the discharge capacity to the battery capacity in 1 hour is the discharge specific capacity.

[0184] The first coulombic efficiency test was conducted on the above 12 groups of batteries on the Landian CT2001A battery testing system. The charge and discharge current was 0.05C, and the first coulombic efficiency was measured.

[0185] The above 12 battery groups were subjected to a 50-cycle test on the Blue Electric CT2001A battery testing system with a charge / discharge current of 0.25C. After 50 cycles, the battery capacity and capacity retention rate after each cycle were calculated.

[0186] The capacity retention rate after 50 cycles at 0.25C is calculated as: discharge capacity of the 50th cycle / discharge capacity of the first cycle * 100%, as shown in Table 2.

[0187] Table 2 Comparison of Parameters and Performance of Various Batteries

[0188] As shown in Table 1-2, to ensure the balance between the specific capacity and cycle life of the negative electrode material, the oxidation level of the silicon particle surface is adjusted by controlling the synthesis process, so that the oxygen protection degree Q value of the silicon-based material is between 1.5 and 4.5. Within this reasonable range, side reactions between the negative electrode material and the electrolyte can be reduced, and an appropriate amount of oxide can be formed on the surface of the silicon-based material as a rigid protective layer, alleviating the volume expansion of the silicon-based material and thus improving the cycle performance of the battery prepared with the negative electrode material. This application, through the synergistic effect of the carbon-based material deposition process and the coating process, controls the protective strength H of the coating layer of the negative electrode material to ≥85%, which can reduce the wetting of active materials such as silicon-based materials in the negative electrode material with the electrolyte, improve the capacity and first-time efficiency of the battery prepared with the negative electrode material, and at the same time alleviate the volume expansion of the silicon-based material, improving the cycle and rate performance of the battery prepared with the negative electrode material.

[0189] Compared to Example 1, Example 2 reduced the amount of metal reducing agent during preparation, resulting in a lower intensity of the first characteristic peak of the anode material. This led to a decrease in the oxygen protection factor Q of the silicon-based material, consequently reducing the cycle retention rate of the composite material in Example 2 and increasing volume expansion. In Example 4, compared to Example 1, the carbon coating process in the vertical fluidized bed was lowered, resulting in a reduced coating effect and a lower carbon content in the anode material. This means the coating layer in the anode material is thinner, accounts for a smaller percentage of the coating mass, and consequently reduces the protective strength of the coating layer, leading to a decrease in the initial coulombic efficiency of the battery prepared from the anode material.

[0190] Compared to Example 2, Example 3 increased the concentration of the etching solution during the preparation process, resulting in a significant decrease in the intensity of the third characteristic peak and a thinner oxide layer on the surface of the silicon-based material. Ultimately, this led to an increase in the oxygen protection degree Q of the silicon-based material in the negative electrode of Example 3, which in turn increased the specific capacity of the negative electrode material in Example 3 and improved the first coulombic efficiency.

[0191] Compared to Example 1, Example 5 reduced the concentration of the etching solution. On the one hand, this resulted in the inability to effectively remove the oxide byproducts generated during the reduction process, leading to a decrease in the intensity of the first characteristic peak. On the other hand, the reduced concentration preferentially etched the amorphous oxides on the surface of the silicon-based material, resulting in a decrease in the intensity of the second characteristic peak. Ultimately, the oxygen protection degree Q of the silicon-based material decreased, and the cycle retention rate and first coulombic efficiency decreased.

[0192] Compared to Example 1, Example 6 extended the etching time of the etching solution, which led to an increase in the porosity of the negative electrode material. Under the same carbon deposition conditions, the carbon coating effect was poor, resulting in a decrease in the protective strength of the coating layer and a deterioration in the cycle performance of the material. However, since sufficient pores were reserved inside the negative electrode material, the volume expansion of the silicon-based material in the negative electrode material could be effectively alleviated, thus reducing the volume expansion rate of the negative electrode material.

[0193] Compared to Example 1, Examples 7 and 8 increased the reaction temperature and carbon source concentration in step (5) during the preparation process, resulting in a significant increase in carbon coating efficiency, carbon content, and density, leading to an increase in the protective strength H of the coating layer. However, the specific capacity of the anode material decreased. Due to the increased temperature and concentration during the coating process, the carbon source concentration increased. Carbon source decomposition is an exothermic reaction, and the increased carbon source concentration leads to a rise in local temperature, which also results in an increase in silicon grain size, leading to a deterioration in cycle performance and expansion performance.

[0194] Compared to Example 1, Comparative Example 1 uses traditional CVD instead of pulsed chemical vapor deposition in the preparation process, which results in low filling efficiency of carbon-based materials in silicon-based materials, increased porosity and specific surface area of ​​the obtained negative electrode material, reduced protective strength H of the coating layer under the same coating conditions, and worsened cycle performance and expansion performance of the battery prepared by the negative electrode material, with a significant reduction in first-efficiency.

[0195] Compared to Example 1, Comparative Example 2 did not add aluminum powder in step (2) of the preparation process, which resulted in a significant decrease in the intensity of the first characteristic peak and an increase in the intensity of the third characteristic peak. Ultimately, this resulted in the oxygen protection degree Q of the silicon-based material being less than 1.5, which led to a decrease in the specific capacity of the battery prepared by the negative electrode material, and thus failed to meet the application requirements.

[0196] Compared to Example 1, Comparative Example 3 showed a significant increase in the amount of metal reducing agent, etching solution content, and concentration during the preparation process. This resulted in an oxygen protection factor Q greater than 4.5 for the silicon-based material, leading to a significant increase in the specific capacity and first-time efficiency of the obtained anode material. However, the oxide layer on the surface of the silicon-based material was relatively thin, which could not effectively reduce the side reactions generated by the contact between the silicon-based material and the electrolyte, nor could it effectively alleviate the volume expansion of the silicon-based material, resulting in poor cycle life of the battery prepared from the anode material.

[0197] In summary, the anode material of this application has advantages such as low expansion and good cycle stability.

[0198] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. Furthermore, any changes or modifications made by those skilled in the art based on the ideas of this application, and on the specific implementation methods and application scope of this application, are all within the scope of protection of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes silicon-carbon material, which includes silicon-based material and carbon-based material, with at least a portion of the carbon-based material distributed within the silicon-based material; The negative electrode material was tested using Raman spectroscopy, and the negative electrode material was measured at 515±10 cm⁻¹. -1 The anode material exhibits a first characteristic peak at a depth of 305±10 cm⁻¹, with a peak intensity of M1. -1 The anode material exhibits a second characteristic peak at a depth of 925±10 cm⁻¹, with a peak intensity of M². -1 The third characteristic peak is defined as M3. Q is defined as the oxygen protection degree of the silicon-based material. The following relationship exists between Q and M1, M2, and M3 of the negative electrode material: Q = M1 / M2 + M1 / M3, 1.5 ≤ Q ≤ 4.5 and M2 > M3.

2. The negative electrode material according to claim 1, characterized in that, The Q value satisfies one of the following conditions: The Q value satisfies 1.5 ≤ Q ≤ 3.35; or The Q value satisfies 3.35 ≤ Q ≤ 4.5; or The Q value is 1.5, 2.0, 2.5, 3.0, 3.35, 3.5, 4.0, 4.5, or any value within the range of any two of the above values.

3. The negative electrode material according to claim 1, characterized in that, The carbon-based materials include at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene.

4. 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 silicon-carbon material. The protective strength of the coating layer is H. The test method for the protective strength H of the coating layer includes: immersing a negative electrode material with a mass of m1 g in a 10*m1 g hydrofluoric acid solution, wherein the mass concentration of hydrofluoric acid in the hydrofluoric acid solution is 20%, mechanically stirring for 2 hours, separating the solid and liquid, washing the residual hydrofluoric acid in the solid material sequentially with deionized water and anhydrous ethanol, and then vacuum drying at 60°C for 12 hours to obtain m2 g of material, where H = m2 / m1 × 100%. The protective strength H value of the coating layer satisfies one of the following conditions: The protective strength H of the covering layer is ≥85%; or The protective strength H of the covering layer is ≥90%; or The protective strength H of the coating layer is 85%, 86%, 87%, 88%, 90%, 95%, 99%, 100%, or any value within the range of any two of the above values.

5. The negative electrode material according to claim 4, characterized in that, The covering layer satisfies at least one of the following conditions: a. The coating layer comprises at least one of carbon materials, metal oxides, and nitrides; b. The coating layer comprises a carbon material, which includes at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, graphene, soft carbon, and hard carbon. c. At least a portion of the carbon-based material is distributed on the surface of the silicon-based material and forms the coating layer; d. The coating layer comprises a metal oxide, wherein the metal oxide comprises at least one selected from titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide; e. The coating layer comprises a nitride, which includes at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

6. The negative electrode material according to claim 4, characterized in that, The coating layer satisfies one of the following conditions: The thickness of the coating layer is 0.1 nm-100 nm; or The thickness of the coating layer is 1nm-50nm; or The thickness of the coating layer is 1nm-20nm; or The thickness of the coating layer is 0.1 nm, 5 nm, 10 nm, 30 nm, 50 nm, 80 nm, 100 nm, or any value within the range of any two of the above values.

7. The negative electrode material according to claim 1, characterized in that, The silicon-based material comprises primary particles, and the primary particles satisfy one of the following conditions: The average particle size of the primary particles is 1nm-20nm; or The average particle size of the primary particles is 1nm, 2nm, 5nm, 8nm, 10nm, 12nm, 15nm, 18nm, 20nm, or any value within the range of any two of the above values.

8. The negative electrode material according to claim 7, characterized in that, The primary particles comprise silicon grains, and the silicon grains satisfy one of the following conditions: The average size of the silicon grains is 0.5nm-10nm; or The average size of the silicon grains is 2nm-10nm; or The average size of the silicon grains is 0.5nm, 0.8nm, 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 8nm, 10nm, or any value within the range of any two of the above values.

9. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies one of the following conditions: The negative electrode material has pores, and the average pore diameter of the negative electrode material is 0.5 nm-50 nm; or The average pore diameter of the negative electrode material is 0.5nm, 1nm, 2nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 40nm, 50nm, or any value within the range of any two of the above values.

10. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies one of the following conditions: The median particle size of the negative electrode material is 0.2 μm to 18 μm; or The median particle size of the negative electrode material is 1μm-18μm; or The median particle size of the negative electrode material is 0.2μm, 0.5μm, 1μm, 2μm, 4μm, 5μm, 8μm, 10μm, 15μm, 18μm, or any value within the range of any two of the above values.

11. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: The specific surface area of ​​the negative electrode material is 0.8 m². 2 / g~25m 2 / g; or The specific surface area of ​​the negative electrode material is 2m². 2 / g-10m 2 / g; or The specific surface area of ​​the negative electrode material is 0.8 m². 2 / g, 1m 2 / g、2m 2 / g、3m 2 / g、5m 2 / g、8m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g or any value within the range of any two of the above values.

12. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies one of the following conditions: The compacted density of the negative electrode material powder is 0.8 g / cm³. 3 ~1.5g / cm 3 ;or The powder compaction density of the negative electrode material is 1 g / cm³. 3 -1.2g / cm 3 ;or The compacted density of the negative electrode material powder is 0.8 g / cm³. 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 Or any value within the range formed by any two of the above values.

13. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies one of the following conditions: Based on the mass of the negative electrode material, the carbon content in the negative electrode material is 15%-65% by mass percentage. Based on the mass of the negative electrode material, the carbon content in the negative electrode material is 20%-60% by mass percentage; or The carbon content in the negative electrode material is 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or any value within the range of any two of the above values.

14. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: Based on the mass of the negative electrode material, the oxygen content in the negative electrode material is ≤10% by mass percentage; or The mass content of oxygen is 1%, 2%, 3%, 4%, 5%, 6%, 8%, or any value within the range of any two of the above values.

15. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies one or more of the following conditions: The negative electrode material has pores, and the porosity of the negative electrode material is 0.5%-15%; or The porosity of the negative electrode material is 0.5%, 1%, 2%, 3%, 5%, 8%, 10%, 15%, or any value within the range of any two of the above values.

16. A secondary battery, characterized in that, Includes the negative electrode material as described in any one of claims 1-15.

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